Mars - Hellas Planitia gravity analysis

NASA Technical Reports Server (NTRS)

Sjogren, W. L.; Wimberley, R. N.

1981-01-01

Doppler radio tracking data from Viking Orbiter 1 has provided new detailed observations of gravity variations over Hellas Planitia. Line-of-sight Bouguer gravity definitely indicates that isostatic adjustment has occurred. Two theoretical models were tested to obtain fits to the gravity data. Results for a surface deficit model, and a model with a surface deficit and a mass excess at depth are displayed. The mass-at-depth model produced very marked improvement in the data fit as compared to the surface deficit model. The optimum depth for the mass excess is 130 km.

Both natural selection and isolation by distance explain phenotypic divergence in bill size and body mass between South Australian little penguin colonies.

PubMed

Colombelli-Négrel, Diane

2016-11-01

Morphological variation between populations of the same species can arise as a response to genetic variation, local environmental conditions, or a combination of both. In this study, I examined small-scale geographic variation in bill size and body mass in little penguins ( Eudyptula minor ) across five breeding colonies in South Australia separated by <150 km. To help understand patterns driving the differences, I investigated these variations in relation to environmental parameters (air temperature, sea surface temperature, and water depth) and geographic distances between the colonies. I found substantial morphological variation among the colonies for body mass and bill measurements (except bill length). Colonies further located from each other showed greater morphological divergence overall than adjacent colonies. In addition, phenotypic traits were somewhat correlated to environmental parameters. Birds at colonies surrounded by hotter sea surface temperatures were heavier with longer and larger bills. Birds with larger and longer bills were also found at colonies surrounded by shallower waters. Overall, the results suggest that both environmental factors (natural selection) and interpopulation distances (isolation by distance) are causes of phenotypic differentiation between South Australian little penguin colonies.

New model for estimating the relationship between surface area and volume in the human body using skeletal remains.

PubMed

Kasabova, Boryana E; Holliday, Trenton W

2015-04-01

A new model for estimating human body surface area and body volume/mass from standard skeletal metrics is presented. This model is then tested against both 1) "independently estimated" body surface areas and "independently estimated" body volume/mass (both derived from anthropometric data) and 2) the cylindrical model of Ruff. The model is found to be more accurate in estimating both body surface area and body volume/mass than the cylindrical model, but it is more accurate in estimating body surface area than it is for estimating body volume/mass (as reflected by the standard error of the estimate when "independently estimated" surface area or volume/mass is regressed on estimates derived from the present model). Two practical applications of the model are tested. In the first test, the relative contribution of the limbs versus the trunk to the body's volume and surface area is compared between "heat-adapted" and "cold-adapted" populations. As expected, the "cold-adapted" group has significantly more of its body surface area and volume in its trunk than does the "heat-adapted" group. In the second test, we evaluate the effect of variation in bi-iliac breadth, elongated or foreshortened limbs, and differences in crural index on the body's surface area to volume ratio (SA:V). Results indicate that the effects of bi-iliac breadth on SA:V are substantial, while those of limb lengths and (especially) the crural index are minor, which suggests that factors other than surface area relative to volume are driving morphological variation and ecogeographical patterning in limb prorportions. © 2014 Wiley Periodicals, Inc.

The interaction of Io's plumes and sublimation atmosphere

NASA Astrophysics Data System (ADS)

McDoniel, William J.; Goldstein, David B.; Varghese, Philip L.; Trafton, Laurence M.

2017-09-01

Io's volcanic plumes are the ultimate source of its SO2 atmosphere, but past eruptions have covered the moon in surface frost which sublimates in sunlight. Today, Io's atmosphere is a result of some combination of volcanism and sublimation, but it is unknown exactly how these processes work together to create the observed atmosphere. We use the direct simulation Monte Carlo (DSMC) method to model the interaction of giant plumes with a sublimation atmosphere. Axisymmetric plume/atmosphere simulations demonstrate that the total mass of SO2 above Io's surface is only poorly approximated as the sum of independent volcanic and sublimated components. A simple analytic model is developed to show how variation in the mass of erupting gas above Io's surface can counteract variation in the mass of its hydrostatic atmosphere as surface temperature changes over a Jupiter year. Three-dimensional, unsteady simulations of giant plumes over an Io day are also presented, showing how plume material becomes suspended in the sublimation atmosphere. We find that a plume which produces some total mass above Io's surface at night will cause a net increase in the noon-time atmosphere of only a fraction of the night-time value. However, as much as seven times the night-side mass of the plume will become suspended in the sublimation atmosphere, altering its composition and displacing sublimated material.

Influence of the surface permeability on the GRACE water mass variations. Case of the Lake Chad basin.

NASA Astrophysics Data System (ADS)

Lopez, T.; Ramillien, G.; Antoine, R.; Darrozes, J.; Rabinowicz, M.

2017-12-01

Since its launch in 2002, the Gravity Recovery And Climate Experiment (GRACE) has been measured the tiny variations of the gravity field due to redistributions of water mass in the surface envelops of Earth. At a spatial resolution of 400 km, these satellite data offer a unique perspective to understand the evolution of continental water storage at regional and global scales, and therefore they enable the monitoring of the hydrological systems such as river basins. It is well known that seasonal cycle, droughts, vegetation and human extractions are the main contributors of the hydrology signals sensed by GRACE. However, the coupling between land surface and the atmosphere is important in semi-arid and arid regions, in particular in West Africa [1]. We propose to quantify the surface water fluxes in the Lake Chad region by using the 10-day water mass solutions of the GRACE mission in the context of the regular West African monsoon. Alternation of the evaporation/condensation cycles during the recent period are interpreted in terms of surface vertical permeability changes that control the thermal evolution in this region [2]. GRACE solutions reveal an interannual increase of surface water mass at the beginning of the dry seasons, especially between 2005 and 2008. We propose that this gain of surface water mass is caused by a seasonal cycle of clay fracturing that controls the evaporation/condensation cycle. [1] Koster et al. (2004). Science, 305, 1138-1140. [2] Lopez et al. (2016). Surv. Geophys., 37 (2), 471-502.

On the capability of Swarm for surface mass variation monitoring: Quantitative assessment based on orbit information from CHAMP, GRACE and GOCE

NASA Astrophysics Data System (ADS)

Baur, Oliver; Weigelt, Matthias; Zehentner, Norbert; Mayer-Gürr, Torsten; Jäggi, Adrian

2014-05-01

In the last decade, temporal variations of the gravity field from GRACE observations have become one of the most ubiquitous and valuable sources of information for geophysical and environmental studies. In the context of global climate change, mass balance of the Arctic and Antarctic ice sheets gained particular attention. Because GRACE has outlived its predicted lifetime by several years already, it is very likely that a gap between GRACE and its successor GRACE follow-on (supposed to be launched in 2017, at the earliest) occurs. The Swarm mission - launched on November 22, 2013 - is the most promising candidate to bridge this potential gap, i.e., to directly acquire large-scale mass variation information on the Earth's surface in case of a gap between the present GRACE and the upcoming GRACE follow-on projects. Although the magnetometry mission Swarm has not been designed for gravity field purposes, its three satellites have the characteristics for such an endeavor: (i) low, near-circular and near-polar orbits, (ii) precise positioning with high-quality GNSS receivers, (iii) on-board accelerometers to measure the influence of non-gravitational forces. Hence, from an orbit analysis point of view the Swarm satellites are comparable to the CHAMP, GRACE and GOCE spacecraft. Indeed and as data analysis from CHAMP has been shown, the detection of annual signals and trends from orbit analysis is possible for long-wavelength features of the gravity field, although the accuracy associated with the inter-satellite GRACE measurements cannot be reached. We assess the capability of the (non-dedicated) mission Swarm for mass variation detection in a real-case environment (opposed to simulation studies). For this purpose, we "approximate" the Swarm scenario by the GRACE+CHAMP and GRACE+GOCE constellations. In a first step, kinematic orbits of the individual satellites are derived from GNSS observations. From these orbits, we compute monthly combined GRACE+CHAMP and GRACE+GOCE time-variable gravity fields; sophisticated techniques based on Kalman filtering are applied to reduce noise in the time series. Finally, we infer mass variation in selected areas from to gravity signal. These results are compared to the findings obtained from mass variation detection exploiting CSR-RL05 gravity fields; due to their superior quality (which is due to the fact that they are derived from inter-satellite GRACE measurements), the CSR-RL05 solutions serve as benchmark. Our quantitative assessment shows the potential and limitations of what can be expected from Swarm with regard to surface mass variation monitoring.

Firn Thickness Changes (1982-2015) Driven by SMB from MERRA-2, RACMO2.3, ERA-Int and AVHRR Surface Temperature and the Impacts to Greenland Ice Sheet Mass Balance

NASA Astrophysics Data System (ADS)

Li, J.; Medley, B.; Neumann, T.; Smith, B. E.; Luthcke, S. B.; Zwally, H. J.

2016-12-01

Surface mass balance (SMB) data are essential in the derivation of ice sheet mass balance. This is because ice sheet mass change consists of short-term and long-term variations. The short-term variations are directly given by the SMB data. For altimetry based ice sheet mass balance studies, these short-term mass changes are converted to firn thickness changes by using a firn densification-elevation model, and then the variations are subtracted from the altimetry measurements to give the long-term ice thickness changes that are associated with the density of ice. So far various SMB data sets such as ERA-Interim, RACMO and MERRA are available and some have been widely used in large number of ice sheet mass balance studies. However theses data sets exhibit the clear discrepancies in both random and systematic manner. In this study, we use our time dependent firn densification- elevation model, driven by the SMB data from MERRA-2, RACMO2.3 and ERA-Int for the period of 1982-2015 and the temperature variations from AVHRR for the same period to examine the corresponding firn thickness variations and the impacts to the mass changes over the Greenland ice sheet. The model was initialized with the1980's climate. Our results show that the relative smaller (centimeter level) differences in the firn thickness driven by the different data set occur at the early stage (1980's) of the model run. As the time progressing, the discrepancies between the SMB data sets accumulate, and the corresponding firn thickness differences quickly become larger with the value > 2m at the end of the period. Although the overall rates for the whole period driven by each of the three data sets are small ranging -0.2 - 0.2 cm a-1 (-3.0-2.7 Gt a-1), the decadal rates can vary greatly with magnitude > 3 cm a-1 and the impact to the Greenland mass change exceeds 30 Gt a-1.

MBE growth of VCSELs for high volume applications

NASA Astrophysics Data System (ADS)

Jäger, Roland; Riedl, Michael C.

2011-05-01

Mass market applications like laser computer mouse or optical data transmission based on vertical-cavity surface-emitting laser (VCSEL) chips need a high over all yield including epitaxy, processing, dicing, mounting and testing. One yield limitation for VCSEL structures is the emission wavelength variation of the substrate surface area leading to the fraction on laser chips which are below or above the specification limits. For most 850 nm VCSEL products a resonator wavelength variation of ±2 nm is common. This represents an average resonator thickness variation of much less than 1% which is quite challenging to be fulfilled on the entire processed wafer surface area. A high over all yield is demonstrated on MBE grown VCSEL structures.

Spatial and temporal variations of aerosols around Beijing in summer 2006: 2. Local and column aerosol optical properties

NASA Astrophysics Data System (ADS)

Matsui, H.; Koike, M.; Kondo, Y.; Takegawa, N.; Fast, J. D.; PöSchl, U.; Garland, R. M.; Andreae, M. O.; Wiedensohler, A.; Sugimoto, N.; Zhu, T.

2010-11-01

Model calculations were conducted using the Weather Research and Forecasting model coupled with chemistry (WRF-chem) for the region around Beijing, China, in the summer of 2006, when the CAREBeijing-2006 intensive campaign was conducted. In this paper, we interpret aerosol optical properties in terms of aerosol mass concentrations and their chemical compositions by linking model calculations with measurements. The model calculations generally captured the observed variability of various surface and column aerosol optical parameters in and around Beijing. At the surface, the spatial and temporal variations of aerosol absorption and scattering coefficients corresponded well to those of elemental carbon and sulfate mass concentrations, respectively, and were controlled by local-scale (<100 km and <24 hours) and regional-scale (<500 km and <3 days) emissions, respectively. The contribution of secondary aerosols and their water uptake increased with altitude within the planetary boundary layer. This variation led to a considerable increase in column aerosol optical depth and was responsible for the differences in regional and temporal variations between surface and column aerosol optical properties around Beijing. These processes are expected to be common in other megacity regions as well. Model calculations, however, underestimated or overestimated the absolute levels of aerosol optical properties in and around Beijing by up to 60%. Sensitivity studies showed that these discrepancies were mostly due to the uncertainties in aerosol mixing state and aerosol density (affecting mass extinction efficiency) in the model calculations. Good agreement with measurements is achieved when these aerosol properties are accurately predicted or assumed; however, significant bias can result when these properties are inadequately treated, even if total aerosol mass concentrations are reproduced well in the model calculations.

Geographic variation in left ventricular mass and mass index: a systematic review.

PubMed

Poppe, K K; Bachmann, M Edgerton; Triggs, C M; Doughty, R N; Whalley, G A

2012-07-01

Left ventricular (LV) hypertrophy, defined as an abnormal increase in LV mass (LVM), is an important prognostic indicator and therapeutic target. LVM is often divided by body surface area to derive indexed mass; however, this does not correctly identify pathological LV hypertrophy in all people, especially when body composition is altered, or in different ethnic groups. We evaluated published ranges of echocardiographic LVM in healthy adult populations from different countries, excluding control groups, and compared them with the American Society of Echocardiography reference ranges. A total of 33 studies met the inclusion criteria. In men and women, there was wide variation in the ranges of LVM with a tendency for the upper limit to increase geographically westward; this variation remained for indexed mass. Several ranges fell outside the upper reference limits: in men, 13 of the mass ranges and 16 of indexed mass; and in women, 8 mass and 16 indexed mass. This review has shown that current guidelines may need revision as some published series suggest that greater LV mass should be considered normal. This may be explained by ethnic differences and supports the need for widely applicable and ethnically diverse reference ranges to be established.

Connectivity between surface and deep waters determines prokaryotic diversity in the North Atlantic Deep Water

PubMed Central

Frank, Alexander H.; Garcia, Juan A. L.; Herndl, Gerhard J.

2016-01-01

Summary To decipher the influence of depth stratification and surface provincialism on the dark ocean prokaryotic community composition, we sampled the major deep‐water masses in the eastern North Atlantic covering three biogeographic provinces. Their diversity was evaluated using ordination and canonical analysis of 454 pyrotag sequences. Variance partitioning suggested that 16% of the variation in the bacterial community composition was based on depth stratification while 9% of the variation was due to geographic location. General linear mixed effect models showed that the community of the subsurface waters was connected to the dark ocean prokaryotic communities in different biogeographic provinces. Cluster analysis indicated that some prokaryotic taxa are specific to distinct regions in bathypelagic water masses. Taken together, our data suggest that the dark ocean prokaryotic community composition of the eastern North Atlantic is primed by the formation and the horizontal transport of water masses. PMID:26914787

Spatial and temporal variations of aerosols around Beijing in summer 2006: 2. Local and column aerosol optical properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsui, Hitoshi; Koike, Makoto; Kondo, Yutaka

Weather Research and Forecasting (WRF)-chem model calculations were conducted to study aerosol optical properties around Beijing, China, during the Campaign of Air Quality Research in Beijing and Surrounding Region 2006 (CAREBeijing-2006) period. In this paper, we interpret aerosol optical properties in terms of aerosol mass concentrations and their chemical compositions by linking model calculations with measurements. In general, model calculations reproduced observed features of spatial and temporal variations of various surface and column aerosol optical parameters in and around Beijing. Spatial and temporal variations of aerosol absorption, scattering, and extinction coefficient corresponded well to those of elemental carbon (primary aerosol),more » sulfate (secondary aerosol), and the total aerosol mass concentration, respectively. These results show that spatial and temporal variations of the absorption coefficient are controlled by local emissions (within 100 km around Beijing during the preceding 24 h), while those of the scattering coefficient are controlled by regional-scale emissions (within 500 km around Beijing during the preceding 3 days) under synoptic-scale meteorological conditions, as discussed in our previous study of aerosol mass concentration. Vertical profiles of aerosol extinction revealed that the contribution of secondary aerosols and their water uptake increased with altitude within the planetary boundary layer, leading to a considerable increase in column aerosol optical depth (AOD) around Beijing. These effects are the main factors causing differences in regional and temporal variations between particulate matter (PM) mass concentration at the surface and column AOD over a wide region in the northern part of the Great North China Plain.« less

Mass Redistribution in the Core and Time-varying Gravity at the Earth's Surface

NASA Technical Reports Server (NTRS)

Kuang, Wei-Jia; Chao, Benjamin F.; Fang, Ming

2003-01-01

The Earth's liquid outer core is in convection, as suggested by the existence of the geomagnetic field in much of the Earth's history. One consequence of the convection is the redistribution of mass resulting from relative motion among fluid parcels with slightly different densities. This time dependent mass redistribution inside the core produces a small perturbation on the gravity field of the Earth. With our numerical dynamo solutions, we find that the mass redistribution (and the resultant gravity field) symmetric about the equator is much stronger than that anti-symmetric about the equator. In particular, J(sub 2) component is the strongest. In addition, the gravity field variation increases with the Rayleigh number that measures the driving force for the geodynamo in the core. With reasonable scaling from the current dynamo solutions, we could expect that at the surface of the Earth, the J(sub 2) variation from the core is on the order of l0(exp -16)/year relative to the mean (i.e. spherically symmetric) gravity field of the Earth. The possible shielding effect due to core-mantle boundary pressure variation loading is likely much smaller and is therefore negligible. Our results suggest that time-varying gravity field perturbation due to core mass redistribution may be measured with modem space geodetic observations, which will result a new means of detecting dynamical processes in the Earth's deep interior.

Seasonal Mass Changes and Crustal Vertical Deformations Constrained by GPS and GRACE in Northeastern Tibet

PubMed Central

Pan, Yuanjin; Shen, Wen-Bin; Hwang, Cheinway; Liao, Chaoming; Zhang, Tengxu; Zhang, Guoqing

2016-01-01

Surface vertical deformation includes the Earth’s elastic response to mass loading on or near the surface. Continuous Global Positioning System (CGPS) stations record such deformations to estimate seasonal and secular mass changes. We used 41 CGPS stations to construct a time series of coordinate changes, which are decomposed by empirical orthogonal functions (EOFs), in northeastern Tibet. The first common mode shows clear seasonal changes, indicating seasonal surface mass re-distribution around northeastern Tibet. The GPS-derived result is then assessed in terms of the mass changes observed in northeastern Tibet. The GPS-derived common mode vertical change and the stacked Gravity Recovery and Climate Experiment (GRACE) mass change are consistent, suggesting that the seasonal surface mass variation is caused by changes in the hydrological, atmospheric and non-tidal ocean loads. The annual peak-to-peak surface mass changes derived from GPS and GRACE results show seasonal oscillations in mass loads, and the corresponding amplitudes are between 3 and 35 mm/year. There is an apparent gradually increasing gravity between 0.1 and 0.9 μGal/year in northeast Tibet. Crustal vertical deformation is determined after eliminating the surface load effects from GRACE, without considering Glacial Isostatic Adjustment (GIA) contribution. It reveals crustal uplift around northeastern Tibet from the corrected GPS vertical velocity. The unusual uplift of the Longmen Shan fault indicates tectonically sophisticated processes in northeastern Tibet. PMID:27490550

Time series of low-degree geopotential coefficients from SLR data: estimation of Earth's figure axis and LOD variations

NASA Astrophysics Data System (ADS)

Luceri, V.; Sciarretta, C.; Bianco, G.

2012-12-01

The redistribution of the mass within the earth system induces changes in the Earth's gravity field. In particular, the second-degree geopotential coefficients reflect the behaviour of the Earth's inertia tensor of order 2, describing the main mass variations of our planet impacting the EOPs. Thanks to the long record of accurate and continuous laser ranging observations to Lageos and other geodetic satellites, SLR is the only current space technique capable to monitor the long time variability of the Earth's gravity field with adequate accuracy. Time series of low-degree geopotential coefficients are estimated with our analysis of SLR data (spanning more than 25 years) from several geodetic satellites in order to detect trends and periodic variations related to tidal effects and atmospheric/oceanic mass variations. This study is focused on the variations of the second-degree Stokes coefficients related to the Earth's principal figure axis and oblateness: C21, S21 and C20. On the other hand, surface mass load variations induce excitations in the EOPs that are proportional to the same second-degree coefficients. The time series of direct estimates of low degree geopotential and those derived from the EOP excitation functions are compared and presented together with their time and frequency analysis.

The variation of polar firn subject to percolation - characterizing processes and glacier mass budget uncertainty using high-resolution instruments

NASA Astrophysics Data System (ADS)

Demuth, M. N.; Marshall, H.; Morris, E. M.; Burgess, D. O.; Gray, L.

2009-12-01

As the Earth's glaciers and ice sheets are subjected to the effects of recent and predicted warming, the distribution of their glaciological facies zones will alter. Percolation and wet snow facies zones will, in general, move upwards; encroaching upon, for some glacier configurations, regions of dry snow facies. Meltwater percolation and internal accumulation processes that characterize these highly variable facies may confound reliable estimates of surface mass budgets based on traditional point measurements alone. If the extents of these zones are indeed increasing, as has been documented through recent analysis of QuickScat data for the ice caps of the Canadian Arctic, then the certainty of glacier mass budget estimates using traditional techniques may be degraded to an as yet un-quantified degree. Indeed, the application of remote sensing, in particular that utilizing repeat altimetry to retrieve surface mass budget estimates, is also subject to the complexity of glacier facies from the standpoint of their near-surface stratigraphy, density variations and rates of compaction. We first review the problem of measuring glacier mass budgets in the context of nested scales of variability, where auto-correlation structure varies with the scale of observation. We then consider specifically firn subject to percolation and describe the application of high-resolution instruments to characterize variability at the field-scale. The data collected include measurements of micro-topography, snow hardness, and snow density and texture; retrieved using airborne scanning lidar, a snow micro-penetrometer, neutron probe and ground-penetrating radars. The analysis suggests corresponding scales of correlation as it concerns the influence of antecedent conditions (surface roughness and hardness, and stratigraphic variability) and post-depositional processes (percolation and refreezing of surface melt water).

Recovery of surface mass redistribution from a joint inversion of GPS and GRACE data - A methodology and results from the Australian and other continents

NASA Astrophysics Data System (ADS)

Han, S. C.; Tangdamrongsub, N.; Razeghi, S. M.

2017-12-01

We present a methodology to invert a regional set of vertical displacement data from Global Positioning System (GPS) to determine surface mass redistribution. It is assumed that GPS deformation is a result of the Earth's elastic response to the surface mass load of hydrology, atmosphere, and ocean. The identical assumption is made when global geopotential change data from Gravity Recovery And Climate Experiment (GRACE) are used to determine surface mass changes. We developed an algorithm to estimate the spectral information of displacements from "regional" GPS data through regional spherical (Slepian) basis functions and apply the load Love numbers to estimate the mass load. We rigorously examine all systematic errors caused by various truncations (spherical harmonic series and Slepian series) and the smoothing constraint applied to the GPS-only inversion. We demonstrate the technique by processing 16 years of daily vertical motions determined from 114 GPS stations in Australia. The GPS inverted surface mass changes are validated against GRACE data, atmosphere and ocean models, and a land surface model. Seasonal and inter-annual terrestrial mass variations from GPS are in good agreement with GRACE data and the water storage models. The GPS recovery compares better with the water storage model around the smaller coastal basins of Australia than two different GRACE solutions. The sub-monthly mass changes from GPS provide meaningful results agreeing with atmospheric mass changes in central Australia. Finally, we integrate GPS data from different continents with GRACE in the least-square normal equations and solve for the global surface mass changes by jointly inverting GPS and GRACE data. We present the results of surface mass changes from the GPS-only inversion and from the joint GPS-GRACE inversion.

Long-period variations in the optical and microphysical parameters of surface aerosol in a Moscow suburb

NASA Astrophysics Data System (ADS)

Isakov, A. A.; Gruzdev, A. N.

2009-04-01

The mass concentration M of surface submicron aerosol and its condensation activity χ were measured at the Zvenigorod Scientific Station of the A.M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, in 2001-2006. Variations in these quantities on scales of several days to several months are analyzed. It is shown that the occurrence of dense and superdense hazes over central Russia became more frequent during these years. This resulted in a change in the character of the seasonal dependence of the mass aerosol concentration M: ordered oscillations whose amplitude increases from year to year appeared in the seasonal cycle of M. Due to more frequent cases of dense and superdense hazes in 2002-2006, a significant monotonic increase is observed in the annual means of M. The annual mean of M increased more than twofold in 2005 (56 μm/m3) compared to 2001 (23 μm/m3). The time regimes of M and χ are characterized by variations with periods in the vicinity of 10, 20, and 40-50 days, as well as variations with longer periods within 70-100 days. In addition, the variability of mass concentration is of a strongly intermittent character. A cross-spectral analysis has shown that, on the whole, variations in M are coherent with those in χ. If the parameters M and χ vary on the same time scales, then, as a rule, variations in M lag behind variations in χ by several days. To understand the relationship between the parameters M and χ, special investigations, including studies of aerosol composition, are needed.

Seasonal Variations of the Earth's Gravitational Field: An Analysis of Atmospheric Pressure, Ocean Tidal, and Surface Water Excitation

NASA Technical Reports Server (NTRS)

Dong, D,; Gross, R.S.; Dickey, J.

1996-01-01

Monthly mean gravitational field parameters (denoted here as C(sub even)) that represent linear combinations of the primarily even degree zonal spherical harmonic coefficients of the Earth's gravitational field have been recovered using LAGEOS I data and are compared with those derived from gridded global surface pressure data of the National meteorological center (NMC) spanning 1983-1992. The effect of equilibrium ocean tides and surface water variations are also considered. Atmospheric pressure and surface water fluctuations are shown to be the dominant cause of observed annual C(sub even) variations. Closure with observations is seen at the 1sigma level when atmospheric pressure, ocean tide and surface water effects are include. Equilibrium ocean tides are shown to be the main source of excitation at the semiannual period with closure at the 1sigma level seen when both atmospheric pressure and ocean tide effects are included. The inverted barometer (IB) case is shown to give the best agreement with the observation series. The potential of the observed C(sub even) variations for monitoring mass variations in the polar regions of the Earth and the effect of the land-ocean mask in the IB calculation are discussed.

Caribbean coral growth influenced by anthropogenic aerosol emissions

NASA Astrophysics Data System (ADS)

Kwiatkowski, Lester; Cox, Peter M.; Economou, Theo; Halloran, Paul R.; Mumby, Peter J.; Booth, Ben B. B.; Carilli, Jessica; Guzman, Hector M.

2013-05-01

Coral growth rates are highly dependent on environmental variables such as sea surface temperature and solar irradiance. Multi-decadal variability in coral growth rates has been documented throughout the Caribbean over the past 150-200 years, and linked to variations in Atlantic sea surface temperatures. Multi-decadal variability in sea surface temperatures in the North Atlantic, in turn, has been linked to volcanic and anthropogenic aerosol forcing. Here, we examine the drivers of changes in coral growth rates in the western Caribbean between 1880 and 2000, using previously published coral growth chronologies from two sites in the region, and a numerical model. Changes in coral growth rates over this period coincided with variations in sea surface temperature and incoming short-wave radiation. Our model simulations show that variations in the concentration of anthropogenic aerosols caused variations in sea surface temperature and incoming radiation in the second half of the twentieth century. Before this, variations in volcanic aerosols may have played a more important role. With the exception of extreme mass bleaching events, we suggest that neither climate change from greenhouse-gas emissions nor ocean acidification is necessarily the driver of multi-decadal variations in growth rates at some Caribbean locations. Rather, the cause may be regional climate change due to volcanic and anthropogenic aerosol emissions.

Surface area-volume ratios in insects.

PubMed

Kühsel, Sara; Brückner, Adrian; Schmelzle, Sebastian; Heethoff, Michael; Blüthgen, Nico

2017-10-01

Body mass, volume and surface area are important for many aspects of the physiology and performance of species. Whereas body mass scaling received a lot of attention in the literature, surface areas of animals have not been measured explicitly in this context. We quantified surface area-volume (SA/V) ratios for the first time using 3D surface models based on a structured light scanning method for 126 species of pollinating insects from 4 orders (Diptera, Hymenoptera, Lepidoptera, and Coleoptera). Water loss of 67 species was measured gravimetrically at very dry conditions for 2 h at 15 and 30 °C to demonstrate the applicability of the new 3D surface measurements and relevance for predicting the performance of insects. Quantified SA/V ratios significantly explained the variation in water loss across species, both directly or after accounting for isometric scaling (residuals of the SA/V ∼ mass 2/3 relationship). Small insects with a proportionally larger surface area had the highest water loss rates. Surface scans of insects to quantify allometric SA/V ratios thus provide a promising method to predict physiological responses, improving the potential of body mass isometry alone that assume geometric similarity. © 2016 Institute of Zoology, Chinese Academy of Sciences.

Connectivity between surface and deep waters determines prokaryotic diversity in the North Atlantic Deep Water.

PubMed

Frank, Alexander H; Garcia, Juan A L; Herndl, Gerhard J; Reinthaler, Thomas

2016-06-01

To decipher the influence of depth stratification and surface provincialism on the dark ocean prokaryotic community composition, we sampled the major deep-water masses in the eastern North Atlantic covering three biogeographic provinces. Their diversity was evaluated using ordination and canonical analysis of 454 pyrotag sequences. Variance partitioning suggested that 16% of the variation in the bacterial community composition was based on depth stratification while 9% of the variation was due to geographic location. General linear mixed effect models showed that the community of the subsurface waters was connected to the dark ocean prokaryotic communities in different biogeographic provinces. Cluster analysis indicated that some prokaryotic taxa are specific to distinct regions in bathypelagic water masses. Taken together, our data suggest that the dark ocean prokaryotic community composition of the eastern North Atlantic is primed by the formation and the horizontal transport of water masses. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.

Background aerosol over the Himalayas and Tibetan Plateau: observed characteristics of aerosol mass loading

NASA Astrophysics Data System (ADS)

Liu, B.; Cong, Z.; Wang, Y.; Xin, J.; Wan, X.; Pan, Y.; Liu, Z.; Wang, Y.; Zhang, G.; Kang, S.

2016-12-01

To investigate the atmospheric aerosols of the Himalayas and Tibetan Plateau (HTP), an observation network was established within the region's various ecosystems, including at Ngari, Qomolangma (QOMS), Nam Co, and SouthEastern Tibetan (SET) stations. In this paper we illustrate aerosol mass loadings by integrating in situ measurements with satellite and ground-based remote sensing datasets for the 2011-2013 period, on both local and large scales. Mass concentrations of these surface atmospheric aerosols were relatively low and varied with land cover, showing a general tendency of Ngari and QOMS (barren sites) > Nam Co (grassland site) > SET (forest site). Bimodal mass distributions of size-segregated particles were found at all sites, with a relatively small peak in accumulation mode and a more notable peak in coarse mode. Diurnal variations in fine aerosol masses generally displayed a bi-peak pattern at the QOMS, Nam Co and SET stations and a single-peak pattern at the Ngari station, controlled by the effects of local geomorphology, mountain-valley breeze circulation and aerosol emissions. Combining surface aerosols data and atmospheric-column aerosol optical properties, the TSP mass and aerosol optical depth (AOD) of the Multi-angle Imaging Spectroradiometer (MISR) generally decreased as land cover changed from barren to forest, in inverse relation to the PM2.5 ratios. The seasonality of aerosol mass parameters was land-cover dependent. Over forest and grassland areas, TSP mass, PM2.5 mass, MISR-AOD and fine-mode AOD were higher in spring and summer, followed by relatively lower values in autumn and winter. At the barren site (the QOMS station), there were inconsistent seasonal variations between surface TSP mass (PM2.5 mass) and atmospheric column AOD (fine-mode AOD). Our findings implicate that, HTP aerosol masses (especially their reginal characteristics and fine particle emissions) need to be treated sensitively in relation to assessments of their climatic effect

Temporal variability of the Antarctic Ice sheet observed from space-based geodesy

NASA Astrophysics Data System (ADS)

Memin, A.; King, M. A.; Boy, J. P.; Remy, F.

2017-12-01

Quantifying the Antarctic Ice Sheet (AIS) mass balance still remains challenging as several processes compete to differing degrees at the basin scale with regional variations, leading to multiple mass redistribution patterns. For instance, analysis of linear trends in surface-height variations from 1992-2003 and 2002-2006 shows that the AIS is subject to decimetric scale variability over periods of a few years. Every year, snowfalls in Antarctica represent the equivalent of 6 mm of the mean sea level. Therefore, any fluctuation in precipitation can lead to changes in sea level. Besides, over the last decade, several major glaciers have been thinning at an accelerating rate. Understanding the processes that interact on the ice sheet is therefore important to precisely determine the response of the ice sheet to a rapid changing climate and estimate its contribution to sea level changes. We estimate seasonal and interannual changes of the AIS between January 2003 and October 2010 and to the end of 2016 from a combined analysis of surface-elevation and surface-mass changes derived from Envisat data and GRACE solutions, and from GRACE solutions only, respectively. While we obtain a good correlation for the interannual signal between the two techniques, important differences (in amplitude, phase, and spatial pattern) are obtained for the seasonal signal. We investigate these discrepancies by comparing the crustal motion observed by GPS and those predicted using monthly surface mass balance derived from the regional atmospheric climate model RACMO.

Arctic Ocean Circulation Patterns Revealed by GRACE

NASA Astrophysics Data System (ADS)

Peralta-Ferriz, Cecilia; Morison, James H.; Wallace, John M.; Bonin, Jennifer A.; Zhang, Jinlun

2013-04-01

EOF analysis of non-seasonal, month-to-month variations in GRACE derived Arctic Ocean bottom pressure (OBP) yield three dominant modes. The first mode is a wintertime basin wide variation in mass associated with high atmospheric pressure (SLP) over Scandinavia. The second mode is a shift of mass from the central Arctic Ocean to the Siberian shelves due to low pressure over the basins, associated with the strength of the Arctic Oscillation. The third mode is a shift in mass between the Eastern and Western Siberian shelves, related to strength of the Beaufort High mainly in summer, and to eastward alongshore winds on the Barents Sea in winter. The PIOMAS and ECCO2 modeled OBP are consistent with the form of these modes and provide context in terms of variations in sea surface height. The models are used to investigate the ocean dynamics associated with each mode of OBP variability.

Geometrical and gravimetrical observations of the Aral Sea and its tributaries along with hydrological models

NASA Astrophysics Data System (ADS)

Singh, A.; Seitz, F.; Schwatke, C.; Güntner, A.

2012-04-01

Satellite altimetry is capable of measuring surface water level changes of large water bodies. This is especially interesting for regions where in-situ gauges are sparse or not available. Temporal variations of coastline and horizontal extent of a water body can be derived from optical remote sensing data. A joint analysis of both data types together with a digital elevation model allows for the estimation of water volume changes. Related variations of water mass map into the observations of the satellite gravity field mission GRACE. In this presentation, we demonstrate the application of heterogeneuous remote sensing methods for studying chages of water volume and mass of the Aral Sea and compare the results with respect to their consistency. Our analysis covers the period 2002-2011. In particular we deal with data from multi-mission radar and laser satellite altimetry that are analyzed in combination with coastlines from Landsat images. The resultant vertical and horizontal variations of the lake surface are geometrically intersected with the bathymetry of the Aral Sea in order to compute volumetric changes. These are transformed into variations of water mass that are subsequently compared with storage changes derived from GRACE satellite gravimetry. Hence we obtain a comprehensive picture of the hydrological changes in the region. Observations from all datasets correspond quite well with each other with respect to their temporal development. However, geometrically determined volume changes and mass changes observed by GRACE agree less well during years of heavy water inflow in to the Aral Sea from its southern tributary 'Amu Darya' since the GRACE signals are contaminated by the large mass of water stored in the river delta and prearalie region On the other hand, GRACE observations of the river basins of Syr Darya and Amu Dayra correspond very well with hydrological models and mass changes computed from the balance of precipitation, evaporation and runoff determined from the atmospheric-terrestrial water balance.

Dynamic surface tension measurements of ionic surfactants using maximum bubble pressure tensiometry

NASA Astrophysics Data System (ADS)

Ortiz, Camilla U.; Moreno, Norman; Sharma, Vivek

Dynamic surface tension refers to the time dependent variation in surface tension, and is intimately linked with the rate of mass transfer of a surfactant from liquid sub-phase to the interface. The diffusion- or adsorption-limited kinetics of mass transfer to interfaces is said to impact the so-called foamability and the Gibbs-Marangoni elasticity of surfaces. Dynamic surface tension measurements carried out with conventional methods like pendant drop analysis, Wilhelmy plate, etc. are limited in their temporal resolution (>50 ms). In this study, we describe design and application of maximum bubble pressure tensiometry for the measurement of dynamic surface tension effects at extremely short (1-50 ms) timescales. Using experiments and theory, we discuss the overall adsorption kinetics of charged surfactants, paying special attention to the influence of added salt on dynamic surface tension.

Surface ozone at Nam Co in the inland Tibetan Plateau: variation, synthesis comparison and regional representativeness

NASA Astrophysics Data System (ADS)

Yin, Xiufeng; Kang, Shichang; de Foy, Benjamin; Cong, Zhiyuan; Luo, Jiali; Zhang, Lang; Ma, Yaoming; Zhang, Guoshuai; Rupakheti, Dipesh; Zhang, Qianggong

2017-09-01

Ozone is an important pollutant and greenhouse gas, and tropospheric ozone variations are generally associated with both natural and anthropogenic processes. As one of the most pristine and inaccessible regions in the world, the Tibetan Plateau has been considered as an ideal region for studying processes of the background atmosphere. Due to the vast area of the Tibetan Plateau, sites in the southern, northern and central regions exhibit different patterns of variation in surface ozone. Here, we present continuous measurements of surface ozone mixing ratios at Nam Co Station over a period of ˜ 5 years (January 2011 to October 2015), which is a background site in the inland Tibetan Plateau. An average surface ozone mixing ratio of 47.6 ± 11.6 ppb (mean ± standard deviation) was recorded, and a large annual cycle was observed with maximum ozone mixing ratios in the spring and minimum ratios during the winter. The diurnal cycle is characterized by a minimum in the early morning and a maximum in the late afternoon. Nam Co Station represents a background region where surface ozone receives negligible local anthropogenic emissions inputs, and the anthropogenic contribution from South Asia in spring and China in summer may affect Nam Co Station occasionally. Surface ozone at Nam Co Station is mainly dominated by natural processes involving photochemical reactions, vertical mixing and downward transport of stratospheric air mass. Model results indicate that the study site is affected differently by the surrounding areas in different seasons: air masses from the southern Tibetan Plateau contribute to the high ozone levels in the spring, and enhanced ozone levels in the summer are associated with air masses from the northern Tibetan Plateau. By comparing measurements at Nam Co Station with those from other sites on the Tibetan Plateau, we aim to expand the understanding of ozone cycles and transport processes over the Tibetan Plateau. This work may provide a reference for future model simulations.

Assessment and application of a snowblow modelling approach for identifying enhanced snow accumulation in areas of former glaciation

NASA Astrophysics Data System (ADS)

Mills, Stephanie; Smith, Michael; Le Brocq, Anne; Ardakova, Ekaterina; Hillier, John; Boston, Clare

2016-04-01

The redistribution of snow by wind can play an important role in providing additional mass to the surface of glaciers and can, therefore, have an impact on the glacier's surface mass balance. In areas of marginal glaciation, this local topo-climatic effect may be prove crucial for the initiation and survival of glaciers, whilst it can also increase heterogeneity in the distribution of snow on ice caps and ice sheets. We present a newly developed snowblow model which calculates spatial variations in relative snow accumulation that result from variations in topography. We apply this model to areas of former marginal glaciation in the Brecon Beacons, Wales and an area of former plateau icefield glaciation in the Monadhliath, Scotland. We can then determine whether redistribution by snow can help explain variations in the estimated equilibrium line altitudes (ELAs) of these former glaciers. Specifically, we compare the areas where snow is modelled as accumulating, to the reconstructed glacier surface, which is based on mapped moraines believed to be of Younger Dryas age. The model is applied to 30 m resolution DEMs and potential snow accumulation is simulated from different wind directions in order to determine the most likely contributing sector. Total snow accumulation in sub-set areas is then calculated and compared to the reconstructed glacier area. The results suggest that areas with larger amounts of snow accumulation often correspond with those where the ELA is lower than surrounding glaciers and vice versa, in both the marginal and icefield setting, suggesting that the role of snowblow in supplying additional mass to the surface of glaciers is significant.

Temporal variations in supraglacial debris distribution on Baltoro Glacier, Karakoram between 2001 and 2012

NASA Astrophysics Data System (ADS)

Gibson, Morgan J.; Glasser, Neil F.; Quincey, Duncan J.; Mayer, Christoph; Rowan, Ann V.; Irvine-Fynn, Tristram D. L.

2017-10-01

Distribution of supraglacial debris in a glacier system varies spatially and temporally due to differing rates of debris input, transport and deposition. Supraglacial debris distribution governs the thickness of a supraglacial debris layer, an important control on the amount of ablation that occurs under such a debris layer. Characterising supraglacial debris layer thickness on a glacier is therefore key to calculating ablation across a glacier surface. The spatial pattern of debris thickness on Baltoro Glacier has previously been calculated for one discrete point in time (2004) using satellite thermal data and an empirically based relationship between supraglacial debris layer thickness and debris surface temperature identified in the field. Here, the same empirically based relationship was applied to two further datasets (2001, 2012) to calculate debris layer thickness across Baltoro Glacier for three discrete points over an 11-year period (2001, 2004, 2012). Surface velocity and sediment flux were also calculated, as well as debris thickness change between periods. Using these outputs, alongside geomorphological maps of Baltoro Glacier produced for 2001, 2004 and 2012, spatiotemporal changes in debris distribution for a sub-decadal timescale were investigated. Sediment flux remained constant throughout the 11-year period. The greatest changes in debris thickness occurred along medial moraines, the locations of mass movement deposition and areas of interaction between tributary glaciers and the main glacier tongue. The study confirms the occurrence of spatiotemporal changes in supraglacial debris layer thickness on sub-decadal timescales, independent of variation in surface velocity. Instead, variation in rates of debris distribution are primarily attributed to frequency and magnitude of mass movement events over decadal timescales, with climate, regional uplift and erosion rates expected to control debris inputs over centurial to millennial timescales. Inclusion of such spatiotemporal variations in debris thickness in distributed surface energy balance models would increase the accuracy of calculated ablation, leading to a more accurate simulation of glacier mass balance through time, and greater precision in quantification of the response of debris-covered glaciers to climatic change.

Field-calibrated model of melt, refreezing, and runoff for polar ice caps: Application to Devon Ice Cap

NASA Astrophysics Data System (ADS)

Morris, Richard M.; Mair, Douglas W. F.; Nienow, Peter W.; Bell, Christina; Burgess, David O.; Wright, Andrew P.

2014-09-01

Understanding the controls on the amount of surface meltwater that refreezes, rather than becoming runoff, over polar ice masses is necessary for modeling their surface mass balance and ultimately for predicting their future contributions to global sea level change. We present a modified version of a physically based model that includes an energy balance routine and explicit calculation of near-surface meltwater refreezing capacity, to simulate the evolution of near-surface density and temperature profiles across Devon Ice Cap in Arctic Canada. Uniquely, our model is initiated and calibrated using high spatial resolution measurements of snow and firn densities across almost the entire elevation range of the ice cap for the summer of 2004 and subsequently validated with the same type of measurements obtained during the very different meteorological conditions of summer 2006. The model captures the spatial variability across the transect in bulk snowpack properties although it slightly underestimates the flow of meltwater into the firn of previous years. The percentage of meltwater that becomes runoff is similar in both years; however, the spatial pattern of this melt-runoff relationship is different in the 2 years. The model is found to be insensitive to variation in the depth of impermeable layers within the firn but is very sensitive to variation in air temperature, since the refreezing capacity of firn decreases with increasing temperature. We highlight that the sensitivity of the ice cap's surface mass balance to air temperature is itself dependent on air temperature.

Precision Determination of Adsorption Layers on Stainless Steel Mass Standards by Mass Comparison and Ellipsometry: Part I: Adsorption Isotherms in Air

NASA Astrophysics Data System (ADS)

Schwartz, R.

1994-01-01

Adsorption layers on stainless steel mass standards (OIML classes E1 and E2) have been determined directly and precisely by the optical method of ellipsometry as a function of relative humidity in the range 0,03 <= h <= 0,77, the relevant influencing factors being surface cleanliness, roughness, steel composition and ambient temperature. Under the same environmental conditions, two pairs of 1 kg artefacts, having geometrical surfaces differing in area by about δ A = 390 cm2, but the same material properties and surface finish as the mass standards, have been compared on a 1 kg mass comparator. The two independent measuring techniques yield strongly correlated results, the standard uncertainties of the measured surface coverings being = 0,7 μg cm-2 show sorption-induced mass variations which are greater by about a factor of 2,5 relative to the clean surfaces.

Satellite Laser Ranging operations

NASA Technical Reports Server (NTRS)

Pearlman, Michael R.

1994-01-01

Satellite Laser Ranging (SLR) is currently providing precision orbit determination for measurements of: 1) Ocean surface topography from satellite borne radar altimetry, 2) Spatial and temporal variations of the gravity field, 3) Earth and ocean tides, 4) Plate tectonic and regional deformation, 5) Post-glacial uplift and subsidence, 6) Variations in the Earth's center-of-mass, and 7) Variations in Earth rotation. SLR also supports specialized programs in time transfer and classical geodetic positioning, and will soon provide precision ranging to support experiments in relativity.

An analytic treatment of gravitational microlensing for sources of finite size at large optical depths

NASA Technical Reports Server (NTRS)

Deguchi, Shuji; Watson, William D.

1988-01-01

Statistical methods are developed for gravitational lensing in order to obtain analytic expressions for the average surface brightness that include the effects of microlensing by stellar (or other compact) masses within the lensing galaxy. The primary advance here is in utilizing a Markoff technique to obtain expressions that are valid for sources of finite size when the surface density of mass in the lensing galaxy is large. The finite size of the source is probably the key consideration for the occurrence of microlensing by individual stars. For the intensity from a particular location, the parameter which governs the importance of microlensing is determined. Statistical methods are also formulated to assess the time variation of the surface brightness due to the random motion of the masses that cause the microlensing.

Variation in foliar respiration and wood CO2 efflux rates among species and canopy layers in a wet tropical forest.

PubMed

Asao, Shinichi; Bedoya-Arrieta, Ricardo; Ryan, Michael G

2015-02-01

As tropical forests respond to environmental change, autotrophic respiration may consume a greater proportion of carbon fixed in photosynthesis at the expense of growth, potentially turning the forests into a carbon source. Predicting such a response requires that we measure and place autotrophic respiration in a complete carbon budget, but extrapolating measurements of autotrophic respiration from chambers to ecosystem remains a challenge. High plant species diversity and complex canopy structure may cause respiration rates to vary and measurements that do not account for this complexity may introduce bias in extrapolation more detrimental than uncertainty. Using experimental plantations of four native tree species with two canopy layers, we examined whether species and canopy layers vary in foliar respiration and wood CO2 efflux and whether the variation relates to commonly used scalars of mass, nitrogen (N), photosynthetic capacity and wood size. Foliar respiration rate varied threefold between canopy layers, ∼0.74 μmol m(-2) s(-1) in the overstory and ∼0.25 μmol m(-2) s(-1) in the understory, but little among species. Leaf mass per area, N and photosynthetic capacity explained some of the variation, but height explained more. Chamber measurements of foliar respiration thus can be extrapolated to the canopy with rates and leaf area specific to each canopy layer or height class. If area-based rates are sampled across canopy layers, the area-based rate may be regressed against leaf mass per area to derive the slope (per mass rate) to extrapolate to the canopy using the total leaf mass. Wood CO2 efflux varied 1.0-1.6 μmol m(-2) s(-1) for overstory trees and 0.6-0.9 μmol m(-2) s(-1) for understory species. The variation in wood CO2 efflux rate was mostly related to wood size, and little to species, canopy layer or height. Mean wood CO2 efflux rate per surface area, derived by regressing CO2 efflux per mass against the ratio of surface area to mass, can be extrapolated to the stand using total wood surface area. The temperature response of foliar respiration was similar for three of the four species, and wood CO2 efflux was similar between wet and dry seasons. For these species and this forest, vertical sampling may yield more accurate estimates than would temporal sampling. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

A Varifold Approach to Surface Approximation

NASA Astrophysics Data System (ADS)

Buet, Blanche; Leonardi, Gian Paolo; Masnou, Simon

2017-11-01

We show that the theory of varifolds can be suitably enriched to open the way to applications in the field of discrete and computational geometry. Using appropriate regularizations of the mass and of the first variation of a varifold we introduce the notion of approximate mean curvature and show various convergence results that hold, in particular, for sequences of discrete varifolds associated with point clouds or pixel/voxel-type discretizations of d-surfaces in the Euclidean n-space, without restrictions on dimension and codimension. The variational nature of the approach also allows us to consider surfaces with singularities, and in that case the approximate mean curvature is consistent with the generalized mean curvature of the limit surface. A series of numerical tests are provided in order to illustrate the effectiveness and generality of the method.

Isotopic Analysis and Evolved Gases

NASA Technical Reports Server (NTRS)

Swindle, Timothy D.; Boynton, William V.; Chutjian, Ara; Hoffman, John H.; Jordan, Jim L.; Kargel, Jeffrey S.; McEntire, Richard W.; Nyquist, Larry

1996-01-01

Precise measurements of the chemical, elemental, and isotopic composition of planetary surface material and gases, and observed variations in these compositions, can contribute significantly to our knowledge of the source(s), ages, and evolution of solar system materials. The analyses discussed in this paper are mostly made by mass spectrometers or some other type of mass analyzer, and address three broad areas of interest: (1) atmospheric composition - isotopic, elemental, and molecular, (2) gases evolved from solids, and (3) solids. Current isotopic data on nine elements, mostly from in situ analysis, but also from meteorites and telescopic observations are summarized. Potential instruments for isotopic analysis of lunar, Martian, Venusian, Mercury, and Pluto surfaces, along with asteroid, cometary and icy satellites, surfaces are discussed.

One hundred years of Arctic ice cover variations as simulated by a one-dimensional, ice-ocean model

NASA Astrophysics Data System (ADS)

Hakkinen, S.; Mellor, G. L.

1990-09-01

A one-dimensional ice-ocean model consisting of a second moment, turbulent closure, mixed layer model and a three-layer snow-ice model has been applied to the simulation of Arctic ice mass and mixed layer properties. The results for the climatological seasonal cycle are discussed first and include the salt and heat balance in the upper ocean. The coupled model is then applied to the period 1880-1985, using the surface air temperature fluctuations from Hansen et al. (1983) and from Wigley et al. (1981). The analysis of the simulated large variations of the Arctic ice mass during this period (with similar changes in the mixed layer salinity) shows that the variability in the summer melt determines to a high degree the variability in the average ice thickness. The annual oceanic heat flux from the deep ocean and the maximum freezing rate and associated nearly constant minimum surface salinity flux did not vary significantly interannually. This also implies that the oceanic influence on the Arctic ice mass is minimal for the range of atmospheric variability tested.

Optimization of Energy Consumption and Mass Transfer Parameters in a Surface Aeration Vessel.

PubMed

Mohammadpour, A; AkhavanBehabadi, M A; Ebrahimzadeh, M; Raisee, M; MajdiNasab, A R; Nosrati, M; Mousavi, S M

2016-04-01

This paper reports tests on a lab-scale surface aeration vessel was equipped with a Rushton turbine to examine its performance in terms of standard aeration efficiency (SAE), mixing time, and void fraction characteristics. These characteristics were investigated by tests using variations of rotor speed, impeller immersion depth, and water level. Results showed that variation of impeller immersion depth had a greater effect on the SAE compared to variation of water level. Moreover, the SAE increased with rotor speeds up to about 150 to 200 rpm and then decreased. In addition, void fraction improved by impeller immersion depth and rotor speed enhancement; however, mixing time and power number were reduced as rotor speed increased. According to the response surface methodology statistical optimizations, optimum values for rotor speed, impeller immersion depth, and water level were 168.90 rpm, 25 mm, and 30 cm, respectively, to achieve the maximum value of SAE.

Use of satellite gravimetry for estimating recent solid Earth changes

NASA Astrophysics Data System (ADS)

Ramillien, Guillaume

2014-05-01

Since its launch in March 2002, the Gravity Recovery & Climate Experiment (GRACE) satellite mission provides a global mapping of the time variations of the Earth's gravity field for the recent period. Official centers such as Center of Space Research (CSR) in Austin, TX, Jet Propulsion Laboratory (JPL) in Pasadena, CA and GeoForschungZentrum (GFZ) in Potsdam, Germany, provide 10-day and monthly solutions of Stokes coefficients (i.e., spherical harmonic coefficients of the geopotential) up to harmonic degree 50-60 (or, equivalently, a spatial resolution of 300-400 km) for the timespan 2002-2012. Tiny variations of the gravity measured by GRACE are mainly due to the total water storage change on continents. Therefore, these solutions of water mass can be used to correct other datasets, and then isolate the gravity signatures of large and sudden earthquakes, as well as of the continuous Post Glacial Rebound (PGR) rate. As these measured seasonal variations of continental hydrology represent the variations of water mass load, it is also possible to derive the deformation of the terrestrial surface associated to this varying load using Love numbers. These latter numbers are obtained by assuming an elastic Earth model. In the center of the Amazon basin, the seasonal displacements of the surface due to hydrology reach amplitudes of a few centimeters typically. Time-series of GRACE-based radial displacement of the surface can be analysed and compared with independent local GPS records for validation.

Total pollen counts do not influence active surface measurements

NASA Astrophysics Data System (ADS)

Moshammer, Hanns; Schinko, Herwig; Neuberger, Manfred

We investigated the temporal association of various aerosol parameters with pollen counts in the pollen season (April 2001) in Linz, Austria. We were especially interested in the relationship between active surface (or Fuchs' surface) because we had shown previously (Atmos. Environ. 37 (2003) 1737-1744) that this parameter during the same observation period was a better predictor for acute respiratory symptoms in school children (like wheezing, shortness of breath, and cough) and reduced lung function on the same day than particle mass (PM 10). While active surface is most sensitive for fine particles with a diameter of less than 100 nm it has no strict upper cut-off regarding particle size and so could eventually be influenced also by larger particles if their numbers were high. All particle mass parameters tested (TSP, PM 10, PM 1) were weakly ( r approximately 0.2) though significantly correlated with pollen counts but neither was active surface nor total particle counts (CPC). The weak association of particle mass and pollen counts was due mainly to similar diurnal variations and a linear trend over time. Only the mass of the coarse fraction (TSP minus PM 10) remained associated with pollen counts significantly after controlling for these general temporal patterns.

Salinity minima, water masses and surface circulation in the Eastern Tropical Pacific off Mexico and surrounding areas

NASA Astrophysics Data System (ADS)

Portela, Esther; Beier, Emilio; Godínez, Victor; Castro, Rubén; Desmond Barton, Eric

2016-04-01

The seasonal variations of the water masses and their interactions are analyzed in the Tropical Pacific off Mexico (TPOM) and four contiguous areas of on the basis of new extensive hydrographic database. The regional water masses intervals are redefined in terms of Absolute Salinity (SA) in g kg-1 and Conservative Temperature (Θ) according to TEOS - 10. The California Current System Water (CCSW) mass is introduced as an improved description of the former California Current Water (CCW) together with the Subarctic Water (SAW) to describe better the characteristics of the components of the California Current System. Hydrographic data, Precipitation-Evaporation balance and geostrophic currents were used to investigate the origin and seasonality of two salinity minima in the area. The shallow salinity minimum of around 33.5 g kg-1 originated in the California Current System and became saltier but less dense water as it traveled to the southeast. It can be identified as a mixture of CCSW and tropical waters. The surface salinity minimum of 32 - 33 g kg-1 was seen as a sharp surface feature in the TPOM from August to November. It was produced by the arrival of tropical waters from the south in combination with the net precipitation in the area during these months. This result provides new evidence of the presence of the poleward-flowing Mexican Coastal Current and, for the first time, of its seasonal pattern of variation.

The topographic development and areal parametric characterization of a stratified surface polished by mass finishing

NASA Astrophysics Data System (ADS)

Walton, Karl; Blunt, Liam; Fleming, Leigh

2015-09-01

Mass finishing is amongst the most widely used finishing processes in modern manufacturing, in applications from deburring to edge radiusing and polishing. Processing objectives are varied, ranging from the cosmetic to the functionally critical. One such critical application is the hydraulically smooth polishing of aero engine component gas-washed surfaces. In this, and many other applications the drive to improve process control and finish tolerance is ever present. Considering its widespread use mass finishing has seen limited research activity, particularly with respect to surface characterization. The objectives of the current paper are to; characterise the mass finished stratified surface and its development process using areal surface parameters, provide guidance on the optimal parameters and sampling method to characterise this surface type for a given application, and detail the spatial variation in surface topography due to coupon edge shadowing. Blasted and peened square plate coupons in titanium alloy are wet (vibro) mass finished iteratively with increasing duration. Measurement fields are precisely relocated between iterations by fixturing and an image superimposition alignment technique. Surface topography development is detailed with ‘log of process duration’ plots of the ‘areal parameters for scale-limited stratified functional surfaces’, (the Sk family). Characteristic features of the Smr2 plot are seen to map out the processing of peak, core and dale regions in turn. These surface process regions also become apparent in the ‘log of process duration’ plot for Sq, where lower core and dale regions are well modelled by logarithmic functions. Surface finish (Ra or Sa) with mass finishing duration is currently predicted with an exponential model. This model is shown to be limited for the current surface type at a critical range of surface finishes. Statistical analysis provides a group of areal parameters including; Vvc, Sq, and Sdq, showing optimal discrimination for a specific range of surface finish outcomes. As a consequence of edge shadowing surface segregation is suggested for characterization purposes.

New Estimates of Hydrological and Oceanic Excitations of Variations of Earth's Rotation, Geocenter and Gravitational Field

NASA Technical Reports Server (NTRS)

Chao, Benjamin F.; Chen, J. L.; Johnson, T.; Au, A. Y.

1998-01-01

Hydrological mass transport in the geophysical fluids of the atmosphere-hydrosphere-solid Earth surface system can excite Earth's rotational variations in both length-of-day and polar motion. These effects can be computed in terms of the hydrological angular momentum by proper integration of global meteorological data. We do so using the 40-year NCEP data and the 18-year NASA GEOS-1 data, where the precipitation and evapotranspiration budgets are computed via the water mass balance of the atmosphere based on Oki et al.'s (1995) algorithm. This hydrological mass redistribution will also cause geocenter motion and changes in Earth's gravitational field, which are similarly computed using the same data sets. Corresponding geodynamic effects due to the oceanic mass transports (i.e. oceanic angular momentum and ocean-induced geocenter/gravity changes) have also been computed in a similar manner. We here compare two independent sets of the result from: (1) non-steric ocean surface topography observations based on Topex/Poseidon, and (2) the model output of the mass field by the Parallel Ocean Climate Model. Finally, the hydrological and the oceanic time series are combined in an effort to better explain the observed non-atmospheric effects. The latter are obtained by subtracting the atmospheric angular momentum from Earth rotation observations, and the atmosphere- induced geocenter/gravity effects from corresponding geodetic observations, both using the above-mentioned atmospheric data sets.

Sequential estimation of surface water mass changes from daily satellite gravimetry data

NASA Astrophysics Data System (ADS)

Ramillien, G. L.; Frappart, F.; Gratton, S.; Vasseur, X.

2015-03-01

We propose a recursive Kalman filtering approach to map regional spatio-temporal variations of terrestrial water mass over large continental areas, such as South America. Instead of correcting hydrology model outputs by the GRACE observations using a Kalman filter estimation strategy, regional 2-by-2 degree water mass solutions are constructed by integration of daily potential differences deduced from GRACE K-band range rate (KBRR) measurements. Recovery of regional water mass anomaly averages obtained by accumulation of information of daily noise-free simulated GRACE data shows that convergence is relatively fast and yields accurate solutions. In the case of cumulating real GRACE KBRR data contaminated by observational noise, the sequential method of step-by-step integration provides estimates of water mass variation for the period 2004-2011 by considering a set of suitable a priori error uncertainty parameters to stabilize the inversion. Spatial and temporal averages of the Kalman filter solutions over river basin surfaces are consistent with the ones computed using global monthly/10-day GRACE solutions from official providers CSR, GFZ and JPL. They are also highly correlated to in situ records of river discharges (70-95 %), especially for the Obidos station where the total outflow of the Amazon River is measured. The sparse daily coverage of the GRACE satellite tracks limits the time resolution of the regional Kalman filter solutions, and thus the detection of short-term hydrological events.

Estimating geocenter motion and barystatic sea-level variability from GRACE observations with explicit consideration of self-attraction and loading effects

NASA Astrophysics Data System (ADS)

Bergmann-Wolf, I.; Dobslaw, H.

2015-12-01

Estimating global barystatic sea-level variations from monthly mean gravity fields delivered by the Gravity Recovery and Climate Experiment (GRACE) satellite mission requires additional information about geocenter motion. These variations are not available directly due to the mission implementation in the CM-frame and are represented by the degree-1 terms of the spherical harmonics expansion. Global degree-1 estimates can be determined with the method of Swenson et al. (2008) from ocean mass variability, the geometry of the global land-sea distribution, and GRACE data of higher degrees and orders. Consequently, a recursive relation between the derivation of ocean mass variations from GRACE data and the introduction of geocenter motion into GRACE data exists.In this contribution, we will present a recent improvement to the processing strategy described in Bergmann-Wolf et al. (2014) by introducing a non-homogeneous distribution of global ocean mass variations in the geocenter motion determination strategy, which is due to the effects of loading and self-attraction induced by mass redistributions at the surface. A comparison of different GRACE-based oceanographic products (barystatic signal for both the global oceans and individual basins; barotropic transport variations of major ocean currents) with degree-1 terms estimated with a homogeneous and non-homogeneous ocean mass representation will be discussed, and differences in noise levels in most recent GRACE solutions from GFZ (RL05a), CSR, and JPL (both RL05) and their consequences for the application of this method will be discussed.

Effects of Extreme Obliquity Variations on the Habitability of Exoplanets

NASA Technical Reports Server (NTRS)

Armstrong, J. C.; Barnes, R.; Domagal-Goldman, S.; Breiner, J.; Quinn, T. R.; Meadows, V. S.

2014-01-01

We explore the impact of obliquity variations on planetary habitability in hypothetical systems with high mutual inclination. We show that large-amplitude, high-frequency obliquity oscillations on Earth-like exoplanets can suppress the ice-albedo feedback, increasing the outer edge of the habitable zone. We restricted our exploration to hypothetical systems consisting of a solar-mass star, an Earth-mass planet at 1 AU, and 1 or 2 larger planets. We verified that these systems are stable for 108 years with N-body simulations and calculated the obliquity variations induced by the orbital evolution of the Earth-mass planet and a torque from the host star. We ran a simplified energy balance model on the terrestrial planet to assess surface temperature and ice coverage on the planet's surface, and we calculated differences in the outer edge of the habitable zone for planets with rapid obliquity variations. For each hypothetical system, we calculated the outer edge of habitability for two conditions: (1) the full evolution of the planetary spin and orbit and (2) the eccentricity and obliquity fixed at their average values. We recovered previous results that higher values of fixed obliquity and eccentricity expand the habitable zone, but we also found that obliquity oscillations further expand habitable orbits in all cases. Terrestrial planets near the outer edge of the habitable zone may be more likely to support life in systems that induce rapid obliquity oscillations as opposed to fixed-spin planets. Such planets may be the easiest to directly characterize with space-borne telescopes.

Effects of extreme obliquity variations on the habitability of exoplanets.

PubMed

Armstrong, J C; Barnes, R; Domagal-Goldman, S; Breiner, J; Quinn, T R; Meadows, V S

2014-04-01

We explore the impact of obliquity variations on planetary habitability in hypothetical systems with high mutual inclination. We show that large-amplitude, high-frequency obliquity oscillations on Earth-like exoplanets can suppress the ice-albedo feedback, increasing the outer edge of the habitable zone. We restricted our exploration to hypothetical systems consisting of a solar-mass star, an Earth-mass planet at 1 AU, and 1 or 2 larger planets. We verified that these systems are stable for 10(8) years with N-body simulations and calculated the obliquity variations induced by the orbital evolution of the Earth-mass planet and a torque from the host star. We ran a simplified energy balance model on the terrestrial planet to assess surface temperature and ice coverage on the planet's surface, and we calculated differences in the outer edge of the habitable zone for planets with rapid obliquity variations. For each hypothetical system, we calculated the outer edge of habitability for two conditions: (1) the full evolution of the planetary spin and orbit and (2) the eccentricity and obliquity fixed at their average values. We recovered previous results that higher values of fixed obliquity and eccentricity expand the habitable zone, but we also found that obliquity oscillations further expand habitable orbits in all cases. Terrestrial planets near the outer edge of the habitable zone may be more likely to support life in systems that induce rapid obliquity oscillations as opposed to fixed-spin planets. Such planets may be the easiest to directly characterize with space-borne telescopes.

Morphological dependency of cutaneous blood flow and sweating during compensable heat stress when heat-loss requirements are matched across participants.

PubMed

Notley, Sean R; Park, Joonhee; Tagami, Kyoko; Ohnishi, Norikazu; Taylor, Nigel A S

2016-07-01

Human heat loss is thought, in part, to be morphologically related. It was therefore hypothesized that when heat-loss requirements and body temperatures were matched, that the mass-specific surface area alone could significantly explain both cutaneous vascular and sudomotor responses during compensable exercise. These thermoeffector responses were examined in 36 men with widely varying mass-specific surface areas (range, 232.3-292.7 cm(2)/kg), but of similar age, aerobic fitness, and adiposity. Subjects completed two trials under compensable conditions (28.1°C, 36.8% relative humidity), each involving rest (20 min) and steady-state cycling (45 min) at two matched metabolic heat-production rates (light, ∼135 W/m(2); moderate, ∼200 W/m(2)). Following equivalent mean body temperature changes, forearm blood flow and vascular conductance (r = 0.63 and r = 0.65) shared significant, positive associations with the mass-specific surface area during light work (P < 0.05), explaining ∼45% of the vasomotor variation. Conversely, during light and moderate work, whole body sweat rate, as well as local sweat rate and sudomotor sensitivity at three of four measured sites, revealed moderate, negative relationships with the mass-specific surface area (correlation coefficient range -0.37 to -0.73, P < 0.05). Moreover, those relationships could uniquely account for between 10 and 53% of those sweating responses (P < 0.05). Therefore, both thermoeffector responses displayed a significant morphological dependency in the presence of equivalent thermoafferent drive. Indeed, up to half of the interindividual variation in these effector responses could now be explained through morphological differences and the first principles governing heat transfer. Copyright © 2016 the American Physiological Society.

Morphological dependency of cutaneous blood flow and sweating during compensable heat stress when heat-loss requirements are matched across participants

PubMed Central

Notley, Sean R.; Park, Joonhee; Tagami, Kyoko; Ohnishi, Norikazu

2016-01-01

Human heat loss is thought, in part, to be morphologically related. It was therefore hypothesized that when heat-loss requirements and body temperatures were matched, that the mass-specific surface area alone could significantly explain both cutaneous vascular and sudomotor responses during compensable exercise. These thermoeffector responses were examined in 36 men with widely varying mass-specific surface areas (range, 232.3-292.7 cm2/kg), but of similar age, aerobic fitness, and adiposity. Subjects completed two trials under compensable conditions (28.1°C, 36.8% relative humidity), each involving rest (20 min) and steady-state cycling (45 min) at two matched metabolic heat-production rates (light, ∼135 W/m2; moderate, ∼200 W/m2). Following equivalent mean body temperature changes, forearm blood flow and vascular conductance (r = 0.63 and r = 0.65) shared significant, positive associations with the mass-specific surface area during light work (P < 0.05), explaining ∼45% of the vasomotor variation. Conversely, during light and moderate work, whole body sweat rate, as well as local sweat rate and sudomotor sensitivity at three of four measured sites, revealed moderate, negative relationships with the mass-specific surface area (correlation coefficient range −0.37 to −0.73, P < 0.05). Moreover, those relationships could uniquely account for between 10 and 53% of those sweating responses (P < 0.05). Therefore, both thermoeffector responses displayed a significant morphological dependency in the presence of equivalent thermoafferent drive. Indeed, up to half of the interindividual variation in these effector responses could now be explained through morphological differences and the first principles governing heat transfer. PMID:27125845

Determination of Interannual to Decadal Changes in Ice Sheet Mass Balance from Satellite Altimetry

NASA Technical Reports Server (NTRS)

Zwally, H. Jay; Busalacchi, Antonioa J. (Technical Monitor)

2001-01-01

A major uncertainty in predicting sea level rise is the sensitivity of ice sheet mass balance to climate change, as well as the uncertainty in present mass balance. Since the annual water exchange is about 8 mm of global sea level equivalent, the +/- 25% uncertainty in current mass balance corresponds to +/- 2 mm/yr in sea level change. Furthermore, estimates of the sensitivity of the mass balance to temperature change range from perhaps as much as - 10% to + 10% per K. Although the overall ice mass balance and seasonal and inter-annual variations can be derived from time-series of ice surface elevations from satellite altimetry, satellite radar altimeters have been limited in spatial coverage and elevation accuracy. Nevertheless, new data analysis shows mixed patterns of ice elevation increases and decreases that are significant in terms of regional-scale mass balances. In addition, observed seasonal and interannual variations in elevation demonstrate the potential for relating the variability in mass balance to changes in precipitation, temperature, and melting. From 2001, NASA's ICESat laser altimeter mission will provide significantly better elevation accuracy and spatial coverage to 86 deg latitude and to the margins of the ice sheets. During 3 to 5 years of ICESat-1 operation, an estimate of the overall ice sheet mass balance and sea level contribution will be obtained. The importance of continued ice monitoring after the first ICESat is illustrated by the variability in the area of Greenland surface melt observed over 17-years and its correlation with temperature. In addition, measurement of ice sheet changes, along with measurements of sea level change by a series of ocean altimeters, should enable direct detection of ice level and global sea level correlations.

Very high resolution surface mass balance over Greenland modeled by the regional climate model MAR with a downscaling technique

NASA Astrophysics Data System (ADS)

Kittel, Christoph; Lang, Charlotte; Agosta, Cécile; Prignon, Maxime; Fettweis, Xavier; Erpicum, Michel

2016-04-01

This study presents surface mass balance (SMB) results at 5 km resolution with the regional climate MAR model over the Greenland ice sheet. Here, we use the last MAR version (v3.6) where the land-ice module (SISVAT) using a high resolution grid (5km) for surface variables is fully coupled while the MAR atmospheric module running at a lower resolution of 10km. This online downscaling technique enables to correct near-surface temperature and humidity from MAR by a gradient based on elevation before forcing SISVAT. The 10 km precipitation is not corrected. Corrections are stronger over the ablation zone where topography presents more variations. The model has been force by ERA-Interim between 1979 and 2014. We will show the advantages of using an online SMB downscaling technique in respect to an offline downscaling extrapolation based on local SMB vertical gradients. Results at 5 km show a better agreement with the PROMICE surface mass balance data base than the extrapolated 10 km MAR SMB results.

Mass change distribution inverted from space-borne gravimetric data using a Monte Carlo method

NASA Astrophysics Data System (ADS)

Zhou, X.; Sun, X.; Wu, Y.; Sun, W.

2017-12-01

Mass estimate plays a key role in using temporally satellite gravimetric data to quantify the terrestrial water storage change. GRACE (Gravity Recovery and Climate Experiment) only observes the low degree gravity field changes, which can be used to estimate the total surface density or equivalent water height (EWH) variation, with a limited spatial resolution of 300 km. There are several methods to estimate the mass variation in an arbitrary region, such as averaging kernel, forward modelling and mass concentration (mascon). Mascon method can isolate the local mass from the gravity change at a large scale through solving the observation equation (objective function) which represents the relationship between unknown masses and the measurements. To avoid the unreasonable local mass inverted from smoothed gravity change map, regularization has to be used in the inversion. We herein give a Markov chain Monte Carlo (MCMC) method to objectively determine the regularization parameter for the non-negative mass inversion problem. We first apply this approach to the mass inversion from synthetic data. Result show MCMC can effectively reproduce the local mass variation taking GRACE measurement error into consideration. We then use MCMC to estimate the ground water change rate of North China Plain from GRACE gravity change rate from 2003 to 2014 under a supposition of the continuous ground water loss in this region. Inversion result show that the ground water loss rate in North China Plain is 7.6±0.2Gt/yr during past 12 years which is coincident with that from previous researches.

Crustal density contrast detection by global gravity and topography models and in-situ gravity observations

NASA Astrophysics Data System (ADS)

Claessens, S. J.

2016-12-01

Mass density contrasts in the Earth's crust can be detected using an inversion of terrestrial or airborne gravity data. This contribution shows a technique to detect short-scale density contrasts using in-situ gravity observations in combination with a high-resolution global gravity model that includes variations in the gravity field due to topography. The technique is exemplified at various test sites using the Global Gravity Model Plus (GGMplus), which is a 7.2 arcsec resolution model of the Earth's gravitational field, covering all land masses and near-coastal areas within +/- 60° latitude. The model is a composite of GRACE and GOCE satellite observations, the EGM2008 global gravity model, and short-scale topographic gravity effects. Since variations in the Earth's gravity field due to topography are successfully modelled by GGMplus, any remaining differences with in-situ gravity observations are primarily due to mass density variations. It is shown that this technique effectively filters out large-scale density variations, and highlights short-scale near-surface density contrasts in the Earth's crust. Numerical results using recent high-density gravity surveys are presented, which indicate a strong correlation between density contrasts found and known lines of geological significance.

Cosmogenic isotope beryllium-7 in the atmosphere: Production versus transport

NASA Astrophysics Data System (ADS)

Pacini, Alessandra; Usoskin, Ilya; Evangelista, Heitor; Echer, Ezequiel; Mursula, Kalevi; Leppanen, Ari-Pekka

Cosmogenic isotope 7 Be measured near the ground can provide information about its produc-tion (that occurs in the atmosphere due to the interaction of cosmic rays and atmospheric constituents) and its deposition processes (that involves air mass dynamics, stratosphere-troposphere coupling and local climatic conditions). We present the results of an investigation of the atmospheric 7 Be temporal variations at different geographic locations (Finland and Brazil). This study was based on an analysis of three time series of 7 Be concentration measured in near-surface air samples from Rovaniemi and Loviisa (Finland) and Rio de Janeiro (Brazil) for the last decades. We made use of the wavelet spectral method to identify the frequency-temporal features of the 7 Be temporal variations that allowed us to determine the relative importance of production and deposition process for the observed data. By comparing these time series with climatic indices and the values of 7 Be concentration expected from the model for the same period, we found that the climate system is the main driver of the surface isotopic modulation, while the imprints of the production variations are geographically dependent. Thus,7 Be can be considered a good tool to monitor the large-scale air mass dynamics.

On the Retrieval of Geocenter Motion from Gravity Data

NASA Astrophysics Data System (ADS)

Rosat, S.; Mémin, A.; Boy, J. P.; Rogister, Y. J. G.

2017-12-01

The center of mass of the whole Earth, the so-called geocenter, is moving with respect to the Center of Mass of the solid Earth because of the loading exerted by the Earth's fluid layers on the solid crust. Space geodetic techniques tying satellites and ground stations (e.g. GNSS, SLR and DORIS) have been widely employed to estimate the geocenter motion. Harmonic degree-1 variations of the gravity field are associated to the geocenter displacement. We show that ground records of time-varying gravity from Superconducting Gravimeters (SGs) can be used to constrain the geocenter motion. Two major difficulties have to be tackled: (1) the sensitivity of surface gravimetric measurements to local mass changes, and in particular hydrological and atmospheric variabilities; (2) the spatial aliasing (spectral leakage) of spherical harmonic degrees higher than 1 induced by the under-sampling of station distribution. The largest gravity variations can be removed from the SG data by subtracting solid and oceanic tides as well as atmospheric and hydrologic effects using global models. However some hydrological signal may still remain. Since surface water content is well-modelled using GRACE observations, we investigate how the spatial aliasing in SG data can be reduced by employing GRACE solutions when retrieving geocenter motion. We show synthetic simulations using complete surface loading models together with GRACE solutions computed at SG stations. In order to retrieve the degree-one gravity variations that are associated with the geocenter motion, we use a multi-station stacking method that performs better than a classical spherical harmonic stacking when the station distribution is inhomogeneous. We also test the influence of the network configuration on the estimate of the geocenter motion. An inversion using SG and GRACE observations is finally presented and the results are compared with previous geocenter estimates.

Stratified turbulent Bunsen flames: flame surface analysis and flame surface density modelling

NASA Astrophysics Data System (ADS)

Ramaekers, W. J. S.; van Oijen, J. A.; de Goey, L. P. H.

2012-12-01

In this paper it is investigated whether the Flame Surface Density (FSD) model, developed for turbulent premixed combustion, is also applicable to stratified flames. Direct Numerical Simulations (DNS) of turbulent stratified Bunsen flames have been carried out, using the Flamelet Generated Manifold (FGM) reduction method for reaction kinetics. Before examining the suitability of the FSD model, flame surfaces are characterized in terms of thickness, curvature and stratification. All flames are in the Thin Reaction Zones regime, and the maximum equivalence ratio range covers 0.1⩽φ⩽1.3. For all flames, local flame thicknesses correspond very well to those observed in stretchless, steady premixed flamelets. Extracted curvature radii and mixing length scales are significantly larger than the flame thickness, implying that the stratified flames all burn in a premixed mode. The remaining challenge is accounting for the large variation in (subfilter) mass burning rate. In this contribution, the FSD model is proven to be applicable for Large Eddy Simulations (LES) of stratified flames for the equivalence ratio range 0.1⩽φ⩽1.3. Subfilter mass burning rate variations are taken into account by a subfilter Probability Density Function (PDF) for the mixture fraction, on which the mass burning rate directly depends. A priori analysis point out that for small stratifications (0.4⩽φ⩽1.0), the replacement of the subfilter PDF (obtained from DNS data) by the corresponding Dirac function is appropriate. Integration of the Dirac function with the mass burning rate m=m(φ), can then adequately model the filtered mass burning rate obtained from filtered DNS data. For a larger stratification (0.1⩽φ⩽1.3), and filter widths up to ten flame thicknesses, a β-function for the subfilter PDF yields substantially better predictions than a Dirac function. Finally, inclusion of a simple algebraic model for the FSD resulted only in small additional deviations from DNS data, thereby rendering this approach promising for application in LES.

Climatic influences on human body size and proportions: ecological adaptations and secular trends.

PubMed

Katzmarzyk, P T; Leonard, W R

1998-08-01

This study reevaluates the long-standing observation that human morphology varies with climate. Data on body mass, the body mass index [BMI; mass (kg)/stature (m)2], the surface area/body mass ratio, and relative sitting height (RSH; sitting height/stature) were obtained for 223 male samples and 195 female samples derived from studies published since D.F. Roberts' landmark paper "Body weight, race, and climate" in 1953 (Am. J. Phys. Anthropol. 11:533-558). Current analyses indicate that body mass varies inversely with mean annual temperature in males (r=-0.27, P < 0.001) and females (r=-0.28, P < 0.001), as does the BMI (males: r=-0.22, P=0.001; females: r=-0.30, P < 0.001). The surface area/body mass ratio is positively correlated with temperature in both sexes (males: r=0.29, P < 0.001; females: r=0.34, P < 0.001), whereas the relationship between RSH and temperature is negative (males: r=-0.37, P < 0.001; females: r=-0.46, P < 0.001). These results are consistent with previous work showing that humans follow the ecological rules of Bergmann and Allen. However, the slope of the best-fit regressions between measures of body mass (i.e., mass, BMI, and surface area/mass) and temperature are more modest than those presented by Roberts. These differences appear to be attributable to secular trends in mass, particularly among tropical populations. Body mass and the BMI have increased over the last 40 years, whereas the surface area/body mass ratio has decreased. These findings indicate that, although climatic factors continue to be significant correlates of world-wide variation in human body size and morphology, differential changes in nutrition among tropical, developing world populations have moderated their influence.

Estimating geocenter motion and barystatic sea-level variability from GRACE observations with explicit consideration of self-attraction and loading effects

NASA Astrophysics Data System (ADS)

Bergmann-Wolf, Inga; Dobslaw, Henryk

2016-04-01

Estimating global barystatic sea-level variations from monthly mean gravity fields delivered by the Gravity Recovery and Climate Experiment (GRACE) satellite mission requires additional information about geocenter motion. These variations are not available directly due to the mission implementation in the CM-frame and are represented by the degree-1 terms of the spherical harmonics expansion. Global degree-1 estimates can be determined with the method of Swenson et al. (2008) from ocean mass variability, the geometry of the global land-sea distribution, and GRACE data of higher degrees and orders. Consequently, a recursive relation between the derivation of ocean mass variations from GRACE data and the introduction of geocenter motion into GRACE data exists. In this contribution, we will present a recent improvement to the processing strategy described in Bergmann-Wolf et al. (2014) by introducing a non-homogeneous distribution of global ocean mass variations in the geocenter motion determination strategy, which is due to the effects of loading and self-attraction induced by mass redistributions at the surface. A comparison of different GRACE-based oceanographic products (barystatic signal for both the global oceans and individual basins; barotropic transport variations of major ocean currents) with degree-1 terms estimated with a homogeneous and non-homogeneous ocean mass representation will be discussed, and differences in noise levels in most recent GRACE solutions from GFZ (RL05a), CSR, and JPL (both RL05) and their consequences for the application of this method will be discussed. Swenson, S., D. Chambers and J. Wahr (2008), Estimating geocenter variations from a combination of GRACE and ocean model output, J. Geophys. Res., 113, B08410 Bergmann-Wolf, I., L. Zhang and H. Dobslaw (2014), Global Eustatic Sea-Level Variations for the Approximation of Geocenter Motion from GRACE, J. Geod. Sci., 4, 37-48

Modeling of Firn Compaction for Estimating Ice-Sheet Mass Change from Observed Ice-Sheet Elevation Change

NASA Technical Reports Server (NTRS)

Li, Jun; Zwally, H. Jay

2011-01-01

Changes in ice-sheet surface elevation are caused by a combination of ice-dynamic imbalance, ablation, temporal variations in accumulation rate, firn compaction and underlying bedrock motion. Thus, deriving the rate of ice-sheet mass change from measured surface elevation change requires information on the rate of firn compaction and bedrock motion, which do not involve changes in mass, and requires an appropriate firn density to associate with elevation changes induced by recent accumulation rate variability. We use a 25 year record of surface temperature and a parameterization for accumulation change as a function of temperature to drive a firn compaction model. We apply this formulation to ICESat measurements of surface elevation change at three locations on the Greenland ice sheet in order to separate the accumulation-driven changes from the ice-dynamic/ablation-driven changes, and thus to derive the corresponding mass change. Our calculated densities for the accumulation-driven changes range from 410 to 610 kg/cu m, which along with 900 kg/cu m for the dynamic/ablation-driven changes gives average densities ranging from 680 to 790 kg/cu m. We show that using an average (or "effective") density to convert elevation change to mass change is not valid where the accumulation and the dynamic elevation changes are of opposite sign.

A New Unified Approach to Determine Geocenter Motion Using Space Geodesy and GRACE Gravity Data

NASA Astrophysics Data System (ADS)

Wu, X.; Kusche, J.; Landerer, F. W.

2016-12-01

Spherical harmonic expansions of Earth's surface mass variations start from three degree-1 terms. These longest-wavelength terms induce geocenter motion between the center-of-mass of the total Earth system (CM) and the center-of-figure of the solid Earth surface (CF), and a degree-1 surface deformation field. For complete spectral coverage and robust assessment of geographic mass budget using GRACE data, very accurate knowledge of geocenter motion between CM and CF is required with precision goals of 0.2 mm in annual amplitude and 0.2 mm/yr leading to equivalent degree-1 coefficients. However, GRACE's K-band ranging data system is not sensitive to these variation modes. Although satellite laser ranging (SLR) system is thought to have the most reliable sensitivity to CM, its surface network is very sparse and can only deliver motion between CM and the center of a changing network (CN) of roughly 20 unevenly distributed stations. Recently, the network has been extended to include 82 stations with their geocentric displacements derived by transferring SLR's CM sensitivity to other technique networks through local tie and co-motion constraints. The CM-CN motion of this network has a better agreement with the geocenter motion result from a global inversion of relative GPS, GRACE, and the ECCO ocean bottom pressure (OBP) model. Still, there is no guarantee that such a CM-CN motion is the same as the CM-CF motion. Also, the global inversion result is subject to the impact of unknown errors in the OBP model. To improve reliability of geocenter motion determination, we use a new unified approach to geocenter motion determination by combining geocentric displacements of ground stations with GRACE gravity data. Both translational and deformational signatures will be exploited for retrieval of the degree-1 surface mass variation coefficients. Higher degree terms are estimated simultaneously using GRACE gravity data, which further improves CF knowledge and reduces aliasing effects. Such a data combination also uses full covariance matrices of all data types to facilitate a reliable variance component estimation. High-precision results for non-linear geocenter motion have been achieved and will be reported. We will also discuss challenges and strategies for improving geocenter velocity determination.

The Eurasia-North Pacific Oscillation in atmospheric mass variations independent of both IHO and AO and its possible impacts on winter climate

NASA Astrophysics Data System (ADS)

Zhang, Qian; Guan, Zhaoyong; Li, Minggang

2018-06-01

Using NCEP/NCAR reanalysis, we have investigated the features of migrations of atmospheric mass (AM) between land and ocean in Eurasia-North Pacific domain in boreal winter after having both signals of Inter-hemispheric Oscillation and Arctic Oscillation removed from the physical quantities. It is found that there is a Eurasia-North Pacific Oscillation (ENPO) in surface air pressure anomalies. This ENPO pattern characterizes with two oppositely signed anomalous surface pressure centers over Eurasia and North Pacific respectively, indicating strong connections between Siberian high and Aleutian low during period 1979-2012. The maintenance of this ENPO teleconnection is significantly associated with three factors including the anomalous AM flows and zonal circulation cell over Eurasia-North Pacific domain, the Rossby wave energy propagations, and the thermal forcing contrasts near the surface between Eurasia and North Pacific during boreal winter. The variations of both wintertime rainfall and temperature over Eurasia may be strongly affected by ENPO. When the ENPO index is positive (negative), there occurs the AM accumulation (depletion) over Eurasia with simultaneous depletion (accumulation) over mid-latitude North-Pacific. Correspondingly, this anomalous surface pressure pattern along with the related circulation anomalies at different isobaric levels possibly results in winter precipitation decreases (increases) over Siberian Plain and East China, whereas increases (decreases) over southeastern Europe, Xinjiang of China, and the west coast of Sea of Okhotsk. On the other hand, surface air temperature decreases (increases) over large areas of Eurasia. These results are helpful for our better understanding the mechanisms behind circulation and winter climate variations over Eurasia-North Pacific region.

Surface flux and ocean heat transport convergence contributions to seasonal and interannual variations of ocean heat content

NASA Astrophysics Data System (ADS)

Roberts, C. D.; Palmer, M. D.; Allan, R. P.; Desbruyeres, D. G.; Hyder, P.; Liu, C.; Smith, D.

2017-01-01

We present an observation-based heat budget analysis for seasonal and interannual variations of ocean heat content (H) in the mixed layer (Hmld) and full-depth ocean (Htot). Surface heat flux and ocean heat content estimates are combined using a novel Kalman smoother-based method. Regional contributions from ocean heat transport convergences are inferred as a residual and the dominant drivers of Hmld and Htot are quantified for seasonal and interannual time scales. We find that non-Ekman ocean heat transport processes dominate Hmld variations in the equatorial oceans and regions of strong ocean currents and substantial eddy activity. In these locations, surface temperature anomalies generated by ocean dynamics result in turbulent flux anomalies that drive the overlying atmosphere. In addition, we find large regions of the Atlantic and Pacific oceans where heat transports combine with local air-sea fluxes to generate mixed layer temperature anomalies. In all locations, except regions of deep convection and water mass transformation, interannual variations in Htot are dominated by the internal rearrangement of heat by ocean dynamics rather than the loss or addition of heat at the surface. Our analysis suggests that, even in extratropical latitudes, initialization of ocean dynamical processes could be an important source of skill for interannual predictability of Hmld and Htot. Furthermore, we expect variations in Htot (and thus thermosteric sea level) to be more predictable than near surface temperature anomalies due to the increased importance of ocean heat transport processes for full-depth heat budgets.

Interannual variation of the Antarctic Ice Sheet from a combined analysis of satellite gravimetry and altimetry data

NASA Astrophysics Data System (ADS)

Mémin, A.; Flament, T.; Alizier, B.; Watson, C.; Rémy, F.

2015-07-01

Assessment of the long term mass balance of the Antarctic Ice Sheet, and thus the determination of its contribution to sea level rise, requires an understanding of interannual variability and associated causal mechanisms. We performed a combined analysis of surface-mass and elevation changes using data from the GRACE and Envisat satellite missions, respectively. Using empirical orthogonal functions and singular value decompositions of each data set, we find a quasi 4.7-yr periodic signal between 08/2002 and 10/2010 that accounts for ∼ 15- 30% of the time variability of the filtered and detrended surface-mass and elevation data. Computation of the density of this variable mass load corresponds to snow or uncompacted firn. Changes reach maximum amplitude within the first 100 km from the coast where it contributes up to 30-35% of the annual rate of accumulation. Extending the analysis to 09/2014 using surface-mass changes only, we have found anomalies with a periodicity of about 4-6 yrs that circle the AIS in about 9-10 yrs. These properties connect the observed anomalies to the Antarctic Circumpolar Wave (ACW) which is known to affect several key climate variables, including precipitation. It suggests that variability in the surface-mass balance of the Antarctic Ice Sheet may also be modulated by the ACW.

Greenland uplift and regional sea level changes from ICESat observations and GIA modelling

NASA Astrophysics Data System (ADS)

Spada, G.; Ruggieri, G.; Sørensen, L. S.; Nielsen, K.; Melini, D.; Colleoni, F.

2012-06-01

We study the implications of a recently published mass balance of the Greenland ice sheet (GrIS), derived from repeated surface elevation measurements from NASA's ice cloud and land elevation satellite (ICESat) for the time period between 2003 and 2008. To characterize the effects of this new, high-resolution GrIS mass balance, we study the time-variations of various geophysical quantities in response to the current mass loss. They include vertical uplift and subsidence, geoid height variations, global patterns of sea level change (or fingerprints), and regional sea level variations along the coasts of Greenland. Long-wavelength uplifts and gravity variations in response to current or past ice thickness variations are obtained solving the sea level equation, which accounts for both the elastic and the viscoelastic components of deformation. To capture the short-wavelength components of vertical uplift in response to current ice mass loss, which is not resolved by satellite gravity observations, we have specifically developed a high-resolution regional elastic rebound (ER) model. The elastic component of vertical uplift is combined with estimates of the viscoelastic displacement fields associated with the process of glacial-isostatic adjustment (GIA), according to a set of published ice chronologies and associated mantle rheological profiles. We compare the sensitivity of global positioning system (GPS) observations along the coasts of Greenland to the ongoing ER and GIA. In notable contrast with past reports, we show that vertical velocities obtained by GPS data from five stations with sufficiently long records and from one tide gauge at the GrIS margins can be reconciled with model predictions based on the ICE-5G deglaciation model and the ER associated with the new ICESat-derived mass balance.

Mass spectrometric analysis of organic compounds, water and volatile constituents in the atmosphere and surface of Mars - The Viking Mars Lander.

NASA Technical Reports Server (NTRS)

Anderson, D. M.; Biemann, K.; Orgel, L. E.; Oro, J.; Owen , T.; Shulman, G. P.; Toulmin, P., III; Urey, H. C.

1972-01-01

An experiment centering around a mass spectrometer is described, which is aimed at the identification of organic substances present in the top 10 cm of the surface of Mars and an analysis of the atmosphere for major and minor constituents as well as isotopic abundances. In addition, an indication of the abundance of water in the surface and some information concerning the mineralogy can be obtained by monitoring the gases produced upon heating the soil sample. The organic material will simply be expelled by heating to 150, 300, and 500 C into the carrier gas stream of a gas chromatograph interfaced to the mass spectrometer or by slowly heating the sample in direct communication with the spectrometer. It is planned to analyze a total of up to nine soil samples in order to study diurnal and seasonal variations. The system is designed to give useful data even for minor constituents if the total of organics should be as low as 5 ppm. The spectrometer covers the mass range of 12-200 with adequate resolution.

Effects of Extreme Obliquity Variations on the Habitability of Exoplanets

PubMed Central

Barnes, R.; Domagal-Goldman, S.; Breiner, J.; Quinn, T.R.; Meadows, V.S.

2014-01-01

Abstract We explore the impact of obliquity variations on planetary habitability in hypothetical systems with high mutual inclination. We show that large-amplitude, high-frequency obliquity oscillations on Earth-like exoplanets can suppress the ice-albedo feedback, increasing the outer edge of the habitable zone. We restricted our exploration to hypothetical systems consisting of a solar-mass star, an Earth-mass planet at 1 AU, and 1 or 2 larger planets. We verified that these systems are stable for 108 years with N-body simulations and calculated the obliquity variations induced by the orbital evolution of the Earth-mass planet and a torque from the host star. We ran a simplified energy balance model on the terrestrial planet to assess surface temperature and ice coverage on the planet's surface, and we calculated differences in the outer edge of the habitable zone for planets with rapid obliquity variations. For each hypothetical system, we calculated the outer edge of habitability for two conditions: (1) the full evolution of the planetary spin and orbit and (2) the eccentricity and obliquity fixed at their average values. We recovered previous results that higher values of fixed obliquity and eccentricity expand the habitable zone, but we also found that obliquity oscillations further expand habitable orbits in all cases. Terrestrial planets near the outer edge of the habitable zone may be more likely to support life in systems that induce rapid obliquity oscillations as opposed to fixed-spin planets. Such planets may be the easiest to directly characterize with space-borne telescopes. Key Words: Exoplanets—Habitable zone—Energy balance models. Astrobiology 14, 277–291. PMID:24611714

Spatio-temporal variation in microclimate, the surface energy balance and ablation over a cirque glacier

NASA Astrophysics Data System (ADS)

Hannah, David M.; Gurnell, Angela M.; McGregor, Glenn R.

2000-06-01

Climatic processes, operating at a range of scales, drive energy fluxes at the glacier surface which control meltwater generation and ultimately runoff. Nevertheless, to date, most glacier microclimate research has been both temporally (short-term) and spatially (single station) restricted. This paper addresses this knowledge gap by reporting on a detailed, empirical study which characterizes spatio-temporal variations in and linkages between glacier microclimate, surface energy and mass exchanges within a small glacierized cirque (Taillon Glacier, French Pyrénées) over two melt seasons. Data collected at five automatic weather stations (AWSs) and over ablation stake networks suggest that topoclimates, altitude and transient snowline position primarily determine the distribution of glacier energy receipt and, in turn, snow- and ice-melt patterns. Generally net radiation is the dominant energy source, followed by sensible heat, while latent heat is an energy sink. However, the magnitude and partitioning of energy balance terms, and consequently ablation, vary across the glacier both seasonally and with prevailing weather conditions. Importantly, this paper demonstrates that such monitoring programmes are required to truly represent and provide a sound basis for modelling glacier energy and mass-balances in both space and time.

Variations of the aerosol concentration and chemical composition over the arid steppe zone of Southern Russia in summer

NASA Astrophysics Data System (ADS)

Artamonova, M. S.; Gubanova, D. P.; Iordanskii, M. A.; Lebedev, V. A.; Maksimenkov, L. O.; Minashkin, V. M.; Obvintsev, Y. I.; Chketiani, O. G.

2016-12-01

Variations in the surface aerosol over the arid steppe zone of Southern Russia have been measured. The parameters of atmospheric aerosol (mass concentration, both dispersed and elemental compositions) and meteorological parameters were measured in Tsimlaynsk raion (Rostov oblast). The chemical composition of aerosol particles in the atmospheric surface layer has been determined, and the coefficients of enrichment of elements with respect to clarkes in the Earth's crust have been calculated. It is shown that, in summer, arid aerosols are transported from both alkaline and sandy soils of Kalmykia to the air basin over the observation zone. Aerosol particles in the surface air layer over this region have been found to contain the products of combustion of oil, coal, and ethylized fuel. These combustion products make a small contribution to the total mass concentration of atmospheric aerosol; however, they are most hazardous to the health of people because of their sizes and heavy-metal contents. A high concentration of submicron sulfur-containing aerosol particles of chemocondensation nature has been recorded. Sources of aerosol of both natural and anthropogenic origins in southern Russia are discussed.

Explanation of observable secular variations of gravity and alternative methods of determination of drift of the center of mass of the Earth

NASA Astrophysics Data System (ADS)

Barkin, Yury

2010-05-01

The summary. On the basis of geodynamic model of the forced relative displacement of the centers of mass of the core and the mantle of the Earth the secular variations of a gravity and heights of some gravimetry stations on a surface of the Earth have ben studied. At the account of secular drift of the center of mass of the Earth which on our geodynamic model is caused by the unidirectional drift of the core of the Earth relatively to the mantle, the full explanation is given to observable secular variations of a gravity at stations Ny-Alesund (Norway), Churchill (Canada), Medicine (Italy), Sayowa (Antarctica), Strastburg (France), Membach (Belgium), Wuhan (China) and Metsahovi (Finland). Two new methods of determination of secular drift of the center of mass of the Earth, alternative to classical method of a space geodesy are offered: 1) on the basis of gravimetry data about secular trends of a gravity at the stations located on all basic regions of the Earth; 2) on the basis of the comparative analysis of altimetry and coastal data about secular changes of sea level also in basic regions of ocean. 1. Secular drift of the center of mass of the core and the center of mass of the Earth. A secular drift of the center of mass of the Earth to the North relatively to special center O on an axis of rotation of the Earth for which the coefficient of third zonal harmonic J3' = 0, has been predicted in the author work [1]. A drift in a direction to a geographical point (pole P) 70°0 N and 104°3 E has been established for the first time theoretically - as a result of the analysis of the global directed redistribution of masses of the Earth, explaining the observed secular drift of the pole of an axis of rotation of the Earth and not tidal acceleration of its axial rotation [2]. In [1] velocity of drift it has been estimated in 1-2 cm/yr. For specified center O the figure of a planet is as though deprived of pure-shaped form (J3' = 0). And in this sense the point O can be conditionally corresponded to the geocenter of the Earth approximately determined by position of stations of satellite observations, as the center of certain mantle systems of coordinates Oxyz. For an explanation of such significant drift of the center of mass of the Earth the mechanism of the unidirectional displacement of the core of the Earth (and its center of mass) relatively to a viscoelastic mantle [1, 2] has been offered. The next years attempts of determination of velocity of secular drift of the center of mass in the mantle reference frame by methods of a space geodesy on the basis of precision satellite observations were repeatedly undertaken. In our work [3] for determination of a trend of the center of mass the data of the International Service of Rotation of the Earth (IERS) for satellite observations of system DORIS have been used. For components of velocity of drift in geocentric Greenwich system of coordinates for period 1999-2007 estimations have been obtained: on coordinate x) -1.46 mm/yr, y) 0.79 mm/yr and z) 5.29 mm/yr (errors of the specified estimations make 5-10 %). The velocity of trend of the center of mass of the Earth and its direction are characterized by values: 5.54 mm/yr; latitude 72°6 N and a longitude 118°4 E. The direction of displacement of the center of mass will well be coordinated with a direction predicted earlier theoretically [2]: latitude 70° N and a longitude 104° E. We shall emphasize, that observable redistributions of superficial masses of the Earth explain only small part of observable displacement of the center of mass. It testifies in favour of a reality of secular relative displacement of the core and the mantle of the Earth. 2 Secular drift of the core to the North and variations of a gravity on the Earth surface. The displaced core of the Earth is characterized by the large superfluous mass approximately in 16.7 masses of the Moon. The superfluous mass is ditermined by contrast values of average densities of the core and the mantle and makes 19.32 % of mass of full the Earth. At displacement of the core relatively to the viscous-elastic mantle its superfluous mass causes observable drift of the center of mass, and also leads to changes of a gravity on the surface of the planet. Except for it the gravitational attraction of a displaced core causes deformations of all layers of the mantle, including a superficial layer. The deformed mantle produses some additional gravitational potential which gives the additional contribution to value of a gravity. Thus, noted factors lead to a secular variation of a gravity which is described by the simple formula [2]: dot g = 2gμmc-(1- h-2- 0.5k-2)ρdot-sin?, μmc = 0.1932m ⊙, g = 9.82022 m -s2 m ⊙ r⊙ (1) Here μmc = 0.1932m⊙ is a superflous mass of the Earth core in the masses of the Earth m⊙. g is an acceleration of free falling. k-2 and h-2 are Love numbers of the order (-2). ρdot is a velocity of the secular drift of the center of mass of the core relatively to the center of mass of the mantle. ?is an angle between dirtection to the pole P (in a direction to which the core of the Earth or its center of mass drifts), and direction to gravimetric station. For rough estimates of gravimetric effects as pole P the North Pole of the Earth has been accepted. Thus ? = ?-2 - φis a co-latitude. At more exact description of the core drift (or the center of mass drift) an angle? is determined by formula: cos? = cosφP cosφcos(λP - λ) + sinφP sinφ, where φP and λP is a latitude and longitude of pole P; φ and λ is a latitude and longitude of station. The Love numbers of the order (-2) in first have been evaluated in the paper [4] and have small values: k-2=-0.005004 and h-2=0.0062154. Approximately we can put ρdot m⊙ = μmcṙC, where ṙC is a velocity of the drift of the center of mass of the Earth. Then, neglecting small effects, for a variation of gravity (1) we obtain a following expression: ? r = 2ṙCg cos?-r⊙. Leaning on results of works [2], [3], we shall accept the following values of parameters of drift of the center of mass: ṙC=5.54 mm/yr, φP=70°0 N, λP=104°3 E. On the other hand a displacement of the center of mass of the Earth leads to effect of slow change of heights of gravimetric station: ḣ = -?dotC cos? = -5.54 × cos? mm/yr. Errors in determination of the specified characteristics in the given work we shall neglect. Besides the gravitational attraction of a displaced core leads also to effect of increase of horizontal component of gravitational force of an attraction of the Earth on its surface directed to the North along the corresponding meridian with pole P. For any point of a surface of the Earth this component of force is determined by the formula ?φ = ṙCg sin?-r⊙ and has positive values. And the maximal values ?φ are reached on equator, which plane is orthogonal to axes of drift of the core OP. Thus, final working formulas for studying of secular variations of components of force of a gravitational attraction of the Earth and for a variation of the heights caused by a drift of the center of mass of the Earth become: ?r = 1.74cos?-r⊙ ?Gal/yr, ?φ = 0.87sin?-r⊙ ?Gal/yr, ḣ = -5.54cos?-r⊙ mm/yr. Calculated values of mentioned gravimetric characteristics (2) for the wide list of gravimetry stations are resulted in work [5] and used in the given work. 3 Explanation of observable secular variations of a gravity and heights on gravimetric stations. We have been analysed observed variations of a gravity and heights available and accessible to us, namely their secular changes, for 8 known gravimetry stations. The periods of observations at mentioned stations make the order of 5-10 years, i.e. are not greater, but nevertheless the obtained results unequivocally testify in favour of that the basic contribution to secular variations of a gravity gives the drifting core of the Earth (by means of direct gravitational influence and due to a contribution to corresponding variations of heights). In the given work we did not consider other factors influencing on gravimetric measurements (superficial redistributions of fluid masses, variations of coefficients of the second and higher harmonics of a geopotential, etc.). As an example here we shall analyse secular variations of a gravity and heights at Ny-Alesund station (geographical coordinates: 78°93 N, 11°87 E, ? =23°16). Linear trends of a gravity and height observable at this station make -2.5±0.9 ?Gal/yr and + (6.9±0.9) mm/yr, accordingly, during 1998-2002 (Sato et.al., 2006). On our model a slow closing of the core to the Ny-Alesund station causes a positive variation of a gravity in 1.60 ?Gal/yr and a negative variation of height of station in -5.09 mm/yr [5]. These data testify a deformation of a surface of the Earth in area of station with a velocity +11.99±0.9 mm/yr owing to which the gravity tests a negative variation -3.74±0.28 ?Gal/yr. Putting effects of a variation of a gravity because of displacement of the core and from deformation of a surface, we obtain negative value for secular trend of gravity in - (2.14±0.28) ?Gal/yr, that within the limits of errors it will be coordinated with observable value - (2.5±0.9) ?Gal/yr. Similar results we have obtained for 7 another's gravimetric stations. All results are summarized in the table 1. Here we have used known data about observable secular trends of gravity and GPS heights at considered here stations of the following authors: Ny-Alesund (Sato et al., 2006); Churchill (Larson et al., 2000); Medicine (Zerbini et al., 2001); Syowa (Fukuda et.al., 2007); Strastburg (Almavict et. al., 2004); Membach (Francis et al., 2004); Wuhan (Xu et al., 2008); Metsahovi (Gitlein et. al., 2009). Table 1. Theoretical and observable values of secular variations of a gravity. Stations Core attractionSurface deformation Theory Observations Ny-Alesund+1.60 ?Gal/yr -(3.77±0.09) ?Gal/yr -(2.17±0.03) ?Gal/yr -(2.5±0.9) ?Gal/yr Churchill +1.11 ?Gal/yr -(3.38±0.28) ?Gal/yr -(2.22±0.28) ?Gal/yr -(2.13±0.23) ?Gal/yr Medicina +1.13 ?Gal/yr +(1.07±0.20) ?Gal/yr+(2.20±0.20) ?Gal/yr+(1.90±0.20) ?Gal/yr Syowa -1.44 ?Gal/yr +(0.63±0.08) ?Gal/yr-(0.81±0.08) ?Gal/yr -0.56 ?Gal/yr Strastburg +1.18 ?Gal/yr +(0.71±0.02) ?Gal/yr+(1.89±0.02) ?Gal/yr+(1.90±0.20) ?Gal/yr Membach +1.21 ?Gal/yr -(1.98±0.16) ?Gal/yr -(0.77±0.16) ?Gal/yr -(0.6±0.1) ?Gal/yr Wuhan +1.34 ?Gal/yr -(0.17±0.05) ?Gal/yr +(1.17±0.05) ?Gal/yr+(1.39±0.02) ?Gal/yr Metsahovi +1.47 ?Gal/yr -(2.82±0.06) ?Gal/yr +(1.35±0.06) ?Gal/yr-(0.88±0.52) ?Gal/yr

Detecting high spatial variability of ice shelf basal mass balance, Roi Baudouin Ice Shelf, Antarctica

NASA Astrophysics Data System (ADS)

Berger, Sophie; Drews, Reinhard; Helm, Veit; Sun, Sainan; Pattyn, Frank

2017-11-01

Ice shelves control the dynamic mass loss of ice sheets through buttressing and their integrity depends on the spatial variability of their basal mass balance (BMB), i.e. the difference between refreezing and melting. Here, we present an improved technique - based on satellite observations - to capture the small-scale variability in the BMB of ice shelves. As a case study, we apply the methodology to the Roi Baudouin Ice Shelf, Dronning Maud Land, East Antarctica, and derive its yearly averaged BMB at 10 m horizontal gridding. We use mass conservation in a Lagrangian framework based on high-resolution surface velocities, atmospheric-model surface mass balance and hydrostatic ice-thickness fields (derived from TanDEM-X surface elevation). Spatial derivatives are implemented using the total-variation differentiation, which preserves abrupt changes in flow velocities and their spatial gradients. Such changes may reflect a dynamic response to localized basal melting and should be included in the mass budget. Our BMB field exhibits much spatial detail and ranges from -14.7 to 8.6 m a-1 ice equivalent. Highest melt rates are found close to the grounding line where the pressure melting point is high, and the ice shelf slope is steep. The BMB field agrees well with on-site measurements from phase-sensitive radar, although independent radar profiling indicates unresolved spatial variations in firn density. We show that an elliptical surface depression (10 m deep and with an extent of 0.7 km × 1.3 km) lowers by 0.5 to 1.4 m a-1, which we tentatively attribute to a transient adaptation to hydrostatic equilibrium. We find evidence for elevated melting beneath ice shelf channels (with melting being concentrated on the channel's flanks). However, farther downstream from the grounding line, the majority of ice shelf channels advect passively (i.e. no melting nor refreezing) toward the ice shelf front. Although the absolute, satellite-based BMB values remain uncertain, we have high confidence in the spatial variability on sub-kilometre scales. This study highlights expected challenges for a full coupling between ice and ocean models.

Technical Note: Stored grain volume measurement using a low density point cloud

USDA-ARS?s Scientific Manuscript database

The mass of stored grain is often determined from volume measurements by crop insurers, government auditors, and stored grain managers conducting inventories. Recent increases in bin size have accentuated the difficulty of accounting for irregularities and variations in surface conditions in calcula...

Models projecting the fate of fish populations under climate change need to be based on valid physiological mechanisms.

PubMed

Lefevre, Sjannie; McKenzie, David J; Nilsson, Göran E

2017-09-01

Some recent modelling papers projecting smaller fish sizes and catches in a warmer future are based on erroneous assumptions regarding (i) the scaling of gills with body mass and (ii) the energetic cost of 'maintenance'. Assumption (i) posits that insurmountable geometric constraints prevent respiratory surface areas from growing as fast as body volume. It is argued that these constraints explain allometric scaling of energy metabolism, whereby larger fishes have relatively lower mass-specific metabolic rates. Assumption (ii) concludes that when fishes reach a certain size, basal oxygen demands will not be met, because of assumption (i). We here demonstrate unequivocally, by applying accepted physiological principles with reference to the existing literature, that these assumptions are not valid. Gills are folded surfaces, where the scaling of surface area to volume is not constrained by spherical geometry. The gill surface area can, in fact, increase linearly in proportion to gill volume and body mass. We cite the large body of evidence demonstrating that respiratory surface areas in fishes reflect metabolic needs, not vice versa, which explains the large interspecific variation in scaling of gill surface areas. Finally, we point out that future studies basing their predictions on models should incorporate factors for scaling of metabolic rate and for temperature effects on metabolism, which agree with measured values, and should account for interspecific variation in scaling and temperature effects. It is possible that some fishes will become smaller in the future, but to make reliable predictions the underlying mechanisms need to be identified and sought elsewhere than in geometric constraints on gill surface area. Furthermore, to ensure that useful information is conveyed to the public and policymakers about the possible effects of climate change, it is necessary to improve communication and congruity between fish physiologists and fisheries scientists. © 2017 John Wiley & Sons Ltd.

Closed Loop Active Flow Separation Detection and Control in a Multistage Compressor

NASA Technical Reports Server (NTRS)

Bright, Michelle M.; Culley, Dennis E.; Braunscheidel, Edward P.; Welch, Gerard E.

2005-01-01

Active closed loop flow control was successfully demonstrated on a full annulus of stator vanes in a low speed axial compressor. Two independent methods of detecting separated flow conditions on the vane suction surface were developed. The first technique detects changes in static pressure along the vane suction surface, while the second method monitors variation in the potential field of the downstream rotor. Both methods may feasibly be used in future engines employing embedded flow control technology. In response to the detection of separated conditions, injection along the suction surface of each vane was used. Injected mass flow on the suction surface of stator vanes is known to reduce separation and the resulting limitation on static pressure rise due to lowered diffusion in the vane passage. A control algorithm was developed which provided a proportional response of the injected mass flow to the degree of separation, thereby minimizing the performance penalty on the compressor system.

The response of glaciers to climate change

NASA Astrophysics Data System (ADS)

Klok, Elisabeth Jantina

2003-12-01

The research described in this thesis addresses two aspects of the response of glaciers to climate change. The first aspect deals with the physical processes that govern the interaction between glaciers and climate change and was treated by (1) studying the spatial and temporal variation of the glacier albedo from satellite images, (2) investigating the spatial distribution of the surface energy and mass balance of a glacier, and (3) investigating the sensitivity of the mass balance to climate change. All of these studies are focused on Morteratschgletscher in Switzerland. The second aspect is the climatic interpretation of glacier length fluctuations. This was studied by developing a model that calculates historical mass balance records from global glacier length fluctuations. To increase our understanding of the variations in glacier albedo, we derived surface albedos from 12 Landsat images. This constituted a stringent test for the retrieval methodology applied because Morteratschgletscher is very steep and rugged, which strongly influences the satellite signal. We aimed to retrieve surface albedos while taking into account all important processes that influence the relationship between the satellite signal and the surface albedo, e.g. the topographic effects on incoming solar radiation, and the anisotropic nature of the reflection pattern of ice and snow surfaces. We then analysed the spatial and temporal pattern of the surface albedo. We developed a two-dimensional mass balance model based on the surface energy balance to study the spatial distribution of the energy and mass balance fluxes of Morteratschgletscher. Meteorological data from weather stations in the vicinity of Morteratschgletscher serve as input for the model. We corrected incoming solar radiation for shading, aspect, slope, reflection from surrounding slopes, and obstruction of the sky. Ignoring these effects results in an increase in solar radiation of 37%, causing a decrease in the mass balance of 0.34 m w.e. We modelled the mass balance for 1999 and 2000 and analysed the spatial distribution. We then ran the model for a period of 23 years and calculated the mass balance sensitivity to climate change by perturbing air temperature and precipitation. The mass balance sensitivity to temperature and precipitation are ˜0.59 m w.e. a-1 K-1 and 0.17 m w.e. a-1 per 10 percent respectively. We also used three other albedo parameterisations to calculate the mass balance sensitivity since albedo parameterisations are often regarded as a main source of error in mass balance models. We concluded that an accurate estimate of the mass balance sensitivity requires a parameterisation that captures the process of a decreasing snow albedo when a snow pack gets older or thinner. To extract a climate signal from worldwide glacier length fluctuations, we developed a simple model. The climate signal is represented as a reconstruction of the mass balance and the equilibrium line altitude (ELA). The model was tested on seventeen European glacier length records and then applied to nineteen glacier length records from different parts of the world. Between 1910 and 1959, the average increase in the reconstructed ELAs is 33 m. This implies that during the first half of the twentieth century, the climate was warmer or drier than before. The reconstructed ELAs decrease to lower elevations after 1960 and up till 1980, when most of the reconstructions end. The results can be translated into a global temperature increase of about 0.8 K for the period 1910-1959

Evidence for Interannual to Decadal Variations in Hadley and Walker Circulations and Links to Water and Energy Fluxes

NASA Technical Reports Server (NTRS)

Robertson, Franklin; Bosilovich, Michael; Miller, Timothy

2007-01-01

Mass and energy transports associated with the Hadley and Walker circulations are important components of the earth s climate system and are strongly linked to hydrologic processes. Interannual to decadal variation in these flows likely signify a combination of natural climate noise as well as a response to anthropgenic forcing. There remains considerable uncertainty in quantifying variations in these flows. Evidence in the surface pressure record supports a weakening of the Walker circulation over the Pacific in recent decades. Conversely the NCEP / NCAR and ERA 40 reanalyses indicate that the Hadley circulation has increased in strength over the last two decades, though these analyses depict significantly different mass circulation changes. Interestingly, the NCEP - II / DOE reanalysis contains essentially no Hadley circulation changes. Most climate model integrations anticipate a weakening of both tropical circulations associated with stronger static stability. Clearly there is much uncertainty not only with the mass transports, but also how they are linked to water and energy balance of the planet through variations in turbulent heat and radiative fluxes and horizontal exports / imports of energy. Here we examine heat and water budget variations from a number of reanalysis products and focus on the linear and nonlinear response of ENSO warm and cold events as opportunities to study budget variations over the past 15-20 years. Our analysis addresses such questions as To what extent do Hadley and Walker Cell variations compensate each other on mass and energy transport? Do static stability adjustments appear to constrain fractional precipitation response vs. fractional water vapor response? We appeal to constraints offered by GPCP precipitation, SSWI ocean evaporation estimates, and ISCCP-FD radiative fluxes, and other satellite data sets to interpret and confirm reanalysis-based diagnostics. Using our findings we also attempt to place in context the recent findings that tropical ocean evaporation increased by order 5% or more during the 1990s, reconciling this with GPCP precipitation variations.

Aircraft Icing Handbook. Volume 1

DTIC Science & Technology

1991-03-01

Maryland - . . . Kohiman Aviation, Lawrence , Kansas Ohio State University, Columbus, Ohio .I --- t-r 1-- - -t I.Q,,- t ../e . Pratt and Whitney...lower; about six percent at -22 ’F (-30 *C). 1.2.3 Variations with Season The summer or warm season months create large warm air masses which can...on Aircraft Surfaces," NASA TM 87184, May 1986. 2-54 Hausman , R.J. and Turnock, S.R., "Investigation of Surface Water Behavior During Glaze Ice

Hydromechanical coupling in fractured rock masses: mechanisms and processes of selected case studies

NASA Astrophysics Data System (ADS)

Zangerl, Christian

2015-04-01

Hydromechanical (HM) coupling in fractured rock play an important role when events including dam failures, landslides, surface subsidences due to water withdrawal or drainage, injection-induced earthquakes and others are analysed. Generally, hydromechanical coupling occurs when a rock mass contain interconnected pores and fractures which are filled with water and pore/fracture pressures evolves. In the on hand changes in the fluid pressure can lead to stress changes, deformations and failures of the rock mass. In the other hand rock mass stress changes and deformations can alter the hydraulic properties and fluid pressures of the rock mass. Herein well documented case studies focussing on surface subsidence due to water withdrawal, reversible deformations of large-scale valley flanks and failure as well as deformation processes of deep-seated rock slides in fractured rock masses are presented. Due to pore pressure variations HM coupling can lead to predominantly reversible rock mass deformations. Such processes can be considered by the theory of poroelasticity. Surface subsidence reaching magnitudes of few centimetres and are caused by water drainage into deep tunnels are phenomenas which can be assigned to processes of poroelasticity. Recently, particular focus was given on large tunnelling projects to monitor and predict surface subsidence in fractured rock mass in oder to avoid damage of surface structures such as dams of large reservoirs. It was found that surface subsidence due to tunnel drainage can adversely effect infrastructure when pore pressure drawdown is sufficiently large and spatially extended and differential displacements which can be amplified due to topographical effects e.g. valley closure are occurring. Reversible surface deformations were also ascertained on large mountain slopes and summits with the help of precise deformation measurements i.e. permanent GPS or episodic levelling/tacheometric methods. These reversible deformations are often in the range of millimetres to a very few centimetres and can be linked to annual groundwater fluctuations. Due to pore pressure variations HM coupling can influence seepage forces and effective stresses in the rock mass. Effective stress changes can adversely affect the stability and deformation behaviour of deep-seated rock slides by influencing the shear strength or the time dependent (viscous) material behaviour of the basal shear zone. The shear strength of active shear zones is often reasonably well described by Coulomb's law. In Coulomb's law the operative normal stresses to the shear surface/zone are effective stresses and hence pore pressures which should be taken into account reduces the shear strength. According to the time dependent material behaviour a few effective stress based viscous models exists which are able to consider pore pressures. For slowly moving rock slides HM coupling could be highly relevant when low-permeability clayey-silty shear zones (fault gouges) are existing. An important parameters therefore is the hydraulic diffusivity, which is controlled by the permeability and fluid-pore compressibility of the shear zone, and by fluid viscosity. Thus time dependent pore pressure diffusion in the shear zone can either control the stability condition or the viscous behaviour (creep) of the rock slide. Numerous cases studies show that HM coupling can effect deformability, shear strength and time dependent behaviour of fractured rock masses. A process-based consideration can be important to avoid unexpected impacts on infrastructures and to understand complex rock mass as well rock slide behaviour.

Powerful non-geoeffective interplanetary disturbance of July 2012 observed by muon hodoscope URAGAN

NASA Astrophysics Data System (ADS)

Astapov, I. I.; Barbashina, N. S.; Petrukhin, A. A.; Shutenko, V. V.; Veselovsky, I. S.

2015-12-01

The most powerful coronal mass ejection of the 24th solar cycle took place on the opposite side of the Sun on July 23, 2012 and had no geomagnetic consequences. Nevertheless, as a result of passing of the ejection through the heliosphere, variations of galactic cosmic rays flux were observed on the Earth. These variations were registered by the muon hodoscope URAGAN (MEPhI, Moscow). Muon flux angular distributions on the Earth's surface are reported and analyzed.

Secular changes in Earth's shape and surface mass loading derived from combinations of reprocessed global GPS networks

NASA Astrophysics Data System (ADS)

Booker, David; Clarke, Peter J.; Lavallée, David A.

2014-09-01

The changing distribution of surface mass (oceans, atmospheric pressure, continental water storage, groundwater, lakes, snow and ice) causes detectable changes in the shape of the solid Earth, on time scales ranging from hours to millennia. Transient changes in the Earth's shape can, regardless of cause, be readily separated from steady secular variation in surface mass loading, but other secular changes due to plate tectonics and glacial isostatic adjustment (GIA) cannot. We estimate secular station velocities from almost 11 years of high quality combined GPS position solutions (GPS weeks 1,000-1,570) submitted as part of the first international global navigation satellite system service reprocessing campaign. Individual station velocities are estimated as a linear fit, paying careful attention to outliers and offsets. We remove a suite of a priori GIA models, each with an associated set of plate tectonic Euler vectors estimated by us; the latter are shown to be insensitive to the a priori GIA model. From the coordinate time series residuals after removing the GIA models and corresponding plate tectonic velocities, we use mass-conserving continental basis functions to estimate surface mass loading including the secular term. The different GIA models lead to significant differences in the estimates of loading in selected regions. Although our loading estimates are broadly comparable with independent estimates from other satellite missions, their range highlights the need for better, more robust GIA models that incorporate 3D Earth structure and accurately represent 3D surface displacements.

Inter-annual Variations in Snow/Firn Density over the Greenland Ice Sheet by Combining GRACE gravimetry and Envisat Altimetry

NASA Astrophysics Data System (ADS)

Su, X.; Shum, C. K.; Guo, J.; Howat, I.; Jezek, K. C.; Luo, Z.; Zhou, Z.

2017-12-01

Satellite altimetry has been used to monitor elevation and volume change of polar ice sheets since the 1990s. In order to derive mass change from the measured volume change, different density assumptions are commonly used in the research community, which may cause discrepancies on accurately estimating ice sheets mass balance. In this study, we investigate the inter-annual anomalies of mass change from GRACE gravimetry and elevation change from Envisat altimetry during years 2003-2009, with the objective of determining inter-annual variations of snow/firn density over the Greenland ice sheet (GrIS). High positive correlations (0.6 or higher) between these two inter-annual anomalies at are found over 93% of the GrIS, which suggests that both techniques detect the same geophysical process at the inter-annual timescale. Interpreting the two anomalies in terms of near surface density variations, over 80% of the GrIS, the inter-annual variation in average density is between the densities of snow and pure ice. In particular, at the Summit of Central Greenland, we validate the satellite data estimated density with the in situ data available from 75 snow pits and 9 ice cores. This study provides constraints on the currently applied density assumptions for the GrIS.

Deriving mass balance and calving variations from reanalysis data and sparse observations, Glaciar San Rafael, northern Patagonia, 1950-2005

NASA Astrophysics Data System (ADS)

Koppes, M.; Conway, H.; Rasmussen, L. A.; Chernos, M.

2011-09-01

Mass balance variations of Glaciar San Rafael, the northernmost tidewater glacier in the Southern Hemisphere, are reconstructed over the period 1950-2005 using NCEP-NCAR reanalysis climate data together with sparse, local historical observations of air temperature, precipitation, accumulation, ablation, thinning, calving, and glacier retreat. The combined observations over the past 50 yr indicate that Glaciar San Rafael has thinned and retreated since 1959, with a total mass loss of ~22 km3 of ice eq. Over that period, except for a short period of cooling from 1998-2003, the climate has become progressively warmer and drier, which has resulted primarily in pervasive thinning of the glacier surface and a decrease in calving rates, with only minor acceleration in retreat of the terminus. A comparison of calving fluxes derived from the mass balance variations and from theoretical calving and sliding laws suggests that calving rates are inversely correlated with retreat rates, and that terminus geometry is more important than balance fluxes to the terminus in driving calving dynamics. For Glaciar San Rafael, regional climate warming has not yet resulted in the significant changes in glacier length seen in other calving glaciers in the region, emphasizing the complex dynamics between climate inputs, topographic constraints and glacier response in calving glacier systems.

Modeling the Martian seasonal CO2 cycle. I - Fitting the Viking Lander pressure curves. II - Interannual variability

NASA Technical Reports Server (NTRS)

Wood, Stephen E.; Paige, David A.

1992-01-01

The present diurnal and seasonal thermal model for Mars, in which surface CO2 frost condensation and sublimation are determined by the net effects of radiation, latent heat, and heat conduction in subsurface soil layers, in order to simulate seasonal exchanges of CO2 between the polar caps and atmosphere, successfully reproduces the measured pressured variations at the Viking Lander 1 site. In the second part of this work, the year-to-year differences between measured surface pressures at Viking sites as a function of season are used as upper limits on the potential magnitudes of interannual variations in the Martian atmosphere's mass. Simulations indicate that the dust layers deposited onto the condensing north seasonal polar cap during dust storms can darken seasonal frost deposits upon their springtime uncovering, while having little effect on seasonal pressure variations.

The relationship between epicuticular long-chained hydrocarbons and surface area - volume ratios in insects (Diptera, Hymenoptera, Lepidoptera)

PubMed Central

Brückner, Adrian; Heethoff, Michael; Blüthgen, Nico

2017-01-01

Long-chain cuticular hydrocarbons (CHCs) are common components of the epicuticle of terrestrial arthropods. CHC serve as a protective barrier against environmental influences but also act as semiochemicals in animal communication. Regarding the latter aspect, species- or intra-functional group specific CHCs composition and variation are relatively well studied. However, comparative knowledge about the relationship of CHC quantity and their relation to surface area—volume ratios in the context of water loss and protection is fragmentary. Hence, we aim to study the taxon-specific relationship of the CHC amount and surface-area to volume ratio related to their functional role (e.g. in water loss). We focused on flower visiting insects and analyzed the CHC amounts of three insect orders (Hymenoptera, Lepidoptera and Diptera) using gas chromatography—mass spectrometry (GC-MS). We included 113 species from two grassland plots, quantified their CHCs, and measured their body mass and surface area. We found differences in the surface area, CHCs per body mass and the CHC density (= amount of CHCs per surface area) across the three insect taxa. Especially the Hymenoptera had a higher CHC density compared to Diptera and Lepidoptera. CHC density could be explained by surface area-volume ratios in Hymenoptera but not in Diptera and Lepidoptera. Unexpectedly, CHC density decreased with increasing surface area—volume ratios. PMID:28384308

Estimates of Ice Sheet Mass Balance from Satellite Altimetry: Past and Future

NASA Technical Reports Server (NTRS)

Zwally, H. Jay; Zukor, Dorothy J. (Technical Monitor)

2001-01-01

A major uncertainty in predicting sea level rise is the sensitivity of ice sheet mass balance to climate change, as well as the uncertainty in present mass balance. Since the annual water exchange is about 8 mm of global sea level equivalent, the 20% uncertainty in current mass balance corresponds to 1.6 mm/yr in sea level change. Furthermore, estimates of the sensitivity of the mass balance to temperature change range from perhaps as much as - 10% to + 10% per K. A principal purpose of obtaining ice sheet elevation changes from satellite altimetry has been estimation of the current ice sheet mass balance. Limited information on ice sheet elevation change and their implications about mass balance have been reported by several investigators from radar altimetry (Seasat, Geosat, ERS-1&2). Analysis of ERS-1&2 data over Greenland for 7 years from 1992 to 1999 shows mixed patterns of ice elevation increases and decreases that are significant in terms of regional-scale mass balances. Observed seasonal and interannual variations in ice surface elevation are larger than previously expected because of seasonal and interannUal variations in precipitation, melting, and firn compaction. In the accumulation zone, the variations in firn compaction are modeled as a function of temperature leaving variations in precipitation and the mass balance trend. Significant interannual variations in elevation in some locations, in particular the difference in trends from 1992 to 1995 compared to 1995 to 1999, can be explained by changes in precipitation over Greenland. Over the 7 years, trends in elevation are mostly positive at higher elevations and negative at lower elevations. In addition, trends for the winter seasons (from a trend analysis through the average winter elevations) are more positive than the corresponding trends for the summer. At lower elevations, the 7-year trends in some locations are strongly negative for summer and near zero or slightly positive for winter. These observations also demonstrate the potential for relating the variability in mass balance to changes in precipitation, temperature, and melting. Beginning in January 2002, NASA's ICESat laser altimeter mission will provide significantly better elevation accuracy and spatial coverage to 86E latitude and to the margins of the ice sheets.

A century of variation in the dependence of Greenland iceberg calving on ice sheet surface mass balance and regional climate change.

PubMed

Bigg, G R; Wei, H L; Wilton, D J; Zhao, Y; Billings, S A; Hanna, E; Kadirkamanathan, V

2014-06-08

Iceberg calving is a major component of the total mass balance of the Greenland ice sheet (GrIS). A century-long record of Greenland icebergs comes from the International Ice Patrol's record of icebergs (I48N) passing latitude 48° N, off Newfoundland. I48N exhibits strong interannual variability, with a significant increase in amplitude over recent decades. In this study, we show, through a combination of nonlinear system identification and coupled ocean-iceberg modelling, that I48N's variability is predominantly caused by fluctuation in GrIS calving discharge rather than open ocean iceberg melting. We also demonstrate that the episodic variation in iceberg discharge is strongly linked to a nonlinear combination of recent changes in the surface mass balance (SMB) of the GrIS and regional atmospheric and oceanic climate variability, on the scale of the previous 1-3 years, with the dominant causal mechanism shifting between glaciological (SMB) and climatic (ocean temperature) over time. We suggest that this is a change in whether glacial run-off or under-ice melting is dominant, respectively. We also suggest that GrIS calving discharge is episodic on at least a regional scale and has recently been increasing significantly, largely as a result of west Greenland sources.

Influence of regional-scale anthropogenic activity in northeast Asia on seasonal variations of surface ozone and carbon monoxide observed at Oki, Japan

NASA Astrophysics Data System (ADS)

Pochanart, Pakpong; Hirokawa, Jun; Kajii, Yoshizumi; Akimoto, Hajime; Nakao, Makoto

1999-02-01

Surface O3 and CO measurements were carried out at Oki, Japan during March 1994 to February 1996 in order to elucidate the processes determining temporal variations of O3 and CO in the northeast Asian Pacific rim region. The isentropic trajectory analysis was applied to sort out the influences of the air mass exchange under the Asian monsoon system and the regional-scale photochemical buildup of O3. The trajectories were categorized into five groups which cover background and regionally polluted air masses. The seasonal cycles of O3 and CO in the background continental air mass revealed spring maximum-summer minimum with averaged concentrations ranging from 32 and 120 ppb to 45 and 208 ppb, respectively. In contrast, O3 concentrations in the regionally polluted continental air mass ranged from 44 to 57 ppb and showed a winter minimum and a spring-summer-autumn broad maximum, which was characterized by photochemical O3 production due to anthropogenic activities in northeast Asia. CO concentrations in the same air mass showed a spring maximum of 271 ppb and a summer-autumn minimum of 180 ppb. The photochemical buildup of O3 resulting from anthropogenic activities in this region was estimated to be 21 ppb in summer, while its production was insignificant, an average 3 ppb, in winter. A comparison between data in northeast Asia and in Europe shows many similarities, supporting the contention that photochemical buildup of O3 from large-scale precursor emissions in both regions is very significant.

Transient Catalytic Combustor Model With Detailed Gas and Surface Chemistry

NASA Technical Reports Server (NTRS)

Struk, Peter M.; Dietrich, Daniel L.; Mellish, Benjamin P.; Miller, Fletcher J.; Tien, James S.

2005-01-01

In this work, we numerically investigate the transient combustion of a premixed gas mixture in a narrow, perfectly-insulated, catalytic channel which can represent an interior channel of a catalytic monolith. The model assumes a quasi-steady gas-phase and a transient, thermally thin solid phase. The gas phase is one-dimensional, but it does account for heat and mass transfer in a direction perpendicular to the flow via appropriate heat and mass transfer coefficients. The model neglects axial conduction in both the gas and in the solid. The model includes both detailed gas-phase reactions and catalytic surface reactions. The reactants modeled so far include lean mixtures of dry CO and CO/H2 mixtures, with pure oxygen as the oxidizer. The results include transient computations of light-off and system response to inlet condition variations. In some cases, the model predicts two different steady-state solutions depending on whether the channel is initially hot or cold. Additionally, the model suggests that the catalytic ignition of CO/O2 mixtures is extremely sensitive to small variations of inlet equivalence ratios and parts per million levels of H2.

Early type galaxies: Mapping out the two-dimensional space of galaxy star formation histories

NASA Astrophysics Data System (ADS)

Graves, Genevieve J.

Early type galaxies form a multi-parameter family, as evidenced by the two- dimensional (2-D) Fundamental Plane relationship. However, their star formation histories are often treated as a one-dimensional mass sequence. This dissertation presents a systematic study of the relationship between the multi- parameter structural properties of early type galaxies and their star formation histoires. We demonstrate that the stellar populations of early type galaxies span a 2-D space, which means that their star formation histories form a two- parameter family. This 2-D family is then mapped onto several familiar early type galaxy scaling relations, including the color-magnitude relation, the Fundamental Plane, and a cross-section through the Fundamental Plane. We find that the stellar population properties, and therefore the star formation histories of early type galaxies depend most strongly on galaxy velocity dispersion (s), rather than on luminosity ( L ), stellar mass ( M [low *] ), or dynamical mass ( M dyn ). Interestingly, stellar populations are independent of the radius ( R e ) of the galaxies. At fixed s, they show correlated residuals through the thickness of the Fundamental Plane (FP) in the surface-brightness ( I e ) dimension, such that low-surface-brightness galaxies are older, less metal-enriched, and more enhanced in Mg relative to Fe than their counterparts at the same s and R e on the FP midplane. Similarly, high- surface-brightness galaxies are younger, more metal-rich, and less Mg-enhanced than their counterparts on the FP midplane. These differences suggest that the duration of star formation varies through the thickness of the FP. If the dynamical mass-to-light ratios of early type galaxies ( M dyn /L ) were constant for all such galaxies, the FP would be equivalent to the plane predicted by the virial relation. However, the observed FP does not exactly match the virial plane. The FP is tilted from the virial plane, indicating that M dyn /L varies systematically across it. Furthermore the FP relation, although relatively tight, shows more scatter in surface brightness (at fixed s and R e ) than is predicted by observational errors. This finite thickness indicates that M dyn /L also varies at a fixed point on the FP. We observe that the stellar populations of early type galaxies vary through the thickness of the FP. These differences translate into variations in the stellar mass-to-light ratio ( M [low *] /L ) that contribute to both the tilt and the thickness of the FP. However, the mass-to-light variations due to stellar population differences are too small to explain either the tilt of the FP or its thickness. This implies that the tilt and thickness of the FP are driven by systematic variations in either the central dark matter fraction in galaxies or in the IMF with which they form stars. Furthermore, because star formation histories can be mapped onto locations in FP-space, the variations in central dark matter fraction or IMF differences must be correlated with differences in the galaxies' star formation histories.

Application of the double paddle oscillator for quantifying environmental, surface mass variation

NASA Astrophysics Data System (ADS)

Wei, Haoyan; Pomeroy, Joshua

2016-04-01

Sub-monolayer sensitivity to controlled gas adsorption and desorption is demonstrated using a double paddle oscillator (DPO) installed within an ultra-high vacuum (UHV) environmental chamber equipped with in situ film deposition, (multi)gas admission and temperature control. This effort is intended to establish a robust framework for quantitatively comparing mass changes due to gas loading and unloading on different materials systems selected or considered for use as mass artefacts. Our apparatus is composed of a UHV chamber with gas introduction and temperature control and in situ materials deposition for future materials testing enabling in situ preparation of virgin surfaces that can be monitored during initial exposure to gasses of interest. These tools are designed to allow us to comparatively evaluate how different materials gain or lose mass due to precisely controlled environmental excursions, with a long term goal of measuring changes in absolute mass. Herein, we provide a detailed experimental description of the apparatus, an evaluation of the initial performance, and demonstration measurements using nitrogen adsorption and desorption directly on the DPO.

Application of the double paddle oscillator for quantifying environmental, surface mass variation

PubMed Central

Wei, Haoyan; Pomeroy, Joshua

2016-01-01

Sub-monolayer sensitivity to controlled gas adsorption and desorption is demonstrated using a double paddle oscillator (DPO) installed within an UHV (ultra-high vacuum) environmental chamber equipped with in situ film deposition, (multi)gas admission and temperature control. This effort is intended to establish a robust framework for quantitatively comparing mass changes due to gas loading and unloading on different materials systems selected or considered for use as mass artifacts. Our apparatus is composed of a UHV chamber with gas introduction and temperature control and in-situ materials deposition for future materials testing enabling in situ preparation of virgin surfaces that can be monitored during initial exposure to gasses of interest. These tools are designed to allow us to comparatively evaluate how different materials gain or lose mass due to precisely controlled environmental excursions, with a long term goal of measuring changes in absolute mass. Herein, we provide a detailed experimental description of the apparatus, an evaluation of the initial performance, and demonstration measurements using nitrogen adsorption and desorption directly on the DPO. PMID:27212736

Seasonal variability of the Red Sea, from GRACE time-variable gravity and altimeter sea surface height measurements

NASA Astrophysics Data System (ADS)

Wahr, John; Smeed, David; Leuliette, Eric; Swenson, Sean

2014-05-01

Seasonal variability of sea surface height and mass within the Red Sea, occurs mostly through the exchange of heat with the atmosphere and wind-driven inflow and outflow of water through the strait of Bab el Mandab that opens into the Gulf of Aden to the south. The seasonal effects of precipitation and evaporation, of water exchange through the Suez Canal to the north, and of runoff from the adjacent land, are all small. The flow through the Bab el Mandab involves a net mass transfer into the Red Sea during the winter and a net transfer out during the summer. But that flow has a multi-layer pattern, so that in the summer there is actually an influx of cool water at intermediate (~100 m) depths. Thus, summer water in the southern Red Sea is warmer near the surface due to higher air temperatures, but cooler at intermediate depths (especially in the far south). Summer water in the northern Red Sea experiences warming by air-sea exchange only. The temperature profile affects the water density, which impacts the sea surface height but has no effect on vertically integrated mass. Here, we study this seasonal cycle by combining GRACE time-variable mass estimates, altimeter (Jason-1, Jason-2, and Envisat) measurements of sea surface height, and steric sea surface height contributions derived from depth-dependent, climatological values of temperature and salinity obtained from the World Ocean Atlas. We find good consistency, particularly in the northern Red Sea, between these three data types. Among the general characteristics of our results are: (1) the mass contributions to seasonal SSHT variations are much larger than the steric contributions; (2) the mass signal is largest in winter, consistent with winds pushing water into the Red Sea through the Strait of Bab el Mandab in winter, and out during the summer; and (3) the steric signal is largest in summer, consistent with summer sea surface warming.

Antarctic Firn Compaction Rates from Repeat-Track Airborne Radar Data: I. Methods

NASA Technical Reports Server (NTRS)

Medley, B.; Ligtenberg, S. R. M.; Joughin, I.; Van Den Broeke, M. R.; Gogineni, S.; Nowicki, S.

2015-01-01

While measurements of ice-sheet surface elevation change are increasingly used to assess mass change, the processes that control the elevation fluctuations not related to ice-flow dynamics (e.g. firn compaction and accumulation) remain difficult to measure. Here we use radar data from the Thwaites Glacier (West Antarctica) catchment to measure the rate of thickness change between horizons of constant age over different time intervals: 2009-10, 2010-11 and 2009-11. The average compaction rate to approximately 25m depth is 0.33ma(exp -1), with largest compaction rates near the surface. Our measurements indicate that the accumulation rate controls much of the spatio-temporal variations in the compaction rate while the role of temperature is unclear due to a lack of measurements. Based on a semi-empirical, steady-state densification model, we find that surveying older firn horizons minimizes the potential bias resulting from the variable depth of the constant age horizon. Our results suggest that the spatiotemporal variations in the firn compaction rate are an important consideration when converting surface elevation change to ice mass change. Compaction rates varied by up to 0.12ma(exp -1) over distances less than 6km and were on average greater than 20% larger during the 2010-11 interval than during 2009-10.

Intracyclic Velocity Variation of the Center of Mass and Hip in Breaststroke Swimming With Maximal Intensity.

PubMed

Gourgoulis, Vassilios; Koulexidis, Stylianos; Gketzenis, Panagiotis; Tzouras, Grigoris

2018-03-01

Gourgoulis, V, Koulexidis, S, Gketzenis, P, and Tzouras, G. Intra-cyclic velocity variation of the center of mass and hip in breaststroke swimming with maximal intensity. J Strength Cond Res 32(3): 830-840, 2018-The aim of the study was to compare the center of mass (CM) and hip (HIP) intracyclic velocity variation in breaststroke swimming using 3-dimensional kinematic analysis. Nine male breaststrokes, of moderate performance level, swam 25-m breaststroke with maximal intensity, and their movements were recorded, both under and above the water surface, using 8 digital cameras. Their CM and HIP velocities and their intracyclic variations were estimated after manual digitization of 28 selected points on the body in a complete arm and leg breaststroke cycle. Paired sample t-tests or Wilcoxon tests, when the assumption of normality was broken, were used for statistical analyses. In both, CM and HIP velocity-time curves, the results revealed a similar pattern of 2 clear peaks associated with the leg and arm propulsive phases and 2 minimal velocities that corresponded to the arm and leg recovery phase and the lag time between the leg and arm propulsive phases, respectively. However, despite this similar general pattern, the HIP minimum resultant velocity was significantly lower, whereas its maximal value was significantly greater, than the corresponding CM values. Consequently, the HIP intracyclic swimming velocity fluctuation significantly overestimates the actual variation of the swimmer's velocity in breaststroke swimming.

Long term ice sheet mass change rates and inter-annual variability from GRACE gravimetry.

NASA Astrophysics Data System (ADS)

Harig, C.

2017-12-01

The GRACE time series of gravimetry now stretches 15 years since its launch in 2002. Here we use Slepian functions to estimate the long term ice mass trends of Greenland, Antarctica, and several glaciated regions. The spatial representation shows multi-year to decadal regional shifts in accelerations, in agreement with increases in radar derived ice velocity. Interannual variations in ice mass are of particular interest since they can directly link changes in ice sheets to the drivers of change in the polar ocean and atmosphere. The spatial information retained in Slepian functions provides a tool to determine how this link varies in different regions within an ice sheet. We present GRACE observations of the 2013-2014 slowdown in mass loss of the Greenland ice sheet, which was concentrated in specific parts of the ice sheet and in certain months of the year. We also discuss estimating the relative importance of climate factors that control ice mass balance, as a function of location of the glacier/ice cap as well as the spatial variation within an ice sheet by comparing gravimetry with observations of surface air temperature, ocean temperature, etc. as well as model data from climate reanalysis products.

Heat and mass transfer in MHD free convection from a moving permeable vertical surface by a perturbation technique

NASA Astrophysics Data System (ADS)

Abdelkhalek, M. M.

2009-05-01

Numerical results are presented for heat and mass transfer effect on hydromagnetic flow of a moving permeable vertical surface. An analysis is performed to study the momentum, heat and mass transfer characteristics of MHD natural convection flow over a moving permeable surface. The surface is maintained at linear temperature and concentration variations. The non-linear coupled boundary layer equations were transformed and the resulting ordinary differential equations were solved by perturbation technique [Aziz A, Na TY. Perturbation methods in heat transfer. Berlin: Springer-Verlag; 1984. p. 1-184; Kennet Cramer R, Shih-I Pai. Magneto fluid dynamics for engineers and applied physicists 1973;166-7]. The solution is found to be dependent on several governing parameter, including the magnetic field strength parameter, Prandtl number, Schmidt number, buoyancy ratio and suction/blowing parameter, a parametric study of all the governing parameters is carried out and representative results are illustrated to reveal a typical tendency of the solutions. Numerical results for the dimensionless velocity profiles, the temperature profiles, the concentration profiles, the local friction coefficient and the local Nusselt number are presented for various combinations of parameters.

Climatic factors contributing to long-term variations in surface fine dust concentration in the United States

NASA Astrophysics Data System (ADS)

Pu, Bing; Ginoux, Paul

2018-03-01

High concentrations of dust particles can cause respiratory problems and increase non-accidental mortality. Studies found fine dust (with an aerodynamic diameter of less than 2.5 µm) is an important component of the total PM2.5 mass in the western and central US in spring and summer and has positive trends. This work examines climatic factors influencing long-term variations in surface fine dust concentration in the US using station data from the Interagency Monitoring Protected Visual Environments (IMPROVE) network during 1990-2015. The variations in the fine dust concentration can be largely explained by the variations in precipitation, surface bareness, and 10 m wind speed. Moreover, including convective parameters such as convective inhibition (CIN) and convective available potential energy (CAPE) that reveal the stability of the atmosphere better explains the variations and trends over the Great Plains from spring to fall.While the positive trend of fine dust concentration in the southwestern US in spring is associated with precipitation deficit, the increase in fine dust over the central Great Plains in summer is largely associated with enhanced CIN and weakened CAPE, which are caused by increased atmospheric stability due to surface drying and lower-troposphere warming. The strengthening of the Great Plains low-level jet also contributes to the increase in fine dust concentration in the central Great Plains in summer via its positive correlation with surface winds and negative correlation with CIN.Summer dusty days in the central Great Plains are usually associated with a westward extension of the North Atlantic subtropical high that intensifies the Great Plains low-level jet and also results in a stable atmosphere with subsidence and reduced precipitation.

A theoretical study of the spheroidal droplet evaporation in forced convection

NASA Astrophysics Data System (ADS)

Li, Jie; Zhang, Jian

2014-11-01

In many applications, the shape of a droplet may be assumed to be an oblate spheroid. A theoretical study is conducted on the evaporation of an oblate spheroidal droplet under forced convection conditions. Closed-form analytical expressions of the mass evaporation rate for an oblate spheroid are derived, in the regime of controlled mass-transfer and heat-transfer, respectively. The variation of droplet size during the evaporation process is presented in the regime of shrinking dynamic model. Comparing with the droplets having the same surface area, an increase in the aspect ratio enhances the mass evaporation rate and prolongs the burnout time.

Connection between Stellar Mass Distributions within Galaxies and Quenching Since z = 2

NASA Astrophysics Data System (ADS)

Mosleh, Moein; Tacchella, Sandro; Renzini, Alvio; Carollo, C. Marcella; Molaeinezhad, Alireza; Onodera, Masato; Khosroshahi, Habib G.; Lilly, Simon

2017-03-01

We study the history from z˜ 2 to z˜ 0 of the stellar mass assembly of quiescent and star-forming galaxies in a spatially resolved fashion. For this purpose, we use multi-wavelength imaging data from the Hubble Space Telescope (HST) over the GOODS fields and the Sloan Digital Sky Survey (SDSS) for the local population. We present the radial stellar mass surface density profiles of galaxies with {M}* > {10}10 {M}⊙ , corrected for mass-to-light ratio ({M}* /L) variations, and derive the half-mass-radius (R m ), central stellar mass surface density within 1 kpc ({{{Σ }}}1) and surface density at R m ({{{Σ }}}m) for star-forming and quiescent galaxies and study their evolution with redshift. At fixed stellar mass, the half-mass sizes of quiescent galaxies increase from z˜ 2 to z˜ 0 by a factor of ˜ 3-5, whereas the half-mass sizes of star-forming galaxies increase only slightly, by a factor of ˜2. The central densities {{{Σ }}}1 of quiescent galaxies decline slightly (by a factor of ≲ 1.7) from z˜ 2 to z˜ 0, while for star-forming galaxies {{{Σ }}}1 increases with time, at fixed mass. We show that the central density {{{Σ }}}1 has a tighter correlation with specific star-formation rate (sSFR) than {{{Σ }}}m and for all masses and redshifts galaxies with higher central density are more prone to be quenched. Reaching a high central density ({{{Σ }}}1≳ {10}10 {M}⊙ {{kpc}}2) seems to be a prerequisite for the cessation of star formation, though a causal link between high {{{Σ }}}1 and quenching is difficult to prove and their correlation can have a different origin.

Optimization of Crew Shielding Requirement in Reactor-Powered Lunar Surface Missions

NASA Technical Reports Server (NTRS)

Barghouty, Abdulnasser F.

2007-01-01

On the surface of the moon -and not only during heightened solar activities- the radiation environment As such that crew protection will be required for missions lasting in excess of six months. This study focuses on estimating the optimized crew shielding requirement for lunar surface missions with a nuclear option. Simple, transport-simulation based dose-depth relations of the three (galactic, solar, and fission) radiation sources am employed in a 1-dimensional optimization scheme. The scheme is developed to estimate the total required mass of lunar-regolith separating reactor from crew. The scheme was applied to both solar maximum and minimum conditions. It is shown that savings of up to 30% in regolith mass can be realized. It is argued, however, that inherent variation and uncertainty -mainly in lunar regolith attenuation properties in addition to the radiation quality factor- can easily defeat this and similar optimization schemes.

Optimization of Crew Shielding Requirement in Reactor-Powered Lunar Surface Missions

NASA Technical Reports Server (NTRS)

Barghouty, A. F.

2007-01-01

On the surface of the moon and not only during heightened solar activities the radiation environment is such that crew protection will be required for missions lasting in excess of six months. This study focuses on estimating the optimized crew shielding requirement for lunar surface missions with a nuclear option. Simple, transport-simulation based dose-depth relations of the three radiation sources (galactic, solar, and fission) are employed in a one-dimensional optimization scheme. The scheme is developed to estimate the total required mass of lunar regolith separating reactor from crew. The scheme was applied to both solar maximum and minimum conditions. It is shown that savings of up to 30% in regolith mass can be realized. It is argued, however, that inherent variation and uncertainty mainly in lunar regolith attenuation properties in addition to the radiation quality factor can easily defeat this and similar optimization schemes.

Satellite remote sensing of surface energy and mass balance - Results from FIFE

NASA Technical Reports Server (NTRS)

Hall, F. G.; Markham, B. J.; Wang, J. R.; Huemmrich, F.; Sellers, P. J.; Strebel, D. E.; Kanemasu, E. T.; Kelly, Robert D.; Blad, Blaine L.

1991-01-01

Results obtained from the FIFE experiments conducted in 1987 and 1989 are summarized. Data analyses indicate that the hypotheses linking energy balance components to surface biology and remote sensing are reasonable at a point level, and that satellite remote sensing can potentially provide useful estimates of the surface energy budget. An investigation of atmospheric scattering and absorption effects on satellite remote sensing of surface radiance shows that the magnitude of atmospheric opacity variations within the FIFE site and with season can have a large effect on satellite measured values of surface radiances. Comparisons of atmospherically corrected TM radiances with surface measured radiances agreed to within about two percent at the visible and near-infrared wavelengths and to 6 percent in the midinfrared.

Parametric Dielectric Model of Comet Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Heggy, E.; Palmer, E. M.; Kofman, W. W.; Clifford, S. M.; Righter, K.; Herique, A.

2012-12-01

In 2014, the European Space Agency's Rosetta mission is scheduled to rendezvous with Comet 67P/Churyumov-Gerasimenko (Comet 67P). Rosetta's CONSERT experiment aims to explore the cometary nucleus' geophysical properties using radar tomography. The expected scientific return and inversion algorithms are mainly dependent on our understanding of the dielectric properties of the comet nucleus and how they vary with the spatial distribution of geophysical parameters. Using observations of comets 9P/Tempel 1 and 81P/Wild 2 in combination with dielectric laboratory measurements of temperature, porosity, and dust-to-ice mass ratio dependencies for cometary analog material, we have constructed two hypothetical three-dimensional parametric dielectric models of Comet 67P's nucleus to assess different dielectric scenarios of the inner structure. Our models suggest that dust-to-ice mass ratios and porosity variations generate the most significant measurable dielectric contrast inside the comet nucleus, making it possible to explore the structural and compositional hypotheses of cometary nuclei. Surface dielectric variations, resulting from temperature changes induced by solar illumination of the comet's faces, have also been modeled and suggest that the real part of the dielectric constant varies from 1.9 to 3.0, hence changing the surface radar reflectivity. For CONSERT, this variation could be significant at low incidence angles, when the signal propagates through a length of dust mantle comparable to the wavelength. The overall modeled dielectric permittivity spatial and temporal variations are therefore consistent with the expected deep penetration of CONSERT's transmitted wave through the nucleus. It is also clear that changes in the physical properties of the nucleus induce sufficient variation in the dielectric properties of cometary material to allow their inversion from radar tomography.

Generalized effective-mass theory of subsurface scanning tunneling microscopy: Application to cleaved quantum dots

NASA Astrophysics Data System (ADS)

Roy, M.; Maksym, P. A.; Bruls, D.; Offermans, P.; Koenraad, P. M.

2010-11-01

An effective-mass theory of subsurface scanning tunneling microscopy (STM) is developed. Subsurface structures such as quantum dots embedded into a semiconductor slab are considered. States localized around subsurface structures match on to a tail that decays into the vacuum above the surface. It is shown that the lateral variation in this tail may be found from a surface envelope function provided that the effects of the slab surfaces and the subsurface structure decouple approximately. The surface envelope function is given by a weighted integral of a bulk envelope function that satisfies boundary conditions appropriate to the slab. The weight function decays into the slab inversely with distance and this slow decay explains the subsurface sensitivity of STM. These results enable STM images to be computed simply and economically from the bulk envelope function. The method is used to compute wave-function images of cleaved quantum dots and the computed images agree very well with experiment.

Real time in situ ellipsometric and gravimetric monitoring for electrochemistry experiments.

PubMed

Broch, Laurent; Johann, Luc; Stein, Nicolas; Zimmer, Alexandre; Beck, Raphaël

2007-06-01

This work describes a new system using real time spectroscopic ellipsometer with simultaneous electrochemical and electrochemical quartz crystal microbalance (EQCM) measurements. This method is particularly adapted to characterize electrolyte/electrode interfaces during electrochemical and chemical processes in liquid medium. The ellipsometer, based on a rotating compensator Horiba Jobin-Yvon ellipsometer, has been adapted to acquire Psi-Delta spectra every 25 ms on a spectral range fixed from 400 to 800 nm. Measurements with short sampling times are only achievable with a fixed analyzer position (A=45 degrees ). Therefore the ellipsometer calibration is extremely important for high precision measurements and we propose a spectroscopic calibration (i.e., determination of the azimuth of elements according to the wavelength) on the whole spectral range. A homemade EQCM was developed to detect mass variations attached to the electrode. This additional instrument provides further information useful for ellipsometric data modeling of complex electrochemical systems. The EQCM measures frequency variations of piezoelectric quartz crystal oscillator working at 5 MHz. These frequency variations are linked to mass variations of electrode surface with a precision of 20 ng cm(-2) every 160 ms. Data acquisition has been developed in order to simultaneously record spectroscopic ellipsometry, EQCM, and electrochemical measurements by a single computer. Finally the electrodeposition of bismuth telluride film was monitored by this new in situ experimental setup and the density of electroplated layers was extracted from the optical thickness and EQCM mass.

Ambient ionisation mass spectrometry for in situ analysis of intact proteins

PubMed Central

Kocurek, Klaudia I.; Griffiths, Rian L.

2018-01-01

Abstract Ambient surface mass spectrometry is an emerging field which shows great promise for the analysis of biomolecules directly from their biological substrate. In this article, we describe ambient ionisation mass spectrometry techniques for the in situ analysis of intact proteins. As a broad approach, the analysis of intact proteins offers unique advantages for the determination of primary sequence variations and posttranslational modifications, as well as interrogation of tertiary and quaternary structure and protein‐protein/ligand interactions. In situ analysis of intact proteins offers the potential to couple these advantages with information relating to their biological environment, for example, their spatial distributions within healthy and diseased tissues. Here, we describe the techniques most commonly applied to in situ protein analysis (liquid extraction surface analysis, continuous flow liquid microjunction surface sampling, nano desorption electrospray ionisation, and desorption electrospray ionisation), their advantages, and limitations and describe their applications to date. We also discuss the incorporation of ion mobility spectrometry techniques (high field asymmetric waveform ion mobility spectrometry and travelling wave ion mobility spectrometry) into ambient workflows. Finally, future directions for the field are discussed. PMID:29607564

Atmospheric Rotational Effects on Mars Based on the NASA Ames General Circulation Model: Angular Momentum Approach

NASA Technical Reports Server (NTRS)

Sanchez, Braulio V.; Haberle, Robert M.; Schaeffer, James

2004-01-01

The objective of the investigation is to determine the motion of the rotational axis of Mars as a result of mass variations in the atmosphere and condensation and sublimation of CO2 ice on the polar caps. A planet experiences this type of motion if it has an atmosphere, which is changing its mass distribution with respect to the solid body of the planet and/or it is asymmetrically changing the amount of ice at the polar caps. The physical principle involved is the conservation of angular momentum, one can get a feeling for it by sitting on a well oiled swivel chair holding a rotating wheel on a horizontal direction and then changing the rotation axis of the wheel to a vertical direction. The person holding the wheel and the chair would begin to rotate in opposite direction to the rotation of the wheel. The motions of Mars atmosphere and the ice caps variations are obtained from a mathematical model developed at the NASA Ames Research Center. The model produces outputs for a time span of one Martian year, which is equivalent to 687 Earth days. The results indicate that Mars axis of rotation moves in a spiral with respect to a reference point on the surface of the planet. It can move as far away as 35.3 cm from the initial location as a result of both mass variations in the atmosphere and asymmetric ice variations at the polar caps. Furthermore the pole performs close to two revolutions around the reference point during a Martian year. This motion is a combination of two motions, one produced by the atmospheric mass variations and another due to the variations in the ice caps. The motion due to the atmospheric variations is a spiral performing about two and a half revolutions around the reference point during which the pole can move as far as 40.9 cm. The motion due to variations in the ice caps is a spiral performing almost three revolutions during which the pole can move as far as 32.8 cm.

Stability analysis of nanoscale surface patterns in stressed solids

NASA Astrophysics Data System (ADS)

Kostyrko, Sergey A.; Shuvalov, Gleb M.

2018-05-01

Here, we use the theory of surface elasticity to extend the morphological instability analysis of stressed solids developed in the works of Asaro, Tiller, Grinfeld, Srolovitz and many others. Within the framework of Gurtin-Murdoch model, the surface phase is assumed to be a negligibly thin layer with the elastic properties which differ from those of the bulk material. We consider the mass transport mechanism driven by the variation of surface and bulk energy along undulated surface of stressed solid. The linearized surface evolution equation is derived in the case of plane strain conditions and describes the amplitude change of surface perturbations with time. A parametric analysis of this equation leads to the definition of critical conditions which depend on undulation wavelength, residual surface stress, applied loading, surface and bulk elastic constants and predict the surface morphological stability.

Deriving mass balance and calving variations from reanalysis data and sparse observations, Glaciar San Rafael, northern Patagonia, 1950-2005

NASA Astrophysics Data System (ADS)

Koppes, M.; Conway, H.; Rasmussen, L. A.; Chernos, M.

2011-04-01

Mass balance variations of Glaciar San Rafael, the most equatorial tidewater glacier in the North Patagonian Icefield, are reconstructed over the period 1950-2005 using NCEP-NCAR reanalysis climate data together with sparse, local historical observations of air temperature, precipitation, accumulation, ablation, thinning, calving, and glacier retreat. The combined observations over the past 50 yr indicate that Glaciar San Rafael has thinned and retreated since 1959, with a total mass loss of ~22 km3 of ice equivalent. Over that period, except for a short period of cooling from 1998-2003, the climate has become progressively warmer and drier, which has resulted primarily in pervasive thinning of the glacier surface and a decrease in calving rates, with only minor acceleration in retreat of the terminus. A comparison of calving fluxes derived from the mass balance variations and from theoretical calving and sliding laws suggest that calving rates are inversely correlated with retreat rates, and that terminus geometry is more important than changes in balance fluxes to the terminus in driving calving dynamics. For Glaciar San Rafael, regional climate warming has not yet resulted in the significant changes in glacier length seen in other calving glaciers in the region, emphasizing the complex dynamics between climate inputs, topographic constraints and glacier response in calving glacier systems.

Three-dimensional biomechanical properties of human vocal folds: parameter optimization of a numerical model to match in vitro dynamics.

PubMed

Yang, Anxiong; Berry, David A; Kaltenbacher, Manfred; Döllinger, Michael

2012-02-01

The human voice signal originates from the vibrations of the two vocal folds within the larynx. The interactions of several intrinsic laryngeal muscles adduct and shape the vocal folds to facilitate vibration in response to airflow. Three-dimensional vocal fold dynamics are extracted from in vitro hemilarynx experiments and fitted by a numerical three-dimensional-multi-mass-model (3DM) using an optimization procedure. In this work, the 3DM dynamics are optimized over 24 experimental data sets to estimate biomechanical vocal fold properties during phonation. Accuracy of the optimization is verified by low normalized error (0.13 ± 0.02), high correlation (83% ± 2%), and reproducible subglottal pressure values. The optimized, 3DM parameters yielded biomechanical variations in tissue properties along the vocal fold surface, including variations in both the local mass and stiffness of vocal folds. That is, both mass and stiffness increased along the superior-to-inferior direction. These variations were statistically analyzed under different experimental conditions (e.g., an increase in tension as a function of vocal fold elongation and an increase in stiffness and a decrease in mass as a function of glottal airflow). The study showed that physiologically relevant vocal fold tissue properties, which cannot be directly measured during in vivo human phonation, can be captured using this 3D-modeling technique. © 2012 Acoustical Society of America

Three-dimensional biomechanical properties of human vocal folds: Parameter optimization of a numerical model to match in vitro dynamics

PubMed Central

Yang, Anxiong; Berry, David A.; Kaltenbacher, Manfred; Döllinger, Michael

2012-01-01

The human voice signal originates from the vibrations of the two vocal folds within the larynx. The interactions of several intrinsic laryngeal muscles adduct and shape the vocal folds to facilitate vibration in response to airflow. Three-dimensional vocal fold dynamics are extracted from in vitro hemilarynx experiments and fitted by a numerical three-dimensional-multi-mass-model (3DM) using an optimization procedure. In this work, the 3DM dynamics are optimized over 24 experimental data sets to estimate biomechanical vocal fold properties during phonation. Accuracy of the optimization is verified by low normalized error (0.13 ± 0.02), high correlation (83% ± 2%), and reproducible subglottal pressure values. The optimized, 3DM parameters yielded biomechanical variations in tissue properties along the vocal fold surface, including variations in both the local mass and stiffness of vocal folds. That is, both mass and stiffness increased along the superior-to-inferior direction. These variations were statistically analyzed under different experimental conditions (e.g., an increase in tension as a function of vocal fold elongation and an increase in stiffness and a decrease in mass as a function of glottal airflow). The study showed that physiologically relevant vocal fold tissue properties, which cannot be directly measured during in vivo human phonation, can be captured using this 3D-modeling technique. PMID:22352511

Improving the detection of tectonic transients in Japan by accounting for Earth's deformation response to surface mass loading

NASA Astrophysics Data System (ADS)

Martens, H. R.; Simons, M.; Moore, A. W.; Owen, S. E.; Rivera, L. A.

2016-12-01

We explore the contributions of oceanic, atmospheric, and hydrologic mass loading to Global Navigation Satellite System (GNSS)-inferred observations of surface displacements in Japan. Surface mass loading (SML) generates mm- to cm-level deformation of the solid Earth on time scales of hours to years, which exceeds the measurement uncertainties of most GNSS position estimates. By improving the efficiency and accuracy of the prediction and empirical estimation of SML response, we aim to reduce the variance of GNSS time series and therefore enhance the ability to resolve subtle tectonic signals, such as aseismic transients associated with subduction zone processes. Using the GIPSY software in precise point positioning mode, we estimate time series of sub-daily receiver positions for the GNSS Earth Observation Network System (GEONET) in Japan. We also model the Earth's elastic deformation response to a variety of surface mass loads, including loads of atmospheric (e.g., ECMWF) and oceanic (e.g., TPXO8-Atlas, ECCO2) origin. We extract periodic signals, such as the ocean tides and seasonal variations in hydrological loading, using harmonic analysis. Deformation caused by non-periodic loads, such as non-tidal oceanic and atmospheric loads, can be predicted and removed to further reduce the variance. We seek to streamline the workflow for estimating SML-induced surface displacements from a variety of sources in order to account for loading signals in routine GNSS data processing, thereby improving the ability to assess the mechanics of plate boundaries.

Translational errors in expression of Shiga toxin from pathogenic Escherichia coli as measured by MALDI-TOF-TOF and Orbitrap mass spectrometry

USDA-ARS?s Scientific Manuscript database

Introduction: Shiga toxin (Stx) is an AB5 toxin expressed by Shiga toxin-producing E. coli (STEC) and Shigella dysenteriae. The Stx holotoxin attaches to surface receptors of eukaryotic cells. After cellular envelopment, the toxin disrupts ribosomal protein synthesis causing cell death. Variations i...

Lunar and Planetary Science XXXV: Outer Solar System

NASA Technical Reports Server (NTRS)

2004-01-01

The session "Outer Solar System" included the following reports:New Data About Seasonal Variations of the North-South Asymmetry of Polarized Light of Jupiter; Appearance of Second Harmonic in the Jupiter Spectrum; Dynamics of Confined Liquid Mass, Spreading on Planet Surface; "Cassini" will Discover 116 New Satellites of Saturn!; Jupiter's Light Reflection Law;and Internal Structure Modelling of Europa.

Mathematical Investigation of Fluid Flow, Mass Transfer, and Slag-steel Interfacial Behavior in Gas-stirred Ladles

NASA Astrophysics Data System (ADS)

Cao, Qing; Nastac, Laurentiu

2018-06-01

In this study, the Euler-Euler and Euler-Lagrange modeling approaches were applied to simulate the multiphase flow in the water model and gas-stirred ladle systems. Detailed comparisons of the computational and experimental results were performed to establish which approach is more accurate for predicting the gas-liquid multiphase flow phenomena. It was demonstrated that the Euler-Lagrange approach is more accurate than the Euler-Euler approach. The Euler-Lagrange approach was applied to study the effects of the free surface setup, injected bubble size, gas flow rate, and slag layer thickness on the slag-steel interaction and mass transfer behavior. Detailed discussions on the flat/non-flat free surface assumption were provided. Significant inaccuracies in the prediction of the surface fluid flow characteristics were found when the flat free surface was assumed. The variations in the main controlling parameters (bubble size, gas flow rate, and slag layer thickness) and their potential impact on the multiphase fluid flow and mass transfer characteristics (turbulent intensity, mass transfer rate, slag-steel interfacial area, flow patterns, etc.,) in gas-stirred ladles were quantitatively determined to ensure the proper increase in the ladle refining efficiency. It was revealed that by injecting finer bubbles as well as by properly increasing the gas flow rate and the slag layer thickness, the ladle refining efficiency can be enhanced significantly.

Morphometric attributes to understand palaeogeomorphological controls on mass-transport deposits offshore Brazil

NASA Astrophysics Data System (ADS)

Piedade, Aldina; Alves, Tiago; Luís Zêzere, José

2017-04-01

Mass-transport deposits form a significant part of the stratigraphic record of ancient and modern deep-water basins worldwide. Three-dimensional (3D) seismic data is used to analyse two different types of buried mass-transport deposits offshore Espírito Santo Basin (SE Brazil. Both types are developed within Early Miocene to Holocene stratigraphic units composed of sandstones, calcarenites, turbidite sands and marls. The high resolution images provided by the interpreted 3D seismic data allowed a detailed analysis of the seismic stratigraphy and internal structure of mass-transport deposits. In addition, improvements in visualisation techniques were used to compute simple morphometric attributes of buried mass-transport deposits in continental slopes. This study classifies the interpreted mass-transport deposits in two different types according to the relationship between the morphology of mass-transport deposits and the surrounding topography. Locally confined mass-transport deposits are laterally constrained by non-deformed strata that surrounds the mass-transport deposit and by the local topography of the depositional surface. Their dimensions are relatively small (area of 5.251 km2). Unconfined mass-transport deposits show a much larger volume compared to the previously type ( 87.180 km2), and local topography does not have control on their geometry. The analysis proves that local topography and geometry of the depositional surface are key controlling factors on the spatial distribution and dimensions of the two types of mass-transport deposits. However, the two types differ in size, geomorphological expression, local structural controls and run-out distance. This work importance is relate variations in the character of the depositional surface with the morphology mass-transport deposits and run-out distance. As a result of the methodology used, two different styles of mass-transport run-out are identified and local factors controlling their morphology are addressed, such as roughness and local morphology of the depositional surface. Separating these two styles, or types, of mass-transport deposits it is of critical importance to understand their mechanisms of gliding, downslope spreading and emplacement.

Seasonal and diurnal variations of ozone at a high-altitude mountain baseline station in East Asia

NASA Astrophysics Data System (ADS)

Ou Yang, Chang-Feng; Lin, Neng-Huei; Sheu, Guey-Rong; Lee, Chung-Te; Wang, Jia-Lin

2012-01-01

Continuous measurements of tropospheric ozone were conducted at the Lulin Atmospheric Background Station (LABS) at an altitude of 2862 m from April 2006 to the end of 2009. Distinct seasonal variations in the ozone concentration were observed at the LABS, with a springtime maximum and a summertime minimum. Based on a backward trajectory analysis, CO data, and ozonesondes, the springtime maximum was most likely caused by the long-range transport of air masses from Southeast Asia, where biomass burning was intense in spring. In contrast, a greater Pacific influence contributed to the summertime minimum. In addition to seasonal variations, a distinct diurnal pattern was also observed at the LABS, with a daytime minimum and a nighttime maximum. The daytime ozone minimum was presumably caused by sinks of dry deposition and NO titration during the up-slope transport of surface air. The higher nighttime values, however, could be the result of air subsidence at night bringing ozone aloft to the LABS. After filtering out the daytime data to remove possible local surface contributions, the average background ozone value for the period of 2006-2009 was approximately 36.6 ppb, increased from 32.3 ppb prior to data filtering, without any changes in the seasonal pattern. By applying HYSPLIT4 model analysis, the origins of the air masses contributing to the background ozone observed at the LABS were investigated.

Evaluation of residual uranium contamination in the dirt floor of an abandoned metal rolling mill.

PubMed

Glassford, Eric; Spitz, Henry; Lobaugh, Megan; Spitler, Grant; Succop, Paul; Rice, Carol

2013-02-01

A single, large, bulk sample of uranium-contaminated material from the dirt floor of an abandoned metal rolling mill was separated into different types and sizes of aliquots to simulate samples that would be collected during site remediation. The facility rolled approximately 11,000 tons of hot-forged ingots of uranium metal approximately 60 y ago, and it has not been used since that time. Thirty small mass (≈ 0.7 g) and 15 large mass (≈ 70 g) samples were prepared from the heterogeneously contaminated bulk material to determine how measurements of the uranium contamination vary with sample size. Aliquots of bulk material were also resuspended in an exposure chamber to produce six samples of respirable particles that were obtained using a cascade impactor. Samples of removable surface contamination were collected by wiping 100 cm of the interior surfaces of the exposure chamber with 47-mm-diameter fiber filters. Uranium contamination in each of the samples was measured directly using high-resolution gamma ray spectrometry. As expected, results for isotopic uranium (i.e., U and U) measured with the large-mass and small-mass samples are significantly different (p < 0.001), and the coefficient of variation (COV) for the small-mass samples was greater than for the large-mass samples. The uranium isotopic concentrations measured in the air and on the wipe samples were not significantly different and were also not significantly different (p > 0.05) from results for the large- or small-mass samples. Large-mass samples are more reliable for characterizing heterogeneously distributed radiological contamination than small-mass samples since they exhibit the least variation compared to the mean. Thus, samples should be sufficiently large in mass to insure that the results are truly representative of the heterogeneously distributed uranium contamination present at the facility. Monitoring exposure of workers and the public as a result of uranium contamination resuspended during site remediation should be evaluated using samples of sufficient size and type to accommodate the heterogeneous distribution of uranium in the bulk material.

Variations of surface ozone concentration across the Klang Valley, Malaysia

NASA Astrophysics Data System (ADS)

Latif, Mohd Talib; Huey, Lim Shun; Juneng, Liew

2012-12-01

Hourly air quality data covering the period 2004-2008 was obtained from the Air Quality Division, the Department of Environment (DOE) through long-term monitoring by Alam Sekitar Sdn. Bhd. (ASMA) were analysed to investigate the variations of surface ozone (O3) in the Klang Valley, Malaysia. A total of nine monitoring stations were selected for analysis in this study and the results show that there are distinct seasonal patterns in the surface O3 across the Klang Valley. A high surface O3 concentration is usually observed between January and April, while a low surface O3 concentration is found between June and August. Analysis of daily variations in surface O3 and the precursors - NO, NO2, CO, NMHC and UVb, indicate that the surface O3 photochemistry in this study area exhibits a positive response to the intensity and wavelength in UVb while being influenced by the concentration of NOx, particularly through tritration processes. Although results from our study suggested that NMHCs may influence the maximum O3 concentration, further investigation is required. Wind direction during different monsoons was found to influence the concentration of O3 around the Klang Valley. HYSPLIT back trajectories (-72 h) were used to indicate the air-mass transport patterns on days with high concentrations of surface O3 in the study area. Results show that 47% of the high O3 days was associated with the localized circulation. The remaining 32% and 22% were associated with mid-range and long-range transport across the South China Sea from the northeast.

Interactions between Lakes and the Atmosphere over the Largest High-Altitude Saline Lake on the Qinghai-Tibet Plateau

NASA Astrophysics Data System (ADS)

Li, X.

2017-12-01

Interactions between lakes and the atmosphere at high-altitudes are still poorly understood due to difficulty in accessibility of direct measurements. This is particularly true for the Qinghai-Tibet Plateau (QTP), where approximately 50% of the lakes in China are located. Continuous direct measurements of the water flux and surface energy budget were made over the largest high-altitude saline lake in China, Qinghai Lake on the northeastern QTP, using the eddy covariance (EC) method from 11 May, 2013 through 10 May, 2015. Results indicated that net radiation and heat storage showed consistent diurnal variation with positive values in the daytime and negative values at night, while latent and sensible heat flux showed little diurnal variation. Nocturnal λE and H contributed to 47.7% and 29.0% of the total heat loss, during the two- year study period. Annual evaporation of Qinghai Lake was 832.5 mm for 2013/2014 and 823.6 mm for 2014/2015, respectively. The surface energy budget and evaporation showed a strong seasonal pattern, with peaks in the latent and sensible heat flux observed in autumn and early winter. There was a 2-3 month delay between the maximum net radiation and maximum latent and sensible heat fluxes. Intraseasonal and seasonal variations in latent and sensible heat flux were strongly affected by different air masses. Westerly cold and dry air masses increased evaporation while southeast moist air mass suppressed evaporation, suggesting that the lakes might serve as an 'air-conditioner' to modify the temporal heat and water flux in QTP. Latent heat flux (λE) during the ice-covered period was less than that during the ice-free period, and lake ice sublimation is perhaps a main possible source for λE during the freeze-up period.

The Importance of the 13C(α,n)16O Reaction in Asymptotic Giant Branch Stars

NASA Astrophysics Data System (ADS)

Cristallo, S.; La Cognata, M.; Massimi, C.; Best, A.; Palmerini, S.; Straniero, O.; Trippella, O.; Busso, M.; Ciani, G. F.; Mingrone, F.; Piersanti, L.; Vescovi, D.

2018-06-01

Low-mass asymptotic giant branch stars are among the most important polluters of the interstellar medium. In their interiors, the main component (A ≳ 90) of the slow neutron capture process (the s-process) is synthesized, the most important neutron source being the 13C(α,n)16O reaction. In this paper, we review its current experimental status, discussing possible future synergies between some experiments currently focused on the determination of its rate. Moreover, in order to determine the level of precision needed to fully characterize this reaction, we present a theoretical sensitivity study, carried out with the FUNS evolutionary stellar code and the NEWTON post-process code. We modify the rate up to a factor of 2 with respect to a reference case. We find that variations of the 13C(α,n)16O rate do not appreciably affect s-process distributions for masses above 3 M ⊙ at any metallicity. Apart from a few isotopes, in fact, the differences are always below 5%. The situation is completely different if some 13C burns in a convective environment: this occurs in FUNS models with M < 3 M ⊙ at solar-like metallicities. In this case, a change of the 13C(α,n)16O reaction rate leads to nonnegligible variations of the element surface distribution (10% on average), with larger peaks for some elements (such as rubidium) and neutron-rich isotopes (such as 86Kr and 96Zr). Larger variations are found in low-mass, low-metallicity models if protons are mixed and burned at very high temperatures. In this case, the surface abundances of the heavier elements may vary by more than a factor of 50.

Antarctic mass balance changes from GRACE

NASA Astrophysics Data System (ADS)

Kallenberg, B.; Tregoning, P.

2012-04-01

The Antarctic ice sheet contains ~30 million km3 of ice and constitutes a significant component of the global water balance with enough freshwater to raise global sea level by ~60 m. Altimetry measurements and climate models suggest variable behaviour across the Antarctic ice sheet, with thickening occurring in a vast area of East Antarctica and substantial thinning in West Antarctica caused by increased temperature gradients in the surrounding ocean. However, the rate at which the polar ice cap is melting is still poorly constrained. To calculate the mass loss of an ice sheet it is necessary to separate present day mass balance changes from glacial isostatic adjustment (GIA), the response of the Earth's crust to mass loss, wherefore it is essential to undertake sufficient geological and geomorphological sampling. As there is only a limited possibility for this in Antarctica, all models (i.e. geological, hydrological as well as atmospheric) are very poorly constrained. Therefore, space-geodetic observations play an important role in detecting changes in mass and spatial variations in the Earth's gravity field. The Gravity Recovery And Climate Experiment (GRACE) observed spatial variations in the Earth's gravity field over the past ten years. The satellite detects mass variations in the Earth system including geophysical, hydrological and atmospheric shifts. GRACE itself is not able to separate the GIA from mass balance changes and, due to the insufficient geological and geomorphological database, it is not possible to model the GIA effect accurately for Antarctica. However, the results from GRACE can be compared with other scientific results, coming from other geodetic observations such as satellite altimetry and GPS or by the use of geological observations. In our contribution we compare the GRACE data with recorded precipitation patterns and mass anomalies over East Antarctica to separate the observed GRACE signal into its two components: GIA as a result of mass loss and present day surface load changes due to possible snow/ice accumulation.

Radial distributions of surface mass density and mass-to-luminosity ratio in spiral galaxies

NASA Astrophysics Data System (ADS)

Sofue, Yoshiaki

2018-03-01

We present radial profiles of the surface mass density (SMD) in spiral galaxies directly calculated using rotation curves of two approximations of flat-disk (SMD-F) and spherical mass distribution (SMD-S). The SMDs are combined with surface brightness using photometric data to derive radial variations of the mass-to-luminosity ratio (ML). It is found that the ML generally has a central peak or a plateau, and decreases to a local minimum at R ˜ 0.1-0.2 h, where R is the radius and h is the scale radius of optical disk. The ML, then, increases rapidly until ˜0.5 h, and is followed by gradual rise till ˜2 h, remaining at around ˜2 [M_{⊙} L^{-1}_{⊙}] in the w1 band (infrared λ3.4 μm) and ˜ 10 [M_⊙ L_⊙ ^{-1}] in the r band (λ6200-7500 Å). Beyond this radius, the ML increases steeply with approaching the observed edges at R ˜ 5 h, attaining to as high values as ˜20 in w1 and ˜ 10^2 [M_⊙ L_⊙ ^{-1}] in the r band, which are indicative of dominant dark matter. The general properties of the ML distributions will be useful for constraining cosmological formation models of spiral galaxies.

Experimental study of ejecta from shock melted lead

NASA Astrophysics Data System (ADS)

Chen, Yongtao; Hu, Haibo; Tang, Tiegang; Ren, Guowu; Li, Qingzhong; Wang, Rongbo; Buttler, William T.

2012-03-01

This effort investigates the dynamic properties of ejecta from explosively shocked, melted Pb targets. The study shows that the ejecta cloud that expands beyond the shocked surface is characterized by a high density and low velocity fragment layer between the free-surface and the high velocity micro-jetting particle cloud. This slow, dense ejecta layer is liquid micro-spall. The properties of micro-spall layer, such as the mass, density and velocity, were diagnosed in a novel application of an Asay window, while micro-jetting particles by lithium niobate piezoelectric pins and high speed photography. The total mass-velocity distribution of ejecta, including micro-spall fragments and micro-jetting particles, is presented. Furthermore, the sensitivity of ejecta production to slight variations in the shockwave drive using the Asay foil is studied.

Three-dimensional investigation of ozone pollution in the lower troposphere using an unmanned aerial vehicle platform.

PubMed

Li, Xiao-Bing; Wang, Dong-Sheng; Lu, Qing-Chang; Peng, Zhong-Ren; Lu, Si-Jia; Li, Bai; Li, Chao

2017-05-01

Potential utilities of instrumented lightweight unmanned aerial vehicles (UAVs) to quickly characterize tropospheric ozone pollution and meteorological factors including air temperature and relative humidity at three-dimensional scales are highlighted in this study. Both vertical and horizontal variations of ozone within the 1000 m lower troposphere at a local area of 4 × 4 km 2 are investigated during summer and autumn times. Results from field measurements show that the UAV platform has a sufficient reliability and precision in capturing spatiotemporal variations of ozone and meteorological factors. The results also reveal that ozone vertical variation is mainly linked to the vertical distribution patterns of air temperature and the horizontal transport of air masses from other regions. In addition, significant horizontal variations of ozone are also observed at different levels. Without major exhaust sources, ozone horizontal variation has a strong correlation with the vertical convection intensity of air masses within the lower troposphere. Higher air temperatures are usually related to lower ozone horizontal variations at the localized area, whereas underlying surface diversity has a week influence. Three-dimensional ozone maps are obtained using an interpolation method based on UAV collected samples, which are capable of clearly demonstrating the diurnal evolution processes of ozone within the 1000 m lower troposphere. Copyright © 2017 Elsevier Ltd. All rights reserved.

Seasonal variability of the Red Sea, from satellite gravity, radar altimetry, and in situ observations

NASA Astrophysics Data System (ADS)

Wahr, John; Smeed, David A.; Leuliette, Eric; Swenson, Sean

2014-08-01

Seasonal variations of sea surface height (SSH) and mass within the Red Sea are caused mostly by exchange of heat with the atmosphere and by flow through the strait opening into the Gulf of Aden to the south. That flow involves a net mass transfer into the Red Sea during fall and out during spring, though in summer there is an influx of cool water at intermediate depths. Thus, summer water in the south is warmer near the surface due to higher air temperatures, but cooler at intermediate depths. Summer water in the north experiences warming by air-sea exchange only. The temperature affects water density, which impacts SSH but has no effect on mass. We study this seasonal cycle by combining GRACE mass estimates, altimeter SSH measurements, and steric contributions derived from the World Ocean Atlas temperature climatology. Among our conclusions are: mass contributions are much larger than steric contributions; the mass is largest in winter, consistent with winds pushing water into the Red Sea in fall and out during spring; the steric signal is largest in summer, consistent with surface warming; and the cool, intermediate-depth water flowing into the Red Sea in spring has little impact on the steric signal, because contributions from the lowered temperature are offset by effects of decreased salinity. The results suggest that the combined use of altimeter and GRACE measurements can provide a useful alternative to in situ data for monitoring the steric signal.

Do Europa's Mountains Have Roots? Erosion of Topography at the Ice-Water Interface via the "Ice Pump"

NASA Astrophysics Data System (ADS)

Goodman, J. C.

2016-12-01

Are topographic features on the surface of Europa and other icy worlds isostatically compensated by variations in shell thickness (Airy isostasy)? This is only possible if variations in shell thickness can remain stable over geologic time. Here we show that melting and freezing driven by the pressure dependence of the melting point of water - the "ice pump" - can rapidly erase topography at the ice/water interface. We consider ice pumps driven by both tidal action and buoyancy-driven flow. We first show that as tidal action drives the ocean up and down along a sloping interface, ice will be melted from areas where it's thickest and deposited where the ice is thinnest. We show that this process causes the ice interface topography to relax according to a simple "diffusion" linear partial differential equation. We estimate that a 10-km-wide topographic feature would be erased by the tidal ice pump in 3000 years if Europa's tidal current amplitude is 1 cm/s; however, this timescale is inversely proportional to the cube of the tidal velocity! Next, we consider an ice pump powered by ascent of meltwater along a sloping ice-water interface. We consider layer-averaged budgets for heat, mass, and momentum, along with turbulent mixing of the meltwater layer with underlying seawater via a Richardson number dependent entrainment process, and use these to estimate the thickness and mass flux of the meltwater layer. From this we estimate the rate of melting and freezing at the interface. These two ice pump processes combine with the glacial flow of warm basal ice to rapidly flatten out any variations in the height of the ice-water interface: Europa's ice/water interface may be perfectly flat! If so, topography at Europa's surface can only be supported by variations in density of the shell or the strength of the brittle surface ice.

Variation of turbulence in a coastal thermal internal boundary layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

SethuRaman, S.; Raynor, G.S.; Brown, R.M.

1981-01-01

Internal boundary layers (IBL) form when an air mass encounters a change in surface characteristics. There are essentially two types of internal boundary layers - one caused by the change in surface roughness and the other by the variation in surface heating. The former is known as the aerodynamic internal boundary layer (AIBL) and the latter the thermal internal boundary layer (TIBL). Change in shear stress generally characterizes the AIBL and change in turbulence the TIBL. Results of some observations of the vertical component of turbulence made in a coastal TIBL over Long Island, New York from 1974 to 1978more » are reported. Vertical turbulence measured by a simple sail plane variometer in a thermal internal boundary layer over Long Island with onshore flows indicates the structure to depend significantly on the land-water temperature difference. The position of the vertical velocity fluctuation maximum seems to vary from one test to another but its variation could not be correlated to other parameters due to lack of a sufficient number of tests. The structure of vertical turbulence was found to be different for sea breeze flows as compared to gradient winds.« less

Spatiotemporal variations in litter mass and their relationships with climate in temperate grassland: A case study from Xilingol grassland, Inner Mongolia (China)

NASA Astrophysics Data System (ADS)

Ren, Hongrui; Zhang, Bei

2018-02-01

Clarifying spatiotemporal variations of litter mass and their relationships with climate factors will advance our understanding of ecosystem structure and functioning in grasslands. Our objective is to investigate the spatiotemporal variations of litter mass in the growing season and their relationships with precipitation and temperature in the Xilingol grassland using MOD09A1 data. With widely used STI (simple tillage index), we firstly estimated the litter mass of Xilingol grassland in the growing season from 2000 to 2014. Then we investigated the variations of litter mass in the growing season at regional and site scales. We further explored the spatiotemporal relationships between litter mass and precipitation and temperature at both scales. The litter mass increased with increasing mean annual precipitation and decreasing mean annual temperature at regional scale. The variations of litter mass at given sites followed quadratic function curves in the growing season, and litter mass generally attained maximums between August 1 and September 1. Positive spatial relationship was observed between litter mass variations and precipitation, and negative spatial relationship was found between litter mass variations and temperature in the growing season. There was no significant relationship between inter-annual variations of litter mass and precipitation and temperature at given sites. Results illustrate that precipitation and temperature are important drivers in shaping ecosystem functioning as reflected in litter mass at regional scale in the Xilingol grassland. Our findings also suggest the action of distinct mechanism in controlling litter mass variations at regional and sites scales.

Short-term variations of Icelandic ice cap mass inferred from cGPS coordinate time series

NASA Astrophysics Data System (ADS)

Compton, Kathleen; Bennett, Richard A.; Hreinsdóttir, Sigrún; van Dam, Tonie; Bordoni, Andrea; Barletta, Valentina; Spada, Giorgio

2017-06-01

As the global climate changes, understanding short-term variations in water storage is increasingly important. Continuously operating Global Positioning System (cGPS) stations in Iceland record annual periodic motion—the elastic response to winter accumulation and spring melt seasons—with peak-to-peak vertical amplitudes over 20 mm for those sites in the Central Highlands. Here for the first time for Iceland, we demonstrate the utility of these cGPS-measured displacements for estimating seasonal and shorter-term ice cap mass changes. We calculate unit responses to each of the five largest ice caps in central Iceland at each of the 62 cGPS locations using an elastic half-space model and estimate ice mass variations from the cGPS time series using a simple least squares inversion scheme. We utilize all three components of motion, taking advantage of the seasonal motion recorded in the horizontal. We remove secular velocities and accelerations and explore the impact that seasonal motions due to atmospheric, hydrologic, and nontidal ocean loading have on our inversion results. Our results match available summer and winter mass balance measurements well, and we reproduce the seasonal stake-based observations of loading and melting within the 1σ confidence bounds of the inversion. We identify nonperiodic ice mass changes associated with interannual variability in precipitation and other processes such as increased melting due to reduced ice surface albedo or decreased melting due to ice cap insulation in response to tephra deposition following volcanic eruptions, processes that are not resolved with once or twice-yearly stake measurements.

Ozone in the marine boundary layer of Bay of Bengal and Arabian Sea during post winter period - continental influence

NASA Astrophysics Data System (ADS)

Nair, Prabha R.; George, Susan K.; David, Liji Mary; Parameswaran, Krishnaswamy

Ozone plays a key role in controlling the oxidation capacity of the troposphere and hence the lifetime of a variety of trace gases in the atmosphere. In pristine marine boundary layer (MBL), entire chemistry is initiated by the photolysis of ozone and the subsequent formation of OH radical from water vapour. Also in such environment, photochemical destruction is considered as a major sink in global ozone budget. Even though large number of studies on near surface ozone has been carried out over land such studies are very few over oceanic environments. This paper presents the observational results on the spatial variations of near-surface ozone over Bay of Bengal and Arabian Sea as revealed by the cruise-based measurements (cruise No. SK223) conducted as part of Integrated Campaign for Aerosol gases and Radiation Budget (ICARB) under the Geosphere Biosphere Programme of Indian Space Research Organisation (IGBP). Online measurements of ozone have been carried out by using a UV Photometric Analyser (model 49C of Thermo Electron Corporation, USA). Ozone mixing ratio was observed to be significantly high over northern Bay of Bengal (20-28 ppb) compared to southern Bay of Bengal and Arabian Sea. Minimum levels of ozone ( 5 ppb) have been measured in the central Bay of Bengal region. Over Arabian Sea latitudinal variation was not prominently observed. The over all latitudinal gradient is estimated to be 1.2 ppb/o latitude over Bay of Bengal with longitudinal gradient showing variation depending on the latitude sector. It was maximum (of 1.2ppb/o longitude) over the mid Bay of Bengal region ( 15o N). Longitudinal variation was not significant over northern and southern regions. A close examination of surface airflow patterns and the air mass back trajectories revealed increase in ozone level associated with continental outflow from the northern and central parts of the subcontinent. The diurnal pattern also showed variations depending on the proximity to inhabited land mass and also with meteorological parameters.

Seasonal gravity change at Yellowstone caldera

NASA Astrophysics Data System (ADS)

Poland, M. P.; de Zeeuw-van Dalfsen, E.

2017-12-01

The driving forces behind Yellowstone's dynamic deformation, vigorous hydrothermal system, and abundant seismicity are usually ascribed to "magmatic fluids," which could refer to magma, water, volatiles, or some combination. Deformation data alone cannot distinguish the relative importance of these fluids. Gravity measurements, however, provide an indication of mass change over time and, when combined with surface displacements, can constrain the density of subsurface fluids. Unfortunately, several decades of gravity surveys at Yellowstone have yielded ambiguous results. We suspect that the difficulty in interpreting Yellowstone gravity data is due to seasonal variations in environmental conditions—especially surface and ground water. Yellowstone gravity surveys are usually carried out at the same time of year (generally late summer) to minimize the impact of seasonality. Nevertheless, surface and subsurface water levels are not likely to be constant from year to year, given annual differences in precipitation. To assess the overall magnitude of seasonal gravity changes, we conducted gravity surveys of benchmarks in and around Yellowstone caldera in May, July, August, and October 2017. Our goal was to characterize seasonal variations due to snow melt/accumulation, changes in river and lake levels, changes in groundwater levels, and changes in hydrothermal activity. We also hope to identify sites that show little variation in gravity over the course of the 2017 surveys, as these locations may be less prone to seasonal changes and more likely to detect small variations due to magmatic processes. Preliminary examination of data collected in May and July 2017 emphasizes the importance of site location relative to sources of water. For example, a site on the banks of the Yellowstone River showed a gravity increase of several hundred microgals associated with a 50 cm increase in the river level. A high-altitude site far from rivers and lakes, in contrast, showed a relatively small gravity increase ( 25 microgals) over the same time period, despite the presence of 1 m of snow during the first survey and none during the second. Reinterpretation of past data collected at sites such as this one, where seasonal variations may be minor, could provide a clearer indication of mass changes in Yellowstone's magmatic system.

Analysis of Seasonal Variability in Gulf of Alaska Glacier Mass Balance using GRACE

NASA Astrophysics Data System (ADS)

Arendt, A. A.; Luthcke, S. B.; Oneel, S.; Gardner, A. S.; Hill, D. F.

2011-12-01

Mass variations of glaciers in Alaska/northwestern Canada must be quantified in order to assess impacts on ecosystems, human infrastructure, and global sea level. Here we combine Gravity Recovery and Climate Experiment (GRACE) observations with a wide range of satellite and field data to investigate drivers of these recent changes, with a focus on seasonal variations. Our central focus will be the exceptionally high mass losses of 2009, which do not correlate with weather station temperature and precipitation data, but may be linked to ash fall from the March 31, 2009 eruption of Mt. Redoubt. The eruption resulted in a significant decrease in MODIS-derived surface albedo over many Alaska glacier regions, and likely contributed to some of the 2009 anomalous mass loss observed by GRACE. We also focus on the Juneau and Stikine Icefield regions that are far from the volcanic eruption but experienced the largest mass losses of any region in 2009. Although rapid drawdown of tidewater glaciers was occurring in southeast Alaska during 2009, we show these changes were probably not sufficiently widespread to explain all of the GRACE signal in those regions. We examine additional field and satellite datasets to quantify potential errors in the climate and GRACE fields that could result in the observed discrepancy.

Relation Between Lightning Activity of Summer and Winter Thunderclouds and Surface Electric Field Variation, Japan

NASA Technical Reports Server (NTRS)

Michimoto, K.; Shimura, T.; Suzuki, T.

1999-01-01

In winter, active convective clouds frequently form along the coastline of the Hokuriku district, in association with strong advection of Siberian air masses over the Sea of Japan. On the other hand, in summer, many thunderclouds form in the Kanto region in the afternoon every day. Summer and winter thunderclouds were investigated by field works, operation of the C- and X-band weather radars and a car-borne fieldmill. The investigation found a very close relation between the temporal variation of 3-dimensional radar echo and surface electric field magnitude detected by a car-borne fieldmill in the case of summer thunderclouds and winter convective clouds or thunderclouds. The study probed the close relation among radar echoes, quantity of thunderclouds and surface electric field magnitude in the summer and winter seasons. We think that summer thundercloud activity can basically be equated with winter thundercloud lightning activity, except that the magnitude of surface electric field under summer thunderclouds in the case of the Kanto region cannot be equated with that under winter thunderclouds in the case of the Hokuriku district in winter.

Fabrication and characterization of bolus material using polydimethyl-siloxane

NASA Astrophysics Data System (ADS)

Wiratma Jaya, Gede; Sutanto, Heri

2018-01-01

Bolus has been used in radiotherapy to reduce tissue harm and to increase the superficial dose for skin cancer treatment. Commonly, a bolus is made of melamine in several hospitals. In this research, polydimethyl-siloxane (PDMS) material was used for bolus fabrication. The aims of the study are to investigate bolus density, percentage surface dose and its structural strength for each various composition. In bolus preparation, bolus material used composition variation between PDMS volume and catalyst volume. Composition variation were 20:1, 22:1, 24:1, 26:1, 28:1, 30:1 and 32:1. PDMS and catalyst were mixed by chemical solution deposition method. Bolus was molded by using glass cast with the size of 10 × 10 × 0.5 cm3. Bolus density was analyzed by mass per volume equation, for bolus radiation was examined by the linear accelerator using two electron energy (5 and 7 MeV) and bolus strain and tensile strength were examined by Brookfield CT 3 machine. The results of bolus density were similar with soft tissue density, while the lowest and highest density each variation are 22:1 and 28:1. In general, the use of bolus has increased the surface dose. Percentage of surface dose at 5 MeV energy is higher than 7 MeV energy. The highest percentage of surface dose at 5 MeV energy with 0.5 and 1.0 cm bolus thickness was achieved at composition of 32:1. For strain and tensile strength result, the lowest and highest strain each variation are 22:1 and 28:1, then the lowest and highest tensile strength each variation are 32:1 and 28:1. These results is important to select composition material for bolus fabrication in radiotherapy treatment.

Results of TV imaging of Phobos - Experiment VSK-Fregat

NASA Technical Reports Server (NTRS)

Avanesov, G.; Zhukov, B.; Ziman, IA.; Kostenko, V.; Kuz'min, A.; Duxbury, T.

1991-01-01

From February to March 1989 the Phobos 2 spacecraft took 37 TV images of Phobos at a distance of 190-1100 km. These images complement Mariner-9 and Viking data by providing higher-resolution coverage of a laarge region west of the crater Stickney (40-160 deg W) and by providing disk-resolved measurements of surface brightness at a greater range of wavelengths and additional phase angles. These images have supported updated mapping and characterization of large craters and grooves, and have provided additional observations of craters' and grooves' bright rims. Variations in surface visible/near-infrared color ratio of almost a factor of 2 have been recognized; these variations appear to be associated with the ejecta of specific large impact craters. Updated determinations of satellite mass and volume allow calculation of a more accurate value of bulk density, 1.90 + or - 0.1 g/cu cm. This is sigificantly lower than the density of meteoritic analogs to Phobos' surface, suggesting a porous interior perhaps containing interstitial ice.

Influence of climate variability on near-surface ozone depletion events in the Arctic spring

NASA Astrophysics Data System (ADS)

Koo, Ja-Ho; Wang, Yuhang; Jiang, Tianyu; Deng, Yi; Oltmans, Samuel J.; Solberg, Sverre

2014-04-01

Near-surface ozone depletion events (ODEs) generally occur in the Arctic spring, and the frequency shows large interannual variations. We use surface ozone measurements at Barrow, Alert, and Zeppelinfjellet to analyze if their variations are due to climate variability. In years with frequent ODEs at Barrow and Alert, the western Pacific (WP) teleconnection pattern is usually in its negative phase, during which the Pacific jet is strengthened but the storm track originated over the western Pacific is weakened. Both factors tend to reduce the transport of ozone-rich air mass from midlatitudes to the Arctic, creating a favorable environment for the ODEs. The correlation of ODE frequencies at Zeppelinfjellet with WP indices is higher in the 2000s, reflecting stronger influence of the WP pattern in recent decade to cover ODEs in broader Arctic regions. We find that the WP pattern can be used to diagnose ODE changes and subsequent environmental impacts in the Arctic spring.

Constraints on Vesta's elemental composition: Fast neutron measurements by Dawn's gamma ray and neutron detector

PubMed Central

Lawrence, David J; Peplowski, Patrick N; Prettyman, Thomas H; Feldman, William C; Bazell, David; Mittlefehldt, David W; Reedy, Robert C; Yamashita, Naoyuki

2013-01-01

Surface composition information from Vesta is reported using fast neutron data collected by the gamma ray and neutron detector on the Dawn spacecraft. After correcting for variations due to hydrogen, fast neutrons show a compositional dynamic range and spatial variability that is consistent with variations in average atomic mass from howardite, eucrite, and diogenite (HED) meteorites. These data provide additional compositional evidence that Vesta is the parent body to HED meteorites. A subset of fast neutron data having lower statistical precision show spatial variations that are consistent with a 400 ppm variability in hydrogen concentrations across Vesta and supports the idea that Vesta's hydrogen is due to long-term delivery of carbonaceous chondrite material. PMID:26074718

Frequency effects on the stability of a journal bearing for periodic loading

NASA Technical Reports Server (NTRS)

Vijayaraghavan, D.; Brewe, D. E.

1991-01-01

The stability of a journal bearing is numerically predicted when a unidirectional periodic external load is applied. The analysis is performed using a cavitation algorithm, which mimics the Jakobsson-Floberg and Olsson (JFO) theory by accounting for the mass balance through the complete bearing. Hence, the history of the film is taken into consideration. The loading pattern is taken to be sinusoidal and the frequency of the load cycle is varied. The results are compared with the predictions using Reynolds boundary conditions for both film rupture and reformation. With such comparisons, the need for accurately predicting the cavitation regions for complex loading patterns is clearly demonstrated. For a particular frequency of loading, the effects of mass, amplitude of load variation and frequency of journal speed are also investigated. The journal trajectories, transient variations in fluid film forces, net surface velocity and minimum film thickness, and pressure profiles are also presented.

Observed temporal variations in the Earth's gravity field from 16-year Starlette orbit analysis

NASA Technical Reports Server (NTRS)

Cheng, M. K.; Eanes, R. L.; Shum, C. K.; Schutz, B. E.; Tapley, B. D.

1992-01-01

Satellite laser ranging data to Starlette, collected during the period from 1975 to 1990, are analyzed to determine yearly values of the second degree annual (Sa) and semiannual (Ssa) tides, simultaneously with average values of other low degree and order tide parameters. The yearly fluctuations in the values for Sa and Ssa are associated with changes in the Earth's second degree zonal harmonic caused by meteorological excitation. The Starlette-determined mean values for the amplitude of the annual and semiannual variations in J2 are 32.3 x 10 exp -11 and 19.5 x 10 exp -11, respectively; while the rms about the mean values are 4.1 x 10 exp -11 and 6.3 x 10 exp -11, respectively. The annual delta-J2 is in good agreement with the value obtained from the combined effects of air mass redistribution without the oceanic inverted-barometer effects (non-IB) and hydrological change. Approximately 90 percent of the observed annual variation from Starlette is attributed to the meteorological mass redistribution occurring on the Earth's surface.

The humidity dependence of ozone deposition onto a variety of building surfaces

NASA Astrophysics Data System (ADS)

Grøntoft, Terje; Henriksen, Jan F.; Seip, Hans M.

Measurements of the dry deposition velocity of O 3 to material samples of calcareous stone, concrete and wood at varying humidity of the air, were performed in a deposition chamber. Equilibrium surface deposition velocities were found for various humidity values by fitting a model to the time-dependent deposition data. A deposition velocity-humidity model was derived giving three separate rate constants for the surface deposition velocities, i.e. on the dry surface, on the first mono-layer of adsorbed water and on additional surface water. The variation in the dry air equilibrium surface deposition velocities among the samples correlated with variations in effective areas, with larger effective areas giving higher measured deposition velocities. A minimum for the equilibrium surface deposition velocity was generally measured at an intermediate humidity close to the humidity found to correspond to one mono-layer of water molecules on the surfaces. At low air humidity the equilibrium surface deposition velocity of O 3 was found to decrease as more adsorbed water prevented direct contact of the O 3 molecules with the surface. This was partly compensated by an increase as more adsorbed water became available for reaction with O 3. At high air humidity the equilibrium surface deposition velocity was found to increase as the mass of water on the surface increased. The deposition velocity on bulk de-ionised water at RH=90% was an order of magnitude lower than on the sample surfaces.

A better GRACE solution for improving the regional Greenland mass balance

NASA Astrophysics Data System (ADS)

Schrama, E.; Xu, Z.

2012-04-01

In most GRACE based researches, a variety of smoothing methods is employed to remove alternating bands of positive and negative stripes stretching in the north-south direction. Many studies have suggested to smooth the GRACE maps, on which mass variations are represented as equivalent water height (EWH). Such maps are capable of exposing the redistribution of earth surface mass over time. In Greenland the shrinking of the ice cap becomes significant in the last decade. Our present study confirms that the dominating melting trends are in the east and southeast coastal zones, however, the smoothed signals along the coastline in these areas do not represent the original but averaged measurements from GRACE satellites which means the signal strength indicating that negative mass variations are mixed with some positive signals that are very close to this area. An exact identification of the topographic edge is not possible and visually the EWH maps appear to be blurred. To improve this, we firstly used spherical harmonic coefficients of GRACE level-2 data from CSR-RL04 and produced a smoothed EWH map. Empirical Orthogonal Functions(EOF)/Principal Component Analysis(PCA) have been introduced as well, in order to extract the melting information associated with the recent warming climate. Next, the Greenland area is redefined by 16 basins and the corresponding melting zones are quantified respectively. Least Squares methods are invoked to interpolate the mass distribution function on each basin. In this way we are able to estimate more accurately regional ice melting rate and we sharpen the EWH map. After comparing our results with a hydrological model the combination SMB - D is established which contains the surface mass balance (SMB) and ice-discharge (D). A general agreement can be reached and it turns out this method is capable to enhance our understanding of the shrinking global cryosphere

Variations in debris distribution and thickness on Himalayan debris-covered glaciers

NASA Astrophysics Data System (ADS)

Gibson, Morgan; Rowan, Ann; Irvine-Fynn, Tristram; Quincey, Duncan; Glasser, Neil

2016-04-01

Many Himalayan glaciers are characterised by extensive supraglacial debris coverage; in Nepal 33% of glaciers exhibit a continuous layer of debris covering their ablation areas. The presence of such a debris layer modulates a glacier's response to climatic change. However, the impact of this modulation is poorly constrained due to inadequate quantification of the impact of supraglacial debris on glacier surface energy balance. Few data exist to describe spatial and temporal variations in parameters such as debris thickness, albedo and surface roughness in energy balance calculations. Consequently, improved understanding of how debris affects Himalayan glacier ablation requires the assessment of surface energy balance model sensitivity to spatial and temporal variability in these parameters. Measurements of debris thickness, surface temperature, reflectance and roughness were collected across Khumbu Glacier during the pre- and post-monsoon seasons of 2014 and 2015. The extent of the spatial variation in each of these parameters are currently being incorporated into a point-based glacier surface energy balance model (CMB-RES, Collier et al., 2014, The Cryosphere), applied on a pixel-by-pixel basis to the glacier surface, to ascertain the sensitivity of glacier surface energy balance and ablation values to these debris parameters. A time series of debris thickness maps have been produced for Khumbu Glacier over a 15-year period (2000-2015) using Mihalcea et al.'s (2008, Cold Reg. Sci. Technol.) method, which utilised multi-temporal ASTER thermal imagery and our in situ debris surface temperature and thickness measurements. Change detection between these maps allowed the identification of variations in debris thickness that could be compared to discrete measurements, glacier surface velocity and morphology of the debris-covered area. Debris thickness was found to vary spatially between 0.1 and 4 metres within each debris thickness map, and temporally on the order of 1 to 2 m. Temporal variability was a result of differential surface lowering, spatial variability in glacier surface velocities and intermittent input of debris to the glacier surface through mass movement. Most debris thickening is seen in initially thin areas of debris (< 0.4 m) or within ~1 km of the glacier terminus. Surface energy balance modelling is currently underway to determine the effect of these variations in debris thickness, and other parameters mentioned previously. Future work will be to calculate debris transport flux on the surface of Khumbu Glacier using the time series of debris thickness maps. Debris flux and refined energy balance calculations will then be incorporated into a 3-D ice flow model to determine the response of Khumbu Glacier to debris transport and climatic changes.

Dust Abundance Variations in the Magellanic Clouds: Probing the Life-cycle of Metals with All-sky Surveys

NASA Astrophysics Data System (ADS)

Roman-Duval, Julia; Bot, Caroline; Chastenet, Jeremy; Gordon, Karl

2017-06-01

Observations and modeling suggest that dust abundance (gas-to-dust ratio, G/D) depends on (surface) density. Variations of the G/D provide timescale constraints for the different processes involved in the life cycle of metals in galaxies. Recent G/D measurements based on Herschel data suggest a factor of 5-10 decrease in dust abundance between the dense and diffuse interstellar media (ISM) in the Magellanic Clouds. However, the relative nature of the Herschel measurements precludes definitive conclusions as to the magnitude of those variations. We investigate variations of the dust abundance in the LMC and SMC using all-sky far-infrared surveys, which do not suffer from the limitations of Herschel on their zero-point calibration. We stack the dust spectral energy distribution (SED) at 100, 350, 550, and 850 microns from IRAS and Planck in intervals of gas surface density, model the stacked SEDs to derive the dust surface density, and constrain the relation between G/D and gas surface density in the range 10-100 M ⊙ pc-2 on ˜80 pc scales. We find that G/D decreases by factors of 3 (from 1500 to 500) in the LMC and 7 (from 1.5× {10}4 to 2000) in the SMC between the diffuse and dense ISM. The surface-density-dependence of G/D is consistent with elemental depletions, and with simple modeling of the accretion of gas-phase metals onto dust grains. This result has important implications for the sub-grid modeling of galaxy evolution, and for the calibration of dust-based gas-mass estimates, both locally and at high redshift.

Forecast skill of a high-resolution real-time mesoscale model designed for weather support of operations at Kennedy Space Center and Cape Canaveral Air Station

NASA Technical Reports Server (NTRS)

Taylor, Gregory E.; Zack, John W.; Manobianco, John

1994-01-01

NASA funded Mesoscale Environmental Simulations and Operations (MESO), Inc. to develop a version of the Mesoscale Atmospheric Simulation System (MASS). The model has been modified specifically for short-range forecasting in the vicinity of KSC/CCAS. To accomplish this, the model domain has been limited to increase the number of horizontal grid points (and therefore grid resolution) and the model' s treatment of precipitation, radiation, and surface hydrology physics has been enhanced to predict convection forced by local variations in surface heat, moisture fluxes, and cloud shading. The objective of this paper is to (1) provide an overview of MASS including the real-time initialization and configuration for running the data pre-processor and model, and (2) to summarize the preliminary evaluation of the model's forecasts of temperature, moisture, and wind at selected rawinsonde station locations during February 1994 and July 1994. MASS is a hydrostatic, three-dimensional modeling system which includes schemes to represent planetary boundary layer processes, surface energy and moisture budgets, free atmospheric long and short wave radiation, cloud microphysics, and sub-grid scale moist convection.

Monitoring massive fracture growth at 2-km depths using surface tiltmeter arrays

USGS Publications Warehouse

Wood, M.D.

1979-01-01

Tilt due to massive hydraulic fractures induced in sedimentary rocks at depths of up to 2.2 km have been recorded by surface tiltmeters. Injection of fluid volumes up to 4 ?? 105 liters and masses of propping agent up to 5 ?? 105 kg is designed to produce fractures approximately 1 km long, 50-100 m high and about 1 cm wide. The surface tilt data adequately fit a dislocation model of a tensional fault in a half-space. Theoretical and observational results indicate that maximum tilt occurs at a distance off the strike of the fracture equivalent to 0.4 of the depth to the fracture. Azimuth and extent of the fracture deduced from the geometry of the tilt field agree with other kinds of geophysical measurements. Detailed correlation of the tilt signatures with pumping parameters (pressure, rate, volume, mass) have provided details on asymmetry in geometry and growth rate. Whereas amplitude variations in tilt vary inversely with the square of the depth, changes in flow rate or pressure gradient can produce a cubic change in width. These studies offer a large-scale experimental approach to the study of problems involving fracturing, mass transport, and dilatancy processes. ?? 1979.

Spectroscopic infrared extinction mapping as a probe of grain growth in IRDCs

NASA Astrophysics Data System (ADS)

Lim, Wanggi; Carey, Sean J.

2014-07-01

We present photometric and spectroscopic tests of MIR to FIR extinction laws toward IRDC G028.36+00.07, a potential site of massive star formation. Lim & Tan (2014, hereafter LT14) developed methods of FIR extinction mapping of this source using Spitzer-MIPS 24 micron and Herschel-PACS 70 micron images, and extending the MIR 8 micron mapping methods of (Butler & Tan 2012, hereafter BT12), finding evidence for grain growth in the highest mass surface density regions. Here we present initial results of spectroscopic infrared extinction (SIREX) mapping using Spitzer-IRS (14 to 38 micron) data of the same IRDC. These methods allow us to measure the SED of the diffuse Galactic ISM, which we compare to theoretical models of Draine & Li (2007), as well as to search for opacity law variations with mass surface density within the IRDC. By comparison with theoretical dust models, e.g., Ossenkopf & Henning (1994) and Ormel et al. (2011), we are able to search for compositional signatures of the grain ices, such as water and methanol. We find evidence for generally flatter MIR to FIR extinction laws as mass surface density increases, strengthening the evidence for grain and ice mantle growth in higher density regions.

Extraction of skin-friction fields from surface flow visualizations as an inverse problem

NASA Astrophysics Data System (ADS)

Liu, Tianshu

2013-12-01

Extraction of high-resolution skin-friction fields from surface flow visualization images as an inverse problem is discussed from a unified perspective. The surface flow visualizations used in this study are luminescent oil-film visualization and heat-transfer and mass-transfer visualizations with temperature- and pressure-sensitive paints (TSPs and PSPs). The theoretical foundations of these global methods are the thin-oil-film equation and the limiting forms of the energy- and mass-transport equations at a wall, which are projected onto the image plane to provide the relationships between a skin-friction field and the relevant quantities measured by using an imaging system. Since these equations can be re-cast in the same mathematical form as the optical flow equation, they can be solved by using the variational method in the image plane to extract relative or normalized skin-friction fields from images. Furthermore, in terms of instrumentation, essentially the same imaging system for measurements of luminescence can be used in these surface flow visualizations. Examples are given to demonstrate the applications of these methods in global skin-friction diagnostics of complex flows.

Mass ejection in failed supernovae: variation with stellar progenitor

NASA Astrophysics Data System (ADS)

Fernández, Rodrigo; Quataert, Eliot; Kashiyama, Kazumi; Coughlin, Eric R.

2018-05-01

We study the ejection of mass during stellar core-collapse when the stalled shock does not revive and a black hole forms. Neutrino emission during the protoneutron star phase causes a decrease in the gravitational mass of the core, resulting in an outward going sound pulse that steepens into a shock as it travels out through the star. We explore the properties of this mass ejection mechanism over a range of stellar progenitors using spherically symmetric, time-dependent hydrodynamic simulations that treat neutrino mass-loss parametrically and follow the shock propagation over the entire star. We find that all types of stellar progenitor can eject mass through this mechanism. The ejected mass is a decreasing function of the surface gravity of the star, ranging from several M⊙ for red supergiants to ˜0.1 M⊙ for blue supergiants and ˜10-3 M⊙ for Wolf-Rayet stars. We find that the final shock energy at the surface is a decreasing function of the core-compactness, and is ≲ 1047-1048 erg in all cases. In progenitors with a sufficiently large envelope, high core-compactness, or a combination of both, the sound pulse fails to unbind mass. Successful mass ejection is accompanied by significant fallback accretion that can last from hours to years. We predict the properties of shock breakout and thermal plateau emission produced by the ejection of the outer envelope of blue supergiant and Wolf-Rayet progenitors in otherwise failed supernovae.

Spatiotemporal Patterns of Ice Mass Variations and the Local Climatic Factors in the Riparian Zone of Central Valley, California

NASA Astrophysics Data System (ADS)

Inamdar, P.; Ambinakudige, S.

2016-12-01

Californian icefields are natural basins of fresh water. They provide irrigation water to the farms in the central valley. We analyzed the ice mass loss rates, air temperature and land surface temperature (LST) in Sacramento and San Joaquin basins in California. The digital elevation models from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) were used to calculate ice mass loss rate between the years 2002 and 2015. Additionally, Landsat TIR data were used to extract the land surface temperature. Data from local weather stations were analyzed to understand the spatiotemporal trends in air temperature. The results showed an overall mass recession of -0.8 ± 0.7 m w.e.a-1. We also noticed an about 60% loss in areal extent of the glaciers in the study basins between 2000 and 2015. Local climatic factors, along with the global climate patterns might have influenced the negative trends in the ice mass loss. Overall, there was an increase in the air temperature by 0.07± 0.02 °C in the central valley between 2000 and 2015. Furthermore, LST increased by 0.34 ± 0.4 °C and 0.55± 0.1 °C in the Sacramento and San Joaquin basins. Our preliminary results show the decrease in area and mass of ice mass in the basins, and changing agricultural practices in the valley.

A Model of the Temporal Variability of Optical Light from Extrasolar Terrestrial Planets

NASA Astrophysics Data System (ADS)

Ford, E. B.; Seager, S.; Turner, E. L.

2001-05-01

New observatories such as TPF (NASA) and Darwin (ESA) are being designed to detect light directly from terrestrial-mass planets. Such observations will provide new data to constrain theories of planet formation and may identify the possible presence of liquid water and even spectroscopic signatures suggestive of life. We model the light scattered by Earth-like planets focusing on temporal variability due to planetary rotation and weather. Since a majority of the scattered light comes from only a small fraction of the planet's surface, significant variations in brightness are possible. The variations can be as large as a factor of two for a cloud-free planet which has a range of albedos similar to those of the different surfaces found on Earth. If a significant fraction of the observed light is scattered by the planet's atmosphere, including clouds, then the amplitude of variations due to surface features will be diluted. Atmospheric variability (e.g. clouds) itself is extremely interesting because it provides evidence for weather. The planet's rotation period, fractional ice and cloud cover, gross distribution of land and water on the surface, large scale weather patterns, large regions of unusual reflectivity or color (such as major desserts or vegetation's "red edge") as well as the geometry of its spin, orbit, and illumination relative to the observer all have substantial effects on the planet's rotational light curve.

Air-surface exchange of nonmethane organic compounds at a grassland site: Seasonal variations and stressed emissions

NASA Astrophysics Data System (ADS)

Fukui, Yoshiko; Doskey, Paul V.

1998-06-01

Emissions of nonmethane organic compounds (NMOCs) were measured by a static enclosure technique at a grassland site in the midwestern United States during the growing seasons over a 2-year period. A mixture of nonmethane hydrocarbons (NMHCs) and oxygenated hydrocarbons (OxHCs) was emitted from the surface at rates exhibiting large seasonal and year-to-year variations. The average emission rate (and standard error) of the total NMOCs around noontime on sunny days during the growing seasons for the 2-year period was 1,300±170 μg m-2 h-1 (mass of the total NMOCs per area of enclosed soil surface per hour) or 5.5±0.9 μg g-1 h-1 (mass of the total NMOCs per mass of dry plant biomass in an enclosure per hour), with about 10% and 70% of the emissions being composed of tentatively identified NMHCs and OxHCs, respectively. Methanol was apparently derived from both the soil and vegetation and exhibited an average emission rate of 460±73 μg m-2 h-1 (1.4±0.2 μg g-1 h-1), which was the largest emission among the NMOCs. The year-to-year variation in the precipitation pattern greatly affected the NMOC emission rates. Emission rates normalized to biomass density exhibited a linear decrease as the growing season progressed. The emission rates of some NMOCs, particularly the OxHCs, from vegetation subjected to hypoxia, frost, and physical stresses were significantly greater than the average values observed at the site. Emissions of monoterpenes (α- and β-pinene, limonene, and myrcene) and cis-3-hexen-l-ol were accelerated during the flowering of the plants and were much greater than those predicted by algorithms that correlated emission rates with temperature. Herbaceous vegetation is estimated to contribute about 40% and 50% of the total NMOC and monoterpene emissions, respectively, in grasslands; the remaining contributions are from woody species within grasslands. Contributions of isoprene emissions from herbaceous vegetation in grasslands are negligible. Grasslands are estimated to contribute about 10% of the total biogenic NMOC emissions in the United States.

Annealing induced low coercivity, nanocrystalline Co-Fe-Si thin films exhibiting inverse cosine angular variation

NASA Astrophysics Data System (ADS)

Hysen, T.; Al-Harthi, Salim; Al-Omari, I. A.; Geetha, P.; Lisha, R.; Ramanujan, R. V.; Sakthikumar, D.; Anantharaman, M. R.

2013-09-01

Co-Fe-Si based films exhibit high magnetic moments and are highly sought after for applications like soft under layers in perpendicular recording media to magneto-electro-mechanical sensor applications. In this work the effect of annealing on structural, morphological and magnetic properties of Co-Fe-Si thin films was investigated. Compositional analysis using X-ray photoelectron spectroscopy and secondary ion mass spectroscopy revealed a native oxide surface layer consisting of oxides of Co, Fe and Si on the surface. The morphology of the as deposited films shows mound like structures conforming to the Volmer-Weber growth model. Nanocrystallisation of amorphous films upon annealing was observed by glancing angle X-ray diffraction and transmission electron microscopy. The evolution of magnetic properties with annealing is explained using the Herzer model. Vibrating sample magnetometry measurements carried out at various angles from 0° to 90° to the applied magnetic field were employed to study the angular variation of coercivity. The angular variation fits the modified Kondorsky model. Interestingly, the coercivity evolution with annealing deduced from magneto-optical Kerr effect studies indicates a reverse trend compared to magetisation observed in the bulk. This can be attributed to a domain wall pinning at native oxide layer on the surface of thin films. The evolution of surface magnetic properties is correlated with morphology evolution probed using atomic force microscopy. The morphology as well as the presence of the native oxide layer dictates the surface magnetic properties and this is corroborated by the apparent difference in the bulk and surface magnetic properties.

Estimation of columnar concentrations of absorbing and scattering fine mode aerosol components using AERONET data

NASA Astrophysics Data System (ADS)

Choi, Yongjoo; Ghim, Young Sung

2016-11-01

Columnar concentrations of absorbing and scattering components of fine mode aerosols were estimated using Aerosol Robotic Network (AERONET) data for a site downwind of Seoul. The study period was between March 2012 and April 2013 including the period of the Distributed Regional Aerosol Gridded Observation Networks (DRAGON)-Asia campaign in March to May 2012. The Maxwell Garnett mixing rule was assumed for insoluble components embedded in a host solution, while the volume average mixing rule was assumed for the aqueous solution of soluble components. During the DRAGON-Asia campaign the surface concentrations of major components of fine particles were measured. The columnar mass fractions of black carbon (BC), organic carbon (OC), mineral dust (MD), and ammonium sulfate (AS) were 1.5, 5.9, 6.6, and 52%, respectively, which were comparable to the mass fractions measured at the surface for BC, OC, and secondary inorganic aerosols at 2.3, 18, and 55%. The vertical distributions of BC and AS were investigated by employing the concept of a column height. While the column height for BC was similar to the planetary boundary layer (PBL) height, that for AS was 4.4 times higher than the PBL height and increased with air temperature from March to May. The monthly variations of the columnar mass concentrations during the study period were generally well explained in term of meteorology and emission characteristics. However, certain variations of MD were different from those typically observed primarily because only fine mode aerosols were considered.

Polymethyl methacrylate-co-methacrylic acid coatings with controllable concentration of surface carboxyl groups: A novel approach in fabrication of polymeric platforms for potential bio-diagnostic devices

NASA Astrophysics Data System (ADS)

Hosseini, Samira; Ibrahim, Fatimah; Djordjevic, Ivan; Koole, Leo H.

2014-05-01

The generally accepted strategy in development of bio-diagnostic devices is to immobilize proteins on polymeric surfaces as a part of detection process for diseases and viruses through antibody/antigen coupling. In that perspective, polymer surface properties such as concentration of functional groups must be closely controlled in order to preserve the protein activity. In order to improve the surface characteristics of transparent polymethacrylate plastics that are used for diagnostic devices, we have developed an effective fabrication procedure of polymethylmetacrylate-co-metacrylic acid (PMMA-co-MAA) coatings with controlled number of surface carboxyl groups. The polymers were processed effectively with the spin-coating technique and the detailed control over surface properties is here by demonstrated through the variation of a single synthesis reaction parameter. The chemical structure of synthesized and processed co-polymers has been investigated with nuclear magnetic resonance spectroscopy (NMR) and matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-ToF-MS). The surface morphology of polymer coatings have been analyzed with atomic force microscopy (AFM) and scanning electron microscopy (SEM). We demonstrate that the surface morphology and the concentration of surface -COOH groups (determined with UV-vis surface titration) on the processed PMMA-co-MAA coatings can be precisely controlled by variation of initial molar ratio of reactants in the free-radical polymerization reaction. The wettability of developed polymer surfaces also varies with macromolecular structure.

Development of a Linear Ion Trap Mass Spectrometer (LITMS) Investigation for Future Planetary Surface Missions

NASA Technical Reports Server (NTRS)

Brinckerhoff, W.; Danell, R.; Van Ameron, F.; Pinnick, V.; Li, X.; Arevalo, R.; Glavin, D.; Getty, S.; Mahaffy, P.; Chu, P.;

Solar Wind sputtering from the surface of Comet Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Wurz, Peter; Rubin, Martin; Altwegg, Kathrin; Balsiger, Hans; Gasc, Sébastien; Galli, André; Jäckel, Annette; Le Roy, Lena; Calmonte, Ursina; Tzou, Chia-Yu; Mall, Urs; Korth, Axel; Fiethe, Björn; De Keyser, Johan; Berthelier, Jean-Jacques; Rème, Henri; Gombosi, Tamas; Fuselier, Steven

2015-04-01

While the European Space Agency's Rosetta spacecraft is orbiting close to the comet 67P/Churyumov-Gerasimenko (67P/C-G) we performed continuous measurements of the chemical inventory of its coma with the the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument suite. ROSINA consists of two mass spectrometers, the Double Focusing Mass Spectrometer (DFMS) and the Reflectron-type Time-Of-Flight (RTOF), as well as the COmet Pressure Sensor (COPS). Most of the observed species in the coma are volatile material that are released from the comet's surface by sublimation, for example H2O, CO, CO2 and many others. The number densities in the coma of these species show temporary variation compatible with the solar illumination (diurnal cycle), with seasonal variation (summer and winter hemispheres), and with compositional heterogeneity of the surface. We can trace back the measurements of the observed species to the cometary surface to create maps of their probable origin on the surface. In addition to the volatile material we detected atoms of Na, K, Si, S, and some more, which cannot or only partially be set free via sublimation. Again, we project these measurements down onto the surface of the comet. These maps for the sputtered atoms differ significantly from the maps for volatile species, like the water map, in some cases they are almost the opposite. Our present understanding is that these atoms are the result of solar wind sputtering of refractory material, i.e., of dust located on the cometary surface. Since the release of material from the surface by sputtering is almost stoichiometric we can infer the chemical composition of major elements for the areas affected by sputtering and the average mineralogy of these locations can be derived. The sputter signal will disappear with the comet getting closer to the Sun and becomes more active. Once the coma is dense enough, the solar wind will be absorbed by the gas layer above the surface and will not propagate to the surface anymore.

Analysis of an electrohydraulic aircraft control surface servo and comparison with test results

NASA Technical Reports Server (NTRS)

Edwards, J. W.

1972-01-01

An analysis of an electrohydraulic aircraft control-surface system is made in which the system is modeled as a lumped, two-mass, spring-coupled system controlled by a servo valve. Both linear and nonlinear models are developed, and the effects of hinge-moment loading are included. Transfer functions of the system and approximate literal factors of the transfer functions for several cases are presented. The damping action of dynamic pressure feedback is analyzed. Comparisons of the model responses with results from tests made on a highly resonant rudder control-surface servo indicate the adequacy of the model. The effects of variations in hinge-moment loading are illustrated.

Analytical mass formula and nuclear surface properties in the ETF approximation. Part I: symmetric nuclei

NASA Astrophysics Data System (ADS)

Aymard, François; Gulminelli, Francesca; Margueron, Jérôme

2016-08-01

The problem of determination of nuclear surface energy is addressed within the framework of the extended Thomas Fermi (ETF) approximation using Skyrme functionals. We propose an analytical model for the density profiles with variationally determined diffuseness parameters. In this first paper, we consider the case of symmetric nuclei. In this situation, the ETF functional can be exactly integrated, leading to an analytical formula expressing the surface energy as a function of the couplings of the energy functional. The importance of non-local terms is stressed and it is shown that they cannot be deduced simply from the local part of the functional, as it was suggested in previous works.

Mass spectrometric analysis of organic compounds, water and volatile constituents in the atmosphere and surface of Mars: The Viking Mars Lander

USGS Publications Warehouse

Anderson, Duwayne M.; Biemann, K.; Orgel, Leslie E.; Oro, John; Owen, Timothy W.; Shulman, Garson P.; Toulmin, Priestley; Urey, H.C.

1972-01-01

An experiment centering around a mass spectrometer is described, which is aimed at the identification of organic substances present in the top 10 cm of the surface of Mars and an analysis of the atmosphere for major and minor constituents as well as isotopic abundances. In addition, an indication of the abundance of water in the surface and some information concerning the mineralogy can be obtained by monitoring the gases produced upon heating the soil sample.The organic material will simply be expelled by heating to 150°, 300°, and 500° into the carrier gas stream of a gas chromatograph interfaced to the mass spectrometer or by slowly heating the sample in direct communication with the spectrometer. It is planned to analyze a total of up to nine soil samples in order to study diurnal and seasonal variations. The system is designed to give useful data even for minor constituents if the total of organics should be as low as 5ppm. The spectrometer covers the mass range of 12–200 with adequate resolution.The results of these experiments, which are deliberately designed to cover a wide spectrum of possibilities independent of terrestrial models, are expected to produce a good picture of the planet's organic chemistry and its possible biological significance as well as allow conclusions regarding the history of the planet's atmosphere.

Hide and Seek: Radial-velocity searches for planets around active stars

NASA Astrophysics Data System (ADS)

Haywood, Raphaelle

2017-01-01

The ultimate obstacle to determining the masses of small, rocky exoplanets through radial-velocity (RV) monitoring is the intrinsic variability of the host stars themselves. For my PhD, I developed an intuitive and robust data analysis framework in which the activity-induced variations are modelled with a Gaussian process that has the frequency structure of the stellar magnetic activity. This allowed me to determine precise and accurate masses of the planets in the CoRoT-7, Kepler-78 and Kepler-10 systems. In parallel, I explored the physical origin of activity-induced RV variations of our best-known star: the Sun. I conducted the first systematic RV campaign of the Sun seen as an exoplanet host star using the 3.6m/HARPS spectrograph, by observing sunlight reflected off the bright asteroid 4/Vesta. I used images from the Solar Dynamics Observatory to reconstruct the RV signals incurred by individual surface features such as sunspots, faculae and granulation. I found that the activity-induced RV variations are driven by the suppression of convective blueshift arising dominantly from the presence of faculae. I also identified the full-disc magnetic flux as an excellent proxy for activity-induced RV variations.I am now pursuing my solar investigations using Sun-as-a-star RV observations acquired with the new solar telescope feed at HARPS-N. In particular, I am investigating the impact of magnetic surface features on the shapes of the spectral line profiles, rather than on the RVs themselves (which are a single moment of these lines). This work is key to developing physically-driven, better-tailored models for activity-induced RV variations, in preparation for the potentially habitable, Earth-like planets to be discovered and characterised in the coming years with TESS and GMT/G-CLEF.This work was funded by the Science and Technology Facilities Council in the United Kingdom and the John Templeton Foundation.

Multi-geodetic characterization of the seasonal signal at the CERGA geodetic reference station, France

NASA Astrophysics Data System (ADS)

Mémin, Anthony; Viswanathan, Vishnu; Fienga, Agnes; Santamarìa-Gómez, Alvaro; Boy, Jean-Paul; Cavalié, Olivier; Deleflie, Florent; Exertier, Pierre; Bernard, Jean-Daniel; Hinderer, Jacques

2017-04-01

Crustal deformations due to surface-mass loading account for a significant part of the variability in geodetic time series. A perfect understanding of the loading signal observed by geodetic techniques should help in improving terrestrial reference frame (TRF) realizations. Yet, discrepancies between crustal motion estimates from models of surface-mass loading and observations are still too large so that no model is currently recommended by the IERS for reducing the observations. We investigate the discrepancy observed in the seasonal variations of the position at the CERGA station, South of France. We characterize the seasonal motions of the reference geodetic station CERGA from GNSS, SLR, LLR and InSAR. We investigate the consistency between the station motions deduced from these geodetic techniques and compare the observed station motion with that estimated using models of surface-mass change. In that regard, we compute atmospheric loading effects using surface pressure fields from ECMWF, assuming an ocean response according to the classical inverted barometer (IB) assumption, considered to be valid for periods typically exceeding a week. We also used general circulation ocean models (ECCO and GLORYS) forced by wind, heat and fresh water fluxes. The continental water storage is described using GLDAS/Noah and MERRA-land models. Using the surface-mass models, we estimate that the seasonal signal due to loading deformation at the CERGA station is about 8-9, 1-2 and 1-2 mm peak-to-peak in Up, North and East component, respectively. There is a very good correlation between GPS observations and non-tidal loading predicted deformation due to atmosphere, ocean and hydrology which is the main driver of seasonal signal at CERGA. Despite large error bars, LLR observations agree reasonably well with GPS and non-tidal loading predictions in Up component. Local deformation as observed by InSAR is very well correlated with GPS observations corrected for non-tidal loading. Finally, we estimate local mass changes using the absolute gravity measurement campaigns available at the station and the global models of surface-mass change. We compute the induced station motion that we compare with the local deformation observed by InSAR and GPS.

Seasonal variability of surface and column carbon monoxide over the megacity Paris, high-altitude Jungfraujoch and Southern Hemispheric Wollongong stations

NASA Astrophysics Data System (ADS)

Té, Yao; Jeseck, Pascal; Franco, Bruno; Mahieu, Emmanuel; Jones, Nicholas; Paton-Walsh, Clare; Griffith, David W. T.; Buchholz, Rebecca R.; Hadji-Lazaro, Juliette; Hurtmans, Daniel; Janssen, Christof

2016-09-01

This paper studies the seasonal variation of surface and column CO at three different sites (Paris, Jungfraujoch and Wollongong), with an emphasis on establishing a link between the CO vertical distribution and the nature of CO emission sources. We find the first evidence of a time lag between surface and free tropospheric CO seasonal variations in the Northern Hemisphere. The CO seasonal variability obtained from the total columns and free tropospheric partial columns shows a maximum around March-April and a minimum around September-October in the Northern Hemisphere (Paris and Jungfraujoch). In the Southern Hemisphere (Wollongong) this seasonal variability is shifted by about 6 months. Satellite observations by the IASI-MetOp (Infrared Atmospheric Sounding Interferometer) and MOPITT (Measurements Of Pollution In The Troposphere) instruments confirm this seasonality. Ground-based FTIR (Fourier transform infrared) measurements provide useful complementary information due to good sensitivity in the boundary layer. In situ surface measurements of CO volume mixing ratios at the Paris and Jungfraujoch sites reveal a time lag of the near-surface seasonal variability of about 2 months with respect to the total column variability at the same sites. The chemical transport model GEOS-Chem (Goddard Earth Observing System chemical transport model) is employed to interpret our observations. GEOS-Chem sensitivity runs identify the emission sources influencing the seasonal variation of CO. At both Paris and Jungfraujoch, the surface seasonality is mainly driven by anthropogenic emissions, while the total column seasonality is also controlled by air masses transported from distant sources. At Wollongong, where the CO seasonality is mainly affected by biomass burning, no time shift is observed between surface measurements and total column data.

A comprehensive analysis of surface acoustic wave reflections

NASA Astrophysics Data System (ADS)

Robinson, H.; Hahn, Y.; Gau, J. N.

1989-06-01

A thorough study of the perturbative and variational approaches is carried out for the surface acoustic wave reflection problem. We have shown that the perturbation treatment by Datta and Hunsinger and potentially powerful variational formulation by Chen and Haus [IEEE Trans. Sonics Ultrason. SU-32, 395 (1985)] are mutually consistent. In their common region of validity, these two approaches yield nearly identical results for the reflection coefficients and velocity shifts due to metal finger and groove overlays. Term-by-term comparison of the mass- and stress-loading effects, and also the electric shorting effect, is carried out to provide a coherent picture of the reflection phenomena. The on- and off-resonance behavior of the reflection coefficient can be described correctly using either one of these theories, with proper inclusion of the overlay shape dependence. A new term for electric shorting is derived for groove overlays.

Seasonal variations of snow depth on Mars.

PubMed

Smith, D E; Zuber, M T; Neumann, G A

2001-12-07

Using topography collected over one martian year from the Mars Orbiter Laser Altimeter on the Mars Global Surveyor (MGS) spacecraft, we have measured temporal changes in the elevation of the martian surface that correlate with the seasonal cycle of carbon dioxide exchange between the surface and atmosphere. The greatest elevation change (1.5 to 2 meters) occurs at high latitudes ( above 80 degrees ), whereas the bulk of the mass exchange occurs at lower latitudes (below 75 degrees N and below 73 degrees S). An unexpected period of sublimation was observed during northern hemisphere autumn, coincident with dust storms in the southern hemisphere. Analysis of MGS Doppler tracking residuals revealed temporal variations in the flattening of Mars that correlate with elevation changes. The combined changes in gravity and elevation constrain the average density of seasonally deposited carbon dioxide to be 910 +/- 230 kilograms per cubic meter, which is considerably denser than terrestrial snow.

Reull Valles in Approximately Natural Color

NASA Technical Reports Server (NTRS)

1995-01-01

Reull Valles, conspicuous southeast-trending fretted channel, dissects wall deposits of the large Hellas impact basin. Center of picture is at latitude 42 degrees S. longitude 258 degrees. Fretted channels are wide, flat-floored channels with steep walls, which may be runoff channels that have been modified and enlarged by mass wasting. Many nearby hills and mountains are surrounded by lobate debris aprons, which may have formed by slow creep of rock deposits aided by the presence of near-surface ice. Layering is exposed in the channel and crater walls. The color variations of the surface are very bland in this region; most of the variations seen in the enhanced-color version (PIA00153) are due to atmospheric scattering. Viking Orbiter Picture Numbers 126A08 (violet), 126A16 (green), and 126A24 (red) at 157 m/pixel resolution. Picture width is 161 km. North is 112 degrees clockwise from top.

Studies on biodegradation of crosslinked hydroxy terminated-poly(proplyene fumarate) and formation of scaffold for orthopedic applications.

PubMed

Shalumon, K T; Jayabalan, M

2009-12-01

Biodegradation of crosslinked-hydroxy terminated-poly(proplyene fumarate) (X-HTPPF) has been studied in simulated physiological media to assess the formation of porous scaffold structure for bone growth and remodeling in load bearing orthopedic applications. Variation in crosslink density and surface hydrophilicity of X-HTPPF are observed due to non-stoichiometric mass of reacting partners. These variations influence absorption of the medium and biodegradation during aging. Though the initial absorption of medium is relatively higher with the crosslinked polymer (PNVP1) having 63.6% HT-PPF and 36.4% comonomer n-vinyl pyrrolidone (NVP) during the initial period of aging, the weight loss due to subsequent degradation with time is relatively lesser. PNVP1 undergo slow degradation with formation of fibril structure on the surface. The present crosslinked material PNVP1 is a candidate for the load bearing orthopedic applications.

Features of Red Sea Water Masses

NASA Astrophysics Data System (ADS)

Kartadikaria, Aditya; Hoteit, Ibrahim

2015-04-01

Features of Red Sea water mass can be divided into three types but best to be grouped into two different classes that are split at the potential density line σθ=27.4. The surface water (0-50 m) and the intermediate water (50-200 m) have nearly identical types of water mass. They appear as a maxima salinity layer for the water mass that has σθ > 26.0, and as a minimum salinity layer for water mass that has σθ < 26.0. These types of water masses are strongly affected by mixing that is controlled by seasonal variability, fresh water intrusion of the Gulf of Aden Intermediate Water (GAIW), and eddies variability. Two types of mixing; isopycnal and diapycnal mixing are part of important physical phenomena that explain the change of water mass in the Red Sea. The isopycnal mixing occurs at the neutral potential density line, connecting the Red Sea with its adjacent channel, the Gulf of Aden. Diapycnal mixing is found as a dominant mixing mode in the surface of the Red Sea Water and mainly due to energetic eddy activity. Density gradients, across which diapycnal mixing occurs, in the Red Sea are mainly due to large variations in salinity. The isolation of an extreme haline water mass below the thermocline contributes to the generation of the latitudinal shift and low diapycnal mixing. This finding further explains the difference of spatial kinetic mixing between the RSW and the Indian Ocean basin.

Variations in body morphology explain sex differences in thermoeffector function during compensable heat stress.

PubMed

Notley, Sean R; Park, Joonhee; Tagami, Kyoko; Ohnishi, Norikazu; Taylor, Nigel A S

2017-05-01

What is the central question of this study? Can sex-related differences in cutaneous vascular and sudomotor responses be explained primarily by variations in the ratio between body surface area and mass during compensable exercise that elicits equivalent heat-loss requirements and mean body temperature changes across participants? What is the main finding and its importance? Mass-specific surface area was a significant determinant of vasomotor and sudomotor responses in men and women, explaining 10-48% of the individual thermoeffector variance. Nonetheless, after accounting for changes in mean body temperature and morphological differences, sex explained only 5% of that inter-individual variability. It was concluded that sex differences in thermoeffector function are morphologically dependent, but not sex dependent. Sex is sometimes thought to be an independent modulator of cutaneous vasomotor and sudomotor function during heat exposure. Nevertheless, it was hypothesized that, when assessed during compensable exercise that evoked equal heat-loss requirements across participants, sex differences in those thermoeffectors would be explained by variations in the ratio between body surface area and mass (specific surface area). To evaluate that possibility, vasomotor and sudomotor functions were assessed in 60 individuals (36 men and 24 women) with widely varying (overlapping) specific surface areas (range, 232.3-292.7 and 241.2-303.1 cm 2  kg -1 , respectively). Subjects completed two trials in compensable conditions (28°C, 36% relative humidity) involving rest (20 min) and steady-state cycling (45 min) at fixed, area-specific metabolic heat-production rates (light, ∼135 W m -2 ; moderate, ∼200 W m -2 ). Equivalent heat-loss requirements and mean body temperature changes were evoked across participants. Forearm blood flow and vascular conductance were positively related to specific surface area during light work in men (r = 0.67 and r = 0.66, respectively; both P < 0.05) and during both exercise intensities in women (light, r = 0.57 and r = 0.69; and moderate, r = 0.64 and r = 0.68; all P < 0.05). Whole-body and local sweat rates were negatively related to that ratio (correlation coefficient range, -0.33 to -0.62; all P < 0.05) during both work rates in men and women. Those relationships accounted for 10-48% of inter-individual thermoeffector variance (P < 0.05). Furthermore, after accounting for morphological differences, sex explained no more than 5% of that variability (P < 0.05). It was concluded that, when assessed during compensable exercise, sex differences in thermoeffector function were largely determined morphologically, rather than being sex dependent. © 2017 The Authors. Experimental Physiology © 2017 The Physiological Society.

Simultaneous solution of the geoid and the surface density anomalies

NASA Astrophysics Data System (ADS)

Ardalan, A. A.; Safari, A.; Karimi, R.; AllahTavakoli, Y.

2012-04-01

The main application of the land gravity data in geodesy is "local geoid" or "local gravity field" modeling, whereas the same data could play a vital role for the anomalous mass-density modeling in geophysical explorations. In the realm of local geoid computations based on Geodetic Boundary Value Problems (GBVP), it is needed that the effect of the topographic (or residual terrain) masses be removed via application of the Newton integral in order to perform the downward continuation in a harmonic space. However, harmonization of the downward continuation domain may not be perfectly possible unless accurate information about the mass-density of the topographic masses be available. On the other hand, from the exploration point of view the unwanted topographical masses within the aforementioned procedure could be regarded as the signal. In order to overcome the effect of the remaining masses within the remove step of the GBVP, which cause uncertainties in mathematical modeling of the problem, here we are proposing a methodology for simultaneous solution of the geoid and residual surface density modeling In other words, a new mathematical model will be offered which both provides the needed harmonic space for downward continuation and at the same time accounts for the non-harmonic terms of gravitational field and makes use of it for residual mass density modeling within the topographic region. The presented new model enjoys from uniqueness of the solution, opposite to the inverse application of the Newton integral for mass density modeling which is non-unique, and only needs regularization to remove its instability problem. In this way, the solution of the model provides both the incremental harmonic gravitational potential on surface of the reference ellipsoid as the gravity field model and the lateral surface mass-density variations via the second derivatives of the non harmonic terms of gravitational field. As the case study and accuracy verification, the proposed methodology is applied for identification of the salt geological structures as well as geoid computations within the northern coasts of Persian Gulf.

Deformable torso phantoms of Chinese adults for personalized anatomy modelling.

PubMed

Wang, Hongkai; Sun, Xiaobang; Wu, Tongning; Li, Congsheng; Chen, Zhonghua; Liao, Meiying; Li, Mengci; Yan, Wen; Huang, Hui; Yang, Jia; Tan, Ziyu; Hui, Libo; Liu, Yue; Pan, Hang; Qu, Yue; Chen, Zhaofeng; Tan, Liwen; Yu, Lijuan; Shi, Hongcheng; Huo, Li; Zhang, Yanjun; Tang, Xin; Zhang, Shaoxiang; Liu, Changjian

2018-04-16

In recent years, there has been increasing demand for personalized anatomy modelling for medical and industrial applications, such as ergonomics device development, clinical radiological exposure simulation, biomechanics analysis, and 3D animation character design. In this study, we constructed deformable torso phantoms that can be deformed to match the personal anatomy of Chinese male and female adults. The phantoms were created based on a training set of 79 trunk computed tomography (CT) images (41 males and 38 females) from normal Chinese subjects. Major torso organs were segmented from the CT images, and the statistical shape model (SSM) approach was used to learn the inter-subject anatomical variations. To match the personal anatomy, the phantoms were registered to individual body surface scans or medical images using the active shape model method. The constructed SSM demonstrated anatomical variations in body height, fat quantity, respiratory status, organ geometry, male muscle size, and female breast size. The masses of the deformed phantom organs were consistent with Chinese population organ mass ranges. To validate the performance of personal anatomy modelling, the phantoms were registered to the body surface scan and CT images. The registration accuracy measured from 22 test CT images showed a median Dice coefficient over 0.85, a median volume recovery coefficient (RC vlm ) between 0.85 and 1.1, and a median averaged surface distance (ASD) < 1.5 mm. We hope these phantoms can serve as computational tools for personalized anatomy modelling for the research community. © 2018 Anatomical Society.

Geographic variation in seed traits within and among forty-two species of Rhododendron (Ericaceae) on the Tibetan plateau: relationships with altitude, habitat, plant height, and phylogeny

PubMed Central

Wang, Yongji; Wang, Jianjian; Lai, Liming; Jiang, Lianhe; Zhuang, Ping; Zhang, Lehua; Zheng, Yuanrun; Baskin, Jerry M; Baskin, Carol C

2014-01-01

Seed mass and morphology are plant life history traits that influence seed dispersal ability, seeding establishment success, and population distribution pattern. Southeastern Tibet is a diversity center for Rhododendron species, which are distributed from a few hundred meters to 5500 m above sea level. We examined intra- and interspecific variation in seed mass and morphology in relation to altitude, habitat, plant height, and phylogeny. Seed mass decreased significantly with the increasing altitude and increased significantly with increasing plant height among populations of the same species. Seed mass differed significantly among species and subsections, but not among sections and subgenera. Seed length, width, surface area, and wing length were significantly negative correlated with altitude and significantly positive correlated with plant height. Further, these traits differed significantly among habitats and varied among species and subsection, but not among sections and subgenera. Species at low elevation had larger seeds with larger wings, and seeds became smaller and the wings of seeds tended to be smaller with the increasing altitude. Morphology of the seed varied from flat round to long cylindrical with increasing altitude. We suggest that seed mass and morphology have evolved as a result of both long-term adaptation and constraints of the taxonomic group over their long evolutionary history. PMID:24963385

Longitudinal Changes in Body Composition Assessed Using DXA and Surface Anthropometry Show Good Agreement in Elite Rugby Union Athletes.

PubMed

Zemski, Adam J; Keating, Shelley E; Broad, Elizabeth M; Slater, Gary J

2018-05-14

Rugby union athletes have divergent body composition based on the demands of their on-field playing position and ethnicity. With an established association between physique traits and positional requirements, body composition assessment is routinely undertaken. Surface anthropometry and dual-energy X-ray absorptiometry (DXA) are the most common assessment techniques utilised, often undertaken synchronously. This study aims to investigate the association between DXA and surface anthropometry when assessing longitudinal changes in fat free mass (FFM) and fat mass (FM) in rugby union athletes. Thirty-nine elite male rugby union athletes (age 25.7 ± 3.1 years; stature 187.6 ± 7.7 cm; mass 104.1 ± 12.2 kg) underwent assessment via DXA and surface anthropometry multiple times over three consecutive international seasons. Changes in the lean mass index (LMI), an empirical measure to assess proportional variation in FFM, showed large agreement with changes in DXA FFM (r=0.54, SEE=1.5%, P<0.001); the strength of association stronger amongst forwards (r=0.63) compared with backs (r=0.38). Changes in the sum of 7 skinfolds (S7SF) showed very large agreement with changes in DXA FM (r=0.73, SEE=5.8%, P<0.001), with meaningful differences observed regardless of ethnicity (Caucasians r=0.75; Polynesians r=0.62). The LMI and S7SF were able to predict the direction of change in FFM and FM, respectively, 86% and 91% of the time when DXA change was >1kg. Surface anthropometry measures provide a robust indication of the direction of change in FFM and FM, although caution may need to be applied when interpreting magnitude of change, particularly with FM.

Monitoring of platinum surface contamination in seven Dutch hospital pharmacies using inductively coupled plasma mass spectrometry

PubMed Central

Huitema, A. D. R.; Bakker, E. N.; Douma, J. W.; Schimmel, K. J. M.; van Weringh, G.; de Wolf, P. J.; Schellens, J. H. M.; Beijnen, J. H.

2007-01-01

Objective: To develop, validate, and apply a method for the determination of platinum contamination, originating from cisplatinum, oxaliplatinum, and carboplatinum. Methods: Inductively coupled plasma mass spectrometry (ICP-MS) was used to determine platinum in wipe samples. The sampling procedure and the analytical conditions were optimised and the assay was validated. The method was applied to measure surface contamination in seven Dutch hospital pharmacies. Results: The developed method allowed reproducible quantification of 0.50 ng l−1 platinum (5 pg/wipe sample). Recoveries for stainless steel and linoleum surfaces ranged between 50.4 and 81.4% for the different platinum compounds tested. Platinum contamination was reported in 88% of the wipe samples. Although a substantial variation in surface contamination of the pharmacies was noticed, in most pharmacies, the laminar-airflow (LAF) hoods, the floor in front of the LAF hoods, door handles, and handles of service hatches showed positive results. This demonstrates that contamination is spread throughout the preparation rooms. Conclusion: We developed and validated an ultra sensitive and reliable ICP-MS method for the determination of platinum in surface samples. Surface contamination with platinum was observed in all hospital pharmacies sampled. The interpretation of these results is, however, complicated. PMID:17377802

Selective nature and inherent variability of interrill erosion across prolonged rainfall simulation

NASA Astrophysics Data System (ADS)

Hu, Y.; Kuhn, N. J.; Fister, W.

2012-04-01

Sediment of interrill erosion has been generally recognized to be selectively enriched with soil organic carbon (SOC) and fine fractions (clay/silt-sized particles or aggregates) in comparison to source area soil. Limited kinetic energy and lack of concentrated runoff are the dominant factors causing selective detachment and transportation. Although enrichment ratios of SOC (ERsoc) in eroded sediment were generally reported > 1, the values varied widely. Causal factors to variation, such as initial soil properties, rainfall properties and experimental conditions, have been extensively discussed. But less attention was directed to the potential influence of prolonged rainfall time onto the temporal pattern of ERsoc. Conservation of mass dictates that ERsoc must be balanced by a decline in the source material which should also lead to a reduced or even negative ERsoc in sediment over time. Besides, the stabilizing effects of structural crust on reducing erosional variation, and the unavoidable variations of erosional response induced by the inherent complexity of interrill erosion, have scarcely been integrated. Moreover, during a prolonged rainfall event surface roughness evolves and affects the movement of eroded aggregates and mineral particles. In this study, two silt loams from Möhlin, Switzerland, organically (OS) and conventionally farmed (CS), were exposed to simulated rainfall of 30 mm h-1 for up to 6 hours. Round donut-flumes with a confined eroding area (1845 cm2) and limited transporting distance (20 cm) were used. Sediments, runoff and subsurface flow were collected in intervals of 30 min. Loose aggregates left on the eroded soil surface, crusts and the soil underneath the crusts were collected after the experiment. All the samples were analyzed for total organic carbon (TOC) content, and texture. Laser scanning of soil surface was applied before and after the rainfall event. The whole experiment was repeated for 10 times. Results from this study showed that: 1) ERsoc in eroded sediment increased at first, then reached steady state and declined afterwards, corresponding well with the formation and completion of structural crust and conservation of mass; 2) the effect of structural crust on stabilizing the surface condition and reducing variation of erosional response was more apparent once steady state discharge was achieved ; and 3) both texture and TOC content in crusts and soil underneath the crusts were comparable to parent soil, explaining the decline in ERsoc. In conclusion, the experiment showed that crusting and conservation of mass lead to a decline and even negative enrichment of organic matter in interrill sediment over time. Enrichment of organic matter should therefore be reported only in conjunction with information about the stage of crust development observed during an erosion event.

Helical variation of density profiles and fluctuations in the tokamak pedestal with applied 3D fields and implications for confinement

DOE PAGES

Wilcox, R. S.; Rhodes, T. L.; Shafer, M. W.; ...

2018-04-19

Smore » mall 3D perturbations to the magnetic field in DIII-D ( δ B / B ~ 2 × 10 - 4 ) result in large modulations of density fluctuation amplitudes in the pedestal, which are shown using Doppler backscattering measurements to vary by a factor of 2. Helical perturbations of equilibrium density within flux surfaces have previously been observed in the pedestal of DIII-D plasmas when 3D fields are applied and were correlated with density fluctuation asymmetries in the pedestal. These intra-surface density and pressure variations are shown through two fluid MHD modeling studies using the M3D-C1 code to be due to the misalignment of the density and temperature equilibrium iso-surfaces in the pedestal region. This modeling demonstrates that the phase shift between the two iso-surfaces corresponds to the diamagnetic direction of the two species, with the mass density surfaces shifted in the ion diamagnetic direction relative to the temperature and magnetic flux iso-surfaces. Finally, the resulting pedestal density, potential, and turbulence asymmetries within flux surfaces near the separatrix may be at least partially responsible for several poorly understood phenomena that occur with the application of 3D fields in tokamaks, including density pump out and the increase in power required to transition from L- to H-mode.« less

Helical variation of density profiles and fluctuations in the tokamak pedestal with applied 3D fields and implications for confinement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilcox, R. S.; Rhodes, T. L.; Shafer, M. W.

Smore » mall 3D perturbations to the magnetic field in DIII-D ( δ B / B ~ 2 × 10 - 4 ) result in large modulations of density fluctuation amplitudes in the pedestal, which are shown using Doppler backscattering measurements to vary by a factor of 2. Helical perturbations of equilibrium density within flux surfaces have previously been observed in the pedestal of DIII-D plasmas when 3D fields are applied and were correlated with density fluctuation asymmetries in the pedestal. These intra-surface density and pressure variations are shown through two fluid MHD modeling studies using the M3D-C1 code to be due to the misalignment of the density and temperature equilibrium iso-surfaces in the pedestal region. This modeling demonstrates that the phase shift between the two iso-surfaces corresponds to the diamagnetic direction of the two species, with the mass density surfaces shifted in the ion diamagnetic direction relative to the temperature and magnetic flux iso-surfaces. Finally, the resulting pedestal density, potential, and turbulence asymmetries within flux surfaces near the separatrix may be at least partially responsible for several poorly understood phenomena that occur with the application of 3D fields in tokamaks, including density pump out and the increase in power required to transition from L- to H-mode.« less

Helical variation of density profiles and fluctuations in the tokamak pedestal with applied 3D fields and implications for confinement

NASA Astrophysics Data System (ADS)

Wilcox, R. S.; Rhodes, T. L.; Shafer, M. W.; Sugiyama, L. E.; Ferraro, N. M.; Lyons, B. C.; McKee, G. R.; Paz-Soldan, C.; Wingen, A.; Zeng, L.

2018-05-01

Small 3D perturbations to the magnetic field in DIII-D ( δB /B ˜2 ×10-4 ) result in large modulations of density fluctuation amplitudes in the pedestal, which are shown using Doppler backscattering measurements to vary by a factor of 2. Helical perturbations of equilibrium density within flux surfaces have previously been observed in the pedestal of DIII-D plasmas when 3D fields are applied and were correlated with density fluctuation asymmetries in the pedestal. These intra-surface density and pressure variations are shown through two fluid MHD modeling studies using the M3D-C1 code to be due to the misalignment of the density and temperature equilibrium iso-surfaces in the pedestal region. This modeling demonstrates that the phase shift between the two iso-surfaces corresponds to the diamagnetic direction of the two species, with the mass density surfaces shifted in the ion diamagnetic direction relative to the temperature and magnetic flux iso-surfaces. The resulting pedestal density, potential, and turbulence asymmetries within flux surfaces near the separatrix may be at least partially responsible for several poorly understood phenomena that occur with the application of 3D fields in tokamaks, including density pump out and the increase in power required to transition from L- to H-mode.

Shape shifting predicts ontogenetic changes in metabolic scaling in diverse aquatic invertebrates

PubMed Central

Glazier, Douglas S.; Hirst, Andrew G.; Atkinson, David

2015-01-01

Metabolism fuels all biological activities, and thus understanding its variation is fundamentally important. Much of this variation is related to body size, which is commonly believed to follow a 3/4-power scaling law. However, during ontogeny, many kinds of animals and plants show marked shifts in metabolic scaling that deviate from 3/4-power scaling predicted by general models. Here, we show that in diverse aquatic invertebrates, ontogenetic shifts in the scaling of routine metabolic rate from near isometry (bR = scaling exponent approx. 1) to negative allometry (bR < 1), or the reverse, are associated with significant changes in body shape (indexed by bL = the scaling exponent of the relationship between body mass and body length). The observed inverse correlations between bR and bL are predicted by metabolic scaling theory that emphasizes resource/waste fluxes across external body surfaces, but contradict theory that emphasizes resource transport through internal networks. Geometric estimates of the scaling of surface area (SA) with body mass (bA) further show that ontogenetic shifts in bR and bA are positively correlated. These results support new metabolic scaling theory based on SA influences that may be applied to ontogenetic shifts in bR shown by many kinds of animals and plants. PMID:25652833

Surface Modification and Surface - Subsurface Exchange Processes on Europa

NASA Astrophysics Data System (ADS)

Phillips, Cynthia B.; Molaro, Jamie; Hand, Kevin P.

2017-10-01

The surface of Jupiter’s moon Europa is modified by exogenic processes such as sputtering, gardening, radiolysis, sulfur ion implantation, and thermal processing, as well as endogenic processes including tidal shaking, mass wasting, and the effects of subsurface tectonic and perhaps cryovolcanic activity. New materials are created or deposited on the surface (radiolysis, micrometeorite impacts, sulfur ion implantation, cryovolcanic plume deposits), modified in place (thermal segregation, sintering), transported either vertically or horizontally (sputtering, gardening, mass wasting, tectonic and cryovolcanic activity), or lost from Europa completely (sputtering, plumes, larger impacts). Some of these processes vary spatially, as visible in Europa’s leading-trailing hemisphere brightness asymmetry.Endogenic geologic processes also vary spatially, depending on terrain type. The surface can be classified into general landform categories that include tectonic features (ridges, bands, cracks); disrupted “chaos-type” terrain (chaos blocks, matrix, domes, pits, spots); and impact craters (simple, complex, multi-ring). The spatial distribution of these terrain types is relatively random, with some differences in apex-antiapex cratering rates and latitudinal variation in chaos vs. tectonic features.In this work, we extrapolate surface processes and rates from the top meter of the surface in conjunction with global estimates of transport and resurfacing rates. We combine near-surface modification with an estimate of surface-subsurface (and vice versa) transport rates for various geologic terrains based on an average of proposed formation mechanisms, and a spatial distribution of each landform type over Europa’s surface area.Understanding the rates and mass balance for each of these processes, as well as their spatial and temporal variability, allows us to estimate surface - subsurface exchange rates over the average surface age (~50myr) of Europa. Quantifying the timescale and volume of transported material will yield insight on whether such a process may provide fuel to sustain a biosphere in Europa’s subsurface ocean, which is relevant to searches for life by a future mission such as a potential Europa Lander.

Surface Modification and Surface - Subsurface Exchange Processes on Europa

NASA Astrophysics Data System (ADS)

Phillips, C. B.; Molaro, J.; Hand, K. P.

2017-12-01

The surface of Jupiter's moon Europa is modified by exogenic processes such as sputtering, gardening, radiolysis, sulfur ion implantation, and thermal processing, as well as endogenic processes including tidal shaking, mass wasting, and the effects of subsurface tectonic and perhaps cryovolcanic activity. New materials are created or deposited on the surface (radiolysis, micrometeorite impacts, sulfur ion implantation, cryovolcanic plume deposits), modified in place (thermal segregation, sintering), transported either vertically or horizontally (sputtering, gardening, mass wasting, tectonic and cryovolcanic activity), or lost from Europa completely (sputtering, plumes, larger impacts). Some of these processes vary spatially, as visible in Europa's leading-trailing hemisphere brightness asymmetry. Endogenic geologic processes also vary spatially, depending on terrain type. The surface can be classified into general landform categories that include tectonic features (ridges, bands, cracks); disrupted "chaos-type" terrain (chaos blocks, matrix, domes, pits, spots); and impact craters (simple, complex, multi-ring). The spatial distribution of these terrain types is relatively random, with some differences in apex-antiapex cratering rates and latitudinal variation in chaos vs. tectonic features. In this work, we extrapolate surface processes and rates from the top meter of the surface in conjunction with global estimates of transport and resurfacing rates. We combine near-surface modification with an estimate of surface-subsurface (and vice versa) transport rates for various geologic terrains based on an average of proposed formation mechanisms, and a spatial distribution of each landform type over Europa's surface area. Understanding the rates and mass balance for each of these processes, as well as their spatial and temporal variability, allows us to estimate surface - subsurface exchange rates over the average surface age ( 50myr) of Europa. Quantifying the timescale and volume of transported material will yield insight on whether such a process may provide fuel to sustain a biosphere in Europa's subsurface ocean, which is relevant to searches for life by a future mission such as a potential Europa Lander.

Thermobaricity, cabbeling, and water-mass conversion

NASA Astrophysics Data System (ADS)

McDougall, Trevor J.

1987-05-01

The efficient mixing of heat and salt along neutral surfaces (by mesoscale eddies) is shown to lead to vertical advection through these neutral surfaces. This is due to the nonlinearities of the equation of state of seawater through terms like ∂2ρ/∂θ∂p (thermobaric effect) and ∂2ρ/∂ θ2 (cabbeling). Cabbeling always causes a sinking or downwelling of fluid through neutral surfaces, whereas thermobaricity can lead to a vertical velocity (relative to neutral surfaces) of either sign. In this paper it is shown that for reasonable values of the lateral scalar diffusivity (especially below a depth of 1000 m), these two processes cause vertical velocities of the order of 10-7 m s-1 through neutral surfaces (usually downward!) and cause water-mass conversion of a magnitude equal to that caused by a vertical diffusivity of 10-4 m2 s-1 (often equivalent to a negative diffusivity). Both thermobaricity and cabbeling can occur in the presence of any nonzero amount of small-scale turbulence and so will not be detected by microstructure measurements. The conservation equations for tracers are considered in a nonorthogonal coordinate frame that moves with neutral surfaces in the ocean. Since only mixing processes cause advection across neutral surfaces, it is useful to regard this vertical advection as a symptom of various mixing processes rather than as a separate physical process. It is possible to derive conservative equations for scalars that do not contain the vertical advective term explicity. In these conservation equations, the terms that represent mixing processes are substantially altered. It is argued that this form of the conservation equations is the most appropriate when considering water-mass transformation, and some examples are given of its application in the North Atlantic. It is shown that the variation of the vertical diffusivity with height does not cause water-mass transformation. Also, salt fingering is often 3-4 times more effective at changing the potential temperature of a water mass than would be implied by simply calculating the vertical derivative of the fingering heat flux.

Heat and mass transfer scale-up issues during freeze-drying, III: control and characterization of dryer differences via operational qualification tests.

PubMed

Rambhatla, S; Tchessalov, S; Pikal, Michael J

2006-04-21

The objective of this research was to estimate differences in heat and mass transfer between freeze dryers due to inherent design characteristics using data obtained from sublimation tests. This study also aimed to provide guidelines for convenient scale-up of the freeze-drying process. Data obtained from sublimation tests performed on laboratory-scale, pilot, and production freeze dryers were used to evaluate various heat and mass transfer parameters: nonuniformity in shelf surface temperatures, resistance of pipe, refrigeration system, and condenser. Emissivity measurements of relevant surfaces such as the chamber wall and the freeze dryer door were taken to evaluate the impact of atypical radiation heat transfer during scale-up. "Hot" and "cold" spots were identified on the shelf surface of different freeze dryers, and the impact of variation in shelf surface temperatures on the primary drying time and the product temperature during primary drying was studied. Calculations performed using emissivity measurements on different freeze dryers suggest that a front vial in the laboratory lyophilizer received 1.8 times more heat than a front vial in a manufacturing freeze dryer operating at a shelf temperature of -25 degrees C and a chamber pressure of 150 mTorr during primary drying. Therefore, front vials in the laboratory are much more atypical than front vials in manufacturing. Steady-state heat and mass transfer equations were used to study a combination of different scale-up issues pertinent during lyophilization cycles commonly used for the freeze-drying of pharmaceuticals.

That gravity thing

NASA Astrophysics Data System (ADS)

Jewess, Mike

2009-05-01

Your news article "New probe plots Earth's gravity field" (March p11) reports on the European Space Agency's Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) - a satellite that will measure the Earth's gravitational field. It describes the way that g, the acceleration of free fall at the Earth's surface, varies with latitude; this variation is great enough to require adjustment of pendulum clocks between latitudes and also the recalibration of all balances that do not directly compare one mass with a reference mass. The article also notes that the spin of the (effectively fluid) Earth causes it to bulge at the equator, a realization that goes back to Newton's Principia.

Mission Implementation Constraints on Planetary Muon Radiography

NASA Technical Reports Server (NTRS)

Jones, Cathleen E.; Kedar, Sharon; Naudet, Charles; Webb, Frank

2011-01-01

Cost: Use heritage hardware, especially use a tested landing system to reduce cost (Phoenix or MSL EDL stage). The sky crane technology delivers higher mass to the surface and enables reaching targets at higher elevation, but at a higher mission cost. Rover vs. Stationary Lander: Rover-mounted instrument enables tomography, but the increased weight of the rover reduces the allowable payload weight. Mass is the critical design constraint for an instrument for a planetary mission. Many factors that are minor factors or do not enter into design considerations for terrestrial operation are important for a planetary application. (Landing site, diurnal temperature variation, instrument portability, shock/vibration)

Influence of indoor environmental factors on mass transfer parameters and concentrations of semi-volatile organic compounds.

PubMed

Wei, Wenjuan; Mandin, Corinne; Ramalho, Olivier

2018-03-01

Semi-volatile organic compounds (SVOCs) in indoor environments can partition among the gas phase, airborne particles, settled dust, and available surfaces. The mass transfer parameters of SVOCs, such as the mass transfer coefficient and the partition coefficient, are influenced by indoor environmental factors. Subsequently, indoor SVOC concentrations and thus occupant exposure can vary depending on environmental factors. In this review, the influence of six environmental factors, i.e., indoor temperature, humidity, ventilation, airborne particle concentration, source loading factor, and reactive chemistry, on the mass transfer parameters and indoor concentrations of SVOCs was analyzed and tentatively quantified. The results show that all mass transfer parameters vary depending on environmental factors. These variations are mostly characterized by empirical equations, particularly for humidity. Theoretical calculations of these parameters based on mass transfer mechanisms are available only for the emission of SVOCs from source surfaces when airborne particles are not present. All mass transfer parameters depend on the temperature. Humidity influences the partition of SVOCs among different phases and is associated with phthalate hydrolysis. Ventilation has a combined effect with the airborne particle concentration on SVOC emission and their mass transfer among different phases. Indoor chemical reactions can produce or eliminate SVOCs slowly. To better model the dynamic SVOC concentration indoors, the present review suggests studying the combined effect of environmental factors in real indoor environments. Moreover, interactions between indoor environmental factors and human activities and their influence on SVOC mass transfer processes should be considered. Copyright © 2017 Elsevier Ltd. All rights reserved.

Local Analysis Approach for Short Wavelength Geopotential Variations

NASA Astrophysics Data System (ADS)

Bender, P. L.

2009-12-01

The value of global spherical harmonic analyses for determining 15 day to 30 day changes in the Earth's gravity field has been demonstrated extensively using data from the GRACE mission and previous missions. However, additional useful information appears to be obtainable from local analyses of the data. A number of such analyses have been carried out by various groups. In the energy approximation, the changes in the height of the satellite altitude geopotential can be determined from the post-fit changes in the satellite separation during individual one-revolution arcs of data from a GRACE-type pair of satellites in a given orbit. For a particular region, it is assumed that short wavelength spatial variations for the arcs crossing that region during a time T of interest would be used to determine corrections to the spherical harmonic results. The main issue in considering higher measurement accuracy in future missions is how much improvement in spatial resolution can be achieved. For this, the shortest wavelengths that can be determined are the most important. And, while the longer wavelength variations are affected by mass distribution changes over much of the globe, the shorter wavelength ones hopefully will be determined mainly by more local changes in the mass distribution. Future missions are expected to have much higher accuracy for measuring changes in the satellite separation than GRACE. However, how large an improvement in the derived results in hydrology will be achieved is still very much a matter of study, particularly because of the effects of uncertainty in the time variations in the atmospheric and oceanic mass distributions. To be specific, it will be assumed that improving the spatial resolution in continental regions away from the coastlines is the objective, and that the satellite altitude is in the range of roughly 290 to 360 km made possible for long missions by drag-free operation. The advantages of putting together the short wavelength results from different arcs crossing the region can be seen most easily for an orbit with moderate inclination, such as 50 to 65 deg., so that the crossing angle between south-to-north (S-N) and N-S passes is fairly large over most regions well away from the poles. In that case, after filtering to pass the shorter wavelengths, the results for a given time interval can be combined to give the short wavelength W-E variations in the geopotential efficiently. For continents with extensive meteorological measurements available, like Europe and North America, a very rough guess at the surface mass density variation uncertainties is about 3 kg/m^2. This is based on the apparent accuracy of carefully calibrated surface pressure measurements. If a substantial part of the resulting uncertainties in the geopotential height at satellite altitude are at wavelengths less than about 1,500 km, they will dominate the measurement uncertainty at short spatial wavelengths for a GRACE-type mission with laser interferometry. This would be the case, even if the uncertainty in the atmospheric and oceanic mass distribution at large distances has a fairly small effect. However, the geopotential accuracy would still be substantially better than for the results achievable with a microwave ranging system.

Two-order parameters theory of the metal-insulator phase transition kinetics in the magnetic field

NASA Astrophysics Data System (ADS)

Dubovskii, L. B.

2018-05-01

The metal-insulator phase transition is considered within the framework of the Ginzburg-Landau approach for the phase transition described with two coupled order parameters. One of the order parameters is the mass density which variation is responsible for the origin of nonzero overlapping of the two different electron bands and the appearance of free electron carriers. This transition is assumed to be a first-order phase one. The free electron carriers are described with the vector-function representing the second-order parameter responsible for the continuous phase transition. This order parameter determines mostly the physical properties of the metal-insulator transition and leads to a singularity of the surface tension at the metal-insulator interface. The magnetic field is involved into the consideration of the system. The magnetic field leads to new singularities of the surface tension at the metal-insulator interface and results in a drastic variation of the phase transition kinetics. A strong singularity in the surface tension results from the Landau diamagnetism and determines anomalous features of the metal-insulator transition kinetics.

The nitrate response of a lowland catchment and groundwater travel times

NASA Astrophysics Data System (ADS)

van der Velde, Ype; Rozemeijer, Joachim; de Rooij, Gerrit; van Geer, Frans

2010-05-01

Intensive agriculture in lowland catchments causes eutrophication of downstream waters. To determine effective measures to reduce the nutrient loads from upstream lowland catchments, we need to understand the origin of long-term and daily variations in surface water nutrient concentrations. Surface water concentrations are often linked to travel time distributions of water passing through the saturated and unsaturated soil of the contributing catchment. This distribution represents the contact time over which sorption, desorption and degradation takes place. However, travel time distributions are strongly influenced by processes like tube drain flow, overland flow and the dynamics of draining ditches and streams and therefore exhibit strong daily and seasonal variations. The study we will present is situated in the 6.6 km2 Hupsel brook catchment in The Netherlands. In this catchment nitrate and chloride concentrations have been intensively monitored for the past 26 years under steadily decreasing agricultural inputs. We described the complicated dynamics of subsurface water fluxes as streams, ditches and tube drains locally switch between active or passive depending on the ambient groundwater level by a groundwater model with high spatial and temporal resolutions. A transient particle tracking approach is used to derive a unique catchment-scale travel time distribution for each day during the 26 year model period. These transient travel time distributions are not smooth distributions, but distributions that are strongly spiked reflecting the contribution of past rainfall events to the current discharge. We will show that a catchment-scale mass response function approach that only describes catchment-scale mixing and degradation suffices to accurately reproduce observed chloride and nitrate surface water concentrations as long as the mass response functions include the dynamics of travel time distributions caused by the highly variable connectivity of the surface water network.

Morphology of a submerged insular shelves in the West Alboran Basin.

NASA Astrophysics Data System (ADS)

Lafosse, Manfred; Le Roy, Pascal; Gorini, Christian; Rabineau, Marina; d'Acremont, Elia; Rabaute, Alain

2017-04-01

The dynamic of the seafloor in the Western Mediterranean Sea reflects the variety of the natural processes shaping it. Each of the sub-surface features is the result of tectonic, sedimentary and oceanic processes and eustatic sea-level variations. This study is focused on the morphology of three flat bathymetric highs and on the continental shelf in the Alboran Sea that show a variety of detailed seabed features that we attribute to a combination of present-day Mediterranean water mass flows, Quaternary active folding and faulting, differential erosion linked to relative-sea-level variation and local hydrodynamic. Swath bathymetry and reflectivity data, 2D seismic lines of multiple resolutions (12 channels, SPARKER source, and TOPAS seismic lines) have been acquired during three successive cruises: the MARLBORO-1 (2011), the MARLBORO-2 (2012) and the SARAS (2012) surveys. Our study deciphers the seabed structure of the banks with morphometric measurements (slope gradient, plan curvature, and topographic index) and correlates these structures to the stratigraphy of surrounding shelf. We show that the competition between active folding of the Miocene units and the erosion linked to the late Quaternary lowstands is creates the topography of the banks. The elevations of the flat surfaces measured on the banks are close to -110m and -80m. They are interpreted as submerged depositional surfaces linked to glacial and post-glacial deposit and wave-ravinement erosional surfaces as observed in other Mediterranean continental shelves. The analysis of the altitudinal spacing of these marine terraces indicates a spatial pattern with varying uplift rates. Furthermore, the characterization of sub-aqueous dune patterns locally linked to potential cold carbonate seamount could reflect the influence of water-masses current on the stratigraphic organization.

Synchrotron based mass spectrometry to investigate the molecular properties of mineral-organic associations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Suet Yi; Kleber, Markus; Takahashi, Lynelle K.

2013-04-01

Soil organic matter (OM) is important because its decay drives life processes in the biosphere. Analysis of organic compounds in geological systems is difficult because of their intimate association with mineral surfaces. To date there is no procedure capable of quantitatively separating organic from mineral phases without creating artifacts or mass loss. Therefore, analytical techniques that can (a) generate information about both organic and mineral phases simultaneously and (b) allow the examination of predetermined high-interest regions of the sample as opposed to conventional bulk analytical techniques are valuable. Laser Desorption Synchrotron Postionization (synchrotron-LDPI) mass spectrometry is introduced as a novelmore » analytical tool to characterize the molecular properties of organic compounds in mineral-organic samples from terrestrial systems, and it is demonstrated that when combined with Secondary Ion Mass Spectrometry (SIMS), can provide complementary information on mineral composition. Mass spectrometry along a decomposition gradient in density fractions, verifies the consistency of our results with bulk analytical techniques. We further demonstrate that by changing laser and photoionization energies, variations in molecular stability of organic compounds associated with mineral surfaces can be determined. The combination of synchrotron-LDPI and SIMS shows that the energetic conditions involved in desorption and ionization of organic matter may be a greater determinant of mass spectral signatures than the inherent molecular structure of the organic compounds investigated. The latter has implications for molecular models of natural organic matter that are based on mass spectrometric information.« less

On the Utilization of Ice Flow Models and Uncertainty Quantification to Interpret the Impact of Surface Radiation Budget Errors on Estimates of Greenland Ice Sheet Surface Mass Balance and Regional Estimates of Mass Balance

NASA Astrophysics Data System (ADS)

Schlegel, N.; Larour, E. Y.; Gardner, A. S.; Lang, C.; Miller, C. E.; van den Broeke, M. R.

2016-12-01

How Greenland ice flow may respond to future increases in surface runoff and to increases in the frequency of extreme melt events is unclear, as it requires detailed comprehension of Greenland surface climate and the ice sheet's sensitivity to associated uncertainties. With established uncertainty quantification tools run within the framework of Ice Sheet System Model (ISSM), we conduct decadal-scale forward modeling experiments to 1) quantify the spatial resolution needed to effectively force distinct components of the surface radiation budget, and subsequently surface mass balance (SMB), in various regions of the ice sheet and 2) determine the dynamic response of Greenland ice flow to variations in components of the net radiation budget. The Glacier Energy and Mass Balance (GEMB) software is a column surface model (1-D) that has recently been embedded as a module within ISSM. Using the ISSM-GEMB framework, we perform sensitivity analyses to determine how perturbations in various components of the surface radiation budget affect model output; these model experiments allow us predict where and on what spatial scale the ice sheet is likely to dynamically respond to changes in these parameters. Preliminary results suggest that SMB should be forced at at least a resolution of 23 km to properly capture dynamic ice response. In addition, Monte-Carlo style sampling analyses reveals that the areas with the largest uncertainty in mass flux are located near the equilibrium line altitude (ELA), upstream of major outlet glaciers in the North and West of the ice sheet. Sensitivity analysis indicates that these areas are also the most vulnerable on the ice sheet to persistent, far-field shifts in SMB, suggesting that continued warming, and upstream shift in the ELA, are likely to result in increased velocities, and consequentially SMB-induced thinning upstream of major outlet glaciers. Here, we extend our investigation to consider various components of the surface radiation budget separately, in order to determine how and where errors in these fields may independently impact ice flow. This work was performed at the California Institute of Technology's Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration's Cryosphere and Interdisciplinary Research in Earth Science Programs.

Herbicide micropollutants in surface, ground and drinking waters within and near the area of Zagreb, Croatia.

PubMed

Fingler, Sanja; Mendaš, G; Dvoršćak, M; Stipičević, S; Vasilić, Ž; Drevenkar, V

2017-04-01

The frequency and mass concentrations of 13 herbicide micropollutants (triazines, phenylureas, chloroacetanilides and trifluralin) were investigated during 2014 in surface, ground and drinking waters in the area of the city of Zagreb and its suburbs. Herbicide compounds were accumulated from water by solid-phase extraction using either octadecylsilica or styrene-divinylbenzene sorbent cartridges and analysed either by high-performance liquid chromatography with UV-diode array detector or gas chromatography with mass spectrometric detection. Atrazine was the most frequently detected herbicide in drinking (84 % of samples) and ground (61 % of samples) waters in mass concentrations of 5 to 68 ng L -1 . It was followed by metolachlor and terbuthylazine, the former being detected in 54 % of drinking (up to 15 ng L -1 ) and 23 % of ground (up to 100 ng L -1 ) waters, and the latter in 45 % of drinking (up to 20 ng L -1 ) and 26 % of ground (up to 25 ng L -1 ) water samples. Acetochlor was the fourth most abundant herbicide in drinking waters, detected in 32 % of samples. Its mass concentrations of 107 to 117 ng L -1 in three tap water samples were the highest of all herbicides measured in the drinking waters. The most frequently (62 % of samples) and highly (up to 887 ng L -1 ) detected herbicide in surface waters was metolachlor, followed by terbuthylazine detected in 49 % of samples in mass concentrations of up to 690 ng L -1 , and atrazine detected in 30 % of samples in mass concentrations of up to 18 ng L -1 . The seasonal variations in herbicide concentrations in surface waters were observed for terbuthylazine, metolachlor, acetochlor, chlortoluron and isoproturon with the highest concentrations measured from April to August.

First Spectroscopic Detection of Surface Structures on a Normal A-Type Star - The Case of Vega

NASA Astrophysics Data System (ADS)

Böhm, Torsten

2018-04-01

For the first time the existence of spots on the surface of the intermediate mass star Vega has been shown. This unexpected result sets new important constraints on the stellar evolution of intermediate mass stars and in particular on the magnetic field generation mechanisms. Vega (α Lyrae) is an intermediate mass star (spectral class A0) in rapid rotation (Prot = 0.68 d). Since more than 150 years it is a stability reference for photometry. Despite the fact that very small sporadic light variations had been announced in the past, no periodicity had been detected in its light curve. In 2009 a very faint magnetic field has been detected on Vega (Lignières et al., 2009, A&A, 500L, 41) and subsequently also on other stars of the same spectral class (A). While the solar magnetic field is generated by a dynamo mechanism in its convective envelope, the origin of magnetic field in stars exempt of convective envelopes, such as Vega, remains mysterious. One of the characteristics of the solar dynamo is its temporal variability revealed by the appearance or disappearance of solar spots. Are there similar structures on the surface of Vega? 2015 A&A, 577, 64. & Nature Research Highlights

Variation in Foot Strike Patterns among Habitually Barefoot and Shod Runners in Kenya.

PubMed

Lieberman, Daniel E; Castillo, Eric R; Otarola-Castillo, Erik; Sang, Meshack K; Sigei, Timothy K; Ojiambo, Robert; Okutoyi, Paul; Pitsiladis, Yannis

2015-01-01

Runners are often categorized as forefoot, midfoot or rearfoot strikers, but how much and why do individuals vary in foot strike patterns when running on level terrain? This study used general linear mixed-effects models to explore both intra- and inter-individual variations in foot strike pattern among 48 Kalenjin-speaking participants from Kenya who varied in age, sex, body mass, height, running history, and habitual use of footwear. High speed video was used to measure lower extremity kinematics at ground contact in the sagittal plane while participants ran down 13 meter-long tracks with three variables independently controlled: speed, track stiffness, and step frequency. 72% of the habitually barefoot and 32% of the habitually shod participants used multiple strike types, with significantly higher levels of foot strike variation among individuals who ran less frequently and who used lower step frequencies. There was no effect of sex, age, height or weight on foot strike angle, but individuals were more likely to midfoot or forefoot strike when they ran on a stiff surface, had a high preferred stride frequency, were habitually barefoot, and had more experience running. It is hypothesized that strike type variation during running, including a more frequent use of forefoot and midfoot strikes, used to be greater before the introduction of cushioned shoes and paved surfaces.

Preliminary design of a large tetrahedral truss/hexagonal heatshield panel aerobrake

NASA Technical Reports Server (NTRS)

Dorsey, John T.; Mikulas, Martin M., Jr.

1989-01-01

An aerobrake structural concept is introduced which consists of two primary components: (1) a lightweight erectable tetrahedral support truss; and (2) sandwich hexagonal heatshield panels which, when attached to the truss, form a continuous impermeable aerobraking surface. Generic finite element models and a general analysis procedure to design tetrahedral truss/hexagonal heatshield panel aerobrakes is developed, and values of the aerobrake design parameters which minimize mass and packaging volume for a 120-foot-diameter aerobrake are determined. Sensitivity of the aerobrake design to variations in design parameters is also assessed. The results show that a 120-foot-diameter aerobrake is viable using the concept presented (i.e., the aerobrake mass is less than or equal to 15 percent of the payload spacecraft mass). Minimizing the aerobrake mass (by increasing the number of rings in the support truss) however, leads to aerobrakes with the highest part count.

Comparison of Grab, Air, and Surface Results for Radiation Site Characterization

NASA Astrophysics Data System (ADS)

Glassford, Eric Keith

2011-12-01

The use of proper sampling methods and sample types for evaluating sites believed to be contaminated with radioactive materials is necessary to avoid misrepresenting conditions at the site. This study was designed to investigate if the site characterization, based upon uranium contamination measured in different types of samples, is dependent upon the mass of the sample collected. A bulk sample of potentially contaminated interior dirt was collected from an abandoned metal processing mill that rolled uranium between 1948 and 1956. The original mill dates from 1910 and has a dirt floor. The bulk sample was a mixture of dirt, black and yellow particles of metal dust, and small fragments of natural debris. Small mass (approximately 0.75 grams (g)) and large mass (approximately 70g) grab samples were prepared from the bulk sample material to simulate collection of a "grab" type sample. Air sampling was performed by re-suspending a portion of the bulk sample material using a vibration table to simulate airborne contamination that might be present during site remediation. Additionally, samples of removable contaminated surface dust were collected on 47 mm diameter filter paper by wiping the surfaces of the exposure chamber used to resuspend the bulk material. Certified reference materials, one containing a precisely known quantity of U 3O8 and one containing a known quantity of natural uranium, were utilized to calibrate the gamma spectrometry measurement system. Non-destructive gamma spectrometry measurements were used to determine the content of uranium-235 (235U) at 185 keV and 143 keV, thorium-234 (234Th) at 63 keV, and protactinium-234m (234mPa) at 1001 keV in each sample. Measurement of natural uranium in small, 1 g samples is usually accomplished by radiochemical analysis in order to measure alpha particles emitted by 238U, 235U, and 234U. However, uranium in larger bulk samples can also be measured non-destructively using gamma spectrometry to detect the low energy photons from 234Th and 234mPa, the short-lived decay products of 238U, and 235U. Two sided t-tests and coefficient of variation were used to compare sampling types. The large grab samples had the lowest calculated coefficient of variation results for activity and atom percentage. The wipe samples had the highest calculated coefficient of variation of mean specific activity (dis/sec/g) for all three energies. The air filter samples had the highest coefficient of variation calculation for mean atom percentage, for both uranium isotopes examined. The data indicated that the large mass sample was the most effective at characterizing the rolling mill radioactive site conditions, since this would indicate which samples had the smallest variations compared to the mean. Additionally, measurement results of natural uranium in the samples indicate that the distribution of radioactive contamination at the sampling location is most likely non-homogeneous and that the size of the sample collected and analyzed must be sufficiently large to insure that the analytical results are truly representative of the activity present.

Correlation of process parameters and properties of TiO2 films grown by ion beam sputter deposition from a ceramic target

NASA Astrophysics Data System (ADS)

Bundesmann, Carsten; Lautenschläge, Thomas; Spemann, Daniel; Finzel, Annemarie; Mensing, Michael; Frost, Frank

2017-10-01

The correlation between process parameters and properties of TiO2 films grown by ion beam sputter deposition from a ceramic target was investigated. TiO2 films were grown under systematic variation of ion beam parameters (ion species, ion energy) and geometrical parameters (ion incidence angle, polar emission angle) and characterized with respect to film thickness, growth rate, structural properties, surface topography, composition, optical properties, and mass density. Systematic variations of film properties with the scattering geometry, namely the scattering angle, have been revealed. There are also considerable differences in film properties when changing the process gas from Ar to Xe. Similar systematics were reported for TiO2 films grown by reactive ion beam sputter deposition from a metal target [C. Bundesmann et al., Appl. Surf. Sci. 421, 331 (2017)]. However, there are some deviations from the previously reported data, for instance, in growth rate, mass density and optical properties.

Vertical self-sorting behavior in juvenile Chinook salmon (Oncorhynchus tshawytscha): evidence for family differences and variation in growth and morphology

USGS Publications Warehouse

Unrein, Julia R.; Billman, E.J.; Cogliati, Karen M.; Chitwood, Rob S.; Noakes, David L. G.; Schreck, Carl B.

2018-01-01

Life history variation is fundamental to the evolution of Pacific salmon and their persistence under variable conditions. We discovered that Chinook salmon sort themselves into surface- and bottom-oriented groups in tanks within days after exogenous feeding. We hypothesised that this behaviour is correlated with subsequent differences in body morphology and growth (as measured by final length and mass) observed later in life. We found consistent morphological differences between surface and bottom phenotypes. Furthermore, we found that surface and bottom orientation within each group is maintained for at least one year after the phenotypes were separated. These surface and bottom phenotypes are expressed across genetic stocks, brood years, and laboratories and we show that the proportion of surface- and bottom-oriented offspring also differed among families. Importantly, feed delivery location did not affect morphology or growth, and the surface fish were longer than bottom fish at the end of the rearing experiment. The body shape of the former correlates with wild individuals that rear in mainstem habitats and migrate in the fall as subyearlings and the latter resemble those that remain in the upper tributaries and migrate as yearling spring migrants. Our findings suggest that early self-sorting behaviour may have a genetic basis and be correlated with other phenotypic traits that are important indicators for juvenile migration timing.

Effect of pressure on the sorption correction to stainless steel, platinum/iridium and silicon mass artefacts

NASA Astrophysics Data System (ADS)

Berry, James; Davidson, Stuart

2014-04-01

This paper reports work undertaken to evaluate the change in mass of platinum/iridium, stainless steel and silicon artefacts measured at atmospheric pressure and in vacuum at a range of pressures typical of those used in vacuum mass comparators and watt balances and for x-ray crystal density (XRCD) measurements. The sets of platinum/iridium, stainless steel and silicon artefacts used in this work have different surface areas and the effect of transferring them between atmospheric pressure and different levels of vacuum was evaluated by measuring the relative changes in mass between them. Reversible variations in the mass differences between the artefacts were found over the pressure range from 0.1 Pa to 100 000 Pa (atmospheric pressure). At lower pressures (0.001 Pa to 0.1 Pa) the mass differences between all the artefacts were stable and no evidence for hysteresis over this range was found when going down in pressure compared with increasing pressure. Therefore consistent results between watt balance, XRCD measurements and vacuum mass measurements can be realized providing the measurements are performed within this pressure range.

Geometric Variational Methods for Controlled Active Vision

DTIC Science & Technology

2006-08-01

Haker , L. Zhu, and A. Tannenbaum, ``Optimal mass transport for registration and warping’’ Int. Journal Computer Vision, volume 60, 2004, pp. 225-240. G...pp. 119-142. A. Angenent, S. Haker , and A. Tannenbaum, ``Minimizing flows for the Monge-Kantorovich problem,’’ SIAM J. Math. Analysis, volume 35...Shape analysis of structures using spherical wavelets’’ (with S. Haker and D. Nain), Proceeedings of MICCAI, 2005. ``Affine surface evolution for 3D

Asymmetry dependence of the caloric curve for mononuclei

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoel, C.; Sobotka, L. G.; Charity, R. J.

2007-01-15

The asymmetry dependence of the caloric curve, for mononuclear configurations, is studied as a function of neutron-to-proton asymmetry with a model that allows for independent variation of the neutron and proton surface diffusenesses. The evolution of the effective mass with density and excitation is included in a schematic fashion and the entropies are extracted in a local density approximation. The plateau in the caloric curve displays only a slight sensitivity to the asymmetry.

Time Series of Greenland Ice-Sheet Elevations and Mass Changes from ICESat 2003-2009

NASA Astrophysics Data System (ADS)

Zwally, H. J.; Li, J.; Medley, B.; Robbins, J. W.; Yi, D.

2015-12-01

We follow the repeat-track analysis (RTA) of ICESat surface-elevation data by a second stage that adjusts the measured elevations on repeat passes to the reference track taking into account the cross-track slope (αc), in order to construct elevation time series. αc are obtained from RTA simultaneous solutions for αc, dh/dt, and h0. The height measurements on repeat tracks are initially interpolated to uniform along-track reference points (every 172 m) and times (ti) giving the h(xi,ti) used in the RTA solutions. The xi are the cross-track spacings from the reference track and i is the laser campaign index. The adjusted elevation measurements at the along-track reference points are hr(ti) = h(xi,ti) - xi tan(αc) - h0. The hr(ti) time series are averaged over 50 km cells creating H(ti) series and further averaged (weighted by cell area) to H(t) time series over drainage systems (DS), elevation bands, regions, and the entire ice sheet. Temperature-driven changes in the rate of firn compaction, CT(t), are calculated for 50 km cells with our firn-compaction model giving I(t) = H(t) - CT(t) - B(t) where B(t) is the vertical motion of the bedrock. During 2003 to 2009, the average dCT(t)/dt in the accumulation zone is -5 cm/yr, which amounts to a -75 km3/yr correction to ice volume change estimates. The I(t) are especially useful for studying the seasonal cycle of mass gains and losses and interannual variations. The H(t) for the ablation zone are fitted with a multi-variate function with a linear component describing the upward component of ice flow plus winter accumulation (fall through spring) and a portion of a sine function describing the superimposed summer melting. During fall to spring the H(t) indicate that the upward motion of the ice flow is at a rate of 1 m/yr, giving an annual mass gain of 180 Gt/yr in the ablation zone. The summer loss from surface melting in the high-melt summer of 2005 is 350 Gt/yr, giving a net surface loss of 170 Gt/yr from the ablation zone for 2005. During 2003-2008, the H(t) for the ablation zone show accelerations of the mass losses in the northwest DS8 and in the west-central DS7 (including Jacobshavn glacier) and offsetting decelerations of the mass losses in the east-central DS3 and southeast DS4, much of which occurred in 2008 possibly due to an eastward shift in the surface mass balance.

Sequential cryogen spraying for heat flux control at the skin surface

NASA Astrophysics Data System (ADS)

Majaron, Boris; Aguilar, Guillermo; Basinger, Brooke; Randeberg, Lise L.; Svaasand, Lars O.; Lavernia, Enrique J.; Nelson, J. Stuart

2001-05-01

Heat transfer rate at the skin-air interface is of critical importance for the benefits of cryogen spray cooling in combination with laser therapy of shallow subsurface skin lesions, such as port-wine stain birthmarks. With some cryogen spray devices, a layer of liquid cryogen builds up on the skin surface during the spurt, which may impair heat transfer across the skin surface due to relatively low thermal conductivity and potentially higher temperature of the liquid cryogen layer as compared to the spray droplets. While the mass flux of cryogen delivery can be adjusted by varying the atomizing nozzle geometry, this may strongly affect other spray properties, such as lateral spread (cone), droplet size, velocity, and temperature distribution. We present here first experiments with sequential cryogen spraying, which may enable accurate mass flux control through variation of spray duty cycle, while minimally affecting other spray characteristics. The observed increase of cooling rate and efficiency at moderate duty cycle levels supports the above described hypothesis of isolating liquid layer, and demonstrates a novel approach to optimization of cryogen spray devices for individual laser dermatological applications.

Millennial-Scale Variability in the Indian Monsoon and Links to Ocean Circulation

NASA Astrophysics Data System (ADS)

DeLong, K. A.; Came, R. E.; Johnson, J. E.; Giosan, L.

2014-12-01

Millennial-scale variability in the Indian monsoon was temporally linked to changes in global ocean circulation during the last glacial period, as evidenced by planktic-benthic foraminiferal stable isotope and trace element results from an intermediate depth sediment core from the northwestern Bay of Bengal. Paired planktic foraminiferal Mg/Ca and δ18Oc constrain sea surface temperatures and isolate millennial-scale variations in the δ18O of surface waters (δ18Osw), which resulted from changes in river runoff in the northwestern Bay. Concurrently with low δ18Osw events, benthic foraminiferal δ13C decreased, suggesting an increased influence of an aged water mass at this intermediate depth site during the low salinity events. Benthic foraminiferal Cd/Ca results support the identification of this water mass as aged Glacial Antarctic Intermediate Water (GAAIW). Lagged correlation analysis (r= 0.41) indicates that changes in subsurface properties led changes in surface properties by an average of 380 years. The implication is that Southern Hemisphere climate exerted a controlling influence on the Indian monsoon during the last glacial period.

Seasonal variations of carbonate system parameters and nutrients at the shellfish-farming bays along the south coast of Korea

NASA Astrophysics Data System (ADS)

Shim, JeongHee; Shim, Jeong-Min; Lee, Yong-Hwa

2017-04-01

About 80 90% of the annual mass production of shellfish in Korea are cultured at the inner bays including Jinhae, Tongyeong and Geoje regions, along the south coast of Korea. To understand coastal carbon and nutrients cycles and those effects/feedbacks on shellfish farming, carbonate (DIC, TA and pH) and environmental parameters were observed at Jinhae, Tongyeong and Geoje Bays 4 times (in Feb., Aug. 2014, Apr. and Oct. 2015 and are considered representative of winter, summer, spring and fall respectively). Surface temperature in the bays showed clear seasonal variation with about 6 12°C and 24 29°C in Feb. and Aug. 2014, respectively and 14 18°C and 22 26°C in Apr. and in Oct. 2015, respectively. Surface pHNBS also ranged with about 8.20 8.53 and 7.28 8.95 in Feb. and Aug. 2014, and 8.04 8.40 and 7.91 8.32 in Apr. and in Oct. 2015. High pH with low salinity in summer resulted from input of land discharge in rainy seasons, however high pH at small bays in Apr. and Oct. 2015 resulted from massive primary production by phytoplankton bloom, supported by high chlorophyll a concentrations. Seasonal variations of DIC and phosphate in the surface and bottom waters correlated largely with salinity, higher in winter and lower in summer. Specifically in shellfish (specially, oyster and mussel) growing season, aragonite saturation state (Ωarag) in bottom water ranged about 0.2 2.9 (mean 2.1) and 2.2 5.0 (mean 3.2) in Feb. 2014 and Oct. 2015, respectively, suggesting low pH environments arose seasonally in coastal area due to some mechanisms. These results suggest that seasonal ocean acidification state might seriously affect shell growth, mass production and thus shellfish industry along the south coast of Korea.

Evolution of X-ray activity of 1-3 Msun late-type stars in early post-main-sequence phases

NASA Astrophysics Data System (ADS)

Pizzolato, N.; Maggio, A.; Sciortino, S.

2000-09-01

We have investigated the variation of coronal X-ray emission during early post-main-sequence phases for a sample of 120 late-type stars within 100 pc, and with estimated masses in the range 1-3 Msun, based on Hipparcos parallaxes and recent evolutionary models. These stars were observed with the ROSAT/PSPC, and the data processed with the Palermo-CfA pipeline, including detection and evaluation of X-ray fluxes (or upper limits) by means of a wavelet transform algorithm. We have studied the evolutionary history of X-ray luminosity and surface flux for stars in selected mass ranges, including stars with inactive A-type progenitors on the main sequence and lower mass solar-type stars. Our stellar sample suggests a trend of increasing X-ray emission level with age for stars with masses M > 1.5 Msun, and a decline for lower-mass stars. A similar behavior holds for the average coronal temperature, which follows a power-law correlation with the X-ray luminosity, independently of their mass and evolutionary state. We have also studied the relationship between X-ray luminosity and surface rotation rate for stars in the same mass ranges, and how this relationships departs from the Lx ~ vrot2 law followed by main-sequence stars. Our results are interpreted in terms of a magnetic dynamo whose efficiency depends on the stellar evolutionary state through the mass-dependent changes of the stellar internal structure, including the properties of envelope convection and the internal rotation profile.

Direct observation of feedout-related areal mass oscillations in planar plastic targets.

NASA Astrophysics Data System (ADS)

Aglitskiy, Y.; Metzler, N.; Velikovich, A. L.; Karasik, M.; Serlin, V.; Pawley, C.; Mostovych, A. N.; Schmitt, A. J.; Obenschain, S. P.; Gardner, J. H.

2001-10-01

"Feedout" means the transfer of mass perturbations from the rear to the front surface of a driven target. The oscillations are expected if the perturbation wavelength λ is not large compared to 2π L_s, where Ls is the shock-compressed target thickness. We report the first direct experimental observation of areal mass oscillation associated with feedout, followed by the onset of exponential RT growth. Our experiments were performed with the Nike KrF laser at irradiation 50 TW/cm^2. The mass redistribution in the target was observed with the aid of monochromatic x-ray imaging coupled to a streak camera. We used 40 to 60 μm thick CH targets rippled on the rear side with wavelengths of either 30 or 45 μm, the ratio 2π L_s/λ thus being close to 2. Two phase reversals of mass variation predicted by the theory and simulations were consistently observed both on the original images and on the time histories of Fourier amplitudes.

Direct Numerical Simulation of Fluid Flow and Mass Transfer in Particle Clusters

PubMed Central

2018-01-01

In this paper, an efficient ghost-cell based immersed boundary method is applied to perform direct numerical simulation (DNS) of mass transfer problems in particle clusters. To be specific, a nine-sphere cuboid cluster and a random-generated spherical cluster consisting of 100 spheres are studied. In both cases, the cluster is composed of active catalysts and inert particles, and the mutual influence of particles on their mass transfer performance is studied. To simulate active catalysts the Dirichlet boundary condition is imposed at the external surface of spheres, while the zero-flux Neumann boundary condition is applied for inert particles. Through our studies, clustering is found to have negative influence on the mass transfer performance, which can be then improved by dilution with inert particles and higher Reynolds numbers. The distribution of active/inert particles may lead to large variations of the cluster mass transfer performance, and individual particle deep inside the cluster may possess a high Sherwood number. PMID:29657359

Early evolution of the Earth: Accretion, atmosphere formation, and thermal history

NASA Astrophysics Data System (ADS)

Abe, Yutaka; Matsui, Takafumi

1986-03-01

Atmospheric and thermal evolution of the earth growing by planetesimal impacts was modeled by taking into account the blanketing effect of an impact-induced H2O atmosphere and the temperature dependence of H2O degassing. When the water content of planetesimals is larger than 0.1% by weight and the accretion time of the earth is less than 5 × 107 years, the surface of the accreting earth melts and thus a “magma ocean” forms and covers the surface. The formation of a “magma ocean” will result in the initiation of core-mantle separation and mantle differentiation during accretion. Once a magma ocean is formed, the surface temperature, the degree of melting in the magma ocean, and the mass of the H2O atmosphere are nearly constant as the protoplanet grows further. The final mass of the H2O atmosphere is about 1021 kg, a value which is insensitive to variations in the model parameter values such as the accretion time and the water content of planetesimals. That the final mass of the H2O atmosphere is close to the mass of the present oceans suggests an impact origin for the earth's hydrosphere. On the other hand, most of the H2O retained in planetesimals will be deposited in the solid earth. Free water within the proto-earth may affect differentiation of the proto-mantle, in particular, the mantle FeO abundance and the incorporation of a light element in the outer core.

The airborne infrared scanner as a geophysical research tool

USGS Publications Warehouse

Friedman, Jules D.

1970-01-01

The infrared scanner is proving to be an effective anomaly-mapping tool, albeit one which depicts surface emission directly and heat mass transfer from depths only indirectly and at a threshold level 50 to 100 times the normal conductive heat flow of the earth. Moreover, successive terrain observations are affected by time-dependent variables such as the diurnal and seasonal warming and cooling cycle of a point on the earth's surface. In planning precise air borne surveys of radiant flux from the earth's surface, account must be taken of background noise created by variations in micrometeorological factors and emissivity of surface materials, as well as the diurnal temperature cycle. The effect of the diurnal cycle may be minimized by planning predawn aerial surveys. In fact, the diurnal change is very small for most water bodies and the emissivity factor for water (e) =~ 1 so a minimum background noise is characteristic of scanner records of calm water surfaces.

Stellar mass and age determinations . I. Grids of stellar models from Z = 0.006 to 0.04 and M = 0.5 to 3.5 M⊙

NASA Astrophysics Data System (ADS)

Mowlavi, N.; Eggenberger, P.; Meynet, G.; Ekström, S.; Georgy, C.; Maeder, A.; Charbonnel, C.; Eyer, L.

2012-05-01

Aims: We present dense grids of stellar models suitable for comparison with observable quantities measured with great precision, such as those derived from binary systems or planet-hosting stars. Methods: We computed new Geneva models without rotation at metallicities Z = 0.006, 0.01, 0.014, 0.02, 0.03, and 0.04 (i.e. [Fe/H] from -0.33 to +0.54) and with mass in small steps from 0.5 to 3.5 M⊙. Great care was taken in the procedure for interpolating between tracks in order to compute isochrones. Results: Several properties of our grids are presented as a function of stellar mass and metallicity. Those include surface properties in the Hertzsprung-Russell diagram, internal properties including mean stellar density, sizes of the convective cores, and global asteroseismic properties. Conclusions: We checked our interpolation procedure and compared interpolated tracks with computed tracks. The deviations are less than 1% in radius and effective temperatures for most of the cases considered. We also checked that the present isochrones provide nice fits to four couples of observed detached binaries and to the observed sequences of the open clusters NGC 3532 and M 67. Including atomic diffusion in our models with M < 1.1 M⊙ leads to variations in the surface abundances that should be taken into account when comparing with observational data of stars with measured metallicities. For that purpose, iso-Zsurf lines are computed. These can be requested for download from a dedicated web page, together with tracks at masses and metallicities within the limits covered by the grids. The validity of the relations linking Z and [Fe/H] is also re-assessed in light of the surface abundance variations in low-mass stars. Table D.1 for the basic tracks is available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/541/A41, and on our web site http://obswww.unige.ch/Recherche/evol/-Database-. Tables for interpolated tracks, iso-Zsurf lines and isochrones can be computed, on demand, from our web site.Appendices are available in electronic form at http://www.aanda.org

Life-history and ecological correlates of geographic variation in egg and clutch mass among passerine species

USGS Publications Warehouse

Martin, T.E.; Bassar, R.D.; Bassar, S.K.; Fontaine, J.J.; Lloyd, P.; Mathewson, Heather A.; Niklison, Alina M.; Chalfoun, A.

2006-01-01

Broad geographic patterns in egg and clutch mass are poorly described, and potential causes of variation remain largely unexamined. We describe interspecific variation in avian egg and clutch mass within and among diverse geographic regions and explore hypotheses related to allometry, clutch size, nest predation, adult mortality, and parental care as correlates and possible explanations of variation. We studied 74 species of Passeriformes at four latitudes on three continents: the north temperate United States, tropical Venezuela, subtropical Argentina, and south temperate South Africa. Egg and clutch mass increased with adult body mass in all locations, but differed among locations for the same body mass, demonstrating that egg and clutch mass have evolved to some extent independent of body mass among regions. A major portion of egg mass variation was explained by an inverse relationship with clutch size within and among regions, as predicted by life-history theory. However, clutch size did not explain all geographic differences in egg mass; eggs were smallest in South Africa despite small clutch sizes. These small eggs might be explained by high nest predation rates in South Africa; life-history theory predicts reduced reproductive effort under high risk of offspring mortality. This prediction was supported for clutch mass, which was inversely related to nest predation but not for egg mass. Nevertheless, clutch mass variation was not fully explained by nest predation, possibly reflecting interacting effects of adult mortality. Tests of the possible effects of nest predation on egg mass were compromised by limited power and by counterposing direct and indirect effects. Finally, components of parental investment, defined as effort per offspring, might be expected to positively coevolve. Indeed, egg mass, but not clutch mass, was greater in species that shared incubation by males and females compared with species in which only females incubate eggs. However, egg and clutch mass were not related to effort of parental care as measured by incubation attentiveness. Ecological and life-history correlates of egg and clutch mass variation found here follow from theory, but possible evolutionary causes deserve further study. ?? 2006 The Society for the Study of Evolution. All rights reserved.

Modes of Arctic Ocean Change from GRACE, ICESat and the PIOMAS and ECCO2 Models of the Arctic Ocean

NASA Astrophysics Data System (ADS)

Peralta Ferriz, C.; Morison, J. H.; Bonin, J. A.; Chambers, D. P.; Kwok, R.; Zhang, J.

2012-12-01

EOF analysis of month-to-month variations in GRACE derived Arctic Ocean bottom pressure (OBP) with trend and seasonal variation removed yield three dominant modes. The first mode is a basin wide variation in mass associated with high atmospheric pressure (SLP) over Scandinavia mainly in winter. The second mode is a shift of mass from the central Arctic Ocean to the Siberian shelves due to low pressure over the basins, associated with the Arctic Oscillation. The third mode is a shift in mass between the Eastern and Western Siberian shelves, related to strength of the Beaufort High mainly in summer, and to eastward alongshore winds on the Barents Sea in winter. The PIOMAS and ECCO2 modeled OBP show fair agreement with the form of these modes and provide context in terms of variations in sea surface height SSH. Comparing GRACE OBP from 2007 to 2011 with GRACE OBP from 2002 to 2006 reveals a rising trend over most of the Arctic Ocean but declines in the Kara Sea region and summer East Siberian Sea. ECCO2 bears a faint resemblance to the observed OBP change but appears to be biased negatively. In contrast, PIOMAS SSH and ECCO2 especially, show changes between the two periods that are muted but similar to ICESat dynamic ocean topography and GRACE-ICESat freshwater trends from 2005 through 2008 [Morison et al., 2012] with a rising DOT and freshening in the Beaufort Sea and a trough with decreased freshwater on the Russian side of the Arctic Ocean. Morison, J., R. Kwok, C. Peralta-Ferriz, M. Alkire, I. Rigor, R. Andersen, and M. Steele (2012), Changing Arctic Ocean freshwater pathways, Nature, 481(7379), 66-70.

The relationship among sea surface roughness variations, oceanographic analyses, and airborne remote sensing analyses

NASA Technical Reports Server (NTRS)

Oertel, G. F.; Wade, T. L.

1981-01-01

The synthetic aperture radar (SAR) was studied to determine whether it could image large scale estuaries and oceanic features such as fronts and to explain the electromagnetic interaction between SAR and the individual surface front features. Fronts were observed to occur at the entrance to the Chesapeake Bay. The airborne measurements consisted of data collection by SAR onboard an F-4 aircraft and real aperture side looking radar (SLAR) in Mohawk aircraft. A total of 89 transects were flown. Surface roughness and color as well as temperature and salinity were evaluated. Cross-frontal surveys were made. Frontal shear and convergence flow were obtained. Surface active organic materials, it was indicated, are present at the air-sea interface. In all, 2000 analyses were conducted to characterize the spatial and temporal variabilities associated with water mass boundaries.

Effects of food supplementation on the physiological ecology of female Western diamond-backed rattlesnakes (Crotalus atrox).

PubMed

Taylor, Emily N; Malawy, Michael A; Browning, Dawn M; Lemar, Shea V; DeNardo, Dale F

2005-06-01

Food availability is an important factor in the life histories of organisms because it is often limiting and thus can affect growth, mass change, reproduction, and behaviors such as thermoregulation, locomotion, and mating. Experimental studies in natural settings allow researchers to examine the effects of food on these parameters while animals are free to behave naturally. The wide variation among organisms in energy demands and among environmental food resources suggest that responses to changes in food availability may vary among organisms. Since most supplemental feeding field experiments have been conducted on species with high energy demands, we conducted a supplemental feeding study on free-ranging, female Western diamond-backed rattlesnakes (Crotalus atrox), a species with low energy demands and infrequent reproductive investment. Snakes were offered thawed rodents 1-4 times per week. Over two active seasons, we collected data on surface activity, home range size, growth, mass change, and reproduction of supplementally fed and control snakes. Fed and control snakes did not differ in surface activity levels (proportion of time encountered above versus below ground) or home range size. Fed snakes grew and gained mass faster, and had a dramatically higher occurrence of reproduction than control snakes. Also, fed snakes were in better body condition following reproduction than snakes that were not fed. However, litter characteristics such as offspring number and size were not increased by feeding, suggesting that these characteristics may be fixed. These data experimentally demonstrate that food availability can directly impact some life history traits (i.e., growth and reproduction for C. atrox), but not others (i.e., surface activity and home range size for C. atrox). The relationship between food availability and life history traits is affected in a complex way by ecological traits and physiological constraints, and thus interspecific variation in this relationship is likely to be high.

Area-variable capacitive microaccelerometer with force-balancing electrodes

NASA Astrophysics Data System (ADS)

Ha, Byeoungju; Lee, Byeungleul; Sung, Sangkyung; Choi, Sangon; Shinn, Meenam; Oh, Yong-Soo; Song, Ci M.

1997-11-01

A surface micromachined accelerometer which senses an inertial motion with an area variation and a force balancing electrodes is developed. The grid-type planar mass of a 7 micrometers thick polysilicon is supported by four thin beams and suspended above a silicon substrate with a 1.5 micrometers air gap. The motion sensing electrodes are formed on the substrate. The sensor is designed as an interdigital rib structure that has a differential capacitor arrangement. The moveable electrodes are mounted on the mass and the pairs of the stationary electrodes are patterned on the substrate. In the accelerometer that has comb-type movable electrodes, the mechanical stress and the electrical pulling effects between a moveable electrodes and the fixed electrodes occur. However this grid-type structure can have a large area variation in a small area relatively without stress and pulling, high sensitivity can be achieved. In order to improve the dynamic rang and a linearity, a pair of comb shape force-balancing electrodes are implemented on both sides of the mass. The force-balancing electrodes are made of the same layer as the mass and anchored on a silicon substrate. When acceleration is applied in the lateral direction, the difference of capacitance results from the area variation between the two capacitors and is measured using a charge amplifier. As AC coupled complimentary pick- off signals are applied in paris of stationary electrodes, the undesirable effects due to temperature and electrical noise are reduced effectively. The accelerometer has a sensitivity of 28mV/g and a bandwidth of DC-120Hz. A resolution of 3mg and a non-linearity of 1.3 percent is achieved for a measurement range of +/- 9 g.

Mercury (Hg) in meteorites: Variations in abundance, thermal release profile, mass-dependent and mass-independent isotopic fractionation

NASA Astrophysics Data System (ADS)

Meier, Matthias M. M.; Cloquet, Christophe; Marty, Bernard

2016-06-01

We have measured the concentration, isotopic composition and thermal release profiles of Mercury (Hg) in a suite of meteorites, including both chondrites and achondrites. We find large variations in Hg concentration between different meteorites (ca. 10 ppb to 14,000 ppb), with the highest concentration orders of magnitude above the expected bulk solar system silicates value. From the presence of several different Hg carrier phases in thermal release profiles (150-650 °C), we argue that these variations are unlikely to be mainly due to terrestrial contamination. The Hg abundance of meteorites shows no correlation with petrographic type, or mass-dependent fractionation of Hg isotopes. Most carbonaceous chondrites show mass-independent enrichments in the odd-numbered isotopes 199Hg and 201Hg. We show that the enrichments are not nucleosynthetic, as we do not find corresponding nucleosynthetic deficits of 196Hg. Instead, they can partially be explained by Hg evaporation and redeposition during heating of asteroids from primordial radionuclides and late-stage impact heating. Non-carbonaceous chondrites, most achondrites and the Earth do not show these enrichments in vapor-phase Hg. All meteorites studied here have however isotopically light Hg (δ202Hg = ∼-7 to -1) relative to the Earth's average crustal values, which could suggest that the Earth has lost a significant fraction of its primordial Hg. However, the late accretion of carbonaceous chondritic material on the order of ∼2%, which has been suggested to account for the water, carbon, nitrogen and noble gas inventories of the Earth, can also contribute most or all of the Earth's current Hg budget. In this case, the isotopically heavy Hg of the Earth's crust would have to be the result of isotopic fractionation between surface and deep-Earth reservoirs.

Modelling the feedbacks between mass balance, ice flow and debris transport to predict the response to climate change of debris-covered glaciers in the Himalaya

NASA Astrophysics Data System (ADS)

Rowan, Ann V.; Egholm, David L.; Quincey, Duncan J.; Glasser, Neil F.

2015-11-01

Many Himalayan glaciers are characterised in their lower reaches by a rock debris layer. This debris insulates the glacier surface from atmospheric warming and complicates the response to climate change compared to glaciers with clean-ice surfaces. Debris-covered glaciers can persist well below the altitude that would be sustainable for clean-ice glaciers, resulting in much longer timescales of mass loss and meltwater production. The properties and evolution of supraglacial debris present a considerable challenge to understanding future glacier change. Existing approaches to predicting variations in glacier volume and meltwater production rely on numerical models that represent the processes governing glaciers with clean-ice surfaces, and yield conflicting results. We developed a numerical model that couples the flow of ice and debris and includes important feedbacks between debris accumulation and glacier mass balance. To investigate the impact of debris transport on the response of a glacier to recent and future climate change, we applied this model to a large debris-covered Himalayan glacier-Khumbu Glacier in Nepal. Our results demonstrate that supraglacial debris prolongs the response of the glacier to warming and causes lowering of the glacier surface in situ, concealing the magnitude of mass loss when compared with estimates based on glacierised area. Since the Little Ice Age, Khumbu Glacier has lost 34% of its volume while its area has reduced by only 6%. We predict a decrease in glacier volume of 8-10% by AD2100, accompanied by dynamic and physical detachment of the debris-covered tongue from the active glacier within the next 150 yr. This detachment will accelerate rates of glacier decay, and similar changes are likely for other debris-covered glaciers in the Himalaya.

Cosmogenic 35S as a Novel Detector of Stratospheric Air at the Earth's Surface: Key Findings from the Western United States and New Insights into the Seasonal Variations of Ozone and Sulfate in East Asia

NASA Astrophysics Data System (ADS)

Lin, M.; Thiemens, M. H.; Shaheen, R.; Biglari, S.; Crocker, D.; Zhang, Z.; Tao, J.; Su, L.; Fung, J. C. H.; Su, B.; Liu, L.

2016-12-01

The extent to which stratospheric intrusions on synoptic scales influence the tropospheric ozone (O3) levels remains poorly understood because quantitative detection of stratosphere air at the Earth's surface has been challenging. Cosmogenic 35S is invaluable in such quantification, but this has not yet been unambiguously demonstrated. As a global hot spot for stratospheric intrusions, the western United States (US) is a natural laboratory for testing the validity of this approach. Here, we present measurements of 35S in sulfate aerosols during a well-defined deep stratospheric intrusion event in the western US, which led to a regional O3 pollution event across southern California. The surprisingly high 35S activity in this episode is greater than any other natural radiogenic sulfate aerosols reported in the literature, providing the first and direct field-based evidence that 35S is a sensitive tracer for air mass of stratospheric origin and transported downward. Using this novel tracer, we quantify the seasonal variation for the strength of downward transport of stratospheric air to the planetary boundary layer in East Asia (EA) and what it may mean for surface O3 and sulfate levels. Our 35S measurements in sulfate aerosols collected from a background site (Mount Wuyi; 27.72°N, 117.68°E) during 2014-2015 show peaks in spring and autumn and the temporal variations of 35S were in tandem with surface O3 levels. These results imply that stratospheric O3 in aged stratospheric air masses may contribute to surface O3 levels in the study region in these two seasons. Along with radiogenic 35S analysis, measuring all seven stable isotopes (16O, 17O, 18O, 32S, 33S, 34S and 36S) in the same sulfate samples provides significantly deeper understanding of the atmospheric sulfur cycle in this region. Triple oxygen isotopes are being measured and preliminary results show that the relative importance of different formation pathways of secondary sulfate in EA is likely altitude-independent. In the future, quadruple sulfur isotopes will be measured to provide a higher resolution description of the source and mechanism of chemical transformation of atmospheric sulfate in this region and reported.

Heat Transfer of Confined Impinging Air-water Mist Jet

NASA Astrophysics Data System (ADS)

Chang, Shyy Woei; Su, Lo May

This paper describes the detailed heat transfer distributions of an atomized air-water mist jet impinging orthogonally onto a confined target plate with various water-to-air mass-flow ratios. A transient technique was used to measure the full field heat transfer coefficients of the impinging surface. Results showed that the high momentum mist-jet interacting with the water-film and wall-jet flows created a variety of heat transfer contours on the impinging surface. The trade-off between the competing influences of the different heat transfer mechanisms involving in an impinging mist jet made the nonlinear variation tendency of overall heat transfer against the increase of water-to-air mass-flow ratio and extended the effective cooling region. With separation distances of 10, 8, 6 and 4 jet-diameters, the spatially averaged heat transfer values on the target plate could respectively reach about 2.01, 1.83, 2.43 and 2.12 times of the equivalent air-jet values, which confirmed the applicability of impinging mist-jet for heat transfer enhancement. The optimal choices of water-to-air mass-flow ratio for the atomized mist jet required the considerations of interactive and combined effects of separation distance, air-jet Reynolds number and the water-to-air mass-flow ratio into the atomized nozzle.

Source and Health Implication of Diurnal Atmospheric PM Mass and Number Concentrations

NASA Astrophysics Data System (ADS)

Li, W.; Olvera, H. A.; Garcia, J. H.; Pingitore, N. E.

2007-12-01

Exposure to atmospheric PM has been known to be associated with adverse health effects, decreased heart-rate variability, and respiratory and cardiopulmonary related morbidity and mortality. New evidence suggests that physical characteristics (mass, size, number, surface area, and morphology) of particles are strongly associated with mortality and morbidity through acute exposure. In particular, as reported in the literature, fine or ultrafine particles are more toxic than coarse particles on an equivalent mass basis while particles of less than 30 nm or greater than 2.5 um in diameter deposit more effectively (approximately 80 percent) in lung versus approximately 18 percent for particles in the range of 100 nm and 1 um. In addition, positive association has been observed between day to day variation in PM2.5 and hospital admissions, mortality and particle surface area, or particle number concentration and oxidative stress-induced DNA damage. This presentation shows the results of a study characterizing the physical properties of PM in El Paso, Texas. Diurnal PM mass concentration peaks previously observed at several other cities along the U.S.-Mexico border and elsewhere in the world were observed in El Paso. The hourly PM particle count varied from less than 10,000 particles/cm3 to greater than 80,000 particles/cm3 during the diurnal PM mass peaks. The total number of PM particles peaked in the morning and in the evening while the mode of the particle size changed from 20 nm to 50 nm, indicating different PM sources may be responsible for the mass and number concentrations and agglomeration of particles in the atmosphere during the day may possibly plays a role. A multivariate regression analysis was performed to correlate the PM mass and number concentrations to environmental variables. Real- time wind statistics were used in conjunction with traffic data at a nearby highway for identifying sources of the PM mass and number concentration peaks. Evaluation of the diurnal variation of PM physical properties and a recent study on PM mass and mortality implies that particle number may be a better environmental indicator for mortality than PM2.5 mass. This publication was made possible by grant number 1 S11 ES013339-01A1 from the National Institute of Environmental Health Sciences (NIEHS), NIH. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIEHS, NIH.

Cross-scale modelling of transpiration from stomata via the leaf boundary layer.

PubMed

Defraeye, Thijs; Derome, Dominique; Verboven, Pieter; Carmeliet, Jan; Nicolai, Bart

2014-09-01

Leaf transpiration is a key parameter for understanding land surface-climate interactions, plant stress and plant structure–function relationships. Transpiration takes place at the microscale level, namely via stomata that are distributed discretely over the leaf surface with a very low surface coverage (approx. 0·2-5%). The present study aims to shed more light on the dependency of the leaf boundary-layer conductance (BLC) on stomatal surface coverage and air speed. An innovative three-dimensional cross-scale modelling approach was applied to investigate convective mass transport from leaves, using computational fluid dynamics. The gap between stomatal and leaf scale was bridged by including all these scales in the same computational model (10⁻⁵-10⁻¹ m), which implies explicitly modelling individual stomata. BLC was strongly dependent on stomatal surface coverage and air speed. Leaf BLC at low surface coverage ratios (CR), typical for stomata, was still relatively high, compared with BLC of a fully wet leaf (hypothetical CR of 100%). Nevertheless, these conventional BLCs (CR of 100%), as obtained from experiments or simulations on leaf models, were found to overpredict the convective exchange. In addition, small variations in stomatal CR were found to result in large variations in BLCs. Furthermore, stomata of a certain size exhibited a higher mass transfer rate at lower CRs. The proposed cross-scale modelling approach allows us to increase our understanding of transpiration at the sub-leaf level as well as the boundary-layer microclimate in a way currently not feasible experimentally. The influence of stomatal size, aperture and surface density, and also flow-field parameters can be studied using the model, and prospects for further improvement of the model are presented. An important conclusion of the study is that existing measures of conductances (e.g. from artificial leaves) can be significantly erroneous because they do not account for microscopic stomata, but instead assume a uniform distribution of evaporation such as found for a fully-wet leaf. The model output can be used to correct or upgrade existing BLCs or to feed into higher-scale models, for example within a multiscale framework.

Light-absorbing Aerosol Properties in the Kathmandu Valley during SusKat-ABC Field Campaign

NASA Astrophysics Data System (ADS)

Kim, S.; Yoon, S.; Kim, J.; Cho, C.; Jung, J.

2013-12-01

Light-absorbing aerosols, such as black carbon (BC), are major contributors to the atmospheric heating and the reduction of solar radiation reaching at the earth's surface. In this study, we investigate light-absorption and scattering properties of aerosols (i.e., BC mass concentration, aerosol solar-absorption/scattering efficiency) in the Kathmandu valley during Sustainable atmosphere for the Kathmandu valley (SusKat)-ABC campaign, from December 2012 to February 2013. Kathmandu City is among the most polluted cities in the world. However, there are only few past studies that provide basic understanding of air pollution in the Kathmandu Valley, which is not sufficient for designing effective mitigation measures (e.g., technological, financial, regulatory, legal and political measures, planning strategies). A distinct diurnal variation of BC mass concentration with two high peaks observed during wintertime dry monsoon period. BC mass concentration was found to be maximum around 09:00 and 20:00 local standard time (LST). Increased cars and cooking activities including substantial burning of wood and other biomass in the morning and in the evening contributed to high BC concentration. Low BC concentrations during the daytime can be explain by reduced vehicular movement and cooking activities. Also, the developmements of the boundary layer height and mountain-valley winds in the Kathmandu Valley paly a crucial role in the temproal variation of BC mass concentrations. Detailed radiative effects of light-absorbing aerosols will be presented.

Investigation of transient chill down phenomena in tubes using liquid nitrogen

NASA Astrophysics Data System (ADS)

Shukla, A. K.; Sridharan, Arunkumar; Atrey, M. D.

2017-12-01

Chill down of cryogenic transfer lines is a crucial part of cryogenic propulsion as chill down ensures transfer of single phase fluid to the storage tanks of cryogenic engines. It also ensures single phase liquid flow at the start of the engine. Chill down time depends on several parameters such as length of the pipe, pipe diameter, orientation, mass flux etc. To understand the effect of these parameters, experiments are carried out in a set up designed and fabricated at Indian Institute of Technology Bombay using tubes of two different diameters. Experiments are conducted at different inlet pressures and mass flow rate values to understand their effect. Two different pipe sizes are taken to study the effect of variation in diameter on chill down time and quantity of cryogen required. Different orientations are taken to understand their effect on the chill down time, heat transfer coefficient and critical heat flux for the same inlet pressure and mass flux. Pipe inner wall temperature, heat transfer coefficient for different boiling regimes and critical heat flux are calculated based on measured outer surface temperature history for each case. A one dimensional energy conservation equation is solved for transient chill down process considering constant mass flux and inlet pressure to predict the chill down time. Temperature variation during chill down obtained from the numerical simulations are compared with the measured temperature history.

Functional Gene Diversity and Metabolic Potential of the Microbial Community in an Estuary-Shelf Environment

PubMed Central

Wang, Yu; Zhang, Rui; He, Zhili; Van Nostrand, Joy D.; Zheng, Qiang; Zhou, Jizhong; Jiao, Nianzhi

2017-01-01

Microbes play crucial roles in various biogeochemical processes in the ocean, including carbon (C), nitrogen (N), and phosphorus (P) cycling. Functional gene diversity and the structure of the microbial community determines its metabolic potential and therefore its ecological function in the marine ecosystem. However, little is known about the functional gene composition and metabolic potential of bacterioplankton in estuary areas. The East China Sea (ECS) is a dynamic marginal ecosystem in the western Pacific Ocean that is mainly affected by input from the Changjiang River and the Kuroshio Current. Here, using a high-throughput functional gene microarray (GeoChip), we analyzed the functional gene diversity, composition, structure, and metabolic potential of microbial assemblages in different ECS water masses. Four water masses determined by temperature and salinity relationship showed different patterns of functional gene diversity and composition. Generally, functional gene diversity [Shannon–Weaner’s H and reciprocal of Simpson’s 1/(1-D)] in the surface water masses was higher than that in the bottom water masses. The different presence and proportion of functional genes involved in C, N, and P cycling among the bacteria of the different water masses showed different metabolic preferences of the microbial populations in the ECS. Genes involved in starch metabolism (amyA and nplT) showed higher proportion in microbial communities of the surface water masses than of the bottom water masses. In contrast, a higher proportion of genes involved in chitin degradation was observed in microorganisms of the bottom water masses. Moreover, we found a higher proportion of nitrogen fixation (nifH), transformation of hydroxylamine to nitrite (hao) and ammonification (gdh) genes in the microbial communities of the bottom water masses compared with those of the surface water masses. The spatial variation of microbial functional genes was significantly correlated with salinity, temperature, and chlorophyll based on canonical correspondence analysis, suggesting a significant influence of hydrologic conditions on water microbial communities. Our data provide new insights into better understanding of the functional potential of microbial communities in the complex estuarine-coastal environmental gradient of the ECS. PMID:28680420

Shape shifting predicts ontogenetic changes in metabolic scaling in diverse aquatic invertebrates.

PubMed

Glazier, Douglas S; Hirst, Andrew G; Atkinson, David

2015-03-07

Metabolism fuels all biological activities, and thus understanding its variation is fundamentally important. Much of this variation is related to body size, which is commonly believed to follow a 3/4-power scaling law. However, during ontogeny, many kinds of animals and plants show marked shifts in metabolic scaling that deviate from 3/4-power scaling predicted by general models. Here, we show that in diverse aquatic invertebrates, ontogenetic shifts in the scaling of routine metabolic rate from near isometry (bR = scaling exponent approx. 1) to negative allometry (bR < 1), or the reverse, are associated with significant changes in body shape (indexed by bL = the scaling exponent of the relationship between body mass and body length). The observed inverse correlations between bR and bL are predicted by metabolic scaling theory that emphasizes resource/waste fluxes across external body surfaces, but contradict theory that emphasizes resource transport through internal networks. Geometric estimates of the scaling of surface area (SA) with body mass (bA) further show that ontogenetic shifts in bR and bA are positively correlated. These results support new metabolic scaling theory based on SA influences that may be applied to ontogenetic shifts in bR shown by many kinds of animals and plants. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Regional Deformation Studies with GRACE and GPS

NASA Technical Reports Server (NTRS)

Davis, J. L.; Elosequi, P.; Tamisiea, M.; Mitrovica, J. X.

2005-01-01

GRACE data indicate large seasonal variations in gravity that have been shown to be to be related to climate-driven fluxes of surface water. Seasonal redistribution of surface mass deforms the Earth, and our previous study using GRACE data demonstrate that annual radial deformations of +/-13 mm in the region of Amazon River Basin were observed by both GRACE and ten GPS sites in the region. For the GRACE determinations, we estimate in a least-squares solution for each Stokes coefficient parameters that represent the amplitudes of the annual variation. We then filter these parameters based on a statistical test that uses the scatter of the postfit residuals. We demonstrate by comparison to the GPS amplitudes that this method is more accurate, for this region, than Gaussian smoothing. Our model for the temporal behavior of the gravity coefficients includes a rate term, and although the time series are noisy, the glacial isostatic adjustment signal over Hudson s Bay can be observed. .

Surface-acoustic-wave (SAW) flow sensor

NASA Astrophysics Data System (ADS)

Joshi, Shrinivas G.

1991-03-01

The use of a surface-acoustic-wave (SAW) device to measure the rate of gas flow is described. A SAW oscillator heated to a suitable temperature above ambient is placed in the path of a flowing gas. Convective cooling caused by the gas flow results in a change in the oscillator frequency. A 73-MHz oscillator fabricated on 128 deg rotated Y-cut lithium niobate substrate and heated to 55 C above ambient shows a frequency variation greater than 142 kHz for flow-rate variation from 0 to 1000 cu cm/min. The output of the sensor can be calibrated to provide a measurement of volume flow rate, pressure differential across channel ports, or mass flow rate. High sensitivity, wide dynamic range, and direct digital output are among the attractive features of this sensor. Theoretical expressions for the sensitivity and response time of the sensor are derived. It is shown that by using ultrasonic Lamb waves propagating in thin membranes, a flow sensor with faster response than a SAW sensor can be realized.

Surface-acoustic-wave (SAW) flow sensor.

PubMed

Joshi, S G

1991-01-01

The use of a surface-acoustic-wave (SAW) device to measure the rate of gas flow is described. A SAW oscillator heated to a suitable temperature above ambient is placed in the path of a flowing gas. Convective cooling caused by the gas flow results in a change in the oscillator frequency. A 73-MHz oscillator fabricated on 128 degrees rotated Y-cut lithium niobate substrate and heated to 55 degrees C above ambient shows a frequency variation greater than 142 kHz for flow-rate variation from 0 to 1000 cm(3)/min. The output of the sensor can be calibrated to provide a measurement of volume flow rate, pressure differential across channel ports, or mass flow rate. High sensitivity, wide dynamic range, and direct digital output are among the attractive features of this sensor. Theoretical expressions for the sensitivity and response time of the sensor are derived. It is shown that by using ultrasonic Lamb waves, propagating in thin membranes, a flow sensor with faster response than a SAW sensor can be realized.

Effects of maternal characteristics and climatic variation on birth masses of Alaskan caribou

USGS Publications Warehouse

Adams, Layne G.

2005-01-01

Understanding factors that influence birth mass of mammals provides insights to nutritional trade-offs made by females to optimize their reproduction, growth, and survival. I evaluated variation in birth mass of caribou (Rangifer tarandus) in central Alaska relative to maternal characteristics (age, body mass, cohort, and nutritional condition as influenced by winter severity) during 11 years with substantial variation in winter snowfall. Snowfall during gestation was the predominant factor explaining variation in birth masses, influencing birth mass inversely and through interactions with maternal age and lactation status. Maternal age effects were noted for females ≤ 5 years old, declining in magnitude with each successive age class. Birth mass as a proportion of autumn maternal mass was inversely related to winter snowfall, even though there was no decrease in masses of adult females in late winter associated with severe winters. I found no evidence of a hypothesized intergenerational effect of lower birth masses for offspring of females born after severe winters. Caribou produce relatively small offspring but provide exceptional lactation support for those that survive. Conservative maternal investment before parturition may represent an optimal reproductive strategy given that caribou experience stochastic variation in winter severity during gestation, uncertainty of environmental conditions surrounding the birth season, and intense predation on neonates.

Massive star formation in 100,000 years from turbulent and pressurized molecular clouds.

PubMed

McKee, Christopher F; Tan, Jonathan C

2002-03-07

Massive stars (with mass m* > 8 solar masses Mmiddle dot in circle) are fundamental to the evolution of galaxies, because they produce heavy elements, inject energy into the interstellar medium, and possibly regulate the star formation rate. The individual star formation time, t*f, determines the accretion rate of the star; the value of the former quantity is currently uncertain by many orders of magnitude, leading to other astrophysical questions. For example, the variation of t*f with stellar mass dictates whether massive stars can form simultaneously with low-mass stars in clusters. Here we show that t*f is determined by the conditions in the star's natal cloud, and is typically about 105yr. The corresponding mass accretion rate depends on the pressure within the cloud--which we relate to the gas surface density--and on both the instantaneous and final stellar masses. Characteristic accretion rates are sufficient to overcome radiation pressure from about 100M middle dot in circle protostars, while simultaneously driving intense bipolar gas outflows. The weak dependence of t*f on the final mass of the star allows high- and low-mass star formation to occur nearly simultaneously in clusters.

Low degree Earth's gravity coefficients determined from different space geodetic observations and climate models

NASA Astrophysics Data System (ADS)

Wińska, Małgorzata; Nastula, Jolanta

2017-04-01

Large scale mass redistribution and its transport within the Earth system causes changes in the Earth's rotation in space, gravity field and Earth's ellipsoid shape. These changes are observed in the ΔC21, ΔS21, and ΔC20 spherical harmonics gravity coefficients, which are proportional to the mass load-induced Earth rotational excitations. In this study, linear trend, decadal, inter-annual, and seasonal variations of low degree spherical harmonics coefficients of Earth's gravity field, determined from different space geodetic techniques, Gravity Recovery and Climate Experiment (GRACE), satellite laser ranging (SLR), Global Navigation Satellite System (GNSS), Earth rotation, and climate models, are examined. In this way, the contribution of each measurement technique to interpreting the low degree surface mass density of the Earth is shown. Especially, we evaluate an usefulness of several climate models from the Coupled Model Intercomparison Project phase 5 (CMIP5) to determine the low degree Earth's gravity coefficients using GRACE satellite observations. To do that, Terrestrial Water Storage (TWS) changes from several CMIP5 climate models are determined and then these simulated data are compared with the GRACE observations. Spherical harmonics ΔC21, ΔS21, and ΔC20 changes are calculated as the sum of atmosphere and ocean mass effect (GAC values) taken from GRACE and a land surface hydrological estimate from the selected CMIP5 climate models. Low degree Stokes coefficients of the surface mass density determined from GRACE, SLR, GNSS, Earth rotation measurements and climate models are compared to each other in order to assess their consistency. The comparison is done by using different types of statistical and signal processing methods.

Pruning The ELM Survey: Characterizing Candidate Low-mass White Dwarfs through Photometric Variability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bell, Keaton J.; Winget, D. E.; Montgomery, M. H.

We assess the photometric variability of nine stars with spectroscopic T {sub eff} and log g values from the ELM Survey that locates them near the empirical extremely low-mass (ELM) white dwarf instability strip. We discover three new pulsating stars: SDSS J135512.34+195645.4, SDSS J173521.69+213440.6, and SDSS J213907.42+222708.9. However, these are among the few ELM Survey objects that do not show radial velocity (RV) variations that confirm the binary nature expected of helium-core white dwarfs. The dominant 4.31 hr pulsation in SDSS J135512.34+195645.4 far exceeds the theoretical cut-off for surface reflection in a white dwarf, and this target is likely amore » high-amplitude δ Scuti pulsator with an overestimated surface gravity. We estimate the probability to be less than 0.0008 that the lack of measured RV variations in four of eight other pulsating candidate ELM white dwarfs could be due to low orbital inclination. Two other targets exhibit variability as photometric binaries. Partial coverage of the 19.342 hr orbit of WD J030818.19+514011.5 reveals deep eclipses that imply a primary radius >0.4 R {sub ⊙}—too large to be consistent with an ELM white dwarf. The only object for which our time series photometry adds support to ELM white dwarf classification is SDSS J105435.78−212155.9, which has consistent signatures of Doppler beaming and ellipsoidal variations. We conclude that the ELM Survey contains multiple false positives from another stellar population at T {sub eff}≲9000 K, possibly related to the sdA stars recently reported from SDSS spectra.« less

Pruning The ELM Survey: Characterizing Candidate Low-mass White Dwarfs through Photometric Variability

NASA Astrophysics Data System (ADS)

Bell, Keaton J.; Gianninas, A.; Hermes, J. J.; Winget, D. E.; Kilic, Mukremin; Montgomery, M. H.; Castanheira, B. G.; Vanderbosch, Z.; Winget, K. I.; Brown, Warren R.

2017-02-01

We assess the photometric variability of nine stars with spectroscopic Teff and log g values from the ELM Survey that locates them near the empirical extremely low-mass (ELM) white dwarf instability strip. We discover three new pulsating stars: SDSS J135512.34+195645.4, SDSS J173521.69+213440.6, and SDSS J213907.42+222708.9. However, these are among the few ELM Survey objects that do not show radial velocity (RV) variations that confirm the binary nature expected of helium-core white dwarfs. The dominant 4.31 hr pulsation in SDSS J135512.34+195645.4 far exceeds the theoretical cut-off for surface reflection in a white dwarf, and this target is likely a high-amplitude δ Scuti pulsator with an overestimated surface gravity. We estimate the probability to be less than 0.0008 that the lack of measured RV variations in four of eight other pulsating candidate ELM white dwarfs could be due to low orbital inclination. Two other targets exhibit variability as photometric binaries. Partial coverage of the 19.342 hr orbit of WD J030818.19+514011.5 reveals deep eclipses that imply a primary radius >0.4 R⊙—too large to be consistent with an ELM white dwarf. The only object for which our time series photometry adds support to ELM white dwarf classification is SDSS J105435.78-212155.9, which has consistent signatures of Doppler beaming and ellipsoidal variations. We conclude that the ELM Survey contains multiple false positives from another stellar population at Teff ≲ 9000 K, possibly related to the sdA stars recently reported from SDSS spectra.

The Lidnis Instrument: Atmosphere And Surface Studies

NASA Astrophysics Data System (ADS)

Leblanc, F.; Chassefiere, E.; Porteneuve, J.; Berthelier, J.-J.; Sarkissian, A.; Meftha, M.; Johnson, R. E.; Chaussidon, M.; Jambon, A.

LIDNIS is a surface instrument for rocky planetary bodies (in particular for Mercury, Mars, the Moon or asteroids) which simultaneously studies the chemical composi- tion of surface material, its gaseous environment and the nature and importance of the atmosphere/surface interaction. A multipurpose mass spectrometer (called NIS for Neutral and Ion spectrometer) placed at the surface of a planetary body would first of all give us information on the local atmosphere, its elementary and isotopic compo- sition and temporal variation. It will also give us the access to the precipitation from the interplanetary space and the products due to this precipitation. The association to NIS of a laser induced desorption (LID) system strong enough to desorb and volatilize the first few tens micro meters of the surface will allow the analysis of the different species present in this layer that is the atmospheric species (volatiles, refractories and products of the interior outgassing), the energetic implanted species along the history of this body (Solar Wind, Solar Energetic Particles and Cosmic Rays) and the inter- nal composition. In the same way as it is usually done in laboratories for the Moon samples, LIDNIS, through a progressive outgassing of the regolith or the rock at the surface, will measure these different groups of species. The purpose of this poster is to describe such an instrument and to show its capabilities with low mass and power to measure efficiently fundamental parameters for our understanding of the origin and evolution of planetary bodies in the solar system.

The Solar Spectrum on the Martian Surface and its Effect on Photovoltaic Performance

NASA Technical Reports Server (NTRS)

Landis, Geoffrey A.; Hyatt, Daniel

2007-01-01

Solar cells operating on the surface of Mars receive a spectrum of illumination different from the AM0 spectrum, since the sunlight is filtered by dust suspended in the atmosphere. This spectrum changes with the amount of dust in the atmosphere, as well as with air mass change due to time of day and season. This spectral variation affects the performance of solar cells. We used data from Mars Exploration Rovers to measure this spectrum. By comparing the measured intensity with the known reflectance of the pancam calibration target on the rovers Spirit and Opportunity, we measure the solar spectrum reaching the surface. The effect of this spectrum on the performance of solar cells is then calculated based on the spectral response of several different solar cell types.

The Solar Spectrum on the Martian Surface and Its Effect on Photovoltaic Performance

NASA Technical Reports Server (NTRS)

Landis, Geoffrey A.; Hyatt, Dan

2006-01-01

Solar cells operating on the surface of Mars receive a spectrum of illumination different from the AM0 spectrum, since the sunlight is filtered by dust suspended in the atmosphere. This spectrum changes with the amount of dust in the atmosphere, as well as with air mass change due to time of day and season. This spectral variation affects the performance of solar cells. We used data from Mars Exploration Rovers to measure this spectrum. By comparing the measured intensity with the known reflectance of the pancam calibration target on the rovers Spirit and Opportunity, we measure the solar spectrum reaching the surface. The effect of this spectrum on the performance of solar cells is then calculated based on the spectral response of several different solar cell types.

Patterns of Cross-Continental Variation in Tree Seed Mass in the Canadian Boreal Forest

PubMed Central

Liu, Jushan; Bai, Yuguang; Lamb, Eric G.; Simpson, Dale; Liu, Guofang; Wei, Yongsheng; Wang, Deli; McKenney, Daniel W.; Papadopol, Pia

2013-01-01

Seed mass is an adaptive trait affecting species distribution, population dynamics and community structure. In widely distributed species, variation in seed mass may reflect both genetic adaptation to local environments and adaptive phenotypic plasticity. Acknowledging the difficulty in separating these two aspects, we examined the causal relationships determining seed mass variation to better understand adaptability and/or plasticity of selected tree species to spatial/climatic variation. A total of 504, 481 and 454 seed collections of black spruce (Picea mariana (Mill.) B.S.P.), white spruce (Picea glauca (Moench) Voss) and jack pine (Pinus banksiana Lamb) across the Canadian Boreal Forest, respectively, were selected. Correlation analyses were used to determine how seed mass vary with latitude, longitude, and altitude. Structural Equation Modeling was used to examine how geographic and climatic variables influence seed mass. Climatic factors explained a large portion of the variation in seed mass (34, 14 and 29%, for black spruce, white spruce and jack pine, respectively), indicating species-specific adaptation to long term climate conditions. Higher annual mean temperature and winter precipitation caused greater seed mass in black spruce, but annual precipitation was the controlling factor for white spruce. The combination of factors such as growing season temperature and evapotranspiration, temperature seasonality and annual precipitation together determined seed mass of jack pine. Overall, sites with higher winter temperatures were correlated with larger seeds. Thus, long-term climatic conditions, at least in part, determined spatial variation in seed mass. Black spruce and Jack pine, species with relatively more specific habitat requirements and less plasticity, had more variation in seed mass explained by climate than did the more plastic species white spruce. As traits such as seed mass are related to seedling growth and survival, they potentially influence forest species composition in a changing climate and should be included in future modeling of vegetation shifts. PMID:23593392

From the Exoplanetary Bestiary to the Exoplanetary Zoo

NASA Astrophysics Data System (ADS)

Unterborn, C. T.; Panero, W. R.; Stixrude, L. P.; Kellogg, L. H.; Lithgow-Bertelloni, C. R.; Diamond, M. R.

2014-12-01

While much attention has been focused on the exoplanetary "bestiary" of super-Earths, lava worlds, and diamond planets, habitable planets are more likely to be found in a more similar exoplanetary "zoo." Many planet-hosting stars are similar in composition to the Sun, with moderate variations in metal abundances. Even for those stars with O and Fe abundances similar to the Sun, many have 100% variations in the refractory, rock-forming elements such as Si, Mg, Al and Ca. For an Earth sized planet, this variation creates planets with drastically different mantle mineral assemblages and variable melting, elastic, and viscous properties, leading to variable dynamical behavior. This dynamical behavior dictates the dominant mode of heat extraction, be it through a conducting rigid lid or via plate tectonics. Without tectonics, there is no mechanism known with which to create a deep water and carbon cycle, thus creating a long-lived habitable surface. We present the results of integrated modeling in which we consider the effects of variations in bulk mantle composition on Earth-mass planets. To explore the variations expected in this planetary zoo, we present condensation sequence calculations for stars of varying refractory element abundances. These calculations constrain the potential refractory mineral reservoir from which Earth-mass terrestrial planets will form. As planets of this size inevitably will convect, the thermal structure of the mantle is controlled by surface melting temperature and the first crust can be estimated from decompression melting of a convecting mantle. The thermodynamic code HeFESTo determines the mineralogy and resulting thermoelastic properties of both the mantle and potential foundering of crustal material. Finally, with parameterized convection modeling and 2- and 3-D convection modeling, we determine terrestrial mantle's convective regime as a function of bulk composition. We therefore consider a planet's potential for Earth-like plate tectonics by applying compositional perturbations from the Earth. Aspects affecting this potential include the location of the basalt-eclogite transition in the upper mantle and the density contrast, and thus negative buoyancy, between the foundering crust and mantle. Portions of this work were initiated at the CIDER 2014 program.

The Sun: Source of the Earth's Energy

NASA Technical Reports Server (NTRS)

Thompson, Barbara J.; Fisher, Richard R. (Technical Monitor)

2001-01-01

The Sun is the primary source of the Earth's energy. However, due to the complexity in the way the energy affects Earth, the various solar sources of the energy, and the variation exhibited by the Sun it is difficult to understand and predict the Earth's response to solar drivers. In addition to visible light the radiant energy of the Sun can exhibit variation in nearly all wavelengths, which can vary over nearly all timescales. Depending on the wavelength of the incident radiation the light can deposit energy in a wide variety or locations and drive processes from below Earth's surface to interplanetary space. Other sources of energy impacting Earth include energetic particles, magnetic fields, and mass and flow variations in the solar wind. Many of these variable energetic processes cannot be coupled and recent results continue to demonstrate that the complex dynamics of the Sun can have a great range of measurable impacts on Earth.

Real time monitoring of the minute dynamic variation at the crude oil-water interface.

PubMed

Duan, Ming; Ding, Ziling; Wang, Hu; Xiong, Yan

2018-02-21

Quantitative recording of the minute dynamic variation at an oil-water interface is always a great challenge. Dual polarization interferometry (DPI) presents an approach in monitoring the variations of mass, thickness, and density at the interface with high resolution. In this study, a planar crude oil-water interface was established by spin-coating on a DPI chip surface. Different concentrations of sodium dodecyl sulphate (SDS) and polyacrylamide (PAM) were injected into the interface. The absorption of free SDS molecules, in low concentrations, can be interpreted as a two-step absorption. With the existence of micelles in higher concentrations, the crude oil molecules tend to be taken away by the micelles. The absorptions of the polymers at the interface are different from SDS. The crude oil can hardly be taken away by the polymers. Instead, the hydrophobic segments of polymers insert into the oil film and hydrophilic groups stretch into the solution.

Gravitational Signal of Mass Redistribution Due to Interannual Meteorological Oscillations in Atmosphere and Ocean

NASA Technical Reports Server (NTRS)

Chao, B. F.; Au, A. Y.; Johnson, T.; Smith, David E. (Technical Monitor)

2001-01-01

Interannual meteorological oscillations (ENSO, QBO, NAO, etc.) have demonstrable influences on Earth's rotation. Here we study their effects on global gravitational field, whose temporal variations are being studied using SLR (satellite laser ranging) data and in anticipation of the new space mission GRACE. The meteorological oscillation modes are identified using the EOF (empirical orthogonal function)/PC (principal component) decomposition of surface fields (in which we take care of issues associated with the area-weighting and non-zero mean). We examine two fields, one for the global surface pressure field for the atmosphere obtained from the NCEP reanalysis (for the past 40 years), one for the surface topography field for the ocean from the Topex/Poseidon (T/P) data (for the past 8 years). We use monthly maps, and remove the mean-monthly ("climatology") values from each grid point, hence focusing only on non-seasonal signals. The T/P data were first subject to a steric correction where the steric contribution to the ocean surface topography was removed according to output of the numerical POCM model. The respective atmospheric and oceanic contributions to the gravitational variation, in terms of harmonic Stokes coefficients, are then combined mode-by-mode. Since the T/P data already contain the oceanic response to overlying atmospheric pressure, no regards to the inverted-barometer behavior for the ocean need be considered. Results for the lowest-degree Stokes coefficients can then be compared with space geodetic observations including the Earth's rotation and the SLR data mentioned above, to identify the importance of each meteorological oscillations in gravitational variation signals.

Variation in body mass of wild canvasback and redhead ducklings

USGS Publications Warehouse

Austin, Jane E.; Serie, Jerome R.

1994-01-01

We assessed variation in body mass of ducklings in single- and mixed-species broods of wild Canvasbacks (Aythya valisineria) and Redheads (Aythya americana) 20-50 days old. Body mass of canvasback ducklings was not affected by year and season (early vs. late hatch date) despite changes in water conditions. Mean body mass of male and female Canvasbacks did not differ in Class IIA but did differ in older age classes. Within-brood differences in body mass tended to be higher in Class IIA ducklings (6-7% of mean body mass for Canvasbacks, 9-11% in Redheads) and generally declined to 4-6% in Class IIC and older ducklings. Some within-brood differences were as high as 20-30% of mean body mass. Tests to assess sources of within-brood variation (age, sex, and season) in body mass for Canvasbacks were inconclusive. Variation within broods was generally less than that among broods for both Canvasbacks and Redheads. The lack of differences in duckling body mass between single- and mixed-species broods for any age class, sex, or species suggests that mass was not affected by interspecific brood parasitism.

Variation in Foot Strike Patterns among Habitually Barefoot and Shod Runners in Kenya

PubMed Central

Lieberman, Daniel E.; Castillo, Eric R.; Otarola-Castillo, Erik; Sang, Meshack K.; Sigei, Timothy K.; Ojiambo, Robert; Okutoyi, Paul; Pitsiladis, Yannis

2015-01-01

Runners are often categorized as forefoot, midfoot or rearfoot strikers, but how much and why do individuals vary in foot strike patterns when running on level terrain? This study used general linear mixed-effects models to explore both intra- and inter-individual variations in foot strike pattern among 48 Kalenjin-speaking participants from Kenya who varied in age, sex, body mass, height, running history, and habitual use of footwear. High speed video was used to measure lower extremity kinematics at ground contact in the sagittal plane while participants ran down 13 meter-long tracks with three variables independently controlled: speed, track stiffness, and step frequency. 72% of the habitually barefoot and 32% of the habitually shod participants used multiple strike types, with significantly higher levels of foot strike variation among individuals who ran less frequently and who used lower step frequencies. There was no effect of sex, age, height or weight on foot strike angle, but individuals were more likely to midfoot or forefoot strike when they ran on a stiff surface, had a high preferred stride frequency, were habitually barefoot, and had more experience running. It is hypothesized that strike type variation during running, including a more frequent use of forefoot and midfoot strikes, used to be greater before the introduction of cushioned shoes and paved surfaces. PMID:26154285

Hydrological storage variations in a lake water balance, observed from multi-sensor satellite data and hydrological models.

NASA Astrophysics Data System (ADS)

Singh, Alka; Seitz, Florian; Schwatke, Christian; Guentner, Andreas

2013-04-01

Freshwater lakes and reservoirs account for 74.5% of continental water storage in surface water bodies and only 1.8% resides in rivers. Lakes and reservoirs are a key component of the continental hydrological cycle but in-situ monitoring networks are very limited either because of sparse spatial distribution of gauges or national data policy. Monitoring and predicting extreme events is very challenging in that case. In this study we demonstrate the use of optical remote sensing, satellite altimetry and the GRACE gravity field mission to monitor the lake water storage variations in the Aral Sea. Aral Sea is one of the most unfortunate examples of a large anthropogenic catastrophe. The 4th largest lake of 1960s has been decertified for more than 75% of its area due to the diversion of its primary rivers for irrigation purposes. Our study is focused on the time frame of the GRACE mission; therefore we consider changes from 2002 onwards. Continuous monthly time series of water masks from Landsat satellite data and water level from altimetry missions were derived. Monthly volumetric variations of the lake water storage were computed by intersecting a digital elevation model of the lake with respective water mask and altimetry water level. With this approach we obtained volume from two independent remote sensing methods to reduce the error in the estimated volume through least square adjustment. The resultant variations were then compared with mass variability observed by GRACE. In addition, GARCE estimates of water storage variations were compared with simulation results of the Water Gap Hydrology Model (WGHM). The different observations from all missions agree that the lake reached an absolute minimum in autumn 2009. A marked reversal of the negative trend occured in 2010 but water storage in the lake decreased again afterwards. The results reveal that water storage variations in the Aral Sea are indeed the principal, but not the only contributor to the GRACE signal of mass variations in this region; this is also verified by WGHM simulations. An important implication of this finding is the possibility of GRACE to analyses storage changes in other hydrological compartments (soil moisture, snow and groundwater) once the signal has been reduced for surface water storage changes. Therefore the congruent use of multi-sensor satellite data for hydrological studies proves to be a great source of information for assessing terrestrial water storage variations.

Study of variation in surface morphology, chemical composition, crystallinity and hardness of laser irradiated silver in dry and wet environments

NASA Astrophysics Data System (ADS)

Ali, Nisar; Bashir, Shazia; Umm-i-Kalsoom; Begum, Narjis; Hussain, Tousif

2017-07-01

Variation in surface morphology, chemical composition, crystallinity and hardness of laser irradiated silver in dry and wet ambient environments has been investigated. For this purpose, the silver targets were exposed for various number of laser pulses in ambient environment of air, ethanol and de-ionized water for various number of laser pulses i.e. 500, 1000, 1500 and 2000. Scanning Electron Microscope (SEM) was employed to investigate the surface morphology of irradiated silver. SEM analysis reveals significant surface variations for both dry and wet ambient environments. For lower number of pulses, in air environment significant mass removal is observed but in case of ethanol no significant change in surface morphology is observed. In case of de-ionized water small sized cavities are observed with formation of protrusions with spherical top ends. For higher number of laser pulses, refilling of cavities by shock liquefied material, globules and protrusions are observed in case of dry ablation. For ablation in ethanol porous and coarse periodic ripples are observed whereas, for de-ionized water increasing density of protrusions is observed for higher number of pulses. EDS analysis exhibits the variation in chemical composition along with an enhanced diffusion of oxygen under both ambient conditions. The crystal structure of the exposed targets were explored by X-ray Diffraction (XRD) technique. XRD results support the EDS results. Formation of Ag2O in case of air and ethanol whereas, Ag2O and Ag3O in case of de-ionized water confirms the diffusion of oxygen into the silver surface after irradiation. Vickers Hardness tester was employed to measure the hardness of laser treated targets. Enhanced hardness is observed after irradiation in both dry and wet ambient environments. Initial decrease and then increase in hardness is observed with increase in number of laser pulses in air environment. In case of ethanol, increase in number of laser pulses results in continuous decrease in hardness. Whereas, in case of de-ionized water hardness increases with increase in number of laser pulses.

Spatial Variations and Sources of Trace Elements in Recent Snow from Glaciers at the Tibetan Plateau

NASA Astrophysics Data System (ADS)

Huang, J.; Li, Y.; Li, Z.; Cozzi, G.; Turetta, C.; Barbante, C.; Xiong, L.

2017-12-01

Various trace element (TEs) could be long-range transported through the atmosphere and deposited onto the snow surface. Recently, with the development of economy of China and the surrounding countries, TEs such as Pb, Cd, Mo and Sb in several glaciers from the Tibetan Plateau (TP) have been gradually affected by anthropogenic activities. This study presents the acid leached concentrations of TEs (e.g., Al, As, Ba, Co, Cr, Cs, Cu, Fe, Li, Mn, Mo, Pb, Rb, Sb, Sr, Ti, Tl, U, V) and dust content sampled from Qiumianleike (QMLK), Meikuang (MK), Yuzhufeng (YZF), Xiaodongkemadi (XDKMD), Gurenhekou (GRHK) glaciers on the TP from April to May of 2013. The different concentrations of TEs in the surface snow and snow pit samples over the five glaciers show that TEs were influenced both by surrounding environment of glaciers and seasonal variations of atmospheric impurity loading. Comparison of TEs concentrations with data of other sites, elevated concentrations of As, Cu, Mo, Pb and Sb were observed in glaciers of TP, showing significant atmospheric TEs pollution. Enrichment factor(EF) analysis indicates that Rb, V, U, Cr, Ba, Cs, Li, As, Co, Mn, Tl, Sr and Cu mainly originated from crustal dust, while anthropogenic inputs such as nonferrous metals melting, coal combustion and traffic emission made an important contribution to the Mo, Pb and Sb. Evidences from air mass back trajectories show the air masses arrived at QMLK mostly came from the Taklimakan desert, the TEs from the Taklimakan desert and the western TP could be transported to the MK and YZF glaciers . The air masses derived from the western TP and the southwestern TP affected the environment of the XDKMD and GRHK glaciers. Futhermore, the air masses passed through some big cities with developed industry and large population such as Urumqi, Bishkek, Dushanbe and some countries such as Pakistan and India could also bring pollutants to the studied glaciers.

Synthesis of carbon nanotube using camphor with SS 316 as catalytic substrate via oxidative heat treatment preparation method

NASA Astrophysics Data System (ADS)

Wulan, Praswasti Pembangun Dyah Kencana; Angelina, Dian

2017-11-01

Carbon nanotube (CNT) is a material that now often become the topic in nanotechnology research. CNT is widely used in the electronics industry especially for TV and computer flat panel displays, devices, automotives for car components, and batteries. Also for defense industries as well as other industries such as sports equipment. Camphor (C10H16O), a botanical hydrocarbon, can be used as a renewable and low cost carbon source for CNT synthesis. Synthesis was performed with stainless steel-316 (SS 316) as substrate, argon as carrier gas, and hydrogen as co-reactant. Preparation of the SS 316 was through a pretreatment by oxidative heat treatment method at a temperature of 850oC for 30 minutes, to remove the layer of chrome and make a rough surface as a growth media for CNT. The operating temperature of the synthesis used was 800oC with a reaction time of 60 minutes. Reactor, which made from stainless steel 316 (SS 316), was used for synthesis CNTs with maximum camphor mass of 20 grams. This research was conducted by varying the number of camphor mass by 5, 7, 10, 12, and 15 grams. The results showed that camphor decomposed into three compounds which are 40% benzene, 8% toluene, and 52% xylene. CNT grows on the surface of the SS 316 plate for each variation. CNTs have grown by follow tips growth model with deformations like buckling growth model and continuous growth model were also founded. The results of XRD showed that CNT were found in every camphor mass variation with high intensity at 2θ angle of 26° and 43°. The best quality and yield of CNT was obtained at camphor mass of 15 grams with carbon percentage of 87,1% and diameter 33 - 44 nm.

Seasonal Ozone Variations in the Isentropic Layer between 330 and 380 K as Observed by SAGE 2: Implications of Extratropical Cross-Tropopause Transport

NASA Technical Reports Server (NTRS)

Wang, Pi-Huan; Cunnold, Derek M.; Zawodny, Joseph M.; Pierce, R. Bradley; Olson, Jennifer R.; Kent, Geoffrey S.; Skeens, Kristi, M.

1998-01-01

To provide observational evidence on the extratropical cross-tropopause transport between the stratosphere and the troposphere via quasi-isentropic processes in the middleworld (the part of the atmosphere in which the isentropic surfaces intersect the tropopause), this report presents an analysis of the seasonal variations of the ozone latitudinal distribution in the isentropic layer between 330 K and 380 K based on the measurements from the Stratospheric Aerosol and Gas Experiment (SAGE) II. The results from SAGE II data analysis are consistent with (1) the buildup of ozone-rich air in the extratropical middleworld through the large-scale descending mass circulation during winter, (2) the spread of ozone-rich air in the isentropic layer from midlatitudes to subtropics via quasi-isentropic transport during spring, (3) significant photochemical ozone removal and the absence of an ozone-rich supply of air to the layer during summer, and (4) air mass exchange between the subtropics and the extratropics during the summer monsoon period. Thus the SAGE II observed ozone seasonal variations in the middleworld are consistent with the existing model calculated annual cycle of the diabatic circulation as well as the conceptual role of the eddy quasi-adiabatic transport in the stratosphere-troposphere exchange reported in the literature.

Interannual variation of the South China Sea circulation during winter: intensified in the southern basin

NASA Astrophysics Data System (ADS)

Zu, Tingting; Xue, Huijie; Wang, Dongxiao; Geng, Bingxu; Zeng, Lili; Liu, Qinyan; Chen, Ju; He, Yunkai

2018-05-01

Surface geostrophic current derived from altimetry remote sensing data, and current profiles observed from in-situ Acoustic Doppler Current Profilers (ADCP) mooring in the northern South China Sea (NSCS) and southern South China Sea (SSCS) are utilized to study the kinetic and energetic interannual variability of the circulation in the South China Sea (SCS) during winter. Results reveal a more significant interannual variation of the circulation and water mass properties in the SSCS than that in the NSCS. Composite ananlysis shows a significantly reduced western boundary current (WBC) and a closed cyclonic eddy in the SSCS at the mature phase of El Niño event, but a strong WBC and an unclosed cyclonic circulation in winter at normal or La Niña years. The SST is warmer while the subsurface water is colder and fresher in the mature phase of El Niño event than that in the normal or La Niña years in the SSCS. Numerical experiments and energy analysis suggest that both local and remote wind stress change are important for the interannual variation in the SSCS, remote wind forcing and Kuroshio intrusion affect the circulation and water mass properties in the SSCS through WBC advection.

Gravity Changes and Internal Processes: Some Results Obtained from Observations at Three Volcanoes

NASA Astrophysics Data System (ADS)

Jentzsch, Gerhard; Weise, Adelheid; Rey, Carlos; Gerstenecker, Carl

Temporal gravity changes provide information about mass and/or density variations within and below the volcano edifice. Three active volcanoes have been under investigation; each of them related to a plate boundary: Mayon/Luzon/Philippines, Merapi/Java/Indonesia, and Galeras/Colombia. The observed gravity changes are smaller than previously expected but significant. For the three volcanoes under investigation, and within the observation period, mainly the increase of gravity is observed, ranging from 1,000 nm-2 to 1,600 nms-2. Unexpectedly, the gravity increase is confined to a rather small area with radii of 5 to 8 km around the summit. At Mayon and Merapi the parallel GPS measurements yield no significant elevation changes. This is crucial for the interpretation, as the internal pressure variations do not lead to significant deformation at the surface. Thus the classical Mogi-model for a shallow extending magma reservoir cannot apply. To confine the possible models, the attraction due to changes of groundwater level or soil moisture is estimated along the slope of Merapi exemplarily by 2-D modelling. Mass redistribution or density changes were evaluated within the vent as well as deeper fluid processes to explain the gravity variations; the results are compared to the model incorporating the additional effect of elastic deformation.

Long-term mass variations from SLR, VLBI and GPS data

NASA Astrophysics Data System (ADS)

Luceri, Vincenza; Sciarretta, Cecilia; Bianco, Giuseppe

2013-04-01

The second-degree geopotential coefficients reflect the behaviour of the Earth's inertia tensor of order 2 which describes the main mass variations of our planet impacting polar motion and length of day (EOP). SLR, VLBI and GPS allow the estimation of those variations, either directly in the case of SLR through its dynamics, and indirectly, for all the three geodetic techniques, by deriving excitation functions from the EOP estimations. The geodetic estimates include the influence of the Earth's atmosphere and oceans, both from their mass and motion components, which can be modelled using the atmospheric and oceanic angular momenta variations. The different C21, S21 and C20 geodetic time series are compared in order to evaluate their coherence and their response to the mass variations after the removal of the motion terms. Moreover, the residual signal contents of the geodetic values, deprived by the atmospheric and oceanic mass and motion components, will be investigated.

Magnetohydrodynamic Convection in the Outer Core and its Geodynamic Consequences

NASA Technical Reports Server (NTRS)

Kuang, Weijia; Chao, Benjamin F.; Fang, Ming

2004-01-01

The Earth's fluid outer core is in vigorous convection through much of the Earth's history. In addition to generating and maintaining Earth s time-varying magnetic field (geodynamo), the core convection also generates mass redistribution in the core and a dynamical pressure field on the core-mantle boundary (CMB). All these shall result in various core-mantle interactions, and contribute to surface geodynamic observables. For example, electromagnetic core-mantle coupling arises from finite electrically conducting lower mantle; gravitational interaction occurs between the cores and the heterogeneous mantle; mechanical coupling may also occur when the CMB topography is aspherical. Besides changing the mantle rotation via the coupling torques, the mass-redistribution in the core shall produce a spatial-temporal gravity anomaly. Numerical modeling of the core dynamical processes contributes in several geophysical disciplines. It helps explain the physical causes of surface geodynamic observables via space geodetic techniques and other means, e.g. Earth's rotation variation on decadal time scales, and secular time-variable gravity. Conversely, identification of the sources of the observables can provide additional insights on the dynamics of the fluid core, leading to better constraints on the physics in the numerical modeling. In the past few years, our core dynamics modeling efforts, with respect to our MoSST model, have made significant progress in understanding individual geophysical consequences. However, integrated studies are desirable, not only because of more mature numerical core dynamics models, but also because of inter-correlation among the geophysical phenomena, e.g. mass redistribution in the outer core produces not only time-variable gravity, but also gravitational core-mantle coupling and thus the Earth's rotation variation. They are expected to further facilitate multidisciplinary studies of core dynamics and interactions of the core with other components of the Earth.

The Southern Ocean's role in ocean circulation and climate transients

NASA Astrophysics Data System (ADS)

Thompson, A. F.; Stewart, A.; Hines, S.; Adkins, J. F.

2017-12-01

The ventilation of deep and intermediate density classes at the surface of the Southern Ocean impacts water mass modification and the air-sea exchange of heat and trace gases, which in turn influences the global overturning circulation and Earth's climate. Zonal variability occurs along the Antarctic Circumpolar Current and the Antarctic margins related to flow-topography interactions, variations in surface boundary conditions, and exchange with northern basins. Information about these zonal variations, and their impact on mass and tracer transport, are suppressed when the overturning is depicted as a two-dimensional (depth-latitude) streamfunction. Here we present an idealized, multi-basin, time-dependent circulation model that applies residual circulation theory in the Southern Ocean and allows for zonal water mass transfer between different ocean basins. This model efficiently determines the temporal evolution of the ocean's stratification, ventilation and overturning strength in response to perturbations in the external forcing. With this model we explore the dynamics that lead to transitions in the circulation structure between multiple, isolated cells and a three-dimensional, "figure-of-eight," circulation in which traditional upper and lower cells are interleaved. The transient model is also used to support a mechanistic explanation of the hemispheric asymmetry and phase lag associated with Dansgaard-Oeschger (DO) events during the last glacial period. In particular, the 200 year lag in southern hemisphere temperatures, following a perturbation in North Atlantic deep water formation, depends critically on the migration of Southern Ocean isopycnal outcropping in response to low-latitude stratification changes. Our results provide a self-consistent dynamical framework to explain various ocean overturning transitions that have occurred over the Earth's last 100,000 years, and motivate an exploration of these mechanisms in more sophisticated climate models.

Multi-geodetic characterization of the seasonal signal at the CERGA geodetic reference, France

NASA Astrophysics Data System (ADS)

Memin, A.; Viswanathan, V.; Fienga, A.; Santamaría-Gómez, A.; Boy, J. P.

2016-12-01

Crustal deformations due to surface-mass loading account for a significant part of the variability in geodetic time series. A perfect understanding of the loading signal observed by geodetic techniques should help in improving terrestrial reference frame (TRF) realizations. Yet, discrepancies between crustal motion estimates from models of surface-mass loading and observations are still too large so that no model is currently recommended by the IERS for reducing the data. We investigate the discrepancy observed in the seasonal variations of the CERGA station, South of France.We characterize the seasonal motions of the reference geodetic station CERGA from GNSS, SLR and LLR. We compare the station motion observed with GNSS and SLR and we estimate changes in the station-to-the-moon distance using an improved processing strategy. We investigate the consistency between these geodetic techniques and compare the observed station motion with that estimated using models of surface-mass change. In that regard, we compute atmospheric loading effects using surface pressure fields from ECMWF, assuming an ocean response according to the classical inverted barometer (IB) assumption, considered to be valid for periods typically exceeding a week. We also used general circulation ocean models (ECCO and GLORYS) forced by wind, heat and fresh water fluxes. The continental water storage is described using GLDAS/Noah and MERRA-land models.Using the surface-mass models, we estimate the amplitude of the seasonal vertical motion of the CERGA station ranging between 5 and 10 mm with a maximum reached in August, mostly due to hydrology. The horizontal seasonal motion of the station may reach up to 3 mm. Such a station motion should induce a change in the distance to the moon reaching up to 10 mm, large enough to be detected in LLR time series and compared to GNSS- and SLR-derived motion.

Bayesian prediction of future ice sheet volume using local approximation Markov chain Monte Carlo methods

NASA Astrophysics Data System (ADS)

Davis, A. D.; Heimbach, P.; Marzouk, Y.

2017-12-01

We develop a Bayesian inverse modeling framework for predicting future ice sheet volume with associated formal uncertainty estimates. Marine ice sheets are drained by fast-flowing ice streams, which we simulate using a flowline model. Flowline models depend on geometric parameters (e.g., basal topography), parameterized physical processes (e.g., calving laws and basal sliding), and climate parameters (e.g., surface mass balance), most of which are unknown or uncertain. Given observations of ice surface velocity and thickness, we define a Bayesian posterior distribution over static parameters, such as basal topography. We also define a parameterized distribution over variable parameters, such as future surface mass balance, which we assume are not informed by the data. Hyperparameters are used to represent climate change scenarios, and sampling their distributions mimics internal variation. For example, a warming climate corresponds to increasing mean surface mass balance but an individual sample may have periods of increasing or decreasing surface mass balance. We characterize the predictive distribution of ice volume by evaluating the flowline model given samples from the posterior distribution and the distribution over variable parameters. Finally, we determine the effect of climate change on future ice sheet volume by investigating how changing the hyperparameters affects the predictive distribution. We use state-of-the-art Bayesian computation to address computational feasibility. Characterizing the posterior distribution (using Markov chain Monte Carlo), sampling the full range of variable parameters and evaluating the predictive model is prohibitively expensive. Furthermore, the required resolution of the inferred basal topography may be very high, which is often challenging for sampling methods. Instead, we leverage regularity in the predictive distribution to build a computationally cheaper surrogate over the low dimensional quantity of interest (future ice sheet volume). Continual surrogate refinement guarantees asymptotic sampling from the predictive distribution. Directly characterizing the predictive distribution in this way allows us to assess the ice sheet's sensitivity to climate variability and change.

Obliquity-paced climate change recorded in Antarctic debris-covered glaciers

PubMed Central

Mackay, Sean L.; Marchant, David R.

2017-01-01

The degree to which debris-covered glaciers record past environmental conditions is debated. Here we describe a novel palaeoclimate archive derived from the surface morphology and internal debris within cold-based debris-covered glaciers in Antarctica. Results show that subtle changes in mass balance impart major changes in the concentration of englacial debris and corresponding surface topography, and that over the past ∼220 ka, at least, the changes are related to obliquity-paced solar radiation, manifest as variations in total summer energy. Our findings emphasize solar radiation as a significant driver of mass balance changes in high-latitude mountain systems, and demonstrate that debris-covered glaciers are among the most sensitive recorders of obliquity-paced climate variability in interior Antarctica, in contrast to most other Antarctic archives that favour eccentricity-paced forcing over the same time period. Furthermore, our results open the possibility that similar-appearing debris-covered glaciers on Mars may likewise hold clues to environmental change. PMID:28186094

Search for companions in visual binary systems using precise radial-velocity measurements

NASA Astrophysics Data System (ADS)

Katoh, Noriyuki; Itoh, Yoichi; Sato, Bun'ei

2018-05-01

The frequency of triple and quadruple systems is considered to be high in the early phase of star formation. Some multiple systems decay in the pre-main-sequence phase. The multiplicity of main-sequence stars provides clues about the evolution of binary systems. This work searched for companions of five components of visual binary systems using precise radial-velocity measurements. Their radial velocities were monitored from 2007 to 2012 using the HIgh Dispersion Echelle Spectrograph (HIDES) installed on the Okayama Astrophysical Observatory (OAO) 1.88 m reflector. In combination with previous work, this work searched for companions with an orbital period of less than 9 yr for the five bodies. We found periodic variations in the radial velocities for ADS 6190 A and BDS 10966A. The radial velocities of ADS 7311 A, 31 Dra A, and 31 Dra B show significant trends. ADS 6190 A is an SB1 binary with an orbital period of 366.2 d. The minimum mass of the secondary star is 0.5^{+0.7}_{-0.2} M_{⊙}. The radial velocity of ADS 7311 A was monitored for an observational span of 3200 d. We rejected a planetary-mass companion as the cause of a decreasing trend in the radial velocity of ADS 7311 A. This work confirmed that the periodic variation in the radial velocity of BDS 10966 A is 771.1 d. Bisector analysis did not reveal a correlation between the asymmetry of a spectral line and the radial velocity of BDS 10966 A. We rejected nonradial oscillation of the photosphere as the source of the radial velocity variation. The variation may be caused by the rotational modulation owing to surface inhomogeneity. The orbital elements of 31 Dra A derived in this paper are consistent with those in a previous paper. 31 Dra A system is an SB1 binary with a minimum mass ratio of 0.30 ± 0.08. 31 Dra B exhibits a periodic variation in radial velocity. The orbital elements derived in this work are consistent with those reported previously by others. The variation is caused by a circumstellar planet.

Linking body mass and group dynamics in an obligate cooperative breeder.

PubMed

Ozgul, Arpat; Bateman, Andrew W; English, Sinead; Coulson, Tim; Clutton-Brock, Tim H

2014-11-01

Social and environmental factors influence key life-history processes and population dynamics by affecting fitness-related phenotypic traits such as body mass. The role of body mass is particularly pronounced in cooperative breeders due to variation in social status and consequent variation in access to resources. Investigating the mechanisms underlying variation in body mass and its demographic consequences can help elucidate how social and environmental factors affect the dynamics of cooperatively breeding populations. In this study, we present an analysis of the effect of individual variation in body mass on the temporal dynamics of group size and structure of a cooperatively breeding mongoose, the Kalahari meerkat, Suricata suricatta. First, we investigate how body mass interacts with social (dominance status and number of helpers) and environmental (rainfall and season) factors to influence key life-history processes (survival, growth, emigration and reproduction) in female meerkats. Next, using an individual-based population model, we show that the models explicitly including individual variation in body mass predict group dynamics better than those ignoring this morphological trait. Body mass influences group dynamics mainly through its effects on helper emigration and dominant reproduction. Rainfall has a trait-mediated, destabilizing effect on group dynamics, whereas the number of helpers has a direct and stabilizing effect. Counteracting effects of number of helpers on different demographic rates, despite generating temporal fluctuations, stabilizes group dynamics in the long term. Our study demonstrates that social and environmental factors interact to produce individual variation in body mass and accounting for this variation helps to explain group dynamics in this cooperatively breeding population. © 2014 The Authors. Journal of Animal Ecology © 2014 British Ecological Society.

Characterizing near-surface firn from the scattered signal component of glacier surface reflections detected in airborne radio-echo sounding measurements

NASA Astrophysics Data System (ADS)

Rutishauser, A.; Grima, C.; Sharp, M. J.; Blankenship, D. D.; Young, D. A.; Cawkwell, F.; Dowdeswell, J. A.

2016-12-01

With recent summer warming, surface melt on Canadian Arctic ice caps has intensified and extended to higher elevations in ice cap accumulation areas. Consequently, more meltwater percolates into the near-surface firn, and refreezes as ice layers where firn temperatures are below freezing. This process can increase firn densification rates, causing a lowering of the glacier surface height even in the absence of mass changes. Thus, knowledge of spatio-temporal variations in the near-surface firn stratigraphy is important for interpreting altimetrically-derived estimates of ice cap mass balance. We investigate the use of the scattering signal component of glacier surface reflections in airborne radio-echo sounding (RES) measurements to characterize the near-surface firn stratigraphy. The scattering signal distribution over Devon Ice Cap is compared to firn stratigraphy derived from ground-based radar data. We identify three distinct firn facies zones at different elevation ranges. The scattered signal component changes significantly between the different firn facies zones: low scattering correlates to laterally homogeneous firn containing thin, flat and continuous ice layers at elevations above 1800 m and below 1200 m, where firn consists mainly of ice. Higher scattering values are found from 1200-1800 m where the firn contains discrete, undulating ice layers. No correlation was found between the scattering component and surface roughness. Modelled scattering values for the measured roughness were significantly less than the observed values, and did not reproduce their observed spatial distribution. This indicates that the scattering component is determined mainly by the structure of near-surface firn. Our results suggest that the scattering component of surface reflections from airborne RES measurements has potential for characterizing heterogeneity in the spatial structure of firn that is affected by melting and refreezing processes.

Gasification Characteristics of Coal/Biomass Mixed Fuels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mitchell, Reginald

2014-09-01

A research project was undertaken that had the overall objective of developing the models needed to accurately predict conversion rates of coal/biomass mixtures to synthesis gas under conditions relevant to a commercially-available coal gasification system configured to co-produce electric power as well as chemicals and liquid fuels. In our efforts to accomplish this goal, experiments were performed in an entrained flow reactor in order to produce coal and biomass chars at high heating rates and temperatures, typical of the heating rates and temperatures fuel particles experience in real systems. Mixed chars derived from coal/biomass mixtures containing up to 50% biomassmore » and the chars of the pure coal and biomass components were subjected to a matrix of reactivity tests in a pressurized thermogravimetric analyzer (TGA) in order to obtain data on mass loss rates as functions of gas temperature, pressure and composition as well as to obtain information on the variations in mass specific surface area during char conversion under kinetically-limited conditions. The experimental data were used as targets when determining the unknown parameters in the chemical reactivity and specific surface area models developed. These parameters included rate coefficients for the reactions in the reaction mechanism, enthalpies of formation and absolute entropies of adsorbed species formed on the carbonaceous surfaces, and pore structure coefficients in the model used to describe how the mass specific surface area of the char varies with conversion. So that the reactivity models can be used at high temperatures when mass transport processes impact char conversion rates, Thiele modulus – effectiveness factor relations were also derived for the reaction mechanisms developed. In addition, the reactivity model and a mode of conversion model were combined in a char-particle gasification model that includes the effects of chemical reaction and diffusion of reactive gases through particle pores and energy exchange between the particle and its environment. This char-particle gasification model is capable of predicting the average mass loss rates, sizes, apparent densities, specific surface areas, and temperatures of the char particles produced when co-firing coal and biomass to the type environments established in entrained flow gasifiers operating at high temperatures and elevated pressures.« less

Recombination energy for negatively charged excitons inside type-II core/shell spherical quantum dots

NASA Astrophysics Data System (ADS)

Chafai, A.; Essaoudi, I.; Ainane, A.; Dujardin, F.; Ahuja, R.

2018-07-01

The recombination energy of isolated neutral exciton and that of isolated negatively charged exciton inside a type-II core/shell spherical quantum dot are studied. Our investigation considers the charge-carriers effective mass discontinuity at the surface contact between the core and shell materials. Although our model omits the effect of the surface polarization, the dielectric-constant mismatch at the nanodot boundaries was taken into account. In order to achieve the exciton and negative trion energies, we proceed by a variational calculation in the framework of the envelope approximation. Our results reveal a strong correlation between the nanodot morphology and the energy spectrum of the neutral and negatively charged exciton.

Electron beam enhanced surface modification for making highly resolved structures

DOEpatents

Pitts, John R.

1986-01-01

A method for forming high resolution submicron structures on a substrate is provided by direct writing with a submicron electron beam in a partial pressure of a selected gas phase characterized by the ability to dissociate under the beam into a stable gaseous leaving group and a reactant fragment that combines with the substrate material under beam energy to form at least a surface compound. Variations of the method provide semiconductor device regions on doped silicon substrates, interconnect lines between active sites, three dimensional electronic chip structures, electron beam and optical read mass storage devices that may include color differentiated data areas, and resist areas for use with selective etching techniques.

Electron beam enhanced surface modification for making highly resolved structures

DOEpatents

Pitts, J.R.

1984-10-10

A method for forming high resolution submicron structures on a substrate is provided by direct writing with a submicron electron beam in a partial pressure of a selected gas phase characterized by the ability to dissociate under the beam into a stable gaseous leaving group and a reactant fragment that combines with the substrate material under beam energy to form at least a surface compound. Variations of the method provide semiconductor device regions on doped silicon substrates, interconnect lines between active sites, three dimensional electronic chip structures, electron beam and optical read mass storage devices that may include color differentiated data areas, and resist areas for use with selective etching techniques.

Au 329–xAg x(SR) 84 Nanomolecules: Plasmonic Alloy Faradaurate-329

DOE PAGES

Kumara, Chanaka; Zuo, Xiaobing; Cullen, David A.; ...

2015-08-10

Though significant progress has been made to improve the monodispersity of larger (>10 nm) alloy metal nanoparticles, there still exists a significant variation in nanoparticle composition, ranging from ±1000s of atoms. Here in this paper, for the first time, we report the synthesis of atomically precise (±0 metal atom variation) Au 329–xAg x(SCH 2CH 2Ph) 84 alloy nanomolecules. The composition was determined using high resolution electrospray ionization mass spectrometry. In contrast to larger (>10 nm) Au–Ag nanoparticles, the surface plasmon resonance (SPR) peak does not show a major shift, but a minor ~10 nm red-shift, upon increasing silver content. Themore » intensity of the SPR peak also varies in an intriguing manner, where a dampening is observed with medium silver incorporation, and a significant sharpening is observed upon higher Ag content. The report outlines (a) an unprecedented advance in nanoparticle mass spectrometry of high mass at atomic precision; and (b) the unexpected optical behavior of Au–Ag alloys in the region where nascent SPR emerges; specifically, in this work, the SPR-like peak does not show a major ~100 nm blue-shift with Ag alloying of Au 329 nanomolecules, as shown to be common in larger nanoparticles.« less

Longest time series of glacier mass changes in the Himalaya based on stereo imagery

NASA Astrophysics Data System (ADS)

Bolch, T.; Pieczonka, T.; Benn, D. I.

2010-12-01

Mass loss of Himalayan glaciers has wide-ranging consequences such as declining water resources, sea level rise and an increasing risk of glacial lake outburst floods (GLOFs). The assessment of the regional and global impact of glacier changes in the Himalaya is, however, hampered by a lack of mass balance data for most of the range. Multi-temporal digital terrain models (DTMs) allow glacier mass balance to be calculated since the availability of stereo imagery. Here we present the longest time series of mass changes in the Himalaya and show the high value of early stereo spy imagery such as Corona (years 1962 and 1970) aerial images and recent high resolution satellite data (Cartosat-1) to calculate a time series of glacier changes south of Mt. Everest, Nepal. We reveal that the glaciers are significantly losing mass with an increasing rate since at least ~1970, despite thick debris cover. The specific mass loss is 0.32 ± 0.08 m w.e. a-1, however, not higher than the global average. The spatial patterns of surface lowering can be explained by variations in debris-cover thickness, glacier velocity, and ice melt due to exposed ice cliffs and ponds.

neoPASCAL: A Cubesat-based approach to validate Mars GCMs using a network of landed sensors

NASA Astrophysics Data System (ADS)

Moores, John; Podmore, Hugh; Lee, Regina S. K.; Haberle, Robert

2017-10-01

Beginning in the 1990s, concepts for a network of 15-20 small (12.8 kg) landers to measure surface pressure across Mars were proposed (Merrihew et al., 1996). Such distributed measurements were seen as particularly valuable as they held the promise of validating Mars Global Circulation Models (GCMs), for which the diurnal and seasonal variations in surface pressure may be diagnostically related to atmospheric parameters (Haberle et al., 1996). MicroMET, later renamed PASCAL, was a Discovery contender, however, the total mass required for the 20 landers and a support orbiter presented a challenge compared to the delivered science.In the 20 years since this concept originated, miniaturization of spacecraft systems, sensors and components has made substantial progress. Several small planetary science spacecraft based on the CubeSat design approach will launch in the next few years. Yet, only one meteorological station (REMS) currently operates on the surface of Mars. Meanwhile, the output from atmospheric models have become ever more critical for understanding key Martian geological processes including volatile transport, identifying the extent and persistence of surface brines, understanding the sources and sinks of methane and investigating the past climate of Mars, to name only a few areas.As such, it is time to reconsider the PASCAL concept. We find that modern equipment opens up payload space in the original 12.8 kg entry-vehicles from 23 g to nearly 1 kg, sufficient for adding small imagers, spectrometers and other additional or alternate payloads to examine atmosphere and surface over a wide geographic range of settings. If, instead, we seek the minimum solution for spacecraft mass, we find that a pressure-sensing vehicle would mass < 250 g at entry making these spacecraft appealing secondary payloads for future Mars missions.

Crustal deformation at very long baseline interferometry sites due to seasonal air-mass and ground water variations

NASA Technical Reports Server (NTRS)

Stolz, A.; Larden, D. R.

1980-01-01

The seasonal deformation normal to the Earth's surface was calculated at stations involved or interested in very long baseline interferometry (VLBI) geodesy and at hypothetical sites in Australia and Brazil using global atmospheric pressure data, values for groundwater storage, and load Love numbers deduced from current Earth models. It was found that the annual range of deformation approached the centimeter level measuring potential of the VLBI technqiue at Greenbank, Haystack, and the Brazil site.

Conditions and constraints of food processing in space

NASA Technical Reports Server (NTRS)

Fu, B.; Nelson, P. E.; Mitchell, C. A. (Principal Investigator)

1994-01-01

Requirements and constraints of food processing in space include a balanced diet, food variety, stability for storage, hardware weight and volume, plant performance, build-up of microorganisms, and waste processing. Lunar, Martian, and space station environmental conditions include variations in atmosphere, day length, temperature, gravity, magnetic field, and radiation environment. Weightlessness affects fluid behavior, heat transfer, and mass transfer. Concerns about microbial behavior include survival on Martian and lunar surfaces and in enclosed environments. Many present technologies can be adapted to meet space conditions.

Cross-scale modelling of transpiration from stomata via the leaf boundary layer

PubMed Central

Defraeye, Thijs; Derome, Dominique; Verboven, Pieter; Carmeliet, Jan; Nicolai, Bart

2014-01-01

Background and Aims Leaf transpiration is a key parameter for understanding land surface–climate interactions, plant stress and plant structure–function relationships. Transpiration takes place at the microscale level, namely via stomata that are distributed discretely over the leaf surface with a very low surface coverage (approx. 0·2–5 %). The present study aims to shed more light on the dependency of the leaf boundary-layer conductance (BLC) on stomatal surface coverage and air speed. Methods An innovative three-dimensional cross-scale modelling approach was applied to investigate convective mass transport from leaves, using computational fluid dynamics. The gap between stomatal and leaf scale was bridged by including all these scales in the same computational model (10−5–10−1 m), which implies explicitly modelling individual stomata. Key Results BLC was strongly dependent on stomatal surface coverage and air speed. Leaf BLC at low surface coverage ratios (CR), typical for stomata, was still relatively high, compared with BLC of a fully wet leaf (hypothetical CR of 100 %). Nevertheless, these conventional BLCs (CR of 100 %), as obtained from experiments or simulations on leaf models, were found to overpredict the convective exchange. In addition, small variations in stomatal CR were found to result in large variations in BLCs. Furthermore, stomata of a certain size exhibited a higher mass transfer rate at lower CRs. Conclusions The proposed cross-scale modelling approach allows us to increase our understanding of transpiration at the sub-leaf level as well as the boundary-layer microclimate in a way currently not feasible experimentally. The influence of stomatal size, aperture and surface density, and also flow-field parameters can be studied using the model, and prospects for further improvement of the model are presented. An important conclusion of the study is that existing measures of conductances (e.g. from artificial leaves) can be significantly erroneous because they do not account for microscopic stomata, but instead assume a uniform distribution of evaporation such as found for a fully-wet leaf. The model output can be used to correct or upgrade existing BLCs or to feed into higher-scale models, for example within a multiscale framework. PMID:24510217

Mars Exospheric studies with MENCA on a Mars Orbiter

NASA Astrophysics Data System (ADS)

Bhardwaj, Anil; Menca Team

2012-07-01

The study of Martian exosphere is important for understanding the escape rate of Martian atmosphere and its impact on Mars' climate change. The neutral density distribution and the composition of Martian exosphere still remain largely unexplored. There are no in-situ measurements of the Martian exosphere; only a few remote sensing measurements have been made and some modelling studies are carried out. We proposed to fly a neutral mass spectrometer, namely "MENCA" (Mars Exospheric Neutral Composition Analyser) to explore the Martian exospheric neutral density and composition at an altitude of ~500 km and above from the surface of Mars, and to study its radial and diurnal variations. MENCA is based on the technique of quadrupole mass spectrometry and has the mass range of 1-300 amu with unit mass resolution. (*) MENCA Team includes: S.V. Mohankumar, T. P. Das, P. Sreelatha, P. Pradeepkumar, B. Sunder, Amarnath Nandi, Neha Naik, G. Supriya, Vipin K. Yadav, M. B. Dhanya, R. Satheesh Thampi, G. P. Padmanabhan

On the probability distribution function of the mass surface density of molecular clouds. II.

NASA Astrophysics Data System (ADS)

Fischera, Jörg

2014-11-01

The probability distribution function (PDF) of the mass surface density of molecular clouds provides essential information about the structure of molecular cloud gas and condensed structures out of which stars may form. In general, the PDF shows two basic components: a broad distribution around the maximum with resemblance to a log-normal function, and a tail at high mass surface densities attributed to turbulence and self-gravity. In a previous paper, the PDF of condensed structures has been analyzed and an analytical formula presented based on a truncated radial density profile, ρ(r) = ρc/ (1 + (r/r0)2)n/ 2 with central density ρc and inner radius r0, widely used in astrophysics as a generalization of physical density profiles. In this paper, the results are applied to analyze the PDF of self-gravitating, isothermal, pressurized, spherical (Bonnor-Ebert spheres) and cylindrical condensed structures with emphasis on the dependence of the PDF on the external pressure pext and on the overpressure q-1 = pc/pext, where pc is the central pressure. Apart from individual clouds, we also consider ensembles of spheres or cylinders, where effects caused by a variation of pressure ratio, a distribution of condensed cores within a turbulent gas, and (in case of cylinders) a distribution of inclination angles on the mean PDF are analyzed. The probability distribution of pressure ratios q-1 is assumed to be given by P(q-1) ∝ q-k1/ (1 + (q0/q)γ)(k1 + k2) /γ, where k1, γ, k2, and q0 are fixed parameters. The PDF of individual spheres with overpressures below ~100 is well represented by the PDF of a sphere with an analytical density profile with n = 3. At higher pressure ratios, the PDF at mass surface densities Σ ≪ Σ(0), where Σ(0) is the central mass surface density, asymptotically approaches the PDF of a sphere with n = 2. Consequently, the power-law asymptote at mass surface densities above the peak steepens from Psph(Σ) ∝ Σ-2 to Psph(Σ) ∝ Σ-3. The corresponding asymptote of the PDF of cylinders for the large q-1 is approximately given by Pcyl(Σ) ∝ Σ-4/3(1 - (Σ/Σ(0))2/3)-1/2. The distribution of overpressures q-1 produces a power-law asymptote at high mass surface densities given by ∝ Σ-2k2 - 1 (spheres) or ∝ Σ-2k2 (cylinders). Appendices are available in electronic form at http://www.aanda.org

Analyses of the long-range transport of nitrogeneous species through the atmosphere from the Asian continent using observational data at Cape Hedo, Okinawa, and CMAQ postanalyses

NASA Astrophysics Data System (ADS)

Sadanaga, Y.; Bandow, H.; Uno, I.; Sera, T.; Yuba, A.; Takenaka, N.; Takami, A.; Kurokawa, J.; Hatakeyama, S.

2010-12-01

The long-term monitoring of air quality has been continuing at the Cape Hedo Atmosphere and Aerosol Monitoring Station (CHAAMS) in Okinawa, Japan in terms of assessing the environmental impact and biogeochemical effect to the marine-surface activities by the economic growth of Asian continent. Among the monitoring data, total odd nitrogen oxides (NOy), HNO3, particulate nitrate (NO3-(p)), NH3, NH4+ and SO42- were analyzed for the period from 16 March to 13 April 2008 as well as the postanalyses of those species by the Community Muti-scale Air Quality model (CMAQ) of those species. NOy and total nitrate (TN = HNO3 + NO3-(p)) concentrations from China (CH) air mass origin were high during the observational period in both observed and model-calculated result. The long-range transport of odd nitrogen species from the Asian continent is supported with respect to both the CMAQ postanalyses and the observations. HNO3 and NO3-(p) concentrations from CH air mass origin were also high during the observational period. However, the HNO3 diurnal variation with daytime peak and nighttime lows suggests that HNO3 around the CHAAMS forms photochemically in situ or in areas relatively close to the CHAAMS. The maximum and minimum concentrations of NH3 were observed at Pacific Ocean (PO) and Middle China air mass origins, respectively, and the observed NH3 concentrations from PO air mass origin were highest. NH3 concentration calculated by the CMAQ failed to reproduce observed variation, this is because the horizontal resolution of CMAQ (-20km) is not sufficient to allocate the land surface/vegetation base NH3 emission. NH4+ and SO42- concentrations from CH air mass origin were high during the observational period for both the observation and the CMAQ calculation. As well as the case of NOy and TN, the long-range transport of ammonium and sulfur compounds from the Asian continent is also supported in terms of both the CMAQ postanalyses and the observations.

Glacier mass variations from recent ITSG-Grace solutions: Experiences with the point-mass modeling technique in the framework of project SPICE.

NASA Astrophysics Data System (ADS)

Reimond, S.; Klinger, B.; Krauss, S.; Mayer-Gürr, T.; Eicker, A.; Zemp, M.

2017-12-01

In recent years, remotely sensed observations have become one of the most ubiquitous and valuable sources of information for glacier monitoring. In addition to altimetry and interferometry data (as observed, e.g., by the CryoSat-2 and TanDEM-X satellites), time-variable gravity field data from the GRACE satellite mission has been used by several authors to assess mass changes in glacier systems. The main challenges in this context are i) the limited spatial resolution of GRACE, ii) the gravity signal attenuation in space and iii) the problem of isolating the glaciological signal from the gravitational signatures as detected by GRACE.In order to tackle the challenges i) and ii), we thoroughly investigate the point-mass modeling technique to represent the local gravity field. Instead of simply evaluating global spherical harmonics, we operate on the normal equation level and make use of GRACE K-band ranging data (available since April 2002) processed at the Graz University of Technology. Assessing such small-scale mass changes from space-borne gravimetric data is an ill-posed problem, which we aim to stabilize by utilizing a Genetic Algorithm based Tikhonov regularization. Concerning issue iii), we evaluate three different hydrology models (i.e. GLDAS, LSDM and WGHM) for validation purposes and the derivation of error bounds. The non-glaciological signal is calculated for each region of interest and reduced from the GRACE results.We present mass variations of several alpine glacier systems (e.g. the European Alps, Svalbard or Iceland) and compare our results to glaciological observations provided by the World Glacier Monitoring Service (WGMS) and alternative inversion methods (surface density modeling).

Articular scaling and body mass estimation in platyrrhines and catarrhines: Modern variation and application to fossil anthropoids.

PubMed

Perry, Jonathan M G; Cooke, Siobhán B; Runestad Connour, Jacqueline A; Burgess, M Loring; Ruff, Christopher B

2018-02-01

Body mass is an important component of any paleobiological reconstruction. Reliable skeletal dimensions for making estimates are desirable but extant primate reference samples with known body masses are rare. We estimated body mass in a sample of extinct platyrrhines and Fayum anthropoids based on four measurements of the articular surfaces of the humerus and femur. Estimates were based on a large extant reference sample of wild-collected individuals with associated body masses, including previously published and new data from extant platyrrhines, cercopithecoids, and hominoids. In general, scaling of joint dimensions is positively allometric relative to expectations of geometric isometry, but negatively allometric relative to expectations of maintaining equivalent joint surface areas. Body mass prediction equations based on articular breadths are reasonably precise, with %SEEs of 17-25%. The breadth of the distal femoral articulation yields the most reliable estimates of body mass because it scales similarly in all major anthropoid taxa. Other joints scale differently in different taxa; therefore, locomotor style and phylogenetic affinity must be considered when calculating body mass estimates from the proximal femur, proximal humerus, and distal humerus. The body mass prediction equations were applied to 36 Old World and New World fossil anthropoid specimens representing 11 taxa, plus two Haitian specimens of uncertain taxonomic affinity. Among the extinct platyrrhines studied, only Cebupithecia is similar to large, extant platyrrhines in having large humeral (especially distal) joints. Our body mass estimates differ from each other and from published estimates based on teeth in ways that reflect known differences in relative sizes of the joints and teeth. We prefer body mass estimators that are biomechanically linked to weight-bearing, and especially those that are relatively insensitive to differences in locomotor style and phylogenetic history. Whenever possible, extant reference samples should be chosen to match target fossils in joint proportionality. Copyright © 2017 Elsevier Ltd. All rights reserved.

On 7Li Enrichment by Low-Mass Metal-Poor Red Giant Branch Stars.

PubMed

de La Reza R; da Silva L; Drake; Terra

2000-06-01

First-ascent red giants with strong and very strong Li lines have just been discovered in globular clusters. Using the stellar internal prompt (7)Li enrichment-mass-loss scenario, we explore the possibility of (7)Li enrichment in the interstellar matter of the globular cluster M3 produced by these Li-rich giants. We found that enrichment as large as 70% or more compared to the initial (7)Li content of M3 can be obtained during the entire life of this cluster. However, because M3 will cross into the Galactic plane several times, the new (7)Li will be very probably removed by ram pressure into the disk. Globular clusters appear then as possible new sources of (7)Li in the Galactic disk. It is also suggested that the known Na/Al variations in stars of globular clusters could be somehow related to the (7)Li variations and that the cool bottom process mixing mechanism acting in the case of (7)Li could also play a role in the case of Na and Al surface enrichments.

Spatial distribution and seasonal variation of four current-use pesticides (CUPs) in air and surface water of the Bohai Sea, China.

PubMed

Liu, Lin; Tang, Jianhui; Zhong, Guangcai; Zhen, Xiaomei; Pan, Xiaohui; Tian, Chongguo

2018-04-15

Current-use pesticides (CUPs) are widely used in agriculture, and some are listed as persistent organic pollutants (POPs) due to their bioaccumulative and toxic properties. China is one of the largest producers and users of pesticides in the world. However, very limited data are available about the environmental fates of CUPs. Four CUPs (trifluralin, chlorothalonil, chlorpyrifos, and dicofol) in surface seawater and low atmospheric samples taken during research cruises on the Bohai Sea in August and December 2016 and February 2017 were analyzed, we added the spring data sampled in May 2012 to the discussion of seasonal variation. In our study, chlorpyrifos was the most abundant CUPs in the gas phase with a mean abundance of 59.06±126.94pgm -3 , and dicofol had the highest concentration dissolved in seawater (mean: 115.94±123.16pgL -1 ). The concentrations of all target compounds were higher during May and August due to intensive use and relatively high temperatures in the spring and summer. Backward trajectories indicated that air masses passing through the eastern coast of the Bohai Sea contained high concentrations of pollutants, while the air masses from the Bohai and Yellow Seas were less polluted. The high concentration of pollutants in seawater was not only influenced by high yields from the source region of production or usage, but also by input from polluted rivers. Volatilization from surface water was found to be an important source of trifluralin and chlorpyrifos in the air. Air-sea gas exchange of chlorothalonil underwent strong net deposition (mean FRs: 51.67), which was driven by higher concentrations in air and indicates that the Bohai Sea acted as a sink for chlorothalonil. Copyright © 2017 Elsevier B.V. All rights reserved.

Investigating the spatio-temporal variability in groundwater and surface water interactions: a multi-technique approach

NASA Astrophysics Data System (ADS)

Unland, N. P.; Cartwright, I.; Andersen, M. S.; Rau, G. C.; Reed, J.; Gilfedder, B. S.; Atkinson, A. P.; Hofmann, H.

2013-09-01

The interaction between groundwater and surface water along the Tambo and Nicholson rivers, southeast Australia, was investigated using 222Rn, Cl, differential flow gauging, head gradients, electrical conductivity (EC) and temperature profiles. Head gradients, temperature profiles, Cl concentrations and 222Rn activities all indicate higher groundwater fluxes to the Tambo River in areas of increased topographic variation where the potential to form large groundwater-surface water gradients is greater. Groundwater discharge to the Tambo River calculated by Cl mass balance was significantly lower (1.48 × 104 to 1.41 × 103 m3 day-1) than discharge estimated by 222Rn mass balance (5.35 × 105 to 9.56 × 103 m3 day-1) and differential flow gauging (5.41 × 105 to 6.30 × 103 m3 day-1) due to bank return waters. While groundwater sampling from the bank of the Tambo River was intended to account for changes in groundwater chemistry associated with bank infiltration, variations in bank infiltration between sample sites remain unaccounted for, limiting the use of Cl as an effective tracer. Groundwater discharge to both the Tambo and Nicholson rivers was the highest under high-flow conditions in the days to weeks following significant rainfall, indicating that the rivers are well connected to a groundwater system that is responsive to rainfall. Groundwater constituted the lowest proportion of river discharge during times of increased rainfall that followed dry periods, while groundwater constituted the highest proportion of river discharge under baseflow conditions (21.4% of the Tambo in April 2010 and 18.9% of the Nicholson in September 2010).

Variation of phytoplankton assemblages along the Mozambique coast as revealed by HPLC and microscopy

NASA Astrophysics Data System (ADS)

Sá, C.; Leal, M. C.; Silva, A.; Nordez, S.; André, E.; Paula, J.; Brotas, V.

2013-05-01

This study is an integrated overview of pigment and microscopic analysis of phytoplankton communities throughout the Mozambican coast. Collected samples revealed notable patterns of phytoplankton occurrence and distribution, with community structure changing between regions and sample depth. Pigment data showed Delagoa Bight, Sofala Bank and Angoche as the most productive regions throughout the sampled area. In general, micro-sized phytoplankton, particularly diatoms, were important contributors to biomass both at surface and sub-surface maximum (SSM) samples, although were almost absent in the northern stations. In contrast, nano- and pico-sized phytoplankton revealed opposing patterns. Picophytoplankton were most abundant at surface, as opposed to nanophytoplankton, which were more abundant at the SSM. Microphytoplankton were associated with cooler southern water masses, while picophytoplankton were related to warmer northern water masses. Nanophytoplankton were found to increase their contribution to biomass with increasing SSM. Microscopy information on the genera and species level revealed the diatoms Chaetoceros spp., Proboscia alata, Pseudo-nitzschia spp., Cylindrotheca closterium and Hemiaulus haukii as the most abundant taxa of the micro-sized phytoplankton. Discosphaera tubifera and Emiliania huxleyi were the most abundant coccolithophores, nano-sized phytoplankton.

Water Mass Classification on a Highly Variable Arctic Shelf Region: Origin of Laptev Sea Water Masses and Implications for the Nutrient Budget

NASA Astrophysics Data System (ADS)

Bauch, D.; Cherniavskaia, E.

2018-03-01

Large gradients and inter annual variations on the Laptev Sea shelf prevent the use of uniform property ranges for a classification of major water masses. The central Laptev Sea is dominated by predominantly marine waters, locally formed polynya waters and riverine summer surface waters. Marine waters enter the central Laptev Sea from the northwestern Laptev Sea shelf and originate from the Kara Sea or the Arctic Ocean halocline. Local polynya waters are formed in the Laptev Sea coastal polynyas. Riverine summer surface waters are formed from Lena river discharge and local melt. We use a principal component analysis (PCA) in order to assess the distribution and importance of water masses within the Laptev Sea. This mathematical method is applied to hydro-chemical summer data sets from the Laptev Sea from five years and allows to define water types based on objective and statistically significant criteria. We argue that the PCA-derived water types are consistent with the Laptev Sea hydrography and indeed represent the major water masses on the central Laptev Sea shelf. Budgets estimated for the thus defined major Laptev Sea water masses indicate that freshwater inflow from the western Laptev Sea is about half or in the same order of magnitude as freshwater stored in locally formed polynya waters. Imported water dominates the nutrient budget in the central Laptev Sea; and only in years with enhanced local polynya activity is the nutrient budget of the locally formed water in the same order as imported nutrients.

Widespread occurrence and seasonal variation of pharmaceuticals in surface waters and municipal wastewater treatment plants in central Finland.

PubMed

Lindholm-Lehto, Petra C; Ahkola, Heidi S J; Knuutinen, Juha S; Herve, Sirpa H

2016-04-01

The presence of five selected pharmaceuticals, consisting of four anti-inflammatory drugs, diclofenac, ibuprofen, ketoprofen, naproxen, and an antiepileptic drug carbamazepine, was determined at four municipal wastewater treatment plants (WWTPs) and in the receiving waterway in central Finland. The samples were taken from influents and effluents of the WWTPs and from surface water of six locations along the water way, including northern Lake Päijänne. In addition, seasonal variation in the area was determined by comparing the concentrations in the winter and summer. The samples were analyzed by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) in the multiple reaction monitoring mode. The concentrations in the influents and effluents ranged from hundreds of nanogram per liter to microgram per liter while ranged from tens of nanogram per liter in northern parts of the waterway to hundreds of nanogram per liter in northern Lake Päijänne near the city area. In addition, the concentrations were higher in the winter compared to summer time in surface water due to decreased temperature and solar irradiation. On the other hand, higher concentrations of ibuprofen, ketoprofen, and naproxen were found in summer at the WWTPs, possibly due to seasonal variations in consumption. In conclusion, there are considerable amounts of pharmaceuticals not only in influents and effluents of the WWTPs but also in lake water along the waterway and in northern Lake Päijänne.

Application of Satellite Gravimetry for Water Resource Vulnerability Assessment

NASA Technical Reports Server (NTRS)

Rodell, Matthew

2012-01-01

The force of Earth's gravity field varies in proportion to the amount of mass near the surface. Spatial and temporal variations in the gravity field can be measured via their effects on the orbits of satellites. The Gravity Recovery and Climate Experiment (GRACE) is the first satellite mission dedicated to monitoring temporal variations in the gravity field. The monthly gravity anomaly maps that have been delivered by GRACE since 2002 are being used to infer changes in terrestrial water storage (the sum of groundwater, soil moisture, surface waters, and snow and ice), which are the primary source of gravity variability on monthly to decadal timescales after atmospheric and oceanic circulation effects have been removed. Other remote sensing techniques are unable to detect water below the first few centimeters of the land surface. Conventional ground based techniques can be used to monitor terrestrial water storage, but groundwater, soil moisture, and snow observation networks are sparse in most of the world, and the countries that do collect such data rarely are willing to share them. Thus GRACE is unique in its ability to provide global data on variations in the availability of fresh water, which is both vital to life on land and vulnerable to climate variability and mismanagement. This chapter describes the unique and challenging aspects of GRACE terrestrial water storage data, examples of how the data have been used for research and applications related to fresh water vulnerability and change, and prospects for continued contributions of satellite gravimetry to water resources science and policy.

Infrared observations of Comet Austin (1990 V) by the COBE/Diffuse Infrared Background Experiment

NASA Technical Reports Server (NTRS)

Lisse, C. M.; Freudenreich, H. T.; Hauser, M. G.; Kelsall, T.; Moseley, S. H.; Reach, W. T.; Silverberg, R. F.

1994-01-01

Comet Austin was observed by the Cosmic Background Explorer (COBE)/Diffuse Infrared Background Experiment (DIRBE) with broadband photometry at 1-240 micrometers during the comet's close passage by Earth in 1990 May. A 6 deg long (6 x 10(exp 6) km) dust tail was found at 12 and 25 micrometers, with detailed structure due to variations in particle properties and mass-loss rate. The spectrum of the central 42 x 42 sq arcmin pixel was found to agree with that of a graybody of temperature 309 +/- 5 K and optical depth 7.3 +/- 10(exp -8). Comparison with IUE and ground-based obervations indicates that particles of radius greater than 20 micrometers predominate by surface area. A mass-loss rate of 510 (+510/-205) kg/s and a total tail mass of 7 +/- 2 x 10(exp 10) kg was found for a model dust tail composed of Mie spheres with a differential particle mass distribution dn/d log m approx. m(exp -0.63) and 2:1 silicate:amorphous carbon composition by mass.

RE-EXAMINING LARSON'S SCALING RELATIONSHIPS IN GALACTIC MOLECULAR CLOUDS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heyer, Mark; Krawczyk, Coleman; Duval, Julia

The properties of Galactic molecular clouds tabulated by Solomon et al. (SRBY) are re-examined using the Boston University-FCRAO Galactic Ring Survey of {sup 13}CO J = 1-0 emission. These new data provide a lower opacity tracer of molecular clouds and improved angular and spectral resolution compared with previous surveys of molecular line emission along the Galactic Plane. We calculate giant molecular cloud (GMC) masses within the SRBY cloud boundaries assuming local thermodynamic equilibrium (LTE) conditions throughout the cloud and a constant H{sub 2} to {sup 13}CO abundance, while accounting for the variation of the {sup 12}C/{sup 13}C with galactocentric radius.more » The LTE-derived masses are typically five times smaller than the SRBY virial masses. The corresponding median mass surface density of molecular hydrogen for this sample is 42 M{sub sun} pc{sup -2}, which is significantly lower than the value derived by SRBY (median 206 M{sub sun} pc{sup -2}) that has been widely adopted by most models of cloud evolution and star formation. This discrepancy arises from both the extrapolation by SRBY of velocity dispersion, size, and CO luminosity to the 1 K antenna temperature isophote that likely overestimates the GMC masses and our assumption of constant {sup 13}CO abundance over the projected area of each cloud. Owing to the uncertainty of molecular abundances in the envelopes of clouds, the mass surface density of GMCs could be larger than the values derived from our {sup 13}CO measurements. From velocity dispersions derived from the {sup 13}CO data, we find that the coefficient of the cloud structure functions, v{sup 0} = {sigma}{sub v}/R {sup 1/2}, is not constant, as required to satisfy Larson's scaling relationships, but rather systematically varies with the surface density of the cloud as {approx}{sigma}{sup 0.5} as expected for clouds in self-gravitational equilibrium.« less

Integrated firn elevation change model for glaciers and ice caps

NASA Astrophysics Data System (ADS)

Saß, Björn; Sauter, Tobias; Braun, Matthias

2016-04-01

We present the development of a firn compaction model in order to improve the volume to mass conversion of geodetic glacier mass balance measurements. The model is applied on the Arctic ice cap Vestfonna. Vestfonna is located on the island Nordaustlandet in the north east of Svalbard. Vestfonna covers about 2400 km² and has a dome like shape with well-defined outlet glaciers. Elevation and volume changes measured by e.g. satellite techniques are becoming more and more popular. They are carried out over observation periods of variable length and often covering different meteorological and snow hydrological regimes. The elevation change measurements compose of various components including dynamic adjustments, firn compaction and mass loss by downwasting. Currently, geodetic glacier mass balances are frequently converted from elevation change measurements using a constant conversion factor of 850 kg m-³ or the density of ice (917 kg m-³) for entire glacier basins. However, the natural conditions are rarely that static. Other studies used constant densities for the ablation (900 kg m-³) and accumulation (600 kg m-³) areas, whereby density variations with varying meteorological and climate conditions are not considered. Hence, each approach bears additional uncertainties from the volume to mass conversion that are strongly affected by the type and timing of the repeat measurements. We link and adapt existing models of surface energy balance, accumulation and snow and firn processes in order to improve the volume to mass conversion by considering the firn compaction component. Energy exchange at the surface is computed by a surface energy balance approach and driven by meteorological variables like incoming short-wave radiation, air temperature, relative humidity, air pressure, wind speed, all-phase precipitation, and cloud cover fraction. Snow and firn processes are addressed by a coupled subsurface model, implemented with a non-equidistant layer discretisation. On our poster we present a general view on the model structure, the input data (model forcing) and finally, an exemplary test case with basic approaches of validation.

Mass-induced sea level variations in the Red Sea from steric-corrected altimetry, GRACE, in-situ bottom pressure records, and hydrographic observations

NASA Astrophysics Data System (ADS)

Feng, Wei; Lemoine, Jean-Michel; Zhong, Min; Xu, Houze

2014-05-01

An annual amplitude of ~18 cm mass-induced sea level variations (SLV) in the Red Sea is detected from steric-corrected altimetry and the Gravity Recovery and Climate Experiment (GRACE) satellites from 2003 to 2011, which dominates the mean sea level in the region. Seawater mass variations here generally reach maximum in late January/early February. The steric component of SLV calculated from oceanographic temperature and salinity data is relatively small and peaks about seven months later than mass variations. The phase difference between the steric SLV and the mass-induced SLV indicates that when the Red Sea gains the mass from inflow water in winter, the steric SLV fall, and vice versa in summer. In-situ bottom pressure records in the eastern coast of the Red Sea validate the high mass variability observed by steric-corrected altimetry and GRACE. Furthermore, we compare the horizontal water mass flux in the Red Sea from steric-corrected altimetry and GRACE with that estimated from hydrographic observations.

Temperature Dependence of Arn+ Cluster Backscattering from Polymer Surfaces: a New Method to Determine the Surface Glass Transition Temperature.

PubMed

Poleunis, Claude; Cristaudo, Vanina; Delcorte, Arnaud

2018-01-01

In this work, time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to study the intensity variations of the backscattered Ar n + clusters as a function of temperature for several amorphous polymer surfaces (polyolefins, polystyrene, and polymethyl methacrylate). For all these investigated polymers, our results show a transition of the ratio Ar 2 + /(Ar 2 + + Ar 3 + ) when the temperature is scanned from -120 °C to +125 °C (the exact limits depend on the studied polymer). This transition generally spans over a few tens of degrees and the temperature of the inflection point of each curve is always lower than the bulk glass transition temperature (T g ) reported for the considered polymer. Due to the surface sensitivity of the cluster backscattering process (several nanometers), the presented analysis could provide a new method to specifically evaluate a surface transition temperature of polymers, with the same lateral resolution as the gas cluster beam. Graphical abstract ᅟ.

Variability in ozone and its precursor gases over the Bay of Bengal during post-monsoon

NASA Astrophysics Data System (ADS)

Mallik, Chinmay; Lal, Shyam; Venkataramani, Sethuram; Naja, Manish; Ojha, Narendra

2013-04-01

O3 and precursor gases were measured during a ship campaign over the Bay of Bengal (BoB) during 28 October -17 November, 2010. The measurements revealed the large spatial heterogeneity in trace gas levels over the BoB during post-monsoon months. The heterogeneity was attributed to unique transport patterns over north and south BoB during this period. Four distinct types of air-masses influenced by heavy pollution from nearby source regions (49% time over North-West Myanmar, East Bangladesh and North-East India), mixed type (25% time over Myanmar, Thailand and Vietnam and 75% time over East BoB), affected by long-range transport of pollutants (59% time over continental South Myanmar, Vietnam and Hong-Kong region of China) and pristine marine (99% time over oceanic regions) were identified. Among these, the continental air masses were fresher compared to marine air masses. High O3 and CO levels were observed in air masses coming from South-East Asia. O3, C4H10 and alkenes were highest in air masses arriving from eastern IGP, Bangladesh, Myanmar via the North BoB. The C2H2 to CO slope of 0.004 and C3H8 to CO slope of 0.003 indicated predominance of biofuel/biomass burning in air masses from South-East Asia. The i-C4H10 to n- C4H10 value of 0.62 indicated contributions of urban/industrial sources in air masses arriving from Bangladesh, India and North-West Myanmar. 'Potential Source Contribution Function' analysis indicated fire impacted South of Myanmar and Thailand regions as potential contributors to high CO levels above 260 ppbv measured on 14 November. Observed enhancements in surface CO during 2-3 November were attributed to the faster transport of continental pollutants associated with cyclonic winds. The O3 e-fold time of 2.3 days indicated the higher rate of O3 destruction over the BoB due to higher precursor levels. Principle component analysis indicated that transport from continental source regions played a major role in determining the chemical composition of the air masses during the campaign and presence of regional sources of NOx. Diurnal variations of surface O3 revealed effects of advection, entrainment and photochemistry. Chemical box model simulations of O3 diurnal variations over the BoB were found to be very sensitive to background O3 and NO2 levels as well as dilution.

Intercomparison of Satellite Derived Gravity Time Series with Inferred Gravity Time Series from TOPEX/POSEIDON Sea Surface Heights and Climatological Model Output

NASA Technical Reports Server (NTRS)

Cox, C.; Au, A.; Klosko, S.; Chao, B.; Smith, David E. (Technical Monitor)

2001-01-01

The upcoming GRACE mission promises to open a window on details of the global mass budget that will have remarkable clarity, but it will not directly answer the question of what the state of the Earth's mass budget is over the critical last quarter of the 20th century. To address that problem we must draw upon existing technologies such as SLR, DORIS, and GPS, and climate modeling runs in order to improve our understanding. Analysis of long-period geopotential changes based on SLR and DORIS tracking has shown that addition of post 1996 satellite tracking data has a significant impact on the recovered zonal rates and long-period tides. Interannual effects such as those causing the post 1996 anomalies must be better characterized before refined estimates of the decadal period changes in the geopotential can be derived from the historical database of satellite tracking. A possible cause of this anomaly is variations in ocean mass distribution, perhaps associated with the recent large El Nino/La Nina. In this study, a low-degree spherical harmonic gravity time series derived from satellite tracking is compared with a TOPEX/POSEIDON-derived sea surface height time series. Corrections for atmospheric mass effects, continental hydrology, snowfall accumulation, and ocean steric model predictions will be considered.

Juvenile body mass estimation: A methodological evaluation.

PubMed

Cowgill, Libby

2018-02-01

Two attempts have been made to develop body mass prediction formulae specifically for immature remains: Ruff (Ruff, C.C., 2007, Body size prediction from juvenile skeletal remains. American Journal Physical Anthropology 133, 698-716) and Robbins et al. (Robbins, G., Sciulli, P.W., Blatt, S.H., 2010. Estimating body mass in subadult human skeletons. American Journal Physical Anthropology 143, 146-150). While both were developed from the same reference population, they differ in their independent variable selection: Ruff (2008) used measures of metaphyseal and articular surface size to predict body mass in immature remains, whereas Robbins et al. (2010) relied on cross-sectional properties. Both methods perform well on independent testing samples; however, differences between the two methods exist in the predicted values. This research evaluates the differences in the body mass estimates from these two methods in seven geographically diverse skeletal samples under the age of 18 (n = 461). The purpose of this analysis is not to assess which method performs with greater accuracy or precision; instead, differences between the two methods are used as a heuristic device to focus attention on the unique challenges affecting the prediction of immature body mass estimates in particular. The two methods differ by population only in some cases, which may be a reflection of activity variation or nutritional status. In addition, cross-sectional properties almost always produce higher estimates than metaphyseal surface size across all age categories. This highlights the difficulty in teasing apart information related to body mass from that relevant to loading, particularly when the original reference population is urban/industrial. Copyright © 2017 Elsevier Ltd. All rights reserved.

Heavy Metals in the Atmosphere over the Northern Coast of Eurasia: Interannual Variations in Winter and Summer

NASA Astrophysics Data System (ADS)

Vinogradova, A. A.; Ivanova, Yu. A.

2017-12-01

Interannual variations in the level of anthropogenic contamination of the surface air in the northern areas of Russia are studied, which are related to a change in the direction of air mass transport. The transport of air and heavy metals to four sites located on territories of nature reserves on the coast of the Arctic Ocean (from the Kola Peninsula to a delta of the Lena River) in winter (January) and summer (July) is analyzed for 2000-2013. Indices of atmospheric circulation and data on the emission of pollutants into the atmosphere in cities and regions of Russia are involved in the analysis. Concentrations of seven heavy metals in the surface air are evaluated in the Arctic regions under study and their interannual, spatial, and seasonal variations are discussed. A strong interannual variability of atmospheric circulation differently influences the variations in the atmosphere contamination with different anthropogenic heavy metals in various areas of the north of Russia. The concentration ratios of heavy metals under study are different for each site in different years. The interannual and seasonal variations in the contamination level have maximum values for heavy metals arriving from most distant sources. Thus, the results of measuring the content of anthropogenic contaminants in the air of reference areas during one season or even one year should not serve a basis for longterm conclusions and forecasts. It would be also unjustified to make general conclusions on the contamination level of the environment from observation results for only one contaminant and/or only at a single site.

Spectro-Interferometry Studies of Velocity-Related Phenomena at the Surface of Stars: Pulsation and Rotation

NASA Astrophysics Data System (ADS)

Mérand, Antoine; Patru, Fabien; Aufdenberg, Jason

We illustrate here two applications of spectro-interferometry to the study of velocity fields at the surface of stars: pulsation and rotation. Stellar pulsation has been resolved spectroscopically for a long time, and interferometry has resolved stellar diameters variations due to pulsation. Combining the two provides unique insights to the study of Cepheids, in particular regarding the structure of the photosphere or investigating the infamous projection factor which biases distances measured by the Baade-Wesselink method. On the other hand, resolving the surface velocity field of rotating stars offers a unique opportunity to potentially study differential rotation in other cases than for the Sun. We also present the model we have implemented recently, as well as two applications to VLTI/AMBER Data: the pulsation of Cepheids and the rotation of intermediate mass main sequence stars.

EVIDENCE FOR A CONSTANT IMF IN EARLY-TYPE GALAXIES BASED ON THEIR X-RAY BINARY POPULATIONS

NASA Astrophysics Data System (ADS)

Zepf, Stephen E.; Maccarone, T. J.; Kundu, A.; Gonzalez, A. H.; Lehmer, B.; Maraston, C.

2014-01-01

A number of recent studies have proposed that the stellar initial mass function (IMF) of early type galaxies varies systematically as a function of galaxy mass, with higher mass galaxies having steeper IMFs. These steeper IMFs have more low-mass stars relative to the number of high mass stars, and therefore naturally result in proportionally fewer neutron stars and black holes. In this paper, we specifically predict the variation in the number of black holes and neutron stars in early type galaxies based on the IMF variation required to reproduce the observed mass-to-light ratio trends with galaxy mass. We then test whether such variations are observed by studying the field low-mass X-ray binary populations (LMXBs) of nearby early-type galaxies. These binaries are field neutron stars or black holes accreting from a low-mass donor star. We specifically compare the number of field LMXBs per K-band light in a well-studied sample of elliptical galaxies, and use this result to distinguish between an invariant IMF and one that is Kroupa/Chabrier-like at low masses and steeper at high masses. We discuss how these observations constrain the possible forms of the IMF variations and how future Chandra observations can enable sharper tests of the IMF.

Automatic Delineation of the Myocardial Wall from CT Images via Shape Segmentation and Variational Region Growing

PubMed Central

Zhu, Liangjia; Gao, Yi; Appia, Vikram; Yezzi, Anthony; Arepalli, Chesnal; Faber, Tracy; Stillman, Arthur; Tannenbaum, Allen

2014-01-01

Prognosis and diagnosis of cardiac diseases frequently require quantitative evaluation of the ventricle volume, mass, and ejection fraction. The delineation of the myocardial wall is involved in all of these evaluations, which is a challenging task due to large variations in myocardial shapes and image quality. In this work, we present an automatic method for extracting the myocardial wall of the left and right ventricles from cardiac CT images. In the method, the left and right ventricles are located sequentially, in which each ventricle is detected by first identifying the endocardium and then segmenting the epicardium. To this end, the endocardium is localized by utilizing its geometric features obtained on-line from a CT image. After that, a variational region-growing model is employed to extract the epicardium of the ventricles. In particular, the location of the endocardium of the left ventricle is determined via using an active contour model on the blood-pool surface. To localize the right ventricle, the active contour model is applied on a heart surface extracted based on the left ventricle segmentation result. The robustness and accuracy of the proposed approach is demonstrated by experimental results from 33 human and 12 pig CT images. PMID:23744658

Background aerosol over the Himalayas and Tibetan Plateau: observed characteristics of aerosol mass loading

NASA Astrophysics Data System (ADS)

Liu, Bin; Cong, Zhiyuan; Wang, Yuesi; Xin, Jinyuan; Wan, Xin; Pan, Yuepeng; Liu, Zirui; Wang, Yonghong; Zhang, Guoshuai; Wang, Zhongyan; Wang, Yongjie; Kang, Shichang

2017-01-01

To investigate the atmospheric aerosols of the Himalayas and Tibetan Plateau (HTP), an observation network was established within the region's various ecosystems, including at the Ngari, Qomolangma (QOMS), Nam Co, and Southeastern Tibetan (SET) stations. In this paper we illustrate aerosol mass loadings by integrating in situ measurements with satellite and ground-based remote sensing datasets for the 2011-2013 period, on both local and large scales. Mass concentrations of these surface atmospheric aerosols were relatively low and varied with land cover, showing a general tendency of Ngari and QOMS (barren sites) > Nam Co (grassland site) > SET (forest site). Daily averages of online PM2.5 (particulates with aerodynamic diameters below 2.5 µm) at these sites were sequentially 18.2 ± 8.9, 14.5 ± 7.4, 11.9 ± 4.9 and 11.7 ± 4.7 µg m-3. Correspondingly, the ratios of PM2.5 to total suspended particles (TSP) were 27.4 ± 6.65, 22.3 ± 10.9, 37.3 ± 11.1 and 54.4 ± 6.72 %. Bimodal mass distributions of size-segregated particles were found at all sites, with a relatively small peak in accumulation mode and a more notable peak in coarse mode. Diurnal variations in fine-aerosol masses generally displayed a bi-peak pattern at the QOMS, Nam Co and SET stations and a single-peak pattern at the Ngari station, controlled by the effects of local geomorphology, mountain-valley breeze circulation and aerosol emissions. Dust aerosol content in PM2.1 samples gave fractions of 26 % at the Ngari station and 29 % at the QOMS station, or ˜ 2-3 times that of reported results at human-influenced sites. Furthermore, observed evidence confirmed the existence of the aerodynamic conditions necessary for the uplift of fine particles from a barren land surface. Combining surface aerosol data and atmospheric-column aerosol optical properties, the TSP mass and aerosol optical depth (AOD) of the Multi-angle Imaging Spectroradiometer (MISR) generally decreased as land cover changed from barren to forest, in inverse relation to the PM2.5 ratios. The seasonality of aerosol mass parameters was land-cover dependent. Over forest and grassland areas, TSP mass, PM2.5 mass, MISR-AOD and fine-mode AOD were higher in spring and summer, followed by relatively lower values in autumn and winter. At the barren site (the QOMS station), there were inconsistent seasonal patterns between surface TSP mass (PM2.5 mass) and atmospheric column AOD (fine-mode AOD). Our findings implicate that HTP aerosol masses (especially their regional characteristics and fine-particle emissions) need to be treated sensitively in relation to assessments of their climatic effect and potential role as cloud condensation nuclei and ice nuclei.

The UF family of hybrid phantoms of the developing human fetus for computational radiation dosimetry

NASA Astrophysics Data System (ADS)

Maynard, Matthew R.; Geyer, John W.; Aris, John P.; Shifrin, Roger Y.; Bolch, Wesley

2011-08-01

Historically, the development of computational phantoms for radiation dosimetry has primarily been directed at capturing and representing adult and pediatric anatomy, with less emphasis devoted to models of the human fetus. As concern grows over possible radiation-induced cancers from medical and non-medical exposures of the pregnant female, the need to better quantify fetal radiation doses, particularly at the organ-level, also increases. Studies such as the European Union's SOLO (Epidemiological Studies of Exposed Southern Urals Populations) hope to improve our understanding of cancer risks following chronic in utero radiation exposure. For projects such as SOLO, currently available fetal anatomic models do not provide sufficient anatomical detail for organ-level dose assessment. To address this need, two fetal hybrid computational phantoms were constructed using high-quality magnetic resonance imaging and computed tomography image sets obtained for two well-preserved fetal specimens aged 11.5 and 21 weeks post-conception. Individual soft tissue organs, bone sites and outer body contours were segmented from these images using 3D-DOCTOR™ and then imported to the 3D modeling software package Rhinoceros™ for further modeling and conversion of soft tissue organs, certain bone sites and outer body contours to deformable non-uniform rational B-spline surfaces. The two specimen-specific phantoms, along with a modified version of the 38 week UF hybrid newborn phantom, comprised a set of base phantoms from which a series of hybrid computational phantoms was derived for fetal ages 8, 10, 15, 20, 25, 30, 35 and 38 weeks post-conception. The methodology used to construct the series of phantoms accounted for the following age-dependent parameters: (1) variations in skeletal size and proportion, (2) bone-dependent variations in relative levels of bone growth, (3) variations in individual organ masses and total fetal masses and (4) statistical percentile variations in skeletal size, individual organ masses and total fetal masses. The resulting series of fetal hybrid computational phantoms is applicable to organ-level and bone-level internal and external radiation dosimetry for human fetuses of various ages and weight percentiles

Surface Texturing-Plasma Nitriding Duplex Treatment for Improving Tribological Performance of AISI 316 Stainless Steel

PubMed Central

Lin, Naiming; Liu, Qiang; Zou, Jiaojuan; Guo, Junwen; Li, Dali; Yuan, Shuo; Ma, Yong; Wang, Zhenxia; Wang, Zhihua; Tang, Bin

2016-01-01

Surface texturing-plasma nitriding duplex treatment was conducted on AISI 316 stainless steel to improve its tribological performance. Tribological behaviors of ground 316 substrates, plasma-nitrided 316 (PN-316), surface-textured 316 (ST-316), and duplex-treated 316 (DT-316) in air and under grease lubrication were investigated using a pin-on-disc rotary tribometer against counterparts of high carbon chromium bearing steel GCr15 and silicon nitride Si3N4 balls. The variations in friction coefficient, mass loss, and worn trace morphology of the tested samples were systemically investigated and analyzed. The results showed that a textured surface was formed on 316 after electrochemical processing in a 15 wt % NaCl solution. Grooves and dimples were found on the textured surface. As plasma nitriding was conducted on a 316 substrate and ST-316, continuous and uniform nitriding layers were successfully fabricated on the surfaces of the 316 substrate and ST-316. Both of the obtained nitriding layers presented thickness values of more than 30 μm. The nitriding layers were composed of iron nitrides and chromium nitride. The 316 substrate and ST-316 received improved surface hardness after plasma nitriding. When the tribological tests were carried out under dry sliding and grease lubrication conditions, the tested samples showed different tribological behaviors. As expected, the DT-316 samples revealed the most promising tribological properties, reflected by the lowest mass loss and worn morphologies. The DT-316 received the slightest damage, and its excellent tribological performance was attributed to the following aspects: firstly, the nitriding layer had high surface hardness; secondly, the surface texture was able to capture wear debris, store up grease, and then provide continuous lubrication. PMID:28773996

How many stakes are required to measure the mass balance of a glacier?

USGS Publications Warehouse

Fountain, A.G.; Vecchia, A.

1999-01-01

Glacier mass balance is estimated for South Cascade Glacier and Maclure Glacier using a one-dimensional regression of mass balance with altitude as an alternative to the traditional approach of contouring mass balance values. One attractive feature of regression is that it can be applied to sparse data sets where contouring is not possible and can provide an objective error of the resulting estimate. Regression methods yielded mass balance values equivalent to contouring methods. The effect of the number of mass balance measurements on the final value for the glacier showed that sample sizes as small as five stakes provided reasonable estimates, although the error estimates were greater than for larger sample sizes. Different spatial patterns of measurement locations showed no appreciable influence on the final value as long as different surface altitudes were intermittently sampled over the altitude range of the glacier. Two different regression equations were examined, a quadratic, and a piecewise linear spline, and comparison of results showed little sensitivity to the type of equation. These results point to the dominant effect of the gradient of mass balance with altitude of alpine glaciers compared to transverse variations. The number of mass balance measurements required to determine the glacier balance appears to be scale invariant for small glaciers and five to ten stakes are sufficient.

Debris-covered Himalayan glaciers under a changing climate: observations and modelling of Khumbu Glacier, Nepal

NASA Astrophysics Data System (ADS)

Rowan, Ann; Quincey, Duncan; Egholm, David; Gibson, Morgan; Irvine-Fynn, Tristram; Porter, Philip; Glasser, Neil

2016-04-01

Many mountain glaciers are characterised in their lower reaches by thick layers of rock debris that insulate the glacier surface from solar radiation and atmospheric warming. Supraglacial debris modifies the response of these glaciers to climate change compared to glaciers with clean-ice surfaces. However, existing modelling approaches to predicting variations in the extent and mass balance of debris-covered glaciers have relied on numerical models that represent the processes governing glaciers with clean-ice surfaces, and yield conflicting results. Moreover, few data exist describing the mass balance of debris-covered glaciers and many observations are only made over short periods of time, but these data are needed to constrain and validate numerical modelling experiments. To investigate the impact of supraglacial debris on the response of a glacier to climate change, we developed a numerical model that couples the flow of ice and debris to include important feedbacks between mass balance, ice flow and debris accumulation. We applied this model to a large debris-covered Himalayan glacier - Khumbu Glacier in the Everest region of Nepal. Our results demonstrate that supraglacial debris prolongs the response of the glacier to warming air temperatures and causes lowering of the glacier surface in situ, concealing the magnitude of mass loss when compared with estimates based on glacierised area. Since the Little Ice Age, the volume of Khumbu Glacier has reduced by 34%, while glacier area has reduced by only 6%. We predict a further decrease in glacier volume of 8-10% by AD2100 accompanied by dynamic and physical detachment of the debris-covered tongue from the active glacier within the next 150 years. For five months during the 2014 summer monsoon, we measured temperature profiles through supraglacial debris and proglacial discharge on Khumbu Glacier. We found that temperatures at the ice surface beneath 0.4-0.7 m of debris were sufficient to promote considerable amounts of ablation. Moreover, although temperatures within the debris layer decreased with depth at the start of the monsoon, later in the monsoon season thicker debris (0.7 m) appeared to retain more heat close to the glacier surface than thin debris (0.4 m). Remote sensing observations indicate that Khumbu Glacier is losing mass more rapidly than is predicted by our model, particularly as ice cliffs and supraglacial ponds enhance ablation locally, and our field observations suggest an additional mechanism for enhanced mass loss.

Revised Atmospheric Angular Momentum Series Related to Earth's Variable Rotation under Consideration of Surface Topography

NASA Technical Reports Server (NTRS)

Zhou, Y. H.; Salstein, D. A.; Chen, J. L.

2006-01-01

The atmospheric angular momentum is closely related to variations in the Earth rotation. The atmospheric excitation function (AEF), or namely atmospheric effective angular momentum function, is introduced in studying the atmospheric excitation of the Earth's variable rotation. It may be separated into two portions, i.e, the "wind" terms due to the atmospheric motion relative to the mantle and the "pressure" terms due to the variations of atmospheric mass distribution evident through surface pressure changes. The AEF wind terms during the period of 1948-2004 are re-processed from the NCEP/NCAR (National Centers for Environmental Prediction-National Center for Atmospheric Research) reanalysis 6-hourly wind and pressure fields. Some previous calculations were approximate, in that the wind terms were integrated from an isobaric lower boundary of 1000 hPa. To consider the surface topography effect, however, the AEF is computed by integration using the winds from the Earth's surface to 10 hPa, the top atmospheric model level, instead of from 1000 hPa. For these two cases, only a minor difference, equivalent to approx. 0.004 milliseconds in length-of-day variation, exists with respect to the axial wind term. However, considerable differences, equivalent to 5-6 milliarcseconds in polar motion, are found regarding equatorial wind terms. We further compare the total equatorial AEF (with and without the topographic effect) with the polar motion excitation function (PMEF) during the period of 1980-2003. The equatorial AEF gets generally closer to the PMEF, and improved coherences are found between them when the topography effect is included. Keywords: Atmospheric angular momentum, Atmospheric excitation function, Earth rotation, Topography, Wind, Pressure.

Global ocean monitoring for the World Climate Research Programme.

PubMed

Revelle, R; Bretherton, F

1986-07-01

Oceanic research and modelling for the World Climate Research Program will utilize several recently-developed instruments and measuring techniques as well as well-tested, long-used instruments. Ocean-scanning satellites will map the component of the ocean-surface topography related to ocean currents and mesoscale eddies and to fluctuating water volumes caused by ocean warming and cooling. Other satellite instruments will measure the direction and magnitude of wind stress on the sea surface, surface water temperatures, the distribution of chlorophyll and other photosynthetic pigments, the characteristics of internal waves, and possible precipitation over the ocean. Networks of acoustic transponders will obtain a three-dimensional picture of the distribution of temperature from the surface down to mid-depth and of long-term changes in temperature at depth. Ocean research vessels will determine the distribution and fate of geochemical tracers and will also make high-precision, deep hydrographic casts. Ships of opportunity, using expendable instruments, will measure temperature, salinity and currents in the upper water layers. Drifting and anchored buoys will also measure these properties as well as those of the air above the sea surface. Tide gauges installed on islands and exposed coastal locations will measure variations in monthly and shorter-period mean sea level. These tide gauges will provide 'ground truth' for the satellite maps of sea-surface topography, and will also determine variations in ocean currents and temperature.All these instruments will be used in several major programs, the most ambitious of which is the World Ocean Circulation Experiment (WOCE) designed to obtain global measurements of major currents throughout the world ocean, greater understanding of the transformation of water masses, and the role of advective, convective, and turbulent processes in exchange of properties between surface and deep-ocean layers.A five- to ten-year experiment-"Tropical Oceans and Global Atmosphere (TOGA)"-will be undertaken to sudy the sequence of events of air-sea interactions in the tropical oceans and their impact on climatic variations on land-for example, variations in the strength and location of the Indian Ocean monsoon, droughts in low latitudes, and climatic fluctuations in temperate latitudes.Experimental and continuing time series will be taken at fixed locations to obtain a better picture of the magnitude and causes of ocean climate variability. National and multinational systematic repeated measurements along selected ocean transects or in specific ocean areas will be taken to determine oceanic variability and teleconnections between oceanic and atmospheric processes. Examples are the long Japanese section along the meridian of 137° E and the 'Sections' program of the USSR and several other countries in Energy-Active zones.The results from this wide range of observations and experiments will be used to guide and define mathematical models of the ocean circulation and its interactions with the atmosphere.It can be shown that biogeochemical processes in the ocean play an important role in determining the carbon dioxide content of the atmosphere and thus in causing long-term climatic changes. Variations in the biological productivity of sub-surface waters cause variations in the effectveness of the biological pump which carries organic carbon down into deeper waters where it is oxidized. Studies of ice cores from 20 000 to 30 000 yr before the present indicate that atmospheric carbon dioxide varied by a factor of 2 within times of the order of 100 yr, and these variations were accompanied by large excursions in atmospheric temperature. Thus, ocean climatic monitoring must take into account measurements of both biological and physical variations in the ocean.

Inhibition and inactivation of Salmonella typhimurium biofilms from polystyrene and stainless steel surfaces by essential oils and phenolic constituent carvacrol.

PubMed

Soni, Kamlesh A; Oladunjoye, Ademola; Nannapaneni, Ramakrishna; Schilling, M Wes; Silva, Juan L; Mikel, Benjy; Bailey, R Hartford

2013-02-01

Persistence of Salmonella biofilms within food processing environments is an important source of Salmonella contamination in the food chain. In this study, essential oils of thyme and oregano and their antimicrobial phenolic constituent carvacrol were evaluated for their ability to inhibit biofilm formation and inactivate preformed Salmonella biofilms. A crystal violet staining assay and CFU measurements were utilized to quantify biofilm cell mass, with evaluating factors such as strain variation, essential oil type, their concentrations, exposure time, as well as biofilm formation surface. Of the three Salmonella strains, Salmonella Typhimurium ATCC 23564 and Salmonella Typhimurium ATCC 19585 produced stronger biofilms than Salmonella Typhimurium ATCC 14028. Biofilm formation by different Salmonella strains was 1.5- to 2-fold higher at 22°C than at 30 or 37°C. The presence of nonbiocidal concentrations of thyme oil, oregano oil, and phenolic carvacrol at 0.006 to 0.012% suppressed Salmonella spp. biofilm formation 2- to 4-fold, but could not completely eliminate biofilm formation. There was high correlation in terms of biofilm inactivation, as determined by the crystal violet-stained optical density (at a 562-nm wavelength) readings and the viable CFU counts. Reduction of biofilm cell mass was dependent on antimicrobial concentration. A minimum concentration of 0.05 to 0.1% of these antimicrobial agents was needed to reduce a 7-log CFU biofilm mass to a nondetectable level on both polystyrene and stainless steel surfaces within 1 h of exposure time.

Spectroscopic Infrared Extinction Mapping as a Probe of Grain Growth in IRDCs

NASA Astrophysics Data System (ADS)

Lim, Wanggi; Carey, Sean J.; Tan, Jonathan C.

2015-11-01

We present spectroscopic tests of MIR to FIR extinction laws in IRDC G028.36+00.07, a potential site of massive star and star cluster formation. Lim & Tan developed methods of FIR extinction mapping of this source using Spitzer-MIPS 24 μm and Herschel-PACS 70 μm images, and by comparing to MIR Spitzer-IRAC 3-8 μm extinction maps, found tentative evidence for grain growth in the highest mass surface density regions. Here we present results of spectroscopic infrared extinction mapping using Spitzer-IRS (14-38 μm) data of the same Infrared dark cloud (IRDC). These methods allow us to first measure the SED of the diffuse Galactic interstellar medium that is in the foreground of the IRDC. We then carry out our primary investigation of measuring the MIR to FIR opacity law and searching for potential variations as a function of mass surface density within the IRDC. We find relatively flat, featureless MIR-FIR opacity laws that lack the ˜12 and ˜35 μm features associated with the thick water ice mantle models of Ossenkopf & Henning. Their thin ice mantle models and the coagulating aggregate dust models of Ormel et al. are a generally better match to the observed opacity laws. We also find evidence for generally flatter MIR to FIR extinction laws as mass surface density increases, strengthening the evidence for grain and ice mantle growth in higher density regions.

SPECTROSCOPIC INFRARED EXTINCTION MAPPING AS A PROBE OF GRAIN GROWTH IN IRDCs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lim, Wanggi; Carey, Sean J.; Tan, Jonathan C.

We present spectroscopic tests of MIR to FIR extinction laws in IRDC G028.36+00.07, a potential site of massive star and star cluster formation. Lim and Tan developed methods of FIR extinction mapping of this source using Spitzer-MIPS 24 μm and Herschel-PACS 70 μm images, and by comparing to MIR Spitzer-IRAC 3–8 μm extinction maps, found tentative evidence for grain growth in the highest mass surface density regions. Here we present results of spectroscopic infrared extinction mapping using Spitzer-IRS (14–38 μm) data of the same Infrared dark cloud (IRDC). These methods allow us to first measure the SED of the diffusemore » Galactic interstellar medium that is in the foreground of the IRDC. We then carry out our primary investigation of measuring the MIR to FIR opacity law and searching for potential variations as a function of mass surface density within the IRDC. We find relatively flat, featureless MIR–FIR opacity laws that lack the ∼12 and ∼35 μm features associated with the thick water ice mantle models of Ossenkopf and Henning. Their thin ice mantle models and the coagulating aggregate dust models of Ormel et al. are a generally better match to the observed opacity laws. We also find evidence for generally flatter MIR to FIR extinction laws as mass surface density increases, strengthening the evidence for grain and ice mantle growth in higher density regions.« less

Flight control actuation system

NASA Technical Reports Server (NTRS)

Wingett, Paul T. (Inventor); Gaines, Louie T. (Inventor); Evans, Paul S. (Inventor); Kern, James I. (Inventor)

2004-01-01

A flight control actuation system comprises a controller, electromechanical actuator and a pneumatic actuator. During normal operation, only the electromechanical actuator is needed to operate a flight control surface. When the electromechanical actuator load level exceeds 40 amps positive, the controller activates the pneumatic actuator to offset electromechanical actuator loads to assist the manipulation of flight control surfaces. The assistance from the pneumatic load assist actuator enables the use of an electromechanical actuator that is smaller in size and mass, requires less power, needs less cooling processes, achieves high output forces and adapts to electrical current variations. The flight control actuation system is adapted for aircraft, spacecraft, missiles, and other flight vehicles, especially flight vehicles that are large in size and travel at high velocities.

The Ice, Cloud, and land Elevation Satellite (ICESat) Summary Mission Timeline and Performance Relative to Pre-Launch Mission Success Criteria

NASA Technical Reports Server (NTRS)

Webb, Charles E.; Zwally H. Jay; Abdalati, Waleed

2012-01-01

The Ice, Cloud and land Elevation Satellite (ICESat) mission was conceived, primarily, to quantify the spatial and temporal variations in the topography of the Greenland and Antarctic ice sheets. It carried on board the Geoscience Laser Altimeter System (GLAS), which measured the round-trip travel time of a laser pulse emitted from the satellite to the surface of the Earth and back. Each range derived from these measurements was combined with precise, concurrent orbit and pointing information to determine the location of the laser spot centroid on the Earth. By developing a time series of precise topographic maps for each ice sheet, changes in their surface elevations can be used to infer their mass balances.

Flight control actuation system

NASA Technical Reports Server (NTRS)

Wingett, Paul T. (Inventor); Gaines, Louie T. (Inventor); Evans, Paul S. (Inventor); Kern, James I. (Inventor)

2006-01-01

A flight control actuation system comprises a controller, electromechanical actuator and a pneumatic actuator. During normal operation, only the electromechanical actuator is needed to operate a flight control surface. When the electromechanical actuator load level exceeds 40 amps positive, the controller activates the pneumatic actuator to offset electromechanical actuator loads to assist the manipulation of flight control surfaces. The assistance from the pneumatic load assist actuator enables the use of an electromechanical actuator that is smaller in size and mass, requires less power, needs less cooling processes, achieves high output forces and adapts to electrical current variations. The flight control actuation system is adapted for aircraft, spacecraft, missiles, and other flight vehicles, especially flight vehicles that are large in size and travel at high velocities.

Photovoltaic power system operation in the Mars environment

NASA Technical Reports Server (NTRS)

Appelbaum, Joseph; Flood, Dennis J.

1989-01-01

Detailed information on the environmental conditions on Mars are very desirable for the design of photovoltaic systems for establishing outposts on the Martian surface. The variation of solar insolation (global, direct, and diffuse) at the Viking lander's locations is addressed. It can be used, to a first approximation, for other latitudes. The radiation data is based on measured optical depth of the Martian atmosphere derived from images taken of the sun with a special diode on the Viking cameras; and computation based on multiple wavelength and multiple scattering of the solar radiation. The data are used to make estimates of photovoltaic system power, area and mass for a surface power system using regenerative fuel cells for storage and nighttime operation.

Method and apparatus for analyzing the internal chemistry and compositional variations of materials and devices

DOEpatents

Kazmerski, Lawrence L.

1989-01-01

A method and apparatus is disclosed for obtaining and mapping chemical compositional data for solid devices. It includes a SIMS mass analyzer or similar system capable of being rastered over a surface of the solid to sample the material at a pattern of selected points, as the surface is being eroded away by sputtering or a similar process. The data for each point sampled in a volume of the solid is digitally processed and indexed by element or molecule type, exact spacial location within the volume, and the concentration levels of the detected element or molecule types. This data can then be recalled and displayed for any desired planar view in the volume.

Method and apparatus for analyzing the internal chemistry and compositional variations of materials and devices

DOEpatents

Kazmerski, L.L.

1985-04-30

A method and apparatus is disclosed for obtaining and mapping chemical compositional data for solid devices. It includes a SIMS mass analyzer or similar system capable of being rastered over a surface of the solid to sample the material at a pattern of selected points, as the surface is being eroded away by sputtering or a similar process. The data for each point sampled in a volume of the solid is digitally processed and indexed by element or molecule type, exact spacial location within the volume, and the concentration levels of the detected element or molecule types. This data can then be recalled and displayed for any desired planar view in the volume.

Tunable surface plasmon devices

DOEpatents

Shaner, Eric A [Rio Rancho, NM; Wasserman, Daniel [Lowell, MA

2011-08-30

A tunable extraordinary optical transmission (EOT) device wherein the tunability derives from controlled variation of the dielectric constant of a semiconducting material (semiconductor) in evanescent-field contact with a metallic array of sub-wavelength apertures. The surface plasmon resonance wavelength can be changed by changing the dielectric constant of the dielectric material. In embodiments of this invention, the dielectric material is a semiconducting material. The dielectric constant of the semiconducting material in the metal/semiconductor interfacial region is controllably adjusted by adjusting one or more of the semiconductor plasma frequency, the concentration and effective mass of free carriers, and the background high-frequency dielectric constant in the interfacial region. Thermal heating and/or voltage-gated carrier-concentration changes may be used to variably adjust the value of the semiconductor dielectric constant.

A Review of Global Satellite-Derived Snow Products

NASA Technical Reports Server (NTRS)

Frei, Allan; Tedesco, Marco; Lee, Shihyan; Foster, James; Hall, Dorothy K.; Kelly, Richard; Robinson, David A.

2011-01-01

Snow cover over the Northern Hemisphere plays a crucial role in the Earth s hydrology and surface energy balance, and modulates feedbacks that control variations of global climate. While many of these variations are associated with exchanges of energy and mass between the land surface and the atmosphere, other expected changes are likely to propagate downstream and affect oceanic processes in coastal zones. For example, a large component of the freshwater flux into the Arctic Ocean comes from snow melt. The timing and magnitude of this flux affects biological and thermodynamic processes in the Arctic Ocean, and potentially across the globe through their impact on North Atlantic Deep Water formation. Several recent global remotely sensed products provide information at unprecedented temporal, spatial, and spectral resolutions. In this article we review the theoretical underpinnings and characteristics of three key products. We also demonstrate the seasonal and spatial patterns of agreement and disagreement amongst them, and discuss current and future directions in their application and development. Though there is general agreement amongst these products, there can be disagreement over certain geographic regions and under conditions of ephemeral, patchy and melting snow

A Review of Global Satellite-Derived Snow Products

NASA Technical Reports Server (NTRS)

Frei, Allan; Tedesco, Marco; Lee, Shihyan; Foster, James; Hall, Dorothy K.; Kelly, Richard; Robinson, David A.

2011-01-01

Snow cover over the Northern Hemisphere plays a crucial role in the Earth's hydrology and surface energy balance, and modulates feedbacks that control variations of global climate. While many of these variations are associated with exchanges of energy and mass between the land surface and the atmosphere, other expected changes are likely to propagate downstream and affect oceanic processes in coastal zones. For example, a large component of the freshwater flux into the Arctic Ocean comes from snow melt. The timing and magnitude of this flux affects biological and thermodynamic processes in the Arctic Ocean, and potentially across the globe through their impact on North Atlantic Deep Water formation. Several recent global remotely sensed products provide information at unprecedented temporal, spatial, and spectral resolutions. In this article we review the theoretical underpinnings and characteristics of three key products. We also demonstrate the seasonal and spatial patterns of agreement and disagreement amongst them, and discuss current and future directions in their application and development. Though there is general agreement amongst these products, there can be disagreement over certain geographic regions and under conditions of ephemeral, patchy and melting snow.

A Review of Global Satellite-derived Snow Products

NASA Technical Reports Server (NTRS)

Frei, Allan; Tedesco, Marco; Lee, Shihyan; Foster, James; Hall, Dorothy K.; Kelly, Richard; Robinson, David A.

2012-01-01

Snow cover over the Northern Hemisphere plays a crucial role in the Earth's hydrology and surface energy balance, and modulates feedbacks that control variations of global climate. While many of these variations are associated with exchanges of energy and mass between the land surface and the atmosphere, other expected changes are likely to propagate downstream and affect oceanic processes in coastal zones. For example, a large component of the freshwater flux into the Arctic Ocean comes from snow melt. The timing and magnitude of this flux affects biological and thermodynamic processes in the Arctic Ocean, and potentially across the globe through their impact on North Atlantic Deep Water formation. Several recent global remotely sensed products provide information at unprecedented temporal, spatial, and spectral resolutions. In this article we review the theoretical underpinnings and characteristics of three key products. We also demonstrate the seasonal and spatial patterns of agreement and disagreement amongst them, and discuss current and future directions in their application and development. Though there is general agreement amongst these products, there can be disagreement over certain geographic regions and under conditions of ephemeral, patchy and melting snow.

Uncovering glacier dynamics beneath a debris mantle

NASA Astrophysics Data System (ADS)

Lefeuvre, P.-M.; Ng, F. S. L.

2012-04-01

Debris-covered glaciers (DCGs) have an extensive sediment mantle whose low albedo influences their surface energy balance to cause a buffering effect that could enhance or reduce ablation rates depending on the sediment thickness. The last effect suggests that some DCGs may be less sensitive to climate change and survive for longer than debris-free (or 'clean') glaciers under sustained climatic warming. However, the origin of DCGs is debated and the precise impact of the debris mantle on their flow dynamics and surface geometry has not been quantified. Here we investigate these issues with a numerical model that encapsulates ice-flow physics and surface debris evolution and transport along a glacier flow-line, as well as couples these with glacier mass balance. We model the impact of surface debris on ablation rates by a mathematical function based on published empirical data (including Ostrem's curve). A key interest is potential positive feedback of ablation on debris thickening and lowering of surface albedo. Model simulations show that when DCGs evolve to attain steady-state profiles, they reach lower elevations than clean glaciers do for the same initial and climatic conditions. Their mass-balance profile at steady state displays an inversion near the snout (where the debris cover is thickest) that is not observed in the clean-glacier simulations. In these cases, where the mantle causes complete buffering to inhibit ablation, the DCG does not reach a steady-state profile, and the sediment thickness evolves to a steady value that depends sensitively on the glacier surface velocities. Variation in the assumed englacial debris concentration in our simulations also determines glacier behaviour. With low englacial debris concentration, the DCG retreats initially while its mass-balance gradient steepens, but the glacier re-advances if it subsequently builds up a thick enough debris cover to cause complete buffering. We identify possible ways and challenges of testing this model with field observations of DCGs, given the inherent difficulty that such glaciers may not be in steady state.

Ambient seismic noise monitoring of a clay landslide: Toward failure prediction

NASA Astrophysics Data System (ADS)

Mainsant, Guénolé; Larose, Eric; Brönnimann, Cornelia; Jongmans, Denis; Michoud, Clément; Jaboyedoff, Michel

2012-03-01

Given that clay-rich landslides may become mobilized, leading to rapid mass movements (earthflows and debris flows), they pose critical problems in risk management worldwide. The most widely proposed mechanism leading to such flow-like movements is the increase in water pore pressure in the sliding mass, generating partial or complete liquefaction. This solid-to-liquid transition results in a dramatic reduction of mechanical rigidity in the liquefied zones, which could be detected by monitoring shear wave velocity variations. With this purpose in mind, the ambient seismic noise correlation technique has been applied to measure the variation in the seismic surface wave velocity in the Pont Bourquin landslide (Swiss Alps). This small but active composite earthslide-earthflow was equipped with continuously recording seismic sensors during spring and summer 2010. An earthslide of a few thousand cubic meters was triggered in mid-August 2010, after a rainy period. This article shows that the seismic velocity of the sliding material, measured from daily noise correlograms, decreased continuously and rapidly for several days prior to the catastrophic event. From a spectral analysis of the velocity decrease, it was possible to determine the location of the change at the base of the sliding layer. These results demonstrate that ambient seismic noise can be used to detect rigidity variations before failure and could potentially be used to predict landslides.

Within-Winter Flexibility in Muscle Masses, Myostatin, and Cellular Aerobic Metabolic Intensity in Passerine Birds.

PubMed

Swanson, David L; King, Marisa O; Culver, William; Zhang, Yufeng

Metabolic rates of passerine birds are flexible traits that vary both seasonally and among and within winters. Seasonal variation in summit metabolic rates (M sum = maximum thermoregulatory metabolism) in birds is consistently correlated with changes in pectoralis muscle and heart masses and sometimes with variation in cellular aerobic metabolic intensity, so these traits might also be associated with shorter-term, within-winter variation in metabolic rates. To determine whether these mechanisms are associated with within-winter variation in M sum , we examined the effects of short-term (ST; 0-7 d), medium-term (MT; 14-30 d), and long-term (LT; 30-yr means) temperature variables on pectoralis muscle and heart masses, pectoralis expression of the muscle-growth inhibitor myostatin and its metalloproteinase activators TLL-1 and TLL-2, and pectoralis and heart citrate synthase (CS; an indicator of cellular aerobic metabolic intensity) activities for two temperate-zone resident passerines, house sparrows (Passer domesticus) and dark-eyed juncos (Junco hyemalis). For both species, pectoralis mass residuals were positively correlated with ST temperature variables, suggesting that cold temperatures resulted in increased turnover of pectoralis muscle, but heart mass showed little within-winter variation for either species. Pectoralis mRNA and protein expression of myostatin and the TLLs were only weakly correlated with ST and MT temperature variables, which is largely consistent with trends in muscle masses for both species. Pectoralis and heart CS activities showed weak and variable trends with ST temperature variables in both species, suggesting only minor effects of temperature variation on cellular aerobic metabolic intensity. Thus, neither muscle or heart masses, regulation by the myostatin system, nor cellular aerobic metabolic intensity varied consistently with winter temperature, suggesting that other factors regulate within-winter metabolic variation in these birds.

Greenland Ice Sheet seasonal and spatial mass variability from model simulations and GRACE (2003-2012)

NASA Astrophysics Data System (ADS)

Alexander, Patrick M.; Tedesco, Marco; Schlegel, Nicole-Jeanne; Luthcke, Scott B.; Fettweis, Xavier; Larour, Eric

2016-06-01

Improving the ability of regional climate models (RCMs) and ice sheet models (ISMs) to simulate spatiotemporal variations in the mass of the Greenland Ice Sheet (GrIS) is crucial for prediction of future sea level rise. While several studies have examined recent trends in GrIS mass loss, studies focusing on mass variations at sub-annual and sub-basin-wide scales are still lacking. At these scales, processes responsible for mass change are less well understood and modeled, and could potentially play an important role in future GrIS mass change. Here, we examine spatiotemporal variations in mass over the GrIS derived from the Gravity Recovery and Climate Experiment (GRACE) satellites for the January 2003-December 2012 period using a "mascon" approach, with a nominal spatial resolution of 100 km, and a temporal resolution of 10 days. We compare GRACE-estimated mass variations against those simulated by the Modèle Atmosphérique Régionale (MAR) RCM and the Ice Sheet System Model (ISSM). In order to properly compare spatial and temporal variations in GrIS mass from GRACE with model outputs, we find it necessary to spatially and temporally filter model results to reproduce leakage of mass inherent in the GRACE solution. Both modeled and satellite-derived results point to a decline (of -178.9 ± 4.4 and -239.4 ± 7.7 Gt yr-1 respectively) in GrIS mass over the period examined, but the models appear to underestimate the rate of mass loss, especially in areas below 2000 m in elevation, where the majority of recent GrIS mass loss is occurring. On an ice-sheet-wide scale, the timing of the modeled seasonal cycle of cumulative mass (driven by summer mass loss) agrees with the GRACE-derived seasonal cycle, within limits of uncertainty from the GRACE solution. However, on sub-ice-sheet-wide scales, some areas exhibit significant differences in the timing of peaks in the annual cycle of mass change. At these scales, model biases, or processes not accounted for by models related to ice dynamics or hydrology, may lead to the observed differences. This highlights the need for further evaluation of modeled processes at regional and seasonal scales, and further study of ice sheet processes not accounted for, such as the role of subglacial hydrology in variations in glacial flow.

Using dual-polarization interferometry to study surface-initiated DNA hybridization chain reactions in real time.

PubMed

Huang, Fujian; Xu, Pingping; Liang, Haojun

2014-01-15

In this study we used dual-polarization interferometry to investigate DNA hybridization chain reactions (HCRs) at solid-liquid interfaces. We monitored the effects of variations in mass, thickness, and density of the immobilized initiator on the subsequent HCRs at various salt concentrations. At low salt concentrations, the single-stranded DNA (ssDNA) initiator was attached uniformly to the chip surface. At high salt concentrations, it lay on the surface at the onset of the immobilization process, but the approaching ssDNA forced the pre-immobilized ssDNA strands to extend into solution as a result of increased electrostatic repulsion between the pre-adsorbed and approaching ssDNA chains. Injection of a mixture of H1 and H2 increased the mass and thickness of the films initially, but thereafter the thickness decreased. These changes indicate that the long double-stranded DNA that formed lay on the surface, rather than extended into the solution, thereby suppressing the subsequent initiation activity of the released single-strand parts of H1 and H2. Increasing the salt concentration increased the HCR efficiency and reaction rate. The HCR efficiency of the initiator ssDNA immobilized on its 5' end was higher than that immobilized on its 3' end, suggesting that the released single-strand parts of H1 and H2 close to the chip surface decreased the initiation activity relative to those of the ones extending into solution. © 2013 Elsevier B.V. All rights reserved.

Light scattering and backscattering by particles suspended in the Baltic Sea in relation to the mass concentration of particles and the proportions of their organic and inorganic fractions

NASA Astrophysics Data System (ADS)

Woźniak, Sławomir B.; Sagan, Sławomir; Zabłocka, Monika; Stoń-Egiert, Joanna; Borzycka, Karolina

2018-06-01

The empirical relationships were examined of spectral characteristics of light scattering and backscattering by particles suspended in seawater in relation to the dry mass concentration of particles and the bulk proportions of their organic and inorganic fractions. The analyses were based on empirical data collected in the surface waters of the southern and central Baltic Sea at different times of the year. It was found that the average scattering and backscattering coefficients, normalized to the dry mass concentration of particles for all our Baltic Sea data (i.e. mass-specific optical coefficients), were characterized by large coefficients of variation (CV) of the order of 30% at all the visible light wavelengths analysed. At wavelength 555 nm the average mass-specific scattering coefficient was ca 0.75 m2 g- 1 (CV = 31%); the corresponding value for backscattering was 0.0072 m2 g- 1 (CV = 29%). The analyses confirmed that some of the observed variations could be explained by changes in the proportions of organic and inorganic fractions of suspended matter. The average organic fraction in all the samples was as high as 83% of the total dry mass concentration but in individual cases it varied between < 50% and up to 100%. Simple, two-variable parameterizations of scattering and backscattering coefficients were derived as functions of the organic and inorganic fraction concentrations. The statistical relationship between the backscattering ratio and the ratio of the organic fraction to the total dry mass of suspended matter was also found: this can be used in practical interpretations of in situ optical measurements. In addition, the variability in particle size distributions recorded with a Coulter counter indicated its potentially highly significant influence on the light scattering properties of particles suspended in Baltic Sea waters.

Mid-Award Progress Report for Department of Energy Office of Science Graduate Student Research Program

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoffman, M. K.

The purpose of the work proposed for this study is to investigate the behavior and transport mechanisms for cesium-137 in soils collected from contaminated sites with distinct source release scenarios. More specifically, this study aims to determine with which elements and minerals cesium-137 associates in these various environments to more reliably predict its migration in the subsurface. This will be achieved using a state-of-the-art analysis technique available at Lawrence Livermore National Laboratory (LLNL) known as NanoSIMS. Nano-scale secondary ion mass spectrometry, or NanoSIMS, is a destructive surface analysis technique in which positive secondary ions are generated from the surface ofmore » a sample and then quantified based on their mass-to-charge ratio (m/z) using mass spectrometry. The data collected about the secondary ions can then be used to create isotope-specific spatial maps with a resolution of a few hundred nanometers and depth profiles that show the variation of the secondary ion intensity with sputtering time. This should be an ideal technique for locating cesium-137 in a sample, as cesium is an easily ionized element, meaning the yield of secondary cesium (Cs) ions produced should be high and making the identification of cesium-137 straight forward.« less

Characterization of extrasolar terrestrial planets from diurnal photometric variability.

PubMed

Ford, E B; Seager, S; Turner, E L

2001-08-30

The detection of massive planets orbiting nearby stars has become almost routine, but current techniques are as yet unable to detect terrestrial planets with masses comparable to the Earth's. Future space-based observatories to detect Earth-like planets are being planned. Terrestrial planets orbiting in the habitable zones of stars-where planetary surface conditions are compatible with the presence of liquid water-are of enormous interest because they might have global environments similar to Earth's and even harbour life. The light scattered by such a planet will vary in intensity and colour as the planet rotates; the resulting light curve will contain information about the planet's surface and atmospheric properties. Here we report a model that predicts features that should be discernible in the light curve obtained by low-precision photometry. For extrasolar planets similar to Earth, we expect daily flux variations of up to hundreds of per cent, depending sensitively on ice and cloud cover as well as seasonal variations. This suggests that the meteorological variability, composition of the surface (for example, ocean versus land fraction) and rotation period of an Earth-like planet could be derived from photometric observations. Even signatures of Earth-like plant life could be constrained or possibly, with further study, even uniquely determined.

Molecular characterization and comparison of shale oils generated by different pyrolysis methods using FT-ICR mass spectrometry

USGS Publications Warehouse

Jin, J.M.; Kim, S.; Birdwell, J.E.

2011-01-01

Fourier transform ion cyclotron resonance mass spectrometry (FT ICR-MS) was applied in the analysis of shale oils generated using two different pyrolysis systems under laboratory conditions meant to simulate surface and in situ oil shale retorting. Significant variations were observed in the shale oils, particularly the degree of conjugation of the constituent molecules. Comparison of FT ICR-MS results to standard oil characterization methods (API gravity, SARA fractionation, gas chromatography-flame ionization detection) indicated correspondence between the average Double Bond Equivalence (DBE) and asphaltene content. The results show that, based on the average DBE values and DBE distributions of the shale oils examined, highly conjugated species are enriched in samples produced under low pressure, high temperature conditions and in the presence of water.

Calibration of the QCM/SAW Cascade Impactor for Measurement of Ozone in the Stratosphere

NASA Technical Reports Server (NTRS)

Wright, Cassandra K.; Sims, S. C.; Peterson, C. B.; Morris, V. R.

1997-01-01

The Quartz Crystal Microbalance Surface Acoustic Wave (QCM/SAW) cascade impactor collects size-fractionated distributions of aerosols on a series of 10 MHz quartz crystals and employs SAW devices coated with chemical sensors for gas detection. Presently, we are calibrating the ER-2 certified QCM/SAW cascade impactor in the laboratory for the detection of ozone. Experiments have been performed to characterize the QCM and SAW mass loading, saturation limits, mass frequency relationships, and sensitivity. We are also characterizing sampling efficiency by measuring the loss of ozone on different materials. There are parallel experiments underway to measure the variations in the sensitivity and response of the QCM/SAW crystals as a function of temperature and pressure. Results of the work to date will be shown.

Membrane reactor for water detritiation: a parametric study on operating parameters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mascarade, J.; Liger, K.; Troulay, M.

2015-03-15

This paper presents the results of a parametric study done on a single stage finger-type packed-bed membrane reactor (PBMR) used for heavy water vapor de-deuteration. Parametric studies have been done on 3 operating parameters which are: the membrane temperature, the total feed flow rate and the feed composition through D{sub 2}O content variations. Thanks to mass spectrometer analysis of streams leaving the PBMR, speciation of deuterated species was achieved. Measurement of the amounts of each molecular component allowed the calculation of reaction quotient at the packed-bed outlet. While temperature variation mainly influences permeation efficiency, feed flow rate perturbation reveals dependencemore » of conversion and permeation properties to contact time between catalyst and reacting mixture. The study shows that isotopic exchange reactions occurring on the catalyst particles surface are not thermodynamically balanced. Moreover, the variation of the heavy water content in the feed exhibits competition between permeation and conversion kinetics.« less

Atmospheric transmission of North Atlantic Heinrich events

USGS Publications Warehouse

Hostetler, S.W.; Clark, P.U.; Bartlein, P.J.; Mix, A.C.; Pisias, N.J.

1999-01-01

We model the response of the climate system during Heinrich event 2 (H2) by employing an atmospheric general circulation model, using boundary conditions based on the concept of a "canonical" Heinrich event. The canonical event is initialized with a full-height Laurentide ice sheet (LIS) and CLIMAP sea surface temperatures (SSTs), followed by lowering of the LIS, then warming of North Atlantic SSTs. Our modeled temperature and wind fields exhibit spatially variable responses over the Northern Hemisphere at each stage of the H2 event. In some regions the climatic responses are additive, whereas in other regions they cancel or are of opposite sign, suggesting that Heinrich event climatic variations may have left complex signatures in geologic records. We find variations in the tropical water balance and the mass balance of ice sheets, and implications for variations in terrestrial methane production from the contraction of northern permafrost regions and the expansion of tropical wetlands. Copyright 1999 by the American Geophysical Union.

Investigation of biogeophysical feedback on the African climate using a two-dimensional model

NASA Technical Reports Server (NTRS)

Xue, Yongkang; Liou, Kuo-Nan; Kasahara, Akira

1990-01-01

A numerical scheme is specifically designed to develop a time-dependent climate model to ensure the conservation of mass, momentum, energy, and water vapor, in order to study the biogeophysical feedback for the climate of Africa. A vegetation layer is incorporated in the present two-dimensional climate model. Using the coupled climate-vegetation model, two tests were performed involving the removal and expansion of the Sahara Desert. Results show that variations in the surface conditions produce a significant feedback to the climate system. It is noted that the simulation responses to the temperature and zonal wind in the case of an expanded desert agree with the climatological data for African dry years. Perturbed simulations have also been performed by changing the albedo only, without allowing the variation in the vegetation layer. It is shown that the variation in latent heat release is significant and is related to changes in the vegetation cover. As a result, precipitation and cloud cover are reduced.

Assessment of Sulphate and Iron Contamination and Seasonal Variations in the Water Resources of a Damodar Valley Coalfield, India: A Case Study.

PubMed

Tiwari, Ashwani Kumar; De Maio, Marina

2018-02-01

The aim of the present study was to assess the sulphate [Formula: see text] and iron (Fe) contamination and seasonal variations in the water resources (groundwater, surface water, and mine water) of the West Bokaro coalfield region, India. One hundred and twenty-four water resources samples were collected from the coalfield during the post- and pre-monsoon seasons. The concentrations of [Formula: see text] were determined using ion chromatography and Fe concentrations were analyzed using inductively coupled plasma mass spectrometry. A statistical analysis was used to easily understand the seasonal variations of the elements in the water resources of the area. The concentrations of [Formula: see text] and Fe in the water resources were higher in the pre-monsoon season than in the post-monsoon season, irrespective of location. The water resources of the coalfield were contaminated with high concentrations of [Formula: see text] and Fe, and would require suitable treatment before drinking, domestic and industrial uses.

Changes in ice dynamics along the northern Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Seehaus, Thorsten; Marinsek, Sebastian; Cook, Alison; Van Wessem, Jan-Melchior; Braun, Matthias

2017-04-01

The climatic conditions along the Antarctic Peninsula have undergone considerable changes during the last 50 years. A period of pronounced air temperature rise, increasing ocean temperatures as well as changes in the precipitation pattern have been reported by various authors. Consequently, the glacial systems showed changes including widespread retreat, surface lowering as well as variations in flow speeds. During the last decades numerous ice shelves along the Antarctic Peninsula retreated, started to break-up or disintegrated completely. The loss of the buttressing effect caused tributary glaciers to accelerate with increasing ice discharge along the Antarctic Peninsula. Quantification of the mass changes is still subject to considerable errors although numbers derived from the different methods are converging. The aim is to study the reaction of glaciers at the northern Antarctic Peninsula to the changing climatic conditions and the readjustments of tributary glaciers to ice shelf disintegration, as well as to better quantify the ice mass loss and its temporal changes. We analysed time series of various satellite sensors (ERS-1/2 SAR, ENVISAT ASAR, RADARSAT-1, ALOS PALSAR, TerraSAR-X/TanDEM-X, ASTER, Landsat) to detect changes in ice dynamics of 74 glacier basins along the northern Antarctic Peninsula (<65°). Intensity feature tracking techniques were applied on data stacks from different SAR satellites over the last 20 years to infer temporal trends in glacier surface velocities. In combination with ice thickness reconstructions and modeled climatic mass balance fields regional imbalances were calculated. Variations in ice front position were mapped based on optical and SAR satellite data sets. Along the west coast of the northern Antarctic Peninsula an increase in flow speeds by 40% between 1992 and 2014 was observed, whereas glaciers on the east side (north of former Prince-Gustav Ice Shelf) showed a strong deceleration. Nearly all former ice shelf tributaries showed similar reactions to ice shelf disintegration, with a significant acceleration and frontal retreat after ice shelf break-up and a subsequent deceleration and front stabilization. In total an ice discharge of 17.93±6.22 Gt/a was estimated for the study region in the period 2010-2014. Regional mass balance estimates indicate nearly balanced mass budgets in the period 1992-1996 and positive imbalances in more recent years (2010-2014), dominated by the clearly positive mass balances along the west coast due to high climatic mass balances. The detailed multi-mission time series analysis of glacier changes supports the interpretation of the ongoing processes in this region and allows multi temporal imbalance estimates.

Seasonal variations of thermocline circulation and ventilation in the Indian Ocean

NASA Astrophysics Data System (ADS)

You, Yuzhu

1997-05-01

Two seasonal hydrographic data sets, including temperature, salinity, dissolved oxygen, and nutrients, are used in a mixing model which combines cluster analysis with optimum multiparameter analysis to determine the spreading and mixing of the thermocline waters in the Indian Ocean. The mixing model comprises a system of four major source water masses, which were identified in the thermocline through cluster analysis. They are Indian Central Water (ICW), North Indian Central Water (NICW) interpreted as aged ICW, Australasian Mediterranean Water (AAMW), and Red Sea Water (RSW)/Persian Gulf Water (PGW). The mixing ratios of these water masses are quantified and mapped on four isopycnal surfaces which span the thermocline from 150 to 600 m in the northern Indian Ocean, on two meridional sections along 60°E and 90°E, and on two zonal sections along 10°S and 6°N. The mixing ratios and pathways of the thermocline water masses show large seasonal variations, particularly in the upper 400-500 m of the thermocline. The most prominent signal of seasonal variation occurs in the Somali Current, the western boundary current, which appears only during the SW (summer) monsoon. The northward spreading of ICW into the equatorial and northern Indian Ocean is by way of the Somali Current centered at 300-400 m on the σθ=26.7 isopycnal surface during the summer monsoon and of the Equatorial Countercurrent during the NE (winter) monsoon. More ICW carried into the northern Indian Ocean during the summer monsoon is seen clearly in the zonal section along 6°N. NICW spreads southward through the western Indian Ocean and is stronger during the winter monsoon. AAMW appears in both seasons but is slightly stronger during the summer in the upper thermocline. The westward flow of AAMW is by way of the South Equatorial Current and slightly bends to the north on the σθ=26.7 isopycnal surface during the summer monsoon, indicative of its contribution to the western boundary current. Outflow of RSW/PGW seems effectively blocked by the continuation of strong northward jet of the Somali Current along the western Arabian Sea during the summer, giving a rather small contribution of only up to 20% in the Arabian Sea. A schematic summer and winter thermocline circulation emerges from this study. Both hydrography and water - mass mixing ratios suggest that the contribution of the water from the South Indian Ocean and from the Indo-Pacific through flow controls the circulation and ventilation in the western boundary region during the summer. However, during the winter the water is carried into the eastern boundary by the Equatorial Countercurrent and leaks into the eastern Bay of Bengal, from where the water is advected into the northwestern Indian Ocean by the North Equatorial Current. The so-called East Madagascar Current as a southward flow occurs only during the summer, as is suggested by both hydrography and water-mass mixing patterns from this paper. During the winter (austral summer) the current seems reversal to a northward flow along east of Madagascar, somewhat symmetrical to the Somali Current in the north.

Combustion dynamics of low vapour pressure nanofuel droplets

NASA Astrophysics Data System (ADS)

Pandey, Khushboo; Chattopadhyay, Kamanio; Basu, Saptarshi

2017-07-01

Multiscale combustion dynamics, shape oscillations, secondary atomization, and precipitate formation have been elucidated for low vapour pressure nanofuel [n-dodecane seeded with alumina nanoparticles (NPs)] droplets. Dilute nanoparticle loading rates (0.1%-1%) have been considered. Contrary to our previous studies of ethanol-water blend (high vapour pressure fuel), pure dodecane droplets do not exhibit internal boiling after ignition. However, variation in surface tension due to temperature causes shape deformations for pure dodecane droplets. In the case of nanofuels, intense heat release from the enveloping flame leads to the formation of micron-size aggregates (of alumina NPS) which serve as nucleation sites promoting heterogeneous boiling. Three boiling regimes (A, B, and C) have been identified with varying bubble dynamics. We have deciphered key mechanisms responsible for the growth, transport, and rupture of the bubbles. Bubble rupture causes ejections of liquid droplets termed as secondary atomization. Ejection of small bubbles (mode 1) resembles the classical vapour bubble collapse mechanism near a flat free surface. However, large bubbles induce severe shape deformations as well as bulk oscillations. Rupture of large bubbles results in high speed liquid jet formation which undergoes Rayleigh-Plateau tip break-up. Both modes contribute towards direct fuel transfer from the droplet surface to flame envelope bypassing diffusion limitations. Combustion lifetime of nanofuel droplets consequently has two stages: stage I (where bubble dynamics are dominant) and stage II (formation of gelatinous mass due to continuous fuel depletion; NP agglomeration). In the present work, variation of flame dynamics and spatio-temporal heat release (HR) have been analysed using high speed OH* chemiluminescence imaging. Fluctuations in droplet shape and flame heat release are found to be well correlated. Droplet flame is bifurcated in two zones (I and II). Flame response is manifested in two frequency ranges: (i) buoyant flame flickering and (ii) auxiliary frequencies arising from high intensity secondary ejections due to bubble ruptures. Addition of alumina NPs enhances the heat absorption rate and ensures the rapid transfer of fuel parcels (detached daughter droplets) from droplet surface to flame front through secondary ejections. Therefore, average HR shows an increasing trend with particle loading rate (PLR). The perikinetic agglomeration model is used to explain the formation of gelatinous sheath during the last phase of droplet burning. Gelatinous mass formed results in bubble entrapment. SEM images of combustion precipitates show entrapped bubble cavities along with surface and sub-surface blowholes. Morphology of combustion precipitate shows a strong variation with PLRs. We have established the coupling mechanisms among heat release, shape oscillations, and secondary atomizations that underline the combustion behaviour of such low vapour pressure nanofuels.

Multi-decadal mass loss of glaciers in the Everest area (Nepal Himalaya) derived from stereo imagery

NASA Astrophysics Data System (ADS)

Bolch, T.; Pieczonka, T.; Benn, D. I.

2011-04-01

Mass loss of Himalayan glaciers has wide-ranging consequences such as changing runoff distribution, sea level rise and an increasing risk of glacial lake outburst floods (GLOFs). The assessment of the regional and global impact of glacier changes in the Himalaya is, however, hampered by a lack of mass balance data for most of the range. Multi-temporal digital terrain models (DTMs) allow glacier mass balance to be calculated. Here, we present a time series of mass changes for ten glaciers covering an area of about 50 km2 south and west of Mt. Everest, Nepal, using stereo Corona spy imagery (years 1962 and 1970), aerial images and recent high resolution satellite data (Cartosat-1). This is the longest time series of mass changes in the Himalaya. We reveal that the glaciers have been significantly losing mass since at least 1970, despite thick debris cover. The specific mass loss for 1970-2007 is 0.32 ± 0.08 m w.e. a-1, however, not higher than the global average. Comparisons of the recent DTMs with earlier time periods indicate an accelerated mass loss. This is, however, hardly statistically significant due to high uncertainty, especially of the lower resolution ASTER DTM. The characteristics of surface lowering can be explained by spatial variations of glacier velocity, the thickness of the debris-cover, and ice melt due to exposed ice cliffs and ponds.

Drought-induced uplift in the western United States as observed by the EarthScope Plate Boundary Observatory GPS network

NASA Astrophysics Data System (ADS)

Borsa, A. A.; Agnew, D. C.; Cayan, D. R.

2014-12-01

The western United States (WUS) has been experiencing severe drought since 2013. The solid earth response to the accompanying loss of surface and near-surface water mass should be a broad region of uplift. We use seasonally-adjusted time series from continuously operating GPS stations in the EarthScope Plate Boundary Observatory and several smaller networks to measure this uplift, which reaches 15 mm in the California Coastal Ranges and Sierra Nevada and has a median value of 4 mm over the entire WUS. The pattern of mass loss due to the drought, which we recover from an inversion of uplift observations, ranges up to 50 cm of water equivalent and is consistent with observed decreases in precipitation and streamflow. We estimate the total deficit to be 240 Gt, equivalent to a uniform 10 cm layer of water over the entire region, or the magnitude of the current annual mass loss from the Greenland Ice Sheet. In the WUS, interannual changes in crustal loading are driven by changes in cool-season precipitation, which cause variations in surface water, snowpack, soil moisture, and groundwater. The results here demonstrate that the existing network of continuous GPS stations can be used to recover loading changes due to both wet and dry climate patterns. This suggests a new role for GPS networks such as that of the Plate Boundary Observatory. The exceptional stability of the GPS monumentation means that this network is also capable of monitoring the long-term effects of regional climate change. Surface displacement observations from GPS have the potential to expand the capabilities of the current hydrological observing network for monitoring current and future hydrological changes, with obvious social and economic benefits.

Spatiotemporal variability of Canadian High Arctic glacier surface albedo from MODIS data, 2001-2016

NASA Astrophysics Data System (ADS)

Mortimer, Colleen A.; Sharp, Martin

2018-02-01

Inter-annual variations and longer-term trends in the annual mass balance of glaciers in Canada's Queen Elizabeth Islands (QEI) are largely attributable to changes in summer melt. The largest source of melt energy in the QEI in summer is net shortwave radiation, which is modulated by changes in glacier surface albedo. We used measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors to investigate large-scale spatial patterns, temporal trends, and variability in the summer surface albedo of QEI glaciers from 2001 to 2016. Mean summer black-sky shortwave broadband albedo (BSA) decreased at a rate of 0.029±0.025 decade-1 over that period. Larger reductions in BSA occurred in July (-0.050±0.031 decade-1). No change in BSA was observed in either June or August. Most of the decrease in BSA, which was greatest at lower elevations around the margins of the ice masses, occurred between 2007 and 2012, when mean summer BSA was anomalously low. The first principal component of the 16-year record of mean summer BSA was well correlated with the mean summer North Atlantic Oscillation index, except in 2006, 2010, and 2016, when the mean summer BSA appears to have been dominated by the August BSA. During the period 2001-2016, the mean summer land surface temperature (LST) over the QEI glaciers and ice caps increased by 0.049±0.038 °C yr-1, and the BSA record was negatively correlated (r: -0.86) with the LST record, indicative of a positive ice-albedo feedback that would increase rates of mass loss from the QEI glaciers.

Seasonal and intraseasonal variations in evaporation and surface energy budget from eddy covariance measurements over an open water surface in Mississippi, U.S.A.

NASA Astrophysics Data System (ADS)

Liu, H.; Zhang, Y.; Williams, Q. L.; Jiang, H.; Sheng, L.

2008-12-01

Understanding seasonal and intraseasonal variations in evaporation over lake/reservoir is important for water resource management as well as predicting variations in hydrology as a result of climate change. Since August of 2007, we have conducted a long-term eddy covariance measurement of evaporation and the surface energy budget over Ross Barnett Reservoir (32o26'N, 90o02'W) in Mississippi, USA. The fetch for eddy covariance system exceeds 2 km in all directions and the water depth is about 4 m around the flux tower. The tower with its height of 4 m stands over a stationary wood platform with its size of 3 m × 3 m and height of about 1 m above the water surface. Along with sensible and latent heat fluxes, microclimate data are also measured, including wind speed, wind direction, relative humidity, solar radiation, net radiation, air temperature at four levels, water surface temperature, and water temperature at eight depths down to about 4 m. Mississippi is subject to frequent influences of different synoptic weather systems in a year around. Incursions of these different systems bring in air masses with different properties in temperature and moisture. Cold fronts, for example, carry them with cold and dry air from north while warm fronts with warm and moist air. Our results indicate that synoptic weather variations play an important role in controlling evaporations and the surface energy budget. For example, daily H and LE (i.e., evaporation) during the passages of cold fronts are around 2-4 times those of normal days and these cold front events lead to an increase in the seasonal H by approximately 420 and LE by 160%. However, the warm weather systems suppress largely the turbulent exchanges of sensible and latent heat, leading to very small evaporation and sensible heat fluxes (even negative). These results imply that future potential changes in cold front activities (intensity, frequency, and duration) as a result of climate change may lead to substantial shifts in regional energy budget and hydrological balance in the southern regions with an abundance of open water bodies (e.g., lakes, reservoirs, swamps etc). Using these datasets, the daytime and nighttime evaporation rates are also analyzed and nighttime evaporative water losses are substantial, contributing a significant portion to the total evaporative water loss.

Three-Dimensional Porous Particles Composed of Curved, Two-Dimensional, Nano-Sized Layers for Li-Ion Batteries

NASA Technical Reports Server (NTRS)

Yushin, Gleb; Evanoff, Kara; Magasinski, Alexander

2012-01-01

Thin Si films coated on porous 3D particles composed of curved 2D graphene sheets have been synthesized utilizing techniques that allow for tunable properties. Since graphene exhibits specific surface area up to 100 times higher than carbon black or graphite, the deposition of the same mass of Si on graphene is much faster in comparison -- a factor which is important for practical applications. In addition, the distance between graphene layers is tunable and variation in the thickness of the deposited Si film is feasible. Both of these characteristics allow for optimization of the energy and power characteristics. Thicker films will allow higher capacity, but slower rate capabilities. Thinner films will allow more rapid charging, or higher power performance. In this innovation, uniform deposition of Si and C layers on high-surface area graphene produced granules with specific surface area (SSA) of 5 sq. m/g.

XPS and ToF-SIMS analysis of natural rubies and sapphires heat-treated in a reducing (5 mol% H 2/Ar) atmosphere

NASA Astrophysics Data System (ADS)

Achiwawanich, S.; James, B. D.; Liesegang, J.

2008-12-01

Surface effects on Mong Hsu rubies and Kanchanaburi sapphires after heat treatment in a controlled reducing atmosphere (5 mol% H 2/Ar) have been investigated using advanced surface science techniques including X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Visual appearance of the gemstones is clearly affected by the heat treatment in a reducing atmosphere. Kanchanaburi sapphires, in particular, exhibit Fe-containing precipitates after the heat treatment which have not been observed in previous studies under an inert atmosphere. Significant correlation between changes in visual appearance of the gemstones and variations in surface concentration of trace elements, especially Ti and Fe are observed. The XPS and ToF-SIMS results suggest that; (1) a reducing atmosphere affects the oxidation state of Fe; (2) dissociation of Fe-Ti interaction may occur during heat treatment.

Unsteady Sisko magneto-nanofluid flow with heat absorption and temperature dependent thermal conductivity: A 3D numerical study

NASA Astrophysics Data System (ADS)

Khan, Masood; Ahmad, Latif; Gulzar, M. Mudassar

2018-03-01

The impact of temperature dependent thermal conductivity and convective surface conditions on unsteady 3D Sisko nanofluid flow over a stretching surface is studied in the presence of heat generation/absorption and magnetic field. The numerical solution of nonlinear coupled equations has been carried out to explore the properties of different physical profiles of the fluid flow with varying of parameters. Specifically, the application of generalized Biot numbers and heat generation/absorption parameter in the sketching of temperature and concentration profiles are explored. The effect of all three parameters is noticed in the increasing order for shear thinning (0 < n < 1) and for shear thickening (n > 1) fluids. Moreover, the influence of Biot number γ1 on heat and mass transfer rates, are found in the enhancement and diminishing conducts respectively, in both cases of shear thinning as well as shear thickening fluids and a reverse trend is observed with the variation of Biot number γ2 . Additionally, the present results are validated through skin friction, heat and mass transfer rate values with the comparable values in the existing previous values.

Thermal advection and stratification effects on surface winds and the low level meridional mass transport

NASA Technical Reports Server (NTRS)

Levy, Gad; Tiu, Felice S.

1990-01-01

Statistical tests are performed on the Seasat scatterometer observations to examine if and to what degree thermal advection and stratification effects manifest themselves in these remotely sensed measurements of mean wind and wind stress over the ocean. On the basis of a two layer baroclinic boundary layer model which is presented, it is shown that the thermal advection and stratification of the entire boundary layer as well as the geostrophic forcing influence the modeled near surface wind and wind stress profiles. Evidence of diurnal variation in the stratification under barotropic conditions is found in the data, with the daytime marine boundary layer being more convective than its nighttime counterpart. The temporal and spacial sampling pattern of the satellite makes it impossible to recover the full diurnal cycle, however. The observed effects of the thermal advection are shown to be statistically significant during the day (and presumed more convective) hours, causing a systematic increase in the poleward transport of mass and heat. The statistical results are in a qualitative agreement with the model simulations and cannot be reproduced in randomized control tests.

Experimental study on heat transfer performance of fin-tube exchanger and PSHE for waste heat recovery

NASA Astrophysics Data System (ADS)

Chen, Ting; Bae, Kyung Jin; Kwon, Oh Kyung

2018-02-01

In this paper, heat transfer characteristics of fin-tube heat exchanger and primary surface heat exchanger (PSHE) used in waste heat recovery were investigated experimentally. The flow in the fin-tube heat exchanger is cross flow and in PSHE counter flow. The variations of friction factor and Colburn j factor with air mass flow rate, and Nu number with Re number are presented. Various comparison methods are used to evaluate heat transfer performance, and the results show that the heat transfer rate of the PSHE is on average 17.3% larger than that of fin-tube heat exchanger when air mass flow rate is ranging from 1.24 to 3.45 kg/min. However, the PSHE causes higher pressure drop, and the fin-tube heat exchanger has a wider application range which leads to a 31.7% higher value of maximum heat transfer rate compared to that of the PSHE. Besides, under the same fan power per unit frontal surface, a higher heat transfer rate value is given in the fin-tube heat exchanger.

Impulsive Injection for Compressor Stator Separation Control

NASA Technical Reports Server (NTRS)

Culley, Dennis E.; Braunscheidel, Edward P.; Bright, Michelle M.

2005-01-01

Flow control using impulsive injection from the suction surface of a stator vane has been applied in a low speed axial compressor. Impulsive injection is shown to significantly reduce separation relative to steady injection for vanes that were induced to separate by an increase in vane stagger angle of 4 degrees. Injected flow was applied to the airfoil suction surface using spanwise slots pitched in the streamwise direction. Injection was limited to the near-hub region, from 10 to 36 percent of span, to affect the dominant loss due to hub leakage flow. Actuation was provided externally using high-speed solenoid valves closely coupled to the vane tip. Variations in injected mass, frequency, and duty cycle are explored. The local corrected total pressure loss across the vane at the lower span region was reduced by over 20 percent. Additionally, low momentum fluid migrating from the hub region toward the tip was effectively suppressed resulting in an overall benefit which reduced corrected area averaged loss through the passage by 4 percent. The injection mass fraction used for impulsive actuation was typically less than 0.1 percent of the compressor through flow.

Greenland ice sheet melt from MODIS and associated atmospheric variability.

PubMed

Häkkinen, Sirpa; Hall, Dorothy K; Shuman, Christopher A; Worthen, Denise L; DiGirolamo, Nicolo E

2014-03-16

Daily June-July melt fraction variations over the Greenland ice sheet (GIS) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) (2000-2013) are associated with atmospheric blocking forming an omega-shape ridge over the GIS at 500 hPa height. Blocking activity with a range of time scales, from synoptic waves breaking poleward (<5 days) to full-fledged blocks (≥5 days), brings warm subtropical air masses over the GIS controlling daily surface temperatures and melt. The temperature anomaly of these subtropical air mass intrusions is also important for melting. Based on the years with the greatest melt (2002 and 2012) during the MODIS era, the area-average temperature anomaly of 2 standard deviations above the 14 year June-July mean results in a melt fraction of 40% or more. Though the summer of 2007 had the most blocking days, atmospheric temperature anomalies were too small to instigate extreme melting. Short-term atmospheric blocking over Greenland contributes to melt episodesAssociated temperature anomalies are equally important for the meltDuration and strength of blocking events contribute to surface melt intensity.

Do digestive contents confound body mass as a measure of relative condition in nestling songbirds?

USGS Publications Warehouse

Streby, Henry M.; Peterson, Sean M.; Lehman, Justin A.; Kramer, Gunnar R.; Vernasco, Ben J.; Andersen, David E.

2014-01-01

Relative nestling condition, typically measured as nestling mass or as an index including nestling mass, is commonly purported to correlate with fledgling songbird survival. However, most studies directly investigating fledgling survival have found no such relationship. We weighed feces and stomach contents of nestling golden-winged warblers (Vermivora chrysoptera) to investigate the potential contribution of variation in digestive contents to differences in nestling mass. We estimated that the mass of a seventh-day (near fledging) nestling golden-winged warbler varies by 0.65 g (approx. 9% of mean nestling mass) depending on the contents of the nestling's digestive system at the time of weighing, and that digestive contents are dissimilar among nestlings at any moment the brood is removed from the nest for weighing. Our conservative estimate of within-individual variation in digestive contents equals 72% and 24% of the mean within-brood and population-wide range in nestling mass, respectively. Based on our results, a substantive but typically unknown amount of the variation in body mass among nestlings is confounded by differences in digestive contents. We conclude that short-term variation in digestive contents likely precludes the use of body mass, and therefore any mass-dependent index, as a measure of relative nestling condition or as a predictor of survival in golden-winged warblers and likely in many other songbirds of similar size.

Modeling of laser-induced ionization of solid dielectrics for ablation simulations: role of effective mass

NASA Astrophysics Data System (ADS)

Gruzdev, Vitaly

2010-11-01

Modeling of laser-induced ionization and heating of conduction-band electrons by laser radiation frequently serves as a basis for simulations supporting experimental studies of laser-induced ablation and damage of solid dielectrics. Together with band gap and electron-particle collision rate, effective electron mass is one of material parameters employed for the ionization modeling. Exact value of the effective mass is not known for many materials frequently utilized in experiments, e.g., fused silica and glasses. Because of that reason, value of the effective mass is arbitrary varied around "reasonable values" for the ionization modeling. In fact, it is utilized as a fitting parameter to fit experimental data on dependence of ablation or damage threshold on laser parameters. In this connection, we study how strong is the influence of variations of the effective mass on the value of conduction-band electron density. We consider influence of the effective mass on the photo-ionization rate and rate of impact ionization. In particular, it is shown that the photo-ionization rate can vary by 2-4 orders of magnitude with variation of effective mass by 50%. Impact ionization shows a much weaker dependence on effective mass, but it significantly enhances the variations of seed-electron density produced by the photo-ionization. Utilizing those results, we demonstrate that variation of effective mass by 50% produces variations of conduction-band electron density by 6 orders of magnitude. In this connection, we discuss the general issues of the current models of laser-induced ionization.

Effect of mass variation on dynamics of tethered system in orbital maneuvering

NASA Astrophysics Data System (ADS)

Sun, Liang; Zhao, Guowei; Huang, Hai

2018-05-01

In orbital maneuvering, the mass variation due to fuel consumption has an obvious impact on the dynamics of tethered system, which cannot be neglected. The contributions of the work are mainly shown in two aspects: 1) the improvement of the model; 2) the analysis of dynamics characteristics. As the mass is variable, and the derivative of the mass is directly considered in the traditional Lagrange equation, the expression of generalized force is complicated. To solve this problem, the coagulated derivative is adopted in the paper; besides, the attitude dynamics equations derived in this paper take into account the effect of mass variation and the drift of orbital trajectory at the same time. The bifurcation phenomenon, the pendular motion angular frequency, and amplitudes of tether vibration revealed in this paper can provide a reference for the parameters and controller design in practical engineering. In the article, a dumbbell model is adopted to analyze the dynamics of tethered system, in which the mass variation of base satellite is fully considered. Considering the practical application, the case of orbital transfer under a transversal thrust is mainly studied. Besides, compared with the analytical solutions of librational angles, the effects of mass variation on stability and librational characteristic are studied. Finally, in order to make an analysis of the effect on vibrational characteristic, a lumped model is introduced, which reveals a strong coupling of librational and vibrational characteristics.

Titan's interior from Cassini-Huygens

NASA Astrophysics Data System (ADS)

Tobie, G.; Baland, R.-M.; Lefevre, A.; Monteux, J.; Cadek, O.; Choblet, G.; Mitri, G.

2013-09-01

The Cassini-Huygens mission has brought many informations about Titan that can be used to infer its interior structure: the gravity field coefficients (up to degree 3, [1]), the surface shape (up to degree 6, [2]), the tidal Love number [1], the electric field [3], and the orientation of its rotation axis [4]. The measured obliquity and gravity perturbation due to tides, as well as the electric field, are lines of evidence for the presence of an internal global ocean beneath the ice surface of Titan [5,1,3]. The observed surface shape and gravity can be used to further constrain the structure of the ice shell above the internal ocean. The presence of a significant topography associated with weak gravity anomalies indicates that deflections of internal interface or lateral density variations may exist to compensate the topography. To assess the sources of compensation, we consider interior models including interface deflections and/or density variations, which reproduces simultaneously the surface gravity and long-wavelength topography data [6]. Furthermore, in order to test the long-term mechanical stability of the internal mass anomalies, we compute the relaxation rate of each internal interface in response to surface mass load. We show that the topography can be explained either by defections of the ocean/ice interface or by density variations in an upper crust [6]. For non-perfectly compensated models of the outer ice shell, the present-day structure is stable only for a conductive layer above a relatively cold ocean (for bottom viscosity > 1016 Pa.s, T < 250 K). For perfectly compensated models, a convective ice shell is stable (with a bottom viscosity lower than 1015 Pas) if the source of compensation is due to density variations in the upper crust (2-3 km below the surface). In this case, deep gravity anomalies are required to explain the observed geoid. Our calculations show that the high pressure ice layer cannot be the source of the residual gravity anomalies. The existence of mass anomalies in the rocky core is a most likely explanation. However, as the observed geoid and topography are mostly sensitive to the lateral structure of the outer ice shell, no information can be retrieved on the ice shell thickness, ocean density and/or size of the rocky core. Constraints on these internal parameters can be obtained from the tidal Love number and the obliquity. To derive the possible density profile, the obliquity is computed from a Cassini state model for a satellite with an internal liquid layer, each layer having an ellipsoidal shape consistent with the measured surface shape and gravity field [7]. We show that, once the observed surface flattening is taken into account, the measured obliquity can be reproduced only for internal models with a dense ocean (between 1275 and 1350 kg.m-3) above a differentiated interior with a full separation of rock and ice [7]. We obtain normalized moments of inertia between 0.31 and 0.33, significantly lower than the expected hydrostatic value (0.34). The tidal Love number is also found to be mostly sensitive to the ocean density and to a lesser extent the ice shell thickness. By combining obliquity and tidal Love number constraints, we show that the thickness of the outer ice shell is at least 40 km and the ocean thickness is less than 100 km, with an averaged density of 1275-1350 kg.m-3. Such a high density indicates that the ocean may contain a significant fraction of salts. Our calculations also imply that there is a significant difference of flattening between the surface and the ice/ocean interface. This is possible only if the ice layer is viscous enough to limit relaxation, as indicated above. This is also consistent with an ocean enriched in salts for which the crystallization point can be several tens of degree below the crystallization point of pure water system. The elevated density (> 3800 kg.m-3) found for the rocky core further suggests that Titan might have a differentiated iron core. The rocky core is likely fully dehydrated at present, suggesting warm conditions during most of its evolution. All the water contained in the deep interior has probably been expelled to the outer regions, thus potentially explaining the salt enrichments.

Additive genetic variation in the craniofacial skeleton of baboons (genus Papio) and its relationship to body and cranial size.

PubMed

Joganic, Jessica L; Willmore, Katherine E; Richtsmeier, Joan T; Weiss, Kenneth M; Mahaney, Michael C; Rogers, Jeffrey; Cheverud, James M

2018-02-01

Determining the genetic architecture of quantitative traits and genetic correlations among them is important for understanding morphological evolution patterns. We address two questions regarding papionin evolution: (1) what effect do body and cranial size, age, and sex have on phenotypic (V P ) and additive genetic (V A ) variation in baboon crania, and (2) how might additive genetic correlations between craniofacial traits and body mass affect morphological evolution? We use a large captive pedigreed baboon sample to estimate quantitative genetic parameters for craniofacial dimensions (EIDs). Our models include nested combinations of the covariates listed above. We also simulate the correlated response of a given EID due to selection on body mass alone. Covariates account for 1.2-91% of craniofacial V P . EID V A decreases across models as more covariates are included. The median genetic correlation estimate between each EID and body mass is 0.33. Analysis of the multivariate response to selection reveals that observed patterns of craniofacial variation in extant baboons cannot be attributed solely to correlated response to selection on body mass, particularly in males. Because a relatively large proportion of EID V A is shared with body mass variation, different methods of correcting for allometry by statistically controlling for size can alter residual V P patterns. This may conflate direct selection effects on craniofacial variation with those resulting from a correlated response to body mass selection. This shared genetic variation may partially explain how selection for increased body mass in two different papionin lineages produced remarkably similar craniofacial phenotypes. © 2017 Wiley Periodicals, Inc.

Anticipated Electrical Environment at Phobos: Nominal and Solar Storm Conditions

NASA Technical Reports Server (NTRS)

Farrell, W. M.; Halekas, J. S.; Fatemi, S.; Poppe, A. R.; Hartzell, C.; Marshall, J. R.; Stubbs, T. J.; Zimmerman, M. I.; Zheng, Y.

2017-01-01

A passing coronal mass ejection (CME) will manifest a different response at an airless body compared to a magnetized planet. Specifically,because the regolith-rich surfaces of airless bodies are directly exposed to the variations in the plasma flow, the surfaces are found to undergo anomalous surface charging during the passing of CME fast plasma events. In this study, we model the surface charging expected at Phobos for nominal solar wind conditions and also those associated with disturbed solar wind conditions during the passage of a CME similar to that observed by MAVEN at Mars in early March 2015. We use an ambipolar diffusion model to examine the development of the trailing wake void in the plasma flow behind Phobos and the formation of mini-wakes within obstruction regions like Stickney Crater. We also consider the roving of an astronaut in Stickney Crater for Phobos positioned near 10 hours Local Time relative to Mars. We examine the plasma dissipation of the collected astronaut charge from contact electrification with the regolith.

Plate Tectonics on Earth-like Planets: Implications for Habitability

NASA Astrophysics Data System (ADS)

Noack, L.; Breuer, D.

2011-12-01

Plate tectonics has been suggested to be essential for life (see e.g. [1]) due to the replenishment of nutrients and its role in the stabilization of the atmosphere temperature through the carbon-silicate cycle. Whether plate tectonics can prevail on a planet should depend on several factors, e.g. planetary mass, age of the planet, water content (at the surface and in the interior), surface temperature, mantle rheology, density variations in the mantle due to partial melting, and life itself by promoting erosion processes and perhaps even the production of continental rock [2]. In the present study, we have investigated how planetary mass, internal heating, surface temperature and water content in the mantle would factor for the probability of plate tectonics to occur on a planet. We allow the viscosity to be a function of pressure [3], an effect mostly neglected in previous discussions of plate tectonics on exoplanets [4, 5]. With the pressure-dependence of viscosity allowed for, the lower mantle may become too viscous in massive planets for convection to occur. When varying the planetary mass between 0.1 and 10 Earth masses, we find a maximum for the likelihood of plate tectonics to occur for planetary masses around a few Earth masses. For these masses the convective stresses acting at the base of the lithosphere are strongest and may become larger than the lithosphere yield strength. The optimum planetary mass varies slightly depending on the parameter values used (e.g. wet or dry rheology; initial mantle temperature). However, the peak in likelihood of plate tectonics remains roughly in the range of one to five Earth masses for reasonable parameter choices. Internal heating has a similar effect on the occurrence of plate tectonics as the planetary mass, i.e. there is a peak in the probability of plate tectonics depending on the internal heating rate. This result suggests that a planet may evolve as a consequence of radioactive decay into and out of the plate tectonics regime. References [1] Parnell, J. (2004): Plate tectonics, surface mineralogy, and the early evolution of life. Int. J. Astrobio. 3(2): 131-137. [2] Rosing, M.T.; D.K. Bird, N.H. Sleep, W. Glassley, and F. Albar (2006): The rise of continents - An essay on the geologic consequences of photosynthesis. Palaeogeography, Palaeoclimatology, Palaeoecology 232 (2006) 99-11. [3] Stamenkovic, V.; D. Breuer and T. Spohn (2011): Thermal and transport properties of mantle rock at high pressure: Applications to super-Earths. Submitted to Icarus. [4] Valencia, D., R.J. O'Connell and D.D. Sasselov (2007): Inevitability of plate tectonics on super-Earths. Astrophys. J. Let. 670(1): 45-48. [5] O'Neill, C. and A. Lenardic (2007). Geological consequences of super-sized Earths. GRL 34: 1-41.

Monitoring Lakes in Africa with Altimetry and GRACE

NASA Astrophysics Data System (ADS)

Carabajal, C. C.; Boy, J. P.

2017-12-01

Thanks to more than two decades of radar altimetry measurements from TOPEX/POSEIDON, Jason 1, 2 and 3, ENVISAT and others, 18 Ice, Cloud and Land Elevation Satellite (ICESat) laser altimeter measurement campaigns over 6 years, and 15 years of Gravity Recovery And Climate Experiment (GRACE) observations, water levels changes of major lakes and reservoirs can be remotely measured regularly with unprecedented precision, facilitating monitoring of continental water storage variations. Smaller footprint laser altimeters like ICESat are more suitable for the retrieval of water level variations of small inland water bodies, better discriminating water returns when water height measurements have the potential to be contaminated by land or vegetation. Using imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS) contemporaneous with the altimetry data collections, in combination with careful examination of the laser waveforms, one can better isolate returns form the water surface. Combining these altimetry observations, we derive and compare water height estimates for several lakes and reservoirs in Africa from radar and laser altimetry measurements, we estimate the surface extent of each individual water body from available MODIS imagery, and derive corresponding estimates of volume variations for each water body. Mass variations from time-variable gravity measurements from the GRACE mission, using the latest one-degree global iterated mascons solution from GSFC are then transformed into volume changes, assuming a constant density, and compared to altimetry plus imagery estimates. These methods demonstrate the power of combined observations to monitor water resources and facilitate their management. Upcoming laser altimetry missions like ICESat-2, with vastly improved coverage and temporal sampling, continuous observations, better measurements techniques, including inland water products specifically formulated for these applications, when combined with SWOT, and GRACE-follow on mission data, will help address the need for continuous monitoring of continental water storage variations from space measurements.

Mesoscale modeling of Central American smoke transport to the United States: 1. ``Top-down'' assessment of emission strength and diurnal variation impacts

NASA Astrophysics Data System (ADS)

Wang, Jun; Christopher, Sundar A.; Nair, U. S.; Reid, Jeffrey S.; Prins, Elaine M.; Szykman, James; Hand, Jenny L.

2006-03-01

As is typical in the Northern Hemisphere spring, during 20 April to 21 May 2003, significant biomass burning smoke from Central America was transported to the southeastern United States (SEUS). A coupled aerosol, radiation, and meteorology model that is built upon the heritage of the Regional Atmospheric Modeling System (RAMS), having newly developed capabilities of Assimilation and Radiation Online Modeling of Aerosols (AROMA) algorithm, was used to simulate the smoke transport and quantify the smoke radiative impacts on surface energetics, boundary layer, and other atmospheric processes. This paper, the first of a two-part series, describes the model and examines the ability of RAMS-AROMA to simulate the smoke transport. Because biomass-burning fire activities have distinct diurnal variations, the FLAMBE hourly smoke emission inventory that is derived from the geostationary satellite (GOES) fire products was assimilated into the model. In the "top-down" analysis, ground-based observations were used to evaluate the model performance, and the comparisons with model-simulated results were used to estimate emission uncertainties. Qualitatively, a 30-day simulation of smoke spatial distribution as well as the timing and location of the smoke fronts are consistent with those identified from the PM2.5 observation network, local air quality reports, and the measurements of aerosol optical thickness (AOT) and aerosol vertical profiles from the Southern Great Plains (SGP) Atmospheric Radiation Measurements (ARM) site in Oklahoma. Quantitatively, the model-simulated daily mean near-surface dry smoke mass correlates well with PM2.5 mass at 34 locations in Texas and with the total carbon mass and nonsoil potassium mass (KNON) at three IMPROVE sites along the smoke pathway (with linear correlation coefficients R = 0.77, 0.74, and 0.69 at the significance level larger than 0.99, respectively). The top-down sensitivity analysis indicates that the total smoke particle emission during the study period is about 1.3 ± 0.2 Tg. The results further indicate that the simulation with a daily smoke emission inventory provides a slightly better correlation with measurements in the downwind region on daily scales but gives an unrealistic diurnal variation of AOT in the smoke source region. This study suggests that the assimilation of emission inventories from geostationary satellites is superior to that of polar orbiting satellites and has important implications for the modeling of air quality in areas influenced by fire-related pollutants from distant sources.

Stable Chlorine Isotopes and Elemental Chlorine by Thermal Ionization Mass Spectrometry and Ion Chromatography; Martian Meteorites, Carbonaceous Chondrites and Standard Rocks

NASA Technical Reports Server (NTRS)

Nakamura, N.; Nyquist, L. E.; Reese, Y.; Shih, C.-Y.; Fujitani, T.; Okano, O.

2011-01-01

Recently significantly large mass fractionation of stable chlorine isotopes has been reported for terrestrial and lunar samples [1,2]. In addition, in view of possible early solar system processes [3] and also potential perchlorate-related fluid/microbial activities on the Martian surface [4,5], a large chlorine isotopic fractionation might be expected for some types of planetary materials. Due to analytical difficulties of isotopic and elemental analyses, however, current chlorine analyses for planetary materials are controversial among different laboratories, particularly between IRMS (gas source mass spectrometry) and TIMS (Thermal Ionization Mass Spectrometry) groups [i.e. 1,6,7] for isotopic analyses, as well as between those doing pyrohydrolysis and other groups [i.e. 6,8]. Additional careful investigations of Cl isotope and elemental abundances are required to confirm real chlorine isotope and elemental variations for planetary materials. We have developed a TIMS technique combined with HF-leaching/ion chromatography at NASA JSC that is applicable to analysis of small amounts of meteoritic and planetary materials. We present here results for several standard rocks and meteorites, including Martian meteorites.

Heparin/heparan sulfate analysis by covalently modified reverse polarity capillary zone electrophoresis-mass spectrometry.

PubMed

Sanderson, Patience; Stickney, Morgan; Leach, Franklin E; Xia, Qiangwei; Yu, Yanlei; Zhang, Fuming; Linhardt, Robert J; Amster, I Jonathan

2018-04-13

Reverse polarity capillary zone electrophoresis coupled to negative ion mode mass spectrometry (CZE-MS) is shown to be an effective and sensitive tool for the analysis of glycosaminoglycan mixtures. Covalent modification of the inner wall of the separation capillary with neutral or cationic reagents produces a stable and durable surface that provides reproducible separations. By combining CZE-MS with a cation-coated capillary and a sheath flow interface, a rapid and reliable method has been developed for the analysis of sulfated oligosaccharides from dp4 to dp12. Several different mixtures have been separated and detected by mass spectrometry. The mixtures were selected to test the capability of this approach to resolve subtle differences in structure, such as sulfation position and epimeric variation of the uronic acid. The system was applied to a complex mixture of heparin/heparan sulfate oligosaccharides varying in chain length from dp3 to dp12 and more than 80 molecular compositions were identified by accurate mass measurement. Copyright © 2018 Elsevier B.V. All rights reserved.

Mass-induced sea level variations in the Red Sea from GRACE, steric-corrected altimetry, in situ bottom pressure records, and hydrographic observations

NASA Astrophysics Data System (ADS)

Feng, W.; Lemoine, J.-M.; Zhong, M.; Hsu, H. T.

2014-08-01

An annual amplitude of ∼18 cm mass-induced sea level variations (SLV) in the Red Sea is detected from the Gravity Recovery and Climate Experiment (GRACE) satellites and steric-corrected altimetry from 2003 to 2011. The annual mass variations in the region dominate the mean SLV, and generally reach maximum in late January/early February. The annual steric component of the mean SLV is relatively small (<3 cm) and out of phase of the mass-induced SLV. In situ bottom pressure records at the eastern coast of the Red Sea validate the high mass variability observed by steric-corrected altimetry and GRACE. In addition, the horizontal water mass flux of the Red Sea estimated from GRACE and steric-corrected altimetry is validated by hydrographic observations.

Variability and change of sea level and its components in the Indo-Pacific region during the altimetry era

NASA Astrophysics Data System (ADS)

Wu, Quran; Zhang, Xuebin; Church, John A.; Hu, Jianyu

2017-03-01

Previous studies have shown that regional sea level exhibits interannual and decadal variations associated with the modes of climate variability. A better understanding of those low-frequency sea level variations benefits the detection and attribution of climate change signals. Nonetheless, the contributions of thermosteric, halosteric, and mass sea level components to sea level variability and trend patterns remain unclear. By focusing on signals associated with dominant climate modes in the Indo-Pacific region, we estimate the interannual and decadal fingerprints and trend of each sea level component utilizing a multivariate linear regression of two adjoint-based ocean reanalyses. Sea level interannual, decadal, and trend patterns primarily come from thermosteric sea level (TSSL). Halosteric sea level (HSSL) is of regional importance in the Pacific Ocean on decadal time scale and dominates sea level trends in the northeast subtropical Pacific. The compensation between TSSL and HSSL is identified in their decadal variability and trends. The interannual and decadal variability of temperature generally peak at subsurface around 100 m but that of salinity tend to be surface-intensified. Decadal temperature and salinity signals extend deeper into the ocean in some regions than their interannual equivalents. Mass sea level (MassSL) is critical for the interannual and decadal variability of sea level over shelf seas. Inconsistencies exist in MassSL trend patterns among various estimates. This study highlights regions where multiple processes work together to control sea level variability and change. Further work is required to better understand the interaction of different processes in those regions.

Electrochemically controlled iron isotope fractionation

NASA Astrophysics Data System (ADS)

Black, Jay R.; Young, Edward D.; Kavner, Abby

2010-02-01

Variations in the stable isotope abundances of transition metals have been observed in the geologic record and trying to understand and reconstruct the physical/environmental conditions that produced these signatures is an area of active research. It is clear that changes in oxidation state lead to large fractionations of the stable isotopes of many transition metals such as iron, suggesting that transition metal stable isotope signatures could be used as a paleo-redox proxy. However, the factors contributing to these observed stable isotope variations are poorly understood. Here we investigate how the kinetics of iron redox electrochemistry generates isotope fractionation. Through a combination of electrodeposition experiments and modeling of electrochemical processes including mass-transport, we show that electron transfer reactions are the cause of a large isotope separation, while mass transport-limited supply of reactant to the electrode attenuates the observed isotopic fractionation. Furthermore, the stable isotope composition of electroplated transition metals can be tuned in the laboratory by controlling parameters such as solution chemistry, reaction overpotential, and solution convection. These methods are potentially useful for generating isotopically-marked metal surfaces for tracking and forensic purposes. In addition, our studies will help interpret stable isotope data in terms of identifying underlying electron transfer processes in laboratory and natural samples.

Development of a Small Area Sniffer

NASA Technical Reports Server (NTRS)

Meade, Laurie A.

1995-01-01

The aim of this project is to develop and implement a sniffer that is capable of measuring the mass flow rate of air through a small area of pinholes whose diameters are on the magnitude of thousandths of an inch. The sniffer is used to scan a strip of a leading edge panel, which is being used in a hybrid laminar flow control experiment, in order to survey the variations in the amount of air that passes through the porous surface at different locations. Spanwise scans are taken at different chord locations by increasing the pressure in a control volume that is connected to the sniffer head, and recording the drop in pressure as the air is allowed to flow through the tiny holes. This information is used to obtain the mass flow through the structure. More importantly, the deviations from the mean flow rate are found and used to determine whether there are any significant variations in the flow rate from one area to the next. The preliminary results show little deviation in the spanwise direction. These results are important when dealing with the location and amount of suction that will be applied to the leading edge in the active laminar flow control experiment.

Variations in rotation rate and polar motion of a non-hydrostatic Titan

NASA Astrophysics Data System (ADS)

Coyette, Alexis; Baland, Rose-Marie; Van Hoolst, Tim

2018-06-01

Observation of the rotation of synchronously rotating satellites can help to probe their interior. Previous studies mostly assume that these large icy satellites are in hydrostatic equilibrium, although several measurements indicate that they deviate from such a state. Here we investigate the effect of non-hydrostatic equilibrium and of flow in the subsurface ocean on the rotation of Titan. We consider the variations in rotation rate and the polar motion due to (1) the gravitational force exerted by Saturn at orbital period and (2) exchanges of angular momentum between the seasonally varying atmosphere and the solid surface. The deviation of the mass distribution from hydrostaticity can significantly increase the diurnal libration and decrease the amplitude of the seasonal libration. The effect of the non-hydrostatic mass distribution is less important for polar motion, which is more sensitive to flow in the subsurface ocean. By including a large spectrum of atmospheric perturbations, the smaller than synchronous rotation rate measured by Cassini in the 2004-2009 period (Meriggiola et al., 2016) could be explained by the atmospheric forcing. If our interpretation is correct, we predict a larger than synchronous rotation rate in the 2009-2014 period.

Interdecadal change in the Eurasia-Pacific anti-phase relation of atmospheric mass and its possible link with PDO

NASA Astrophysics Data System (ADS)

Zhang, Qian; Guan, Zhaoyong

2017-02-01

Based on the known climatic shift that occurred in 1976, we divide the present study period into two epochs: epoch-I, for 1958-1976; and epoch-II, for 1977-2002. Using ERA-40 and the 20th century reanalysis data, we investigate the interdecadal change in the Eurasia-Pacific anti-phase relation (EPAR) pattern of atmospheric mass (AM) during boreal winter before and after 1976. It is found that anomalous AM over lands is highly and negatively correlated with anomalous AM over oceans in the Northern Hemisphere during the winter season. This correlation does not change much from epoch-I to epoch-II. However, the correlation pattern of surface air pressure anomalies with variations of anomalous AM over lands changes remarkably from epoch-I to epoch-II; the EPAR pattern emerges evidently in the later period, whereas it is not significant in epoch-I. The occurrence of the EPAR pattern in epoch-II may be attributable to the Pacific Decadal Oscillation (PDO). The PDO may modulate the EPAR pattern in two ways. Firstly, the interdecadal component of the PDO as a background may modulate the intensities of the Aleutian low, East Asian trough, and westerly flow, acting as a waveguide during the warm phase (epoch-II) of the PDO. Secondly, the interannual variations of sea surface temperature anomalies in the North Pacific, in association with the PDO, may affect the interannual variations of AM, which facilitates the existence of the EPAR pattern in epoch-II only. With the teleconnection pattern having changed before and after 1976, winter climate anomalies, including rainfall and temperature, are found to be different in many regions in the Northern Hemisphere between epoch-I and epoch-II. All the results of the present work are meaningful for a better understanding of climate anomalies during boreal winter.

Cosmic-ray record in solar system matter

NASA Technical Reports Server (NTRS)

Reedy, R. C.; Arnold, J. R.; Lal, D.

1983-01-01

The interaction of galactic cosmic rays (GCR) and solar cosmic rays (SCR) with bodies in the solar system is discussed, and what the record of that interaction reveals about the history of the solar system is considered. The influence of the energy, charge, and mass of the particles on the interaction is addressed, showing long-term average fluxes of solar protons, predicted production rates for heavy-nuclei tracks and various radionuclides as a function of depth in lunar rock, and integral fluxes of protons emitted by solar flares. The variation of the earth's magnetic field, the gardening of the lunar surface, and the source of meteorites and cosmic dust are studied using the cosmic ray record. The time variation of GCR, SCR, and VH and VVH nuclei is discussed for both the short and the long term.

Isogeometric Divergence-conforming B-splines for the Steady Navier-Stokes Equations

DTIC Science & Technology

2012-04-01

discretizations produce pointwise divergence-free velocity elds and hence exactly satisfy mass conservation. Consequently, discrete variational formulations...cretizations produce pointwise divergence-free velocity fields and hence exactly satisfy mass conservation. Consequently, discrete variational ... variational formulation. Using a combination of an advective for- mulation, SUPG, PSPG, and grad-div stabilization, provably convergent numerical methods

Hot-spots of primary productivity: An Alternative interpretation to Conventional upwelling models

NASA Astrophysics Data System (ADS)

van Ruth, Paul D.; Ganf, George G.; Ward, Tim M.

2010-12-01

The eastern Great Australian Bight (EGAB) forms part of the Southern and Indian Oceans and is an area of high ecological and economic importance. Although it supports a commercial fishery, quantitative estimates of the primary productivity underlying this industry are open to debate. Estimates range from <100 mg C m -2 day -1 to > 500 mg C m -2 day -1. Part of this variation may be due to the unique upwelling circulation of shelf waters in summer/autumn (November-April), which shares some similarities with highly productive eastern boundary current upwelling systems, but differs due to the influence of a northern boundary current, the Flinders current, and a wide continental shelf. This study examines spatial variations in primary productivity in the EGAB during the upwelling seasons of 2005 and 2006. Daily integral productivity calculated using the vertically generalised production model (VGPM) showed a high degree of spatial variation. Productivity was low (<800 mg C m -2 day -1) in offshore central and western regions of the EGAB. High productivities (1600-3900 mg C m -2 day -1) were restricted to hotspots in the east that were influenced by the upwelled water mass. There was a strong correlation between the depth of the euphotic zone and the depth of the mixed layer that suggested that ˜50% of the euphotic zone lay below the mixed layer depth. As a result, high rates of primary productivity did not require upwelled water to reach the surface. A significant proportion of total productivity in the euphotic zone (57% in 2005 and 65% in 2006) occurred in the upwelled water mass below the surface mixed layer. This result has implications for daily integral productivities modelled with the VGPM, which uses surface measures of phytoplankton biomass to calculate productivity. Macro-nutrient concentrations could not be used to explain the difference in the low and high productivities (silica > 1 μmol L -1, nitrate/nitrite > 0.4 μmol L -1, phosphate > 0.1 μmol L -1). Mixing patterns or micro-nutrient concentrations are possible explanations for spatial variations in primary productivity in the EGAB. On a global scale, daily rates of primary productivity of the EGAB lie between the highly productive eastern boundary current upwelling systems, and less productive coastal regions of western and south eastern Australia, and the oligotrophic ocean. However, daily productivity rates in the upwelling hotspots of the EGAB rival productivities in Benguela and Humboldt currents.

Kinematics and depth-integrated terms in surf zone waves from laboratory measurement

NASA Astrophysics Data System (ADS)

Stansby, Peter K.; Feng, Tong

2005-04-01

Kinematics of nominally periodic surf zone waves have been measured in the laboratory using LDA (laser Doppler anemometry), above trough level as well as below, for weakly plunging breakers transforming into bores in shallower water. The aim was to determine, through phase- or ensemble-averaging, periodic flow structures in a two-dimensional vertical plane, from large-scale down to small-scale vortical structures. Coherent multiple vortical structures were evident at the initiation of breaking, becoming elongated along the surface during bore propagation. The initial region is likely to become more extensive as waves become more strongly plunging and could explain the difference in turbulence characteristics between plunging and spilling breakers observed elsewhere. Comparison of vorticity magnitudes with hydraulic-jump measurements showed some similarities during the initial stages of breaking, but these quickly grew less as breaking progressed into shallower water. Period-averaged kinematics and vorticity were also obtained showing shoreward mass transport above trough level and undertow below, with a thick layer of vorticity at trough level and a thin layer of vorticity of opposite rotation at the bed. There were also concentrated regions of mean vorticity near the end of the plunging region. Residual turbulence of relatively high frequency was presented as Reynolds stresses, showing marked anisotrophy. Dynamic pressure (pressure minus its hydrostatic component) was determined from the kinematics. The magnitudes of different effects were evaluated through the depth-integrated Reynolds-averaged Navier-Stokes (RANS) equations, which may be reduced to nine terms (the standard inviscid terms of the shallow-water equations conserving mass and momentum with hydrostatic pressure, and six additional terms), assuming that the complex, often aerated, free surface is treated as a simple interface. All terms were evaluated, assuming that a space/time transformation was justified with a slowly varying phase speed, and the net balance was always small in relation to the maxima of the larger terms. Terms due to dynamic pressure and vertical dispersion (due to the vertical variation of velocity) were as significant as the three terms in the inviscid shallow-water equations; terms involving residual turbulence were insignificant. The r.m.s. (root mean square) variation of each along the slope is highly irregular, with the inertia term due to (Eulerian) acceleration always greatest. This is consistent with complex, though repetitive, coherent structures. Modelling the flow with the shallow-water equations, using the surface elevation variation at the break point as input, nevertheless gave a good prediction of the wave height variation up the slope.

Seismologic applications of GRACE time-variable gravity measurements

NASA Astrophysics Data System (ADS)

Li, Jin; Chen, Jianli; Zhang, Zizhan

2014-04-01

The Gravity Recovery and Climate Experiment (GRACE) has been measuring temporal and spatial variations of mass redistribution within the Earth system since 2002. As large earthquakes cause significant mass changes on and under the Earth's surface, GRACE provides a new means from space to observe mass redistribution due to earthquake deformations. GRACE serves as a good complement to other earthquake measurements because of its extensive spatial coverage and being free from terrestrial restriction. During its over 10 years mission, GRACE has successfully detected seismic gravitational changes of several giant earthquakes, which include the 2004 Sumatra-Andaman earthquake, 2010 Maule (Chile) earthquake, and 2011 Tohoku-Oki (Japan) earthquake. In this review, we describe by examples how to process GRACE time-variable gravity data to retrieve seismic signals, and summarize the results of recent studies that apply GRACE observations to detect co- and post-seismic signals and constrain fault slip models and viscous lithospheric structures. We also discuss major problems and give an outlook in this field of GRACE application.

The Effect of CO2 Ice Cap Sublimation on Mars Atmosphere

NASA Technical Reports Server (NTRS)

Batterson, Courtney

2016-01-01

Sublimation of the polar CO2 ice caps on Mars is an ongoing phenomenon that may be contributing to secular climate change on Mars. The transfer of CO2 between the surface and atmosphere via sublimation and deposition may alter atmospheric mass such that net atmospheric mass is increasing despite seasonal variations in CO2 transfer. My study builds on previous studies by Kahre and Haberle that analyze and compare data from the Phoenix and Viking Landers 1 and 2 to determine whether secular climate change is happening on Mars. In this project, I use two years worth of temperature, pressure, and elevation data from the MSL Curiosity rover to create a program that allows for successful comparison of Curiosity pressure data to Viking Lander pressure data so a conclusion can be drawn regarding whether CO2 ice cap sublimation is causing a net increase in atmospheric mass and is thus contributing to secular climate change on Mars.

Interannual Variation of Surface Circulation in the Japan/East Sea due to External Forcings and Intrinsic Variability

NASA Astrophysics Data System (ADS)

Choi, Byoung-Ju; Cho, Seong Hun; Jung, Hee Seok; Lee, Sang-Ho; Byun, Do-Seong; Kwon, Kyungman

2018-03-01

The interannual variation of surface ocean currents can be as large as seasonal variation in the Japan/East Sea (JES). To identify the major factors that cause such interannual variability of surface ocean circulation in the JES, surface circulation was simulated from 1998 to 2009 using a three-dimensional model. Contributions of atmospheric forcing (ATM), open boundary data (OBC), and intrinsic variability (ITV) of the surface flow in the JES on the interannual variability of surface ocean circulation were separately examined using numerical simulations. Variability in surface circulation was quantified in terms of variance in sea surface height, 100-m depth water temperature, and surface currents. ITV was found to be the dominant factor that induced interannual variabilities of surface circulation, the main path of the East Korea Warm Current (EKWC), and surface kinetic energy on a time scale of 2-4 years. OBC and ATM were secondary factors contributing to the interannual variation of surface circulation. Interannual variation of ATM changed the separation latitude of EKWC and increased the variability of surface circulation in the Ulleung Basin. Interannual variation of OBC enhanced low-frequency changes in surface circulation and eddies in the Yamato Basin. It also modulated basin-wide uniform oscillations of sea level. This study suggests that precise estimation of initial conditions using data assimilation is essential for long-term prediction of surface circulation in the JES.

Clumping in the Cassini Division and C Ring: Constraints from Stellar Occultations

NASA Astrophysics Data System (ADS)

Colwell, J. E.; Jerousek, R. G.; Esposito, L. W.

2014-12-01

Particles in Saturn's rings are engaged in a constant tug-of-war between interparticle gravitational and adhesive forces that lead to clumping, on the one hand, and Keplerian shear that inhibits accretion on the other. Depending on the surface mass density of the rings and the local orbital velocity, ephemeral clumps or self-gravity wakes can form, giving the rings granularity on the scale of the most-unstable length scale against gravitational collapse. The A ring and many regions of the B ring are dominated by self-gravity wakes with a typical radial wavelength of ~50-100 m. A characteristic of self-gravity wakes is that they can effectively shadow the relatively empty spaces in between them, depending on viewing geometry. This leads to geometry-dependent measurements of optical depth in occultations of the rings. The C ring and Cassini Division have significantly lower surface mass densities than the A and B ring such that in most of these regions the most-unstable wavelength is comparable to the size of the ring particles (~1 m) so that self-gravity wake formation is not expected nor have its characteristics in various measurements been observed. Here we present measurements of the optical depth of the C ring and Cassini Division with the Cassini Ultraviolet Imaging Spectrograph (UVIS) showing variations with viewing geometry in the "ramp" regions and the Cassini Division "triple band". These variations are characteristic of self-gravity wakes. We place limits on clumping in other regions of the C ring and Cassini Division.

Chemical durability of alkali-borosilicate glasses studied by analytical SEM, IBA, isotopic-tracing and SIMS

NASA Astrophysics Data System (ADS)

Trocellier, P.; Djanarthany, S.; Chêne, J.; Haddi, A.; Brass, A. M.; Poissonnet, S.; Farges, F.

2005-10-01

Simple and complex alkali-borosilicate glasses were submitted to aqueous corrosion at room temperature, 60 and 90 °C in solutions with pH ranging between 0 and 12. Analytical scanning electron microscopy (SEM), ion beam analysis (IBA) techniques, isotopic tracing and secondary ion mass-depth profiling (SIMS) have been used to investigate the variations of the surface composition of glass. In acidic medium, the glass surface is generally covered by a thick hydrated silica layer, mobile elements like Li, Na and B and transition elements (Fe, Zr, Mo, etc.) are strongly depleted. Near pH 7, relative enrichments of aluminium, iron and rare earths are shown together with strong Li, Na and B depletions. In basic medium, the glass surface exhibits relative enrichments of the major part of transition metals (from Cr to U) whereas mobile elements seem to be kept close to their nominal concentration level at the glass surface and Si is severely impoverished. Hydrogen incorporated at the glass surface after leaching is much more immobile in neutral and basic media than in acid medium.

COMBINED ANALYSIS OF THORIUM AND FAST NEUTRON DATA AT THE LUNAR SURFACE

DOE Office of Scientific and Technical Information (OSTI.GOV)

O. GASNAULT; W. FELDMAN; ET AL

2001-01-01

The global distribution of the radioactive elements (U, K, Th) at the lunar surface is an important parameter for an understanding of lunar evolution, because they have provided continuous heat over the lifetime of the Moon. Today, only the thorium distribution is available for the whole lunar surface [1]. Another key parameter that characterize the surface of the Moon is the presence of mare basalts. These basalts are concentrated on the nearside and are represented by materials with high-Fe content, sometimes associated with high-Ti. We demonstrated elsewhere that the fast neutron measurement made by Lunar Prospector is representative of themore » average soil atomic mass [2]. is primarily dominated by Fe and Ti in basaltic terranes, and therefore the map of the fast neutrons provides a good delineation of mare basalts. We focus here on the correlated variations of thorium abundances and fast neutron fluxes averaged over areas of 360 km in diameter, in an attempt to provide a better understanding of the thorium emplacement on the surface of the Moon.« less

Seismological properties of intermediate-mass stars

NASA Astrophysics Data System (ADS)

Audard, N.; Provost, J.

1994-02-01

Stars more massive than about 1.2 solar mass are characterized by a convective core, which induces at its frontier a rapid variation of the density, sound speed and Brunt-Vaisala frequency, close to a discontinuity. For three stars of 1, 1.5 and 2 solar mass we have studied the properties of p-mode frequencies of high radial order and low degree, and we present results on the effects on p-mode oscillations of some rapid variations of the internal structure. We first point out the difficulties of the classical asymptotic theory to represent with accuracy the p-mode spectrum of the stars considered. We compare the numerical frequencies with asymptotic and polynomial approximations obtained from fits. The variation of the derived global coefficients characterizing the p-mode spectrum along the evolutionary tracks has been estimated; it would help to separate the effects of age and mass of intermediate-mass stars. The sensitivity of these coefficients to stellar parameters substantially depends on the stellar mass and must be considered for asteroseismic calibration. The effects of rapid variations in the stellar internal structure are finally considered. An asymptotic formula taking into account the rapid variation of the sound speed at the convective core boundary of the 1.5 and 2 solar mass stars predicts an oscillatory behavior of the frequencies with a very large period. We also show that the second frequency difference delta2nu = nun, l - 2nun-1, l + nun-2, l exhibits a substantial oscillation which corresponds to the region of the He II ionization of the 1, 1.5 and 2 solar mass stars.

CFD Based Added Mass Prediction in Cruise Condition of Underwater Vehicle Dynamic

NASA Astrophysics Data System (ADS)

Agoes Moelyadi, Mochammad; Bambang Riswandi, Bagus

2018-04-01

One of the unsteady flow behavior on the hydrodynamic characteristics of underwater vehicle is the presence of added mass. In cruising conditions, the underwater vehicle may require the addition of speed or experience the disturbance in the form of unsteady flow so that cause the hydrodynamic interaction between the surface of the vehicle with the surrounding fluid. This leads to the rise of local velocity of flow and the great changes of hydrodynamic forces which are very influential on the stability of the underwater vehicle. One of the result is an additional force called added mass. It is very useful parameter to control underwater vehicle dynamic.This paper reports the research on the added mass coefficient of underwater vehicles obtained through the Computational Fluid Dynmaic (CFD) simulation method using CFX software. Added mass coefficient is calculated by performing an unsteady simulation or known as transient simulation. Computational simulations are based on the Reynold Average Navier- Stokes (RANS) equation solution. The simulated vehicle moves forward and backward according to the sinus function, with a frequency of 0.25 Hz, a 2 m amplitude, a cruising depth of 10 m below sea level, and Vcruise 1.54 m / s (Re = 9.000.000). Simulation result data includes velocity contour, variation of force and acceleration to frequency, and added mass coefficient.

Comparison of hydrological and GRACE-based excitation functions of polar motion in the seasonal spectral band

NASA Astrophysics Data System (ADS)

Nastula, J.; Kolaczek, B.; Salstein, D. A.

2008-04-01

Understanding changes in the global balance of the Earths angular momentum due to the mass redistribution of geophysical fluids is needed to explain the observed polar motion. The impact of continental hydrologic signals, from land water, snow, and ice, on polar motion excitation (hydrological angular momentum-HAM), is still inadequately known. Although estimates of HAM have been made from several models of global hydrology based upon the observed distribution of surface water, snow, and soil moisture, the relatively sparse observation network and the presence of errors in the data and the geophysical fluid models preclude a full understanding of the HAM influence on polar motion variations. Recently the GRACE mission monitoring Earths time variable gravity field has allowed us to determine the mass term of polar motion excitation functions and compare them with the mass term derivable as a residual from the geodetic excitation functions and geophysical fluid motion terms on seasonal time scales. Differences between these mass terms in the years 2004 - 2005.5 are still on the order of 20 mas. Besides the overall mass excitation of polar motion comparisons with GRACE (RL04-release), we also intercompare the non-atmospheric, non-oceanic signals in the mass term of geodetic polar motion excitation with hydrological excitation of polar motion.

Precise stellar surface gravities from the time scales of convectively driven brightness variations

PubMed Central

Kallinger, Thomas; Hekker, Saskia; García, Rafael A.; Huber, Daniel; Matthews, Jaymie M.

2016-01-01

A significant part of the intrinsic brightness variations in cool stars of low and intermediate mass arises from surface convection (seen as granulation) and acoustic oscillations (p-mode pulsations). The characteristics of these phenomena are largely determined by the stars’ surface gravity (g). Detailed photometric measurements of either signal can yield an accurate value of g. However, even with ultraprecise photometry from NASA’s Kepler mission, many stars are too faint for current methods or only moderate accuracy can be achieved in a limited range of stellar evolutionary stages. This means that many of the stars in the Kepler sample, including exoplanet hosts, are not sufficiently characterized to fully describe the sample and exoplanet properties. We present a novel way to measure surface gravities with accuracies of about 4%. Our technique exploits the tight relation between g and the characteristic time scale of the combined granulation and p-mode oscillation signal. It is applicable to all stars with a convective envelope, including active stars. It can measure g in stars for which no other analysis is now possible. Because it depends on the time scale (and no other properties) of the signal, our technique is largely independent of the type of measurement (for example, photometry or radial velocity measurements) and the calibration of the instrumentation used. However, the oscillation signal must be temporally resolved; thus, it cannot be applied to dwarf stars observed by Kepler in its long-cadence mode. PMID:26767193

Precise stellar surface gravities from the time scales of convectively driven brightness variations.

PubMed

Kallinger, Thomas; Hekker, Saskia; García, Rafael A; Huber, Daniel; Matthews, Jaymie M

2016-01-01

A significant part of the intrinsic brightness variations in cool stars of low and intermediate mass arises from surface convection (seen as granulation) and acoustic oscillations (p-mode pulsations). The characteristics of these phenomena are largely determined by the stars' surface gravity (g). Detailed photometric measurements of either signal can yield an accurate value of g. However, even with ultraprecise photometry from NASA's Kepler mission, many stars are too faint for current methods or only moderate accuracy can be achieved in a limited range of stellar evolutionary stages. This means that many of the stars in the Kepler sample, including exoplanet hosts, are not sufficiently characterized to fully describe the sample and exoplanet properties. We present a novel way to measure surface gravities with accuracies of about 4%. Our technique exploits the tight relation between g and the characteristic time scale of the combined granulation and p-mode oscillation signal. It is applicable to all stars with a convective envelope, including active stars. It can measure g in stars for which no other analysis is now possible. Because it depends on the time scale (and no other properties) of the signal, our technique is largely independent of the type of measurement (for example, photometry or radial velocity measurements) and the calibration of the instrumentation used. However, the oscillation signal must be temporally resolved; thus, it cannot be applied to dwarf stars observed by Kepler in its long-cadence mode.

Reflection of a shock wave from a thermally accommodating wall - Molecular simulation.

NASA Technical Reports Server (NTRS)

Deiwert, G. S.

1973-01-01

Reflection of a plane shock wave from a wall has been simulated on a microscopic scale using a direct simulation Monte Carlo technique of the type developed by Bird. A monatomic gas model representing argon was used to describe the fluid medium and a simple one-parameter accommodation coefficient model was used to describe the gas-surface interaction. The influence of surface accommodation was studied parametrically by varying the accommodation coefficient from zero to one. Results are presented showing the temporal variations of flow field density, and mass, momentum, and energy fluxes to the wall during the shock wave reflection process. The energy flux was used to determine the wall temperature history. Comparisons with experiment are found to be satisfactory where data are available.

Estimation of the reactive mineral surface area during CO2-rich fluid-rock interaction: the influence of neogenic phases

NASA Astrophysics Data System (ADS)

Scislewski, A.; Zuddas, P.

2010-12-01

Mineral dissolution and precipitation reactions actively participate to control fluid chemistry during water-rock interaction. It is however, difficult to estimate and well normalize bulk reaction rates if the mineral surface area exposed to the aqueous solution and effectively participating on the reactions is unknown. We evaluated the changing of the reactive mineral surface area during the interaction between CO2-rich fluids and Albitite/Granitoid rocks (similar mineralogy but different abundances), reacting under flow-through conditions. Our methodology, adopting an inverse modeling approach, is based on the estimation of dissolution rate and reactive surface area of the different minerals participating in the reactions by the reconstruction the chemical evolution of the interacting fluids. The irreversible mass-transfer processes is defined by a fractional degree of advancement, while calculations were carried out for Albite, Microcline, Biotite and Calcite assuming that the ion activity of dissolved silica and aluminium ions was limited by the equilibrium with quartz and kaolinite. Irrespective of the mineral abundance in granite and albitite, we found that mineral dissolution rates did not change significantly in the investigated range of time where output solution’s pH remained in the range between 6 and 8, indicating that the observed variation in fluid composition depends not on pH but rather on the variation of the parent mineral’s reactive surface area. We found that the reactive surface area of Albite varied by more than 2 orders of magnitude, while Microcline, Calcite and Biotite surface areas changed by 1-2 orders of magnitude. We propose that parent mineral chemical heterogeneity and, particularly, the stability of secondary mineral phases may explain the observed variation of the reactive surface area of the minerals. Formation of coatings at the dissolving parent mineral surfaces significantly reduced the amount of surface available to react with CO2-rich fluids, decreasing the effective reactive surface area. Predictive models of CO2 sequestration under geological conditions should take into account the inhibiting role of surface coating formation. The CO2 rich fluid-rock interactions may also have significant consequences on metal mobilization. Our results indicated that the formation of stable carbonate complexes enhances the solubility of uranium minerals of both albitite and granite, facilitating the U(IV) oxidation, and limiting the extent of uranium adsorption onto particles in oxidized waters. This clearly produces an increase of the uranium mobility with significant consequences for the environment.

Stochastic and compensatory effects limit persistence of variation in body mass of young caribou

USGS Publications Warehouse

Dale, Bruce W.; Adams, Layne G.; Collins, William B.; Joly, Kyle; Valkenburg, Patrick; Tobey, Robert

2008-01-01

Nutritional restriction during growth can have short- and long-term effects on fitness; however, animals inhabiting uncertain environments may exhibit adaptations to cope with variation in food availability. We examined changes in body mass in free-ranging female caribou (Rangifer tarandus) by measuring mass at birth and at 4, 11, and 16 months of age to evaluate the relative importance of seasonal nutrition to growth, the persistence of cohort-specific variation in body mass through time, and compensatory growth of individuals. Relative mean body mass of cohorts did not persist through time. Compensatory growth of smaller individuals was not observed in summer; however, small calves exhibited more positive change in body mass than did large calves. Compensation occurred during periods of nutritional restriction (winter) rather than during periods of rapid growth (summer) thus differing from the conventional view of compensatory growth.

Atmospheric and oceanic excitation of decadal-scale Earth orientation variations

NASA Astrophysics Data System (ADS)

Gross, Richard S.; Fukumori, Ichiro; Menemenlis, Dimitris

2005-09-01

The contribution of atmospheric wind and surface pressure and oceanic current and bottom pressure variations during 1949-2002 to exciting changes in the Earth's orientation on decadal timescales is investigated using an atmospheric angular momentum series computed from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis project and an oceanic angular momentum series computed from a near-global ocean model that was forced by surface fluxes from the NCEP/NCAR reanalysis project. Not surprisingly, since decadal-scale variations in the length of day are caused mainly by interactions between the mantle and core, the effect of the atmosphere and oceans is found to be only about 14% of that observed. More surprisingly, it is found that the effect of atmospheric and oceanic processes on decadal-scale changes in polar motion is also only about 20% (x component) and 38% (y component) of that observed. Therefore redistribution of mass within the atmosphere and oceans does not appear to be the main cause of the Markowitz wobble. It is also found that on timescales between 10 days and 4 years the atmospheric and oceanic angular momentum series used here have very little skill in explaining Earth orientation variations before the mid to late 1970s. This is attributed to errors in both the Earth orientation observations prior to 1976 when measurements from the accurate space-geodetic techniques became available and to errors in the modeled atmospheric fields prior to 1979 when the satellite era of global weather observing systems began.

Do Knickpoints Unzip Watersheds? Longitudinal Observations of Terrace and Hillslope Response to Mainstem Incision along the South Fork Eel River, California

NASA Astrophysics Data System (ADS)

Wehrs, K.; Crosby, B. T.

2017-12-01

River response to changes in climate and relative base level often leave behind a legacy of transient landforms that enable the interpretation of past events. The dominant paradigm is that base level fall initiates a wave of mainstem incision that progressively transmits change upstream. Mainstem-adjacent hillslopes coupled to the channel subsequently respond as their toe slopes are steepened. To test this paradigm, we first use a longitudinal set of mainstem terrace ages to evaluate whether incision incrementally progresses upstream or is contemporaneous. Second, we explore longitudinal variations in mainstem-adjacent mass movements to evaluate whether they reflect a time and space progression in response. The South Fork Eel River in northern California contains over 600 mainstem-adjacent mass movements and 60 m tall, longitudinally extensive strath terraces that record a landscape response to river incision. We use Optically Stimulated Luminescence, with feldspars and coarse-grained sampling technique, to determine the depositional age of alluvial fill atop the strath terrace. If terrace abandonment progressively young upstream, this suggests that base level fall was not spatially contemporaneous, but rather time progressive. As a consequence, the age, form, and extent of mass wasting events should also vary longitudinally. Because terraces isolate hillslopes from the base level fall signal, we use these surfaces to quantify hillslope form and function independent of that forcing. Preliminary results using mainstem-parallel, 1 m LiDAR, show significant variation in size of mass movements throughout the basin, with planar, linearly moving translational landslides dominating throughout the catchment. In the lower basin, well downstream of the current knickzone, we see an increase in mass movement concentration, reactivation, and overall extent of mass movements. Multiple factors confound our interpretation of hillslope morphology and response, due to changes in lithology, climate, and river sinuosity throughout the catchment.

Summary of the SeaRISE Project's Experiments on Modeled Ice-Sheet Contributions to Future Sea Level: Linearities and Non-linearities

NASA Astrophysics Data System (ADS)

Bindschadler, Robert

2013-04-01

The SeaRISE (Sea-level Response to Ice Sheet Evolution) project achieved ice-sheet model ensemble responses to a variety of prescribed changes to surface mass balance, basal sliding and ocean boundary melting. Greenland ice sheet models are more sensitive than Antarctic ice sheet models to likely atmospheric changes in surface mass balance, while Antarctic models are most sensitive to basal melting of its ice shelves. An experiment approximating the IPCC's RCP8.5 scenario produces first century contributions to sea level of 22.3 and 7.3 cm from Greenland and Antarctica, respectively, with a range among models of 62 and 17 cm, respectively. By 200 years, these projections increase to 53.2 and 23.4 cm, respectively, with ranges of 79 and 57 cm. The considerable range among models was not only in the magnitude of ice lost, but also in the spatial pattern of response to identical forcing. Despite this variation, the response of any single model to a large range in the forcing intensity was remarkably linear in most cases. Additionally, the results of sensitivity experiments to single types of forcing (i.e., only one of the surface mass balance, or basal sliding, or ocean boundary melting) could be summed to accurately predict any model's result for an experiment when multiple forcings were applied simultaneously. This suggests a limited amount of feedback through the ice sheet's internal dynamics between these types of forcing over the time scale of a few centuries (SeaRISE experiments lasted 500 years).

Feedback control of thermal lensing in a high optical power cavity.

PubMed

Fan, Y; Zhao, C; Degallaix, J; Ju, L; Blair, D G; Slagmolen, B J J; Hosken, D J; Brooks, A F; Veitch, P J; Munch, J

2008-10-01

This paper reports automatic compensation of strong thermal lensing in a suspended 80 m optical cavity with sapphire test mass mirrors. Variation of the transmitted beam spot size is used to obtain an error signal to control the heating power applied to the cylindrical surface of an intracavity compensation plate. The negative thermal lens created in the compensation plate compensates the positive thermal lens in the sapphire test mass, which was caused by the absorption of the high intracavity optical power. The results show that feedback control is feasible to compensate the strong thermal lensing expected to occur in advanced laser interferometric gravitational wave detectors. Compensation allows the cavity resonance to be maintained at the fundamental mode, but the long thermal time constant for thermal lensing control in fused silica could cause difficulties with the control of parametric instabilities.

Radioactive impact in South Korea from the damaged nuclear reactors in Fukushima: evidence of long and short range transport.

PubMed

Hong, G H; Hernández-Ceballos, M A; Lozano, R L; Kim, Y I; Lee, H M; Kim, S H; Yeh, S-W; Bolívar, J P; Baskaran, M

2012-12-01

Traces of long-lived fallout-derived radioisotopes ((134)Cs and (137)Cs) were found in wet and dry deposition samples collected from the west and east coasts of South Korea from March to May 2011 following the release of radionuclides from the damaged nuclear power plants in Fukushima, Japan. The analysis of air mass back trajectory and atmospheric pressure systems indicated that the Fukushima-derived radiocaesium had predominantly reached South Korea from the west by surface westerlies from 11 March to 5 April; however, after 6 April, air masses arrived from Japan directly due to a high pressure system that developed to the east of Japan. Spatial variation of deposition fluxes of radiocaesium in South Korea was partly attributed to the presence of local longitudinal orography.

Towards an estimation of water masses formation areas from SMOS-based TS diagrams

NASA Astrophysics Data System (ADS)

Klockmann, Marlene; Sabia, Roberto; Fernandez-Prieto, Diego; Donlon, Craig; Font, Jordi

2014-05-01

Temperature-Salinity (TS) diagrams emphasize the mutual variability of ocean temperature and salinity values, relating them to the corresponding density. Canonically used in oceanography, they provide a means to characterize and trace ocean water masses. In [1], a first attempt to estimate surface-layer TS diagrams based on satellite measurements has been performed, profiting from the recent availability of spaceborne salinity data. In fact, the Soil Moisture and Ocean Salinity (SMOS, [2]) and the Aquarius/SAC-D [3] satellite missions allow to study the dynamical patterns of Sea Surface Salinity (SSS) for the first time on a global scale. In [4], given SMOS and Aquarius salinity estimates, and by also using Sea Surface Temperature (SST) from the Operational Sea Surface Temperature and Sea Ice Analysis (OSTIA, [5]) effort, experimental satellite-based TS diagrams have been routinely derived for the year 2011. They have been compared with those computed from ARGO-buoys interpolated fields, referring to a customised partition of the global ocean into seven regions, according to the water masses classification of [6]. In [7], moreover, besides using TS diagrams as a diagnostic tool to evaluate the temporal variation of SST and SSS (and their corresponding density) as estimated by satellite measurements, the emphasis was on the interpretation of the geographical deviations with respect to the ARGO baseline (aiming at distinguishing between the SSS retrieval errors and the additional information contained in the satellite data with respect to ARGO). In order to relate these mismatches to identifiable oceanographic structures and processes, additional satellite datasets of ocean currents, evaporation/precipitation fluxes, and wind speed have been super-imposed. Currently, the main focus of the study deals with the exploitation of these TS diagrams as a prognostic tool to derive water masses formation areas. Firstly, following the approach described in [8], the surface density flux (i.e., the change in density induced by surface heat and freshwater fluxes) is computed, characterizing how the buoyancy of a water parcel is being transformed, by increasing or decreasing its density. Afterwards, integrating over a certain time/space and deriving with respect to density, the formation (in Sv) of water masses themselves can be computed, pinpointing the range of SST and SSS in the TS diagrams where a specific water mass is formed. A geographical representation of these points, ultimately, allows to provide a relevant temporal series of the spatial extent of the water masses formation areas (in the specific test zones chosen). This can be then extended over challenging ocean regions, also evaluating the sensitivity of the performances to the datasets used. With this approach, known water masses can be identified and their formation traced in time and space. Longer time series will give further insights by helping to identify inter-annual water mass formation variability and trends in the TS/geographical domains. Future work aims at exploring additional datasets and at connecting the surface information to the vertical structure and to buoyancy-driven ocean circulation processes. References [1] Sabia, R., J. Ballabrera, G. Lagerloef, E. Bayler, M. Talone, Y. Chao, C. Donlon, D. Fernández-Prieto, J. Font, "Derivation of an Experimental Satellite-based T-S Diagram", In Proceedings of IGARSS '12 , Munich, Germany, pp. 5760-5763, 2012. [2] Font, J., A. Camps, A. Borges, M. Martín-Neira, J. Boutin, N. Reul, Y. H. Kerr, A. Hahne, and S. Mecklenburg, "SMOS: The challenging sea surface salinity measurement from space," Proceedings of the IEEE, vol. 98, pp. 649-665, 2010. [3] Le Vine, D.M.; Lagerloef, G.S.E.; Torrusio, S.E.; "Aquarius and Remote Sensing of Sea Surface Salinity from Space," Proceedings of the IEEE , vol.98, no.5, pp.688-703, May 2010, doi: 10.1109/JPROC.2010.2040550. [4] Sabia, R., M. Klockmann, D. Fernández-Prieto, C. Donlon, E. Bayler, J. Font, G. Lagerloef, "Satellite-based T/S Diagrams and Surface Ocean Water Masses", SMOS-Aquarius Science Workshop, Brest, France, April 2013. [5] Donlon, C. J., M. Martin, J. D. Stark, J. Roberts-Jones, E. Fiedler and W. Wimmer, "The Operational Sea Surface Temperature and Sea Ice analysis (OSTIA)", Remote Sensing of the Environment. doi: 10.1016/j.rse.2010.10.017 2011. [6] Emery, W. J., "Water Types and Water Masses", Ocean Circulation, Elsevier science, pp 1556-1567, 2003. [7] Sabia, R., M. Klockmann, C. Donlon, D. Fernández-Prieto, M. Talone, J. Ballabrera, "Satellite-based T-S Diagrams: a prospective diagnostic tool to trace ocean water masses", Living Planet Symposium 2013, Edinburgh, UK, September 2013. [8] Speer, K., E. Tzipermann, "Rates of Water Mass Transformation in the North Atlantic", Journal of Physical Oceanography, 22, 93 - 104, 1992.

The influence of thermal inertia on Mars' seasonal pressure variation and the effect of the weather component

NASA Technical Reports Server (NTRS)

Wood, S. E.; Paige, D. A.

1993-01-01

Using a Leighton-Murray type diurnal and seasonal Mars thermal model, we found that it is possible to reproduce the seasonal variation in daily-averaged pressures (approximately 680-890 Pa) measured by Viking Lander 1 (VL1), during years without global dust storms, with a standard deviation of less than 5 Pa. In this simple model, surface CO2, frost condensation, and sublimation rates at each latitude are determined by the net effects of radiation, latent heat, and heat conduction in subsurface soil layers. An inherent assumption of our model is that the seasonal pressure variation is due entirely to the exchange of mass between the atmosphere and polar caps. However, the results of recent Mars GCM modeling have made it clear that there is a significant dynamical contribution to the seasonal pressure variation. This 'weather' component is primarily due to large-scale changes in atmospheric circulation, and its magnitude depends somewhat on the dust content of the atmosphere. The overall form of the theoretical weather component at the location of VL1, as calculated by the AMES GCM, remains the same over the typical range of Mars dust opacities.

An X-ray method for detecting substructure in galaxy clusters - Application to Perseus, A2256, Centaurus, Coma, and Sersic 40/6

NASA Technical Reports Server (NTRS)

Mohr, Joseph J.; Fabricant, Daniel G.; Geller, Margaret J.

1993-01-01

We use the moments of the X-ray surface brightness distribution to constrain the dynamical state of a galaxy cluster. Using X-ray observations from the Einstein Observatory IPC, we measure the first moment FM, the ellipsoidal orientation angle, and the axial ratio at a sequence of radii in the cluster. We argue that a significant variation in the image centroid FM as a function of radius is evidence for a nonequilibrium feature in the intracluster medium (ICM) density distribution. In simple terms, centroid shifts indicate that the center of mass of the ICM varies with radius. This variation is a tracer of continuing dynamical evolution. For each cluster, we evaluate the significance of variations in the centroid of the IPC image by computing the same statistics on an ensemble of simulated cluster images. In producing these simulated images we include X-ray point source emission, telescope vignetting, Poisson noise, and characteristics of the IPC. Application of this new method to five Abell clusters reveals that the core of each one has significant substructure. In addition, we find significant variations in the orientation angle and the axial ratio for several of the clusters.

Environmental variation at the onset of independent foraging affects full-grown body mass in the red fox

PubMed Central

Soulsbury, Carl D; Iossa, Graziella; Baker, Philip J; Harris, Stephen

2008-01-01

The period following the withdrawal of parental care has been highlighted as a key developmental period for juveniles. One reason for this is that juveniles cannot forage as competently as adults, potentially placing them at greater risk from environmentally-induced changes in food availability. However, no study has examined this topic. Using a long-term dataset on red foxes (Vulpes vulpes), we examined (i) dietary changes that occurred in the one-month period following the attainment of nutritional independence, (ii) diet composition in relation to climatic variation, and (iii) the effect of climatic variation on subsequent full-grown mass. Diet at nutritional independence contained increased quantities of easy-to-catch food items (earthworms and insects) when compared with pre-independence. Interannual variation in the volume of rainfall at nutritional independence was positively correlated to the proportion of earthworms in cub diet. Pre-independence cub mass and rainfall immediately following nutritional independence explained a significant proportion of variance in full-grown mass, with environmental variation affecting full-grown mass of the entire cohorts. Thus, weather-mediated availability of easy-to-catch food items at a key developmental stage has lifelong implications for the development of juvenile foxes by affecting full-grown mass, which in turn appears to be an important component of individual reproductive potential. PMID:18628118

Significance of groundwater flux on contaminant concentration and mass discharge in the nonaqueous phase liquid (NAPL) contaminated zone.

PubMed

Zhu, Jianting; Sun, Dongmin

2016-09-01

Groundwater flowing through residual nonaqueous phase liquid (NAPL) source zone will cause NAPL dissolution and generate large contaminant plume. The use of contaminant mass discharge (CMD) measurements in addition to NAPL aqueous phase concentration to characterize site conditions and assess remediation performance is becoming popular. In this study, we developed new and generic numerical models to investigate the significance of groundwater flux temporal variations on the NAPL source dynamics. The developed models can accommodate any temporal variations of groundwater flux in the source zone. We examined the various features of groundwater flux using a few selected functional forms of linear increase/decrease, gradual smooth increase/decrease, and periodic fluctuations with a general trend. Groundwater flux temporal variations have more pronounced effects on the contaminant mass discharge dynamics than the aqueous concentration. If the groundwater flux initially increases, then the reduction in contaminant mass discharge (CMDR) vs. NAPL mass reduction (MR) relationship is mainly downward concave. If the groundwater flux initially decreases, then CMDR vs. MR relationship is mainly upward convex. If the groundwater flux variations are periodic, the CMDR vs. MR relationship tends to also have periodic variations ranging from upward convex to downward concave. Eventually, however, the CMDR vs. MR relationship approaches 1:1 when majority of the NAPL mass becomes depleted. Copyright © 2016 Elsevier B.V. All rights reserved.

Monitoring stress-related mass variations in Amazon trees using accelerometers

NASA Astrophysics Data System (ADS)

van Emmerik, T. H. M.; Steele-Dunne, S. C.; Gentine, P.; Hut, R.; Guerin, M. F.; Leus, G.; Oliveira, R. S.; Van De Giesen, N.

2016-12-01

Containing half of the world's rainforests, the Amazon plays a key role in the global water and carbon budget. However, the Amazon remains poorly understood, but appears to be vulnerable to increasing moisture stress, and future droughts have the potential to considerably change the global water and carbon budget. Field measurements will allow further investigations of the effects of moisture stress and droughts on tree dynamics, and its impact on the water and carbon budget. This study focuses on studying the diurnal mass variations of seven Amazonian tree species. The mass of trees is influenced by physiological processes within the tree (e.g. transpiration and root water uptake), as well as external loads (e.g. intercepted precipitation). Depending on the physiological traits of an individual tree, moisture stress and drought affect processes such as photosynthesis, assimilation, transpiration, and root water uptake. In turn, these have their influence on diurnal mass variations of a tree. Our study uses measured three-dimensional displacement and acceleration of trees, to detect and quantify their diurnal (bio)mass variations. Nineteen accelerometers and dendrometers were installed on seven different tree species in the Amazon rainforest, covering an area of 250 x 250 m. The selected species span a wide range in wood density (0.5 - 1.1), diameter (15 - 40 cm) and height (25 - 60 m). Acceleration was measured with a frequency of 10 Hz, from August 2015 to June 2016, covering both the wet and dry season. On-site additional measurements of net radiation, wind speed at three heights, temperature, and precipitation as available every 15 minutes. Dendrometers measured variation in xylem and bark thickness every 5 minutes. The MUltiple SIgnal Classification (MUSIC) algorithm was applied to the acceleration time series to estimate the frequency spectrum of each tree. A correction was necessary to account for the dominant effect of wind. The resulting spectra reveal clear diurnal variations, as well as changes during precipitation events. Comparison with ancillary data suggests that we can extract information on diurnal mass variations from the accelerometer data. This may provide valuable insight into the effects of water stress on mass variations in different Amazon tree species.

Rapid recovery from the Late Ordovician mass extinction

NASA Technical Reports Server (NTRS)

Krug, A. Z.; Patzkowsky, M. E.

2004-01-01

Understanding the evolutionary role of mass extinctions requires detailed knowledge of postextinction recoveries. However, most models of recovery hinge on a direct reading of the fossil record, and several recent studies have suggested that the fossil record is especially incomplete for recovery intervals immediately after mass extinctions. Here, we analyze a database of genus occurrences for the paleocontinent of Laurentia to determine the effects of regional processes on recovery and the effects of variations in preservation and sampling intensity on perceived diversity trends and taxonomic rates during the Late Ordovician mass extinction and Early Silurian recovery. After accounting for variation in sampling intensity, we find that marine benthic diversity in Laurentia recovered to preextinction levels within 5 million years, which is nearly 15 million years sooner than suggested by global compilations. The rapid turnover in Laurentia suggests that processes such as immigration may have been particularly important in the recovery of regional ecosystems from environmental perturbations. However, additional regional studies and a global analysis of the Late Ordovician mass extinction that accounts for variations in sampling intensity are necessary to confirm this pattern. Because the record of Phanerozoic mass extinctions and postextinction recoveries may be compromised by variations in preservation and sampling intensity, all should be reevaluated with sampling-standardized analyses if the evolutionary role of mass extinctions is to be fully understood.

Diurnal variations of aerosol characteristics at a rural measuring site close to the Ruhr-Area, Germany

NASA Astrophysics Data System (ADS)

Kuhlbusch, T. A. J.; John, A. C.; Fissan, H.

PM10, PM2.5, and Black Carbon (BC) mass concentrations as well as number size distributions were measured quasi-online at a rural sampling site from 18 September to 17 October 1997. Average PM10, PM2.5, and BC mass concentrations were 37 ± 25, 25 ± 23, and 2 ± 1 μgm -3, respectively. All determined aerosol characteristics showed significant diurnal variations with generally higher concentrations during daytime compared to nights. Maxima in mass concentrations were around 11 AM and 8 PM during weekdays, most likely caused by commuter traffic. Decreased mass concentrations, changes in chemical composition and size distribution have been observed for the time from 12 to 5 PM. Diurnal variations of the BC/PM2.5 mass ratio revealed a minimum between 12 and 4 PM. The ratio of particle volume (0.5-2.5 μm) to particle mass (PM2.5) called 'potential density' also showed significant diurnal changes. These changes could be attributed to increasing in mixing height and windspeed. The determined diurnal variations in particle mass, composition, and size distribution may be relevant for epidemiological studies. We propose that diurnally weighted averages of relevant aerosol characteristics, which take diurnal patterns of human activities into account, should be used in epidemiological studies.

Estimation of root zone storage capacity at the catchment scale using improved Mass Curve Technique

NASA Astrophysics Data System (ADS)

Zhao, Jie; Xu, Zongxue; Singh, Vijay P.

2016-09-01

The root zone storage capacity (Sr) greatly influences runoff generation, soil water movement, and vegetation growth and is hence an important variable for ecological and hydrological modelling. However, due to the great heterogeneity in soil texture and structure, there seems to be no effective approach to monitor or estimate Sr at the catchment scale presently. To fill the gap, in this study the Mass Curve Technique (MCT) was improved by incorporating a snowmelt module for the estimation of Sr at the catchment scale in different climatic regions. The "range of perturbation" method was also used to generate different scenarios for determining the sensitivity of the improved MCT-derived Sr to its influencing factors after the evaluation of plausibility of Sr derived from the improved MCT. Results can be showed as: (i) Sr estimates of different catchments varied greatly from ∼10 mm to ∼200 mm with the changes of climatic conditions and underlying surface characteristics. (ii) The improved MCT is a simple but powerful tool for the Sr estimation in different climatic regions of China, and incorporation of more catchments into Sr comparisons can further improve our knowledge on the variability of Sr. (iii) Variation of Sr values is an integrated consequence of variations in rainfall, snowmelt water and evapotranspiration. Sr values are most sensitive to variations in evapotranspiration of ecosystems. Besides, Sr values with a longer return period are more stable than those with a shorter return period when affected by fluctuations in its influencing factors.

Observed Luminosity Spread in Young Clusters and FU Ori Stars: A Unified Picture

NASA Astrophysics Data System (ADS)

Baraffe, I.; Vorobyov, E.; Chabrier, G.

2012-09-01

The idea that non-steady accretion during the embedded phase of protostar evolution can produce the observed luminosity spread in the Herzsprung-Russell diagram (HRD) of young clusters has recently been called into question. Observations of FU Ori, for instance, suggest an expansion of the star during strong accretion events, whereas the luminosity spread implies a contraction of the accreting objects, decreasing their radiating surface. In this paper, we present a global scenario based on calculations coupling episodic accretion histories derived from numerical simulations of collapsing cloud prestellar cores of various masses and subsequent protostar evolution. Our calculations show that, assuming an initial protostar mass Mi ~ 1 M Jup, typical of the second Larson's core, both the luminosity spread in the HRD and the inferred properties of FU Ori events (mass, radius, accretion rate) can be explained by this scenario, providing two conditions. First, there must be some variation within the fraction of accretion energy absorbed by the protostar during the accretion process. Second, the range of this variation should increase with increasing accretion burst intensity and thus with the initial core mass and final star mass. The numerical hydrodynamics simulations of collapsing cloud prestellar cores indeed show that the intensity of the accretion bursts correlates with the mass and initial angular momentum of the prestellar core. Massive prestellar cores with high initial angular momentum are found to produce intense bursts characteristic of FU Ori-like events. Our results thus suggest a link between the burst intensities and the fraction of accretion energy absorbed by the protostar, with some threshold in the accretion rate, of the order of 10-5 M ⊙ yr-1, delimitating the transition from "cold" to "hot" accretion. Such a transition might reflect a change in the accretion geometry with increasing accretion rate, i.e., a transition from magnetospheric or thin-disk to thick-disk accretion, or in the magnetospheric interaction between the star and the disk. Conversely, the luminosity spread can also be explained by a variation of the initial protostar mass within the ~1-5 M Jup range, although it is unclear for now whether such a spread among the second Larson's core can be produced during the prestellar core second collapse. This unified picture confirms the idea that early accretion during protostar and proto-brown dwarf formation/evolution can explain the observed luminosity spread in young clusters without invoking any significant age spread, and that the concept of a well-defined birthline does not apply for low-mass objects. Finally, we examine the impact of accretion on the determination of the initial mass function in young clusters.

The Arctic clouds from model simulations and long-term observations at Barrow, Alaska

NASA Astrophysics Data System (ADS)

Zhao, Ming

The Arctic is a region that is very sensitive to global climate change while also experiencing significant changes in its surface air temperature, sea-ice cover, atmospheric circulation, precipitation, snowfall, biogeochemical cycling, and land surface. Although previous studies have shown that the arctic clouds play an important role in the arctic climate changes, the arctic clouds are poorly understood and simulated in climate model due to limited observations. Furthermore, most of the studies were based on short-term experiments and typically only cover the warm seasons, which do not provide a full understanding of the seasonal cycle of arctic clouds. To address the above concerns and to improve our understanding of arctic clouds, six years of observational and retrieval data from 1999 to 2004 at the Atmospheric Radiation Management (ARM) Climate Research Facility (ACRF) North Slope of Alaska (NSA) Barrow site are used to understand the arctic clouds and related radiative processes. In particular, we focus on the liquid-ice mass partition in the mixed-phase cloud layer. Statistical results show that aerosol type and concentration are important factors that impact the mixed-phase stratus (MPS) cloud microphysical properties: liquid water path (LWP) and liquid water fraction (LWF) decrease with the increase of cloud condensation nuclei (CCN) number concentration; the high dust loading and dust occurrence in the spring are possible reasons for the much lower LWF than the other seasons. The importance of liquid-ice mass partition on surface radiation budgets was analyzed by comparing cloud longwave radiative forcings under the same LWP but different ice water path (IWP) ranges. Results show the ice phase enhance the surface cloud longwave (LW) forcing by 8˜9 W m-2 in the moderately thin MPS. This result provides an observational evidence on the aerosol glaciation effect in the moderately thin MPS, which is largely unknown so far. The above new insights are important to guide the model parameterizations of liquid-ice mass partition in arctic mixed-phase clouds, and are served as a test bed to cloud models and cloud microphysical schemes. The observational data between 1999 and 2007 are used to assess the performance of the European Center for Medium-Range Weather Forecasts (ECMWF) model in the Arctic region. The ECMWF model-simulated near-surface humidity had seasonal dependent biases as large as 20%, while also experiencing difficulty representing boundary layer (BL) temperature inversion height and strength during the transition seasons. Although the ECMWF model captured the seasonal variation of surface heat fluxes, it had sensible heat flux biases over 20 W m-2 in most of the cold months. Furthermore, even though the model captured the general seasonal variations of low-level cloud fraction (LCF) and LWP, it still overestimated the LCF by 20% or more and underestimated the LWP over 50% in the cold season. On average, the ECMWF model underestimated LWP by ˜30 g m-2 but more accurately predicted ice water path for BL clouds. For BL mixed-phase clouds, the model predicted water-ice mass partition was significantly lower than the observations, largely due to the temperature dependence of water-ice mass partition used in the model. The new cloud and BL schemes of the ECMWF model that were implemented after 2003 only resulted in minor improvements in BL cloud simulations in summer. These results indicate that significant improvements in cold season BL and mixed-phase cloud processes in the model are needed. In this study, single-layer MPS clouds were simulated by the Weather Research and Forecasting (WRF) model under different microphysical schemes and different ice nuclei (IN) number concentrations. Results show that by using proper IN concentration, the WRF model incorporated with Morrison microphysical scheme can reasonably capture the observed seasonal differences in temperature dependent liquid-ice mass partition. However, WRF simulations underestimate both LWP and IWP indicating its deficiency in capturing the radiative impacts of arctic MPS clouds.

Causes of plasma column contraction in surface-wave-driven discharges in argon at atmospheric pressure

NASA Astrophysics Data System (ADS)

Ridenti, Marco Antonio; de Amorim, Jayr; Dal Pino, Arnaldo; Guerra, Vasco; Petrov, George

2018-01-01

In this work we compute the main features of a surface-wave-driven plasma in argon at atmospheric pressure in view of a better understanding of the contraction phenomenon. We include the detailed chemical kinetics dynamics of Ar and solve the mass conservation equations of the relevant neutral excited and charged species. The gas temperature radial profile is calculated by means of the thermal diffusion equation. The electric field radial profile is calculated directly from the numerical solution of the Maxwell equations assuming the surface wave to be propagating in the TM00 mode. The problem is considered to be radially symmetrical, the axial variations are neglected, and the equations are solved in a self-consistent fashion. We probe the model results considering three scenarios: (i) the electron energy distribution function (EEDF) is calculated by means of the Boltzmann equation; (ii) the EEDF is considered to be Maxwellian; (iii) the dissociative recombination is excluded from the chemical kinetics dynamics, but the nonequilibrium EEDF is preserved. From this analysis, the dissociative recombination is shown to be the leading mechanism in the constriction of surface-wave plasmas. The results are compared with mass spectrometry measurements of the radial density profile of the ions Ar+ and Ar2+. An explanation is proposed for the trends seen by Thomson scattering diagnostics that shows a substantial increase of electron temperature towards the plasma borders where the electron density is small.

Mercury Detection with Gold Nanoparticles: Investigating Fundamental Phenomena and Expanding Applications

NASA Astrophysics Data System (ADS)

Crosby, Jeffrey Scott

Mercury is a pollutant of grave concern with well documented neurological and developmental health impacts. Better sensing methodology would improve detection and control of mercury and thus reduce its health burden. Gold nanoparticles provide a sensing medium with potential advantages in sensitivity, selectivity, robustness, and cost over established techniques. Mercury readily adsorbs onto the surface of the gold changing the localized surface plasmon resonance which is measured as a shift in the peak optical absorbance wavelength. This shift is dependent on the mercury concentration and predictable with classical electromagnetism. This work investigates some of the fundamental relationships driving sensor response. The effects of mass transfer and surface kinetics on mercury/gold nanoparticle adsorption are determined with analytical models and experimental results based on impinging flow geometry. To decouple mass transfer and surface kinetics adsorption, electrical analogy models are constructed and fit to the experimental data. The models can account for variations in flow conditions and surface coatings on the nanoparticles. These models are generalizable to other systems. Results from these fundamental investigations are used to improve and extend sensor performance. The time response or collection efficiency is optimized depending on system requirements. Using the knowledge gained, the applicability of gold nanoparticle mercury sensors is extended to a fiber optic based system and aqueous detection. Nanorods deposited on the surface of a fiber optic cable have a linear response with concentration and are able to detect mercury down to 1.0 mug/m3. The modification of an established oxidation/reduction scheme for use with the sensor allows for the detection of ionic and organic mercury from water samples which ordinarily would not be reactive with gold nanoparticles. The aqueous sensor was able to detect mercury below the EPA's drinking water limit.

The New Horizons Radio Science Experiment: Expected Performance in Measurements of Pluto's Atmospheric Structure, Surface Pressure, and Surface Temperature

NASA Astrophysics Data System (ADS)

Hinson, D. P.; Linscott, I.; Woods, W. W.; Tyler, G. L.; Bird, M. K.; Paetzold, M.; Strobel, D. F.

2014-12-01

The New Horizons (NH) payload includes a Radio Science Experiment (REX) for investigating key characteristics of Pluto and Charon during the upcoming flyby in July 2015. REX flight equipment augments the NH radio transceiver used for spacecraft communications and tracking. The REX hardware implementation requires 1.6 W and 160 g. This presentation will focus on the final design and the predicted performance of two high-priority observations. First, REX will receive signals from a pair of 70-m antennas on Earth - each transmitting 20 kW at 4.2-cm wavelength - during a diametric radio occultation by Pluto. The data recorded by REX will reveal the surface pressure, the temperature structure of the lower atmosphere, and the surface radius. Second, REX will measure the thermal emission from Pluto at 4.2-cm wavelength during two linear scans across the disk at close range when both the dayside and the nightside are visible, allowing the surface temperature and its spatial variations to be determined. Both scans extend from limb to limb with a resolution of about 10 pixels; one bisects Pluto whereas the second crosses the winter pole. We will illustrate the capabilities of REX by reviewing the method of analysis and the precision achieved in a lunar occultation observed by New Horizons in May 2011. Re-analysis of radio occultation measurements by Voyager 2 at Triton is also under way. More generally, REX objectives include a radio occultation search for Pluto's ionosphere; examination of Charon through both radio occultation and radiometry; a search for a radar echo from Pluto's surface; and improved knowledge of the Pluto system mass and the Pluto-Charon mass ratio from a combination of two-way and one-way Doppler frequency measurements.

How reactive fluids alter fracture walls and affect shale-matrix accessibility

NASA Astrophysics Data System (ADS)

Fitts, J. P.; Deng, H.; Peters, C. A.

2014-12-01

Predictions of mass transfer across fracture boundaries and fluid flow in fracture networks provide fundamental inputs into risk and life cycle assessments of geologic energy technologies including oil and gas extraction, geothermal energy systems and geologic CO2 storage. However, major knowledge gaps exist due to the lack of experimental observations of how reactive fluids alter the pore structures and accessible surface area within fracture boundaries that control the mass transfer of organics, metals and salts, and influence fluid flow within the fracture. To investigate the fracture and rock matrix properties governing fracture boundary alteration, we developed a new flow-through cell that enables time-dependent 2D x-ray imaging of mineral dissolution and/or precipitation at a fracture surface. The parallel plate design provides an idealized fracture geometry to investigate the relationship between flow rate, reaction rate, and mineral spatial heterogeneity and variation. In the flow-cell, a carbonate-rich sample of Eagle Ford shale was reacted with acidified brine. The extent and rate of mineral dissolution were correlated with calcite abundance relative to less soluble silicate minerals. Three-dimensional x-ray tomography of the reacted fracture wall shows how calcite dissolution left behind a porous network of silicate minerals. And while this silicate network essentially preserved the location of the initial fracture wall, the pore network structures within the fracture boundary were dramatically altered, such that the accessible surface area of matrix components increased significantly. In a second set of experiments with a limestone specimen, however, the extent of dissolution and retreat of the fracture wall was not strictly correlated with the occurrence of calcite. Instead, the pattern and extent of dissolution suggested secondary causes such as calcite morphology, the presence of argillaceous minerals and other diagenetic features. Our experiments show that while calcite dissolution is the primary geochemical driver of fracture wall alterations, hydrodynamic properties and matrix accessibility within fracture boundaries evolve based on a complex relationship between mineral spatial heterogeneity and variation, fluid chemistry and flow rate.

Deposition measurement of particulate matter in connection with corrosion studies.

PubMed

Ferm, Martin; Watt, John; O'Hanlon, Samantha; De Santis, Franco; Varotsos, Costas

2006-03-01

A new passive particle collector (inert surrogate surface) that collects particles from all directions has been developed. It was used to measure particle deposition at 35 test sites as part of a project that examined corrosion of materials in order that variation in particulate material could be used in development of dose-response functions in a modern multi-pollutant environment. The project, MULTI-ASSESS, was funded by the EU to examine the effects of air pollution on cultural heritage. Passive samplers were mounted rain-protected, and both in wind-protected and wind-exposed positions, to match the exposure of the samples for corrosion studies. The particle mass and its chemical content (nitrate, ammonium, sulfate, calcium, sodium, chloride, magnesium and potassium) were analysed. The loss of light reflectance on the surrogate surface was also measured. Very little ammonium and potassium was found, and one or more anions are missing in the ion balance. There were many strong correlations between the analysed species. The mass of analysed water-soluble ions was fairly constant at 24% of the total mass. The particle mass deposited to the samplers in the wind-protected position was about 25% of the particles deposited to an openly exposed sampler. The Cl-/Na+ ratios indicate a reaction between HNO(3) and NaCl. The deposited nitrate flux corresponds to the missing chloride. The Ca2+ deposition equals the SO4(2-) deposition and the anion deficiency. The SO4(2-) deposition most likely originates from SO2 that has reacted with basic calcium-containing particles either before or after they were deposited. The particle depositions at the urban sites were much higher than in nearby rural sites. The deposited mass correlated surprisingly well with the PM(10) concentration, except at sites very close to traffic.

Dietary pattern, the metabolic syndrome, and left ventricular mass and systolic function: the Multi-Ethnic Study of Atherosclerosis.

PubMed

Liu, Longjian; Nettleton, Jennifer A; Bertoni, Alain G; Bluemke, David A; Lima, João A; Szklo, Moyses

2009-08-01

Little is known about the relations between dietary patterns, metabolic dysfunction, and left ventricular (LV) function. The objective was to examine associations of dietary patterns with LV mass and function and to explore the potential role of metabolic dysfunction in the association between diet and LV function. Dietary patterns that maximally explained the variation in metabolic syndrome (MetSyn) components were derived by using reduced rank regression (RRR). LV mass, stroke volume, and LV ejection fraction (LVEF) were measured by magnetic resonance imaging. Associations between dietary pattern and LV indexes were analyzed cross-sectionally. A total of 4601 participants aged 45-84 y and free of clinical cardiovascular disease were studied. The primary RRR dietary pattern score was positively correlated with intake of foods with a high glycemic index, high-fat meats, cheeses, and processed foods and negatively correlated with low intakes of vegetables, soy, fruit, green and black tea, low-fat dairy desserts, seeds and nuts, and fish. Multivariate analyses showed that each 1-unit increase in the RRR dietary pattern score was associated with a 0.32-g/m(2) increase in LV mass/body surface area, a 0.43-mL/m(2) decrease in stroke volume/body surface area, and a 0.21% decrease in LVEF. The associations of the RRR dietary pattern score with LV mass and stroke indexes were attenuated and became nonsignificant after adjustment for all MetSyn components (P > 0.05). The results suggest that the RRR dietary pattern is significantly associated with unfavorable LV function, and this association might be mediated by metabolic dysfunction. Given the cross-sectional nature of our study, these results must be confirmed with the use of longitudinal data.

Identifying water mass depletion in Northern Iraq observed by GRACE

NASA Astrophysics Data System (ADS)

Mulder, G.; Olsthoorn, T. N.; Al-Manmi, D. A. M. A.; Schrama, E. J. O.; Smidt, E. H.

2014-10-01

Observations acquired by Gravity Recovery And Climate Experiment (GRACE) mission indicate a mass loss of 31 ± 3 km3 or 130 ± 14 mm in Northern Iraq between 2007 and 2009. This data is used as an independent validation of a hydrologic model of the region including lake mass variations. We developed a rainfall-runoff model for five tributaries of the Tigris River, based on local geology and climate conditions. Model inputs are precipitation from Tropical Rainfall Measurement Mission (TRMM) observations, and potential evaporation from GLDAS model parameters. Our model includes a representation of the karstified aquifers that cause large natural groundwater variations in this region. Observed river discharges were used to calibrate our model. In order to get the total mass variations, we corrected for lake mass variations derived from Moderate Resolution Imaging Spectroradiometer (MODIS) in combination with satellite altimetry and some in-situ data. Our rainfall-runoff model confirms that Northern Iraq suffered a drought between 2007 and 2009 and is consistent with the mass loss observed by GRACE over that period. Also, GRACE observed the annual cycle predicted by the rainfall-runoff model. The total mass depletion seen by GRACE between 2007 and 2009 is mainly explained by a lake mass depletion of 74 ± 4 mm and a natural groundwater depletion of 37 ± 6 mm. Our findings indicate that man-made groundwater extraction has a minor influence in this region while depletion of lake mass and geology play a key role.

Geochemical investigation of weathering processes in a forested headwater catchment: Mass-balance weathering fluxes

USGS Publications Warehouse

Jones, B.F.; Herman, J.S.

2008-01-01

Geochemical research on natural weathering has often been directed towards explanations of the chemical composition of surface water and ground water resulting from subsurface water-rock interactions. These interactions are often defined as the incongruent dissolution of primary silicates, such as feldspar, producing secondary weathering products, such as clay minerals and oxyhydroxides, and solute fluxes (Meunier and Velde, 1979). The chemical composition of the clay-mineral product is often ignored. However, in earlier investigations, the saprolitic weathering profile at the South Fork Brokenback Run (SFBR) watershed, Shenandoah National Park, Virginia, was characterized extensively in terms of its mineralogical and chemical composition (Piccoli, 1987; Pochatila et al., 2006; Jones et al., 2007) and its basic hydrology. O'Brien et al. (1997) attempted to determine the contribution of primary mineral weathering to observed stream chemistry at SFBR. Mass-balance model results, however, could provide only a rough estimate of the weathering reactions because idealized mineral compositions were utilized in the calculations. Making use of detailed information on the mineral occurrence in the regolith, the objective of the present study was to evaluate the effects of compositional variation on mineral-solute mass-balance modelling and to generate plausible quantitative weathering reactions that support both the chemical evolution of the surface water and ground water in the catchment, as well as the mineralogical evolution of the weathering profile. ?? 2008 The Mineralogical Society.

Tree-to-tree variation in seed size and its consequences for seed dispersal versus predation by rodents.

PubMed

Wang, Bo; Ives, Anthony R

2017-03-01

Individual variation in seed size and seed production is high in many plant species. How does this variation affect seed-dispersing animals and, in turn, the fitness of individual plants? In this study, we first surveyed intraspecific variation in seed mass and production in a population of a Chinese white pine, Pinus armandii. For 134 target trees investigated in 2012, there was very high variation in seed size, with mean seed mass varying among trees almost tenfold, from 0.038 to 0.361 g. Furthermore, 30 of the 134 trees produced seeds 2 years later, and for these individuals there was a correlation in seed mass of 0.59 between years, implying consistent differences among individuals. For a subset of 67 trees, we monitored the foraging preferences of scatter-hoarding rodents on a total of 15,301 seeds: 8380 were ignored, 3184 were eaten in situ, 2651 were eaten after being cached, and 395 were successfully dispersed (cached and left intact). At the scale of individual seeds, seed mass affected almost every decision that rodents made to eat, remove, and cache individual seeds. At the level of individual trees, larger seeds had increased probabilities of both predation and successful dispersal: the effects of mean seed size on costs (predation) and benefits (caching) balanced out. Thus, despite seed size affecting rodent decisions, variation among trees in dispersal success associated with mean seed size was small once seeds were harvested. This might explain, at least in part, the maintenance of high variation in mean seed mass among tree individuals.

Evolution of complex organic molecules in hot molecular cores. Synthetic spectra at (sub-)mm wavebands

NASA Astrophysics Data System (ADS)

Choudhury, R.; Schilke, P.; Stéphan, G.; Bergin, E.; Möller, T.; Schmiedeke, A.; Zernickel, A.

2015-03-01

Context. Hot molecular cores (HMCs) are intermediate stages of high-mass star formation and are also known for their rich chemical reservoirs and emission line spectra at (sub-)mm wavebands. Complex organic molecules (COMs) such as methanol (CH3OH), ethanol (C2H5OH), dimethyl ether (CH3OCH3), and methyl formate (HCOOCH3) produce most of these observed lines. The observed spectral feature of HMCs such as total number of emission lines and associated line intensities are also found to vary with evolutionary stages. Aims: We aim to investigate the spectral evolution of these COMs to explore the initial evolutionary stages of high-mass star formation including HMCs. Methods: We developed various 3D models for HMCs guided by the evolutionary scenarios proposed by recent empirical and modeling studies. We then investigated the spatio-temporal variation of temperature and molecular abundances in HMCs by consistently coupling gas-grain chemical evolution with radiative transfer calculations. We explored the effects of varying physical conditions on molecular abundances including density distribution and luminosity evolution of the central protostar(s) among other parameters. Finally, we simulated the synthetic spectra for these models at different evolutionary timescales to compare with observations. Results: Temperature has a profound effect on the formation of COMs through the depletion and diffusion on grain surface to desorption and further gas-phase processing. The time-dependent temperature structure of the hot core models provides a realistic framework for investigating the spatial variation of ice mantle evaporation as a function of evolutionary timescales. We find that a slightly higher value (15 K) than the canonical dark cloud temperature (10 K) provides a more productive environment for COM formation on grain surface. With increasing protostellar luminosity, the water ice evaporation font (~100 K) expands and the spatial distribution of gas phase abundances of these COMs also spreads out. We calculated the temporal variation of the radial profiles of these COMs for different hot core models. These profiles resemble the so-called jump profiles with relative abundances higher than 10-9 within the evaporation font will furthermore be useful to model the observed spectra of hot cores. We present the simulated spectra of these COMs for different hot core models at various evolutionary timescales. A qualitative comparison of the simulated and observed spectra suggests that these self-consistent hot core models can reproduce the notable trends in hot core spectral variation within the typical hot core timescales of 105 year. These models predict that the spatial distribution of various emission line maps will also expand with evolutionary time; this feature can be used to constrain the relative desorption energies of the molecules that mainly form on the grain surface and return to the gas phase via thermal desorption. The detailed modeling of the thermal structure of hot cores with similar masses along with the characterization of the desorption energies of different molecules can be used to constrain the luminosity evolution of the central protostars. The model predictions can be compared with high resolution observation that can probe scales of a few thousand AU in high-mass star forming regions such as from Atacama Large Millimeter/submillimeter Array (ALMA). We used a spectral fitting method to analyze the simulated spectra and find that it significantly underestimates some of the physical parameters such as temperature. The coupling of chemical evolution with radiative transfer models will be particularly useful to decipher the physical structure of hot cores and also to constrain the initial evolutionary stages of high-mass star formation. Appendices are available in electronic form at http://www.aanda.org

Regional variability in sea ice melt in a changing Arctic

PubMed Central

Perovich, Donald K.; Richter-Menge, Jacqueline A.

2015-01-01

In recent years, the Arctic sea ice cover has undergone a precipitous decline in summer extent. The sea ice mass balance integrates heat and provides insight on atmospheric and oceanic forcing. The amount of surface melt and bottom melt that occurs during the summer melt season was measured at 41 sites over the time period 1957 to 2014. There are large regional and temporal variations in both surface and bottom melting. Combined surface and bottom melt ranged from 16 to 294 cm, with a mean of 101 cm. The mean ice equivalent surface melt was 48 cm and the mean bottom melt was 53 cm. On average, surface melting decreases moving northward from the Beaufort Sea towards the North Pole; however interannual differences in atmospheric forcing can overwhelm the influence of latitude. Substantial increases in bottom melting are a major contributor to ice losses in the Beaufort Sea, due to decreases in ice concentration. In the central Arctic, surface and bottom melting demonstrate interannual variability, but show no strong temporal trends from 2000 to 2014. This suggests that under current conditions, summer melting in the central Arctic is not large enough to completely remove the sea ice cover. PMID:26032323

Quantum confined Stark effects of single dopant in polarized hemispherical quantum dot: Two-dimensional finite difference approach and Ritz-Hassé variation method

NASA Astrophysics Data System (ADS)

El Harouny, El Hassan; Nakra Mohajer, Soukaina; Ibral, Asmaa; El Khamkhami, Jamal; Assaid, El Mahdi

2018-05-01

Eigenvalues equation of hydrogen-like off-center single donor impurity confined in polarized homogeneous hemispherical quantum dot deposited on a wetting layer, capped by insulated matrix and submitted to external uniform electric field is solved in the framework of the effective mass approximation. An infinitely deep potential is used to describe effects of quantum confinement due to conduction band offsets at surfaces where quantum dot and surrounding materials meet. Single donor ground state total and binding energies in presence of electric field are determined via two-dimensional finite difference approach and Ritz-Hassé variation principle. For the latter method, attractive coulomb correlation between electron and ionized single donor is taken into account in the expression of trial wave function. It appears that off-center single dopant binding energy, spatial extension and radial probability density are strongly dependent on hemisphere radius and single dopant position inside quantum dot. Influence of a uniform electric field is also investigated. It shows that Stark effect appears even for very small size dots and that single dopant energy shift is more significant when the single donor is near hemispherical surface.

Analytical solution for heat transfer in three-dimensional porous media including variable fluid properties

NASA Technical Reports Server (NTRS)

Siegel, R.; Goldstein, M. E.

1972-01-01

An analytical solution is obtained for flow and heat transfer in a three-dimensional porous medium. Coolant from a reservoir at constant pressure and temperature enters one portion of the boundary of the medium and exits through another portion of the boundary which is at a specified uniform temperature and uniform pressure. The variation with temperature of coolant density and viscosity are both taken into account. A general solution is found that provides the temperature distribution in the medium and the mass and heat fluxes along the portion of the surface through which the coolant is exiting.

Seasonal 7Be and 137Cs activities in surface air before and after the Chernobyl event.

PubMed

Kulan, A

2006-01-01

Seasonal fluctuations of cosmogenic (7)Be (T(1/2)=53.4 days) and anthropogenic (137)Cs (T(1/2)=30 years) activities in surface air (aerosols) have been extracted from a long data record (1972-2000) at high latitude (56 degrees N-68 degrees N, Sweden). Normalization to weekly average values was used to control long-term trends so that cyclical trends could be investigated. Enhanced (7)Be activity was observed in spring and summer seasons and likely relates to the seasonal thinning of the tropopause. Variations in the (137)Cs activity record seem to reflect how the isotope was injected in the atmosphere (stratospheric from bomb tests and tropospheric from the Chernobyl accident) and subsequent transport mechanisms. Accordingly, until 1986, the surface air (137)Cs activity was strongly related to nuclear weapons test fallout and exhibits temporal fluctuations resembling the (7)Be. Conversely, since 1986 the Chernobyl-produced (137)Cs dominates the long-term record that shows annual cycles that are strongly controlled by atmospheric boundary layer conditions. Additionally, short-term data within the post-Chernobyl period suggest subtle intrusion of air masses rich in (137)Cs that may occur throughout the year, and differences resulting from spatial occurrence at these latitudes. This is an important observation that may have to do with year-to-year variation and calls for caution when interpreting short-term data records.

Southern Ocean Mixed-Layer Seasonal and Interannual Variations From Combined Satellite and In Situ Data

NASA Astrophysics Data System (ADS)

Buongiorno Nardelli, B.; Guinehut, S.; Verbrugge, N.; Cotroneo, Y.; Zambianchi, E.; Iudicone, D.

2017-12-01

The depth of the upper ocean mixed layer provides fundamental information on the amount of seawater that directly interacts with the atmosphere. Its space-time variability modulates water mass formation and carbon sequestration processes related to both the physical and biological pumps. These processes are particularly relevant in the Southern Ocean, where surface mixed-layer depth estimates are generally obtained either as climatological fields derived from in situ observations or through numerical simulations. Here we demonstrate that weekly observation-based reconstructions can be used to describe the variations of the mixed-layer depth in the upper ocean over a range of space and time scales. We compare and validate four different products obtained by combining satellite measurements of the sea surface temperature, salinity, and dynamic topography and in situ Argo profiles. We also compute an ensemble mean and use the corresponding spread to estimate mixed-layer depth uncertainties and to identify the more reliable products. The analysis points out the advantage of synergistic approaches that include in input the sea surface salinity observations obtained through a multivariate optimal interpolation. Corresponding data allow to assess mixed-layer depth seasonal and interannual variability. Specifically, the maximum correlations between mixed-layer anomalies and the Southern Annular Mode are found at different time lags, related to distinct summer/winter responses in the Antarctic Intermediate Water and Sub-Antarctic Mode Waters main formation areas.

Contribution of myostatin gene polymorphisms to normal variation in lean mass, fat mass and peak BMD in Chinese male offspring.

PubMed

Yue, Hua; He, Jin-wei; Zhang, Hao; Wang, Chun; Hu, Wei-wei; Gu, Jie-mei; Ke, Yao-hua; Fu, Wen-zhen; Hu, Yun-qiu; Li, Miao; Liu, Yu-juan; Wu, Song-hua; Zhang, Zhen-lin

2012-05-01

Myostatin gene is a member of the transforming growth factor-β (TGF-β) family that negatively regulates skeletal muscle growth. Genetic polymorphisms in Myostatin were found to be associated with the peak bone mineral density (BMD) in Chinese women. The purpose of this study was to investigate whether myostatin played a role in the normal variation in peak BMD, lean mass (LM), and fat mass (FM) of Chinese men. Four hundred male-offspring nuclear families of Chinese Han ethnic group were recruited. Anthropometric measurements, including the peak BMD, body LM and FM were measured using dual-energy X-ray absorptiometry (DXA). The single nucleotide polymorphisms (SNPs) studied were tag-SNPs selected by sequencing. Both rs2293284 and +2278GA were genotyped using TaqMan assay, and rs3791783 was genotyped with PCR-restriction fragment length polymorphism (RFLP) analysis. The associations of the SNPs with anthropometric variations were analyzed using the quantitative transmission disequilibrium test (QTDT). Using QTDT to detect within-family associations, neither single SNP nor haplotype was found to be associated with peak BMD at any bone site. However, rs3791783 was found to be significantly associated with fat mass of the trunk (P<0.001). Moreover, for within-family associations, haplotypes AGG, AAA, and TGG were found to be significantly associated with the trunk fat mass (all P<0.001). Our results suggest that genetic variation within myostatin may play a role in regulating the variation in fat mass in Chinese males. Additionally, the myostatin gene may be a candidate that determines body fat mass in Chinese men.

Energy Levels in Quantum Wells.

NASA Astrophysics Data System (ADS)

Zang, Jan Xin

Normalized analytical equations for eigenstates of an arbitrary one-dimensional configuration of square potentials in a well have been derived. The general formulation is used to evaluate the energy levels of a particle in a very deep potential well containing seven internal barriers. The configuration can be considered as a finite superlattice sample or as a simplified model for a sample with only several atom layers. The results are shown in graphical forms as functions of the height and width of the potential barriers and as functions of the ratio of the effective mass in barrier to the mass in well. The formation of energy bands and surface eigenstates from eigenstates of a deep single well, the coming close of two energy bands and a surface state which are separate ordinarily, and mixing of the wave function of a surface state with the bulk energy bands are seen. Then the normalized derivation is extended to study the effect of a uniform electric field applied across a one-dimensional well containing an internal configuration of square potentials The general formulation is used to calculate the electric field dependence of the energy levels of a deep well with five internal barriers. Typical results are shown in graphical forms as functions of the barrier height, barrier width, barrier effective mass and the field strength. The formation of Stark ladders and surface states from the eigenstates of a single deep well in an electric field, the localization process of wave functions with changing barrier height, width, and field strength and their anticrossing behaviors are seen. The energy levels of a hydrogenic impurity in a uniform medium and in a uniform magnetic field are calculated with variational methods. The energy eigenvalues for the eigenstates with major quantum number less than or equal to 3 are obtained. The results are consistent with previous results. Furthermore, the energy levels of a hydrogenic impurity at the bottom of a one-dimensional parabolic quantum well with a magnetic field normal to the plane of the well are calculated with the finite-basis-set variational method. The limit of small radial distance and the limit of great radial distance are considered to choose a set of proper basis functions. It is found that the energy levels increase with increasing parabolic parameter alpha and increase with increasing normalized magnetic field strength gamma except those levels with magnetic quantum number m < 0 at small gamma.

Religious Attendance and Body Mass: An Examination of Variations by Race and Gender.

PubMed

Godbolt, Dawn; Vaghela, Preeti; Burdette, Amy M; Hill, Terrence D

2017-08-30

Studies of the association between religious attendance and body mass have yielded mixed results. In this paper, we consider intersectional variations by race and gender to advance our understanding of these inconsistencies. We use data from the 2006-2008 Health and Retirement Study to examine the association between religious attendance and three indicators of body mass: overall body mass index, waist circumference, and waist-to-height ratio (n = 11,457). For White women, attendance is either protective or unrelated to body mass. For Black women, attendance is consistently associated with increased body mass. We find that religious attendance is not associated with body mass among the men.

An overview of surface radiance and biology studies in FIFE

NASA Astrophysics Data System (ADS)

Blad, B. L.; Schimel, D. S.

1992-11-01

The use of satellite data to study and to understand energy and mass exchanges between the land surface and the atmosphere requires information about various biological processes and how various reflected or emitted spectral radiances are influenced by or manifested in these processes. To obtain such information, studies were conducted by the First ISLSCP Field Experiment (FIFE) surface radiances and biology (SRB) group using surface, near-surface, helicopter, and aircraft measurements. The two primary objectives of this group were to relate radiative fluxes to biophysical parameters and physiological processes and to assess how various management treatments affect important biological processes. This overview paper summarizes the results obtained by various SRB teams working in nine different areas: (1) measurement of bidirectional reflectance and estimation of hemispherical albedo; (2) evaluation of spatial and seasonal variability of spectral reflectance and vegetation indices; (3) determination of surface and radiational factors and their effects on vegetation indices and PAR relationships; (4) use of surface temperatures to estimate sensible heat flux; (5) controls over photosynthesis and respiration at small scales; (6) soil surface CO2 fluxes and grassland carbon budget; (7) landscape variations in controls over gas exchange and energy partitioning; (8) radiometric response of prairie to management and topography; and (9) determination of nitrogen gas exchanges in a tallgrass prairie.

The emergence of the galactic stellar mass function from a non-universal IMF in clusters

NASA Astrophysics Data System (ADS)

Dib, Sami; Basu, Shantanu

2018-06-01

We investigate the dependence of a single-generation galactic mass function (SGMF) on variations in the initial stellar mass functions (IMF) of stellar clusters. We show that cluster-to-cluster variations of the IMF lead to a multi-component SGMF where each component in a given mass range can be described by a distinct power-law function. We also show that a dispersion of ≈0.3 M⊙ in the characteristic mass of the IMF, as observed for young Galactic clusters, leads to a low-mass slope of the SGMF that matches the observed Galactic stellar mass function even when the IMFs in the low-mass end of individual clusters are much steeper.

A monolithic Lagrangian approach for fluid-structure interaction problems

NASA Astrophysics Data System (ADS)

Ryzhakov, P. B.; Rossi, R.; Idelsohn, S. R.; Oñate, E.

2010-11-01

Current work presents a monolithic method for the solution of fluid-structure interaction problems involving flexible structures and free-surface flows. The technique presented is based upon the utilization of a Lagrangian description for both the fluid and the structure. A linear displacement-pressure interpolation pair is used for the fluid whereas the structure utilizes a standard displacement-based formulation. A slight fluid compressibility is assumed that allows to relate the mechanical pressure to the local volume variation. The method described features a global pressure condensation which in turn enables the definition of a purely displacement-based linear system of equations. A matrix-free technique is used for the solution of such linear system, leading to an efficient implementation. The result is a robust method which allows dealing with FSI problems involving arbitrary variations in the shape of the fluid domain. The method is completely free of spurious added-mass effects.

Understanding Space Weather: The Sun as a Variable Star

NASA Technical Reports Server (NTRS)

Strong, Keith; Saba, Julia; Kucera, Therese

2011-01-01

The Sun is a complex system of systems and until recently, less than half of its surface was observable at any given time and then only from afar. New observational techniques and modeling capabilities are giving us a fresh perspective of the solar interior and how our Sun works as a variable star. This revolution in solar observations and modeling provides us with the exciting prospect of being able to use a vastly increased stream of solar data taken simultaneously from several different vantage points to produce more reliable and prompt space weather forecasts. Solar variations that cause identifiable space weather effects do not happen only on solar-cycle timescales from decades to centuries; there are also many shorter-term events that have their own unique space weather effects and a different set of challenges to understand and predict, such as flares, coronal mass ejections, and solar wind variations

Understanding Space Weather: The Sun as a Variable Star

NASA Technical Reports Server (NTRS)

Strong, Keith; Saba, Julia; Kucera, Therese

2012-01-01

The Sun is a complex system of systems and until recently, less than half of its surface was observable at any given time and then only from afar. New observational techniques and modeling capabilities are giving us a fresh perspective of the solar interior and how our Sun works as a variable star. This revolution in solar observations and modeling provides us with the exciting prospect of being able to use a vastly increased stream of solar data taken simultaneously from several different vantage points to produce more reliable and prompt space weather forecasts. Solar variations that cause identifiable space weather effects do not happen only on solar-cycle timescales from decades to centuries; there are also many shorter-term events that have their own unique space weather effects and a different set of challenges to understand and predict, such as flares, coronal mass ejections, and solar wind variations.

Spatial and seasonal variations of elemental composition in Mt. Everest (Qomolangma) snow/firn

NASA Astrophysics Data System (ADS)

Kang, Shichang; Zhang, Qianggong; Kaspari, Susan; Qin, Dahe; Cong, Zhiyuan; Ren, Jiawen; Mayewski, Paul A.

In May 2005, a total of 14 surface snow (0-10 cm) samples were collected along the climbing route from the advanced base camp to the summit (6500-8844 m a.s.l.) on the northern slope of Mt. Everest (Qomolangma). A 108 m firn/ice core was retrieved from the col of the East Rongbuk Glacier (28.03°N, 86.96°E, 6518 m a.s.l.) on the north eastern saddle of Mt. Everest in September 2002. Surface snow and the upper 3.5 m firn samples from the core were analyzed for major and trace elements by inductively coupled plasma mass spectroscopy (ICP-MS). Measurements show that crustal elements dominated both surface snow and the firn core, suggesting that Everest snow chemistry is mainly influenced by crustal aerosols from local rock or prevalent spring dust storms over southern/central Asia. There are no clear trends for element variations with elevation due to local crustal aerosol inputs or redistribution of surface snow by strong winds during the spring. Seasonal variability in snow/firn elements show that high elemental concentrations occur during the non-monsoon season and low values during the monsoon season. Ca, Cr, Cs, and Sr display the most distinct seasonal variations. Elemental concentrations (especially for heavy metals) at Mt. Everest are comparable with polar sites, generally lower than in suburban areas, and far lower than in large cities. This indicates that anthropogenic activities and heavy metal pollution have little effect on the Mt. Everest atmospheric environment. Everest firn core REE concentrations are the first reported in the region and seem to be comparable with those measured in modern and Last Glacial Maximum snow/ice samples from Greenland and Antarctica, and with precipitation samples from Japan and the East China Sea. This suggests that REE concentrations measured at Everest are representative of the background atmospheric environment.

Surface layer characteristics derived from fast-response micrometeorological observations over a mountain peak in the central Himalayas

NASA Astrophysics Data System (ADS)

Solanki, Raman; Dhaka, Surendra; Rajeev, Kunjukrishnapillai; Singh, Narendra; Nadimpally, Kirankumar

Diurnal evolution of atmospheric boundary layer over hilly terrains is highly complex and least understood. Fast-response micrometeorological observations carried out at Manora Peak, Nainital (29.2°N, 79.3°E, 1960 m ASL), a hill station located in the Central Himalayas during March-2013 to February-2014 has been used to investigate diurnal variations in the surface layer characteristics, energy budget and atmospheric circulation over complex terrains. This study mainly employs tower-based sonic anemometer observations (25 Hz) carried out at two levels (12 m and 27 m above the ground level) which are used to derive the variations of zonal, meridional and vertical winds, virtual temperature, momentum flux, turbulent kinetic energy, and Monin-Obukhov stability parameter during fair-weather conditions. In general, this station is manifested by warm and dry conditions as well as relatively high wind speed during pre-monsoon season (March-May); while highly moist conditions prevail during the summer monsoon season (June-September). The sensible heat flux (SHF) undergoes a prominent diurnal variation during winter and pre-monsoon seasons with peak values (200 to 400 Wm-2) occurring between 11-15 Local Time (LT) and weakly negative values (typically -20 Wm-2) during night, the latter indicating a downward transfer of heat from atmosphere to surface. The noon-time peak values systematically increases from winter to pre-monsoon season. Remarkably, the large noon-time values of SHF observed during the pre-monsoon season over this station (peak SHF of more than 400 Wm-2 during May) arise from the forced lifting of air masses, caused by the prevailing horizontal winds that blow perpendicular to the mountain. The intricate details of the surface layer parameters and fluxes over this site will assist in investigating how such a complex topography influences the flux generation process.

Recent evolution and mass balance of Cordón Martial glaciers, Cordillera Fueguina Oriental

NASA Astrophysics Data System (ADS)

Strelin, Jorge; Iturraspe, Rodolfo

2007-10-01

Past and present glacier changes have been studied at Cordón Martial, Cordillera Fueguina Oriental, Tierra del Fuego, providing novel data for the Holocene deglaciation history of southern South America and extrapolating as well its future behavior based on predicted climatic changes. Regional geomorphologic and stratigraphic correlations indicate that the last glacier advance deposited the ice-proximal ("internal") moraines of Cordón Martial, around 330 14C yr BP, during the Late Little Ice Age (LLIA). Since then glaciers have receded slowly, until 60 years ago, when major glacier retreat started. There is a good correspondence for the past 100 years between the surface area variation of four small cirque glaciers at Cordón Martial and the annual temperature and precipitation data of Ushuaia. Between 1984 and 1998, Martial Este Glacier lost 0.64 ± 0.02 × 10 6 m 3 of ice mass (0.59 ± 0.02 × 10 6 m 3 w.e.), corresponding to an average ice thinning of 7.0 ± 0.2 m (6.4 ± 0.2 m w.e), according to repeated topographic mapping. More detailed climatic data have been obtained since 1998 at the Martial Este Glacier, including air temperature, humidity and solar radiation. These records, together with the monthly mass balance measured since March 2000, document the annual response of the Martial Este Glacier to the climate variation. Mass balances during hydrological years were positive in 2000, negative in 2001 and near equilibrium in 2002. Finally, using these data and the regional temperature trend projections, modeled for different future scenarios by the Atmosphere-Ocean Model (GISS-NASA/GSFC), potential climatic-change effects on this mountain glacier were extrapolated. The analysis shows that only the Martial Este Glacier may survive this century.

An Ultra-short Period Rocky Super-Earth with a Secondary Eclipse and a Neptune-like Companion around K2-141

NASA Astrophysics Data System (ADS)

Malavolta, Luca; Mayo, Andrew W.; Louden, Tom; Rajpaul, Vinesh M.; Bonomo, Aldo S.; Buchhave, Lars A.; Kreidberg, Laura; Kristiansen, Martti H.; Lopez-Morales, Mercedes; Mortier, Annelies; Vanderburg, Andrew; Coffinet, Adrien; Ehrenreich, David; Lovis, Christophe; Bouchy, Francois; Charbonneau, David; Ciardi, David R.; Collier Cameron, Andrew; Cosentino, Rosario; Crossfield, Ian J. M.; Damasso, Mario; Dressing, Courtney D.; Dumusque, Xavier; Everett, Mark E.; Figueira, Pedro; Fiorenzano, Aldo F. M.; Gonzales, Erica J.; Haywood, Raphaëlle D.; Harutyunyan, Avet; Hirsch, Lea; Howell, Steve B.; Johnson, John Asher; Latham, David W.; Lopez, Eric; Mayor, Michel; Micela, Giusi; Molinari, Emilio; Nascimbeni, Valerio; Pepe, Francesco; Phillips, David F.; Piotto, Giampaolo; Rice, Ken; Sasselov, Dimitar; Ségransan, Damien; Sozzetti, Alessandro; Udry, Stéphane; Watson, Chris

2018-03-01

Ultra-short period (USP) planets are a class of low-mass planets with periods shorter than one day. Their origin is still unknown, with photo-evaporation of mini-Neptunes and in situ formation being the most credited hypotheses. Formation scenarios differ radically in the predicted composition of USP planets, and it is therefore extremely important to increase the still limited sample of USP planets with precise and accurate mass and density measurements. We report here the characterization of a USP planet with a period of 0.28 days around K2-141 (EPIC 246393474), and the validation of an outer planet with a period of 7.7 days in a grazing transit configuration. We derived the radii of the planets from the K2 light curve and used high-precision radial velocities gathered with the HARPS-N spectrograph for mass measurements. For K2-141b, we thus inferred a radius of 1.51 ± 0.05 R {}\\oplus and a mass of 5.08 ± 0.41 M {}\\oplus , consistent with a rocky composition and lack of a thick atmosphere. K2-141c is likely a Neptune-like planet, although due to the grazing transits and the non-detection in the RV data set, we were not able to put a strong constraint on its density. We also report the detection of secondary eclipses and phase curve variations for K2-141b. The phase variation can be modeled either by a planet with a geometric albedo of 0.30 ± 0.06 in the Kepler bandpass, or by thermal emission from the surface of the planet at ∼3000 K. Only follow-up observations at longer wavelengths will allow us to distinguish between these two scenarios.

Feeling Gravity's Pull: Gravity Modeling. The Gravity Field of Mars

NASA Technical Reports Server (NTRS)

Lemoine, Frank; Smith, David; Rowlands, David; Zuber, Maria; Neumann, G.; Chinn, Douglas; Pavlis, D.

2000-01-01

Most people take the constant presence of gravitys pull for granted. However, the Earth's gravitational strength actually varies from location to location. This variation occurs because mass, which influences an object's gravitational pull, is not evenly distributed within the planet. Changes in topography, such as glacial movement, an earthquake, or a rise in the ocean level, can subtly affect the gravity field. An accurate measurement of the Earth's gravity field helps us understand the distribution of mass beneath the surface. This insight can assist us in locating petroleum, mineral deposits, ground water, and other valuable substances. Gravity mapping can also help notice or verify changes in sea surface height and other ocean characteristics. Such changes may indicate climate change from polar ice melting and other phenomena. In addition, gravity mapping can indicate how land moves under the surface after earthquakes and other plate tectonic processes. Finally, changes in the Earth's gravity field might indicate a shift in water distribution that could affect agriculture, water supplies for population centers, and long-term weather prediction. Scientists can map out the Earth's gravity field by watching satellite orbits. When a satellite shifts in vertical position, it might be passing over an area where gravity changes in strength. Gravity is only one factor that may shape a satellite's orbital path. To derive a gravity measurement from satellite movement, scientists must remove other factors that might affect a satellite's position: 1. Drag from atmospheric friction. 2. Pressure from solar radiation as it heads toward Earth and. as it is reflected off the surface of the Earth 3. Gravitational pull from the Sun, the Moon, and other planets in the Solar System. 4. The effect of tides. 5. Relativistic effects. Scientists must also correct for the satellite tracking process. For example, the tracking signal must be corrected for refraction through the atmosphere of the Earth. Supercomputers can calculate the effect of gravity for specific locations in space following a mathematical process known as spherical harmonics, which quantifies the gravity field of a planetary body. The process is based on Laplace's fundamental differential equation of gravity. The accuracy of a spherical harmonic solution is rated by its degree and order. Minute variations in gravity are measured against the geoid, a surface of constant gravity acceleration at mean sea level. The geoid reference gravity model strength includes the central body gravitational attraction (9.8 m/sq s) and a geopotential variation in latitude partially caused by the rotation of the Earth. The rotational effect modifies the shape of the geoid to be more like an ellipsoid, rather than a perfect, circle. Variations of gravity strength from the ellipsoidal reference model are measured in units called milli-Galileos (mGals). One mGal equals 10(exp -5) m/sq s. Research projects have also measured the gravity fields of other planetary bodies, as noted in the user profile that follows. From this information, we may make inferences about our own planet's internal structure and evolution. Moreover, mapping the gravity fields of other planets can help scientists plot the most fuel-efficient course for spacecraft expeditions to those planets.

ORIGINS OF SCATTER IN THE RELATIONSHIP BETWEEN HCN 1-0 AND DENSE GAS MASS IN THE GALACTIC CENTER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mills, Elisabeth A. C.; Battersby, Cara, E-mail: elisabeth.mills@sjsu.edu

We investigate the correlation of HCN 1-0 with gas mass in the central 300 pc of the Galaxy. We find that on the ∼10 pc size scale of individual cloud cores, HCN 1-0 is well correlated with dense gas mass when plotted as a log–log relationship. There is ∼0.75 dex of scatter in this relationship from clouds like Sgr B2, which has an integrated HCN 1-0 intensity of a cloud less than half its mass, and others that have HCN 1-0 enhanced by a factor of 2–3 relative to clouds of comparable mass. We identify the two primary sources ofmore » scatter to be self-absorption and variations in HCN abundance. We also find that the extended HCN 1-0 emission is more intense per unit mass than in individual cloud cores. In fact the majority (80%) of HCN 1-0 emission comes from extended gas with column densities below 7 × 10{sup 22} cm{sup −2}, accounting for 68% of the total mass. We find variations in the brightness of HCN 1-0 would only yield a ∼10% error in the dense gas mass inferred from this line in the Galactic center. However, the observed order of magnitude HCN abundance variations, and the systematic nature of these variations, warn of potential biases in the use of HCN as dense gas mass tracer in more extreme environments such as an active galactic nucleus and shock-dominated regions. We also investigate other 3 mm tracers, finding that HNCO is better correlated with mass than HCN, and might be a better tracer of cloud mass in this environment.« less

Changes in ground-level PM mass concentration and column aerosol optical depth over East Asia during 2004-2014

NASA Astrophysics Data System (ADS)

Nam, J.; Kim, S. W.; Park, R.; Yoon, S. C.; Sugimoto, N.; Park, J. S.; Hong, J.

2015-12-01

Multi-year records of moderate resolution imaging spectroradiometer (MODIS), ground-level particulate matter (PM) mass concentration, cloud-aerosol lidar with orthogonal polarization (CALIOP), and ground-level lidar were analyzed to investigate seasonal and annual changes of aerosol optical depth (AOD) and PM mass concentration over East Asia. Least mean square fit method is applied to detect the trends and their magnitudes for each selected regions and stations. Eleven-year MODIS measurements show generally increasing trends in both AOD (1.18 % yr-1) and Ångström exponent (0.98 % yr-1), especially over the east coastal industrialized region in China. Monthly variation of AOD show maximum value at April-July, which were related to the progress of summer monsoon rain band and stationary continental air mass on the northeast of Asia. Increasing trends of AOD were found for eight cites in China (0.80 % yr-1) and Seoul site, Korea (0.40 % yr-1), whereas no significant change were shown in Gosan background site (0.04 % yr-1) and decreasing trend at five background sites in Japan (-0.42 % yr-1). Contrasting to AOD trend, all fifteen sites in China (-1.28 % yr-1), Korea (-2.77 % yr-1), and Japan (-2.03 % yr-1) showed decreasing trend of PM10 mass concentration. Also, PM2.5 mass concentration at Beijing, Seoul, Rishiri, and Oki show significant decreasing trend of -1.16 % yr-1. To further discuss the opposite trend of surface PM mass concentration and column AOD, we investigate vertical aerosol profile from lidar measurements. AOD estimated for planetary boundary layer (surface~1.5 km altitude; AODPBL) from CALIOP measurements over East China show decreasing trend of -1.71 % yr-1 over the period of 2007-2014, wherever AOD estimated for free troposphere (1.5 km~5 km altitude; AODFT) show increasing trend of 2.92 % yr-1. In addition, ground-level lidar measurements in Seoul show decreasing AODPBL trend of -2.57 % yr-1, whereas, AODFT show no significant change (-0.44 % yr-1) between 2007 and 2014. This significant decreasing AODPBL and increasing AODFT trend is attributable to the relative contribution of complex processes that may include decrease of coarse particles near surface following the implementation of numerous air pollution control and changes in meteorological factors (convection, precipitation, etc.).

Degradation of blending vulcanized natural rubber and nitril rubber (NR/NBR) by dimethyl ether through variation of elastomer ratio

NASA Astrophysics Data System (ADS)

Saputra, A. H.; Juneva, S.; Sari, T. I.; Cifriadi, A.

2018-04-01

Dimethyl ether can cause degradation of the rubber material seal in some applications. In order to use of natural rubber in industry, research about a blending of natural rubber (NR) and nitrile rubber (NBR) to produce rubber to meet the standard seal material application were conducted. This study will observe the degradation mechanisms that occur in the blending natural rubber and nitrile rubber (NR/NBR) by dimethyl ether. Nitrile rubber types used in this study is medium quality nitrile rubber with 33% of acrylonitrile content (NBR33). The observed parameters are percent change in mass, mechanical properties and surface morphology. This study is limited to see the effect of variation vulcanized blending ratio (NR/NBR33) against to swelling. The increase of nitrile rubber (NBR33) ratio of blending rubber vulcanized can reduce the tensile strength and elongation. The best elastomer variation was obtained after comparing with the standard feasibility material of seal is rubber vulcanized blending (NR/NBR33) with ratio 40:60 NR: NBR.

Estimating continental water storage variations in Central Asia area using GRACE data

NASA Astrophysics Data System (ADS)

Dapeng, Mu; Zhongchang, Sun; Jinyun, Guo

2014-03-01

The goal of GRACE satellite is to determine time-variations of the Earth's gravity, and particularly the effects of fluid mass redistributions at the surface of the Earth. This paper uses GRACE Level-2 RL05 data provided by CSR to estimate water storage variations of four river basins in Asia area for the period from 2003 to 2011. We apply a two-step filtering method to reduce the errors in GRACE data, which combines Gaussian averaging function and empirical de-correlation method. We use GLDAS hydrology to validate the result from GRACE. Special averaging approach is preformed to reduce the errors in GLDAS. The results of former three basins from GRACE are consistent with GLDAS hydrology model. In the Tarim River basin, there is more discrepancy between GRACE and GLDAS. Precipitation data from weather station proves that the results of GRACE are more plausible. We use spectral analysis to obtain the main periods of GRACE and GLDAS time series and then use least squares adjustment to determine the amplitude and phase. The results show that water storage in Central Asia is decreasing.

Near-surface density profiling of Fe ion irradiated Si (100) using extremely asymmetric x-ray diffraction by variation of the wavelength

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khanbabaee, B., E-mail: khanbabaee@physik.uni-siegen.de; Pietsch, U.; Facsko, S.

2014-10-20

In this work, we report on correlations between surface density variations and ion parameters during ion beam-induced surface patterning process. The near-surface density variations of irradiated Si(100) surfaces were investigated after off-normal irradiation with 5 keV Fe ions at different fluences. In order to reduce the x-ray probing depth to a thickness below 5 nm, the extremely asymmetrical x-ray diffraction by variation of wavelength was applied, exploiting x-ray refraction at the air-sample interface. Depth profiling was achieved by measuring x-ray rocking curves as function of varying wavelengths providing incidence angles down to 0°. The density variation was extracted from the deviationsmore » from kinematical Bragg angle at grazing incidence angles due to refraction of the x-ray beam at the air-sample interface. The simulations based on the dynamical theory of x-ray diffraction revealed that while a net near-surface density decreases with increasing ion fluence which is accompanied by surface patterning, there is a certain threshold of ion fluence to surface density modulation. Our finding suggests that the surface density variation can be relevant with the mechanism of pattern formation.« less

Movement simulation of the variable masses in the Gylden-Meshcherskii problem

DOE Office of Scientific and Technical Information (OSTI.GOV)

Starinova, Olga L.; Salmin, Vadim V.

The Gylden-Meshcherskii problem is used for various cases of dynamics of two points of the variable mass. For example, it describes of double star evolution due to mass loss at the photon expense and the corpuscular activity. Except, it is mathematical model for the movement of spacecraft with propulsion system. In the present work the mass variation laws, allowing a stationary form of the movement differential equations are considered. Movement simulation for all cases was conducted. The relative movement trajectories was constructed as for known Eddington-Jeans laws and for other mass variation laws.

Long-term Variation of Ventilation System in the East Sea (Japan Sea) Revealed by Heat Content Change and Water Mass Analysis

NASA Astrophysics Data System (ADS)

Yoon, S.; Chang, K. I.; Kim, K. R.; Lobanov, V. B.

2016-02-01

The semi-enclosed East Sea (ES) is called a miniature ocean with its own thermohaline circulation characterized by the formation of deep and intermediate water masses in the Japan Basin, southward discharge of those subsurface water masses towards the Ulleung and Yamato basins, and northward heat transport by the Tsushima Warm Current in the upper layer. Reports have been given of rapid changes of physical and biogeochemical properties associated with its ventilation system. We present results on upper ocean heat content variations and changes in water mass structure and properties from the analysis of historical and most recent hydrographic data. The analysis of non-seasonal heat content (HCA) variations in the upper 500 m from 1976 to 2007 highlights the 2-year lagged in-phase decadal-scale HCA variations in the eastern and western ES until 1995 followed by uncorrelated variations between two regions thereafter with pronounced interannual variations. Long-term trend of HCA in the entire ES shows an increasing trend, but with a large increase in the eastern part and relatively weaker but statistically significant decrease in the western part. The thickness variation of water warmer than 10°C mainly contributes to the HCA variation. Analyses of upper circulation in conjunction with climate indices suggest the importance of the wind-stress curl pattern represented by the Western Pacific index in the western ES and the influence of the Siberian High in the eastern ES. The thickness and temperature variation of 1-5°C representing the East Sea Intermediate Water (ESIW) is relatively minor contributor to the HCA variation in the upper 500 m. However, the thickness (temperature) of the ESIW has been increased (decreased) in the entire ES since 1992, which implies that the formation of the ESIW has been activated in recent decades. To investigate water mass changes in deeper than 500 m, we use full-depth CTD data obtained from CREAMS expeditions from 1993 to 2015. Temperature deeper than 1000 m has been increased about 0.03°C during 20 years and the depth of deep salinity minimum depth which is the lower (upper) limit of the East Sea Central Water (Deep Water) has been deepened. Other characteristics of water mass structure and property changes will be presented.

Pedogenesis on ice (Invited)

NASA Astrophysics Data System (ADS)

Hodson, A. J.

2010-12-01

It is well known from ice cores that organic and mineral debris accumulates within glacier ice following atmospheric deposition. However, the concentrations of such debris are usually greatest upon the ice surface, especially at the margins of continental glaciers and ice sheets, where it forms mm-scale aggregate particles called “cryoconite”. According to the literature, cryoconite covers about 2 % of the ablation areas of glaciers outside Greenland and Antarctica, equivalent to a mass loading of ca. 25 g/m2. Of the great ice sheets not included in this figure, Greenland is the easiest to estimate, and new observations from the NE and SW sectors indicate mass loadings in the range 17 - 440 g/m2. Studies of cryoconite often report the presence of a significant biomass (usually 10^4 - 10^7 cells/g) that is capable of a wide range of biogeochemical functions. The first part of this presentation will therefore explore the contention that the formation of cryoconite represents the first stages of pedogenesis, resulting in the production of soil-type aggregates that inoculate glacial forefields following glacier retreat. Emphasis will be given to the relevant processes that result in aggregate formation, including rapid cell-mineral attachment within melting snowpacks and the slower, biological processes of cementation within thermodynamically stable habitats such as cryoconite holes. The second part of the presentation will use examples from Svalbard, Greenland and Antarctica to consider the carbon balance of the cryoconite during the longest phase of its life cycle: upon the ice. It will be demonstrated how the efficacy of photosynthesis is strongly influenced by thermodynamic conditions at or near this surface. Data from the Greenland and Antarctic ice sheets will show how thermal equilibration decouples variations in photosynthesis from variations in incident radiation over timescales > 1 d, resulting in an equitable, low-carbon economy for aggregates within deep cryoconite holes. Here rates of primary production can be low (e.g. average 2.2 µg C/g (cryoconite)/d in East Antarctica). However, upon maritime glaciers and perhaps parts of the Greenland Ice Sheet margin, high rates of sensible heat transfer maintain cryoconite aggregates close to or upon the ice surface, rendering a communal existence far less likely. This near-surface habitat enables higher rates of photosynthesis (e.g. average 17 µgC/g/d in Svalbard), but also means the probability of meltwater flushing from the ice surface is greatly increased.

Constant-Distance Mode Nanospray Desorption Electrospray Ionization Mass Spectrometry Imaging of Biological Samples with Complex Topography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Son N.; Liyu, Andrey V.; Chu, Rosalie K.

A new approach for constant distance mode mass spectrometry imaging of biological samples using nanospray desorption electrospray ionization (nano-DESI MSI) was developed by integrating a shear-force probe with nano-DESI probe. The technical concept and basic instrumental setup as well as general operation of the system are described. Mechanical dampening of resonant oscillations due to the presence of shear forces between the probe and the sample surface enables constant-distance imaging mode via a computer controlled closed feedback loop. The capability of simultaneous chemical and topographic imaging of complex biological samples is demonstrated using living Bacillus Subtilis ATCC 49760 colonies on agarmore » plates. The constant-distance mode nano-DESI MSI enabled imaging of many metabolites including non-ribosomal peptides (surfactin, plipastatin and iturin) and iron-bound heme on the surface of living bacterial colonies ranging in diameter from 10 mm to 13 mm with height variations of up to 0.8 mm above the agar plate. Co-registration of ion images to topographic images provided higher-contrast images. Constant-mode nano-DESI MSI is ideally suited for imaging biological samples of complex topography in their native state.« less

Theoretical and experimental analysis of an equivalent circuit model for the investigation of shallow landmines with acoustic methods

NASA Astrophysics Data System (ADS)

Borgioli, G.; Bulletti, A.; Calzolai, M.; Capineri, L.; Falorni, P.; Masotti, L.; Valentini, S.; Windsor, C.

2007-10-01

Acoustic methods have been recently investigated for the detection of shallow landmines. Some plastic landmines have a flexible case which can made to vibrate by an airborne excitation like a loudspeaker. The soil-mine system shows a resonant behavior which is used as a signature to discriminate from other rigid objects. The mechanical resonance can be detected at the soil surface by a remote sensing systems like a laser interferometer. An equivalent physical model of the mine-soil system has been investigated having the known physical characteristics of mine simulants. The authors designed and built a test-object with known mechanical characteristics (mass, elasticity, damping factor). The model has been characterized in laboratory and the results compared with the classic mass-spring loss oscillator described by Voigt. The vibrations at the soil surface have been measured in various positions with a micro machined accelerometer. The results of the simulations for the acceleration of the soil-mine system agree well with the experiment. The calibrated mine model is useful to investigate the variation of the resonance frequency for various buried depths and to compare the results for different soils in different environmental conditions.

Widespread albedo decreasing and induced melting of Himalayan snow and ice in the early 21st century.

PubMed

Ming, Jing; Wang, Yaqiang; Du, Zhencai; Zhang, Tong; Guo, Wanqin; Xiao, Cunde; Xu, Xiaobin; Ding, Minghu; Zhang, Dongqi; Yang, Wen

2015-01-01

The widely distributed glaciers in the greater Himalayan region have generally experienced rapid shrinkage since the 1850s. As invaluable sources of water and because of their scarcity, these glaciers are extremely important. Beginning in the twenty-first century, new methods have been applied to measure the mass budget of these glaciers. Investigations have shown that the albedo is an important parameter that affects the melting of Himalayan glaciers. The surface albedo based on the Moderate Resolution Imaging Spectroradiometer (MODIS) data over the Hindu Kush, Karakoram and Himalaya (HKH) glaciers is surveyed in this study for the period 2000-2011. The general albedo trend shows that the glaciers have been darkening since 2000. The most rapid decrease in the surface albedo has occurred in the glacial area above 6000 m, which implies that melting will likely extend to snow accumulation areas. The mass-loss equivalent (MLE) of the HKH glacial area caused by surface shortwave radiation absorption is estimated to be 10.4 Gt yr-1, which may contribute to 1.2% of the global sea level rise on annual average (2003-2009). This work probably presents a first scene depicting the albedo variations over the whole HKH glacial area during the period 2000-2011. Most rapidly decreasing in albedo has been detected in the highest area, which deserves to be especially concerned.

Impact of data assimilation on Eulerian versus Lagrangian estimates of upper ocean transport

NASA Astrophysics Data System (ADS)

Sperrevik, Ann Kristin; Röhrs, Johannes; Christensen, Kai Hâkon

2017-07-01

Using four-dimensional variational analysis, we produce an estimate of the state of a coastal region in Northern Norway during the late winter and spring in 1984. We use satellite sea surface temperature and in situ observations from a series of intensive field campaigns, and obtain a more realistic distribution of water masses both in the horizontal and the vertical than a pure downscaling approach can achieve. Although the distribution of Eulerian surface current speeds are similar, we find that they are more variable and less dependent on model bathymetry in our reanalysis compared to a hindcast produced using the same modeling system. Lagrangian drift currents on the other hand are significantly changed, with overall higher kinetic energy levels in the reanalysis than in the hindcast, particularly in the superinertial frequency band.

Tuning structure of oppositely charged nanoparticle and protein complexes

NASA Astrophysics Data System (ADS)

Kumar, Sugam; Aswal, V. K.; Callow, P.

2014-04-01

Small-angle neutron scattering (SANS) has been used to probe the structures of anionic silica nanoparticles (LS30) and cationic lyszyme protein (M.W. 14.7kD, I.P. ˜ 11.4) by tuning their interaction through the pH variation. The protein adsorption on nanoparticles is found to be increasing with pH and determined by the electrostatic attraction between two components as well as repulsion between protein molecules. We show the strong electrostatic attraction between nanoparticles and protein molecules leads to protein-mediated aggregation of nanoparticles which are characterized by fractal structures. At pH 5, the protein adsorption gives rise to nanoparticle aggregation having surface fractal morphology with close packing of nanoparticles. The surface fractals transform to open structures of mass fractal morphology at higher pH (7 and 9) on approaching isoelectric point (I.P.).

Typhoon-Induced Ground Deformation

NASA Astrophysics Data System (ADS)

Mouyen, M.; Canitano, A.; Chao, B. F.; Hsu, Y.-J.; Steer, P.; Longuevergne, L.; Boy, J.-P.

2017-11-01

Geodetic instruments now offer compelling sensitivity, allowing to investigate how solid Earth and surface processes interact. By combining surface air pressure data, nontidal sea level variations model, and rainfall data, we systematically analyze the volumetric deformation of the shallow crust at seven borehole strainmeters in Taiwan induced by 31 tropical cyclones (typhoons) that made landfall to the island from 2004 to 2013. The typhoon's signature consists in a ground dilatation due to air pressure drop, generally followed by a larger ground compression. We show that this compression phase can be mostly explained by the mass loading of rainwater that falls on the ground and concentrates in the valleys towards the strainmeter sensitivity zone. Further, our analysis shows that borehole strainmeters can help quantifying the amount of rainwater accumulating and flowing over a watershed during heavy rainfalls, which is a useful constraint for building hydrological models.

Variations in body weight, food intake and body composition after long-term high-fat diet feeding in C57BL/6J Mice

PubMed Central

Yang, Yongbin; Smith, Daniel L.; Keating, Karen D.; Allison, David B.; Nagy, Tim R.

2014-01-01

Objective To investigate the variations in body weight, food intake and body composition of both male and female C57BL/6J mice during a diet-induced obesity (DIO) model with high-fat diet (HFD) feeding. Design and Methods Mice were individually housed and fed ad libitum either a low-fat diet (LFD, 10% calories from fat; n=15 male, n=15 female) or high-fat diet (HFD, 45% calories from fat; n=277 male, n=278 female) from 8 to 43 weeks of age. Body weight, food intake and body composition were routinely measured. Results Body weight was significantly increased with HFD (vs. LFD) in males from week 14 (p=0.0221) and in females from week 27 (P=0.0076). Fat mass and fat-free mass of all groups were significantly increased over time (all p<0.0001), with a large variation observed in fat mass. Baseline fat mass, fat-free mass and daily energy intake were significant predictors of future body weight for both sexes (p<0.0001). Baseline fat mass was a significant predictor of future body fat (p<0.0001). Conclusions Both males and females have large variations in fat mass, and this variability increases over time, while that of fat-free mass remains relatively stable. Sex differences exist in HFD responses and multivariate predicting models of body weight. PMID:24942674

Variations in Below Canopy Turbulent Flux From Snow in North American Mountain Environments

NASA Astrophysics Data System (ADS)

Essery, R.; Marks, D.; Pomeroy, J.; Grangere, R.; Reba, M.; Hedstrom, N.; Link, T.; Winstral, A.

2004-12-01

Sensible and latent heat and mass fluxes from the snow surface are modulated by site canopy density and structure. Forest and shrub canopies reduce wind speeds and alter the radiation and thermal environment which will alter the below canopy energetics that control the magnitude of turbulent fluxes between the snow surface and the atmosphere. In this study eddy covariance (EC) systems were located in three experimental catchments along a mountain transect through the North American Cordillera. Within each catchment, a variety of sites representing the local range of climate, weather, and canopy conditions were selected for measurement of sensible and latent heat and mass flux from the snow surface. EC measurements were made 1) below a uniform pine canopy (2745m) in the Fraser Experimental Forest in Colorado from February through June melt-out in 2003; 2) at an open, unforested site (2100m), and below an Aspen canopy (2055m) within a small headwater catchment in the Reynolds Creek Experimental Watershed, Owyhee Mts., Idaho from October, 2003, through June melt-out, 2004; and 3) at five sites, representing a range of conditions: a) below a dense spruce forest (750m); b) a north-facing shrub-tundra slope (1383m); c) a south-facing shrub-tundra slope; d) the valley bottom between b) and c) (1363m); and e) a tundra site (1402m) in the Wolf Creek Research Basin (WCRB) in the Yukon, Canada during the 2001 and 2002 snow seasons. Summary data from all sites are presented and compared including the relative significance of sublimation losses at each site, the importance of interception losses to the snowcover mass balance, and the occurrence of condensation events. Site and weather conditions that inhibit or enhance flux from the snow surface are discussed. This research will improve snow modeling by allowing better representation of turbulent fluxes from snow in forested regions, and improved simulation of the snowcover mass balance over low deposition, high latitude sites such as WCRB, and during drought conditions at mid-latitude sites such as Fraser, Colorado, and RCEW in Idaho.

Interactions Between Wind Erosion, Vegetation Structure, and Soil Stability in Groundwater Dependent Plant Communities

NASA Astrophysics Data System (ADS)

Vest, K. R.; Elmore, A. J.; Okin, G. S.

2009-12-01

Desertification is a human induced global phenomenon causing a loss of biodiversity and ecosystem productivity. Semi-arid grasslands are vulnerable to anthropogenic impacts (i.e., groundwater pumping and surface water diversion) that decrease vegetation cover and increase bare soil area leading to a greater probability of soil erosion, potentially enhancing feedback processes associated with desertification. To enhance our understanding of interactions between anthropogenic, physical, and biological factors causing desertification, this study used a combination of modeling and field observations to examine the relationship between chronic groundwater pumping and vegetation cover change and its effects on soil erosion and stability. The work was conducted in Owens Valley California, where a long history of groundwater pumping and surface water diversion has lead to documented vegetation changes. The work examined hydrological, ecological and biogeochemical factors across thirteen sites in Owens Valley. We analyzed soil stability, vegetation and gap size, soil organic carbon, and we also installed Big Spring Number Eight (BSNE) catchers to calculate mass transport of aeolian sediment across sites. Mass transport calculations were used to validate a new wind erosion model that represents the effect of porous vegetation on surface windshear velocity. Results across two field seasons show that the model can be used to predict mass transport, and areas with increased groundwater pumping show a greater susceptibility to erosion. Sediment collected in BSNE catchers was positively correlated with site gap size. Additionally, areas with larger gap sizes have a greater threshold shear velocity and soil stability, yet mass transport was greater at these sites than at sites with smaller gap sizes. Although modeling is complicated by spatial variation in multiple model parameters (e.g., gap size, threshold shear velocity in gaps), our results support the hypothesis that soils with high organic matter are being eroded following the loss of vegetation cover due to groundwater decline leaving behind bare soil surfaces with less fertility hampering vegetation reestablishment. Desertification in this system is apparently easily initiated through groundwater decline due to the high friability of these meadow soils.

Hydrographic characterization of southeast Arabian Sea during the wane of southwest monsoon and spring intermonsoon.

PubMed

Vimal Kumar, K G; Dinesh Kumar, P K; Smitha, B R; Habeeb Rahman, H; Josia, Jacob; Muraleedharan, K R; Sanjeevan, V N; Achuthankutty, C T

2008-05-01

Seasonal variation of the hydrography along the southeast Arabian Sea is described using data collected onboard FORV Sagar Sampada in September--October 2003 (later phase of Southwest monsoon, SWM) and March--April 2004 (Spring inter monsoon, SIM). During the later phase of the SWM, upwelling was in the withdrawal phase and the frontal structure was clearer in the northern sections (13 and 15 degrees N lat) indicating strong upwelling in the area. The driving force of upwelling is identified as the combination of alongshore wind stress and remote forcing with a latitudinal variability. Although a more prominent upwelling was found in the north, a maximum surface Chlorophyll-a was found in the south (10 degrees N). During the SIM, the area was characterized by oligotrophic water with relatively high Sea Surface Temperature (>29 degrees C) and low salinity (33.8 to 35.4). During March, the surface hydrography was found to be controlled mainly by the intrusion of low-saline waters from the south, while during September by the high saline water from the north. The presence of various water masses [Arabian Sea High Salinity Water (ASHSW), Persian Gulf Water (PGW), Red Sea Water (RSW)] and their seasonal variations in the region is discussed and their decreasing influence towards the south is noted during both periods of observation. During the SWM, the dynamic topography showed the equator-ward flow of the West India Coastal Current (WICC) at the surface and a pole-ward coastal under current at sub-thermocline depth. During the SIM, surface circulation revealed the WICC flowing pole-ward north of 13 degrees N, but equator-ward flow in the south, with a clockwise circulation around the Lakshadweep High.

Spacebased Observation of Water Balance Over Global Oceans

NASA Astrophysics Data System (ADS)

Liu, W.; Xie, X.

2008-12-01

We demonstrated that ocean surface fresh water flux less the water discharge into the ocean from river and ice melt balances the mass loss in the ocean both in magnitude and in the phase of annual variation. The surface water flux was computed from the divergence of the water transport integrated over the depth of the atmosphere. The atmospheric water transport is estimated from the precipitable water measured by Special Sensor Microwave Imager, the surface wind vector by QuikSCAT, and the NOAA cloud drift wind through a statistical model. The transport has been extensively validated using global radiosonde and data and operational numerical weather prediction results. Its divergence has been shown to agree with the difference between evaporation estimated from the Advanced Microwave Scanning Radiometer data and the precipitation measured by Tropical Rain Measuring Mission over the global tropical and subtropical oceans both in magnitude and geographical distribution for temporal scales ranging from intraseasonal to interannual. The water loss rate in the ocean is estimated by two methods, one is from Gravity Recovery and Climate Experiment and the other is by subtracting the climatological steric change from the sea level change measured by radar altimeter on Jason. Only climatological river discharge and ice melt from in situ measurements are available and the lack of temporal variation may contribute to discrepancies in the balance. We have successfully used the spacebased surface fluxes to estimate to climatological mean heat transport in the Atlantic ocean and is attempting to estimate the meridional fresh water (or salt) transport from the surface flux. The approximate closure of the water balance gives a powerful indirect validation of the spacebased products.

Conarticular congruence of the hominoid subtalar joint complex with implications for joint function in Plio-Pleistocene hominins.

PubMed

Prang, Thomas C

2016-07-01

The purpose of this study is to test the hypothesis that conarticular surfaces areas and curvatures are correlates of mobility at the hominoid talocalcaneal and talonavicular joints. Articular surface areas and curvatures of the talonavicular, anterior talocalcaneal, and posterior talocalcaneal joints were quantified using a total of 425 three-dimensional surface models of extant hominoid and fossil hominin tali, calcanei, and naviculars. Quadric surface fitting was used to calculate curvatures, pairwise comparisons were used to evaluate statistical differences between taxa, and regression was used to test for the effects of allometry. Pairwise comparisons show that the distributions of values for joint curvature indices follow the predicted arboreal-terrestrial morphocline in hominoid primates with no effect of body mass (PGLS p > 0.05). OH 8 (Homo habilis) and LB 1 (Homo floresiensis) can be accommodated within the range of human variation for the talonavicular joint, whereas MH2 (Australopithecus sediba) falls within the ranges of variation for Pan troglodytes and Gorilla gorilla in measures of posterior talocalcaneal joint congruity. Joint curvature indices are better discriminators than joint surface area indices, which may reflect a greater contribution of rotation, rather than translation, to joint movement in plantigrade taxa due to discrepancies in conarticular congruence and the "convex-concave" rule. The pattern of joint congruence in Au. sediba contributes to other data on the foot and ankle suggesting that the lateral side of the foot was more mobile than the medial side, which is consistent with suggestions of increased medial weight transfer associated with hyperpronation. Am J Phys Anthropol 160:446-457, 2016. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Corotation lag limit on mass-loss rate from Io

NASA Astrophysics Data System (ADS)

Huang, T. S.; Siscoe, G. L.

1987-08-01

Considering rapid escape of H2O from Io during an early hot evolutionary epoch, an H2O plasma torus is constructed by balancing dissociation and ionization products against centrifugally driven diffusion, including for the first time the effects of corotation lag resulting from mass loading. Two fundamental limits are found as the mass injection rate increases: (1) an 'ignition' limit of 1.1 x 10 to the 6th kg/s, beyond which the torus cannot ionize itself and photoionization dominates; and (2) the ultimate mass loading limit of 1.3 x 10 to the 7th kg/s, which occurs when neutrals newly created by charge exchange and recombination cannot leave the torus, thereby bringing magnetospherically driven transport to a halt. Connecting this limit with the variations of Io's temperature in its early evolution epoch gives an estimate of the upper limit on the total mass loss from Io, about 3.0 x 10 to the 20th kg (for high-opacity nebula) and about 8.9 x 10 to the 20th kg (for low-opacity nebula). These limits correspond to eroding 8 km and 22 km of H2O from the surface. It is concluded that compared to the other Galilean satellites, Io was created basically dry.

Viscous slip coefficients for binary gas mixtures measured from mass flow rates through a single microtube

NASA Astrophysics Data System (ADS)

Yamaguchi, H.; Takamori, K.; Perrier, P.; Graur, I.; Matsuda, Y.; Niimi, T.

2016-09-01

The viscous slip coefficient for helium-argon binary gas mixture is extracted from the experimental values of the mass flow rate through a microtube. The mass flow rate is measured by the constant-volume method. The viscous slip coefficient was obtained by identifying the measured mass flow rate through a microtube with the corresponding analytical expression, which is a function of the Knudsen number. The measurements were carried out in the slip flow regime where the first-order slip boundary condition can be applied. The measured viscous slip coefficients of binary gas mixtures exhibit a concave function of the molar ratio of the mixture, showing a similar profile with numerical results. However, from the detailed comparison between the measured and numerical values with the complete and incomplete accommodation at a surface, it is inappropriate to estimate the viscous slip coefficient for the mixture numerically by employing separately measured tangential momentum accommodation coefficient for each component. The time variation of the molar ratio in the downstream chamber was measured by sampling the gas from the chamber using the quadrupole mass spectrometer. In our measurements, it is indicated that the volume flow rate of argon is larger than that of helium because of the difference in the tangential momentum accommodation coefficient.

Colliding Winds in Massive Binaries

NASA Astrophysics Data System (ADS)

Thaller, M. L.

1998-12-01

In close binary systems of massive stars, the individual stellar winds will collide and form a bow shock between the stars, which may have significant impact on the mass-loss and evolution of the system. The existence of such a shock can be established through orbital-phase related variations in the UV resonance lines and optical emission lines. High density regions near the shock will produce Hα and Helium I emission which can be used to map the mass-flow structure of the system. The shock front between the stars may influence the balance of mass-loss versus mass-transfer in massive binary evolution, as matter lost to one star due to Roche lobe overflow may hit the shock and be deflected before it can accrete onto the surface of the other star. I have completed a high-resolution spectroscopic survey of 37 massive binaries, and compared the incidence and strength of emission to an independent survey of single massive stars. Binary stars show a statistically significant overabundance of optical emission, especially when one of the binary stars is in either a giant or supergiant phase of evolution. Seven systems in my survey exhibited clear signs of orbital phase related emission, and for three of the stars (HD 149404, HD 152248, and HD 163181), I present qualitative models of the mass-flow dynamics of the systems.

Seasonal air and water mass redistribution effects on LAGEOS and Starlette

NASA Technical Reports Server (NTRS)

Gutierrez, Roberto; Wilson, Clark R.

1987-01-01

Zonal geopotential coefficients have been computed from average seasonal variations in global air and water mass distribution. These coefficients are used to predict the seasonal variations of LAGEOS' and Starlette's orbital node, the node residual, and the seasonal variation in the 3rd degree zonal coefficient for Starlette. A comparison of these predictions with the observed values indicates that air pressure and, to a lesser extent, water storage may be responsible for a large portion of the currently unmodeled variation in the earth's gravity field.

Recent glacier retreat over Kerguelen archipelago (49°S, 69°E) derived from field data, satellite imagery and modelling

NASA Astrophysics Data System (ADS)

Verfaillie, Deborah; Favier, Vincent; Dumont, Marie; Jomelli, Vincent; Gilbert, Adrien; Brunstein, Daniel; Frenot, Yves

2013-04-01

Situated in the Indian Ocean at 49° S, 69° E, Kerguelen archipelago represents a unique sub-polar observational site. Located at low altitude and on islands, the glaciers are particularly sensitive to oceanic and atmospheric variations (e.g. Poggi, 1977a,b; Vallon, 1987). The cryosphere on Kerguelen showed important fluctuations during the last 2 centuries (Frenot et al., 1993). After a small stable period until 1961, the ice cap showed a huge and extremely quick retreat, losing 20% of its surface during the last 40 years (Berthier et al., 2009). Relating directly this acceleration with the fluctuations of temperature and precipitation inferred from direct meteorological measurements is attractive and was generally performed (e.g. Frenot et al., 1993, 1997; Berthier et al., 2009). However, it was recently discovered that the drastic temperature change may be mainly due to changes in meteorological station characteristics in 1973 (Météo France, personal communication), challenging previous interpretation. The analysis of field data collected on Ampere glacier since 2010 presented here provides a first approach in our aim to understand the recent rapid retreat of its cryosphere. In this area, short term mass balance data from previous studies (Vallon 1977a,b, 1987) were compared to recent mass balance measurements. The analysis revealed that the spatial distribution of SMB significantly changed in 40 years. Collecting spatially distributed data of the surface characteristics and ablation was crucial to better interpret our field data. Recent variations (from 2000 to 2012) of the equilibrium line altitude (ELA) of Cook ice cap derived from MODIS imagery confirmed that the ELA rose about 100m since 2000. Additionally, we analysed meteorological and reanalysis data over Kerguelen from 1950 to 2012, in order to assess the causes and processes involved in the retreat of the ice cap, and present additional SMB and ELA estimates from a simple positive degree-day model. We concluded that the parameter with the largest variation was precipitation, which was associated to a decrease in cloud cover. The direct impact of these changes was a rise of the 0°C level that led to a reduction of the occurrence of solid precipitation at low elevation. These retroactions demonstrate that Kerguelen's glaciers are extremely sensitive to small climatic changes. These results on glaciological processes of Ampere glacier are an important base to constrain modelling approaches to assess past, present and future ice cap variations. In this framework, regional scale simulations of mass balance processes over Kerguelen archipelago have been initiated with a downscaling scheme (SMHiL) and with the regional climate model MAR (Modèle Atmosphérique Régional).

Surface Mass Balance of the Columbia Glacier, Alaska, 1978 and 2010 Balance Years

USGS Publications Warehouse

O'Neel, Shad

2012-01-01

Although Columbia Glacier is one of the largest sources of glacier mass loss in Alaska, surface mass balance measurements are sparse, with only a single data set available from 1978. The dearth of surface mass-balance data prohibits partitioning of the total mass losses between dynamics and surface forcing; however, the accurate inclusion of calving glaciers into predictive models requires both dynamic and climatic forcing of total mass balance. During 2010, the U.S. Geological Survey collected surface balance data at several locations distributed over the surface of Columbia Glacier to estimate the glacier-wide annual balance for balance year 2010 using the 2007 area-altitude distribution. This report also summarizes data collected in 1978, calculates the 1978 annual surface balance, and uses these observations to constrain the 2010 values, particularly the shape of the balance profile. Both years exhibit balances indicative of near-equilibrium surface mass-balance conditions, and demonstrate the importance of dynamic processes during the rapid retreat.

Low Energy Nuclear Reaction Products at Surfaces

NASA Astrophysics Data System (ADS)

Nagel, David J.

2008-03-01

This paper examines the evidence for LENR occurring on or very near to the surface of materials. Several types of experimental indications for LENR surface reactions have been reported and will be reviewed. LENR result in two types of products, energy and the appearance of new elements. The level of instantaneous power production can be written as the product of four factors: (1) the total area of the surface on which the reactions can occur, (2) the fraction of the area that is active at any time, (3) the reaction rate, that is, the number of reactions per unit active area per second, and (4) the energy produced per reaction. Each of these factors, and their limits, are reviewed. A graphical means of relating these four factors over their wide variations has been devised. The instantaneous generation of atoms of new elements can also be written as the product of the first three factors and the new elemental mass produced per reaction. Again, a graphical means of presenting the factors and their results over many orders of magnitude has been developed.

Identifying water mass depletion in Northern Iraq observed by GRACE

NASA Astrophysics Data System (ADS)

Mulder, Gert; Olsthoorn, Theo; Al-Manmi, Diary; Schrama, Ernst; Smidt, Ebel

2014-05-01

Observations acquired by Gravity Recovery And Climate Experiment (GRACE) mission indicates a mass loss of 31±3 km3 or 130±14 mm in Northern Iraq between 2006 and 2009. This data is used as an independent validation of a hydrologic model of the region including lake mass variations. We developed a rainfall-runoff model for five tributaries of the Tigris River, based on local geology and climate conditions. Model inputs are precipitation data from Tropical Rainfall Measurement Mission (TRMM) observations, and potential evaporation from GLDAS parameters. Our model includes an extensive network of karstified aquifers that causes large natural groundwater variations in this region. Observed river discharges have been used to calibrate our model. In order to get the total mass variations, we correct for lake mass variations derived from Moderate Resolution Imaging Spectroradiometer (MODIS) data in combination with satellite altimetry and some in-situ data. Our rainfall-runoff model confirms that Northern Iraq suffered a drought between 2006 and 2009 and is consistent with the mass loss observed by GRACE in that period. Also, GRACE picks up the annual cycle predicted by the rainfall-runoff model. The total mass depletion seen by GRACE between 2006 and 2009 is 130±14 mm, which is mainly explained by a lake mass depletion of 74±4 mm and a natural groundwater depletion of approximately 50 mm. Our findings indicate that man-made groundwater extraction has a minor influence in this region while depletion of lake mass and geology play a key role.

Variations in thermospheric composition: A model based on mass-spectrometer and satellite-drag data

NASA Technical Reports Server (NTRS)

Jacchia, L. G.

1973-01-01

The seasonal-latitudinal and the diurnal variations of composition observed by mass spectrometers on the OGO 6 satellite are represented by two simple empirical formulae, each of which uses only one numerical parameter. The formulae are of a very general nature and predict the behavior of these variations at all heights and for all levels of solar activity; they yield a satisfactory representation of the corresponding variations in total density as derived from satellite drag. It is suggested that a seasonal variation of hydrogen might explain the abnormally low hydrogen densities at high northern latitudes in July 1964.

A combined surface/volume scattering retracking algorithm for ice sheet satellite altimetry

NASA Technical Reports Server (NTRS)

Davis, Curt H.

1992-01-01

An algorithm that is based upon a combined surface-volume scattering model is developed. It can be used to retrack individual altimeter waveforms over ice sheets. An iterative least-squares procedure is used to fit the combined model to the return waveforms. The retracking algorithm comprises two distinct sections. The first generates initial model parameter estimates from a filtered altimeter waveform. The second uses the initial estimates, the theoretical model, and the waveform data to generate corrected parameter estimates. This retracking algorithm can be used to assess the accuracy of elevations produced from current retracking algorithms when subsurface volume scattering is present. This is extremely important so that repeated altimeter elevation measurements can be used to accurately detect changes in the mass balance of the ice sheets. By analyzing the distribution of the model parameters over large portions of the ice sheet, regional and seasonal variations in the near-surface properties of the snowpack can be quantified.

Water droplet evaporation from sticky superhydrophobic surfaces

NASA Astrophysics Data System (ADS)

Lee, Moonchan; Kim, Wuseok; Lee, Sanghee; Baek, Seunghyeon; Yong, Kijung; Jeon, Sangmin

2017-07-01

The evaporation dynamics of water from sticky superhydrophobic surfaces was investigated using a quartz crystal microresonator and an optical microscope. Anodic aluminum oxide (AAO) layers with different pore sizes were directly fabricated onto quartz crystal substrates and hydrophobized via chemical modification. The resulting AAO layers exhibited hydrophobic or superhydrophobic characteristics with strong adhesion to water due to the presence of sealed air pockets inside the nanopores. After placing a water droplet on the AAO membranes, variations in the resonance frequency and Q-factor were measured throughout the evaporation process, which were related to changes in mass and viscous damping, respectively. It was found that droplet evaporation from a sticky superhydrophobic surface followed a constant contact radius (CCR) mode in the early stage of evaporation and a combination of CCR and constant contact angle modes without a Cassie-Wenzel transition in the final stage. Furthermore, AAO membranes with larger pore sizes exhibited longer evaporation times, which were attributed to evaporative cooling at the droplet interface.

Mars Express 10 years at Mars: Observations by the Mars Express Radio Science Experiment (MaRS)

NASA Astrophysics Data System (ADS)

Pätzold, M.; Häusler, B.; Tyler, G. L.; Andert, T.; Asmar, S. W.; Bird, M. K.; Dehant, V.; Hinson, D. P.; Rosenblatt, P.; Simpson, R. A.; Tellmann, S.; Withers, P.; Beuthe, M.; Efimov, A. I.; Hahn, M.; Kahan, D.; Le Maistre, S.; Oschlisniok, J.; Peter, K.; Remus, S.

2016-08-01

The Mars Express spacecraft is operating in Mars orbit since early 2004. The Mars Express Radio Science Experiment (MaRS) employs the spacecraft and ground station radio systems (i) to conduct radio occultations of the atmosphere and ionosphere to obtain vertical profiles of temperature, pressure, neutral number densities and electron density, (ii) to conduct bistatic radar experiments to obtain information on the dielectric and scattering properties of the surface, (iii) to investigate the structure and variation of the crust and lithosphere in selected target areas, (iv) to determine the mass, bulk and internal structure of the moon Phobos, and (v) to track the MEX radio signals during superior solar conjunction to study the morphology of coronal mass ejections (CMEs). Here we report observations, results and discoveries made in the Mars environment between 2004 and 2014 over almost an entire solar cycle.

Quantification of Glacier Depletion in the Central Tibetan Plateau by Using Integrated Satellite Remote Sensing and Gravimetry

NASA Astrophysics Data System (ADS)

Tseng, K.-H.; Liu, K. T.; Shum, C. K.; Jia, Y.; Shang, K.; Dai, C.

2016-06-01

Glaciers over the Tibetan Plateau have experienced accelerated depletion in the last few decades due primarily to the global warming. The freshwater drained into brackish lakes is also observed by optical remote sensing and altimetry satellites. However, the actual water storage change is difficult to be quantified since the altimetry or remote sensing only provide data in limited dimensions. The altimetry data give an elevation change of surface while the remote sensing images provide an extent variation in horizontal plane. Hence a data set used to describe the volume change is needed to measure the exact mass transition in a time span. In this study, we utilize GRACE gravimetry mission to quantify the total column mass change in the central Tibetan Plateau, especially focused on the lakes near Tanggula Mountains. By removing these factors, the freshwater storage change of glacier system at study area can be potentially isolated.

Monoatomic and cluster beam effect on ToF-SIMS spectra of self-assembled monolayers on gold

NASA Astrophysics Data System (ADS)

Tuccitto, N.; Torrisi, V.; Delfanti, I.; Licciardello, A.

2008-12-01

Self-assembled monolayers represent well-defined systems that is a good model surface to study the effect of primary ion beams used in secondary ion mass spectrometry. The effect of polyatomic primary beams on both aliphatic and aromatic self-assembled monolayers has been studied. In particular, we analysed the variation of the relative secondary ion yield of both substrate metal-cluster (Au n-) in comparison with the molecular ions (M -) and clusters (M xAu y-) by using Bi +, Bi 3+, Bi 5+ beams. Moreover, the differences in the secondary ion generation efficiency are discussed. The main effect of the cluster beams is related to an increased formation of low-mass fragments and to the enhancement of the substrate related gold-clusters. The results show that, at variance of many other cases, the static SIMS of self-assembled monolayers does not benefit of the use of polyatomic primary ions.

Greenland Ice Sheet Melt from MODIS and Associated Atmospheric Variability

NASA Technical Reports Server (NTRS)

Hakkinen, Sirpa; Hall, Dorothy K.; Shuman, Christopher A.; Worthen, Denise L.; DiGirolamo, Nicolo E.

2014-01-01

Daily June-July melt fraction variations over the Greenland Ice Sheet (GIS) derived from the MODerate-resolution Imaging Spectroradiometer (MODIS) (2000-2013) are associated with atmospheric blocking forming an omega-shape ridge over the GIS at 500hPa height (from NCEPNCAR). Blocking activity with a range of time scales, from synoptic waves breaking poleward ( 5 days) to full-fledged blocks (5 days), brings warm subtropical air masses over the GIS controlling daily surface temperatures and melt. The temperature anomaly of these subtropical air mass intrusions is also important for melting. Based on the largest MODIS melt years (2002 and 2012), the area-average temperature anomaly of 2 standard deviations above the 14-year June-July mean, results in a melt fraction of 40 or more. Summer 2007 had the most blocking days, however atmospheric temperature anomalies were too small to instigate extreme melting.

Brown dwarfs as close companions to white dwarfs

NASA Technical Reports Server (NTRS)

Stringfellow, Guy S.; Bodenheimer, Peter; Black, David C.

1990-01-01

The influence of the radiation flux emitted by a white dwarf primary on the evolution of a closely orbiting brown dwarf (BD) companion is investigated. Full stellar evolutionary calculations are presented for both isolated and thermal bath cases, including effects of large variations in the atmospheric grain opacities. High grain opacities significantly increase the radii of the BDs, but the thermal bath does not. The major influence of the thermal bath is to increase substantially the surface temperature and luminosity of the BD at a given age. These results are compared with the observational properties of the possible BD companion of the white dwarf G29-38. Inclusion of both physical effects, high grain opacities and thermal bath, increases the mass range (0.034-0.063 solar masses) of viable models significantly, yet the final determination of whether the object is indeed a BD requires improvements in the observations of the system's properties.

A feasibility study of developing toroidal tanks for a spinning spacecraft

NASA Technical Reports Server (NTRS)

Anderson, J. E.; Fester, D. A.

1973-01-01

A study was made to determine the feasibility of developing toroidal propellant tanks for a bipropellant (N204/MMH) propulsion system to be used in a proposed advanced Pioneer spin-stabilized vehicle intended for a Jupiter-orbiter and possibly a Saturn-orbiter mission. The rationale for considering the use of two toroidal tanks rather than the proposed use of four spherical tanks includes the belief that a more symmetrical distribution of propellant mass and a smaller variation in the position of the vehicle center-of-mass during propellant consumption would result, reducing requirements for attitude-control propellants, for balance weight, and for other weights associated with the dynamics of the spinning spacecraft. Results lead to the conclusion that a toroidal tank containing an effective, passive surface tension propellant acquisition device could be fabricated with available manufacturing methods and could be used interchangeably for either fuel or oxidizer.

Extrema of mass, first law of black hole mechanics, and a staticity theorem in Einstein-Maxwell-axion-dilaton gravity

NASA Astrophysics Data System (ADS)

Rogatko, Marek

1998-08-01

Using the ADM formulation of the Einstein-Maxwell axion-dilaton gravity we derive the formulas for the variation of mass and other asymptotic conserved quantities in the theory under consideration. Generalizing this kind of reasoning to the initial data for the manifold with an interior boundary we get the generalized first law of black hole mechanics. We consider an asymptotically flat solution to the Einstein-Maxwell axion-dilaton gravity describing a black hole with a Killing vector field timelike at infinity, the horizon of which comprises a bifurcate Killing horizon with a bifurcate surface. Supposing that the Killing vector field is asymptotically orthogonal to the static hypersurface with boundary S and a compact interior, we find that the solution is static in the exterior world, when the timelike vector field is normal to the horizon and has vanishing electric and axion-electric fields on static slices.

Isostatic models and isostatic gravity anomalies of the Arabian plate and surroundings

NASA Astrophysics Data System (ADS)

Kaban, Mikhail K.; El Khrepy, Sami; Al-Arifi, Nassir

2015-04-01

Isostaic anomalies represent one of the most useful "geological" reduction of the gravity field. With the isostatic correction it is possible to remove a significant part of the effect of deep density heterogeneity, which dominates in the Bouguer gravity anomalies. This correction is based on the fact that a major part of the near-surface load is compensated by variations of the lithosphere boundaries (chiefly the Moho and LAB) and by density variations within the crust and upper mantle. It is usually supposed that it is less important to a first order, what is the actual compensation model when reducing the effect of compensating masses, since their total weight is exactly opposite to the near-surface load. We compare several compensating models for the Arabian plate and surrounding area. The Airy model gives very significant regional isostatic anomalies, which can not be explained by the upper crust structure or disturbances of the isostatic equilibrium. Also the predicted "isostatic" Moho is very different from the existing observations. The second group of the isostatic models includes the Moho, which is based on existing seismic determinations. Additional compensation is provided by density variations within the lithosphere (chiefly in the upper mantle). In this way we minimize regional anomalies over the Arabian plate. The residual local anomalies well correspond to tectonic structure of the plate. Still very significant anomalies are associated with the Zagros fold belt, the collision zone of the Arabian and Eurasian plates.

Seasonal variations in shallow Alaska seismicity and stress modulation from GRACE derived hydrological loading

NASA Astrophysics Data System (ADS)

Johnson, C. W.; Fu, Y.; Burgmann, R.

2017-12-01

Shallow (≤50 km), low magnitude (M≥2.0) seismicity in southern Alaska is examined for seasonal variations during the annual hydrological cycle. The seismicity is declustered with a spatio-temporal epidemic type aftershock sequence (ETAS) model. The removal of aftershock sequences allows detailed investigation of seismicity rate changes, as water and ice loads modulate crustal stresses throughout the year. The GRACE surface loads are obtained from the JPL mass concentration blocks (mascons) global land and ocean solutions. The data product is smoothed with a 9˚ Gaussian filter and interpolated on a 25 km grid. To inform the surface loading model, the global solutions are limited to the region from -160˚ to -120˚ and 50˚ to 70˚. The stress changes are calculated using a 1D spherical layered earth model at depth intervals of 10 km from 10 - 50 km in the study region. To evaluate the induced seasonal stresses, we use >30 years of earthquake focal mechanisms to constrain the background stress field orientation and assess the stress change with respect to the principal stress orientation. The background stress field is assumed to control the preferred orientation of faulting, and stress field perturbations are expected to increase or decrease seismicity. The number of excess earthquakes is calculated with respect to the background seismicity rates. Here, we present preliminary results for the shallow seismicity variations and quantify the seasonal stresses associated with changes in hydrological loading.

μ Eridani from MOST and from the ground: an orbit, the SPB component's fundamental parameters and the SPB frequencies

NASA Astrophysics Data System (ADS)

Jerzykiewicz, M.; Lehmann, H.; Niemczura, E.; Molenda-Żakowicz, J.; Dymitrov, W.; Fagas, M.; Guenther, D. B.; Hartmann, M.; Hrudková, M.; Kamiński, K.; Moffat, A. F. J.; Kuschnig, R.; Leto, G.; Matthews, J. M.; Rowe, J. F.; Ruciński, S. M.; Sasselov, D.; Weiss, W. W.

2013-06-01

MOST time series photometry of μ Eri, an SB1 eclipsing binary with a rapidly rotating SPB primary, is reported and analysed. The analysis yields a number of sinusoidal terms, mainly due to the intrinsic variation of the primary, and the eclipse light curve. New radial-velocity observations are presented and used to compute parameters of a spectroscopic orbit. Frequency analysis of the radial-velocity residuals from the spectroscopic orbital solution fails to uncover periodic variations with amplitudes greater than 2 km s-1. A Rossiter-McLaughlin anomaly is detected from observations covering ingress. From archival photometric indices and the revised Hipparcos parallax, we derive the primary's effective temperature, surface gravity, bolometric correction and the luminosity. An analysis of a high signal-to-noise spectrogram yields the effective temperature and surface gravity in good agreement with the photometric values. From the same spectrogram, we determine the abundance of He, C, N, O, Ne, Mg, Al, Si, P, S, Cl and Fe. The eclipse light curve is solved by means of EBOP. For a range of mass of the primary, a value of mean density, very nearly independent of assumed mass, is computed from the parameters of the system. Contrary to a recent report, this value is approximately equal to the mean density obtained from the star's effective temperature and luminosity. Despite limited frequency resolution of the MOST data, we were able to recover the closely spaced SPB frequency quadruplet discovered from the ground in 2002-2004. The other two SPB terms seen from the ground were also recovered. Moreover, our analysis of the MOST data adds 15 low-amplitude SPB terms with frequencies ranging from 0.109 to 2.786 d-1.

Applications of Satellite Geodesy in Environmental and Climate Change

NASA Astrophysics Data System (ADS)

Yang, Qian

Satellite geodesy plays an important role in earth observation. This dissertation presents three applications of satellite geodesy in environmental and climate change. Three satellite geodesy techniques are used: high-precision Global Positioning System (GPS), the Gravity Recovery and Climate Experiment (GRACE) and Interferometric Synthetic Aperture Radar (InSAR). In the first study, I use coastal uplift observed by GPS to study the annual changes in mass loss of the Greenland ice sheet. The data show both spatial and temporal variations of coastal ice mass loss and suggest that a combination of warm atmospheric and oceanic condition drove these variations. In the second study, I use GRACE monthly gravity change estimates to constrain recent freshwater flux from Greenland. The data show that Arctic freshwater flux started to increase rapidly in the mid-late 1990s, coincident with a decrease in the formation of dense Labrador Sea Water, a key component of the deep southward return flow od the Atlantic Meridional Overturning Circulation (AMOC). Recent freshening of the polar oceans may be reducing formation of Labrador Sea Water and hence may be weakening the AMOC. In the third study, I use InSAR to monitor ground deformation caused by CO2 injection at an enhanced oil recovery site in west Texas. Carbon capture and storage can reduce CO 2 emitted from power plants, and is a promising way to mitigate anthropogenic warming. From 2007 to 2011, ~24 million tons of CO2 were sequestered in this field, causing up to 10 MPa pressure buildup in a reservoir at depth, and surface uplift up to 10 cm. This study suggests that surface displacement observed by InSAR is a cost-effective way to estimate reservoir pressure change and monitor the fate of injected fluids at waste disposal and CO2 injection sites.

Radar observations and shape model of asteroid 16 Psyche

NASA Astrophysics Data System (ADS)

Shepard, Michael K.; Richardson, James; Taylor, Patrick A.; Rodriguez-Ford, Linda A.; Conrad, Al; de Pater, Imke; Adamkovics, Mate; de Kleer, Katherine; Males, Jared R.; Morzinski, Katie M.; Close, Laird M.; Kaasalainen, Mikko; Viikinkoski, Matti; Timerson, Bradley; Reddy, Vishnu; Magri, Christopher; Nolan, Michael C.; Howell, Ellen S.; Benner, Lance A. M.; Giorgini, Jon D.; Warner, Brian D.; Harris, Alan W.

2017-01-01

Using the S-band radar at Arecibo Observatory, we observed 16 Psyche, the largest M-class asteroid in the main belt. We obtained 18 radar imaging and 6 continuous wave runs in November and December 2015, and combined these with 16 continuous wave runs from 2005 and 6 recent adaptive-optics (AO) images (Drummond et al., 2016) to generate a three-dimensional shape model of Psyche. Our model is consistent with a previously published AO image (Hanus et al., 2013) and three multi-chord occultations. Our shape model has dimensions 279 × 232 × 189 km (± 10%), Deff = 226 ± 23 km, and is 6% larger than, but within the uncertainties of, the most recently published size and shape model generated from the inversion of lightcurves (Hanus et al., 2013). Psyche is roughly ellipsoidal but displays a mass-deficit over a region spanning 90° of longitude. There is also evidence for two ∼50-70 km wide depressions near its south pole. Our size and published masses lead to an overall bulk density estimate of 4500 ± 1400 kgm-3. Psyche's mean radar albedo of 0.37 ± 0.09 is consistent with a near-surface regolith composed largely of iron-nickel and ∼40% porosity. Its radar reflectivity varies by a factor of 1.6 as the asteroid rotates, suggesting global variations in metal abundance or bulk density in the near surface. The variations in radar albedo appear to correlate with large and small-scale shape features. Our size and Psyche's published absolute magnitude lead to an optical albedo of pv = 0.15 ± 0.03, and there is evidence for albedo variegations that correlate with shape features.

Asteroid 16 Psyche: Radar Observations and Shape Model

NASA Astrophysics Data System (ADS)

Shepard, Michael K.; Richardson, James E.; Taylor, Patrick A.; Rodriguez-Ford, Linda A.; Conrad, Al; de Pater, Imke; Adamkovics, Mate; de Kleer, Katherine R.; Males, Jared; Morzinski, Kathleen M.; Miller Close, Laird; Kaasalainen, Mikko; Viikinkoski, Matti; Timerson, Bradley; Reddy, Vishnu; Magri, Christopher; Nolan, Michael C.; Howell, Ellen S.; Warner, Brian D.; Harris, Alan W.

2016-10-01

We observed 16 Psyche, the largest M-class asteroid in the main belt, using the S-band radar at Arecibo Observatory. We obtained 18 radar imaging and 6 continuous wave runs in November and December 2015, and combined these with 16 continuous wave runs from 2005 and 6 recent adaptive-optics (AO) images to generate a three-dimensional shape model of Psyche. Our model is consistent with a previously published AO image [Hanus et al. Icarus 226, 1045-1057, 2013] and three multi-chord occultations. Our shape model has dimensions 279 x 232 x 189 km (±10%), Deff = 226 ± 23 km, and is 6% larger than, but within the uncertainties of, the most recently published size and shape model generated from the inversion of lightcurves [Hanus et al., 2013]. Psyche is roughly ellipsoidal but displays a mass-deficit over a region spanning 90° of longitude. There is also evidence for two ~50-70 km wide depressions near its south pole. Our size and published masses lead to an overall bulk density estimate of 4500 ± 1400 kg m-3. Psyche's mean radar albedo of 0.37 ± 0.09 is consistent with a near-surface regolith composed largely of iron-nickel and ~40% porosity. Its radar reflectivity varies by a factor of 1.6 as the asteroid rotates, suggesting global variations in metal abundance or bulk density in the near surface. The variations in radar albedo appear to correlate with large and small-scale shape features. Our size and Psyche's published absolute magnitude lead to an optical albedo of pv = 0.15 ± 0.03, and there is evidence for albedo variegations that correlate with shape features.

Soil respiration and aboveground litter dynamics of a tropical transitional forest in northwest Mato Grosso, Brazil

NASA Astrophysics Data System (ADS)

Valentini, Carla Maria Abido; Sanches, Luciana; de Paula, Sérgio Roberto; Vourlitis, George Louis; de Souza Nogueira, José; Pinto, Osvaldo Borges; de Almeida Lobo, Francisco

2008-12-01

Measurements of soil CO2 efflux, litter production, and the surface litter pool biomass were made over a 1 year period in a tropical transitional forest near Sinop, Mato Grosso, Brazil with the aim of quantifying the seasonal variation in soil respiration and litter decomposition and the annual contribution of litter decomposition to soil CO2 efflux. Average annual soil CO2 efflux (+/-95% confidence interval (CI)) was 7.91 +/- 1.16 g C m-2 d-1. Soil CO2 efflux was highest during the November-February wet season (9.15 +/- 0.90 g C m-2 d-1) and lowest during the May-September dry season (6.19 +/- 1.40 g C m-2 d-1), and over 60% of the variation in seasonal soil CO2 efflux was explained by seasonal variations in soil temperature and moisture. Mass balance estimates of mean (+/-95% CI) decomposition rates were statistically different between the wet and dry seasons (0.66 +/- 0.08 and 1.65 +/- 0.10 g C m-2 d-1, respectively), and overall, decomposition of leaf litter comprised 16% of the average annual soil respiration. Leaf litter production was higher during the dry season, and mean (+/-95% CI) leaf litter fall (5.6 +/- 1.7 Mg ha-1) comprised 73% of the total litter fall (7.8 +/- 2.3 Mg ha-1). Average (+/-95% CI) annual litter pool biomass was estimated to be 5.5 +/- 0.3 Mg ha-1, which was similar to the measured pool size (5.7 +/- 2.2 Mg ha-1). Overall, seasonal variations in environmental variables, specifically water availability (soil moisture and rainfall), had a profound influence on litter production, soil respiration, and surface litter decomposition.

Metagenomic covariation along densely sampled environmental gradients in the Red Sea

PubMed Central

Thompson, Luke R; Williams, Gareth J; Haroon, Mohamed F; Shibl, Ahmed; Larsen, Peter; Shorenstein, Joshua; Knight, Rob; Stingl, Ulrich

2017-01-01

Oceanic microbial diversity covaries with physicochemical parameters. Temperature, for example, explains approximately half of global variation in surface taxonomic abundance. It is unknown, however, whether covariation patterns hold over narrower parameter gradients and spatial scales, and extending to mesopelagic depths. We collected and sequenced 45 epipelagic and mesopelagic microbial metagenomes on a meridional transect through the eastern Red Sea. We asked which environmental parameters explain the most variation in relative abundances of taxonomic groups, gene ortholog groups, and pathways—at a spatial scale of <2000 km, along narrow but well-defined latitudinal and depth-dependent gradients. We also asked how microbes are adapted to gradients and extremes in irradiance, temperature, salinity, and nutrients, examining the responses of individual gene ortholog groups to these parameters. Functional and taxonomic metrics were equally well explained (75–79%) by environmental parameters. However, only functional and not taxonomic covariation patterns were conserved when comparing with an intruding water mass with different physicochemical properties. Temperature explained the most variation in each metric, followed by nitrate, chlorophyll, phosphate, and salinity. That nitrate explained more variation than phosphate suggested nitrogen limitation, consistent with low surface N:P ratios. Covariation of gene ortholog groups with environmental parameters revealed patterns of functional adaptation to the challenging Red Sea environment: high irradiance, temperature, salinity, and low nutrients. Nutrient-acquisition gene ortholog groups were anti-correlated with concentrations of their respective nutrient species, recapturing trends previously observed across much larger distances and environmental gradients. This dataset of metagenomic covariation along densely sampled environmental gradients includes online data exploration supplements, serving as a community resource for marine microbial ecology. PMID:27420030

Study of seasonal and long-term vertical deformation in Nepal based on GPS and GRACE observations

NASA Astrophysics Data System (ADS)

Zhang, Tengxu; Shen, WenBin; Pan, Yuanjin; Luan, Wei

2018-02-01

Lithospheric deformation signal can be detected by combining data from continuous global positioning system (CGPS) and satellite observations from the Gravity Recovery and Climate Experiment (GRACE). In this paper, we use 2.5- to 19-year-long time series from 35 CGPS stations to estimate vertical deformation rates in Nepal, which is located in the southern side of the Himalaya. GPS results were compared with GRACE observations. Principal component analysis was conducted to decompose the time series into three-dimensional principal components (PCs) and spatial eigenvectors. The top three high-order PCs were calculated to correct common mode errors. Both GPS and GRACE observations showed significant seasonal variations. The observed seasonal GPS vertical variations are in good agreement with those from the GRACE-derived results, particularly for changes in surface pressure, non-tidal oceanic mass loading, and hydrologic loading. The GPS-observed rates of vertical deformation obtained for the region suggest both tectonic impact and mass decrease. The rates of vertical crustal deformation were estimated by removing the GRACE-derived hydrological vertical rates from the GPS measurements. Most of the sites located in the southern part of the Main Himalayan Thrust subsided, whereas the northern part mostly showed an uplift. These results may contribute to the understanding of secular vertical crustal deformation in Nepal.

Variations of surface ozone at Ieodo Ocean Research Station in the East China Sea and the influence of Asian outflows

NASA Astrophysics Data System (ADS)

Han, J.; Shin, B.; Lee, M.; Hwang, G.; Kim, J.; Shim, J.; Lee, G.; Shim, C.

2015-11-01

Ieodo Ocean Research Station (IORS), a research tower (~ 40 m a.s.l.) for atmospheric and oceanographic observations, is located in the East China Sea (32.07° N, 125.10° E). The IORS is almost equidistant from South Korea, China, and Japan and, therefore, it is an ideal place to observe Asian outflows without local emission effects. The seasonal variation of ozone was distinct, with a minimum in August (37 ppbv) and two peaks in April and October (62 ppbv), and was largely affected by the seasonal wind pattern over east Asia. At IORS, six types of air masses were distinguished with different levels of O3 concentrations by the cluster analysis of backward trajectories. Marine air masses from the Pacific Ocean represent a relatively clean background air with a lowest ozone level of 32 ppbv, which was most frequently observed in summer (July-August). In spring (March-April) and winter (December-February), the influence of Chinese outflows was dominant with higher ozone concentrations of 62 and 49 ppbv, respectively. This study confirms that the influence of Chinese outflows was the main factor determining O3 levels at IORS and its extent was dependent on meteorological state, particularly at a long-term scale.

Migrating pattern of deformation prior to the Tohoku-Oki earthquake revealed by GRACE data

NASA Astrophysics Data System (ADS)

Panet, Isabelle; Bonvalot, Sylvain; Narteau, Clément; Remy, Dominique; Lemoine, Jean-Michel

2018-05-01

Understanding how and when far-field continuous motions lead to giant subduction earthquakes remains a challenge. An important limitation comes from an incomplete description of aseismic mass fluxes at depth along plate boundaries. Here we analyse Earth's gravity field variations derived from GRACE satellite data in a wide space-time domain surrounding the Mw 9.0 2011 Tohoku-Oki earthquake. We show that this earthquake is the extreme expression of initially silent deformation migrating from depth to the surface across the entire subduction system. Our analysis indeed reveals large-scale gravity and mass changes throughout three tectonic plates and connected slabs, starting a few months before March 2011. Before the Tohoku-Oki earthquake rupture, the gravity variations can be explained by aseismic extension of the Pacific plate slab at mid-upper mantle depth, concomitant with increasing seismicity in the shallower slab. For more than two years after the rupture, the deformation propagated far into the Pacific and Philippine Sea plate interiors, suggesting that subduction accelerated along 2,000 km of the plate boundaries in March 2011. This gravitational image of the earthquake's long-term dynamics provides unique information on deep and crustal processes over intermediate timescales, which could be used in seismic hazard assessment.

Particle emissions from diesel passenger cars equipped with a particle trap in comparison to other technologies.

PubMed

Mohr, Martin; Forss, Anna-Maria; Lehmann, Urs

2006-04-01

Tail pipe particle emissions of passenger cars, with different engine and aftertreatment technologies, were determined with special focus on diesel engines equipped with a particle filter. The particle number measurements were performed, during transient tests, using a condensation particle counter. The measurement procedure complied with the draft Swiss ordinance, which is based on the findings of the UN/ECE particulate measurement program. In addition, particle mass emissions were measured by the legislated and a modified filter method. The results demonstrate the high efficiency of diesel particle filters (DPFs) in curtailing nonvolatile particle emissions over the entire size range. Higher emissions were observed during short periods of DPF regeneration and immediately afterward, when a soot cake has not yet formed on the filter surface. The gasoline vehicles exhibited higher emissions than the DPF equipped diesel vehicles but with a large variation depending on the technology and driving conditions. Although particle measurements were carried out during DPF regeneration, it was impossible to quantify their contribution to the overall emissions, due to the wide variation in intensity and frequency of regeneration. The numbers counting method demonstrated its clear superiority in sensitivity to the mass measurement. The results strongly suggest the application of the particle number counting to quantify future low tailpipe emissions.

Insights into Seasonal Variations in Phosphorus Concentrations and Cycling in Monterey Bay

NASA Astrophysics Data System (ADS)

Kong, M.; Defforey, D.; Paytan, A.; Roberts, K.

2014-12-01

Phosphorus (P) is an essential nutrient for life as it is a structural constituent in many cell components and a key player in cellular energy metabolism. Therefore, P availability can impact primary productivity. Here we quantify dissolved and particulate P compounds and trace P sources and cycling in Monterey Bay over the course of a year. This time series gives insights into monthly and seasonal variations in the surface water chemistry of this region. Preliminary characterization of seawater samples involves measuring total P and soluble reactive P (SRP) concentrations. 31P nuclear magnetic resonance spectroscopy (31P NMR) is used to determine the chemical structure of organic phosphorus compounds present in surface seawater. The isotopic signature of phosphatic oxygen (δ18Op) is used as a proxy for studying P cycling and sources. Oxygen isotope ratios in phosphate are determined by continuous-flow isotope mass ratio spectrometry (CF-IRMS) following purification of dissolved P from seawater samples and precipitation as silver phosphate. We expect to observe seasonal changes in P concentrations, as well as differences in organic P composition and P sources. The chemical structure of organic P compounds will affect their bioavailability and thus the extent to which they can fuel primary productivity in Monterey Bay. δ18Op will reflect source signatures and provide information on turnover rates of P in surface waters. Results from this work will provide valuable insights into seasonal changes in P cycling in surface waters and have important implications for understanding primary productivity in the Monterey Bay ecosystem.

Mechanisms of the formation of low spatial frequency LIPSS on Ni/  Ti reactive multilayers

NASA Astrophysics Data System (ADS)

Cangueiro, Liliana T.; Cavaleiro, André J.; Morgiel, Jerzy; Vilar, Rui

2016-09-01

The present paper aims at investigating the mechanisms of imprinting LIPSS (laser-induced periodic surface structures), arrangements of parallel ripples with a periodicity slightly smaller than the radiation wavelength, on metallic surfaces. To this end, Ni/Ti multi-layered samples produced by magnetron sputtering were textured with LIPSS using a 1030 nm, 560 fs pulse duration laser and pulse frequency of 1 kHz, and the resulting surfaces were investigated by scanning and transmission electron microscopies. The results obtained show that the core of the ripples remains in the solid state during the laser treatment, except for a layer of material about 30 nm thick at the valleys and 65-130 nm thick at the top of the crests, which melts and solidifies forming NiTi with an amorphous structure. A layer of ablation debris composed of amorphous NiTi nanoparticles was redeposited on the LIPSS crests. The results achieved indicate that the periodic variation of the absorbed radiation intensity leads to a variation of the predominant ablation mechanisms and, consequently, of the ablation rate, thus explaining the rippled surface topography. The comparison with theoretical predictions suggests that in the intensity maxima (corresponding to the valleys) the material is removed by liquid spallation, while at its minima (the crests) the predominant material removal mechanism is melting and vaporization. These results support Sipe et al LIPSS formation theory and are in contradiction with the theories that explain the formation of LIPSS by convective fluid flow or self-organized mass transport of a laser-induced instability.

Controls on the chemical composition of saline surface crusts and emitted dust from a wet playa in the Mojave Desert (USA)

USGS Publications Warehouse

Goldstein, Harland L.; Breit, George N.; Reynolds, Richard L.

2017-01-01

Saline-surface crusts and their compositions at ephemeral, dry, and drying lakes are important products of arid-land processes. Detailed understanding is lacking, however, about interactions among locally variable hydrogeologic conditions, compositional control of groundwater on vadose zone and surface salts, and dust composition. Chemical and physical data from groundwater, sediments, and salts reveal compositional controls on saline-surface crusts across a wet playa, Mojave Desert, with bearing on similar settings elsewhere. The compositions of chemically and isotopically distinctive shallow (<3 m) water masses are recorded in the composition of associated salts. In areas with deeper and more saline groundwater, however, not all ions are transported through the vadose zone. Retention of arsenic and other elements in the vadose zone diminishes the concentrations of potentially toxic elements in surface salts, but creates a reservoir of these elements that may be brought to the surface during wetter conditions or by human disturbance. Selective wind-erosion loss of sulfate salts was identified by the compositional contrast between surface salt crusts and underlying groundwater. At the sub-basin scale, compositional links exist among groundwater, salt crusts, and dust from wet playas. Across the study basin, however, lateral variations in groundwater and solid-salt compositions are produced by hydrogeologic heterogeneity.

A CANDELS-3D-HST synergy: Resolved Star Formation Patterns at 0.7 < z < 1.5

NASA Astrophysics Data System (ADS)

Wuyts, Stijn; Förster Schreiber, Natascha M.; Nelson, Erica J.; van Dokkum, Pieter G.; Brammer, Gabe; Chang, Yu-Yen; Faber, Sandra M.; Ferguson, Henry C.; Franx, Marijn; Fumagalli, Mattia; Genzel, Reinhard; Grogin, Norman A.; Kocevski, Dale D.; Koekemoer, Anton M.; Lundgren, Britt; Lutz, Dieter; McGrath, Elizabeth J.; Momcheva, Ivelina; Rosario, David; Skelton, Rosalind E.; Tacconi, Linda J.; van der Wel, Arjen; Whitaker, Katherine E.

2013-12-01

We analyze the resolved stellar populations of 473 massive star-forming galaxies at 0.7 < z < 1.5, with multi-wavelength broadband imaging from CANDELS and Hα surface brightness profiles at the same kiloparsec resolution from 3D-HST. Together, this unique data set sheds light on how the assembled stellar mass is distributed within galaxies, and where new stars are being formed. We find the Hα morphologies to resemble more closely those observed in the ACS I band than in the WFC3 H band, especially for the larger systems. We next derive a novel prescription for Hα dust corrections, which accounts for extra extinction toward H II regions. The prescription leads to consistent star formation rate (SFR) estimates and reproduces the observed relation between the Hα/UV luminosity ratio and visual extinction, on both a pixel-by-pixel and a galaxy-integrated level. We find the surface density of star formation to correlate with the surface density of assembled stellar mass for spatially resolved regions within galaxies, akin to the so-called "main sequence of star formation" established on a galaxy-integrated level. Deviations from this relation toward lower equivalent widths are found in the inner regions of galaxies. Clumps and spiral features, on the other hand, are associated with enhanced Hα equivalent widths, bluer colors, and higher specific SFRs compared to the underlying disk. Their Hα/UV luminosity ratio is lower than that of the underlying disk, suggesting that the ACS clump selection preferentially picks up those regions of elevated star formation activity that are the least obscured by dust. Our analysis emphasizes that monochromatic studies of galaxy structure can be severely limited by mass-to-light ratio variations due to dust and spatially inhomogeneous star formation histories.

A CANDELS-3d-HST Synergy: Resolved Star Formation Patterns at 0.7 less than z less than 1.5

NASA Technical Reports Server (NTRS)

Wuyts, Stijn; Foerster Schreiber, Natascha M.; Nelson, Erica J.; Van Dokkum, Pieter G.; Brammer, Gabe; Chang, Yu-Yen; Faber, Sandra M.; Ferguson, Henry C.; Franx, Marijn; Fumagalli, Mattia;

Egg size and asymmetric sibling rivalry in red-winged blackbirds.

PubMed

Forbes, Scott; Wiebe, Mark

2010-06-01

How big to make an egg is a life history decision that in birds is made coincident with a series of other similar decisions (how many eggs to have, whether to fortify them with maternally derived hormones or immune system boosters, whether to hatch the eggs synchronously or asynchronously). Though within-population variation in egg size in birds has been well studied, its adaptive significance, if any, is unclear. Here we examine within-population variation in egg size in relation to asymmetric sibling rivalry in a 17-year study of red-winged blackbirds (Agelaius phoeniceus), an altricial songbird. Egg mass showed a twofold range of variation, with roughly 80% of the variation occurring across clutches. By commencing incubation before the clutch is complete, mothers create advantaged core and disadvantaged marginal elements within their brood. Previous work on this system has shown that sibling competition is asymmetric, and that core offspring enjoy priority access to food, and as a consequence show higher growth and lower mortality than marginal offspring. Here we examine the effect of initial egg size on nestling growth and survival in relation to these competitive asymmetries. Egg mass was strongly linked to hatchling mass, and remained significantly related to the mass of both core and marginal nestlings; the effect of egg size was stronger for core offspring early in the nestling period, but the disparity between core and marginal nestlings narrowed as they approached fledging age, and slower growing marginals fell victim to brood reduction. The effect of egg mass on survival differed dramatically between core and marginal nestlings. Egg mass was significantly related to the survival of marginal but not core nestlings: below average egg mass was associated primarily with very early mortality. Asymmetric sibling competition is clearly a strong determinant of the consequences of egg size variation.

Earth rotation excitation mechanisms derived from geodetic space observations

NASA Astrophysics Data System (ADS)

Göttl, F.; Schmidt, M.

2009-04-01

Earth rotation variations are caused by mass displacements and motions in the subsystems of the Earth. Via the satellite Gravity and Climate Experiment (GRACE) gravity field variations can be identified which are caused by mass redistribution in the Earth system. Therefore time variable gravity field models (GFZ RL04, CSR RL04, JPL RL04, ITG-Grace03, GRGS, ...) can be used to derive different impacts on Earth rotation. Furthermore satellite altimetry provides accurate information on sea level anomalies (AVISO, DGFI) which are caused by mass and volume changes of seawater. Since Earth rotation is solely affected by mass variations and motions the volume (steric) effect has to be reduced from the altimetric observations in order to infer oceanic contributions to Earth rotation variations. Therefore the steric effect is estimated from physical ocean parameters such as temperature and salinity changes in the oceans (WOA05, Ishii). In this study specific individual geophysical contributions to Earth rotation variations are identified by means of a multitude of accurate geodetic space observations in combination with a realistic error propagation. It will be shown that due to adjustment of altimetric and/or gravimetric solutions the results for polar motion excitations can be improved.

Mass balance model parameter transferability on a tropical glacier

NASA Astrophysics Data System (ADS)

Gurgiser, Wolfgang; Mölg, Thomas; Nicholson, Lindsey; Kaser, Georg

2013-04-01

The mass balance and melt water production of glaciers is of particular interest in the Peruvian Andes where glacier melt water has markedly increased water supply during the pronounced dry seasons in recent decades. However, the melt water contribution from glaciers is projected to decrease with appreciable negative impacts on the local society within the coming decades. Understanding mass balance processes on tropical glaciers is a prerequisite for modeling present and future glacier runoff. As a first step towards this aim we applied a process-based surface mass balance model in order to calculate observed ablation at two stakes in the ablation zone of Shallap Glacier (4800 m a.s.l., 9°S) in the Cordillera Blanca, Peru. Under the tropical climate, the snow line migrates very frequently across most of the ablation zone all year round causing large temporal and spatial variations of glacier surface conditions and related ablation. Consequently, pronounced differences between the two chosen stakes and the two years were observed. Hourly records of temperature, humidity, wind speed, short wave incoming radiation, and precipitation are available from an automatic weather station (AWS) on the moraine near the glacier for the hydrological years 2006/07 and 2007/08 while stake readings are available at intervals of between 14 to 64 days. To optimize model parameters, we used 1000 model simulations in which the most sensitive model parameters were varied randomly within their physically meaningful ranges. The modeled surface height change was evaluated against the two stake locations in the lower ablation zone (SH11, 4760m) and in the upper ablation zone (SH22, 4816m), respectively. The optimal parameter set for each point achieved good model skill but if we transfer the best parameter combination from one stake site to the other stake site model errors increases significantly. The same happens if we optimize the model parameters for each year individually and transfer these combinations to the other year. We show that multi-site and multi-year analyses are crucial before extrapolating ablation modeling to larger glacier areas. So far tested surface albedo schemes and respective parameterizations can obviously not satisfyingly reproduce the dynamics of glacier surface conditions at our study site and new solutions to the problem have to be explored.