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1

THE MEASURE OF RATES OF NUTRIENT FLUXES BETWEEN TAMPA BAY SEDIMENTS AND THE OVERLYING WATER COLUMN  

EPA Science Inventory

The project will measure rates of nutrient fluxes between Tampa Bay sediments and the ovrelying water column. This information has been lacking from previous nitrogen budgets for Tampa Bay, potentially hampering their accuracy and effectiveness. Refined nitrogen budgets based o...

2

FFTF (FAST FLUX TEST FACILITY) REACTOR CHARACTERIZATION PROGRAM ABSOLUTE FISSION RATE MEASUREMENTS  

SciTech Connect

Absolute fission rate measurements using modified National Bureau of Standards fission chambers were performed in the Fast Flux Test Facility at two core locations for isotopic deposits of {sup 232}Th, {sup 233}U, {sup 235}U, {sup 238}U, {sup 237}Np, {sup 239}Pu, {sup 240}Pu, and {sup 241}Pu. Monitor chamber results at a third location were analyzed to support other experiments involving passive dosimeter fission rate determinations.

FULLER JL; GILLIAM DM; GRUNDL JA; RAWLINS JA; DAUGHTRY JW

1981-05-01

3

Heat flux measurements  

SciTech Connect

A new automated, computer controlled heat flux measurement facility is described. Continuous transient and steady-state surface heat flux values varying from about 0.3 to 6 MW/sq m over a temperature range of 100 to 1200 K can be obtained in the facility. An application of this facility is the development of heat flux gauges for continuous fast transient surface heat flux measurement on turbine blades operating in space shuttle main engine turbopumps. The facility is useful for durability testing at fast temperature transients.

Liebert, C.H.; Weikle, D.H.

1989-01-01

4

Heat flux microsensor measurements  

NASA Technical Reports Server (NTRS)

A thin-film heat flux sensor has been fabricated on a stainless steel substrate. The thermocouple elements of the heat flux sensor were nickel and nichrome, and the temperature resistance sensor was platinum. The completed heat flux microsensor was calibrated at the AEDC radiation facility. The gage output was linear with heat flux with no apparent temperature effect on sensitivity. The gage was used for heat flux measurements at the NASA Langley Vitiated Air Test Facility. Vitiated air was expanded to Mach 3.0 and hydrogen fuel was injected. Measurements were made on the wall of a diverging duct downstream of the injector during all stages of the hydrogen combustion tests. Because the wall and the gage were not actively cooled, the wall temperature reached over 1000 C (1900 F) during the most severe test.

Terrell, J. P.; Hager, J. M.; Onishi, S.; Diller, T. E.

1992-01-01

5

Measurements of Nuclear Heating Rate and Neutron Flux in HANARO CN Hole for Designing the Moderator Cell of Cold Neutron Source  

Microsoft Academic Search

The design of the cold neutron source(CNS) facility for HANARO, a 30 MW research reactor, is in progress. In order to measure the nuclear heating rate and thermal neutron flux in the CN hole of HANARO, a calorimeter based on the concept of the heat flow calorimeter is designed and constructed. The calorimeter sensor consists of a cylindrical Al sample,

Myong-Seop KIM; Sung-Yul HWANG; Hoan-Sung JUNG; Kye-Hong LEE

6

Ionization chamber for measuring the exposure dose rate of intense pulsed fluxes of X rays and ?-radiation  

Microsoft Academic Search

Measurements of the exposure dose rate of powerful pulsed sources of bremsstrahlung xrays and y-radiation are very difficult because a standard of pulsed radiation is not available. The presently employed measuring means are based on scintillation, semiconductor, and pyroelectric devices [1-3] and are characterized by adequate resolution on the time scale and a satisfactory dynamic range, but cannot be successfully

N. D. Villeval'de; N. N. Morozov; A. V. Oborin; B. M. Stepanov; V. I. Fominykh

1981-01-01

7

Measuring surface fluxes in CAPE  

NASA Technical Reports Server (NTRS)

Two stations (site 1612 and site 2008) were operated by the University of Georgia group from 6 July 1991 to 18 August 1991. The following data were collected continuously: surface energy fluxes (i.e., net radiation, soil heat fluxes, sensible heat flux and latent heat flux), air temperature, vapor pressure, soil temperature (at 1 cm depth), and precipitation. Canopy reflectance and light interception data were taken three times at each site between 6 July and 18 August. Soil moisture content was measured twice at each site.

Kanemasu, E. T.; D-Shah, T.; Nie, Dalin

1992-01-01

8

Assessing Photosynthetic Energy Fluxes Within Microbial Communities Using Continuous Ship-Based Fast Repetition Rate (FRR) Fluorescence Measurements.  

NASA Astrophysics Data System (ADS)

Microbial life in the ocean is sustained by photosynthetically-derived energy at a power level of about 5*1014 W. Assuming photosynthetic efficiency of about 20%, this mechanism consumes less than 10% of photosynthetically-available radiation (PAR) incident on the ocean surface. Life in the ocean operates under condition of excess energy, where factors such as nutrients/trace metals availability or prevalence of nitrogen fixation limit photosynthetic light utilization. To investigate these factors we have performed fast repetition rate (FRR) fluorescence measurements, continuously, over a period of one year, along the cruise track of R/V Kilo Moana. We have identified photosynthetic signatures of Trichodesmium blooms during two cruises in 2007 and 2008, and we have used these signatures to infer the presence of Trichodesmium along the cruise track. Most surface enhancements in photosynthetic rates and the chlorophyll biomass were observed in peripheral areas between cyclonic and anticyclonic eddies. It appears that local shear zones in these areas induce small-scale vertical mixing capable of supporting near-surface blooms. Our data indicate that the gradients in the sea surface height, rather than local minima/maxima, determine the occurrence of small-scale surface blooms in the North Pacific Subtropical Gyre.

Kolber, Z. S.; Tozzi, S.; Klimov, D.

2008-12-01

9

A process-based model to estimate gas exchange and monoterpene emission rates in the mediterranean maquis - comparisons between modelled and measured fluxes at different scales  

NASA Astrophysics Data System (ADS)

This paper concerns the application of a process-based model (MOCA, Modelling of Carbon Assessment) as an useful tool for estimating gas exchange, and integrating the empirical algorithms for calculation of monoterpene fluxes, in a Mediterranean maquis of central Italy (Castelporziano, Rome). Simulations were carried out for a range of hypothetical but realistic canopies of the evergreen Quercus ilex (holm oak), Arbutus unedo (strawberry tree) and Phillyrea latifolia. More, the dependence on total leaf area and leaf distribution of monoterpene fluxes at the canopy scale has been considered in the algorithms. Simulation of the gas exchange rates showed higher values for P. latifolia and A. unedo (2.39±0.30 and 3.12±0.27 gC m-2 d-1, respectively) with respect to Q. ilex (1.67±0.08 gC m-2 d-1) in the measuring campaign (May-June). Comparisons of the average Gross Primary Production (GPP) values with those measured by eddy covariance were well in accordance (7.98±0.20 and 6.00±1.46 gC m-2 d-1, respectively, in May-June), although some differences (of about 30%) were evident in a point-to-point comparison. These differences could be explained by considering the non uniformity of the measuring site where diurnal winds blown S-SW direction affecting thus calculations of CO2 and water fluxes. The introduction of some structural parameters in the algorithms for monoterpene calculation allowed to simulate monoterpene emission rates and fluxes which were in accord to those measured (6.50±2.25 vs. 9.39±4.5?g g-1DW h-1 for Q. ilex, and 0.63±0.207?g g-1DW h-1 vs. 0.98±0.30?g g-1DW h-1 for P. latifolia). Some constraints of the MOCA model are discussed, but it is demonstrated to be an useful tool to simulate physiological processes and BVOC fluxes in a very complicated plant distributions and environmental conditions, and necessitating also of a low number of input data.

Vitale, M.; Matteucci, G.; Fares, S.; Davison, B.

2009-02-01

10

Errors in airborne flux measurements  

NASA Astrophysics Data System (ADS)

We present a general approach for estimating systematic and random errors in eddy correlation fluxes and flux gradients measured by aircraft in the convective boundary layer as a function of the length of the flight leg, or of the cutoff wavelength of a highpass filter. The estimates are obtained from empirical expressions for various length scales in the convective boundary layer and they are experimentally verified using data from the First ISLSCP (International Satellite Land Surface Climatology Experiment) Field Experiment (FIFE), the Air Mass Transformation Experiment (AMTEX), and the Electra Radome Experiment (ELDOME). We show that the systematic flux and flux gradient errors can be important if fluxes are calculated from a set of several short flight legs or if the vertical velocity and scalar time series are high-pass filtered. While the systematic error of the flux is usually negative, that of the flux gradient can change sign. For example, for temperature flux divergence the systematic error changes from negative to positive about a quarter of the way up in the convective boundary layer.

Mann, Jakob; Lenschow, Donald H.

1994-07-01

11

Relationships between enzymatic flux capacities and metabolic flux rates: Nonequilibrium reactions in?muscle?glycolysis  

PubMed Central

The rules that govern the relationships between enzymatic flux capacities (Vmax) and maximum physiological flux rates (v) at enzyme-catalyzed steps in pathways are poorly understood. We relate in vitro Vmax values with in vivo flux rates for glycogen phosphorylase, hexokinase, and phosphofructokinase, enzymes catalyzing nonequilibrium reactions, from a variety of muscle types in fishes, insects, birds, and mammals. Flux capacities are in large excess over physiological flux rates in low-flux muscles, resulting in low fractional velocities (%Vmax = v/Vmax × 100) in vivo. In high-flux muscles, close matches between flux capacities and flux rates (resulting in fractional velocities approaching 100% in vivo) are observed. These empirical observations are reconciled with current concepts concerning enzyme function and regulation. We suggest that in high-flux muscles, close matches between enzymatic flux capacities and metabolic flux rates (i.e., the lack of excess capacities) may result from space constraints in the sarcoplasm. PMID:9192692

Suarez, R. K.; Staples, J. F.; Lighton, J. R. B.; West, T. G.

1997-01-01

12

Latent Heat in Soil Heat Flux Measurements  

Technology Transfer Automated Retrieval System (TEKTRAN)

The surface energy balance includes a term for soil heat flux. Soil heat flux is difficult to measure because it includes conduction and convection heat transfer processes. Accurate representation of soil heat flux is an important consideration in many modeling and measurement applications. Yet, the...

13

Measurement of the rates of acetyl-CoA hydrolysis and synthesis from acetate in rat hepatocytes and the role of these fluxes in substrate cycling.  

PubMed Central

1. Acetyl-CoA hydrolysis, acetyl-CoA synthesis from acetate and several related fluxes were measured in rat hepatocytes. 2. In contrast with acetyl-CoA hydrolysis, most of the acetyl-CoA synthesis from acetate occurred in the mitochondria. 3. Acetyl-CoA hydrolysis was not significantly affected by 24 h starvation or (-)-hydroxycitrate. 4. In the cytoplasm there was a net flux of acetyl-CoA to acetate, and substrate cycling between acetate and acetyl-CoA in this compartment was very low, accounting for less than 0.1% of the total heat production by the animal. 5. A larger cycle, involving mitochondrial and cytoplasmic acetate and acetyl-CoA, may operate in fed animals, but would account for only approx 1% of total heat production. 6. It is proposed that the opposing fluxes of mitochondrial acetate utilization and cytoplasmic net acetate production may provide sensitivity, feedback and buffering, even when these fluxes are not linked to form a conventional substrate cycle. PMID:2396982

Crabtree, B; Gordon, M J; Christie, S L

1990-01-01

14

Quantifying the "chamber effect" in CO2 flux measurements  

NASA Astrophysics Data System (ADS)

The significance of aquatic CO2 emissions has received attention in recent years. For example annual aquatic emissions in the Amazon basin have been estimated as 500 Mt of carbon1. Methods for determining the flux rates include eddy covariance flux tower measurements, flux estimates calculated from partial pressure of CO2 (pCO2) in water and the use floating flux chambers connected to an infra-red gas analyser. The flux chamber method is often used because it is portable, cheaper and allows smaller scale measurements. It is also a direct method and hence avoids problems related to the estimation of the gas transfer coefficient that is required when fluxes are calculated from pCO2. However, the use of a floating chamber may influence the flux measurements obtained. The chamber shields the water underneath from effects of wind which could lead to lower flux estimates. Wind increases the flux rate by i) causing waves which increase the surface area for efflux, and ii) removing CO2 build up above the water surface, hence maintaining a higher concentration gradient. Many floating chambers have an underwater extension of the chamber below the float to ensure better seal to water surface and to prevent any ingress of atmospheric air when waves rock the chamber. This extension may cause additional turbulence in flowing water and hence lead to overestimation of flux rates. Some groups have also used a small fan in the chamber headspace to ensure thorough mixing of air in the chamber. This may create turbulence inside the chamber which could increase the flux rate. Here we present results on the effects of different chamber designs on the detected flux rates. 1Richey et al. 2002. Outgassing from Amazonian rivers and wetlands as a large tropical source of atmospheric CO2. Nature 416: 617-620.

Vihermaa, Leena; Childs, Amy; Long, Hazel; Waldron, Susan

2014-05-01

15

Flux-based environmental management: the future of integrated passive flux measurements in groundwater  

NASA Astrophysics Data System (ADS)

The measurement and interpretation of parameter mass fluxes and discharges is gaining more and more importance. Especially in the frame of soil and groundwater contamination, remediation and related environmental risks, water management and ecosystem management, the interpretation of mass fluxes is essential. Current legislation already includes a mass flux approach today (e.g. EU Water Framework Directive and Groundwater Daughter Directive). Environmental management actions regarding groundwater pollutions and ecosystem research and management are mostly driven by parameter concentrations. Since concentration estimates are highly uncertain and do not include the fluctuations caused by spatially and temporally varying conditions, decisions about these actions can be improved by also considering parameter mass fluxes (mass of parameter passing per unit time per unit area, or flow rate of these parameters per unit area) and parameter mass discharges (sum of all mass flux measures across an entire plume). The mass that effectively reaches a downgradient receptor, determines the actual situation and risks, and should therefore be monitored. It is essential to determine mass fluxes directly instead of estimating mass flux based on concentration data and estimates of groundwater velocity. The direct determination of contaminant mass fluxes in soil and groundwater systems is possible with the Passive Flux Meter (PFM) technology. The PFM is a recently developed passive sampling device that provides simultaneous in situ point measurements of a time-averaged contaminant mass flux and water flux. The device, with a suite of tracers, is placed in a monitoring well or borehole for a known exposure period, where it intercepts the groundwater flow and captures contaminants from it. The measurements of the contaminants and the remaining resident tracer can then be used to estimate groundwater and contaminant fluxes. Today, an increasing demand from different sectors for the combined determination of multiple parameter mass fluxes, has stimulated us to optimize the technology and develop an integrated flux measurement device which targets the combined mass flux determination of multiple parameter types. The principles of flux-based environmental management will be presented, with a special focus on the application and future of integrated passive flux measurements in groundwater.

Verreydt, Goedele; Struyf, Eric; Van Keer, Ilse; Meire, Patrick; Bronders, Jan; Seuntjens, Piet

2014-05-01

16

Measurement of trace gas fluxes over an unfertilized agricultural field using the flux-gradient technique.  

PubMed

Trace gas fluxes exhibit extensive spatial and temporal variability that is dependent on a number of factors, including meteorology, ambient concentration, and emission source size. Previous studies have found that agricultural fertilization contributes to higher fluxes of certain gases. The magnitude of trace gas fluxes over unfertilized crops is still uncertain. In the present study, deposition of ammonia (NH), nitric acid (HNO), and sulfur dioxide (SO) was measured over unfertilized soybean using the flux-gradient technique. The eddy diffusivity was estimated from eddy covariance measurements of temperature fluxes, resulting in K of 0.64 ± 0.30 m s. Flux means and standard deviations were -0.14 ± 0.13, -0.22 ± 0.19, and -0.38 ± 0.54 ?g m s for NH, HNO, and SO, respectively. Low concentrations of NH and HNO increased the relative uncertainties in the deposition velocities estimated from measured fluxes. This contributed to dissimilarities between deposition velocities estimated from the resistance analogy and deposition velocities estimated from fluxes. However, wet canopy conditions during the study may have led to an underestimation of deposition by the resistance analogy because the resistance method does not accurately describe the enhanced deposition rates that occur after dew formation. Quantification of vegetation characteristics, such as leaf wetness and apoplast chemistry, would be beneficial in future studies to more accurately determine stomatal resistance and its influence on fluxes. PMID:21869497

Myles, Latoya; Kochendorfer, John; Heuer, Mark W; Meyers, Tilden P

2011-01-01

17

Calving fluxes and basal melt rates of Antarctic ice shelves.  

PubMed

Iceberg calving has been assumed to be the dominant cause of mass loss for the Antarctic ice sheet, with previous estimates of the calving flux exceeding 2,000?gigatonnes per year. More recently, the importance of melting by the ocean has been demonstrated close to the grounding line and near the calving front. So far, however, no study has reliably quantified the calving flux and the basal mass balance (the balance between accretion and ablation at the ice-shelf base) for the whole of Antarctica. The distribution of fresh water in the Southern Ocean and its partitioning between the liquid and solid phases is therefore poorly constrained. Here we estimate the mass balance components for all ice shelves in Antarctica, using satellite measurements of calving flux and grounding-line flux, modelled ice-shelf snow accumulation rates and a regional scaling that accounts for unsurveyed areas. We obtain a total calving flux of 1,321?±?144?gigatonnes per year and a total basal mass balance of -1,454?±?174?gigatonnes per year. This means that about half of the ice-sheet surface mass gain is lost through oceanic erosion before reaching the ice front, and the calving flux is about 34 per cent less than previous estimates derived from iceberg tracking. In addition, the fraction of mass loss due to basal processes varies from about 10 to 90 per cent between ice shelves. We find a significant positive correlation between basal mass loss and surface elevation change for ice shelves experiencing surface lowering and enhanced discharge. We suggest that basal mass loss is a valuable metric for predicting future ice-shelf vulnerability to oceanic forcing. PMID:24037377

Depoorter, M A; Bamber, J L; Griggs, J A; Lenaerts, J T M; Ligtenberg, S R M; van den Broeke, M R; Moholdt, G

2013-10-01

18

Epistasis for growth rate and total metabolic flux in yeast.  

PubMed

Studies of interactions between gene deletions repeatedly show that the effect of epistasis on the growth of yeast cells is roughly null or barely positive. These observations relate generally to the pace of growth, its costs in terms of required metabolites and energy are unknown. We measured the maximum rate at which yeast cultures grow and amounts of glucose they consume per synthesized biomass for strains with none, single, or double gene deletions. Because all strains were maintained under a fermentative mode of growth and thus shared a common pattern of metabolic processes, we used the rate of glucose uptake as a proxy for the total flux of metabolites and energy. In the tested sample, the double deletions showed null or slightly positive epistasis both for the mean growth and mean flux. This concordance is explained by the fact that average efficiency of converting glucose into biomass was nearly constant, that is, it did not change with the strength of growth effect. Individual changes in the efficiency caused by gene deletions did have a genetic basis as they were consistent over several environments and transmitted between single and double deletion strains indicating that the efficiency of growth, although independent of its rate, was appreciably heritable. Together, our results suggest that data on the rate of growth can be used as a proxy for the rate of total metabolism when the goal is to find strong individual interactions or estimate the mean epistatic effect. However, it may be necessary to assay both growth and flux in order to detect smaller individual effects of epistasis. PMID:22412994

Jakubowska, Agata; Korona, Ryszard

2012-01-01

19

Eddy Correlation Flux Measurement System (ECOR) Handbook  

SciTech Connect

The eddy correlation (ECOR) flux measurement system provides in situ, half-hour measurements of the surface turbulent fluxes of momentum, sensible heat, latent heat, and carbon dioxide (CO2) (and methane at one Southern Great Plains extended facility (SGP EF) and the North Slope of Alaska Central Facility (NSA CF). The fluxes are obtained with the eddy covariance technique, which involves correlation of the vertical wind component with the horizontal wind component, the air temperature, the water vapor density, and the CO2 concentration.

Cook, DR

2011-01-31

20

4, 66036643, 2004 Flux measurements  

E-print Network

deciduous forest site in North-Western Germany using the eddy covari- ance (EC) technique. The measurement site was characterised by a forest of inho-5 mogeneous composition, complex canopy structure, limited this forest, with average emissions10 (normalised to 30 C and 1000 µmoles m-2 s-1 PAR) of 1.5 and 0.39 µg m-2

Boyer, Edmond

21

Cosmic muon flux measurements at the Kimballton Underground Research Facility  

NASA Astrophysics Data System (ADS)

In this article, the results from a series of muon flux measurements conducted at the Kimballton Underground Research Facility (KURF), Virginia, United States, are presented. The detector employed for these investigations, is made of plastic scintillator bars readout by wavelength shifting fibers and multianode photomultiplier tubes. Data was taken at several locations inside KURF, spanning rock overburden values from ~ 200 to 1450 m.w.e. From the extracted muon rates an empirical formula was devised, that estimates the muon flux inside the mine as a function of the overburden. The results are in good agreement with muon flux calculations based on analytical models and MUSIC.

Kalousis, L. N.; Guarnaccia, E.; Link, J. M.; Mariani, C.; Pelkey, R.

2014-08-01

22

Experimental flux measurements on a network scale  

SciTech Connect

Metabolic flux is a fundamental property of living organisms. In recent years, methods for measuring metabolic flux in plants on a network scale have evolved further. One major challenge in studying flux in plants is the complexity of the plant's metabolism. In particular, in the presence of parallel pathways in multiple cellular compartments, the core of plant central metabolism constitutes a complex network. Hence, a common problem with the reliability of the contemporary results of {sup 13}C-Metabolic Flux Analysis in plants is the substantial reduction in complexity that must be included in the simulated networks; this omission partly is due to limitations in computational simulations. Here, I discuss recent emerging strategies that will better address these shortcomings.

Schwender, J.

2011-10-11

23

Dual neutron flux/temperature measurement sensor  

DOEpatents

Simultaneous measurement of neutron flux and temperature is provided by a single sensor which includes a phosphor mixture having two principal constituents. The first constituent is a neutron sensitive 6LiF and the second is a rare-earth activated Y203 thermophosphor. The mixture is coated on the end of a fiber optic, while the opposite end of the fiber optic is coupled to a light detector. The detected light scintillations are quantified for neutron flux determination, and the decay is measured for temperature determination.

Mihalczo, John T. (Oak Ridge, TN); Simpson, Marc L. (Knoxville, TN); McElhaney, Stephanie A. (Oak Ridge, TN)

1994-01-01

24

Dual neutron flux/temperature measurement sensor  

DOEpatents

Simultaneous measurement of neutron flux and temperature is provided by a single sensor which includes a phosphor mixture having two principal constituents. The first constituent is a neutron sensitive 6LiF and the second is a rare-earth activated Y203 thermophosphor. The mixture is coated on the end of a fiber optic, while the opposite end of the fiber optic is coupled to a light detector. The detected light scintillations are quantified for neutron flux determination, and the decay is measured for temperature determination. 3 figs.

Mihalczo, J.T.; Simpson, M.L.; McElhaney, S.A.

1994-10-04

25

Regional airborne flux measurements in Europe  

NASA Astrophysics Data System (ADS)

The problem of identifying the spatial and temporal distribution of sources and sinks of atmospheric CO2 is the subject of considerable scientific and political debate. Even if it is now possible to estimate within reasonable accuracy the sink strength of European forests at the local scale, difficulties still exist in determining the partitioning of the sinks at the global and regional scales. The aim of the EU-project RECAB (Regional Assessment of the Carbon Balance in Europe) that is coordinated by Alterra, Wageningen (NL), is to bridge the gap between local scale flux measurements and continental scale inversion models by a generic modelling effort and measurement program, focussing on a limited number of selected regions in Europe for which previous measurements exists. This required the establishment of a European facility for airborne measurement of surface fluxes of CO2 at very low altitude, and a research aircraft capable of performing airborne eddy covariance measurements has been acquired by this project and used on several occasions at the different RECAB sites. The aircraft is the italian Sky Arrows ERA (Environmental Research Aircraft) equipped with the NOAA/ARA Mobile Flux Platform (MFP), and a commercial open-path infrared gas analyser. Airborne eddy covariance measurements were made from June 2001 onwards in Southern Spain near Valencia (June and December 2001), in Central Germany near Jena (July 2001), in Sweden near Uppsala (August 2001), in The Netherlands near Wageningen (January and July 2002) and in Italy near Rome (June 2002). Flux towers were present at each site to provide a validation of airborne eddy covariance measurements. This contribution reports some validation results based on the comparison between airborne and ground based flux measurements and some regional scale results for different locations and different seasons, in a wide range of meteorological and ecological settings.

Gioli, B.; Miglietta, F.; Vaccari, F. P.; Zaldei, A.; Hutjes, R. W. A.

2003-04-01

26

An Apparatus for Absolute Neutron Flux Measurement  

NASA Astrophysics Data System (ADS)

A fully-absorbing neutron detector is being developed to measure the absolute flux (s-1) of a cold neutron beam at the level of 0.1,%. The device will be used to calibrate a neutron flux monitor used in an in-beam neutron lifetime measurement performed at NIST (?n= (886.3 ±3.4) s). The precision of the measurement was limited by the uncertainty in the efficiency of the neutron flux monitor (0.3,%). The flux monitor operates by counting charged particles produced when neutrons impinge on a ^6Li (or ^10B) foil. Its efficiency was calculated from the cross section, the solid angle subtended by the charged particle detectors, and the amount of neutron-absorbing material present on the foil. Successful calibration would reduce the neutron lifetime uncertainty to approximately 0.25,%. In addition, using the measured solid angle and amount of material on the deposit, a new experimental value for the ^6Li or (^10B) capture cross section will be obtained. Details of the apparatus and the measurement technique along with the status of the experiment will be discussed.

Yue, A.; Greene, G.; Dewey, M. S.; Gilliam, D.; Nico, J.; Laptev, A.

2007-10-01

27

Fluid flow rate, temperature and heat flux at Mohns Ridge vent fields: evidence from isosampler measurements for phase separated hydrothermal circulation along the arctic ridge system  

NASA Astrophysics Data System (ADS)

An expedition to the Mohns Ridge in the Norwegian-Greenland sea was carried out in July-August 2005 as part of BIODEEP, lead by University of Bergen (UoB). UoB had previously detected water column methane along this very slow spreading ridge. Previous ROV observations along the ridge (71 deg 18'N, 5 deg 47'W, 605 mbsl) near Jan Mayen had uncovered a broad area of ferric hydroxide-rich bacterial/mineral assemblages, comprising large populations of gallionella bacteria. This area was revisted in 2005. Characteristic of sections of this area ("Gallionella Garden") are chimney-like structures standing ~15 cm tall, often topped by a sea lily (heliometra glacialis). The interior of the structures comprised quasi-concentric bands with vertically-oriented channels. The Oregon State University/Cardiff University Isosampler sensor determined that some of these assemblages support fluid flow through their interior. The outflow from the chimney structures was typically +0.5 deg C, against background temperatures of -0.3 deg C. Flow anomalies were also identified atop extensive bacterial mats. Gallionella Gardens is several km in extent with active, albeit extremely low temperature hydrothermal flow. A field of active high temperature smoker chimney structures was located near Gallionella Garden at 540 mbsl. This field extends ~500 m along a scarp wall, with hydrothermal mounds extending along faults running perpendicular to the scarp, each of which has multiple smoker vents and areas of diffuse flow. There was evidence for phase separation, with a negatively buoyant fluid phase exiting some vent orifices and descending along the vent wall; and evidence for gas phase condensing after leaving some vent orifices. Gas bubble emissions were not uncommon. Isosampler sensors were available that were configured for lower temperature measurements at Gallionella Garden. While capable of detecting variations in effluent at the 4 millidegree level, the temperature ceiling for the sensor tips available aboard ship was 260 deg C (800 deg C-capable isosampler sensors will be available for the 2006 field season). At this depth the phase separation point of seawater is 263 deg C. An isosampler sensor was deployed directly atop an apparently phase-separated white smoker chimney. The sensor indicated 260 deg C before terminating measurement. This was repeated at another vent site, indicating that the fluids were venting at the point of phase separation. Indicated smoker plume flow rates were approximately 1/2 meter per second. A second field "Soria Moria" of high temperature vents was discovered. This field is ~100 m on a side, and is densely populated by active white smoker chimneys, also with evidence for phase-separated flow. These vent fields comprise the first ever arctic vent plume sources ever visited by ROV and measured directly at the source of emission. A return to this area, and exploration and measurement further north is anticipated for 2006. The planned work includes comprehensive Isosampler and bioreactor fluid flow, sampling, geochemical and biogeochemical sampling and incubation.

Schultz, A.; Pedersen, R. B.; Thorseth, I. H.; Taylor, P.; Flynn, M.

2005-12-01

28

Instruments for measuring radiant thermal fluxes  

NASA Technical Reports Server (NTRS)

An absolute two-sided radiometer, designed on the principle of replacing absorbed radiant energy with electrical energy, is described. The sensitive element of the detector is a thermoelectric transducer of thermal flux. The fabrication technology, methods of measurement, technical characteristics, and general operation of the instrument are presented.

Gerashenko, O. A.; Sazhina, S. A.

1974-01-01

29

Plasma momentum meter for momentum flux measurements  

DOEpatents

Invention comprises an instrument in which momentum flux onto a biasable target plate is transferred via a suspended quartz tube onto a sensitive force transducer--a capacitance-type pressure gauge. The transducer is protected from thermal damage, arcing and sputtering, and materials used in the target and pendulum are electrically insulating, rigid even at elevated temperatures, and have low thermal conductivity. The instrument enables measurement of small forces (10.sup.-5 to 10.sup.3 N) accompanied by high heat fluxes which are transmitted by energetic particles with 10's of eV of kinetic energy in a intense magnetic field and pulsed plasma environment.

Zonca, Fulvio (Rome, IT); Cohen, Samuel A. (Hopewell, NJ); Bennett, Timothy (Princeton, NJ); Timberlake, John R. (Allentown, NJ)

1993-01-01

30

Aerosol flux measurements above a mixed forest at Borden, Ontario  

NASA Astrophysics Data System (ADS)

Aerosol fluxes were measured above a mixed forest by Eddy Covariance (EC) with a Fast Mobility Particle Sizer (FMPS) at the Borden Forest Research Station in Ontario, Canada between 13 July and 12 August 2009. The FMPS, mounted at a height of 33 m (approximately 10 m above the canopy top) and housed in a temperature controlled enclosure, measured size-resolved particle concentrations for 3 to 410 nm at a rate of 1 Hz. For the size range 20fluxes were upward. The exchange velocity is between -0.5 and 2.0 mm s-1, with median values near 0.5 mm s-1 for all sizes between 24 and 280 nm. The net production rate of particles is highest for 75 nm particles and is near 0.4×106 m-2 s-1. Results indicate a decoupling of the above and below canopy spaces, whereby particles are stored in the canopy space at night, and are then diluted with cleaner air above during the day. Chemically speciated flux measurements from a previous study at the same location using a Quadrupole Aerosol Mass Spectrometer (Q-AMS) demonstrate a tendency towards downward fluxes, which may be due to an organic particle component which can not be resolved by the flux mode of the Q-AMS.

Gordon, M.; Staebler, R. M.; Liggio, J.; Vlasenko, A.; Li, S.-M.; Hayden, K.

2010-10-01

31

An investigation of the consistency of the ionospheric measurements of the photoelectron flux and solar EUV flux  

NASA Technical Reports Server (NTRS)

This paper demonstrates that there is an inconsistency between ionospheric measurements of the photoelectron flux and the solar EUV flux. The problem which occurs for EUV wavelengths near 250 A or photoelectron energies near 35 eV has serious implications for theoretical photoelectron flux calculations and could help to explain up to 40 percent of the difference between calculated and measured photoelectron fluxes for electron energies below 35 eV. It is also shown that: (1) only photons with wavelengths shorter than 310 A are of importance in producing photoelectrons; (2) above 20 eV, the photoelectron flux is controlled by the production of primary photoelectrons, while below 20 eV the flux is controlled by degraded photoelectrons; (3) the calculated cascading production rate is insensitive to the cross sections used for the calculation; and (4) the photoelectron flux is inversely proportional to the total inelastic cross sections.

Richards, P. G.; Torr, D. G.

1984-01-01

32

HONO Flux Measurement at a Forested Site in Northern Michigan  

NASA Astrophysics Data System (ADS)

Nitrous acid (HONO) is an important precursor of hydroxyl radical and plays an important role in the terrestrial boundary layer photochemistry. HONO is produced from various heterogeneous processes on surfaces, including photo-induced reactions involving NOx and HNO3. To quantitatively assess the HONO source strength at the forest canopy surface, we have deployed a Relaxed Eddy Accumulation (REA) method coupled with 2 LOng Path Absorption Photometers (LOPAP) for the measurement of HONO flux on PROPHET tower in the University of Michigan Biological Station during summer of 2008. Overall positive fluxes were observed, in consistent with our understanding that canopy surface is mainly a HONO source. A composite plot based on all measurement data shows a distinct diurnal variation pattern in HONO flux, with a low exchange rate (0.1 "Ýmoles m-2 hr-1) during the night and a maximum upward flux (0.7 "Ýmoles m-2 hr- 1) during noontime and early afternoon, suggesting that HONO production on canopy surface is photochemically related. The daytime upward HONO flux may counter a significant fraction of the NOy downward flux, a maximum of ~1.5 "Ýmoles m-2 hr-1 measured in August 2005. Some strong downward fluxes (up to 2 "Ýmoles m-2 hr-1) were found to be associated with rain and dew events, as a result of enhanced HONO dry deposition on wet surfaces. We will further examine the relationship between HONO flux and other parameters, such as ambient NOx, HNO3/nitrate loading on leaves, light intensity, relative humidity, and air mass back trajectories.

Zhou, X.; Zhang, N.; Tang, D.; Bertman, S.; Teravest, M.; Alaghmand, M.; Shepson, P.; Carroll, M.

2008-12-01

33

Micrometeorological flux measurements at a coastal site  

NASA Astrophysics Data System (ADS)

The eddy covariance (EC) technique is the only direct measurement of the momentum, heat, and trace gas (e.g. water vapor, CO2 and ozone) fluxes. The measurements are expected to be most accurate over flat terrain where there is an extended homogenous surface upwind from the tower, and when the environmental conditions are steady. Additionally, the one dimensional approach assumes that vertical turbulent exchange is the dominant flux, whereas advective influences should be negligible. The application of EC method under non-ideal conditions, for example in complex terrain, has yet to be fully explored. To explore the possibilities and limitations of EC technique under non-ideal conditions, an EC system was set up at Selles beach, Crete, Greece (35.33°N, 25.71°E) in the beginning of July 2012. The dominant wind direction was west, parallel to the coast. The EC system consisted of a sonic anemometer (CSAT3 Campbell Scientific), an infrared open-path CO2/H2O gas analyzer (LI-7500, Li-COR Biosciences) and a fast chemiluminescence ozone analyzer (enviscope GmbH). All the signals of these fast response instruments were sampled at 10 Hz and the measurement height was 3 m. Besides, another gradient system was setup. Air temperature, relative humidity (HYGROMER MP 103 A), and wind speed (WMT700 Vaisala) were measured every 10 seconds at 3 heights (0.7, 1.45, 3 m). Air intakes were set up at 0.7m and 3m. A pump drew the air through a flow system and a telflon valve alternately switched between the two heights every 30 seconds. H2O, CO2 (LI-840A, Li-COR Biosciences) and ozone mixing ratio s (model 205, 2BTechnologies) were measured every 10 seconds. Momentum, heat, CO2 and ozone fluxes were evaluated by both EC and gradient technique. For the calculation of turbulent fluxes, TK3 algorithm (Department of Micrometeorology, University Bayreuth, Germany) was applied. We will present the measured fluxes of the two systems and assess the data quality under such non-ideal condition.

Song, Guozheng; Meixner, Franz X.; Bruse, Michael; Mamtimin, Buhalqem

2014-05-01

34

Infrared Camera Diagnostic for Heat Flux Measurements on NSTX  

SciTech Connect

An infrared imaging system has been installed on NSTX (National Spherical Torus Experiment) at the Princeton Plasma Physics Laboratory to measure the surface temperatures on the lower divertor and center stack. The imaging system is based on an Indigo Alpha 160 x 128 microbolometer camera with 12 bits/pixel operating in the 7-13 {micro}m range with a 30 Hz frame rate and a dynamic temperature range of 0-700 degrees C. From these data and knowledge of graphite thermal properties, the heat flux is derived with a classic one-dimensional conduction model. Preliminary results of heat flux scaling are reported.

D. Mastrovito; R. Maingi; H.W. Kugel; A.L. Roquemore

2003-03-25

35

Measurement of the Meteoroid Flux at Mars  

NASA Astrophysics Data System (ADS)

In the fall of 2005, a dedicated meteor observing campaign was carried out by the Panoramic Camera (Pancam) onboard the Mars Exploration Rover (MER) Spirit to determine the viability of using MER cameras as meteor detectors and to obtain the first experimental estimate of the meteoroid flux at Mars. Our observing targets included both the sporadic meteoroid background and two predicted martian meteor showers: one associated with comet 1P/Halley and a potential stream associated with 2001/R1 LONEOS. A total of 353 images covering 2.7 h of net exposure time were analyzed with no conclusive meteor detections. From these data, we estimate the upper limit to the background meteoroid flux at Mars to be < 4.4 x 10-6 meteoroids km-2hr-1 for meteoroids with mass larger than 4 g. The estimated flux to this same mass limit at the Earth is 10-6 meteoroids km-2hr-1(Grün et al. 1985). This result is qualitatively consistent, within error bounds, with theoretical models predicting martian fluxes of 50% that at Earth for meteoroids of mass 10-3-101 g (Adolfsson et al. 1996). Our analysis also suggests that the event reported as the first martian meteor (Selsis et al. 2005) is more likely to be a grazing cosmic ray impact, which we found to be a major source of confusion with potential meteors in all Pancam images. Domokos, A., Bell III, J.F., Brown, P., Lemmon, M.T., Suggs, R., Vaubaillon, J., 2007. Measurement of the Meteoroid Flux at Mars. Icarus, in press. doi: 10.1016/j.icarus.2007.04.017

Domokos, Andrea; Bell, J. F., III; Brown, P.; Lemmon, M. T.; Suggs, R.; Vaubaillon, J.; Cooke, W.

2007-12-01

36

Rapid and Precise Determination of Cellular Amino Acid Flux Rates  

E-print Network

Rapid and Precise Determination of Cellular Amino Acid Flux Rates Using HPLC with Automated in complete cell media using an Agilent 1100 HPLC with a ZORBAX Eclipse Plus C18 column with absorbance synthesis may consume larger quantities of amino acids than other cell types. HPLC with precolumn

Wikswo, John

37

High heat flux measurements and experimental calibrations/characterizations  

NASA Technical Reports Server (NTRS)

Recent progress in techniques employed in the measurement of very high heat-transfer rates in reentry-type facilities at the Arnold Engineering Development Center (AEDC) is described. These advances include thermal analyses applied to transducer concepts used to make these measurements; improved heat-flux sensor fabrication methods, equipment, and procedures for determining the experimental time response of individual sensors; performance of absolute heat-flux calibrations at levels above 2,000 Btu/cu ft-sec (2.27 kW/cu cm); and innovative methods of performing in-situ run-to-run characterizations of heat-flux probes installed in the test facility. Graphical illustrations of the results of extensive thermal analyses of the null-point calorimeter and coaxial surface thermocouple concepts with application to measurements in aerothermal test environments are presented. Results of time response experiments and absolute calibrations of null-point calorimeters and coaxial thermocouples performed in the laboratory at intermediate to high heat-flux levels are shown. Typical AEDC high-enthalpy arc heater heat-flux data recently obtained with a Calspan-fabricated null-point probe model are included.

Kidd, Carl T.

1992-01-01

38

ACCURACY OF SOIL HEAT FLUX MEASUREMENTS MADE WITH FLUX PLATES OF CONTRASTING PROPERTIES  

Technology Transfer Automated Retrieval System (TEKTRAN)

Flux plate measurements of soil heat flux (G) may include significant errors unless the plates are carefully installed and known errors accounted for. The objective of this research was to quantify potential errors in G when using soil heat flux plates of contrasting designs. Five flux plates with...

39

Measurements of diffusive sublayer thicknesses in the ocean by alabaster dissolution, and their implications for the measurements of benthic fluxes  

Microsoft Academic Search

Fluxes of reactive chemical species across the sediment-water interface can profoundly influence the dominant biogeochemical cycles in the worlds ocean. However, reliable in-situ measurements of benthic fluxes of many reactive species cannot be carried out without adjustments of stirring rates inside benthic flux chambers to match boundary layer conditions prevailing outside. A simple method to compare flow levels consists of

Peter H. Santschi; Robert F. Anderson; Walter Bowles

1991-01-01

40

Suggestions for the measurement and derivation of fluxes and flux divergences from a satellite  

NASA Technical Reports Server (NTRS)

Consideration is given to the determination of the optimal bands for measuring and deriving the total outgoing longwave radiation (OLR), surface downward flux (SDF), and cooling rates (CRs) using linear regression. The optimal bands are determined from scatter plots of total fluxes and cooling rates associated with the various bands. It is found that the best band for OLR is between 800 and 1200/cm, while the best band for SDF is between 500 and 660/cm or between 660 and 800/cm. For CRs, it is shown that the best band is also between 660 and 800/cm. It is noted that the AVHRR OLR is damped compared with the Nimbus-7 earth radiation budget (ERB) OLR derived from the broadband, narrow FOV ERB instrument.

Wu, Man-Li C.

1990-01-01

41

A storage-extended rating curve for sediment flux estimation  

NASA Astrophysics Data System (ADS)

An empirical suspended sediment concentration (SSC) estimation method was tested, which incorporates sediment storage, erosion, and sedimentation history of the upstream river system. It is based on the common rating curve method of which inaccurate SSC estimation is prevailingly caused by the assumption of an over-proportional relationship between SSC and discharge. However, this ignores the fact that SSC depends on the availability of sediments in the river basin as well. Hence, the tested method includes non-linear processes such as the clockwise and counter-clockwise hysteresis during flood discharges. The main characteristic of this new approach is that sediment flux is described as a composition of (i) the base transport of sediments from the catchment area into the river system, (ii) erosion, and (iii) in-situ sedimentation. The first two components are approximated with classical rating curves. The second component depends on (i) a threshold discharge for erosion and (ii) on the sediment availability. Sedimentation is factored as a constant value and it is zero if the discharge exceeds the threshold value. This new model formulation was tested with daily SSC and discharge measurements from the Alpine Rhine River for the period 1 June 2012 to 31 May 2013 at gauging station Diepoldsau, which is located a few kilometres upstream of Lake Constance. The seven empirical parameters of the model were estimated by using an evolutionary algorithm. This optimization algorithm found a threshold for erosion at a discharge of about 500 m3 s-1, a mean concentration of 124 mg l-1 that is lost due to sedimentation, and the mean content of sediment storage in the river bed of about 1.82×1011 kg, which is available for erosion. The results show an clear improvement of SSC estimation: R2 increased to 0.93 while it was 0.73 for the rating curve. Moreover, the new method calculated flood loads, which fitted perfect to measured sediments: e.g. the measured flood load of 7392 mg l-1 (4 June 2013) was approximated with 7357 mg l-1 by the model. To conclude, the additional consideration of erosion and sedimentation processes significantly improves SSC estimations especially during flood events and it offers a reliable way to estimate SSC time series with runoff data.

Fink, Gabriel; Wüest, Alfred

2014-05-01

42

An evaluation of sediment rating curves for estimating suspended sediment concentrations for subsequent flux calculations  

USGS Publications Warehouse

In the absence of actual suspended sediment concentration (SSC) measurements, hydrologists have used sediment rating (sediment transport) curves to estimate (predict) SSCs for subsequent flux calculations. Various evaluations of the sediment rating-curve method were made using data from long-term, daily sediment-measuring sites within large (>1 000 000 km2), medium ( 1000 km2), and small (<1000 km2) river basins in the USA and Europe relative to the estimation of suspended sediment fluxes. The evaluations address such issues as the accuracy of flux estimations for various levels of temporal resolution as well as the impact of sampling frequency on the magnitude of flux estimation errors. The sediment rating-curve method tends to underpredict high, and overpredict low SSCs. As such, the range of errors associated with concomitant flux estimates for relatively short time-frames (e.g. daily, weekly) are likely to be substantially larger than those associated with longer time-frames (e.g. quarterly, annually) because the over- and underpredictions do not have sufficient time to balance each other. Hence, when error limits must be kept under ??20%, temporal resolution probably should be limited to quarterly or greater. The evaluations indicate that over periods of 20 or more years, errors of <1% can be achieved using a single sediment rating curve based on data spanning the entire period. However, somewhat better estimates for the entire period, and markedly better annual estimates within the period, can be obtained if individual annual sediment rating curves are used instead. Relatively accurate (errors fluxes can be obtained from hydrologically based monthly measurements/samples. For 5-year periods or longer, similar results can be obtained from measurements/samples collected once every 2 months. In either case, hydrologically based sampling, as opposed to calendar-based sampling is likely to limit the magnitude of flux estimation errors. Published in 2003 by John Wiley and Sons, Ltd.

Horowitz, A.J.

2003-01-01

43

FAST NEUTRON FLUX MEASUREMENTS FOR SHIELDING APPLICATIONS  

Microsoft Academic Search

Pressed sulfur pellets, irradiated for two hours at 10 w yielded ;\\u000a satisfactory counting rates on an internal proportional counter for measuring ;\\u000a fast neutrons. The pellets were counted in their original form and an equation ;\\u000a applicable to thick sources was applied to obtain disintegration rates. Decay ;\\u000a data and beta energy analyses indicated that the induced activity was

Roy

1959-01-01

44

Elementary heating events - magnetic interactions between two flux sources. II. Rates of flux reconnection  

NASA Astrophysics Data System (ADS)

Magnetic fragments in the photosphere are in continuous motion and, due to the complex nature of the magnetic field in the solar atmosphere, these motions are likely to drive a lucrative coronal energy source: the passing of initially-unconnected opposite-polarity fragments that release energy through both closing and then re-opening the same fieldlines. Three-dimensional, time-dependent MHD and potential models are used to investigate the passing of fragments in an overlying field. The processes of closing and opening the field generally occur through separator and separatrix reconnection, respectively. The rates of flux reconnection in these processes are determined. They are found to be dependent on the direction of the surrounding magnetic field relative to the motion of the fragments and the velocity of the sources. In particular, separator reconnection rates (closing) and separatrix-surface reconnection rates (opening) are directly related to the rate of flux transport perpendicular to the current sheet (overlying field). The results suggest that both types of reconnection are fast with the peak rates of separator and separatrix reconnection occurring at 58% and 29% of the peak potential reconnection rate, respectively, when the sources are driven at a hundredth of the peak Alfvén velocity in the box. Moreover, the slower the system is driven the closer the flux reconnection rates are to the instantaneous potential rates. Furthermore, there is a maximum reconnection rate for both types of reconnection as the driving speed tends to the Alfvén speed with the separatrix reconnection rate typically half that of separator reconnection. These results suggest that, on the Sun, reconnection driven by the passing of small-scale network and intranetwork fragments is a highly efficient process that is very likely to contribute significantly to the heating of the background solar corona. The three-dimensional reconnection processes are efficient because, unlike in two-dimensions, there are many places within the current sheets where reconnection can take place simultaneously giving rise to fine-scale structure along the boundaries between the open, closed and re-opened flux. Furthermore, due to the complexity of the magnetic field above the photosphere the reconnection all takes place low down at less than a quarter of the separation of the initial fragments above the photosphere.

Parnell, C. E.; Galsgaard, K.

2004-12-01

45

An Alpha-Gamma Counter for Absolute Neutron Flux Measurement  

NASA Astrophysics Data System (ADS)

An alpha-gamma counter was used to measure the absolute neutron flux of a monochromatic cold neutron beam to sub-0.1,% precision. Simultaneously, the counter was used to calibrate a thin neutron flux monitor based on neutron absorption on ^6Li to the same precision. This monitor was used in the most precise beam-based measurement of the neutron lifetime, where the limiting systematic effect was the uncertainty in the neutron counting efficiency (0.3,%). The counter uses a thick target of ^10B-enriched boron carbide to completely absorb the beam. The rate of absorbed neutrons is determined by counting 478 keV gamma rays from neutron capture on ^10B with calibrated high-purity germanium detectors. The calibration results and the implications for the neutron lifetime will be discussed.

Yue, A.; Greene, G.; Dewey, M.; Gilliam, D.; Nico, J.; Laptev, A.

2012-03-01

46

Plasma momentum meter for momentum flux measurements  

DOEpatents

An apparatus is described for measuring momentum flux from an intense plasma stream, comprising: refractory target means oriented normal to the flow of said plasma stream for bombardment by said plasma stream where said bombardment by said plasma stream applies a pressure to said target means, pendulum means for communicating a translational displacement of said target to a force transducer where said translational displacement of said target is transferred to said force transducer by an elongated member coupled to said target, where said member is suspended by a pendulum configuration means and where said force transducer is responsive to said translational displacement of said member, and force transducer means for outputting a signal representing pressure data corresponding to said displacement.

Zonca, F.; Cohen, S.A.; Bennett, T.; Timberlake, J.R.

1993-08-24

47

Latent heat sink in soil heat flux measurements  

Technology Transfer Automated Retrieval System (TEKTRAN)

The surface energy balance includes a term for soil heat flux. Soil heat flux is difficult to measure because it includes conduction and convection heat transfer processes. Accurate representation of soil heat flux is an important consideration in many modeling and measurement applications. Yet, the...

48

Measurement of local high-level, transient surface heat flux  

SciTech Connect

This study is part of a continuing investigation to develop methods for measuring local transient surface heat flux. A method is presented for simultaneous measurements of dual heat fluxes at a surface location by considering the heat flux as a separate function of heat stored and heat conducted within a heat flux gage. Surface heat flux information is obtained from transient temperature measurements taken at points within the gage. Heat flux was determined over a range of 4 to 22 MW/sq m. It was concluded that the method is feasible. Possible applications are for heat flux measurements on the turbine blade surfaces of space shuttle main engine turbopumps and on the component surfaces of rocket and advanced gas turbine engines and for testing sensors in heat flux gage calibrators.

Liebert, C.H.

1988-09-01

49

Measurement of local high-level, transient surface heat flux  

NASA Technical Reports Server (NTRS)

This study is part of a continuing investigation to develop methods for measuring local transient surface heat flux. A method is presented for simultaneous measurements of dual heat fluxes at a surface location by considering the heat flux as a separate function of heat stored and heat conducted within a heat flux gage. Surface heat flux information is obtained from transient temperature measurements taken at points within the gage. Heat flux was determined over a range of 4 to 22 MW/sq m. It was concluded that the method is feasible. Possible applications are for heat flux measurements on the turbine blade surfaces of space shuttle main engine turbopumps and on the component surfaces of rocket and advanced gas turbine engines and for testing sensors in heat flux gage calibrators.

Liebert, Curt H.

1988-01-01

50

In situ measurement of mesopelagic particle sinking rates and the control of carbon transfer to the ocean interior during the Vertical Flux in the Global Ocean (VERTIGO) voyages in the North Pacific  

NASA Astrophysics Data System (ADS)

Among the parameters affecting carbon transfer to the ocean interior, particle sinking rates vary three orders of magnitude and thus more than primary production, f-ratios, or particle carbon contents [e.g., Boyd, P.W., Trull, T.W., 2006. Understanding the export of marine biogenic particles: is there consensus? Progress in Oceanography 4, 276-312, doi:10.1016/j.pocean.2006.10.007]. Very few data have been obtained from the mesopelagic zone where the majority of carbon remineralization occurs and the attenuation of the sinking flux is determined. Here, we report sinking rates from ˜300 m depth for the subtropical (station ALOHA, June 2004) and subarctic (station K2, July 2005) North Pacific Ocean, obtained from short (6.5 day) deployments of an indented rotating sphere (IRS) sediment trap operating as an in situ settling column [Peterson, M.L., Wakeham, S.G., Lee, C., Askea, M.A., Miquel, J.C., 2005. Novel techniques for collection of sinking particles in the ocean and determining their settling rates. Limnology and Oceanography Methods 3, 520-532] to separate the flux into 11 sinking-rate fractions ranging from >820 to >2 m d -1 that are collected by a carousel for further analysis. Functioning of the IRS trap was tested using a novel programming sequence to check that all particles have cleared the settling column prior to the next delivery of particles by the 6-hourly rotation cycle of the IRS. There was some evidence (from the flux distribution among the cups and photomicroscopy of the collected particles) that very slow-sinking particles may have been under-collected because they were unable to penetrate the brine-filled collection cups, but good evidence for appropriate collection of fast-settling fractions. Approximately 50% of the particulate organic carbon (POC) flux was sinking at greater than 100 m d -1 at both stations. At ALOHA, more than 15% of the POC flux sank at >820 m d -1, but low fluxes make this uncertain, and precluded resolution of particles sinking slower than 137 m d -1. At K2, less than 1% of the POC flux sank at >820 m d -1, but a large fraction (˜15-45%) of the flux was contributed by other fast-sinking classes (410 and 205 m d -1). PIC and BSi minerals were not present in higher proportions in the faster sinking fractions, but the observations were too limited to rule out a ballasting contribution to the control of sinking rates. Photographic evidence for a wide range of particle types within individual sinking-rate fractions suggests that biological processes that set the porosity and shape of particles are also important and may mask the role of minerals. Comparing the spectrum of sinking rates observed at K2 with the power-law profile of flux attenuation with depth obtained from other VERTIGO sediment traps deployed at multiple depths [Buesseler, K.O., Lamborg, C.H., Boyd, P.W., Lam, P.J., Trull, T.W., Bidigare, R.R., Bishop, J.K.B., Casciotti, K.L., Dehairs, F., Elskens, M., Honda, M., Karl, D.M., Siegel, D., Silver, M., Steinberg, D., Valdes, J., Van Mooy, B., Wilson, S.E., 2007b. Revisiting carbon flux through the Ocean's twilight zone. Science 316(5824), 567-570, doi: 10.1126/science.1137959] emphasizes the importance of particle transformations within the mesopelagic zone in the control of carbon transport to the ocean interior.

Trull, T. W.; Bray, S. G.; Buesseler, K. O.; Lamborg, C. H.; Manganini, S.; Moy, C.; Valdes, J.

2008-07-01

51

Sensor for Injection Rate Measurements  

PubMed Central

A vast majority of the medium and high speed Diesel engines are equipped with multi-hole injection nozzles nowadays. Inaccuracies in workmanship and changing hydraulic conditions in the nozzles result in differences in injection rates between individual injection nozzle holes. The new deformational measuring method described in the paper allows injection rate measurement in each injection nozzle hole. The differences in injection rates lead to uneven thermal loads of Diesel engine combustion chambers. All today known measuring method, such as Bosch and Zeuch give accurate results of the injection rate in diesel single-hole nozzles. With multihole nozzles they tell us nothing about possible differences in injection rates between individual holes of the nozzle. At deformational measuring method, the criterion of the injected fuel is expressed by the deformation of membrane occurring due to the collision of the pressure wave against the membrane. The pressure wave is generated by the injection of the fuel into the measuring space. For each hole of the nozzle the measuring device must have a measuring space of its own into which fuel is injected as well as its measuring membrane and its own fuel outlet. During measurements procedure the measuring space must be filled with fuel to maintain an overpressure of 5 kPa. Fuel escaping from the measuring device is conducted into the graduated cylinders for measuring the volumetric flow through each hole of the nozzle.The membrane deformation is assessed by strain gauges. They are glued to the membrane and forming the full Wheatstone's bridge. We devoted special attention to the membrane shape and temperature compensation of the strain gauges.

Marcic, Milan

2006-01-01

52

Predicting terrestrial 222Rn flux using gamma dose rate as a proxy  

NASA Astrophysics Data System (ADS)

222Rn is commonly used as a natural tracer for validating climate models. To improve such models a better source term for 222Rn than currently used is necessary. The aim of this work is to establish a method for mapping this source term by using a commonly measured proxy, the gamma dose rate (GDR). Automatic monitoring of GDR has been networked in 25 European countries by the Institute for Environment and Sustainability at the Joint Research Centre (JRC IES) in Ispra, Italy, using a common data format. We carried out simultaneous measurements of 222Rn flux and GDR at 63 locations in Switzerland, Germany, Finland and Hungary in order to cover a wide range of GDR. Spatial variations in GDR resulted from different radionuclide concentrations in soil forming minerals. A relatively stable fraction (20%) of the total terrestrial GDR originates from the 238U decay series, of which 222Rn is a member. Accordingly, spatial variation in terrestrial GDR was found to describe almost 60% of the spatial variation in 222Rn flux. Furthermore, temporal variation in GDR and 222Rn was found to be correlated. Increasing soil moisture reduces gas diffusivity and the rate of 222Rn flux but it also decreases GDR through increased shielding of photons. Prediction of 222Rn flux through GDR for individual measurement points is imprecise but un-biased. Verification of larger scale prediction showed that estimates of mean 222Rn fluxes were not significantly different from the measured mean values.

Szegvary, T.; Leuenberger, M. C.; Conen, F.

2007-06-01

53

Predicting terrestrial 222Rn flux using gamma dose rate as a proxy  

NASA Astrophysics Data System (ADS)

222Rn is commonly used as a natural tracer for validating climate models. To improve such models a better source term for 222Rn than currently used is necessary. The aim of this work is to establish a method for mapping this source term by using a commonly measured proxy, the gamma dose rate (GDR). Automatic monitoring of GDR has been networked in 25 European countries by the Institute for Environment and Sustainability at the Joint Research Centre (JRC IES) in Ispra, Italy, using a common data format. We carried out simultaneous measurements of 222Rn flux and GDR at 63 locations in Switzerland, Germany, Finland and Hungary in order to cover a wide range of GDR. Spatial variations in GDR resulted from different radionuclide concentrations in soil forming minerals. A relatively stable fraction (20%) of the total terrestrial GDR originates from the 238U decay series, of which 222Rn is a member. Accordingly, spatial variation in terrestrial GDR was found to describe almost 60% of the spatial variation in 222Rn flux. Furthermore, temporal variation in GDR and 222Rn was found to be correlated. Increasing soil moisture reduces gas diffusivity and the rate of 222Rn flux but it also decreases GDR through increased shielding of photons. Prediction of 222Rn flux through GDR for individual measurement points is imprecise but un-biased. Verification of larger scale prediction showed that estimates of mean 222Rn fluxes were not significantly different from the measured mean values.

Szegvary, T.; Leuenberger, M. C.; Conen, F.

2007-02-01

54

Measuring Longwave Radiative Flux Divergence in an Urban Canyon  

NASA Astrophysics Data System (ADS)

There has been very little measurement of longwave radiation divergence since the urban studies of Fuggle, Oke and Nunez in the mid 1970's or the rural work of Funk in the early 1960's. Although radiative divergence has been widely ignored for sometime there is the belief that it may play an important role in balancing nocturnal energy budgets in a range of environments. For example, in urban environments surface temperature relates well to the energy balance whereas air temperature does not, even in non-turbulent conditions. This is probably due at least in part to the effects of longwave divergence. To help answer issues related to longwave divergence a new dual-channel infrared radiometer (DCIR) has been developed. The DCIR, as the name implies, measures the directional infrared radiation in two wavebands and can, through differencing of the signals and further signal processing, give a direct measurement of longwave radiative flux divergence. The DCIR was deployed for the first time as part of a larger study (BUBBLE) of the urban boundary layer of Basel, Switzerland. The objective is to further study the thermal regime of a city at the canyon scale. To this end, a street canyon was carefully selected, in the city of Basel. The canyon surface and air volume were instrumented, including turbulent and conductive fluxes, and standard meteorological variables in addition to radiation. A unique data set was obtained to allow the complete energy balance of the canyon system to be evaluated without the need to resort to using residuals to quantify the magnitude of the longwave radiative flux divergence. Measured values of longwave flux-divergence are converted to cooling rates to compare with measured air temperature cooling. Preliminary results show that at the onset of canyon air-volume cooling, measured cooling rates are slightly lower than radiative cooling rates. The differences are less than 0.5° C. This contrasts sharply with previously measured above roof level and rural differences of greater than 5° C. The difference between the rural and above-canyon case and the in-canyon case is most likely a result of differences in radiative environments and wind and temperature fields. The differences illustrate the strong role of urbanization on the surface energy budget.

Soux, A.; Oke, T. R.; Nunez, M.; Wilson, M.

2003-12-01

55

Flux Rope Acceleration and Enhanced Magnetic Reconnection Rate  

SciTech Connect

A physical mechanism of flares, in particular for the flare rise phase, has emerged from our 2-1/2-dimensional resistive MHD simulations. The dynamical evolution of current-sheet formation and magnetic reconnection and flux-rope acceleration subject to continuous, slow increase of magnetic shear in the arcade are studied by employing a non-uniform anomalous resistivity in the reconnecting current sheet under gravity. The simulation results directly relate the flux rope's accelerated rising motion with an enhanced magnetic reconnection rate and thus an enhanced reconnection electric field in the current sheet during the flare rise phase. The simulation results provide good quantitative agreements with observations of the acceleration of flux rope, which manifests in the form of SXR ejecta or erupting filament or CMEs, in the low corona. Moreover, for the X-class flare events studied in this paper the peak reconnection electric field is about O(10{sup 2} V/m) or larger, enough to accelerate p articles to over 100 keV in a field-aligned distance of 10 km. Nonthermal electrons thus generated can produce hard X-rays, consistent with impulsive HXR emission observed during the flare rise phase.

C.Z. Cheng; Y. Ren; G.S. Choe; Y.-J. Moon

2003-03-25

56

Wind tunnels vs. flux chambers: Area source emission measurements and the necessity for VOC and odour correction factors  

Technology Transfer Automated Retrieval System (TEKTRAN)

Wind tunnels and flux chambers have been used to measure fluxes of volatile organic compounds (VOC), odour, and ammonia (NH3) with little regard to air velocity or sweep air flow rates. As a result, flux measurements have been highly variable and scientists have been in disagreement as to the better...

57

Dual physiological rate measurement instrument  

NASA Technical Reports Server (NTRS)

The object of the invention is to provide an instrument for converting a physiological pulse rate into a corresponding linear output voltage. The instrument which accurately measures the rate of an unknown rectangular pulse wave over an extended range of values comprises a phase-locked loop including a phase comparator, a filtering network, and a voltage-controlled oscillator, arranged in cascade. The phase comparator has a first input responsive to the pulse wave and a second input responsive to the output signal of the voltage-controlled oscillator. The comparator provides a signal dependent on the difference in phase and frequency between the signals appearing on the first and second inputs. A high-input impedance amplifier accepts an output from the filtering network and provides an amplified output DC signal to a utilization device for providing a measurement of the rate of the pulse wave.

Cooper, Tommy G. (inventor)

1990-01-01

58

Heat flux measurements on ceramics with thin film thermocouples  

NASA Technical Reports Server (NTRS)

Two methods were devised to measure heat flux through a thick ceramic using thin film thermocouples. The thermocouples were deposited on the front and back face of a flat ceramic substrate. The heat flux was applied to the front surface of the ceramic using an arc lamp Heat Flux Calibration Facility. Silicon nitride and mullite ceramics were used; two thicknesses of each material was tested, with ceramic temperatures to 1500 C. Heat flux ranged from 0.05-2.5 MW/m2(sup 2). One method for heat flux determination used an approximation technique to calculate instantaneous values of heat flux vs time; the other method used an extrapolation technique to determine the steady state heat flux from a record of transient data. Neither method measures heat flux in real time but the techniques may easily be adapted for quasi-real time measurement. In cases where a significant portion of the transient heat flux data is available, the calculated transient heat flux is seen to approach the extrapolated steady state heat flux value as expected.

Holanda, Raymond; Anderson, Robert C.; Liebert, Curt H.

1993-01-01

59

Thrombin Flux and Wall Shear Rate Regulate Fibrin Fiber Deposition State during Polymerization under Flow  

PubMed Central

Thrombin is released as a soluble enzyme from the surface of platelets and tissue-factor-bearing cells to trigger fibrin polymerization during thrombosis under flow conditions. Although isotropic fibrin polymerization under static conditions involves protofibril extension and lateral aggregation leading to a gel, factors regulating fiber growth are poorly quantified under hemodynamic flow due to the difficulty of setting thrombin fluxes. A membrane microfluidic device allowed combined control of both thrombin wall flux (10?13 to 10?11 nmol/?m2 s) and the wall shear rate (10–100 s?1) of a flowing fibrinogen solution. At a thrombin flux of 10?12 nmol/?m2 s, both fibrin deposition and fiber thickness decreased as the wall shear rate increased from 10 to 100 s?1. Direct measurement and transport-reaction simulations at 12 different thrombin flux-wall shear rate conditions demonstrated that two dimensionless numbers, the Peclet number (Pe) and the Damkohler number (Da), defined a state diagram to predict fibrin morphology. For Da < 10, we only observed thin films at all Pe. For 10 < Da < 900, we observed either mat fibers or gels, depending on the Pe. For Da > 900 and Pe < 100, we observed three-dimensional gels. These results indicate that increases in wall shear rate quench first lateral aggregation and then protofibril extension. PMID:20371335

Neeves, K.B.; Illing, D.A.R.; Diamond, S.L.

2010-01-01

60

The accuracy of oxygen flux measurements using microelectrodes  

Microsoft Academic Search

An electrochemical analog of a biofilm was constructed to test the accuracy of oxygen flux measurements using microelectrodes. We used a cathodically polarized graphite felt attached to the bottom of a flat plate open channel reactor as the reactive surface consuming oxygen. The oxygen flux to the felt was calculated from the polarization current. Microelectrodes were used to measure the

Kjetil Rasmussen; Zbigniew Lewandowski

1998-01-01

61

Heat flux measurement in SSME turbine blade tester  

SciTech Connect

Surface heat flux values were measured in the turbine blade thermal cycling tester located at NASA-Marshall. This is the first time heat flux has been measured in a space shuttle main engine turbopump environment. Plots of transient and quasi-steady state heat flux data over a range of about 0 to 15 MW/sq m are presented. Data were obtained with a miniature heat flux gage device developed at NASA-Lewis. The results from these tests are being incorporated into turbine design models. Also, these gages are being considered for airfoil surface heat flux measurement on turbine vanes mounted in SSME turbopump test bed engine nozzles at Marshall. Heat flux effects that might be observed on degraded vanes are discussed.

Liebert, C.H.

1990-11-01

62

Heat flux measurement in SSME turbine blade tester  

NASA Technical Reports Server (NTRS)

Surface heat flux values were measured in the turbine blade thermal cycling tester located at NASA-Marshall. This is the first time heat flux has been measured in a space shuttle main engine turbopump environment. Plots of transient and quasi-steady state heat flux data over a range of about 0 to 15 MW/sq m are presented. Data were obtained with a miniature heat flux gage device developed at NASA-Lewis. The results from these tests are being incorporated into turbine design models. Also, these gages are being considered for airfoil surface heat flux measurement on turbine vanes mounted in SSME turbopump test bed engine nozzles at Marshall. Heat flux effects that might be observed on degraded vanes are discussed.

Liebert, Curt H.

1990-01-01

63

Sound power flux measurements in strongly exited ducts with flow  

NASA Astrophysics Data System (ADS)

This contribution describes new robust procedures for the measurement of sound power flux at appropriate axial positions along a duct with flow, using pairs of flush wall mounted microphones, or pressure transducers. The technology includes the application of selective averaging, order tracking, and optimized sampling rate methods to identify the small fraction of the total fluctuating wave energy that is being propagated along the flow path in a reverberent, or highly reactive duct system. Such measurements can also be used to quantify the local acoustic characteristics that govern the generation, transfer, and propagation of wave energy in the system. Illustrative examples include the determination of the acoustic characteristics of individual silencing elements installed in IC engine intakes and exhausts both on the flow bench and during controlled acceleration or run down on a test bed, where the wave component spectral levels approached 170 dB.

Holland, Keith R.; Davies, Peter O. A. L.; van der Walt, Danie C.

2002-12-01

64

Sound power flux measurements in strongly exited ducts with flow.  

PubMed

This contribution describes new robust procedures for the measurement of sound power flux at appropriate axial positions along a duct with flow, using pairs of flush wall mounted microphones, or pressure transducers. The technology includes the application of selective averaging, order tracking, and optimized sampling rate methods to identify the small fraction of the total fluctuating wave energy that is being propagated along the flow path in a reverberent, or highly reactive duct system. Such measurements can also be used to quantify the local acoustic characteristics that govern the generation, transfer, and propagation of wave energy in the system. Illustrative examples include the determination of the acoustic characteristics of individual silencing elements installed in IC engine intakes and exhausts both on the flow bench and during controlled acceleration or run down on a test bed, where the wave component spectral levels approached 170 dB. PMID:12509008

Holland, Keith R; Davies, Peter O A L; van der Walt, Danie C

2002-12-01

65

Measurement of Flux Density of Cas A at Low Frequencies  

NASA Astrophysics Data System (ADS)

Cas A is used as a flux calibrator throughout the radio spectrum. Therefore it is important to know the spectral and secular variations in its flux density. Earlier observations by Scott et. al. (1969) and Baars et. al. (1972) suggested a secular decrease in flux density of Cas A at a rate of about 1% per year at all frequencies. However later observations by Erickson & Perley (1975) and Read (1977) indicated anomalously high flux from Cas A at 38 MHz. Also, these observations suggested that the original idea of faster decay of the flux density rate at low frequencies may be in error or that something more complex than simple decay is affecting the flux density at low frequencies. The source changes at 38 MHz still remains a mystery. We intend to present the results of follow up observations made from 1995 to 1998 with a three element interferometer in Green Bank operating in frequency range 30 to 120 MHz. We will discuss the problems at such low frequencies due to large beamwidth and unstable ionosphere. We will also discuss the strategies we have used so far to to find the flux density of Cas A by calculating the ratio of flux density of Cas A to that of Cyg A, assuming flux density of Cyg A to be constant. Above mentioned work was performed in summer student program sponsored by National Radio Astronomy Observatory.

Patil, Ajinkya; Fisher, R.

2012-01-01

66

Precise, Facile Initial Rate Measurements  

PubMed Central

Progress curve analysis has been used sparingly in studies of enzyme-catalyzed reactions due largely to the complexity of the integrated rate expressions used in data analysis. Using an experimental design that simplifies the analysis, the advantages and limitations of progress curve experiments are explored in a study of four different enzyme-catalyzed reactions. The approach involves relatively simple protocols, requires 20–25% of the materials, and provides 10- to 20-fold signal enhancements compared to analogous initial rate studies. Product inhibition, which complicates integrated rate analysis, was circumvented using cloned, purified enzymes that remove the products and draw the reaction forward. The resulting progress curves can be transformed into the equivalent of thousands of initial rate and [S] measurements and, due to the absence of product inhibition, are plotted in the familiar, linear double-reciprocal format. Allowing product to accumulate during a reaction produces a continuously changing substrate/product ratio that can be used as the basis for obtaining product inhibition constants and to distinguish among the three classical inhibition mechanisms. Algebraic models describing the double-reciprocal patterns obtained from such inhibition studies are presented. The virtual continuum of substrate concentrations that occurs during a progress curve experiment provides a nearly errorless set of relative concentrations that results in remarkably precise data; kinetic constant standard deviations are on the order of 0.5%. PMID:20735055

Tang, Qingxiu; Leyh, Thomas S.

2010-01-01

67

Some potential errors in the measurement of mercury gas exchange at the soil surface using a dynamic flux chamber.  

PubMed

A series of controlled environment experiments were conducted to examine the use of a dynamic flux chamber to measure soil emission and absorption of total gaseous mercury (TGM). Uncertainty about the appropriate airflow rates through the chamber and chamber exposure to ambient wind are shown to be major sources of potential error. Soil surface mercury flux measurements over a range of chamber airflow rates showed a positive linear relationship between flux rates and airflow rate through the chamber. Mercury flux measurements using the chamber in an environmental wind tunnel showed that exposure of the system to ambient winds decreased the measured flux rates by 40% at a wind speed of 1.0 m s(-1) and 90% at a wind speed of 2 m s(-1). Wind tunnel measurements also showed that the chamber footprint was limited to the area of soil inside the chamber and there is little uncertainty of the footprint size in dry soil. PMID:11032126

Gillis, A; Miller, D R

2000-10-01

68

Quantitative Comparison of Measured Plasma Sheet Electron Energy Flux and Remotely Sensed Auroral Electron Energy Flux  

NASA Astrophysics Data System (ADS)

In situ plasma sheet observations and auroral images give us two views of magnetospheric dynamics. With in situ observations, we get a detailed point measurement; auroral images give us a global view. Previous studies have shown an excellent correlation between dynamic plasma behavior in the plasma sheet and auroral activity. Here we extend the previous work with quantitative comparisons between the two regions. We directly compare the electron energy flux measured in the plasma sheet with the electron energy flux into the ionosphere inferred from auroral images. We find that during quiet times, the plasma sheet is able to supply the aurora with nearly all of the observed energy flux. During intervals of intense auroral emission, the electron spectrum in the conjugate region of the plasma sheet changes, increasing the amount of energy flux incident on the ionosphere. However, the increases in the plasma sheet energy flux is not enough to account for the inferred energy flux into the ionosphere from the images by nearly an order of magnitude. This implies that additional energy flux must be entering the loss cone through pitch angle diffusion or through the presence of parallel electric fields between the plasma sheet and the ionosphere during intervals of intense auroral emission. A likely source of this additional energy flux is the low altitude auroral acceleration region. >http://www.ess.washington.edu/People/Students/matt/AGU2001/

Fillingim, M. O.; Parks, G. K.; Chua, D.; Germany, G. A.; Lin, R. P.; McCarthy, M.

2001-12-01

69

Measurements of muon flux in the Pyhäsalmi underground laboratory  

NASA Astrophysics Data System (ADS)

The cosmic-ray induced muon flux was measured at several depths in the Pyhäsalmi mine (Finland) using a plastic scintillator telescope mounted on a trailer. The flux was determined at four different depths underground at 400 m (980 m.w.e), at 660 m (1900 m.w.e), at 990 m (2810 m.w.e) and at 1390 m (3960 m.w.e) with the trailer, and also at the ground surface. In addition, previously measured fluxes from depths of 90 m (210 m.w.e) and 210 m (420 m.w.e) are shown. A relation was obtained for the underground muon flux as a function of the depth. The measured flux follows well the general behaviour and is consistent with results determined in other underground laboratories.

Enqvist, T.; Mattila, A.; Föhr, V.; Jämsén, T.; Lehtola, M.; Narkilahti, J.; Joutsenvaara, J.; Nurmenniemi, S.; Peltoniemi, J.; Remes, H.; Sarkamo, J.; Shen, C.; Usoskin, I.

2005-12-01

70

Flux gradient measurements from a catamaran buoy in SEMAPHORE  

SciTech Connect

During the SEMAPHORE Structure des Echanges Mer Atmosphere Proprietes des Heterogeneities de L`Ocean leur Repartition (Structure of Exchanges with the Marine Atmosphere, Properties of Heterogeneities of the Ocean and their Repartition) experiment in the fall of 1993, a large catamaran buoy, the MENTOR, was set adrift in the Azores region. The purpose of the buoy was to provide measurements for testing flux-profile relations over the sea, and to measure the influence of sea state on the turbulent fluxes and atmospheric profiles and the effects of atmospheric and radiative fluxes on near surface temperature structure in the ocean. In addition, the buoy measurements were to provide an anchor point for calibrating mesoscale bulk surface flux estimates over the SEMAPHORE domain and to provide intercomparison data for dissipation estimates of fluxes from the R/V Le Suroit.

Katsaros, K.B. [Univ. of Washington, Seattle, WA (United States). Dept. of Atmospheric Sciences; Drennan, W.M.; Donelan, M.A. [Canada Centre for Inland Waters, Burlington, Ontario (Canada)

1994-12-31

71

Measurements of muon flux in the Pyhäsalmi underground laboratory  

E-print Network

The cosmic-ray induced muon flux was measured at several depths in the Pyh\\"asalmi mine (Finland) using a plastic scintillator telescope mounted on a trailer. The flux was determined at four different depths underground at 400 m (980 m.w.e), at 660 m (1900 m.w.e), at 990 m (2810 m.w.e) and at 1390 m (3960 m.w.e) with the trailer, and also at the ground surface. In addition, previously measured fluxes from depths of 90 m (210 m.w.e) and 210 m (420 m.w.e) are shown. A relation was obtained for the underground muon flux as a function of the depth. The measured flux follows well the general behaviour and is consistent with results determined in other underground laboratories.

T. Enqvist; A. Mattila; V. Föhr; T. Jämsén; M. Lehtola; J. Narkilahti; J. Joutsenvaara; S. Nurmenniemi; J. Peltoniemi; H. Remes; J. Sarkamo; C. Shen; I. Usoskin

2005-06-13

72

Sensitivity of shortwave radiative flux density, forcing, and heating rates to the aerosol vertical profile  

SciTech Connect

The effect of the aerosol vertical distribution on the solar radiation profiles, for idealized and measured profiles of optical properties (extinction and single-scattering albedo (SSA)) during the May 2003 Atmospheric Radiation Measurement (ARM) Aerosol Intensive Observation Period (AIOP), has been investigated using the Rapid Radiative Transfer Model Shortwave (RRTM_SW) code. Calculated profiles of down-welling and up-welling solar fluxes during the AIOP have been compared with the data measured by up- and down-looking solar broadband radiometers aboard a profiling research aircraft. The measured profiles of aerosol extinction, SSA, and water vapor obtained from the same aircraft that carried the radiometers served as the inputs for the model calculations. It is noteworthy that for this study, the uplooking radiometers were mounted on a stabilized platform that kept the radiometers parallel with respect to the earth’s horizontal plane. The results indicate that the shape of the aerosol extinction profiles has very little impact on direct radiative forcings at the top of atmosphere and surface in a cloud-free sky. However, as long as the aerosol is not purely scattering, the shape of the extinction profiles is important for forcing profiles. Identical extinction profiles with different absorption profiles drastically influence the forcing and heating rate profiles. Using aircraft data from 19 AIOP profiles over the Southern Great Plains (SGP), we are able to achieve broadband down-welling solar flux closure within 0.8% (bias difference) or 1.8% (rms difference), well within the expected measurement uncertainty of 1 to 3%. The poorer agreement in up-welling flux (bias -3.7%, rms 10%) is attributed to the use of inaccurate surface albedo data. The sensitivity tests reveal the important role accurate, vertically resolved aerosol extinction data plays in tightening flux closure. This study also suggests that in the presence of a strongly absorbing substance, aircraft flux measurements from a stabilized platform have the potential to determine heating rate profiles. These measurement-based heating rate profiles provide useful data for heating rate closure studies and indirect estimates of single scattering albedo assumed in radiative transfer calculations.

Guan, Hong; Schmid, Beat; Bucholtz, Anthony; Bergstrom, Robert

2010-03-31

73

FLUX MEASUREMENTS FROM A TALL TOWER IN A COMPLEX LANDSCAPE  

SciTech Connect

The accuracy and representativeness of flux measurements from a tall tower in a complex landscape was assessed by examining the vertical and sector variability of the ratio of wind speed to momentum flux and the ratio of vertical advective to eddy flux of heat. The 30-60 m ratios were consistent with theoretical predictions which indicate well mixed flux footprints. Some variation with sector was observed that were consistent with upstream roughness. Vertical advection was negligible compared with vertical flux except for a few sectors at night. This implies minor influence from internal boundary layers. Flux accuracy is a function of sector and stability but 30-60 m fluxes were found to be generally representative of the surrounding landscape. This paper will study flux data from a 300 m tower, with 4 levels of instruments, in a complex landscape. The surrounding landscape will be characterized in terms of the variation in the ratio of mean wind speed to momentum flux as a function of height and wind direction. The importance of local advection will be assessed by comparing vertical advection with eddy fluxes for momentum and heat.

Kurzeja, R.; Weber, A.; Chiswell, S.; Parker, M.

2010-07-22

74

Eddy Covariance Measurements Of CO2 Fluxes Above Lake Superior  

NASA Astrophysics Data System (ADS)

Lake Superior has been reported to be seasonally supersaturated with respect to atmospheric CO2, and fluxes estimated from measured pCO2 would be regionally significant. Comparison of pCO2 within the lake and atmospheric CO2 measured 400 m above ground at a site 100 km south of the lake suggest that ?pCO2 (difference between air and water) is 0-400 ?atm. Application of empirical gas exchange models suggests that the flux out of the lake is 0.1-0.4 g C m-2 d-1. While these fluxes are small compared to daily or monthly averages over nearby terrestrial systems (-8 to +4 g C m-2 d-1), the annual fluxes for the lake (~140 g C m-2 yr-1) are comparable in magnitude but opposite in direction to fluxes over nearby forests (-120 to -300 g C m-2 yr-1). Given the large surface area of Lake Superior, annual emissions of CO2 from the lake (~11 Tg C yr-1) may be regionally significant. To better assess the magnitude of the flux, eddy covariance (EC) measurements of the CO2 flux above the lake were made on six occasions between August 2007 and October 2008. Measurements were made at fixed stations that were 1-20 km from shore in the central region of the lake. EC instrumentation was mounted on top of a 10-m pneumatic mast on board the R/V Agassiz. A Crossbow AHRS300CA was mounted level with the sonic anemometer to enable measured wind vectors to be corrected for ship motion. The adequacy of the motion correction was verified by power spectral analysis of vertical wind speeds, comparison of EC fluxes with bulk aerodynamic calculations, and comparison of latent and sensible heat fluxes with other estimates of these fluxes. Measurements were conducted for an hour at each station; 10-minute average fluxes were computed, and these were then averaged to yield hourly means. The EC CO2 fluxes were in the range of 0.15 to 0.63 g C m-2 d-1 which is similar to the range of estimates cited above, though all measurements were made at times of low wind speeds (1 - 6 m s-1). The mean (± 95% CI) of all measured fluxes (0.28 ± 0.15 g C m-2 d-1 or 100 g C m-2 yr-1) supports the conclusion that Lake Superior is a regionally significant source of CO2 to the atmosphere.

Mwangi, J. M.; Urban, N. R.; Perlinger, J. A.; Bariteau, L.; Fairall, C. W.

2008-12-01

75

Measurement of advective soil gas flux: Results of field and laboratory experiments with CO2  

SciTech Connect

We modified our multi-channel, steady-state flow-through (SSFT), soil-CO2 flux monitoring system to include an array of inexpensive pyroelectric non-dispersive infrared detectors for full-range (0-100%) coverage of CO2 concentrations without dilution, and a larger-diameter vent tube. We then conducted field testing of this system from late July through mid-September 2010 at the Zero Emissions Research and Technology (ZERT) project site located in Bozeman, MT, and subsequently, laboratory testing at the Pacific Northwest National Laboratory (PNNL) in Richland, WA using a flux bucket filled with dry sand. In the field, an array of twenty-five SSFT and three non-steady-state (NSS) flux chambers was installed in a 10x4 m area, the long boundary of which was directly above a shallow (2-m depth) horizontal injection well located 0.5 m below the water table. Two additional chambers (one SSFT and one NSS) were installed 10 m from the well for background measurements. Volumetric soil moisture sensors were installed at each SSFT chamber to measure mean levels in the top 0.15 m of soil. A total flux of 52 kg CO2 d-1 was injected into the well for 27 d and the efflux from the soil was monitored by the chambers before, during, and for 27 d after the injection. Overall, the results were consistent with those from previous years, showing a radial efflux pattern centered on a known “hot spot”, rapid responses to changes in injection rate and wind power, evidence for movement of the CO2 plume during the injection, and nominal flux levels from the SSFT chambers that were up to 6-fold higher than those measured by adjacent NSS chambers. Soil moisture levels varied during the experiment from moderate to near saturation with the highest levels occurring consistently at the hot spot. The effects of wind on measured flux were complex and decreased as soil moisture content increased. In the laboratory, flux bucket testing with the SSFT chamber showed large measured-flux enhancement due to the Venturi effect on the chamber vent, but an overall decrease in measured flux when wind also reached the sand surface. Flux-bucket tests at a high flux (comparable to that at the hot spot) also showed that the measured flux levels increase linearly with the chamber-flushing rate until the actual level is reached. At the SSFT chamber-flushing rate used in the field experiment the measured flux in the laboratory was only about a third of the actual flux. The ratio of measured to actual flux increased logarithmically as flux decreased, and reached parity at low levels typical of diffusive flux systems. Taken together, our results suggest that values for advective CO2 flux measured by SSFT and NSS chamber systems are likely to be significantly lower than the actual values due to back pressure developed in the chamber that diverts flux from entering the chamber. Chamber designs that counteract the back pressure and also avoid large Venturi effects associated with vent tubes, such as the SSFT with a narrow vent tube operated at a high chamber-flushing rate, are likely to yield flux measurements closer to the true values.

Amonette, James E.; Barr, Jonathan L.; Erikson, Rebecca L.; Dobeck, Laura M.; Barr, Jamie L.; Shaw, Joseph A.

2013-10-01

76

Flux Measurements of Volatile Organic Compounds from an Urban Landscape  

SciTech Connect

Direct measurements of volatile organic compound (VOC) emissions that include all anthropogenic and biogenic emission sources in urban areas are a missing requirement to evaluate emission inventories and constrain current photochemical modelling practices. Here we demonstrate the use of micrometeorological techniques coupled with fast-response sensors to measure urban VOC fluxes from a neighborhood of Mexico City, where the spatial variability of surface cover and roughness is high. Fluxes of olefins, methanol, acetone, toluene and C2-benzenes were measured and compared with the local gridded emission inventory. VOC fluxes exhibited a clear diurnal pattern with a strong relationship to vehicular traffic. Recent photochemical modeling results suggest that VOC emissions are significantly underestimated in Mexico City1, but the measured VOC fluxes described here indicate that the official emission inventory2 is essentially correct. Thus, other explanations are needed to explain the photochemical modelling results.

Velasco, E.; Lamb, Brian K.; Pressley, S.; Allwine, Eugene J.; Westberg, Halvor; Jobson, B Tom T.; Alexander, M. Lizabeth; Prazeller, Peter; Molina, Luisa; Molina, Mario J.

2005-10-19

77

High rates of energy expenditure and water flux in free-ranging Point Reyes mountain beavers Aplodontia rufa phaea  

USGS Publications Warehouse

We measured water flux and energy expenditure in free-ranging Point Reyes mountain beavers Aplodontia rufa phaea by using the doubly labeled water method. Previous laboratory investigations have suggested weak urinary concentrating ability, high rates of water flux, and low basal metabolic rates in this species. However, free-ranging measurements from hygric mammals are rare, and it is not known how these features interact in the environment. Rates of water flux (210 ?? 32 mL d-1) and field metabolic rates (1,488 ?? 486 kJ d-1) were 159% and 265%, respectively, of values predicted by allometric equations for similar-sized herbivores. Mountain beavers can likely meet their water needs through metabolic water production and preformed water in food and thus remain in water balance without access to free water. Arginine-vasopressin levels were strongly correlated with rates of water flux and plasma urea : creatinine ratios, suggesting an important role for this hormone in regulating urinary water loss in mountain beavers. High field metabolic rates may result from cool burrow temperatures that are well below lower critical temperatures measured in previous laboratory studies and suggest that thermoregulation costs may strongly influence field energetics and water flux in semifossorial mammals. ?? 2007 by The University of Chicago. All rights reserved.

Crocker, D.E.; Kofahl, N.; Fellers, G.D.; Gates, N.B.; Houser, D.S.

2007-01-01

78

Standardization of flux chamber and wind tunnel flux measurements for quantifying volatile organic compound and ammonia emissions from area sources at animal feeding operations  

NASA Astrophysics Data System (ADS)

A variety of portable wind tunnels and flux chambers have been used to measure fluxes of volatile organic compounds (VOC) and ammonia (NH3) at animal feeding operations (AFO). However, there has been little regard to the extreme variation and potential inaccuracies caused by air velocity or sweep air flow rates that are either too low or too high to simulate field conditions. There is a need for correction factors to standardize flux chamber and wind tunnel measurements. In this manuscript, we present results of water evaporative flux and VOC flux measurements with the EPA flux chamber and a small wind tunnel. In the EPA flux chamber, water evaporative flux was positively correlated with sweep air flow rate (SAFR) between 1 and 20 L min-1 (r2 = 0.981-0.999) and negatively correlated with sweep air relative humidity between 0 and 80% (r2 = 0.982-0.992). Emissions of gas-film controlled compounds like NH3 and VOC at AFOs were positively correlated with evaporation rates between 0.6 and 2.8 mm d-1. We demonstrate a simple methodology for standardizing and comparing different chamber types by measuring water evaporation within the chamber using a gravimetric mass balance approach under controlled laboratory conditions. A water evaporative flux ratio correction factor (EFRCF) was used to improve the accuracy of field-measured VOC and NH3 chamber flux measurements. In a field study, both the EPA flux chamber (SAFR = 5 L min-1) and small wind tunnel (SAFR = 1 L min-1) underestimated the true field emissions of VOC, with EFRCFs of 2.42 and 3.84, respectively. EFRCFs are recommended for all but the driest of soil and manure conditions.

Parker, David; Ham, Jay; Woodbury, Bryan; Cai, Lingshuang; Spiehs, Mindy; Rhoades, Marty; Trabue, Steve; Casey, Ken; Todd, Rick; Cole, Andy

2013-02-01

79

Intercalibration of benthic flux chambers I. Accuracy of flux measurements and influence of chamber hydrodynamics  

Microsoft Academic Search

The hydrodynamic properties and the capability to measure sediment–water solute fluxes, at assumed steady state conditions, were compared for three radically different benthic chamber designs: the “Microcosm”, the “Mississippi” and the “Göteborg” chambers. The hydrodynamic properties were characterized by mounting a PVC bottom in each chamber and measuring mixing time, diffusive boundary layer thickness (DBL thickness) shear velocity (u?), and

A. Tengberg; H. Stahl; G. Gust; V. Müller; U. Arning; H. Andersson; P. O. J. Hall

2004-01-01

80

Radiant Flux of Near Field in Temperature Measurements  

SciTech Connect

In this work we present a calculation of the radiant flux exiting from an object which is at a constant temperature. The flux calculation is based in the propagation model of irradiance and it permit to predict the small variations in measurements of infrared radiation sources when the pyrometer is going far from the source, this variation is known as distance effect. The classical radiometry defines the quantity radiance, which is used in temperature measurements of objects through the infrared radiation they emit. Unfortunately the radiance does not permit to take into account the variations of the radiant flux measured by the pyrometer due to the wave propagation of the radiation given that the radiance definition is based in ray propagation, the geometrical model. Due to the anterior in this work we present a radiant flux calculation using wave model and considering the approximation of the near field or Fresnel approximation. We show experimental results that confirm our proposal.

Suarez-Romero, J. G.; Resendiz Barron, A. J. [Instituto Tecnologico de Queretaro, Av. Tecnologico SN, esq. Escobedo, Centro, Queretaro, Qro. 76000. MEXICO (Mexico); Farias Arguello, J. O. [Centro de Ingenieria y Desarrollo Industrial, Av. Playa Pie de la Cuesta 702, Desarrollo San Pablo, Queretaro, Qro. 76130 (Mexico)

2008-04-15

81

ADcp Measurements of Suspended Sediment Fluxes in Banat Rivers, Romania  

E-print Network

ADcp Measurements of Suspended Sediment Fluxes in Banat Rivers, Romania Eugenia Rotaru1 , Jérôme Le sediment, aDcp, river discharge measurement, hydrometry Introduction Suspended load represents a huge used to perform river discharge measurements. Water velocity profiles are computed from the Doppler

Paris-Sud XI, Université de

82

Hybrid heat flux measurement system for solar central receiver evaluation  

Microsoft Academic Search

A hybrid heat flux measurement system has been designed, built and mounted on top of the SSPS-CRS tower at the Plataforma Solar de Almería (PSA) to measure the incident solar power that is concentrated by a heliostat field on the flat aperture of a central receiver. This device is composed of two measurement systems, one direct and the other indirect.

J. Ballestrín; R. Monterreal

2004-01-01

83

Design of a differential radiometer for atmospheric radiative flux measurements  

SciTech Connect

The Hemispherical Optimized NEt Radiometer (HONER) is an instrument under development at the Los Alamos National Laboratory for deployment on an unmanned aerospace vehicle as part of the Atmospheric Radiation Measurements (ARM/UAV) program. HONER is a differential radiometer which will measure the difference between the total upwelling and downwelling fluxes and is intended to provide a means of measuring the atmospheric radiative flux divergence. Unlike existing instruments which measure the upwelling and downwelling fluxes separately, HONER will achieve an optical difference by chopping the two fluxes alternately onto a common pyroelectric detector. HONER will provide data resolved into two spectral bands; one covering the solar dominated region from less than 0.4 micrometer to approximately 4.5 micrometers and the other covering the region from approximately 4.5 micrometers to greater than 50 micrometers, dominated by thermal radiation. The means of separating the spectral regions guarantees seamless summation to calculate the total flux. The fields-of-view are near-hemispherical, upward and downward. The instrument can be converted, in flight, from the differential mode to absolute mode, measuring the upwelling and downwelling fluxes separately and simultaneously. The instrument also features continuous calibration from on-board sources. We will describe the design and operation of the sensor head and the on-board reference sources as well as the means of deployment.

LaDelfe, P.C.; Weber, P.G.; Rodriguez, C.W.

1994-11-01

84

Airborne flux measurements of biogenic volatile organic compounds over California  

NASA Astrophysics Data System (ADS)

Biogenic Volatile Organic Compound (BVOC) fluxes were measured onboard the CIRPAS Twin Otter aircraft as part of the California Airborne BVOC Emission Research in Natural Ecosystem Transects (CABERNET) campaign during June 2011. The airborne virtual disjunct eddy covariance (AvDEC) approach used measurements from a PTR-MS and a wind radome probe to directly determine fluxes of isoprene, MVK + MAC, methanol, monoterpenes, and MBO over ∼10 000 km of flight paths focusing on areas of California predicted to have the largest emissions of isoprene. The Fast Fourier Transform (FFT) approach was used to calculate fluxes over long transects of more than 15 km, most commonly between 50 and 150 km. The Continuous Wavelet Transformation (CWT) approach was used over the same transects to also calculate "instantaneous" fluxes with localization of both frequency and time independent of non-stationarities. Vertical flux divergence of isoprene is expected due to its relatively short lifetime and was measured directly using "racetrack" profiles at multiple altitudes. It was found to be linear and in the range 5% to 30% depending on the ratio of aircraft altitude to PBL height (z / zi). Fluxes were generally measured by flying consistently at 400 ± 50 m (a.g.l.) altitude, and extrapolated to the surface according to the determined flux divergence. The wavelet-derived surface fluxes of isoprene averaged to 2 km spatial resolution showed good correspondence to Basal Emission Factor (BEF) landcover datasets used to drive biogenic VOC (BVOC) emission models. The surface flux of isoprene was close to zero over Central Valley crops and desert shrublands, but was very high (up to 15 mg m-2 h-1) above oak woodlands, with clear dependence of emissions on temperature and oak density. Isoprene concentrations of up to 8 ppb were observed at aircraft height on the hottest days and over the dominant source regions. While isoprene emissions from agricultural crop regions, shrublands, and coniferous forests were extremely low, high concentrations of methanol and monoterpenes were found above some of these regions. These observations demonstrate the ability to measure fluxes from specific sources by eddy covariance from an aircraft, and suggest the utility of measurements using fast response chemical sensors to constrain emission inventories and map out source distributions for a much broader array of trace gases than was observed in this study. This paper reports the first regional direct eddy covariance fluxes of isoprene. The emissions of VOCs measured from aircraft with 2 km spatial resolution can quantify the distribution of major sources providing the observations required for testing statewide emission inventories of these important trace gases. These measurements will be used in a future study to assess BVOC emission models and their driving variable datasets.

Misztal, P. K.; Karl, T.; Weber, R.; Jonsson, H. H.; Guenther, A. B.; Goldstein, A. H.

2014-03-01

85

High rates of soil respiration suggest large fluxes of labile C in a turfgrass system  

NASA Astrophysics Data System (ADS)

We measured high rates of soil respiration (up to 19 ?mol C m-2 sec-1) in a study of management effects on turfgrass lawns. Estimates based on these measurements indicate that annual soil respiration is on the order of 15-30 Mg C ha-1, which seems high, given measured NPP of 3-6 Mg C ha-1 yr-1 and 0-10 cm soil C pools of 15-20 Mg C ha-1 which showed no net change over the study period. We contend that this flux is plausible, given irrigation and fertilizer applications, and hypothesize that in this context, soil respiration is driven largely by assimilate availability. We provide several lines of evidence supporting the idea that large fluxes of readily labile C move through this system: Biomass growth rates were highly correlated with soil respiration rates; we observed statistically significant variation in soil C stocks, dramatic changes in microbial biomass stoichiometry, and major shifts in N mineralization and nitrification over the course of a single growing season; and long-term soil incubations appear to show the accumulation and depletion of a substantial pool of labile C.

Lilly, P.; Jenkins, J. C.; Carroll, M.

2013-12-01

86

Measurement and modelling of methane fluxes from UK peatlands  

NASA Astrophysics Data System (ADS)

Nearly 5000 chamber measurements of CH4 flux were collated from 21 sites across the UK, covering a range of soil and vegetation types, to derive a parsimonious model that explains as much of the variability as possible, with the least input requirements. Less than half of the observed variability in instantaneous fluxes could be explained by the independent variables measured. Measurement error is one reason for this, and here we analyse several of the uncertainties inherent in these measurements, including the choice of model used to calculate the flux. Other reasons include the stochastic nature of some of the transport processes and the poor correspondence between the independent variables measured and the actual variables influencing the processes underlying methane production, transport and oxidation. Alternative measurement methods are considered which may circumvent some of these problems. When temporal variation was removed, and the fluxes averaged at larger spatial scales, simple models explained up to ~75 % of the variance in CH4 fluxes. Soil carbon, peat depth, soil moisture and pH together provided the best sub-set of explanatory variables. To estimate the impact of changes in peatland water table on CH4 emissions in the UK, an emission factor of +0.4 g CH4 m-2 y-1 per cm increase in water table was derived from the data. As an alternative approach, vegetation species composition provides a long-term integrator of environmental conditions, which may correlate with methane flux. Here, we used a "weighted averaging" approach to predict methane flux from plant species composition at a range of sites in the UK, continental Europe and Canada. Species were classified into functional groups, defined by a number of qualitative traits considered relevant to methane dynamics. We compared the results based on this functional classification with those based on the original species composition data with a purely taxonomic classification.

Levy, P. E.; Gray, A.

2012-12-01

87

The Airborne Measurements of Methane Fluxes (AIRMETH) Arctic Campaign (Invited)  

NASA Astrophysics Data System (ADS)

One of the most pressing questions with regard to climate feedback processes in a warming Arctic is the regional-scale methane release from Arctic permafrost areas. The Airborne Measurements of Methane Fluxes (AIRMETH) campaign is designed to quantitatively and spatially explicitly address this question. Ground-based eddy covariance (EC) measurements provide continuous in-situ observations of the surface-atmosphere exchange of methane. However, these observations are rare in the Arctic permafrost zone and site selection is bound by logistical constraints among others. Consequently, these observations cover only small areas that are not necessarily representative of the region of interest. Airborne measurements can overcome this limitation by covering distances of hundreds of kilometers over time periods of a few hours. Here, we present the potential of environmental response functions (ERFs) for quantitatively linking methane flux observations in the atmospheric surface layer to meteorological and biophysical drivers in the flux footprints. For this purpose thousands of kilometers of AIRMETH data across the Alaskan North Slope are utilized, with the aim to extrapolate the airborne EC methane flux observations to the entire North Slope. The data were collected aboard the research aircraft POLAR 5, using its turbulence nose boom and fast response methane and meteorological sensors. After thorough data pre-processing, Reynolds averaging is used to derive spatially integrated fluxes. To increase spatial resolution and to derive ERFs, we then use wavelet transforms of the original high-frequency data. This enables much improved spatial discretization of the flux observations, and the quantification of continuous and biophysically relevant land cover properties in the flux footprint of each observation. A machine learning technique is then employed to extract and quantify the functional relationships between the methane flux observations and the meteorological and biophysical drivers in the flux footprints. Lastly, the resulting ERFs are used to extrapolate the methane release over spatio-temporally explicit grids of the Alaskan North Slope. Metzger et al. (2013) have demonstrated the efficacy of this technique for regionalizing airborne EC heat flux observations to within an accuracy of ?18% and a precision of ?5%. Here, we show for the first time results from applying the ERF procedure to airborne methane EC measurements, and report its potential for spatio-temporally explicit inventories of the regional-scale methane exchange. References: Metzger, S., Junkermann, W., Mauder, M., Butterbach-Bahl, K., Trancón y Widemann, B., Neidl, F., Schäfer, K., Wieneke, S., Zheng, X. H., Schmid, H. P., and Foken, T.: Spatially explicit regionalization of airborne flux measurements using environmental response functions, Biogeosciences, 10, 2193-2217, doi:10.5194/bg-10-2193-2013, 2013.

Serafimovich, A.; Metzger, S.; Hartmann, J.; Kohnert, K.; Sachs, T.

2013-12-01

88

Flux measurement and modeling in a typical mediterranean vineyard  

NASA Astrophysics Data System (ADS)

Vineyard ecosystems are typical in the Mediterranean area, since wine is one of the most important economic sectors. Nevertheless, only a few studies have been conducted to investigate the interactions between this kind of vegetation and the atmosphere. These information are important both to understand the behaviour of such ecosystems in different environmental conditions, and are crucial to parameterize crop and flux simulation models. Combining direct measurements and modelling can obtain reliable estimates of surface fluxes and crop evapotranspiration. This study would contribute both to (1) directly measure energy fluxes and evapotranspiration in a typical Mediterranean vineyard, located in the South of Sardinia (Italy), through the application of the Eddy Covariance micrometeorological technique and to (2) evaluate the land surface model ACASA (Advanced-Canopy-Atmosphere-Soil Algorithm) in simulating energy fluxes and evapotranspiration over vineyard. Independent datasets of direct measurements were used to calibrate and validate model results during the growing period. Statistical analysis was performed to evaluate model performance and accuracy in predicting surface fluxes. Results will be showed as well as the model capability to be used for future studies to predict energy fluxes and crop water requirements under actual and future climate.

Marras, Serena; Bellucco, Veronica; Pyles, David R.; Falk, Matthias; Sirca, Costantino; Duce, Pierpaolo; Snyder, Richard L.; Tha Paw U, Kyaw; Spano, Donatella

2014-05-01

89

Infrared calorimeter for time-resolved plasma energy flux measurement  

SciTech Connect

An infrared calorimeter system for measuring energy flux in a noisy electromagnetic environment has been developed. A thin (13 ..mu..) oxidized stainless-steel foil is heated by energy flux and its temperature is determined by measuring the infrared emission from the back surface of the foil. The radiation is transported to the detector, which is located inside a double-shielded enclosure, through a nylon-tube infrared telescope. The calculated response time is 12 ..mu..s, and the measured peak-to-peak noise is equivalent to 0.4 mJ/cm/sup 2/ deposited energy.

Ingraham, J.C.; Miller, G.

1983-06-01

90

Accuracy of quantum sensors measuring yield photon flux and photosynthetic photon flux  

NASA Technical Reports Server (NTRS)

Photosynthesis is fundamentally driven by photon flux rather than energy flux, but not all absorbed photons yield equal amounts of photosynthesis. Thus, two measures of photosynthetically active radiation have emerged: photosynthetic photon flux (PPF), which values all photons from 400 to 700 nm equally, and yield photon flux (YPF), which weights photons in the range from 360 to 760 nm according to plant photosynthetic response. We selected seven common radiation sources and measured YPF and PPF from each source with a spectroradiometer. We then compared these measurements with measurements from three quantum sensors designed to measure YPF, and from six quantum sensors designed to measure PPF. There were few differences among sensors within a group (usually <5%), but YPF values from sensors were consistently lower (3% to 20%) than YPF values calculated from spectroradiometric measurements. Quantum sensor measurements of PPF also were consistently lower than PPF values calculated from spectroradiometric measurements, but the differences were <7% for all sources, except red-light-emitting diodes. The sensors were most accurate for broad-band sources and least accurate for narrow-band sources. According to spectroradiometric measurements, YPF sensors were significantly less accurate (>9% difference) than PPF sensors under metal halide, high-pressure sodium, and low-pressure sodium lamps. Both sensor types were inaccurate (>18% error) under red-light-emitting diodes. Because both YPF and PPF sensors are imperfect integrators, and because spectroradiometers can measure photosynthetically active radiation much more accurately, researchers should consider developing calibration factors from spectroradiometric data for some specific radiation sources to improve the accuracy of integrating sensors.

Barnes, C.; Tibbitts, T.; Sager, J.; Deitzer, G.; Bubenheim, D.; Koerner, G.; Bugbee, B.; Knott, W. M. (Principal Investigator)

1993-01-01

91

Accuracy of quantum sensors measuring yield photon flux and photosynthetic photon flux.  

PubMed

Photosynthesis is fundamentally driven by photon flux rather than energy flux, but not all absorbed photons yield equal amounts of photosynthesis. Thus, two measures of photosynthetically active radiation have emerged: photosynthetic photon flux (PPF), which values all photons from 400 to 700 nm equally, and yield photon flux (YPF), which weights photons in the range from 360 to 760 nm according to plant photosynthetic response. We selected seven common radiation sources and measured YPF and PPF from each source with a spectroradiometer. We then compared these measurements with measurements from three quantum sensors designed to measure YPF, and from six quantum sensors designed to measure PPF. There were few differences among sensors within a group (usually <5%), but YPF values from sensors were consistently lower (3% to 20%) than YPF values calculated from spectroradiometric measurements. Quantum sensor measurements of PPF also were consistently lower than PPF values calculated from spectroradiometric measurements, but the differences were <7% for all sources, except red-light-emitting diodes. The sensors were most accurate for broad-band sources and least accurate for narrow-band sources. According to spectroradiometric measurements, YPF sensors were significantly less accurate (>9% difference) than PPF sensors under metal halide, high-pressure sodium, and low-pressure sodium lamps. Both sensor types were inaccurate (>18% error) under red-light-emitting diodes. Because both YPF and PPF sensors are imperfect integrators, and because spectroradiometers can measure photosynthetically active radiation much more accurately, researchers should consider developing calibration factors from spectroradiometric data for some specific radiation sources to improve the accuracy of integrating sensors. PMID:11537894

Barnes, C; Tibbitts, T; Sager, J; Deitzer, G; Bubenheim, D; Koerner, G; Bugbee, B

1993-12-01

92

Surface Catalysis and Oxidation on Stagnation Point Heat Flux Measurements in High Enthalpy Arc Jets  

NASA Technical Reports Server (NTRS)

Heat flux sensors are routinely used in arc jet facilities to determine heat transfer rates from plasma plume. The goal of this study is to assess the impact of surface composition changes on these heat flux sensors. Surface compositions can change due to oxidation and material deposition from the arc jet. Systematic surface analyses of the sensors were conducted before and after exposure to plasma. Currently copper is commonly used as surface material. Other surface materials were studied including nickel, constantan gold, platinum and silicon dioxide. The surfaces were exposed to plasma between 0.3 seconds and 3 seconds. Surface changes due to oxidation as well as copper deposition from the arc jets were observed. Results from changes in measured heat flux as a function of surface catalycity is given, along with a first assessment of enthalpy for these measurements. The use of cupric oxide is recommended for future heat flux measurements, due to its consistent surface composition arc jets.

Nawaz, Anuscheh; Driver, David M.; Terrazas-Salinas

2013-01-01

93

Analysis of field measurements of carbon dioxide and water vapor fluxes  

NASA Technical Reports Server (NTRS)

Analysis of the field measurements of carbon dioxide and water vapor fluxes is discussed. These data were examined in conjunction with reflectance obtained from helicopter mounted Modular Multiband Radiometer. These measurements are representative of the canopy scale (10 to 100 m)(exp 2) and provide a good basis for investigating the hypotheses/relationship potentially useful in remote sensing applications. All the micrometeorological data collected during FIFE-89 were processed and fluxes of CO2, water vapor, and sensible heat were calculated. Soil CO2 fluxes were also estimated. Employing these soil CO2 flux values, in conjunction with micrometeorological measurements, canopy photosynthesis is being estimated. A biochemical model of leaf photosynthesis was adapted to the prairie vegetation. The modeled leaf photosynthesis rates were scaled up to the canopy level. This model and a multiplicative stomatal conductance model are also used to calculate canopy conductance.

Verma, Shashi B.

1991-01-01

94

Air-sea flux of bromoform: Controls, rates, and implications  

Microsoft Academic Search

Bromoform (CHBr3) is the largest single source of atmospheric organic bromine and therefore of importance as a source of reactive halogens to the troposphere and lower stratosphere. The sea-to-air flux, originating with macroalgal and planktonic sources, is the main source for atmospheric bromoform. We review bromoform's contribution to atmospheric chemistry, its atmospheric and oceanic distributions and its oceanic sources and

Birgit Quack; D. W. R. Wallace

2003-01-01

95

Measuring flux of soil fumigants using the aerodynamic and dynamic flux chamber methods.  

PubMed

Methods for measuring and estimating flux density of soil fumigants under field conditions are important for the purpose of providing inputs to air dispersion models and for comparing the effects of management practices on emission reduction. The objective of this study was to measure the flux of 1,3-dichloropropene (1,3-D) and chloropicrin at a site in Georgia (GA) using the aerodynamic method and the dynamic flux chamber (FC) method. A secondary objective was to compare the effects of high density polyethylene (HDPE), and virtually impermeable film (VIF) tarps on fumigant flux at a site in Florida (FL). Chloropicrin and 1,3-D were applied by surface drip application of In-Line soil fumigant on vegetable beds covered by low density polyethylene (LDPE), HDPE, or VIF. The surface drip fumigation using In-Line and LDPE tarp employed in this study resulted in volatilization of 26.5% of applied 1,3-D and 11.2% of the applied chloropicrin at the GA site, as determined using the aerodynamic method. Estimates of mass loss obtained from dynamic FCs were 23.6% for 1,3-D and 18.0% for chloropicrin at the GA site. Flux chamber trials at the FL site indicate significant additional reduction in flux density, and cumulative mass loss when VIF tarp is used. This study supports the use of dynamic FCs as a valuable tool for estimating gas flux density from agricultural soils, and evaluating best management practices for reducing fumigant emissions to the atmosphere. PMID:17412897

van Wesenbeeck, I J; Knuteson, J A; Barnekow, D E; Phillips, A M

2007-01-01

96

Airborne Solar Radiant Flux Measurements During ACE-2  

NASA Technical Reports Server (NTRS)

Aerosol effects on atmospheric radiative fluxes provide a forcing function that can change the climate in potentially significant ways. This aerosol radiative forcing is a major source of uncertainty in understanding the climate change of the past century and predicting future climate. To help reduce this uncertainty, the 1996 Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) and the 1997 Aerosol Characterization Experiment (ACE-2) measured the properties and radiative effects of aerosols over the Atlantic Ocean. In the ACE 2 program the solar radiant fluxes were measured on the Pelican aircraft and the UK Met Office C130. This poster will show results from the measurements for the aerosol effects during the clear column days. We will compare the results with calculations of the radiant fluxes.

Bergstrom, Robert W.; Russell, Philip B.; Jonsson, Haflidi

2000-01-01

97

Flux measurements of biogenic VOCs during ECHO 2003  

NASA Astrophysics Data System (ADS)

Within the framework of the AFO 2000 project ECHO, two PTR-MS instruments were operated in combination with sonic anemometers to determine biogenic VOC fluxes from a mixed deciduous forest site in North-Western Germany using the eddy covariance (EC) technique. The measurement site was characterised by a forest of inhomogeneous composition, complex canopy structure, limited extension in certain wind directions and frequent calm wind conditions during night time. As a consequence, a considerable fraction of the measurements did not qualify for flux calculations by EC and had to be discarded. The validated results show light and temperature dependent emissions of isoprene and monoterpenes from this forest, with average emissions (normalised to 30°C and 1000 µmoles m-2 s-1 PAR) of 1.5 and 0.39 µg m-2 s-1, respectively. Emissions of methanol reached on average 0.087 µg m-2 s-1 during daytime, but fluxes were too small to be detected during night time. Upward fluxes of the isoprene oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) were also found, being two orders of magnitude lower than those of isoprene. The observed fluxes are consistent with upscalings from leaf-level emission measurements of representative tree species in this forest and, in the case of MVK and MACR, can plausibly be explained by chemical production through oxidation of isoprene within the canopy. Calculations with an analytical footprint model indicate that the observed isoprene fluxes correlate with the fraction of oaks within the footprints of the flux measurement.

Spirig, C.; Neftel, A.; Ammann, C.; Dommen, J.; Grabmer, W.; Thielmann, A.; Schaub, A.; Beauchamp, J.; Wisthaler, A.; Hansel, A.

2004-10-01

98

Uncertainty of calorimeter measurements at NREL's high flux solar furnace  

NASA Astrophysics Data System (ADS)

The uncertainties of the calorimeter and concentration measurements at the High Flux Solar Furnace (HFSF) at the National Renewable Energy Laboratory (NREL) are discussed. Two calorimeter types have been used to date. One is an array of seven commercially available circular foil calorimeters (gardon or heat flux gages) for primary concentrator peak flux (up to 250 W/sq cm). The second is a cold-water calorimeter designed and built by the University of Chicago to measure the average exit power of the reflective compound parabolic secondary concentrator used at the HFSF (over 3.3 kW across a 1.6/sq cm) exit aperture, corresponding to a flux of about 2 kW/sq cm. This paper discussed the uncertainties of the calorimeter and pyrheliometer measurements and resulting concentration calculations. The measurement uncertainty analysis is performed according to the ASME/ANSI standard PTC 19.1 (1985). Random and bias errors for each portion of the measurement are analyzed. The results show that as either the power or the flux is reduced, the uncertainties increase. Another calorimeter is being designed for a new, refractive secondary which will use a refractive material to produce a higher average flux (5 kW/sq cm) than the reflective secondary. The new calorimeter will use a time derivative of the fluid temperature as a key measurement of the average power out of the secondary. A description of this calorimeter and test procedure is also presented, along with a pre-test estimate of major sources of uncertainty.

Bingham, C. E.

1991-12-01

99

Densitometric tomography using the measurement of muon flux  

NASA Astrophysics Data System (ADS)

The knowledge of the subsurface properties is essentially obtained by geophysical methods, e.g. seismic imaging, electric prospection or gravimetry. The present work develops a recent method to investigate the in situ density of rocks using atmospheric the muon flux measurement , its attenuation depending on the rock density and thickness. This new geophysical technique have been mainly applied in volcanology (Lesparre N., 2011) using scintillator detectors. The present project (T2DM2) aims to realize underground muons flux measurements in order to characterizing the rock massif density variations above the LSBB underground research facility in Rustrel (France). The muon flux will be measure with a new Muon telescope instrumentation using Micromegas detectors in Time Projection Chambers (TPC) configuration. The first step of the work presented considers the muon flux simulation using the Gaisser model, for the interactions between muons and atmospheric particles, and the MUSIC code (Kudryavtsev V. A., 2008) for the muons/rock interactions. The results show that the muon flux attenuation caused by density variations are enough significant to be observed until around 500 m depth and for period of time in the order of one month. Such a duration scale and depth of investigation is compatible with the duration of the water transfer processes involved within the Karst unsaturated zone where LSBB is located. Our work now concentrates on the optimization of the spatial distribution of detectors that will be deployed in future.

Hivert, F.; Busto, J.; Brunner, J.; Salin, P.; Gaffet, S.

2013-12-01

100

Thermal neutron flux measurements in the STAR experimental hall  

NASA Astrophysics Data System (ADS)

We report measurements of thermal neutron fluxes at different locations in the STAR experimental hall during RHIC Run 13 with proton-proton collisions at ?{s}=510 GeV. We compare these measurements to calculations based on PYTHIA as a minimum bias event generator, detailed GEANT3 simulation of the STAR detector and experimental hall, and with GCALOR as the neutron transport code. A fairly good agreement was found between simulation and measurements.

Fisyak, Yuri; Tsai, Oleg; Videbæk, Flemming; Xu, Zhangbu

2014-08-01

101

Long Term Isoprene Flux Measurements Above a Northern Hardwood Forest  

NASA Astrophysics Data System (ADS)

Canopy scale emissions of isoprene from a northern hardwood forest in Michigan were measured using the eddy covariance technique during the summer growing periods from 1999 through 2001. The goal of this work was to improve our understanding of isoprene emissions from forest ecosystems to better describe the role of isoprene in local and regional atmospheric chemical cycles. A second objective of this work was to contribute to the Program for Research on Oxidants: PHotochemistry, Emissions, and Transport (PROPHET) goal of characterizing the role of biogenic emissions in processing atmospheric nitrogen. Isoprene is one of the most abundant hydrocarbons in the atmosphere, and it is very reactive in the atmosphere. Long-term flux measurements are important for investigating the interannual variability in emissions due to interannual variability in climate. In addition, continuous flux data are useful for verifying canopy scale models that are used to generate emission inventories for regional photochemical models. Measurements were made in collaboration with the AmeriFlux site located at the University of Michigan Biological Station (UMBS) and the (PROPHET) site located within 100 m of the AmeriFlux Tower. The site is a 90-year old stand classified as mid-aged conifer and deciduous, with aspen and oak two of the dominant species. Fluxes of isoprene, CO2, H2O, and sensible heat were measured using a fast response isoprene sensor (FIS), an open-path infrared gas analyzer, and a 3-D sonic anemometer. Concurrent measurements of these canopy scale fluxes are useful for understanding the physiological controls on isoprene emissions and potential links between isoprene emissions and other forest ecosystem dynamics. The multi-year data set will be presented and year-to-year variations in isoprene emissions will be explored in the context of interannual variations among the other canopy scale parameters.

Pressley, S. N.; Lamb, B.; Westberg, H.; Hatten, G.; Flaherty, J.

2002-12-01

102

Flux measurements of volatile organic compounds from an urban landscape  

NASA Astrophysics Data System (ADS)

Direct measurements of volatile organic compound (VOC) emissions that include all sources in urban areas are a missing requirement to evaluate emission inventories and constrain current photochemical modelling practices. Here we demonstrate the use of micrometeorological techniques coupled with fast-response sensors to measure urban VOC fluxes from a neighbourhood of Mexico City, where the spatial variability of surface cover and roughness is high. Fluxes of olefins, methanol, acetone, toluene and C2-benzenes were measured and compared with the local gridded emissions inventory. VOC fluxes exhibited a clear diurnal pattern with a strong relationship to vehicular traffic. Recent photochemical modelling results suggest that VOC emissions are significantly underestimated in Mexico City, but for the olefin class, toluene, C2-benzenes, and acetone fluxes measured in this work, the results show general agreement with the gridded emissions inventory. While these measurements do not address the full suite of VOC emissions, the comparison with the inventory suggests that other explanations may be needed to explain the photochemical modelling results.

Velasco, E.; Lamb, B.; Pressley, S.; Allwine, E.; Westberg, H.; Jobson, B. T.; Alexander, M.; Prazeller, P.; Molina, L.; Molina, M.

2005-10-01

103

Primary Cosmic Ray Proton Flux Measured by AMS-02  

E-print Network

The Alpha Magnetic Spectrometer (AMS-02) is a high energy particle detector designed to study origin and nature of cosmic rays up to a few TV from space. It was installed on the International Space Station (ISS) on May 19, 2011. During the first two years of operation AMS-02 performed precise measurements of the proton flux. In the low rigidity range, from 1 GV to 20 GV, the proton flux was daily measured with a statistical error less than 1%. In the same rigidity range a gradual decrease due to Solar modulation effect and transit variations due to Solar Flares and Coronal Mass Ejection were also observed. In the rigidity range from 20 GV up to 100 GV instead, AMS-02 data show no drastic variation and the results are consistent with other experiments. Above 100 GV, AMS-02 proton flux exhibits a single power low behavior with no fine structures nor brakes.

C. Consolandi; on Behalf of the AMS-02 Collaboration

2014-02-03

104

From Satellite ion flux data to SEU rate estimation  

Microsoft Academic Search

During a solar particle event (SPE) a spacecraft can suffer a large number of single event effect (SEE) anomalies due to the enhanced energetic ion environment. Throughout satellite design, simulations can be made to estimate the mission single event upset (SEU) rate. One of the most used models to predict in-orbit SEU rate is cosmic ray effects on microelectronics (CREME96).

S. Esteve Hoyos; Hugh Evans; Eamonn Daly

2004-01-01

105

Biogenic silica fluxes and accumulation rates in the Gulf of California  

SciTech Connect

The Gulf of California, though small in size, plays an important role in the global silica cycle. The seasonal pattern of biogenic silica flux in the gulf is closely related to that of phytoplankton biomass levels and is controlled by changes in weather and hydrographic conditions. The highest opal fluxes ([approximately] 0.35 g[center dot]m[sup [minus]2][center dot]d[sup [minus]1]) occur during winter and spring, and they are comparable to those measured in some of the most productive ecosystems of the world. Approximately 15%-25% of the biogenic silica produced in surface waters is preserved in gulf sediments, a figure significantly higher than the average global ocean preservation rate. However, the flux of opal at 500 m water depth is less than 25% of that being produced at the surface, suggesting that most of the recycling of biogenic silica in the Gulf of California occurs in the upper water column. 28 refs., 3 figs.

Thunell, R.C.; Pride, C.J.; Tappa, E. (Univ. of South Carolina, Columbia, SC (United States)); Muller-Karger, F.E. (Univ. of South Florida, St. Petersburg, FL (United States))

1994-04-01

106

A PROBLEM WITH FLUX CHAMBER MEASUREMENTS OF BIOGENIC SULFUR EMISSIONS  

EPA Science Inventory

Problems associated with identifying and quantifying factors that influence liquid-phase controlled evolution of hydrogen sulfide and organic sulfides through the air-water interface are briefly reviewed. It was found that at present flux chamber measurements of the release of th...

107

Corer–Reactors for Contaminant Flux Measurement in Sediments  

Microsoft Academic Search

disturbance to the sediment. This apparatus has been used in our laboratory for a number of years (Jones and Design details and operating instructions are provided for a sedi- Jung, 1996; Jung et al., 1997) and has generated useful ment corer that can be converted into a reactor for the measurement of the fluxes of contaminants from sediments to overlying

R. F. Jung; D. R. Jones; G. E. Batley

2003-01-01

108

Estimation of wet surface evaporation from sensible heat flux measurements  

Microsoft Academic Search

A new method is proposed to estimate wet surface evaporation by means of measurements of sensible heat flux and of air temperature, relative humidity, and wind speed at one level only. This formulation is made possible by the linearization of the Bowen ratio, a common assumption in other methods, such as Penman's model and its derivatives. The method will be

Nikki Vercauteren; Elie Bou-Zeid; Hendrik Huwald; Marc B. Parlange; Wilfried Brutsaert

2009-01-01

109

Estimating terrestrial uranium and thorium by antineutrino flux measurements  

E-print Network

Estimating terrestrial uranium and thorium by antineutrino flux measurements Stephen T. Dye, and approved November 16, 2007 (received for review July 11, 2007) Uranium and thorium within the Earth produce of uranium and thorium concentrations in geological reservoirs relies largely on geochemi- cal model

Mcdonough, William F.

110

Airborne flux measurements of Biogenic Isoprene over California  

SciTech Connect

Biogenic Volatile Organic Compound (BVOC) fluxes were measured onboard the CIRPAS Twin Otter aircraft as part of the California Airborne BVOC Emission Research in Natural Ecosystem Transects (CABERNET) campaign during June 2011. The airborne virtual disjunct eddy covariance (AvDEC) approach used measurements from a PTR-MS and a wind radome probe to directly determine fluxes of isoprene, MVK+MAC, methanol, monoterpenes, and MBO over ~10,000-km of flight paths focusing on areas of California predicted to have the largest emissions of isoprene. The Fast Fourier Transform (FFT) approach was used to calculate fluxes over long transects of more than 15 km, most commonly between 50 and 150 km. The Continuous Wavelet Transformation (CWT) approach was used over the same transects to also calculate "instantaneous" fluxes with localization of both frequency and time independent of non-stationarities. Vertical flux divergence of isoprene is expected due to its relatively short lifetime and was measured directly using "racetrack" profiles at multiple altitudes. It was found to be linear and in the range 5% to 30% depending on the ratio of aircraft altitude to PBL height (z/zi). Fluxes were generally measured by flying consistently 1 at 400 m ±50 m (a.g.l.) altitude, and extrapolated to the surface according to the determined flux divergence. The wavelet-derived surface fluxes of isoprene averaged to 2 km spatial resolution showed good correspondence to Basal Emission Factor (BEF) landcover datasets used to drive biogenic VOC (BVOC) emission models. The surface flux of isoprene was close to zero over Central Valley crops and desert shrublands, but was very high (up to 15 mg m-2 h-1) above oak woodlands, with clear dependence of emissions on temperature and oak density. Isoprene concentrations of up to 8 ppb were observed at aircraft height on the hottest days and over the dominant source regions. While isoprene emissions from agricultural crop regions, shrublands, and coniferous forests were extremely low, high concentrations of methanol and monoterpenes were found above some of these regions. These observations demonstrate the ability to measure fluxes from specific sources by eddy covariance from an aircraft, and suggest the utility of measurements using fast response chemical sensors to constrain emission inventories and map out source distributions for a much broader array of trace gases than was observed in this study. This paper reports the first regional direct eddy covariance fluxes of isoprene. The emissions of VOCs measured from aircraft with 2 km spatial resolution can quantify the distribution of major sources providing the observations required for testing statewide emission inventories of these important trace gases. These measurements will be used in a future study to assess BVOC emission models and their driving variable datasets.

Misztal, P.; Karl, Thomas G.; Weber, Robin; Jonsson, H. H.; Guenther, Alex B.; Goldstein, Allen H.

2014-10-10

111

Advances in Air-Sea Flux Measurement by Eddy Correlation  

NASA Astrophysics Data System (ADS)

Eddy-correlation measurements of the oceanic flux are useful for the development and validation of air-sea gas exchange models and for analysis of the marine carbon cycle. Results from more than a decade of published work and from two recent field programs illustrate the principal interferences from water vapour and motion, demonstrating experimental approaches for improving measurement precision and accuracy. Water vapour cross-sensitivity is the greatest source of error for flux measurements using infrared gas analyzers, often leading to a ten-fold bias in the measured flux. Much of this error is not related to optical contamination, as previously supposed. While various correction schemes have been demonstrated, the use of an air dryer and closed-path analyzer is the most effective way to eliminate this interference. This approach also obviates density corrections described by Webb et al. (Q J R Meteorol 106:85-100, 1980). Signal lag and frequency response are a concern with closed-path systems, but periodic gas pulses at the inlet tip provide for precise determination of lag time and frequency attenuation. Flux attenuation corrections are shown to be 5 % for a cavity ring-down analyzer (CRDS) and dryer with a 60-m inlet line. The estimated flux detection limit for the CRDS analyzer and dryer is a factor of ten better than for IRGAs sampling moist air. While ship-motion interference is apparent with all analyzers tested in this study, decorrelation or regression methods are effective in removing most of this bias from IRGA measurements and may also be applicable to the CRDS.

Blomquist, Byron W.; Huebert, Barry J.; Fairall, Christopher W.; Bariteau, Ludovic; Edson, James B.; Hare, Jeffrey E.; McGillis, Wade R.

2014-09-01

112

A Novel Detector for High Neutron Flux Measurements  

SciTech Connect

Measuring alpha particles from a neutron induced break-up reaction with a mass spectrometer can be an excellent tool for detecting neutrons in a high neutron flux environment. Break-up reactions of {sup 6}Li and {sup 12}C can be used in the detection of slow and fast neutrons, respectively. A high neutron flux detection system that integrates the neutron energy sensitive material and helium mass spectrometer has been developed. The description of the detector configuration is given and it is soon to be tested at iThemba LABS, South Africa.

Singo, T. D.; Wyngaardt, S. M. [Department of Physics, University of Stellenbosch, Private bag X1, Matieland, Stellenbosch (South Africa); Papka, P. [Department of Physics, University of Stellenbosch, Private bag X1, Matieland, Stellenbosch (South Africa); Nuclear Physics group, iThemba labs, P. O. Box 722, Somerset West 7129 (South Africa); Dobson, R. T. [Department of Mechanical and Mechatronic Engineering, University of Stellenbosch, Private bag X1, Matieland, Stellenbosch (South Africa)

2010-01-05

113

A semiclassical reactive flux method for the calculation of condensed phase activated rate constants  

Microsoft Academic Search

A semiclassical reactive flux algorithm for calculating thermally activated rate constants is presented which is based on a semiclassical transition state theory due to Chapman, Garrett, and Miller J. This reactive flux technique, when combined with the semiclassical TST, enables one to describe dynamical recrossings of the transition state on the same footing as tunneling effects. Most importantly, the method

Diane E. Sagnella; Jianshu Cao; Gregory A. Voth

1994-01-01

114

Balloon-borne measurement of energetic electron fluxes inside thunderclouds  

NASA Astrophysics Data System (ADS)

High-energy radiation is routinely produced by thunderclouds and lightning. This radiation is in the form of x-rays and gamma-rays with timescales ranging from sub-microsecond (x-rays associated with lightning leaders), to sub-millisecond (Terrestrial Gamma-ray Flashes), to minute long glows (Gamma-ray Glows from thunderclouds seen on the ground and in or near the cloud by aircrafts and balloons). It is generally accepted that these emissions originate from bremsstrahlung interactions of relativistic runaway electrons with air, which can be accelerated in the thundercloud/lightning electric fields and gain up to multi-MeV energies. However, the exact physical details of the mechanism that produces these runaway electrons are still unknown. In order to better understand the source of energetic radiation inside thunderclouds, we have begun a campaign of balloon-borne instruments to directly measure the flux of energetic electrons inside thunderclouds. In the current configuration, each balloon carries Geiger counters to record the energetic particles. Geiger counters are well suited for directly measuring energetic electrons and positrons and have the advantage of being lightweight and dependable. We transmit data at 900MHz, ISM band, with 115.2 kb/s transmission rate. This would provide us a high resolution radiation profile over a relatively large distance. Due to the nature of the thunderstorm environment, the campaign has many design, communication, and safety challenges. In this presentation we will report on the status of the campaign and some of the physical insights gained from the data collected by our instruments. This work was supported in part by the NASA grant NNX12A002H and by DARPA grant HR0011-1-10-1-0061.

Arabshahi, Shahab; Vodopiyanov, Igor; Dwyer, Joseph; Rassoul, Hamid

2014-05-01

115

Ecosystem photosynthesis inferred from measurements of carbonyl sulphide flux  

NASA Astrophysics Data System (ADS)

Limited understanding of carbon dioxide sinks and sources on land is often linked to the inability to distinguish between the carbon dioxide taken up by photosynthesis, and that released by respiration. Carbonyl sulphide, a sulphur-containing analogue of carbon dioxide, is also taken up by plants, and could potentially serve as a powerful proxy for photosynthetic carbon dioxide uptake, which cannot be directly measured above the leaf scale. Indeed, variations in atmospheric concentrations of carbonyl sulphide are closely related to those of carbon dioxide at regional, local and leaf scales. Here, we use eddy covariance and laser spectroscopy to estimate the net exchange of carbon dioxide and carbonyl sulphide across three pine forests, a cotton field and a wheat field in Israel. We estimate gross primary productivity--a measure of ecosystem photosynthesis--directly from the carbonyl sulphide fluxes, and indirectly from carbon dioxide fluxes. The two estimates agree within an error of +/-15%. The ratio of carbonyl sulphide to carbon dioxide flux at the ecosystem scale was consistent with the variability in mixing ratios observed on seasonal timescales in the background atmosphere. We suggest that atmospheric measurements of carbonyl sulphide flux could provide an independent constraint on estimates of gross primary productivity, key to projecting the response of the land biosphere to climate change.

Asaf, David; Rotenberg, Eyal; Tatarinov, Fyodor; Dicken, Uri; Montzka, Stephen A.; Yakir, Dan

2013-03-01

116

EURISOL Multi-MW Target Station - MAFF Configuration - Neutron Fluxes, Fission Rates, Dose Rates and Activation  

E-print Network

The EURISOL (The EURopean Isotope Separation On-Line Radioactive Ion Beam) project aims atproducing high intensity radioactive ion beams produced by neutron-induced fission on fissile targets(235U) surrounding a liquid mercury converter. A proton beam of 1GeV and 4MW impinges on theconverter, generating, by spallation reactions, high neutron fluxes that induce fission in thesurrounding fissile targets.In this work the state-of-the-art Monte Carlo codes MCNPX and FLUKA were used to assess theneutronics performance of the system, which geometry, inspired in the MAFF concept, allows aversatile manipulation of the fission targets. The first objective of the study was to optimize thegeometry and the materials used in the fuel and reflector elements of the system, in order to achievethe highest possible fission rates. Indeed, it is shown that the appropriate combination of fission targetmaterial and surrounding reflector material leads to the aimed value of 1015 fissions/s per fissiontarget. The second part of this...

Luis, R; Goncalves, I. F; Vaz, P; Kadi, Y; Kharoua, C; Rocca, R; Bermudez, J; Tecchio, L; Negoita, F; Ene, D; David, J.C

117

Measuring methane emission rates of a dairy cow herd by two micrometeorological techniques  

Microsoft Academic Search

Two well-known micrometeorological techniques were used to measure methane emission rates from a herd of dairy cows freely grazing within a fenced paddock. The integrated horizontal flux technique (IHF) was preferable to the flux-gradient technique (FG) because it does not rely on similarity assumptions, and because it had the smaller measurement error. Both techniques were comparable, within estimated errors, with

Johannes Laubach; Francis M. Kelliher

2004-01-01

118

Scales, Growth Rates, and Spectral Fluxes of Baroclinic Instability in the Ocean  

E-print Network

An observational, modeling, and theoretical study of the scales, growth rates, and spectral fluxes of baroclinic instability in the ocean is presented, permitting a discussion of the relation between the local instability ...

Tulloch, Ross

119

Nitrous Oxide Fluxes in Turfgrass: Effects of Nitrogen Fertilization Rates and Types Dale J. Bremer*  

E-print Network

Nitrous Oxide Fluxes in Turfgrass: Effects of Nitrogen Fertilization Rates and Types Dale J. Bremer* ABSTRACT Urban ecosystems are rapidly expanding and their effects on atmo- spheric nitrous oxide (N2O

120

How are Rainfall Rates Measured?  

NSDL National Science Digital Library

In this problem-based learning activity, students learn about weather forecasting and the role of the TRMM (Tropical Rainfall Measuring Mission) satellite in data collection. Assuming the role of climatologists, students assist a reporter in determining the accuracy of weather predictions published in The Old Farmer's Almanac. The lesson requires a street map of the local community, acetate sheets to cover the map, materials needed to build a homemade rain gauge, and sample pages of the almanac. Teacher notes, student worksheet, glossary and an appendix introducing problem-based learning are included. This resource is the first of the 3-part learning module, Investigating the Climate System: Precipitation.

121

[Estimation of CO2 fluxes from rice paddies based on transparent chamber measurement].  

PubMed

Closed chamber provide a valuable tool for measuring CO2 exchange fluxes. In general, the change rate of CO2 concentration is assumed to be constant in the short measurement time and a linear regression method is used to estimate the CO2 fluxes. However, due to the physical and physiological effects, the change rate of CO2 is not always constant. A linear regression method and an exponential regression method are compared in this study. Results show that during the growing stages except for the ripening, nonlinear relationship of CO2 concentration versus time was estimated in the sunny daytime. Absolute values of CO2 fluxes calculated by linear regression were lower than that by exponential regression. Whereas, CO2 concentration changed linearly with time in cloudy days or in nighttime. And no significant difference was found between the results calculated with these two methods. Accumulative CO2-C fluxes with exponential and linear regressions were compared with the values of net ecosystem exchange of CO2-C (NEE), which were calculated by net primary production (NPP) minus soil respiration. The values with the exponential regression method were closer to NEE than those with linear regression. Therefore, the linear regression method could result in underestimation of carbon budget of ecosystem. Based on transparent chamber measurement, the exponential regression is more feasible to calculate CO2 fluxes than the linear regression. PMID:16447420

Zhu, Yong-li; Tong, Cheng-li; Wu, Jin-shui; Zhou, Wei-jun

2005-11-01

122

Measurement of Heat Flux at Metal-Mold Interface during Casting Solidification  

SciTech Connect

All previous studies on interfacial heat transfer coefficient have been based on indirect methods for estimating the heat flux that employed either inverse heat transfer analysis procedures or instrumentation arrangements to measure temperatures and displacements near the metal-mold interface. In this paper, the heat transfer at the metal-mold interfaces is investigated using a sensor for the direct measurement of heat flux. The heat flux sensor (HFS) was rated for 700oC and had a time response of less than 10 ms. Casting experiments were conducted using graphite molds for aluminum alloy A356. Several casting experiments were performed using a graphite coating and a boron nitride coating. The measurement errors were estimated. The temperature of the mold surface was provided by the HFS while the temperature of the casting surface was measured using a thermocouple. Results for the heat transfer coefficients were obtained based on measured heat flux and temperatures. Four stages were clearly identified for the variation in time of the heat flux. Values of the heat transfer coefficient were in good agreement with data from previous studies.

Sabau, Adrian S [ORNL

2006-01-01

123

Saharan Airborne Dust Flux Measurements from the Fennec Campaign  

NASA Astrophysics Data System (ADS)

The Fennec campaign of 2011involved deployment of the Facility for Airborne Atmospheric Measurements BAe 146 (FAAM Bae 146) scientific research aircraft to Fuerteventura with research flights over the remote Saharan desert in Mali and Mauritania. The aims of the Fennec campaign were to characterise the dynamics, radiation and dust environment in this inaccessible region. The FAAM BAe 146 operated a suite of instruments which measured size distributions of dust including a Passive Cavity Aerosol Spectrometer Probe, a Cloud Droplet Probe and a Cloud Imaging Probe (part of a Cloud, Aerosol and Precipitation Spectrometer). These instruments were able to reliably generate particle size distributions over the approximate range 0.1 to 200 ?m and for the first time were simultaneously operated at high temporal resolution of at least 10 Hz. Combining these dust measurements with the measured 3D wind vectors has allowed size resolved dust flux estimates to be derived using the eddy covariance method. To the authors' knowledge this is the first time such estimates have been successfully derived from aircraft data. Although the FAAM BAe 146 is capable of low level flying with straight and level runs at minimum altitudes of ~100 m (higher in poor visibility), this is still significantly higher than mast based flux measurements making comparison of the total flux with surface based observations difficult. However, these observations give useful measures of the size dependence of the particle flux and the spectral signature of the dynamics of vertical dust transport. The size resolved measurements show that dust mass flux includes significant contributions up to particle diameters ~100 ?m. This is much larger than the limit seen by other studies and is even more surprising given that the measurements were made at heights so far above the saltation layer. Spectral analysis shows three distinct dynamical regimes. The first appears to be linked to chaotic turbulence with horizontal scales of ~100 m. The second seems to be linked to features on scales ~1 km, similar to the order of the boundary layer depth. Finally, in the third regime, the concentration and wind measurements have a very asymmetric cross correlation series in the along flight direction which may indicate a preferred orientation for turbulent eddies caused buy e.g. shear. These characteristics are linked to the weather conditions and dust uplift mechanisms for each case.

Rosenberg, Phil; Parker, Doug; Ryder, Claire; Garcia-Carreras, Luis; Marsham, John; Dorsey, James; Brooks, Ian; Dean, Angela; Crosier, Jonathan; McQuaid, Jim; Washington, Richard

2013-04-01

124

EISCAT observations of pump-enhanced plasma temperature and optical emission excitation rate as a function of power flux  

NASA Astrophysics Data System (ADS)

We analyze optical emissions and enhanced electron temperatures induced by high power HF radio waves as a function of power flux using the EISCAT heater with a range of effective radiated powers. The UHF radar was used to measure the electron temperatures and densities. The Digital All Sky Imager was used to record the 630.0 nm optical emission intensities. We quantify the HF flux loss due to self-absorption in the D-region (typically 3-11 dB) and refraction in the F-region to determine the flux which reaches the upper-hybrid resonance height. We find a quasi-linear relationship between the HF flux and both the temperature enhancement and the optical emission excitation rate with a threshold at ˜37.5 ?Wm-2. On average ˜70% of the HF flux at the upper-hybrid resonance height goes in to heating the electrons for fluxes above the threshold compared to ˜40% for fluxes below the threshold.

Bryers, C. J.; Kosch, M. J.; Senior, A.; Rietveld, M. T.; Yeoman, T. K.

2012-09-01

125

Initial assessment of multi-scale measures of C02 and H20flux in the Siberian taiga  

Microsoft Academic Search

We measured C02 and HzO fluxes between undis- turbed Larix gmelinii forest and the atmosphere at a remote Eastern Siberian site in July 1993. Scaled-up leaf-level porom- eter measurements agreed with those derived from the eddy correlation technique for the canopy fluxes of COz and HzO. Patch-scale measurements of ecosystem C02 exchange agreed in turn with regional CO2 exchange rates

D. Y. HOLLINGER; F. M. KELLIHER; E.-D. SCHULZE; N. N. VYGODSKAYA; A. VARLAGIN

126

Time and Space Resolved Heat Flux Measurements During Nucleate Boiling with Constant Heat Flux Boundary Conditions  

NASA Technical Reports Server (NTRS)

The lack of temporally and spatially resolved measurements under nucleate bubbles has complicated efforts to fully explain pool-boiling phenomena. The objective of this current work was to acquire time and space resolved temperature distributions under nucleating bubbles on a constant heat flux surface using a microheater array with 100x 100 square microns resolution, then numerically determine the wall to liquid heat flux. This data was then correlated with high speed (greater than l000Hz) visual recordings of The bubble growth and departure from the heater surface acquired from below and from the side of the heater. The data indicate that microlayer evaporation and contact line heat transfer are not major heat transfer mechanisms for bubble growth. The dominant heat transfer mechanism appears to be transient conduction into the liquid as the liquid rewets the wall during the bubble departure process.

Yerramilli, Vamsee K.; Myers, Jerry G.; Hussey, Sam W.; Yee, Glenda F.; Kim, Jungho

2005-01-01

127

Airborne flux measurements of biogenic isoprene over California  

NASA Astrophysics Data System (ADS)

Biogenic isoprene fluxes were measured onboard the CIRPAS Twin Otter aircraft as part of the California Airborne Biogenic volatile organic compound (BVOC) Emission Research in Natural Ecosystem Transects (CABERNET) campaign during June 2011. The airborne virtual disjunct eddy covariance (AvDEC) approach used measurements from a proton transfer reaction mass spectrometer (PTR-MS) and a wind radome probe to directly determine fluxes of isoprene over 7400 km of flight paths focusing on areas of California predicted to have the largest emissions. The fast Fourier transform (FFT) approach was used to calculate fluxes of isoprene over long transects of more than 15 km, most commonly between 50 and 150 km. The continuous wavelet transformation (CWT) approach was used over the same transects to also calculate instantaneous isoprene fluxes with localization of both frequency and time independent of non-stationarities. Fluxes were generally measured by flying consistently at 400 m ± 50 m (a.g.l.) altitude, and extrapolated to the surface according to the determined flux divergence determined in the racetrack-stacked profiles. The wavelet-derived surface fluxes of isoprene averaged to 2 km spatial resolution showed good correspondence to basal emission factor (BEF) land-cover data sets used to drive BVOC emission models. The surface flux of isoprene was close to zero over Central Valley crops and desert shrublands, but was very high (up to 15 mg m-2 h-1) above oak woodlands, with clear dependence of emissions on temperature and oak density. Isoprene concentrations of up to 8 ppb were observed at aircraft height on the hottest days and over the dominant source regions. Even though the isoprene emissions from agricultural crop regions, shrublands, and coniferous forests were extremely low, observations at the Walnut Grove tower south of Sacramento demonstrate that isoprene oxidation products from the high emitting regions in the surrounding oak woodlands accumulate at night in the residual layer above the valley and mix down into the valley in the morning. Thus, the isoprene emissions surrounding the valley have relevance for the regional photochemistry that is not immediately apparent solely from the direct emission flux distribution. This paper reports the first regional observations of fluxes from specific sources by eddy covariance from an aircraft which can finally constrain statewide isoprene emission inventories used for ozone simulations by state agencies. While previously there was no available means to constrain the biogenic models, our results provide a good understanding of what the major sources of isoprene are in California, their magnitude, and how they are distributed. This data set on isoprene fluxes will be particularly useful for evaluating potential model alternatives which will be dealt with in a separate paper to assess isoprene emission models and their driving variable data sets.

Misztal, P. K.; Karl, T.; Weber, R.; Jonsson, H. H.; Guenther, A. B.; Goldstein, A. H.

2014-10-01

128

CAN COSMIC-RAY NUCLEON MEASUREMENTS BE USED TO SCALE PRODUCTION RATES OF COSMOGENIC NUCLIDES?  

E-print Network

CAN COSMIC-RAY NUCLEON MEASUREMENTS BE USED TO SCALE PRODUCTION RATES OF COSMOGENIC NUCLIDES variability of nuclide production rates on the earth's surface. Direct measurements of cosmic-ray fluxes have spatial variations of cosmic-ray neu- tron intensity and production rates of in-situ cosmogenic nuclides

Zreda, Marek

129

Impact of CO2 measurement bias on CarbonTracker surface flux estimates  

NASA Astrophysics Data System (ADS)

For over 20 years, atmospheric measurements of CO2 dry air mole fractions have been used to derive estimates of CO2 surface fluxes. Historically, only a few research laboratories made these measurements. Today, many laboratories are making CO2 observations using a variety of analysis techniques and, in some instances, using different calibration scales. As a result, the risk of biases in individual CO2 mole fraction records, or even in complete monitoring networks, has increased over the last decades. Ongoing experiments comparing independent, well-calibrated measurements of atmospheric CO2 show that biases can and do exist between measurement records. Biases in measurements create artificial spatial and temporal CO2 gradients, which are then interpreted by an inversion system, leading to erroneous flux estimates. Here we evaluate the impact of a constant bias introduced into the National Oceanic and Atmospheric Administration (NOAA) quasi-continuous measurement record at the Park Falls, Wisconsin (LEF), tall tower site on CarbonTracker flux estimates. We derive a linear relationship between the magnitude of the introduced bias at LEF and the CarbonTracker surface flux responses. Temperate North American net flux estimates are most sensitive to a bias at LEF in our CarbonTracker inversion, and its linear response rate is 68 Tg C yr-1 (˜10% of the estimated North American annual terrestrial uptake) for every 1 ppm of bias in the LEF record. This sensitivity increases when (1) measurement biases approached assumed model errors and (2) fewer other measurement records are available to anchor the flux estimates despite the presence of bias in one record. Flux estimate errors are also calculated beyond North America. For example, biospheric uptake in Europe and boreal Eurasia combined increases by 25 Tg C yr-1 per ppm CO2 to partially compensate for changes in the North American flux totals. These results illustrate the importance of well-calibrated, high-precision CO2 dry air mole fraction measurements, as well as the value of an effective strategy for detecting bias in measurements. This study stresses the need for a monitoring network with the necessary density to anchor regional, continental, and hemispheric fluxes more tightly and to lessen the impact of potentially undetected biases in observational networks operated by different national and international research programs.

Masarie, K. A.; PéTron, G.; Andrews, A.; Bruhwiler, L.; Conway, T. J.; Jacobson, A. R.; Miller, J. B.; Tans, P. P.; Worthy, D. E.; Peters, W.

2011-09-01

130

Estimating terrestrial uranium and thorium by antineutrino flux measurements  

PubMed Central

Uranium and thorium within the Earth produce a major portion of terrestrial heat along with a measurable flux of electron antineutrinos. These elements are key components in geophysical and geochemical models. Their quantity and distribution drive the dynamics, define the thermal history, and are a consequence of the differentiation of the Earth. Knowledge of uranium and thorium concentrations in geological reservoirs relies largely on geochemical model calculations. This article describes the methods and criteria to experimentally determine average concentrations of uranium and thorium in the continental crust and in the mantle by using site-specific measurements of the terrestrial antineutrino flux. Optimal, model-independent determinations involve significant exposures of antineutrino detectors remote from nuclear reactors at both a midcontinental and a midoceanic site. This would require major, new antineutrino detection projects. The results of such projects could yield a greatly improved understanding of the deep interior of the Earth. PMID:18172211

Dye, Stephen T.; Guillian, Eugene H.

2008-01-01

131

A method to measure cardiac autophagic flux in vivo.  

PubMed

Autophagy, a highly conserved cellular mechanism wherein various cellular components are broken down and recycled through lysosomes, has been implicated in the development of heart failure. However, tools to measure autophagic flux in vivo have been limited. Here, we tested whether monodansylcadaverine (MDC) and the lysosomotropic drug chloroquine could be used to measure autophagic flux in both in vitro and in vivo model systems. Using HL-1 cardiac-derived myocytes transfected with GFP-tagged LC3 to track changes in autophagosome formation, autophagy was stimulated by mTOR inhibitor rapamycin. Administration of chloroquine to inhibit lysosomal activity enhanced the rapamycin-induced increase in the number of cells with numerous GFP-LC3-positive autophagosomes. The chloroquine-induced increase of autophagosomes occurred in a dose-dependent manner between 1 microM and 8 microM, and reached a maximum 2 hour after treatment. Chloroquine also enhanced the accumulation of autophagosomes in cells stimulated with hydrogen peroxide, while it attenuated that induced by Bafilomycin A1, an inhibitor of V-ATPase that interferes with fusion of autophagosomes with lysosomes. The accumulation of autophagosomes was inhibited by 3-methyladenine, which is known to inhibit the early phase of the autophagic process. Using transgenic mice expressing 3 mCherry-LC3 exposed to rapamycin for 4 hr, we observed an increase in mCherry-LC3-labeled autophagosomes in myocardium, which was further increased by concurrent administration of chloroquine, thus allowing determination of flux as a more precise measure of autophagic activity in vivo. MDC injected 1 hr before sacrifice colocalized with mCherry-LC3 puncta, validating its use as a marker of autophagosomes. This study describes a method to measure autophagic flux in vivo even in non-transgenic animals, using MDC and chloroquine. PMID:18216495

Iwai-Kanai, Eri; Yuan, Hua; Huang, Chengqun; Sayen, M Richard; Perry-Garza, Cynthia N; Kim, Lucy; Gottlieb, Roberta A

2008-04-01

132

DIRECT MEASUREMENT OF HEAT FLUX FROM COOLING LAKE THERMAL IMAGERY  

SciTech Connect

Laboratory experiments show a linear relationship between the total heat flux from a water surface to air and the standard deviation of the surface temperature field, {sigma}, derived from thermal images of the water surface over a range of heat fluxes from 400 to 1800 Wm{sup -2}. Thermal imagery and surface data were collected at two power plant cooling lakes to determine if the laboratory relationship between heat flux and {sigma} exists in large heated bodies of water. The heat fluxes computed from the cooling lake data range from 200 to 1400 Wm{sup -2}. The linear relationship between {sigma} and Q is evident in the cooling lake data, but it is necessary to apply band pass filtering to the thermal imagery to remove camera artifacts and non-convective thermal gradients. The correlation between {sigma} and Q is improved if a correction to the measured {sigma} is made that accounts for wind speed effects on the thermal convection. Based on more than a thousand cooling lake images, the correlation coefficients between {sigma} and Q ranged from about 0.8 to 0.9.

Garrett, A; Eliel Villa-Aleman, E; Robert Kurzeja, R; Malcolm Pendergast, M; Timothy Brown, T; Saleem Salaymeh, S

2007-12-19

133

First measurement of the flux of solar neutrinos from the sun at the Sudbury Neutrino Observatory  

NASA Astrophysics Data System (ADS)

The Sudbury Neutrino Observatory (SNO) is a second generation solar neutrino detector. SNO is the first experiment that is able to measure both the electron neutrino flux and a flavor-blind flux of all active neutrino types, allowing a model-independent determination if the deficit of solar neutrinos known as the solar neutrino problem is due to neutrino oscillation. The Sudbury Neutrino Observatory started taking production data in November, 1999. A measurement of the charged current rate will be the first indication if SNO too sees a suppression of the solar neutrino signal relative to the theoretical predictions. Such a confirmation is the first step in SNO's ambitious science program. In this thesis, we present evidence that SNO is seeing solar neutrinos and a preliminary ratio of the measured vs predicted rate of electrons as induced by 8B neutrinos in the ?e, + d --> p + p + e charged-current (CC) reaction.

Wittich, Peter

2000-12-01

134

Measurement of diffusive flux of ammonia from water.  

PubMed

An instrument was developed for the measurement of gaseous ammonia concentration, NH(3(sw,eq)), in equilibrium with surface waters, notably ocean water. The instrument measures the ammonia flux from a flowing water surface under defined conditions and allows the calculation of NH(3(sw,eq)) from the principles of Fickian diffusion. The flux collector resembles a wetted parallel plate denuder previously developed for air sampling. The sample under study runs on one plate of the device; the ammonia released from the sample is collected by a slow flow of a receptor liquid on the other plate. The NH(3) + NH(4)(+) (hereinafter called N(T)) in the effluent receptor liquid is preconcentrated on a silica gel column and subsequently measured by a fluorometric flow injection analysis (FIA) system. With a 6-min cycle (4-min load, 2-min inject), the analytical system can measure down to 0.3 nM N(T) in the receptor liquid. Coupled with the flux collector, it is sufficiently sensitive to measure the ammonia flux from seawater. The instrument design is such that it is little affected by ambient ammonia. In both laboratory (N(T) 0.2-50 ?M), and field investigations (N(T) 0.18-1.7 ?M) good linearity between the ammonia flux and the N(T) concentration in seawater (spiked, synthetic, natural) was observed, although aged seawater, with depleted N(T) content, behaves in an unusual fashion upon N(T) addition, showing the existence of an "ammonia demand". NH(3(sw,eq)) levels from ocean water measured in the Coconut Island Laboratory, HI, ranged from 6.6 to 33 nmol/m(3) with an average of 17.4 ± 6.9 nmol/m(3), in comparison to 2.8-21 nmol/m(3) (average 10 ± 7 nmol/m(3)) NH(3(sw,eq)) values previously reported for the Central Pacific Ocean (Quinn, P. K.; et al. J. Geophys. Res. 1990, 95, 16405-16416). PMID:21644712

Genfa, Z; Uehara, T; Dasgupta, P K; Clarke, A D; Winiwarter, W

1998-09-01

135

An ecosystem-scale perspective of the net land methanol flux: synthesis of micrometeorological flux measurements  

NASA Astrophysics Data System (ADS)

Methanol is the second most abundant volatile organic compound in the troposphere and plays a significant role in atmospheric chemistry. While there is consensus about the dominant role of living plants as the major source and the reaction with OH as the major sink of methanol, global methanol budgets diverge considerably in terms of source/sink estimates reflecting uncertainties in the approaches used to model, and the empirical data used to separately constrain these terms. Here we compiled micrometeorological methanol flux data from eight different study sites and reviewed the corresponding literature in order to provide a first cross-site synthesis of the terrestrial ecosystem-scale methanol exchange and present an independent data-driven view of the land-atmosphere methanol exchange. Our study shows that the controls of plant growth on the production, and thus the methanol emission magnitude, and stomatal conductance on the hourly methanol emission variability, established at the leaf level, hold across sites at the ecosystem-level. Unequivocal evidence for bi-directional methanol exchange at the ecosystem scale is presented. Deposition, which at some sites even exceeds methanol emissions, represents an emerging feature of ecosystem-scale measurements and is likely related to environmental factors favouring the formation of surface wetness. Methanol may adsorb to or dissolve in this surface water and eventually be chemically or biologically removed from it. Management activities in agriculture and forestry are shown to increase local methanol emission by orders of magnitude; they are however neglected at present in global budgets. While contemporary net land methanol budgets are overall consistent with the grand mean of the micrometeorological methanol flux measurements, we caution that the present approach of simulating methanol emission and deposition separately is prone to opposing systematic errors and does not allow taking full advantage of the rich information content of micrometeorological flux measurements.

Wohlfahrt, G.; Amelynck, C.; Ammann, C.; Arneth, A.; Bamberger, I.; Goldstein, A. H.; Gu, L.; Guenther, A.; Hansel, A.; Heinesch, B.; Holst, T.; Hörtnagl, L.; Karl, T.; Laffineur, Q.; Neftel, A.; McKinney, K.; Munger, J. W.; Pallardy, S. G.; Schade, G. W.; Seco, R.; Schoon, N.

2015-01-01

136

Momentum Flux Measuring Instrument for Neutral and Charged Particle Flows  

NASA Technical Reports Server (NTRS)

An instrument to measure the momentum flux (total pressure) of plasma and neutral particle jets onto a surface has been developed. While this instrument was developed for magnetized plasmas, the concept works for non-magnetized plasmas as well. We have measured forces as small as 10(exp -4) Newtons on a surface immersed in the plasma where small forces are due to ionic and neutral particles with kinetic energies on the order of a few eV impacting the surface. This instrument, a force sensor, uses a target plate (surface) that is immersed in the plasma and connected to one end of an alumina rod while the opposite end of the alumina rod is mechanically connected to a titanium beam on which four strain gauges are mounted. The force on the target generates torque causing strain in the beam. The resulting strain measurements can be correlated to a force on the target plate. The alumina rod electrically and thermally isolates the target plate from the strain gauge beam and allows the strain gauges to be located out of the plasma flow while also serving as a moment arm of several inches to increase the strain in the beam at the strain gauge location. These force measurements correspond directly to momentum flux and may be used with known plasma conditions to place boundaries on the kinetic energies of the plasma and neutral particles. The force measurements may also be used to infer thrust produced by a plasma propulsive device. Stainless steel, titanium, molybdenum, and aluminum flat target plates have been used. Momentum flux measurements of H2, D2, He, and Ar plasmas produced in a magnetized plasma device have been performed.

Chavers, Greg; Chang-Diaz, Franklin; Schafer, Charles F. (Technical Monitor)

2002-01-01

137

Controlling quantum flux through measurement: An idealised example  

NASA Astrophysics Data System (ADS)

Classically, no transfer occurs between two equally filled reservoirs, no matter how one looks at them, but the situation can be different quantum-mechanically. This paradoxically surprising phenomenon rests on the distinctive property of the quantum world that one cannot stare at a system without disturbing it. It was recently discovered that this seemingly annoying feature could be harnessed to control small quantum systems using weak measurements. Here we present one of the simplest models —an idealised double quantum dot—where by toying with the dot measurement strength, i.e. the intensity of the look, it is possible to create a particle flux in an otherwise completely symmetric system. The basic property underlying this phenomena is that measurement disturbances are very different on a system evolving unitarily and a system evolving dissipatively. This effect shows that adaptive measurements can have dramatic effects enabling transport control but possibly inducing biases in the measurement of macroscopic quantities if not handled with care.

Tilloy, A.; Bauer, M.; Bernard, D.

2014-07-01

138

Spatial and temporal variations of methane flux measured by autochambers in a temperate ombrotrophic peatland  

NASA Astrophysics Data System (ADS)

measured CH4 flux at high temporal resolution with triplicate autochambers from three different plant communities at the ombrotrophic Mer Bleue bog in Canada to investigate the spatial and temporal variations, and factors that related to the CH4 flux. Our results show that seasonal mean CH4 fluxes from the Eriophorum-dominated community were 1.4-2.2 and 3.7-5.5 times higher than those from Maianthemum/Ledum and Chamaedaphne communities, respectively. Significant interannual variations in CH4 flux were observed in Maianthemum/Ledum and Chamaedaphne communities, attributable to a 55-60% reduction of mean summer (July-September) CH4 flux in 2010 as a consequence of a 5.5-9.0 cm lower mean summer water table compared to 2009. The Eriophorum community showed a much larger rate of increase in CH4 flux with peat temperature in the early growing season than in midsummer, which might be caused by a concomitant increase in root exudation of labile carbon for methanogenesis. Temporal variability of log-transformed CH4 flux was correlated (r ? 0.4) with peat temperature only when water table was less than 20, 30, and 40 cm below the peat surface for Maianthemum/Ledum, Chamaedaphne, and Eriophorum communities, respectively. This difference in water table threshold among communities might partly be related to differences in rooting depth and hence the ability of plants to sustain CH4 flux in dry conditions. These results suggest that modeling of CH4 flux from ombrotrophic peatlands over time should take into account the role of different vegetation types, since the relationships between CH4 emissions and environmental factors vary among vascular plant communities.

Lai, Derrick Y. F.; Moore, Tim R.; Roulet, Nigel T.

2014-05-01

139

Method to Determine the Global Thermogenic Methane Seepage Rate from the Helium Flux of the Continents  

NASA Astrophysics Data System (ADS)

Bottom-up assessments of the contribution of natural hydrocarbon seepage from the earth to the global methane budget have quantified the emissions from small areas and attempted to extrapolate those measurements to a cumulative global emission rate, resulting in estimates of 18-48 Tg/yr (3-9% of the global methane budget). An alternative top-down method using helium is proposed to estimate the total emission rate of methane from natural hydrocarbon seepage worldwide from the equation: Qseeps = 4J 4 f g-1 f b c m c T c a where Qseeps is the quantity of methane emitted to the atmosphere annually (in Tg yr-1). 4J is the average flux of 4He atoms from the surface of the continents (4.18 x 1010atoms m-2 s-1), 4 f g-1 is the inverse of the global average fraction of natural hydrocarbon gases comprised of 4He in the subsurface, expressed as CH 4 (vol) / 4He (vol). The other variable is the fraction of the continents that are covered by sedimentary basins (f b ~0.4), which reduces the helium flux to the fraction that migrates through hydrocarbon reservoirs on the way to the surface. The constants convert 4He atoms m-2 s-1into 4He mass flux per m2 per year (c m = 2.11 x 10-16), 4He grams into CH 4 Teragrams (c T = 4.0 x 10-12) and c a is the area of the continents (1.53 x 1014 m2). This approach assumes the 4He flux from the continents is the same from basement shield areas as from sedimentary basins, and that the average 4He content of natural hydrocarbon seeps is the same as the 4He content of natural gases in subsurface reservoirs exploited for hydrocarbons worldwide. An internally consistent estimate of the 4He content of these gases can be determined from the increase in the 4He content of the atmosphere in the past 30 years, because this would be attributable to the worldwide hydrocarbon production during that period. A most likely increase of 4 x 1010 4He mol yr-1 and a maximum increase of 1.3 x 1011 4He mol y-1 has been measured at the experimental limit from the change in 3He/4He in the atmosphere, which implies a 4He content of 300 ppm and an upper limit of <1000 ppm for produced natural gases, consistent with the observed 4He content of produced hydrocarbon gases along the continental margins. Using this estimate gives a value for 4 f g-1 of 1000 and 3333, which results in a calculated minimum natural thermogenic methane seepage rate for the earth of >2 Tg yr-1 and a most likely rate of ~6-8 Tg yr-1 (~1% of the global methane budget). The validity of this method could be tested by measuring the helium content of natural gas seeps in comparison with the helium content of the underlying natural gas reservoirs.

Hornafius, J. S.

2012-12-01

140

The Adjustment of Avian Metabolic Rates and Water Fluxes to Desert Environments  

E-print Network

461 The Adjustment of Avian Metabolic Rates and Water Fluxes to Desert Environments B. Irene on phylogenetically independent contrasts, we showed that birds from desert habitats have re- duced basal and field metabolic rates compared with species from mesic areas. Previous work showed that desert birds have reduced

Williams, Jos. B.

141

TITLE: Effects of Nitrogen Fertilizer Types and Rates and Irrigation on Nitrous Oxide Fluxes in Turfgrass  

E-print Network

28 TITLE: Effects of Nitrogen Fertilizer Types and Rates and Irrigation on Nitrous Oxide Fluxes; and 2) determine how nitrogen (N)-fertilization rates, N-fertilizer types, and irrigation affect N2O, which are fertilized with nitrogen (N) and irrigated (Figure 1). Urbanization in the United States

142

Momentum Flux Measurements Using an Impact Thrust Stand  

NASA Technical Reports Server (NTRS)

A device has been developed to measure the force caused by a beam of charged and neutral particles impacting a target plate. This device, an impact thrust stand, was developed to allow thrusters, during early stages of development, to be quickly and easily exhausted and compared to other thrusters. Since some thruster concepts are tested using laboratory equipment that is heavy and cumbersome, measuring the momentum flux of the particles in the plume can be much simpler than placing the entire thruster on a thrust stand. Conservation of momentum requires the momentum flux measured in the plume to be related to the thrust produced by the thruster. The impact thrust stand was designed to be placed in the plume of an electric thruster and has been tested and compared to the thrust measured from a Hall thruster placed on a pendulum thrust stand. Force measurements taken at several axial locations in the magnetic nozzle region of the Variable Specific Impulse Magnetoplasma Rocket will be presented.

Chavers, Greg; Chang-Diaz, Franklin; Breizman, Boris; Bengtson, Roger

2004-01-01

143

Eddy covariance measurements of the sea spray aerosol flux over the open ocean  

E-print Network

Eddy covariance measurements of the sea spray aerosol flux over the open ocean Sarah J. Norris,1 eddy covariance measurements of size-segregated sea spray aerosol fluxes over the open Atlantic Ocean the high variability in sea spray aerosol flux compared with other air-sea fluxes, both between individual

Brooks, Ian M.

144

Development of a Passive Sensor for Measuring Water and Solute Mass Flux in the Hyporheic Zone  

NASA Astrophysics Data System (ADS)

Measuring water, pollutant and nutrient exchange at the groundwater-surface water interface is challenging due to the dynamic nature of the hyporheic zone. Quantifying the exchange is critical to understanding mass balance across this interface. Technologies currently exist to identify groundwater discharge zones and infer estimates of contaminant mass flux based on total contaminant concentration in bulk sediment, though it is generally accepted that freely dissolved concentration in pore water is a better measure of potential exposure. Laboratory and preliminary field testing has been completed to demonstrate a new tool with potential to provide more accurate characterization of water, pollutant and nutrient flux at the groundwater-surface water interface through direct in-situ measurement. The sediment bed passive flux meter (SBPFM) was designed for passively and directly providing in-situ measurements of volumetric water flux and solute mass flux vertically through the upper surface sediment layer and into the overlying water column. The SBPFM consists of an internal permeable sorbent which is impregnated with one or more water soluble tracers (typically alcohols) and is contained in a dedicated drive-point with upper and lower screened openings for fluid intake and exhaust. This configuration generates water flow through the device proportional to the vertical gradient between the sediment bed and the water column. Once the SBPFM has been deployed, the tracers are displaced from the sorbent at rates proportional to the average vertical specific discharge. The mass loss of tracers during deployment can be used to calculate the cumulative water flux. Similarly, the cumulative mass of sorbed pollutants or nutrients provide a direct measurement of the vertical mass flux during deployment. The SBPFM prototype has been tested in controlled laboratory sediment interface models. The results show good agreement between the SBPFM calculated and the applied water and contaminant fluxes through the laboratory aquifer model. Flow reversals are anticipated for tidal sites and sorbent layers within the PFM are segmented and used to determine next flux magnitude and direction averaged over the deployment period. Preliminary field testing is underway focusing on an areas with chlorinated solvent contamination discharging to surface water. The SBPFM is deployed to quantify the net mass discharge of contaminants to a small stream over a short reach. The integrated mass discharge can be compared to concentrations and mass discharge observed in surface water. The SBPFM provides a new tool to assess water and solute flux at point locations and can provide spatial variability that can be integrated to support mass balance studies on segments of surface water reaches.

Annable, Michael D.; Layton, Leif; Hatfield, Kirk; Newman, Mark C.; Cho, Jaehyun; Klammler, Harald

2014-05-01

145

Fetch effects of forest canopy on flux measurements  

NASA Astrophysics Data System (ADS)

The flux measured above a canopy often deviates from the source strength due to the consequence of limited fetch. Any natural surface is commonly more or less heterogeneous, which violates the assumption of horizontal homogeneity for most micrometeorological measurement methods. This affects methods such as the eddy covariance technique where fluxes are measured in situ from a mast and the source area (or footprint) of the measurements lies upwind from the mast. Hence, in order to understand how the horizontal scale of heterogeneity influences scalar transport as well as the footprint of the measurements, we study the effects of the scale of surface heterogeneity to the measurements conducted at different measurement heights. Numerical simulations of flow over forest canopy with varying scales of heterogeneity were performed using a large eddy simulation (LES) model PALM. LES provides us a means of studying detailed and highly resolved turbulence and understanding the combined effects of forest terrain. The results show that the flow over canopy is sensitive to the size of homogenous fetch and the complexity of terrain. In particular, when the size of fetch is getting smaller and more complex, the local turbulence affects scalar transportation strongly. This has implications for the transport of scalars in the forest canopy. The blending height of scalar in relation to the scale of heterogeneity, measurement height and site location are also discussed. Furthermore, these results show great potential of LES for a wide range of applications in the field of micrometeorology including the determination of placing of instruments and the interpretation of measurements in complex forest terrain.

Tu, Sofia M.; Nordbo, Annika; Kanani, Farah; Rinne, Janne; Raasch, Siegfried; Vesala, Timo; Hellsten, Antti

2014-05-01

146

SIERRA-Flux: Measuring Regional Surface Fluxes of Carbon Dioxide, Methane, and Water Vapor from an Unmanned Aircraft System  

NASA Technical Reports Server (NTRS)

The Eddy-Covariance Method for quantifying surface-atmosphere fluxes is a foundational technique for measuring net ecosystem exchange and validating regional-to-global carbon cycle models. While towers or ships are the most frequent platform for measuring surface-atmosphere exchange, experiments using aircraft for flux measurements have yielded contributions to several large-scale studies including BOREAS, SMACEX, RECAB by providing local-to-regional coverage beyond towers. The low-altitude flight requirements make airborne flux measurements particularly dangerous and well suited for unmanned aircraft.

Fladeland; Yates, Emma Louise; Bui, Thaopaul Van; Dean-Day, Jonathan; Kolyer, Richard

2011-01-01

147

Progress on a Rayleigh Scattering Mass Flux Measurement Technique  

NASA Technical Reports Server (NTRS)

A Rayleigh scattering diagnostic has been developed to provide mass flux measurements in wind tunnel flows. Spectroscopic molecular Rayleigh scattering is an established flow diagnostic tool that has the ability to provide simultaneous density and velocity measurements in gaseous flows. Rayleigh scattered light from a focused 10 Watt continuous-wave laser beam is collected and fiber-optically transmitted to a solid Fabry-Perot etalon for spectral analysis. The circular interference pattern that contains the spectral information that is needed to determine the flow properties is imaged onto a CCD detector. Baseline measurements of density and velocity in the test section of the 15 cm x 15 cm Supersonic Wind Tunnel at NASA Glenn Research Center are presented as well as velocity measurements within a supersonic combustion ramjet engine isolator model installed in the tunnel test section.

Mielke-Fagan, Amy F.; Clem, Michelle M.; Elam, Kristie A.; Hirt, Stefanie M.

2010-01-01

148

The effect of sparging rate on transmembrane pressure and critical flux in an AnMBR.  

PubMed

Anaerobic membrane bioreactors (AnMBRs) have been shown to be successful units for the treatment of low strength wastewaters, however, the issue of membrane fouling is still a major problem in terms of economic viability. Biogas sparging has been shown to reduce fouling substantially, and hence this study monitored the effect of biogas sparging rate on an AnMBR. The critical flux under a sparging rate of 6 l per minute (LPM) was found to be 11.8 l m(-2) h(-1) (LMH), however, membrane hysteresis was found to have an effect on the critical flux, and where the AnMBR had previously been operated with a 2 LPM sparging rate, the critical flux fell to 7.2 LMH. The existence of a "critical sparging rate" was also investigated under the condition that 'there exists a sparging rate beyond which any further decrease in sparging rate will cause a dramatic rise in TMP'. For an AnMBR operating at a flux of 7.2 LMH the critical sparging rate was found to be 4 LPM. PMID:25577705

Fox, R A; Stuckey, D C

2015-03-15

149

VARIABILITY IN MEASURED BEDLOAD-TRANSPORT RATES.  

USGS Publications Warehouse

During a four-day period of nearly constant water discharge, four sets of consecutively collected bedload samples, ranging from 43 to 120 samples, were obtained at the same cross channel location using a standard 65-pound Helley-Smith bedload sampler. When the measured transport rates are converted to dimensionless rates and plotted as cumulative frequency distributions, they show good agreement with a theoretical probability distribution function of rates derived for the case of ripples on dunes. The distributions show that during constant water discharge individual measured rates at a fixed point vary from near zero to four times the mean rate, and 60 percent of the sampled rates will be less than the mean.

Carey, William P.

1985-01-01

150

Imposing strong constraints on tropical terrestrial CO2 fluxes using passenger aircraft based measurements  

NASA Astrophysics Data System (ADS)

Because very few measurements of atmospheric carbon dioxide (CO2) are available in the tropics, estimates of surface CO2 fluxes in tropical regions are beset with considerable uncertainties. To improve estimates of tropical terrestrial fluxes, atmospheric CO2 inversion was performed using passenger aircraft based measurements of the Comprehensive Observation Network for Trace gases by Airliner (CONTRAIL) project in addition to the surface measurement data set of GLOBALVIEW-CO2. Regional monthly fluxes at the earth's surface were estimated using the Bayesian synthesis approach focusing on the period 2006-2008 using the Nonhydrostatic Icosahedral Atmospheric Model-based Transport Model (NICAM-TM). By adding the aircraft to the surface data, the posterior flux errors were greatly reduced; specifically, error reductions of up to 64% were found for tropical Asia regions. This strong impact is closely related to efficient vertical transport in the tropics. The optimized surface fluxes using the CONTRAIL data were evaluated by comparing the simulated atmospheric CO2 distributions with independent aircraft measurements of the Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container (CARIBIC) project. The inversion with the CONTRAIL data yields the global carbon sequestration rates of 2.22 ± 0.28 Pg C yr-1 for the terrestrial biosphere and 2.24 ± 0.27 Pg C yr-1 for the oceans (the both are adjusted by riverine input of CO2). For the first time the CONTRAIL CO2 measurements were used in an inversion system to identify the areas of greatest impact in terms of reducing flux uncertainties.

Niwa, Yosuke; Machida, Toshinobu; Sawa, Yousuke; Matsueda, Hidekazu; Schuck, Tanja J.; Brenninkmeijer, Carl A. M.; Imasu, Ryoichi; Satoh, Masaki

2012-06-01

151

A time series of benthic flux measurements from Monterey Bay, CA  

Microsoft Academic Search

In situ incubation chamber measurements of benthic nutrient recycling rates were made on the Monterey Bay shelf at 100m during various years and seasons. Variability in nutrient (Si, PO42+, NH3, NO3?) and trace metal (Mn, Fe (II), Cu) fluxes correlate with variability in the amount of organic carbon oxidized on the sea floor. Patterns of primary productivity show a mid-year

William Berelson; Jim McManus; Kenneth Coale; Ken Johnson; David Burdige; Tammy Kilgore; Debbie Colodner; Francisco Chavez; Rafael Kudela; Joceline Boucher

2003-01-01

152

Angular-Rate Estimation Using Quaternion Measurements  

NASA Technical Reports Server (NTRS)

In most spacecraft (SC) there is a need to know the SC angular rate. Precise angular rate is required for attitude determination, and a coarse rate is needed for attitude control damping. Classically, angular rate information is obtained from gyro measurements. These days, there is a tendency to build smaller, lighter and cheaper SC, therefore the inclination now is to do away with gyros and use other means and methods to determine the angular rate. The latter is also needed even in gyro equipped satellites when performing high rate maneuvers whose angular-rate is out of range of the on board gyros or in case of gyro failure. There are several ways to obtain the angular rate in a gyro-less SC. When the attitude is known, one can differentiate the attitude in whatever parameters it is given and use the kinematics equation that connects the derivative of the attitude with the satellite angular-rate and compute the latter. Since SC usually utilize vector measurements for attitude determination, the differentiation of the attitude introduces a considerable noise component in the computed angular-rate vector.

Azor, Ruth; Bar-Itzhack, Y.; Deutschmann, Julie K.; Harman, Richard R.

1998-01-01

153

The AmeriFlux Network of Long-Term CO{sub 2} Flux Measurement Stations: Methodology and Intercomparability  

SciTech Connect

A portable flux measurement system has been used within the AmeriFlux network of CO{sub 2} flux measurement stations to enhance the comparability of data collected across the network. No systematic biases were observed in a comparison between portable system and site H, LE, or CO{sub 2} flux values although there were biases observed between the portable system and site measurement of air temperature and PPFD. Analysis suggests that if values from two stations differ by greater than 26% for H, 35% for LE, and 32% for CO{sub 2} flux they are likely to be significant. Methods for improving the intercomparability of the network are also discussed.

Hollinger, D. Y.; Evans, R. S.

2003-05-20

154

System having unmodulated flux locked loop for measuring magnetic fields  

DOEpatents

A system (10) for measuring magnetic fields, wherein the system (10) comprises an unmodulated or direct-feedback flux locked loop (12) connected by first and second unbalanced RF coaxial transmission lines (16a, 16b) to a superconducting quantum interference device (14). The FLL (12) operates for the most part in a room-temperature or non-cryogenic environment, while the SQUID (14) operates in a cryogenic environment, with the first and second lines (16a, 16b) extending between these two operating environments.

Ganther, Jr., Kenneth R. (Olathe, KS); Snapp, Lowell D. (Blue Springs, MO)

2006-08-15

155

Measurement of autophagy flux in the nervous system in vivo  

PubMed Central

Accurate methods to measure autophagic activity in vivo in neurons are not available, and most of the studies are based on correlative and static measurements of autophagy markers, leading to conflicting interpretations. Autophagy is an essential homeostatic process involved in the degradation of diverse cellular components including organelles and protein aggregates. Autophagy impairment is emerging as a relevant factor driving neurodegeneration in many diseases. Moreover, strategies to modulate autophagy have been shown to provide protection against neurodegeneration. Here we describe a novel and simple strategy to express an autophagy flux reporter in the nervous system of adult animals by the intraventricular delivery of adeno-associated viruses (AAV) into newborn mice. Using this approach we efficiently expressed a monomeric tandem mCherry-GFP-LC3 construct in neurons of the peripheral and central nervous system, allowing the measurement of autophagy activity in pharmacological and disease settings. PMID:24232093

Castillo, K; Valenzuela, V; Matus, S; Nassif, M; Oñate, M; Fuentealba, Y; Encina, G; Irrazabal, T; Parsons, G; Court, F A; Schneider, B L; Armentano, D; Hetz, C

2013-01-01

156

Standardization of flux chamber and wind tunnel flux measurements for quantifying emissions from area sources at animal feeding operations  

Technology Transfer Automated Retrieval System (TEKTRAN)

A variety of wind tunnels and flux chambers have been used to measure fluxes of volatile organic compounds (VOC) and ammonia (NH3) at animal feeding operations (AFO). However, there has been little regard to the extreme variation and inaccuracy caused by inappropriate air velocity or sweep air flow...

157

Effects of measurement resolution and random measurement error on temperature based estimates of vertical stream-aquifer flux  

NASA Astrophysics Data System (ADS)

The use of temperature measurements to describe or quantify stream-aquifer interaction has received much attention within the hydrologic community. One common method to infer infiltration rates makes use of diurnal temperature fluctuations of the stream and streambed sediments. In this study a synthetic stream-aquifer interaction experiment was conducted to quantify the effects of temperature measurement resolution and measurement error on inferred vertical water fluxes using Stallman’s solution. Hydrus-1D was used to generate synthetic thermographs at multiple depths in a simulated streambed in response to a sinusoidally varying surface temperature across a range of vertical water fluxes. To simulate real instruments, these thermographs were filtered at different levels or corrupted with different levels of random error to represent ranges of reduced measurement resolution or random measurement error, respectively. As expected, the sensitivity of the temperature tracer method decreases with decreased downward or increased upward flux as well as increased depth. The study also showed that the effects of temperature measurement error and measurement resolution on estimates of vertical water fluxes have disproportionately large impacts under upward flow conditions (Fig. 1). The effects of decreased sensitivity under these flow conditions are magnified by low sensor resolution and by large sensor depths and offer very little flexibility on sensor selection and placement. Therefore, under upward flow we recommend that sensors with high measurement resolution (<0.05 °C) and medium to low uncertainty (<0.5 °C) should be used and placed within the uppermost 0.3 m of the streambed where possible. Finally, we describe how these results can be tailored to site specific parameters to improve on the experimental application of temperature as a tracer. Figure 1: [A,B] Inferred vertical flux bias with discrete thermographs and [C,D] average inferred vertical flux bias with error corrupted thermographs as a function of measurement depth and applied flux. Each panel represents a different temperature discretization interval (TDI) level or temperature error (TE) level. The white/hashed represent the region where the absolute measurement bias is greater than 10%.

Soto, C. D.; Meixner, T.; Ferre, T. A.

2010-12-01

158

Measurement of Tree Stems O2 and CO2 Fluxes -New Approach in Tree Respiration B. Hilman* and A. Angert  

E-print Network

Measurement of Tree Stems O2 and CO2 Fluxes - New Approach in Tree Respiration B. Hilman* and A are major players in the global carbon cycle and emit respired CO2 at a rate which is estimated to be about 50% of the annual gross photosynthesis rate1 . Therefore, tree respiration has an important global

Simon, Emmanuel

159

Heat flux measurements for use in physiological and clothing research.  

PubMed

Scientists use passive heat flow meters to measure body heat exchanges with the environment. In recent years, several such sensors have been developed and concerns about their proper calibration have been addressed. However, calibration methods have differed in the geometry of the heated device as well as in the heat transfer mechanism. Therefore, a comparison of calibration methods is needed in order to understand the obtained differences in calibration lines. We chose three commercially available heat flux sensors and placed them on four different heated devices: a hot plate, double hot plate, nude cylinder and a cylinder covered with a spacer material. We found differences between the calibration line of the manufacturer and our own measurements, especially when forced convection was involved as the main heat transfer mechanism. The results showed clearly that the calibration method should be chosen according to the intended purpose of use. In addition, we recommend use a thin, light heat flux sensor with good thermal conduction in human subject studies. PMID:23824222

Niedermann, R; Psikuta, A; Rossi, R M

2014-08-01

160

Comparison of buried soil sensors, surface chambers and above ground measurements of carbon dioxide fluxes  

Technology Transfer Automated Retrieval System (TEKTRAN)

Soil carbon dioxide (CO2) flux is an important component of the terrestrial carbon cycle. Accurate measurements of soil CO2 flux aids determinations of carbon budgets. In this study, we investigated soil CO2 fluxes with time and depth and above ground CO2 fluxes in a bare field. CO2 concentrations w...

161

Wintertime Air-Sea Gas Transfer Rates and Air Injection Fluxes at Station Papa in the NE Pacific  

NASA Astrophysics Data System (ADS)

In recent studies of air-sea fluxes of N2 and O2 in hurricanes, McNeil and D'Asaro (2007) used a simplified model formulation of air-sea gas flux to estimate simultaneous values of gas transfer rate, KT, and air injection flux, VT. The model assumes air-sea gas fluxes at high to extreme wind speeds can be explained by a combination of two processes: 1) air injection, by complete dissolution of small bubbles drawn down into the ocean boundary layer by turbulent currents, and 2) near-surface equilibration processes, such as occurs within whitecaps. This analysis technique relies on air-sea gas flux estimates for two gases, N2 and O2, to solve for the two model parameters, KT and VT. We present preliminary results of similar analysis of time series data collected during winter storms at Station Papa in the NE Pacific during 2003/2004. The data show a clear increase in KT and VT with increasing NCEP derived wind speeds and acoustically measured bubble penetration depth.

McNeil, C.; Steiner, N.; Vagle, S.

2008-12-01

162

Fieldable computer system for determining gamma-ray pulse-height distributions, flux spectra, and dose rates from Little Boy  

SciTech Connect

Our system consists of a LeCroy 3500 data acquisition system with a built-in CAMAC crate and eight bismuth-germanate detectors 7.62 cm in diameter and 7.62 cm long. Gamma-ray pulse-height distributions are acquired simultaneously for up to eight positions. The system was very carefully calibrated and characterized from 0.1 to 8.3 MeV using gamma-ray spectra from a variety of radioactive sources. By fitting the pulse-height distributions from the sources with a function containing 17 parameters, we determined theoretical repsonse functions. We use these response functions to unfold the distributions to obtain flux spectra. A flux-to-dose-rate conversion curve based on the work of Dimbylow and Francis is then used to obtain dose rates. Direct use of measured spectra and flux-to-dose-rate curves to obtain dose rates avoids the errors that can arise from spectrum dependence in simple gamma-ray dosimeter instruments. We present some gamma-ray doses for the Little Boy assembly operated at low power. These results can be used to determine the exposures of the Hiroshima survivors and thus aid in the establishment of radation exposure limits for the nuclear industry.

Moss, C.E.; Lucas, M.C.; Tisinger, E.W.; Hamm, M.E.

1984-01-01

163

Just Breathe Green: Measuring Transpiration Rates  

NSDL National Science Digital Library

Through multi-trial experiments, students are able to see and measure something that is otherwise invisible to them—seeing plants breathe. Student groups are given two small plants of native species and materials to enclose them after watering with colored water. After being enclosed for 5, 10 and 15 minutes, teams collect and measure the condensed water from the plants' "breathing," and then calculate the rates at which the plants breathe. A plant's breath is known as transpiration, which is the flow of water from the ground where it is taken up by roots (plant uptake) and then lost through the leaves. Students plot volume/time data for three different native plant species, determine and compare their transpiration rates to see which had the highest reaction rate and consider how a plant's unique characteristics (leaf surface area, transpiration rate) might figure into engineers' designs for neighborhood stormwater management plans.

2014-09-18

164

Ways of measuring rates of recurrent events.  

PubMed Central

Recurrent events are common in medical research, yet the best ways to measure their occurrence remain controversial. Moreover, the correct statistical techniques to compare the occurrence of such events across populations or treatment groups are not widely known. In both observational studies and randomised clinical trials one natural and intuitive measure of occurrence is the event rate, defined as the number of events (possibly including multiple events per person) divided by the total person-years of experience. This is often a more relevant and clinically interpretable measure of disease burden in a population than considering only the first event that occurs. Appropriate statistical tests to compare such event rates among treatment groups or populations require the recognition that some individuals may be especially likely to experience recurrent events. Straightforward approaches are available to account for this tendency in crude and stratified analyses. Recently developed regression models can appropriately examine the association of several variables with rates of recurrent events. PMID:8611837

Glynn, R. J.; Buring, J. E.

1996-01-01

165

Effect of wind tunnel air velocity on VOC flux rates from CAFO manure and wastewater  

Technology Transfer Automated Retrieval System (TEKTRAN)

Wind tunnels and flux chambers are often used to estimate volatile organic compound (VOC) emissions from animal feeding operations (AFOs) without regard to air velocity or sweep air flow rates. Laboratory experiments were conducted to evaluate the effect of wind tunnel air velocity on VOC emission ...

166

Segregation Effects and their Impact on Chemical Transformation Rates and Vertical Fluxes of Atmospheric Trace Constituents  

NASA Astrophysics Data System (ADS)

Results of segregation effects determined during the SANA field experiment "Eisdorf" for the chemical reactions of ozone with NO and NO2 are to be presented and their impact on the corresponding reaction rates and the vertical fluxes of these trace species are to be pointed out.

Kramm, G.; Meixner, F. X.

2002-05-01

167

Initiation of methane turbulent flux measurements over a grazed grassland in Belgium  

NASA Astrophysics Data System (ADS)

Methane fluxes emitted by a grazed meadow were measured continuously during the 2012 grazing season at the Dorinne Terrestrial Observatory (50° 18' 44" N; 4° 58' 07" E; 248 m asl.) in Belgium. Measurements were made with the eddy covariance technique, using a fast CH4 analyzer (Picarro G2311-f). Carbon dioxide fluxes (LI-7000) and various micro-meteorological and soil variables, biomass growth and stocking rate evolution were also measured at the site. The site is an intensively pastured meadow of 4.2 ha managed according to the regional usual practices where up to 30 cows are grazing simultaneously. N2O emissions are currently measured through dynamic closed chambers (Beekkerk van Ruth et al., Geophysical Research Abstracts. Vol. 15, EGU2013-3211, 2013) and the carbon budget of the site has already been investigated (Jerome et al. Geophysical Research Abstracts, Vol. 15, EGU2013-6989, 2013). As no CH4 measurements were available, CH4 fluxes were estimated on the basis of dry matter intake by the cows and a conversion factor obtained from a literature review. We want to improve this estimation by measuring CH4 fluxes, identifying their main environmental drivers and understanding diurnal and annual exchange patterns. Methane emissions were found strongly related with cattle stocking rate with a slope of 7.34±0.78 mol CH4 day-1 LSU-1. Up to now, no methane absorption has been observed, the meadow behaving as a methane emitter, even in the absence of cows. In the absence of cows, no significant relation can be established up to now between methane emissions and environmental parameters. No clear diurnal evolution is observed, neither during grazing periods nor during cow free periods. During cow presence periods, fluxes are highly variable, probably due to cow movements in and out the measurement footprint and cow digestion rhythm. Further developments are ongoing in order to improve cattle geo-localization through individual home-made GPS devices and infra-red cameras. The two systems will be compared in terms of cost, efficiency and ease of use. Key words: grassland, methane fluxes, eddy covariance, cattle emissions

Dumortier, Pierre; Aubinet, Marc; Chopin, Henri; Debacq, Alain; Jérome, Elisabeth; Beckers, Yves; Heinesch, Bernard

2013-04-01

168

Local Heat Flux Measurements with Single Element Coaxial Injectors  

NASA Technical Reports Server (NTRS)

To support the mission for the NASA Vision for Space Exploration, the NASA Marshall Space Flight Center conducted a program in 2005 to improve the capability to predict local thermal compatibility and heat transfer in liquid propellant rocket engine combustion devices. The ultimate objective was to predict and hence reduce the local peak heat flux due to injector design, resulting in a significant improvement in overall engine reliability and durability. Such analyses are applicable to combustion devices in booster, upper stage, and in-space engines, as well as for small thrusters with few elements in the injector. In this program, single element and three-element injectors were hot-fire tested with liquid oxygen and ambient temperature gaseous hydrogen propellants at The Pennsylvania State University Cryogenic Combustor Laboratory from May to August 2005. Local heat fluxes were measured in a 1-inch internal diameter heat sink combustion chamber using Medtherm coaxial thermocouples and Gardon heat flux gauges. Injectors were tested with shear coaxial and swirl coaxial elements, including recessed, flush and scarfed oxidizer post configurations, and concentric and non-concentric fuel annuli. This paper includes general descriptions of the experimental hardware, instrumentation, and results of the hot-fire testing for three of the single element injectors - recessed-post shear coaxial with concentric fuel, flush-post swirl coaxial with concentric fuel, and scarfed-post swirl coaxial with concentric fuel. Detailed geometry and test results will be published elsewhere to provide well-defined data sets for injector development and model validatation.

Jones, Gregg; Protz, Christopher; Bullard, Brad; Hulka, James

2006-01-01

169

Occurrence rates of magnetic activities and flux maintenance in quiet regions  

NASA Astrophysics Data System (ADS)

We investigate occurrence rates of magnetic activities, namely merging, splitting, cancellation, and emergence as functions of flux content in quiet regions by means of feature tracking technique. The structure of magnetic field on the solar surface is important not only because it is the but also because it is actual magneto-convection on the stellar surface which we can observe for the most details. Recent satellite observation reveals scaling nature of magnetic patches on the solar surface. Parnell et al. (2009) found a power-law distribution with an index of -1.85 for flux content in each magnetic patch and Thornton & Parnell (2011) found a power-law distribution with an index of -2.7 for flux content of emerging flux. However, it is not still understood what mechanism makes these power-law nature. We try this issue by developing auto-tracking technique and quantization of patch activities. We use two data sets of line-of-sight magnetograms by Solar Optical Telescope (SOT)/ Narrowband Filter Imager (NFI) on board Hinode satellite. One has the high temporal cadence, 1 minute, and the other has the longest observational period, 140 hours. More than 3000 and 40000 patches are tracked in the data sets, respectively. We found that the occurrence of merging and splitting is larger than those of emergence and cancellation by one-order of magnitude, which means that the frequency distribution of flux content is maintained by the surface activities not by flux supply itself. The frequency dependence of cancellation on flux amount is also investigated. We found that a power-law distribution with an index of -2.48 with an error bar of 0.24, which is same as that of emergence in Thornton & Parnell (2011). In the discussion, we want to suggest flux re-cycling in quiet regions, which can explain these characters. begin{enumerate} Frequency distribution of flux content is formed to a power-law distribution by merging and splitting on the solar surface. Transport of patches of surface convection results in steep power-law distribution of flux content of cancellation. The submerged fluxes though cancellations re-appear to the solar surface, which results in small-scale flux emergences on the solar surface.

Iida, Yusuke

170

Measuring Degradation Rates Without Irradiance Data  

SciTech Connect

A method to report PV system degradation rates without using irradiance data is demonstrated. First, a set of relative degradation rates are determined by comparing daily AC final yields from a group of PV systems relative to the average final yield of all the PV systems. Then, the difference between relative and absolute degradation rates is found from a statistical analysis. This approach is verified by comparing to methods that utilize irradiance data. This approach is significant because PV systems are often deployed without irradiance sensors, so the analysis method described here may enable measurements of degradation using data that were previously thought to be unsuitable for degradation studies.

Pulver, S.; Cormode, D.; Cronin, A.; Jordan, D.; Kurtz, S.; Smith, R.

2011-02-01

171

Measuring star formation rates in blue galaxies  

NASA Technical Reports Server (NTRS)

The problems associated with measurements of star formation rates in galaxies are briefly reviewed, and specific models are presented for determinations of current star formation rates from H alpha and Far Infrared (FIR) luminosities. The models are applied to a sample of optically blue irregular galaxies, and the results are discussed in terms of star forming histories. It appears likely that typical irregular galaxies are forming stars at nearly constant rates, although a few examples of systems with enhanced star forming activity are found among HII regions and luminous irregular galaxies.

Gallagher, John S., III; Hunter, Deidre A.

1987-01-01

172

Comparative soil CO2 flux measurements and geostatistical estimation methods on Masaya volcano, Nicaragua  

USGS Publications Warehouse

We present a comparative study of soil CO2 flux (FCO2) measured by five groups (Groups 1-5) at the IAVCEI-CCVG Eighth Workshop on Volcanic Gases on Masaya volcano, Nicaragua. Groups 1-5 measured (FCO2) using the accumulation chamber method at 5-m spacing within a 900 m2 grid during a morning (AM) period. These measurements were repeated by Groups 1-3 during an afternoon (PM) period. Measured (FCO2 ranged from 218 to 14,719 g m-2 day-1. The variability of the five measurements made at each grid point ranged from ??5 to 167%. However, the arithmetic means of fluxes measured over the entire grid and associated total CO2 emission rate estimates varied between groups by only ??22%. All three groups that made PM measurements reported an 8-19% increase in total emissions over the AM results. Based on a comparison of measurements made during AM and PM times, we argue that this change is due in large part to natural temporal variability of gas flow, rather than to measurement error. In order to estimate the mean and associated CO2 emission rate of one data set and to map the spatial FCO2 distribution, we compared six geostatistical methods: Arithmetic and minimum variance unbiased estimator means of uninterpolated data, and arithmetic means of data interpolated by the multiquadric radial basis function, ordinary kriging, multi-Gaussian kriging, and sequential Gaussian simulation methods. While the total CO2 emission rates estimated using the different techniques only varied by ??4.4%, the FCO2 maps showed important differences. We suggest that the sequential Gaussian simulation method yields the most realistic representation of the spatial distribution of FCO2, but a variety of geostatistical methods are appropriate to estimate the total CO2 emission rate from a study area, which is a primary goal in volcano monitoring research. ?? Springer-Verlag 2005.

Lewicki, J.L.; Bergfeld, D.; Cardellini, C.; Chiodini, G.; Granieri, D.; Varley, N.; Werner, C.

2005-01-01

173

Interplanetary dust fluxes measurements using the Waves instrument on STEREO  

NASA Astrophysics Data System (ADS)

Dust particles provide an important fraction of the matter composing the interplanetary medium, their mass density at 1 A.U. being comparable to the one of the solar wind. The impact of a dust particle on a spacecraft produces a plasma cloud whose associated electric field is detected by the on-board electric antennas. The signal measured by the wave instruments thus reveals the dust properties. We analyse the dust particle impacts on the STEREO spacecraft during the 2007-2010 period. We use the TDS waveform sampler of the STEREO/WAVES instrument, which enables us to deduce considerably more informations than in a previous study based on the LFR spectral analyzer [Meyer-Vernet et al., 2009]. We observe two distinct populations of dust that we infer to be nano and micron sized dust particles and we derive their fluxes at 1 AU and the evolution of these fluxes with time (and solar longitude). The observations are also in accord with the dynamics of nanometer-sized and micrometer-sized dust particles in the interplanetary medium.

Zaslavsky, A.; Meyer-Vernet, N.; Mann, I.; Czechowski, A.; Issautier, K.; Le Chat, G.; Maksimovic, M.; Kasper, J. C.

2010-12-01

174

Measurements for the JASPER Program Flux Monitor Experiment  

SciTech Connect

The Flux Monitor Experiment was conducted at the Oak Ridge National Laboratory (ORNL) Tower Shielding Facility (TSF) during the months of May and June 1992, as part of the continuing series of eight experiments planned for the Japanese-American Shielding Program for Experimental Research (JASPER) program that was started in 1986. This series of experiments was designed to examine shielding concerns and radiation transport effects pertaining to in-vessel flux monitoring systems (FMS) in current reactor shield designs proposed for both the Advanced Liquid Metal Reactor (ALMR) design and the Japanese loop-type design. The program is a cooperative effort between the United States Department of Energy (US DOE) and the Japanese Power Reactor and Nuclear Fuel Development Corporation (PNC). The Tower Shielding Reactor H (TSR-II) neutron source was altered by the spectrum modifier (SM) used previously in the Axial Shield Experiment, and part of the Japanese Removable Radial Shield (RRS) before reaching the axial shield. In the axial shield were placed six homogeneous boron carbide (B{sub 4}C) hexagons around a center hexagon of aluminum used to represent sodium. Shield designs to be studied were placed beyond the axial shield, each design forming a void directly behind the axial shield. Measurements were made in the void and behind each slab as successive slabs were added.

Muckenthaler, F.J.; Spencer, R.R.; Hunter, H.T.; Hull, J.L. [Oak Ridge National Lab., TN (United States); Shono, A. [Power Reactor and Nuclear Fuel Development Corp., Oarai, Ibaraki (Japan). Oarai Engineering Center

1993-02-01

175

Direct measurement of the 7Be solar neutrino flux with 192 days of borexino data.  

PubMed

We report the direct measurement of the 7Be solar neutrino signal rate performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso. The interaction rate of the 0.862 MeV 7Be neutrinos is 49+/-3stat+/-4syst counts/(day.100 ton). The hypothesis of no oscillation for 7Be solar neutrinos is inconsistent with our measurement at the 4sigma C.L. Our result is the first direct measurement of the survival probability for solar nu(e) in the transition region between matter-enhanced and vacuum-driven oscillations. The measurement improves the experimental determination of the flux of 7Be, pp, and CNO solar nu(e), and the limit on the effective neutrino magnetic moment using solar neutrinos. PMID:18851600

Arpesella, C; Back, H O; Balata, M; Bellini, G; Benziger, J; Bonetti, S; Brigatti, A; Caccianiga, B; Cadonati, L; Calaprice, F; Carraro, C; Cecchet, G; Chavarria, A; Chen, M; Dalnoki-Veress, F; D'Angelo, D; de Bari, A; de Bellefon, A; de Kerret, H; Derbin, A; Deutsch, M; di Credico, A; di Pietro, G; Eisenstein, R; Elisei, F; Etenko, A; Fernholz, R; Fomenko, K; Ford, R; Franco, D; Freudiger, B; Galbiati, C; Gatti, F; Gazzana, S; Giammarchi, M; Giugni, D; Goeger-Neff, M; Goldbrunner, T; Goretti, A; Grieb, C; Hagner, C; Hampel, W; Harding, E; Hardy, S; Hartman, F X; Hertrich, T; Heusser, G; Ianni, Aldo; Ianni, Andrea; Joyce, M; Kiko, J; Kirsten, T; Kobychev, V; Korga, G; Korschinek, G; Kryn, D; Lagomarsino, V; Lamarche, P; Laubenstein, M; Lendvai, C; Leung, M; Lewke, T; Litvinovich, E; Loer, B; Lombardi, P; Ludhova, L; Machulin, I; Malvezzi, S; Manecki, S; Maneira, J; Maneschg, W; Manno, I; Manuzio, D; Manuzio, G; Martemianov, A; Masetti, F; Mazzucato, U; McCarty, K; McKinsey, D; Meindl, Q; Meroni, E; Miramonti, L; Misiaszek, M; Montanari, D; Monzani, M E; Muratova, V; Musico, P; Neder, H; Nelson, A; Niedermeier, L; Oberauer, L; Obolensky, M; Orsini, M; Ortica, F; Pallavicini, M; Papp, L; Parmeggiano, S; Perasso, L; Pocar, A; Raghavan, R S; Ranucci, G; Rau, W; Razeto, A; Resconi, E; Risso, P; Romani, A; Rountree, D; Sabelnikov, A; Saldanha, R; Salvo, C; Schimizzi, D; Schönert, S; Shutt, T; Simgen, H; Skorokhvatov, M; Smirnov, O; Sonnenschein, A; Sotnikov, A; Sukhotin, S; Suvorov, Y; Tartaglia, R; Testera, G; Vignaud, D; Vitale, S; Vogelaar, R B; von Feilitzsch, F; von Hentig, R; von Hentig, T; Wojcik, M; Wurm, M; Zaimidoroga, O; Zavatarelli, S; Zuzel, G

2008-08-29

176

Chamber and Diffusive Based Carbon Flux Measurements in an Alaskan Arctic Ecosystem  

NASA Astrophysics Data System (ADS)

Eric Wilkman, Walter Oechel, Donatella Zona Comprising an area of more than 7 x 106 km2 and containing over 11% of the world's organic matter pool, Arctic terrestrial ecosystems are vitally important components of the global carbon cycle, yet their structure and functioning are sensitive to subtle changes in climate and many of these functional changes can have large effects on the atmosphere and future climate regimes (Callaghan & Maxwell 1995, Chapin et al. 2002). Historically these northern ecosystems have acted as strong C sinks, sequestering large stores of atmospheric C due to photosynthetic dominance in the short summer season and low rates of decomposition throughout the rest of the year as a consequence of cold, nutrient poor, and generally water-logged conditions. Currently, much of this previously stored carbon is at risk of loss to the atmosphere due to accelerated soil organic matter decomposition in warmer future climates (Grogan & Chapin 2000). Although there have been numerous studies on Arctic carbon dynamics, much of the previous soil flux work has been done at limited time intervals, due to both the harshness of the environment and labor and time constraints. Therefore, in June of 2013 an Ultraportable Greenhouse Gas Analyzer (UGGA - Los Gatos Research Inc.) was deployed in concert with the LI-8100A Automated Soil Flux System (LI-COR Biosciences) in Barrow, AK to gather high temporal frequency soil CO2 and CH4 fluxes from a wet sedge tundra ecosystem. An additional UGGA in combination with diffusive probes, installed in the same location, provides year-round soil and snow CO2 and CH4 concentrations. When used in combination with the recently purchased AlphaGUARD portable radon monitor (Saphymo GmbH), continuous soil and snow diffusivities and fluxes of CO2 and CH4 can be calculated (Lehmann & Lehmann 2000). Of particular note, measuring soil gas concentration over a diffusive gradient in this way allows one to separate both net production and consumption, whereas chamber and eddy covariance methodologies only document net production from the surface. Also, the capability to measure spring, summer and fall chamber fluxes, and to continuously determine year-round CO2 and CH4 fluxes under even the most extreme weather conditions, allows an unprecedented level of data continuity and local spatial coverage. Comparison to a nearby eddy covariance tower measuring CO2 and CH4 fluxes with an LGR Fast Greenhouse Gas Analyzer add additional power to this set of measurements. Thus, inter-comparison between diffusive, chamber, and tower-based carbon fluxes should lend much insight into the spatial and temporal controls on carbon cycling in this ecosystem.

Wilkman, E.; Oechel, W. C.; Zona, D.

2013-12-01

177

Evidence for electron neutrino flavor change through measurement of the (8)B solar neutrino flux at the Sudbury Neutrino Observatory  

NASA Astrophysics Data System (ADS)

The Sudbury Neutrino Observatory (SNO) is a water Cerenkov detector designed to study solar neutrinos. Using 1 kiloton of heavy water as the target and detection medium, SNO is able to separately determine the flux of electron neutrinos (?e) and the flux of all active neutrinos from the Sun by measuring the rate of charged current (CC) and neutral current (NC) interactions with deuterons. A comparison of these interaction rates allows for direct observation of solar neutrino oscillations. SNO can also search for oscillations by comparing the rate of CC and neutrino- electron elastic scattering (ES) events, since ES has both charged current and neutral current sensitivity. In this thesis, we present measurement of the 8B solar ? e flux of 1.78+0.13-0.14 (stat+syst) × 106cm-2s -1 (35% BP2000 SSM) through measurement of the CC rate over 169.3 days of livetime. We have also measured the 8B flux from the ES reaction to be 2.56+0.48-0.45 (stat+syst), consistent with measurements by previous water Cerenkov experiments. A flavor analysis comparing the CC measured flux with that determined through ES by SuperKamiokande yields a non- ?e active neutrino flux from 8B of 3.62+1.06-1.08 × 106cm-2s-1 , providing evidence for ?e --> ? ?,? oscillations as a solution to the solar neutrino problem. This result excludes pure solar ?e --> ? s oscillations at greater than the 99.7% C.I. The total active 8B neutrino flux has been measured to be 5.39+1.07-1.09 × 106cm-2s-1 , consistent with BP2000 SSM predictions. First analyses of the CC (NHit) spectrum and hep flux in SNO are presented. The CC spectrum is found to be a good fit to expectations from an undistorted 8B spectrum, and global best fit vacuum oscillation solutions are disfavored over the other solutions by the data. Through observations near the 8B endpoint with consideration of energy systematics, hep flux limits of 4.1 (90% C.I.) and 6.9 (99% C.I.) times SSM expectations are obtained. A statistical fit for the hep flux signal yields a 3? upper limit of 3.2 times the SSM expected flux.

Neubauer, Mark Stephen

2001-11-01

178

Measuring fluxes of mineral nutrients and toxicants in plants with radioactive tracers.  

PubMed

Unidirectional influx and efflux of nutrients and toxicants, and their resultant net fluxes, are central to the nutrition and toxicology of plants. Radioisotope tracing is a major technique used to measure such fluxes, both within plants, and between plants and their environments. Flux data obtained with radiotracer protocols can help elucidate the capacity, mechanism, regulation, and energetics of transport systems for specific mineral nutrients or toxicants, and can provide insight into compartmentation and turnover rates of subcellular mineral and metabolite pools. Here, we describe two major radioisotope protocols used in plant biology: direct influx (DI) and compartmental analysis by tracer efflux (CATE). We focus on flux measurement of potassium (K(+)) as a nutrient, and ammonia/ammonium (NH3/NH4(+)) as a toxicant, in intact seedlings of the model species barley (Hordeum vulgare L.). These protocols can be readily adapted to other experimental systems (e.g., different species, excised plant material, and other nutrients/toxicants). Advantages and limitations of these protocols are discussed. PMID:25177829

Coskun, Devrim; Britto, Dev T; Hamam, Ahmed M; Kronzucker, Herbert J

2014-01-01

179

The measurable heat flux that accompanies active transport Dick Bedeauxw and Signe Kjelstrupw  

E-print Network

The measurable heat flux that accompanies active transport by Ca2+ -ATPase Dick Bedeauxw and Signe of the fluxes far from global equilibrium. An asymmetric set of transport coefficients is obtained, by assuming how the measurable heat flux and the heat production under isothermal conditions, as well

Kjelstrup, Signe

180

Standardization of flux chambers and wind tunnels for area source emission measurements at animal feeding operations  

Technology Transfer Automated Retrieval System (TEKTRAN)

Researchers and practitioners have used many varied designs of wind tunnels and flux chambers to measure the flux of volatile organic compounds, odor, and ammonia from area sources at animal feeding operations. The measured fluxes are used to estimate emission factors or compare treatments. We sho...

181

Applying thermodynamics constraints to the model achieves higher growth rates and flux efficiency while still adhering to  

E-print Network

· Applying thermodynamics constraints to the model achieves higher growth rates and flux efficiency RHA1 that Accounts for Thermodynamics Constraints Timothy Cheung, Mohammad Tajparast, Dominic Frigon Optimize: Z=c.v Subject to: Flux Balance and i vi i Flux Balance Analysis (FBA) Thermodynamics

Barthelat, Francois

182

Air/water subchannel measurements of the equilibrium quality and mass-flux distribution in a rod bundle. [BWR  

SciTech Connect

Subchannel measurements were performed in order to determine the equilibrium quality and mass flux distribution in a four rod bundle, using air/water flow. An isokinetic technique was used to sample the flow in the center, side and corner subchannels of this test section. Flow rates of the air and water in each sampled subchannel were measured. Experiments were performed for two test-section-average mass fluxes (0.333x10/sup 6/ and 0.666x10/sup 6/ lb/sub m//h-ft/sup 2/), and the test-section-average quality was varied from 0% to 0.54% for each mass flux. Single-phase liquid, bubbly, slug and churn-turbulent two-phase flow regimes were achieved. The observed data trends agreed with previous diabatic measurements in which the center subchannel had the highest quality and mass flux, while the corner subchannel had the lowest.

Sterner, R.W.; Lahey, R.T. Jr.

1983-07-01

183

Measurement of particulate matter emission fluxes from a beef cattle feedlot using Flux-gradient technique  

Technology Transfer Automated Retrieval System (TEKTRAN)

Data on air emissions from open-lot beef cattle feedlots are limited. This research was conducted to determine PM10 emission fluxes from a commercial beef cattle feedlot in Kansas using the flux-gradient technique, a widely-used micrometeorological method for gaseous emissions from open sources. V...

184

Optimization of magnetic flux density measurement using multiple RF receiver coils and multi-echo in MREIT  

NASA Astrophysics Data System (ADS)

Magnetic Resonance Electrical Impedance Tomography (MREIT) is an MRI method that enables mapping of internal conductivity and/or current density via measurements of magnetic flux density signals. The MREIT measures only the z-component of the induced magnetic flux density B = (Bx, By, Bz) by external current injection. The measured noise of Bz complicates recovery of magnetic flux density maps, resulting in lower quality conductivity and current-density maps. We present a new method for more accurate measurement of the spatial gradient of the magnetic flux density gradient (? Bz). The method relies on the use of multiple radio-frequency receiver coils and an interleaved multi-echo pulse sequence that acquires multiple sampling points within each repetition time. The noise level of the measured magnetic flux density Bz depends on the decay rate of the signal magnitude, the injection current duration, and the coil sensitivity map. The proposed method uses three key steps. The first step is to determine a representative magnetic flux density gradient from multiple receiver coils by using a weighted combination and by denoising the measured noisy data. The second step is to optimize the magnetic flux density gradient by using multi-echo magnetic flux densities at each pixel in order to reduce the noise level of ? Bz and the third step is to remove a random noise component from the recovered ? Bz by solving an elliptic partial differential equation in a region of interest. Numerical simulation experiments using a cylindrical phantom model with included regions of low MRI signal to noise (‘defects’) verified the proposed method. Experimental results using a real phantom experiment, that included three different kinds of anomalies, demonstrated that the proposed method reduced the noise level of the measured magnetic flux density. The quality of the recovered conductivity maps using denoised ? Bz data showed that the proposed method reduced the conductivity noise level up to 3-4 times at each anomaly region in comparison to the conventional method.

Jeong, Woo Chul; Chauhan, Munish; Sajib, Saurav Z. K.; Kim, Hyung Joong; Serša, Igor; In Kwon, Oh; Woo, Eung Je

2014-09-01

185

Energetic ion diagnostics using neutron flux measurements during pellet injection  

SciTech Connect

Neutron measurements during injection of deuterium pellets into deuterium plasmas on the Tokamak Fusion Test Reactor (TFTR) indicate that the fractional increase in neutron emission about 0.5 msec after pellet injection is proportional to the fraction of beam-plasma reactions to total fusion reactions in the unperturbed plasma. These observations suggest three diagnostic applications of neutron measurements during pellet injection: (1) measurement of the beam-plasma reaction rate in deuterium plasmas for use in determining the fusion Q in an equivalent deuterium-tritium plasma, (2) measurement of the radial profile of energetic beam ions by varying the pellet size and velocity, and (3) measurement of the ''temperature'' of ions accelerated during wave heating. 18 refs., 3 figs.

Heidbrink, W.W.

1986-01-01

186

A high sensitivity momentum flux measuring instrument for plasma thruster exhausts and diffusive plasmas  

SciTech Connect

A high sensitivity momentum flux measuring instrument based on a compound pendulum has been developed for use with electric propulsion devices and radio frequency driven plasmas. A laser displacement system, which builds upon techniques used by the materials science community for surface stress measurements, is used to measure with high sensitivity the displacement of a target plate placed in a plasma thruster exhaust. The instrument has been installed inside a vacuum chamber and calibrated via two different methods and is able to measure forces in the range of 0.02-0.5 mN with a resolution of 15 {mu}N. Measurements have been made of the force produced from the cold gas flow and with a discharge ignited using argon propellant. The plasma is generated using a Helicon Double Layer Thruster prototype. The instrument target is placed about 1 mean free path for ion-neutral charge exchange collisions downstream of the thruster exit. At this position, the plasma consists of a low density ion beam (10%) and a much larger downstream component (90%). The results are in good agreement with those determined from the plasma parameters measured with diagnostic probes. Measurements at various flow rates show that variations in ion beam velocity and plasma density and the resulting momentum flux can be measured with this instrument. The instrument target is a simple, low cost device, and since the laser displacement system used is located outside the vacuum chamber, the measurement technique is free from radio frequency interference and thermal effects. It could be used to measure the thrust in the exhaust of other electric propulsion devices and the momentum flux of ion beams formed by expanding plasmas or fusion experiments.

West, Michael D.; Charles, Christine; Boswell, Rod W. [Space Plasma, Power and Propulsion Group, Research School of Physics and Engineering, Australian National University, Canberra ACT 0200 (Australia)

2009-05-15

187

A high sensitivity momentum flux measuring instrument for plasma thruster exhausts and diffusive plasmas  

NASA Astrophysics Data System (ADS)

A high sensitivity momentum flux measuring instrument based on a compound pendulum has been developed for use with electric propulsion devices and radio frequency driven plasmas. A laser displacement system, which builds upon techniques used by the materials science community for surface stress measurements, is used to measure with high sensitivity the displacement of a target plate placed in a plasma thruster exhaust. The instrument has been installed inside a vacuum chamber and calibrated via two different methods and is able to measure forces in the range of 0.02-0.5mN with a resolution of 15?N. Measurements have been made of the force produced from the cold gas flow and with a discharge ignited using argon propellant. The plasma is generated using a Helicon Double Layer Thruster prototype. The instrument target is placed about 1 mean free path for ion-neutral charge exchange collisions downstream of the thruster exit. At this position, the plasma consists of a low density ion beam (10%) and a much larger downstream component (90%). The results are in good agreement with those determined from the plasma parameters measured with diagnostic probes. Measurements at various flow rates show that variations in ion beam velocity and plasma density and the resulting momentum flux can be measured with this instrument. The instrument target is a simple, low cost device, and since the laser displacement system used is located outside the vacuum chamber, the measurement technique is free from radio frequency interference and thermal effects. It could be used to measure the thrust in the exhaust of other electric propulsion devices and the momentum flux of ion beams formed by expanding plasmas or fusion experiments.

West, Michael D.; Charles, Christine; Boswell, Rod W.

2009-05-01

188

The Design of a Calorimeter to Measure Concentrated Solar Flux  

NASA Astrophysics Data System (ADS)

A water-cooled, cavity calorimeter was designed to accurately measure concentrated solar thermal power produced by the University of Minnesota's solar simulator. The cavity is comprised of copper tubing bent into spiral and helical coils for the base and cylindrical walls, respectively. Insulation surrounds the cavity to reduce heat transfer to the ambient, and a water- cooled aperture cover is positioned at the open end of the cavity. The calorimeter measures the heat gain of water flowing through the system as radiant energy is passed through the aperture. Chilled water flows through the tubing, and the energy incident on the cavity surface is conducted through the wall and convected to the flowing water. The energy increase in the water can be observed by an increase in fluid temperature. A Monte Carlo ray tracing method is used to predict the incident flux distribution and corresponding power on the surfaces of the cavity. These values are used to estimate the thermal losses of the system, and it is found that they account for less that 1% of the total power passed through the aperture. The overall uncertainty of the calorimeter is found by summing the measured uncertainty and the estimated heat loss and is found to be +/-2.5% for 9.2 kW of power output and +/-3.4% for 3 kW.

Sefkow, Elizabeth Anne Bennett

189

Effect on Autochamber Flux Measurements in an Ombrotrophic Peatland from Atmospheric Turbulence and Deployment Time  

NASA Astrophysics Data System (ADS)

Accurate quantification of soil-atmosphere gas exchange is essential for understanding the magnitude and controls of soil respiration as well as modelling the effects of various perturbations on soil carbon dynamics. We investigated the influence of atmospheric turbulence and chamber deployment time on CO2 and CH4 fluxes measured by closed, dynamic automatic chambers in the ombrotrophic Mer Bleue peatland near Ottawa, Canada. With a short deployment time of 2.5 minutes, autochamber CH4 flux exhibited a strong diurnal pattern that was highly and negatively correlated with friction velocity. We also found a significant, negative relationship between friction velocity and CO2 concentration gradient in the top 20 cm surface peat. This demonstrated a mass flow of gas from peat pore space to the atmosphere under highly turbulent conditions. Consequently, it is hypothesized that the transient low gas fluxes obtained could be due to insufficient time allowed for re-establishment of a diffusive concentration gradient with short duration deployment. On the other hand, the high CO2 and CH4 effluxes measured under calm conditions were possibly artefacts of chamber closure and headspace mixing by fans that enhanced near surface gas emissions when concentration gradients were large. Results of a test with a 30-minute deployment time showed that CO2 and CH4 efflux rates reached a constant rate after about 13 minutes of chamber closure. Methane fluxes calculated using the headspace concentration after this duration had no significant relationship with friction velocity and exhibited little diurnal variation. The above results suggest there is considerable potential bias in chamber flux measurements under both high and low turbulence conditions when sampling porous soils with a short deployment time. This bias is expected to be of particular concern in ecosystems with highly porous and aerated soils like those at Mer Bleue which has a relatively low water table (30 cm or more) and a peat soil with a porosity of more than 94% in the top 30 cm though we suspect it also exists to a lesser extent in other less porous soils. In these situations, the time required to reach a steady rate of increase in headspace concentration should be determined for each site to minimize bias in calculated fluxes.

Lai, D.; Roulet, N. T.; Dalva, M.; Humphreys, E. R.; Moore, T. R.

2010-12-01

190

Nonlinear Dependency of Intracellular Fluxes on Growth Rate in Miniaturized Continuous Cultures of Escherichia coli†  

PubMed Central

A novel mini-scale chemostat system was developed for the physiological characterization of 10-ml cultures. The parallel operation of eight such mini-scale chemostats was exploited for systematic 13C analysis of intracellular fluxes over a broad range of growth rates in glucose-limited Escherichia coli. As expected, physiological variables changed monotonously with the dilution rate, allowing for the assessment of maintenance metabolism. Despite the linear dependence of total cellular carbon influx on dilution rate, the distribution of almost all major fluxes varied nonlinearly with dilution rate. Most prominent were the distinct maximum of glyoxylate shunt activity and the concomitant minimum of tricarboxylic acid cycle activity at low to intermediate dilution rates of 0.05 to 0.2 h?1. During growth on glucose, this glyoxylate shunt activity is best understood from a network perspective as the recently described phosphoenolpyruvate (PEP)-glyoxylate cycle that oxidizes PEP (or pyruvate) to CO2. At higher or extremely low dilution rates, in vivo PEP-glyoxylate cycle activity was low or absent. The step increase in pentose phosphate pathway activity at around 0.2 h?1 was not related to the cellular demand for the reduction equivalent NADPH, since NADPH formation was 20 to 50% in excess of the anabolic demand at all dilution rates. The results demonstrate that mini-scale continuous cultivation enables quantitative and parallel characterization of intra- and extracellular phenotypes in steady state, thereby greatly reducing workload and costs for stable-isotope experiments. PMID:16461663

Nanchen, Annik; Schicker, Alexander; Sauer, Uwe

2006-01-01

191

Controls on Flux Rates of Dissolved Gaseous Mercury Emitted from an Estuarine Water Column to the Atmosphere in Eastern New Jersey.  

NASA Astrophysics Data System (ADS)

The emission rate of mercury from a water surface is influenced by a matrix of water quality parameters, including dissolved organic material (DOM), incident radiation, pH, salinity, and dissolved oxygen. As part of a larger project examining the total flux of dissolved gaseous mercury (DGM) from water, land, and plant surfaces, this work attempts to characterize the variables that control the emission of mercury from a estuarine water surface. The project's principal field site is a long recognized site of historic mercury contamination, the Ventron/Velsicol Superfund site located near the headwaters of Berry's Creek in eastern New Jersey. A number of field sites were selected longitudinally along a gradient of aqueous mercury concentration, DOM concentration, and salinity. Mercury fluxes at one site were measured over a continuous 55-hour period using flux chambers and field portable mercury analyzers, including those that measure absorbance (Mercury Instruments UT-3000) and those that measure fluorescence (Tekran). Here we report on fluxes of mercury from the water column as a function of water quality parameters. Measured mercury flux rates from the water surface ranged from near zero to almost 70 ng/m2/h. During the daytime, flux rates covaried positively with incoming solar radiation, with best fits approximated by a logarithmic relationship. Surprisingly, the highest mercury flux rates were observed at night. Nighttime fluxes appear to occur after a transition from daytime dissolved oxygen oversaturated conditions due to algal photosynthesis, to lower dissolved oxygen at nighttime. Clear relations between mercury flux rate and turbidity, pH, temperature, and salinity were not observed. Regionally elevated mercury concentrations may be sourced from this site, as the atmospheric mercury concentration measured 2m above the water surface varied inversely with windspeed. Maximum flux rates decreased with distance downstream, from near 70 ng/m2/h adjacent to the Superfund site to ~30-40 ng/m2/h approximately 3 km downstream. The comparison of fluorescence and absorbance analytical techniques was favorable, with a correlation coefficient greater than 0.90 on parallel simultaneous measurements.

Peters, S.; Wollenberg, J.

2006-12-01

192

The effect of cumulus cloud field anisotropy on solar radiative fluxes and atmospheric heating rates  

NASA Astrophysics Data System (ADS)

The effect of fair-weather cumulus cloud field anisotropy on domain average surface fluxes and atmospheric heating profiles was studied. Causes of anisotropy were investigated using a large-eddy simulation (LES) model. Cloud formation under a variety of environmental conditions was simulated and the degree of anisotropy in the output fields was calculated. Wind shear was found to be the single greatest factor in the development of both vertically tilted and horizontally stretched cloud structures. A stochastic field generation algorithm was used to produce twenty three-dimensional liquid water content fields based on the statistical properties of the LES cloud scenes. Progressively greater degrees of tilt and stretching were imposed on each of these scenes, so that an ensemble of scenes were produced for each level of distortion. The resulting scenes were used as input to a three-dimensional Monte Carlo model. Domain-average transmission, reflection, and absorption of broadband solar radiation were computed for each scene along with the average heating rate profile. Both tilt and horizontal stretching were found to significantly affect calculated fluxes, with the amount and sign of flux differences depending strongly on sun position relative to cloud distortion geometry. For nearly all solar geometries, domain-averaged fluxes and atmospheric heating rate profiles calculated using the Independent Pixel Approximation differed substantially from the corresponding three-dimensional Monte Carlo results.

Hinkelman, Laura M.

193

Weighted mean method for eddy covariance flux measurement  

NASA Astrophysics Data System (ADS)

The study to monitor the exchange of energy, water vapor and carbon dioxide between the atmosphere and terrestrial ecosystem has been carried out with eddy covariance method throughout the world. The monitored exchange quantity, named flux F , is conventionally determined by a mean of 1 hr or 30 min interval because no technique have been fortified to directly measure a momentary F itself at an instant of time. Therefore, the posterior analysis with this sampling should be paid attention to those spatial or temporal averaging and summation in the consideration of the sampling uncertainty. In particular, the averaging calcurated by arithmetic mean Fa might be inappropriate because the sample F used in this averaging has nonidentical inherent quality within one another according to different micrometeorological and ecophysiological conditions while those are observed under the same instruments. To overcome this issue, we propose the weighted mean Fw using a relative sampling error estimated by a sampling F and its error, and introduce Fw performance tested with EC measurements for 3 years at tangerine orchard.

Kim, W.; Cho, J.; Seo, H.; Oki, T.

2013-12-01

194

Effect of magnetic field strength on deposition rate and energy flux in a dc magnetron sputtering system  

SciTech Connect

Variations in the magnetic field strongly affect the plasma parameters in a magnetron sputtering system. This in turn affects the throughput as well as the energy flux to the substrate. The variation in the magnetic field in this study, for a dc magnetron process, is achieved by shifting the magnet assembly slightly away from the target. Measurements of the plasma parameters show that while the electron density at the substrate increases with decrease in magnetic field, the electron temperature decreases. The cooling of the electron temperature is consistent with results reported elsewhere. The deposition rate per input magnetron power is found to increase slightly with the decrease in magnetic field for the process conditions considered in this study. Results suggest that the energy flux to the substrate tends to show a general decrease with the shift in the magnet assembly.

Ekpe, Samuel D.; Jimenez, Francisco J.; Field, David J.; Davis, Martin J.; Dew, Steven K. [Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta T6G 2V4 (Canada); NUCRYST Pharmaceuticals, 10102-114 st., Fort Saskatchewan, Alberta T8L 3W4 (Canada); Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta T6G 2V4 (Canada)

2009-11-15

195

MEASURING TINY MASS ACCRETION RATES ONTO YOUNG BROWN DWARFS  

SciTech Connect

We present low-resolution Keck I/LRIS spectra spanning from 3200 to 9000 A of nine young brown dwarfs and three low-mass stars in the TW Hya Association and in Upper Sco. The optical spectral types of the brown dwarfs range from M5.5 to M8.75, though two have near-IR spectral types of early L dwarfs. We report new accretion rates derived from excess Balmer continuum emission for the low-mass stars TW Hya and Hen 3-600A and the brown dwarfs 2MASS J12073347-3932540, UScoCTIO 128, SSSPM J1102-3431, USco J160606.29-233513.3, DENIS-P J160603.9-205644, and Oph J162225-240515B, and upper limits on accretion for the low-mass star Hen 3-600B and the brown dwarfs UScoCTIO 112, Oph J162225-240515A, and USco J160723.82-221102.0. For the six brown dwarfs in our sample that are faintest at short wavelengths, the accretion luminosity or upper limit is measurable only when the image is binned over large wavelength intervals. This method extends our sensitivity to accretion rate down to {approx}10{sup -13} M{sub sun}yr{sup -1} for brown dwarfs. Since the ability to measure an accretion rate from excess Balmer continuum emission depends on the contrast between excess continuum emission and the underlying photosphere, for objects with earlier spectral types the upper limit on accretion rate is much higher. Absolute uncertainties in our accretion rate measurements of {approx}3-5 include uncertainty in accretion models, brown dwarf masses, and distance. The accretion rate of 2 x 10{sup -12} M {sub sun} yr{sup -1} onto 2MASS J12073347-3932540 is within 15% of two previous measurements, despite large changes in the H{alpha} flux.

Herczeg, Gregory J.; Cruz, Kelle L.; Hillenbrand, Lynne A., E-mail: gregoryh@mpe.mpg.de

2009-05-10

196

Heat flux measured acoustically at Grotto Vent, a hydrothermal vent cluster on the Endeavour Segment, Juan de Fuca Ridge  

NASA Astrophysics Data System (ADS)

Over the past several decades, quantifying the heat output has been a unanimous focus of studies at hydrothermal vent fields discovered around the global ocean. Despite their importance, direct measurements of hydrothermal heat flux are very limited due to the remoteness of most vent sites and the complexity of hydrothermal venting. Moreover, almost all the heat flux measurements made to date are snapshots and provide little information on the temporal variation that is expected from the dynamic nature of a hydrothermal system. The Cabled Observatory Vent Imaging Sonar (COVIS, https://sites.google.com/a/uw.edu/covis/) is currently connected to the Endeavour node of the NEPTUNE Canada observatory network (http://www.neptunecanada.ca) to monitor the hydrothermal plumes issuing from a vent cluster (Grotto) on the Endeavour Segment of the Juan de Fuca Ridge. COVIS is acquiring a long-term (20-months to date) time series of the vertical flow rate and volume flux of the hydrothermal plume above Grotto through the Doppler analysis of the acoustic backscatter data (Xu et al., 2013). We then estimate the plume heat flux from vertical flow rate and volume flux using our newly developed inverse method. In this presentation, we will briefly summarize the derivation of the inverse method and present the heat-flux time series obtained consequently with uncertainty quantification. In addition, we compare our heat-flux estimates with the one estimated from the plume in-situ temperatures measured using a Remotely Operative Vehicle (ROV) in 2012. Such comparison sheds light on the uncertainty of our heat flux estimation. Xu, G., Jackson, D., Bemis, K., and Rona, P., 2013, Observations of the volume flux of a seafloor hydrothermal plume using an acoustic imaging sonar, Geochemistry, Geophysics Geosystems, 2013 (in press).

Xu, G.; Jackson, D. R.; Bemis, K. G.; Rona, P. A.

2013-12-01

197

A highly portable, rapidly deployable system for eddy covariance measurements of CO2 fluxes  

SciTech Connect

To facilitate the study of flux heterogeneity within a region, the authors have designed, built, and field-tested a highly portable, rapidly deployable, eddy covariance CO{sub 2} flux measurement system. The system is built from off-the-shelf parts and was assembled at a minimal cost. The unique combination of features of this system allow for a very rapid deployment with a minimal number of field personnel. The system is capable of making high precision, unattended measurements of turbulent CO{sub 2} fluxes, latent heat (LE) fluxes, sensible heat fluxes (H), and momentum transfer fluxes. In addition, many of the meteorological and ecosystem variables necessary for quality control of the fluxes and for running ecosystem models are measured. A side-by-side field comparison of the system at a pair of established AmeriFlux sites has verified that, for single measurements, the system is capable of CO{sub 2} flux accuracy of about {+-} 1.2 {micro}mole/m{sup 2}/sec, LE flux accuracy of about {+-} 15 Watts/m{sup 2}, H flux accuracy of about {+-} 7 Watts/m{sup 2}, and momentum transfer flux accuracy of about {+-} 11 gm-m/sec/sec. System deployment time is between 2 and 4 hours by a single person. The system was measured to draw between 30 and 35 Watts of power and may be run from available line power, storage batteries, or solar panels.

Billesbach, David P.; Fischer, Marc L.; Torn, Margaret S.; Berry, Joe A.

2001-09-19

198

A scintillating fission detector for neutron flux measurements  

SciTech Connect

Neutron flux monitors are commonly used for a variety of nuclear physics applications. A scintillating neutron detector, consisting of a liquid scintillator loaded with fissionable material, has been developed, characterized, and tested in the beam line at the Los Alamos Neutron Science Center, and shows a significant improvement in neutron sensitivity compared with a conventional fission chamber. Recent research on nanocomposite-based scintillators for gamma-ray detection indicates that this approach can be extended to load nanoparticles of fissionable material into a scintillating matrix, with up to three orders of magnitude higher loading than typical fission chambers. This will result in a rugged, cost-efficient detector with high efficiency, a short signal rise time, and the ability to be used in low neutron-flux environments. Initial efforts to utilize the luminescence of uranyl oxide to eliminate the need for wavelength-shifting dyes were unsuccessful. Excitation of uranyl compounds has been reported at wavelengths ranging from 266 nm to 532 nm. However, neither the 300 nm emission of toluene, nor the 350 nm emission of PPO, nor the 410 nm emission of POPOP resulted in significant excitation of and emission by uranyl oxide. As indicated by UV/visible spectroscopy, light emitted at these wavelengths was absorbed by the colored solution. {sup 235}U remains the most attractive candidate for a fissionable scintillator, due to its high fission cross-section and lack of a threshold fission energy, but all solutions containing molecular uranium compounds will be colored, most more highly than the U{sup 6+} compounds used here. Research is therefore continuing toward the fabrication of uranium nanoparticles, in which, due to Rayleigh scattering, the coloration should be less pronounced. The characterization of the thorium-loaded liquid scintillator and the fabrication of the 100 mL detectors for use at LANSCE demonstrated the feasibility of loading fissionable material into a liquid scintillator. Analysis of beam line experiments using the thorium-loaded scintillator is underway to determine the fission event rate in the detector, for comparison with a conventional fission chamber as well as with an unloaded liquid scintillator.

Stange, Sy [Los Alamos National Laboratory; Esch, Ernst I [Los Alamos National Laboratory; Burgett, Eric A [Los Alamos National Laboratory; May, Iain [Los Alamos National Laboratory; Muenchausen, Ross E [Los Alamos National Laboratory; Taw, Felicia [Los Alamos National Laboratory; Tovesson, Fredrik K [Los Alamos National Laboratory

2010-01-01

199

Continuous monitoring of fluid flow rate and contemporaneous biogeochemical fluxes in the sub-seafloor; the Mosquito flux meter  

NASA Astrophysics Data System (ADS)

Fluid flow through marine sediments and oceanic crust impacts seawater chemistry as well as diagenetic, thermal, seismic, and magmatic processes at plate boundaries, creates ore and gas hydrate deposits at and below seafloor, and establishes and maintains deep microbial ecosystems. However, steady-state fluid flow rates, as well as the temporal and spatial variability of fluid flow and composition are poorly constrained in many marine environments. A new, low-cost instrument deployable by ROV or submersible, named the Mosquito, was recently developed to provide continuous, long-term and campaign style monitoring of fluid flow rate and contemporaneous solute fluxes at multiple depths below the sea floor. The Mosquito consists of a frame that houses several osmotic pumps (Osmo-Samplers [OS]) connected to coils of tubing that terminate with an attachment to long thin titanium (Ti) needles, all of which are mounted to a release plate. The OS's consist of an acrylic housing which contains a brine chamber (BC) and a distilled water chamber (DWC) separated by semi permeable membranes. The osmotic gradient between the chambers drives the flow of distilled water into the BC. The DWC is connected to the Teflon tubing coil and a Ti needle, both of which are also filled with distilled water, thus the OS pulls fluid from the base of the needle through the tubing coil. One central Ti needle is attached to a custom-made tracer injection assembly, filled with a known volume of tracer, which is triggered, injecting a point source in the sediment. On a typical Mosquito, 4 needles are mounted vertically at varying depths with respect to the tracer injection needle, and 4 needles are mounted at equal depth but set at variable horizontal distances away from the tracer injection. Once the Mosquito has been placed on the seafloor, the release plate is manually triggered pushing the Ti needles into the sediment, then the tracer injection assembly is actuated. As the tracer is advected, the OS's monitor the tracer concentrations through time, which are modeled for fluid flow rates. Simultaneously the Mosquito provides a continuous record of fluid, at high-resolution, for chemical analysis. The fluid chemistry time series, in combination with the fluid flow rate record, provide a serial record of biogeochemical fluxes. The robust nature and adaptable layout of the Mosquito allows for a wide variety of deployment settings from mid ocean ridges to the continental shelf as well as lacustrine environments. Preliminary results are being presented for three major deployments of the new flow meters; a 5-day campaign style deployment at Hydrate Ridge offshore of Oregon, a recently recovered 2-year deployment at Hydrate Ridge, and two transects of Mosquito deployments spanning from the deformation front to the upper slope at the Cascadia subduction zone off the coast of Washington.

Culling, D. P.; Solomon, E. A.; Kastner, M.; Berg, R. D.

2013-12-01

200

Soft defect printability: correlation to optical flux-area measurements  

NASA Astrophysics Data System (ADS)

Soft defects on photomasks have, historically, been difficult to measure, and predict how the measured size of a soft defect will correlate to what prints, if at all. Over the past few years KLA-Tencor STARlight surface inspection has become the inspection of choice for soft defects. Though the capture rate of this tool is exceptional, the defect sizing capability has lacked in accuracy. Customer specifications have traditionally been built around defect size and transmission. If a given defect cannot be accurately sized then it cannot be accurately dispositioned. In this study we are attempting to show a correlation between the AVI defect measurement tool sizing and what actually prints on the wafer. We will show defect sizing both from the KLA-Tencor STARlight and pattern tools, the AVI tool, AIMS and VSS printability data.

Taylor, Darren; Fiekowsky, Peter

2001-01-01

201

Carbon fluxes of surfaces vs. ecosystems: advantages of measuring eddy covariance and soil respiration simultaneously in dry grassland ecosystems  

NASA Astrophysics Data System (ADS)

An automated open system for measurement of soil CO2 efflux (Rsc) was developed and calibrated against known fluxes. The system was tested in the field, while estimating soil respiration simultaneously by the gradient method (Rsg) at a dry, sandy grassland site (Bugac, Hungary). Ecosystem respiration (Rego) was measured using the eddy covariance technique. The small chamber size (5 cm in diameter) made it possible to use the chambers in vegetation gaps, thereby avoiding the necessity of removing shoots and disturbing the spatial structure of vegetation and the upper soil layer. Low air flow rates associated with small chamber volume and chamber design allowed the overpressure range to stabilize between 0.05-0.12 Pa. The correlation between ecosystem and soil CO2 efflux rates as measured by the independent methods was significant, Reco rates were similar or even lower than Rsc in the low flux (up to 2 ?mol CO2 m-2 s-1) range but the differences were within the uncertainty limits for the two fluxes. Rsc from trenched and non-trenched plots amounted to 16 % and 44 % of Reco, respectively. The gradient method showed both up and downward CO2 fluxes originating from the main rooting zone after rains. Diffusive retardation played a smaller role than CO2 production considering the soil air CO2 concentration increase after rains in a given layer. Downward fluxes within the soil profile amounted to 15 % of the simultaneous upward fluxes and to ~7.6 % of the total (upward) effluxes during the 3-month study. The upper 5 cm soil layer contributed to ~50 % of the total soil CO2 efflux. Downward fluxes are expected to seriously affect (1) the Reco vs. temperature response functions and (2) the net ecosystem exchange of CO2 (NEE) vs. photon flux density response functions, therefore potentially affecting the gap filling procedures and to lead to a situation (3) when the measured surface and the real time ecosystem fluxes will necessarily differ in the short term. Simultaneous measurements of Reco and soil CO2 effluxes may reveal the timing and magnitude of the decoupling, thereby contributing to decreasing uncertainty associated with eddy flux measurements over flat terrains. While the correlations between CO2 effluxes measured by independent systems are strong, Rsg was generally larger than Rsc or Reco, mainly due to overestimation of effective diffusivity in the soil.

Nagy, Z.; Pintér, K.; Pavelka, M.; Darenová, E.; Balogh, J.

2011-09-01

202

Measurements of Correlation-Enhanced Collision Rates  

NASA Astrophysics Data System (ADS)

We measure the perp-to-parallel collision rate ?| in laser-cooled Magnesium ion plasmas in the strongly-magnetized and correlated regime; and obtain close agreement with the ``Salpeter correlation enhancement'' first studied for fusion in dense plasmas such as stars. The cyclotron energy, like nuclear energy, is released only through rare close-range collisions. These close collisions are suppressed by strong magnetization, because collisional impact distances are rarely as small as a cyclotron radius rc. However, theory predicts that particle correlations reduce this suppression of collisionality, enhancing the rare close collisions by e^?, where ??e^2 / aT is the correlation parameter. We control the plasma temperature over the range 4 0-6 < T < 1eV, giving correlation parameters up to ? 0, with measured collision rates 2 < ?| 2 10^4 sec-1. At low temperatures, the measured ?| are enhanced by up to 10^9 compared to uncorrelated theory, consistent with the predicted correlation enhancement. When the plasma density is reduced from 2 to 0.12 x10^7cm-3, the correlations are eliminated and the measured ?| agree with uncorrelated theory. E.E. Salpeter and H.M. Van Horn, Astrophys. J. 155, 183 (1969). D.H.E. Dubin, Phys. Rev. Lett. 94, 025002 (2005).

Anderegg, F.; Dubin, D. H. E.; O'Neil, T. M.; Driscoll, C. F.

2008-11-01

203

MEASURED AND PREDICTED FLUXES OF BIOGENIC SILICA IN LAKE MICHIGAN  

EPA Science Inventory

Diatom production in the offshore waters of Lake Michigan is limited by silica supplies in late summer and can be predicted from the seasonal disappearance of silica from the trophogenic zone. Biogenic silica fluxes obtained from sediment trap collections were compared with fluxe...

204

Sparking rates measured on the CRITS RFQ  

SciTech Connect

During the test of the LEDA injector on the CRITS RFQ, an automatic data acquisition system has been implemented. The purpose was to measure the sparking rate of this CW RFQ. The RF level has some influences on vacuum, but there is no evidence of any reciprocal effect. The raw sparking rate is very difficult to interpret, since burst of sparks bias the statistics. A more convenient and useful interpretation is the number of sparking seconds. At the nominal field level (1.75 Kilp), the sparking-second rate is 0.5 per minute without beam. It strongly depends on the field, with a logarithmic law: 4.5 decade/Kilp. With beam, the sparking rate jumps to 3.0 per minute. As far as tested, it depends neither on the beam current (20 to 80 mA) nor on the field (1.5 to 1.7 Kilp tested). With sparking rates as measured here, one could not hope to build an RFQ that would be free of sparks over a several months continuous operation. Such a requirement, based on an extrapolation of the curves presented here, would lead to a maximal electric field much lower than the Kilpatrick value, an unreasonable requirement for a functional RFQ. A conclusion is that a sparkless RFQ is hopeless, even with a very carefully conditioned cavity. It will probably be necessary to deal with a few sparks per day, and the linac must be able to restart automatically after a short beam interruption.

Balleyguier, P.

1998-05-28

205

Airborne Flux Measurements of Volatile Organic Compounds and NOx over a European megacity  

NASA Astrophysics Data System (ADS)

Ground level ozone (O3) and nitrogen dioxide (NO2) are priority pollutants whose concentrations are closely regulated by European Union Air Quality Directive 2008/50/EC. O3 is a secondary pollutant, produced from a complex chemical interplay between oxides of nitrogen (NOx = NO + NO2) and volatile organic compounds (VOCs). Whilst the basic atmospheric chemistry leading to O3 formation is generally well understood, there are substantial uncertainties associated with the magnitude of emissions of both VOCs and NOx. At present our knowledge of O3 precursor emissions in the UK is primarily derived from National Atmospheric Emission inventories (NAEI) that provide spatially disaggregated estimates at 1x1km resolution, and these are not routinely tested at city or regional scales. Uncertainties in emissions propagate through into uncertainties in predictions of air quality in the future, and hence the likely effectiveness of control policies on both background and peak O3 and NO2 concentrations in the UK. The Ozone Precursor Fluxes in the Urban Environment (OPFUE) project aims to quantify emission rates for NOx and selected VOCs in and around the megacity of London using airborne eddy covariance (AEC). The mathematical foundation for AEC has been extensively reviewed and AEC measurements of ozone, dimethyl sulphide, CO2 and VOCs have been previously reported. During the summer of 2013, approximately 30 hours of airborne flux measurements of toluene, benzene, NO and NO2 were obtained from the NERC Airborne Research and Survey Facility's (ARSF) Dornier-228 aircraft. Over SE England, flights involved repeated south west to north east transects of ~50 km each over Greater London and it's surrounding suburbs and rural areas, flying at the aircraft's minimum operating flight altitude and airspeed (~300m, 80m/s). Mixing ratios of benzene and toluene were acquired at 2Hz using a proton transfer reaction mass spectrometer (PTR-MS) and compared to twice hourly whole air canister samples (WAS) which were quantitatively determined post-flight via TD-GCMS. Mixing ratios between the PTR-MS and WAS-TD-GCMS were in good agreement with R2 values of 0.8 and 1.0 for Toluene and Benzene respectively. Mixing ratios of NO and NO2 were acquired at 10Hz using a 2 channel NOx chemiluminescence detector with photolytic converter. These measurements were used with 20 Hz 3-D wind vector data from an AIMMS-20 turbulence probe on the aircraft to calculate highly spatially resolved (1 km) surface-to-atmosphere emission flux rates of these compounds using the eddy covariance method of Karl et al. (2013). Measured surface to atmosphere emission fluxes of NOx, benzene and toluene from London were between 40 - 91 mg m2 h-1, 0.1 - 0.4 mg m2 h-1 and 0.2 - 2 mg m2 h-1 respectively, showing the spatial flux heterogeneity over the city. This demonstrates for the first time the feasibility of airborne eddy covariance flux measurements of reactive NOx species. We also show the applicability of wavelet analysis using virtually disjunct eddy covariance measurements of anthropogenic compounds in estimating regional fluxes over a European megacity. We compare our measured emission rates with those estimated from 'bottom-up' emissions inventories and highlight the agreement between the two.

Shaw, Marvin; Lee, James; Davison, Brian; Misztal, Pawel; Karl, Thomas; Hewitt, Nick; Lewis, Alistair

2014-05-01

206

The preliminary results of fast neutron flux measurements in the DULB laboratory at Baksan  

Microsoft Academic Search

One of the main sources of a background in underground physics experiments (such as the investigation of solar neutrino flux, neutrino oscillations, neutrinoless double beta decay, and the search for annual and daily Cold Dark Matter particle flux modulation) are fast neutrons originating from the surrounding rocks. The measurements of fast neutron flux in the new DULB Laboratory situated at

J. N. Abdurashitov; V. N. Gavrin; A. V. Kalikhov; A. A. Shikhin; V. E. Yants; O. S. Zaborskaya; A. A. Klimenko; S. B. Osetrov; A. A. Smolnikov; S. I. Vasiliev

2000-01-01

207

TEST OF A PROTOTYPE EDDY ACCUMULATOR FOR MEASURING ATMOSPHERIC VERTICAL FLUXES OF WATER VAPOR AND PARTICULATE SULFATE  

EPA Science Inventory

An eddy accumulator offers an appealing approach to measuring fluxes of species for which fast-response sensors are not available. The device accumulates trace atmospheric species into an updraft sampler and a downdraft sampler at rates proportional to the vertical wind speed. Th...

208

Wide Range Neutron Flux Measuring Channel for Aerospace Application  

SciTech Connect

The use of classical techniques for neutron flux measurements in nuclear reactors involves the switching between several detection chains as the power grows up to 10 decades. In space applications where mass and size constraints are of key significance, such volume of hardware represents a clear disadvantage. Instead of requiring different instruments for each reactor operating range (start-up, ramping-up, and nominal power), a single instrument chain should be desirable. A Wide Range Neutron Detector (WRND) system, combining a classic pulse Counting Channel with a Campbell's theorem based Fluctuation Channel can be implemented for the monitoring and control of a space nuclear reactor. Such an instrument will allow for a reduction in the complexity of space-based nuclear instrumentation and control systems. In this presentation we will discuss the criteria and tradeoffs involved in the development of such a system. We will focus particularly on the characteristics of the System On Chip (SOC) and the DSP board used to implement this instrument.

Cibils, R. M.; Busto, A.; Gonella, J. L.; Martinez, R.; Chielens, A. J.; Otero, J. M.; Nunez, M. [INVAP S.E., Moreno 1089, 8400 Bariloche, Rio Negro (Argentina); Tropea, S. E. [INTI, Av. Gral. Paz 5445, 1650 San Martin, Buenos Aires (Argentina)

2008-01-21

209

An unmanned aircraft vehicle system for boundary-layer flux measurements over forest canopies  

Microsoft Academic Search

Describes a system design of an unmanned aircraft vehicle (UAV) system for boundary-layer measurements of carbon dioxide fluxes, particularly of those fluxes over forest canopies. The system is aircraft-based, which permits measurements that are difficult to obtain by ground-based line-of-sight instruments (e.g., lidar). The system is unmanned, which permits flux measurements to as low as 5 m above a forest

Jason M. Daida; P. B. Russell; Timothy L. Crawford; J. F. Vesecky

1994-01-01

210

In Situ Measurement of Energetic Electron Fluxes Inside Thunderclouds  

NASA Astrophysics Data System (ADS)

It is now well established that high-energy radiation is routinely produced by thunderclouds and lightning. This radiation is in the form of x-rays and gamma-rays with timescales ranging from sub-microsecond (x-rays associated with lightning leaders), to sub-millisecond (Terrestrial Gamma-ray Flashes), to minute long glows (Gamma-ray Glows from thunderclouds seen on the ground and in or near the cloud by aircrafts and balloons). It is generally accepted that these emissions originate from bremsstrahlung interactions of relativistic runaway electrons with air, which can be accelerated in the thundercloud/lightning electric fields and gain up to multi-MeV energies. However, the exact physical details of the mechanism that produces these runaway electrons are still unknown. In order to better understand the source of energetic radiation inside thunderclouds, we have begun a campaign of balloon-borne instruments to directly measure the flux of energetic electrons inside thunderclouds. In the current configuration, each balloon carries Geiger counters to record the energetic particles. Geiger counters are well suited for directly measuring energetic electrons and positrons and have the advantage of being lightweight and dependable. Due to the nature of the thunderstorm environment, the campaign has many design, communication, and safety challenges. In this presentation we will report on the status of the campaign and some of the physical insights gained from the data collected by our instruments. This work was supported in part by the NASA grant NNX12A002H and by DARPA grant HR0011-1-10-1-0061.

Arabshahi, S.; Vodopiyanov, I. B.; Dwyer, J. R.; Rassoul, H.

2013-12-01

211

Influence of thermal and resonance neutron on fast neutron flux measurement by 239Pu fission chamber  

NASA Astrophysics Data System (ADS)

The 239Pu fission chambers are widely used to measure fission spectrum neutron flux due to a flat response to fast neutrons. However, in the meantime the resonance and thermal neutrons can cause a significant influence on the measurement if they are moderated, which could be eliminated by using 10B and Cd covers. At a column enriched uranium fast neutron critical assembly, the fission reaction rates of 239Pu are measured as 1.791×10?16, 2.350×10?16 and 1.385×10?15 per second for 15 mm thick 10B cover, 0.5 mm thick Cd cover, and no cover respectively, while the fission reaction rate of 239Pu is rapidly increased to 2.569×10?14 for a 20 mm thick polythene covering fission chamber. The average 239Pu fission cross-section of thermal and resonance neutrons is calculated to be 500 b and 24.95 b with the assumption of 1/v and 1/E spectra respectively, then thermal, resonance and fast neutron flux are achieved to be 2.30×106, 2.24×106 and 1.04×108 cm?2·s?1.

Zeng, Li-Na; Wang, Qiang; Song, Ling-Li; Zheng, Chun

2015-01-01

212

New Measurements of Inner Belt Proton Flux Gradients From the Van Allen Probes Mission  

NASA Astrophysics Data System (ADS)

Prior studies of 10's of MeV inner belt protons in low Earth orbit have established that the atmospheric density gradient produces a proton flux gradient because of losses to the atmosphere and the comparable sizes of the proton qyroradius and atmosphere scale height. The observable is an east-west asymmetry in the proton flux that has been reported using many low-Earth orbit missions going back to the first nuclear emulsion flights in 1963. We will revisit this low-altitude east-west effect as well as higher-altitude gradients with new measurements from the Relativistic Proton Spectrometer (RPS) on the Van Allen Probes spacecraft. RPS is a particle spectrometer designed to measure the flux, angular distribution, and energy spectrum of protons from ~60 MeV to ~2000 MeV with good rejection of penetrating backgrounds by requiring a 10-fold coincidence in its stack of silicon detectors. The Van Allen Probes orbit allows for a survey of proton gradients not only at low altitudes but also as high as the outer trapping limit at McIlwain L shell L~3 corresponding to ~13,000 km altitude. The 60 MeV proton gyroradius varies from ~50 to 700 km in this altitude range. The 1-second sampling of RPS and the nominal 5 rpm rotation rate of the Van Allen Probes yields a sensitive measure of proton gradients. This is the first time that a single mission can address the gradients and trapping of high-energy protons throughout the inner belt. We will report on preliminary flux gradients of >61 MeV protons observed during the first year of the mission using RPS and ancillary geophysical data.

Mazur, J. E.; O'Brien, T. P.; Looper, M. D.; George, J. S.; Blake, J. B.

2013-12-01

213

COMPARISON OF FLUX MEASUREMENTS WITH OPEN-AND CLOSED-PATH GAS ANALYZERS ABOVE AN AGRICULTURAL  

E-print Network

COMPARISON OF FLUX MEASUREMENTS WITH OPEN- AND CLOSED-PATH GAS ANALYZERS ABOVE AN AGRICULTURAL 16 March, 1993) Abstract. Comparison was made of the flux measurements of a closed-path CO2/H20), the measurement can be made using the eddy correlation technique with a velocity sensor and an adjacent open

Lee, Xuhui

214

Estimation of hydrocarbon biodegradation rates in gasoline-contaminated sediment from measured respiration rates  

USGS Publications Warehouse

An open microcosm method for quantifying microbial respiration and estimating biodegradation rates of hydrocarbons in gasoline-contaminated sediment samples has been developed and validated. Stainless-steel bioreactors are filled with soil or sediment samples, and the vapor-phase composition (concentrations of oxygen (O2), nitrogen (N2), carbon dioxide (CO2), and selected hydrocarbons) is monitored over time. Replacement gas is added as the vapor sample is taken, and selection of the replacement gas composition facilitates real-time decision-making regarding environmental conditions within the bioreactor. This capability allows for maintenance of field conditions over time, which is not possible in closed microcosms. Reaction rates of CO2 and O2 are calculated from the vapor-phase composition time series. Rates of hydrocarbon biodegradation are either measured directly from the hydrocarbon mass balance, or estimated from CO2 and O2 reaction rates and assumed reaction stoichiometries. Open microcosm experiments using sediments spiked with toluene and p-xylene were conducted to validate the stoichiometric assumptions. Respiration rates calculated from O2 consumption and from CO2 production provide estimates of toluene and p- xylene degradation rates within about ??50% of measured values when complete mineralization stoichiometry is assumed. Measured values ranged from 851.1 to 965.1 g m-3 year-1 for toluene, and 407.2-942.3 g m-3 year-1 for p- xylene. Contaminated sediment samples from a gasoline-spill site were used in a second set of microcosm experiments. Here, reaction rates of O2 and CO2 were measured and used to estimate hydrocarbon respiration rates. Total hydrocarbon reaction rates ranged from 49.0 g m-3 year-1 in uncontaminated (background) to 1040.4 g m-3 year-1 for highly contaminated sediment, based on CO2 production data. These rate estimates were similar to those obtained independently from in situ CO2 vertical gradient and flux determinations at the field site. In these experiments, aerobic conditions were maintained in the microcosms by using air as the replacement gas, thus preserving the ambient aerobic environment of the subsurface near the capillary zone. This would not be possible with closed microcosms.

Baker, R.J.; Baehr, A.L.; Lahvis, M.A.

2000-01-01

215

Comparison of floating chamber and eddy covariance measurements of lake greenhouse gas fluxes  

NASA Astrophysics Data System (ADS)

Fluxes of carbon dioxide (CO2) and methane (CH4) from lakes may have a large impact on the magnitude of the terrestrial carbon sink. Traditionally lake fluxes have been measured using the floating chamber (FC) technique; however, several recent studies use the eddy covariance (EC) method. We present simultaneous flux measurements using both methods at lake Tämnaren in Sweden during field campaigns in 2011 and 2012. Only very few similar studies exist. For CO2 flux, the two methods agree relatively well during some periods, but deviate substantially at other times. The large discrepancies might be caused by heterogeneity of partial pressure of CO2 (pCO2w) in the EC flux footprint. The methods agree better for CH4 fluxes. It is, however, clear that short-term discontinuous FC measurements are likely to miss important high flux events.

Podgrajsek, E.; Sahlée, E.; Bastviken, D.; Holst, J.; Lindroth, A.; Tranvik, L.; Rutgersson, A.

2014-08-01

216

Solids flow rate measurement in dense slurries  

SciTech Connect

Accurate and rapid flow rate measurement of solids in dense slurries remains an unsolved technical problem, with important industrial applications in chemical processing plants and long-distance solids conveyance. In a hostile two-phase medium, such a measurement calls for two independent parameter determinations, both by non-intrusive means. Typically, dense slurries tend to flow in laminar, non-Newtonian mode, eliminating most conventional means that usually rely on calibration (which becomes more difficult and costly for high pressure and temperature media). These issues are reviewed, and specific solutions are recommended in this report. Detailed calculations that lead to improved measuring device designs are presented for both bulk density and average velocity measurements. Cross-correlation, chosen here for the latter task, has long been too inaccurate for practical applications. The cause and the cure of this deficiency are discussed using theory-supported modeling. Fluid Mechanics are used to develop the velocity profiles of laminar non-Newtonian flow in a rectangular duct. This geometry uniquely allows the design of highly accurate `capacitive` devices and also lends itself to gamma transmission densitometry on an absolute basis. An absolute readout, though of less accuracy, is also available from a capacitive densitometer and a pair of capacitive sensors yields signals suitable for cross-correlation velocity measurement.

Porges, K.G.; Doss, E.D.

1993-09-01

217

Chemical weathering rates of a soil chronosequence on granitic alluvium: III. Hydrochemical evolution and contemporary solute fluxes and rates  

USGS Publications Warehouse

Although long-term changes in solid-state compositions of soil chronosequences have been extensively investigated, this study presents the first detailed description of the concurrent hydrochemical evolution and contemporary weathering rates in such sequences. The most direct linkage between weathering and hydrology over 3 million years of soil development in the Merced chronosequence in Central California relates decreasing permeability and increasing hydrologic heterogeneity to the development of secondary argillic horizons and silica duripans. In a highly permeable, younger soil (40 kyr old), pore water solutes reflect seasonal to decadal-scale variations in rainfall and evapotranspiration (ET). This climate signal is strongly damped in less permeable older soils (250 to 600 kyr old) where solutes increasingly reflect weathering inputs modified by heterogeneous flow. Elemental balances in the soils are described in terms of solid state, exchange and pore water reservoirs and input/output fluxes from precipitation, ET, biomass, solute discharge and weathering. Solute mineral nutrients are strongly dependent on biomass variations as evidenced by an apparent negative K weathering flux reflecting aggradation by grassland plants. The ratios of solute Na to other base cations progressively increase with soil age. Discharge fluxes of Na and Si, when integrated over geologic time, are comparable to solid-state mass losses in the soils, implying similar past weathering conditions. Similarities in solute and sorbed Ca/Mg ratios reflect short-term equilibrium with the exchange reservoir. Long-term consistency in solute ratios, when contrasted against progressive decreases in solid-state Ca/Mg, requires an additional Ca source, probably from dry deposition. Amorphous silica precipitates from thermodynamically-saturated pore waters during periods of high evapotranspiration and result in the formation of duripans in the oldest soils. The degree of feldspar and secondary gibbsite and kaolinite saturation varies both spatially and temporally due to the seasonality of plant-respired CO2 and a decrease in organically complexed Al. In deeper pore waters, K-feldspar is in equilibrium and plagioclase is about an order of magnitude undersaturated. Hydrologic heterogeneity produces a range of weathering gradients that are constrained by solute distributions and matrix and macropore flow regimes. Plagioclase weathering rates, based on precipitation-corrected Na gradients, vary between 3 and 7 ?? 10-16 mol m-2 s-1. These rates are similar to previously determined solid-state rates but are several orders of magnitude slower than for experimental plagioclase dissolution indicating strong inhibitions to natural weathering, partly due to near-equilibrium weathering reactions. Copyright ?? 2005 Elsevier Ltd.

White, A.F.; Schulz, M.S.; Vivit, D.V.; Blum, A.E.; Stonestrom, D.A.; Harden, J.W.

2005-01-01

218

Spatially explicit surface energy budget and partitioning with remote sensing and flux measurements in a boreal region of Interior Alaska  

NASA Astrophysics Data System (ADS)

Extrapolating energy fluxes between the ground surface and the atmospheric boundary layer from point-based measurements to spatially explicit landscape estimation is critical to understand and quantify the energy balance components and exchanges in the hydrosphere, atmosphere, and biosphere. This information is difficult to quantify and are often lacking. Using a Landsat image (acquired on 5 August 2004), the flux measurements from three eddy covariance flux towers (a 1987 burn, a 1999 burn, and an unburned control site) and a customized satellite-based surface energy balance model of Mapping Evapotranspiration at High Resolution with Internalized Calibration (METRIC), we estimated net radiation, sensible heat flux ( H), latent heat flux (LE), and soil heat flux ( G) for the boreal Yukon River Basin of Interior Alaska. The model requires user selection of two extreme conditions present within the image area to calibrate and anchor the sensible flux output. One is the "hot" condition which refers to a bare soil condition with specified residual evaporation rates. Another one is the "cold" condition which refers to a fully transpiring vegetation such as full-cover agricultural crops. We selected one bare field as the "hot" condition while we explored three different scenarios for the "cold" pixel because of the absence of larger expanses of agricultural fields within the image area. For this application over boreal forest, selecting agricultural fields whose evapotranspiration was assumed to be 1.05 times the alfalfa-based reference evapotranspiration as the "cold" pixel could result in large errors. Selecting an unburned flux tower site as the "cold" pixel could achieve acceptable results, but uncertainties remain about the energy balance closure of the flux towers. We found that METRIC performs reasonably well in partitioning energy fluxes in a boreal landscape.

Huang, Shengli; Dahal, Devendra; Singh, Ramesh; Liu, Heping; Young, Claudia; Liu, Shuguang

2013-08-01

219

Measurement of photon flux with a miniature gas ionization chamber in a Material Testing Reactor  

NASA Astrophysics Data System (ADS)

Nuclear heating measurements in Material Testing Reactors (MTR) are crucial for the design of the experimental devices and the prediction of the temperature of the hosted samples. Nuclear heating in MTR materials (except fuel) is mainly due to the energy deposition by the photon flux. Therefore, the photon flux is a key input parameter for the computer codes which simulate nuclear heating and temperature reached by samples/devices under irradiation. In the Jules Horowitz MTR under construction at the CEA Cadarache, the maximal expected nuclear heating levels will be about 15 to 18 W g-1 and it will be necessary to assess this parameter with the best accuracy. An experiment was performed at the OSIRIS reactor to combine neutron flux, photon flux and nuclear heating measurements to improve the knowledge of the nuclear heating in MTR. There are few appropriate sensors for selective measurement of the photon flux in MTR even if studies and developments are ongoing. An experiment, called CARMEN-1, was conducted at the OSIRIS MTR and we used in particular a gas ionization chamber based on miniature fission chamber design to measure the photon flux. In this paper, we detail Monte-Carlo simulations to analyze the photon fluxes with ionization chamber measurements and we compare the photon flux calculations to the nuclear heating measurements. These results show a good accordance between photon flux measurements and nuclear heating measurement and allow improving the knowledge of these parameters.

Fourmentel, D.; Filliatre, P.; Villard, J. F.; Lyoussi, A.; Reynard-Carette, C.; Carcreff, H.

2013-10-01

220

Surface Fluxes, Dissipation Rate of Tke and Temperature Structure Parameter Determined From Scintillometers.  

NASA Astrophysics Data System (ADS)

The objective of this paper is to present some recent results of scintillometry research carried out by the Meteorology and Air Quality Group of the Wageningen University in collaboration with others such as KNMI (Royal Neth. Met. Inst.) and DWD (Ger- man Weath. Serv.). The paper deals with: 1. Application of long path scintillometers over heterogeneous terrain to determine the sensible and latent heat flux. This concerns a long-path large aperture scintillometer (LAS) as well as a long-path radio-wave scin- tillometer (RWS). 2. Applications of small aperture laser scintillometers to determine the dissipation rate of TKE and the temperature structure parameter as well as the fluxes of sensible heat and momentum. Experimental results will be presented of the WINTEX (1997, Sweden), FLEVOPOLDER (1998, the Netherlands), the LITFASS (1998-, Germany), RAPID (USA, 1999), CASES-99 (1999, USA) and the YAQUI (2000, NW-Mexico).

de Bruin, H. A. R.; Meijninger, W. M. L.; Hartogensis, O. K.; Beyrich, F.; Kohsiek, W.; Moene, A.

221

Simultaneous bidirectional magnesium ion flux measurements in single barnacle muscle cells by mass spectrometry.  

PubMed Central

Stable isotopes of Mg were used to measure bidirectional magnesium ion fluxes in single barnacle giant muscle fibers immersed in Ca- and Na-free, isosmotic media. Measurements were made using a mass spectrometric technique, thermal ionization mass spectrometry (TIMS), in conjunction with atomic absorption spectroscopy. Kinetic relations based on a first-order model were developed that permit the determination of unidirectional rate coefficients for Mg influx, ki, and efflux, ke, in the same experiment from knowledge of initial conditions and the initial and final ratios of 26Mg/24Mg and 25Mg/24Mg in ambient solutions (i.e., by isotope dilution). Such determinations were made for three values of the external Mg ion concentration: 5, 25, and 60 mM. At the concentration [Mg+2]o = 5 mM, ki and ke were about equal at a value of 0.01 min-1. At the higher values of [Mg+2]o, the values of ke increased along a curve suggesting saturation, whereas the values of ki remained essentially constant. As could be expected on the basis of a constant ki, the initial influx rate varied in direct linear proportion to [Mg+2]o, and was 11.8 pmol/cm2s when [Mg+2]o was 5 mM. However, the initial efflux rate appeared to increase nonlinearly with [Mg+2]o, varying from 13.4 pmol/cm2s ([ Mg+2]o = 5 mM) to approximately 80 pmol/cm2s ([ Mg+2]o = 60 mM). The results are consistent with a model that assumes Mg influx to be mainly an electrodiffusive inward leak with PMg = 0.07 cm/s and Mg efflux to be almost entirely by active transport processes. Where comparisons can be made, the rate coefficients determined from stable isotope measurements agree with those previously obtained using radioactive Mg. The rate coefficients can be used to correctly predict time-dependent changes in total fiber Mg content. The results support the conclusion that nonradioactive tracers can be used to measure ion fluxes and ion flux ratios in excitable cells; it is expected that this method will greatly assist in the study of Mg regulation in general. PMID:2477072

Montes, J G; Sjodin, R A; Yergey, A L; Vieira, N E

1989-01-01

222

Mild solutions to a measure-valued mass evolution problem with flux boundary conditions  

E-print Network

We investigate the well-posedness and approximation of mild solutions to a class of linear transport equations on the unit interval $[0,1]$ endowed with a linear discontinuous production term, formulated in the space $\\mathcal{M}([0,1])$ of finite Borel measures. Our working technique includes a detailed boundary layer analysis in terms of a semigroup representation of solutions in spaces of measures able to cope with the passage to the singular limit where thickness of the layer vanishes. We obtain not only a suitable concept of solutions to the chosen measure-valued evolution problem, but also derive convergence rates for the approximation procedure and get insight in the structure of flux boundary conditions for the limit problem.

Joep H. M. Evers; Sander C. Hille; Adrian Muntean

2014-12-20

223

Comparison of measured and modeled radiation, heat and water vapor fluxes: FIFE pilot study  

NASA Technical Reports Server (NTRS)

The feasibility of using radio frequency receivers to collect data from automated weather stations to model fluxes of latent heat, sensible heat, and radiation using routine weather data collected by automated weather stations was tested and the estimated fluxes were compared with fluxes measured over wheat. The model Cupid was used to model the fluxes. Two or more automated weather stations, interrogated by radio frequency and other means, were utilized to examine some of the climatic variability of the First ISLSCP (International Satellite Land-Surface Climatology Project) Field Experiment (FIFE) site, to measure and model reflected and emitted radiation streams from various locations at the site and to compare modeled latent and sensible heat fluxes with measured values. Some bidirectional reflected and emitted radiation data were collected from 23 locations throughout the FIFE site. Analysis of these data along with analysis of the measured sensible and latent heat fluxes is just beginning.

Blad, Blaine L.; Hubbard, Kenneth G.; Verma, Shashi B.; Starks, Patrick; Norman, John M.; Walter-Shea, Elizabeth

1987-01-01

224

Measurements of NO(x) and NO(y) concentrations and fluxes over Arctic tundra  

NASA Technical Reports Server (NTRS)

Measurements of the atmospheric concentrations of NO, NO2, total NO(y), and O3 were made during the NASA Arctic Boundary Layer Expedition (ABLE 3A) at a remote location in a tundra bog ecosystem in southeastern Alaska during the growing season (July-August 1988). Concentrations of NO(x) and NO(y) were found to be very low compared to other remote continental sites, indicating that anthropogenic influences were small at this site during this time of year. The NO(y) emission rate from the soil were 0.13 +/- 0.05 x 10 exp 9 molecules/sq cm/s. Direct measurements of the flux of total NO(y) were made for the first time, indicating downward flux of NO(y) at all times of day, with maximum deposition of 2.5 +/- 0.9 x 10 exp 9 molecules/sq cm/s in the afternoon. Deposition of HNO3 appears to dominate the atmosphere/surface exchange of NO(y). The mean dry deposition rate of NO(y) to the tundra was 1.8 +/- 1.0 x 10 exp 9 molecules/sq cm/s.

Bakwin, Peter S.; Wofsy, Steven C.; Fan, Song-Miao; Fitzjarrald, David R.

1992-01-01

225

Measurements of NO(x) and NO(y) concentrations and fluxes over Arctic tundra  

SciTech Connect

Measurements of the atmospheric concentrations of NO, NO[sub 2], total NO(y), and O[sub 3] were made during the NASA Arctic Boundary Layer Expedition (ABLE 3A) at a remote location in a tundra bog ecosystem in southeastern Alaska during the growing season (July-August 1988). Concentrations of NO(x) and NO(y) were found to be very low compared to other remote continental sites, indicating that anthropogenic influences were small at this site during this time of year. The NO(y) emission rate from the soil were 0.13 +/- 0.05 x 10 exp 9 molecules/sq cm/s. Direct measurements of the flux of total NO(y) were made for the first time, indicating downward flux of NO(y) at all times of day, with maximum deposition of 2.5 +/- 0.9 x 10 exp 9 molecules/sq cm/s in the afternoon. Deposition of HNO3 appears to dominate the atmosphere/surface exchange of NO(y). The mean dry deposition rate of NO(y) to the tundra was 1.8 +/- 1.0 x 10 exp 9 molecules/sq cm/s. 58 refs.

Bakwin, P.S.; Wofsy, S.C.; Fan, Songmiao; Fitzjarrald, D.R. (Harvard Univ., Cambridge, MA (United States) New York State Univ., Albany (United States))

1992-10-01

226

A new measurement of the singlet delta pooling rate  

Microsoft Academic Search

The singlet delta pooling rate has been measured in a chemical generator using gas phase laser Raman spectroscopy. The measured rate is four times the currently accepted pooling rate constant. Our measurement also agrees with recent ab initio rate calculations. This rate is one of the most important losses in the COIL laser and is believed responsible for the production

William E. McDermott; Keith Hobbs; Thomas Henshaw

2008-01-01

227

REDUCING THE UNCERTAINTY OF NORTH AMERICAN CARBON FLUX ESTIMATES USING AN EXTENDED ATMOSPHERIC CARBON DIOXIDE MEASUREMENT NETWORK.  

E-print Network

??We evaluate North American carbon fluxes using a monthly global Bayesian synthesis inversion that includes well-calibrated carbon dioxide concentrations measured at continental flux towers. We… (more)

Butler, Martha

2010-01-01

228

Arrangement Analysis of Leaves Optimized on Photon Flux Density or Photosynthetic Rate  

NASA Astrophysics Data System (ADS)

By clarifying a plant evolutive process, useful information may be obtained on engineering. Consequently, an analysis algorithm that investigates the optimal arrangement of plant leaves was developed. In the developed algorithm, the Monte Carlo method is introduced and sunlight is simulated. Moreover, the arrangement optimization of leaves is analyzed using a Genetic Algorithm (GA). The number of light quanta (photon flux density) that reaches leaves, or the average photosynthetic rate of the same was set as the objective function, and leaf models of a dogwood and a ginkgo tree were analyzed. The number of leaf models was set between two to four, and the position of the leaf was expressed in terms of the angle of direction, elevation angle, rotation angle, and the representative length of the branch of a leaf. The chromosome model introduced into GA consists of information concerning the position of the leaf. Based on the analysis results, the characteristics of the leaf of an actual plant could be simulated by ensuring the algorithm had multiple constrained conditions. The optimal arrangement of leaves differs in maximization of the photon flux density, and that of the average value of a photosynthetic rate. Furthermore, the leaf form affecting the optimal arrangement of leave and also having a significant influence also on a photosynthetic rate was shown.

Obara, Shin'ya; Tanno, Itaru

229

Eddy covariance flux measurements of gaseous elemental mercury using cavity ring-down spectroscopy.  

PubMed

A newly developed pulsed cavity ring-down spectroscopy (CRDS) system for measuring atmospheric gaseous elemental mercury (GEM) concentrations at high temporal resolution (25 Hz) was used to successfully conduct the first eddy covariance (EC) flux measurements of GEM. GEM is the main gaseous atmospheric form, and quantification of bidirectional exchange between the Earth's surface and the atmosphere is important because gas exchange is important on a global scale. For example, surface GEM emissions from natural sources, legacy emissions, and re-emission of previously deposited anthropogenic pollution may exceed direct primary anthropogenic emissions. Using the EC technique for flux measurements requires subsecond measurements, which so far has not been feasible because of the slow time response of available instrumentation. The CRDS system measured GEM fluxes, which were compared to fluxes measured with the modified Bowen ratio (MBR) and a dynamic flux chamber (DFC). Measurements took place near Reno, NV, in September and October 2012 encompassing natural, low-mercury (Hg) background soils and Hg-enriched soils. During nine days of measurements with deployment of Hg-enriched soil in boxes within 60 m upwind of the EC tower, the covariance of GEM concentration and vertical wind speed was measured, showing that EC fluxes over an Hg-enriched area were detectable. During three separate days of flux measurements over background soils (without Hg-enriched soils), no covariance was detected, indicating fluxes below the detection limit. When fluxes were measurable, they strongly correlated with wind direction; the highest fluxes occurred when winds originated from the Hg-enriched area. Comparisons among the three methods showed good agreement in direction (e.g., emission or deposition) and magnitude, especially when measured fluxes originated within the Hg-enriched soil area. EC fluxes averaged 849 ng m(-2) h(-1), compared to DFC fluxes of 1105 ng m(-2) h(-1) and MBR fluxes of 1309 ng m(-2) h(-1). This study demonstrated that a CRDS system can be used to measure GEM fluxes over Hg-enriched areas, with a conservative detection limit estimate of 32 ng m(-2) h(-1). PMID:25608027

Pierce, Ashley M; Moore, Christopher W; Wohlfahrt, Georg; Hörtnagl, Lukas; Kljun, Natascha; Obrist, Daniel

2015-02-01

230

Measurements of Correlation-Enhanced Collision Rates  

NASA Astrophysics Data System (ADS)

This talk presents the first detailed experimental measurements of the Salpeter collisional enhancement factor g ( ?) in strongly correlated plasmas. This factor is predicted to enhance the nuclear reaction rate in dense strongly-correlated plasmas, such as in giant planet interiors, brown dwarfs and degenerate stars;footnotetextE.E. Salpeter and H.M. Van Horn, Astrophys. J. 155, 183 (1969). and recent theory establishes that it also applies to the perpendicular-to-parallel collisions in magnetized plasmas described here.footnotetextD.H.E. Dubin, Phys. Rev. Lett. 94, 025002 (2005). The enhancement is caused by plasma screening of the repulsive Coulomb potential between charges, allowing closer collisions for a given particle energy. The enhancement factor is predicted to be large when the plasma correlation parameter ??e^2 /aT is larger than unity, scaling as g ( ?) ˜e^?. The perp-to-parallel collision rate is then ?|= n v b^2 ,( ? ) ,( ?), where I ( ? ) decreases precipitously below ( 8 ?? / 15 ) ? in the highly magnetized regime of ? ??2 ,/ rc1. Our measurementsfootnotetextF. Anderegg et al., Phys. Rev. Lett. 102, 185001 (2009); F. Anderegg et al., Phys. Plasmas 16, 055705 (2009). of ?| in Mg^+ pure ion plasmas are consistent with the predicted Salpeter correlation enhancement, with the comparison limited mainly by systematic spatial variations in the plasma temperature. The plasma temperatures are controlled over the range 4 x10-6 < T < 1eV, with the outer radii being up to 2x hotter. Bulk-averaged collision rates of 1 < ?|< 2 x10^4 sec-1 are measured by 2 techniques: for slow collisions, T| is heated or cooled, and the subsequent relaxation is directly observed; for rapid collisions, sinusoidal modulation of the plasma length at frequency fmod gives maximal heating when fmod = ?|/ 2 ?c (?), where c ( ?) is the specific heat. Two densities are used, 2.0 and 0.12 x10^7 cm-3; the lower density has ˜2.5 x less correlation at any temperature. Experiments clearly show the expected ?|T-3/2 regime at high temperatures, and show the strong I ( ? ) suppression of ?| for b / rc1. At low temperatures and high density, the measured ?| is enhanced by up to g ˜10^12 over the uncorrelated prediction, consistent with the Salpeter-enhanced prediction. At low (uncorrelated) densities, no enhancement is observed. Future experiments may be able to image ``burn fronts'' propagating from hot regions to cold regions.

Driscoll, C. Fred

2009-11-01

231

Measuring Mars Sand Flux Seasonality from a Time Series of Hirise Images  

NASA Astrophysics Data System (ADS)

The volumetric transport rate of sand, or flux, is a fundamental quantity that relates to the rate of landscape evolution through surface deposition and erosion. Measuring this quantity on Mars is particularly relevant as wind is the dominant geomorphic agent active at present on the planet. Measuring sand flux on Mars has been made possible thanks to the availability of times series of high resolution images acquired by the High Resolution Imaging Science Experiment (HiRISE) and precise image registration and correlation methods which permits the quantification of movement to sub-pixel precision. In this study, focused on the Nili Patera dune field, we first measured the migration rate of sand ripples and dune lee fronts over 105 days, using a pair of HiRISE images acquired in 2007, correlated and co-registered with COSI-Corr. From these measurements and the estimation of the ripple and dune heights, we derived the reptation and saltation sand fluxes. We next applied the same methodology to a time-series of eight images acquired in 2010-2011 covering one Mars year. Pairs of sequential images, were processed with COSI-Corr yielding a times series of 8 displacement maps. A Principal Component Analysis (PCA) was applied to the time-series to quantify more robustly the time evolution of the signal and filter out noise, in particular due to misalignment of CCDs. Using the first two components, which account for 84% of the variance, the seasonal variation of the ripple migration rate was estimated. We clearly observe continuously active migration throughout the year with a strong seasonal quasi-sinusoidal variation which peaks at perihelion. Ripple displacement orientation is stable in time, toward ~N115°E. The wind direction is thus relatively constant in this area, a finding consistent with the barchan morphology and orientation of the dunes. The dataset require that sand moving winds must occur daily to weekly throughout the year. The amplitude of the seasonal variation is about twice the mean signal.

Ayoub, F.; Avouac, J.; Bridges, N. T.; Leprince, S.; Lucas, A.

2012-12-01

232

New Heat Transfer Correlation for an HCCI Engine Derived from Measurements of Instantaneous Surface Heat Flux  

Microsoft Academic Search

An experimental study has been carried out to provide qualitative and quantitative insight into gas to wall heat transfer in a gasoline fueled Homogeneous Charge Compression Ignition (HCCI) engine. Fast response thermocouples are embedded in the piston top and cylinder head surface to measure instantaneous wall temperature and heat flux. Heat flux measurements obtained at multiple locations show small spatial

Junseok Chang; Orgun Güralp; Zoran Filipi; Dennis Assanis; Tang-Wei Kuo; Paul Najt; Rod Rask

233

Continental Shelf Research 23 (2003) 457481 A time series of benthic flux measurements from  

E-print Network

Continental Shelf Research 23 (2003) 457­481 A time series of benthic flux measurements from September 2002; accepted 3 December 2002 Abstract In situ incubation chamber measurements of benthic. Variability in nutrient (Si, PO4 2+ , NH3, NO3 � ) and trace metal (Mn, Fe (II), Cu) fluxes correlate

Burdige, David

234

LEAF, BRANCH, STAND & LANDSCAPE SCALE MEASUREMENTS OF VOLATILE ORGANIC COMPOUND FLUXES FROM U.S. WOODLANDS  

EPA Science Inventory

Natural volatile organic compounds (VOC) fluxes were measured in three U.S. woodlands in summer 1993. Fluxes from individual leaves and branches were estimated with enclosure techniques and used to initialize and evaluate VOC emission model estimates. Ambient measurements were us...

235

MERCURY FLUX MEASUREMENTS OVER AIR AND WATER IN KEJIMKUJIK NATIONAL PARK, NOVA SCOTIA  

E-print Network

MERCURY FLUX MEASUREMENTS OVER AIR AND WATER IN KEJIMKUJIK NATIONAL PARK, NOVA SCOTIA F. S. BOUDALA. Mercury flux measurements were conducted at two lakes and three soil sites in Kejimkujik National Park, located in the eastern Canadian province of Nova Scotia. One of the lakes had high levels of both mercury

Folkins, Ian

236

Measurement of the cosmic ray and neutrino-induced muon flux at the Sudbury neutrino observatory  

Microsoft Academic Search

Results are reported on the measurement of the atmospheric neutrino-induced muon flux at a depth of 2 kilometers below the Earth's surface from 1229 days of operation of the Sudbury Neutrino Observatory (SNO). By measuring the flux of through-going muons as a function of zenith angle, the SNO experiment can distinguish between the oscillated and unoscillated portion of the neutrino

B. Aharmim; S. N. Ahmed; T. C. Andersen; A. E. Anthony; N. Barros; E. W. Beier; A. Bellerive; B. Beltran; M. Bergevin; S. D. Biller; K. Boudjemline; M. G. Boulay; T. H. Burritt; B. Cai; Y. D. Chan; M. Chen; M. C. Chon; B. T. Cleveland; G. A. Cox-Mobrand; C. A. Currat; X. Dai; F. Dalnoki-Veress; H. Deng; J. Detwiler; P. J. Doe; R. S. Dosanjh; G. Doucas; P.-L. Drouin; F. A. Duncan; M. Dunford; S. R. Elliott; H. C. Evans; G. T. Ewan; J. Farine; H. Fergani; F. Fleurot; R. J. Ford; J. A. Formaggio; N. Gagnon; J. T. M. Goon; K. Graham; D. R. Grant; E. Guillian; S. Habib; R. L. Hahn; A. L. Hallin; E. D. Hallman; C. K. Hargrove; P. J. Harvey; R. Hazama; K. M. Heeger; W. J. Heintzelman; J. Heise; R. L. Helmer; R. J. Hemingway; R. Henning; A. Hime; C. Howard; M. A. Howe; M. Huang; B. Jamieson; N. A. Jelley; J. R. Klein; M. Kos; A. Krüger; C. Kraus; C. B. Krauss; T. Kutter; C. C. M. Kyba; R. Lange; J. Law; I. T. Lawson; K. T. Lesko; J. R. Leslie; I. Levine; J. C. Loach; S. Luoma; R. MacLellan; S. Majerus; H. B. Mak; J. Maneira; A. D. Marino; R. Martin; N. McCauley; A. B. McDonald; S. McGee; C. Mifflin; M. L. Miller; B. Monreal; J. Monroe; A. J. Noble; N. S. Oblath; C. E. Okada; H. M. O'Keeffe; Y. Opachich; G. D. Orebi Gann; S. M. Oser; R. A. Ott; S. J. M. Peeters; A. W. P. Poon; G. Prior; K. Rielage; B. C. Robertson; R. G. H. Robertson; E. Rollin; M. H. Schwendener; J. A. Secrest; S. R. Seibert; O. Simard; J. J. Simpson; D. Sinclair; P. Skensved; M. W. E. Smith; T. J. Sonley; T. D. Steiger; L. C. Stonehill; N. Tagg; G. Tesic; N. Tolich; T. Tsui; R. G. van de Water; B. A. Vandevender; C. J. Virtue; D. Waller; C. E. Waltham; H. Wan Chan Tseung; D. L. Wark; P. Watson; J. Wendland; J. F. Wilkerson; J. R. Wilson; J. M. Wouters; A. Wright; M. Yeh; F. Zhang; K. Zuber

2009-01-01

237

Aerosol Fluxes over Amazon Rain Forest Measured with the Eddy Covariance Method  

Microsoft Academic Search

We present measurements of vertical aerosol fluxes over the Amazon carried out on top of K34, a 50 meter high tower in the Cuieiras Reserve about 50 km north of Manaus in northern Brazil. The turbulent fluxes were measured with the eddy covariance method. The covariance of vertical wind speed from a sonic anemometer Gill Windmaster and total aerosol number

L. Ahlm; E. D. Nilsson; R. Krejci; E. M. Mårtensson; M. Vogt; P. Artaxo

2008-01-01

238

Measuring radon flux across active faults: Relevance of excavating and possibility of satellite discharges  

E-print Network

Measuring radon flux across active faults: Relevance of excavating and possibility of satellite January 2010 Keywords: Exhalation flux Radon-222 Carbon dioxide Faults Earthquake Trench a b s t r a c on the Xidatan segment of the Kunlun Fault, Qinghai Province, China, using measurement of the radon- 222

Klinger, Yann

239

FLUX MEASUREMENTS OF OZONE AND NITRIC ACID AT COASTAL AND MID-CONTINENTAL SITES  

EPA Science Inventory

A system for measuring the turbulent fluxes of ozone, nitric acid, and other gases was operated at two sites in 1994. hese direct measurements of fluxes are for comparison with those calculated for National Dry Deposition Network sites using an inferential model approach. zone fl...

240

A comparison of methods for deriving solute flux rates using long-term data from streams in the mirror lake watershed  

USGS Publications Warehouse

Calculation of chemical flux rates for streams requires integration of continuous measurements of discharge with discrete measurements of solute concentrations. We compared two commonly used methods for interpolating chemistry data (time-averaging and flow-weighting) to determine whether discrepancies between the two methods were large relative to other sources of error in estimating flux rates. Flux rates of dissolved Si and SO42- were calculated from 10 years of data (1981-1990) for the NW inlet and Outlet of Mirror Lake and for a 40-day period (March 22 to April 30, 1993) during which we augmented our routine (weekly) chemical monitoring with collection of daily samples. The time-averaging method yielded higher estimates of solute flux during high-flow periods if no chemistry samples were collected corresponding to peak discharge. Concentration-discharge relationships should be used to interpolate stream chemistry during changing flow conditions if chemical changes are large. Caution should be used in choosing the appropriate time-scale over which data are pooled to derive the concentration-discharge regressions because the model parameters (slope and intercept) were found to be sensitive to seasonal and inter-annual variation. Both methods approximated solute flux to within 2-10% for a range of solutes that were monitored during the intensive sampling period. Our results suggest that errors arising from interpolation of stream chemistry data are small compared with other sources of error in developing watershed mass balances.

Bukaveckas, P.A.; Likens, G.E.; Winter, T.C.; Buso, D.C.

1998-01-01

241

Heat flux measurement from vertical temperature profile and thermal infrared imagery in low-flux fumarolic zones  

NASA Astrophysics Data System (ADS)

Hydrothermal systems are associated to most of the dormant volcanoes. Heat is transported by steam from the hot magma body in the connected porosity and the fissures of the rock to the surface. If the flux is low enough (<500 W/m²), the steam mainly condensates in the soil close to surface, and a significant proportion of the heat is transported to the surface by conduction, producing a gradient of temperature and a thermal anomaly detectable at the surface. Detecting and monitoring these fluxes is crucial for hazard management, since it reflects the state of the magma body in depth. In order to quantify this flux two methods are considered. First, a vertical profile of temperature is measured by a series of thermocouples, and the conducted flux is estimated thanks to the Fourier law. Secondly, a more recent method uses the thermal infrared imagery to monitor the surface temperature anomaly (STA) between the studied zone and an equivalent zone not affected by the geothermal flux. The heat flux from the soil to the atmosphere is computed as the sum of (1) the radiative flux, (2) the sensible flux and (3) the residual steam flux. These two methods are complementary and have an equivalent uncertainty of approximately 20%, which would allow to track the major changes in the hydrothermal system. However, the surface and sub-surface temperatures are strongly influenced by the climate. For instance, it has been widely demonstrated that the surface temperature dramatically decreases after a rainfall. In order to estimate the reliability of the measurements, a numerical model simulating the evolution of the subsurface temperature in low flux fumarolic zone has been built. In depth, the heat can be transported either by conduction, or by the rising steam, or by condensed water. In surface, both the radiative flux and the sensible flux (convection of the atmosphere) are taken into account. This model allows to estimate the changes of temperature due to a variation of solar illumination, wind, or rainfalls. It has been successfully tested during 5 months with a permanent station built on the Ty fault on La Soufrière volcano (Guadeloupe, Lesser Antilles). Results show that the diurnal cycle has a significant influence on the temperature up to ca. 30 cm depth, hindering the use of the thermal gradient in this zone, while the STA has a negligible variation. Rain has a more dramatic influence: the surface temperature and the STA are significantly affected, even for small rains. The model shows that the drop of temperature and the affected thickness are mainly controlled by the amount of rain, while the relaxation time is primarily a function of the heat flux. These results have strong implications in the interpretation and the reliability of the temperature surveys, and could be used to correct them from the climate fluctuations.

Gaudin, Damien; Finizola, Anthony; Beauducel, François; Brothelande, Elodie; Allemand, Pascal; Delacourt, Christophe; Delcher, Eric; Peltier, Aline

2014-05-01

242

Sizes of nanobubbles from nucleation rate measurements  

NASA Astrophysics Data System (ADS)

In homogeneous bubble nucleation, the critical nucleus typically has nanometer dimensions. The volume V of a critical bubble can be determined from the simple equation (partial W/partial p)_T=V, where W is the reversible work of nucleus formation and p is the ambient pressure of the liquid phase in which bubble formation is occurring. The relation, W/kT=-ln J+ln A, where J is the steady state nucleation rate and A is the weakly pressure-dependent kinetic prefactor, allows V to be determined from rate measurements. The original derivation of this equation for V from the nucleation theorem was limited to one-component, ideal gas bubbles with a gas density much smaller than that of the ambient liquid. [D. Kashchiev, Nucleation: basic theory with applications (Butterworth-Heinemann, Oxford, 2000) p. 226.] The result is actually much more general, and it will be shown that it applies to multi-component, nonideal gas bubbles, provided the same density inequality holds. When the bubble phase and liquid densities are comparable, a more complicated, but also general and rigorous result is found.

Wilemski, G.

2003-03-01

243

SkyLine and SkyGas: Novel automated technologies for automatic GHG flux measurements  

NASA Astrophysics Data System (ADS)

1. Concerns for the future of the Earth's climate centre around the anthropogenically-driven continuing increases in atmospheric concentrations of the major 'greenhouse gases' (GHGs) which include CO2, CH4 and N2O. A major component of the global budgets for all three of these gases is the flux between the atmosphere and terrestrial ecosystems. 2. Currently, these fluxes are poorly quantified, largely due to technical limitations associated with making these flux measurements. Whilst eddy covariance systems have greatly improved such measurements at the ecosystem scale, flux measurements at the plot scale are commonly made using labour intensive traditional 'cover box' approaches; technical limitations have frequently been a bottle-neck in producing adequate and appropriate GHG flux data necessary for making land management decisions. For example, there are almost no night time flux data for N2O fluxes, and frequently such data are only measured over bare soil patches. 3. We have been addressing the design of novel field equipment for the automation of GHG flux measurements at the chamber and plot scale and will present here some of the technical solutions we have developed. These solutions include the development of the SkyLine and SkyGas approaches which resolve many of the common problems associated with making high frequency, sufficiently replicated GHG flux measurements under field conditions. 4. Unlike most other automated systems, these technologies 'fly' a single chamber to the measurement site, rather than have multiple replicated chambers and analysers. We will present data showing how such systems can deliver high time and spatial resolution flux data, with a minimum of operator intervention and, potentially, at relatively low per plot cost. We will also show how such measurements can be extended to monitoring fluxes from freshwater features in the landscape.

Ineson, Philip; Stockdale, James

2014-05-01

244

Area-Averaged Surface Fluxes Over the Litfass Region Based on Eddy-Covariance Measurements  

NASA Astrophysics Data System (ADS)

Micrometeorological measurements (including eddy-covariance measurements of the surface fluxes of sensible and latent heat) were performed during the LITFASS-2003 experiment at 13 field sites over different types of land use (forest, lake, grassland, various agricultural crops) in a 20 × 20 km2 area around the Meteorological Observatory Lindenberg (MOL) of the German Meteorological Service (Deutscher Wetterdienst, DWD). Significant differences in the energy fluxes could be found between the major land surface types (forest, farmland, water), but also between the different agricultural crops (cereals, rape, maize). Flux ratios between the different surfaces changed during the course of the experiment as a result of increased water temperature of the lake, changing soil moisture, and of the vegetation development at the farmland sites. The measurements over grass performed at the boundary-layer field site Falkenberg of the MOL were shown to be quite representative for the farmland part of the area. Measurements from the 13 sites were composed into a time series of the area-averaged surface flux by taking into account the data quality of the single flux values from the different sites and the relative occurrence of each surface type in the area. Such composite fluxes could be determined for about 80% of the whole measurement time during the LITFASS-2003 experiment. Comparison of these aggregated surface fluxes with area-averaged fluxes from long-range scintillometer measurements and from airborne measurements showed good agreement.

Beyrich, Frank; Leps, Jens-Peter; Mauder, Matthias; Bange, Jens; Foken, Thomas; Huneke, Sven; Lohse, Horst; Lüdi, Andreas; Meijninger, Wouter M. L.; Mironov, Dmitrii; Weisensee, Ulrich; Zittel, Peter

2006-10-01

245

MEASURING CO2 FLUX OVER NORTHERN GREAT PLAINS RANGELANDS  

Technology Transfer Automated Retrieval System (TEKTRAN)

The role of rangelands in regulating atmospheric CO2 levels is a critical issue in global climate change research. Rangelands are complex systems occupying more than 40% of the land area in the world and USA. We studied the effects of seasonal grazing on CO2 flux on small plots located on a silty ra...

246

A bottom-up perspective of the net land methanol flux: synthesis of global eddy covariance flux measurements  

NASA Astrophysics Data System (ADS)

Methanol (CH3OH) is, after methane, the second most abundant VOC in the troposphere and globally represents nearly 20% of the total biospheric VOC emissions. With typical concentrations of 1-10 ppb in the continental boundary layer, methanol plays a crucial role in atmospheric chemistry, which needs to be evaluated in the light of ongoing changes in land use and climate. Previous global methanol budgets have approached the net land flux by summing up the various emission terms (namely primary biogenic and anthropogenic emissions, plant decay and biomass burning) and by subtracting dry and wet deposition, resulting in a net land flux in the range of 75-245 Tg y-1. The data underlying these budget calculations largely stem from small-scale leaf gas exchange measurements and while recently column-integrated remotely sensed methanol concentrations have become available for constraining budget calculations, there have been few attempts to contrast model calculations with direct net ecosystem-scale methanol flux measurements. Here we use eddy covariance methanol flux measurements from 8 sites in Europe and North America to study the magnitude of and controls on the diurnal and seasonal variability in the net ecosystem methanol flux. In correspondence with leaf-level literature, our data show that methanol emission and its strong environmental and biotic control (by temperature and stomatal conductance) prevailed at the more productive (agricultural) sites and at a perturbed forest site. In contrast, at more natural, less productive sites substantial deposition of methanol occurred, in particular during periods of surface wetness. These deposition processes are poorly represented by currently available temperature/light and/or production-driven modelling algorithms. A new framework for modelling the bi-directional land-atmosphere methanol exchange is proposed which accounts for the production of methanol in leaves, the regulation of leaf methanol emission by stomatal conductance and the bi-directional methanol exchange within plant canopies as governed by surface wetness and ambient methanol concentrations.

Wohlfahrt, Georg; Amelynck, Crist; Ammann, Christof; Arneth, Almut; Bamberger, Ines; Goldstein, Allen; Hansel, Armin; Heinesch, Bernhard; Holst, Thomas; Hörtnagl, Lukas; Karl, Thomas; Neftel, Albrecht; McKinney, Karena; Munger, William; Schade, Gunnar; Schoon, Niels

2014-05-01

247

Influence of Steel Grade on Surface Cooling Rates and Heat Flux during Quenching  

NASA Astrophysics Data System (ADS)

Immersion quenching is one of the most widely used processes for achieving martensitic and bainitic steels. The efficiency and quality of quenching are generally tested using standard quench probes for obtaining the cooling curves. A host of parameters like quenchant type, steel grade, bath agitation, section thickness, etc., affect the cooling curves. Cooling curve analyses covered under ASTM standards cannot be used to assess the performance of a quenchant for different grades of steel, as they use a common material for the probe. This article reports the development of equipment, which, in conjunction with mathematical models, can be used for obtaining cooling curves for a specific steel/quenchant combination. The mathematical models couple nonlinear transient inverse heat transfer with phase transformation, resulting in cooling curves specific to the steel grade-quenchant combination. The austenite decomposition models were based on an approach consistent with both the TTT diagram of the steel and Fe-C equilibrium phase diagrams. The TTT diagrams for the specific chemistry of the specimens and the thermophysical properties of the individual phases as functions of temperature were obtained using JMatPro software. Experiments were conducted in the laboratory for computing surface temperature and heat flux at the mid-section of a 25-mm diameter by 100-mm-long cylindrical specimen of two types of steels in two different quenchants. A low alloy steel (EN19) and a plain carbon steel (C45) were used for bringing out the influence of austenite transformation on surface cooling rates and heat flux. Two types of industrial quenchants (i) a mineral oil, and (ii) an aqueous solution of polymer were used. The results showed that the cooling curves, cooling rate curves, and the surface heat flux depended on the steel grade with the quenchant remaining the same.

Prasanna Kumar, T. S.

2013-07-01

248

Rn-222 tracing and stable isotope measurements of biogenic gas fluxes from methane saturated sediments  

NASA Technical Reports Server (NTRS)

Transport of reduced biogenic gases from anoxic sediments and soils to the atmosphere can be quantitatively studied through measurement of radon-222/radium-226 disequilibrium. In previous work, seasonal variations in biogenic gas transport mechanisms, net fluxes and overall composition were documented. Now presented are direct field measurements of radon-222 activity in gases exiting organic rich sediments which show their usefulness for tracing of the stripping of dissolved biogenic gases from within the sediment column and transport via bubble ebullition. Methane is depleted in deuterium during the summer as compared with winter months and is in general lighter than in most marine sediments signaling the probable importance of acetate as an important precursor molecule. The significant seasonal isotopic variations observed illustrate the importance of understanding mechanisms and rates of biogenic gas production in order to interpret observed tropospheric isotopic data.

Martens, Christopher S.; Green, C. D.; Blair, Neal; Chanton, J. P.

1985-01-01

249

Comparison of Two Chamber Methods for Measuring Soil Trace-gas Fluxes in Bioenergy Cropping Systems  

NASA Astrophysics Data System (ADS)

Greenhouse gas emissions from soils are often measured using trace-gas flux chamber techniques without a standardized protocol, raising concerns about measurement accuracy and consistency. To address this, we compared measurements from non-steady-state non-through-flow (NTF) chambers with a non-steady-state through-flow (TF) chamber system in three bioenergy cropping systems located in Wisconsin. Additionally, we investigated the effects of NTF flux calculation method and deployment time on flux measurements. In all cropping systems, when NTF chambers were deployed for 60 min and a linear (LR) flux calculation was used, soil CO2 and N2O fluxes were, on average, 18% and 12% lower, respectively, than fluxes measured with a 15 min deployment. Fluxes calculated with the HMR method, a hybrid of non-linear and linear approaches, showed no deployment time effects for CO2 and N2O and produced 27-32% higher CO2 fluxes and 28-33% higher N2O fluxes in all crops than the LR approach with 60 min deployment. Across all crops, CO2 fluxes measured with the TF chamber system were higher by 24.4 to 84.9 mg CO2-C m-2 h-1, than fluxes measured with NTF chambers using either flux calculation method. These results suggest NTF chamber deployment time should be shortened if the LR approach is used though detection limits should be considered, and the HMR approach may be more appropriate when long deployment times are necessary. Significant differences in absolute flux values with different chamber types highlight the need for significant effort in determining the accuracy of methods or alternative flux measurement technologies. N2O fluxes with chamber deployment time for (a) all crops (switchgrass, corn, hybrid poplar) using both linear (LR) and HMR flux calculation methods, (b) each crop individually using LR approach, and (c) each crop individually using HMR approach. Given are seasonal (May-August) means + standard error. Letters indicate significant differences among deployment times (p<0.05, Tukey-Kramer test). Because there were no significant crop x deployment time interactions, significance letters are not shown in (b) and (c).

Duran, B. E.; Kucharik, C. J.

2013-12-01

250

Determination of solar proton fluxes and energies at high solar latitudes by UV radiation measurements  

NASA Technical Reports Server (NTRS)

The latitudinal variation of the solar proton flux and energy causes a density increase at high solar latitudes of the neutral gas penetrating the heliosphere. Measurements of the neutral density by UV resonance radiation observations from interplanetary spacecraft thus permit deductions on the dependence of the solar proton flux on heliographic latitude. Using both the results of Mariner 10 measurements and of other off-ecliptic solar wind observations, the values of the solar proton fluxes and energies at polar heliographic latitudes are determined for several cases of interest. The Mariner 10 analysis, together with IPS results, indicate a significant decrease of the solar proton flux at polar latitudes.

Witt, N.; Blum, P. W.; Ajello, J. M.

1981-01-01

251

Improved radon-flux-measurement system for uranium-tailings pile measurement  

SciTech Connect

The Pacific Northwest Laboratory (PNL) is developing cover technology for uranium mill tailings that will inhibit the diffusion of radon to the atmosphere. As part of this cover program, an improved radon flux measurement system has been developed. The radon measurement system is a recirculating, pressure-balanced, flow-through system that uses activated carbon at ambient temperatures to collect the radon. With the system, an area of 0.93 m/sup 2/ is sampled for periods ranging from 1 to 12 h. The activated carbon is removed from the radon trap and the collected radon is determined by counting the /sup 214/Bi daughter product. Development of the system included studies to determine the efficiency of activated carbon, relative calibration measurements and field measurements made during 1980 at the inactive tailings pile in Grand Junction, Colorado. Results of these studies are presented.

Freeman, H.D.

1981-10-01

252

Measuring the energy flux at the substrate position during magnetron sputter deposition processes  

SciTech Connect

In this work, the energetic conditions at the substrate were investigated in dc magnetron sputtering (DCMS), pulsed dc magnetron sputtering (pDCMS), and high power impulse magnetron sputtering (HiPIMS) discharges by means of an energy flux diagnostic based on a thermopile sensor, the probe being set at the substrate position. Measurements were performed in front of a titanium target for a highly unbalanced magnetic field configuration. The average power was always kept to 400 W and the probe was at the floating potential. Variation of the energy flux against the pulse peak power in HiPIMS was first investigated. It was demonstrated that the energy per deposited titanium atom is the highest for short pulses (5 {mu}s) high pulse peak power (39 kW), as in this case, the ion production is efficient and the deposition rate is reduced by self-sputtering. As the argon pressure is increased, the energy deposition is reduced as the probability of scattering in the gas phase is increased. In the case of the HiPIMS discharge run at moderate peak power density (10 kW), the energy per deposited atom was found to be lower than the one measured for DCMS and pDCMS discharges. In these conditions, the HiPIMS discharge could be characterized as soft and close to a pulsed DCMS discharge run at very low duty cycle. For the sake of comparison, measurements were also carried out in DCMS mode with a balanced magnetron cathode, in the same working conditions of pressure and power. The energy flux at the substrate is significantly increased as the discharge is generated in an unbalanced field.

Cormier, P.-A.; Thomann, A.-L.; Dussart, R.; Semmar, N.; Mathias, J. [GREMI, Universite d'Orleans, 14 rue d'Issoudun, B.P. 6744, 45067 Orleans Cedex 2 (France); Balhamri, A. [Laboratoire de Chimie des Interactions Plasma-Surface, Universite de Mons, 23 Place du Parc, 7000 Mons (Belgium); Laboratoire Rayonnement and Matiere: Laboratoire d'Optique Appliquee et Transfert d'Energie (LOPATE), Faculte des Sciences et Techniques de Settat, Universite Hassan 1, B.P. 461 Settat (Morocco); Snyders, R. [Laboratoire de Chimie des Interactions Plasma-Surface, Universite de Mons, 23 Place du Parc, 7000 Mons (Belgium); Materia Nova R and D Center, Avenue Copernic 1, Mons (Belgium); Konstantinidis, S. [Laboratoire de Chimie des Interactions Plasma-Surface, Universite de Mons, 23 Place du Parc, 7000 Mons (Belgium)

2013-01-07

253

Integral equations of the photon fluence rate and flux based on a generalized Delta-Eddington phase function  

PubMed Central

We present a generalized Delta-Eddington phase function to simplify the radiative transfer equation to integral equations with respect to both photon fluence rate and flux vector. The photon fluence rate and flux can be solved from the system of integral equations. By comparing to the Monte Carlo simulation results, the solutions of the system of integral equations accurately model the photon propagation in biological tissue over a wide range of optical parameters. PMID:18465979

Cong, Wenxiang; Shen, Haiou; Cong, Alexander X.; Wang, Ge

2009-01-01

254

Quantitative method for measuring heat flux emitted from a cryogenic object  

DOEpatents

The present invention is a quantitative method for measuring the total heat flux, and of deriving the total power dissipation, of a heat-fluxing object which includes the steps of placing an electrical noise-emitting heat-fluxing object in a liquid helium bath and measuring the superfluid transition temperature of the bath. The temperature of the liquid helium bath is thereafter reduced until some measurable parameter, such as the electrical noise, exhibited by the heat-fluxing object or a temperature-dependent resistive thin film in intimate contact with the heat-fluxing object, becomes greatly reduced. The temperature of the liquid helum bath is measured at this point. The difference between the superfluid transition temperature of the liquid helium bath surrounding the heat-fluxing object, and the temperature of the liquid helium bath when the electrical noise emitted by the heat-fluxing object becomes greatly reduced, is determined. The total heat flux from the heat-fluxing object is determined as a function of this difference between these temperatures. In certain applications, the technique can be used to optimize thermal design parameters of cryogenic electronics, for example, Josephson junction and infra-red sensing devices.

Duncan, Robert V. (Tijeras, NM)

1993-01-01

255

Comparative soil CO2 flux measurements and geostatisticalestimation methods on masaya volcano, nicaragua  

SciTech Connect

We present a comparative study of soil CO{sub 2} flux (F{sub CO2}) measured by five groups (Groups 1-5) at the IAVCEI-CCVG Eighth Workshop on Volcanic Gases on Masaya volcano, Nicaragua. Groups 1-5 measured F{sub CO2} using the accumulation chamber method at 5-m spacing within a 900 m{sup 2} grid during a morning (AM) period. These measurements were repeated by Groups 1-3 during an afternoon (PM) period. All measured F{sub CO2} ranged from 218 to 14,719 g m{sup -2}d{sup -1}. Arithmetic means and associated CO{sub 2} emission rate estimates for the AM data sets varied between groups by {+-}22%. The variability of the five measurements made at each grid point ranged from {+-}5 to 167% and increased with the arithmetic mean. Based on a comparison of measurements made by Groups 1-3 during AM and PM times, this variability is likely due in large part to natural temporal variability of gas flow, rather than to measurement error. We compared six geostatistical methods (arithmetic and minimum variance unbiased estimator means of uninterpolated data, and arithmetic means of data interpolated by the multiquadric radial basis function, ordinary kriging, multi-Gaussian kriging, and sequential Gaussian simulation methods) to estimate the mean and associated CO{sub 2} emission rate of one data set and to map the spatial F{sub CO2} distribution. While the CO{sub 2} emission rates estimated using the different techniques only varied by {+-}1.1%, the F{sub CO2} maps showed important differences. We suggest that the sequential Gaussian simulation method yields the most realistic representation of the spatial distribution of F{sub CO2} and is most appropriate for volcano monitoring applications.

Lewicki, J.L.; Bergfeld, D.; Cardellini, C.; Chiodini, G.; Granieri, D.; Varley, N.; Werner, C.

2004-04-27

256

Intercomparison of fast response commercial gas analysers for nitrous oxide flux measurements under field conditions  

NASA Astrophysics Data System (ADS)

Four gas analysers capable of measuring nitrous oxide (N2O) concentration at a response time necessary for eddy covariance flux measurements were operated from spring until winter 2011 over a field cultivated with reed canary grass (RCG, Phalaris arundinacea, L.), a perennial bioenergy crop in eastern Finland. The instruments were TGA100A (Campbell Scientific Inc.), CW-TILDAS-CS (Aerodyne Research Inc.), N2O / CO-23d (Los Gatos Research Inc.) and QC-TILDAS-76-CS (Aerodyne Research Inc.). The period with high emissions, lasting for about 2 weeks after fertilization in late May, was characterized by an up to 2 orders of magnitude higher emission, whereas during the rest of the campaign the N2O fluxes were small, from 0.01 to 1 nmol m-2 s-1. Two instruments, CW-TILDAS-CS and N2O / CO-23d, determined the N2O exchange with minor systematic difference throughout the campaign, when operated simultaneously. TGA100A produced the cumulatively highest N2O estimates (with 29% higher values during the period when all instruments were operational). QC-TILDAS-76-CS obtained 36% lower fluxes than CW-TILDAS-CS during the first period, including the emission episode, whereas the correspondence with other instruments during the rest of the campaign was good. The reasons for systematic differences were not identified, suggesting further need for detailed evaluation of instrument performance under field conditions with emphasis on stability, calibration and any other factors that can systematically affect the accuracy of flux measurements. The instrument CW-TILDAS-CS was characterized by the lowest noise level (with a standard deviation of around 0.12 ppb at 10 Hz sampling rate) as compared to N2O / CO-23d and QC-TILDAS-76-CS (around 0.50 ppb) and TGA100A (around 2 ppb). We identified that for all instruments except CW-TILDAS-CS the random error due to instrumental noise was an important source of uncertainty at the 30 min averaging level and the total stochastic error was frequently of the same magnitude as the fluxes when N2O exchange was small at the measurement site. Both instruments based on continuous-wave quantum cascade laser, CW-TILDAS-CS and N2O / CO-23d, were able to determine the same sample of low N2O fluxes with a high mutual coefficient of determination at the 30 min averaging level and with minor systematic difference over the observation period of several months. This enables us to conclude that the new-generation instrumentation is capable of measuring small N2O exchange with high precision and accuracy at sites with low fluxes.

Rannik, Ü.; Haapanala, S.; Shurpali, N. J.; Mammarella, I.; Lind, S.; Hyvönen, N.; Peltola, O.; Zahniser, M.; Martikainen, P. J.; Vesala, T.

2015-01-01

257

Aerosol Fluxes over Amazon Rain Forest Measured with the Eddy Covariance Method  

NASA Astrophysics Data System (ADS)

We present measurements of vertical aerosol fluxes over the Amazon carried out on top of K34, a 50 meter high tower in the Cuieiras Reserve about 50 km north of Manaus in northern Brazil. The turbulent fluxes were measured with the eddy covariance method. The covariance of vertical wind speed from a sonic anemometer Gill Windmaster and total aerosol number concentration from a condensation particle counter (CPC) TSI 3010 provided the total number flux (diameter >0.01 ?m). The covariance of vertical wind speed and size resolved number concentrations from an optical particle counter (OPC) Grimm 1.109 provided size resolved number fluxes in 15 bins from 0.25 ?m to 2.5 ?m diameter. Additionally fluxes of CO2 and H2O were derived from Li-7500 observations. The observational period, from early March to early August, includes both wet and dry season. OPC fluxes generally show net aerosol deposition both during wet and dry season with the largest downward fluxes during midday. CPC fluxes show different patterns in wet and dry season. During dry season, when number concentrations are higher, downward fluxes clearly dominate. In the wet season however, when number concentrations are lower, our data indicates that upward and downward fluxes are quite evenly distributed during course of a day. On average there is a peak in upward flux during late morning and another peak during the afternoon. Since the OPC fluxes in the same time show net deposition, there is an indication of net source of primary aerosol particles with diameters between 10 and 250 nm emitted from the rain forest. Future data analysis will hopefully shed light on origin and formation mechanism of these particles and thus provide a deeper insight in the rain forest - atmosphere interactions. The aerosol flux measurements were carried out as a part of the AMAZE project in collaboration with University of Sao Paulo, Brazil, and financial support was provided by Swedish International Development Cooperation Agency (SIDA).

Ahlm, L.; Nilsson, E. D.; Krejci, R.; Mårtensson, E. M.; Vogt, M.; Artaxo, P.

2008-12-01

258

A fast gauge for energy flux density measurement  

NASA Astrophysics Data System (ADS)

Herein, the design and characterization of a fast energy flux density gauge are described. The gauge is based on a thermoelectrical pair with the junction made of a thin layer of silver. High absorptivity is attained by an electrolytic deposit of platinum black on the silver coat. Dynamic calibration gives a response time below 100 microsec. Computer methods to obtain the energy flux density from temperature-time history were evaluated. The results of the tests performed with igniters of pelleted boron/potassium nitrate and black powder, used in solid propellant ignition, are shown. The gauge developed can be applied to fast processes which require small response time. The gauge does not need previous calibration, it is resistant to vibrations and accelerations, and, at the same time, it is small in size, economical, and easy to build.

Garcia, Jorge; Bana de Schor, Beatriz

1990-01-01

259

Evaluating the value of enhanced atmospheric measurements and models to improve interpretation of flux data  

NASA Astrophysics Data System (ADS)

Gaps in trace-gas fluxes measured via eddy-covariance occur for many reasons. One of these reasons is that many sites are equipped with flux measurements at only one height above the canopy. The optimal height for detecting fluxes, however, changes in time with the environmental conditions at the site. In some instances, a measurement such as friction velocity (u*) can indicate when data should be eliminated. When u* is high however, data are not eliminated but sensors may not actually be detecting fluxes from the ecosystem of interest. This latter scenario often occurs at night when the surface layer of the atmosphere is stably stratified and may be lower than the tower measurement height. Here, we propose that increased information about atmospheric structure near the surface and the processes occurring within the surface layer can inform an improved interpretation of fluxes as measured at a single point above the canopy. We adjusted and tuned the Advanced Canopy-Atmosphere-Soil Algorithm (ACASA) for modeling a California mediterranean oak savanna, the Tonzi AmeriFlux Site near Ione, CA, USA. We fused datasets of wind profiles, temperature profiles, and fluxes from standard eddy-covariance measurements, radiosonde launches, and upward-facing LIDAR measurements to determine surface layer depth and then drive ACASA from the top of the surface layer. By combining modeled profiles of the surface layer with flux measurements above and below the canopy, we were able to better interpret when flux signals were true indications of canopy processes, and the sources of flux anomalies.

Osuna, J. L.; Wharton, S.; Falk, M.; Pyles, R. D.; Ma, S.; Baldocchi, D. D.

2013-12-01

260

Measurement of auroral Birkeland currents and energetic particle fluxes  

Microsoft Academic Search

A rocket-borne experiment containing a vector magnetometer and a set of ; charged-particle detectors was launched from Poker Flat, Alaska, at 2217 LT on ; February 13, 1971, over a single auroral arc. Particle data in the energy range ; 0.5-20 kev, obtained during part of the night, show a peak incident flux of 4x10\\/; sup 7\\/ el\\/cm² sec ster

P. A. Cloutier; B. R. Sandel; H. R. Anderson; P. M. Pazich; R. J. Spiger

1973-01-01

261

Soil CO 2 flux measurements in volcanic and geothermal areas  

Microsoft Academic Search

The accumulation chamber methodology allows one to obtain reliable values of the soil CO2 flux, ?soil CO2, in the range 0.2 to over 10?000 g m?2 d?1, as proven by both laboratory tests and field surveys in geothermal and volcanic areas. A strong negative correlation is observed between ??soil CO2\\/?t and ?Patm\\/?t. Maps of classes of log ?soil CO2 for

G. Chiodini; R. Cioni; M. Guidi; B. Raco; L. Marini

1998-01-01

262

Measured and simulated nitrogen fluxes after field application of food-processing and municipal organic wastes.  

PubMed

The aims of this study were to (i) assess N fluxes (mineralization, volatilization, denitrification, leaching) caused by spreading various organic wastes from food-processing industries during a field experiment, and (ii) to identify the main factors affecting N transformation processes after field spreading. Experimental treatments including the spreading of six types of waste and a control soil were set up in August 2000 and studied for 22 mo under bare soil conditions. Ammonia and nitrous oxide emissions, and nitrogen mineralization were measured in experimental devices and extrapolated to field conditions or computed in calculation models. The ammonia emissions varied from 80 to 580 g kg(-1) NH4+-N applied, representing 0 to 90 g N kg(-1) total N applied. Under these meteorologically favorable conditions (dry and warm weather), waste pH was the main factor affecting volatilization rates. Cumulated N2O-N fluxes were estimated at 2 to 5 g kg(-1) total N applied, which was quite low due to the low soil water content during the experimental period; water-filled pore space (WFPS) was confirmed as the main factor affecting N2O fluxes. Nitrogen mineralization from wastes represented 126 to 723 g N kg(-1) organic N added from the incorporation date to 14 May 2001 and was not related to the organic C to organic N ratio of wastes. Nitrogen lost by leaching during the equivalent period ranged from 30 to 890 g kg(-1) total N applied. The highest values were obtained for wastes having the highest inorganic N content and mineralization rates. PMID:19141817

Parnaudeau, V; Génermont, S; Hénault, C; Farrugia, A; Robert, P; Nicolardot, B

2009-01-01

263

Long-term isoprene flux measurements above a northern hardwood forest  

Microsoft Academic Search

We report continuous whole canopy isoprene emission fluxes from a northern hardwood forest in Michigan for the 1999–2002 growing seasons. The eddy covariance fluxes of isoprene, CO2, latent heat, and sensible heat are presented along with an analysis of the seasonal and year-to-year variations. Measurements were made in collaboration with the AmeriFlux site located at the University of Michigan Biological

Shelley Pressley; Brian Lamb; Hal Westberg; Julia Flaherty; Jack Chen; Christoph Vogel

2005-01-01

264

The measurement of absolute thermal neutron flux using liquid scintillation counting techniques  

E-print Network

factor for flux depression due to a neutron absorbing indium foil. Later Tittle (2, 3) studied the same problem and extended Bothe's re- sults to a more useful form. To minimize flux depression and also the self absorption of the induced radioactivity... of the foil, the use of very thin foils has become a standard practice . Greenfield et al . (4) have described in detail the conventional techniques for measuring absolute thermal neutron flux with thin indium foils. The authors discuss the importance...

Walker, Jack Vernon

2012-06-07

265

Remote Measurement of Heat Flux from Power Plant Cooling Lakes  

SciTech Connect

Laboratory experiments have demonstrated a correlation between the rate of heat loss q? from an experimental fluid to the air above and the standard deviation ? of the thermal variability in images of the fluid surface. These experimental results imply that q? can be derived directly from thermal imagery by computing ?. This paper analyses thermal imagery collected over two power plant cooling lakes to determine if the same relationship exists. Turbulent boundary layer theory predicts a linear relationship between q? and ? when both forced (wind driven) and free (buoyancy driven) convection are present. Datasets derived from ground- and helicopter-based imagery collections had correlation coefficients between ? and q? of 0.45 and 0.76, respectively. Values of q? computed from a function of ? and friction velocity u* derived from turbulent boundary layer theory had higher correlations with measured values of q? (0.84 and 0.89). This research may be applicable to the problem of calculating losses of heat from the ocean to the atmosphere during high-latitude cold-air outbreaks because it does not require the information typically needed to compute sensible, evaporative, and thermal radiation energy losses to the atmosphere.

Garrett, A.; Kurzeja, R.; Villa-Aleman, E.; Bollinger, J.

2013-01-01

266

Novel Surface Thermocouple Probes for Divertor Heat Flux Measurement  

NASA Astrophysics Data System (ADS)

An array of novel surface thermocouple probes have been installed and tested in the outer divertor of Alcator C-Mod. These sensors can, in principle, record divertor surface temperatures with fast time response (? >= 10 ? sec), allowing a direct estimate of the plasma heat flux to be inferred. The design is an adaptation of a commercially available device(``The Self-Renewing Thermocouple,'' Nanmac Corp., Framingham, MA), employing a coaxial-like geometry with a single tungsten-rhenium ribbon wire embedded inside a 6.35 mm diameter molybdenum rod. Various prototypes were tested, including probes with flush and 5^circ angles with respect to the divertor surface, and probes with and without protective surface coatings. Typical surface temperature rises are ~ 300-700 ^circC, corresponding to signals of ~ 3-9 mV. RC filters with 10 ms time constants are used to reduce noise introduced by the plasma environment. The surface temperature corresponding to typical RMS noise levels is ~ 25 ^circC. Using a one-dimensional, semi-infinite slab model, parallel heat fluxes in the range of 50-500 MW/m^2 are estimated. A comparison with heat flux estimates from Langmuir probes located adjacent to the thermocouple array will be presented. Supported by U.S. DOE Contract No. DE-AC02-78ET51013

Gangadhara, S.; Labombard, B.; Lipschultz, B.; Pierce, N.

1996-11-01

267

Wind erosion flux measurements and variability on traditionally cultivated fields in South West Niger: crop residues and soils crust impacts.  

NASA Astrophysics Data System (ADS)

In the Sahel, crop residues are well known to reduce wind erosion. But these crop residues were studied on controlled experimental plots with amounts much higher than those traditionally encountered on cultivated fields. This work aims i) to monitor crop residues on traditional field and to quantify its influence on wind erosion ii) to characterize the impacts of soils crusting on erosion flux. At Banizoumbou in Niger, crop residues cover rates (%) and wind erosion fluxes (kg m-1 per event) have been measured for six seasons on two plots: PA (1,5 ha) maintained bare and PB (1,5 ha) traditionally cultivated. Results showed that crop residues efficiently prevent cultivated fields from wind erosion during the dry season and considerably reduce erosion fluxes at the beginning of the rainy season. A minimal cover rate of about 2 % (100 Kg.ha-1) appears as critical to limit wind erosion. Below this rate, soil losses by wind erosion would dramatically increase as observed on plot PA. On this plot, the area covered with erosion crusts increased at the soil surface from the first year of measurements during each rainy season. They are due to the combined effect of wind erosion and rainfall, but not to water erosion as the plot is not sloped. After soils crusting wind erosion flux regularly decreases on plot PA. This decrease seems to be due to supply limitation in erodible sediment.

Abdourhamane Touré, A.; Rajot, J. L.; Garba, Z.; Marticorena, B.; Petit, C.; Sebag, D.; Malam Issa, O.

2012-04-01

268

Time and Space Resolved Wall Temperature Measurements during Nucleate Boiling with Constant Heat Flux Boundary Conditions  

NASA Technical Reports Server (NTRS)

The lack of temporally and spatially resolved measurements under nucleate bubbles has complicated efforts to fully explain pool-boiling phenomena. The objective of this current work is to acquire time and space resolved temperature distributions under nucleate bubbles on a constant heat flux surface. This was performed using a microheater array with 100 micron resolution that allowed effectively simultaneous measurements of surface temperature while supplying a constant dissipative heat flux. This data is then correlated with high speed (> 1000Hz) visual recordings of the bubble growth and departure from the heater surface acquired from below and from the side of the heater. The data indicate that a significant source of energy during bubble nucleation and initial growth is the superheated layer around the bubble. Bubble coalescence was not observed to decrease surface temperature as significantly as bubble departure from the surface. Since bubble departure is typically followed by a sharp increase in the heater surface temperature, it is surmised that the departing bubble effectively removes the superheated layer, allowing a high local heat transfer rate with the bulk fluid through transient conduction/micro-convection during rewetting.

Myers, Jerry G.; Hussey, Sam W.; Yee, Glenda F.; Yerramilli, Vamsee K.; Kim, Jungho

2005-01-01

269

Up-scaling methods of greenhouse gas fluxes between the soil and the atmosphere using a measuring tunnel as well as open-path measurement techniques for the flux-gradient method  

NASA Astrophysics Data System (ADS)

For up-scaling the emissions of N2O, CO2 and CH4 (GHG) from arable field soils a measuring tunnel for controlled enrichment of released gases was installed at the soil surface covering an area of 495 or 306 m2. The concentrations of GHG and humidity were measured by the path-averaging, multi-component Fourier Transform Infrared (FTIR) absorption spectrometry at an open path of 100 m length across the whole measuring tunnel. During a 2-years-time frame the N2O fluxes between the soil and the atmosphere at the agricultural field varied between 1.0 and 21 µg N2O-N m-2 h-1. These results were compared with N2O emission rates that were simultaneously measured with a conventional closed chamber technique. The resulting N2O fluxes between the soil and the atmosphere of both methods had the same order of magnitude. However, we found an extreme spatial variability of N2O fluxes at the scale of the closed chambers. The hypothesis that an enlargement of the measured soil surface area is an appropriate measure to avoid the problems of up-scaling results of small scale chamber measurements was confirmed by the results obtained with the measuring tunnel. Currently, a non-intrusive emission and flux measurement method at a scale from 100 m up to. 27.000 m2 on the basis of the flux-gradient method (0.50 and 2.70 m height above surface) is developed and tested by means of open-path multi-component measurement methods (FTIR, GHG) and area averaging meteorological measurements (determination of horizontal winds, friction velocity using acoustic tomography). Two campaigns in October 2007 and June 2008 were performed with this new methodology when wind speeds were low. Due to the very low wind speeds and insufficient turbulence for the application of the usual flux-gradient method a new concept introducing the viscosity instead of stability corrections was developed. It requires a direct measurement of the friction velocity and the vertical gradient of the horizontal wind speeds by ultra-sonic anemometers. The mean results of this measurement method during both campaigns and the measuring tunnel results differ by about 25 % to the mean measuring tunnel results. The calculated single values on the basis of 10-minutes-mean data varied from 2 up to 42 µg N2O-N m-2 h-1.

Schäfer, K.; Jahn, C.; Emeis, S.; Wiwiorra, M.; von der Heide, C.; Böttcher, J.; Deurer, M.; Weymann, D.; Schleichardt, A.; Raabe, A.

2009-09-01

270

Measurement of the Cosmic Ray and Neutrino-Induced Muon Flux at the Sudbury Neutrino Observatory  

SciTech Connect

Results are reported on the measurement of the atmospheric neutrino-induced muon flux at a depth of 2 kilometers below the Earth's surface from 1229 days of operation of the Sudbury Neutrino Observatory (SNO). By measuring the flux of through-going muons as a function of zenith angle, the SNO experiment can distinguish between the oscillated and un-oscillated portion of the neutrino flux. A total of 514 muon-like events are measured between -1 {le} cos {theta}{sub zenith} 0.4 in a total exposure of 2.30 x 10{sup 14} cm{sup 2} s. The measured flux normalization is 1.22 {+-} 0.09 times the Bartol three-dimensional flux prediction. This is the first measurement of the neutrino-induced flux where neutrino oscillations are minimized. The zenith distribution is consistent with previously measured atmospheric neutrino oscillation parameters. The cosmic ray muon flux at SNO with zenith angle cos {theta}{sub zenith} > 0.4 is measured to be (3.31 {+-} 0.01 (stat.) {+-} 0.09 (sys.)) x 10{sup -10} {micro}/s/cm{sup 2}.

SNO collaboration; Aharmim, B.; Ahmed, S.N.; Andersen, T.C.; Anthony, A.E.; Barros, N.; Beier, E.W.; Bellerive, A.; Beltran, B.; Bergevin, M.; Biller, S.D.; Boudjemline, K.; Boulay, M.G.; Burritt, T.H.; Cai, B.; Chan, Y.D.; Chen, M.; Chon, M.C.; Cleveland, B.T.; Cox-Mobrand, G.A.; Currat, C.A.; Dai, X.; Dalnoki-Veress, F.; Deng, H.; Detwiler, J.; Doe, P.J.; Dosanjh, R.S.; Doucas, G.; Drouin, P.-L.; Duncan, F.A.; Dunford, M.; Elliott, S.R.; Evans, H.C.; Ewan, G.T.; Farine, J.; Fergani, H.; Fleurot, F.; Ford, R.J.; Formaggio, J.A.; Gagnon, N.; Goon, J.TM.; Grant, D.R.; Guillian, E.; Habib, S.; Hahn, R.L.; Hallin, A.L.; Hallman, E.D.; Hargrove, C.K.; Harvey, P.J.; Harvey, P.J.; Heeger, K.M.; Heintzelman, W.J.; Heise, J.; Helmer, R.L.; Hemingway, R.J.; Henning, R.; Hime, A.; Howard, C.; Howe, M.A.; Huang, M.; Jamieson, B.; Jelley, N.A.; Klein, J.R.; Kos, M.; Kruger, A.; Kraus, C.; Krauss, C.B.; Kutter, T.; Kyba, C.C.M.; Lange, R.; Law, J.; Lawson, I.T.; Lesko, K.T.; Leslie, J.R.; Levine, I.; Loach, J.C.; Luoma, S.; MacLellan, R.; Majerus, S.; Mak, H.B.; Maneira, J.; Marino, A.D.; Martin, R.; McCauley, N.; McDonald, A.B.; McGee, S.; Mifflin, C.; Miller, M.L.; Monreal, B.; Monroe, J.; Noble, A.J.; Oblath, N.S.; Okada, C.E.; O?Keeffe, H.M.; Opachich, Y.; Orebi Gann, G.D.; Oser, S.M.; Ott, R.A.; Peeters, S.J.M.; Poon, A.W.P.; Prior, G.; Rielage, K.; Robertson, B.C.; Robertson, R.G.H.; Rollin, E.; Schwendener, M.H.; Secrest, J.A.; Seibert, S.R.; Simard, O.; Simpson, J.J.; Sinclair, D.; Skensved, P.; Smith, M.W.E.; Sonley, T.J.; Steiger, T.D.; Stonehill, L.C.; Tagg, N.; Tesic, G.; Tolich, N.; Tsui, T.; Van de Water, R.G.; VanDevender, B.A.; Virtue, C.J.; Waller, D.; Waltham, C.E.; Wan Chan Tseung, H.; Wark, D.L.; Watson, P.; Wendland, J.; West, N.; Wilkerson, J.F.; Wilson, J.R.; Wouters, J.M.; Wright, A.; Yeh, M.; Zhang, F.; Zuber, K.

2009-02-16

271

A comparison of six methods for measuring soil-surface carbon dioxide fluxes  

NASA Astrophysics Data System (ADS)

Measurements of soil-surface CO2 fluxes are important for characterizing the carbon budget of boreal forests because these fluxes can be the second largest component of the budget. Several methods for measuring soil-surface CO2 fluxes are available: (1) closed-dynamic-chamber systems, (2) closed-static-chamber systems, (3) open-chamber systems, and (4) eddy covariance systems. This paper presents a field comparison of six individual systems for measuring soil-surface CO2 fluxes with each of the four basic system types represented. A single system is used as a reference and compared to each of the other systems individually in black spruce (Picea mariana), jack pine (Pinus banksiana), or aspen (Populus tremuloides) forests. Fluxes vary from 1 to 10 ?mol CO2 m-2 s-1. Adjustment factors to bring all of the systems into agreement vary from 0.93 to 1.45 with an uncertainty of about 10-15%.

Norman, J. M.; Kucharik, C. J.; Gower, S. T.; Baldocchi, D. D.; Crill, P. M.; Rayment, M.; Savage, K.; Striegl, R. G.

1997-12-01

272

A comparison of six methods for measuring soil-surface carbon dioxide fluxes  

USGS Publications Warehouse

Measurements of soil-surface CO2 fluxes are important for characterizing the carbon budget of boreal forests because these fluxes can be the second largest component of the budget. Several methods for measuring soil-surface CO2 fluxes are available: (1) closed-dynamic-chamber systems, (2) closed-static-chamber systems, (3) open-chamber systems, and (4) eddy covariance systems. This paper presents a field comparison of six individual systems for measuring soil-surface CO2 fluxes with each of the four basic system types represented. A single system is used as a reference and compared to each of the other systems individually in black spruce (Picea mariana), jack pine (Pinus banksiana), or aspen (Populus tremuloides) forests. Fluxes vary from 1 to 10 ??mol CO2 m-2 s-1. Adjustment factors to bring all of the systems into agreement vary from 0.93 to 1.45 with an uncertainty of about 10-15%.

Norman, J.M.; Kucharik, C.J.; Gower, S.T.; Baldocchi, D.D.; Crill, P.M.; Rayment, M.; Savage, K.; Striegl, R.G.

1997-01-01

273

Independent Measurement of the Total Active B8 Solar Neutrino Flux Using an Array of He3 Proportional Counters at the Sudbury Neutrino Observatory  

Microsoft Academic Search

The Sudbury Neutrino Observatory (SNO) used an array of He3 proportional counters to measure the rate of neutral-current interactions in heavy water and precisely determined the total active (nux) B8 solar neutrino flux. This technique is independent of previous methods employed by SNO. The total flux is found to be 5.54-0.31+0.33(stat)-0.34+0.36(syst)×106cm-2s-1, in agreement with previous measurements and standard solar models.

B. Aharmim; S. N. Ahmed; J. F. Amsbaugh; A. E. Anthony; J. Banar; N. Barros; E. W. Beier; A. Bellerive; B. Beltran; M. Bergevin; S. D. Biller; K. Boudjemline; M. G. Boulay; T. J. Bowles; M. C. Browne; T. V. Bullard; T. H. Burritt; B. Cai; Y. D. Chan; D. Chauhan; M. Chen; B. T. Cleveland; G. A. Cox-Mobrand; C. A. Currat; X. Dai; H. Deng; J. Detwiler; M. Dimarco; P. J. Doe; G. Doucas; P.-L. Drouin; C. A. Duba; F. A. Duncan; M. Dunford; E. D. Earle; S. R. Elliott; H. C. Evans; G. T. Ewan; J. Farine; H. Fergani; F. Fleurot; R. J. Ford; J. A. Formaggio; M. M. Fowler; N. Gagnon; J. V. Germani; A. Goldschmidt; J. T. M. Goon; K. Graham; E. Guillian; S. Habib; R. L. Hahn; A. L. Hallin; E. D. Hallman; A. A. Hamian; G. C. Harper; P. J. Harvey; R. Hazama; K. M. Heeger; W. J. Heintzelman; J. Heise; R. L. Helmer; R. Henning; A. Hime; C. Howard; M. A. Howe; M. Huang; P. Jagam; B. Jamieson; N. A. Jelley; K. J. Keeter; J. R. Klein; L. L. Kormos; M. Kos; A. Krüger; C. Kraus; C. B. Krauss; T. Kutter; C. C. M. Kyba; R. Lange; J. Law; I. T. Lawson; K. T. Lesko; J. R. Leslie; J. C. Loach; R. MacLellan; S. Majerus; H. B. Mak; J. Maneira; R. Martin; K. McBryde; N. McCauley; A. B. McDonald; S. McGee; C. Mifflin; G. G. Miller; M. L. Miller; B. Monreal; J. Monroe; B. Morissette; A. Myers; B. G. Nickel; A. J. Noble; N. S. Oblath; H. M. O'Keeffe; R. W. Ollerhead; G. D. Orebi Gann; S. M. Oser; R. A. Ott; S. J. M. Peeters; A. W. P. Poon; G. Prior; S. D. Reitzner; K. Rielage; B. C. Robertson; R. G. H. Robertson; E. Rollin; M. H. Schwendener; J. A. Secrest; S. R. Seibert; O. Simard; J. J. Simpson; L. Sinclair; P. Skensved; M. W. E. Smith; T. D. Steiger; L. C. Stonehill; G. Tesic; P. M. Thornewell; N. Tolich; T. Tsui; C. D. Tunnell; T. van Wechel; R. van Berg; B. A. Vandevender; C. J. Virtue; T. J. Walker; B. L. Wall; D. Waller; H. Wan Chan Tseung; J. Wendland; J. B. Wilhelmy; J. F. Wilkerson; J. R. Wilson; J. M. Wouters; A. Wright; M. Yeh; F. Zhang; K. Zuber

2008-01-01

274

A comparison of two nitrification inhibitors used to measure nitrification rates in estuarine sediments  

USGS Publications Warehouse

Nitrification rates were measured using intact sediment cores from South San Francisco Bay and two different nitrification inhibitors: acetylene and methyl fluoride. Sediment oxygen consumption and ammonium and nitrate fluxes were also measured in these cores. Four experiments were conducted in the spring, and one in the fall of 1993. There was no significant difference in nitrification rates measured using the two inhibitors, which suggests that methyl fluoride can be used as an effective inhibitor of nitrification. Nitrification was positively correlated with sediment oxygen consumption and numbers of macrofauna. This suggests that bioturbation by macrofauna is an important control of nitrification rates. Irrigation by the tube-dwelling polychaete, Asychis elongata, which dominates the benthic biomass at this location, appears particularly important. Ammonium fluxes out of the sediment were greatest about one week after the spring bloom, while nitrification peaked about one month later.

Caffrey, J.M.; Miller, L.G.

1995-01-01

275

Measurement of erosion rate by absorption spectroscopy in a Hall thruster  

SciTech Connect

The erosion rate of a Hall thruster was estimated with the objective of building a real-time erosion rate monitoring system using a 1 kW class anode layer type Hall thruster. This system aids the understanding of the tradeoff between lifetime and performance. To estimate the flux of the sputtered wall material, the number density of the sputtered iron was measured by laser absorption spectroscopy using an absorption line from ground atomic iron at 371.9935 nm. An ultravioletAl{sub x}In{sub y}Ga{sub (1-x-y)}N diode laser was used as the probe. The estimated number density of iron was 1.1x10{sup 16} m{sup -3}, which is reasonable when compared with that measured by duration erosion tests. The relation between estimated erosion rate and magnetic flux density also agreed with that measured by duration erosion tests.

Yamamoto, Naoji; Yokota, Shigeru; Matsui, Makoto; Komurasaki, Kimiya; Arakawa, Yoshihiro [Department of Advanced Energy Engineering Science, Kyushu University, 6-1 Kasuga-kouen, Kasuga, Fukuoka 816-8580 (Japan); Department of Aeronautics and Astronautics, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656 (Japan); Department of Advanced Energy, The University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba 277-8562 (Japan); Department of Aeronautics and Astronautics, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656 (Japan)

2005-08-15

276

Field measurement of small ozone fluxes to snow, wet bare soil, and lake water  

Microsoft Academic Search

Eddy-correlation measurements over snow, wet bare soil, and lake water indicate very small vertical ozone fluxes. Adjustments to the small vertical fluxes are needed to take into account the effect of mean Stefan flow associated with evaporation at the surface and the effects of correlation between density variations and vertical wind fluctuations. For snow, the residual resistance calculated for the

M. L. Wesely; D. R. Cook; R. M. Williams

1981-01-01

277

Balloon-borne measurements of the ultraviolet flux in the Arctic stratosphere during winter  

NASA Technical Reports Server (NTRS)

Filter radiometers sensitive from 280 to 320 nm and from 280 to 400 nm, respectively, were used for measurements of the actinic flux in the stratosphere. Since the instruments are calibrated for absolute spectral sensitivity the data can be compared with model calculations of the actinic flux. Data were obtained during seven balloon flights during the European Arctic Stratospheric Ozone Experiment (EASOE).

Schiller, Cornelius; Mueller, Martin; Klein, Erich; Schmidt, Ulrich; Roeth, Ernst-Peter

1994-01-01

278

Eddy covariance flux measurements of biogenic VOCs during ECHO 2003 using proton transfer reaction mass spectrometry  

NASA Astrophysics Data System (ADS)

Within the framework of the AFO 2000 project ECHO, two PTR-MS instruments were operated in combination with sonic anemometers to determine biogenic VOC fluxes from a mixed deciduous forest site in North-Western Germany. The measurement site was characterised by a forest of inhomogeneous composition, complex canopy structure, limited extension in certain wind directions and frequent calm wind conditions during night time. The eddy covariance (EC) technique was applied since it represents the most direct flux measurement approach on the canopy scale and is, therefore, least susceptible to these non-ideal conditions. A specific flux calculation method was used to account for the sequential multi-component PTR-MS measurements and allowing an individual delay time adjustment as well as a rigorous quality control based on cospectral analysis. The validated flux results are consistent with light and temperature dependent emissions of isoprene and monoterpenes from this forest, with average daytime emissions of 0.94 and 0.3µg m-2s-1, respectively. Emissions of methanol reached on average 0.087µg m-2s-1 during daytime, but fluxes were too small to be detected during night time. Upward fluxes of the isoprene oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) were also found, being two orders of magnitude lower than those of isoprene. Calculations with an analytical footprint model indicate that the observed isoprene fluxes correlate with the fraction of oaks within the footprints of the flux measurement.

Spirig, C.; Neftel, A.; Ammann, C.; Dommen, J.; Grabmer, W.; Thielmann, A.; Schaub, A.; Beauchamp, J.; Wisthaler, A.; Hansel, A.

2005-02-01

279

A comparison of measured and modeled turbulent fluxes over snow based on site characteristics  

Technology Transfer Automated Retrieval System (TEKTRAN)

Sensible and latent heat and mass flux represent a significant component of the snowcover energy and mass balance in mountain environments. Though these fluxes are computed in energy balance snow models, limited measurements exist for comparison or validation in complex, mountainous sites. Sensibl...

280

Determination of longwave heat flux at the air-sea interface using measurements from buoy platforms  

Microsoft Academic Search

A theory for pyrgeometer operation is utilized for determining downwelling longwave radiation. Errors in downwelling longwave radiation measurements are due to differences in pyrgeometer body and dome temperatures compared to that of the atmosphere. Additionally, incident shortwave radiation fluxes may be important. Using the present theory along with laboratory and field observations, it appears that downwelling longwave heat fluxes can

T. D. Dickey; D. V. Manov; R. A. Weller; D. A. Siegel

1994-01-01

281

Two years of continuous CO 2 eddy-flux measurements over a Danish beech forest  

Microsoft Academic Search

As part of the EUROFLUX network a long-term monitoring station for fluxes of CO2 and water vapour has been established in an 80-year old beech forest in Denmark. The station has been in continuous operation since June 1996 and will be so at least to the end of 2002. A primary goal of EUROFLUX is to combine flux measurements on

K Pilegaard; P Hummelshøj; N. O Jensen; Z Chen

2001-01-01

282

Quantifying particle size and turbulent scale dependence of dust flux in the Sahara using aircraft measurements  

NASA Astrophysics Data System (ADS)

first size-resolved airborne measurements of dust fluxes and the first dust flux measurements from the central Sahara are presented and compared with a parameterization by Kok (2011a). High-frequency measurements of dust size distribution were obtained from 0.16 to 300 µm diameter, and eddy covariance fluxes were derived. This is more than an order of magnitude larger size range than previous flux estimates. Links to surface emission are provided by analysis of particle drift velocities. Number flux is described by a -2 power law between 1 and 144 µm diameter, significantly larger than the 12 µm upper limit suggested by Kok (2011a). For small particles, the deviation from a power law varies with terrain type and the large size cutoff is correlated with atmospheric vertical turbulent kinetic energy, suggesting control by vertical transport rather than emission processes. The measured mass flux mode is in the range 30-100 µm. The turbulent scales important for dust flux are from 0.1 km to 1-10 km. The upper scale increases during the morning as boundary layer depth and eddy size increase. All locations where large dust fluxes were measured had large topographical variations. These features are often linked with highly erodible surface features, such as wadis or dunes. We also hypothesize that upslope flow and flow separation over such features enhance the dust flux by transporting large particles out of the saltation layer. The tendency to locate surface flux measurements in open, flat terrain means these favored dust sources have been neglected in previous studies.

Rosenberg, Philip D.; Parker, Douglas J.; Ryder, Claire L.; Marsham, John H.; Garcia-Carreras, Luis; Dorsey, James R.; Brooks, Ian M.; Dean, Angela R.; Crosier, Jonathon; McQuaid, James B.; Washington, Richard

2014-06-01

283

Absolute beam flux measurement at NDCX-I using gold-melting calorimetry technique  

SciTech Connect

We report on an alternative way to measure the absolute beam flux at the NDCX-I, LBNL linear accelerator. Up to date, the beam flux is determined from the analysis of the beam-induced optical emission from a ceramic scintilator (Al-Si). The new approach is based on calorimetric technique, where energy flux is deduced from the melting dynamics of a gold foil. We estimate an average 260 kW/cm2 beam flux over 5 {micro}s, which is consistent with values provided by the other methods. Described technique can be applied to various ion species and energies.

Ni, P.A.; Bieniosek, F.M.; Lidia, S.M.; Welch, J.

2011-04-01

284

Comparison of surface fluxes and boundary-layer measurements at Arctic terrestrial sites  

NASA Astrophysics Data System (ADS)

Observational evidence suggests that atmospheric energy fluxes are a major contributor to the decrease of the Arctic pack ice, seasonal land snow cover and the warming of the surrounding land areas and permafrost layers. To better understand the atmosphere-surface exchange mechanisms, improve models, and to diagnose climate variability in the Arctic, accurate measurements are required of all components of the net surface energy budget and the carbon dioxide cycle over representative areas and over multiple years. This study analyzes and discusses variability of surface fluxes and basic meteorological parameters based on measurements made at several long-term research observatories near the coast of the Arctic Ocean located in USA (Barrow), Canada (Eureka), and Russia (Tiksi). Tower-based eddy covariance and solar radiation measurements provide a long-term near continuous temporal record of hourly average mass and energy fluxes respectively. The turbulent fluxes of the momentum, sensible heat, water vapor, and carbon dioxide are supported by additional atmospheric and surface/snow/permafrost measurements (mean wind speed, air temperature and humidity, upwelling and downwelling short-wave and long-wave atmospheric and surface radiation, snow depth, surface albedo, soil heat flux, active layer temperature profiles etc.) In this study we compare annual cycles of surface fluxes including solar radiation and other ancillary data to describe four seasons in the Arctic including spring onset of melt and fall onset of snow accumulation. Particular interest is a transition through freezing point, i.e. during transition from winter to spring and from summer to fall, when the carbon dioxide and/or water vapor turbulent fluxes change their direction. According to our data, in a summer period observed temporal variability of the carbon dioxide flux was generally in anti-phase with water vapor flux (downward CO2 flux and upward H2O flux). On average the turbulent flux of carbon dioxide was mostly negative (uptake by the surface) in summer indicating that the Arctic terrestrial sites are generally net sinks for atmospheric CO2 during the growing season when surface is extensively covered with vegetation. This study also shows that the sensible heat flux, water vapor, and carbon dioxide fluxes as well as air temperature exhibit clear diurnal cycles during the Arctic summer. During the Polar winter and cold seasons, the sensible heat flux, water vapor and carbon dioxide fluxes were small and mostly irregular when the ground is covered with snow and air temperatures are sufficiently below freezing. The work is supported by the U.S. National Science Foundation (NSF) with award ARC 11-07428 and by the U.S. Civilian Research & Development Foundation (CRDF) with award RUG1-2976-ST-10.

Grachev, Andrey; Uttal, Taneil; Persson, Ola; Stone, Robert; Crepinsek, Sara; Albee, Robert; Makshtas, Alexander; Kustov, Vasily; Repina, Irina; Artamonov, Arseniy

2014-05-01

285

Measurement of NOx fluxes by eddy covariance from the BT tower, London during the ClearfLo project  

NASA Astrophysics Data System (ADS)

The vast majority of air pollutants are emitted directly into the atmosphere from activities occurring at the Earth's surface. One of the key anthropogenic pollutants is NOx (defined as the sum of NO and NO2), which is emitted as a result of most anthropogenic combustion processes. Whilst the chemical reactions and atmospheric processing of NOx are reasonably well understood, and can be modelled with some skill, large uncertainties arise in models due to uncertainty associated with the rate of emissions. In recent years it has become clear that measured trends in certain pollutants, for example NO2, have not followed trends predicted by inventories. Continued exceedances of certain air pollution targets are of significant concern to governments, who have identified reducing this uncertainty associated with emissions as key evidence need. As part of the UK Natural Environment Research Council (NERC) Clean Air for London (ClearfLo) project, concentrations and fluxes of NOx were measured from the top of the BT tower, which is a 188m high telecommunications tower, situated in central London (51o31'17.4'N; 0o8'20.04W). The tower is surrounded by a mixture of commercial and residential buildings with an average height of 15 m. The typical daytime flux footprint of the tower is dominated by commercial/residential buildings and roads (82%) but also includes urban parkland (13%) and impervious ground (5%). High time resolution (10 Hz) chemiluminescence measurements of NO and NO2 (photolytic conversion to NO followed by chemiluminescence) were combined with fast turbulence measurements from a sonic anemometer to calculate fluxes using the eddy covariance technique. In brief, NOx fluxes per notional half-hourly averaging period were obtained by maximising the covariance between instantaneous (i.e. mean for the averaging period subtracted from each 10 Hz data point) fluctuations of NOx mixing ratio and vertical wind velocity. 24 hour NOx flux measurements were made on 36 days during June, July and August 2012 and 28 days in March and April 2013. The data showed a clear diurnal cycle, with NOx flux broadly following measured traffic flow in the surrounding streets, with a typical maximum daytime flux of 4?g m-2 s-1. Mixing ratios of NOx can be seen to be a function of the NOx flux and the boundary layer height evolution during the day. A clear weekday / weekend dependence is seen on the NOx flux measurements, again following the traffic flow data. The measured fluxes were averaged over 24 hours and scaled up to give a 'top down' estimate of the annual emission rate of 79.6 T km-2 yr-1. This compares well to estimates from the UK National Atmospheric Emissions Inventory, however some differences are seen when the data is separated into different wind sectors. Conversely, a 'bottom up' dispersion model (ADMS-Urban) was run using measured meteorological data and the detailed London Atmospheric Emissions Inventory as input. ADMS-Urban has previously been validated using near-surface measurements, but the current work demonstrates that the model gives good agreement with the flux measurements, both in terms of magnitude and diurnal cycle.

Lee, James; Helfter, Carole; Nemitz, Eiko; Tremper, Anja; Stocker, Jenny; Carruthers, David

2014-05-01

286

Measurements of suprathermal hydrogen flux in CASTOR tokamak  

NASA Astrophysics Data System (ADS)

A study of the non-equilibrium absorption of hydrogen particles by a plasma-facing absorption probe (AP) made of Group V metals in the CASTOR tokamak environment has been undertaken with the main purposes: (1) to investigate the role of nonmetallic coatings upon plasma-facing materials in D/T inventory and recycling and (2) to develop a method of the registration and diagnostic of the flux of suprathermal hydrogen. Two series of experiments were performed: with AP of Nb and of V. The absorption of suprathermal hydrogen particles coming from the tokamak plasma was investigated as a function of AP temperature, AP distance from the plasma, AP bias and of plasma pulse duration. The possibility of a reliable registration of suprathermal hydrogen was demonstrated in spite of the short plasma pulse duration and a relatively high background H 2 pressure. The composition of the hydrogen flux (molecules, atoms, ions) impinging on the tokamak walls was analyzed, including ion energy distribution.

Notkin, M. E.; Livshits, A. I.; Hron, M.; Stockel, J.

2006-10-01

287

A framework to utilize turbulent flux measurements for mesoscale models and remote sensing applications  

NASA Astrophysics Data System (ADS)

Meteorologically measured fluxes of energy and matter between the surface and the atmosphere originate from a source area of certain extent, located in the upwind sector of the device. The spatial representativeness of such measurements is strongly influenced by the heterogeneity of the landscape. The footprint concept is capable of linking observed data with spatial heterogeneity. This study aims at upscaling eddy covariance derived fluxes to a grid size of 1 km edge length, which is typical for mesoscale models or low resolution remote sensing data. Here an upscaling strategy is presented, utilizing footprint modelling and SVAT modelling as well as observations from a target land-use area. The general idea of this scheme is to model fluxes from adjacent land-use types and combine them with the measured flux data to yield a grid representative flux according to the land-use distribution within the grid cell. The performance of the upscaling routine is evaluated with real datasets, which are considered to be land-use specific fluxes in a grid cell. The measurements above rye and maize fields stem from the LITFASS experiment 2003 in Lindenberg, Germany and the respective modelled timeseries were derived by the SVAT model SEWAB. Contributions from each land-use type to the observations are estimated using a forward lagrangian stochastic model. A representation error is defined as the error in flux estimates made when accepting the measurements unchanged as grid representative flux and ignoring flux contributions from other land-use types within the respective grid cell. Results show that this representation error can be reduced up to 56 % when applying the spatial integration. This shows the potential for further application of this strategy, although the absolute differences between flux observations from rye and maize were so small, that the spatial integration would be rejected in a real situation. Corresponding thresholds for this decision have been estimated as a minimum mean absolute deviation in modelled timeseries of the different land-use types with 35 W m-2 for the sensible heat flux and 50 W m-2 for the latent heat flux. Finally, a quality lagging scheme to classify the data with respect to representativeness for a given grid cell is proposed, based on an overall flux error estimate. This enables the data user to infer the uncertainty of mesoscale models and remote sensing products with respect to ground observations. Major uncertainty sources remaining are the lack of an adequate method for energy balance closure correction as well as model structure and parameter estimation, when applying the model for surfaces without flux measurements.

Babel, W.; Huneke, S.; Foken, T.

2011-05-01

288

The Role of Water Movement and Spatial Scaling for Measurement of Dissolved Inorganic Nitrogen Fluxes in Intertidal Sediments  

NASA Astrophysics Data System (ADS)

Fluxes of dissolved inorganic nitrogen (ammonium and nitrate) across the sediment-water interface were determined at intertidal locations in Königshafen, northern Wadden Sea, North Sea. Three different incubation techniques were compared: closed sediment cores (small scale), closed bell jars (medium scale) and an open flow system (Sylt flume, large scale). Water movement in the two closed systems was maintained below the resuspension limit by spinning magnets (cores, incubated in the laboratory) or by transfer of wave action through flexible plastic foil (bell jars, in situ), whereas in the flume system ( in situ) water movement was unidirectional, driven by currents and waves. Data sets from several years of core measurements (1992-94), bell jar measurements (1980) and flume campaigns (1990-93) served as the basis for a comparison of dissolved inorganic nitrogen fluxes. Fluxes of ammonium and nitrate were within the same order of magnitude in closed cores and bell jars, while flume rates of ammonium were considerably higher. The high flume rates were caused by advective flushing due to tidal water movement and wave action. The release of ammonium increased significantly with current velocity between 1 and 13 cm s -1. Fluxes of ammonium were higher in sediments with Arenicola marinacompared to those without this bioturbating species. The influence of benthic microalgae was evident only in the small and medium scale core and bell jar systems as reduced ammonium release during light exposure. Nitrate was consumed by sediments in both closed systems at a rate proportional to the nitrate concentration in the overlying water. Nitrate fluxes in the large scale Sylt flume were low with an average of only 7% of the ammonium fluxes, probably due to low concentrations in tidal waters during measurements (summer). Both closed, small scale or open, large scale techniques can be applied successfully for benthic flux studies, but the actual choice depends on the purpose of the investigation. Small enclosures, either in the field (bell jars) or in the laboratory (cores) are well suited to examine controlling factors for benthic microbial metabolism and nutrient exchange across the sediment-water interface. Fluxes in benthic-pelagic subsystems need larger, open tools where the effect of entire benthic communities and especially the influence of waves and currents can be evaluated.

Asmus, R. M.; Jensen, M. H.; Jensen, K. M.; Kristensen, E.; Asmus, H.; Wille, A.

1998-02-01

289

Methodological approach to field measurement of mercury vapor flux using portable devices in a mineralized volcanic realm: Rodalquilar (SE Spain)  

NASA Astrophysics Data System (ADS)

The measurement of mercury vapor flux is a technique that has been applied to the exploration of buried sulfide deposits. This is due to the general presence of mercury in sulfide ore deposits and the mobility of released mercury gas, that is able to ascend to the surface where can be detected and measured as an indication of the deep presence of such deposits. We tried this technique as a pilot study at the Rodalquilar Valley (Almería SE Spain), where alluvial and colluvial sedimentary deposits cover epithermal veins and strongly altered volcanic rocks. We used portable analytical devices including a LUMEX RA915+ mercury vapor analyzer and an Oxford X-MET3000TXS X Ray Fluorescence multielemental device. The pilot survey consisted in measurements of mercury emissions in the alluvial and colluvial soils, using an opaque flux chamber. The usage of opaque flux chambers minimizes the effect of different sun radiation. We also dug ~ 1.5 cm (diameter) vertical holes in the sampling area to observe whether these channels allowed enhanced rates of mercury flux. The results put forward differential emissions, in particular with the measurements corresponding to 15 cm deep holes.

Higueras, Pablo; Oyarzun, Roberto; María Esbrí, José; Martínez-Coronado, Alba

2010-05-01

290

Description of heat flux measurement methods used in hydrocarbon and propellant fuel fires at Sandia.  

SciTech Connect

The purpose of this report is to describe the methods commonly used to measure heat flux in fire applications at Sandia National Laboratories in both hydrocarbon (JP-8 jet fuel, diesel fuel, etc.) and propellant fires. Because these environments are very severe, many commercially available heat flux gauges do not survive the test, so alternative methods had to be developed. Specially built sensors include 'calorimeters' that use a temperature measurement to infer heat flux by use of a model (heat balance on the sensing surface) or by using an inverse heat conduction method. These specialty-built sensors are made rugged so they will survive the environment, so are not optimally designed for ease of use or accuracy. Other methods include radiometers, co-axial thermocouples, directional flame thermometers (DFTs), Sandia 'heat flux gauges', transpiration radiometers, and transverse Seebeck coefficient heat flux gauges. Typical applications are described and pros and cons of each method are listed.

Nakos, James Thomas

2010-12-01

291

Eddy covariance flux measurements of pollutant gases in urban Mexico City  

NASA Astrophysics Data System (ADS)

Eddy covariance (EC) flux measurements of the atmosphere/surface exchange of gases over an urban area are a direct way to improve and evaluate emissions inventories, and, in turn, to better understand urban atmospheric chemistry and the role that cities play in regional and global chemical cycles. As part of the MCMA-2003 study, we demonstrated the feasibility of using eddy covariance techniques to measure fluxes of selected volatile organic compounds (VOCs) and CO2 from a residential district of Mexico City (Velasco et al., 2005a, b). During the MILAGRO/MCMA-2006 field campaign, a second flux measurement study was conducted in a different district of Mexico City to corroborate the 2003 flux measurements, to expand the number of species measured, and to obtain additional data for evaluation of the local emissions inventory. Fluxes of CO2 and olefins were measured by the conventional EC technique using an open path CO2 sensor and a Fast Isoprene Sensor calibrated with a propylene standard. In addition, fluxes of toluene, benzene, methanol and C2-benzenes were measured using a virtual disjunct EC method with a Proton Transfer Reaction Mass Spectrometer. The flux measurements were analyzed in terms of diurnal patterns and vehicular activity and were compared with the most recent gridded local emissions inventory. In both studies, the results showed that the urban surface of Mexico City is a net source of CO2 and VOCs with significant contributions from vehicular traffic. Evaporative emissions from commercial and other anthropogenic activities were significant sources of toluene and methanol. The results show that the emissions inventory is in reasonable agreement with measured olefin and CO2 fluxes, while C2-benzenes and toluene emissions from evaporative sources are overestimated in the inventory. It appears that methanol emissions from mobile sources occur, but are not reported in the mobile emissions inventory.

Velasco, E.; Pressley, S.; Grivicke, R.; Allwine, E.; Coons, T.; Foster, W.; Jobson, B. T.; Westberg, H.; Ramos, R.; Hernández, F.; Molina, L. T.; Lamb, B.

2009-10-01

292

Eddy covariance flux measurements of pollutant gases in urban Mexico City  

NASA Astrophysics Data System (ADS)

Eddy covariance (EC) flux measurements of the atmosphere/surface exchange of gases over an urban area are a direct way to improve and evaluate emissions inventories, and, in turn, to better understand urban atmospheric chemistry and the role that cities play in regional and global chemical cycles. As part of the MCMA-2003 study, we demonstrated the feasibility of using eddy covariance techniques to measure fluxes of selected volatile organic compounds (VOCs) and CO2 from a residential district of Mexico City (Velasco et al., 2005a, b). During the MILAGRO/MCMA-2006 field campaign, a second flux measurement study was conducted in a different district of Mexico City to corroborate the 2003 flux measurements, to expand the number of species measured, and to obtain additional data for evaluation of the local emissions inventory. Fluxes of CO2 and olefins were measured by the conventional EC technique using an open path CO2 sensor and a Fast Isoprene Sensor calibrated with a propylene standard. In addition, fluxes of toluene, benzene, methanol and C2-benzenes were measured using a virtual disjunct EC method with a Proton Transfer Reaction Mass Spectrometer. The flux measurements were analyzed in terms of diurnal patterns and vehicular activity and were compared with the most recent gridded emissions inventory. In both studies, the results showed that the urban surface of Mexico City is a net source of CO2 and VOCs with significant contributions from vehicular traffic. Evaporative emissions from commercial and other anthropogenic activities were significant sources of toluene and methanol. The data show that the emissions inventory is in reasonable agreement with measured olefin and CO2 fluxes, while C2-benzenes and toluene emissions from evaporative sources are overestimated in the inventory. It appears that methanol emissions from mobile sources occur, but are not present in the mobile emissions inventory.

Velasco, E.; Pressley, S.; Grivicke, R.; Allwine, E.; Coons, T.; Foster, W.; Jobson, T.; Westberg, H.; Ramos, R.; Hernández, F.; Molina, L. T.; Lamb, B.

2009-03-01

293

Measuring diurnal cycles of plant transpiration fluxes in the Arctic with an automated clear chamber  

NASA Astrophysics Data System (ADS)

Evapotranspiration is an important greenhouse gas and a major component of the hydrological cycle, but methodological challenges still limit our knowledge of this flux. Measuring evapotranspiration is even more difficult when aiming to partition plant transpiration and soil evaporation. Information on this process for arctic systems is very limited. In order to decrease this gap, our objective was to directly measure plant transpiration in Barrow, Alaska (71.3°N 156.7°W). A commercial system allows measuring carbon soil respiration fluxes with an automated clear chamber connected to an infrared gas-analyzer (Licor 8100), and while it simultaneously measures water concentrations, it is not calibrated to measure vapor fluxes. We calibrated the clear chamber against a previously established method based on a Licor 6400 soil chamber, and we developed a code to calculate fluxes. We performed laboratory comparisons in New Mexico and field comparisons in the Arctic, suggesting that this is a valid tool for a large range of climates. In the field we found a strong correlation between the two instruments with R2 of 0.79. Even with 24 hours of daylight in the Arctic, the system captures a clear diurnal transpiration flux, peaking at 0.9 mmol m-2 s-1 and showing no flux at the lowest points. This new method should be a powerful approach for long term measurements of specific vegetation types or surface features. Such Data can also be used to help understand controls on larger scale eddy covariance tower measurements of evapotranspiration.

Cohen, L. R.; Raz Yaseef, N.; Curtis, J. B.; Rahn, T. A.; Young, J. M.; Newman, B. D.

2013-12-01

294

Eddy covariance flux measurements of pollutant gases in urban Mexico City  

E-print Network

Eddy covariance (EC) flux measurements of the atmosphere/surface exchange of gases over an urban area are a direct way to improve and evaluate emissions inventories, and, in turn, to better understand urban atmospheric ...

Velasco, Erik

295

Measuring Radiation Heat Fluxes from a Jet Fire Using a Lumped Capacitance Model  

Microsoft Academic Search

This paper presents an experimental methodology for measuring the incident radiation heat flux distribution surrounding a\\u000a jet fire. The methodology uses a line of surface thermocouples attached to a steel bar. The thermocouples measure the temperature\\u000a time history of the steel bar in response to an imposed incident radiation heat flux. The theoretical basis of the methodology\\u000a is an energy

Peter S. Cumber

2011-01-01

296

Eddy Covariance Flux Measurements of Urban Aerosols During the MILAGRO Mexico City Field Campaign  

NASA Astrophysics Data System (ADS)

Expansive urban development in the fast growing number of megacities around the world raises concerns regarding the pollution levels in such sites. The Mexico City MILAGRO 2006 (Megacity Initiative: Local and Global Research Observations) field campaign was a worldwide initiative aiming to understand sources, chemical nature and evolution of pollution in one of the largest urban developments. As part of the MILAGRO campaign, urban fluxes of aerosols and related trace gases were measured near the centre of Mexico City at 42 m above street level. Aerosol concentrations (1 min. averages) and aerosol fluxes (10 Hz, selected ion monitoring) were measured with an Aerodyne quadrupole aerosol mass spectrometer operated in an alternating 30 minute mode of ambient concentrations and fluxes. The fluxes were derived using eddy covariance calculations. The aerosol flux data were supported by additional flux measurements of CO2 and a number of gas phase VOC species using a combination of techniques, including Proton Transfer Reaction Mass Spectrometry using a disjunct eddy covariance technique and GC-FID analysis of samples from a disjunct eddy accumulation sampler. Preliminary results of aerosol concentrations and flux measurements indicate that the urban landscape is a significant source of organic aerosols.

Grivicke, R.; Pressley, S.; Jimenez, J.; Nemitz, E.; Alexander, L.; Velasco, E.; Allwine, E.; Jobson, T.; Westberg, H.; Ramos, R.; Molina, L.; Lamb, B.

2007-12-01

297

Estimating regional methane surface fluxes: the relative importance of surface and GOSAT mole fraction measurements  

NASA Astrophysics Data System (ADS)

We use an ensemble Kalman filter (EnKF), together with the GEOS-Chem chemistry transport model, to estimate regional monthly methane (CH4) fluxes for the period June 2009-December 2010 using proxy dry-air column-averaged mole fractions of methane (XCH4) from GOSAT (Greenhouse gases Observing SATellite) and/or NOAA ESRL (Earth System Research Laboratory) and CSIRO GASLAB (Global Atmospheric Sampling Laboratory) CH4 surface mole fraction measurements. Global posterior estimates using GOSAT and/or surface measurements are between 510-516 Tg yr-1, which is less than, though within the uncertainty of, the prior global flux of 529 ± 25 Tg yr-1. We find larger differences between regional prior and posterior fluxes, with the largest changes in monthly emissions (75 Tg yr-1) occurring in Temperate Eurasia. In non-boreal regions the error reductions for inversions using the GOSAT data are at least three times larger (up to 45%) than if only surface data are assimilated, a reflection of the greater spatial coverage of GOSAT, with the two exceptions of latitudes >60° associated with a data filter and over Europe where the surface network adequately describes fluxes on our model spatial and temporal grid. We use CarbonTracker and GEOS-Chem XCO2 model output to investigate model error on quantifying proxy GOSAT XCH4 (involving model XCO2) and inferring methane flux estimates from surface mole fraction data and show similar resulting fluxes, with differences reflecting initial differences in the proxy value. Using a series of observing system simulation experiments (OSSEs) we characterize the posterior flux error introduced by non-uniform atmospheric sampling by GOSAT. We show that clear-sky measurements can theoretically reproduce fluxes within 10% of true values, with the exception of tropical regions where, due to a large seasonal cycle in the number of measurements because of clouds and aerosols, fluxes are within 15% of true fluxes. We evaluate our posterior methane fluxes by incorporating them into GEOS-Chem and sampling the model at the location and time of surface CH4 measurements from the AGAGE (Advanced Global Atmospheric Gases Experiment) network and column XCH4 measurements from TCCON (Total Carbon Column Observing Network). The posterior fluxes modestly improve the model agreement with AGAGE and TCCON data relative to prior fluxes, with the correlation coefficients (r2) increasing by a mean of 0.04 (range: -0.17 to 0.23) and the biases decreasing by a mean of 0.4 ppb (range: -8.9 to 8.4 ppb).

Fraser, A.; Palmer, P. I.; Feng, L.; Boesch, H.; Cogan, A.; Parker, R.; Dlugokencky, E. J.; Fraser, P. J.; Krummel, P. B.; Langenfelds, R. L.; O'Doherty, S.; Prinn, R. G.; Steele, L. P.; van der Schoot, M.; Weiss, R. F.

2013-06-01

298

Estimating regional methane surface fluxes: the relative importance of surface and GOSAT mole fraction measurements  

NASA Astrophysics Data System (ADS)

We use an ensemble Kalman filter (EnKF), together with the GEOS-Chem chemistry transport model, to estimate regional monthly methane (CH4) fluxes for the period June 2009-December 2010 using proxy dry-air column-averaged mole fractions of methane (XCH4) from GOSAT (Greenhouse gases Observing SATellite) and/or NOAA ESRL (Earth System Research Laboratory) and CSIRO GASLAB (Global Atmospheric Sampling Laboratory) CH4 surface mole fraction measurements. Global posterior estimates using GOSAT and/or surface measurements are between 510-516 Tg yr-1, which is less than, though within the uncertainty of, the prior global flux of 529 ± 25 Tg yr-1. We find larger differences between regional prior and posterior fluxes, with the largest changes (75 Tg yr-1) occurring in Temperate Eurasia. In non-boreal regions the error reductions for inversions using the GOSAT data are at least three times larger (up to 45%) than if only surface data are assimilated, a reflection of the greater spatial coverage of GOSAT, with the two exceptions of latitudes > 60° associated with a data filter and over Europe where the surface network adequately describes fluxes on our model spatial and temporal grid. We use CarbonTracker and GEOS-Chem XCO2 model output to investigate model error on quantifying proxy GOSAT XCH4 (involving model XCO2) and inferring methane flux estimates from surface mole fraction data and show similar resulting fluxes, with differences reflecting initial differences in the proxy value. Using a series of observing system simulation experiments (OSSEs) we characterize the posterior flux error introduced by non-uniform atmospheric sampling by GOSAT. We show that clear-sky measurements can theoretically reproduce fluxes within 5% of true values, with the exception of South Africa and Tropical South America where, due to a large seasonal cycle in the number of measurements because of clouds and aerosols, fluxes are within 17% and 19% of true fluxes, respectively. We evaluate our posterior methane fluxes by incorporating them into GEOS-Chem and sampling the model at the location and time of independent surface CH4 measurements from the AGAGE (Advanced Global Atmospheric Gases Experiment) network and column XCH4 measurements from TCCON (Total Carbon Column Observing Network). The posterior fluxes modestly improve the model agreement with AGAGE and TCCON data relative to prior fluxes, with the correlation coefficients (r2) increasing by a mean of 0.04 (range: -0.17, 0.23) and the biases decreasing by a mean of 0.4 ppb (range: -8.9, 8.4 ppb).

Fraser, A.; Palmer, P. I.; Feng, L.; Boesch, H.; Cogan, A.; Parker, R.; Dlugokencky, E. J.; Fraser, P. J.; Krummel, P. B.; Langenfelds, R. L.; O'Doherty, S.; Prinn, R. G.; Steele, L. P.; van der Schoot, M.; Weiss, R. F.

2012-12-01

299

Annual sediment flux estimates in a tidal strait using surrogate measurements  

USGS Publications Warehouse

Annual suspended-sediment flux estimates through Carquinez Strait (the seaward boundary of Suisun Bay, California) are provided based on surrogate measurements for advective, dispersive, and Stokes drift flux. The surrogates are landward watershed discharge, suspended-sediment concentration at one location in the Strait, and the longitudinal salinity gradient. The first two surrogates substitute for tidally averaged discharge and velocity-weighted suspended-sediment concentration in the Strait, thereby providing advective flux estimates, while Stokes drift is estimated with suspended-sediment concentration alone. Dispersive flux is estimated using the product of longitudinal salinity gradient and the root-mean-square value of velocity-weighted suspended-sediment concentration as an added surrogate variable. Cross-sectional measurements validated the use of surrogates during the monitoring period. During high freshwater flow advective and dispersive flux were in the seaward direction, while landward dispersive flux dominated and advective flux approached zero during low freshwater flow. Stokes drift flux was consistently in the landward direction. Wetter than average years led to net export from Suisun Bay, while dry years led to net sediment import. Relatively low watershed sediment fluxes to Suisun Bay contribute to net export during the wet season, while gravitational circulation in Carquinez Strait and higher suspended-sediment concentrations in San Pablo Bay (seaward end of Carquinez Strait) are responsible for the net import of sediment during the dry season. Annual predictions of suspended-sediment fluxes, using these methods, will allow for a sediment budget for Suisun Bay, which has implications for marsh restoration and nutrient/contaminant transport. These methods also provide a general framework for estimating sediment fluxes in estuarine environments, where temporal and spatial variability of transport are large. ?? 2006 Elsevier Ltd. All rights reserved.

Ganju, N.K.; Schoellhamer, D.H.

2006-01-01

300

Standard Test Method for Measuring Heat Flux Using a Copper-Constantan Circular Foil, Heat-Flux Transducer  

E-print Network

1.1 This test method describes the measurement of radiative heat flux using a transducer whose sensing element (1,2 ) is a thin circular metal foil. These sensors are often called Gardon Gauges. 1.2 The values stated in SI units are to be regarded as the standard. The values stated in parentheses are provided for information only. 1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

American Society for Testing and Materials. Philadelphia

2007-01-01

301

Cluster electric current density measurements within a magnetic flux rope in the plasma sheet  

NASA Technical Reports Server (NTRS)

On August 22, 2001 all 4 Cluster spacecraft nearly simultaneously penetrated a magnetic flux rope in the tail. The flux rope encounter took place in the central plasma sheet, Beta(sub i) approx. 1-2, near the leading edge of a bursty bulk flow. The "time-of-flight" of the flux rope across the 4 spacecraft yielded V(sub x) approx. 700 km/s and a diameter of approx.1 R(sub e). The speed at which the flux rope moved over the spacecraft is in close agreement with the Cluster plasma measurements. The magnetic field profiles measured at each spacecraft were first modeled separately using the Lepping-Burlaga force-free flux rope model. The results indicated that the center of the flux rope passed northward (above) s/c 3, but southward (below) of s/c 1, 2 and 4. The peak electric currents along the central axis of the flux rope predicted by these single-s/c models were approx.15-19 nA/sq m. The 4-spacecraft Cluster magnetic field measurements provide a second means to determine the electric current density without any assumption regarding flux rope structure. The current profile determined using the curlometer technique was qualitatively similar to those determined by modeling the individual spacecraft magnetic field observations and yielded a peak current density of 17 nA/m2 near the central axis of the rope. However, the curlometer results also showed that the flux rope was not force-free with the component of the current density perpendicular to the magnetic field exceeding the parallel component over the forward half of the rope, perhaps due to the pressure gradients generated by the collision of the BBF with the inner magnetosphere. Hence, while the single-spacecraft models are very successful in fitting flux rope magnetic field and current variations, they do not provide a stringent test of the force-free condition.

Slavin, J. A.; Lepping, R. P.; Gjerloev, J.; Goldstein, M. L.; Fairfield, D. H.; Acuna, M. H.; Balogh, A.; Dunlop, M.; Kivelson, M. G.; Khurana, K.

2003-01-01

302

Application of an energy balance correction method for turbulent flux measurements based on buoyancy  

NASA Astrophysics Data System (ADS)

The energy imbalance in flux measurements between the atmosphere and the surface is a well-known problem, but unsolved due to the complexity of possible reasons and potential error sources. In order to provide unbiased budgets, however, eddy-covariance measurements of sensible and latent heat flux should be corrected according to the closure gap. Recent studies utilising turbulent flux data and LES models suggest that the transport of the missing turbulent flux is triggered by meso-scale circulations, not detected by eddy-covariance measurements within typical averaging intervals of 30 minutes. These motions on longer timescales are driven by buoyancy, suggesting that the missing turbulent flux is a missing buoyancy flux. Based on this assumption we present an energy balance closure correction method according to the buoyancy flux. The effects are compared with the results obtained by the commonly used correction according to the Bowen ratio (Twine et al., Agr. Forest Meteorol., 2000). We show that in general both correction methods could be applied to daytime fluxes and conditions with positive Bowen ratios. Finally the corrected turbulent fluxes are compared with different simulations of SVAT-type models for Tibetan grassland sites and a central European spruce forest site. The model performance with respect to the used data correction method is linked to the different mechanism of closing the energy balance within the model. Model validation requires energy balance closure correction in case the model relies on the energy balance equation. We conclude that mechanistic model development of turbulent flux parameterisations should recognize the recent hypotheses concerning the energy balance closure rather than fitting just to the uncorrected eddy-covariance data.

Babel, Wolfgang; Charuchittipan, Doojdao; Zhao, Peng; Biermann, Tobias; Gatzsche, Kathrin; Foken, Thomas

2014-05-01

303

A flux-gradient system for simultaneous measurement of the CH4, CO2, and H2O fluxes at a lake-air interface.  

PubMed

Inland lakes play important roles in water and greenhouse gas cycling in the environment. This study aims to test the performance of a flux-gradient system for simultaneous measurement of the fluxes of water vapor, CO2, and CH4 at a lake-air interface. The concentration gradients over the water surface were measured with an analyzer based on the wavelength-scanned cavity ring-down spectroscopy technology, and the eddy diffusivity was measured with a sonic anemometer. Results of a zero-gradient test indicate a flux measurement precision of 4.8 W m(-2) for water vapor, 0.010 mg m(-2) s(-1) for CO2, and 0.029 ?g m(-2) s(-1) for CH4. During the 620 day measurement period, 97%, 69%, and 67% of H2O, CO2, and CH4 hourly fluxes were higher in magnitude than the measurement precision, which confirms that the flux-gradient system had adequate precision for the measurement of the lake-air exchanges. This study illustrates four strengths of the flux-gradient method: (1) the ability to simultaneously measure the flux of H2O, CO2, and CH4; (2) negligibly small density corrections; (3) the ability to resolve small CH4 gradient and flux; and (4) continuous and noninvasive operation. The annual mean CH4 flux (1.8 g CH4 m(-2) year(-1)) at this hypereutrophic lake was close to the median value for inland lakes in the world (1.6 g CH4 m(-2) year(-1)). The system has adequate precision for CH4 flux for broad applications but requires further improvement to resolve small CO2 flux in many lakes. PMID:25377990

Xiao, Wei; Liu, Shoudong; Li, Hanchao; Xiao, Qitao; Wang, Wei; Hu, Zhenghua; Hu, Cheng; Gao, Yunqiu; Shen, Jing; Zhao, Xiaoyan; Zhang, Mi; Lee, Xuhui

2014-12-16

304

VOC flux measurements using a novel Relaxed Eddy Accumulation GC-FID system in urban Houston, Texas  

NASA Astrophysics Data System (ADS)

Houston experiences higher ozone production rates than most other major cities in the US, which is related to high anthropogenic VOC emissions from both area/mobile sources (car traffic) and a large number of petrochemical facilities. The EPA forecasts that Houston is likely to still violate the new 8-h NAAQS in 2020. To monitor neighborhood scale pollutant fluxes, we established a tall flux tower installation a few kilometers north of downtown Houston. We measure energy and trace gas fluxes, including VOCs from both anthropogenic and biogenic emission sources in the urban surface layer using eddy covariance and related techniques. Here, we describe a Relaxed Eddy Accumulation (REA) system combined with a dual-channel GC-FID used for VOC flux measurements, including first results. Ambient air is sampled at approximately 15 L min-1 through a 9.5 mm OD PFA line from 60 m above ground next to a sonic anemometer. Subsamples of this air stream are extracted through an ozone scrubber and pushed into two Teflon bag reservoirs, from which they are transferred to the GC pre-concentration units consisting of carbon-based adsorption traps encapsulated in heater blocks for thermal desorption. We discuss the performance of our system and selected measurement results from the 2008 spring and summer seasons in Houston. We present diurnal variations of the fluxes of the traffic tracers benzene, toluene, ethylbenzene, and xylenes (BTEX) during different study periods. Typical BTEX fluxes ranged from -0.36 to 3.10 mg m-2 h-1 for benzene, and -0.47 to 5.04 mg m-2 h-1 for toluene, and exhibited diurnal cycles with two dominant peaks related to rush-hour traffic. A footprint analysis overlaid onto a geographic information system (GIS) will be presented to reveal the dominant emission sources and patterns in the study area.

Park, C.; Schade, G.; Boedeker, I.

2008-12-01

305

Radiative transfer in cirrus clouds from airborne flux and microphysical measurements during FIRE 86  

NASA Technical Reports Server (NTRS)

Microphysical and radiation measurements from three case studies during FIRE 86 are presented and analyzed. Calculated solar and infrared flux profiles are compared to measured flux values for the studies. The flux comparison shows that the modeled cirrus cloud underestimates cloud extinction, especially near the cloud base, where modeled extinctions are largest. The large downward solar attenuation near the cloud base cannot be matched, while the modeled solar reflection is too small. Most of this difference is attributed to an underestimation of cloud optical depth in the model. Modeling difficulties and difficulties in the measurements are discussed. It is proposed that, in order to assure a more useful flux comparison, field experiment set-ups and instrumentation as well as the modeling of cirrus clouds need to be improved.

Kinne, S.; Ackerman, T.; Heymsfield, A.; Miller, K.

1990-01-01

306

Flux correction for closed-path laser spectrometers without internal water vapor measurements  

NASA Astrophysics Data System (ADS)

Recently, instruments became available on the market that provide the possibility to perform eddy covariance flux measurements of CH4 and many other trace gases, including the traditional CO2 and H2O. Most of these instruments employ laser spectroscopy, where a cross-sensitivity to H2O is frequently observed leading to an increased dilution effect. Additionally, sorption processes at the intake tube walls modify and delay the observed H2O signal in closed-path systems more strongly than the signal of the sampled trace gas. Thereby, a phase shift between the trace gas and H2O fluctuations is introduced that dampens the H2O flux observed in the sampling cell. For instruments that do not provide direct H2O measurement in the sampling cell, transfer functions from externally measured H2O fluxes are needed to estimate the effect of H2O on trace gas flux measurements. The effects of cross-sensitivity and the damping are shown for an eddy covariance setup with the Fast Greenhouse Gas Analyzer (FGGA, Los Gatos Research Inc.) that measures CO2, CH4, and H2O fluxes. This instrument is technically identical with the Fast Methane Analyzer (FMA, Los Gatos Research Inc.) that does not measure H2O concentrations. Hence, we used measurements from a FGGA to derive a modified correction for the FMA accounting for dilution as well as phase shift effects in our instrumental setup. With our specific setup for eddy covariance flux measurements, the cross-sensitivity counteracts the damping effects, which compensate each other. Hence, the new correction only deviates very slightly from the traditional Webb, Pearman, and Leuning density correction, which is calculated from separate measurements of the atmospheric water vapor flux.

Hiller, R. V.; Zellweger, C.; Knohl, A.; Eugster, W.

2012-01-01

307

A non-water-cooled heat flux measurement system under concentrated solar radiation conditions  

Microsoft Academic Search

This paper presents a brief description of a direct heat flux measurement system to measure the concentrated solar power delivered by a heliostat field onto the flat aperture of solar central receiver prototypes. The main advantages of this device are the low measurement uncertainty and the non-requirement of water-cooling. This system has been designed, mounted and used successfully on top

Jesus Ballestrin

2002-01-01

308

Elemental weathering fluxes and saprolite production rate in a Central African lateritic terrain (Nsimi, South Cameroon)  

NASA Astrophysics Data System (ADS)

The comparison between contemporary and long-term weathering has been carried out in the Small Experimental Watershed (SEW) of Nsimi, South Cameroon in order to quantify the export fluxes of major and trace elements and the residence time of the lateritic weathering cover. We focus on the hillside system composed of a thick lateritic weathering cover topped by a soil layer. This study is built on the recent improvements of the hillside hydrological functioning and on the analyses of major and trace elements. The mass balance calculation at the weathering horizon scale performed with the parent rock as reference indicates (i) strong depletion profiles for alkalis (Na, K, Rb) and alkaline earths (Mg, Ca, Sr, Ba), (ii) moderate depletion profiles for Si, P, Cd, Cu, Zn, Ni and Co, (iii) depletion/enrichment profiles for Al, Ga, Ge, Sn, Pb, LREE, HREE, Y, U, Fe, V, Cr, Mn. It is noteworthy that (i) Mn and Ce are not significantly redistributed according to oxidative processes as it is the case for Fe, V and Cr, and (ii) Ge is fractionated compared to silica with enrichment in Fe-rich horizons. The calculations performed for the topsoil with iron crust as parent material reference reveal that the degradation of the iron crust is accompanied by the loss of most of the constituting elements, among which are those specifically accumulated as the redox sensitive elements (Fe, V, Cr) and iron oxide related elements like Th. The overall current elemental fluxes from the hillside system at the springs and the seepage zones are extremely low due to the inert lateritic mineralogy. Ninety-four percent of the whole Na flux generated from the hillside corrected from atmospheric deposits (77 mol/ha/yr) represents the current weathering rates of plagioclase (oligoclase) in the system, the other remaining 6% may be attributed to the dissolution of hornblende. The silica hillside flux is 300 mol/ha/yr and can be mostly attributed to the plagioclase and kaolinite dissolution. Al and Ga are exported from the lateritic regolith and maybe due to the dissolution of kaolinite crystals. Compared to the other immobile elements (Zr, Hf, Nb and Th), Ti is significantly exported. Among redox-sensitive elements (Fe, V, Cr, Mn, Ce), only Ce and Mn are exported out of the hillside system. The other elements (Fe, V, Cr) are likely able to be mobilized but over a short distance only. Rb, Sr, Ba, Ni, Cu, Zn are affected by export processes. LREE and Y are exported but in very low amounts (in the range from ?mol/ha/yr to mmol/ha/yr) while HREE and U are exported in negligible quantities. A first attempt is carried out to compare the mature ridge top profile from Nsimi SEW with the immature ridge top weathering profile from the Mule Hole SEW (South India), developed on similar granodioritic basement, in order to get deeper insight into (i) the contemporary saprolite production rates and (ii) the combined effect of precipitation (in terms of Mean Annual Rainfall, MAR) and evapotranspiration on the aggressiveness of the draining solutions. Considering (i) the contemporary Na flux as representative of the dissolution of plagioclase crystals and conservative during saprolitization processes and (ii) steady state of the inter-annual recharge (R) over a 10 years period, the current saprolite production rates (?r) are of 22 mm/kyr for Mule Hole SEW and 2 mm/kyr for Nsimi SEW, respectively. Even with a very low R/MAR ratio (0.04) compared to Nsimi, the chemical weathering at Mule Hole is active and related to the groundwater exports. At Mule Hole, plagioclase crystals are still present in the saprolite and the soil cover leading to a diffuse weathering front. The high Nsimi R/MAR ratio (0.2) allows the solution to be still aggressive with respect to the plagioclase and other weatherable minerals at the bedrock interface resulting in their complete breakdown in a few centimetres (sharp weathering front) leading to a mature saprolite. For the Nsimi SEW, if we consider (i) the low contemporary saprolite production rate (2 mm/kyr), (ii) the Miocene age (average 15 Myr) o

Braun, Jean-Jacques; Marechal, Jean-Christophe; Riotte, Jean; Boeglin, Jean-Loup; Bedimo Bedimo, Jean-Pierre; Ndam Ngoupayou, Jules Remy; Nyeck, Brunot; Robain, Henri; Sekhar, M.; Audry, Stéphane; Viers, Jérôme

2012-12-01

309

Rates of insulin secretion in INS-1 cells are enhanced by coupling to anaplerosis and Kreb's cycle flux independent of ATP synthesis  

SciTech Connect

Highlights: Black-Right-Pointing-Pointer We studied media effects on mechanisms of insulin secretion of INS-1 cells. Black-Right-Pointing-Pointer Insulin secretion was higher in DMEM than KRB despite identical ATP synthesis rates. Black-Right-Pointing-Pointer Insulin secretion rates correlated with rates of anaplerosis and TCA cycle. Black-Right-Pointing-Pointer Mitochondria metabolism and substrate cycles augment secretion signal of ATP. -- Abstract: Mechanistic models of glucose stimulated insulin secretion (GSIS) established in minimal media in vitro, may not accurately describe the complexity of coupling metabolism with insulin secretion that occurs in vivo. As a first approximation, we have evaluated metabolic pathways in a typical growth media, DMEM as a surrogate in vivo medium, for comparison to metabolic fluxes observed under the typical experimental conditions using the simple salt-buffer of KRB. Changes in metabolism in response to glucose and amino acids and coupling to insulin secretion were measured in INS-1 832/13 cells. Media effects on mitochondrial function and the coupling efficiency of oxidative phosphorylation were determined by fluorometrically measured oxygen consumption rates (OCRs) combined with {sup 31}P NMR measured rates of ATP synthesis. Substrate preferences and pathways into the TCA cycle, and the synthesis of mitochondrial 2nd messengers by anaplerosis were determined by {sup 13}C NMR isotopomer analysis of the fate of [U-{sup 13}C] glucose metabolism. Despite similar incremental increases in insulin secretion, the changes of OCR in response to increasing glucose from 2.5 to 15 mM were blunted in DMEM relative to KRB. Basal and stimulated rates of insulin secretion rates were consistently higher in DMEM, while ATP synthesis rates were identical in both DMEM and KRB, suggesting greater mitochondrial uncoupling in DMEM. The relative rates of anaplerosis, and hence synthesis and export of 2nd messengers from the mitochondria were found to be similar in DMEM to those in KRB. And, the correlation of total PC flux with insulin secretion rates in DMEM was found to be congruous with the correlation in KRB. Together, these results suggest that signaling mechanisms associated with both TCA cycle flux and with anaplerotic flux, but not ATP production, may be responsible for the enhanced rates of insulin secretion in more complex, and physiologically-relevant media.

Cline, Gary W., E-mail: gary.cline@yale.edu [The Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06520 (United States); Department of Surgery, University of Minnesota-Twin Cities, Minneapolis, MN 55455 (United States); Pongratz, Rebecca L.; Zhao, Xiaojian [The Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06520 (United States)] [The Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06520 (United States); Papas, Klearchos K. [Department of Surgery, University of Minnesota-Twin Cities, Minneapolis, MN 55455 (United States)] [Department of Surgery, University of Minnesota-Twin Cities, Minneapolis, MN 55455 (United States)

2011-11-11

310

Respiration rate measurement in a submerged fixed bed reactor.  

PubMed

A novel method is presented to measure the overall biofilm respiration rate in a submerged fixed bed reactor. The method, named "double gassing-out" is based on the measurement of the oxygen uptake rate under two different conditions: (i) replacing the air flow rate by nitrogen in the biological reactor, ensuring the conservation of the same hydraulic conditions and (ii) measuring the oxygen displacement rate by nitrogen in an identical reactor design with no microorganisms. The difference between these measurements gives the overall biofilm respiration rate. Results obtained in a nitrifying fixed bed reactor are presented, compared to classical techniques and discussed. PMID:12701929

Carrión, M; Asaff, A; Thalasso, F

2003-01-01

311

Direct measurements of CO2 fluxes in an urban area of Beijing city  

NASA Astrophysics Data System (ADS)

Direct measurements of CO2 fluxes in an urban area of Beijing city Huizhi Liu and Jianwu Feng LAPC, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029 Abstract Direct measurements of CO2 fluxes using an eddy covariance (EC) system were conducted from 2006 to 2008 in an urban environment of Beijing city. The EC measurements were made at the height of 47 m above the canopy on a 325 m tower. Stationarity test and cospectral analyses of the turbulence measurements met the requirement of EC assumptions. Analyses of the data revealed a clear annual cycle of CO2 fluxes with the maximum in the winter and the minimum in the summer. The positive fluxes of CO2 demonstrated that the urban surface was consistently a net source of CO2 emissions to the atmosphere. The mean daily CO2 fluxes were 0.48 ± 0.17 mg m-2 s-1 and 0.78 ± 0.28 mg m-2 s-1 (mean ± std) in the summer and the winter respectively, indicating that vehicle emissions and residential heating both contributed to the higher magnitude of CO2 fluxes in winter time. Diurnal pattern of CO2 fluxes were largely associated with traffic volumn. Two distinct peaks were observed in the morning and evening traffic peak hours, with the winter morning peak averaging up to 1.3 mg m-2 s-1. Minimum CO2 fluxes usually occurred before sunrise. The two peaks of CO2 fluxes in the weekend were a little lower than in the weekday all the year around. In summer time, the two peaks occurred about 2 hour later in the weekend compared to the weekday, but this phenomenon was not obvious in the winter. Restricted driving and other related measures to reduce CO2 emission during the time of Olympic Games (July 20 to September 20, 2008) had significant impact on the magnitude of CO2 fluxes, resulting in a mean daily value of 0.39 ± 0.13 mg m-2 s-1 (mean ± std). This research in Beijing city aims at furthering the understanding of the level and dynamics of CO2 fluxes in mega cities in China. Keywords: Carbon dioxide fluxes, eddy covariance, urban area, Beijing

Liu, H.; Feng, J.

2009-12-01

312

Feed rate measuring method and system  

DOEpatents

A system and method are provided for establishing the feed rate of a workpiece along a feed path with respect to a machine device. First and second sensors each having first and second sensing electrodes which are electrically isolated from the workpiece are positioned above, and in proximity to the desired surfaces of the workpiece along a feed path. An electric field is developed between the first and second sensing electrodes of each sensor and capacitance signals are developed which are indicative of the contour of the workpiece. First and second image signals representative of the contour of the workpiece along the feed path are developed by an image processor. The time delay between corresponding portions of the first and second image signals are then used to determine the feed rate based upon the separation of the first and second sensors and the amount of time between corresponding portions of the first and second image signals.

Novak, James L. (Albuquerque, NM); Wiczer, James J. (Albuquerque, NM)

1995-01-01

313

Feed rate measuring method and system  

DOEpatents

A system and method are provided for establishing the feed rate of a workpiece along a feed path with respect to a machine device. First and second sensors each having first and second sensing electrodes which are electrically isolated from the workpiece are positioned above, and in proximity to the desired surfaces of the workpiece along a feed path. An electric field is developed between the first and second sensing electrodes of each sensor and capacitance signals are developed which are indicative of the contour of the workpiece. First and second image signals representative of the contour of the workpiece along the feed path are developed by an image processor. The time delay between corresponding portions of the first and second image signals are then used to determine the feed rate based upon the separation of the first and second sensors and the amount of time between corresponding portions of the first and second image signals. 18 figs.

Novak, J.L.; Wiczer, J.J.

1995-12-05

314

Areal-averaged trace gas emission rates from long-range open-path measurements in stable boundary layer conditions  

NASA Astrophysics Data System (ADS)

Measurements of land-surface emission rates of greenhouse and other gases at large spatial scales (10 000 m2) are needed to assess the spatial distribution of emissions. This can be more readily done using spatial-integrating micro-meteorological methods than the widely-utilized small chamber measurements. Several micro-meteorological flux-gradient methods utilizing a non-intrusive path-averaging measurement method were evaluated for determining land-surface emission rates of trace gases under stable boundary layers. Successful application of a flux-gradient method requires confidence in the gradients of trace gas concentration and wind and in the applicability of boundary-layer turbulence theory. While there is relatively high confidence in flux measurements made under unstable atmospheres with mean winds greater than 1 m s-1, there is greater uncertainty in flux measurements made under free convective or stable conditions. The study involved quality-assured determinations of fluxes under low wind, stable or night-time atmospheric conditions when the continuous "steady-state" turbulence of the surface boundary layer breaks down and the layer has intermittent turbulence. Results indicate that the Monin-Obukhov similarity theory (MOST) flux-gradient methods that assume a log-linear profile of the wind speed and concentration gradient incorrectly determine vertical profiles and thus fluxes in the stable boundary layer.

Schäfer, K.; Grant, R. H.; Emeis, S.; Raabe, A.; von der Heide, C.; Schmid, H. P.

2012-02-01

315

Measuring and modeling near surface reflected and emitted radiation fluxes at the FIFE site  

NASA Technical Reports Server (NTRS)

Research was conducted during the four Intensive Field Campaigns (IFC) of the FIFE project in 1987. The research was done on a tall grass prairie with specific measurement sites on and near the Konza Prairie in Kansas. Measurements were made to help meet the following objectives: determination of the variability in reflected and emitted radiation fluxes in selected spectral wavebands as a function of topography and vegetative community; development of techniques to account for slope and sun angle effects on the radiation fluxes; estimation of shortwave albedo and net radiation fluxes using the reflected and emitted spectral measurements described; estimation of leaf and canopy spectral properties from calculated normalized differences coupled with off-nadir measurements using inversion techniques; estimation of plant water status at several locations with indices utilizing plant temperature and other environmental parameters; and determination of relationships between estimated plant water status and measured soil water content. Results are discussed.

Blad, Blaine L.; Norman, John M.; Walter-Shea, Elizabeth; Starks, Patrick; Vining, Roel; Hays, Cynthia

1988-01-01

316

Preliminary energy-flux measurements on ZT-40M  

SciTech Connect

Bolometer measurements indicate that 15 to 20% of the plasma losses from ZT-40M are due to radiation for a 190-kA, 1.6-mtorr discharge. The fraction of radiation losses increases slightly as the current is decreased. Thermistor measurements of the bellows temperature rise following a 190-kA discharge show large shot-to-shot variation on bellows peaks (relative to the plasma), with bellows peaks at large major radii being heated considerably more than bellows peaks at small major radii.

Ingraham, J.C.; Miller, G.

1982-05-01

317

ELF-magnetic flux densities measured in a city environment in summer and winter.  

PubMed

Epidemiological studies have indicated a connection between extremely low frequency magnetic flux densities above 0.4 microT (time weighted average) and childhood leukemia risks. This conclusion is based mainly on indoor exposure measurements. We therefore regarded it important to map outdoor magnetic flux densities in public areas in Trondheim, Norway. Because of seasonal power consumption variations, the fields were measured during both summer and winter. Magnetic flux density was mapped 1.0 m above the ground along 17 km of pavements in downtown Trondheim. The spectrum was measured at some spots and the magnetic flux density emanated mainly from the power frequency of 50 Hz. In summer less than 4% of the streets showed values exceeding 0.4 microT, increasing to 29% and 34% on cold and on snowy winter days, respectively. The average levels were 0.13 microT (summer), 0.85 microT (winter, cold), and 0.90 microT (winter, snow), with the highest recorded value of 37 microT. High spot measurements were usually encountered above underground transformer substations. In winter electric heating of pavements also gave rise to relatively high flux densities. There was no indication that the ICNIRP basic restriction was exceeded. It would be of interest to map the flux density situation in other cities and towns with a cold climate. PMID:17786926

Straume, Aksel; Johnsson, Anders; Oftedal, Gunnhild

2008-01-01

318

Analysis of actinic flux profiles measured from an ozone sonde balloon  

NASA Astrophysics Data System (ADS)

A green light sensor has been developed at KNMI to measure actinic flux profiles using an ozone sonde balloon. In total, 63 launches with ascending and descending profiles were performed between 2006 and 2010. The measured uncalibrated actinic flux profiles are analyzed using the Doubling Adding KNMI (DAK) radiative transfer model. Values of the cloud optical thickness (COT) along the flight track were taken from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) Cloud Physical Properties (CPP) product. The impact of clouds on the actinic flux profile is evaluated on the basis of the cloud modification factor (CMF) at the cloud top and cloud base, which is the ratio between the actinic fluxes for cloudy and clear-sky scenes. The impact of clouds on the actinic flux is clearly detected: the largest enhancement occurs at the cloud top due to multiple scattering. The actinic flux decreases almost linearly from cloud top to cloud base. Above the cloud top the actinic flux also increases compared to clear-sky scenes. We find that clouds can increase the actinic flux to 2.3 times of the clear-sky value at cloud top and decrease it to about 0.05 at cloud base. The relationship between CMF and COT agrees well with DAK simulations, except for a few outliers. Good agreement is found between the DAK simulated actinic flux profiles and the observations for single layer clouds in fully overcast scenes. The instrument is suitable for operational balloon measurements because of its simplicity and low cost. It is worth to further develop the instrument and launch it together with atmospheric chemistry composition sensors.

Wang, P.; Allaart, M.; Knap, W. H.; Stammes, P.

2014-12-01

319

Lidar Based Particulate Flux Measurements of Agricultural Field  

Technology Transfer Automated Retrieval System (TEKTRAN)

A three-wavelength portable scanning lidar system was developed to derive information on particulate spatial aerosol distribution over remote distances. The lidar system and retrieval approach has been tested during several field campaigns measuring agricultural emissions from a swine feeding operat...

320

CO{sub 2} flux measurements across portions of the Dixie Valley geothermal system, Nevada  

SciTech Connect

A map of the CO{sub 2} flux across a newly formed area of plant kill in the NW part of the Dixie Valley geothermal system was constructed to monitor potential growth of a fumarole field. Flux measurements were recorded using a LI-COR infrared analyzer. Sample locations were restricted to areas within and near the dead zone. The data delineate two areas of high CO{sub 2} flux in different topographic settings. Older fumaroles along the Stillwater range front produce large volumes of CO{sub 2} at high temperatures. High CO{sub 2} flux values were also recorded at sites along a series of recently formed ground fractures at the base of the dead zone. The two areas are connected by a zone of partial plant kill and moderate flux on an alluvial fan. Results from this study indicate a close association between the range front fumaroles and the dead zone fractures. The goals of this study are to characterize recharge to the geothermal system, provide geochemical monitoring of reservoir fluids and to examine the temporal and spatial distribution of the CO{sub 2} flux in the dead zone. This paper reports the results of the initial CO{sub 2} flux measurements taken in October, 1997.

Bergfeld, D.; Goff, F. [Los Alamos National Lab., NM (United States). Earth and Environmental Sciences Div.; Janik, C.J. [Geological Survey, Menlo Park, CA (United States); Johnson, S.D. [Oxbow Power Services, Reno, NV (United States)

1998-12-31

321

Rotation Rate of Saturn's Magnetosphere using CAPS Plasma Measurements  

NASA Technical Reports Server (NTRS)

We present the present status of an investigation of the rotation rate of Saturn's magnetosphere using a 3D velocity moment technique being developed at Goddard which is similar to the 2D version used by Sittler et al. for SOI and similar to that used by Thomsen et al.. This technique allows one to nearly cover the full energy range of the Cassini Plasma Spectrometer (CAPS) IMS from 1 V . E/Q < 50 kV. Since our technique maps the observations into a local inertial frame, it does work during roll maneuvers. We make comparisons with the bi-Maxwellian fitting technique developed by Wilson et al. and the similar velocity moment technique by Thomsen et al. . We concentrate our analysis when ion composition data is available, which is used to weight the non-compositional data, referred to as singles data, to separate H+, H2+ and water group ions (W+) from each other. The chosen periods have high enough telemetry rates (4 kbps or higher) so that coincidence ion data, similar to that used by Sittler et al. for SOI is available. The ion data set is especially valuable for measuring flow velocities for protons, which are more difficult to derive using singles data within the inner magnetosphere, where the signal is dominated by heavy ions (i.e., proton peak merges with W+ peak as low energy shoulder). Our technique uses a flux function, which is zero in the proper plasma flow frame, to estimate fluid parameter uncertainties. The comparisons investigate the experimental errors and potential for systematic errors in the analyses, including ours. The rolls provide the best data set when it comes to getting 4PI coverage of the plasma but are more susceptible to time aliasing effects. In the future we will then make comparisons with magnetic field observations, Saturn ionosphere conductivities as presently known and the field aligned currents necessary for the planet to enforce corotation of the rotating plasma.

Sittler, E.; Cooper, J.; Hartle, R.; Simpson, D.; Johnson, R.; Thomsen, M.; Arridge, C.

2011-01-01

322

Measurements of upward turbulent ozone fluxes above a subalpine spruce-fir forest  

NASA Astrophysics Data System (ADS)

High rural concentrations of ozone (O3) are thought to be either stratospheric in origin, advected from upwind urban sources, or photochemically generated locally as a result of natural trace gas emissions. Ozone is known to be transported vertically downward from the above-canopy atmospheric surface layer and destroyed within stomata or on other biological and mineral surfaces. However, here we report winter-time eddy correlation measurements of vertical O3 flux above a subalpine canopy of Picea engelmannii and Abies lasiocarpa in the Snowy Range Mountains of Wyoming that indicate anomalous upward O3 fluxes Upward fluxes of 0.5 µg m-2 s-1 (11 kg km-2 day-1) were routinely measured during the 1991-92 winter season. Decreasing O3 concentration from several hours to several days that relate to increasing positive O3 flux magnitudes and visa versa, suggest O3 may be temporarily stored in the snow base.

Zeller, Karl; Hehn, Ted

323

Can CO2 Turbulent Flux Be Measured by Lidar? A Preliminary Study  

NASA Technical Reports Server (NTRS)

The vertical profiling ofCO2 turbulent fluxes in the atmospheric boundary layer (ABL) is investigated using a coherent differential absorption lidar (CDIAL) operated nearby a tall tower in Wisconsin during June 2007. A CDIAL can perform simultaneous range-resolved CO2 DIAL and velocity measurements. The lidar eddy covariance technique is presented. The aims of the study are (i) an assessment of performance and current limitation of available CDIAL for CO2 turbulent fluxes and (ii) the derivation of instrument specifications to build a future CDIAL to perform accurate range-resolved CO2 fluxes. Experimental lidar CO2 mixing ratio and vertical velocity profiles are successfully compared with in situ sensors measurements. Time and space integral scales of turbulence in the ABL are addressed that result in limitation for time averaging and range accumulation. A first attempt to infer CO2 fluxes using an eddy covariance technique with currently available 2-mm CDIAL dataset is reported.

Gilbert, Fabien; Koch, Grady; Beyon, Jeffrey Y.; Hilton, Timothy W.; Davis, Kenneth J.; Andrews, Arlyn; Flamant, Pierre H.; Singh, Upendra N.

2011-01-01

324

Direct measurement of the oceanic carbon monoxide flux by eddy correlation  

NASA Astrophysics Data System (ADS)

This report presents results from a field trial of ship-based air-sea flux measurements of carbon monoxide (CO) by direct eddy correlation with an infrared-laser trace gas analyzer. The analyzer utilizes Off-Axis Integrated-Cavity-Output Spectroscopy (OA-ICOS) to achieve high selectivity for CO, rapid response (~2 Hz) and low noise. Over a two-day sea trial, peak daytime seawater CO concentrations were ~1.5 nM and wind speeds were consistently 10-12 m s-1. A clear diel cycle in CO flux with an early afternoon maximum was observed. An analysis of flux error suggests the effects of non-stationarity are important, and air-sea CO flux measurements are best performed in regions remote from continental pollution sources.

Blomquist, B. W.; Fairall, C. W.; Huebert, B. J.; Wilson, S. T.

2012-12-01

325

Direct measurement of the oceanic carbon monoxide flux by eddy correlation  

NASA Astrophysics Data System (ADS)

This report presents results from a field trial of ship-based air-sea flux measurements of carbon monoxide (CO) by direct eddy correlation using an infrared-laser trace gas analyzer. The analyzer utilizes Off-Axis Integrated-Cavity-Output Spectroscopy (OA-ICOS) to achieve high selectivity for CO, rapid response (10 Hz) and low noise. Over a two-day sea trial, peak daytime seawater CO concentrations were ~ 1.5 nM and wind speeds were consistently 10-12 m s-1. A clear diel cycle in CO flux with an early afternoon maximum was observed. An analysis of flux error sources suggests air-sea CO flux measurements are best performed in regions remote from continental pollution sources.

Blomquist, B. W.; Fairall, C. W.; Huebert, B. J.; Wilson, S. T.

2012-07-01

326

Assessing Tower Flux Footprint Climatology and Scaling Between Remotely Sensed and Eddy Covariance Measurements  

NASA Astrophysics Data System (ADS)

We describe pragmatic and reliable methods to examine the influence of patch-scale heterogeneities on the uncertainty in long-term eddy-covariance (EC) carbon flux data and to scale between the carbon flux estimates derived from land surface optical remote sensing and directly derived from EC flux measurements on the basis of the assessment of footprint climatology. Three different aged Douglas-fir stands with EC flux towers located on Vancouver Island and part of the Fluxnet Canada Research Network were selected. Monthly, annual and interannual footprint climatologies, unweighted or weighted by carbon fluxes, were produced by a simple model based on an analytical solution of the Eulerian advection-diffusion equation. The dimensions and orientation of the flux footprint depended on the height of the measurement, surface roughness length, wind speed and direction, and atmospheric stability. The weighted footprint climatology varied with the different carbon flux components and was asymmetrically distributed around the tower, and its size and spatial structure significantly varied monthly, seasonally and inter-annually. Gross primary productivity (GPP) maps at 10-m resolution were produced using a tower-mounted multi-angular spectroradiometer, combined with the canopy structural information derived from airborne laser scanning (Lidar) data. The horizontal arrays of footprint climatology were superimposed on the 10-m-resolution GPP maps. Monthly and annual uncertainties in EC flux caused by variations in footprint climatology of the 59-year-old Douglas-fir stand were estimated to be approximately 15-20% based on a comparison of GPP estimates derived from EC and remote sensing measurements, and on sensor location bias analysis. The footprint-variation-induced uncertainty in long-term EC flux measurements was mainly dependent on the site spatial heterogeneity. The bias in carbon flux estimates using spatially-explicit ecological models or tower-based remote sensing at finer scales can be estimated by comparing the footprint-weighted and EC-derived flux estimates. This bias is useful for model parameter optimizing. The optimization of parameters in remote-sensing algorithms or ecosystem models using satellite data will, in turn, increase the accuracy in the upscaled regional carbon flux estimation.

Chen, Baozhang; Black, T. Andrew; Coops, Nicholas C.; Hilker, Thomas; (Tony) Trofymow, J. A.; Morgenstern, Kai

2009-02-01

327

Improved Eddy Flux Measurements by Open-Path Gas Analyzer and Sonic Anemometer Co-Location  

NASA Astrophysics Data System (ADS)

A novel instrument design combines the sensing paths of an open-path gas analyzer and a 3-D sonic anemometer and integrates the sensors in a single aerodynamic body. Common electronics provide fast-response, synchronized measurements of wind vector, sonic temperature, CO2 and H2O densities, and atmospheric pressure. An instantaneous CO2 mixing ratio, relative to dry air, is computed in real time. The synergy of combined sensors offers an alternative to the traditional density-based flux calculation method historically used for standalone open-path analyzers. A simple method is described for a direct, in-situ, mixing-ratio-based flux calculation. The method consists of: (i) correcting sonically derived air temperature for humidity effects using instantaneous water vapor density and atmospheric pressure measurements, (ii) computing water vapor pressure based on water-vapor density and humidity-corrected sonic temperature, (iii) computing fast-response CO2 mixing ratio based on CO2 density, sonic temperature, water vapor, and atmospheric pressures, and (iv) computing CO2 flux from the covariance of the vertical wind speed and the CO2 mixing ratio. Since CO2 mixing ratio is a conserved quantity, the proposed method simplifies the calculations and eliminates the need for corrections in post-processing by accounting for temperature, water-vapor, and pressure-fluctuation effects on the CO2 density. A field experiment was conducted using the integrated sensor to verify performance of the mixing-ratio method and to quantify the differences with density-derived CO2 flux corrected for sensible and latent-heat fluxes. The pressure term of the density corrections was also included in the comparison. Results suggest that the integrated sensor with co-located sonic and gas sensing paths and the mixing-ratio-based method minimize or eliminate the following uncertainties in the measured CO2 flux: (i) correcting for frequency-response losses due to spatial separation of measured quantities, (ii) correcting sonically-derived, sensible-heat flux for humidity, (iii) correcting latent-heat flux for sensible-heat flux and water-vapor self-dilution, (iv) correcting CO2 flux for sensible- and latent-heat fluxes, (v) correcting CO2 flux for pressure-induced density fluctuations.

Bogoev, Ivan

2014-05-01

328

Leak rate measurements and detection systems  

SciTech Connect

A research program is under way to evaluate and develop improve leak detection systems. The primary focus of the work has been on acoustic emission detection of leaks. Leaks from artificial flaws, laboratory-generated IGSCCs and thermal fatigue cracks, and field-induced intergranular stress corrosion cracks (IGSCCs) from reactor piping have been examined. The effects of pressure, temperature, and leak rate and geometry on the acoustic signature are under study. The use of cross-correlation techniques for leak location and pattern recognition and autocorrelation for source discrimination is also being considered.

Kupperman, D.; Shack, W.J.; Claytor, T.

1983-10-01

329

Infiltration rate measurement by active perfluorocarbon monitoring  

SciTech Connect

The rate of air infiltration in homes and buildings is a significant factor affecting the magnitude of human exposure to air pollutants in the indoor environment. Several techniques have been utilized for the determination of air infiltration. These include building pressurization and tracer analysis, e.g., SF/sub 6/. Dietz and Cote at Brookhaven National Laboratory (BNL) have developed a simple, steady-state tracer kit that can be utilized by homeowners. This kit includes a source(s) of perfluorocarbon, i.e., perfluoromethylcyclohexane (PMCH) or perfluorodimethylcyclohexane (PDCH), and a passive sampling tube containing Ambersorb XE-347. Typically, the sampling tube is deployed for several days and then returned to a laboratory for analysis by thermal desorption/gas chromatography/electron capture detection. The authors developed an alternative sampling and analysis technique for PMCH/PDCH in homes. In order to facilitate monitoring of short-term infiltration rates (i.e., less than one day) they developed an active sorbent sampling method and solvent desorption/gas chromatography/electron capture detection analytical method. The method is based on the collection of PMCH on charcoal. The method validation, which is discussed in this article, includes analytical method development, selection of a solid sorbent, determination of desorption efficiency, analysis of breakthrough, testing of storage stability, and assessment of precision and accuracy in both the laboratory and field environment.

Menzies, K.T.; Pong, C.M.; Randel, M.A. (Arthur D. Little, Inc., Cambridge, MA (US))

1987-01-01

330

A Local Heat Flux Measurement Technique for Inclined Heat Exchanger Tubes  

Microsoft Academic Search

This article presents the design, fabrication, and calibration of thermocouple pairs for local heat flux measurement. The intended application of the thermocouple pairs is on the tubes of phase-change heat exchangers experiencing heat fluxes on the order of 10 W\\/m. Particular advantages of this technique are that it is accurate even for thin-wall tubes, there are no restrictions on the

T. Wu; K. Vierow

2006-01-01

331

Spatially explicit regionalization of airborne flux measurements using environmental response functions  

NASA Astrophysics Data System (ADS)

The goal of this study is to characterize the sensible (H) and latent (LE) heat exchange for different land covers in the heterogeneous steppe landscape of the Xilin River catchment, Inner Mongolia, China. Eddy-covariance flux measurements at 50-100 m above ground were conducted in July 2009 using a weight-shift microlight aircraft. Wavelet decomposition of the turbulence data enables a spatial discretization of 90 m of the flux measurements. For a total of 8446 flux observations during 12 flights, MODIS land surface temperature (LST) and enhanced vegetation index (EVI) in each flux footprint are determined. Boosted regression trees are then used to infer an environmental response function (ERF) between all flux observations (H, LE) and biophysical (LST, EVI) and meteorological drivers. Numerical tests show that ERF predictions covering the entire Xilin River catchment (?3670 km2) are accurate to ?18% (1 ?). The predictions are then summarized for each land cover type, providing individual estimates of source strength (36 W m-2 < H < 364 W m-2, 46 W m-2 < LE < 425 W m-2) and spatial variability (11 W m-2 < ?H < 169 W m-2, 14 W m-2 < ?LE < 152 W m-2) to a precision of ?5%. Lastly, ERF predictions of land cover specific Bowen ratios are compared between subsequent flights at different locations in the Xilin River catchment. Agreement of the land cover specific Bowen ratios to within 12 ± 9% emphasizes the robustness of the presented approach. This study indicates the potential of ERFs for (i) extending airborne flux measurements to the catchment scale, (ii) assessing the spatial representativeness of long-term tower flux measurements, and (iii) designing, constraining and evaluating flux algorithms for remote sensing and numerical modelling applications.

Metzger, S.; Junkermann, W.; Mauder, M.; Butterbach-Bahl, K.; Trancón y Widemann, B.; Neidl, F.; Schäfer, K.; Wieneke, S.; Zheng, X. H.; Schmid, H. P.; Foken, T.

2013-04-01

332

Measurement of the flux and energy spectrum of cosmic-ray induced neutrons on the ground  

Microsoft Academic Search

New ground-based measurements of the cosmic-ray induced neutron flux and its energy distribution have been made at several locations across the United States using an extended-energy Bonner sphere spectrometer. The data cover over twelve decades of neutron energy, from meV to GeV. An expression to scale the flux to other locations has been developed from a fit to the altitude

M. S. Gordon; P. Goldhagen; K. P. Rodbell; T. H. Zabel; H. H. K. Tang; J. M. Clem; P. Bailey

2004-01-01

333

Comparison of in-situ measured ground heat fluxes within a heteorogeneous urban ballast layer  

Microsoft Academic Search

Summary  This study concentrates on measurements of ground heat fluxes within a porous urban ballast layer that were conducted from\\u000a June to September 2002 at the goods station in Osnabrück, Germany. To account for the limitation of accurately installing\\u000a sensors within the heterogeneous and porous ballast bulk, the heat fluxes were calculated from four different methods to compare\\u000a their variability, dynamics

S. Weber

2006-01-01

334

Surface turbulent flux measurements over the Loess Plateau for a semi-arid climate change study  

Microsoft Academic Search

In order to provide high quality data for climate change studies, the data quality of turbulent flux measurements at the station\\u000a of SACOL (Semi-Arid Climate & Environment Observatory of Lanzhou University), which is located on a semi-arid grassland over\\u000a the Loess Plateau in China, has been analyzed in detail. The effects of different procedures of the flux corrections on CO2,

Jinqing Zuo; Jianping Huang; Jiemin Wang; Wu Zhang; Jianrong Bi; Guoyin Wang; Weijing Li; Peijian Fu

2009-01-01

335

Vertical helicity flux in atmospheric vortices as a measure of their intensity  

Microsoft Academic Search

It is suggested that the downward helicity flux (through the upper boundary of the viscous turbulent boundary layer) be treated\\u000a as a measure of the intensity of atmospheric vortices, including tropical cyclones, tornadoes, and dust devils. As follows\\u000a immediately from the general helicity balance equation known in the literature, this flux is determined by the product of\\u000a the cubed maximum

M. V. Kurgansky

2008-01-01

336

Measurement of oxygen flux as a function of oxygen activity for selected ceramic materials  

NASA Astrophysics Data System (ADS)

For materials that possess an ionic conductivity that is dependent upon the oxygen activity, such as those used for gas separation membranes, it is difficult to relate the oxygen flux generated by a material under an oxygen chemical potential gradient to the actual ionic conductivity values. It is possible to determine average values for the ionic conductivity or to indirectly measure it at a single oxygen activity using some electrical and thermodynamic measurements. In real gas separation systems, however, it would be beneficial to use actual oxygen flux measurements when determining the oxygen activity dependence of the ionic conductivity. This measurement would be a more direct approach than others and would be performed under the actual conditions that a material would be exposed to in a real system. When making these measurements of the oxygen flux, however, it is important to consider the influence of adding oxygen into the reducing gas stream. This additional oxygen, which may arise from a leak in the seal or delivery systems or due to the oxygen flux itself, can shift the oxygen activity of the reducing gas and limit the oxygen flux. A method for calculating the ionic conductivity as a function of oxygen activity has been developed. This method requires that the oxygen flux be measured as the oxygen activity is systematically changed on one side of the oxygen chemical potential gradient. Corrections can be made to the oxygen flux for leaks into the system and also for the shift in the oxygen chemical potential due to the addition of oxygen into the reducing gas. This method was used to determine the ionic conductivity of (Lasb{0.80}Srsb{0.20})(Cosb{0.20}Fesb{0.80})Osb3 membranes and to correlate it to the defect chemistry of the material.

Stephens, Walter Timothy

337

Urban greenhouse gas mole fraction in-situ measurements: Results from the Indianapolis Flux Experiment (INFLUX)  

NASA Astrophysics Data System (ADS)

The Indianapolis Flux Experiment (INFLUX) was designed to develop and evaluate methods for the measurement and modeling of greenhouse gas fluxes from urban environments. Determination of greenhouse gas fluxes and uncertainty bounds is essential for the evaluation of the effectiveness of mitigation strategies. The current INFLUX observation network includes twelve in-situ tower-based, continuous measurements of CO2, CO, and CH4, flask sampling of 14CO2 and other trace gases, and periodic aircraft sampling of greenhouse gases and meteorological conditions. Eddy covariance and radiative flux are measured at four of the tower sites, and a scanning Doppler lidar was installed in April 2013; both are used to quantify key boundary layer meteorological properties and evaluate model performance. Additionally, a total carbon column observing network (TCCON) column remote sensing station was deployed August - December 2012. The data from the towers, TCCON, and aircraft measurements are being used in an inverse-modeling approach to yield estimates of the urban area flux at 1 km2 resolution. Very high space/time resolution estimates of fossil fuel carbon emissions (Hestia project) offer state-of-the-art "bottom up" emissions estimates for the city and its surroundings. Here we present an overview of the progress from INFLUX, with a focus on tower-based results. With this high density of urban tower-based greenhouse gas measurements, we will quantify horizontal and vertical spatial patterns in atmospheric mole fractions of CO2, CO, and CH4 in Indianapolis. The consistency of the observed horizontal gradients with that expected based on differences in land-cover contributions according to footprint analysis will be evaluated. The ability to correctly model transport and mixing in the atmospheric boundary layer, responsible for carrying greenhouse gases from their source to the point of measurement, is essential. Thus we investigate differences between the modeled and observed sensible heat flux, latent heat flux, air temperature, and wind speed.

Miles, Natasha; Lauvaux, Thomas; Davis, Kenneth; Richardson, Scott; Sarmiento, Daniel; Sweeney, Colm; Karion, Anna; Hardesty, Robert Michael; Turnbull, Jocelyn; Iraci, Laura; Gurney, Kevin; Razlivanov, Igor; Obiminda Cambaliza, Maria; Shepson, Paul; Whetstone, James

2014-05-01

338

Measuring Transpiration to Regulate Winter Irrigation Rates  

SciTech Connect

Periodic transpiration (monthly sums) in a young loblolly pine plantation between ages 3 and 6 was measured using thermal dissipation probes. Fertilization and fertilization with irrigation were better than irrigation alone in increasing transpiration of young loblolly pines during winter months, apparently because of increased leaf area in fertilized trees. Irrigation alone did not significantly increase transpiration compared with the non-fertilized and non-irrigated control plots.

Samuelson, Lisa [Auburn University] [Auburn University

2006-11-08

339

Measurement uncertainties in quantifying aeolian mass flux: evidence from wind tunnel and field site data  

PubMed Central

Aeolian sediment traps are widely used to estimate the total volume of wind-driven sediment transport, but also to study the vertical mass distribution of a saltating sand cloud. The reliability of sediment flux estimations from such measurements are dependent upon the specific configuration of the measurement compartments and the analysis approach used. In this study, we analyse the uncertainty of these measurements by investigating the vertical cumulative distribution and relative sediment flux derived from both wind tunnel and field studies. Vertical flux data was examined using existing data in combination with a newly acquired dataset; comprising meteorological data and sediment fluxes from six different events, using three customized catchers at Ameland beaches in northern Netherlands. Fast-temporal data collected in a wind tunnel shows that the median transport height has a scattered pattern between impact and fluid threshold, that increases linearly with shear velocities above the fluid threshold. For finer sediment, a larger proportion was transported closer to the surface compared to coarser sediment fractions. It was also shown that errors originating from the distribution of sampling compartments, specifically the location of the lowest sediment trap relative to the surface, can be identified using the relative sediment flux. In the field, surface conditions such as surface moisture, surface crusts or frozen surfaces have a more pronounced but localized effect than shear velocity. Uncertainty in aeolian mass flux estimates can be reduced by placing multiple compartments in closer proximity to the surface. PMID:25071984

Keijsers, Joep G.S.; Maroulis, Jerry; Visser, Saskia M.

2014-01-01

340

Measurement uncertainties in quantifying aeolian mass flux: evidence from wind tunnel and field site data.  

PubMed

Aeolian sediment traps are widely used to estimate the total volume of wind-driven sediment transport, but also to study the vertical mass distribution of a saltating sand cloud. The reliability of sediment flux estimations from such measurements are dependent upon the specific configuration of the measurement compartments and the analysis approach used. In this study, we analyse the uncertainty of these measurements by investigating the vertical cumulative distribution and relative sediment flux derived from both wind tunnel and field studies. Vertical flux data was examined using existing data in combination with a newly acquired dataset; comprising meteorological data and sediment fluxes from six different events, using three customized catchers at Ameland beaches in northern Netherlands. Fast-temporal data collected in a wind tunnel shows that the median transport height has a scattered pattern between impact and fluid threshold, that increases linearly with shear velocities above the fluid threshold. For finer sediment, a larger proportion was transported closer to the surface compared to coarser sediment fractions. It was also shown that errors originating from the distribution of sampling compartments, specifically the location of the lowest sediment trap relative to the surface, can be identified using the relative sediment flux. In the field, surface conditions such as surface moisture, surface crusts or frozen surfaces have a more pronounced but localized effect than shear velocity. Uncertainty in aeolian mass flux estimates can be reduced by placing multiple compartments in closer proximity to the surface. PMID:25071984

Poortinga, Ate; Keijsers, Joep G S; Maroulis, Jerry; Visser, Saskia M

2014-01-01

341

Inaccuracies in soil heat flux measurement and modeling: a matter of vertical and temporal resolution?  

NASA Astrophysics Data System (ADS)

We here demonstrate with a conceptual model of the land-atmosphere interaction and a high vertical resolution Soil Vegetation Atmosphere Transfer model that the high daily frequencies of incoming radiation play a fundamental role in the soil heat flux signal. These high frequencies remain concentrated in a very shallow layer at the surface of about 1cm, which precludes the use of deeper measurement to accurately describe the surface soil heat flux signal. Current measurement techniques lead to important errors in the surface energy budget. In addition the currently-used calorimetric method is demonstrated to be unable to characterize the variability, magnitude and phase in the surface soil heat flux. In consequence, these results call for a higher-resolution sampling of soil heat flux, both in time and vertically near the surface, in order to accurately quantify the surface soil heat flux and to account for its rapid variations, especially in cloudy situations. In addition those results demonstrate the need for high vertical and temporal resolution in the modeling of the soil surface in order to describe the diurnal course of the surface soil heat flux. Coarser resolutions are shown to miss most of the soil heat flux signal since it acts as a high-pass filter of incoming radiation. Finally this works points out important limitations of the assimilation of infrared surface temperature because of the rapid fluctuations in solar radiation (weather noise). Comparison of the soil heat flux at different depth obtained with SVAT (continuous line) and conceptual land-atmosphere model (dashed line) over 135 days of data from the SUDMED project. The conceptual model captures the emergent behavior of the soil heat flux response. Soil heat flux at the surface is mostly influenced by high frequencies, whereas the high-frequency component of the signal has almost disappeared at typical soil heat flux measurement depth (2.5 or 5cm). This shows the limitation of current soil heat flux methodology since they do not capture most of the surface signal and cannot therefore close the surface energy partitioning.

Gentine, P.; Entekhabi, D.

2010-12-01

342

Eddy Covariance Measurements of Methane Fluxes from an Arctic Sedge Wetland  

NASA Astrophysics Data System (ADS)

Concern and uncertainty regarding the magnitude of greenhouse gas emissions from permafrost regions has prompted a new field study on the North Slope of Alaska. In support of an aircraft eddy covariance campaign beginning in 2013, a CH4 and CO2 eddy covariance flux tower was installed in a wet sedge ecosystem along the aircraft measurement transect, south of Prudhoe Bay, AK. The tower-based results indicate that this ecosystem is a strong source of CH4 to the atmosphere, with preliminary fluxes of approximately 100 mg CH4 m-2 day-1 measured in late July. Prior to installation in Alaska, the tower and aircraft flux measurement systems were also compared for one week over a salt marsh on Wallops Is, VA in June, 2013. The flux of CH4 to the atmosphere was significantly smaller than at the sedge site in Alaska, and was measured by the eddy covariance tower to be about 10 mg CH4 m-2 day-1. Results from this study will be presented, with a specific focus on the tower-based CH4 flux measurements and their correlation with soil temperature.

Kochendorfer, J.; Heuer, M.; Dumas, E.; Meyers, T. P.; Baker, B.; Healy, C. E.; Munster, J.; Sayres, D. S.; Anderson, J. G.

2013-12-01

343

Measurement of turbulent water vapor fluxes using a lightweight unmanned aerial vehicle system  

NASA Astrophysics Data System (ADS)

We present here the first application of a lightweight unmanned aerial vehicle (UAV) system designed to measure turbulent properties and vertical latent heat fluxes (?E). Such measurements are crucial to improve our understanding of linkages between surface moisture supply and boundary layer clouds and phenomena such as atmospheric rivers. The application of UAVs allows for measurements on spatial scales complimentary to satellite, aircraft, and tower derived fluxes. Key system components are: a turbulent gust probe; a fast response water vapor sensor; an inertial navigation system (INS) coupled to global positioning system (GPS); and a 100 Hz data logging system. We present measurements made in the continental boundary layer at the National Aeronautics and Space Administration (NASA) Dryden Research Flight Facility located in the Mojave Desert. Two flights consisting of several horizontal straight flux run legs up to ten kilometers in length and between 330 and 930 m above ground level (m a.g.l.) are compared to measurement from a surface tower. Surface measured ?E ranged from -53 W m-2 to 41 W m-2, and the application of a Butterworth High Pass Filter (HPF) to the datasets improved agreement to within +/-12 W m-2 for 86% of flux runs, by removing improperly sampled low frequency flux contributions. This result, along with power and co-spectral comparisons and consideration of the differing spatial scales indicates the system is able to resolve vertical fluxes for the measurement conditions encountered. Challenges remain, and the outcome of these measurements will be used to inform future sampling strategies and further system development.

Thomas, R. M.; Lehmann, K.; Nguyen, H.; Jackson, D. L.; Wolfe, D.; Ramanathan, V.

2012-01-01

344

Measurement of turbulent water vapor fluxes using a lightweight unmanned aerial vehicle system  

NASA Astrophysics Data System (ADS)

We present here the first application of a lightweight unmanned aerial vehicle (UAV) system designed to measure turbulent properties and vertical latent heat fluxes (?E). Such measurements are crucial to improve our understanding of linkages between surface moisture supply and boundary layer clouds and phenomena such as atmospheric rivers. The application of UAVs allows for measurements on spatial scales complimentary to satellite, aircraft, and tower derived fluxes. Key system components are: a turbulent gust probe; a fast response water vapor sensor; an inertial navigation system (INS) coupled to global positioning system (GPS); and a 100 Hz data logging system. We present measurements made in the continental boundary layer at the National Aeronautics and Space Administration (NASA) Dryden Research Flight Facility located in the Mojave Desert. Two flights consisting of several horizontal straight flux run legs up to ten kilometers in length and between 330 and 930 m above ground level (m a.g.l.) are compared to measurement from a surface tower. Surface measured ?E ranged from -53 W m-2 to 41 W m-2, and the application of a Butterworth High Pass Filter (HPF) to the datasets improved agreement to within ± 12 W m-2 for 86 % of flux runs, by removing improperly sampled low frequency flux contributions. This result, along with power and co-spectral comparisons and consideration of the differing spatial scales indicates the system is able to resolve vertical fluxes for the measurement conditions encountered. Challenges remain, and the outcome of these measurements will be used to inform future sampling strategies and further system development.

Thomas, R. M.; Lehmann, K.; Nguyen, H.; Jackson, D. L.; Wolfe, D.; Ramanathan, V.

2011-08-01

345

Standardization of flux chamber and wind tunnel flux measurements for quantifying volatile organic compound and ammonia emissions from area sources at animal feeding operations  

Technology Transfer Automated Retrieval System (TEKTRAN)

A variety of wind tunnels and flux chambers have been used to measure fluxes of volatile organic compounds (VOC) and ammonia (NH3) at animal feeding operations (AFO). However, there has been little regard to the extreme variation and potential inaccuracies caused by inappropriate air velocity or sw...

346

Multireaction Spallation Detectors for Measuring Fluxes and Energy Spectra of High Energy Hadrons  

Microsoft Academic Search

A method is described for measuring fluxes and energy spectra of high energy hadron cascade particles in the energy range of tens to hundreds of MeV. A multitude of spallation reactions induced in copper foils are identified and quantitatively measured by the use of high resolution Ge(Li) gamma spectroscopy and computerized analysis. Calculated spallation cross sections are used to estimate

J T Routti

1974-01-01

347

DESIGN AND IMPLEMENTATION OF A TRANSPORTABLE SYSTEM FOR DIRECT MEASUREMENT OF DRY DEPOSITION FLUXES  

EPA Science Inventory

Dry deposition of air pollutants is expensive and difficult to measure. icks et al. (1985) proposed the dry deposition inferential model determines dry deposition fluxes as the product of a measured concentration and a modeled deposition velocity. eposition velocity is calculated...

348

Characterisation of radiation and flux measurements on a neutraliser plate of the Tore Supra ergodic divertor  

Microsoft Academic Search

A recent extensive experimental study of impurity production and penetration for various density regimes is described. Deuterium and carbon emissions near a neutraliser plate (NP) of the Tore Supra Ergodic Divertor (ED) has been measured with an absolutely calibrated visible endoscope, for high- and low-density plasma regimes. From these radiation measurements, we have deduced an effective carbon flux, and at

Y. Corre; R. Giannella; C. De Michelis; R. Guirlet; A. Azeroual; E. Chareyre; L. Costanzo; A. Escarguel; E. Gauthier; P. Ghendrih; J. Gunn; J. Hogan; P. Monier-Garbet; B. Pégourié; A. Pospieszczyk; E. Tsitrone

2001-01-01

349

ODOR FLUX MEASUREMENTS AT A FACULTATIVE SWINE LAGOON STRATIFIED BY SURFACE AERATION  

Microsoft Academic Search

Odor-related complaints are a major concern of pork producers. Open manure storage and treatment facilities such as uncovered anaerobic treatment lagoons are a major contributor to odor nuisance. Repeatable and valid field measurement techniques are needed for evaluating baseline odor emissions from existing livestock facilities and the effectiveness of odor abatement technologies. A buoyant convective flux chamber (BCFC) for measuring

A. J. Heber; J.-Q. Ni; T. T. Lim

350

A novel method for measurement of crystal growth rate  

NASA Astrophysics Data System (ADS)

A new method for measurement of crystal growth rate is proposed, in an attempt to make the measuring of growth rate more convenient than the existing methods. In this newly proposed method, the point of nucleation under a constant cooling rate condition was measured as changing the amount of seeds. The growth kinetics parameters were then estimated using the experimental data to match the points of nucleation. Experiments were performed with potash alum in the water system and growth kinetic parameters were estimated. Compared with existing results, the proposed method showed tolerable discrepancy in the growth kinetic parameters. The proposed method can be an alternative technique for measurement of growth rate.

Kim, Do Yeon; Yang, Dae Ryook

2013-06-01

351

Use of footprint modelling for the characterisation of complex meteorological flux measurement sites  

NASA Astrophysics Data System (ADS)

A tool for the evaluation of complex flux measurement sites has been developed which combines existing quality assessment tools for flux measurements with footprint modelling. In this way it is possible to define the spatial context of the fluxes measured, and to include both topographical and land use features of the surrounding terrain and micrometeorological flux data in the analysis. This approach allows us to determine the flux data quality for different wind sectors and meteorological conditions, and thus to identify the most suitable situations for the collection of high-quality data sets. To prepare the input data set for the quality assessment tool, data quality flags have to be assigned for the flux measurements and the source area has to be calculated. The quality flag assignment adopted within this program is based on FOKEN &WICHURA (1996), while the footprint routine used in the actual version of the quality assessment software is the FSAM-model proposed by SCHMID (1997). To produce the overall performance of the flux data quality for a specific site, the results of those two analyses are combined. This process is termed source weight synthesis because the products of the procedure are two-dimensional matrices and graphs which form a combination of all the footprint analyses for the specific site. The software for this purpose, which was produced in the course of this quality assessment approach, is termed TERRAFEX. This software has been tested thoroughly within the frame of the CARBOEUROFLUX project and the German Program on Atmospheric research, AFO 2000, sub-project VERTIKO. The results can be provided in tabulated form or illustrated by 3-dimensional graphs, indicating the computed flux property for discrete grid cells in the area surrounding the tower. These graphs are routinely produced for - the flux contribution to the total flux. - the quality assessment of the fluxes of momentum, sensible heat, latent heat and CO2. - the vertical wind speed, with respect to the topography of the area. - the percentage of the land use type of interest. As an example the results for the Waldstein/Weidenbrunnen site in the Fichtelgebirge mountains near Bayreuth, Germany, will be presented.

Goeckede, M.; Rebmann, C.; Foken, Th.

2003-04-01

352

A computationally efficient iron loss model for brushless AC machines that caters for rated flux and field weakened operation  

Microsoft Academic Search

This paper presents a simple and computationally efficient approach for predicting iron loss within a field orientated controlled brushless AC permanent magnet machine which can cater for both rated flux and field weakened operation. The proposed method is readily incorporated as part of the design process and is based on two discrete time step 2D magnetostatic finite element field solutions

P. H. Mellor; R. Wrobel; D. Holliday

2009-01-01

353

Comparative Biochemistry and Physiology Part A 127 (2000) 8187 Effects of acute fresh water exposure on water flux rates  

E-print Network

to fresh water were quantified. Salt-water adapted turtles were exposed to fresh water for 4 d before being in sea turtles may be adrenocortically mediated. In another group of marine adapted reptiles, sea snakes exposure on water flux rates and osmotic responses in Kemp's ridley sea turtles (Lepidochelys kempi ) Rudy

Ortiz, Rudy M.

354

Radon-222 activity flux measurement using activated charcoal canisters: revisiting the methodology.  

PubMed

The measurement of radon ((222)Rn) activity flux using activated charcoal canisters was examined to investigate the distribution of the adsorbed (222)Rn in the charcoal bed and the relationship between (222)Rn activity flux and exposure time. The activity flux of (222)Rn from five sources of varying strengths was measured for exposure times of one, two, three, five, seven, 10, and 14 days. The distribution of the adsorbed (222)Rn in the charcoal bed was obtained by dividing the bed into six layers and counting each layer separately after the exposure. (222)Rn activity decreased in the layers that were away from the exposed surface. Nevertheless, the results demonstrated that only a small correction might be required in the actual application of charcoal canisters for activity flux measurement, where calibration standards were often prepared by the uniform mixing of radium ((226)Ra) in the matrix. This was because the diffusion of (222)Rn in the charcoal bed and the detection efficiency as a function of the charcoal depth tended to counterbalance each other. The influence of exposure time on the measured (222)Rn activity flux was observed in two situations of the canister exposure layout: (a) canister sealed to an open bed of the material and (b) canister sealed over a jar containing the material. The measured (222)Rn activity flux decreased as the exposure time increased. The change in the former situation was significant with an exponential decrease as the exposure time increased. In the latter case, lesser reduction was noticed in the observed activity flux with respect to exposure time. This reduction might have been related to certain factors, such as absorption site saturation or the back diffusion of (222)Rn gas occurring at the canister-soil interface. PMID:24412530

Alharbi, Sami H; Akber, Riaz A

2014-03-01

355

Denitrification in the Upper Mississippi River: Rates, controls, and contribution to nitrate flux  

USGS Publications Warehouse

We evaluated patterns of denitrification and factors effecting denitrification in the upper Mississippi River. Measurements were taken over 2 years, during which river discharge ranged from record flooding to base flow conditions. Over the period of study, average denitrification enzyme activity was highest in backwater lakes and lowest in the main channel. Throughout the study reach, highest denitrification enzyme activity occurred during fall and lowest occurred in winter. Rates during spring floods (2001) were only slightly higher than during the preceding winter. Mean unamended denitrification rates ranged from 0.02 (fall 2001 in backwaters) to 0.40 ??g N??cm -2??h-1 (spring 2001 in backwaters). Laboratory experiments showed that denitrification rates increased significantly with addition of NO3- regardless of sediment C content, while rates increased little with addition of labile C (glucose). Denitrification in this reach of the upper Mississippi River appears to be NO3- limited throughout the growing season and the delivery of NO 3- is strongly controlled by river discharge and hydrologie connectivity across the floodplain. We estimate that denitrification removes 6939 t N??year-1 or 6.9% of the total annual NO 3- input to the reach. Hydrologic connectivity and resultant NO3- delivery to high-C sediments is a critical determinant of reach-scale processing of N in this floodplain system.

Richardson, W.B.; Strauss, E.A.; Bartsch, L.A.; Monroe, E.M.; Cavanaugh, J.C.; Vingum, L.; Soballe, D.M.

2004-01-01

356

Measuring Mass Loss Rates from Galactic Satellites  

E-print Network

We present the results of a study that uses numerical simulations to interpret observations of tidally disturbed satellites around the Milky Way. When analysing the simulations from the viewpoint of an observer, we find a break in the slope of the star count and velocity dispersion profiles in our models at the location where unbound stars dominate. We conclude that `extra-tidal' stars and enhanced velocity dispersions observed in the outskirts of Galactic satellites are due to contamination by stellar debris from the tidal interaction with the Milky Way. However, a significant bound population can exist beyond the break radius and we argue that it should not be identified with the tidal radius of the satellite. We also develop and test a method for determining the mass loss rate from a Galactic satellite using its extra-tidal population. We apply this method to observations of globular clusters and dwarf spheroidal satellites of the Milky Way, and conclude that a significant fraction of both satellite systems are likely be destroyed within the next Hubble time. Finally, we demonstrate that this mass loss estimate allows us to place some limits on the initial mass function (IMF) of stars in a cluster from the radial dependence of its present day mass function (PDMF).

Kathryn V. Johnston; Steinn Sigurdsson; Lars Hernquist

1998-05-21

357

Measurements and Models of Heat Flux Magnitude and Variance from the Main Endeavour Hydrothermal Vent Field  

NASA Astrophysics Data System (ADS)

Precise measurement of the total heat flux from the Main Endeavour hydrothermal vent field (MEF) to the Northeast Pacific Ocean is confounded by tidal and topographically-controlled currents within the axial valley of the Endeavour segment. The magnitude of the total heat flux is dominated by vertical flux through a horizontal plane 75m above the vent field, observed to be 590+/-51MW. The variance of the vertical flux, based on 12 surveys of velocity and hydrography over the MEF made by the Autonomous Benthic Explorer (ABE), compares well with the variance expected at the survey elevation from a model of axisymmetric hydrothermal plumes. In contrast to the vertical flux, the horizontal flux of heat, advected laterally by currents through the MEF perimeter (<75m above the bottom), has a low observed mean magnitude of order 10MW. The horizontal flux, estimated by interpreting CTD and current data in multiple ways, has a high variance which is explained by an advection/diffusion, or ``puff,'' model initialized with current meter data acquired near the MEF. >http://www2.ocean.washington.edu/ ~scottv/research/2001agu/

Veirs, S. R.; Stahr, F. R.; McDuff, R. E.; Thomson, R. E.; Yoerger, D. R.; Bradley, A. M.

2001-12-01

358

A literature overview of micrometeorological CH4 and N2O flux measurements in terrestrial ecosystems  

NASA Astrophysics Data System (ADS)

The use of micrometeorological (MM) techniques for methane (CH4) and nitrous oxide (N2O) flux measurements in terrestrial ecosystems is increasing and a general outline which summarizes key results is needed. This work provides an overview of the current status of global flux measurements of CH4 and N2O by MM techniques in terrestrial ecosystems. Published studies were grouped into four main terrestrial land cover categories and the reported flux ranges, the consistency of different MM approaches over the same ecosystem types, the variability of the MM technique performances as regards the flux detection limit and environmental conditions, were analysed. Furthermore, the issue of the comparability between MM and soil chambers measurements was evaluated. The existing dataset, although temporally and spatially limited, shows that CH4 and N2O fluxes are extremely variable in both time and space with mean fluxes spanning within interquartile ranges of 1.33 ÷ 5.45, 11.02 ÷ 68.48, 5.38 ÷ 29.28, 13.87·103 ÷ 47.60·103 nmol CH4 m-2 s-1 in forest, wetlands, croplands and artificial lands respectively, and of 0.09 ÷ 0.42, 0.24 ÷ 1.47, 9.13 ÷ 20.89 nmol N2O m-2 s-1 in forest, croplands and artificial lands (no published works were found for wetlands). When environmental conditions were comparable, a general agreement of flux ranges was found within each ecosystem type, in particular when estimates were based on accurate footprint analysis. Exceptions were mainly related to site-specific aspects or to particular measurement periods. Not all the measurement set-ups were suitable for all ecosystems, environmental conditions, turbulence characteristics and flux intensity, however the latest technological improvements make the detection of fluxes feasible virtually in all ecosystems. MM studies of CH4 and N2O fluxes were unevenly distributed around the globe and, in particular, were lacking in sensitive areas like Africa, South America and Central Asia.

Nicolini, Giacomo; Castaldi, Simona; Fratini, Gerardo; Valentini, Riccardo

2013-12-01

359

Areal-averaged trace gas emission rates from long-range open-path measurements in stable boundary layer conditions  

NASA Astrophysics Data System (ADS)

Measurements of land-surface emission rates of greenhouse and other gases at large spatial scales (10 000 m2) are needed to assess the spatial distribution of emissions. This can be readily done using spatial-integrating micro-meteorological methods like flux-gradient methods which were evaluated for determining land-surface emission rates of trace gases under stable boundary layers. Non-intrusive path-integrating measurements are utilized. Successful application of a flux-gradient method requires confidence in the gradients of trace gas concentration and wind, and in the applicability of boundary-layer turbulence theory; consequently the procedures to qualify measurements that can be used to determine the flux is critical. While there is relatively high confidence in flux measurements made under unstable atmospheres with mean winds greater than 1 m s-1, there is greater uncertainty in flux measurements made under free convective or stable conditions. The study of N2O emissions of flat grassland and NH3 emissions from a cattle lagoon involves quality-assured determinations of fluxes under low wind, stable or night-time atmospheric conditions when the continuous "steady-state" turbulence of the surface boundary layer breaks down and the layer has intermittent turbulence. Results indicate that following the Monin-Obukhov similarity theory (MOST) flux-gradient methods that assume a log-linear profile of the wind speed and concentration gradient incorrectly determine vertical profiles and thus flux in the stable boundary layer. An alternative approach is considered on the basis of turbulent diffusivity, i.e. the measured friction velocity as well as height gradients of horizontal wind speeds and concentrations without MOST correction for stability. It is shown that this is the most accurate of the flux-gradient methods under stable conditions.

Schäfer, K.; Grant, R. H.; Emeis, S.; Raabe, A.; von der Heide, C.; Schmid, H. P.

2012-07-01

360

``Designing Lagrangian experiments to measure regional-scale trace gas fluxes''  

E-print Network

are incorporated into planning of Lagrangian experiments using statistics of wind errors derived by comparison gas fluxes at the land surface is essential for understanding the impact of human activities locations, rate of dispersion of air parcels, and proper assessment of forecast errors. We describe

361

Uncertainty analysis of steady state incident heat flux measurements in hydrocarbon fuel fires.  

SciTech Connect

The objective of this report is to develop uncertainty estimates for three heat flux measurement techniques used for the measurement of incident heat flux in a combined radiative and convective environment. This is related to the measurement of heat flux to objects placed inside hydrocarbon fuel (diesel, JP-8 jet fuel) fires, which is very difficult to make accurately (e.g., less than 10%). Three methods will be discussed: a Schmidt-Boelter heat flux gage; a calorimeter and inverse heat conduction method; and a thin plate and energy balance method. Steady state uncertainties were estimated for two types of fires (i.e., calm wind and high winds) at three times (early in the fire, late in the fire, and at an intermediate time). Results showed a large uncertainty for all three methods. Typical uncertainties for a Schmidt-Boelter gage ranged from {+-}23% for high wind fires to {+-}39% for low wind fires. For the calorimeter/inverse method the uncertainties were {+-}25% to {+-}40%. The thin plate/energy balance method the uncertainties ranged from {+-}21% to {+-}42%. The 23-39% uncertainties for the Schmidt-Boelter gage are much larger than the quoted uncertainty for a radiative only environment (i.e ., {+-}3%). This large difference is due to the convective contribution and because the gage sensitivities to radiative and convective environments are not equal. All these values are larger than desired, which suggests the need for improvements in heat flux measurements in fires.

Nakos, James Thomas

2005-12-01

362

Eddy covariance measurements of nitric oxide flux within an Amazonian rain forest  

NASA Astrophysics Data System (ADS)

NO flux measurements by the eddy covariance technique were performed within a tropical rain forest 1 m and 11 m above the forest floor. A fast-response chemiluminescence NO analyzer with a sampling tube of 25 m length was used for the gas measurements. Nighttime similarity between the cospectra of sensible heat and the NO flux offered the possibility to quantify the high-frequency attenuation of the NO eddy covariance by spectral analysis. Integrated flux correction factors of about 21% for the system at 1 m and 5% for the one at 11 m above ground were calculated by transfer functions adopted from the literature and confirmed experimentally. For an independent validation the results of the eddy covariance system were compared with the NO soil emissions obtained by dynamic chambers. For nighttime averages, good agreement within 10% was found. The obtained NO fluxes were 3.5 ± 0.14 and 4.8 ± 0.39 ng N m-2 s-1 for the two investigated periods at 1 and 11 m heights, respectively. During the day, chemical reaction with ozone entrained from aloft reduced the fraction of the soil-emitted NO that reached the measuring height of the eddy covariance system. The average flux showed a reduction of 48% at 1 m and 92% at 11 m height compared to the corresponding soil emission measured by the chamber system.

Rummel, , U.; Ammann, , C.; Gut, , A.; Meixner, , F. X.; Andreae, M. O.

2002-10-01

363

Flux compression measurements in sintered bulk Ba2YCu3O7  

NASA Technical Reports Server (NTRS)

Trapping of magnetic fields and subsequent flux compression have been realized in sintered bulk Ba2YCu3O7 superconductors at 77 K. The field is trapped in two interconnected holes of 0.95-cm and 0.52-cm diameter, respectively. By inserting a superconducting plunger with a diameter of 0.93 cm into the larger hole, the trapped flux is compressed into the smaller hole, where the flux density is measured with a Hall probe. The ratio of the areas available for the magnetic flux before and after compression is 3.7. Deviations from this compression ratio are observed to increase as the trapped field is increased, demonstrating penetration of magnetic flux into the interior of the superconductor. Using a simple extension of the critical state model, the authors demonstrate how the flux compression technique can be used to test the validity of the model and also to calculate the critical current density of the superconductor directly from the measurements.

Israelsson, U. E.; Strayer, D. M.

1991-01-01

364

Snow, Shrubs, Grasses, and Footprint Theory: Measuring Moisture and Energy Fluxes in Patchy Landscapes  

NASA Astrophysics Data System (ADS)

When measuring sensible and latent heat flux from a tower within a heterogeneous landscape, one must consider which part of the landscape influences the flux sampled by the instruments. This variable landscape fraction, known as a footprint, is dependent upon wind direction, wind speed and atmospheric stability (thermal and mechanical). From 1 December 2002 - 31 March 2003, the FLuxes Over Snow Surfaces II (FLOSS II) field campaign measured sensible and latent heat fluxes at various heights on a 34 m tower in North Park, Colorado. North Park is an intermountain basin covered with a mixture of shrubs and graminoids (grasses and sedges) that interact with winter snow and wind to produce heterogeneous snow covers and, depending on the depth, protruding vegetation. During this period, snow depth measurements were made along transects extending 400-600 m upwind of the tower roughly every ten days. These snow depth data, in combination with blowing-snow model (SnowTran-3D) simulations, provided daily snow-depth distributions on a 1-meter grid over the area surrounding the flux tower. In addition, shrub height and vertical biomass profiles were measured and combined with a vegetation map having a 1-meter sampling scale. Merging the snow-depth distributions with the vegetation-height map allowed us to quantify the amount of vegetation protruding above the snow. This, in turn, allowed us to analyze the influence of exposed vegetation on observed energy and moisture fluxes. In this poster we describe our model for identifying the landscape fraction gauged by the flux-tower instruments as a function of commonly observed atmospheric conditions.

Strack, J. E.; Liston, G. E.; Hiemstra, C. A.; Pielke, R. A.

2004-12-01

365

Development of a benthic-flux chamber for measurement of ground-water seepage and water sampling for mercury analysis at the sediment-water interface  

USGS Publications Warehouse

A benthic-flux chamber was constructed to collect data to determine the relation between ground- and surface-water interaction and mercury concentrations in water at the sediment- water interface. The benthic-flux chamber was successfully used to measure the rate of ground water seeping to surface water or surface water seeping to ground water, and to collect water samples for mercury analysis from the sedimentwater interface in a lake setting. The benthic-flux chamber was designed to be deployed in relatively calm fresh water lakes, in areas of water less than 2 meters deep. The groundwater seepage rate data were comparable to data from an in-line flow meter in a calibration tank and with data from two 55-gallon drum seepage meters concurrently deployed in two different lakes. The benthic-flux chamber was used to collect possible water samples for analysis of total mercury and methylmercury concentrations.

Menheer, M.A.

2004-01-01

366

Measured and parameterized energy fluxes estimated for Atlantic transects of RV Polarstern  

NASA Astrophysics Data System (ADS)

Even to date energy fluxes over the oceans are difficult to assess. As an example the relative paucity of evaporation observations and the uncertainties of currently employed empirical approaches lead to large uncertainties of evaporation products over the ocean (e.g. Large and Yeager, 2009). Within the frame of OCEANET (Macke et al., 2010) we performed such measurements on Atlantic transects between Bremerhaven (Germany) and Cape Town (South Africa) or Punta Arenas (Chile) onboard RV Polarstern during the recent years. The basic measurements of sensible and latent heat fluxes are inertial-dissipation (e.g. Dupuis et al., 1997) flux estimates and measurements of the bulk variables. Turbulence measurements included a sonic anemometer and an infrared hygrometer, both mounted on the crow's nest. Mean meteorological sensors were those of the ship's operational measurement system. The global radiation and the down terrestrial radiation were measured on the OCEANET container placed on the monkey island. At least about 1000 time series of 1 h length were analyzed to derive bulk transfer coefficients for the fluxes of sensible and latent heat. The bulk transfer coefficients were applied to the ship's meteorological data to derive the heat fluxes at the sea surface. The reflected solar radiation was estimated from measured global radiation. The up terrestrial radiation was derived from the skin temperature according to the Stefan-Boltzmann law. Parameterized heat fluxes were compared to the widely used COARE-parameterization (Fairall et al., 2003), the agreement is excellent. Measured and parameterized heat and radiation fluxes gave the total energy budget at the air sea interface. As expected the mean total flux is positive, but there are also areas, where it is negative, indicating an energy loss of the ocean. It could be shown that the variations in the energy budget are mainly due to insolation and evaporation. A comparison between the mean values of measured and parameterized sensible and latent heat fluxes shows that the data are suitable to validate satellite derived fluxes at the sea surface and re-analysis data. References Dupuis, H., P. K. Taylor, A. Weill, and K. Katsaros, 1997: Inertial dissipation method applied to derive turbulent fluxes over the ocean during the surface of the ocean. J. Geophys. Res., 102 (C9), 21 115-21 129. Fairall, C. W., E. F. Bradley, J. E. Hare, A. A. Grachev, J. B. Edson, 2003: Bulk Parameterization of Air-Sea Fluxes: Updates and Verification for the COARE Algorithm. J. Climate, 16, 571-591. Large, W.G., and S.G. Yeager, 2009: The global climatology of an interannually varying air-sea flux data set. Climate Dynamics 33, 341-364. Macke, A., Kalisch, J., Zoll, Y., and Bumke, K., 2010: Radiative effects of the cloudy atmosphere from ground and satellite based observations, EPJ Web of Conferences, 5 9, 83-94

Bumke, Karl; Macke, Andreas; Kalisch, John; Kleta, Henry

2013-04-01

367

Development of airborne eddy-correlation flux measurement capabilities for reactive oxides of nitrogen  

NASA Technical Reports Server (NTRS)

This research is aimed at producing a fundamental new research tool for characterizing the source strength of the most important compound controlling the hemispheric and global scale distribution of tropospheric ozone. Specifically, this effort seeks to demonstrate the proof-of-concept of a new general purpose laser-induced fluorescence based spectrometer for making airborne eddy-correlation flux measurements of nitric oxide (NO) and other reactive nitrogen compounds. The new all solid-state laser technology being used in this advanced sensor will produce a forerunner of the type of sensor technology that should eventually result in highly compact operational systems. The proof-of-concept sensor being developed will have over two orders-of-magnitude greater sensitivity than present-day instruments. In addition, this sensor will offer the possibility of eventual extension to airborne eddy-correlation flux measurements of nitrogen dioxide (NO2) and possibly other compounds, such as ammonia (NH3), peroxyradicals (HO2), nitrateradicals (NO3) and several iodine compounds (e.g., I and IO). Demonstration of the new sensor's ability to measure NO fluxes will occur through a series of laboratory and field tests. This proof-of-concept demonstration will show that not only can airborne fluxes of important ultra-trace compounds be made at the few parts-per-trillion level, but that the high accuracy/precision measurements currently needed for predictive models can also. These measurement capabilities will greatly enhance our current ability to quantify the fluxes of reactive nitrogen into the troposphere and significantly impact upon the accuracy of predictive capabilities to model O3's distribution within the remote troposphere. This development effort also offers a timely approach for producing the reactive nitrogen flux measurement capabilities that will be needed by future research programs such as NASA's planned 1999 Amazon Biogeochemistry and Atmospheric Chemistry Experimental portion of LBA.

Bradshaw, John (Principal Investigator); Zheng, Xiaonan; Sandholm, Scott T.

1996-01-01

368

Analysis of the PKT correction for direct CO2 flux measurements over the ocean  

NASA Astrophysics Data System (ADS)

Eddy covariance measurements of air-sea CO2 fluxes can be affected by cross-sensitivities of the CO2 measurement to water vapour, resulting in order-of-magnitude biases. Well-established causes for these biases are (i) cross-sensitivity of the broadband non-dispersive infrared sensors due to band-broadening and spectral overlap (commercial sensors typically correct for this) and (ii) the effect of air density fluctuations (removed by determining the dry air CO2 mixing ratio). Another bias related to water vapour fluctuations has recently been observed with open-path sensors, attributed to sea salt build-up and water films on sensor optics. Two very different approaches have been used to deal with these water vapour-related biases. Miller et al. (2010) employed a membrane drier to physically eliminate 97% of the water vapour fluctuations in the sample air before it entered a closed-path gas analyser. Prytherch et al. (2010a) employed the empirical (Peter K. Taylor, PKT) post-processing correction to correct open-path sensor data. In this paper, we test these methods side by side using data from the Surface Ocean Aerosol Production (SOAP) experiment in the Southern Ocean. The air-sea CO2 flux was directly measured with four closed-path analysers, two of which were positioned down-stream of a membrane dryer. The CO2 fluxes from the two dried gas analysers matched each other and were in general agreement with common parameterisations. The flux estimates from the un-dried sensors agreed with the dried sensors only during periods with low latent heat flux (≤7 W m-2). When latent heat flux was higher, CO2 flux estimates from the un-dried sensors exhibited large scatter and an order-of-magnitude bias. Applying the PKT correction to the flux data from the un-dried analysers did not remove the bias when compared to the data from the dried gas analyser. The results of this study demonstrate the validity of measuring CO2 fluxes using a pre-dried air stream and show that the PKT correction is not valid for the correction of CO2 fluxes.

Landwehr, S.; Miller, S. D.; Smith, M. J.; Saltzman, E. S.; Ward, B.

2014-04-01

369

Continuous In Situ Measurements of Near Bottom Chemistry and Sediment-Water Fluxes with the Chimney Sampler Array (CSA)  

NASA Astrophysics Data System (ADS)

The Chimney Sampler Array (CSA) was designed to measure in situ chemical and physical parameters within the benthic boundary layer plus methane and oxygen sediment-water chemical fluxes at upper slope sites in the northern Gulf of Mexico. The CSA can monitor temporal changes plus help to evaluate oceanographic and sub-seafloor processes that can influence the formation and stability of gas hydrates in underlying sediments. The CSA consists of vertical cylinders (chimneys) equipped with internal chemical sensors and with laboratory flume-calibrated washout rates. Chimney washout rates multiplied by chimney mean versus ambient concentrations allow calculation of net O2 and methane sediment-water fluxes. The CSA is emplaced on the seafloor by a ROVARD lander using a ROV for chimney deployments. The CSA presently includes two 30 cm diameter by 90 cm length cylinders that seal against the sediment with lead pellet beanbags; within each chimney cylinder are optode, conductivity and methane sensors. The CSA's data logger platform also includes pressure and turbidity sensors external to the chimneys along with an acoustic Doppler current meter to measure temporal variation in ambient current velocity and direction. The CSA was deployed aboard a ROVARD lander on 9/13/2010 in the northern Gulf of Mexico (Lat. 28 51.28440, Long. 088 29.39421) on biogeochemically active sediments within Block MC-118. A ROV was utilized for chimney deployment away from the ROVARD lander. The CSA monitored temporal changes in water column physical parameters, obtained near-bottom chemical data to compare with pore fluid and sediment core measurements and measured temporal variability in oxygen and methane sediment-water fluxes at two closely spaced stations at MC-118. A continuous, three-week data set was obtained that revealed daily cycles in chemical parameters and episodic flux events. Lower than ambient chimney dissolved O2 concentrations controlled by temporal variability in washout rates were used to calculate sediment O2 demand. Episodic events yielding turbidity spikes produced episodic spikes in chimney methane concentrations and sediment-water fluxes. The robust data set reveals new capabilities for long-term monitoring of near-bottom processes in biogeochemically active, continental margin environments.

Martens, C. S.; Mendlovitz, H. P.; White, B. L.; Hoer, D.; Sleeper, K.; Chanton, J.; Wilson, R.; Lapham, L.

2011-12-01

370

Marine particle dynamics : sinking velocities, size distributions, fluxes, and microbial degradation rates  

E-print Network

The sinking flux of particulate matter into the ocean interior is an oceanographic phenomenon that fuels much of the metabolic demand of the subsurface ocean and affects the distribution of carbon and other elements ...

McDonnell, Andrew M. P

2011-01-01

371

Measuring Fluxes with Better Certainty without a Need for Density Corrections or Pressure Term  

NASA Astrophysics Data System (ADS)

Eddy Covariance flux measurements using gas analyzers of an enclosed design rely on the covariance between instantaneous vertical wind speed and instantaneous output of gas mixing ratio, such that density data are corrected on-the-fly using instantaneous water vapor, temperature and pressure measurements in the cell, collected and aligned with CO2 or other gas of interest. This approach implicitly accounts for the effects of fluctuations in water vapor, temperature and pressure on the density of the gas of interest. Therefore no sensible heat or latent heat portions of Webb-Pearman-Leuning density corrections (WPL) are required, and the pressure term, which is usually neglected in traditional WPL implementation, is accounted for in these mixing ratio-based measurements. A somewhat similar way of calculating fluxes has been used frequently with traditional closed-path analyzers, with some assumptions: (i) slow temperature measurements were used to convert from density to mixing ratio, assuming fast fluctuations of the air temperature to be fully attenuated in the long intake tube; (ii) slow pressure measurements were used, assuming negligible instantaneous pressure fluctuations. Nine field experiments were conducted in a wide range of environmental conditions from Florida to Alaska using an enclosed CO2/H2O gas analyzer. These experiments presented an opportunity to verify the performance of the mixing ratio approach, and examine the differences from traditional density-based measurements. Results indicate that the mixing ratio-based approach helps to minimize or eliminate a number of uncertainties associated with traditional density-based approach, including: (i) uncertainties associated with correcting the product of fast covariances of gas density using sensible and latent heat flux calculated over half-hour or an hour; (ii) uncertainties in the magnitudes of the sensible and latent heat fluxes used in correcting gas flux; (iii) bias in long-term accumulated CO2 flux due to the neglected pressure term. The latest findings on the importance of fast temperature and pressure measurements for CO2 flux on hourly and long-term scales for open-path, closed-path and enclosed designs are discussed. Fundamental differences between gas density and gas mixing ratio for flux measurements are also examined.

Burba, G.; Nakai, T.; Schmidt, A.; Scott, R.; Kathilankal, J.; Fratini, G.; Hanson, C.; Law, B.; McDermitt, D.; Eckles, R.

2012-04-01

372

DETECTION AND FLUX DENSITY MEASUREMENTS OF THE MILLISECOND PULSAR J2145–0750 BELOW 100 MHz  

SciTech Connect

We present flux density measurements and pulse profiles for the millisecond pulsar PSR J2145–0750 spanning 37 to 81 MHz using data obtained from the first station of the Long Wavelength Array. These measurements represent the lowest frequency detection of pulsed emission from a millisecond pulsar to date. We find that the pulse profile is similar to that observed at 102 MHz. We also find that the flux density spectrum between ?40 MHz to 5 GHz is suggestive of a break and may be better fit by a model that includes spectral curvature with a rollover around 730 MHz rather than a single power law.

Dowell, J.; Taylor, G. B.; Craig, J.; Henning, P. A.; Schinzel, F. [Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM 87131 (United States)] [Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM 87131 (United States); Ray, P. S. [Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States)] [Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States); Blythe, J. N. [School of Physics, Georgia Institute of Technology, Atlanta, GA 3033 (United States)] [School of Physics, Georgia Institute of Technology, Atlanta, GA 3033 (United States); Clarke, T.; Helmboldt, J. F. [U.S. Naval Research Laboratory, Washington, DC 20375 (United States)] [U.S. Naval Research Laboratory, Washington, DC 20375 (United States); Ellingson, S. W.; Wolfe, C. N. [Bradley Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, VA 24061 (United States)] [Bradley Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, VA 24061 (United States); Lazio, T. J. W. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)] [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Stovall, K., E-mail: jdowell@unm.edu [Center for Gravitational Wave Astronomy and Department of Physics and Astronomy, University of Texas at Brownsville, Brownsville, TX 78520 (United States)

2013-09-20

373

Influence Of Subsurface Biosphere On Geochemical Fluxes From Diffuse Hydrothermal Fluids: Direct Measurement Of Subsurface Hydrogen Oxidation  

NASA Astrophysics Data System (ADS)

After decades of research on hydrothermal vent biogeochemistry, quantification of low-temperature diffusive geochemical fluxes remains elusive and limits our ability to place constraints on their role in global geochemical cycles. Quantifying the relative differences in geochemical composition, in particular of energy-rich compounds such as H2 and CH4, between focused high-temperature and diffuse low-temperature hydrothermal fluids can allow the estimation of metabolic rates in the underlying subsurface biosphere. Towards shortening the gap in our understanding of geochemical and microbial dynamics of the subsurface biosphere, we deployed an in situ mass spectrometer (ISMS) and low flow meter to quantify biologically relevant volatiles in a wide range of flow regimes and temperatures. Here we present coupled in situ chemical analyses and flow measurements that enable quantification of geochemical fluxes from a diversity of