Agriculture's impact on microbial diversity and associated fluxes of carbon dioxide and methane

PubMed Central

Levine, Uri Y; Teal, Tracy K; Robertson, G Philip; Schmidt, Thomas M

2011-01-01

Agriculture has marked impacts on the production of carbon dioxide (CO2) and consumption of methane (CH4) by microbial communities in upland soils—Earth's largest biological sink for atmospheric CH4. To determine whether the diversity of microbes that catalyze the flux of these greenhouse gases is related to the magnitude and stability of these ecosystem-level processes, we conducted molecular surveys of CH4-oxidizing bacteria (methanotrophs) and total bacterial diversity across a range of land uses and measured the in situ flux of CH4 and CO2 at a site in the upper United States Midwest. Conversion of native lands to row-crop agriculture led to a sevenfold reduction in CH4 consumption and a proportionate decrease in methanotroph diversity. Sites with the greatest stability in CH4 consumption harbored the most methanotroph diversity. In fields abandoned from agriculture, the rate of CH4 consumption increased with time along with the diversity of methanotrophs. Conversely, estimates of total bacterial diversity in soil were not related to the rate or stability of CO2 emission. These combined results are consistent with the expectation that microbial diversity is a better predictor of the magnitude and stability of processes catalyzed by organisms with highly specialized metabolisms, like CH4 oxidation, as compared with processes driven by widely distributed metabolic processes, like CO2 production in heterotrophs. The data also suggest that managing lands to conserve or restore methanotroph diversity could mitigate the atmospheric concentrations of this potent greenhouse gas. PMID:21490688

Medusae Fossae-Elysium Region, Mars: Depression in the HEND/Odyssey Map of Mars Epithermal Neutrons

NASA Technical Reports Server (NTRS)

Ivanov, M. A.; Litvak, M. L.; Mitrofanov, I. G.; Boynton, W.; Saunders, R. S.

2003-01-01

The first data from the Gamma Ray Spectrometer (GRS) onboard Mars Odyssey spacecraft showed that the low neutron fluxes characterize both subpolar regions of Mars. The low neutron fluxes mean the presence of hydrogen-rich soils and have been interpreted as an indication on abundant water ice in these areas. The equatorial region of Mars (equatorward of approx. 50 deg) is characterized by higher fluxes of both epithermal (0.4 eV-100 keV, come from depth 1-2 m) and fast (3.4-7.3 MeV, come from depth 0.2-0.3 m) neutrons meaning that this area is mostly dry. The pattern of distribution of the neutron fluxes is in a good agreement with the theoretical predictions on the stability of ground ice on present Mars. The actual distribution of the ice, however, depends on variations of thermal inertia of soils and albedo of the surface. The flux of the epithermal neutrons detected by the HEND instrument, which is part of GRS, has two noticeable depressions in the equatorial region, one in Arabia Terra and another in the Medusae Fossae-Elysium region (MFER). Here we present the initial results of analysis of characteristics of the neutron fluxes and regional geological setting of the epithermal neutron depression in this area. The main goal of our study was to put some constraints on the time of the anomaly formation and to assess possible form of hydrogen (ground ice vs. chemically bound water) there.

Advanced Organic Electro-Optic Materials for Integrated Device Applications

DTIC Science & Technology

2001-06-01

Electro - optic chromophores (FTC and CLD) were synthesized in bulk (kilogram) quantities and were distributed to the participants of this program...to stabilize electro - optic activity for operation at elevated temperatures and photon flux levels. Over 100 variants of these chromophores were...1.5-2.0 improvement over FTC and CLD chromophores in terms of electro - optic activity at telecommunication wavelengths. They also have proven more

How do Stability Corrections Perform in the Stable Boundary Layer Over Snow?

NASA Astrophysics Data System (ADS)

Schlögl, Sebastian; Lehning, Michael; Nishimura, Kouichi; Huwald, Hendrik; Cullen, Nicolas J.; Mott, Rebecca

2017-10-01

We assess sensible heat-flux parametrizations in stable conditions over snow surfaces by testing and developing stability correction functions for two alpine and two polar test sites. Five turbulence datasets are analyzed with respect to, (a) the validity of the Monin-Obukhov similarity theory, (b) the model performance of well-established stability corrections, and (c) the development of new univariate and multivariate stability corrections. Using a wide range of stability corrections reveals an overestimation of the turbulent sensible heat flux for high wind speeds and a generally poor performance of all investigated functions for large temperature differences between snow and the atmosphere above (>10 K). Applying the Monin-Obukhov bulk formulation introduces a mean absolute error in the sensible heat flux of 6 W m^{-2} (compared with heat fluxes calculated directly from eddy covariance). The stability corrections produce an additional error between 1 and 5 W m^{-2}, with the smallest error for published stability corrections found for the Holtslag scheme. We confirm from previous studies that stability corrections need improvements for large temperature differences and wind speeds, where sensible heat fluxes are distinctly overestimated. Under these atmospheric conditions our newly developed stability corrections slightly improve the model performance. However, the differences between stability corrections are typically small when compared to the residual error, which stems from the Monin-Obukhov bulk formulation.

Assessing the severity of rainfall-derived infiltration and inflow and sewer deterioration based on the flux stability of sewage markers.

PubMed

Shelton, Jessica M; Kim, Lavane; Fang, Jiasong; Ray, Chittaranjan; Yan, Tao

2011-10-15

This study investigated the flux stability of select chemical and biological sewage markers, including caffeine, total nitrogen (TN), total suspended solids (TSS), E. coli, and enterococci, and their suitability in assessing the severity of rainfall-derived infiltration and inflow (RDII) in a residential sewershed. To quantify and compare marker flux stability, concentrations of the candidate markers in two dry-weather periods were determined and the one-day lag autocorrelation coefficients (r) of their mass fluxes were calculated. TN (r = 0.82-0.88) exhibited higher and more consistent flux stability than TSS (r = 0.49-0.82), caffeine (r = 0.56-0.58), E. coli (r = 0.36-0.87), and enterococci (by culture; r = 0.40-0.52), all of which except enterococci by qPCR (r = -0.10-0.21) showed significant autocorrelation. Sewage flows and marker concentrations were also monitored in two wet-weather periods, and the severity of RDII (R(RDII)) were calculated using either flow measurements or marker concentrations independently. Corresponding to its outstanding flux stability, R(RDII) values estimated by TN predicted all severe RDII instances and gave the highest and most consistent correlation (r = 0.74-0.78) among the different sewage markers. Overall, the study illustrated the feasibility of using the flux stability of sewage markers in assessing the severity of RDII and thereby deterioration levels in sewer systems.

Evidence for elevated and spatially variable geothermal flux beneath the West Antarctic Ice Sheet

PubMed Central

Schroeder, Dustin M.; Blankenship, Donald D.; Young, Duncan A.; Quartini, Enrica

2014-01-01

Heterogeneous hydrologic, lithologic, and geologic basal boundary conditions can exert strong control on the evolution, stability, and sea level contribution of marine ice sheets. Geothermal flux is one of the most dynamically critical ice sheet boundary conditions but is extremely difficult to constrain at the scale required to understand and predict the behavior of rapidly changing glaciers. This lack of observational constraint on geothermal flux is particularly problematic for the glacier catchments of the West Antarctic Ice Sheet within the low topography of the West Antarctic Rift System where geothermal fluxes are expected to be high, heterogeneous, and possibly transient. We use airborne radar sounding data with a subglacial water routing model to estimate the distribution of basal melting and geothermal flux beneath Thwaites Glacier, West Antarctica. We show that the Thwaites Glacier catchment has a minimum average geothermal flux of ∼114 ± 10 mW/m2 with areas of high flux exceeding 200 mW/m2 consistent with hypothesized rift-associated magmatic migration and volcanism. These areas of highest geothermal flux include the westernmost tributary of Thwaites Glacier adjacent to the subaerial Mount Takahe volcano and the upper reaches of the central tributary near the West Antarctic Ice Sheet Divide ice core drilling site. PMID:24927578

Interactions between aerosol absorption, thermodynamics, dynamics, and microphysics and their impacts on a multiple-cloud system

NASA Astrophysics Data System (ADS)

Lee, Seoung Soo; Li, Zhanqing; Mok, Jungbin; Ahn, Myoung-Hwan; Kim, Byung-Gon; Choi, Yong-Sang; Jung, Chang-Hoon; Yoo, Hye Lim

2017-12-01

This study investigates how the increasing concentration of black carbon aerosols, which act as radiation absorbers as well as agents for the cloud-particle nucleation, affects stability, dynamics and microphysics in a multiple-cloud system using simulations. Simulations show that despite increases in stability due to increasing concentrations of black carbon aerosols, there are increases in the averaged updraft mass fluxes (over the whole simulation domain and period). This is because aerosol-enhanced evaporative cooling intensifies convergence near the surface. This increase in the intensity of convergence induces an increase in the frequency of updrafts with the low range of speeds, leading to the increase in the averaged updraft mass fluxes. The increase in the frequency of updrafts induces that in the number of condensation entities and this leads to more condensation and cloud liquid that acts to be a source of the accretion of cloud liquid by precipitation. Hence, eventually, there is more accretion that offsets suppressed autoconversion, which results in negligible changes in cumulative precipitation as aerosol concentrations increase. The increase in the frequency of updrafts with the low range of speeds alters the cloud-system organization (represented by cloud-depth spatiotemporal distributions and cloud-cell population) by supporting more low-depth clouds. The altered organization in turn alters precipitation spatiotemporal distributions by generating more weak precipitation events. Aerosol-induced reduction in solar radiation that reaches the surface induces more occurrences of small-value surface heat fluxes, which in turn supports the more low-depth clouds and weak precipitation together with the greater occurrence of low-speed updrafts.

Synchronization stability and pattern selection in a memristive neuronal network.

PubMed

Wang, Chunni; Lv, Mi; Alsaedi, Ahmed; Ma, Jun

2017-11-01

Spatial pattern formation and selection depend on the intrinsic self-organization and cooperation between nodes in spatiotemporal systems. Based on a memory neuron model, a regular network with electromagnetic induction is proposed to investigate the synchronization and pattern selection. In our model, the memristor is used to bridge the coupling between the magnetic flux and the membrane potential, and the induction current results from the time-varying electromagnetic field contributed by the exchange of ion currents and the distribution of charged ions. The statistical factor of synchronization predicts the transition of synchronization and pattern stability. The bifurcation analysis of the sampled time series for the membrane potential reveals the mode transition in electrical activity and pattern selection. A formation mechanism is outlined to account for the emergence of target waves. Although an external stimulus is imposed on each neuron uniformly, the diversity in the magnetic flux and the induction current leads to emergence of target waves in the studied network.

Synchronization stability and pattern selection in a memristive neuronal network

NASA Astrophysics Data System (ADS)

Wang, Chunni; Lv, Mi; Alsaedi, Ahmed; Ma, Jun

2017-11-01

Spatial pattern formation and selection depend on the intrinsic self-organization and cooperation between nodes in spatiotemporal systems. Based on a memory neuron model, a regular network with electromagnetic induction is proposed to investigate the synchronization and pattern selection. In our model, the memristor is used to bridge the coupling between the magnetic flux and the membrane potential, and the induction current results from the time-varying electromagnetic field contributed by the exchange of ion currents and the distribution of charged ions. The statistical factor of synchronization predicts the transition of synchronization and pattern stability. The bifurcation analysis of the sampled time series for the membrane potential reveals the mode transition in electrical activity and pattern selection. A formation mechanism is outlined to account for the emergence of target waves. Although an external stimulus is imposed on each neuron uniformly, the diversity in the magnetic flux and the induction current leads to emergence of target waves in the studied network.

Extension of lattice Boltzmann flux solver for simulation of compressible multi-component flows

NASA Astrophysics Data System (ADS)

Yang, Li-Ming; Shu, Chang; Yang, Wen-Ming; Wang, Yan

2018-05-01

The lattice Boltzmann flux solver (LBFS), which was presented by Shu and his coworkers for solving compressible fluid flow problems, is extended to simulate compressible multi-component flows in this work. To solve the two-phase gas-liquid problems, the model equations with stiffened gas equation of state are adopted. In this model, two additional non-conservative equations are introduced to represent the material interfaces, apart from the classical Euler equations. We first convert the interface equations into the full conservative form by applying the mass equation. After that, we calculate the numerical fluxes of the classical Euler equations by the existing LBFS and the numerical fluxes of the interface equations by the passive scalar approach. Once all the numerical fluxes at the cell interface are obtained, the conservative variables at cell centers can be updated by marching the equations in time and the material interfaces can be identified via the distributions of the additional variables. The numerical accuracy and stability of present scheme are validated by its application to several compressible multi-component fluid flow problems.

A Multiyear Dataset of SSM/I-Derived Global Ocean Surface Turbulent Fluxes

NASA Technical Reports Server (NTRS)

Chou, Shu-Hsien; Shie, Chung-Lin; Atlas, Robert M.; Ardizzone, Joe; Nelkin, Eric; Einaudi, Franco (Technical Monitor)

2001-01-01

The surface turbulent fluxes of momentum, latent heat, and sensible heat over global oceans are essential to weather, climate and ocean problems. Evaporation is a key component of the hydrological cycle and the surface heat budget, while the wind stress is the major forcing for driving the oceanic circulation. The global air-sea fluxes of momentum, latent and sensible heat, radiation, and freshwater (precipitation-evaporation) are the forcing for driving oceanic circulation and, hence, are essential for understanding the general circulation of global oceans. The global air-sea fluxes are required for driving ocean models and validating coupled ocean-atmosphere global models. We have produced a 7.5-year (July 1987-December 1994) dataset of daily surface turbulent fluxes over the global oceans from the Special Sensor microwave/Imager (SSM/I) data. Daily turbulent fluxes were derived from daily data of SSM/I surface winds and specific humidity, National Centers for Environmental Prediction (NCEP) sea surface temperatures, and European Centre for Medium-Range Weather Forecasts (ECMWF) air-sea temperature differences, using a stability-dependent bulk scheme. The retrieved instantaneous surface air humidity (with a 25-km resolution) validated well with that of the collocated radiosonde observations over the global oceans. Furthermore, the retrieved daily wind stresses and latent heat fluxes were found to agree well with that of the in situ measurements (IMET buoy, RV Moana Wave, and RV Wecoma) in the western Pacific warm pool during the TOGA COARE intensive observing period (November 1992-February 1993). The global distributions of 1988-94 seasonal-mean turbulent fluxes will be presented. In addition, the global distributions of 1990-93 annual-means turbulent fluxes and input variables will be compared with those of UWM/COADS covering the same period. The latter is based on the COADS (comprehensive ocean-atmosphere data set) and is recognized to be one of the best climatological analyses of fluxes derived from ship observations.

Suppression of Self-Induced Flavor Conversion in the Supernova Accretion Phase

NASA Astrophysics Data System (ADS)

Sarikas, Srdjan; Raffelt, Georg G.; Hüdepohl, Lorenz; Janka, Hans-Thomas

2012-02-01

Self-induced flavor conversions of supernova (SN) neutrinos can strongly modify the flavor-dependent fluxes. We perform a linearized flavor stability analysis with accretion-phase matter profiles of a 15M⊙ spherically symmetric model and corresponding neutrino fluxes. We use realistic energy and angle distributions, the latter deviating strongly from quasi-isotropic emission, thus accounting for both multiangle and multienergy effects. For our matter and neutrino density profile we always find stable conditions: flavor conversions are limited to the usual Mikheyev-Smirnov-Wolfenstein effect. In this case one may distinguish the neutrino mass hierarchy in a SN neutrino signal if the mixing angle θ13 is as large as suggested by recent experiments.

Suppression of self-induced flavor conversion in the supernova accretion phase.

PubMed

Sarikas, Srdjan; Raffelt, Georg G; Hüdepohl, Lorenz; Janka, Hans-Thomas

2012-02-10

Self-induced flavor conversions of supernova (SN) neutrinos can strongly modify the flavor-dependent fluxes. We perform a linearized flavor stability analysis with accretion-phase matter profiles of a 15M[symbol: see text] spherically symmetric model and corresponding neutrino fluxes. We use realistic energy and angle distributions, the latter deviating strongly from quasi-isotropic emission, thus accounting for both multiangle and multienergy effects. For our matter and neutrino density profile we always find stable conditions: flavor conversions are limited to the usual Mikheyev-Smirnov-Wolfenstein effect. In this case one may distinguish the neutrino mass hierarchy in a SN neutrino signal if the mixing angle θ13 is as large as suggested by recent experiments.

Convective stability of a plasma in a system of coupled adiabatic open cells in the Kruskal-Oberman model

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

Arsenin, V. V.; Terekhin, P. N.

2010-08-15

The Kruskal-Oberman kinetic model is used to determine the conditions for the convective stability of a plasma in a system of coupled axisymmetric adiabatic open cells in which the magnetic field curvature has opposite signs. For a combination of a nonparaxial simple mirror cell and a semicusp, the boundaries of the interval of values of the flux coordinate where the plasma can be stable are determined, as well as the range in which the ratio of the pressures in the component cells should lie. Numerical simulations were carried out for different particle distributions over the pitch angle.

Quantifying the Impact of Background Atmospheric Stability on Air-Ice-Ocean Interactions the Arctic Ocean During the Fall Freeze-Up

NASA Astrophysics Data System (ADS)

Guest, P. S.; Persson, O. P. G.; Blomquist, B.; Fairall, C. W.

2016-02-01

"Background" stability refers to the effect of vertical virtual temperature variations above the surface layer on fluxes within the surface layer. This is different from the classical surface layer stability quantified by the Obhukhov length scale. In most locations, changes in the background stability do not have a significant direct impact on surface fluxes. However in polar regions, where there is usually a strong low-level temperature inversion capping the boundary layer, changes in background stability can have big impacts on surface fluxes. Therefore, in the Arctic, there is potential for a positive feedback effect between ice cover and surface wind speed (and momentum flux) due to the background stability effects. As the surface becomes more ice free, heat fluxes from the surface weaken the temperature inversion which in turn increases the surface wind speed which further increases the surface turbulent heat fluxes and removes more sea ice by melting or advection. It is not clear how important feedbacks involving the background stability are during the fall freeze up of the Arctic Ocean; that will be the focus of this study. As part of an ONR-sponsored cruise in the fall of 2015 to examine sea state and boundary layer processes in the Beaufort Sea on the R/V Sikuliaq, the authors will perform a variety of surface layer and upper level atmospheric measurements of temperature, humidity and wind vector using ship platform instruments, radiosonde weather balloons, tethered balloons, kites, and miniature quad-rotor unmanned aerial vehicles. In addition, the authors will deploy a full suite of turbulent and radiational flux measurements from the vessel. These measurements will be used to quantify the impact of changing surface conditions on atmospheric structure and vice-versa. The goal is to directly observe how the surface and atmosphere above the surface layer interact and feedback with each other through radiational and turbulent fluxes.

Turbulent transport stabilization by ICRH minority fast ions in low rotating JET ILW L-mode plasmas

NASA Astrophysics Data System (ADS)

Bonanomi, N.; Mantica, P.; Di Siena, A.; Delabie, E.; Giroud, C.; Johnson, T.; Lerche, E.; Menmuir, S.; Tsalas, M.; Van Eester, D.; Contributors, JET

2018-05-01

The first experimental demonstration that fast ion induced stabilization of thermal turbulent transport takes place also at low values of plasma toroidal rotation has been obtained in JET ILW (ITER-like wall) L-mode plasmas with high (3He)-D ICRH (ion cyclotron resonance heating) power. A reduction of the gyro-Bohm normalized ion heat flux and higher values of the normalized ion temperature gradient have been observed at high ICRH power and low NBI (neutral beam injection) power and plasma rotation. Gyrokinetic simulations indicate that ITG (ion temperature gradient) turbulence stabilization induced by the presence of high-energetic 3He ions is the key mechanism in order to explain the experimental observations. Two main mechanisms have been identified to be responsible for the turbulence stabilization: a linear electrostatic wave-fast particle resonance mechanism and a nonlinear electromagnetic mechanism. The dependence of the stabilization on the 3He distribution function has also been studied.

On the stability of fast rotating magentodiscs

NASA Astrophysics Data System (ADS)

Neupane, B. R.; Delamere, P. A.; Ma, X.

2016-12-01

In this study, a steady-state, self-consistent magnetodisc model (i.e., Caudal [1986] model based on in-situ observational temperature and density profile) has been developed to systematically investigate the stability of fast rotationing magnetodiscs, which is fundamentally important to the dynamics of Jupiter's and Saturn's magnetospheres. Comparison between model and observational data (magnetic field component normal to the equatorial plane) suggests that Saturn's magnetodisc equilibrium is dominated by the heavy and cold plasma, where the centrifugal force cannot be ignored. In contrast, the hot tenuous plasma contribution, in which the centrifugal force can be ignored, should be small. In general, the stability of the Saturn's magnetosphere is determined by the competition between the radial decrease of flux tube content and radial increase of flux tube entropy. The profiles of flux tube content and flux tube entropy are expected to vary under different solar wind dynamic pressure conditions, consequently changing the stability of the magnetosphere. We will discuss stability during solar wind compression and expansion.

Stability analysis of feedforward anticipation optimal flux difference in traffic lattice hydrodynamic theory

NASA Astrophysics Data System (ADS)

Sun, Di-Hua; Zhang, Geng; Zhao, Min; Cheng, Sen-Lin; Cao, Jian-Dong

2018-03-01

Recently, the influence of driver's individual behaviors on traffic stability is research hotspot with the fasting developing transportation cyber-physical systems. In this paper, a new traffic lattice hydrodynamic model is proposed with consideration of driver's feedforward anticipation optimal flux difference. The neutral stability condition of the new model is obtained through linear stability analysis theory. The results show that the stable region will be enlarged on the phase diagram when the feedforward anticipation optimal flux difference effect is taken into account. In order to depict traffic jamming transition properties theoretically, the mKdV equation near the critical point is derived via nonlinear reductive perturbation method. The propagation behavior of traffic density waves can be described by the kink-antikink solution of the mKdV equation. Numerical simulations are conducted to verify the analytical results and all the results confirms that traffic stability can be enhanced significantly by considering the feedforward anticipation optimal flux difference in traffic lattice hydrodynamic theory.

Effect of operation parameters on the flux stabilization of gravity-driven membrane (GDM) filtration system for decentralized water supply.

PubMed

Tang, Xiaobin; Ding, An; Qu, Fangshu; Jia, Ruibao; Chang, Haiqing; Cheng, Xiaoxiang; Liu, Bin; Li, Guibai; Liang, Heng

2016-08-01

A pilot-scale gravity-driven membrane (GDM) filtration system under low gravitational pressure without any pre-treatment, backwash, flushing, or chemical cleaning was carried out to investigate the effect of operation parameters (including operation pressure, aeration mode, and intermittent filtration) on the effluent quality and permeability development. The results revealed that GDM system exhibited an efficient performance for the removal of suspended substances and organic compounds. The stabilization of flux occurred and the average values of stable flux were 6.6, 8.1, and 8.6 Lm(-2) h(-1) for pressures of 65, 120, and 200 mbar, respectively. In contrast, flux stabilization was not observed under continuous and intermittent aeration conditions. However, aeration (especially continuous aeration) was effective to improve flux and alleviate membrane fouling during 1-month operation. Moreover, intermittent filtration would influence the stabilization of permeate flux, resulting in a higher stable flux (ranging from 6 to 13 Lm(-2) h(-1)). The stable flux significantly improved with the increase of intermittent period. Additionally, GDM systems exhibited an efficient recovery of flux after simple physical cleaning and the analyses of resistance reversibility demonstrated that most of the total resistance was hydraulic reversible resistance (50-75 %). Therefore, it is expected that the results of this study can develop strategies to increase membrane permeability and reduce energy consumption in GDM systems for decentralized water supply.

Nonlinear Stability and Saturation of Ballooning Modes in Tokamaks*

NASA Astrophysics Data System (ADS)

Ham, C. J.; Cowley, S. C.; Brochard, G.; Wilson, H. R.

2016-06-01

The theory of tokamak stability to nonlinear "ballooning" displacements of elliptical magnetic flux tubes is presented. Above a critical pressure profile the energy stored in the plasma may be lowered by finite (but not infinitesimal) displacements of such tubes (metastability). Above a higher pressure profile, the linear stability boundary, such tubes are linearly and nonlinearly unstable. The predicted saturated flux tube displacement can be of the order of the pressure gradient scale length. Plasma transport from these displaced flux tubes may explain the rapid loss of confinement in some experiments.

Soil property effects on wind erosion of organic soils

NASA Astrophysics Data System (ADS)

Zobeck, Ted M.; Baddock, Matthew; Scott Van Pelt, R.; Tatarko, John; Acosta-Martinez, Veronica

2013-09-01

Histosols (also known as organic soils, mucks, or peats) are soils that are dominated by organic matter (OM > 20%) in half or more of the upper 80 cm. Forty two states have a total of 21 million ha of Histosols in the United States. These soils, when intensively cropped, are subject to wind erosion resulting in loss of crop productivity and degradation of soil, air, and water quality. Estimating wind erosion on Histosols has been determined by USDA-Natural Resources Conservation Service (NRCS) as a critical need for the Wind Erosion Prediction System (WEPS) model. WEPS has been developed to simulate wind erosion on agricultural land in the US, including soils with organic soil material surfaces. However, additional field measurements are needed to understand how soil properties vary among organic soils and to calibrate and validate estimates of wind erosion of organic soils using WEPS. Soil properties and sediment flux were measured in six soils with high organic contents located in Michigan and Florida, USA. Soil properties observed included organic matter content, particle density, dry mechanical stability, dry clod stability, wind erodible material, and geometric mean diameter of the surface aggregate distribution. A field portable wind tunnel was used to generate suspended sediment and dust from agricultural surfaces for soils ranging from 17% to 67% organic matter. The soils were tilled and rolled to provide a consolidated, friable surface. Dust emissions and saltation were measured using an isokinetic vertical slot sampler aspirated by a regulated suction source. Suspended dust was sampled using a Grimm optical particle size analyzer. Particle density of the saltation-sized material (>106 μm) was inversely related to OM content and varied from 2.41 g cm-3 for the soil with the lowest OM content to 1.61 g cm-3 for the soil with highest OM content. Wind erodible material and the geometric mean diameter of the surface soil were inversely related to dry clod stability. The effect of soil properties on sediment flux varied among flux types. Saltation flux was adequately predicted with simple linear regression models. Dry mechanical stability was the best single soil property linearly related to saltation flux. Simple linear models with soil properties as independent variables were not well correlated with PM10E values (mass flux). A second order polynomial equation with OM as the independent variable was found to be most highly correlated with PM10E values. These results demonstrate that variations in sediment and dust emissions can be linked to soil properties using simple models based on one or more soil properties to estimate saltation mass flux and PM10E values from organic and organic-rich soils.

Strength and stability of microbial plugs in porous media

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

Sarkar, A.K.; Sharma, M.M.; Georgiou, G.

1995-12-31

Mobility reduction induced by the growth and metabolism of bacteria in high-permeability layers of heterogeneous reservoirs is an economically attractive technique to improve sweep efficiency. This paper describes an experimental study conducted in sandpacks using an injected bacterium to investigate the strength and stability of microbial plugs in porous media. Successful convective transport of bacteria is important for achieving sufficient initial bacteria distribution. The chemotactic and diffusive fluxes are probably not significant even under static conditions. Mobility reduction depends upon the initial cell concentrations and increase in cell mass. For single or multiple static or dynamic growth techniques, permeability reductionmore » was approximately 70% of the original permeability. The stability of these microbial plugs to increases in pressure gradient and changes in cell physiology in a nutrient-depleted environment needs to be improved.« less

Levitation in the field of a nonsuperconducting coil with magnetic flux stabilization

NASA Astrophysics Data System (ADS)

Koshurnikov, E. K.

2013-09-01

A method providing the "frozen flux" conditions in a nonsuperconducting coil is suggested and demonstrated with a model. The feasibility of permanent magnet stable levitation in the field of the coil with magnetic flux stabilization and mean current control is shown. The method allows researchers to exploit permanent magnet-superconducting body interaction in physical devices, for example, to reproduce, using nonsuperconducting coils, the frozen magnetic flux conditions required for the stable levitation of the magnet over a superconducting body.

Analysis of edge stability for models of heat flux width

DOE PAGES

Makowski, Michael A.; Lasnier, Charles J.; Leonard, Anthony W.; ...

2017-05-12

Detailed measurements of the n e, and T e, and T i profiles in the vicinity of the separatrix of ELMing H-mode discharges have been used to examine plasma stability at the extreme edge of the plasma and assess stability dependent models of the heat flux width. The results are strongly contrary to the critical gradient model, which posits that a ballooning instability determines a gradient scale length related to the heat flux width. The results of this analysis are not sensitive to the choice of location to evaluate stability. Significantly, it is also found that the results are completelymore » consistent with the heuristic drift model for the heat flux width. Here the edge pressure gradient scales with plasma density and is proportional to the pressure gradient inferred from the equilibrium in accordance with the predictions of that theory.« less

Tropical Ocean Surface Energy Balance Variability: Linking Weather to Climate Scales

NASA Technical Reports Server (NTRS)

Roberts, J. Brent; Clayson, Carol Anne

2013-01-01

Radiative and turbulent surface exchanges of heat and moisture across the atmosphere-ocean interface are fundamental components of the Earth s energy and water balance. Characterizing the spatiotemporal variability of these exchanges of heat and moisture is critical to understanding the global water and energy cycle variations, quantifying atmosphere-ocean feedbacks, and improving model predictability. These fluxes are integral components to tropical ocean-atmosphere variability; they can drive ocean mixed layer variations and modify the atmospheric boundary layer properties including moist static stability, thereby influencing larger-scale tropical dynamics. Non-parametric cluster-based classification of atmospheric and ocean surface properties has shown an ability to identify coherent weather regimes, each typically associated with similar properties and processes. Using satellite-based observational radiative and turbulent energy flux products, this study investigates the relationship between these weather states and surface energy processes within the context of tropical climate variability. Investigations of surface energy variations accompanying intraseasonal and interannual tropical variability often use composite-based analyses of the mean quantities of interest. Here, a similar compositing technique is employed, but the focus is on the distribution of the heat and moisture fluxes within their weather regimes. Are the observed changes in surface energy components dominated by changes in the frequency of the weather regimes or through changes in the associated fluxes within those regimes? It is this question that the presented work intends to address. The distribution of the surface heat and moisture fluxes is evaluated for both normal and non-normal states. By examining both phases of the climatic oscillations, the symmetry of energy and water cycle responses are considered.

Experimental Verification of the Kruskal-Shafranov Stability Limit in Line-Tied Partial Toroidal Plasmas

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

Oz, E.; Myers, C. E.; Yamada, M.

2011-07-19

The stability properties of partial toroidal flux ropes are studied in detail in the laboratory, motivated by ubiquitous arched magnetic structures found on the solar surface. The flux ropes studied here are magnetized arc discharges formed between two electrodes in the Magnetic Reconnection Experiment (MRX) [Yamada et al., Phys. Plasmas, 4, 1936 (1997)]. The three dimensional evolution of these flux ropes is monitored by a fast visible light framing camera, while their magnetic structure is measured by a variety of internal magnetic probes. The flux ropes are consistently observed to undergo large-scale oscillations as a result of an external kinkmore » instability. Using detailed scans of the plasma current, the guide field strength, and the length of the flux rope, we show that the threshold for kink stability is governed by the Kruskal-Shafranov limit for a flux rope that is held fixed at both ends (i.e., qa = 1).« less

Experimental verification of the Kruskal-Shafranov stability limit in line-tied partial-toroidal plasmas

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

Oz, E.; Myers, C. E.; Yamada, M.

2011-10-15

The stability properties of partial-toroidal flux ropes are studied in detail in the laboratory, motivated by ubiquitous arched magnetic structures found on the solar surface. The flux ropes studied here are magnetized arc discharges formed between two electrodes in the Magnetic Reconnection Experiment (MRX) [Yamada et al., Phys. Plasmas 4, 1936 (1997)]. The three dimensional evolution of these flux ropes is monitored by a fast visible light framing camera, while their magnetic structure is measured by a variety of internal magnetic probes. The flux ropes are consistently observed to undergo large-scale oscillations as a result of an external kink instability.more » Using detailed scans of the plasma current, the guide field strength, and the length of the flux rope, we show that the threshold for kink stability is governed by the Kruskal-Shafranov limit for a flux rope that is held fixed at both ends (i.e., q{sub a} = 1).« less

Formation of a compound flux rope by the merging of two filament channels, the associated dynamics, and its stability

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

Joshi, Navin Chandra; Inoue, Satoshi; Magara, Tetsuya, E-mail: navin@khu.ac.kr, E-mail: njoshi98@gmail.com

2014-11-01

We present observations of compound flux rope formation, which occurred on 2014 January 1, via merging of two nearby filament channels, the associated dynamics, and its stability using multiwavelength data. We also discuss the dynamics of cool and hot plasma moving along the newly formed compound flux rope. The merging started after the interaction between the southern leg of the northward filament and the northern leg of the southward filament at ≈01:21 UT and continued until a compound flux rope formed at ≈01:33 UT. During the merging, the cool filament plasma heated up and started to move along both sidesmore » of the compound flux rope, i.e., toward the north (≈265 km s{sup –1}) and south (≈118 km s{sup –1}) from the point of merging. After traveling a distance of ≈150 Mm toward the north, the plasma cooled down and started to return back to the south (≈14 km s{sup –1}) after ≈02:00 UT. The observations provide a clear example of compound flux rope formation via merging of two different flux ropes and the occurrence of a flare through tether cutting reconnection. However, the compound flux rope remained stable in the corona and had a confined eruption. The coronal magnetic field decay index measurements revealed that both the filaments and the compound flux rope axis lie within the stability domain (decay index <1.5), which may be the possible cause for their stability. The present study also deals with the relationship between the filament's chirality (sinistral) and the helicity (positive) of the surrounding flux rope.« less

On the use of flux limiters in the discrete ordinates method for 3D radiation calculations in absorbing and scattering media

NASA Astrophysics Data System (ADS)

Godoy, William F.; DesJardin, Paul E.

2010-05-01

The application of flux limiters to the discrete ordinates method (DOM), SN, for radiative transfer calculations is discussed and analyzed for 3D enclosures for cases in which the intensities are strongly coupled to each other such as: radiative equilibrium and scattering media. A Newton-Krylov iterative method (GMRES) solves the final systems of linear equations along with a domain decomposition strategy for parallel computation using message passing libraries in a distributed memory system. Ray effects due to angular discretization and errors due to domain decomposition are minimized until small variations are introduced by these effects in order to focus on the influence of flux limiters on errors due to spatial discretization, known as numerical diffusion, smearing or false scattering. Results are presented for the DOM-integrated quantities such as heat flux, irradiation and emission. A variety of flux limiters are compared to "exact" solutions available in the literature, such as the integral solution of the RTE for pure absorbing-emitting media and isotropic scattering cases and a Monte Carlo solution for a forward scattering case. Additionally, a non-homogeneous 3D enclosure is included to extend the use of flux limiters to more practical cases. The overall balance of convergence, accuracy, speed and stability using flux limiters is shown to be superior compared to step schemes for any test case.

Funneled potential and flux landscapes dictate the stabilities of both the states and the flow: Fission yeast cell cycle.

PubMed

Luo, Xiaosheng; Xu, Liufang; Han, Bo; Wang, Jin

2017-09-01

Using fission yeast cell cycle as an example, we uncovered that the non-equilibrium network dynamics and global properties are determined by two essential features: the potential landscape and the flux landscape. These two landscapes can be quantified through the decomposition of the dynamics into the detailed balance preserving part and detailed balance breaking non-equilibrium part. While the funneled potential landscape is often crucial for the stability of the single attractor networks, we have uncovered that the funneled flux landscape is crucial for the emergence and maintenance of the stable limit cycle oscillation flow. This provides a new interpretation of the origin for the limit cycle oscillations: There are many cycles and loops existed flowing through the state space and forming the flux landscapes, each cycle with a probability flux going through the loop. The limit cycle emerges when a loop stands out and carries significantly more probability flux than other loops. We explore how robustness ratio (RR) as the gap or steepness versus averaged variations or roughness of the landscape, quantifying the degrees of the funneling of the underlying potential and flux landscapes. We state that these two landscapes complement each other with one crucial for stabilities of states on the cycle and the other crucial for the stability of the flow along the cycle. The flux is directly related to the speed of the cell cycle. This allows us to identify the key factors and structure elements of the networks in determining the stability, speed and robustness of the fission yeast cell cycle oscillations. We see that the non-equilibriumness characterized by the degree of detailed balance breaking from the energy pump quantified by the flux is the cause of the energy dissipation for initiating and sustaining the replications essential for the origin and evolution of life. Regulating the cell cycle speed is crucial for designing the prevention and curing strategy of cancer.

Funneled potential and flux landscapes dictate the stabilities of both the states and the flow: Fission yeast cell cycle

PubMed Central

2017-01-01

Using fission yeast cell cycle as an example, we uncovered that the non-equilibrium network dynamics and global properties are determined by two essential features: the potential landscape and the flux landscape. These two landscapes can be quantified through the decomposition of the dynamics into the detailed balance preserving part and detailed balance breaking non-equilibrium part. While the funneled potential landscape is often crucial for the stability of the single attractor networks, we have uncovered that the funneled flux landscape is crucial for the emergence and maintenance of the stable limit cycle oscillation flow. This provides a new interpretation of the origin for the limit cycle oscillations: There are many cycles and loops existed flowing through the state space and forming the flux landscapes, each cycle with a probability flux going through the loop. The limit cycle emerges when a loop stands out and carries significantly more probability flux than other loops. We explore how robustness ratio (RR) as the gap or steepness versus averaged variations or roughness of the landscape, quantifying the degrees of the funneling of the underlying potential and flux landscapes. We state that these two landscapes complement each other with one crucial for stabilities of states on the cycle and the other crucial for the stability of the flow along the cycle. The flux is directly related to the speed of the cell cycle. This allows us to identify the key factors and structure elements of the networks in determining the stability, speed and robustness of the fission yeast cell cycle oscillations. We see that the non-equilibriumness characterized by the degree of detailed balance breaking from the energy pump quantified by the flux is the cause of the energy dissipation for initiating and sustaining the replications essential for the origin and evolution of life. Regulating the cell cycle speed is crucial for designing the prevention and curing strategy of cancer. PMID:28892489

[Simulation of CO2 exchange between forest canopy and atmosphere].

PubMed

Diao, Yiwei; Wang, Anzhi; Jin, Changjie; Guan, Dexin; Pei, Tiefan

2006-12-01

Estimating the scalar source/sink distribution of CO2 and its vertical fluxes within and above forest canopy continues to be a critical research problem in biosphere-atmosphere exchange processes and plant ecology. With broad-leaved Korean pine forest in Changbai Mountains as test object, and based on Raupach's localized near field theory, the source/sink and vertical flux distribution of CO2 within and above forest canopy were modeled through an inverse Lagrangian dispersion analysis. This model correctly predicted a strong positive CO2 source strength in the deeper layers of the canopy due to soil-plant respiration, and a strong CO2 sink in the upper layers of the canopy due to the assimilation by sunlit foliage. The foliage in the top layer of canopy changed from a CO2 source in the morning to a CO2 sink in the afternoon, while the soil constituted a strong CO2 source all the day. The simulation results accorded well with the eddy covariance CO2 flux measurements within and above the canopy, and the average precision was 89%. The CO2 exchange predicted by the analysis was averagely 15% higher than that of the eddy correlation, but exhibited identical temporal trend. Atmospheric stability remarkably affected the CO2 exchange between forest canopy and atmosphere.

On the Impact of Wind Farms on a Convective Atmospheric Boundary Layer

NASA Astrophysics Data System (ADS)

Lu, Hao; Porté-Agel, Fernando

2015-10-01

With the rapid growth in the number of wind turbines installed worldwide, a demand exists for a clear understanding of how wind farms modify land-atmosphere exchanges. Here, we conduct three-dimensional large-eddy simulations to investigate the impact of wind farms on a convective atmospheric boundary layer. Surface temperature and heat flux are determined using a surface thermal energy balance approach, coupled with the solution of a three-dimensional heat equation in the soil. We study several cases of aligned and staggered wind farms with different streamwise and spanwise spacings. The farms consist of Siemens SWT-2.3-93 wind turbines. Results reveal that, in the presence of wind turbines, the stability of the atmospheric boundary layer is modified, the boundary-layer height is increased, and the magnitude of the surface heat flux is slightly reduced. Results also show an increase in land-surface temperature, a slight reduction in the vertically-integrated temperature, and a heterogeneous spatial distribution of the surface heat flux.

Parametrizing Evaporative Resistance for Heterogeneous Sparse Canopies through Novel Wind Tunnel Experimentation

NASA Astrophysics Data System (ADS)

Sloan, B.; Ebtehaj, A. M.; Guala, M.

2017-12-01

The understanding of heat and water vapor transfer from the land surface to the atmosphere by evapotranspiration (ET) is crucial for predicting the hydrologic water balance and climate forecasts used in water resources decision-making. However, the complex distribution of vegetation, soil and atmospheric conditions makes large-scale prognosis of evaporative fluxes difficult. Current ET models, such as Penman-Monteith and flux-gradient methods, are challenging to apply at the microscale due to ambiguity in determining resistance factors to momentum, heat and vapor transport for realistic landscapes. Recent research has made progress in modifying Monin-Obukhov similarity theory for dense plant canopies as well as providing clearer description of diffusive controls on evaporation at a smooth soil surface, which both aid in calculating more accurate resistance parameters. However, in nature, surfaces typically tend to be aerodynamically rough and vegetation is a mixture of sparse and dense canopies in non-uniform configurations. The goal of our work is to parameterize the resistances to evaporation based on spatial distributions of sparse plant canopies using novel wind tunnel experimentation at the St. Anthony Falls Laboratory (SAFL). The state-of-the-art SAFL wind tunnel was updated with a retractable soil box test section (shown in Figure 1), complete with a high-resolution scale and soil moisture/temperature sensors for recording evaporative fluxes and drying fronts. The existing capabilities of the tunnel were used to create incoming non-neutral stability conditions and measure 2-D velocity fields as well as momentum and heat flux profiles through PIV and hotwire anemometry, respectively. Model trees (h = 5 cm) were placed in structured and random configurations based on a probabilistic spacing that was derived from aerial imagery. The novel wind tunnel dataset provides the surface energy budget, turbulence statistics and spatial soil moisture data under varying atmospheric stability for each sparse canopy configuration. We will share initial data results and progress toward the development of new parametrizations that can account for the evolution of a canopy roughness sublayer on the momentum, heat and vapor resistance terms as a function of a stochastic representation of canopy spacing.

Electrospun Superhydrophobic Organic/Inorganic Composite Nanofibrous Membranes for Membrane Distillation.

PubMed

Li, Xiong; Yu, Xufeng; Cheng, Cheng; Deng, Li; Wang, Min; Wang, Xuefen

2015-10-07

Electrospun superhydrophobic organic/inorganic composite nanofibrous membranes exhibiting excellent direct contact membrane distillation (DCMD) performance were fabricated by a facile route combining the hydrophobization of silica nanoparticles (SiO2 NPs) and colloid electrospinning of the hydrophobic silica/poly(vinylidene fluoride) (PVDF) matrix. Benefiting from the utilization of SiO2 NPs with three different particle sizes, the electrospun nanofibrous membranes (ENMs) were endowed with three different delicate nanofiber morphologies and fiber diameter distribution, high porosity, and superhydrophobic property, which resulted in excellent waterproofing and breathability. Significantly, structural attributes analyses have indicated the major contributing role of fiber diameter distribution on determining the augment of permeate vapor flux through regulating mean flow pore size (MFP). Meanwhile, the extremely high liquid entry pressure of water (LEPw, 2.40 ± 0.10 bar), robust nanofiber morphology of PVDF immobilized SiO2 NPs, remarkable mechanical properties, thermal stability, and corrosion resistance endowed the as-prepared membranes with prominent desalination capability and stability for long-term MD process. The resultant choreographed PVDF/silica ENMs with optimized MFP presented an outstanding permeate vapor flux of 41.1 kg/(m(2)·h) and stable low permeate conductivity (∼2.45 μs/cm) (3.5 wt % NaCl salt feed; ΔT = 40 °C) over a DCMD test period of 24 h without membrane pores wetting detected. This result was better than those of typical commercial PVDF membranes and PVDF and modified PVDF ENMs reported so far, suggesting them as promising alternatives for MD applications.

Forbidden territories in the string landscape

NASA Astrophysics Data System (ADS)

Kumar, Alok; Mukhopadhyay, Subir; Ray, Koushik

2007-12-01

Problems of stabilizing moduli of the type-IIB string theory on toroidal orientifolds T6/Z2, in presence of worldvolume fluxes on various D-branes, are considered. For Z2 actions, introducing either O9 or O3 planes, we rule out the possibility of moduli stabilization in a wide class of models with Script N = 1 supersymmetry, characterized by the type of fluxes turned on along D-brane worldvolume. Our results, in particular, imply that Abelian worldvolume fluxes can not by themselves stabilize closed string moduli, in a consistent supersymmtric model, for above orientifold compactifications. We also discuss other Z2 orientifolds of T6 and show that certain other brane wrappings are also ruled out by similar consistency requirements. In specific setups we consider examples with D9-branes wrapping on a complex three-torus with its world-volume fluxes taken to be semi-homogeneous bundles and D7-branes wrapping holomorphic four-cycles of the complex three-torus carrying world-volume fluxes.

Experimental study of the impact of large-scale wind farms on land-atmosphere exchanges

NASA Astrophysics Data System (ADS)

Zhang, wei; Markfort, Corey; Porté-Agel, Fernando

2013-04-01

Wind energy is one of the fastest growing sources of renewable energy world-wide, and it is expected that many more large-scale wind farms will be built and cover a significant portion of land and ocean surfaces. By extracting kinetic energy from the atmospheric boundary layer and converting it to electricity, wind farms may affect the transport of momentum, heat, moisture and trace gases (e.g. CO2) between the atmosphere and the land surface locally and globally. Understanding wind farm-atmosphere interactions and subsequent environmental impacts are complicated by the effects of turbine array configuration, wind farm size, land-surface characteristics and atmospheric thermal stability. In particular, surface scalar flux is influenced by wind farms and needs to be appropriately parameterized in meso-scale and/or high-resolution numerical models. Wind-tunnel experiments of model wind farms with perfectly aligned and staggered configurations, having the same turbine distribution density, were conducted in a neutral turbulent boundary layer with a surface heat source. Turbulent flow and fluxes over and through the wind farm were measured using a custom x-wire/cold-wire anemometer; and surface scalar flux was measured with an array of surface-mounted heat flux sensors within the quasi-developed flow regime. Although the overall surface heat flux change produced by the wind farms was found to be small, with a net reduction of 4% for the staggered wind farm and nearly zero for the aligned wind farm, the highly heterogeneous spatial distribution of the surface heat flux, dependent on wind farm layout, is significant. The difference between the minimum and maximum surface heat fluxes could be up to 12% and 7% in aligned and staggered wind farms, respectively. This finding is important for planning intensive agriculture practices and optimizing agricultural land use with regard to wind energy project development. The well-controlled wind-tunnel experiments presented here also provide a first comprehensive dataset on turbulent flow and scalar transport in wind farms, which can be further used to develop and validate new parameterizations for surface scalar fluxes in numerical models.

Distribution Functions of Sizes and Fluxes Determined from Supra-Arcade Downflows

NASA Technical Reports Server (NTRS)

McKenzie, D.; Savage, S.

2011-01-01

The frequency distributions of sizes and fluxes of supra-arcade downflows (SADs) provide information about the process of their creation. For example, a fractal creation process may be expected to yield a power-law distribution of sizes and/or fluxes. We examine 120 cross-sectional areas and magnetic flux estimates found by Savage & McKenzie for SADs, and find that (1) the areas are consistent with a log-normal distribution and (2) the fluxes are consistent with both a log-normal and an exponential distribution. Neither set of measurements is compatible with a power-law distribution nor a normal distribution. As a demonstration of the applicability of these findings to improved understanding of reconnection, we consider a simple SAD growth scenario with minimal assumptions, capable of producing a log-normal distribution.

Comparing Multiple Scales of CH4 Fluxes in a Boreal Transition Forest - from Soil-Chambers to Eddy Covariance

NASA Astrophysics Data System (ADS)

Savage, K. E.; Shoemaker, J.; Hollinger, D. Y.

2017-12-01

Boreal-transition forests contain a range of soil moisture conditions, from drier "uplands" to embedded wetlands, with transitional soils in between. This creates a complex topography of methane (CH4) producing and consuming patches. Seasonally, CH4 production in wet environments can be orders of magnitude greater than methane uptake rates in drier soils, as well as being much more episodic. The spatial and temporal variability in flux magnitudes from these drainage conditions creates a challenge for constraining the contribution of these forests to the global CH4 cycle. Ground based chambers capture small-scale fluxes, and are often distributed to capture specific soil conditions. Soil chambers have been the primary tool for assessing CH4 fluxes from natural soils, with observations being scaled up to represent broader regions. The study of CH4 biogeochemistry lacked meso-scale measurements to provide checks between the global atmospheric data and the soil chambers. Recent advances in the technology of fast response CH4 analyzers have led to increased use of the eddy-flux covariance (EC) method to capture CH4 fluxes over a larger landscape-scale. The EC method captures net exchange at the top of the vegetation canopy, across a footprint of varying size, dependent on wind-speed, direction, surface roughness, turbulence, sensor height and atmospheric stability. Simultaneous deployment of EC and soil chambers provide a critical means to reconcile bottom up with top down approaches to quantify CH4 fluxes. Two years of CH4 flux data from an EC tower in Howland forest, a boreal-transition forest in north-central Maine, USA, are compared with concurrent automated soil chamber data collected within the tower footprint and distributed among soil drainage classes. An EC footprint model was used to determine a daily and sub-daily tower footprint. Using a published soil analysis of the Howland tower area, and Lidar imagery of tree canopy, we explore various strategies for upscaling chamber fluxes: footprint estimates, aerial weighting by drainage class, and canopy density; and compare to measurements from the EC tower. Analyzing simultaneous flux data from both scales over multiple years, will enable us to evaluate these methodologies and enhance our understanding of CH4 biogeochemistry at all scales.

Performance of low resistance microchannel plate stacks

NASA Technical Reports Server (NTRS)

Siegmund, O. H. W.; Stock, J.

1991-01-01

Results are presented from an evaluation of three sets of low resistance microchannel plate (MCP) stacks; the tests encompassed gain, pulse-height distribution, background rate, event rate capacity as a function of illuminated area, and performance changes due to high temperature bakeout and high flux UV scrub. The MCPs are found to heat up, requiring from minutes to hours to reach stabilization. The event rate is strongly dependent on the size of the area being illuminated, with larger areas experiencing a gain drop onset at lower rates than smaller areas.

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

NASA Astrophysics Data System (ADS)

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

2012-07-01

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.

Towards an emergent model of solitonic particles from non-trivial vacuum structure

NASA Astrophysics Data System (ADS)

Gillard, Adam B.; Gresnigt, Niels G.

2017-12-01

We motivate and introduce what we refer to as the principles of Lie-stability and Hopf-stability and see what the physical theories must look like. Lie-stability is needed on the classical side and Hopf-stability is needed on the quantum side. We implement these two principles together with Lie-deformations consistent with basic constraints on the classical kinematical variables to arrive at the form of a theory that identifies standard model fermions with quantum solitonic trefoil knotted flux tubes which emerge from a flux tube vacuum network. Moreover, twisted unknot fluxtubes form natural dark matter candidates

Hydrate Formation in Gas-Rich Marine Sediments: A Grain-Scale Model

NASA Astrophysics Data System (ADS)

Holtzman, R.; Juanes, R.

2009-12-01

We present a grain-scale model of marine sediment, which couples solid- and multiphase fluid-mechanics together with hydrate kinetics. The model is applied to investigate the spatial distribution of the different methane phases - gas and hydrate - within the hydrate stability zone. Sediment samples are generated from three-dimensional packs of spherical grains, mapping the void space into a pore network by tessellation. Gas invasion into the water-saturated sample is simulated by invasion-percolation, coupled with a discrete element method that resolves the grain mechanics. The coupled model accounts for forces exerted by the fluids, including cohesion associated with gas-brine surface tension. Hydrate growth is represented by a hydrate film along the gas-brine interface, which increases sediment cohesion by cementing the grain contacts. Our model of hydrate growth includes the possible rupture of the hydrate layer, which leads to the creation of new gas-water interface. In previous work, we have shown that fine-grained sediments (FGS) exhibit greater tendency to fracture, whereas capillary invasion is the preferred mode of methane gas transport in coarse-grained sediments (CGS). The gas invasion pattern has profound consequences on the hydrate distribution: a larger area-to-volume ratio of the gas cluster leads to a larger drop in gas pressure inside the growing hydrate shell, causing it to rupture. Repeated cycles of imbibition and hydrate growth accompanied by trapping of gas allow us to determine the distribution of hydrate and gas within the sediment as a function of time. Our pore-scale model suggests that, even when film rupture takes place, the conversion of gas to hydrate is slow. This explains two common field observations: the coexistence of gas and hydrate within the hydrate stability zone in CGS, and the high methane fluxes through fracture conduits in FGS. These results demonstrate the importance of accounting for the strong coupling among multiphase flow, sediment mechanics, and hydrate formation. Our model explains the remarkable differences in hydrate distribution and saturation between fine- and coarse-grained sediments, and promotes the quantitative understanding of the role of methane hydrate in seafloor stability and the global carbon cycle, including the size of the hydrate energy resource, and estimates of methane fluxes into the ocean and the atmosphere.

Effect of Stability on Mixing in Open Canopies. Chapter 4

NASA Technical Reports Server (NTRS)

Lee, Young-Hee; Mahrt, L.

2005-01-01

In open canopies, the within-canopy flux from the ground surface and understory can account for a significant fraction of the total flux above the canopy. This study incorporates the important influence of within-canopy stability on turbulent mixing and subcanopy fluxes into a first-order closure scheme. Toward this goal, we analyze within-canopy eddy-correlation data from the old aspen site in the Boreal Ecosystem - Atmosphere Study (BOREAS) and a mature ponderosa pine site in Central Oregon, USA. A formulation of within-canopy transport is framed in terms of a stability- dependent mixing length, which approaches Monin-Obukhov similarity theory above the canopy roughness sublayer. The new simple formulation is an improvement upon the usual neglect of the influence of within-canopy stability in simple models. However, frequent well-defined cold air drainage within the pine subcanopy inversion reduces the utility of simple models for nocturnal transport. Other shortcomings of the formulation are discussed.

Stability of a two-volume MRxMHD model in slab geometry

NASA Astrophysics Data System (ADS)

Tuen, Li Huey

Ideal MHD models are known to be inadequate to describe various physical attributes of a toroidal field with non-continuous symmetry, such as magnetic islands and stochastic regions. Motivated by this omission, a new variational principle MRXMHD was developed; rather than include an infinity of magnetic flux surfaces, MRxMHD has a finite number of flux surfaces, and thus supports partial plasma relaxation. The model comprises of relaxed plasma regions which are separated by nested ideal MHD interfaces (flux surfaces), and can be encased in a perfectly conducting wall. In each region the pressure is constant, but can jump across interfaces. The field and field pitch, or rotational transform, can also jump across the interfaces. Unlike ideal MHD, MRxMHD plasmas can support toroidally non-axisymmetric confined magnetic fields, magnetic islands and stochastic regions. In toroidally non-axisymmetric plasma, the existence of interfaces in MRxMHD is contingent on the irrationality of the rotational transform of flux surfaces. That is, the KAM theorem shows that invariant tori (flux surfaces) continue to exist for sufficiently small perturbations to an integrable system (which describes flux surfaces), provided that the rotational transform is sufficiently irrational. Building upon the MRxMHD stability model, we study the effects of irrationality of the rotational transform at interfaces in MRxMHD on plasma stability. We present an MRxMHD equilibrium model to investigate the effects of magnetic field pitch within the plasma and across the aforementioned flux surfaces within a chosen geometry. In this model, it is found that the 2D system stability conditions are dependent on the interface and resonant surface magnetic field pitch at minimised energy states, and the stability of a system as a function of magnetic field pitch destabilises at particular values of magnetic field pitch. We benchmark the treatment of a two-volume system, along with the calculations for background and perturbed magnetic fields to existing cylindrical working. An expression is formulated for the stability eigenvalues by creating a model for the slab geometry system. The eigenvalues for system stability at a minimum energy state are found to depend upon the rationality of the magnetic field pitch at resonant surfaces. Various system parameter scans are conducted to determine their affect upon system stability and their implications. While tearing instabilities exist at low order rational resonances, investigating the instability of high-order rationals requires study of pressure-driven instabilities.

Doping and defect structure of mixed-conducting ceramics for gas separation

NASA Astrophysics Data System (ADS)

Zuo, Chendong

A worldwide energy crisis and increasing environmental concerns are strong incentives for using hydrogen as a sustainable and clean energy source. "Hydrogen economy" has been around since 1970s, but it started to look practicable only in recent years. The trend in the future is to switch from using hydrogen as the basic raw material in the chemical industry to the energy carrier in the transportation and distributed energy industries. To meet the expected rising demand, hydrogen has to be generated in a more cost-effective manner. As one of the most important operation units in the hydrogen production, a high performance hydrogen separation membrane system is essential to the coming hydrogen economy. The project of hydrogen separation membrane based on Mixed ionic and electronic conductor (MIEC) composite was initiated by DoE years ago, and the MIEC membrane has been developed in Argonne National Laboratory (ANL) for several years. The goal at ANL is to develop a dense, ceramic-based MIEC membrane that is highly selective, chemical stable in practical environments at operative temperatures up to ≈900°C, and can separate hydrogen from mixed gases at commercially significant fluxes under industrially relevant operating conditions, without the need for electrodes or electrical circuitry. The effort at ANL initially focused on BCY20 (BaCe0.8Y 0.2O3). BCY20 forms the matrix of ANL-1a and -2a ceramic-metal composite membranes (40-50 vol.% of a metal is dispersed in a ceramic matrix) and its bulk transport properties, including ionic transfer number, ionic and electronic conductivity, and chemical and mechanical stability have been systematically studied. However, exposure to CO2 and H2O-containing atmospheres, as would be present in a practical environment, will degrade the material as it reacts to form insulating barium carbonate (BaCO3 ) and cerium oxide (CeO2). This decomposition greatly limits its applicability in hydrogen separation, despite the promising properties of this material. The combination of high proton conductivity and good chemical stability, which is a prerequisite for the application of MIEC compounds, is generally considered to be a key problem. In choosing good materials for H2 separation membrane, defect structure, and hence transport properties of perovskites, which are strongly influenced by the oxidation states and ionic radii of dopants, are very critical. Therefore it is the goal of this research to gain a fundamental understanding of the correlation between the defect chemistry and the properties of perovskite structure materials, so as to allow the engineering of these materials with the desired properties for the application in industry, such as developing membranes of mixed conductors which have good stability in practical atmospheres. With respect to thermodynamic stability, water solubility limit and mobility of protonic defects the occupation of the A-site does not require much of a compromise. Except for the stability with acidic gases, which is almost independent of the choice of the A-cation, all relevant properties are superior for an A-site occupation by the big barium compared to other alkaline earth ions. Addition of acceptor dopants into ABO3 is crucial to proton uptake. A high concentration of protonic defects requires a high acceptor dopants concentration. Dopants are incorporated into the lattice at either A or B-sites with the respective creation of charge-compensating oxygen vacancies and A-site vacancies. Smaller dopants preferentially substitute at the B-site, while larger cations substitute at the A-site. Partial occupation of the A sublattice can explain the low uptake of protons. The yttrium seems to be perfect acceptor dopant choice for BaZrO3, BaCeO3-based materials, and both the proton mobility and the thermodynamics of hydration are practically unchanged for dopant levels up to 20% Y. The choice of the B-cation, however, requires some compromising. It should be of medium size. High packing densities as a result of small B-cations reduce the water solubility limit, while though the high proton mobilities are compatible with loosely packed structure; the poor compatibility of big B-cations with the perovskite structure reduces the thermodynamic stability including the stability in acidic gases. Empirically high chemical stability and high proton conductivity still seem to exclude one another for simple alkaline earth perovskites. But there is seemingly still room for discoveries among 'old and new' oxide material. We are investigating various possible alternatives to BCY based on the understanding of defect chemistry of doped perovskite structure materials. BCY20 is one of the best proton conductors among this class of conductors, however, not stable in the CO2, H2O-containing atmospheres. In contrast, yttrium-doped barium zirconates have good chemical stability but are undesirable because of their relatively low conductivity and high sintering temperature. Since BaCeO3 and BaZrO3 can easily form solid solutions, it is possible to replace any desired fraction of the Ce in BaCeO3 with Zr, and the solid solution between cerate and zirconate has both high protonic conductivity and good chemical stability. BZCY proton conductors with various compositions (0.0≤x≤0.8) have been synthesized and characterized. The absence of low-angle supercell reflections indicates a random B-site cation distribution. The substitution of Zr led to a decrease in cell volume and an enhanced structural stability against reactions with CO2. The total conductivity for BZCY pellets of all composition increased with temperature increased and decreased as the zirconium content increased from 10% to 40% at each fixed temperature in wet 4% H2/N2 atmosphere. BZCY7 [Ba(Zr0.1Ce 0.7Y0.2)O3] showed pronounced proton conduction within the bulk and along the grain boundaries. Total conductivity increased from 0.015 S/cm at 550°C to 0.043 S/cm at 850°C for BZCY7 smaple, which is highest among all Ba(Zr0.8-xCexY0.2)O 3 (0.4≤x≤0.7) compositions. However, the relatively low electronic conductivity is not adequate for the hydrogen separation membrane to be used in a non-galvanic operation mode, electronic conduction must been introduced into the proton conductor to create mixed ionic-electronic conductors. Dense Ni-BZCY [Ni-Ba(Zr0.8-xCexY0.2)O 3-alpha] cermet composite membranes have been successfully fabricated for evaluating hydrogen permeability, and stability. Nickel phase enhances the hydrogen permeability of the ceramic phase by increasing the electronic conductivity of the composite, surface exchange kinetics, and improving mechanical stability. By comparing the BEI images of BZCY cermets with different Zirconium content, we can tell the grain size, shape and distribution of two phases are insensitive to the zirconium content. Doping Zirconium in the B-site only slightly reduced the hydrogen permeation at high temperatures (e.g. 900°C), but dramatically increased the chemical stability in CO2- and H2O-containing gases. The hydrogen permeation fluxes of Ni-BZCY cermet membrane increased with temperature for all the compositions and the flux decreased as the zirconium content increased at each fixed temperature, but they are comparable to that of Ni-BCY for the lower zirconium content samples (x=0.6, 0.7). While the hydrogen permeation flux through a Ni-BCY cermet membrane decreased sharply upon exposure to wet CO2 atmospheres, the hydrogen permeation flux of a Ni-BZCY was relatively stable for 80 h in atmospheres containing up to 30% CO2 at 900°C after a small initial decrease. Among the compositions studied (0.4≤x≤0.7), the Ni-BZCY7 (x=0.7) composition exhibited both highest H2 permeation rate and good chemistry stability, thus having potential for practical applications. The Ni-BZCY7 membrane was chose to further study based on the best overall performance. The hydrogen flux through a Ni-BZCY7 cermet membrane increased with temperature under both dry and wet conditions. The fact of increasing hydrogen flux by adding moisture to the feed gas or increasing the hydrogen partial pressure gradient across the membrane implies that the hydrogen flux through the Ni-BZCY7 cermet membrane is limited by the proton transport through the ceramic BZCY7 phase. The dependence of hydrogen flux on membrane thickness indicates that the flux is limited by the bulk diffusion of hydrogen through the ceramic phase over the range of thicknesses that were studied (0.25-1.0 mm). Although interfacial reactions are expected to become important for thinner membranes, these results suggest that we can further increase the hydrogen flux by decreasing the membrane thickness. The highest measured hydrogen flux was 0.805 cm3/min-cm 2 for a dense 266-mum-thick membrane at 900°C using 100% H 2 as the feed gas. The hydrogen fluxes through membrane were stable, after a small initial decrease, for 80 h in atmospheres containing up to 30% CO2 at 900°C, implying that Ni-BZCY7 membranes might be suitable for practical applications.

Feedback control of persistent-current oscillation based on the atomic-clock technique

NASA Astrophysics Data System (ADS)

Yu, Deshui; Dumke, Rainer

2018-05-01

We propose a scheme of stabilizing the persistent-current Rabi oscillation based on the flux qubit-resonator-atom hybrid structure. The low-Q L C resonator weakly interacts with the flux qubit and maps the persistent-current Rabi oscillation of the flux qubit onto the intraresonator electric field. This oscillating electric field is further coupled to a Rydberg-Rydberg transition of the 87Rb atoms. The Rabi-frequency fluctuation of the flux qubit is deduced from measuring the atomic population via the fluorescence detection and stabilized by feedback controlling the external flux bias. Our numerical simulation indicates that the feedback-control method can efficiently suppress the background fluctuations in the flux qubit, especially in the low-frequency limit. This technique may be extensively applicable to different types of superconducting circuits, paving a way to long-term-coherence superconducting quantum information processing.

On the Asymptotic Stability of Steady Flows with Nonzero Flux in Two-Dimensional Exterior Domains

NASA Astrophysics Data System (ADS)

Guillod, Julien

2017-05-01

The Navier-Stokes equations in a two-dimensional exterior domain are considered. The asymptotic stability of stationary solutions satisfying a general hypothesis is proven under any L 2-perturbation. In particular, the general hypothesis is valid if the steady solution is the sum of the critically decaying flux carrier with flux {| Φ | < 2 π} and a small subcritically decaying term. Under the central symmetry assumption, the general hypothesis is also proven for any critically decaying steady solutions under a suitable smallness condition.

Structure of an energetic narrow discrete arc

NASA Technical Reports Server (NTRS)

Mcfadden, J. P.; Carlson, C. W.; Boehm, M. H.

1990-01-01

Particle distributions, waves, dc electric fields, and magnetic fields were measured by two sounding rockets at altitudes of 950 and 430 km through an energetic (greater than 5 keV) narrow (about 10 km) stable discrete arc. Although the payloads' magnetic footprints were separated by only 50 km, differences in the arc's structure were observed including the spatial width, peak energy, and characteristic spectra. The energetic electron precipitation included both slowly varying isotropic fluxes that formed an inverted-V energy-time signature and rapidly varying field-aligned fluxes at or below the isotropic spectral peak. The isotropic precipitation had a flux discontinuity inside the arc indicating the arc was present on a boundary between two different magnetospheric plasmas. Dispersive and nondispersive bursts of field-aligned electrons were measured throughout the arc, appearing over broad energy ranges or as monoenergetic beams. Dispersive bursts gave variable source distances less than 8000 km. Plateauing of some of the most intense bursts suggests that waves stabilized these electrons. During the lower altitude arc crossing, the field-aligned component formed a separate inverted-V energy-time signature whose peak energy was half the isotropic peak energy.

Nonequilibrium segregation and phase instability in alloy films during elevated-temperature irradiation in a high-voltage electron microscope

NASA Astrophysics Data System (ADS)

Lam, N. Q.; Okamoto, P. R.

1984-05-01

The effects of defect-production rate gradients, caused by the radial nonuniformity in the electron flux distribution, on solute segregation and phase stability in alloy films undergoing high-voltage electron-microscope (HVEM) irradiation at high temperatures are assessed. Two-dimensional (axially symmetric) compositional redistributions were calculated, taking into account both axial and transverse radial defect fluxes. It was found that when highly focused beams were employed radiation-induced segregation consisted of two stages: dominant axial segregation at the film surfaces at short irradiation times and competitive radial segregation at longer times. The average alloy composition within the irradiated region could differ greatly from that irradiated with a uniform beam, because of the additional atom transport from or to the region surrounding the irradiated zone under the influence of radial fluxes. Damage-rate gradient effects must be taken into account when interpreting in-situ HVEM observations of segregation-induced phase instabilities. The theoretical predictions are compared with experimental observations of the temporal and spatial dependence of segregation-induced precipitation in thin films of Ni-Al, Ni-Ge and Ni-Si solid solutions.

Measuring Fast Calcium Fluxes in Cardiomyocytes

PubMed Central

Golebiewska, Urszula; Scarlata, Suzanne

2011-01-01

Cardiomyocytes have multiple Ca2+ fluxes of varying duration that work together to optimize function 1,2. Changes in Ca2+ activity in response to extracellular agents is predominantly regulated by the phospholipase Cβ- Gαq pathway localized on the plasma membrane which is stimulated by agents such as acetylcholine 3,4. We have recently found that plasma membrane protein domains called caveolae5,6 can entrap activated Gαq7. This entrapment has the effect of stabilizing the activated state of Gαq and resulting in prolonged Ca2+ signals in cardiomyocytes and other cell types8. We uncovered this surprising result by measuring dynamic calcium responses on a fast scale in living cardiomyocytes. Briefly, cells are loaded with a fluorescent Ca2+ indicator. In our studies, we used Ca2+ Green (Invitrogen, Inc.) which exhibits an increase in fluorescence emission intensity upon binding of calcium ions. The fluorescence intensity is then recorded for using a line-scan mode of a laser scanning confocal microscope. This method allows rapid acquisition of the time course of fluorescence intensity in pixels along a selected line, producing several hundreds of time traces on the microsecond time scale. These very fast traces are transferred into excel and then into Sigmaplot for analysis, and are compared to traces obtained for electronic noise, free dye, and other controls. To dissect Ca2+ responses of different flux rates, we performed a histogram analysis that binned pixel intensities with time. Binning allows us to group over 500 traces of scans and visualize the compiled results spatially and temporally on a single plot. Thus, the slow Ca2+ waves that are difficult to discern when the scans are overlaid due to different peak placement and noise, can be readily seen in the binned histograms. Very fast fluxes in the time scale of the measurement show a narrow distribution of intensities in the very short time bins whereas longer Ca2+ waves show binned data with a broad distribution over longer time bins. These different time distributions allow us to dissect the timing of Ca2+fluxes in the cells, and to determine their impact on various cellular events. PMID:22143396

Measuring fast calcium fluxes in cardiomyocytes.

PubMed

Golebiewska, Urszula; Scarlata, Suzanne

2011-11-29

Cardiomyocytes have multiple Ca(2+) fluxes of varying duration that work together to optimize function (1,2). Changes in Ca(2+) activity in response to extracellular agents is predominantly regulated by the phospholipase Cβ- Gα(q;) pathway localized on the plasma membrane which is stimulated by agents such as acetylcholine (3,4). We have recently found that plasma membrane protein domains called caveolae(5,6) can entrap activated Gα(q;)(7). This entrapment has the effect of stabilizing the activated state of Gα(q;) and resulting in prolonged Ca(2+) signals in cardiomyocytes and other cell types(8). We uncovered this surprising result by measuring dynamic calcium responses on a fast scale in living cardiomyocytes. Briefly, cells are loaded with a fluorescent Ca(2+) indicator. In our studies, we used Ca(2+) Green (Invitrogen, Inc.) which exhibits an increase in fluorescence emission intensity upon binding of calcium ions. The fluorescence intensity is then recorded for using a line-scan mode of a laser scanning confocal microscope. This method allows rapid acquisition of the time course of fluorescence intensity in pixels along a selected line, producing several hundreds of time traces on the microsecond time scale. These very fast traces are transferred into excel and then into Sigmaplot for analysis, and are compared to traces obtained for electronic noise, free dye, and other controls. To dissect Ca(2+) responses of different flux rates, we performed a histogram analysis that binned pixel intensities with time. Binning allows us to group over 500 traces of scans and visualize the compiled results spatially and temporally on a single plot. Thus, the slow Ca(2+) waves that are difficult to discern when the scans are overlaid due to different peak placement and noise, can be readily seen in the binned histograms. Very fast fluxes in the time scale of the measurement show a narrow distribution of intensities in the very short time bins whereas longer Ca(2+) waves show binned data with a broad distribution over longer time bins. These different time distributions allow us to dissect the timing of Ca(2+)fluxes in the cells, and to determine their impact on various cellular events.

Numerical investigations on the characteristics of thermomagnetic instability in MgB2 bulks

NASA Astrophysics Data System (ADS)

Xia, Jing; Li, Maosheng; Zhou, Youhe

2017-07-01

This paper presents the characteristics of thermomagnetic instability in MgB2 bulks by numerically solving the macroscopic dynamics of thermomagnetic interaction governed by the coupled magnetic and heat diffusion equations in association with a modified E-J power-law relationship. The finite element method is used to discretize the system of partial differential equations. The calculated magnetization loops with flux jumps are consistent with the experimental results for MgB2 slabs bathed in a wide range of ambient temperatures. We reveal the evolution process of the thermomagnetic instability and present the distributions of the magnetic field, temperature, and current density before and after flux jumps. A 2D axisymmetric model is used to study the thermomagnetic instability in cylindrical MgB2 bulks. It is found that the number of flux jumps monotonously reduces as the ambient temperature rises and no flux jump appears when the ambient temperature exceeds a certain value. Moreover, the flux-jump phenomenon exists in a wide range of the ramp rate of the applied external field, i.e. 10-2-102 T s-1. Furthermore, the dependences of the first flux-jump field on the ambient temperature, ramp rate, and bulk thickness are investigated. The critical bulk thicknesses for stability are obtained for different ambient temperatures and sample radii. In addition, the influence of the capability of the interfacial heat transfer on the temporal response of the bulk temperature is discussed. We also find that the prediction of thermomagnetic instability is sensitive to the employment of the flux creep exponent in the simulations.

On the stability treatment in WAsP

NASA Astrophysics Data System (ADS)

Giebel, G.; Gryning, S.-E.

2003-04-01

An assessment of the treatment of atmospheric stability in the standard package for wind resource estimation, WAsP (from Risø National Laboratory), is presented. Emphasis is on the vertical wind profiles in WAsP and the treatment of stability therein, under special consideration of the nightly situation. The study starts with an introduction to WAsP and the way it treats the vertical extrapolation, under special consideration of the stability. The two parameters available for changing the stability treatment in WAsP are identified as RMS heat flux and offset heat flux. Four years worth of data from the meteorological mast at Risø, plus data from Egypt and Bermuda, is used for the identification of the parameter settings for stable conditions. To this aim, the measured heat fluxes from the mast were used to extract three data sets with successively higher stability in four different heights. These data sets were then run through the Observed Wind Climate Wizard (part of the WAsP package), resulting in Weibull fits to the data. Using these observed wind climates, a prediction of the highest level wind climate using the lowest level wind climate under all different stable conditions is undertaken and compared with the measured data set. To expand on this study, a systematic variation of the two heat flux parameters in WAsP is done, finding the parameters yielding the lowest overall errors for the predictions. Parts of this study were financed by the Landesumweltamt Brandenburg.

Classical and quantum stability in putative landscapes

DOE PAGES

Dine, Michael

2017-01-18

Landscape analyses often assume the existence of large numbers of fields, N, with all of the many couplings among these fields (subject to constraints such as local supersymmetry) selected independently and randomly from simple (say Gaussian) distributions. We point out that unitarity and perturbativity place significant constraints on behavior of couplings with N, eliminating otherwise puzzling results. In would-be flux compactifications of string theory, we point out that in order that there be large numbers of light fields, the compactification radii must scale as a positive power of N; scaling of couplings with N may also be necessary for perturbativity.more » We show that in some simple string theory settings with large numbers of fields, for fixed R and string coupling, one can bound certain sums of squares of couplings by order one numbers. This may argue for strong correlations, possibly calling into question the assumption of uncorrelated distributions. Finally, we consider implications of these considerations for classical and quantum stability of states without supersymmetry, with low energy supersymmetry arising from tuning of parameters, and with dynamical breaking of supersymmetry.« less

Classical and quantum stability in putative landscapes

NASA Astrophysics Data System (ADS)

Dine, Michael

2017-01-01

Landscape analyses often assume the existence of large numbers of fields, N , with all of the many couplings among these fields (subject to constraints such as local supersymmetry) selected independently and randomly from simple (say Gaussian) distributions. We point out that unitarity and perturbativity place significant constraints on behavior of couplings with N , eliminating otherwise puzzling results. In would-be flux compactifications of string theory, we point out that in order that there be large numbers of light fields, the compactification radii must scale as a positive power of N ; scaling of couplings with N may also be necessary for perturbativity. We show that in some simple string theory settings with large numbers of fields, for fixed R and string coupling, one can bound certain sums of squares of couplings by order one numbers. This may argue for strong correlations, possibly calling into question the assumption of uncorrelated distributions. We consider implications of these considerations for classical and quantum stability of states without supersymmetry, with low energy supersymmetry arising from tuning of parameters, and with dynamical breaking of supersymmetry.

A dynamical stabilizer in the climate system: a mechanism suggested by a simple model

NASA Astrophysics Data System (ADS)

Bates, J. R.

1999-05-01

A simple zonally averaged hemispheric model of the climate system is constructed, based on energy equations for two ocean basins separated at 30° latitude with the surface fluxes calculated explicitly. A combination of empirical input and theoretical calculation is used to determine an annual mean equilibrium climate for the model and to study its stability with respect to small perturbations. The insolation, the mean albedos and the equilibrium temperatures for the two model zones are prescribed from observation. The principal agent of interaction between the zones is the vertically integrated poleward transport of atmospheric angular momentum across their common boundary. This is parameterized using an empirical formula derived from a multiyear atmospheric data set. The surface winds are derived from the angular momentum transport assuming the atmosphere to be in a state of dynamic balance on the climatic timescales of interest. A further assumption that the air sea temperature difference and low level relative humidity remain fixed at their mean observed values then allows the surface fluxes of latent and sensible heat to be calculated. Results from a radiative model, which show a positive lower tropospheric water vapour/infrared radiative feedback on SST perturbations in both zones, are used to calculate the net upward infrared radiative fluxes at the surface. In the model's equilibrium climate, the principal processes balancing the solar radiation absorbed at the surface are evaporation in the tropical zone and net infrared radiation in the extratropical zone. The stability of small perturbations about the equilibrium is studied using a linearized form of the ocean energy equations. Ice-albedo and cloud feedbacks are omitted and attention is focussed on the competing effects of the water vapour/infrared radiative feedback and the turbulent surface flux and oceanic heat transport feedbacks associated with the angular momentum cycle. The perturbation equations involve inter-zone coupling and have coefficients dependent on the values of the equilibrium fluxes and the sensitivity of the angular momentum transport. Analytical solutions for the perturbations are obtained. These provide criteria for the stability of the equilibrium climate. If the evaporative feedback on SST perturbations is omitted, the equilibrium climate is unstable due to the influence of the water vapour/infrared radiative feedback, which dominates over the effects of the sensible heat and ocean heat transport feedbacks. The inclusion of evaporation gives a negative feedback which is of sufficient strength to stabilize the system. The stabilizing mechanism involves wind and humidity factors in the evaporative fluxes that are of comparable magnitude. Both factors involve the angular momentum transport. In including angular momentum and calculating the surface fluxes explicitly, the model presented here differs from the many simple climate models based on the Budyko Sellers formulation. In that formulation, an atmospheric energy balance equation is used to eliminate surface fluxes in favour of top-of-the-atmosphere radiative fluxes and meridional atmospheric energy transports. In the resulting models, infrared radiation appears as a stabilizing influence on SST perturbations and the dynamical stabilizing mechanism found here cannot be identified.

Characterization of extreme air-sea turbulent fluxes

NASA Astrophysics Data System (ADS)

Gulev, Sergey; Belyaev, Konstantin

2017-04-01

Extreme ocean-atmosphere turbulent fluxes play a critical role in the convective processes in the mid and subpolar latitudes and may also affect a variety of atmospheric processes, such as generation and re-intensification of extreme cyclones in the areas of the mid latitude storm tracks. From the ocean dynamics perspective, specifically for quantifying extreme vertical mixing, characterization of the extreme fluxes requires, besides estimation of the extreme events, also consideration of the relative extremeness of surface fluxes and their timing, e.g. the duration of periods of high surface fluxes. In order to comprehensively characterize extreme turbulent fluxes at sea surface we propose a formalism based upon probability density distributions of surface turbulent fluxes and flux-related variables. Individual absolute flux extremes were derived using Modified Fisher-Tippett (MFT) distribution of turbulent fluxes. Then, we extend this distribution to the fractional distribution, characterizing the fraction of time-integrated turbulent heat flux provided by the fluxes exceeding a given percentile. Finally, we consider the time durations during which fluxes of a given intensity provide extreme accumulations of heat loss from the surface. For estimation of these characteristics of surface fluxes we use fluxes recomputed from the state variables available from modern era reanalyses (ERA-Interim, MERRA and CFSR) for the period from 1979 onwards. Applications of the formalism to the VOS (Voluntary Observing Ship) - based surface fluxes are also considered. We discuss application of the new metrics of mesoscale and synoptic variability of surface fluxes to the dynamics of mixed layer depth in the North Atlantic.

Nature of convection-stabilized dc arcs in dual-flow nozzle geometry. I - The cold flow field and dc arc characteristics. II - Optical diagnostics and theory

NASA Astrophysics Data System (ADS)

Serbetci, Ilter; Nagamatsu, H. T.

1990-02-01

Steady-state low-current air arcs in a dual-flow nozzle system are studied experimentally. The cold flow field with no arc is investigated using a 12.7-mm diameter dual-flow nozzle in a steady-flow facility. Mach number and mass flux distributions are determined for various nozzle-pressure ratios and nozzle-gap spacing. It is found that the shock waves in the converging-diverging nozzles result in a decrease in overal resistance by about 15 percent. Also, Schlieren and differential interferometry techniques are used to visualize the density gradients within the arc plasma and thermal mantle. Both optical techniques reveal a laminar arc structure for a reservoir pressure of 1 atm at various current levels. Experimentally determined axial static pressure and cold-flow mass flux rate distributions and a channel-flow model with constant arc temperatre are used to solve the energy integral for the arc radius as a function of axial distance. The arc electric field strength, voltage, resistance, and power are determined with Ohm's law and the total heat transfer is related to arc power.

Magnet safety and stability related coolant states: critical fluid dynamics at peak flux

NASA Astrophysics Data System (ADS)

Ravikumar, K. V.; Carandang, R. M.; Frederking, T. H. K.

The stability of superconducting magnets is endangered under certain distinct conditions of the fluid serving as magnet coolant. A severe compromising of safety takes place at the peak heat flux of nucleate boiling. Progress in analysing first order phase transitions for cryoliquids and room temperature liquids, in the presence of heat flow, has led to better understanding of the parameters related to vapour bubble phenomena. The present work addresses the consequences arising from bubble frequency results, including model calculations for the effective masses of the saturated fluids involved in the two-phase transport at the peak flux.

Kinetic Properties of the Neutral Solar Wind

NASA Astrophysics Data System (ADS)

Florinski, V.; Heerikhuisen, J.

2017-03-01

Charge-exchange collisions between the solar wind protons and interstellar hydrogen produce a distinctive population of neutral hydrogen streaming radially at nearly the solar-wind speed. This tenuous population, known as the neutral solar wind (NSW) is thought to play a key role in the appearance of the Interplanetary Boundary EXplorer ribbon, a bright circular band in the sky that is the source of neutral hydrogen with energies near 1 keV. According to the leading model of the ribbon, the velocity distribution of NSW hydrogen is imparted on the pickup ions (PUIs) generated via charge exchange with the interstellar protons beyond the heliopause, and in this way controls the stability of the resulting ring distribution of PUIs against hydromagnetic wave generation. In this paper, we examine the velocity distributions of the NSW atoms in the heliosphere and the outer heliosheath regions by following the phase-space trajectories of the Boltzmann equation. It is demonstrated that these distributions are highly anisotropic, with the parallel (radial) temperature greatly exceeding the perpendicular temperature. Ions picked up near 90° from the anisotropic NSW would form a stable ring distribution capable of generating the ribbon flux. We also discuss a second population of neutrals born in charge transfer collisions with interstellar PUIs, the so-called neutralized pickup ion (NPI) component. Their high thermal velocities translate into large parallel velocity spread of the daughter ribbon PUIs, which would adversely affect plasma stability in local interstellar space.

Three-Dimensional Radiative Hydrodynamics for Disk Stability Simulations: A Proposed Testing Standard and New Results

NASA Astrophysics Data System (ADS)

Boley, Aaron C.; Durisen, Richard H.; Nordlund, Åke; Lord, Jesse

2007-08-01

Recent three-dimensional radiative hydrodynamics simulations of protoplanetary disks report disparate disk behaviors, and these differences involve the importance of convection to disk cooling, the dependence of disk cooling on metallicity, and the stability of disks against fragmentation and clump formation. To guarantee trustworthy results, a radiative physics algorithm must demonstrate the capability to handle both the high and low optical depth regimes. We develop a test suite that can be used to demonstrate an algorithm's ability to relax to known analytic flux and temperature distributions, to follow a contracting slab, and to inhibit or permit convection appropriately. We then show that the radiative algorithm employed by Mejía and Boley et al. and the algorithm employed by Cai et al. pass these tests with reasonable accuracy. In addition, we discuss a new algorithm that couples flux-limited diffusion with vertical rays, we apply the test suite, and we discuss the results of evolving the Boley et al. disk with this new routine. Although the outcome is significantly different in detail with the new algorithm, we obtain the same qualitative answers. Our disk does not cool fast due to convection, and it is stable to fragmentation. We find an effective α~10-2. In addition, transport is dominated by low-order modes.

Measurement and simulation of thermal neutron flux distribution in the RTP core

NASA Astrophysics Data System (ADS)

Rabir, Mohamad Hairie B.; Jalal Bayar, Abi Muttaqin B.; Hamzah, Na'im Syauqi B.; Mustafa, Muhammad Khairul Ariff B.; Karim, Julia Bt. Abdul; Zin, Muhammad Rawi B. Mohamed; Ismail, Yahya B.; Hussain, Mohd Huzair B.; Mat Husin, Mat Zin B.; Dan, Roslan B. Md; Ismail, Ahmad Razali B.; Husain, Nurfazila Bt.; Jalil Khan, Zareen Khan B. Abdul; Yakin, Shaiful Rizaide B. Mohd; Saad, Mohamad Fauzi B.; Masood, Zarina Bt.

2018-01-01

The in-core thermal neutron flux distribution was determined using measurement and simulation methods for the Malaysian’s PUSPATI TRIGA Reactor (RTP). In this work, online thermal neutron flux measurement using Self Powered Neutron Detector (SPND) has been performed to verify and validate the computational methods for neutron flux calculation in RTP calculations. The experimental results were used as a validation to the calculations performed with Monte Carlo code MCNP. The detail in-core neutron flux distributions were estimated using MCNP mesh tally method. The neutron flux mapping obtained revealed the heterogeneous configuration of the core. Based on the measurement and simulation, the thermal flux profile peaked at the centre of the core and gradually decreased towards the outer side of the core. The results show a good agreement (relatively) between calculation and measurement where both show the same radial thermal flux profile inside the core: MCNP model over estimation with maximum discrepancy around 20% higher compared to SPND measurement. As our model also predicts well the neutron flux distribution in the core it can be used for the characterization of the full core, that is neutron flux and spectra calculation, dose rate calculations, reaction rate calculations, etc.

Saturation Length of Erodible Sediment Beds Subject to Shear Flow

NASA Astrophysics Data System (ADS)

Casler, D. M.; Kahn, B. P.; Furbish, D. J.; Schmeeckle, M. W.

2016-12-01

We examine the initial growth and wavelength selection of sand ripples based on probabilistic formulations of the flux and the Exner equation. Current formulations of this problem as a linear stability analysis appeal to the idea of a saturation length-the lag between the bed stress and the flux-as a key stabilizing influence leading to selection of a finite wavelength. We present two contrasting formulations. The first is based on the Fokker-Planck approximation of the divergence form of the Exner equation, and thus involves particle diffusion associated with variations in particle activity, in addition to the conventionally assumed advective term. The role of a saturation length associated with the particle activity is similar to previous analyses. However, particle diffusion provides an attenuating influence on the growth of small wavelengths, independent of a saturation length, and is thus a sufficient, if not necessary, condition contributing to selection of a finite wavelength. The second formulation is based on the entrainment form of the Exner equation. As a precise, probabilistic formulation of conservation, this form of the Exner equation does not distinguish between advection and diffusion, and, because it directly accounts for all particle motions via a convolution of the distribution of particle hop distances, it pays no attention to the idea of a saturation length. The formulation and resulting description of initial ripple growth and wavelength selection thus inherently subsume the effects embodied in the ideas of advection, diffusion, and a saturation length as used in other formulations. Moreover, the formulation does not distinguish between bed load and suspended load, and is thus broader in application. The analysis reveals that the length scales defined by the distribution of hop distances are more fundamental than the saturation length in determining the initial growth or decay of bedforms. Formulations involving the saturation length coincide with the special case of an exponential distribution of hop distance, where the saturation length is equal to the mean hop distance.

Stepwise inference of likely dynamic flux distributions from metabolic time series data.

PubMed

Faraji, Mojdeh; Voit, Eberhard O

2017-07-15

Most metabolic pathways contain more reactions than metabolites and therefore have a wide stoichiometric matrix that corresponds to infinitely many possible flux distributions that are perfectly compatible with the dynamics of the metabolites in a given dataset. This under-determinedness poses a challenge for the quantitative characterization of flux distributions from time series data and thus for the design of adequate, predictive models. Here we propose a method that reduces the degrees of freedom in a stepwise manner and leads to a dynamic flux distribution that is, in a statistical sense, likely to be close to the true distribution. We applied the proposed method to the lignin biosynthesis pathway in switchgrass. The system consists of 16 metabolites and 23 enzymatic reactions. It has seven degrees of freedom and therefore admits a large space of dynamic flux distributions that all fit a set of metabolic time series data equally well. The proposed method reduces this space in a systematic and biologically reasonable manner and converges to a likely dynamic flux distribution in just a few iterations. The estimated solution and the true flux distribution, which is known in this case, show excellent agreement and thereby lend support to the method. The computational model was implemented in MATLAB (version R2014a, The MathWorks, Natick, MA). The source code is available at https://github.gatech.edu/VoitLab/Stepwise-Inference-of-Likely-Dynamic-Flux-Distributions and www.bst.bme.gatech.edu/research.php . mojdeh@gatech.edu or eberhard.voit@bme.gatech.edu. Supplementary data are available at Bioinformatics online. © The Author (2017). Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com

On the relationship between finger width, velocity, and fluxes in thermohaline convection

NASA Astrophysics Data System (ADS)

Sreenivas, K. R.; Singh, O. P.; Srinivasan, J.

2009-02-01

Double-diffusive finger convection occurs in many natural processes. The theories for double-diffusive phenomena that exist at present consider systems with linear stratification in temperature and salinity. The double-diffusive systems with step change in salinity and temperature are, however, not amenable to simple stability analysis. Hence factors that control the width of the finger, velocity, and fluxes in systems that have step change in temperature and salinity have not been understood so far. In this paper we provide new physical insight regarding factors that influence finger convection in two-layer double-diffusive system through two-dimensional numerical simulations. Simulations have been carried out for density stability ratios (Rρ) from 1.5 to 10. For each density stability ratio, the thermal Rayleigh number (RaT) has been systematically varied from 7×103 to 7×108. Results from these simulations show how finger width, velocity, and flux ratios in finger convection are interrelated and the influence of governing parameters such as density stability ratio and the thermal Rayleigh number. The width of the incipient fingers at the time of onset of instability has been shown to vary as RaT-1/3. Velocity in the finger varies as RaT1/3/Rρ. Results from simulation agree with the scale analysis presented in the paper. Our results demonstrate that wide fingers have lower velocities and flux ratios compared to those in narrow fingers. This result contradicts present notions about the relation between finger width and flux ratio. A counterflow heat-exchanger analogy is used in understanding the dependence of flux ratio on finger width and velocity.

BSRs Elevated by Fluid Upwelling on the Upper Amazon Fan : Bottom-up Controls on Gas Hydrate Stability

NASA Astrophysics Data System (ADS)

Praeg, D.; Silva, C. G.; dos Reis, A. T.; Ketzer, J. M.; Unnithan, V.; Perovano Da Silva, R. J.; Cruz, A. M.; Gorini, C.

2017-12-01

The stability of natural gas hydrate accumulations on continental margins has mainly been considered in terms of changes in seawater pressures and temperatures driven from above by climate. We present evidence from the Amazon deep-sea fan for stability zone changes driven from below by fluid upwelling. A grid of 2D and 3D multichannel seismic data show the upper Amazon fan in water depths of 1200-2000 m to contain a discontinuous bottom-simulating seismic reflection (BSR) that forms `patches' 10-50 km wide and up to 140 km long, over a total area of at least 5000 km2. The elongate BSR patches coincide with anticlinal thrust-folds that record on-going gravitational collapse of the fan above décollements at depths of up to 10 km. The BSR lies within 100-300 m of seafloor, in places rising beneath features that seafloor imagery show to be pockmarks and mud volcanoes, some venting gas to the water column. The BSR patches are up to 500 m shallower than predicted for methane hydrate based on geothermal gradients as low as 17˚C/km measured within the upper fan, and inversion of the BSR to obtain temperatures at the phase boundary indicates gradients 2-5 times background levels. We interpret the strongly elevated BSR patches to record upwelling of warm gas-rich fluids through thrust-fault zones 101 km wide. We infer this process to favour gas hydrate occurrences that are concentrated in proportion to flux and locally pierced by vents, and that will be sensitive to temporal variations in the upward flux of heat and gas. Thus episodes of increased flux, e.g. during thrusting, could dissociate gas hydrates to trigger slope failures and/or enhanced gas venting to the ocean. Structurally-driven fluid flow episodes could account for evidence of recurrent large-scale failures from the compressive belt on the upper fan during its Neogene collapse, and provide a long-term alternative to sea level triggering. The proposed mechanism of upward flux links the distribution and stability of gas hydrate occurrences (and gas vents) to the internal dynamics of deep-sea depocentres, in all water depths that structural pathways for fluid migration may form. Gravitational collapse is increasingly recognized to affect passive continental margins, and our findings challenge global models of hydrate inventory over time based solely on in situ methanogenesis.

High time resolution characteristics of intermediate ion distributions upstream of the earth's bow shock

NASA Technical Reports Server (NTRS)

Potter, D. W.

1985-01-01

High time resolution particle data upstream of the bow shock during time intervals that have been identified as having intermediate ion distributions often show high amplitude oscillations in the ion fluxes of energy 2 and 6 keV. These ion oscillations, observed with the particle instruments of the University of California, Berkeley, on the ISEE 1 and 2 spacecraft, are at the same frequency (about 0.04 Hz) as the magnetic field oscillations. Typically, the 6-keV ion flux increases then the 2-keV flux increases followed by a decrease in the 2-keV flux and then the 6-keV flux decreases. This process repeats many times. Although there is no entirely satisfactory explanation, the presence of these ion flux oscillations suggests that distributions often are misidentified as intermediate ion distributions.

Non-equilibrium physics of neural networks for leaning, memory and decision making: landscape and flux perspectives

NASA Astrophysics Data System (ADS)

Wang, Jin

Cognitive behaviors are determined by underlying neural networks. Many brain functions, such as learning and memory, can be described by attractor dynamics. We developed a theoretical framework for global dynamics by quantifying the landscape associated with the steady state probability distributions and steady state curl flux, measuring the degree of non-equilibrium through detailed balance breaking. We found the dynamics and oscillations in human brains responsible for cognitive processes and physiological rhythm regulations are determined not only by the landscape gradient but also by the flux. We found that the flux is closely related to the degrees of the asymmetric connections in neural networks and is the origin of the neural oscillations. The neural oscillation landscape shows a closed-ring attractor topology. The landscape gradient attracts the network down to the ring. The flux is responsible for coherent oscillations on the ring. We suggest the flux may provide the driving force for associations among memories. Both landscape and flux determine the kinetic paths and speed of decision making. The kinetics and global stability of decision making are explored by quantifying the landscape topography through the barrier heights and the mean first passage time. The theoretical predictions are in agreement with experimental observations: more errors occur under time pressure. We quantitatively explored two mechanisms of the speed-accuracy tradeoff with speed emphasis and further uncovered the tradeoffs among speed, accuracy, and energy cost. Our results show an optimal balance among speed, accuracy, and the energy cost in decision making. We uncovered possible mechanisms of changes of mind and how mind changes improve performance in decision processes. Our landscape approach can help facilitate an understanding of the underlying physical mechanisms of cognitive processes and identify the key elements in neural networks.

Enthalpy Distributions of Arc Jet Flow Based on Measured Laser Induced Fluorescence, Heat Flux and Stagnation Pressure Distributions

NASA Technical Reports Server (NTRS)

Suess, Leonard E.; Milhoan, James D.; Oelke, Lance; Godfrey, Dennis; Larin, Maksim Y.; Scott, Carl D.; Grinstead, Jay H.; DelPapa, Steven

2011-01-01

The centerline total enthalpy of arc jet flow is determined using laser induced fluorescence of oxygen and nitrogen atoms. Each component of the energy, kinetic, thermal, and chemical can be determined from LIF measurements. Additionally, enthalpy distributions are inferred from heat flux and pressure probe distribution measurements using an engineering formula. Average enthalpies are determined by integration over the radius of the jet flow, assuming constant mass flux and a mass flux distribution estimated from computational fluid dynamics calculations at similar arc jet conditions. The trends show favorable agreement, but there is an uncertainty that relates to the multiple individual measurements and assumptions inherent in LIF measurements.

Electrical transport property, thermal stability and oxidation resistance of single crystalline β-Zn4Sb3 prepared using the Bi-Sn mixed-flux method

NASA Astrophysics Data System (ADS)

Deng, Shuping; Li, Decong; Chen, Zhong; Tang, Yu; Shen, Lanxian; Deng, Shukang

2017-12-01

Single crystal samples β-Zn4Sb3 have been prepared by using Bi-Sn mixed-flux method. The obtained crystals exhibit p-type conduction behavior with carrier concentration varying from 4.40 × 1019 to 18.12 × 1019 cm-3 as carrier mobility changes from 25.8 to 61.5 cm2 V-1 s-1 at room temperature. Electrical transport properties of the samples were optimized by Bi-Sn co-doped, which brought by Bi-Sn mixed-flux. And the maximal power factor of 1.45 × 10-3 W m-1 K-2 is achieved at 510 K for the sample with Bi flux content x = 0.5. Consequently, the oxidation resistance of the sample was determined by exploring the effects of heat treatment in air on electrical transport properties and thermal stability, which the single crystalline β-Zn4Sb3 still possess an excellent oxidation resistance and thermal stability after the heat treatment process.

Using a spatially-distributed hydrologic biogeochemistry model with nitrogen transport to study the spatial variation of carbon stocks and fluxes in a Critical Zone Observatory

NASA Astrophysics Data System (ADS)

Shi, Y.; Eissenstat, D. M.; He, Y.; Davis, K. J.

2017-12-01

Most current biogeochemical models are 1-D and represent one point in space. Therefore, they cannot resolve topographically driven land surface heterogeneity (e.g., lateral water flow, soil moisture, soil temperature, solar radiation) or the spatial pattern of nutrient availability. A spatially distributed forest biogeochemical model with nitrogen transport, Flux-PIHM-BGC, has been developed by coupling a 1-D mechanistic biogeochemical model Biome-BGC (BBGC) with a spatially distributed land surface hydrologic model, Flux-PIHM, and adding an advection dominated nitrogen transport module. Flux-PIHM is a coupled physically based model, which incorporates a land-surface scheme into the Penn State Integrated Hydrologic Model (PIHM). The land surface scheme is adapted from the Noah land surface model, and is augmented by adding a topographic solar radiation module. Flux-PIHM is able to represent the link between groundwater and the surface energy balance, as well as land surface heterogeneities caused by topography. In the coupled Flux-PIHM-BGC model, each Flux-PIHM model grid couples a 1-D BBGC model, while nitrogen is transported among model grids via surface and subsurface water flow. In each grid, Flux-PIHM provides BBGC with soil moisture, soil temperature, and solar radiation, while BBGC provides Flux-PIHM with spatially-distributed leaf area index. The coupled Flux-PIHM-BGC model has been implemented at the Susquehanna/Shale Hills Critical Zone Observatory. The model-predicted aboveground vegetation carbon and soil carbon distributions generally agree with the macro patterns observed within the watershed. The importance of abiotic variables (including soil moisture, soil temperature, solar radiation, and soil mineral nitrogen) in predicting aboveground carbon distribution is calculated using a random forest. The result suggests that the spatial pattern of aboveground carbon is controlled by the distribution of soil mineral nitrogen. A Flux-PIHM-BGC simulation without the nitrogen transport module is also executed. The model without nitrogen transport fails in predicting the spatial patterns of vegetation carbon, which indicates the importance of having a nitrogen transport module in spatially distributed ecohydrologic modeling.

Spectral unfolding of fast neutron energy distributions

NASA Astrophysics Data System (ADS)

Mosby, Michelle; Jackman, Kevin; Engle, Jonathan

2015-10-01

The characterization of the energy distribution of a neutron flux is difficult in experiments with constrained geometry where techniques such as time of flight cannot be used to resolve the distribution. The measurement of neutron fluxes in reactors, which often present similar challenges, has been accomplished using radioactivation foils as an indirect probe. Spectral unfolding codes use statistical methods to adjust MCNP predictions of neutron energy distributions using quantified radioactive residuals produced in these foils. We have applied a modification of this established neutron flux characterization technique to experimentally characterize the neutron flux in the critical assemblies at the Nevada National Security Site (NNSS) and the spallation neutron flux at the Isotope Production Facility (IPF) at Los Alamos National Laboratory (LANL). Results of the unfolding procedure are presented and compared with a priori MCNP predictions, and the implications for measurements using the neutron fluxes at these facilities are discussed.

Multi-year Estimates of Methane Fluxes in Alaska from an Atmospheric Inverse Model

NASA Astrophysics Data System (ADS)

Miller, S. M.; Commane, R.; Chang, R. Y. W.; Miller, C. E.; Michalak, A. M.; Dinardo, S. J.; Dlugokencky, E. J.; Hartery, S.; Karion, A.; Lindaas, J.; Sweeney, C.; Wofsy, S. C.

2015-12-01

We estimate methane fluxes across Alaska over a multi-year period using observations from a three-year aircraft campaign, the Carbon Arctic Reservoirs Vulnerability Experiment (CARVE). Existing estimates of methane from Alaska and other Arctic regions disagree in both magnitude and distribution, and before the CARVE campaign, atmospheric observations in the region were sparse. We combine these observations with an atmospheric particle trajectory model and a geostatistical inversion to estimate surface fluxes at the model grid scale. We first use this framework to estimate the spatial distribution of methane fluxes across the state. We find the largest fluxes in the south-east and North Slope regions of Alaska. This distribution is consistent with several estimates of wetland extent but contrasts with the distribution in most existing flux models. These flux models concentrate methane in warmer or more southerly regions of Alaska compared to the estimate presented here. This result suggests a discrepancy in how existing bottom-up models translate wetland area into methane fluxes across the state. We next use the inversion framework to explore inter-annual variability in regional-scale methane fluxes for 2012-2014. We examine the extent to which this variability correlates with weather or other environmental conditions. These results indicate the possible sensitivity of wetland fluxes to near-term variability in climate.

Disparity between online and offline tests in accelerated aging tests of LED lamps under electric stress.

PubMed

Wang, Yao; Jing, Lei; Ke, Hong-Liang; Hao, Jian; Gao, Qun; Wang, Xiao-Xun; Sun, Qiang; Xu, Zhi-Jun

2016-09-20

The accelerated aging tests under electric stress for one type of LED lamp are conducted, and the differences between online and offline tests of the degradation of luminous flux are studied in this paper. The transformation of the two test modes is achieved with an adjustable AC voltage stabilized power source. Experimental results show that the exponential fitting of the luminous flux degradation in online tests possesses a higher fitting degree for most lamps, and the degradation rate of the luminous flux by online tests is always lower than that by offline tests. Bayes estimation and Weibull distribution are used to calculate the failure probabilities under the accelerated voltages, and then the reliability of the lamps under rated voltage of 220 V is estimated by use of the inverse power law model. Results show that the relative error of the lifetime estimation by offline tests increases as the failure probability decreases, and it cannot be neglected when the failure probability is less than 1%. The relative errors of lifetime estimation are 7.9%, 5.8%, 4.2%, and 3.5%, at the failure probabilities of 0.1%, 1%, 5%, and 10%, respectively.

Using isotopes to quantify evaporation and non-stationary transit times distributions in lake water budgets

NASA Astrophysics Data System (ADS)

Smith, A. A.; Tetzlaff, D.; Soulsby, C.

2017-12-01

Evaporative fluxes from northern lakes are essential components of catchment water balances, providing large supplies of water to the atmosphere, and affecting downstream water availability. However, measurement of lake evaporation is difficult in many catchments due to remoteness and inaccessibility. Evaporative flux may also influence mean transit times of lakes and catchments, identified through water- and tracer mass-balance. We combined stable water isotopes (δ2H and δ18O), transit, and residence time distributions in a non-stationary transit time model to estimate the evaporative flux from two lakes in the Scottish Highlands. The lakes were in close proximity to each other ( 2km), shallow (mean depth, 1.5 m) with one large (0.88km2) and one small (0.4km2). Model calibration used measurements of precipitation, air temperature, water level, and isotopic stream compositions of lake inflow and outflows. Evaporation flux was identified using lake fractionation of δ2H and δ18O. Mixing patterns of the lakes and their respective outlet isotopic compositions were accounted for by comparing three probability distributions for discharge and evaporation. We found that the evaporation flux was strongly influenced by these discharge and evaporation distributions. Decreased mixing within the lake resulted in greater evaporation fluxes. One of the three distributions yielded similar mean daily evaporation and uncertainty for both lakes (max 5mm/day), while evaporation using the other two distributions was inconsistent between the lakes. Importantly, our approach also estimated distributions of evaporation age, which were significantly different between the lakes, reflecting a combination of inflow stream magnitude and the mixing regimes. The mean evaporation flux age of the large lake was 160 days, and 14 days for the small lake. Our integrated approach of stable isotopes, time variant transit time distributions has shown to be a useful tool for quantifying evaporative fluxes and closing the water balance, while simultaneously providing useful transit times of fluxes for lake dominated catchments.

Measurement of cosmic muon angular distribution and vertical integrated flux by 2 m × 2 m RPC stack at IICHEP-Madurai

NASA Astrophysics Data System (ADS)

Pethuraj, S.; Datar, V. M.; Majumder, G.; Mondal, N. K.; Ravindran, K. C.; Satyanarayana, B.

2017-09-01

The 50 kton INO-ICAL is a proposed underground high energy physics experiment at Theni, India (9o57'N, 77o16'E) to study the neutrino oscillation parameters using atmospheric neutrinos. The Resistive Plate Chamber (RPC) has been chosen as the active detector element for the ICAL detector. An experimental setup consisting of 12 layers of glass RPCs of size 2 m × 2 m has been built at IICHEP, Madurai to study the long term stability and performance of RPCs which are produced on a large scale in Indian industry. In this paper, the studies on the performance of RPCs are presented along with the angular distribution of muons at Madurai (9o56'N,78o00'E and Altitude ≈ 160 m from sea level).

A scaling theory for number-flux distributions generated during steady-state coagulation and settling and application to particles in Lake Zurich, Switzerland.

PubMed

Boehm, Alexandria B

2002-10-15

In this study, we extend the established scaling theory for cluster size distributions generated during unsteady coagulation to number-flux distributions that arise during steady-state coagulation and settling in an unmixed water mass. The scaling theory predicts self-similar number-flux distributions and power-law decay of total number flux with depth. The shape of the number-flux distributions and the power-law exponent describing the decay of the total number flux are shown to depend on the homogeneity and small i/j limit of the coagulation kernel and the exponent kappa, which describes the variation in settling velocity with cluster volume. Particle field measurements from Lake Zurich, collected by U. Weilenmann and co-workers (Limnol. Oceanogr.34, 1 (1989)), are used to illustrate how the scaling predictions can be applied to a natural system. This effort indicates that within the mid-depth region of Lake Zurich, clusters of the same size preferentially interact and large clusters react with one another more quickly than small ones, indicative of clusters coagulating in a reaction-limited regime.

Turbulent flow and scalar transport in a large wind farm

NASA Astrophysics Data System (ADS)

Porte-Agel, F.; Markfort, C. D.; Zhang, W.

2012-12-01

Wind energy is one of the fastest growing sources of renewable energy world-wide, and it is expected that many more large-scale wind farms will be built and cover a significant portion of land and ocean surfaces. By extracting kinetic energy from the atmospheric boundary layer and converting it to electricity, wind farms may affect the transport of momentum, heat, moisture and trace gases (e.g. CO_2) between the atmosphere and the land surface locally and globally. Understanding wind farm-atmosphere interaction is complicated by the effects of turbine array configuration, wind farm size, land-surface characteristics, and atmospheric thermal stability. A wind farm of finite length may be modeled as an added roughness or as a canopy in large-scale weather and climate models. However, it is not clear which analogy is physically more appropriate. Also, surface scalar flux is affected by wind farms and needs to be properly parameterized in meso-scale and/or high-resolution numerical models. Experiments involving model wind farms, with perfectly aligned and staggered configurations, having the same turbine distribution density, were conducted in a thermally-controlled boundary-layer wind tunnel. A neutrally stratified turbulent boundary layer was developed with a surface heat source. Measurements of the turbulent flow and fluxes over and through the wind farm were made using a custom x-wire/cold-wire anemometer; and surface scalar flux was measured with an array of surface-mounted heat flux sensors far within the quasi-developed region of the wind-farm. The turbulence statistics exhibit similar properties to those of canopy-type flows, but retain some characteristics of surface-layer flows in a limited region above the wind farms as well. The flow equilibrates faster and the overall momentum absorption is higher for the staggered compared to the aligned farm, which is consistent with canopy scaling and leads to a larger effective roughness. Although the overall surface heat flux change produced by the wind farms is found to be small, with a net reduction of 4% for the staggered wind farm and nearly zero change for the aligned wind farm, the highly heterogeneous spatial distribution of the surface heat flux, dependent on wind farm layout, is significant. This comprehensive first wind-tunnel dataset on turbulent flow and scalar transport in wind farms will be further used to develop and validate new parameterizations of surface fluxes in numerical models.

Characterization of Deuteron-Deuteron Neutron Generators

NASA Astrophysics Data System (ADS)

Waltz, Cory Scott

A facility based on a next-generation, high-flux D-D neutron generator (HFNG) was commissioned at the University of California Berkeley. The characterization of the HFNG is presented in the following study. The current generator design produces near mono-energetic 2.45 MeV neutrons at outputs of 108 n/s. Calculations provided show that future conditioning at higher currents and voltages will allow for a production rate over 1010 n/s. Characteristics that effect the operational stability include the suppression of the target-emitted back streaming electrons, target sputtering and cooling, and ion beam optics. Suppression of secondary electrons resulting from the deuterium beam striking the target was achieved via the implementation of an electrostatic shroud with a voltage offset of greater than -400 V relative to the target. Ion beam optics analysis resulted in the creation of a defocussing extraction nozzle, allowing for cooler target temperatures and a more compact design. To calculate the target temperatures, a finite difference method (FDM) solver incorporating the additional heat removal effects of subcooled boiling was developed. Validation of the energy balance results from the finite difference method calculations showed the iterative solver converged to heat removal results within about 3% of the expected value. Testing of the extraction nozzle at 1.43 mA and 100 kV determined that overheating of the target did not occur as the measured neutron flux of the generator was near predicted values. Many factors, including the target stopping power, deuterium atomic species, and target loading ratio, affect the flux distribution of the HFNG neutron generator. A detailed analysis to understand these factors effects is presented. Comparison of the calculated flux of the neutron generator using deuteron depth implantation data, neutron flux distribution data, and deuterium atomic species data matched the experimentally calculated flux determined from indium foil irradiations. An overview of experiments using the HFNG, including medical isotope cross section measurements, geochronology, delayed gamma measurements from uranium fission, and single event upset of cpu's is discussed. Future work should focus on the reduction of beam induced arcing between the shroud and the vacuum chamber. Investigation of insulator charge build-up, as well as electrical ash-over of insulators should be explored. The reduction of beam induced arcing will allow for larger beam currents and acceleration voltages, therefore increasing the neutron flux.

Effects of Geostrophic Kinetic Energy on the Distribution of Mesopelagic Fish Larvae in the Southern Gulf of California in Summer/Fall Stratified Seasons.

PubMed

Contreras-Catala, Fernando; Sánchez-Velasco, Laura; Beier, Emilio; Godínez, Victor M; Barton, Eric D; Santamaría-Del-Angel, Eduardo

2016-01-01

Effects of geostrophic kinetic energy flux on the three-dimensional distribution of fish larvae of mesopelagic species (Vinciguerria lucetia, Diogenichthys laternatus, Benthosema panamense and Triphoturus mexicanus) in the southern Gulf of California during summer and fall seasons of stronger stratification were analyzed. The greatest larval abundance was found at sampling stations in geostrophic kinetic energy-poor areas (<7.5 J/m3), where the distribution of the dominant species tended to be stratified. Larvae of V. lucetia (average abundance of 318 larvae/10m2) and B. panamense (174 larvae/10m2) were mostly located in and above the pycnocline (typically ~ 40 m depth). In contrast, larvae of D. laternatus (60 larvae/10m2) were mainly located in and below the pycnocline. On the other hand, in sampling stations from geostrophic kinetic energy-rich areas (> 21 J/m3), where mesoscale eddies were present, the larvae of the dominant species had low abundance and were spread more evenly through the water column, in spite of the water column stratification. For example, in a cyclonic eddy, V. lucetia larvae (34 larvae/10m2) extended their distribution to, at least, the limit of sampling 200 m depth below the pycnocline, while D. laternatus larvae (29 larvae/10m2) were found right up to the surface, both probably as a consequence mixing and secondary circulation in the eddy. Results showed that the level of the geostrophic kinetic energy flux affects the abundance and the three-dimensional distribution of mesopelagic fish larvae during the seasons of stronger stratification, indicating that areas with low geostrophic kinetic energy may be advantageous for feeding and development of mesopelagic fish larvae because of greater water column stability.

Effects of Geostrophic Kinetic Energy on the Distribution of Mesopelagic Fish Larvae in the Southern Gulf of California in Summer/Fall Stratified Seasons

PubMed Central

Contreras-Catala, Fernando; Beier, Emilio; Godínez, Victor M.; Barton, Eric D.; Santamaría-del-Angel, Eduardo

2016-01-01

Effects of geostrophic kinetic energy flux on the three-dimensional distribution of fish larvae of mesopelagic species (Vinciguerria lucetia, Diogenichthys laternatus, Benthosema panamense and Triphoturus mexicanus) in the southern Gulf of California during summer and fall seasons of stronger stratification were analyzed. The greatest larval abundance was found at sampling stations in geostrophic kinetic energy-poor areas (<7.5 J/m3), where the distribution of the dominant species tended to be stratified. Larvae of V. lucetia (average abundance of 318 larvae/10m2) and B. panamense (174 larvae/10m2) were mostly located in and above the pycnocline (typically ~ 40 m depth). In contrast, larvae of D. laternatus (60 larvae/10m2) were mainly located in and below the pycnocline. On the other hand, in sampling stations from geostrophic kinetic energy-rich areas (> 21 J/m3), where mesoscale eddies were present, the larvae of the dominant species had low abundance and were spread more evenly through the water column, in spite of the water column stratification. For example, in a cyclonic eddy, V. lucetia larvae (34 larvae/10m2) extended their distribution to, at least, the limit of sampling 200 m depth below the pycnocline, while D. laternatus larvae (29 larvae/10m2) were found right up to the surface, both probably as a consequence mixing and secondary circulation in the eddy. Results showed that the level of the geostrophic kinetic energy flux affects the abundance and the three-dimensional distribution of mesopelagic fish larvae during the seasons of stronger stratification, indicating that areas with low geostrophic kinetic energy may be advantageous for feeding and development of mesopelagic fish larvae because of greater water column stability. PMID:27760185

Are There Different Populations of Flux Ropes in the Solar Wind?

NASA Astrophysics Data System (ADS)

Janvier, M.; Démoulin, P.; Dasso, S.

2014-07-01

Flux ropes are twisted magnetic structures that can be detected by in-situ measurements in the solar wind. However, different properties of detected flux ropes suggest different types of flux-rope populations. As such, are there different populations of flux ropes? The answer is positive and is the result of the analysis of four lists of flux ropes, including magnetic clouds (MCs), observed at 1 AU. The in-situ data for the four lists were fitted with the same cylindrical force-free field model, which provides an estimate of the local flux-rope parameters such as its radius and orientation. Since the flux-rope distributions have a broad dynamic range, we went beyond a simple histogram analysis by developing a partition technique that uniformly distributes the statistical fluctuations across the radius range. By doing so, we found that small flux ropes with radius R<0.1 AU have a steep power-law distribution in contrast to the larger flux ropes (identified as MCs), which have a Gaussian-like distribution. Next, from four CME catalogs, we estimated the expected flux-rope frequency per year at 1 AU. We found that the predicted numbers are similar to the frequencies of MCs observed in-situ. However, we also found that small flux ropes are at least ten times too abundant to correspond to CMEs, even to narrow ones. Investigating the different possible scenarios for the origin of these small flux ropes, we conclude that these twisted structures can be formed by blowout jets in the low corona or in coronal streamers.

On the Consequences of Clausius-Duhem Inequality for Electrolyte Solutions

NASA Astrophysics Data System (ADS)

Reis, Martina; Bassi, Adalberto Bono Maurizio Sacchi

2014-03-01

Based on the fundamentals of thermo-statics, non-equilibrium thermodynamics theories frequently employ an entropy inequality, where the entropy flux is collinear to the heat flux, and the entropy supply is proportional to the energy supply. Although this assumption is suitable for many material bodies, e.g. heat-conducting viscous fluids, there is a class of materials for which these assumptions are not valid. By assuming that the entropy flux and the entropy supply are constitutive quantities, in this work it is demonstrated that the entropy flux for a reacting ionic mixture of non-volatile solutes presents a non-collinear term due to the diffusive fluxes. The consequences of the collinearity between the entropy flux and the heat flux, as well as the proportionality of the entropy supply and the energy supply on the stability of chemical systems are also investigated. Furthermore, by considering an electrolyte solution of non-volatile solutes in phase equilibrium with water vapor, and the constitutive nature of the entropy flux, the stability of a vapor-electrolyte solution interface is studied. Despite this work only deals with electrolyte solutions, the results presented can be easily extended to more complex chemical reacting systems. The first author acknowledges financial support from CNPq (National Counsel of Technological and Scientific Development).

The flow structure of jets from transient sources and implications for modeling short-duration explosive volcanic eruptions

NASA Astrophysics Data System (ADS)

Chojnicki, K. N.; Clarke, A. B.; Adrian, R. J.; Phillips, J. C.

2014-12-01

We used laboratory experiments to examine the rise process in neutrally buoyant jets that resulted from an unsteady supply of momentum, a condition that defines plumes from discrete Vulcanian and Strombolian-style eruptions. We simultaneously measured the analog-jet discharge rate (the supply rate of momentum) and the analog-jet internal velocity distribution (a consequence of momentum transport and dilution). Then, we examined the changes in the analog-jet velocity distribution over time to assess the impact of the supply-rate variations on the momentum-driven rise dynamics. We found that the analog-jet velocity distribution changes significantly and quickly as the supply rate varied, such that the whole-field distribution at any instant differed considerably from the time average. We also found that entrainment varied in space and over time with instantaneous entrainment coefficient values ranging from 0 to 0.93 in an individual unsteady jet. Consequently, we conclude that supply-rate variations exert first-order control over jet dynamics, and therefore cannot be neglected in models without compromising their capability to predict large-scale eruption behavior. These findings emphasize the fundamental differences between unsteady and steady jet dynamics, and show clearly that: (i) variations in source momentum flux directly control the dynamics of the resulting flow; (ii) impulsive flows driven by sources of varying flux cannot reasonably be approximated by quasi-steady flow models. New modeling approaches capable of describing the time-dependent properties of transient volcanic eruption plumes are needed before their trajectory, dilution, and stability can be reliably computed for hazards management.

An extended lattice model accounting for traffic jerk

NASA Astrophysics Data System (ADS)

Redhu, Poonam; Siwach, Vikash

2018-02-01

In this paper, a flux difference lattice hydrodynamics model is extended by considering the traffic jerk effect which comes due to vehicular motion of non-motor automobiles. The effect of traffic jerk has been examined through linear stability analysis and shown that it can significantly enlarge the unstable region on the phase diagram. To describe the phase transition of traffic flow, mKdV equation near the critical point is derived through nonlinear stability analysis. The theoretical findings have been verified using numerical simulation which confirms that the jerk parameter plays an important role in stabilizing the traffic jam efficiently in sensing the flux difference of leading sites.

Large dimensions and small curvatures from supersymmetric brane back-reaction

NASA Astrophysics Data System (ADS)

Burgess, C. P.; van Nierop, L.

2011-04-01

We compute the back-reaction of pairs of codimension-two branes within an explicit flux-stabilized compactification, to trace how its properties depend on the parameters that define the brane-bulk couplings. Both brane tension and magnetic couplings to the stabilizing flux play an important role in the resulting dynamics, with the magnetic coupling allowing some of the flux to be localized on the branes (thus changing the flux-quantization conditions). We find that back-reaction lifts the classical flat directions of the bulk supergravity, and we calculate both the scalar potential and changes to the extra-dimensional and on-brane geometries that result, as functions of the assumed brane couplings. When linearized about simple rugby-ball geometries the resulting solutions allow a systematic exploration of the system's response. Several of the systems we explore have remarkable properties. Among these are a propensity for the extra dimensions to stabilize at exponentially large sizes, providing a mechanism for generating extremely large volumes. In some circumstances the brane-dilaton coupling allows the bulk dilaton to adjust to suppress the on-brane curvature parametrically below the change in brane tension, potentially providing a mechanism for reducing the vacuum energy. We explore the stability of this suppression to quantum effects in the case where their strength is controlled by the value of the field along the classical flat direction, and find it can (but need not) be stable.

`Surface-Layer' momentum fluxes in nocturnal slope flows over steep terrain

NASA Astrophysics Data System (ADS)

Oldroyd, H. J.; Pardyjak, E.; Higgins, C. W.; Parlange, M. B.

2017-12-01

A common working definition for the `surface layer' is the lowest 10% of the atmospheric boundary layer (ABL) where the turbulent fluxes are essentially constant. The latter part of this definition is a critical assumption that must hold for accurate flux estimations from land-surface models, wall models, similarity theory, flux-gradient relations and bulk transfer methods. We present cases from observed momentum fluxes in nocturnal slope flows over steep (35.5 degree), alpine terrain in Val Ferret, Switzerland that satisfy the classical definitions of the surface layer and other cases where no traditional surface layer is observed. These cases broadly fall into two distinct flow regimes occurring under clear-sky conditions: (1) buoyancy-driven, `katabatic flow', characterized by an elevated velocity maximum (katabatic jet peak) and (2) `downslope winds', for which larger-scale forcing prevents formation of a katabatic jet. Velocity profiles in downslope wind cases are quite similar to logarithmic profiles typically observed over horizontal and homogeneous terrain, and the corresponding momentum fluxes roughly resemble a constant-flux surface-layer. Contrastingly, velocity profiles in the katabatic regime exhibit a jet-like shape. This jet strongly modulates the corresponding momentum fluxes, which exhibit strong gradients over the shallow katabatic layer and usually change sign near the jet peak, where the velocity gradients also change sign. However, a counter-gradient momentum flux is frequently observed near the jet peak (and sometimes at higher levels), suggesting strong non-local turbulent transport within the katabatic jet layer. We compare our observations with katabatic flow theories and observational studies over shallow-angle slopes and use co-spectral analyses to better identify and understand the non-local transport dynamics. Finally, we show that because of the counter-gradient momentum fluxes, surface layer stability and even local stability can be difficult to characterize because the counter-gradient momentum flux represents a sink in the shear term of turbulence kinetic energy budget equation. These results have broad implications for stability-based modeling and general definitions and assumptions used for the ABL and so-called `surface layer' over steep terrain.

The role of large-scale eddies in the climate equilibrium. Part 2: Variable static stability

NASA Technical Reports Server (NTRS)

Zhou, Shuntai; Stone, Peter H.

1993-01-01

Lorenz's two-level model on a sphere is used to investigate how the results of Part 1 are modified when the interaction of the vertical eddy heat flux and static stability is included. In general, the climate state does not depend very much on whether or not this interaction is included, because the poleward eddy heat transport dominates the eddy forcing of mean temperature and wind fields. However, the climatic sensitivity is significantly affected. Compared to two-level model results with fixed static stability, the poleward eddy heat flux is less sensitive to the meridional temperature gradient and the gradient is more sensitive to the forcing. For example, the logarithmic derivative of the eddy flux with respect to the gradient has a slope that is reduced from approximately 15 on a beta-plane with fixed static stability and approximately 6 on a sphere with fixed static stability, to approximately 3 to 4 in the present model. This last result is more in line with analyses from observations. The present model also has a stronger baroclinic adjustment than that in Part 1, more like that in two-level beta-plane models with fixed static stability, that is, the midlatitude isentropic slope is very insensitive to the forcing, the diabatic heating, and the friction, unless the forcing is very weak.

An experimental study of air-assist atomizer spray flames

NASA Technical Reports Server (NTRS)

Mao, Chien-Pei; Wang, Geng; Chigier, Norman

1988-01-01

It is noted that air-assisted atomizer spray flames encountered in furnaces, boilers, and gas turbine combustors possess a more complex structure than homogeneous turbulent diffusion flames, due to the swirling motion introduced into the fuel and air flows for the control of flame stability, length, combustion intensity, and efficiency. Detailed comparisons are presented between burning and nonburning condition measurements of these flames obtained by nonintrusive light scattering phase/Doppler detection. Spray structure is found to be drastically changed within the flame reaction zone, with changes in the magnitude and shape of drop number density, liquid flux, mean drop size diameter, and drop mean axial velocity radial distributions.

Effects of mantle rheologies on viscous heating induced by Glacial Isostatic Adjustment

NASA Astrophysics Data System (ADS)

Huang, PingPing; Wu, Patrick; van der Wal, Wouter

2018-04-01

It has been argued that viscous dissipation from mantle flow in response to surface loading during glacial cycles can result in short-term heating and thus trigger transient volcanism or changes in mantle properties, which may in turn affect mantle dynamics. Furthermore, heating near the Earth's surface can also affect the stability of ice sheets. We have studied the magnitude and spatial-temporal distribution of viscous heating induced in the mantle by the realistic ice model ICE-6G and gravitationally consistent ocean loads. Three types of mantle rheologies, including linear, non-linear and composite rheologies are considered to see if non-linear creep can induce larger viscous heating than linear rheology. We used the Coupled-Laplace-Finite-Element model of Glacial Isostatic Adjustment (GIA) to compute the strain, stress and shear heating during a glacial cycle. We also investigated the upper bound of temperature change and surface heat flux change due to viscous heating. We found that maximum viscous heating occurs near the end of deglaciation near the edge of the ice sheet with amplitude as high as 120 times larger than that of the chondritic radioactive heating. The maximum heat flux due to viscous heating can reach 30 mW m-2, but the area with large heat flux is small and the timescale of heating is short. As a result, the upper bound of temperature change due to viscous heating is small. Even if 30 glacial cycles are included, the largest temperature change can be of the order of 0.3 °C. Thus, viscous heating induced by GIA cannot induce volcanism and cannot significantly affect mantle material properties, mantle dynamics nor ice-sheet stability.

Surface flux density distribution characteristics of bulk high- Tc superconductor in external magnetic field

NASA Astrophysics Data System (ADS)

Torii, S.; Yuasa, K.

2004-10-01

Various magnetic levitation systems using oxide superconductors are developed as strong pinning forces are obtained in melt-processed bulk. However, the trapped flux of superconductor is moved by flux creep and fluctuating magnetic field. Therefore, to examine the internal condition of superconductor, the authors measure the dynamic surface flux density distribution of YBCO bulk. Flux density measurement system has a structure with the air-core coil and the Hall sensors. Ten Hall sensors are arranged in series. The YBCO bulk, which has 25 mm diameter and 13 mm thickness, is field cooled by liquid nitrogen. After that, magnetic field is changed by the air-core coil. This paper describes about the measured results of flux density distribution of YBCO bulk in the various frequencies of air-core coils currents.

The heliolongitudinal distribution of solar flares associated with solar proton events.

PubMed

Smart, D F; Shea, M A

1996-01-01

We find that the heliolongitudinal distribution of solar flares associated with earth-observed solar proton events is a function of the particle measurement energy. For solar proton events containing fluxes with energies exceeding 1 GeV, we find a Gaussian distribution about the probable root of the Archimedean spiral favorable propagation path leading from the earth to the sun. This distribution is modified as the detection threshold is lowered. For > 100 MeV solar proton events with fluxes > or = 10 protons (cm2-sec-ster)-1 we find the distribution becomes wider with a secondary peak near the solar central meridian. When the threshold is lowered to 10 MeV the distribution further evolves. For > 10 MeV solar proton events having a flux threshold at 10 protons (cm2-sec-ster)-1 the distribution can be considered to be a composite of two Gaussians. One distribution is centered about the probable root of the Archimedean spiral favorable propagation path leading from the earth to the sun, and the other is centered about the solar central meridian. For large flux solar proton events, those with flux threshold of 1000 (cm2-sec-ster)-1 at energies > 10 MeV, we find the distribution is rather flat for about 40 degrees either side of central meridian.

Magnetically-guided assembly of microfluidic fibers for ordered construction of diverse netlike modules

NASA Astrophysics Data System (ADS)

Li, Xingfu; Shi, Qing; Wang, Huaping; Sun, Tao; Huang, Qiang; Fukuda, Toshio

2017-12-01

In this paper, a magnetically-guided assembly method is proposed to methodically construct diverse modules with a microfiber-based network for promoting nutrient circulation and waste excretion of cell culture. The microfiber is smoothly spun from the microfluidic device via precise control of the volumetric flow rate, and superparamagnetic nanoparticles within the alginate solution of the microfluidic fiber enable its magnetic response. The magnetized device is used to effectively capture the microfiber using its powerful magnetic flux density and high magnetic field gradient. Subsequently, the dot-matrix magnetic flux density is used to distribute the microfibers in an orderly fashion that depends on the array structure of the magnetized device. Furthermore, the magnetic microfluidic fibers are spatially organized into desired locations and are cross-aligned to form highly interconnected netlike modules in a liquid environment. Therefore, the experimental results herein demonstrate the structural controllability and stability of various modules and establish the effectiveness of the proposed method.

Nonlinear stability of solar type 3 radio bursts. 2: Application to observations near 1 AU

NASA Technical Reports Server (NTRS)

Goldstein, M. L.; Smith, R. A.; Papadopoulos, K.

1978-01-01

A set of rate equations including strong turbulence effects and anomalous resitivity are solved using parmeters which model several solar type 3 bursts. Exciter distributions observed at 1 AU are excitation of the linear bump-in-tail instability, amplifying Langmuir waves above the threshold for the oscillating two stream instability (OTSI). The OTSI, and the attendant anomalous resistivity produce a rapid spectral transfer of Langmuir waves to short wavelengths, out of resonance with the electron exciter. Further energy loss of the beam is thus precluded. The various parameters needed to model the bursts are extrapolated inside 1 AU with similar results. Again, the OTSI is excited and decouples the electron beam from the Langmuir radiation. Reabsorption of the Langmuir waves by the beam is shown to be unimportant in all cases, even at 0.1 AU. The theory provides a natural explanation for the observed realationship between radio flux, and the electron flux.

Impact of bootstrap current and Landau-fluid closure on ELM crashes and transport

NASA Astrophysics Data System (ADS)

Chen, J. G.; Xu, X. Q.; Ma, C. H.; Lei, Y. A.

2018-05-01

Results presented here are from 6-field Landau-Fluid simulations using shifted circular cross-section tokamak equilibria on BOUT++ framework. Linear benchmark results imply that the collisional and collisionless Landau resonance closures make a little difference on linear growth rate spectra which are quite close to the results with the flux limited Spitzer-Härm parallel flux. Both linear and nonlinear simulations show that the plasma current profile plays dual roles on the peeling-ballooning modes that it can drive the low-n peeling modes and stabilize the high-n ballooning modes. For fixed total pressure and current, as the pedestal current decreases due to the bootstrap current which becomes smaller when the density (collisionality) increases, the operational point is shifted downwards vertically in the Jped - α diagram, resulting in threshold changes of different modes. The bootstrap current can slightly increase radial turbulence spreading range and enhance the energy and particle transports by increasing the perturbed amplitude and broadening cross-phase frequency distribution.

Gas Flux and Density Surrounding a Cylindrical Aperture in the Free Molecular Flow Regime

NASA Technical Reports Server (NTRS)

Soulas, George C.

2011-01-01

The equations for rigorously calculating the particle flux and density surrounding a cylindrical aperture in the free molecular flow regime are developed and presented. The fundamental equations for particle flux and density from a reservoir and a diffusely reflecting surface will initially be developed. Assumptions will include a Maxwell-Boltzmann speed distribution, equal particle and wall temperatures, and a linear flux distribution along the cylindrical aperture walls. With this information, the equations for axial flux and density surrounding a cylindrical aperture will be developed. The cylindrical aperture will be divided into multiple volumes and regions to rigorously determine the surrounding axial flux and density, and appropriate limits of integration will be determined. The results of these equations will then be evaluated. The linear wall flux distribution assumption will be assessed. The axial flux and density surrounding a cylindrical aperture with a thickness-to-radius ratio of 1.25 will be presented. Finally, the equations determined in this study will be verified using multiple methods.

A random wave model for the Aharonov-Bohm effect

NASA Astrophysics Data System (ADS)

Houston, Alexander J. H.; Gradhand, Martin; Dennis, Mark R.

2017-05-01

We study an ensemble of random waves subject to the Aharonov-Bohm effect. The introduction of a point with a magnetic flux of arbitrary strength into a random wave ensemble gives a family of wavefunctions whose distribution of vortices (complex zeros) is responsible for the topological phase associated with the Aharonov-Bohm effect. Analytical expressions are found for the vortex number and topological charge densities as functions of distance from the flux point. Comparison is made with the distribution of vortices in the isotropic random wave model. The results indicate that as the flux approaches half-integer values, a vortex with the same sign as the fractional part of the flux is attracted to the flux point, merging with it in the limit of half-integer flux. We construct a statistical model of the neighbourhood of the flux point to study how this vortex-flux merger occurs in more detail. Other features of the Aharonov-Bohm vortex distribution are also explored.

Martian CH(4): sources, flux, and detection.

PubMed

Onstott, T C; McGown, D; Kessler, J; Lollar, B Sherwood; Lehmann, K K; Clifford, S M

2006-04-01

Recent observations have detected trace amounts of CH(4) heterogeneously distributed in the martian atmosphere, which indicated a subsurface CH(4) flux of ~2 x 10(5) to 2 x 10(9) cm(2) s(1). Four different origins for this CH(4) were considered: (1) volcanogenic; (2) sublimation of hydrate- rich ice; (3) diffusive transport through hydrate-saturated cryosphere; and (4) microbial CH(4) generation above the cryosphere. A diffusive flux model of the martian crust for He, H(2), and CH(4) was developed based upon measurements of deep fracture water samples from South Africa. This model distinguishes between abiogenic and microbial CH(4) sources based upon their isotopic composition, and couples microbial CH(4) production to H(2) generation by H(2)O radiolysis. For a He flux of approximately 10(5) cm(2) s(1) this model yields an abiogenic CH(4) flux and a microbial CH(4) flux of approximately 10(6) and approximately 10(9) cm(2) s(1), respectively. This flux will only reach the martian surface if CH(4) hydrate is saturated in the cryosphere; otherwise it will be captured within the cryosphere. The sublimation of a hydrate-rich cryosphere could generate the observed CH(4) flux, whereas microbial CH(4) production in a hypersaline environment above the hydrate stability zone only seems capable of supplying approximately 10(5) cm(2) s(1) of CH(4). The model predicts that He/H(2)/CH(4)/C(2)H(6) abundances and the C and H isotopic values of CH(4) and the C isotopic composition of C(2)H(6) could reveal the different sources. Cavity ring-down spectrometers represent the instrument type that would be most capable of performing the C and H measurements of CH(4) on near future rover missions and pinpointing the cause and source of the CH(4) emissions.

The effect of heating on mineral composition and grain size distribution of flux calcined porcelanites from the Gafsa-Metlaoui basin, southwestern Tunisia

NASA Astrophysics Data System (ADS)

Saidi, Raja; Tlili, Ali; Jamoussi, Fakher

2016-12-01

The porcelanite rock of Ypresian phosphatic series of the Gafsa-Metlaoui basin (south-western Tunisia), is composed mainly of opal CT, and presents a variable percentage of carbonates and fibrous clays. This rock is treated with flux calcination at different temperatures in order to prepare a specific filter aid for cleaning melting sulfur which can be used for the production of sulfuric acid. This work presents the effect of heating on the mineralogy and grain size distribution of carbonate-rich porcelanite (Tm1) and clay-rich porcelanite (Gh) compared to flux calcined silica-rich porcelanite (CHM3) and diatomaceous filtration aids. The porcelanite samples used in this work come from three localities of the Gafsa-Metlaoui basin: Kef El Ghis (Gh), Tamarza (Tm1) and Mides (CHM3). Flux calcination at 1000 °C provokes a mineralogical transformation on carbonate-rich porcelanite samples. The opal CT transforms to opal C and becomes neater and more stable. The Thermal treatment of porcelanite (Tm1) incites also the apparition of new peaks of wollastonite. However, the structural change of opal CT to opal C by heat treatment is blocked for flux calcination of clay-rich porcelanite. The opal CT of fluxing clay-rich porcelanite becomes more ordered without significant change to opal C. The difference between fluxing carbonate-rich porcelanite (Tm1) and fluxing clay-rich porcelanite (Gh) appears also with granulometric distribution histogram of the tow heated samples. All raw samples have unimodal granulometric distribution (1-100 μm). After calcination with alkaline flux at 1000 °C fluxing carbonate-rich porcelanite displays bimodal granulometric distribution and a new mode appears systematically, between 0.1 μm and 1 μm. This occurs for fluxing silica-riche porcelanite and diatomaceous filtration aids as well and corresponds to the opal C formed after heat treatment. Whereas fluxing clay-rich porcelanite present trimodal granulometric distribution and a third mode appears (100-300 μm), which due to silica glass phase. Since, the granulometric rearrangement of porcelanite during thermal treatment may due to mineralogical transformation of opal CT to opal C and crystal grow.

The temperature and density structures of an X-ray flare during the decay phase. [Skylab observations

NASA Technical Reports Server (NTRS)

Silk, J. K.; Kahler, S. W.; Krieger, A. S.; Vaiana, G. S.

1976-01-01

The X-ray flare of 9 August 1973 was characterized by a spatially small kernel structure which persisted throughout its duration. The decay phase of this flare was observed in the objective grating mode of the X-ray telescope aboard the Skylab. Data analysis was carried out by scanning the images with a microdensitometer, converting the density arrays to energy using laboratory film calibration data and taking cross sections of the energy images. The 9 August flare shows two distinct periods in its decay phase, involving both cooling and material loss. The objective grating observations reveal that the two phenomena are separated in time. During the earlier phase of the flare decay, the distribution of emission measure as a function of temperature is changing, the high temperature component of the distribution being depleted relative to the cooler body of plasma. As the decay continues, the emission measure distribution stabilizes and the flux diminishes as the amount of material at X-ray emitting temperatures decreases.

Optimization of naltrexone diclofenac codrugs for sustained drug delivery across microneedle-treated skin.

PubMed

Ghosh, Priyanka; Lee, DoMin; Kim, Kyung Bo; Stinchcomb, Audra L

2014-01-01

The purpose of this work was to optimize the structure of codrugs for extended delivery across microneedle treated skin. Naltrexone, the model compound was linked with diclofenac, a nonspecific cyclooxygenase inhibitor to enhance the pore lifetime following microneedle treatment and develop a 7 day transdermal system for naltrexone. Four different codrugs of naltrexone and diclofenac were compared in terms of stability and solubility. Transdermal flux, permeability and skin concentration of both parent drugs and codrugs were quantified to form a structure permeability relationship. The results indicated that all codrugs bioconverted in the skin. The degree of conversion was dependent on the structure, phenol linked codrugs were less stable compared to the secondary alcohol linked structures. The flux of naltrexone across microneedle treated skin and the skin concentration of diclofenac were higher for the phenol linked codrugs. The polyethylene glycol link enhanced solubility of the codrugs, which translated into flux enhancement. The current studies indicated that formulation stability of codrugs and the flux of naltrexone can be enhanced via structure design optimization. The polyethylene glycol linked naltrexone diclofenac codrug is better suited for a 7 day drug delivery system both in terms of stability and drug delivery.

Influence of Oxygen on Cu Distribution Behavior Between Molten Iron and FeS-Based Flux

NASA Astrophysics Data System (ADS)

Kang, Youngjo; Shin, Kil-Sun; Morita, Kazuki

2018-06-01

Cu distribution behavior between molten iron and a sulfide flux was investigated under different oxygen contents in the sulfide flux to clarify the effect of oxygen content in FeS-based flux on Cu removal. The activity coefficient of CuS0.5 could be experimentally estimated according to the oxygen content. Based on the present result, the possibility of Cu removal by sulfide flux containing a certain amount of oxide was discussed.

Understanding the role of pore size homogeneity in the water transport through graphene layers.

PubMed

Su, Jiaye; Zhao, Yunzhen; Fang, Chang

2018-06-01

Graphene is a versatile 2D material and attracts an increasing amount of attention from a broad scientific community, including novel nanofluidic devices. In this work, we use molecular dynamics simulations to study the pressure driven water transport through graphene layers, focusing on the pore size homogeneity, realized by the arrangement of two pore sizes. For a given layer number, we find that water flux exhibits an excellent linear behavior with pressure, in agreement with the prediction of the Hagen-Poiseuille equation. Interestingly, the flux for concentrated pore size distribution is around two times larger than that of a uniform distribution. More surprisingly, under a given pressure, the water flux changes in an opposite way for these two distributions, where the flux ratio almost increases linearly with the layer number. For the largest layer number, more distributions suggest the same conclusion that higher water flux can be attained for more concentrated pore size distributions. Similar differences for the water translocation time and occupancy are also identified. The major reason for these results should clearly be due to the hydrogen bond and density profile distributions. Our results are helpful to delineate the exquisite role of pore size homogeneity, and should have great implications for the design of high flux nanofluidic devices and inversely the detection of pore structures.

Understanding the role of pore size homogeneity in the water transport through graphene layers

NASA Astrophysics Data System (ADS)

Su, Jiaye; Zhao, Yunzhen; Fang, Chang

2018-06-01

Graphene is a versatile 2D material and attracts an increasing amount of attention from a broad scientific community, including novel nanofluidic devices. In this work, we use molecular dynamics simulations to study the pressure driven water transport through graphene layers, focusing on the pore size homogeneity, realized by the arrangement of two pore sizes. For a given layer number, we find that water flux exhibits an excellent linear behavior with pressure, in agreement with the prediction of the Hagen–Poiseuille equation. Interestingly, the flux for concentrated pore size distribution is around two times larger than that of a uniform distribution. More surprisingly, under a given pressure, the water flux changes in an opposite way for these two distributions, where the flux ratio almost increases linearly with the layer number. For the largest layer number, more distributions suggest the same conclusion that higher water flux can be attained for more concentrated pore size distributions. Similar differences for the water translocation time and occupancy are also identified. The major reason for these results should clearly be due to the hydrogen bond and density profile distributions. Our results are helpful to delineate the exquisite role of pore size homogeneity, and should have great implications for the design of high flux nanofluidic devices and inversely the detection of pore structures.

Method and system using power modulation and velocity modulation producing sputtered thin films with sub-angstrom thickness uniformity or custom thickness gradients

DOEpatents

Montcalm, Claude [Livermore, CA; Folta, James Allen [Livermore, CA; Walton, Christopher Charles [Berkeley, CA

2003-12-23

A method and system for determining a source flux modulation recipe for achieving a selected thickness profile of a film to be deposited (e.g., with highly uniform or highly accurate custom graded thickness) over a flat or curved substrate (such as concave or convex optics) by exposing the substrate to a vapor deposition source operated with time-varying flux distribution as a function of time. Preferably, the source is operated with time-varying power applied thereto during each sweep of the substrate to achieve the time-varying flux distribution as a function of time. Preferably, the method includes the steps of measuring the source flux distribution (using a test piece held stationary while exposed to the source with the source operated at each of a number of different applied power levels), calculating a set of predicted film thickness profiles, each film thickness profile assuming the measured flux distribution and a different one of a set of source flux modulation recipes, and determining from the predicted film thickness profiles a source flux modulation recipe which is adequate to achieve a predetermined thickness profile. Aspects of the invention include a computer-implemented method employing a graphical user interface to facilitate convenient selection of an optimal or nearly optimal source flux modulation recipe to achieve a desired thickness profile on a substrate. The method enables precise modulation of the deposition flux to which a substrate is exposed to provide a desired coating thickness distribution.

Discontinuous Galerkin Method with Numerical Roe Flux for Spherical Shallow Water Equations

NASA Astrophysics Data System (ADS)

Yi, T.; Choi, S.; Kang, S.

2013-12-01

In developing the dynamic core of a numerical weather prediction model with discontinuous Galerkin method, a numerical flux at the boundaries of grid elements plays a vital role since it preserves the local conservation properties and has a significant impact on the accuracy and stability of numerical solutions. Due to these reasons, we developed the numerical Roe flux based on an approximate Riemann problem for spherical shallow water equations in Cartesian coordinates [1] to find out its stability and accuracy. In order to compare the performance with its counterpart flux, we used the Lax-Friedrichs flux, which has been used in many dynamic cores such as NUMA [1], CAM-DG [2] and MCore [3] because of its simplicity. The Lax-Friedrichs flux is implemented by a flux difference between left and right states plus the maximum characteristic wave speed across the boundaries of elements. It has been shown that the Lax-Friedrichs flux with the finite volume method is more dissipative and unstable than other numerical fluxes such as HLLC, AUSM+ and Roe. The Roe flux implemented in this study is based on the decomposition of flux difference over the element boundaries where the nonlinear equations are linearized. It is rarely used in dynamic cores due to its complexity and thus computational expensiveness. To compare the stability and accuracy of the Roe flux with the Lax-Friedrichs, two- and three-dimensional test cases are performed on a plane and cubed-sphere, respectively, with various numbers of element and polynomial order. For the two-dimensional case, the Gaussian bell is simulated on the plane with two different numbers of elements at the fixed polynomial orders. In three-dimensional cases on the cubed-sphere, we performed the test cases of a zonal flow over an isolated mountain and a Rossby-Haurwitz wave, of which initial conditions are the same as those of Williamson [4]. This study presented that the Roe flux with the discontinuous Galerkin method is less dissipative and has stronger numerical stability than the Lax-Friedrichs. Reference 1. 2002, Giraldo, F.X., Hesthaven, J.S. and Warburton, T., "Nodal High-Order Discontinous Galerkin Methods for the Spherical Shallow Water Equations," Journal of Computational Physics, Vol.181, pp.499-525. 2. 2005, Nair, R.D., Thomas, S.J. and Loft, R.D., "A Discontinuous Galerkin Transport Scheme on the Cubed Sphere," Monthly Weather Review, Vol.133, pp.814-828. 3. 2010, Ullrich, P.A., Jablonowski, C. and Leer, van B., "High-Order Finite-Volume Methods for the Shallow-Water Equations on the Sphere," Journal of Computational Physics, Vol.229, pp.6104-6134. 4. 1992, Williamson, D.L., Drake, J.B., Hack, J., Jacob, R. and Swartztrauber, P.N., "A Standard Test Set for Numerical Approximations to the Shallow Water Equations in Spherical Geometry," Journal of Computational Physics, Vol.102, pp.211-224.

DistributedFBA.jl: High-level, high-performance flux balance analysis in Julia

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

Heirendt, Laurent; Thiele, Ines; Fleming, Ronan M. T.

Flux balance analysis and its variants are widely used methods for predicting steady-state reaction rates in biochemical reaction networks. The exploration of high dimensional networks with such methods is currently hampered by software performance limitations. DistributedFBA.jl is a high-level, high-performance, open-source implementation of flux balance analysis in Julia. It is tailored to solve multiple flux balance analyses on a subset or all the reactions of large and huge-scale networks, on any number of threads or nodes. DistributedFBA.jl is a high-level, high-performance, open-source implementation of flux balance analysis in Julia. It is tailored to solve multiple flux balance analyses on amore » subset or all the reactions of large and huge-scale networks, on any number of threads or nodes.« less

DistributedFBA.jl: High-level, high-performance flux balance analysis in Julia

DOE PAGES

Heirendt, Laurent; Thiele, Ines; Fleming, Ronan M. T.

2017-01-16

Flux balance analysis and its variants are widely used methods for predicting steady-state reaction rates in biochemical reaction networks. The exploration of high dimensional networks with such methods is currently hampered by software performance limitations. DistributedFBA.jl is a high-level, high-performance, open-source implementation of flux balance analysis in Julia. It is tailored to solve multiple flux balance analyses on a subset or all the reactions of large and huge-scale networks, on any number of threads or nodes. DistributedFBA.jl is a high-level, high-performance, open-source implementation of flux balance analysis in Julia. It is tailored to solve multiple flux balance analyses on amore » subset or all the reactions of large and huge-scale networks, on any number of threads or nodes.« less

Magnetopause modeling - Flux transfer events and magnetosheath quasi-trapped distributions

NASA Technical Reports Server (NTRS)

Speiser, T. W.; Williams, D. J.

1982-01-01

Three-dimensional distribution functions for energetic ions are studied numerically in the magnetosphere, through the magnetopause, and in the magnetosheath using a simple one-dimensional quasi-static model and ISEE 1 magnetopause crossing data for November 10, 1977. Quasi-trapped populations in the magnetosheath observed near flux transfer events (FTEs) are investigated, and it is shown that the population in the sheath appears to sandwich the FTE distributions. These quasi-trapped distributions are due to slow, large pitch angle, outward moving particles left behind by the outward rush of the ions more field-aligned at the time the flux was opened. It is found that sheath convective flows can map along the connected flux tube without drastically changing the distribution function, and results suggest that localized tangential fields above the upper limit may exist.

Retrieving SW fluxes from geostationary narrowband radiances for the NASA-CERES SYN1deg product

NASA Astrophysics Data System (ADS)

Wrenn, F. J., IV; Doelling, D. R.; Liang, L.

2016-12-01

The CERES mission was designed to measure the natural variability of the net TOA flux over long time scales relevant to climate monitoring. To achieve this goal, CERES provides the level-3 SSF1deg, SYN1deg, and EBAF monthly 1° by 1° regional TOA flux. The single satellite (Terra or Aqua) SSF1deg 24-hour shortwave flux is based on one daytime measurements and assumes constant meteorology to model the diurnal change in albedo. To accurately describe regions with a prominent diurnal signal, the SYN1deg Edition4 dataset employs hourly geostationary (GEO) measurements. This improves upon Edition3, which used 3-hourly GEO measurements and with temporal interpolation. The EBAF product combines the temporal stability of the SSF1deg product with the diurnal information from SYN1deg and removes the CERES instrument calibration bias by constraining the net flux balance to the ocean heat storage term. The SYN-1deg product retrieves hourly SW fluxes from GEO measurements. Over regions with large diurnal cycles, such as maritime stratus and land afternoon convective locations, the GEO derived SW fluxes will capture the diurnal flux not observed with Terra or Aqua sun-synchronous satellites. Obtaining fluxes from geostationary satellite radiance is a multistep process. First, most GEO visible imagers lack calibration and must be calibrated to MODIS and VIIRS. Second, the GEO imager visible channel radiances are converted to broadband radiances using empirical and theoretical models. The lack of coincident, collocated, and co-angled GEO and CERES measurements makes building an empirical model difficult. The narrowband to broadband models are a function of surface and cloud conditions, which are difficult to identify due to the inconsistent cloud retrievals between the 16 GEO imagers used in the CERES record. Third, the GEO derived broadband radiances are passed through the CERES angular distribution model (ADM) to convert the radiances to fluxes. Lastly, the GEO derived broadband fluxes are normalized with CERES fluxes in order to preserve the CERES instrument calibration. Validation is performed by comparing the GEO converted fluxes against CERES observations using coincident and collocated data. This work will focus on the GEO visible radiance conversion, validation approach, and Edition4 improvements.

Retrieving SW fluxes from geostationary narrowband radiances for the NASA-CERES SYN1deg product

NASA Astrophysics Data System (ADS)

Wrenn, F. J., IV; Doelling, D. R.; Liang, L.

2017-12-01

The CERES mission was designed to measure the natural variability of the net TOA flux over long time scales relevant to climate monitoring. To achieve this goal, CERES provides the level-3 SSF1deg, SYN1deg, and EBAF monthly 1° by 1° regional TOA flux. The single satellite (Terra or Aqua) SSF1deg 24-hour shortwave flux is based on one daytime measurements and assumes constant meteorology to model the diurnal change in albedo. To accurately describe regions with a prominent diurnal signal, the SYN1deg Edition4 dataset employs hourly geostationary (GEO) measurements. This improves upon Edition3, which used 3-hourly GEO measurements and with temporal interpolation. The EBAF product combines the temporal stability of the SSF1deg product with the diurnal information from SYN1deg and removes the CERES instrument calibration bias by constraining the net flux balance to the ocean heat storage term. The SYN-1deg product retrieves hourly SW fluxes from GEO measurements. Over regions with large diurnal cycles, such as maritime stratus and land afternoon convective locations, the GEO derived SW fluxes will capture the diurnal flux not observed with Terra or Aqua sun-synchronous satellites. Obtaining fluxes from geostationary satellite radiance is a multistep process. First, most GEO visible imagers lack calibration and must be calibrated to MODIS and VIIRS. Second, the GEO imager visible channel radiances are converted to broadband radiances using empirical and theoretical models. The lack of coincident, collocated, and co-angled GEO and CERES measurements makes building an empirical model difficult. The narrowband to broadband models are a function of surface and cloud conditions, which are difficult to identify due to the inconsistent cloud retrievals between the 16 GEO imagers used in the CERES record. Third, the GEO derived broadband radiances are passed through the CERES angular distribution model (ADM) to convert the radiances to fluxes. Lastly, the GEO derived broadband fluxes are normalized with CERES fluxes in order to preserve the CERES instrument calibration. Validation is performed by comparing the GEO converted fluxes against CERES observations using coincident and collocated data. This work will focus on the GEO visible radiance conversion, validation approach, and Edition4 improvements.

An analytical method based on multipole moment expansion to calculate the flux distribution in Gammacell-220

NASA Astrophysics Data System (ADS)

Rezaeian, P.; Ataenia, V.; Shafiei, S.

2017-12-01

In this paper, the flux of photons inside the irradiation cell of the Gammacell-220 is calculated using an analytical method based on multipole moment expansion. The flux of the photons inside the irradiation cell is introduced as the function of monopole, dipoles and quadruples in the Cartesian coordinate system. For the source distribution of the Gammacell-220, the values of the multipole moments are specified by direct integrating. To confirm the validation of the presented methods, the flux distribution inside the irradiation cell was determined utilizing MCNP simulations as well as experimental measurements. To measure the flux inside the irradiation cell, Amber dosimeters were employed. The calculated values of the flux were in agreement with the values obtained by simulations and measurements, especially in the central zones of the irradiation cell. In order to show that the present method is a good approximation to determine the flux in the irradiation cell, the values of the multipole moments were obtained by fitting the simulation and experimental data using Levenberg-Marquardt algorithm. The present method leads to reasonable results for the all source distribution even without any symmetry which makes it a powerful tool for the source load planning.

Stability of isolated Barchan dunes

NASA Astrophysics Data System (ADS)

Fourrière, Antoine; Charru, François

2010-11-01

When sand grains are entrained by an air flow over a non-erodible ground, or with limited sediment supply from the bed, they form isolated dunes showing a remarkable crescentic shape with horns pointing downstream. These dunes, known as Barchan dunes, are commonly observed in deserts, with height of a few meters and velocity of a few meters per year (Bagnold 1941). These dunes also exist under water, at a much smaller, centimetric size (Franklin & Charru 2010). Their striking stability properties are not well understood yet. Two phenomena are likely to be involved in this stability: (i) relaxation effects of the sand flux which increases from the dune foot up to the crest, related to grain inertia or deposition, and (ii) a small transverse sand flux due to slope effects and the divergence of the streamlines of the fluid flow. We reproduced aqueous Barchan dunes in a channel, and studied their geometrical and dynamic properties (in particular their shape, velocity, minimum size, and rate of erosion). Using coloured glass beads (see the figure), we were then able to measure the particle flux over the whole dune surface. We will discuss the stability of these dunes in the light of our measurements.

The potential and flux landscape theory of evolution.

PubMed

Zhang, Feng; Xu, Li; Zhang, Kun; Wang, Erkang; Wang, Jin

2012-08-14

We established the potential and flux landscape theory for evolution. We found explicitly the conventional Wright's gradient adaptive landscape based on the mean fitness is inadequate to describe the general evolutionary dynamics. We show the intrinsic potential as being Lyapunov function(monotonically decreasing in time) does exist and can define the adaptive landscape for general evolution dynamics for studying global stability. The driving force determining the dynamics can be decomposed into gradient of potential landscape and curl probability flux. Non-zero flux causes detailed balance breaking and measures how far the evolution from equilibrium state. The gradient of intrinsic potential and curl flux are perpendicular to each other in zero fluctuation limit resembling electric and magnetic forces on electrons. We quantified intrinsic energy, entropy and free energy of evolution and constructed non-equilibrium thermodynamics. The intrinsic non-equilibrium free energy is a Lyapunov function. Both intrinsic potential and free energy can be used to quantify the global stability and robustness of evolution. We investigated an example of three allele evolutionary dynamics with frequency dependent selection (detailed balance broken). We uncovered the underlying single, triple, and limit cycle attractor landscapes. We found quantitative criterions for stability through landscape topography. We also quantified evolution pathways and found paths do not follow potential gradient and are irreversible due to non-zero flux. We generalized the original Fisher's fundamental theorem to the general (i.e., frequency dependent selection) regime of evolution by linking the adaptive rate with not only genetic variance related to the potential but also the flux. We show there is an optimum potential where curl flux resulting from biotic interactions of individuals within a species or between species can sustain an endless evolution even if the physical environment is unchanged. We offer a theoretical basis for explaining the corresponding Red Queen hypothesis proposed by Van Valen. Our work provides a theoretical foundation for evolutionary dynamics.

On Magnetic Flux Trapping by Surface Superconductivity

NASA Astrophysics Data System (ADS)

Podolyak, E. R.

2018-03-01

The magnetic flux trapping by surface superconductivity is considered. The stability of the state localized at the cylindrical sample surface upon a change in the external magnetic field is tested. It is shown that as the magnetic field decreases, the sample acquires a positive magnetic moment due to magnetic flux trapping; i.e., the magnetization curve of surface superconductivity is "paramagnetic" by nature.

The Potential and Flux Landscape Theory of Ecology

PubMed Central

Zhang, Kun; Wang, Erkang; Wang, Jin

2014-01-01

The species in ecosystems are mutually interacting and self sustainable stable for a certain period. Stability and dynamics are crucial for understanding the structure and the function of ecosystems. We developed a potential and flux landscape theory of ecosystems to address these issues. We show that the driving force of the ecological dynamics can be decomposed to the gradient of the potential landscape and the curl probability flux measuring the degree of the breaking down of the detailed balance (due to in or out flow of the energy to the ecosystems). We found that the underlying intrinsic potential landscape is a global Lyapunov function monotonically going down in time and the topology of the landscape provides a quantitative measure for the global stability of the ecosystems. We also quantified the intrinsic energy, the entropy, the free energy and constructed the non-equilibrium thermodynamics for the ecosystems. We studied several typical and important ecological systems: the predation, competition, mutualism and a realistic lynx-snowshoe hare model. Single attractor, multiple attractors and limit cycle attractors emerge from these studies. We studied the stability and robustness of the ecosystems against the perturbations in parameters and the environmental fluctuations. We also found that the kinetic paths between the multiple attractors do not follow the gradient paths of the underlying landscape and are irreversible because of the non-zero flux. This theory provides a novel way for exploring the global stability, function and the robustness of ecosystems. PMID:24497975

A Correction for IUE UV Flux Distributions from Comparisons with CALSPEC

NASA Astrophysics Data System (ADS)

Bohlin, Ralph C.; Bianchi, Luciana

2018-04-01

A collection of spectral energy distributions (SEDs) is available in the Hubble Space Telescope (HST) CALSPEC database that is based on calculated model atmospheres for pure hydrogen white dwarfs (WDs). A much larger set (∼100,000) of UV SEDs covering the range (1150–3350 Å) with somewhat lower quality are available in the IUE database. IUE low-dispersion flux distributions are compared with CALSPEC to provide a correction that places IUE fluxes on the CALSPEC scale. While IUE observations are repeatable to only 4%–10% in regions of good sensitivity, the average flux corrections have a precision of 2%–3%. Our re-calibration places the IUE flux scale on the current UV reference standard and is relevant for any project based on IUE archival data, including our planned comparison of GALEX to the corrected IUE fluxes. IUE SEDs may be used to plan observations and cross-calibrate data from future missions, so the IUE flux calibration must be consistent with HST instrumental calibrations to the best possible precision.

SEM-EDS Analyses of Small Craters in Stardust Aluminum Foils: Implications for the Wild-2 Dust Distribution

NASA Technical Reports Server (NTRS)

Borg, J.; Horz, F.; Bridges, J. C.; Burchell, M. J.; Djouadi, Z.; Floss, C.; Graham, G. A.; Green, S. F.; Heck, P. R.; Hoppe, P.;

Measurement of cosmic muon angular distribution and vertical integrated flux by 2 m × 2 m RPC stack at IICHEP-Madurai

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

Pethuraj, S.; Datar, V.M.; Majumder, G.

2017-09-01

The 50 kton INO-ICAL is a proposed underground high energy physics experiment at Theni, India (9{sup o}57' N , 77{sup o}16' E ) to study the neutrino oscillation parameters using atmospheric neutrinos. The Resistive Plate Chamber (RPC) has been chosen as the active detector element for the ICAL detector. An experimental setup consisting of 12 layers of glass RPCs of size 2 m × 2 m has been built at IICHEP, Madurai to study the long term stability and performance of RPCs which are produced on a large scale in Indian industry. In this paper, the studies on the performancemore » of RPCs are presented along with the angular distribution of muons at Madurai (9{sup o}56' N ,78{sup o}00' E and Altitude ≈ 160 m from sea level).« less

Sensitivity Analysis of Flux Determination in Heart by H2 18O -provided Labeling Using a Dynamic Isotopologue Model of Energy Transfer Pathways

PubMed Central

Schryer, David W.; Peterson, Pearu; Illaste, Ardo; Vendelin, Marko

2012-01-01

To characterize intracellular energy transfer in the heart, two organ-level methods have frequently been employed: inversion and saturation transfer, and dynamic labeling. Creatine kinase (CK) fluxes obtained by following oxygen labeling have been considerably smaller than the fluxes determined by saturation transfer. It has been proposed that dynamic labeling determines net flux through CK shuttle, whereas saturation transfer measures total unidirectional flux. However, to our knowledge, no sensitivity analysis of flux determination by oxygen labeling has been performed, limiting our ability to compare flux distributions predicted by different methods. Here we analyze oxygen labeling in a physiological heart phosphotransfer network with active CK and adenylate kinase (AdK) shuttles and establish which fluxes determine the labeling state. A mathematical model consisting of a system of ordinary differential equations was composed describing enrichment in each phosphoryl group and inorganic phosphate. By varying flux distributions in the model and calculating the labeling, we analyzed labeling sensitivity to different fluxes in the heart. We observed that the labeling state is predominantly sensitive to total unidirectional CK and AdK fluxes and not to net fluxes. We conclude that measuring dynamic incorporation of into the high-energy phosphotransfer network in heart does not permit unambiguous determination of energetic fluxes with a higher magnitude than the ATP synthase rate when the bidirectionality of fluxes is taken into account. Our analysis suggests that the flux distributions obtained using dynamic labeling, after removing the net flux assumption, are comparable with those from inversion and saturation transfer. PMID:23236266

Photoelectron escape fluxes over the equatorial and midlatitude regions

NASA Technical Reports Server (NTRS)

Narasingarao, B. C.; Singh, R. N.; Maier, E. J.

1972-01-01

Satellite measurements of photoelectron escape flux around noontime made by Explorer 31 in 600-800 km altitude range are reported for the equatorial and midlatitude regions. The pitch angle distributions and the spectral distributions are derived from the data. Analyzed data show that the flux for equatorial regions is lower by a factor 2 to 3 in comparison to that of midlatitude regions. Theoretical calculations are also made to compare with observed escape fluxes.

Determination of meteor flux distribution over the celestial sphere

NASA Technical Reports Server (NTRS)

Andreev, V. V.; Belkovich, O. I.; Filimonova, T. K.; Sidorov, V. V.

1992-01-01

A new method of determination of meteor flux density distribution over the celestial sphere is discussed. The flux density was derived from observations by radar together with measurements of angles of arrival of radio waves reflected from meteor trails. The role of small meteor showers over the sporadic background is shown.

Steady-state distributions of probability fluxes on complex networks

NASA Astrophysics Data System (ADS)

Chełminiak, Przemysław; Kurzyński, Michał

2017-02-01

We consider a simple model of the Markovian stochastic dynamics on complex networks to examine the statistical properties of the probability fluxes. The additional transition, called hereafter a gate, powered by the external constant force breaks a detailed balance in the network. We argue, using a theoretical approach and numerical simulations, that the stationary distributions of the probability fluxes emergent under such conditions converge to the Gaussian distribution. By virtue of the stationary fluctuation theorem, its standard deviation depends directly on the square root of the mean flux. In turn, the nonlinear relation between the mean flux and the external force, which provides the key result of the present study, allows us to calculate the two parameters that entirely characterize the Gaussian distribution of the probability fluxes both close to as well as far from the equilibrium state. Also, the other effects that modify these parameters, such as the addition of shortcuts to the tree-like network, the extension and configuration of the gate and a change in the network size studied by means of computer simulations are widely discussed in terms of the rigorous theoretical predictions.

Size Distributions of Solar Flares and Solar Energetic Particle Events

NASA Technical Reports Server (NTRS)

Cliver, E. W.; Ling, A. G.; Belov, A.; Yashiro, S.

2012-01-01

We suggest that the flatter size distribution of solar energetic proton (SEP) events relative to that of flare soft X-ray (SXR) events is primarily due to the fact that SEP flares are an energetic subset of all flares. Flares associated with gradual SEP events are characteristically accompanied by fast (much > 1000 km/s) coronal mass ejections (CMEs) that drive coronal/interplanetary shock waves. For the 1996-2005 interval, the slopes (alpha values) of power-law size distributions of the peak 1-8 Angs fluxes of SXR flares associated with (a) >10 MeV SEP events (with peak fluxes much > 1 pr/sq cm/s/sr) and (b) fast CMEs were approx 1.3-1.4 compared to approx 1.2 for the peak proton fluxes of >10 MeV SEP events and approx 2 for the peak 1-8 Angs fluxes of all SXR flares. The difference of approx 0.15 between the slopes of the distributions of SEP events and SEP SXR flares is consistent with the observed variation of SEP event peak flux with SXR peak flux.

Evaporation Flux Distribution of Drops on a Hydrophilic or Hydrophobic Flat Surface by Molecular Simulations.

PubMed

Xie, Chiyu; Liu, Guangzhi; Wang, Moran

2016-08-16

The evaporation flux distribution of sessile drops is investigated by molecular dynamic simulations. Three evaporating modes are classified, including the diffusion dominant mode, the substrate heating mode, and the environment heating mode. Both hydrophilic and hydrophobic drop-substrate interactions are considered. To count the evaporation flux distribution, which is position dependent, we proposed an azimuthal-angle-based division method under the assumption of spherical crown shape of drops. The modeling results show that the edge evaporation, i.e., near the contact line, is enhanced for hydrophilic drops in all the three modes. The surface diffusion of liquid molecular absorbed on solid substrate for hydrophilic cases plays an important role as well as the space diffusion on the enhanced evaporation rate at the edge. For hydrophobic drops, the edge evaporation flux is higher for the substrate heating mode, but lower than elsewhere of the drop for the diffusion dominant mode; however, a nearly uniform distribution is found for the environment heating mode. The evidence shows that the temperature distribution inside drops plays a key role in the position-dependent evaporation flux.

Aerosol Radiative Forcing Derived From SeaWIFS - Retrieved Aerosol Optical Properties

NASA Technical Reports Server (NTRS)

Chou, Mong-Dah; Chan, Pui-King; Wang, Menghua; Einaudi, Franco (Technical Monitor)

2000-01-01

To understand climatic implications of aerosols over global oceans, the aerosol optical properties retrieved from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) are analyzed, and the effects of the aerosols on the Earth's radiation budgets (aerosol radiative forcing, ARF) are computed using a radiative transfer model. It is found that the distribution of the SeaWiFS-retrieved aerosol optical thickness is distinctively zonal. The maximum in the equatorial region coincides with the Intertropical Convergence Zone, and the maximum in the Southern Hemispheric high latitudes coincides with the region of prevailing westerlies. The minimum aerosol optical thickness is found in the subtropical high pressure regions, especially in the Southern Hemisphere. These zonal patterns clearly demonstrate the influence of atmospheric circulation on the oceanic aerosol distribution. Over global oceans, aerosols reduce the annual mean net downward solar flux by 5.4 W m-2 at the top of the atmosphere and by 6.1 W m-2 at the surface. The largest ARF is found in the tropical Atlantic, Arabian Sea, Bay of Bengal, the coastal regions of Southeast and East Asia, and the Southern Hemispheric high latitudes. During the period of the Indonesian big fires (September-December 1997), the cooling due to aerosols is greater than 15 W m-2 at the top of the atmosphere and greater than 30 W m(exp -1) at the surface in the vicinity of the maritime continents. The atmosphere receives extra solar radiation by greater than 15 W m(exp -1) over a large area. These large changes in radiative fluxes are expected to have enhanced the atmospheric stability, weakened the atmospheric circulation, and augmented the drought condition during that period. It would be very instructive to simulate the regional climatic. The model-calculated clear sky solar flux at the top of the atmosphere is compared with that derived from the Clouds and the Earth's Radiant Energy System (CERES). The net downward solar flux of CERES is systematically larger than the model calculations by -3 W M-2. In the equatorial region, the CERES-derived net downward solar flux is even larger than the model calculations without including aerosols. It is possible that the CERES incorrectly identified regions of high humidity and high aerosol concentration as being cloud contaminated and, hence, overestimated the clear sky net downward solar flux.

Tritium Plume Dynamics in the Shallow Unsaturated Zone Adjacent to an Arid Waste Disposal Facility

NASA Astrophysics Data System (ADS)

Maples, S.; Andraski, B. J.; Stonestrom, D. A.; Cooper, C. A.; Michel, R. L.; Pohll, G. M.

2012-12-01

Previous studies at the U.S. Geological Survey's Amargosa Desert Research Site (ADRS) in southern Nevada have documented two plumes of tritiated water-vapor (3HHOg) adjacent to a closed, commercial low-level radioactive waste disposal facility. Wastes were disposed on-site from 1962-92. Tritium has moved long distances (> 400 m) through a shallow (1-2-m depth) dry gravelly layer—orders of magnitude further than anticipated by standard transport models. Geostatistical methods, spatial moment analyses and tritium flux calculations were applied to assess shallow plume dynamics. A grid-based plant-water sampling method was utilized to infer detailed, field-scale 3HHOg concentrations at 5-yr intervals during 2001-11. Results indicate that gravel-layer 3HHOg mass diminished faster than would be expected from radioactive decay (~70% in 10 yr). Both plumes exhibited center-of-mass stability, suggesting that bulk-plume movement is minimal during the period of study. Nonetheless, evidence of localized lateral advancement along some margins, combined with increases in the spatial covariance of concentration distribution, indicates intra-plume mass redistribution is ongoing. Previous studies have recognized that vertical movement of tritiated water from sub-root-zone gravel into the root-zone contributes to atmospheric release via evapotranspiration. Estimates of lateral and vertical tritium fluxes during the study period indicate (1) vertical tritiated water fluxes were dominated by diffusive-vapor fluxes (> 90%), and (2) vertical diffusive-vapor fluxes were roughly an order of magnitude greater than lateral diffusive-vapor fluxes. This behavior highlights the importance of the atmosphere as a tritium sink. Estimates of cumulative vertical diffusive-vapor flux and radioactive decay with time were comparable to observed declines in total shallow plume mass with time. This suggests observed changes in plume mass may (1) be attributed, in considerable part, to these removal mechanisms, and (2) appreciable input from the adjacent disposal facility is not occurring at this time.

Gravity Wave Dynamics in a Mesospheric Inversion Layer: 2. Instabilities, Turbulence, Fluxes, and Mixing

NASA Astrophysics Data System (ADS)

Fritts, David C.; Wang, Ling; Laughman, Brian; Lund, Thomas S.; Collins, Richard L.

2018-01-01

A companion paper by Fritts, Laughman, et al. (2017) employed an anelastic numerical model to explore the dynamics of gravity waves (GWs) encountering a mesospheric inversion layer (MIL) having a moderate static stability enhancement and a layer of weaker static stability above. That study revealed that MIL responses, including GW transmission, reflection, and instabilities, are sensitive functions of GW parameters. This paper expands on two of the Fritts, Laughman, et al. (2017) simulations to examine GW instability dynamics and turbulence in the MIL; forcing of the mean wind and stability environments by GW, instability, and turbulence fluxes; and associated heat and momentum transports. These direct numerical simulations resolve turbulence inertial-range scales and yield the following results: GW breaking and turbulence in the MIL occur below where they would otherwise, due to enhancements of GW amplitudes and shears in the MIL. 2-D GW and instability heat and momentum fluxes are 20-30 times larger than 3-D instability and turbulence fluxes. Mean fields are driven largely by 2-D GW and instability dynamics rather than 3-D instabilities and turbulence. 2-D and 3-D heat fluxes in regions of strong turbulence yield small departures from initial T(z) and N2(z) profiles, hence do not yield nearly adiabatic "mixed" layers. Our MIL results are consistent with the relation between the turbulent vertical velocity variance and energy dissipation rate proposed by Weinstock (1981) for the limited intervals evaluated.

How Cells Can Control Their Size by Pumping Ions.

PubMed

Kay, Alan R

2017-01-01

The ability of all cells to set and regulate their size is a fundamental aspect of cellular physiology. It has been known for sometime but not widely so, that size stability in animal cells is dependent upon the operation of the sodium pump, through the so-called pump-leak mechanism (Tosteson and Hoffman, 1960). Impermeant molecules in cells establish an unstable osmotic condition, the Donnan effect, which is counteracted by the operation of the sodium pump, creating an asymmetry in the distribution of Na + and K + staving off water inundation. In this paper, which is in part a tutorial, I show how to model quantitatively the ion and water fluxes in a cell that determine the cell volume and membrane potential. The movement of water and ions is constrained by both osmotic and charge balance, and is driven by ion and voltage gradients and active ion transport. Transforming these constraints and forces into a set of coupled differential equations allows us to model how the ion distributions, volume and voltage change with time. I introduce an analytical solution to these equations that clarifies the influence of ion conductances, pump rates and water permeability in this multidimensional system. I show that the number of impermeant ions ( x ) and their average charge have a powerful influence on the distribution of ions and voltage in a cell. Moreover, I demonstrate that in a cell where the operation of active ion transport eliminates an osmotic gradient, the size of the cell is directly proportional to x . In addition, I use graphics to reveal how the physico-chemical constraints and chemical forces interact with one another in apportioning ions inside the cell. The form of model used here is applicable to all membrane systems, including mitochondria and bacteria, and I show how pumps other than the sodium pump can be used to stabilize cells. Cell biologists may think of electrophysiology as the exclusive domain of neuroscience, however the electrical effects of ion fluxes need to become an intimate part of cell biology if we are to understand a fundamental process like cell size regulation.

The influence of surface roughness and turbulence on heat fluxes from an oil palm plantation in Jambi, Indonesia

NASA Astrophysics Data System (ADS)

June, Tania; Meijide, Ana; Stiegler, Christian; Purba Kusuma, Alan; Knohl, Alexander

2018-05-01

Oil palm plantations are expanding vastly in Jambi, resulted in altered surface roughness and turbulence characteristics, which may influence exchange of heat and mass. Micrometeorological measurements above oil palm canopy were conducted for the period 2013–2015. The oil palms were 12.5 years old, canopy height 13 meters and 1.5 years old canopy height 2.5 m. We analyzed the influence of surface roughness and turbulence strenght on heat (sensible and latent) fluxes by investigating the profiles and gradient of wind speed, and temperature, surface roughness (roughness length, zo, and zero plane displacement, d), and friction velocity u*. Fluxes of heat were calculated using profile similarity methods taking into account atmospheric stability calculated using Richardson number Ri and the generalized stability factor ζ. We found that roughness parameters (zo, d, and u*) directly affect turbulence in oil palm canopy and hence heat fluxes; they are affected by canopy height, wind speed and atmospheric stability. There is a negative trend of d towards air temperature above the oil palm canopy, indicating the effect of plant volume and height in lowering air temperature. We propose studying the relation between zero plane displacement d with a remote sensing vegetation index for scaling up this point based analysis.

Climate Quality Broadband and Narrowband Solar Reflected Radiance Calibration Between Sensors in Orbit

NASA Technical Reports Server (NTRS)

Wielicki, Bruce A.; Doelling, David R.; Young, David F.; Loeb, Norman G.; Garber, Donald P.; MacDonnell, David G.

2008-01-01

vAs the potential impacts of global climate change become more clear [1], the need to determine the accuracy of climate prediction over decade-to-century time scales has become an urgent and critical challenge. The most critical tests of climate model predictions will occur using observations of decadal changes in climate forcing, response, and feedback variables. Many of these key climate variables are observed by remotely sensing the global distribution of reflected solar spectral and broadband radiance. These "reflected solar" variables include aerosols, clouds, radiative fluxes, snow, ice, vegetation, ocean color, and land cover. Achieving sufficient satellite instrument accuracy, stability, and overlap to rigorously observe decadal change signals has proven very difficult in most cases and has not yet been achieved in others [2]. One of the earliest efforts to make climate quality observations was for Earth Radiation Budget: Nimbus 6/7 in the late 1970s, ERBE in the 1980s/90s, and CERES in 2000s are examples of the most complete global records. The recent CERES data products have carried out the most extensive intercomparisons because if the need to merge data from up to 11 instruments (CERES, MODIS, geostationary imagers) on 7 spacecraft (Terra, Aqua, and 5 geostationary) for any given month. In order to achieve climate calibration for cloud feedbacks, the radiative effect of clear-sky, all-sky, and cloud radiative effect must all be made with very high stability and accuracy. For shortwave solar reflected flux, even the 1% CERES broadband absolute accuracy (1-sigma confidence bound) is not sufficient to allow gaps in the radiation record for decadal climate change. Typical absolute accuracy for the best narrowband sensors like SeaWiFS, MISR, and MODIS range from 2 to 4% (1-sigma). IPCC greenhouse gas radiative forcing is approx. 0.6 W/sq m per decade or 0.6% of the global mean shortwave reflected flux, so that a 50% cloud feedback would change the global reflected flux by approx. 0.3 W/sq m or 0.3% per decade in broadband SW calibration change. Recent results comparing CERES reflected flux changes with MODIS, MISR, and SeaWiFS narrowband changes concluded that only SeaWiFS and CERES were approaching sufficient stability in calibration for decadal climate change [3]. Results using deep convective clouds in the optically thick limit as a stability target may prove very effective for improving past data sets like ISCCP. Results for intercalibration of geostationary imagers to CERES using an entire month of regional nearly coincident data demonstrates new approaches to constraining the calibration of current geostationary imagers. The new Decadal Survey Mission CLARREO is examining future approaches to a "NIST-in-Orbit" approach of very high absolute accuracy reference radiometers that cover the full solar and infrared spectrum at high spectral resolution but at low spatial resolution. Sampling studies have shown that a precessing CLARREO mission could calibrate other geo and leo reflected solar radiation and thermal infrared sensors.

Magnetic flux in modeled magnetic clouds at 1 AU and some specific comparisons to associated photospheric flux

NASA Technical Reports Server (NTRS)

Lepping, R. P.; Szabo, A.; DeForest, C. E.; Thompson, B. J.

1997-01-01

In order to better understand the solar origins of magnetic clouds, statistical distributions of the estimated axial magnetic flux of 30 magnetic clouds at 1 AU, separated according to their occurrence during the solar cycle, were obtained and a comparison was made of the magnetic flux of a magnetic cloud to the aggregate flux of apparently associated photospheric magnetic flux tubes, for some specific cases. The 30 magnetic clouds comprise 12 cases from WIND, and the remainder from IMP-8, earlier IMPs, the International Sun-Earth Explorer (ISEE) 3 and HELIOS. The total magnetic flux along the cloud axis was estimated using a constant alpha, cylindrical, force-free flux rope model to determine cloud diameter and axial magentic field strength. The distribution of magentic fluxes for the 30 clouds is shown to be in the form of a skewed Gaussian.

Decentralized Fuzzy MPC on Spatial Power Control of a Large PHWR

NASA Astrophysics Data System (ADS)

Liu, Xiangjie; Jiang, Di; Lee, Kwang Y.

2016-08-01

Reliable power control for stabilizing the spatial oscillations is quite important for ensuring the safe operation of a modern pressurized heavy water reactor (PHWR), since these spatial oscillations can cause “flux tilting” in the reactor core. In this paper, a decentralized fuzzy model predictive control (DFMPC) is proposed for spatial control of PHWR. Due to the load dependent dynamics of the nuclear power plant, fuzzy modeling is used to approximate the nonlinear process. A fuzzy Lyapunov function and “quasi-min-max” strategy is utilized in designing the DFMPC, to reduce the conservatism. The plant-wide stability is achieved by the asymptotically positive realness constraint (APRC) for this decentralized MPC. The solving optimization problem is based on a receding horizon scheme involving the linear matrix inequalities (LMIs) technique. Through dynamic simulations, it is demonstrated that the designed DFMPC can effectively suppress spatial oscillations developed in PHWR, and further, shows the advantages over the typical parallel distributed compensation (PDC) control scheme.

Simulated sensitivity of the tropical cyclone eyewall replacement cycle to the ambient temperature profile

NASA Astrophysics Data System (ADS)

Ma, Xulin; He, Jie; Ge, Xuyang

2017-09-01

In this study, the impacts of the environmental temperature profile on the tropical cyclone eyewall replacement cycle are examined using idealized numerical simulations. It is found that the environmental thermal condition can greatly affect the formation and structure of a secondary eyewall and the intensity change during the eyewall replacement cycle. Simulation with a warmer thermal profile produces a larger moat and a prolonged eyewall replacement cycle. It is revealed that the enhanced static stability greatly suppresses convection, and thus causes slow secondary eyewall formation. The possible processes influencing the decay of inner eyewall convection are investigated. It is revealed that the demise of the inner eyewall is related to a choking effect associated with outer eyewall convection, the radial distribution of moist entropy fluxes within the moat region, the enhanced static stability in the inner-core region, and the interaction between the inner and outer eyewalls due to the barotropic instability. This study motivates further research into how environmental conditions influence tropical cyclone dynamics and thermodynamics.

Compact toroid generation, lifetime, and stability studies in linear reversed-field theta pinch geometries, (TRX-1): Second annual and final report, June 1981-March 1983

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

Hoffman, A.L.; Slough, J.T.

1983-09-01

Four major areas have been investigated in the triggered reconnection experiment (TRX) program. These areas are flux trapping; formation (reconnection and axial dynamics); stability; and lifetime. This report describes the progress in each of these areas. Flux trapping for relatively slow field reversal rates due to the formation of a wall sheath has been accomplished and techniques have been developed for both triggered and programmed reconnection and the formation process has been optimized for maximum flux retention. Rotational n=2 instability has been controlled through the use of octopole barrier fields and long particle lifetimes have been achieved through optimization ofmore » the formation process. 46 refs., 63 figs., 4 tabs. (FI)« less

Emergent properties of climate-vegetation feedbacks in the North American Monsoon Macrosystem

NASA Astrophysics Data System (ADS)

Mathias, A.; Niu, G.; Zeng, X.

2012-12-01

The ability of ecosystems to adapt naturally to climate change and associated disturbances (e.g. wildfires, spread of invasive species) is greatly affected by the stability of feedback interactions between climate and vegetation. In order to study climate-vegetation interactions, such as CO2 and H2O exchange in the North American Monsoon System (NAMS), we plan to couple a community land surface model (NoahMP or CLM) used in regional climate models (WRF) with an individual based, spatially explicit vegetation model (ECOTONE). Individual based modeling makes it possible to link individual plant traits with properties of plant communities. Community properties, such as species composition and species distribution arise from dynamic interactions of individual plants with each other, and with their environment. Plants interact with each other through intra- and interspecific competition for resources (H2O, nitrogen), and the outcome of these interactions depends on the properties of the plant community and the environment itself. In turn, the environment is affected by the resulting change in community structure, which may have an impact on the drivers of climate change. First, we performed sensitivity tests of ECOTONE to assess its ability to reproduce vegetation distribution in the NAMS. We compared the land surface model and ECOTONE with regard to their capability to accurately simulate soil moisture, CO2 flux and above ground biomass. For evaluating the models we used the eddy-correlation sensible and latent heat fluxes, CO2 flux and observations of other climate and environmental variables (e.g. soil temperature and moisture) from the Santa Rita experimental range. The model intercomparison helped us understand the advantages and disadvantages of each model, providing us guidance for coupling the community land surface model (NoahMP or CLM) with ECOTONE.

Flux concentrations on solar dynamic components due to mispointing

NASA Technical Reports Server (NTRS)

Rylicki, Daniel S.

1992-01-01

Mispointing of the solar dynamic (SD) concentrator designed for use on Space Station Freedom (SSF) causes the optical axis of the concentrator to be nonparallel to the incoming rays from the Sun. This causes solar flux not to be focused into the aperture hole of the receiver and may position the flux on other SSF components. A Rocketdyne analysis has determined the thermal impact of off-axis radiation due to mispointing on elements of the SD module and photovoltaic (PV) arrays. The conclusion was that flux distributions on some of the radiator components, the two-axis gimbal rings, the truss, and the PV arrays could present problems. The OFFSET computer code was used at Lewis Research Center to further investigate these flux distributions incident on components. The Lewis study included distributions for a greater range of mispoint angles than the Rocketdyne study.

Gravity wave momentum flux estimation from CRISTA satellite data

NASA Astrophysics Data System (ADS)

Ern, M.; Preusse, P.; Alexander, M. J.; Offermann, D.

2003-04-01

Temperature altitude profiles measured by the CRISTA satellite were analyzed for gravity waves (GWs). Amplitudes, vertical and horizontal wavelengths of GWs are retrieved by applying a combination of maximum entropy method (MEM) and harmonic analysis (HA) to the temperature height profiles and subsequently comparing the so retrieved GW phases of adjacent altitude profiles. From these results global maps of the absolute value of the vertical flux of horizontal momentum have been estimated. Significant differences between distributions of the temperature variance and distributions of the momentum flux exist. For example, global maps of the momentum flux show a pronounced northward shift of the equatorial maximum whereas temperature variance maps of the tropics/subtropics are nearly symmetric with respect to the equator. This indicates the importance of the influence of horizontal and vertical wavelength distribution on global structures of the momentum flux.

Evaluation of Surface Flux Parameterizations with Long-Term ARM Observations

DOE PAGES

Liu, Gang; Liu, Yangang; Endo, Satoshi

2013-02-01

Surface momentum, sensible heat, and latent heat fluxes are critical for atmospheric processes such as clouds and precipitation, and are parameterized in a variety of models ranging from cloud-resolving models to large-scale weather and climate models. However, direct evaluation of the parameterization schemes for these surface fluxes is rare due to limited observations. This study takes advantage of the long-term observations of surface fluxes collected at the Southern Great Plains site by the Department of Energy Atmospheric Radiation Measurement program to evaluate the six surface flux parameterization schemes commonly used in the Weather Research and Forecasting (WRF) model and threemore » U.S. general circulation models (GCMs). The unprecedented 7-yr-long measurements by the eddy correlation (EC) and energy balance Bowen ratio (EBBR) methods permit statistical evaluation of all six parameterizations under a variety of stability conditions, diurnal cycles, and seasonal variations. The statistical analyses show that the momentum flux parameterization agrees best with the EC observations, followed by latent heat flux, sensible heat flux, and evaporation ratio/Bowen ratio. The overall performance of the parameterizations depends on atmospheric stability, being best under neutral stratification and deteriorating toward both more stable and more unstable conditions. Further diagnostic analysis reveals that in addition to the parameterization schemes themselves, the discrepancies between observed and parameterized sensible and latent heat fluxes may stem from inadequate use of input variables such as surface temperature, moisture availability, and roughness length. The results demonstrate the need for improving the land surface models and measurements of surface properties, which would permit the evaluation of full land surface models.« less

TORT/MCNP coupling method for the calculation of neutron flux around a core of BWR.

PubMed

Kurosawa, Masahiko

2005-01-01

For the analysis of BWR neutronics performance, accurate data are required for neutron flux distribution over the In-Reactor Pressure Vessel equipments taking into account the detailed geometrical arrangement. The TORT code can calculate neutron flux around a core of BWR in a three-dimensional geometry model, but has difficulties in fine geometrical modelling and lacks huge computer resource. On the other hand, the MCNP code enables the calculation of the neutron flux with a detailed geometry model, but requires very long sampling time to give enough number of particles. Therefore, a TORT/MCNP coupling method has been developed to eliminate the two problems mentioned above in each code. In this method, the TORT code calculates angular flux distribution on the core surface and the MCNP code calculates neutron spectrum at the points of interest using the flux distribution. The coupling method will be used as the DOT-DOMINO-MORSE code system. This TORT/MCNP coupling method was applied to calculate the neutron flux at points where induced radioactivity data were measured for 54Mn and 60Co and the radioactivity calculations based on the neutron flux obtained from the above method were compared with the measured data.

The Ability of Atmospheric Data to Reduce Disagreements in Wetland Methane Flux Estimates over North America

NASA Astrophysics Data System (ADS)

Miller, S. M.; Andrews, A. E.; Benmergui, J. S.; Commane, R.; Dlugokencky, E. J.; Janssens-Maenhout, G.; Melton, J. R.; Michalak, A. M.; Sweeney, C.; Worthy, D. E. J.

2015-12-01

Existing estimates of methane fluxes from wetlands differ in both magnitude and distribution across North America. We discuss seven different bottom-up methane estimates in the context of atmospheric methane data collected across the US and Canada. In the first component of this study, we explore whether the observation network can even detect a methane pattern from wetlands. We find that the observation network can identify a methane pattern from Canadian wetlands but not reliably from US wetlands. Over Canada, the network can even identify spatial patterns at multi-provence scales. Over the US, by contrast, anthropogenic emissions and modeling errors obscure atmospheric patterns from wetland fluxes. In the second component of the study, we then use these observations to reconcile disagreements in the magnitude, seasonal cycle, and spatial distribution of existing estimates. Most existing estimates predict fluxes that are too large with a seasonal cycle that is too narrow. A model known as LPJ-Bern has a spatial distribution most consistent with atmospheric observations. By contrast, a spatially-constant model outperforms the distribution of most existing flux estimates across Canada. The results presented here provide several pathways to reduce disagreements among existing wetland flux estimates across North America.

Evaluation of methane oxidation activity in waste biocover soil during landfill stabilization.

PubMed

He, Ruo; Wang, Jing; Xia, Fang-Fang; Mao, Li-Juan; Shen, Dong-Sheng

2012-10-01

Biocover soil has been demonstrated to have high CH(4) oxidation capacity and is considered as a good alternative cover material to mitigate CH(4) emission from landfills, yet the response of CH(4) oxidation activity of biocover soils to the variation of CH(4) loading during landfill stabilization is poorly understood. Compared with a landfill cover soil (LCS) collected from Hangzhou Tianziling landfill cell, the development of CH(4) oxidation activity of waste biocover soil (WBS) was investigated using simulated landfill systems in this study. Although a fluctuation of influent CH(4) flux occurred during landfill stabilization, the WBS covers showed a high CH(4) removal efficiency of 94-96% during the entire experiment. In the LCS covers, the CH(4) removal efficiencies varied with the fluctuation of CH(4) influent flux, even negative ones occurred due to the storage of CH(4) in the soil porosities after the high CH(4) influent flux of ~137 gm(-2) d(-1). The lower concentrations of O(2) and CH(4) as well as the higher concentration of CO(2) were observed in the WBS covers than those in the LCS covers. The highest CH(4) oxidation rates of the two types of soil covers both occurred in the bottom layer (20-30 cm). Compared to the LCS, the WBS showed higher CH(4) oxidation activity and methane monooxygenase activity over the course of the experiment. Overall, this study indicated the WBS worked well for the fluctuation of CH(4) influent flux during landfill stabilization. Copyright © 2012 Elsevier Ltd. All rights reserved.

Viscosity and viscoelasticity of two-phase systems having diffuse interfaces

NASA Technical Reports Server (NTRS)

Hopper, R. W.

1976-01-01

The equilibrium stability criterion for diffuse interfaces in a two-component solution with a miscibility gap requires that the interdiffusion flux vanish. If the system is continuously deformed, convective fluxes disrupt the equilibrium in the interface regions and induce a counter diffusive flux, which is dissipative and contributes to the apparent viscosity of the mixture. Chemical free energy is recoverably stored, causing viscoelastic phenomena. Both effects are significant.

Actively heated high-resolution fiber-optic-distributed temperature sensing to quantify streambed flow dynamics in zones of strong groundwater upwelling

USGS Publications Warehouse

Briggs, Martin A.; Buckley, Sean F.; Bagtzoglou, Amvrossios C.; Werkema, Dale D.; Lane, John W.

2016-01-01

Zones of strong groundwater upwelling to streams enhance thermal stability and moderate thermal extremes, which is particularly important to aquatic ecosystems in a warming climate. Passive thermal tracer methods used to quantify vertical upwelling rates rely on downward conduction of surface temperature signals. However, moderate to high groundwater flux rates (>−1.5 m d−1) restrict downward propagation of diurnal temperature signals, and therefore the applicability of several passive thermal methods. Active streambed heating from within high-resolution fiber-optic temperature sensors (A-HRTS) has the potential to define multidimensional fluid-flux patterns below the extinction depth of surface thermal signals, allowing better quantification and separation of local and regional groundwater discharge. To demonstrate this concept, nine A-HRTS were emplaced vertically into the streambed in a grid with ∼0.40 m lateral spacing at a stream with strong upward vertical flux in Mashpee, Massachusetts, USA. Long-term (8–9 h) heating events were performed to confirm the dominance of vertical flow to the 0.6 m depth, well below the extinction of ambient diurnal signals. To quantify vertical flux, short-term heating events (28 min) were performed at each A-HRTS, and heat-pulse decay over vertical profiles was numerically modeled in radial two dimension (2-D) using SUTRA. Modeled flux values are similar to those obtained with seepage meters, Darcy methods, and analytical modeling of shallow diurnal signals. We also observed repeatable differential heating patterns along the length of vertically oriented sensors that may indicate sediment layering and hyporheic exchange superimposed on regional groundwater discharge.

GREEN BANK TELESCOPE AND SWIFT X-RAY TELESCOPE OBSERVATIONS OF THE GALACTIC CENTER RADIO MAGNETAR SGR J1745–2900

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

Lynch, Ryan S.; Archibald, Robert F.; Kaspi, Victoria M.

We present results from eight months of Green Bank Telescope 8.7 GHz observations and nearly 18 months of Swift X-ray telescope observations of the radio magnetar SGR J1745–2900. We tracked the radio and X-ray flux density, polarization properties, profile evolution, rotation, and single-pulse behavior. We identified two main periods of activity. The first is characterized by approximately 5.5 months of relatively stable evolution in radio flux density, rotation, and profile shape, while in the second these properties varied substantially. Specifically, a third profile component emerged and the radio flux also became more variable. The single pulse properties also changed, mostmore » notably with a larger fraction of pulses with pulse widths ∼5–20 ms in the erratic state. Bright single pulses are well described by a log-normal energy distribution at low energies, but with an excess at high energies. The 2–10 keV flux decayed steadily since the initial X-ray outburst, while the radio flux remained stable to within ∼20% during the stable state. A joint pulsar timing analysis of the radio and X-ray data shows a level of timing noise unprecedented in a radio magnetar, though during the time covered by the radio data alone the timing noise was at a level similar to that observed in other radio magnetars. While SGR J1745–2900 is similar to other radio magnetars in many regards, it differs by having experienced a period of relative stability in the radio that now appears to have ended, while the X-ray properties evolved independently.« less

Effects of GAC layer on the performance of gravity-driven membrane filtration (GDM) system for rainwater recycling.

PubMed

Ding, An; Wang, Jinlong; Lin, Dachao; Zeng, Rong; Yu, Shengping; Gan, Zhendong; Ren, Nanqi; Li, Guibai; Liang, Heng

2018-01-01

Gravity-driven membrane filtration (GDM) is promising for decentralized rainwater recycling, owing to low maintenance and energy consumption. However, the organic removal by GDM process is sometimes undesirable and the quality of the permeate cannot meet the standard of water reuse. To improve this, granular activate carbon (GAC) was added as a particle layer on the membrane surface of GDM system. Additionally, a system with sand addition and a system with no particle addition were trialed as comparisons, to study the combined effects of particle hindering and adsorption on the removal efficacy of organics and the development of permeate flux. Results showed that GDM with a GAC layer improved removal efficiency of organics by 25%, and that GAC enhanced removal of florescent compounds (e.g., aromatic proteins, tryptophan proteins and humics), compared with the other two systems. Additionally, the permeate flux in three systems stabilized after Day 25, and kept stable until the end of the operation. However, the presence of GAC layer decreased the level of stable flux (3.2 L/m 2 h) compared with the control system (4.5 L/m 2 h). The factors responsible for the lower flux and severe membrane fouling in GAC layer assisted system were the combined effects of particle and adsorption which led to a denser bio-fouling layer with higher amount of biomass and extracellular polymeric substances contents (proteins and polysaccharides). Resistance distribution analyses revealed that GAC layer mainly increased hydraulically reversible resistance (occupied 93%) of the total resistance, indicating that the flux could be recovered easily by simple physical cleaning. Copyright © 2017 Elsevier Ltd. All rights reserved.

A coupled distributed hydrological-stability analysis on a terraced slope of Valtellina (northern Italy)

NASA Astrophysics Data System (ADS)

Camera, C.; Apuani, T.; Masetti, M.

2013-02-01

The aim of this work was to understand and reproduce the hydrological dynamics of a slope, which was terraced using dry-stone retaining walls and its response to these processes in terms of stability at the slope scale. The slope studied is located in Valtellina (northern Italy), near the village of Tresenda, and in the last 30 yr has experienced several soil slip/debris flow events. In 1983 alone, such events caused the death of 18 people. Direct observation of the events of 1983 enabled the principal triggering cause of these events to be recognized in the formation of an overpressure at the base of a dry-stone wall, which caused its failure. To perform the analyses it is necessary to include the presence of dry-stone walls, considering the importance they have in influencing hydrological and geotechnical processes at the slope scale. This requires a very high resolution DEM (1 m × 1 m because the walls are from 0.60 m to 1.0 m wide) that has been appositely derived. A hydrogeological raster-based model, which takes into account both the unsaturated and saturated flux components, was applied. This was able to identify preferential infiltration zones and was rather precise in the prediction of maximum groundwater levels, providing valid input for the distributed stability analysis. Results of the hydrogeological model were used for the successive stability analysis. Sections of terrace were identified from the downslope base of a retaining wall to the top of the next downslope retaining wall. Within each section a global method of equilibrium was applied to determine its safety factor. The stability model showed a general tendency to overestimate the amount of unstable areas. An investigation of the causes of this unexpected behavior was, therefore, also performed in order to progressively improve the reliability of the model.

On contemporary sedimentation at the titanic survey area

NASA Astrophysics Data System (ADS)

Lukashin, V. N.

2009-12-01

The basic parameters of the sedimentation environment are considered: the Western Boundary Deep Current that transports sedimentary material and distributes it on the survey area; the nepheloid layer, its features, and the distribution of the concentrations and particulate standing crop in it; the distribution of the horizontal and vertical fluxes of the sedimentary material; and the bottom sediments and their absolute masses. The comparison of the vertical fluxes of the particulate matter and the absolute masses of the sediments showed that the contemporary fluxes of sedimentary material to the bottom provided the distribution of the absolute masses of the sediments in the survey area during the Holocene.

An automated model-based aim point distribution system for solar towers

NASA Astrophysics Data System (ADS)

Schwarzbözl, Peter; Rong, Amadeus; Macke, Ansgar; Säck, Jan-Peter; Ulmer, Steffen

2016-05-01

Distribution of heliostat aim points is a major task during central receiver operation, as the flux distribution produced by the heliostats varies continuously with time. Known methods for aim point distribution are mostly based on simple aim point patterns and focus on control strategies to meet local temperature and flux limits of the receiver. Lowering the peak flux on the receiver to avoid hot spots and maximizing thermal output are obviously competing targets that call for a comprehensive optimization process. This paper presents a model-based method for online aim point optimization that includes the current heliostat field mirror quality derived through an automated deflectometric measurement process.

Ondansetron Suppositories: Extemporaneous Preparation, Drug Release, Stability and Flux through Rabbit Rectal Membrane.

PubMed

Tenjarla, S N; Ward, E S; Fox, J L

1998-01-01

The objective of this study was to determine the feasibility and develop a formulation for an extemporaneously prepared ondansetron suppository form Zofran 8-mg tablets. The stability of the formulation over 28 days of refrigerated storage and the initial and poststorage drug-release profiles were evaluated. The ondansetron flux in an in vitro model (a rabbit rectal membrane) from each formulation was determined. Suppositories containing 8 or 16 mg ondansetron were made using commercially available hydrophobic and hydrophilic suppository bases. A sensitive, stability-indication high-performance liquid chromatography assay was used for the analysis of ondansetron. The partition coefficient (octanol/water) of ondansetron and the displacement factor of tablets with each of the two bases were determined . The suppositories, formed in disposable molds, were kept in plastic wwrap and stored at 5 deg C in the refrigerator. The effect of storage on ondansetron release from the suppository base and the stability of ondansetron in the two suppository bases were evaluated over a period of 28 days. The dissolution study provided data on the release profile of the drug over 28 days, as well as the stabilty of the drug during the storage period. Ondansetron flux through rabbit rectal membrane from the various formulations was determined in vitro using modified Franz diffusion cells. Greater than 90% of the intiial amount (8 or 16 mg) of ondansetron was retained in the suppositories after 28-day storage at 5 deg C for both hydrophilic and hydrophobic formulations. There was no statistically siginificant difference in the drug-release profiles during this period. Ondansetron flux through the rabbit rectal membrane from 8- and 16-mg hydrophobic suppositories was 393 +/- 58 and 76.2 +/- 13.8 micrograms per centimeters squared -hour, respectively (n=6). The corresponding flux from 8- and 16-mg hydrophilic suppositories was 37.8 +/- 16 and 81.7 +/- 22.9 micrograms per centimeter squared - hour, respectively. The variablility in the flux required further study but the levels achieved indicated that extemporaneous preparation of ondansetron suppositories is reasonable using commercially available components.

Measurement of air and VOC vapor fluxes during gas-driven soil remediation: bench-scale experiments.

PubMed

Kim, Heonki; Kim, Taeyun; Shin, Seungyeop; Annable, Michael D

2012-09-04

In this laboratory study, an experimental method was developed for the quantitative analyses of gas fluxes in soil during advective air flow. One-dimensional column and two- and three-dimensional flow chamber models were used in this study. For the air flux measurement, n-octane vapor was used as a tracer, and it was introduced in the air flow entering the physical models. The tracer (n-octane) in the gas effluent from the models was captured for a finite period of time using a pack of activated carbon, which then was analyzed for the mass of n-octane. The air flux was calculated based on the mass of n-octane captured by the activated carbon and the inflow concentration. The measured air fluxes are in good agreement with the actual values for one- and two-dimensional model experiments. Using both the two- and three-dimensional models, the distribution of the air flux at the soil surface was measured. The distribution of the air flux was found to be affected by the depth of the saturated zone. The flux and flux distribution of a volatile contaminant (perchloroethene) was also measured by using the two-dimensional model. Quantitative information of both air and contaminant flux may be very beneficial for analyzing the performance of gas-driven subsurface remediation processes including soil vapor extraction and air sparging.

Investigating Coastal Processes Responsible for Large-Scale Shoreline Responses to Human Shoreline Stabilization

NASA Astrophysics Data System (ADS)

Slott, J. M.; Murray, A. B.; Ashton, A. D.

2006-12-01

Human shoreline stabilization practices, such as beach nourishment (i.e. placing sand on an eroding beach), have become more prevalent as erosion threatens coastal communities. On sandy shorelines, recent experiments with a numerical model of shoreline change (Slott, et al., in press) indicate that moderate shifts in storminess patterns, one possible outcome of global warming, may accelerate the rate at which shorelines erode or accrete, by altering the angular distribution of approaching waves (the `wave climate'). Accelerated erosion would undoubtedly place greater demands on stabilization. Scientists and coastal engineers have typically only considered the site-specific consequences of shoreline stabilization; here we explore the coastal processes responsible for large-scale (10's kms) and long-term (decades) effects using a numerical model developed by Ashton, et al. (2001). In this numerical model, waves breaking at oblique angles drive a flux of sediment along the shoreline, where gradients in this flux can shape the coastline into surprisingly complex forms (e.g. cuspate-capes found on the Carolina coast). Wave "shadowing" plays a major role in shoreline evolution, whereby coastline features may block incoming waves from reaching distant parts. In this work, we include beach nourishment in the Ashton, et al. (2001) model. Using a cuspate-cape shoreline as our initial model condition, we conducted pairs of experiments and varied the wave-climate forcing across each pair, each representing different storminess scenarios. Here we report on one scenario featuring increased extra-tropical storm influence. For each experiment-pair we ran a control experiment with no shoreline stabilization and a second where a beach nourishment project stabilized a cape tip. By comparing the results of these two parallel runs, we isolate the tendency of the shoreline to migrate landward or seaward along the domain due solely to beach nourishment. Significant effects from beach nourishment reached several tens of kilometers away from the nourishment project. The magnitude of these effects rivaled the erosion we expect from sea-level rise alone over the coming century. Furthermore, the nature of the effects were unexpected: where we expect beach nourishment sand to spread laterally in the direction of net alongshore sediment transport (e.g. to the right looking off-shore), coastline segments to the right of the cape should tend to migrate seaward, while segments to the left of the cape might naively be expected to feel little effects. We observed, however, that shoreline segments to the left (right) of the stabilized cape tip tended to migrate seaward (landward). Two statistics we collected for each model run--the extent of wave shadowing and the net flux of sediment at each alongshore position--helped explain the surprising behavior. By pinning the location of the cape tip, beach nourishment altered the way in which the cape shadowed adjacent coastlines. The stabilized cape-tip shadowed segments to the left more often, increasing the influence from left-approaching waves. These shoreline segments shifted seaward, relative to the non-nourishment case, through a convergence in alongshore sediment transport from increased transport from the left, rather than from laterally-spreading beach nourishment sand. The stabilized cape-tip shadowed segments to the right less often, increasing the influence of left-approaching waves. These segments shifted landward through a divergence in alongshore sediment transport from increased transport to the right.

Including metabolite concentrations into flux balance analysis: thermodynamic realizability as a constraint on flux distributions in metabolic networks

PubMed Central

Hoppe, Andreas; Hoffmann, Sabrina; Holzhütter, Hermann-Georg

2007-01-01

Background In recent years, constrained optimization – usually referred to as flux balance analysis (FBA) – has become a widely applied method for the computation of stationary fluxes in large-scale metabolic networks. The striking advantage of FBA as compared to kinetic modeling is that it basically requires only knowledge of the stoichiometry of the network. On the other hand, results of FBA are to a large degree hypothetical because the method relies on plausible but hardly provable optimality principles that are thought to govern metabolic flux distributions. Results To augment the reliability of FBA-based flux calculations we propose an additional side constraint which assures thermodynamic realizability, i.e. that the flux directions are consistent with the corresponding changes of Gibb's free energies. The latter depend on metabolite levels for which plausible ranges can be inferred from experimental data. Computationally, our method results in the solution of a mixed integer linear optimization problem with quadratic scoring function. An optimal flux distribution together with a metabolite profile is determined which assures thermodynamic realizability with minimal deviations of metabolite levels from their expected values. We applied our novel approach to two exemplary metabolic networks of different complexity, the metabolic core network of erythrocytes (30 reactions) and the metabolic network iJR904 of Escherichia coli (931 reactions). Our calculations show that increasing network complexity entails increasing sensitivity of predicted flux distributions to variations of standard Gibb's free energy changes and metabolite concentration ranges. We demonstrate the usefulness of our method for assessing critical concentrations of external metabolites preventing attainment of a metabolic steady state. Conclusion Our method incorporates the thermodynamic link between flux directions and metabolite concentrations into a practical computational algorithm. The weakness of conventional FBA to rely on intuitive assumptions about the reversibility of biochemical reactions is overcome. This enables the computation of reliable flux distributions even under extreme conditions of the network (e.g. enzyme inhibition, depletion of substrates or accumulation of end products) where metabolite concentrations may be drastically altered. PMID:17543097

Localized Artificial Viscosity Stabilization of Discontinuous Galerkin Methods for Nonhydrostatic Mesoscale Atmospheric Modeling

DTIC Science & Technology

2014-01-01

with a Riemann flux !"#! (!! ,!!!,), where !!! denotes the solution outside the current element !. Various (approximate) Riemann solvers ...can be used to calculate the Riemann flux, and the Rusanov Riemann solver is adopted in this paper. Then Eq. (7) can be rewritten as !

Self-equilibration of the radius distribution in self-catalyzed GaAs nanowires

NASA Astrophysics Data System (ADS)

Leshchenko, E. D.; Turchina, M. A.; Dubrovskii, V. G.

2016-08-01

This work addresses the evolution of radius distribution function in self-catalyzed vapor-liquid-solid growth of GaAs nanowires from Ga droplets. Different growth regimes are analyzed depending on the V/III flux ratio. In particular, we find a very unusual selfequilibration regime in which the radius distribution narrows up to a certain stationary radius regardless of the initial size distribution of Ga droplets. This requires that the arsenic vapor flux is larger than the gallium one and that the V/III influx imbalance is compensated by a diffusion flux of gallium adatoms. Approximate analytical solution is compared to the numerical radius distribution obtained by solving the corresponding Fokker-Planck equation by the implicit difference scheme.

Measurement of Solar pp-neutrino flux with Borexino: results and implications

NASA Astrophysics Data System (ADS)

Smirnov, O. Yu; Agostini, M.; Appel, S.; Bellini, G.; Benziger, J.; Bick, D.; Bonfini, G.; Bravo, D.; Caccianiga, B.; Calaprice, F.; Caminata, A.; Cavalcante, P.; Chepurnov, A.; D'Angelo, D.; Davini, S.; Derbin, A.; Di Noto, L.; Drachnev, I.; Etenko, A.; Fomenko, K.; Franco, D.; Gabriele, F.; Galbiati, C.; Ghiano, C.; Giammarchi, M.; Goeger-Neff, M.; Goretti, A.; Gromov, M.; Hagner, C.; Hungerford, E.; Ianni, Aldo; Ianni, Andrea; Jedrzejczak, K.; Kaiser, M.; Kobychev, V.; Korablev, D.; Korga, G.; Kryn, D.; Laubenstein, M.; Lehnert, B.; Litvinovich, E.; Lombardi, F.; Lombardi, P.; Ludhova, L.; Lukyanchenko, G.; Machulin, O.; Manecki, S.; Maneschg, W.; Marcocci, S.; Meroni, E.; Meyer, M.; Miramonti, L.; Misiaszek, M.; Montuschi, M.; Mosteiro, P.; Muratova, V.; Neumair, B.; Oberauer, L.; Obolensky, M.; Ortica, F.; Pallavicini, M.; Papp, L.; Perasso, L.; Pocar, A.; Ranucci, G.; Razeto, A.; Re, A.; Romani, A.; Roncin, R.; Rossi, N.; Schönert, S.; Semenov, D.; Simgen, H.; Skorokhvatov, M.; Sotnikov, A.; Sukhotin, S.; Suvorov, Y.; Tartaglia, R.; Testera, G.; Thurn, J.; Toropova, M.; Unzhakov, E.; Vishneva, A.; Vogelaar, R. B.; von Feilitzsch, F.; Wang, H.; Weinz, S.; Winter, J.; Wojcik, M.; Wurm, M.; Yokley, Z.; Zaimidoroga, O.; Zavatarelli, S.; Zuber, K.; Zuzel, G.

2016-02-01

Measurement of the Solar pp-neutrino flux completed the measurement of Solar neutrino fluxes from the pp-chain of reactions in Borexino experiment. The result is in agreement with the prediction of the Standard Solar Model and the MSW/LMA oscillation scenario. A comparison of the total neutrino flux from the Sun with Solar luminosity in photons provides a test of the stability of the Sun on the 105 years time scale, and sets a strong limit on the power production by the unknown energy sources in the Sun.

An implicit flux-split algorithm to calculate hypersonic flowfields in chemical equilibrium

NASA Technical Reports Server (NTRS)

Palmer, Grant

1987-01-01

An implicit, finite-difference, shock-capturing algorithm that calculates inviscid, hypersonic flows in chemical equilibrium is presented. The flux vectors and flux Jacobians are differenced using a first-order, flux-split technique. The equilibrium composition of the gas is determined by minimizing the Gibbs free energy at every node point. The code is validated by comparing results over an axisymmetric hemisphere against previously published results. The algorithm is also applied to more practical configurations. The accuracy, stability, and versatility of the algorithm have been promising.

Control of wave-driven turbulence and surface heating on the mixing of microplastic marine debris

NASA Astrophysics Data System (ADS)

Kukulka, T.; Lavender Law, K. L.; Proskurowski, G. K.

2016-02-01

Buoyant microplastic marine debris (MPMD) is a pollutant in the ocean surface boundary layer (OSBL) that is submerged by turbulent transport processes. Langmuir circulation (LC) is a turbulent process driven by wind and surface waves that enhances mixing in the OSBL. Sea surface cooling also contributes to OSBL turbulence by driving convection. On the other hand, sea surface heating stratifies and stabilizes the water column to reduce turbulent motion. We analyze observed MPMD surface concentrations in the Atlantic and Pacific Oceans to reveal a significant increase in MPMD concentrations during surface heating and a decrease during surface cooling. Turbulence resolving large eddy simulations of the OSBL for an idealized diurnal heating cycle suggest that turbulent downward fluxes of buoyant tracers are enhanced at night, facilitating deep submergence of plastics, and suppressed in heating conditions, resulting in surface trapped MPMD. Simulations agree with observations if enhanced mixing due to LC is included. Our results demonstrate the controlling influence of surface heat fluxes and LC on turbulent transport in the OSBL and on vertical distributions of buoyant marine particles.

SEPARATION OF THE RIBBON FROM GLOBALLY DISTRIBUTED ENERGETIC NEUTRAL ATOM FLUX USING THE FIRST FIVE YEARS OF IBEX OBSERVATIONS

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

Schwadron, N. A.; Moebius, E.; Kucharek, H.

2014-11-01

The Interstellar Boundary Explorer (IBEX) observes the IBEX ribbon, which stretches across much of the sky observed in energetic neutral atoms (ENAs). The ribbon covers a narrow (∼20°-50°) region that is believed to be roughly perpendicular to the interstellar magnetic field. Superimposed on the IBEX ribbon is the globally distributed flux that is controlled by the processes and properties of the heliosheath. This is a second study that utilizes a previously developed technique to separate ENA emissions in the ribbon from the globally distributed flux. A transparency mask is applied over the ribbon and regions of high emissions. We thenmore » solve for the globally distributed flux using an interpolation scheme. Previously, ribbon separation techniques were applied to the first year of IBEX-Hi data at and above 0.71 keV. Here we extend the separation analysis down to 0.2 keV and to five years of IBEX data enabling first maps of the ribbon and the globally distributed flux across the full sky of ENA emissions. Our analysis shows the broadening of the ribbon peak at energies below 0.71 keV and demonstrates the apparent deformation of the ribbon in the nose and heliotail. We show global asymmetries of the heliosheath, including both deflection of the heliotail and differing widths of the lobes, in context of the direction, draping, and compression of the heliospheric magnetic field. We discuss implications of the ribbon maps for the wide array of concepts that attempt to explain the ribbon's origin. Thus, we present the five-year separation of the IBEX ribbon from the globally distributed flux in preparation for a formal IBEX data release of ribbon and globally distributed flux maps to the heliophysics community.« less

Combined point and distributed techniques for multidimensional estimation of spatial groundwater-stream water exchange in a heterogeneous sand bed-stream.

NASA Astrophysics Data System (ADS)

Gaona Garcia, J.; Lewandowski, J.; Bellin, A.

2017-12-01

Groundwater-stream water interactions in rivers determine water balances, but also chemical and biological processes in the streambed at different spatial and temporal scales. Due to the difficult identification and quantification of gaining, neutral and losing conditions, it is necessary to combine techniques with complementary capabilities and scale ranges. We applied this concept to a study site at the River Schlaube, East Brandenburg-Germany, a sand bed stream with intense sediment heterogeneity and complex environmental conditions. In our approach, point techniques such as temperature profiles of the streambed together with vertical hydraulic gradients provide data for the estimation of fluxes between groundwater and surface water with the numerical model 1DTempPro. On behalf of distributed techniques, fiber optic distributed temperature sensing identifies the spatial patterns of neutral, down- and up-welling areas by analysis of the changes in the thermal patterns at the streambed interface under certain flow. The study finally links point and surface temperatures to provide a method for upscaling of fluxes. Point techniques provide point flux estimates with essential depth detail to infer streambed structures while the results hardly represent the spatial distribution of fluxes caused by the heterogeneity of streambed properties. Fiber optics proved capable of providing spatial thermal patterns with enough resolution to observe distinct hyporheic thermal footprints at multiple scales. The relation of thermal footprint patterns and temporal behavior with flux results from point techniques enabled the use of methods for spatial flux estimates. The lack of detailed information of the physical driver's spatial distribution restricts the spatial flux estimation to the application of the T-proxy method, whose highly uncertain results mainly provide coarse spatial flux estimates. The study concludes that the upscaling of groundwater-stream water interactions using thermal measurements with combined point and distributed techniques requires the integration of physical drivers because of the heterogeneity of the flux patterns. Combined experimental and modeling approaches may help to obtain more reliable understanding of groundwater-surface water interactions at multiple scales.

[Spectra and thermal analysis of the arc in activating flux plasma arc welding].

PubMed

Chai, Guo-Ming; Zhu, Yi-Feng

2010-04-01

In activating flux plasma arc welding the welding arc was analyzed by spectra analysis technique, and the welding arc temperature field was measured by the infrared sensing and computer image technique. The distribution models of welding arc heat flow density of activating flux PAW welding were developed. The composition of welding arc affected by activated flux was studied, and the welding arc temperature field was studied. The results show that the spectral lines of argon atom and ionized argon atom of primary ionization are the main spectra lines of the conventional plasma welding arc. The spectra lines of weld metal are inappreciable in the spectra lines of the conventional plasma welding arc. The gas particle is the main in the conventional plasma welding arc. The conventional plasma welding arc is gas welding arc. The spectra lines of argon atom and ionized argon atom of primary ionization are intensified in the activating flux plasma welding arc, and the spectra lines of Ti, Cr and Fe elements are found in the activating flux plasma welding arc. The welding arc temperature distribution in activating flux plasma arc welding is compact, the outline of the welding arc temperature field is narrow, the range of the welding arc temperature distribution is concentrated, the welding arc radial temperature gradient is large, and the welding arc radial temperature gradient shows normal Gauss distribution.

A mobile ferromagnetic shape detection sensor using a Hall sensor array and magnetic imaging.

PubMed

Misron, Norhisam; Shin, Ng Wei; Shafie, Suhaidi; Marhaban, Mohd Hamiruce; Mailah, Nashiren Farzilah

2011-01-01

This paper presents a mobile Hall sensor array system for the shape detection of ferromagnetic materials that are embedded in walls or floors. The operation of the mobile Hall sensor array system is based on the principle of magnetic flux leakage to describe the shape of the ferromagnetic material. Two permanent magnets are used to generate the magnetic flux flow. The distribution of magnetic flux is perturbed as the ferromagnetic material is brought near the permanent magnets and the changes in magnetic flux distribution are detected by the 1-D array of the Hall sensor array setup. The process for magnetic imaging of the magnetic flux distribution is done by a signal processing unit before it displays the real time images using a netbook. A signal processing application software is developed for the 1-D Hall sensor array signal acquisition and processing to construct a 2-D array matrix. The processed 1-D Hall sensor array signals are later used to construct the magnetic image of ferromagnetic material based on the voltage signal and the magnetic flux distribution. The experimental results illustrate how the shape of specimens such as square, round and triangle shapes is determined through magnetic images based on the voltage signal and magnetic flux distribution of the specimen. In addition, the magnetic images of actual ferromagnetic objects are also illustrated to prove the functionality of mobile Hall sensor array system for actual shape detection. The results prove that the mobile Hall sensor array system is able to perform magnetic imaging in identifying various ferromagnetic materials.

A Mobile Ferromagnetic Shape Detection Sensor Using a Hall Sensor Array and Magnetic Imaging

PubMed Central

Misron, Norhisam; Shin, Ng Wei; Shafie, Suhaidi; Marhaban, Mohd Hamiruce; Mailah, Nashiren Farzilah

2011-01-01

This paper presents a Mobile Hall Sensor Array system for the shape detection of ferromagnetic materials that are embedded in walls or floors. The operation of the Mobile Hall Sensor Array system is based on the principle of magnetic flux leakage to describe the shape of the ferromagnetic material. Two permanent magnets are used to generate the magnetic flux flow. The distribution of magnetic flux is perturbed as the ferromagnetic material is brought near the permanent magnets and the changes in magnetic flux distribution are detected by the 1-D array of the Hall sensor array setup. The process for magnetic imaging of the magnetic flux distribution is done by a signal processing unit before it displays the real time images using a netbook. A signal processing application software is developed for the 1-D Hall sensor array signal acquisition and processing to construct a 2-D array matrix. The processed 1-D Hall sensor array signals are later used to construct the magnetic image of ferromagnetic material based on the voltage signal and the magnetic flux distribution. The experimental results illustrate how the shape of specimens such as square, round and triangle shapes is determined through magnetic images based on the voltage signal and magnetic flux distribution of the specimen. In addition, the magnetic images of actual ferromagnetic objects are also illustrated to prove the functionality of Mobile Hall Sensor Array system for actual shape detection. The results prove that the Mobile Hall Sensor Array system is able to perform magnetic imaging in identifying various ferromagnetic materials. PMID:22346653

LAD Dissertation Prize: Laboratory Identification of Magnetohydrodynamic Eruption Criteria in the Solar Corona

NASA Astrophysics Data System (ADS)

Myers, Clayton E.; Yamada, Masaaki; Ji, Hantao

2018-06-01

Ideal magnetohydrodynamic instabilities such as the kink and torus instabilities are believed to play an important role in driving storage-and-release eruptions in the solar corona. These instabilities act on long-lived, arched magnetic flux ropes that are line-tied to the solar surface. In spite of numerous observational and computational studies, the conditions under which these instabilities produce an eruption remain a subject of intense debate. In this paper, we use a line-tied, arched flux rope experiment to systematically study storage-and-release eruption mechanisms in the laboratory [1]. Thin in situ magnetic probes facilitate the study of both the equilibrium and the stability of these laboratory flux ropes. In particular, they permit the direct measurement of magnetic (J×B) forces, both in equilibrium [2] and during dynamic events [3, 4]. Regarding stability and eruptions, two major results are reported: First, a new stability regime is identified where torus-unstable flux ropes fail to erupt. In this ‘failed torus’ regime, the flux rope is torus-unstable but kink-stable. Under these conditions, a dynamic toroidal field tension force surges in magnitude and prevents the flux rope from erupting [3, 4]. This dynamic tension force, which is missing from existing eruption models, is generated by magnetic self-organization events within the line-tied flux rope. Second, a clear torus instability threshold is observed in the kink-unstable regime. This latter result, which is consistent with existing theoretical [5] and numerical [6] results, verifies the key role of the torus instability in driving flux rope eruptions in the solar corona.[1] C. E. Myers, Ph.D. Thesis, Princeton University (2015)[2] C. E. Myers et al., Phys. Plasmas 23, 112102 (2016)[3] C. E. Myers et al., Nature 528, 526 (2015)[4] C. E. Myers et al., Plasma Phys. Control. Fusion 59, 014048 (2017)[5] O. Olmedo & J. Zhang, Astrophys. J. 718, 433 (2010)[6] T. Török & B. Kliem, Astrophys. J. 630, L97 (2005)This research is supported by DoE Contract DE-AC02-09CH11466 and by the NSF/DoE Center for Magnetic Self-Organization (CMSO).

Buoyant Turbulence Kinetic Energy (TKE) Production in Katabatic Flow Despite Stable Thermal Stratification

NASA Astrophysics Data System (ADS)

Oldroyd, H. J.; Pardyjak, E.; Higgins, C. W.; Parlange, M. B.

2015-12-01

As micrometeorological research shifts to increasingly non-idealized environments, the lens through which we view classical atmospheric boundary layer theory must also shift to accommodate unfamiliar behavior. We present observations of katabatic flow over a steep (35.5 degree), alpine slope and draw comparisons with classical theory for nocturnal boundary layers (NBL) over flat terrain to delineate key physical differences and similarities. In both cases, the NBL is characterized by a strong, terrain-aligned thermal stratification. Over flat terrain, this temperature inversion tends to stabilize perturbations and suppresses vertical motions. Hence, the buoyancy term in the TKE budget equation acts as a sink. In contrast, the steep-slope katabatic flow regime is characterized by buoyant TKE production despite NBL thermal stratification. This buoyant TKE production occurs because streamwise (upslope) heat fluxes, which are typically treated as unimportant over flat terrain, contribute to the total vertical buoyancy flux since the gravity vector is not terrain-normal. Due to a relatively small number of observations over steep terrain, the turbulence structure of such flows and the implications of buoyant TKE production in the NBL have gone largely unexplored. As an important consequence of this characteristic, we show that conventional stability characterizations require careful coordinate system alignment and interpretation for katabatic flows. The streamwise heat fluxes play an integral role in characterizing stability and turbulent transport, more broadly, in katabatic flows. Therefore, multi-scale statistics and budget analyses describing physical interactions between turbulent fluxes at various scales are presented to interpret similarities and differences between the observations and classical theories regarding streamwise heat fluxes.

Using a spatially-distributed hydrologic biogeochemistry model to study the spatial variation of carbon processes in a Critical Zone Observatory

NASA Astrophysics Data System (ADS)

Shi, Y.; Eissenstat, D. M.; Davis, K. J.; He, Y.

2016-12-01

Forest carbon processes are affected by, among other factors, soil moisture, soil temperature, soil nutrients and solar radiation. Most of the current biogeochemical models are 1-D and represent one point in space. Therefore, they cannot resolve the topographically driven hill-slope land surface heterogeneity or the spatial pattern of nutrient availability. A spatially distributed forest ecosystem model, Flux-PIHM-BGC, has been developed by coupling a 1-D mechanistic biogeochemical model Biome-BGC (BBGC) with a spatially distributed land surface hydrologic model, Flux-PIHM. Flux-PIHM is a coupled physically based model, which incorporates a land-surface scheme into the Penn State Integrated Hydrologic Model (PIHM). The land surface scheme is adapted from the Noah land surface model. Flux-PIHM is able to represent the link between groundwater and the surface energy balance, as well as the land surface heterogeneities caused by topography. In the coupled Flux-PIHM-BGC model, each Flux-PIHM model grid couples a 1-D BBGC model, while soil nitrogen is transported among model grids via subsurface water flow. In each grid, Flux-PIHM provides BBGC with soil moisture, soil temperature, and solar radiation information, while BBGC provides Flux-PIHM with leaf area index. The coupled Flux-PIHM-BGC model has been implemented at the Susquehanna/Shale Hills critical zone observatory (SSHCZO). Model results suggest that the vegetation and soil carbon distribution is primarily constrained by nitorgen availability (affected by nitorgen transport via topographically driven subsurface flow), and also constrained by solar radiation and root zone soil moisture. The predicted vegetation and soil carbon distribution generally agrees with the macro pattern observed within the watershed. The coupled ecosystem-hydrologic model provides an important tool to study the impact of topography on watershed carbon processes, as well as the impact of climate change on water resources.

The current impact flux on Mars and its seasonal variation

NASA Astrophysics Data System (ADS)

JeongAhn, Youngmin; Malhotra, Renu

2015-12-01

We calculate the present-day impact flux on Mars and its variation over the martian year, using the current data on the orbital distribution of known Mars-crossing minor planets. We adapt the Öpik-Wetherill formulation for calculating collision probabilities, paying careful attention to the non-uniform distribution of the perihelion longitude and the argument of perihelion owed to secular planetary perturbations. We find that, at the current epoch, the Mars crossers have an axial distribution of the argument of perihelion, and the mean direction of their eccentricity vectors is nearly aligned with Mars' eccentricity vector. These previously neglected angular non-uniformities have the effect of depressing the mean annual impact flux by a factor of about 2 compared to the estimate based on a uniform random distribution of the angular elements of Mars-crossers; the amplitude of the seasonal variation of the impact flux is likewise depressed by a factor of about 4-5. We estimate that the flux of large impactors (of absolute magnitude H < 16) within ±30° of Mars' aphelion is about three times larger than when the planet is near perihelion. Extrapolation of our results to a model population of meter-size Mars-crossers shows that if these small impactors have a uniform distribution of their angular elements, then their aphelion-to-perihelion impact flux ratio would be 11-15, but if they track the orbital distribution of the large impactors, including their non-uniform angular elements, then this ratio would be about 3. Comparison of our results with the current dataset of fresh impact craters on Mars (detected with Mars-orbiting spacecraft) appears to rule out the uniform distribution of angular elements.

A diagnostic study of the forcing of the Ferrel cell by eddies, with latent heat effects included

NASA Technical Reports Server (NTRS)

Salustri, G.; Stone, P. H.

1983-01-01

A diagnostic study of the forcing of the Ferrel cell by eddy fluxes in the Northern Hemisphere is carried out. The quasi-geostrophic omega equation, and Oort and Rasmusson's (1971) data set, are used. The effects of condensation associated with the large scale motions are introduced to the omega equation by using the quasi-geostrophic moisture conservation equation. Thus, the dry static stability is replaced by a moist static stability, and the forcing of the Ferrel cell by eddy latent heat fluxes as well as sensible heat and momentum fluxes is included. Both effects tend to enhance the forcing of the Ferrel cell. The numerical analysis indicates that the effects are small in January, but in July the maximum vertical velocities are enhanced by about 30 percent.

Systems with a constant heat flux with applications to radiative heat transport across nanoscale gaps and layers

NASA Astrophysics Data System (ADS)

Budaev, Bair V.; Bogy, David B.

2018-06-01

We extend the statistical analysis of equilibrium systems to systems with a constant heat flux. This extension leads to natural generalizations of Maxwell-Boltzmann's and Planck's equilibrium energy distributions to energy distributions of systems with a net heat flux. This development provides a long needed foundation for addressing problems of nanoscale heat transport by a systematic method based on a few fundamental principles. As an example, we consider the computation of the radiative heat flux between narrowly spaced half-spaces maintained at different temperatures.

The distribution of ion orbit loss fluxes of ions and energy from the plasma edge across the last closed flux surface into the scrape-off layer

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

Stacey, Weston M.; Schumann, Matthew T.

A more detailed calculation strategy for the evaluation of ion orbit loss of thermalized plasma ions in the edge of tokamaks is presented. In both this and previous papers, the direct loss of particles from internal flux surfaces is calculated from the conservation of canonical angular momentum, energy, and magnetic moment. The previous result that almost all of the ion energy and particle fluxes crossing the last closed flux surface are in the form of ion orbit fluxes is confirmed, and the new result that the distributions of these fluxes crossing the last closed flux surface into the scrape-off layermore » are very strongly peaked about the outboard midplane is demonstrated. Previous results of a preferential loss of counter current particles leading to a co-current intrinsic rotation peaking just inside of the last closed flux surface are confirmed. Various physical details are discussed.« less

MHD Stability in Compact Stellarators

NASA Astrophysics Data System (ADS)

Fu, Guoyong

1999-11-01

A key issue for current carrying compact stellarators(S.P. Hirshman et al., "Physics of compact stellarators", Phys. Plasmas 6, 1858 (1999).) is the stability of ideal MHD modes. We present recent stability results of external kink modes, ballooning mode, and vertical modes in Quasi-axisymmetric Stellarators (QAS)( A. Reiman et al, "Physics issue in the design of a high beta Quasi-Axisymmetric Stellarator" the 17th IAEA Fusion Energy conference, (Yokohama, Japan, October 1998), Paper ICP/06.) as well as Quasi-Omnigeneous Stellarators (QOS)^2. The 3D stability code Terpsichore(W. A. Cooper et al., Phys. Plasmas 3, 275 (1996)) is used in this study. The vertical stability in a current carrying stellarator is studied for the first time. The vertical mode is found to be stabilized by externally generated poloidal flux(G.Y. Fu et al., "Stability of vertical mode in a current carrying stellarator"., to be submitted). Physically, this is because the external poloidal flux enhances the field line bending energy relative to the current drive term in the MHD energy principle, δ W. A simple stability criteria is derived in the limit of large aspect ratio and constant current density. For wall at infinite distance from the plasma, the amount of external flux needed for stabilization is given by f=(κ^2-κ)/(κ^2+1) where κ is the axisymmetric elongation and f is the fraction of the external rotational transform at the plasma edge. A systematic parameter study shows that the external kink in QAS can be stabilized at high beta ( ~ 5%) without a conducting wall by combination of edge magnetic shear and 3D shaping(G. Y. Fu et al., "MHD stability calculations of high-beta Quasi-Axisymmetric Stellarators", the 17th IAEA Fusion Energy conference, (Yokohama, Japan, October 1998), paper THP1/07.). The optimal shaping is obtained by using an optimizer with kink stability included in its objective function. The physics mechanism for the kink modes is studied by examining relative contributions of individual terms in δ W. It is found the external kinks are mainly driven by the parallel current. The pressure contributes significantly to the overall drive through the curvature term and the Pfirsch-Schluter current. These results demonstrate potential of QAS and QOS for disruption-free operations at high-beta without a close-fitting conducting wall and feedback stabilization.

Balanced sediment fluxes in southern California’s Mediterranean-climate zone salt marshes

USGS Publications Warehouse

Rosencranz, Jordan A.; Ganju, Neil K.; Ambrose, Richard F.; Brosnahan, Sandra M.; Dickhudt, Patrick J.; Guntenspergen, Glenn R.; MacDonald, Glen M.; Takekawa, John Y.; Thorne, Karen M.

2016-01-01

Salt marsh elevation and geomorphic stability depends on mineral sedimentation. Many Mediterranean-climate salt marshes along southern California, USA coast import sediment during El Niño storm events, but sediment fluxes and mechanisms during dry weather are potentially important for marsh stability. We calculated tidal creek sediment fluxes within a highly modified, sediment-starved, 1.5-km2 salt marsh (Seal Beach) and a less modified 1-km2marsh (Mugu) with fluvial sediment supply. We measured salt marsh plain suspended sediment concentration and vertical accretion using single stage samplers and marker horizons. At Seal Beach, a 2014 storm yielded 39 and 28 g/s mean sediment fluxes and imported 12,000 and 8800 kg in a western and eastern channel. Western channel storm imports offset 8700 kg exported during 2 months of dry weather, while eastern channel storm imports augmented 9200 kg imported during dry weather. During the storm at Mugu, suspended sediment concentrations on the marsh plain increased by a factor of four; accretion was 1–2 mm near creek levees. An exceptionally high tide sequence yielded 4.4 g/s mean sediment flux, importing 1700 kg: 20 % of Mugu’s dry weather fluxes. Overall, low sediment fluxes were observed, suggesting that these salt marshes are geomorphically stable during dry weather conditions. Results suggest storms and high lunar tides may play large roles, importing sediment and maintaining dry weather sediment flux balances for southern California salt marshes. However, under future climate change and sea level rise scenarios, results suggest that balanced sediment fluxes lead to marsh elevational instability based on estimated mineral sediment deficits.

Evaluation of parameterization for turbulent fluxes of momentum and heat in stably stratified surface layers

NASA Astrophysics Data System (ADS)

Sodemann, H.; Foken, Th.

2003-04-01

General Circulation Models calculate the energy exchange between surface and atmosphere by means of parameterisations for turbulent fluxes of momentum and heat in the surface layer. However, currently implemented parameterisations after Louis (1979) create large discrepancies between predictions and observational data, especially in stably stratified surface layers. This work evaluates a new surface layer parameterisation proposed by Zilitinkevich et al. (2002), which was specifically developed to improve energy flux predictions in stable stratification. The evaluation comprises a detailed study of important surface layer characteristics, a sensitivity study of the parameterisation, and a direct comparison to observational data from Antarctica and predictions by the Louis (1979) parameterisation. The stability structure of the stable surface layer was found to be very complex, and strongly influenced fluxes in the surface layer. The sensitivity study revealed that the new parameterisation depends strongly on the ratio between roughness length and roughness temperature, which were both observed to be very variable parameters. The comparison between predictions and measurements showed good agreement for momentum fluxes, but large discrepancies for heat fluxes. A stability dependent evaluation of selected data showed better agreement for the new parameterisation of Zilitinkevich et al. (2002) than for the Louis (1979) scheme. Nevertheless, this comparison underlines the need for more detailed and physically sound concepts for parameterisations of heat fluxes in stably stratified surface layers. Zilitinkevich, S. S., V. Perov and J. C. King (2002). "Near-surface turbulent fluxes in stable stratification: Calculation techniques for use in General Circulation Models." Q. J. R. Meteorol. Soc. 128(583): 1571--1587. Louis, J. F. (1979). "A Parametric Model of Vertical Eddy Fluxes in the Atmosphere." Bound.-Layer Meteor. 17(2): 187--202.

Improvement of stability of Nb 3 Sn superconductors by introducing high specific heat substances

DOE PAGES

Xu, X.; Li, P.; Zlobin, A. V.; ...

2018-01-24

High-J c Nb 3Sn conductors have low stability against perturbations, which accounts for the slow training rates of high-field Nb 3Sn magnets. While it is known that adding substances with high specific heat (C) into Nb 3Sn wires can increase their overall specific heat and thus improve their stability, there has not been a practical method that is compatible with the fabrication of long-length conductors. In this work, we put forward a scheme to introduce such substances to distributed-barrier Nb 3Sn wires, which adds minimum difficulty to the wire manufacturing process. Multifilamentary wires using a mixture of Cu and high-Cmore » Gd 2O 3 powders have been successfully fabricated along this line. Measurements showed that addition of Gd 2O 3 had no negative effects on residual resitivity ratio or non-Cu J c, and that flux jumps were remarkably reduced, and minimum quench energy values at 4.2 K, 14 T were increased by a factor of three, indicating that stability was significantly improved. We also discussed the influences of the positioning of high-C substances and their thermal diffusivity on their effectiveness in reducing the superconductor temperature rise against perturbations. Based on these results, we proposed an optimized conductor architecture to maximize the effectiveness of this approach.« less

Improvement of stability of Nb 3 Sn superconductors by introducing high specific heat substances

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

Xu, X.; Li, P.; Zlobin, A. V.

High-J c Nb 3Sn conductors have low stability against perturbations, which accounts for the slow training rates of high-field Nb 3Sn magnets. While it is known that adding substances with high specific heat (C) into Nb 3Sn wires can increase their overall specific heat and thus improve their stability, there has not been a practical method that is compatible with the fabrication of long-length conductors. In this work, we put forward a scheme to introduce such substances to distributed-barrier Nb 3Sn wires, which adds minimum difficulty to the wire manufacturing process. Multifilamentary wires using a mixture of Cu and high-Cmore » Gd 2O 3 powders have been successfully fabricated along this line. Measurements showed that addition of Gd 2O 3 had no negative effects on residual resitivity ratio or non-Cu J c, and that flux jumps were remarkably reduced, and minimum quench energy values at 4.2 K, 14 T were increased by a factor of three, indicating that stability was significantly improved. We also discussed the influences of the positioning of high-C substances and their thermal diffusivity on their effectiveness in reducing the superconductor temperature rise against perturbations. Based on these results, we proposed an optimized conductor architecture to maximize the effectiveness of this approach.« less

Tropical Gravity Wave Momentum Fluxes and Latent Heating Distributions

NASA Technical Reports Server (NTRS)

Geller, Marvin A.; Zhou, Tiehan; Love, Peter T.

2015-01-01

Recent satellite determinations of global distributions of absolute gravity wave (GW) momentum fluxes in the lower stratosphere show maxima over the summer subtropical continents and little evidence of GW momentum fluxes associated with the intertropical convergence zone (ITCZ). This seems to be at odds with parameterizations forGWmomentum fluxes, where the source is a function of latent heating rates, which are largest in the region of the ITCZ in terms of monthly averages. The authors have examined global distributions of atmospheric latent heating, cloud-top-pressure altitudes, and lower-stratosphere absolute GW momentum fluxes and have found that monthly averages of the lower-stratosphere GW momentum fluxes more closely resemble the monthly mean cloud-top altitudes rather than the monthly mean rates of latent heating. These regions of highest cloud-top altitudes occur when rates of latent heating are largest on the time scale of cloud growth. This, plus previously published studies, suggests that convective sources for stratospheric GW momentum fluxes, being a function of the rate of latent heating, will require either a climate model to correctly model this rate of latent heating or some ad hoc adjustments to account for shortcomings in a climate model's land-sea differences in convective latent heating.

Dynamics of low- and high-Z metal ions emitted during nanosecond laser-produced plasmas

NASA Astrophysics Data System (ADS)

Elsied, Ahmed M.; Diwakar, Prasoon K.; Polek, Mathew; Hassanein, Ahmed

2016-11-01

Dynamics of metal ions during laser-produced plasmas was studied. A 1064 nm, Nd: YAG laser pulse was used to ablate pure Al, Fe, Co, Mo, and Sn samples. Ion flux and velocity were measured using Faraday cup ion collector. Time-of-flight measurements showed decreasing ion flux and ion velocity with increasing atomic weight, and heavy metal ion flux profile exhibited multiple peaks that was not observed in lighter metals. Slow peak was found to follow shifted Maxwell Boltzmann distribution, while the fast peak was found to follow Gaussian distribution. Ion flux angular distribution that was carried out on Mo and Al using fixed laser intensity 2.5 × 1010 W/cm2 revealed that the slow ion flux peaks at small angles, that is, close to normal to the target ˜0° independent of target's atomic weight, and fast ion flux for Mo peaks at large angles ˜40° measured from the target normal, while it completely absents for Al. This difference in spatial and temporal distribution reveals that the emission mechanism of the fast and slow ions is different. From the slow ion flux angular distribution, the measured plume expansion ratio (plume forward peaking) was 1.90 and 2.10 for Al and Mo, respectively. Moreover, the effect of incident laser intensity on the ion flux emission as well as the emitted ion velocity were investigated using laser intensities varying from 2.5 × 1010 W/cm2 to 1.0 × 1011 W/cm2. Linear increase of fast ion flux and velocity, and quadratic increase of slow ion flux and velocity were observed. For further understanding of plume dynamics, laser optical emission spectroscopy was used to characterize Sn plasma by measuring the temporal and spatial evolution of plasma electron density Ne and electron temperature Te. At 3.5 mm away from the target, plasma density showed slow decrease with time, however electron temperature was observed to decrease dramatically. The maximum plasma density and temperature occurred at 0.5 mm away from target and were measured to be 8.0 × 1017 cm-3 and 1.3 eV, respectively.

Dean vortices with wall flux in a curved channel membrane system. 2: The velocity field

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

Chung, K.Y.; Brewster, M.E.; Belfort, G.

1996-02-01

The velocity and pressure fields and the effect of wall flux on these fields in a spiral channel are presented. As fluid flows inward through a spiral channel with constant gap and permeable walls, the streamwise flux decreases while the curvature increases. Thus, by balancing the stabilizing effect of wall suction with the destabilizing effect of increasing curvature, established vortices can be maintained along the spiral channel. This approach is used to prescribe spiral geometries with different wall fluxes. Using a weakly nonlinear stability analysis, the influence of wall flux on the characteristics of Dean vortices is obtained. The criticalmore » Dean number is reduced when suction is through the inner wall only, is slightly reduced when suction is equal through both walls, and is increased when suction is through the outer wall only. The magnitude of change is proportional to a ratio of small numbers that measures the importance of the effect of curvature. In membrane filtration applications the wall flux is typically 2 to 5 orders of magnitude less than the streamwise flow. If the radius of curvature of the channel is of the order of 100 times the channel gap, the effect on the critical Dean number is within 2% of the no-wall flux case. If the radius of curvature is sufficiently large, however, it is possible to observe effects on the critical Dean number that approach O(1) in magnitude for certain parameter ranges.« less

Representation of the Geosynchronous Plasma Environment in Spacecraft Charging Calculations

NASA Technical Reports Server (NTRS)

Davis, V. A.; Mandell, M. J.; Thomsen, M. F.

2006-01-01

Historically, our ability to predict and postdict spacecraft surface charging has been limited by the characterization of the plasma environment. One difficulty lies in the common practice of fitting the plasma data to a Maxwellian or Double Maxwellian distribution function, which may not represent the data well for charging purposes. We use electron and ion flux spectra measured by the Los Alamos National Laboratory (LANL) Magnetospheric Plasma Analyzer (MPA) to examine how the use of different spectral representations of the charged particle environment in computations of spacecraft potentials during magnetospheric substorms affects the accuracy of the results. We calculate the spacecraft potential using both the measured fluxes and several different fits to these fluxes. These measured fluxes have been corrected for the difference between the measured and calculated potential. The potential computed using the measured fluxes and the best available material properties of graphite carbon, with a secondary electron escape fraction of 81%, is within a factor of three of the measured potential for 87% of the data. Potentials calculated using a Kappa function fit to the incident electron flux distribution function and a Maxwellian function fit to the incident ion flux distribution function agree with measured potentials nearly as well as do potentials calculated using the measured fluxes. Alternative spectral representations gave less accurate estimates of potential. The use of all the components of the net flux, along with spacecraft specific average material properties, gives a better estimate of the spacecraft potential than the high energy flux alone.

Comparison between measured and computed magnetic flux density distribution of simulated transformer core joints assembled from grain-oriented and non-oriented electrical steel

NASA Astrophysics Data System (ADS)

Shahrouzi, Hamid; Moses, Anthony J.; Anderson, Philip I.; Li, Guobao; Hu, Zhuochao

2018-04-01

The flux distribution in an overlapped linear joint constructed in the central region of an Epstein Square was studied experimentally and results compared with those obtained using a computational magnetic field solver. High permeability grain-oriented (GO) and low permeability non-oriented (NO) electrical steels were compared at a nominal core flux density of 1.60 T at 50 Hz. It was found that the experimental results only agreed well at flux densities at which the reluctance of different paths of the flux are similar. Also it was revealed that the flux becomes more uniform when the working point of the electrical steel is close to the knee point of the B-H curve of the steel.

Dynamics and mechanics of motor-filament systems

NASA Astrophysics Data System (ADS)

Kruse, K.; Jülicher, F.

2006-08-01

Motivated by the cytoskeleton of eukaryotic cells, we develop a general framework for describing the large-scale dynamics of an active filament network. In the cytoskeleton, active cross-links are formed by motor proteins that are able to induce relative motion between filaments. Starting from pair-wise interactions of filaments via such active processes, our framework is based on momentum conservation and an analysis of the momentum flux. This allows us to calculate the stresses in the filament network generated by the action of motor proteins. We derive effective theories for the filament dynamics which can be related to continuum theories of active polar gels. As an example, we discuss the stability of homogenous isotropic filament distributions in two spatial dimensions.

Characteristics of Low-latitude Coronal Holes near the Maximum of Solar Cycle 24

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

Hofmeister, Stefan J.; Veronig, Astrid; Reiss, Martin A.

We investigate the statistics of 288 low-latitude coronal holes extracted from SDO /AIA-193 filtergrams over the time range of 2011 January 01–2013 December 31. We analyze the distribution of characteristic coronal hole properties, such as the areas, mean AIA-193 intensities, and mean magnetic field densities, the local distribution of the SDO /AIA-193 intensity and the magnetic field within the coronal holes, and the distribution of magnetic flux tubes in coronal holes. We find that the mean magnetic field density of all coronal holes under study is 3.0 ± 1.6 G, and the percentaged unbalanced magnetic flux is 49 ± 16%.more » The mean magnetic field density, the mean unsigned magnetic field density, and the percentaged unbalanced magnetic flux of coronal holes depend strongly pairwise on each other, with correlation coefficients cc > 0.92. Furthermore, we find that the unbalanced magnetic flux of the coronal holes is predominantly concentrated in magnetic flux tubes: 38% (81%) of the unbalanced magnetic flux of coronal holes arises from only 1% (10%) of the coronal hole area, clustered in magnetic flux tubes with field strengths >50 G (10 G). The average magnetic field density and the unbalanced magnetic flux derived from the magnetic flux tubes correlate with the mean magnetic field density and the unbalanced magnetic flux of the overall coronal hole (cc>0.93). These findings give evidence that the overall magnetic characteristics of coronal holes are governed by the characteristics of the magnetic flux tubes.« less

Determination of Fluxes and their Source Partitioning from high-resolution Profile Measurements of Wind Speed and Scalars within and above short Canopies

NASA Astrophysics Data System (ADS)

Graf, A.; Ney, P.

2017-12-01

A continuously moving elevator-based system is described to measure vertical profiles of wind speed, temperature, CO2 and H2O within and above short plant canopies with a vertical resolution in the centimeter range. On sample days in 2015 to 2017, we measured profiles from the soil surface to 2 m a.g.l. in a crop rotation including wheat, barley, bare soil, winter catch crops and sugarbeet, with canopy heights of up to 1 m. Profiles over bare soil or very short canopies could be described well by fitting Monin-Obukhov-like profiles, and the derived fluxes of momentum and all three scalars matched well those of a nearby eddy-covariance station. In green canopies during the day, CO2 profiles clearly indicated the plant sink and soil source by a local minimum in the canopy and a maximum at the soil surface. H2O profiles, indicating sources both in the canopy and at the soil surface, did or did not show a local minimum between both, depending on canopy structure and turbulence. Temperature profiles showed various shapes including solar incident angle effects, and often the expected opposing signs of thermal stability between the subcanopy and the roughness sublayer. Finally, we test different existing parametrizations to estimate the vertical source / sink distribution from the measured profiles, compare the resulting vertically integrated fluxes to eddy-covariance based net fluxes, and discuss limitations and needed improvements to quantify subcanopy soil respiration and evaporation from such approaches.

A model for the flux-r.m.s. correlation in blazar variability or the minijets-in-a-jet statistical model

NASA Astrophysics Data System (ADS)

Biteau, J.; Giebels, B.

2012-12-01

Very high energy gamma-ray variability of blazar emission remains of puzzling origin. Fast flux variations down to the minute time scale, as observed with H.E.S.S. during flares of the blazar PKS 2155-304, suggests that variability originates from the jet, where Doppler boosting can be invoked to relax causal constraints on the size of the emission region. The observation of log-normality in the flux distributions should rule out additive processes, such as those resulting from uncorrelated multiple-zone emission models, and favour an origin of the variability from multiplicative processes not unlike those observed in a broad class of accreting systems. We show, using a simple kinematic model, that Doppler boosting of randomly oriented emitting regions generates flux distributions following a Pareto law, that the linear flux-r.m.s. relation found for a single zone holds for a large number of emitting regions, and that the skewed distribution of the total flux is close to a log-normal, despite arising from an additive process.

Bayesian Hierarchical Model Characterization of Model Error in Ocean Data Assimilation and Forecasts

DTIC Science & Technology

2013-09-30

wind ensemble with the increments in the surface momentum flux control vector in a four-dimensional variational (4dvar) assimilation system. The...stability  effects?   surface  stress   Surface   Momentum  Flux  Ensembles  from  Summaries  of  BHM  Winds  (Mediterranean...surface wind speed given ensemble winds from a Bayesian Hierarchical Model to provide surface momentum flux ensembles. 3 Figure 2: Domain of

Estimating the potential for methane clathrate instability in the 1%-CO2 IPCC AR-4 simulations

NASA Astrophysics Data System (ADS)

Lamarque, Jean-François

2008-10-01

The recent work of Reagan and Moridis (2007) has shown that even a limited warming of 1 K over 100 years can lead to clathrate destabilization, leading to a significant flux of methane into the ocean water, at least for shallow deposits. Here we study the potential for methane clathrate destabilization by identifying the 100-year temperature increase in the available IPCC (Intergovernmental Panel on Climate Change) AR-4 1%-CO2 increase per year (up to doubling over pre-industrial conditions, which occurs after 70 years) simulations. Depending on assumptions made on the possible locations (in this case, only depth) of methane clathrates and on temperature dependence, our calculation leads to an estimated model-mean release of methane at the bottom of the ocean of approximately 560-2140 Tg(CH4)/year; as no actual geographical distribution of methane clathrates is considered here, these flux estimates must be viewed as upper bound estimates. Using an observed 1% ratio to estimate the amount of methane reaching the atmosphere, our analysis leads to a relatively small methane flux of approximately 5-21 Tg(CH4)/year, with an estimated inter-model standard deviation of approximately 30%. The role of sea-level rise by 2100 will be to further stabilize methane clathrates, albeit to a small amount as the sea-level rise is expected to be less than a few meters.

Reconstructing metabolic flux vectors from extreme pathways: defining the alpha-spectrum.

PubMed

Wiback, Sharon J; Mahadevan, Radhakrishnan; Palsson, Bernhard Ø

2003-10-07

The move towards genome-scale analysis of cellular functions has necessitated the development of analytical (in silico) methods to understand such large and complex biochemical reaction networks. One such method is extreme pathway analysis that uses stoichiometry and thermodynamic irreversibly to define mathematically unique, systemic metabolic pathways. These extreme pathways form the edges of a high-dimensional convex cone in the flux space that contains all the attainable steady state solutions, or flux distributions, for the metabolic network. By definition, any steady state flux distribution can be described as a nonnegative linear combination of the extreme pathways. To date, much effort has been focused on calculating, defining, and understanding these extreme pathways. However, little work has been performed to determine how these extreme pathways contribute to a given steady state flux distribution. This study represents an initial effort aimed at defining how physiological steady state solutions can be reconstructed from a network's extreme pathways. In general, there is not a unique set of nonnegative weightings on the extreme pathways that produce a given steady state flux distribution but rather a range of possible values. This range can be determined using linear optimization to maximize and minimize the weightings of a particular extreme pathway in the reconstruction, resulting in what we have termed the alpha-spectrum. The alpha-spectrum defines which extreme pathways can and cannot be included in the reconstruction of a given steady state flux distribution and to what extent they individually contribute to the reconstruction. It is shown that accounting for transcriptional regulatory constraints can considerably shrink the alpha-spectrum. The alpha-spectrum is computed and interpreted for two cases; first, optimal states of a skeleton representation of core metabolism that include transcriptional regulation, and second for human red blood cell metabolism under various physiological, non-optimal conditions.

Watershed Scale Shear Stress From Tethersonde Wind Profile Measurements Under Near Neutral and Unstable Atmospheric Stability

NASA Astrophysics Data System (ADS)

Parlange, M. B.; Katul, G. G.

1995-04-01

Mean wind speed profiles were measured in the atmospheric surface layer, using a tethersonde system, above the Ojai Valley Watershed in southern California. The valley is mainly planted with mature avocado and orange trees. The surface shear stress and latent and sensible heat fluxes were measured above the trees which are up to 9 m in height. Near-neutral wind speed profile measurements allowed the determination of the watershed surface roughness (z0 = 1.4 m) and the momentum displacement height (d0 = 7.0 m). The wind speed measurements obtained under unstable atmospheric stability were analyzed using Monin-Obukhov similarity theory. New stability correction functions proposed based on theory and experiments of Kader-Yaglom as well as the now classic Businger-Dyer type functions were tested. The watershed shear stress values calculated using the surface layer wind speed profiles with the new Monin-Obukhov stability functions were found to be improved in comparison with the values obtained with the Businger-Dyer functions under strongly unstable stability conditions. The Monin-Obukhov model with the Businger-Dyer stability correction function underpredicted the momentum flux by 25% under strongly unstable stability conditions, while the new Kader-Yaglom formulation compared well on average (R2 = 0.77) with the surface eddy correlation measurements for all atmospheric stability conditions. The unstable 100-m drag coefficient was found to be u*2/V1002 = 0.0182.

Estimation of the average exchanges in momentum and latent heat between the atmosphere and the oceans with Seasat observations

NASA Technical Reports Server (NTRS)

Liu, W. T.

1983-01-01

Ocean-surface momentum flux and latent heat flux are determined from Seasat-A data from 1978 and compared with ship observations. Momentum flux was measured using the Seasat-A scatterometer system (SASS) heat flux, with the scanning multichannel MW radiometer (SMMR). Ship measurements were quality selected and averaged to increase their reliability. The fluxes were computed using a bulk parameterization technique. It is found that although SASS effectively measures momentum flux, variations in atmospheric stability and sea-surface temperature cause deviations which are not accounted for by the present data-processing algorithm. The SMMR-latent-heat-flux algorithm, while needing refinement, is shown to given estimations to within 35 W/sq m in its present form, which removes systematic error and uses an empirically determined transfer coefficient.

Using a spatially-distributed hydrologic biogeochemistry model with a nitrogen transport module to study the spatial variation of carbon processes in a Critical Zone Observatory

DOE PAGES

Shi, Yuning; Eissenstat, David M.; He, Yuting; ...

2018-05-12

Terrestrial carbon processes are affected by soil moisture, soil temperature, nitrogen availability and solar radiation, among other factors. Most of the current ecosystem biogeochemistry models represent one point in space, and have limited characterization of hydrologic processes. Therefore these models can neither resolve the topographically driven spatial variability of water, energy, and nutrient, nor their effects on carbon processes. A spatially-distributed land surface hydrologic biogeochemistry model, Flux-PIHM-BGC, is developed by coupling the Biome-BGC model with a physically-based land surface hydrologic model, Flux-PIHM. In the coupled system, each Flux-PIHM model grid couples a 1-D Biome-BGC model. In addition, a topographic solarmore » radiation module and an advection-driven nitrogen transport module are added to represent the impact of topography on nutrient transport and solar energy distribution. Because Flux-PIHM is able to simulate lateral groundwater flow and represent the land surface heterogeneities caused by topography, Flux-PIHM-BGC is capable of simulating the complex interaction among water, energy, nutrient, and carbon in time and space. The Flux-PIHM-BGC model is tested at the Susquehanna/Shale Hills Critical Zone Observatory. Model results show that distributions of carbon and nitrogen stocks and fluxes are strongly affected by topography and landscape position, and tree growth is nitrogen limited. The predicted aboveground and soil carbon distributions generally agree with the macro patterns observed. Although the model underestimates the spatial variation, the predicted watershed average values are close to the observations. Lastly, the coupled Flux-PIHM-BGC model provides an important tool to study spatial variations in terrestrial carbon and nitrogen processes and their interactions with environmental factors, and to predict the spatial structure of the responses of ecosystems to climate change.« less

Using a spatially-distributed hydrologic biogeochemistry model with a nitrogen transport module to study the spatial variation of carbon processes in a Critical Zone Observatory

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

Shi, Yuning; Eissenstat, David M.; He, Yuting

Terrestrial carbon processes are affected by soil moisture, soil temperature, nitrogen availability and solar radiation, among other factors. Most of the current ecosystem biogeochemistry models represent one point in space, and have limited characterization of hydrologic processes. Therefore these models can neither resolve the topographically driven spatial variability of water, energy, and nutrient, nor their effects on carbon processes. A spatially-distributed land surface hydrologic biogeochemistry model, Flux-PIHM-BGC, is developed by coupling the Biome-BGC model with a physically-based land surface hydrologic model, Flux-PIHM. In the coupled system, each Flux-PIHM model grid couples a 1-D Biome-BGC model. In addition, a topographic solarmore » radiation module and an advection-driven nitrogen transport module are added to represent the impact of topography on nutrient transport and solar energy distribution. Because Flux-PIHM is able to simulate lateral groundwater flow and represent the land surface heterogeneities caused by topography, Flux-PIHM-BGC is capable of simulating the complex interaction among water, energy, nutrient, and carbon in time and space. The Flux-PIHM-BGC model is tested at the Susquehanna/Shale Hills Critical Zone Observatory. Model results show that distributions of carbon and nitrogen stocks and fluxes are strongly affected by topography and landscape position, and tree growth is nitrogen limited. The predicted aboveground and soil carbon distributions generally agree with the macro patterns observed. Although the model underestimates the spatial variation, the predicted watershed average values are close to the observations. Lastly, the coupled Flux-PIHM-BGC model provides an important tool to study spatial variations in terrestrial carbon and nitrogen processes and their interactions with environmental factors, and to predict the spatial structure of the responses of ecosystems to climate change.« less

Moduli stabilization in stringy ISS models

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

Nakayama, Yu; Nakayama, Yu; Yamazaki, Masahito

2007-09-28

We present a stringy realization of the ISS metastable SUSY breaking model with moduli stabilization. The mass moduli of the ISS model is stabilized by gauging of a U(1) symmetry and its D-term potential. The SUSY is broken both by F-terms and D-terms. It is possible to obtain de Sitter vacua with a vanishingly small cosmological constant by an appropriate fine-tuning of flux parameters.

Bond rupture between colloidal particles with a depletion interaction

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

Whitaker, Kathryn A.; Furst, Eric M., E-mail: furst@udel.edu

The force required to break the bonds of a depletion gel is measured by dynamically loading pairs of colloidal particles suspended in a solution of a nonadsorbing polymer. Sterically stabilized poly(methyl methacrylate) colloids that are 2.7 μm diameter are brought into contact in a solvent mixture of cyclohexane-cyclohexyl bromide and polystyrene polymer depletant. The particle pairs are subject to a tensile load at a constant loading rate over many approach-retraction cycles. The stochastic nature of the thermal rupture events results in a distribution of bond rupture forces with an average magnitude and variance that increases with increasing depletant concentration. The measuredmore » force distribution is described by the flux of particle pairs sampling the energy barrier of the bond interaction potential based on the Asakura–Oosawa depletion model. A transition state model demonstrates the significance of lubrication hydrodynamic interactions and the effect of the applied loading rate on the rupture force of bonds in a depletion gel.« less

The development and stability of non-thermal plasma in space

NASA Astrophysics Data System (ADS)

Kasper, Justin

2017-10-01

This talk will review our understanding of non-thermal ion and electron velocity distribution functions (VDFs) in space plasma, with a focus on pressure anisotropy and unequal temperatures in the solar wind and corona. Under typical solar wind plasma conditions, which are common for a range of astrophysical plasmas, relaxation processes such as Coulomb collisions are sufficiently slow compared to interactions between particles and electromagnetic fluctuations that ion and electron VDFs can depart significantly from the classical Maxwell-Boltzmann distribution and maintain these non-thermal features for times greater than the dynamical scales of the system. These non-thermal properties of the plasma are very important as they can significantly modify aspects of the plasma such as heat flux, susceptibility to kinetic instabilities, and interaction with waves and turbulence. Major open questions in the field will be reviewed, along with current and planned observational capabilities of instruments on spacecraft such as Wind and the upcoming Parker Solar Probe, with an eye to potential crossover with laboratory plasma experiments.

Stability mechanical considerations, and AC loss in HTSC monoliths, coils, and wires

NASA Technical Reports Server (NTRS)

Sumption, M. D.; Collings, E. W.

1995-01-01

For monolithic high-T(sub c) superconductors (HTSC's) calculations are presented of: (1) the initial flux jump field, H(sub fj), in melt-processed YBCO based on a field and temperature dependent J(sub c), and (2) the radial and circumferential stresses in solid and hollow cylinders containing trapped magnetic flux. For model multi filamentary (MF) HTSC/Ag strands calculations are presented of: (1) the limiting filament diameters for adiabatic and dynamic stability, and (2) the hysteretic and eddy current components of AC loss. Again for MF HTSC/Ag composite strands the need for filamentary subdivision and twisting is discussed.

Comparison of eigenvectors for coupled seismo-electromagnetic layered-Earth modelling

NASA Astrophysics Data System (ADS)

Grobbe, N.; Slob, E. C.; Thorbecke, J. W.

2016-07-01

We study the accuracy and numerical stability of three eigenvector sets for modelling the coupled poroelastic and electromagnetic layered-Earth response. We use a known eigenvector set, its flux-normalized version and a newly derived flux-normalized set. The new set is chosen such that the system is properly uncoupled when the coupling between the poroelastic and electromagnetic fields vanishes. We carry out two different numerical stability tests: the first test focuses on the internal system, eigenvector and eigenvalue consistency; the second test investigates the stability and preciseness of the flux-normalized systems by looking at identity relations. We find that the known set shows the largest deviation for both tests, whereas the new set performs best. In two additional numerical modelling experiments, these numerical inaccuracies are shown to generate numerical noise levels comparable to small signals, such as signals coming from the important interface conversion responses, especially when the coupling coefficient is small. When coupling vanishes completely, the known set does not produce proper results. The new set produces numerically stable and accurate results in all situations. We therefore strongly recommend to use this newly derived set for future layered-Earth seismo-electromagnetic modelling experiments.

Investigation of the influence of atmospheric stability and turbulence on land-atmosphere exchange

NASA Astrophysics Data System (ADS)

Osibanjo, O.; Holmes, H.

2015-12-01

Surface energy fluxes are exchanged between the surface of the earth and the atmosphere and impact weather, climate, and air quality. The radiation from the sun triggers the surface-atmosphere interaction during the day as heat is transmitted to the surface and the surface heats the air directly above generating wind (i.e., thermal turbulence) that transports heat, moisture, and momentum in the atmospheric boundary layer (ABL). This process is impacted by greenhouse gasses (i.e., water vapor, carbon dioxide and other trace gases) that absorb heat emitted by the earth's surface. The concentrations of atmospheric greenhouse gasses are increasing leading to changes in ABL dynamics as a result of the changing surface energy balance. The ABL processes are important to characterize because they are difficult to parameterize in global and regional scale atmospheric models. Empirical data can be collected using eddy covariance micrometeorological methods to measure turbulent fluxes (e.g., sensible heat, moisture, and CO2) and quantify the exchange between the surface and the atmosphere. The objective of this work is to calculate surface fluxes using observational data collected during one week in September 2014 from a monitoring site in Echo, Oregon. The site is located in the Columbia Basin with rolling terrain, irrigated farmland, and over 100 wind turbines. The 10m tower was placed in a small valley depression to isolate nighttime cold air pools. This work will present observations of momentum, sensible heat, moisture, and carbon dioxide fluxes from data collected at a sampling frequency of 10Hz at four heights. Atmospheric stability is determined using Monin-Obukov length and flux Richardson number, and the impact of stability on surface-atmosphere exchange is investigated. This work will provide a better understanding of surface fluxes and mixing, particularly during stable ABL periods, and the results can be used to compare with numerical models.

Analysis of solar receiver flux distributions for US/Russian solar dynamic system demonstration on the MIR Space Station

NASA Technical Reports Server (NTRS)

Kerslake, Thomas W.; Fincannon, James

1995-01-01

The United States and Russia have agreed to jointly develop a solar dynamic (SD) system for flight demonstration on the Russian MIR space station starting in late 1997. Two important components of this SD system are the solar concentrator and heat receiver provided by Russia and the U.S., respectively. This paper describes optical analysis of the concentrator and solar flux predictions on target receiver surfaces. The optical analysis is performed using the code CIRCE2. These analyses account for finite sun size with limb darkening, concentrator surface slope and position errors, concentrator petal thermal deformation, gaps between petals, and the shading effect of the receiver support struts. The receiver spatial flux distributions are then combined with concentrator shadowing predictions. Geometric shadowing patterns are traced from the concentrator to the target receiver surfaces. These patterns vary with time depending on the chosen MIR flight attitude and orbital mechanics of the MIR spacecraft. The resulting predictions provide spatial and temporal receiver flux distributions for any specified mission profile. The impact these flux distributions have on receiver design and control of the Brayton engine are discussed.

Soil-atmosphere trace gas exchange from tropical oil palm plantations on peat

NASA Astrophysics Data System (ADS)

Arn Teh, Yit; Manning, Frances; Zin Zawawi, Norliyana; Hill, Timothy; Chocholek, Melanie; Khoon Kho, Lip

2015-04-01

Oil palm is the largest agricultural crop in the tropics, accounting for 13 % of all tropical land cover. Due to its large areal extent, oil palm cultivation may have important implications not only for terrestrial stores of C and N, but may also impact regional and global exchanges of material and energy, including fluxes of trace gases and water vapor. In particular, recent expansion of oil palm into tropical peatlands has raised concerns over enhanced soil C emissions from degradation of peat, and elevated N-gas fluxes linked to N fertilizer application. Here we report our preliminary findings on soil carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes from a long-term, multi-scale project investigating the C, N and greenhouse gas (GHG) dynamics of oil palm ecosystems established on peat soils in Sarawak, Malaysian Borneo. Flux chamber measurements indicate that soil CO2, CH4 and N2O fluxes averaged 20.0 ± 16.0 Mg CO2-C ha-1 yr-1, 37.4 ± 29.9 kg CH4-C ha-1 yr-1 and 4.7 ± 4.2 g N2O-N ha-1 yr-1, respectively. Soil CO2 fluxes were on par with other drained tropical peatlands; whereas CH4 fluxes exceeded observations from similar study sites elsewhere. Nitrous oxide fluxes were in a similar range to fluxes from other drained tropical peatlands, but lower than emissions from mineral-soil plantations by up to three orders of magnitude. Fluxes of soil CO2 and N2O were spatially stratified, and contingent upon the distribution of plants, deposited harvest residues, and soil moisture. Soil CO2 fluxes were most heavily influenced by the distribution of palms and their roots. On average, autotrophic (root) respiration accounted for approximately 78 % of total soil CO2 flux, and total soil respiration declined steeply away from palms; e.g. soil CO2 fluxes in the immediate 1 m radius around palms were up to 6 times greater than fluxes in inter-palm spaces due to higher densities of roots. Placement of harvest residues played an important - but secondary - role in modulating soil CO2 fluxes; soil respiration rates doubled in areas where harvest residues were deposited, reflecting an enhanced input of labile organic matter for decomposition. In contrast, N2O fluxes were best-predicted by the distribution of harvest residues, and were only weakly related to plant distributions or soil moisture. For example, N2O fluxes from harvest residue piles were up to twice of the overall plot-average. In contrast, N2O fluxes showed no clear pattern around palms or in inter-palm spaces; this finding is surprising because N fertilizers are applied within the 1 m radius around palms, and we expected to observe enhanced N2O fluxes in areas of greater fertilizer input. This suggests that palms may be a strong competitor for N in these ecosystems, and that fertilizer application may more closely match overall plant demand than in mineral-soil plantations. Overall, the spatial patterning of soil CO2 and N2O fluxes implies that soil biogeochemical processes are predictably distributed in space, potentially making it easier to model and constrain fluxes of these soil-derived GHGs.

Novel Sensor for the In Situ Measurement of Uranium Fluxes

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

Hatfield, Kirk

2015-02-10

The goal of this project was to develop a sensor that incorporates the field-tested concepts of the passive flux meter to provide direct in situ measures of flux for uranium and groundwater in porous media. Measurable contaminant fluxes [J] are essentially the product of concentration [C] and groundwater flux or specific discharge [q ]. The sensor measures [J] and [q] by changes in contaminant and tracer amounts respectively on a sorbent. By using measurement rather than inference from static parameters, the sensor can directly advance conceptual and computational models for field scale simulations. The sensor was deployed in conjunction withmore » DOE in obtaining field-scale quantification of subsurface processes affecting uranium transport (e.g., advection) and transformation (e.g., uranium attenuation) at the Rifle IFRC Site in Rifle, Colorado. Project results have expanded our current understanding of how field-scale spatial variations in fluxes of uranium, groundwater and salient electron donor/acceptors are coupled to spatial variations in measured microbial biomass/community composition, effective field-scale uranium mass balances, attenuation, and stability. The coupling between uranium, various nutrients and micro flora can be used to estimate field-scale rates of uranium attenuation and field-scale transitions in microbial communities. This research focuses on uranium (VI), but the sensor principles and design are applicable to field-scale fate and transport of other radionuclides. Laboratory studies focused on sorbent selection and calibration, along with sensor development and validation under controlled conditions. Field studies were conducted at the Rifle IFRC Site in Rifle, Colorado. These studies were closely coordinated with existing SBR (formerly ERSP) projects to complement data collection. Small field tests were conducted during the first two years that focused on evaluating field-scale deployment procedures and validating sensor performance under controlled field conditions. In the third and fourth year a suite of larger field studies were conducted. For these studies, the uranium flux sensor was used with uranium speciation measurements and molecular-biological tools to characterize microbial community and active biomass at synonymous wells distributed in a large grid. These field efforts quantified spatial changes in uranium flux and field-scale rates of uranium attenuation (ambient and stimulated), uranium stability, and quantitatively assessed how fluxes and effective reaction rates were coupled to spatial variations in microbial community and active biomass. Analyses of data from these field experiments were used to generate estimates of Monod kinetic parameters that are ‘effective’ in nature and optimal for modeling uranium fate and transport at the field-scale. This project provided the opportunity to develop the first sensor that provides direct measures of both uranium (VI) and groundwater flux. A multidisciplinary team was assembled to include two geochemists, a microbiologist, and two quantitative contaminant hydrologists. Now that the project is complete, the sensor can be deployed at DOE sites to evaluate field-scale uranium attenuation, source behavior, the efficacy of remediation, and off-site risk. Because the sensor requires no power, it can be deployed at remote sites for periods of days to months. The fundamental science derived from this project can be used to advance the development of predictive models for various transport and attenuation processes in aquifers. Proper development of these models is critical for long-term stewardship of contaminated sites in the context of predicting uranium source behavior, remediation performance, and off-site risk.« less

The Intensity Distribution for Gamma-Ray Bursts Observed with BATSE

NASA Technical Reports Server (NTRS)

Pendleton, Geoffrey N.; Mallozzi, Robert S.; Paciesas, William S.; Briggs, Michael S.; Preece, Robert D.; Koshut, Tom M.; Horack, John M.; Meegan, Charles A.; Fishman, Gerald J.; Hakkila, Jon;

Seasonal Clear-Sky Flux and Cloud Radiative Effect Anomalies in the Arctic Atmospheric Column Associated with the Arctic Oscillation and Arctic Dipole

NASA Technical Reports Server (NTRS)

Hegyi, Bradley M.; Taylor, Patrick C.

2017-01-01

The impact of the Arctic Oscillation (AO) and Arctic Dipole (AD) on the radiative flux into the Arctic mean atmospheric column is quantified. 3-month-averaged AO and AD indices are regressed with corresponding surface and top-of-atmosphere (TOA) fluxes from the CERES-SFC and CERES-TOA EBAF datasets over the period 2000-2014. An increase in clear-sky fluxes into the Arctic mean atmospheric column during fall is the largest net flux anomaly associated with AO, primarily driven by a positive net longwave flux anomaly (i.e. increase of net flux into the atmospheric column) at the surface. A decrease in the Arctic mean atmospheric column cloud radiative effect during winter and spring is the largest flux anomaly associated with AD, primarily driven by a change in the longwave cloud radiative effect at the surface. These prominent responses to AO and AD are widely distributed across the ice-covered Arctic, suggesting that the physical process or processes that bring about the flux change associated with AO and AD are distributed throughout the Arctic.

Measurement of limiter particle fluxes and carbon erosion in the helical scrape-off layer of startup plasmas at W7-X

NASA Astrophysics Data System (ADS)

Winters, V.; Biedermann, C.; Brezinsek, S.; Effenberg, F.; Frerichs, H.; Harris, J.; Schmitz, O.; Stephey, L.; Unterberg, E.; Wurden, G.; W7-X Team

2016-10-01

Measurement of the 2D recycling flux and calculations of the carbon erosion from the limiter in startup plasmas of W7-X provides a first insight into neutral particle release and impurity inflow into the helical scrape-off layer. H-alpha, C-II (514.5nm) and C-III (465.1nm) line emissions were collected with filter-scopes and a visible camera aimed at limiter 3 of W7-X. Local plasma parameters are considered to estimate physical and chemical sputtering contributions. The analytical model for chemical sputtering by Roth is used to convert the measured particle flux into a chemically eroded C flux. The particle flux as well as the extracted C erosion pattern deviates from the measured heat flux distribution and also from the predicted particle flux distribution from EMC3-EIRENE. Candidates to resolve this discrepancy are measurement uncertainties and physics related (e.g. asymmetry in the last closed flux surface position). Post-mortem analysis of the limiter will be taken into account and compared to these in-situ measurements to gather first detailed insight on the net C erosion distribution and the impurity sourcing into the helical scrape-off layer. This work was funded by DE-SC0014210, DE-AC5206NA25396, DE-AC05-00OR22725 and by EUROfusion under Grant No 633053.

Energy-Efficient and Environmentally Friendly Solid Oxide Membrane Electrolysis Process for Magnesium Oxide Reduction: Experiment and Modeling

NASA Astrophysics Data System (ADS)

Guan, Xiaofei; Pal, Uday B.; Powell, Adam C.

2014-06-01

This paper reports a solid oxide membrane (SOM) electrolysis experiment using an LSM(La0.8Sr0.2MnO3-δ)-Inconel inert anode current collector for production of magnesium and oxygen directly from magnesium oxide at 1423 K (1150 °C). The electrochemical performance of the SOM cell was evaluated by means of various electrochemical techniques including electrochemical impedance spectroscopy, potentiodynamic scan, and electrolysis. Electronic transference numbers of the flux were measured to assess the magnesium dissolution in the flux during SOM electrolysis. The effects of magnesium solubility in the flux on the current efficiency and the SOM stability during electrolysis are discussed. An inverse correlation between the electronic transference number of the flux and the current efficiency of the SOM electrolysis was observed. Based on the experimental results, a new equivalent circuit of the SOM electrolysis process is presented. A general electrochemical polarization model of SOM process for magnesium and oxygen gas production is developed, and the maximum allowable applied potential to avoid zirconia dissociation is calculated as well. The modeling results suggest that a high electronic resistance of the flux and a relatively low electronic resistance of SOM are required to achieve membrane stability, high current efficiency, and high production rates of magnesium and oxygen.

SMALL-SCALE AND GLOBAL DYNAMOS AND THE AREA AND FLUX DISTRIBUTIONS OF ACTIVE REGIONS, SUNSPOT GROUPS, AND SUNSPOTS: A MULTI-DATABASE STUDY

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

Muñoz-Jaramillo, Andrés; Windmueller, John C.; Amouzou, Ernest C.

2015-02-10

In this work, we take advantage of 11 different sunspot group, sunspot, and active region databases to characterize the area and flux distributions of photospheric magnetic structures. We find that, when taken separately, different databases are better fitted by different distributions (as has been reported previously in the literature). However, we find that all our databases can be reconciled by the simple application of a proportionality constant, and that, in reality, different databases are sampling different parts of a composite distribution. This composite distribution is made up by linear combination of Weibull and log-normal distributions—where a pure Weibull (log-normal) characterizesmore » the distribution of structures with fluxes below (above) 10{sup 21}Mx (10{sup 22}Mx). Additionally, we demonstrate that the Weibull distribution shows the expected linear behavior of a power-law distribution (when extended to smaller fluxes), making our results compatible with the results of Parnell et al. We propose that this is evidence of two separate mechanisms giving rise to visible structures on the photosphere: one directly connected to the global component of the dynamo (and the generation of bipolar active regions), and the other with the small-scale component of the dynamo (and the fragmentation of magnetic structures due to their interaction with turbulent convection)« less

High power LED standard light sources for photometric applications

NASA Astrophysics Data System (ADS)

Ivashin, Evgeniy; Ogarev, Sergey; Khlevnoy, Boris; Shirokov, Stanislav; Dobroserdov, Dmitry; Sapritsky, Victor

2018-02-01

High power LED light sources have been developed as possible new VNIIOFI standard sources for luminous intensity, luminous flux and colour measurements. Stability, repeatability and spatial uniformity of the sources were investigated and demonstrated high accuracy and homogeneity. The paper describes different tests on one of the manufactured sources. In the future, these LED light sources are planned to be used as standard luminous flux sources to transfer the units of luminous intensity and luminous flux from gonio-spectrometer to sphere-spectrometer.

Method and system using power modulation for maskless vapor deposition of spatially graded thin film and multilayer coatings with atomic-level precision and accuracy

DOEpatents

Montcalm, Claude [Livermore, CA; Folta, James Allen [Livermore, CA; Tan, Swie-In [San Jose, CA; Reiss, Ira [New City, NY

2002-07-30

A method and system for producing a film (preferably a thin film with highly uniform or highly accurate custom graded thickness) on a flat or graded substrate (such as concave or convex optics), by sweeping the substrate across a vapor deposition source operated with time-varying flux distribution. In preferred embodiments, the source is operated with time-varying power applied thereto during each sweep of the substrate to achieve the time-varying flux distribution as a function of time. A user selects a source flux modulation recipe for achieving a predetermined desired thickness profile of the deposited film. The method relies on precise modulation of the deposition flux to which a substrate is exposed to provide a desired coating thickness distribution.

Validation of absolute axial neutron flux distribution calculations with MCNP with 197Au(n,γ)198Au reaction rate distribution measurements at the JSI TRIGA Mark II reactor.

PubMed

Radulović, Vladimir; Štancar, Žiga; Snoj, Luka; Trkov, Andrej

2014-02-01

The calculation of axial neutron flux distributions with the MCNP code at the JSI TRIGA Mark II reactor has been validated with experimental measurements of the (197)Au(n,γ)(198)Au reaction rate. The calculated absolute reaction rate values, scaled according to the reactor power and corrected for the flux redistribution effect, are in good agreement with the experimental results. The effect of different cross-section libraries on the calculations has been investigated and shown to be minor. Copyright © 2013 Elsevier Ltd. All rights reserved.

Influence of the late winter bloom on migrant zooplankton metabolism and its implications on export fluxes

NASA Astrophysics Data System (ADS)

Putzeys, S.; Yebra, L.; Almeida, C.; Bécognée, P.; Hernández-León, S.

2011-12-01

Studies on carbon active fluxes due to diel migrants are scarce and critical for carbon flux models and biogeochemical estimates. We studied the temporal variability and vertical distribution of biomass, indices of feeding and respiration of the zooplanktonic community north off the Canary Islands during the end of the late winter bloom, in order to assess vertical carbon fluxes in this area. Biomass distribution during the day presented two dense layers of organisms at 0-200 m and around 500 m, whereas at night, most of the biomass concentrated in the epipelagic layer. The gut pigment flux (0.05-0.18 mgC·m - 2 ·d - 1 ) represented 0.22% of the estimated passive export flux (POC flux) while potential ingestion represented 3.91% of the POC (1.24-3.40 mgC·m - 2 ·d - 1 ). The active respiratory flux (0.50-1.36 mgC·m - 2 ·d - 1 ) was only 1.57% of the POC flux. The total carbon flux mediated by diel migrants (respiration plus potential ingestion) ranged between 3.37 and 9.22% of the POC flux; which is three-fold higher than calculating ingestion fluxes from gut pigments. Our results suggest that the fluxes by diel migrants play a small role in the downward flux of carbon in the open ocean during the post-bloom period.

Extreme air-sea surface turbulent fluxes in mid latitudes - estimation, origins and mechanisms

NASA Astrophysics Data System (ADS)

Gulev, Sergey; Natalia, Tilinina

2014-05-01

Extreme turbulent heat fluxes in the North Atlantic and North Pacific mid latitudes were estimated from the modern era and first generation reanalyses (NCEP-DOE, ERA-Interim, MERRA NCEP-CFSR, JRA-25) for the period from 1979 onwards. We used direct surface turbulent flux output as well as reanalysis state variables from which fluxes have been computed using COARE-3 bulk algorithm. For estimation of extreme flux values we analyzed surface flux probability density distribution which was approximated by Modified Fisher-Tippett distribution. In all reanalyses extreme turbulent heat fluxes amount to 1500-2000 W/m2 (for the 99th percentile) and can exceed 2000 W/m2 for higher percentiles in the western boundary current extension (WBCE) regions. Different reanalyses show significantly different shape of MFT distribution, implying considerable differences in the estimates of extreme fluxes. The highest extreme turbulent latent heat fluxes are diagnosed in NCEP-DOE, ERA-Interim and NCEP-CFSR reanalyses with the smallest being in MERRA. These differences may not necessarily reflect the differences in mean values. Analysis shows that differences in statistical properties of the state variables are the major source of differences in the shape of PDF of fluxes and in the estimates of extreme fluxes while the contribution of computational schemes used in different reanalyses is minor. The strongest differences in the characteristics of probability distributions of surface fluxes and extreme surface flux values between different reanalyses are found in the WBCE extension regions and high latitudes. In the next instance we analyzed the mechanisms responsible for forming surface turbulent fluxes and their potential role in changes of midlatitudinal heat balance. Midlatitudinal cyclones were considered as the major mechanism responsible for extreme turbulent fluxes which are typically occur during the cold air outbreaks in the rear parts of cyclones when atmospheric conditions provide locally high winds and air-sea temperature gradients. For this purpose we linked characteristics of cyclone activity over the midlatitudinal oceans with the extreme surface turbulent heat fluxes. Cyclone tracks and parameters of cyclone life cycle (deepening rates, propagation velocities, life time and clustering) were derived from the same reanalyses using state of the art numerical tracking algorithm. The main questions addressed in this study are (i) through which mechanisms extreme surface fluxes are associated with cyclone activity? and (ii) which types of cyclones are responsible for forming extreme turbulent fluxes? Our analysis shows that extreme surface fluxes are typically associated not with cyclones themselves but rather with cyclone-anticyclone interaction zones. This implies that North Atlantic and North Pacific series of intense cyclones do not result in the anomalous surface fluxes. Alternatively, extreme fluxes are most frequently associated with blocking situations, particularly with the intensification of the Siberian and North American Anticyclones providing cold-air outbreaks over WBC regions.

Scaling-up of CO2 fluxes to assess carbon sequestration in rangelands of Central Asia

Treesearch

Bruce K. Wylie; Tagir G. Gilmanov; Douglas A. Johnson; Nicanor Z. Saliendra; Larry L. Tieszen; Ruth Anne F. Doyle; Emilio A. Laca

2006-01-01

Flux towers provide temporal quantification of local carbon dynamics at specific sites. The number and distribution of flux towers, however, are generally inadequate to quantify carbon fluxes across a landscape or ecoregion. Thus, scaling up of flux tower measurements through use of algorithms developed from remote sensing and GIS data is needed for spatial...

The impact of land-surface wetness heterogeneity on mesoscale heat fluxes

NASA Technical Reports Server (NTRS)

Chen, Fei; Avissar, Roni

1994-01-01

Vertical heat fluxes associated with mesoscale circulations generated by land-surface wetness discontinuities are often stronger than turbulent fluxes, especially in the upper part of the atmospheric planetary boundary layer. As a result, they contribute significantly to the subgrid-scale fluxes in large-scale atmospheric models. Yet they are not considered in these models. To provide some insights into the possible parameterization of these fluxes in large-scale models, a state-of-the-art mesoscale numerical model was used to investigate the relationships between mesoscale heat fluxes and atmospheric and land-surface characteristics that play a key role in the generation of mesoscale circulations. The distribution of land-surface wetness, the wavenumber and the wavelength of the land-surface discontinuities, and the large-scale wind speed have a significant impact on the mesoscale heat fluxes. Empirical functions were derived to characterize the relationships between mesoscale heat fluxes and the spatial distribution of land-surface wetness. The strongest mesoscale heat fluxes were obtained for a wavelength of forcing corresponding approximately to the local Rossby deformation radius. The mesoscale heat fluxes are weakened by large-scale background winds but remain significant even with moderate winds.

An Equivalent cross-section Framework for improving computational efficiency in Distributed Hydrologic Modelling

NASA Astrophysics Data System (ADS)

Khan, Urooj; Tuteja, Narendra; Ajami, Hoori; Sharma, Ashish

2014-05-01

While the potential uses and benefits of distributed catchment simulation models is undeniable, their practical usage is often hindered by the computational resources they demand. To reduce the computational time/effort in distributed hydrological modelling, a new approach of modelling over an equivalent cross-section is investigated where topographical and physiographic properties of first-order sub-basins are aggregated to constitute modelling elements. To formulate an equivalent cross-section, a homogenization test is conducted to assess the loss in accuracy when averaging topographic and physiographic variables, i.e. length, slope, soil depth and soil type. The homogenization test indicates that the accuracy lost in weighting the soil type is greatest, therefore it needs to be weighted in a systematic manner to formulate equivalent cross-sections. If the soil type remains the same within the sub-basin, a single equivalent cross-section is formulated for the entire sub-basin. If the soil type follows a specific pattern, i.e. different soil types near the centre of the river, middle of hillslope and ridge line, three equivalent cross-sections (left bank, right bank and head water) are required. If the soil types are complex and do not follow any specific pattern, multiple equivalent cross-sections are required based on the number of soil types. The equivalent cross-sections are formulated for a series of first order sub-basins by implementing different weighting methods of topographic and physiographic variables of landforms within the entire or part of a hillslope. The formulated equivalent cross-sections are then simulated using a 2-dimensional, Richards' equation based distributed hydrological model. The simulated fluxes are multiplied by the weighted area of each equivalent cross-section to calculate the total fluxes from the sub-basins. The simulated fluxes include horizontal flow, transpiration, soil evaporation, deep drainage and soil moisture. To assess the accuracy of equivalent cross-section approach, the sub-basins are also divided into equally spaced multiple hillslope cross-sections. These cross-sections are simulated in a fully distributed settings using the 2-dimensional, Richards' equation based distributed hydrological model. The simulated fluxes are multiplied by the contributing area of each cross-section to get total fluxes from each sub-basin referred as reference fluxes. The equivalent cross-section approach is investigated for seven first order sub-basins of the McLaughlin catchment of the Snowy River, NSW, Australia, and evaluated in Wagga-Wagga experimental catchment. Our results show that the simulated fluxes using an equivalent cross-section approach are very close to the reference fluxes whereas computational time is reduced of the order of ~4 to ~22 times in comparison to the fully distributed settings. The transpiration and soil evaporation are the dominant fluxes and constitute ~85% of actual rainfall. Overall, the accuracy achieved in dominant fluxes is higher than the other fluxes. The simulated soil moistures from equivalent cross-section approach are compared with the in-situ soil moisture observations in the Wagga-Wagga experimental catchment in NSW, and results found to be consistent. Our results illustrate that the equivalent cross-section approach reduces the computational time significantly while maintaining the same order of accuracy in predicting the hydrological fluxes. As a result, this approach provides a great potential for implementation of distributed hydrological models at regional scales.

Inverse modeling of Asian (222)Rn flux using surface air (222)Rn concentration.

PubMed

Hirao, Shigekazu; Yamazawa, Hiromi; Moriizumi, Jun

2010-11-01

When used with an atmospheric transport model, the (222)Rn flux distribution estimated in our previous study using soil transport theory caused underestimation of atmospheric (222)Rn concentrations as compared with measurements in East Asia. In this study, we applied a Bayesian synthesis inverse method to produce revised estimates of the annual (222)Rn flux density in Asia by using atmospheric (222)Rn concentrations measured at seven sites in East Asia. The Bayesian synthesis inverse method requires a prior estimate of the flux distribution and its uncertainties. The atmospheric transport model MM5/HIRAT and our previous estimate of the (222)Rn flux distribution as the prior value were used to generate new flux estimates for the eastern half of the Eurasian continent dividing into 10 regions. The (222)Rn flux densities estimated using the Bayesian inversion technique were generally higher than the prior flux densities. The area-weighted average (222)Rn flux density for Asia was estimated to be 33.0 mBq m(-2) s(-1), which is substantially higher than the prior value (16.7 mBq m(-2) s(-1)). The estimated (222)Rn flux densities decrease with increasing latitude as follows: Southeast Asia (36.7 mBq m(-2) s(-1)); East Asia (28.6 mBq m(-2) s(-1)) including China, Korean Peninsula and Japan; and Siberia (14.1 mBq m(-2) s(-1)). Increase of the newly estimated fluxes in Southeast Asia, China, Japan, and the southern part of Eastern Siberia from the prior ones contributed most significantly to improved agreement of the model-calculated concentrations with the atmospheric measurements. The sensitivity analysis of prior flux errors and effects of locally exhaled (222)Rn showed that the estimated fluxes in Northern and Central China, Korea, Japan, and the southern part of Eastern Siberia were robust, but that in Central Asia had a large uncertainty.

Glucose metabolic flux distribution of Lactobacillus amylophilus during lactic acid production using kitchen waste saccharified solution.

PubMed

Liu, Jianguo; Wang, Qunhui; Zou, Hui; Liu, Yingying; Wang, Juan; Gan, Kemin; Xiang, Juan

2013-11-01

The (13) C isotope tracer method was used to investigate the glucose metabolic flux distribution and regulation in Lactobacillus amylophilus to improve lactic acid production using kitchen waste saccharified solution (KWSS). The results demonstrate that L. amylophilus is a homofermentative bacterium. In synthetic medium, 60.6% of the glucose entered the Embden-Meyerhof-Parnas (EMP) to produce lactic acid, whereas 36.4% of the glucose entered the pentose phosphate metabolic pathway (HMP). After solid-liquid separation of the KWSS, the addition of Fe(3+) during fermentation enhanced the NADPH production efficiency and increased the NADH content. The flux to the EMP was also effectively increased. Compared with the control (60.6% flux to EMP without Fe(3+) addition), the flux to the EMP with the addition of Fe(3+) (74.3%) increased by 23.8%. In the subsequent pyruvate metabolism, Fe(3+) also increased lactate dehydrogenase activity, and inhibited alcohol dehydrogenase, pyruvate dehydrogenase and pyruvate carboxylase, thereby increasing the lactic acid production to 9.03 g l(-1) , an increase of 8% compared with the control. All other organic acid by-products were lower than in the control. However, the addition of Zn(2+) showed an opposite effect, decreasing the lactic acid production. In conclusion it is feasible and effective means using GC-MS, isotope experiment and MATLAB software to integrate research the metabolic flux distribution of lactic acid bacteria, and the results provide the theoretical foundation for similar metabolic flux distribution. © 2013 The Authors. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology.

Magnetic flux amplification by Lenz lenses.

PubMed

Schoenmaker, J; Pirota, K R; Teixeira, J C

2013-08-01

Tailoring magnetic flux distribution is highly desirable in a wide range of applications such as magnetic sensors and biomedicine. In this paper we study the manipulation of induced currents in passive devices in order to engineer the distribution of magnetic flux intensity in a given region. We propose two different approaches, one based on especially designed wire loops (Lenz law) and the other based on solid conductive pieces (eddy currents). The gain of such devices is mainly determined by geometry giving perspective of high amplification. We consistently modeled, simulated, and executed the proposed devices. Doubled magnetic flux intensity is demonstrated experimentally for a moderate aspect ratio.

Magnetic flux amplification by Lenz lenses

NASA Astrophysics Data System (ADS)

Schoenmaker, J.; Pirota, K. R.; Teixeira, J. C.

2013-08-01

Tailoring magnetic flux distribution is highly desirable in a wide range of applications such as magnetic sensors and biomedicine. In this paper we study the manipulation of induced currents in passive devices in order to engineer the distribution of magnetic flux intensity in a given region. We propose two different approaches, one based on especially designed wire loops (Lenz law) and the other based on solid conductive pieces (eddy currents). The gain of such devices is mainly determined by geometry giving perspective of high amplification. We consistently modeled, simulated, and executed the proposed devices. Doubled magnetic flux intensity is demonstrated experimentally for a moderate aspect ratio.

Entropy Stable Wall Boundary Conditions for the Compressible Navier-Stokes Equations

NASA Technical Reports Server (NTRS)

Parsani, Matteo; Carpenter, Mark H.; Nielsen, Eric J.

2014-01-01

Non-linear entropy stability and a summation-by-parts framework are used to derive entropy stable wall boundary conditions for the compressible Navier-Stokes equations. A semi-discrete entropy estimate for the entire domain is achieved when the new boundary conditions are coupled with an entropy stable discrete interior operator. The data at the boundary are weakly imposed using a penalty flux approach and a simultaneous-approximation-term penalty technique. Although discontinuous spectral collocation operators are used herein for the purpose of demonstrating their robustness and efficacy, the new boundary conditions are compatible with any diagonal norm summation-by-parts spatial operator, including finite element, finite volume, finite difference, discontinuous Galerkin, and flux reconstruction schemes. The proposed boundary treatment is tested for three-dimensional subsonic and supersonic flows. The numerical computations corroborate the non-linear stability (entropy stability) and accuracy of the boundary conditions.

Entropy Stable Wall Boundary Conditions for the Three-Dimensional Compressible Navier-Stokes Equations

NASA Technical Reports Server (NTRS)

Parsani, Matteo; Carpenter, Mark H.; Nielsen, Eric J.

2015-01-01

Non-linear entropy stability and a summation-by-parts framework are used to derive entropy stable wall boundary conditions for the three-dimensional compressible Navier-Stokes equations. A semi-discrete entropy estimate for the entire domain is achieved when the new boundary conditions are coupled with an entropy stable discrete interior operator. The data at the boundary are weakly imposed using a penalty flux approach and a simultaneous-approximation-term penalty technique. Although discontinuous spectral collocation operators on unstructured grids are used herein for the purpose of demonstrating their robustness and efficacy, the new boundary conditions are compatible with any diagonal norm summation-by-parts spatial operator, including finite element, finite difference, finite volume, discontinuous Galerkin, and flux reconstruction/correction procedure via reconstruction schemes. The proposed boundary treatment is tested for three-dimensional subsonic and supersonic flows. The numerical computations corroborate the non-linear stability (entropy stability) and accuracy of the boundary conditions.

Magnetic field distribution in superconducting composites as revealed by ESR-probe and magnetization

NASA Astrophysics Data System (ADS)

Davidov, D.; Bontemps, N.; Golosovsky, M.; Waysand, G.

1998-03-01

The distribution of a static magnetic field in superconductor-insulator composites consisting of BSCCO (YBCO) powder in paraffin wax is studied by ESR bulk probing and magnetization. The average field and field variance in the non-superconducting host are measured as function of temperature and volume fraction of superconductor. We develop a model of the field distribution in dilute magnetic and superconducting composites that relates the field inhomogeneity to magnetization and particle shape. We find that this model satisfactorily describes field distribution in our superconducting composites in the regime of strong flux pinning, i.e. below irreversibility line. We find deviations from the model above the irreversibility line and attribute this to flux motion. We show that the field distribution in superconducting composites is determined not only by magnetization and particle shape, but is strongly affected by the flux profile within the superconducting particles.

Estimation of in-canopy flux distributions of reactive nitrogen and sulfur within a mixed hardwood forest in southern Appalachia

EPA Science Inventory

Estimating the source/sink distribution and vertical fluxes of air pollutants within and above forested canopies is critical for understanding biological, physical, and chemical processes influencing the soil-vegetation-atmosphere exchange. The vertical source-sink profiles of re...

In-situ measurement of concentrated solar flux and distribution at the aperture of a central solar receiver

NASA Astrophysics Data System (ADS)

Ferriere, Alain; Volut, Mikael; Perez, Antoine; Volut, Yann

2016-05-01

A flux mapping system has been designed, implemented and experimented at the top of the Themis solar tower in France. This system features a moving bar associated to a CCD video camera and a flux gauge mounted onto the bar used as reference measurement for calibration purpose. Images and flux signal are acquired separately. The paper describes the equipment and focus on the data processing to issue the distribution of flux density and concentration at the aperture of the solar receiver. Finally, the solar power entering into the receiver is estimated by integration of flux density. The processing is largely automated in the form of a dedicated software with fast execution. A special attention is paid to the accuracy of the results, to the robustness of the algorithm and to the velocity of the processing.

Evidence for ion heat flux in the light ion polar wind

NASA Technical Reports Server (NTRS)

Biddle, A. P.; Moore, T. E.; Chappell, C. R.

1985-01-01

Cold flowing hydrogen and helium ions have been observed using the retarding ion mass spectrometer on board the Dynamics Explorer 1 spacecraft in the dayside magnetosphere at subauroral latitudes. The ions show a marked flux asymmetry with respect to the relative wind direction. The observed data are fitted by a model of drifting Maxwellian distributions perturbed by a first order-Spritzer-Haerm heat flux distribution function. It is shown that both ion species are supersonic just equatorward of the auroral zone at L = 14, and the shape of asymmetry and direction of the asymmetry are consistent with the presence of an upward heat flux. At L = 6, both species evolve smoothly into warmer subsonic upward flows with downward heat fluxes. In the case of subsonic flows the downward heat flux implies a significant heat source at higher altitudes. Spin curves of the spectrometer count rate versus the spin phase angle are provided.

PVDF flux/mass/velocity/trajectory systems and their applications in space

NASA Technical Reports Server (NTRS)

Tuzzolino, Anthony J.

1994-01-01

The current status of the University of Chicago Polyvinylidene Fluoride (PVDF) flux/mass/velocity/trajectory instrumentation is summarized. The particle response and thermal stability characteristics of pure PVDF and PVDF copolymer sensors are described, as well as the characteristics of specially constructed two-dimensional position-sensing PVDF sensors. The performance of high-flux systems and of velocity/trajectory systems using these sensors is discussed, and the objectives and designs of a PVDF velocity/trajectory dust instrument for launch on the Advanced Research and Global Observation Satellite (ARGOS) in 1995 and of a high-flux dust instrument for launch on the Cassini spacecraft to Saturn in 1997 are summarized.

On the structure and stability of magnetic tower jets

DOE PAGES

Huarte-Espinosa, M.; Frank, A.; Blackman, E. G.; ...

2012-09-05

Modern theoretical models of astrophysical jets combine accretion, rotation, and magnetic fields to launch and collimate supersonic flows from a central source. Near the source, magnetic field strengths must be large enough to collimate the jet requiring that the Poynting flux exceeds the kinetic energy flux. The extent to which the Poynting flux dominates kinetic energy flux at large distances from the engine distinguishes two classes of models. In magneto-centrifugal launch models, magnetic fields dominate only at scales <~ 100 engine radii, after which the jets become hydrodynamically dominated (HD). By contrast, in Poynting flux dominated (PFD) magnetic tower models,more » the field dominates even out to much larger scales. To compare the large distance propagation differences of these two paradigms, we perform three-dimensional ideal magnetohydrodynamic adaptive mesh refinement simulations of both HD and PFD stellar jets formed via the same energy flux. We also compare how thermal energy losses and rotation of the jet base affects the stability in these jets. For the conditions described, we show that PFD and HD exhibit observationally distinguishable features: PFD jets are lighter, slower, and less stable than HD jets. Here, unlike HD jets, PFD jets develop current-driven instabilities that are exacerbated as cooling and rotation increase, resulting in jets that are clumpier than those in the HD limit. Our PFD jet simulations also resemble the magnetic towers that have been recently created in laboratory astrophysical jet experiments.« less

Theory and Performance of AIMS for Active Interrogation

NASA Astrophysics Data System (ADS)

Walters, William J.; Royston, Katherine E. K.; Haghighat, Alireza

2014-06-01

A hybrid Monte Carlo and deterministic methodology has been developed for application to active interrogation systems. The methodology consists of four steps: i) determination of neutron flux distribution due to neutron source transport and subcritical multiplication; ii) generation of gamma source distribution from (n, γ) interactions; iii) determination of gamma current at a detector window; iv) detection of gammas by the detector. This paper discusses the theory and results of the first three steps for the case of a cargo container with a sphere of HEU in third-density water. In the first step, a response-function formulation has been developed to calculate the subcritical multiplication and neutron flux distribution. Response coefficients are pre-calculated using the MCNP5 Monte Carlo code. The second step uses the calculated neutron flux distribution and Bugle-96 (n, γ) cross sections to find the resulting gamma source distribution. Finally, in the third step the gamma source distribution is coupled with a pre-calculated adjoint function to determine the gamma flux at a detector window. A code, AIMS (Active Interrogation for Monitoring Special-Nuclear-materials), has been written to output the gamma current for an source-detector assembly scanning across the cargo using the pre-calculated values and takes significantly less time than a reference MCNP5 calculation.

High-flux source of low-energy neutral beams using reflection of ions from metals

NASA Technical Reports Server (NTRS)

Cuthbertson, John W.; Motley, Robert W.; Langer, William D.

1992-01-01

Reflection of low-energy ions from surfaces can be applied as a method of producing high-flux beams of low-energy neutral particles, and is an important effect in several areas of plasma technology, such as in the edge region of fusion devices. We have developed a beam source based on acceleration and reflection of ions from a magnetically confined coaxial RF plasma source. The beam provides a large enough flux to allow the energy distribution of the reflected neutrals to be measured despite the inefficiency of detection, by means of an electrostatic cylindrical mirror analyzer coupled with a quadrupole mass spectrometer. Energy distributions have been measured for oxygen, nitrogen, and inert gas ions incident with from 15 to 70 eV reflected from amorphous metal surfaces of several compositions. For ions of lighter atomic mass than the reflecting metal, reflected beams have peaked energy distributions; beams with the peak at 4-32 eV have been measured. The energy and mass dependences of the energy distributions as well as measurements of absolute flux, and angular distribution and divergence are reported. Applications of the neutral beams produced are described.

Hidden regularity and universal classification of fast side chain motions in proteins

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

Rajeshwar, Rajitha; Smith, Jeremy C.; Krishnam, Marimuthu

Proteins display characteristic dynamical signatures that appear to be universal across all proteins regardless of topology and size. Here, we systematically characterize the universal features of fast side chain motions in proteins by examining the conformational energy surfaces of individual residues obtained using enhanced sampling molecular dynamics simulation (618 free energy surfaces obtained from 0.94 s MD simulation). The side chain conformational free energy surfaces obtained using the adaptive biasing force (ABF) method for a set of eight proteins with different molecular weights and secondary structures are used to determine the methyl axial NMR order parameters (O axis 2), populationsmore » of side chain rotamer states (ρ), conformational entropies (S conf), probability fluxes, and activation energies for side chain inter-rotameric transitions. The free energy barriers separating side chain rotamer states range from 0.3 to 12 kcal/mol in all proteins and follow a trimodal distribution with an intense peak at ~5 kcal/mol and two shoulders at ~3 and ~7.5 kcal/mol, indicating that some barriers are more favored than others by proteins to maintain a balance between their conformational stability and flexibility. The origin and the influences of the trimodal barrier distribution on the distribution of O axis 2 and the side chain conformational entropy are discussed. A hierarchical grading of rotamer states based on the conformational free energy barriers, entropy, and probability flux reveals three distinct classes of side chains in proteins. A unique nonlinear correlation is established between O axis 2 and the side chain rotamer populations (ρ). In conclusion, the apparent universality in O axis 2 versus correlation, trimodal barrier distribution, and distinct characteristics of three classes of side chains observed among all proteins indicates a hidden regularity (or commonality) in the dynamical heterogeneity of fast side chain motions in proteins.« less

DETECTION OF FLUX EMERGENCE, SPLITTING, MERGING, AND CANCELLATION OF NETWORK FIELD. I. SPLITTING AND MERGING

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

Iida, Y.; Yokoyama, T.; Hagenaar, H. J.

2012-06-20

Frequencies of magnetic patch processes on the supergranule boundary, namely, flux emergence, splitting, merging, and cancellation, are investigated through automatic detection. We use a set of line-of-sight magnetograms taken by the Solar Optical Telescope (SOT) on board the Hinode satellite. We found 1636 positive patches and 1637 negative patches in the data set, whose time duration is 3.5 hr and field of view is 112'' Multiplication-Sign 112''. The total numbers of magnetic processes are as follows: 493 positive and 482 negative splittings, 536 positive and 535 negative mergings, 86 cancellations, and 3 emergences. The total numbers of emergence and cancellationmore » are significantly smaller than those of splitting and merging. Further, the frequency dependence of the merging and splitting processes on the flux content are investigated. Merging has a weak dependence on the flux content with a power-law index of only 0.28. The timescale for splitting is found to be independent of the parent flux content before splitting, which corresponds to {approx}33 minutes. It is also found that patches split into any flux contents with the same probability. This splitting has a power-law distribution of the flux content with an index of -2 as a time-independent solution. These results support that the frequency distribution of the flux content in the analyzed flux range is rapidly maintained by merging and splitting, namely, surface processes. We suggest a model for frequency distributions of cancellation and emergence based on this idea.« less

Exchange biased and closed-flux pseudo spin-valve materials, device applications, and electrical reliability

NASA Astrophysics Data System (ADS)

Bae, Seongtae

Since giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) spinvalve effects were developed for the last two decades after discovered, world wide researches on applying these effects for various kinds of solid state active devices has provided a strong impact on challenging new functional micro-magnetoelectronic devices. In particular, recently developed nano-structured magnetic spin-valve thin film materials for spin-electronic devices are now considered as building blocks of state-of-the-art electronic engineering. This research has been concentrated on developing and designing magneto-electronic solid state devices with high thermal and electrical stability using an alpha-Fe 2O3 and NiO oxide anti-ferromagnetic exchange biased GMR bottom spin-valves (BSV), NiFe/Cu/Co and NiFe/Cu/CoFe based closed-flux metallic pseudo spin-valves, and PtMn exchange biased TMR spin-valves. The category covering this research is divided into four main research steps. First is to investigate exchange bias coupling characteristics of alpha-Fe2 O3 and NiO oxide Anti-ferromagnetic materials (AF)/Ferromagnetic (F) layer systems for optimizing exchange biased BSV and to study magnetic properties of various kinds of magnetic thin films including single through multi-layered structures for the fundamental research on NiFe/Cu/Co and NiFe/Cu/CoFe closed-flux metallic pseudo spin-valves. Second is to develop and improve new kinds of BSVs and closed-flux metallic spinvalves by controlling process parameters in terms of crystalline orientation texture of AF and F layers, interfacial surface roughness, grain size (its size distribution), chemical composition, and kinetics of sputtering film growth. Third is to design, to fabricate, and to investigate the magnetic and electrical properties of magneto-electronic devices as well as their applications such as GMR magnetoresistive random access memory (MRAM), GMR read head, TMR read head, and new kinds of GMR solid state devices, which can be promisingly substituted for current microelectronic devices. Finally, the last is to focus on studying electrical reliability of GMR read sensor and GMR MRAM cell in terms of electromigration-induced failures of various kinds of magnetic thin films, which are currently used in GMR spin-valve materials, and is to investigate the effects of current (or voltage) induced dielectric breakdown in aluminum oxide tunnel barrier under various testing conditions on the electrical stability of real TMR read sensors.

Towards natural inflation from weakly coupled heterotic string theory

NASA Astrophysics Data System (ADS)

Abe, Hiroyuki; Kobayashi, Tatsuo; Otsuka, Hajime

2015-06-01

We propose natural inflation from the heterotic string theory on the "Swiss-Cheese" Calabi-Yau manifold with multiple U(1) magnetic fluxes. Such multiple U(1) magnetic fluxes stabilize the same number of the linear combination of the universal axion and Kähler axions, and one of the Kähler axions is identified as the inflaton. This axion decay constant can be determined by the size of one-loop corrections to the gauge kinetic function of the hidden gauge groups, which leads effectively to the trans-Planckian axion decay constant consistent with the Planck data. During the inflation, the real parts of the moduli are also stabilized by employing the nature of the "Swiss-Cheese" Calabi-Yau manifold.

Evaluation of a 6-wire thermocouple psychrometer for determination of in-situ water potentials

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

Loskot, C.L.; Rousseau, J.P.; Kurzmack, M.A.

1994-12-31

The US Geological Survey has been conducting investigations at Yucca Mountain, Nevada, to provide information about the hydrologic and geologic suitability of this site for storing high-level nuclear wastes in an underground mined repository. Test drilling and instrumentation are a principal method of investigation. The main objectives of the deep unsaturated-zone testhole program are: (1) to determine the flux of water moving through the unsaturated welded and nonwelded tuff units, (2) to determine the vertical and lateral distribution of moisture content, water potential, and other important geohydrologic characteristics in the rock units penetrated, and (3) to monitor stability and changesmore » in in-situ fluid potentials with time. Thermocouple psychrometers will be used to monitor in-situ water potentials.« less

Inhibition of electron thermal conduction by electromagnetic instabilities. [in stellar coronas

NASA Technical Reports Server (NTRS)

Levinson, Amir; Eichler, David

1992-01-01

Heat flux inhibition by electromagnetic instabilities in a hot magnetized plasma is investigated. Low-frequency electromagnetic waves become unstable due to anisotropy of the electron distribution function. The chaotic magnetic field thus generated scatters the electrons with a specific effective mean free path. Saturation of the instability due to wave-wave interaction, nonlinear scattering, wave propagation, and collisional damping is considered. The effective mean free path is found self-consistently, using a simple model to estimate saturation level and scattering, and is shown to decrease with the temperature gradient length. The results, limited to the assumptions of the model, are applied to astrophysical systems. For some interstellar clouds the instability is found to be important. Collisional damping stabilizes the plasma, and the heat conduction can be dominated by superthermal electrons.

Stability Analysis of Distributed Order Fractional Chen System

PubMed Central

Aminikhah, H.; Refahi Sheikhani, A.; Rezazadeh, H.

2013-01-01

We first investigate sufficient and necessary conditions of stability of nonlinear distributed order fractional system and then we generalize the integer-order Chen system into the distributed order fractional domain. Based on the asymptotic stability theory of nonlinear distributed order fractional systems, the stability of distributed order fractional Chen system is discussed. In addition, we have found that chaos exists in the double fractional order Chen system. Numerical solutions are used to verify the analytical results. PMID:24489508

Modelling the Surface Distribution of Magnetic Activity on Sun-Like Stars

NASA Astrophysics Data System (ADS)

Isik, Emre

2018-04-01

With the advent of high-precision space-borne stellar photometry and prospects for direct imaging, it is timely and essential to improve our understanding of stellar magnetic activity in rotational time scales. We present models for 'younger suns' with rotation and flux emergence rates between 1 and 16 times the solar rate. The models provide latitudinal distributions and tilt angles of bipolar magnetic regions, using flux tube rise simulations. Using these emergence patterns, we model the subsequent surface flux transport, to predict surface distributions of star-spots. Based on these models, we present preliminary results from our further modelling of the observed azimuthal magnetic fields, which strengthen for more rapidly rotating Sun-like stars.

Thermally Driven One-Fluid Electron-Proton Solar Wind: Eight-Moment Approximation

NASA Astrophysics Data System (ADS)

Olsen, Espen Lyngdal; Leer, Egil

1996-05-01

In an effort to improve the "classical" solar wind model, we study an eight-moment approximation hydrodynamic solar wind model, in which the full conservation equation for the heat conductive flux is solved together with the conservation equations for mass, momentum, and energy. We consider two different cases: In one model the energy flux needed to drive the solar wind is supplied as heat flux from a hot coronal base, where both the density and temperature are specified. In the other model, the corona is heated. In that model, the coronal base density and temperature are also specified, but the temperature increases outward from the coronal base due to a specified energy flux that is dissipated in the corona. The eight-moment approximation solutions are compared with the results from a "classical" solar wind model in which the collision-dominated gas expression for the heat conductive flux is used. It is shown that the "classical" expression for the heat conductive flux is generally not valid in the solar wind. In collisionless regions of the flow, the eight-moment approximation gives a larger thermalization of the heat conductive flux than the models using the collision-dominated gas approximation for the heat flux, but the heat flux is still larger than the "saturation heat flux." This leads to a breakdown of the electron distribution function, which turns negative in the collisionless region of the flow. By increasing the interaction between the electrons, the heat flux is reduced, and a reasonable shape is obtained on the distribution function. By solving the full set of equations consistent with the eight-moment distribution function for the electrons, we are thus able to draw inferences about the validity of the eight-moment description of the solar wind as well as the validity of the very commonly used collision-dominated gas approximation for the heat conductive flux in the solar wind.

Submarine melt rates under Greenland's ice tongues

NASA Astrophysics Data System (ADS)

Wilson, Nat; Straneo, Fiametta; Heimbach, Patrick; Cenedese, Claudia

2017-04-01

The few remaining ice tongues (ice-shelf like extensions) of Greenland's glaciers are undergoing rapid changes with potential implications for the stability of the ice sheet. Submarine melting is recognized as a major contributor to mass loss, yet the magnitude and spatial distribution of melt are poorly known or understood. Here, we use high resolution satellite imagery to infer the magnitude and spatial variability of melt rates under Greenland's largest remaining ice tongues: Ryder Glacier, Petermann Glacier and Nioghalvfjerdsbræ (79 North Glacier). We find that submarine plus aerial melt approximately balance the ice flux from the grounded ice sheet for the first two while at Nioghalvfjerdsbræ the total melt flux exceeds the inflow of ice indicating thinning of the ice tongue. We also show that melt rates under the ice tongues vary considerably, exceeding 60 m yr-1 near the grounding zone and decaying rapidly downstream. Channels, likely originating from upstream subglacial channels, give rise to large melt variations across the ice tongues. Using derived melt rates, we test simplified melt parameterizations appropriate for ice sheet models and find the best agreement with those that incorporate ice tongue geometry in the form of depth and slope.

Implicit flux-split Euler schemes for unsteady aerodynamic analysis involving unstructured dynamic meshes

NASA Technical Reports Server (NTRS)

Batina, John T.

1990-01-01

Improved algorithms for the solution of the time-dependent Euler equations are presented for unsteady aerodynamic analysis involving unstructured dynamic meshes. The improvements have been developed recently to the spatial and temporal discretizations used by unstructured grid flow solvers. The spatial discretization involves a flux-split approach which is naturally dissipative and captures shock waves sharply with at most one grid point within the shock structure. The temporal discretization involves an implicit time-integration shceme using a Gauss-Seidel relaxation procedure which is computationally efficient for either steady or unsteady flow problems. For example, very large time steps may be used for rapid convergence to steady state, and the step size for unsteady cases may be selected for temporal accuracy rather than for numerical stability. Steady and unsteady flow results are presented for the NACA 0012 airfoil to demonstrate applications of the new Euler solvers. The unsteady results were obtained for the airfoil pitching harmonically about the quarter chord. The resulting instantaneous pressure distributions and lift and moment coefficients during a cycle of motion compare well with experimental data. The paper presents a description of the Euler solvers along with results and comparisons which assess the capability.

Implicit flux-split Euler schemes for unsteady aerodynamic analysis involving unstructured dynamic meshes

NASA Technical Reports Server (NTRS)

Batina, John T.

1990-01-01

Improved algorithm for the solution of the time-dependent Euler equations are presented for unsteady aerodynamic analysis involving unstructured dynamic meshes. The improvements were developed recently to the spatial and temporal discretizations used by unstructured grid flow solvers. The spatial discretization involves a flux-split approach which is naturally dissipative and captures shock waves sharply with at most one grid point within the shock structure. The temporal discretization involves an implicit time-integration scheme using a Gauss-Seidel relaxation procedure which is computationally efficient for either steady or unsteady flow problems. For example, very large time steps may be used for rapid convergence to steady state, and the step size for unsteady cases may be selected for temporal accuracy rather than for numerical stability. Steady and unsteady flow results are presented for the NACA 0012 airfoil to demonstrate applications of the new Euler solvers. The unsteady results were obtained for the airfoil pitching harmonically about the quarter chord. The resulting instantaneous pressure distributions and lift and moment coefficients during a cycle of motion compare well with experimental data. A description of the Euler solvers is presented along with results and comparisons which assess the capability.

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

Desai, M. I.; Dayeh, M. A.; Allegrini, F.

We investigate the latitude, energy, and temporal variations of the ∼0.5–6 keV energetic neutral atom (ENA) fluxes and spectral indices measured by the Interstellar Boundary Explorer ( IBEX ) outside of the Ribbon from 2009 to 2013. By combining all-sky maps for years 1–3 and years 4–5, we find that the >1.2 keV globally distributed (GD) ENA fluxes at all latitudes decrease by ∼25% from years 1–3 to years 4–5, but there is no change (<5%) in the corresponding spectral indices. We also show that the latitudinal profile and energy-dependence of the ≥1 keV ENA spectral indices outside the Ribbonmore » exhibit no significant time differences between years 1–3 and 4–5, lending strong support for the notion that the highly organized, persistent energy dependence and latitudinal pattern of the ENA spectral indices during 2009–2014 are determined by that of the solar wind (SW) speed observed in the inner heliosphere during the deep solar minimum conditions of 2006–2010. In contrast, the ∼25% decrease in the >1.2 keV ENA fluxes at all latitudes from years 1–3 to years 4–5 occurs because the magnitude of the driving SW parameters (SW density or dynamic pressure) diminished significantly from 2006 to 2010. Based on the reconstructed latitudinal and temporal profiles of SW parameters from 2011 to 2014, i.e., during the rising phase of solar cycle 24, we suggest that the GD ENA fluxes in years 2014–2017, i.e., in maps 6–9, will either stabilize or increase and the latitudinal pattern and energy dependence of the corresponding spectral indices will be disrupted.« less

The Near-Earth Meteoroid Flux, Speed Distribution, and Uncertainty

NASA Technical Reports Server (NTRS)

Moorhead, Althea; Cooke, William J.; Brown, Peter G.; Campbell-Brown, Margaret; Moser, Danielle E.

2016-01-01

Meteoroids are known to pose a threat to spacecraft; they can puncture components, disturb spacecraft attitude, and possibly create secondary electrical effects. Accurate environment models are therefore critical for mitigating meteoroid-related risks. While there are several meteoroid environment models available for assessing spacecraft risk, the uncertainties associated with these models are not well understood. Because meteoroid properties are derived from indirect observations such as meteors and impact craters, the uncertainty in the meteoroid flux is potentially quite large. We combine existing meteoroid flux measurements with new radar and optical meteor data to improve our characterization of the meteoroid flux onto the Earth and its velocity distribution. We use data extracted from the NASA all-sky network, the Canadian Automated Meteor Observatory, and the Canadian Meteor Orbit Radar. We improve our characterization of the observed meteoroid speed distribution by incorporating modern descriptions of the ionization efficiency (e.g., Thomas et al., 2016). We also present estimates of the uncertainties associated with our meteoroid flux distribution. Finally, we discuss the implications for spacecraft. Our model is constrained by the cratering rate on the space-facing surface of LDEF, and thus the risk posed to spacecraft by meteoroid-induced physical damage is the least uncertain component of our model. Other sources of risk, however, may vary. For instance, a lower average meteoroid speed would require a higher meteoroid mass flux in order to match the LDEF crater counts, leading to higher predicted rates of attitude disturbances.

Adaptive Discontinuous Evolution Galerkin Method for Dry Atmospheric Flow

DTIC Science & Technology

2013-04-02

standard one-dimensional approximate Riemann solver used for the flux integration demonstrate better stability, accuracy as well as reliability of the...discontinuous evolution Galerkin method for dry atmospheric convection. Comparisons with the standard one-dimensional approximate Riemann solver used...instead of a standard one- dimensional approximate Riemann solver , the flux integration within the discontinuous Galerkin method is now realized by

A 7.5-Year Dataset of SSM/I-Derived Surface Turbulent Fluxes Over Global Oceans

NASA Technical Reports Server (NTRS)

Chou, Shu-Hsien; Shie, Chung-Lin; Atlas, Robert M.; Ardizzone, Joe; Nelkin, Eric; Einaudi, Franco (Technical Monitor)

2001-01-01

The surface turbulent fluxes of momentum, latent heat, and sensible heat over global oceans are essential to weather, climate and ocean problems. Wind stress is the major forcing for driving the oceanic circulation, while Evaporation is a key component of hydrological cycle and surface heat budget. We have produced a 7.5-year (July 1987-December 1994) dataset of daily, individual monthly-mean and climatological (1988-94) monthly-mean surface turbulent fluxes over the global oceans from measurements of the Special Sensor Microwave/Imager (SSM/I) on board the US Defense Meteorological Satellite Program F8, F10, and F11 satellites. It has a spatial resolution of 2.0x2.5 latitude-longitude. Daily turbulent fluxes are derived from daily data of SSM/I surface winds and specific humidity, National Centers for Environmental Prediction (NCEP) sea surface temperatures, and European Centre for Medium-Range Weather Forecasts (ECMWF) air-sea temperature differences, using a stability-dependent bulk scheme. The retrieved instantaneous surface air humidity (with a 25-km resolution) IS found to be generally accurate as compared to the collocated radiosonde observations over global oceans. The surface wind speed and specific humidity (latent heat flux) derived from the F10 SSM/I are found to be -encrally smaller (larger) than those retrieved from the F11 SSM/I. The F11 SSM/I appears to have slightly better retrieval accuracy for surface wind speed and humidity as compared to the F10 SSM/I. This difference may be due to the orbital drift of the F10 satellite. The daily wind stresses and latent heat fluxes retrieved from F10 and F11 SSM/Is show useful accuracy as verified against the research quality in si -neasurerrients (IMET buoy, RV Moana Wave, and RV Wecoma) in the western Pacific warm pool during the TOGA COARE Intensive observing period (November 1992-February 1993). The 1988-94 seasonal-mean turbulent fluxes and input variables derived from FS and F11 SSM/Is show reasonable patterns related to seasonal variations of atmospheric general circulation. This dataset of SSM/I-derived turbulent fluxes is useful for climate studies, forcing of ocean models, and validation of coupled ocean-atmosphere global models and can be accessed through the NASA/GSFC Distributed Active Archive Center.

Stabilizing all geometric moduli in heterotic Calabi-Yau vacua

DOE PAGES

Anderson, Lara B.; Gray, James; Lukas, Andre; ...

2011-05-27

We propose a scenario to stabilize all geometric moduli - that is, the complex structure, Kähler moduli and the dilaton - in smooth heterotic Calabi-Yau compactifications without Neveu-Schwarz three-form flux. This is accomplished using the gauge bundle required in any heterotic compactification, whose perturbative effects on the moduli are combined with non-perturbative corrections. We argue that, for appropriate gauge bundles, all complex structure and a large number of other moduli can be perturbatively stabilized - in the most restrictive case, leaving only one combination of Kähler moduli and the dilaton as a flat direction. At this stage, the remaining modulimore » space consists of Minkowski vacua. That is, the perturbative superpotential vanishes in the vacuum without the necessity to fine-tune flux. Finally, we incorporate non-perturbative effects such as gaugino condensation and/or instantons. These are strongly constrained by the anomalous U(1) symmetries which arise from the required bundle constructions. We present a specific example, with a consistent choice of non-perturbative effects, where all remaining flat directions are stabilized in an AdS vacuum.« less

Flux tubes in the SU(3) vacuum

NASA Astrophysics Data System (ADS)

Cardaci, M. S.; Cea, P.; Cosmai, L.; Falcone, R.; Papa, A.

We analyze the distribution of the chromoelectric field generated by a static quark-antiquark pair in the SU(3) vacuum. We find that the transverse profile of the flux tube resembles the dual version of the Abrikosov vortex field distribution and give an estimate of the London penetration length in the confined vacuum.

Point and Compact Hα Sources in the Interior of M33

NASA Astrophysics Data System (ADS)

Moody, J. Ward; Hintz, Eric G.; Joner, Michael D.; Roming, Peter W. A.; Hintz, Maureen L.

2017-12-01

A variety of interesting objects such as Wolf-Rayet stars, tight OB associations, planetary nebulae, X-ray binaries, etc., can be discovered as point or compact sources in Hα surveys. How these objects distribute through a galaxy sheds light on the galaxy star formation rate and history, mass distribution, and dynamics. The nearby galaxy M33 is an excellent place to study the distribution of Hα-bright point sources in a flocculant spiral galaxy. We have reprocessed an archived WIYN continuum-subtracted Hα image of the inner 6.‧5 × 6.‧5 of M33 and, employing both eye and machine searches, have tabulated sources with a flux greater than approximately 10-15 erg cm-2s-1. We have effectively recovered previously mapped H II regions and have identified 152 unresolved point sources and 122 marginally resolved compact sources, of which 39 have not been previously identified in any archive. An additional 99 Hα sources were found to have sufficient archival flux values to generate a Spectral Energy Distribution. Using the SED, flux values, Hα flux value, and compactness, we classified 67 of these sources.

Exact analytic flux distributions for two-dimensional solar concentrators.

PubMed

Fraidenraich, Naum; Henrique de Oliveira Pedrosa Filho, Manoel; Vilela, Olga C; Gordon, Jeffrey M

2013-07-01

A new approach for representing and evaluating the flux density distribution on the absorbers of two-dimensional imaging solar concentrators is presented. The formalism accommodates any realistic solar radiance and concentrator optical error distribution. The solutions obviate the need for raytracing, and are physically transparent. Examples illustrating the method's versatility are presented for parabolic trough mirrors with both planar and tubular absorbers, Fresnel reflectors with tubular absorbers, and V-trough mirrors with planar absorbers.

Effect of boundary heat flux on columnar formation in binary alloys: A phase-field study

NASA Astrophysics Data System (ADS)

Du, Lifei; Zhang, Peng; Yang, Shaomei; Chen, Jie; Du, Huiling

2018-02-01

A non-isothermal phase-field model was employed to simulate the columnar formation during rapid solidification in binary Ni-Cu alloy. Heat flux at different boundaries was applied to investigate the temperature gradient effect on the morphology, concentration and temperature distributions during directional solidifications. With the heat flux input/extraction from boundaries, coupling with latent heat release and initial temperature gradient, temperature distributions are significantly changed, leading to solute diffusion changes during the phase-transition. Thus, irregular columnar structures are formed during the directional solidification, and the concentration distribution in solid columnar arms could also be changed due to the different growing speeds and temperature distributions at the solid-liquid interfaces. Therefore, applying specific heat conditions at the solidifying boundaries could be an efficient way to control the microstructure during solidifications.

Transition from eruptive to confined flares in the same active region

NASA Astrophysics Data System (ADS)

Zuccarello, F. P.; Chandra, R.; Schmieder, B.; Aulanier, G.; Joshi, R.

2017-05-01

Context. Solar flares are sudden and violent releases of magnetic energy in the solar atmosphere that can be divided into two classes: eruptive flares, where plasma is ejected from the solar atmosphere resulting in a coronal mass ejection (CME), and confined flares, where no CME is associated with the flare. Aims: We present a case study showing the evolution of key topological structures, such as spines and fans, which may determine the eruptive versus non-eruptive behavior of the series of eruptive flares followed by confined flares, which all originate from the same site. Methods: To study the connectivity of the different flux domains and their evolution, we compute a potential magnetic field model of the active region. Quasi-separatrix layers are retrieved from the magnetic field extrapolation. Results: The change in behavior of the flares from one day to the next - from eruptive to confined - can be attributed to the change in orientation of the magnetic field below the fan with respect to the orientation of the overlaying spine rather than an overall change in the stability of the large-scale field. Conclusions: Flares tend to be more confined when the field that supports the filament and the overlying field gradually becomes less anti-parallel as a direct result of changes in the photospheric flux distribution, being themselves driven by continuous shearing motions of the different magnetic flux concentrations. Movies associated to Figs. 2, 3, and 5 are available at http://www.aanda.org

Linear stability analysis of the three-dimensional thermally-driven ocean circulation: application to interdecadal oscillations

NASA Astrophysics Data System (ADS)

Huck, Thierry; Vallis, Geoffrey K.

2001-08-01

What can we learn from performing a linear stability analysis of the large-scale ocean circulation? Can we predict from the basic state the occurrence of interdecadal oscillations, such as might be found in a forward integration of the full equations of motion? If so, do the structure and period of the linearly unstable modes resemble those found in a forward integration? We pursue here a preliminary study of these questions for a case in idealized geometry, in which the full nonlinear behavior can also be explored through forward integrations. Specifically, we perform a three-dimensional linear stability analysis of the thermally-driven circulation of the planetary geostrophic equations. We examine the resulting eigenvalues and eigenfunctions, comparing them with the structure of the interdecadal oscillations found in the fully nonlinear model in various parameter regimes. We obtain a steady state by running the time-dependent, nonlinear model to equilibrium using restoring boundary conditions on surface temperature. If the surface heat fluxes are then diagnosed, and these values applied as constant flux boundary conditions, the nonlinear model switches into a state of perpetual, finite amplitude, interdecadal oscillations. We construct a linearized version of the model by empirically evaluating the tangent linear matrix at the steady state, under both restoring and constant-flux boundary conditions. An eigen-analysis shows there are no unstable eigenmodes of the linearized model with restoring conditions. In contrast, under constant flux conditions, we find a single unstable eigenmode that shows a striking resemblance to the fully-developed oscillations in terms of three-dimensional structure, period and growth rate. The mode may be damped through either surface restoring boundary conditions or sufficiently large horizontal tracer diffusion. The success of this simple numerical method in idealized geometry suggests applications in the study of the stability of the ocean circulation in more realistic configurations, and the possibility of predicting potential oceanic modes, even weakly damped, that might be excited by stochastic atmospheric forcing or mesoscale ocean eddies.

Oxygen permeation and stability of La 0.4Ca 0.6Fe 1-xCo xO 3-δ ( x = 0, 0.25, 0.5) membranes

NASA Astrophysics Data System (ADS)

Diethelm, S.; Van herle, J.; Middleton, P. H.; Favrat, D.

Three perovskite-type compounds of composition La 0.4Ca 0.6Fe 1- xCo xO 3- δ ( x=0, 0.25 and 0.5) were investigated for use as oxygen separation membranes for the partial oxidation (POX) of methane to syngas. Special attention was given to the question of their stability in real operating conditions. A permeation set-up was specially designed to measure oxygen fluxes through these materials when placed in a strong pO 2 gradient. It also facilitated testing the long-term stability of the specimen. Permeation measurements performed in an air/argon gradient between 800 and 1000 °C showed that the highest fluxes were obtained with the highest content of cobalt (La 0.4Ca 0.6Fe 0.5Co 0.5O 3- δ ≅ La 0.4Ca 0.6Fe 0.75Co 0.25O 3- δ > La 0.4Ca 0.6FeO 3- δ). In addition, comparison between the fluxes of samples of different thickness gave clear evidence of surface limitations in the oxygen transport. The long-term stability test showed opposite trends: only the two lowest Co containing compounds ( x=0 and 0.25) sustained an air/(Ar+H 2) gradient over more than 600 h. The other ( x=0.5) broke shortly after the introduction of H 2. In the presence of H 2, the oxygen flux was increased by a factor 10 compared to Ar and reached 0.83 μmol/cm 2 s for La 0.4Ca 0.6Fe 0.75Co 0.25O 3- δ at 900 °C. Post-operation SEM examination of the cross-section and both surfaces revealed that the surface exposed to H 2 had started to decompose resulting in the formation of a thin porous layer but the bulk of the material remained unchanged.

Empirical effective temperatures and bolometric corrections for early-type stars

NASA Technical Reports Server (NTRS)

Code, A. D.; Bless, R. C.; Davis, J.; Brown, R. H.

1976-01-01

An empirical effective temperature for a star can be found by measuring its apparent angular diameter and absolute flux distribution. The angular diameters of 32 bright stars in the spectral range O5f to F8 have recently been measured with the stellar interferometer at Narrabri Observatory, and their absolute flux distributions have been found by combining observations of ultraviolet flux from the Orbiting Astronomical Observatory (OAO-2) with ground-based photometry. In this paper, these data have been combined to derive empirical effective temperatures and bolometric corrections for these 32 stars.

In situ stabilization of NAPL contaminant source-zones as a remediation technique to reduce mass discharge and flux to groundwater.

PubMed

Mateas, Douglas J; Tick, Geoffrey R; Carroll, Kenneth C

2017-09-01

Widely used flushing and in-situ destruction based remediation techniques (i.e. pump-and treat, enhanced-solubilization, and chemical oxidation/reduction) for sites contaminated by nonaqueous phase liquid (NAPL) contaminant sources have been shown to be ineffective at complete mass removal and reducing aqueous-phase contaminant of concern (COC) concentrations to levels suitable for site closure. A remediation method was developed to reduce the aqueous solubility and mass-flux of COCs within NAPL through the in-situ creation of a NAPL mixture source-zone. In contrast to remediation techniques that rely on the rapid removal of contaminant mass, this technique relies on the stabilization of difficult-to-access NAPL sources to reduce COC mass flux to groundwater. A specific amount (volume) of relatively insoluble n-hexadecane (HEXDEC) or vegetable oil (VO) was injected into a trichloroethene (TCE) contaminant source-zone through a bench-scale flow cell port (i.e. well) to form a NAPL mixture of targeted mole fraction (TCE:HEXDEC or TCE:VO). NAPL-aqueous phase batch tests were conducted prior to the flow-cell experiments to evaluate the effects of various NAPL mixture ratios on equilibrium aqueous-phase concentrations of TCE to design optimal NAPL (HEXDEC or VO) injection volumes for the flow-cell experiments. The NAPL-stabilization flow-cell experiments initiated and sustained significant reductions in COC concentration and mass flux due to a combination of both reduced relative permeability (increased NAPL-saturation) and via modification of NAPL composition (decreased TCE mole fraction). Variations in remediation performance (i.e. impacts on TCE concentration and mass flux reduction) between the different HEXDEC injection volumes were relatively minor, and therefore inconsistent with Raoult's Law predictions. This phenomenon likely resulted from non-uniform mixing of the injected HEXDEC with TCE in the source-zone. VO injection caused TCE concentrations and mass-flux to decrease more rapidly than with HEXDEC injections. This phenomenon occurred because the injected VO was observed to mix more uniformly with TCE in the source-zone due to a lower mobilization potential. The relative lower density differences (buoyancy effects) between VO and the flushing solution (water) was the primary factor contributing to the lower mobilization potential for VO. Overall, this study indicated that the delivery of HEXDEC or VO into the toxic TCE source-zone was effective in significantly reducing contaminant aqueous-phase concentration and mass-flux. However, the effectiveness of this in-situ NAPL stabilization technique depends on source delivery, uniform mixing of amendment, and that the amendment remains immobilized within and around the NAPL contaminant source. Copyright © 2017 Elsevier B.V. All rights reserved.

Resistivity analysis of epitaxially grown, doped semiconductors using energy dependent secondary ion mass spectroscopy

NASA Astrophysics Data System (ADS)

Burnham, Shawn D.; Thomas, Edward W.; Doolittle, W. Alan

2006-12-01

A characterization technique is discussed that allows quantitative optimization of doping in epitaxially grown semiconductors. This technique uses relative changes in the host atom secondary ion (HASI) energy distribution from secondary ion mass spectroscopy (SIMS) to indicate relative changes in conductivity of the material. Since SIMS is a destructive process due to sputtering through a film, a depth profile of the energy distribution of sputtered HASIs in a matrix will contain information on the conductivity of the layers of the film as a function of depth. This process is demonstrated with Mg-doped GaN, with the Mg flux slowly increased through the film. Three distinct regions of conductivity were observed: one with Mg concentration high enough to cause compensation and thus high resistivity, a second with moderate Mg concentration and low resistivity, and a third with little to no Mg doping, causing high resistivity due to the lack of free carriers. During SIMS analysis of the first region, the energy distributions of sputtered Ga HASIs were fairly uniform and unchanging for a Mg flux above the saturation, or compensation, limit. For the second region, the Ga HASI energy distributions shifted and went through a region of inconsistent energy distributions for Mg flux slightly below the critical flux for saturation, or compensation. Finally, for the third region, the Ga HASI energy distributions then settled back into another fairly unchanging, uniform pattern. These three distinct regions were analyzed further through growth of Mg-doped step profiles and bulk growth of material at representative Mg fluxes. The materials grown at the two unchanging, uniform regions of the energy distributions yielded highly resistive material due to too high of Mg concentration and low to no Mg concentration, respectively. However, material grown in the transient energy distribution region with Mg concentration between that of the two highly resistive regions yielded low resistivity (0.59Ωcm) and highly p-type (1.2×1018cm-3 holes) Mg-doped GaN.

Quantifying trace element and isotope fluxes at the ocean-sediment boundary: a review.

PubMed

Homoky, William B; Weber, Thomas; Berelson, William M; Conway, Tim M; Henderson, Gideon M; van Hulten, Marco; Jeandel, Catherine; Severmann, Silke; Tagliabue, Alessandro

2016-11-28

Quantifying fluxes of trace elements and their isotopes (TEIs) at the ocean's sediment-water boundary is a pre-eminent challenge to understand their role in the present, past and future ocean. There are multiple processes that drive the uptake and release of TEIs, and properties that determine their rates are unevenly distributed (e.g. sediment composition, redox conditions and (bio)physical dynamics). These factors complicate our efforts to find, measure and extrapolate TEI fluxes across ocean basins. GEOTRACES observations are unveiling the oceanic distributions of many TEIs for the first time. These data evidence the influence of the sediment-water boundary on many TEI cycles, and underline the fact that our knowledge of the source-sink fluxes that sustain oceanic distributions is largely missing. Present flux measurements provide low spatial coverage and only part of the empirical basis needed to predict TEI flux variations. Many of the advances and present challenges facing TEI flux measurements are linked to process studies that collect sediment cores, pore waters, sinking material or seawater in close contact with sediments. However, such sampling has not routinely been viable on GEOTRACES expeditions. In this article, we recommend approaches to address these issues: firstly, with an interrogation of emergent data using isotopic mass-balance and inverse modelling techniques; and secondly, by innovating pursuits of direct TEI flux measurements. We exemplify the value of GEOTRACES data with a new inverse model estimate of benthic Al flux in the North Atlantic Ocean. Furthermore, we review viable flux measurement techniques tailored to the sediment-water boundary. We propose that such activities are aimed at regions that intersect the GEOTRACES Science Plan on the basis of seven criteria that may influence TEI fluxes: sediment provenance, composition, organic carbon supply, redox conditions, sedimentation rate, bathymetry and the benthic nepheloid inventory.This article is part of the themed issue 'Biological and climatic impacts of ocean trace element chemistry'. © 2015 The Authors.

Quantifying trace element and isotope fluxes at the ocean-sediment boundary: a review

NASA Astrophysics Data System (ADS)

Homoky, William B.; Weber, Thomas; Berelson, William M.; Conway, Tim M.; Henderson, Gideon M.; van Hulten, Marco; Jeandel, Catherine; Severmann, Silke; Tagliabue, Alessandro

2016-11-01

Quantifying fluxes of trace elements and their isotopes (TEIs) at the ocean's sediment-water boundary is a pre-eminent challenge to understand their role in the present, past and future ocean. There are multiple processes that drive the uptake and release of TEIs, and properties that determine their rates are unevenly distributed (e.g. sediment composition, redox conditions and (bio)physical dynamics). These factors complicate our efforts to find, measure and extrapolate TEI fluxes across ocean basins. GEOTRACES observations are unveiling the oceanic distributions of many TEIs for the first time. These data evidence the influence of the sediment-water boundary on many TEI cycles, and underline the fact that our knowledge of the source-sink fluxes that sustain oceanic distributions is largely missing. Present flux measurements provide low spatial coverage and only part of the empirical basis needed to predict TEI flux variations. Many of the advances and present challenges facing TEI flux measurements are linked to process studies that collect sediment cores, pore waters, sinking material or seawater in close contact with sediments. However, such sampling has not routinely been viable on GEOTRACES expeditions. In this article, we recommend approaches to address these issues: firstly, with an interrogation of emergent data using isotopic mass-balance and inverse modelling techniques; and secondly, by innovating pursuits of direct TEI flux measurements. We exemplify the value of GEOTRACES data with a new inverse model estimate of benthic Al flux in the North Atlantic Ocean. Furthermore, we review viable flux measurement techniques tailored to the sediment-water boundary. We propose that such activities are aimed at regions that intersect the GEOTRACES Science Plan on the basis of seven criteria that may influence TEI fluxes: sediment provenance, composition, organic carbon supply, redox conditions, sedimentation rate, bathymetry and the benthic nepheloid inventory. This article is part of the themed issue 'Biological and climatic impacts of ocean trace element chemistry'.

Quantifying trace element and isotope fluxes at the ocean–sediment boundary: a review

PubMed Central

Berelson, William M.; Severmann, Silke

2016-01-01

Quantifying fluxes of trace elements and their isotopes (TEIs) at the ocean's sediment–water boundary is a pre-eminent challenge to understand their role in the present, past and future ocean. There are multiple processes that drive the uptake and release of TEIs, and properties that determine their rates are unevenly distributed (e.g. sediment composition, redox conditions and (bio)physical dynamics). These factors complicate our efforts to find, measure and extrapolate TEI fluxes across ocean basins. GEOTRACES observations are unveiling the oceanic distributions of many TEIs for the first time. These data evidence the influence of the sediment–water boundary on many TEI cycles, and underline the fact that our knowledge of the source–sink fluxes that sustain oceanic distributions is largely missing. Present flux measurements provide low spatial coverage and only part of the empirical basis needed to predict TEI flux variations. Many of the advances and present challenges facing TEI flux measurements are linked to process studies that collect sediment cores, pore waters, sinking material or seawater in close contact with sediments. However, such sampling has not routinely been viable on GEOTRACES expeditions. In this article, we recommend approaches to address these issues: firstly, with an interrogation of emergent data using isotopic mass-balance and inverse modelling techniques; and secondly, by innovating pursuits of direct TEI flux measurements. We exemplify the value of GEOTRACES data with a new inverse model estimate of benthic Al flux in the North Atlantic Ocean. Furthermore, we review viable flux measurement techniques tailored to the sediment–water boundary. We propose that such activities are aimed at regions that intersect the GEOTRACES Science Plan on the basis of seven criteria that may influence TEI fluxes: sediment provenance, composition, organic carbon supply, redox conditions, sedimentation rate, bathymetry and the benthic nepheloid inventory. This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’. PMID:29035270

Eddington-limited X-Ray Bursts as Distance Indicators. I. Systematic Trends and Spherical Symmetry in Bursts from 4U 1728-34

NASA Astrophysics Data System (ADS)

Galloway, Duncan K.; Psaltis, Dimitrios; Chakrabarty, Deepto; Muno, Michael P.

2003-06-01

We investigate the limitations of thermonuclear X-ray bursts as a distance indicator for the weakly magnetized accreting neutron star 4U 1728-34. We measured the unabsorbed peak flux of 81 bursts in public data from the Rossi X-Ray Timing Explorer (RXTE). The distribution of peak fluxes was bimodal: 66 bursts exhibited photospheric radius expansion (presumably reaching the local Eddington limit) and were distributed about a mean bolometric flux of 9.2×10-8ergscm-2s-1, while the remaining (non-radius expansion) bursts reached 4.5×10-8ergscm-2s-1, on average. The peak fluxes of the radius expansion bursts were not constant, exhibiting a standard deviation of 9.4% and a total variation of 46%. These bursts showed significant correlations between their peak flux and the X-ray colors of the persistent emission immediately prior to the burst. We also found evidence for quasi-periodic variation of the peak fluxes of radius expansion bursts, with a timescale of ~=40 days. The persistent flux observed with RXTE/ASM over 5.8 yr exhibited quasi-periodic variability on a similar timescale. We suggest that these variations may have a common origin in reflection from a warped accretion disk. Once the systematic variation of the peak burst fluxes is subtracted, the residual scatter is only ~=3%, roughly consistent with the measurement uncertainties. The narrowness of this distribution strongly suggests that (1) the radiation from the neutron star atmosphere during radius expansion episodes is nearly spherically symmetric and (2) the radius expansion bursts reach a common peak flux that may be interpreted as a standard candle intensity. Adopting the minimum peak flux for the radius expansion bursts as the Eddington flux limit, we derive a distance for the source of 4.4-4.8 kpc (assuming RNS=10 km), with the uncertainty arising from the probable range of the neutron star mass MNS=1.4-2 Msolar.

Beyond topology: coevolution of structure and flux in metabolic networks.

PubMed

Morrison, E S; Badyaev, A V

2017-10-01

Interactions between the structure of a metabolic network and its functional properties underlie its evolutionary diversification, but the mechanism by which such interactions arise remains elusive. Particularly unclear is whether metabolic fluxes that determine the concentrations of compounds produced by a metabolic network, are causally linked to a network's structure or emerge independently of it. A direct empirical study of populations where both structural and functional properties vary among individuals' metabolic networks is required to establish whether changes in structure affect the distribution of metabolic flux. In a population of house finches (Haemorhous mexicanus), we reconstructed full carotenoid metabolic networks for 442 individuals and uncovered 11 structural variants of this network with different compounds and reactions. We examined the consequences of this structural diversity for the concentrations of plumage-bound carotenoids produced by flux in these networks. We found that concentrations of metabolically derived, but not dietary carotenoids, depended on network structure. Flux was partitioned similarly among compounds in individuals of the same network structure: within each network, compound concentrations were closely correlated. The highest among-individual variation in flux occurred in networks with the strongest among-compound correlations, suggesting that changes in the magnitude, but not the distribution of flux, underlie individual differences in compound concentrations on a static network structure. These findings indicate that the distribution of flux in carotenoid metabolism closely follows network structure. Thus, evolutionary diversification and local adaptations in carotenoid metabolism may depend more on the gain or loss of enzymatic reactions than on changes in flux within a network structure. © 2017 European Society For Evolutionary Biology. Journal of Evolutionary Biology © 2017 European Society For Evolutionary Biology.

Impact of phenazine-1-carboxylic acid upon iron speciation and microbial biomass in the rhizosphere of wheat

NASA Astrophysics Data System (ADS)

LeTourneau, M.; Marshall, M.; Grant, M.; Freeze, P.; Cliff, J. B.; Lai, B.; Strawn, D. G.; Thomashow, L. S.; Weller, D. M.; Harsh, J. B.

2015-12-01

Phenazine-1-carboxylic acid (PCA) is a redox-active antibiotic produced by diverse bacterial taxa, and has been shown to facilitate interactions between biofilms and iron (hydr)oxides in culture systems (Wang et al. 2011, J Bacteriol 192: 365). Because rhizobacterial biofilms are a major sink for plant-derived carbon and source for soil organic matter (SOM), and Fe (hydr)oxides have reactive surfaces that influence the stability of microbial biomass and SOM, PCA-producing rhizobacteria could influence soil carbon fluxes. Large populations of Pseudomonas fluorescens strains producing PCA in concentrations up to 1 μg/g root have been observed in the rhizosphere of non-irrigated wheat fields covering 1.56 million hectares of central Washington state. This is one of the highest concentrations ever reported for a natural antibiotic in a terrestrial ecosystem (Mavrodi et al. 2012, Appl Environ Microb 78: 804). Microscopic comparisons of PCA-producing (PCA+) and non-PCA-producing (PCA-) rhizobacterial colony morphologies, and comparisons of Fe extractions from rhizosphere soil inoculated with PCA+ and PCA- strains suggest that PCA promotes biofilm development as well as dramatic Fe transformations throughout the rhizosphere (unpublished data). In order to illustrate PCA-mediated interactions between biofilms and Fe (hydr)oxides in the rhizosphere, identify the specific Fe phases favored by PCA, and establish the ramifications for stability and distribution of microbial biomass and SOM, we have collected electron micrographs, X-ray fluorescence images, X-ray absorption near-edge spectra, and secondary-ion mass spectrometry images of wheat root sections inoculated with 15N-labelled PCA+ or PCA- rhizobacteria. These images and spectra allow us to assess the accumulation, turnover, and distribution of microbial biomass, the associations between Fe and other nutrients such as phosphorus, and the redox status and speciation of iron in the presence and absence of PCA. This information provides a starting point to model the impact of PCA upon carbon fluxes in Columbia Basin agro-ecosystems and other environments where PCA-producing bacteria are prevalent.

Density variations of meteor flux along the Earth's orbit

NASA Technical Reports Server (NTRS)

Svetashkova, N. T.

1987-01-01

No model of distribution of meteor substance is known to explain the observed diurnal and annual variations of meteor rates, if that distribution is assumed to be constant during the year. Differences between the results of observations and the prediction of diurnal variation rates leads to the conclusion that the density of the orbits of meteor bodies changes with the motion of the Earth along its orbit. The distributions of the flux density over the celestial sphere are obtained by the method described previously by Svetashkova, 1984. The results indicate that the known seasonal and latitudinal variations of atmospheric conditions does not appear to significantly affect the value of the mean flux density of meteor bodies and the matter influx onto the Earth.

New experimental research stand SVICKA neutron field analysis using neutron activation detector technique

NASA Astrophysics Data System (ADS)

Varmuza, Jan; Katovsky, Karel; Zeman, Miroslav; Stastny, Ondrej; Haysak, Ivan; Holomb, Robert

2018-04-01

Knowledge of neutron energy spectra is very important because neutrons with various energies have a different material impact or a biological tissue impact. This paper presents basic results of the neutron flux distribution inside the new experimental research stand SVICKA which is located at Brno University of Technology in Brno, Czech Republic. The experiment also focused on the investigation of the sandwich biological shielding quality that protects staff against radiation effects. The set of indium activation detectors was used to the investigation of neutron flux distribution. The results of the measurement provide basic information about the neutron flux distribution inside all irradiation channels and no damage or cracks are present in the experimental research stand biological shielding.

Lamination effects on a 3D model of the magnetic core of power transformers

NASA Astrophysics Data System (ADS)

Poveda-Lerma, Antonio; Serrano-Callergues, Guillermo; Riera-Guasp, Martin; Pineda-Sanchez, Manuel; Puche-Panadero, Ruben; Perez-Cruz, Juan

2017-12-01

In this paper the lamination effect on the model of a power transformer's core with stacked E-I structure is analyzed. The distribution of the magnetic flux in the laminations depends on the stacking method. In this work it is shown, using a 3D FEM model and an experimental prototype, that the non-uniform distribution of the flux in a laminated E-I core with alternate-lap joint stack increases substantially the average value of the magnetic flux density in the core, compared with a butt joint stack. Both the simulated model and the experimental tests show that the presence of constructive air-gaps in the E-I junctions gives rise to a zig-zag flux in the depth direction. This inter-lamination flux reduces the magnetic flux density in the I-pieces and increases substantially the magnetic flux density in the E-pieces, with highly saturated points that traditional 2D analysis cannot reproduce. The relation between the number of laminations included in the model, and the computational resourses needed to build it, is also evaluated in this work.

Predictability of dune activity in real dune fields under unidirectional wind regimes

NASA Astrophysics Data System (ADS)

Barchyn, Thomas E.; Hugenholtz, Chris H.

2015-02-01

We present an analysis of 10 dune fields to test a model-derived hypothesis of dune field activity. The hypothesis suggests that a quantifiable threshold exists for stabilization in unidirectional wind regimes: active dunes have slipface deposition rates that exceed the vegetation deposition tolerance, and stabilizing dunes have the opposite. We quantified aeolian sand flux, slipface geometry, and vegetation deposition tolerance to directly test the hypothesis at four dune fields (Bigstick, White Sands Stable, White Sands Active, and Cape Cod). We indirectly tested the hypothesis at six additional dune fields with limited vegetation data (Hanford, Año Nuevo, Skagen Odde, Salton Sea, Oceano Stable, and Oceano Active, "inverse calculation sites"). We used digital topographic data and estimates of aeolian sand flux to approximate the slipface deposition rates prior to stabilization. Results revealed a distinct, quantifiable, and consistent pattern despite diverse environmental conditions: the modal peak of prestabilization slipface deposition rates was 80% of the vegetation deposition tolerance at stabilized or stabilizing dune fields. Results from inverse calculation sites indicate deposition rates at stabilized sites were near a hypothesized maximum vegetation deposition tolerance (1 m a-1), and active sites had slipface deposition rates much higher. Overall, these results confirm the hypothesis and provide evidence of a globally applicable, simple, and previously unidentified predictor for the dynamics of vegetation cover in dune fields under unidirectional wind regimes.

Dynamics, Stability, and Evolutionary Patterns of Mesoscale Intrathermocline Vortices

DTIC Science & Technology

2016-12-01

physical oceanography, namely, the link between the basin-scale forcing of the ocean by air-sea fluxes and the dissipation of energy and thermal variance...at the microscale. 14. SUBJECT TERMS Meddy, intrathermocline, double diffusion, energy cascade, eddy, MITgcm, numerical simulation, interleaving...lateral intrusions, lateral diffusivity, heat flux 15. NUMBER OF PAGES 69 16. PRICE CODE 17. SECURITY CLASSIFICATION OF REPORT Unclassified 18

Strong plume fluxes at Mars observed by MAVEN: An important planetary ion escape channel

NASA Astrophysics Data System (ADS)

Dong, Y.; Fang, X.; Brain, D. A.; McFadden, J. P.; Halekas, J. S.; Connerney, J. E.; Curry, S. M.; Harada, Y.; Luhmann, J. G.; Jakosky, B. M.

2015-11-01

We present observations by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission of a substantial plume-like distribution of escaping ions from the Martian atmosphere, organized by the upstream solar wind convection electric field. From a case study of MAVEN particle-and-field data during one spacecraft orbit, we identified three escaping planetary ion populations: plume fluxes mainly along the upstream electric field over the north pole region of the Mars-Sun-Electric field (MSE) coordinate system, antisunward ion fluxes in the tail region, and much weaker upstream pickup ion fluxes. A statistical study of O+ fluxes using 3 month MAVEN data shows that the plume is a constant structure with strong fluxes widely distributed in the MSE northern hemisphere, which constitutes an important planetary ion escape channel. The escape rate through the plume is estimated to be ~30% of the tailward escape and ~23% of the total escape for > 25 eV O+ ions.

SGR-like behaviour of the repeating FRB 121102

NASA Astrophysics Data System (ADS)

Wang, F. Y.; Yu, H.

2017-03-01

Fast radio bursts (FRBs) are millisecond-duration radio signals occurring at cosmological distances. However the physical model of FRBs is mystery, many models have been proposed. Here we study the frequency distributions of peak flux, fluence, duration and waiting time for the repeating FRB 121102. The cumulative distributions of peak flux, fluence and duration show power-law forms. The waiting time distribution also shows power-law distribution, and is consistent with a non-stationary Poisson process. These distributions are similar as those of soft gamma repeaters (SGRs). We also use the statistical results to test the proposed models for FRBs. These distributions are consistent with the predictions from avalanche models of slowly driven nonlinear dissipative systems.

Investigation of the mechanical behaviour of gas-hydrate bearing clayey sediments from the Gulf of Guinea using in-situ geotechnical measurements

NASA Astrophysics Data System (ADS)

Taleb, F.; Garziglia, S.; Sultan, N.

2017-12-01

Expanding needs for energy resources and concerns about climate change have moved industrial and academic interests towards regions where specific thermobaric conditions allow the formation of gas hydrates (GH). While significant advances have been made to characterize the fabric and structure of these metastable geo-compounds, considerable uncertainty remains regarding the impact of their mechanical properties on the seafloor morphology and stability. This is particularly true for gas hydrates-bearing fine-grained sediments, which remain challenging to preserve or synthesise prior to laboratory testing. As a step towards understanding the mechanical consequences of the concentration and distribution of GH in this type of sediments, this work uses acoustic and geotechnical in situ measurements collected in a high gas flux system offshore Nigeria. Acoustic measurements of compressional wave velocity were shown to be convenient means of both detecting and quantifying gas hydrates in marine sediments. Geotechnical data derived from piezocone readings and their distribution in normalised soil classification charts allowed identifying distinct features of gas hydrates-bearing clayey sediments; such as a mechanical behaviour sharing similarities with that of cemented clays. Correlations between acoustic and piezocone data showed that the stiffness and strength tend to generally increase with increasing GH concentrations. However, several sediment intervals sharing the same hydrates concentration have revealed different features of mechanical behaviour. This was linked to the presence of various GH morphologies within the marine sediments such as groups of hydrate veins or massive hydrate nodules. This in-situ approach allowing both understanding the heterogeneous distribution of GH and characterising their host sediment seems key to assess the potential link between seafloor stability and GH dissociation/dissolution caused by human activities or by natural environmental changes.

Global Flux Balance in the Terrestrial H2O Cycle: Reconsidering the Post-Arc Subducted H2O Flux

NASA Astrophysics Data System (ADS)

Parai, R.; Mukhopadhyay, S.

2010-12-01

Quantitative estimates of H2O fluxes between the mantle and the exosphere (i.e., the atmosphere, oceans and crust) are critical to our understanding of the chemistry and dynamics of the solid Earth: the abundance and distribution of water in the mantle has dramatic impacts upon mantle melting, degassing history, structure and style of convection. Water is outgassed from the mantle is association with volcanism at mid-ocean ridges, ocean islands and convergent margins. H2O is removed from the exosphere at subduction zones, and some fraction of the subducted flux may be recycled past the arc into the Earth’s deep interior. Estimates of the post-arc subducted H2O flux are primarily based on the stability of hydrous phases at subduction zone pressures and temperatures (e.g. Schmidt and Poli, 1998; Rüpke et al., 2004; Hacker, 2008). However, the post-arc H2O flux remains poorly quantified, in part due to large uncertainties in the water content of the subducting slab. Here we evaluate estimated post-arc subducted fluxes in the context of mantle-exosphere water cycling, using a Monte Carlo simulation of the global H2O cycle. Literature estimates of primary magmatic H2O abundances and magmatic production rates at different tectonic settings are used with estimates of the total subducted H2O flux to establish the parameter space under consideration. Random sampling of the allowed parameter space affords insight into which input and output fluxes satisfy basic constraints on global flux balance, such as a limit on sea-level change over time. The net flux of H2O between mantle and exosphere is determined by the total mantle output flux (via ridges and ocean islands, with a small contribution from mantle-derived arc output) and the input flux subducted beyond the arc. Arc and back-arc output is derived mainly from the slab, and therefore cancels out a fraction of the trench intake in an H2O subcycle. Limits on sea-level change since the end of the Archaean place constraints on the magnitude of the post-arc subducted H2O flux that can be accommodated by the global water cycle. Estimates of the post-arc subducted flux are up to an order of magnitude larger than the estimated mantle output flux. If the marked imbalance in the estimated global water cycle is accurate, then it must be a recent phenomenon: if propagated back in time, modeled net inward fluxes would consume half a present-day ocean volume of water in as little as 500 Myr (corresponding to ~1200 meters of sea level change given present-day hypsometry). Such changes are inconsistent with the limited sea level changed inferred from the geologic record since the end of the Archaean. The literature post-arc flux estimates reflect water carried to depth via a layer of serpentinized lithospheric mantle within the slab; however, the extent to which oceanic lithosphere may be serpentinized remains poorly constrained. A smaller post-arc subducted H2O flux of 2.3 x108 Tg/Ma would perfectly balance our mean modeled total mantle output. Such a post-arc flux corresponds to ~2% serpentinization of a 10 km thick layer of lithospheric mantle (i.e., a mean water content of ~0.25 wt% H2O).

Decoupling suspension controller based on magnetic flux feedback.

PubMed

Zhang, Wenqing; Li, Jie; Zhang, Kun; Cui, Peng

2013-01-01

The suspension module control system model has been established based on MIMO (multiple input and multiple output) state feedback linearization. We have completed decoupling between double suspension points, and the new decoupling method has been applied to CMS04 magnetic suspension vehicle in national mid-low-speed maglev experiment field of Tangshan city in China. Double suspension system model is very accurate for investigating stability property of maglev control system. When magnetic flux signal is taken back to the suspension control system, the suspension module's antijamming capacity for resisting suspension load variety has been proved. Also, the external force interference has been enhanced. As a result, the robustness and stability properties of double-electromagnet suspension control system have been enhanced.

Decoupling Suspension Controller Based on Magnetic Flux Feedback

PubMed Central

Zhang, Wenqing; Li, Jie; Zhang, Kun; Cui, Peng

2013-01-01

The suspension module control system model has been established based on MIMO (multiple input and multiple output) state feedback linearization. We have completed decoupling between double suspension points, and the new decoupling method has been applied to CMS04 magnetic suspension vehicle in national mid-low-speed maglev experiment field of Tangshan city in China. Double suspension system model is very accurate for investigating stability property of maglev control system. When magnetic flux signal is taken back to the suspension control system, the suspension module's antijamming capacity for resisting suspension load variety has been proved. Also, the external force interference has been enhanced. As a result, the robustness and stability properties of double-electromagnet suspension control system have been enhanced. PMID:23844415

Membrane penetration enhancement of ibuprofen using supersaturation.

PubMed

Iervolino, M; Raghavan, S L; Hadgraft, J

2000-04-05

Permeation enhancement of ibuprofen from supersaturated solutions formed using the cosolvent technique was investigated using silicone as a model membrane. Hydroxpropyl methyl cellulose and hydroxpropyl-beta-cyclodextrin were used to stabilise the supersaturated states. Physical stability studies showed best results for low drug concentrations in a 40:60 propylene glycol/water cosolvent system. Variations in flux across model silicone membranes from saturated solutions were observed as the PG content was increased. The flux of IBU increased with the degree of saturation for solutions prepared in a 40:60 PG/water cosolvent mixture. HPMC and CD were found to be effective in enhancing the stability of supersaturated solutions of IBU. The mechanisms of action are different for the two additives and are discussed.

IMF Control of Alfvénic Energy Transport and Deposition at High Latitudes

NASA Astrophysics Data System (ADS)

Hatch, Spencer M.; LaBelle, James; Lotko, William; Chaston, Christopher C.; Zhang, Binzheng

2017-12-01

We investigate the influence of the interplanetary magnetic field (IMF) clock angle ϕIMF on high-latitude inertial Alfvén wave (IAW) activity in the magnetosphere-ionosphere transition region using Fast Auroral SnapshoT (FAST) satellite observations. We find evidence that negative IMF Bz coincides with nightside IAW power generation and enhanced rates of IAW-associated electron energy deposition, while positive IMF Bz coincides with enhanced dayside wave and electron energy deposition. Large (≳ 5 nT) negative IMF By coincides with enhanced postnoon IAW power, while large positive IMF By coincides with enhanced but relatively weaker prenoon IAW power. For each ϕIMF orientation we compare IAW Poynting flux and IAW-associated electron energy flux distributions with previously published distributions of Alfvénic Poynting flux over ˜2-22 mHz, as well as corresponding wave-driven electron energy deposition derived from Lyon-Fedder-Mobarry global MHD simulations. We also compare IAW Poynting flux distributions with distributions of broad and diffuse electron number flux, categorized using an adaptation of the Newell et al. (2009) precipitation scheme for FAST. Under negative IMF Bz in the vicinity of the cusp (9.5-14.5 magnetic local time), regions of intense dayside IAW power correspond to enhanced diffuse electron number flux but relatively weaker broadband electron precipitation. Differences between cusp region IAW activity and broadband precipitation illustrate the need for additional information, such as fields or pitch angle measurements, to identify the physical mechanisms associated with electron precipitation in the vicinity of the cusp.

Advanced divertor configurations with large flux expansion

NASA Astrophysics Data System (ADS)

Soukhanovskii, V. A.; Bell, R. E.; Diallo, A.; Gerhardt, S.; Kaye, S.; Kolemen, E.; LeBlanc, B. P.; McLean, A.; Menard, J. E.; Paul, S. F.; Podesta, M.; Raman, R.; Ryutov, D. D.; Scotti, F.; Kaita, R.; Maingi, R.; Mueller, D. M.; Roquemore, A. L.; Reimerdes, H.; Canal, G. P.; Labit, B.; Vijvers, W.; Coda, S.; Duval, B. P.; Morgan, T.; Zielinski, J.; De Temmerman, G.; Tal, B.

2013-07-01

Experimental studies of the novel snowflake divertor concept (D. Ryutov, Phys. Plasmas 14 (2007) 064502) performed in the NSTX and TCV tokamaks are reviewed in this paper. The snowflake divertor enables power sharing between divertor strike points, as well as the divertor plasma-wetted area, effective connection length and divertor volumetric power loss to increase beyond those in the standard divertor, potentially reducing heat flux and plasma temperature at the target. It also enables higher magnetic shear inside the separatrix, potentially affecting pedestal MHD stability. Experimental results from NSTX and TCV confirm the predicted properties of the snowflake divertor. In the NSTX, a large spherical tokamak with a compact divertor and lithium-coated graphite plasma-facing components (PFCs), the snowflake divertor operation led to reduced core and pedestal impurity concentration, as well as re-appearance of Type I ELMs that were suppressed in standard divertor H-mode discharges. In the divertor, an otherwise inaccessible partial detachment of the outer strike point with an up to 50% increase in divertor radiation and a peak divertor heat flux reduction from 3-7 MW/m2 to 0.5-1 MW/m2 was achieved. Impulsive heat fluxes due to Type-I ELMs were significantly dissipated in the high magnetic flux expansion region. In the TCV, a medium-size tokamak with graphite PFCs, several advantageous snowflake divertor features (cf. the standard divertor) have been demonstrated: an unchanged L-H power threshold, enhanced stability of the peeling-ballooning modes in the pedestal region (and generally an extended second stability region), as well as an H-mode pedestal regime with reduced (×2-3) Type I ELM frequency and slightly increased (20-30%) normalized ELM energy, resulting in a favorable average energy loss comparison to the standard divertor. In the divertor, ELM power partitioning between snowflake divertor strike points was demonstrated. The NSTX and TCV experiments are providing support for the snowflake divertor as a viable solution for the outstanding tokamak plasma-material interface issues.

Evaluating competing forces constraining glacial grounding-line stability (Invited)

NASA Astrophysics Data System (ADS)

Powell, R. D.

2013-12-01

Stability of grounding lines of marine-terminating glaciers and ice sheets is of concern due to their importance in governing rates of ice mass loss and consequent sea level rise during global warming. Although processes are similar at tidewater and floating grounding zones their relative magnitudes in terms of their influence on grounding-line stability vary between these two end members. Processes considered Important for this discussion are ice dynamics, ice surface melting and crevassing, ocean dynamics, subglacial sediment and water dynamics, and subglacial bed geometries. Models have continued to improve in their representation of these complex interactions but reliable field measurements and data continue to be hard earned and too few to properly constrain the range of boundary conditions in this complicated system. Some data will be presented covering a range of regimes from Alaska, Svalbard and Antarctica. Certainly more data are required on subglacial sediment/water dynamics and fluxes to fully represent the spectrum of glacial regimes and to assess the significance of grounding-zone sediment systems in counteracting the other processes to force grounding-line stability. Especially important here is constraining the duration of the stability that could be maintained by sediment flux - present data appear to show that it is likely to be a limited period.

Scanning micro-Hall probe mapping of magnetic flux distributions and current densities in YBa2Cu3O7 thin films

NASA Technical Reports Server (NTRS)

Xing, W.; Heinrich, B.; Zhou, HU; Fife, A. A.; Cragg, A. R.; Grant, P. D.

1995-01-01

Mapping of the magnetic flux density B(sub z) (perpendicular to the film plane) for a YBa2Cu3O7 thin-film sample was carried out using a scanning micro-Hall probe. The sheet magnetization and sheet current densities were calculated from the B(sub z) distributions. From the known sheet magnetization, the tangential (B(sub x,y)) and normal components of the flux density B were calculated in the vicinity of the film. It was found that the sheet current density was mostly determined by 2B(sub x,y)/d, where d is the film thickness. The evolution of flux penetration as a function of applied field will be shown.

Distribution of flux-pinning energies in YBa2Cu3O(7-delta) and Bi2Sr2CaCu2O(8+delta) from flux noise

NASA Astrophysics Data System (ADS)

Ferrari, M. J.; Johnson, Mark; Wellstood, Frederick C.; Clarke, John; Mitzi, D.

1990-01-01

The spectral density of the magnetic flux noise measured in high-temperature superconductors in low magnetic fields scales approximately as the inverse of the frequency and increases with temperature. The temperature and frequency dependence of the noise are used to determine the pinning energies of individual flux vortices in thermal equilibrium. The distribution of pinning energies below 0.1 eV in YBa(2)Cu(3)O(7-delta) and near 0.2 eV in Bi(2)Sr(2)CaCu(2)O(8+delta). The noise power is proportional to the ambient magnetic field, indicating that the vortex motion is uncorrelated.

A metabolite-centric view on flux distributions in genome-scale metabolic models

PubMed Central

2013-01-01

Background Genome-scale metabolic models are important tools in systems biology. They permit the in-silico prediction of cellular phenotypes via mathematical optimisation procedures, most importantly flux balance analysis. Current studies on metabolic models mostly consider reaction fluxes in isolation. Based on a recently proposed metabolite-centric approach, we here describe a set of methods that enable the analysis and interpretation of flux distributions in an integrated metabolite-centric view. We demonstrate how this framework can be used for the refinement of genome-scale metabolic models. Results We applied the metabolite-centric view developed here to the most recent metabolic reconstruction of Escherichia coli. By compiling the balance sheets of a small number of currency metabolites, we were able to fully characterise the energy metabolism as predicted by the model and to identify a possibility for model refinement in NADPH metabolism. Selected branch points were examined in detail in order to demonstrate how a metabolite-centric view allows identifying functional roles of metabolites. Fructose 6-phosphate aldolase and the sedoheptulose bisphosphate bypass were identified as enzymatic reactions that can carry high fluxes in the model but are unlikely to exhibit significant activity in vivo. Performing a metabolite essentiality analysis, unconstrained import and export of iron ions could be identified as potentially problematic for the quality of model predictions. Conclusions The system-wide analysis of split ratios and branch points allows a much deeper insight into the metabolic network than reaction-centric analyses. Extending an earlier metabolite-centric approach, the methods introduced here establish an integrated metabolite-centric framework for the interpretation of flux distributions in genome-scale metabolic networks that can complement the classical reaction-centric framework. Analysing fluxes and their metabolic context simultaneously opens the door to systems biological interpretations that are not apparent from isolated reaction fluxes. Particularly powerful demonstrations of this are the analyses of the complete metabolic contexts of energy metabolism and the folate-dependent one-carbon pool presented in this work. Finally, a metabolite-centric view on flux distributions can guide the refinement of metabolic reconstructions for specific growth scenarios. PMID:23587327

Determination of Formulation Conditions Allowing Double Emulsions Stabilized by PGPR and Sodium Caseinate to Be Used as Capsules.

PubMed

Nollet, Maxime; Laurichesse, Eric; Besse, Samantha; Soubabère, Olivier; Schmitt, Véronique

2018-02-27

Water-in-oil-in-water (W 1 /O/W 2 ) double emulsions stabilized by polyglycerol polyricinoleate (PGPR), a lipophilic food grade small polymer, and sodium caseinate, a hydrophilic milk protein, were developed to encapsulate vitamin B12, a model hydrophilic substance easy to titrate. Using rheology, sensitive to drop size evolution and water fluxes, static light scattering, and microscopy both giving the evolution of drops' size and vitamin B12 titration assessing the encapsulation, we were able to detect independently the double emulsion drop size, the encapsulation loss, and the flux of water as a function of time. By differentiating the PGPR required to cover the W 1 -droplets' surface from PGPR in excess in the oil phase, we built a PGPR-inner droplet volume fraction diagram highlighting the domains where the double emulsion is stable toward encapsulation and/or water fluxes. We demonstrated the key role played by nonadsorbed PGPR concentration in the intermediate sunflower oil phase on the emulsion stability while, surprisingly, the inner droplet volume fraction had no effect on the emulsion stability. At low PGPR concentration, a release of vitamin B12 was observed and the leakage mechanism of coalescence between droplets and oil-water interface of the oily drops (also called globules hereafter), was identified using confocal microscopy. For high enough PGPR content, the emulsions were stable and may therefore serve as efficient capsules without need of an additional gelling, thickening, complexion or interface rigidifying agent. We generalized these results with the encapsulation of an insecticide: Cydia pomonella granulovirus used in organic arboriculture.

SYMMETRY OF THE IBEX RIBBON OF ENHANCED ENERGETIC NEUTRAL ATOM (ENA) FLUX

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

Funsten, H. O.; Cai, D. M.; Higdon, D. M.

2015-01-20

The circular ribbon of enhanced energetic neutral atom (ENA) emission observed by the Interstellar Boundary Explorer (IBEX) mission remains a critical signature for understanding the interaction between the heliosphere and the interstellar medium. We study the symmetry of the ribbon flux and find strong, spectrally dependent reflection symmetry throughout the energy range 0.7-4.3 keV. The distribution of ENA flux around the ribbon is predominantly unimodal at 0.7 and 1.1 keV, distinctly bimodal at 2.7 and 4.3 keV, and a mixture of both at 1.7 keV. The bimodal flux distribution consists of partially opposing bilateral flux lobes, located at highest and lowest heliographic latitude extentsmore » of the ribbon. The vector between the ribbon center and heliospheric nose (which defines the so-called BV plane) appears to play an organizing role in the spectral dependence of the symmetry axis locations as well as asymmetric contributions to the ribbon flux. The symmetry planes at 2.7 and 4.3 keV, derived by projecting the symmetry axes to a great circle in the sky, are equivalent to tilting the heliographic equatorial plane to the ribbon center, suggesting a global heliospheric ordering. The presence and energy dependence of symmetric unilateral and bilateral flux distributions suggest strong spectral filtration from processes encountered by an ion along its journey from the source plasma to its eventual detection at IBEX.« less

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

PubMed Central

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

2014-01-01

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

SteadyCom: Predicting microbial abundances while ensuring community stability

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

Chan, Siu Hung Joshua; Simons, Margaret N.; Maranas, Costas D.

Genome-scale metabolic modeling has become widespread for analyzing microbial metabolism. Extending this established paradigm to more complex microbial communities is emerging as a promising way to unravel the interactions and biochemical repertoire of these omnipresent systems. While several modeling techniques have been developed for microbial communities, little emphasis has been placed on the need to impose a time-averaged constant growth rate across all members for a community to ensure co-existence and stability. In the absence of this constraint, the faster growing organism will ultimately displace all other microbes in the community. This is particularly important for predicting steady-state microbiota compositionmore » as it imposes significant restrictions on the allowable community membership, composition and phenotypes. In this study, we introduce the SteadyCom optimization framework for predicting metabolic flux distributions consistent with the steady-state requirement. SteadyCom can be rapidly converged by iteratively solving linear programming (LP) problem and the number of iterations is independent of the number of organisms. A significant advantage of SteadyCom is compatibility with flux variability analysis. SteadyCom is first demonstrated for a community of four E. coli double auxotrophic mutants and is then applied to a gut microbiota model consisting of nine species, with representatives from the phyla Bacteroidetes, Firmicutes, Actinobacteria and Proteobacteria. In contrast to the direct use of FBA, SteadyCom is able to predict the change in species abundance in response to changes in diets with minimal additional imposed constraints on the model. Furthermore, by randomizing the uptake rates of microbes, an abundance profile with a good agreement to experimental gut microbiota is inferred. SteadyCom provides an important step towards the cross-cutting task of predicting the composition of a microbial community in a given environment.« less

SteadyCom: Predicting microbial abundances while ensuring community stability

DOE PAGES

Chan, Siu Hung Joshua; Simons, Margaret N.; Maranas, Costas D.; ...

2017-05-15

Genome-scale metabolic modeling has become widespread for analyzing microbial metabolism. Extending this established paradigm to more complex microbial communities is emerging as a promising way to unravel the interactions and biochemical repertoire of these omnipresent systems. While several modeling techniques have been developed for microbial communities, little emphasis has been placed on the need to impose a time-averaged constant growth rate across all members for a community to ensure co-existence and stability. In the absence of this constraint, the faster growing organism will ultimately displace all other microbes in the community. This is particularly important for predicting steady-state microbiota compositionmore » as it imposes significant restrictions on the allowable community membership, composition and phenotypes. In this study, we introduce the SteadyCom optimization framework for predicting metabolic flux distributions consistent with the steady-state requirement. SteadyCom can be rapidly converged by iteratively solving linear programming (LP) problem and the number of iterations is independent of the number of organisms. A significant advantage of SteadyCom is compatibility with flux variability analysis. SteadyCom is first demonstrated for a community of four E. coli double auxotrophic mutants and is then applied to a gut microbiota model consisting of nine species, with representatives from the phyla Bacteroidetes, Firmicutes, Actinobacteria and Proteobacteria. In contrast to the direct use of FBA, SteadyCom is able to predict the change in species abundance in response to changes in diets with minimal additional imposed constraints on the model. Furthermore, by randomizing the uptake rates of microbes, an abundance profile with a good agreement to experimental gut microbiota is inferred. SteadyCom provides an important step towards the cross-cutting task of predicting the composition of a microbial community in a given environment.« less

Solar Wind Strahl Observations and Their Implication to the Core-Halo Formation due to Scattering

NASA Technical Reports Server (NTRS)

Vinas, Adolfo F.

2011-01-01

A study of the kinetic properties of the strahl electron velocity distribution functions (VDF?s) in the solar wind is presented. This study focuses on the mechanisms that control and regulate the electron VDF?s and the stability of the strahl electrons in the solar wind; mechanisms that are not yet well understood. Various parameters are investigated such as the strahl-electron density, temperature anisotropy, and electron heat-flux. These parameters are used to investigate the stability of the strahl population. The analysis check for whether the strahl electrons are constrained by some instability (e.g., the whistler or KAW instabilities), or are maintained by other types of processes. The electron heat-flux and temperature anisotropy are determined by modeling of the 3D-VDF?s from which the moments properties of the various populations are obtained. The results of this study have profound implication on the current hypothesis about the probable formation of the solar wind halo electrons produced from the scattering of the strahl population. This hypothesis is strengthened by direct observations of the strahl electrons being scattered into the core-halo in an isolated event. The observation implies that the scattering of the strahl is not a continuous process but occurs in bursts in regions where conditions for wave growth providing the scattering are optimum. Sometimes, observations indicate that the strahl component is anisotropic (Tper/Tpal approx. 2). This provides a possible free energy source for the excitation of whistler waves as a possible scattering mechanism, however this condition is not always observed. The study is based on high time resolution data from the Cluster/PEACE electron spectrometer.

Utility of 222Rn as a passive tracer of subglacial distributed system drainage

NASA Astrophysics Data System (ADS)

Linhoff, Benjamin S.; Charette, Matthew A.; Nienow, Peter W.; Wadham, Jemma L.; Tedstone, Andrew J.; Cowton, Thomas

2017-03-01

Water flow beneath the Greenland Ice Sheet (GrIS) has been shown to include slow-inefficient (distributed) and fast-efficient (channelized) drainage systems, in response to meltwater delivery to the bed via both moulins and surface lake drainage. This partitioning between channelized and distributed drainage systems is difficult to quantify yet it plays an important role in bulk meltwater chemistry and glacial velocity, and thus subglacial erosion. Radon-222, which is continuously produced via the decay of 226Ra, accumulates in meltwater that has interacted with rock and sediment. Hence, elevated concentrations of 222Rn should be indicative of meltwater that has flowed through a distributed drainage system network. In the spring and summer of 2011 and 2012, we made hourly 222Rn measurements in the proglacial river of a large outlet glacier of the GrIS (Leverett Glacier, SW Greenland). Radon-222 activities were highest in the early melt season (10-15 dpm L-1), decreasing by a factor of 2-5 (3-5 dpm L-1) following the onset of widespread surface melt. Using a 222Rn mass balance model, we estimate that, on average, greater than 90% of the river 222Rn was sourced from distributed system meltwater. The distributed system 222Rn flux varied on diurnal, weekly, and seasonal time scales with highest fluxes generally occurring on the falling limb of the hydrograph and during expansion of the channelized drainage system. Using laboratory based estimates of distributed system 222Rn, the distributed system water flux generally ranged between 1-5% of the total proglacial river discharge for both seasons. This study provides a promising new method for hydrograph separation in glacial watersheds and for estimating the timing and magnitude of distributed system fluxes expelled at ice sheet margins.

Forward Modeling of Atmospheric Carbon Dioxide in GEOS-5: Uncertainties Related to Surface Fluxes and Sub-Grid Transport

NASA Technical Reports Server (NTRS)

Pawson, Steven; Ott, Lesley E.; Zhu, Zhengxin; Bowman, Kevin; Brix, Holger; Collatz, G. James; Dutkiewicz, Stephanie; Fisher, Joshua B.; Gregg, Watson W.; Hill, Chris;

Characterization of a 5-eV neutral atomic oxygen beam facility

NASA Technical Reports Server (NTRS)

Vaughn, J. A.; Linton, R. C.; Carruth, M. R., Jr.; Whitaker, A. F.; Cuthbertson, J. W.; Langer, W. D.; Motley, R. W.

1991-01-01

An experimental effort to characterize an existing 5-eV neutral atomic oxygen beam facility being developed at Princeton Plasma Physics Laboratory is described. This characterization effort includes atomic oxygen flux and flux distribution measurements using a catalytic probe, energy determination using a commercially designed quadrupole mass spectrometer (QMS), and the exposure of oxygen-sensitive materials in this beam facility. Also, comparisons were drawn between the reaction efficiencies of materials exposed in plasma ashers, and the reaction efficiencies previously estimated from space flight experiments. The results of this study show that the beam facility is capable of producing a directional beam of neutral atomic oxygen atoms with the needed flux and energy to simulate low Earth orbit (LEO) conditions for real time accelerated testing. The flux distribution in this facility is uniform to +/- 6 percent of the peak flux over a beam diameter of 6 cm.

LDEF Interplanetary Dust Experiment (IDE) results

NASA Technical Reports Server (NTRS)

Oliver, John P.; Singer, S. F.; Weinberg, J. L.; Simon, C. G.; Cooke, W. J.; Kassel, P. C.; Kinard, W. H.; Mulholland, J. D.; Wortman, J. J.

1995-01-01

The Interplanetary Dust Experiment (IDE) provided high time resolution detection of microparticle impacts on the Long Duration Exposure Facility satellite. Particles, in the diameter range from 0.2 microns to several hundred microns, were detected impacting on six orthogonal surfaces of the gravity-gradient stabilized LDEF spacecraft. The total sensitive surface area was about one square meter, distributed between LDEF rows 3 (Wake or West), 6 (South), 9 (Ram or East), 12 (North), as well as the Space and Earth ends of LDEF. The time of each impact is known to an accuracy that corresponds to better than one degree in orbital longitude. Because LDEF was gravity-gradient stabilized and magnetically damped, the direction of the normal to each detector panel is precisely known for each impact. The 11 1/2 month tape-recorded data set represents the most extensive record gathered of the number, orbital location, and incidence direction for microparticle impacts in low Earth orbit. Perhaps the most striking result from IDE was the discovery that microparticle impacts, especially on the Ram, South, and North surfaces, were highly episodic. Most such impacts occurred in localized regions of the orbit for dozens or even hundreds of orbits in what we have termed Multiple Orbit Event Sequences (MOES). In addition, more than a dozen intense and short-lived 'spikes' were seen in which impact fluxes exceeded the background by several orders of magnitude. These events were distributed in a highly non-uniform fashion in time and terrestrial longitude and latitude.

Entropy and optimality in river deltas

NASA Astrophysics Data System (ADS)

Tejedor, Alejandro; Longjas, Anthony; Edmonds, Douglas A.; Zaliapin, Ilya; Georgiou, Tryphon T.; Rinaldo, Andrea; Foufoula-Georgiou, Efi

2017-10-01

The form and function of river deltas is intricately linked to the evolving structure of their channel networks, which controls how effectively deltas are nourished with sediments and nutrients. Understanding the coevolution of deltaic channels and their flux organization is crucial for guiding maintenance strategies of these highly stressed systems from a range of anthropogenic activities. To date, however, a unified theory explaining how deltas self-organize to distribute water and sediment up to the shoreline remains elusive. Here, we provide evidence for an optimality principle underlying the self-organized partition of fluxes in delta channel networks. By introducing a suitable nonlocal entropy rate (nER) and by analyzing field and simulated deltas, we suggest that delta networks achieve configurations that maximize the diversity of water and sediment flux delivery to the shoreline. We thus suggest that prograding deltas attain dynamically accessible optima of flux distributions on their channel network topologies, thus effectively decoupling evolutionary time scales of geomorphology and hydrology. When interpreted in terms of delta resilience, high nER configurations reflect an increased ability to withstand perturbations. However, the distributive mechanism responsible for both diversifying flux delivery to the shoreline and dampening possible perturbations might lead to catastrophic events when those perturbations exceed certain intensity thresholds.

Martian electron foreshock from MAVEN observations

NASA Astrophysics Data System (ADS)

Meziane, K.; Mazelle, C. X.; Romanelli, N.; Mitchell, D. L.; Espley, J. R.; Connerney, J. E. P.; Hamza, A. M.; Halekas, J.; McFadden, J. P.; Jakosky, B. M.

2017-02-01

Flux enhancements of energetic electrons are always observed when the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft is magnetically connected to the shock. The observations indicate that the foreshock electrons consist of two populations. The most energetic (E≥237 eV) originate from a narrow region at the nearly perpendicular shock. They always appear as spikes, and their flux level reaches a maximum when the angle θBn approaches 90°. The other population emanates from the entire Martian bow shock surface, and the flux level decreases slightly from the quasi-parallel to quasi-perpendicular regions. A detailed examination of the pitch angle distribution shows that the enhanced fluxes are associated with electrons moving sunward. Annulus centered along the interplanetary magnetic field direction is the most stringent feature of the 3-D angular distribution. The gyrotropic character is observed over the whole range of shock geometry. Although such signatures in the electron pitch angle distribution function strongly suggest that the reflection off the shock of a fraction of the solar wind electrons is the main mechanism for the production of Martian foreshock electrons, the decay of the flux of the second population on the other hand has yet to be understood.

Estimation of electrical conductivity distribution within the human head from magnetic flux density measurement.

PubMed

Gao, Nuo; Zhu, S A; He, Bin

2005-06-07

We have developed a new algorithm for magnetic resonance electrical impedance tomography (MREIT), which uses only one component of the magnetic flux density to reconstruct the electrical conductivity distribution within the body. The radial basis function (RBF) network and simplex method are used in the present approach to estimate the conductivity distribution by minimizing the errors between the 'measured' and model-predicted magnetic flux densities. Computer simulations were conducted in a realistic-geometry head model to test the feasibility of the proposed approach. Single-variable and three-variable simulations were performed to estimate the brain-skull conductivity ratio and the conductivity values of the brain, skull and scalp layers. When SNR = 15 for magnetic flux density measurements with the target skull-to-brain conductivity ratio being 1/15, the relative error (RE) between the target and estimated conductivity was 0.0737 +/- 0.0746 in the single-variable simulations. In the three-variable simulations, the RE was 0.1676 +/- 0.0317. Effects of electrode position uncertainty were also assessed by computer simulations. The present promising results suggest the feasibility of estimating important conductivity values within the head from noninvasive magnetic flux density measurements.

Stability and Multiattractor Dynamics of a Toggle Switch Based on a Two-Stage Model of Stochastic Gene Expression

PubMed Central

Strasser, Michael; Theis, Fabian J.; Marr, Carsten

2012-01-01

A toggle switch consists of two genes that mutually repress each other. This regulatory motif is active during cell differentiation and is thought to act as a memory device, being able to choose and maintain cell fate decisions. Commonly, this switch has been modeled in a deterministic framework where transcription and translation are lumped together. In this description, bistability occurs for transcription factor cooperativity, whereas autoactivation leads to a tristable system with an additional undecided state. In this contribution, we study the stability and dynamics of a two-stage gene expression switch within a probabilistic framework inspired by the properties of the Pu/Gata toggle switch in myeloid progenitor cells. We focus on low mRNA numbers, high protein abundance, and monomeric transcription-factor binding. Contrary to the expectation from a deterministic description, this switch shows complex multiattractor dynamics without autoactivation and cooperativity. Most importantly, the four attractors of the system, which only emerge in a probabilistic two-stage description, can be identified with committed and primed states in cell differentiation. To begin, we study the dynamics of the system and infer the mechanisms that move the system between attractors using both the quasipotential and the probability flux of the system. Next, we show that the residence times of the system in one of the committed attractors are geometrically distributed. We derive an analytical expression for the parameter of the geometric distribution, therefore completely describing the statistics of the switching process and elucidate the influence of the system parameters on the residence time. Moreover, we find that the mean residence time increases linearly with the mean protein level. This scaling also holds for a one-stage scenario and for autoactivation. Finally, we study the implications of this distribution for the stability of a switch and discuss the influence of the stability on a specific cell differentiation mechanism. Our model explains lineage priming and proposes the need of either high protein numbers or long-term modifications such as chromatin remodeling to achieve stable cell fate decisions. Notably, we present a system with high protein abundance that nevertheless requires a probabilistic description to exhibit multistability, complex switching dynamics, and lineage priming. PMID:22225794

Mechanistic principles of colloidal crystal growth by evaporation-induced convective steering.

PubMed

Brewer, Damien D; Allen, Joshua; Miller, Michael R; de Santos, Juan M; Kumar, Satish; Norris, David J; Tsapatsis, Michael; Scriven, L E

2008-12-02

We simulate evaporation-driven self-assembly of colloidal crystals using an equivalent network model. Relationships between a regular hexagonally close-packed array of hard, monodisperse spheres, the associated pore space, and selectivity mechanisms for face-centered cubic microstructure propagation are described. By accounting for contact line rearrangement and evaporation at a series of exposed menisci, the equivalent network model describes creeping flow of solvent into and through a rigid colloidal crystal. Observations concerning colloidal crystal growth are interpreted in terms of the convective steering hypothesis, which posits that solvent flow into and through the pore space of the crystal may play a major role in colloidal self-assembly. Aspects of the convective steering and deposition of high-Peclet-number rigid spherical particles at a crystal boundary are inferred from spatially resolved solvent flow into the crystal. Gradients in local flow through boundary channels were predicted due to the channels' spatial distribution relative to a pinned free surface contact line. On the basis of a uniform solvent and particle flux as the criterion for stability of a particular growth plane, these network simulations suggest the stability of a declining {311} crystal interface, a symmetry plane which exclusively propagates fcc microstructure. Network simulations of alternate crystal planes suggest preferential growth front evolution to the declining {311} interface, in consistent agreement with the proposed stability mechanism for preferential fcc microstructure propagation in convective assembly.

A Fluid Pulse on the Hikurangi Subduction Margin: Evidence From a Heat Flux Transect Across the Upper Limit of Gas Hydrate Stability

NASA Astrophysics Data System (ADS)

Pecher, I. A.; Villinger, H.; Kaul, N.; Crutchley, G. J.; Mountjoy, J. J.; Huhn, K.; Kukowski, N.; Henrys, S. A.; Rose, P. S.; Coffin, R. B.

2017-12-01

A transect of seafloor heat probe measurements on the Hikurangi Margin shows a significant increase of thermal gradients upslope of the updip limit of gas hydrate stability at the seafloor. We interpret these anomalously high thermal gradients as evidence for a fluid pulse leading to advective heat flux, while endothermic cooling from gas hydrate dissociation depresses temperatures in the hydrate stability field. Previous studies predict a seamount on the subducting Pacific Plate to cause significant overpressure beneath our study area, which may be the source of the fluid pulse. Double-bottom simulating reflections are present in our study area and likely caused by uplift based on gas hydrate phase boundary considerations, although we cannot exclude a thermogenic origin. We suggest that uplift may be associated with the leading edge of the subducting seamount. Our results provide further evidence for the transient nature of fluid expulsion in subduction zones.

Two new methods used to simulate the circumferential solar flux density concentrated on the absorber of a parabolic trough solar collector

NASA Astrophysics Data System (ADS)

Guo, Minghuan; Wang, Zhifeng; Sun, Feihu

2016-05-01

The optical efficiencies of a solar trough concentrator are important to the whole thermal performance of the solar collector, and the outer surface of the tube absorber is a key interface of energy flux. So it is necessary to simulate and analyze the concentrated solar flux density distributions on the tube absorber of a parabolic trough solar collector for various sun beam incident angles, with main optical errors considered. Since the solar trough concentrators are linear focusing, it is much of interest to investigate the solar flux density distribution on the cross-section profile of the tube absorber, rather than the flux density distribution along the focal line direction. Although a few integral approaches based on the "solar cone" concept were developed to compute the concentrated flux density for some simple trough concentrator geometries, all those integral approaches needed special integration routines, meanwhile, the optical parameters and geometrical properties of collectors also couldn't be changed conveniently. Flexible Monte Carlo ray trace (MCRT) methods are widely used to simulate the more accurate concentrated flux density distribution for compound parabolic solar trough concentrators, while generally they are quite time consuming. In this paper, we first mainly introduce a new backward ray tracing (BRT) method combined with the lumped effective solar cone, to simulate the cross-section flux density on the region of interest of the tube absorber. For BRT, bundles of rays are launched at absorber-surface points of interest, directly go through the glass cover of the absorber, strike on the uniformly sampled mirror segment centers in the close-related surface region of the parabolic reflector, and then direct to the effective solar cone around the incident sun beam direction after the virtual backward reflection. All the optical errors are convoluted into the effective solar cone. The brightness distribution of the effective solar cone is supposed to be circular Gaussian type. Then a parabolic trough solar collector of Euro Trough 150 is used as an example object to apply this BRT method. Euro Trough 150 is composed of RP3 mirror facets, with the focal length of 1.71m, aperture width of 5.77m, outer tube diameter of 0.07m. Also to verify the simulated flux density distributions, we establish a modified MCRT method. For this modified MCRT method, the random rays with weighted energy elements are launched in the close-related rectangle region in the aperture plane of the parabolic concentrator and the optical errors are statistically modeled in the stages of forward ray tracing process. Given the same concentrator geometric parameters and optical error values, the simulated results from these two ray tracing methods are in good consistence. The two highlights of this paper are the new optical simulation method, BRT, and figuring out the close-related mirror surface region for BRT and the close-related aperture region for MCRT in advance to effectively simulate the solar flux distribution on the absorber surface of a parabolic trough collector.

Evidence for Spiral Magnetic Structures at the Magnetopause: A Case for Multiple Reconnections

NASA Technical Reports Server (NTRS)

Vaisberg, O. L.; Smirnov, V. N.; Avanov, L. A.; Moore, T. E.

2003-01-01

We analyze plasma structures within the low latitude boundary layer (LLBL) observed by the lnterball Tail spacecraft under southward interplanetary magnetic field. Ion velocity distributions observed in the LLBL under these conditions fall into three categories: (a) D-shaped distributions, (b) ion velocity distributions consisting of two counterstreaming magnetosheath-type, and (c) distributions with three components where one of them has nearly zero velocity parallel to magnetic field (VlI), while the other two are counter-streaming components. D-shaped ion velocity distributions (a) correspond to magnetosheath plasma injections into reconnected flux tubes, as influenced by spacecraft location relative to the reconnection site. Simultaneous counter-streaming injections (b) suggest multiple reconnections. Three-component ion velocity distributions (c) and theii evolution with decreasing number density in the LLBL are consistent v behavior expected on long spiral flux tube islands at the magnetopaus as has been proposed and found to occur in magnetopause simulatior We interpret these distributions as a natural consequence of the formation of spiral magnetic flux tubes consisting of a mixture of alternating segments originating from the magnetosheath and magnetospheric plasmas. We suggest that multiple reconnections pla! an important role in the formation of the LLBL.

Satellite-Derived Distributions, Inventories and Fluxes of Dissolved and Particulate Organic Matter Along the Northeastern U.S. Continental Margin

NASA Technical Reports Server (NTRS)

Mannino, A.; Hooker, S. B.; Hyde, K.; Novak, M. G.; Pan, X.; Friedrichs, M.; Cahill, B.; Wilkin, J.

2011-01-01

Estuaries and the coastal ocean experience a high degree of variability in the composition and concentration of particulate and dissolved organic matter (DOM) as a consequence of riverine and estuarine fluxes of terrigenous DOM, sediments, detritus and nutrients into coastal waters and associated phytoplankton blooms. Our approach integrates biogeochemical measurements, optical properties and remote sensing to examine the distributions and inventories of organic carbon in the U.S. Middle Atlantic Bight and Gulf of Maine. Algorithms developed to retrieve colored DOM (CDOM), Dissolved (DOC) and Particulate Organic Carbon (POC) from NASA's MODIS-Aqua and SeaWiFS satellite sensors are applied to quantify the distributions and inventories of DOC and POC. Horizontal fluxes of DOC and POC from the continental margin to the open ocean are estimated from SeaWiFS and MODIS-Aqua distributions of DOC and POC and horizontal divergence fluxes obtained from the Northeastern North Atlantic ROMS model. SeaWiFS and MODIS imagery reveal the importance of estuarine outflow to the export of CDOM and DOC to the coastal ocean and a net community production of DOC on the shelf.

Fast Radio Bursts’ Recipes for the Distributions of Dispersion Measures, Flux Densities, and Fluences

NASA Astrophysics Data System (ADS)

Niino, Yuu

2018-05-01

We investigate how the statistical properties of dispersion measure (DM) and apparent flux density/fluence of (nonrepeating) fast radio bursts (FRBs) are determined by unknown cosmic rate density history [ρ FRB(z)] and luminosity function (LF) of the transient events. We predict the distributions of DMs, flux densities, and fluences of FRBs taking account of the variation of the receiver efficiency within its beam, using analytical models of ρ FRB(z) and LF. Comparing the predictions with the observations, we show that the cumulative distribution of apparent fluences suggests that FRBs originate at cosmological distances and ρ FRB increases with redshift resembling the cosmic star formation history (CSFH). We also show that an LF model with a bright-end cutoff at log10 L ν (erg s‑1 Hz‑1) ∼ 34 are favored to reproduce the observed DM distribution if ρ FRB(z) ∝ CSFH, although the statistical significance of the constraints obtained with the current size of the observed sample is not high. Finally, we find that the correlation between DM and flux density of FRBs is potentially a powerful tool to distinguish whether FRBs are at cosmological distances or in the local universe more robustly with future observations.

Linking Carbon Flux Dynamics and Soil Structure in Dryland Soils

NASA Astrophysics Data System (ADS)

DeCarlo, K. F.; Caylor, K. K.

2016-12-01

Biological sources in the form of microbes and plants play a fundamental role in determining the magnitude of carbon flux. However, the geophysical structure of the soil (which the carbon must pass through before entering the atmosphere) often serves as a constraining entity, which has the potential to serve as instigators or mitigators of those carbon and hydrologic flux processes. We characterized soil carbon dynamics in three dryland soil systems: bioturbated soils, biocompacted soils, and undisturbed soils. Carbon fluxes were characterized using a closed-system respiration chamber, with CO2 concentration differences measured using an infrared gas analyzer (IRGA). Structure of the soil systems, with a focus on the macro-crack structure, were characterized using a combined resin-casting/X-ray imaging technique. Results show fundamental differences in carbon dynamics between the different soil systems/structures: control soils have gaussian distributions of carbon flux that decrease with progressive drying of the soil, while biocompacted soils exhibit exponentially distributed fluxes that do not regularly decrease with increased drying of the soil. Bioturbated soils also exhibit an exponential distribution of carbon flux, though at a much higher magnitude. These differences are evaluated in the context of the underlying soil structure: while the control soils exhibit a shallow and narrow crack structure, the biocompacted soils exhibit a "systematic" crack network with moderate cracking intensity and large depth. The deep crack networks of the biocompacted soils may serve to physically enhance an otherwise weak source of carbon via advection and/or convection, inducing fluxes that are equal or greater than an otherwise carbon-rich soil. The bioturbated soils exhibit a "surficial" crack network that is shallow but extensive, but additionally have deep holes known to convectively vent carbon, which may explain their periodically large carbon fluxes. Our results suggest that variability in soil structure, as well as carbon source, plays a fundamental role in carbon flux dynamics, and the importance of evaluating biological carbon source and geophysical soil structure in a dryland environment.

Nitrogen Flux in Watersheds: The Role of Soil Distributions and Climate in Nitrogen Flux to the Coastal Ecosystems

NASA Astrophysics Data System (ADS)

Showers, W. J.; Reyes, M. M.; Genna, B. J.

2009-12-01

Quantifying the flux of nitrate from different landscape sources in watersheds is important to understand the increased flux of nitrogen to coastal ecosystems. Recent technological advances in chemical sensor networks has demonstrated that chemical variability in aquatic environments are chronically under-sampled, and that many nutrient monitoring programs with monthly or daily sampling rates are inadequate to characterize the dominate seasonal, daily or semi-diurnal fluxes in watersheds. The RiverNet program has measured the nitrate flux in the Neuse River Basin, NC on a 15 minute interval over the past eight years. Significant diurnal variation has been observed in nitrate concentrations during high and low flow periods associated with waste water treatment plants in urban watersheds that are not present in agricultural watersheds. Discharge and N flux in the basin also has significant inter-annual variations associated with El Nino oscillations modified by the North Atlantic oscillation. Positive JMA and NAO indexes are associated with increased groundwater levels, nutrient fluxes, and estuary fish kills. To understand how climate oscillation affect discharge and nutrient fluxes, we have monitored runoff/drainages and groundwater inputs adjacent to a large waste application field over the past 4 years, and used the nitrate inputs as a tracer. Surface water run off is well correlated to precipitation patterns and is the largest nutrient flux into the river. Groundwater inputs are variable spatially and temporally, and are controlled by geology and groundwater levels. Hydric soil spatial distributions are an excellent predictor of nutrient transport across landscapes, and is related to the distribution of biogeochemical “hotspots” The isotopic composition of oxygen and nitrogen in dissolved nitrate indicate that sources change with discharge state, and that atmospherically deposited nitrogen is only important to river fluxes in forested and urban watersheds. These results also indicate that the contribution of wastewater treatment plants from urban watersheds has been greatly under-estimated in current models. Prediction of future changes in discharge and nutrient flux by the modeling of climate oscillations has important implications for water resources policy and drought management for public policy and utility managers.

A new lattice hydrodynamic model based on control method considering the flux change rate and delay feedback signal

NASA Astrophysics Data System (ADS)

Qin, Shunda; Ge, Hongxia; Cheng, Rongjun

2018-02-01

In this paper, a new lattice hydrodynamic model is proposed by taking delay feedback and flux change rate effect into account in a single lane. The linear stability condition of the new model is derived by control theory. By using the nonlinear analysis method, the mKDV equation near the critical point is deduced to describe the traffic congestion. Numerical simulations are carried out to demonstrate the advantage of the new model in suppressing traffic jam with the consideration of flux change rate effect in delay feedback model.

Estimation of m.w.e (meter water equivalent) depth of the salt mine of Slanic Prahova, Romania

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

Mitrica, B.; Margineanu, R.; Stoica, S.

2010-11-24

A new mobile detector was developed in IFIN-HH, Romania, for measuring muon flux at surface and in underground. The measurements have been performed in the salt mines of Slanic Prahova, Romania. The muon flux was determined for 2 different galleries of the Slanic mine at different depths. In order to test the stability of the method, also measurements of the muon flux at surface at different altitudes were performed. Based on the results, the depth of the 2 galleries was established at 610 and 790 m.w.e. respectively.

Flux Measurements of Trace Gases, Aerosols and Energy from the Urban Core of Mexico City

NASA Astrophysics Data System (ADS)

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

2007-05-01

As part of the MILAGRO field campaign in March 2006 we deployed a flux system in a busy district of Mexico City surrounded by congested avenues. The flux system consisted of a tall tower instrumented with fast-response sensors coupled with eddy covariance (EC) techniques to measure fluxes of volatile organic compounds (VOCs), CO2, CO, aerosols and energy. The measured fluxes represent direct measurements of emissions that include all major and minor emission sources from a typical residential and commercial district. In a previous study we demonstrated that the EC techniques are valuable tools to evaluate emissions inventories in urban areas, and understand better the atmospheric chemistry and the role that megacities play in global change. We measured fluxes of olefins using a Fast Olefin Sensor (FOS) and the EC technique, fluxes of aromatic and oxygenated VOCs by Proton Transfer Reaction-Mass Spectroscopy (PTR-MS) and the disjunct eddy covariance (DEC) technique, fluxes of CO2 and H2O with an open path Infrared Gas Analyzer (IRGA) and the EC technique, fluxes of CO using a modified gradient method and a commercial CO instrument, and fluxes of aerosols (organics, nitrates and sulfates) using an Aerodyne Aerosol Mass Spectrometer (AMS) and the EC technique. In addition we used a disjunct eddy accumulation (DEA) system to extend the number of VOCs. This system collected whole air samples as function of the direction of the vertical wind component, and the samples were analyzed on site using gas chromatography / flame ionization detection (GC-FID). We also measured fluxes of sensible and latent heat by EC and the radiation components with a net radiometer. Overall, these flux measurements confirm the results of our previous flux measurements in Mexico City in terms of the magnitude, composition, and distribution. We found that the urban surface is a net source of CO2 and VOCs. The diurnal patterns show clear anthropogenic signatures, with important contributions from vehicular traffic. The DEA results for individual hydrocarbons show that the alkane fluxes are considerably higher than alkene fluxes, which is consistent with ambient concentration measurements and with the emission inventory for Mexico City. CO fluxes, estimated from a modified gradient technique, were more than 10% of the measured CO2 fluxes (on a molar basis) which is much higher than is generally expected for combustion efficiencies in mobile and other sources. Investigation of this result is underway. The energy balance distribution and radiative parameters observed are similar to distributions and parameters reported for other urban sites.

Ion distributions in RC at different energy levels retrieved from TWINS ENA images by voxel CT tech

NASA Astrophysics Data System (ADS)

Ma, S. Y.; McComas, David; Xu, Liang; Goldstein, Jerry; Yan, Wei-Nan

2012-07-01

Distributions of energetic ions in the RC regions in different energy levels are retrieved by using 3-D voxel CT inversion method from ENA measurements onboard TWINS constellation during the main phase of a moderate geomagnetic storm. It is assumed that the ion flux distribution in the RC is anisotropic in regard to pitch angle which complies with the adiabatic invariance of the magnetic moment as ion moving in the dipole magnetic mirror field. A semi-empirical model of the RC ion distribution in the magnetic equator is quoted to form the ion flux distribution shape at off-equatorial latitudes by mapping. For the concerned time interval, the two satellites of the TWINS flying in double Molnia orbits were located in nearly the same meridian plane at vantage points widely separated in magnetic local time, and both more than 5 RE geocentric distance from the Earth. The ENA data used in this study are differential fluxes averaged over 12 sweeps (corresponding to an interval of 16 min.) at different energy levels ranging from about 1 to 100 keV. The retrieved ion distributions show that in total the main part of the RC is located in the region with L value larger than 4, tending to increase at larger L. It reveals that there are two distinct dominant energy bands at which the ion fluxes are significantly larger magnitude than at other energy levels, one is at lower level around 2 keV and the other at higher level of 30-100 keV. Furthermore, it is very interesting that the peak fluxes of the RC ions at the two energy bands occurred in different magnetic local time, low energy ions appear preferentially in after midnight, while the higher energy ions mainly distributed around midnight and pre-midnight. This new profile is worthy of further study and needs to be demonstrated by more cases.

Studies of heat source driven natural convection

NASA Technical Reports Server (NTRS)

Kulacki, F. A.; Nagle, M. E.; Cassen, P.

1974-01-01

Natural convection energy transport in a horizontal layer of internally heated fluid with a zero heat flux lower boundary, and an isothermal upper boundary, has been studied. Quantitative information on the time-mean temperature distribution and the fluctuating component of temperature about the mean temperature in steady turbulent convection are obtained from a small thermocouple inserted into the layer through the upper bounding plate. Data are also presented on the development of temperature at several vertical positions when the layer is subject to both a sudden increase and to a sudden decrease in power input. For changes of power input from zero to a value corresponding to a Rayleigh number much greater than the critical linear stability theory value, a slight hysteresis in temperature profiles near the upper boundary is observed between the heat-up and cool-down modes.

Muon Simulation at the Daya Bay SIte

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

Mengyun, Guan; Jun, Cao; Changgen, Yang

2006-05-23

With a pretty good-resolution mountain profile, we simulated the underground muon background at the Daya Bay site. To get the sea-level muon flux parameterization, a modification to the standard Gaisser's formula was introduced according to the world muon data. MUSIC code was used to transport muon through the mountain rock. To deploy the simulation, first we generate a statistic sample of sea-level muon events according to the sea-level muon flux distribution formula; then calculate the slant depth of muon passing through the mountain using an interpolation method based on the digitized data of the mountain; finally transport muons through rockmore » to get underground muon sample, from which we can get results of muon flux, mean energy, energy distribution and angular distribution.« less

Optimality and self-organization in river deltas

NASA Astrophysics Data System (ADS)

Tejedor, A.; Longjas, A.; Edmonds, D. A.; Zaliapin, I. V.; Georgiou, T. T.; Rinaldo, A.; Foufoula-Georgiou, E.

2017-12-01

Deltas are nourished by channel networks, whose connectivity constrains, if not drives, the evolution, functionality and resilience of these systems. Understanding the coevolution of deltaic channels and their flux organization is crucial for guiding maintenance strategies of these highly stressed systems from a range of anthropogenic activities. However, in contrast to tributary channel networks, to date, no theory has been proposed to explain how deltas self-organize to distribute water and sediment to the delta top and the shoreline. Here, we hypothesize the existence of an optimality principle underlying the self-organized partition of fluxes in delta channel networks. Specifically, we hypothesize that deltas distribute water and sediment fluxes on a given delta topology such as to maximize the diversity of flux delivery to the shoreline. By introducing the concept of nonlocal Entropy Rate (nER) and analyzing ten field deltas in diverse environments, we present evidence that supports our hypothesis, suggesting that delta networks achieve dynamically accessible maxima of their nER. Furthermore, by analyzing six simulated deltas using the Delf3D model and following their topologic and flux re-organization before and after major avulsions, we further study the evolution of nER and confirm our hypothesis. We discuss how optimal flux distributions in terms of nER, when interpreted in terms of resilience, are configurations that reflect an increased ability to withstand perturbations.

Ballooning modes localized near the null point of a divertor

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

Farmer, W. A.; Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, California 94550

2014-04-15

The stability of ballooning modes localized to the null point in both the standard and snowflake divertors is considered. Ideal magnetohydrodynamics is used. A series expansion of the flux function is performed in the vicinity of the null point with the lowest, non-vanishing term retained for each divertor configuration. The energy principle is used with a trial function to determine a sufficient instability threshold. It is shown that this threshold depends on the orientation of the flux surfaces with respect to the major radius with a critical angle appearing due to the convergence of the field lines away from themore » null point. When the angle the major radius forms with respect to the flux surfaces exceeds this critical angle, the system is stabilized. Further, the scaling of the instability threshold with the aspect ratio and the ratio of the scrape-off-layer width to the major radius is shown. It is concluded that ballooning modes are not a likely candidate for driving convection in the vicinity of the null for parameters relevant to existing machines. However, the results place a lower bound on the width of the heat flux in the private flux region. To explain convective mixing in the vicinity of the null point, new consideration should be given to an axisymmetric mixing mode [W. A. Farmer and D. D. Ryutov, Phys. Plasmas 20, 092117 (2013)] as a possible candidate to explain current experimental results.« less

Design and use of a sparged platform for energy flux measurements over lakes

NASA Astrophysics Data System (ADS)

Gijsbers, S.; Wenker, K.; van Emmerik, T.; de Jong, S.; Annor, F.; Van De Giesen, N.

2012-12-01

Energy flux measurements over lakes or reservoirs demand relatively stable platforms. Platforms can not be stabilized by fixing them on the bottom of the lake when the water body is too deep or when water levels show significant fluctuations. We present the design and first operational results of a sparged platform. The structure consists of a long PVC pipe, the sparge, which is closed at the bottom. On the PVC pipe rests an aluminum frame platform that carries instrumentation and solar power panel. In turn, the platform rests partially on a large inflated tire. At the bottom of the PVC pipe, lead weights and batteries were placed to ensure a very low point of gravity to minimize wave impact on the platform movement. The tire ensures a large second moment of the water plane. The overall volume of displacement is small in this sparged design. The combination of large second momentum of the water plane and small displacement ensure a high placement of the metacenter. The distance between the point of gravity and the metacenter is relatively long and the weight is large due to the weights and batteries. This ensures that the eigenfrequency of the platform is very low. The instrumentation load consisted of a WindMaster Pro (sonic anemometer for 3D wind speed and air temperature to perform eddy covariance measurements of sensible heat flux), a NR Lite (net radiometer), and air temperature and relative humidity sensors. The platform had a wind vane and the sparge could turn freely around its anchor cable to ensure that the anemometer always faced upwind. A compass in the logger completed this setup. The stability was measured with an accelerometer. In addition to the design and its stability, some first energy flux results will be presented.

Effects of Dendrimer-Like Biopolymers on Physical Stability of Amorphous Solid Dispersions and Drug Permeability Across Caco-2 Cell Monolayers.

PubMed

Lavan, Monika; Knipp, Gregory

2018-06-04

The potential applications of dendrimer-like biopolymers (DLB) as stabilizing excipients for amorphous solid dispersion (ASD) of niclosamide, celecoxib, and resveratrol were evaluated based on (1) the formation and physical stability of the ASD and (2) the permeability and flux of the agents across Caco-2 cell monolayers. The evaluation was made by comparing the performance of prototype phytoglycogen derivatives (DLB1, DLB2, and DLB3) with commonly used polymers such as HPMCAS, PVPVA, and Soluplus®. PXRD was used to confirm the formation of the dispersions and detect crystallinity peaks formed during 2- and 4-week storage at 40°C/75% RH. At concentrations below 2 g/mL, the viability of Caco-2 cells remained above 80% for all DLB samples compared to untreated cells in the MTT assay. Permeability studies revealed a repeating pattern in which an increase in the initial concentration (C 0 ) was associated with a concomitant decrease in the apparent permeability (P app ) which we theorize is due to differences in drug-polymer interactions. Niclosamide-DLB1 dispersion had the lowest flux due to a significant reduction in P app . The high increase in the C 0 of celecoxib-DLB2, however, made up for the reduction in the P app and produced the highest flux values compared to other polymers. Resveratrol-DLB3 had a 5× reduction in P app , but C 0 increased from 25.8 to 176 μg/mL led to a higher flux compared to the crystalline drug without polymer. Collectively, these results provide a "proof-of-concept" basis to demonstrate that DLB excipients have the ability to increase apparent solubility (Sol app ), most likely due to drug-binding capacity.

Determination of the thermal, oxidative and photochemical degradation rates of scintillator liquid by fluorescence EEM spectroscopy.

PubMed

Andrews, N L P; Fan, J Z; Forward, R L; Chen, M C; Loock, H-P

2016-12-21

The thermal, oxidative and photochemical stability of the scintillator liquid proposed for the SNO+ experiment has been tested experimentally using accelerated aging methods. The stability of the scintillator constituents was determined through fluorescence excitation emission matrix (EEM) spectroscopy and absorption spectroscopy, using parallel factor analysis (PARAFAC) as an multivariate analysis tool. By exposing the scintillator liquid to a well-known photon flux at 365 nm and by measuring the decay rate of the fluorescence shifters and the formation rate of their photochemical degradation products, we can place an upper limit on the acceptable photon flux as 1.38 ± 0.09 × 10 -11 photon mol L -1 . Similarly, the oxidative stability of the scintillator liquid was determined by exposure to air at several elevated temperatures. Through measurement of the corresponding activation energy it was determined that the average oxygen concentration would have to be kept below 4.3-7.1 ppb w (headspace partial pressure below 24 ppm v ). On the other hand, the thermal stability of the scintillator cocktail in the absence of light and oxygen was remarkable and poses no concern to the SNO+ experiment.

Connection stiffness and dynamical docking process of flux pinned spacecraft modules

NASA Astrophysics Data System (ADS)

Lu, Yong; Zhang, Mingliang; Gao, Dong

2014-02-01

This paper describes a novel kind of potential flux pinned docking system that consists of guidance navigation and control system, the traditional extrusion type propulsion system, and a flux pinned docking interface. Because of characteristics of passive stability of flux pinning, the docking control strategy of flux pinned docking system only needs a series of sequential control rather than necessary active feedback control, as well as avoidance of hazardous collision accident. The flux pinned force between YBaCuO (YBCO) high temperature superconductor bulk and permanent magnet is able to be given vent based on the identical current loop model and improved image dipole model, which can be validated experimentally. Thus, the connection stiffness between two flux pinned spacecraft modules can be calculated based on Hooke's law. This connection stiffness matrix at the equilibrium position has the positive definite performance, which can validate the passively stable connection of two flux pinned spacecraft modules theoretically. Furthermore, the relative orbital dynamical equation of two flux pinned spacecraft modules can be established based on Clohessy-Wiltshire's equations and improved image dipole model. The dynamical docking process between two flux pinned spacecraft modules can be obtained by way of numerical simulation, which suggests the feasibility of flux pinned docking system.

Connection stiffness and dynamical docking process of flux pinned spacecraft modules

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

Lu, Yong; Zhang, Mingliang, E-mail: niudun12@126.com; Gao, Dong

2014-02-14

This paper describes a novel kind of potential flux pinned docking system that consists of guidance navigation and control system, the traditional extrusion type propulsion system, and a flux pinned docking interface. Because of characteristics of passive stability of flux pinning, the docking control strategy of flux pinned docking system only needs a series of sequential control rather than necessary active feedback control, as well as avoidance of hazardous collision accident. The flux pinned force between YBaCuO (YBCO) high temperature superconductor bulk and permanent magnet is able to be given vent based on the identical current loop model and improvedmore » image dipole model, which can be validated experimentally. Thus, the connection stiffness between two flux pinned spacecraft modules can be calculated based on Hooke's law. This connection stiffness matrix at the equilibrium position has the positive definite performance, which can validate the passively stable connection of two flux pinned spacecraft modules theoretically. Furthermore, the relative orbital dynamical equation of two flux pinned spacecraft modules can be established based on Clohessy-Wiltshire's equations and improved image dipole model. The dynamical docking process between two flux pinned spacecraft modules can be obtained by way of numerical simulation, which suggests the feasibility of flux pinned docking system.« less

SGR-like behaviour of the repeating FRB 121102

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

Wang, F.Y.; Yu, H., E-mail: fayinwang@nju.edu.cn, E-mail: yuhai@smail.nju.edu.cn

2017-03-01

Fast radio bursts (FRBs) are millisecond-duration radio signals occurring at cosmological distances. However the physical model of FRBs is mystery, many models have been proposed. Here we study the frequency distributions of peak flux, fluence, duration and waiting time for the repeating FRB 121102. The cumulative distributions of peak flux, fluence and duration show power-law forms. The waiting time distribution also shows power-law distribution, and is consistent with a non-stationary Poisson process. These distributions are similar as those of soft gamma repeaters (SGRs). We also use the statistical results to test the proposed models for FRBs. These distributions are consistentmore » with the predictions from avalanche models of slowly driven nonlinear dissipative systems.« less

Enrichment Ratio and Aggregate Stability Dynamics in Intensely Managed Landscapes

NASA Astrophysics Data System (ADS)

Wacha, K.; Papanicolaou, T.; Filley, T. R.; Hou, T.; Abban, B. K.; Wilson, C. G.; Boys, J.

2015-12-01

Challenges in understanding the soil carbon dynamics within intensely managed landscapes (IMLs), found throughout much the US Midwest, is highly complex due to the presence of heterogeneous landscape features and properties, as well as a mosaic of physical and biogeochemical processes occurring at different time scales. In addition, rainfall events exacerbate the effects of tillage by the impact of raindrops, which break down aggregates that encase carbon and dislodge and entrain soil particles and aggregates along the downslope. The redistribution of soil and carbon can have huge implications on biogeochemical cycling and overall carbon budgeting. In this study, we provide some rare field data on the mechanisms impacting aggregate stability, enrichment ratio values to estimate fluxes of carbon, as well as lignin chemistry to see influences on oxidation/mineralization rates. Rainfall simulation experiments were conducted within agricultural fields. Experiments were performed on the midslope (eroding) and toeslope (depositional) sections of representative hillslopes, under a variety of land managements, including row crop (conventional and conservation) and restored grasslands. Sensors were utilized to capture the evolution of soil moisture, temperature, microbial respiration pulses, and discharge rates to identify pseudo-steady state conditions. Samples collected at the weir outlet were tested for sediment concentrations and size fractions, as well as carbon and lignin fluxes. Preliminary findings show that conservation management practices have higher aggregate stability and decreased mass fluxes of carbon in the downslope than conventional tillage techniques.

Partnership for Edge Physics Simulation

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

Kritz, Arnold H.; Rafiq, Tariq

A major goal of our participation in the Edge Physics Simulation project has been to contribute to the understanding of the self-organization of tokamak turbulence fluctuations resulting in the formation of a staircase structure in the ion temperature. A second important goal is to demonstrate how small scale turbulence in plasmas self-organizes with dynamically driven quasi-stationary flow shear. These goals have been accomplished through the analyses of the statistical properties of XGC1 flux driven Gyrokinetic electrostatic ion temperature gradient (ITG) turbulence simulation data in which neutrals are included. The ITG turbulence data, and in particular fluctuation data, were obtained frommore » a massively parallel flux-driven gyrokinetic full-f particle-in-cell simulation of a DIII-D like equilibrium. Below some the findings are summarized. It was observed that the emergence of staircase structure is related to the variations in the normalized temperature gradient length (R/LT) and the poloidal flow shear. Average turbulence intensity is found to be large in the vicinity of minima in R/LTi, where ITG growth is expected to be lower. The distributions of the occurrences of potential fluctuation are found to be Gaussian away from the staircase-step locations, but they are found to be non-Gaussian in the vicinity of staircase-step locations. The results of analytically derived expressions for the distribution of the occurrences of turbulence intensity and intensity flux were compared with the corresponding quantities computed using XGC1 simulation data and good agreement is found. The derived expressions predicts inward and outward propagation of turbulence intensity flux in an intermittent fashion. The outward propagation of turbulence intensity flux occurs at staircase-step locations and is related to the change in poloidal flow velocity shear and to the change in the ion temperature gradient. The standard deviation, skewness and kurtosis for turbulence quantities were computed and found to be large in the vicinity of the staircase-step structures. Large values of skewness and kurtosis can be explained by a temporary opening and closing of the structure which allows turbulence intensity events to propagate. The staircase patterns may reduce the ion heat transport and a manipulation of these patterns may be used to optimize heat transport in tokamaks. An additional objective of the research in support of the Edge Physics Simulation initiative has been to improve the understanding of scrape-off layer thermal transport. In planning experiments and designing future tokamaks, it is important to understand the physical effects that contribute to divertor heat-load fluxes. The research accomplished will contribute to developing new models for the scrape-off layer region. The XGC0 code was used to compute the heat fluxes and the heat-load width in the outer divertor plates of C-Mod and DIII-D tokamaks. It was observed that the width of the XGC0 neoclassical heat-load was approximately inversely proportional to the total plasma current. Anomalous transport in the H-mode pedestal region of five Alcator C-Mod discharges, representing a collisionality scan, was analyzed. The understanding of anomalous transport in the pedestal region is important for the development of a comprehensive model for the H-mode pedestal slope. It was found that the electron thermal anomalous diffusivities at the pedestal top increase with the electron collisionality. This dependence can point to the DRIBM as the modes that drive the anomalous transport in the plasma edge of highly collisional discharges. The effects of plasma shaping on the H-mode pedestal structure was also investigated. The differences in the predicted H-mode pedestal width and height for the DIII-D discharges with different elongation and triangularities were discussed. For the discharges with higher elongation, it was found that the gradients of the plasma profiles in the H-mode pedestal reach semi-steady states. In these simulations, the pedestal slowly continued to evolve to higher pedestal pressures and bootstrap currents until the peeling ballooning stability conditions were satisfied. The discharges with lower elongation do not reach the semi-steady state, and ELM crashes were triggered at earlier times. The plasma elongation was found to have a stronger stabilizing effect than the plasma triangularity. For the discharges with lower elongation and lower triangularity, the ELM frequency was large, and the H-mode pedestal evolves rapidly. It was found that the temperature of neutrals in the scrape-off-layer region can affect the dynamics of the H-mode pedestal buildup. However, the final pedestal profiles were nearly independent of the neutral temperature. The elongation and triangularity affected the pedestal widths of plasma density and electron temperature profiles differently. This study illustrated a new mechanism for controlling the pedestal bootstrap current and the pedestal stability.« less

Flow instabilities of magnetic flux tubes. IV. Flux storage in the solar overshoot region

NASA Astrophysics Data System (ADS)

Işık, E.; Holzwarth, V.

2009-12-01

Context: Flow-induced instabilities of magnetic flux tubes are relevant to the storage of magnetic flux in the interiors of stars with outer convection zones. The stability of magnetic fields in stellar interiors is of importance to the generation and transport of solar and stellar magnetic fields. Aims: We consider the effects of material flows on the dynamics of toroidal magnetic flux tubes located close to the base of the solar convection zone, initially within the overshoot region. The problem is to find the physical conditions in which magnetic flux can be stored for periods comparable to the dynamo amplification time, which is of the order of a few years. Methods: We carry out nonlinear numerical simulations to investigate the stability and dynamics of thin flux tubes subject to perpendicular and longitudinal flows. We compare the simulations with the results of simplified analytical approximations. Results: The longitudinal flow instability induced by the aerodynamic drag force is nonlinear in the sense that the growth rate depends on the perturbation amplitude. This result is consistent with the predictions of linear theory. Numerical simulations without friction show that nonlinear Parker instability can be triggered below the linear threshold of the field strength, when the difference in superadiabaticity along the tube is sufficiently large. A localised downflow acting on a toroidal tube in the overshoot region leads to instability depending on the parameters describing the flow, as well as the magnetic field strength. We determined ranges of the flow parameters for which a linearly Parker-stable magnetic flux tube is stored in the middle of the overshoot region for a period comparable to the dynamo amplification time. Conclusions: The longitudinal flow instability driven by frictional interaction of a flux tube with its surroundings is relevant to determining the storage time of magnetic flux in the solar overshoot region. The residence time for magnetic flux tubes with 2 × 1021 Mx in the convective overshoot layer can be comparable to the dynamo amplification time, provided that the average speed and the duration of an external downflow do not exceed about 50 m s -1 and 100 days, respectively, and that the lateral extension of the flow is smaller than about 10°. Appendix C and movies are only available in electronic form at http://www.aanda.org

Convection and reaction in a diffusive boundary layer in a porous medium: nonlinear dynamics.

PubMed

Andres, Jeanne Therese H; Cardoso, Silvana S S

2012-09-01

We study numerically the nonlinear interactions between chemical reaction and convective fingering in a diffusive boundary layer in a porous medium. The reaction enhances stability by consuming a solute that is unstably distributed in a gravitational field. We show that chemical reaction profoundly changes the dynamics of the system, by introducing a steady state, shortening the evolution time, and altering the spatial patterns of velocity and concentration of solute. In the presence of weak reaction, finger growth and merger occur effectively, driving strong convective currents in a thick layer of solute. However, as the reaction becomes stronger, finger growth is inhibited, tip-splitting is enhanced and the layer of solute becomes much thinner. Convection enhances the mass flux of solute consumed by reaction in the boundary layer but has a diminishing effect as reaction strength increases. This nonlinear behavior has striking differences to the density fingering of traveling reaction fronts, for which stronger chemical kinetics result in more effective finger merger owing to an increase in the speed of the front. In a boundary layer, a strong stabilizing effect of reaction can maintain a long-term state of convection in isolated fingers of wavelength comparable to that at onset of instability.

Flux cutting in high- T c superconductors

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

Vlasko-Vlasov, V.; Koshelev, A.; Glatz, A.

We performed magneto-optical study of flux distributions in a YBCO crystal under various applied crossed- field orientations to elucidate the complex nature of magnetic flux cutting in superconductors. Our study reveals unusual vortex patterns induced by the interplay between flux-cutting and vortex pinning. We observe strong flux penetration anisotropy of the normal flux B⊥ in the presence of an in-plane field H|| and associate the modified flux dynamics with staircase structure of tilted vortices in YBCO and the flux-cutting process. We demonstrate that flux-cutting can effectively delay vortex entry in the direction transverse to H||. Finally, we elucidate details ofmore » the vortex-cutting and reconnection process using time-dependent Ginzburg-Landau simulations.« less

Heat-Flux Measurements in Laser-Produced Plasmas Using Thomson Scattering from Electron Plasma Waves

NASA Astrophysics Data System (ADS)

Henchen, R. J.; Goncharov, V. N.; Cao, D.; Katz, J.; Froula, D. H.; Rozmus, W.

2017-10-01

An experiment was designed to measure heat flux in coronal plasmas using collective Thomson scattering. Adjustments to the electron distribution function resulting from heat flux affect the shape of the collective Thomson scattering features through wave-particle resonance. The amplitude of the Spitzer-Härm electron distribution function correction term (f1) was varied to match the data and determines the value of the heat flux. Independent measurements of temperature and density obtained from Thomson scattering were used to infer the classical heat flux (q = - κ∇Te) . Time-resolved Thomson-scattering data were obtained at five locations in the corona along the target normal in a blowoff plasma formed from a planar Al target with 1.5 kJ of 351-nm laser light in a 2-ns square pulse. The flux measured through the Thomson-scattering spectra is a factor of 5 less than the κ∇Te measurements. The lack of collisions of heat-carrying electrons suggests a nonlocal model is needed to accurately describe the heat flux. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Distributed Sensible Heat Flux Measurements for Wireless Sensor Networks

NASA Astrophysics Data System (ADS)

Huwald, H.; Brauchli, T.; Lehning, M.; Higgins, C. W.

2015-12-01

The sensible heat flux component of the surface energy balance is typically computed using eddy covariance or two point profile measurements while alternative approaches such as the flux variance method based on convective scaling has been much less explored and applied. Flux variance (FV) certainly has a few limitations and constraints but may be an interesting and competitive method in low-cost and power limited wireless sensor networks (WSN) with the advantage of providing spatio-temporal sensible heat flux over the domain of the network. In a first step, parameters such as sampling frequency, sensor response time, and averaging interval are investigated. Then we explore the applicability and the potential of the FV method for use in WSN in a field experiment. Low-cost sensor systems are tested and compared against reference instruments (3D sonic anemometers) to evaluate the performance and limitations of the sensors as well as the method with respect to the standard calculations. Comparison experiments were carried out at several sites to gauge the flux measurements over different surface types (gravel, grass, water) from the low-cost systems. This study should also serve as an example of spatially distributed sensible heat flux measurements.

The Distribution and Behaviour of Photospheric Magnetic Features

NASA Astrophysics Data System (ADS)

Parnell, C. E.; Lamb, D. A.; DeForest, C. E.

2014-12-01

Over the past two decades enormous amounts of data on the magnetic fields of the solar photosphere have been produced by both ground-based (Kitt Peak & SOLIS), as well as space-based instruments (MDI, Hinode & HMI). In order to study the behaviour and distribution of photospheric magnetic features, efficient automated detection routines need to be utilised to identify and track magnetic features. In this talk, I will discuss the pros and cons of different automated magnetic feature identification and tracking routines with a special focus on the requirements of these codes to deal with the large data sets produced by HMI. By patching together results from Hinode and MDI (high-res & full-disk), the fluxes of magnetic features were found to follow a power-law over 5 orders of magnitude. At the strong flux tail of this distribution, the power law was found to fall off at solar minimum, but was maintained over all fluxes during solar maximum. However, the point of deflection in the power-law distribution occurs at a patching point between instruments and so questions remain over the reasons for the deflection. The feature fluxes determined from the superb high-resolution HMI data covers almost all of the 5 orders of magnitude. Considering both solar mimimum and solar maximum HMI data sets, we investigate whether the power-law over 5 orders of magnitude in flux still holds. Furthermore, we investigate the behaviour of magnetic features in order to probe the nature of their origin. In particular, we analyse small-scale flux emergence events using HMI data to investigate the existence of a small-scale dynamo just below the solar photosphere.

Methane exchange at the peatland forest floor - automatic chamber system exposes the dynamics of small fluxes

NASA Astrophysics Data System (ADS)

Korkiakoski, Mika; Tuovinen, Juha-Pekka; Aurela, Mika; Koskinen, Markku; Minkkinen, Kari; Ojanen, Paavo; Penttilä, Timo; Rainne, Juuso; Laurila, Tuomas; Lohila, Annalea

2017-04-01

We measured methane (CH4) exchange rates with automatic chambers at the forest floor of a nutrient-rich drained peatland in 2011-2013. The fen, located in southern Finland, was drained for forestry in 1969 and the tree stand is now a mixture of Scots pine, Norway spruce, and pubescent birch. Our measurement system consisted of six transparent chambers and stainless steel frames, positioned on a number of different field and moss layer compositions. Gas concentrations were measured with an online cavity ring-down spectroscopy gas analyzer. Fluxes were calculated with both linear and exponential regression. The use of linear regression resulted in systematically smaller CH4 fluxes by 10-45 % as compared to exponential regression. However, the use of exponential regression with small fluxes ( < 2.5 µg CH4 m-2 h-1) typically resulted in anomalously large absolute fluxes and high hour-to-hour deviations. Therefore, we recommend that fluxes are initially calculated with linear regression to determine the threshold for low fluxes and that higher fluxes are then recalculated using exponential regression. The exponential flux was clearly affected by the length of the fitting period when this period was < 190 s, but stabilized with longer periods. Thus, we also recommend the use of a fitting period of several minutes to stabilize the results and decrease the flux detection limit. There were clear seasonal dynamics in the CH4 flux: the forest floor acted as a CH4 sink particularly from early summer until the end of the year, while in late winter the flux was very small and fluctuated around zero. However, the magnitude of fluxes was relatively small throughout the year, ranging mainly from -130 to +100 µg CH4 m-2 h-1. CH4 emission peaks were observed occasionally, mostly in summer during heavy rainfall events. Diurnal variation, showing a lower CH4 uptake rate during the daytime, was observed in all of the chambers, mainly in the summer and late spring, particularly in dry conditions. It was attributed more to changes in wind speed than air or soil temperature, which suggest that physical rather than biological phenomena are responsible for the observed variation. The annual net CH4 exchange varied from -104 ± 30 to -505 ± 39 mg CH4 m-2 yr-1 among the six chambers, with an average of -219 mg CH4 m-2 yr-1 over the 2-year measurement period.

Broadening of the divertor heat flux footprint with increasing number of ELM filaments in NSTX

NASA Astrophysics Data System (ADS)

Ahn, Joon-Wook

2014-10-01

We report on the broadening (narrowing) of the ELM heat flux footprint with increasing (decreasing) number of filamentary striations from in-depth thermography measurements in NSTX. Edge localized modes (ELMs) represent a challenge to future fusion devices, due to the high heat fluxes on plasma facing surfaces. One ameliorating factor has been that the divertor heat flux characteristic profile width (λq) has been observed to broaden with the size of ELM, as compared with the inter-ELM λq, which keeps the peak heat flux (qpeak) from increasing. In contrast, λq has been observed to narrow during ELMs under certain conditions in NSTX, for both naturally occurring and 3-D fields triggered ELMs. Fast thermographic measurements and detailed analysis demonstrate that the ELM λq increases with the number of observed filamentary striations, i . e . , profile narrowing (broadening) occurs when the number of striations is smaller (larger) than 3-4. With profile narrowing, qpeak at ELM peak times is inversely related (proportional) to λq (the ELM size), exacerbating the heat flux problem. Edge stability analysis shows that NSTX ELMs almost always lie on the current-driven kink/peeling mode side with low toroidal mode number (n = 1--5), consistent with the typical numbers of striations in NSTX (0-8) in comparison 10--15 striations are normally observed in intermediate-n peeling-ballooning ELMs, e.g., from JET. The NSTX characteristics may translate directly to ITER, which is also projected to lie on the low-n kink/peeling stability boundary. This work was supported by the U.S. DOE, Contract DE-AC05-00OR22725 (ORNL) and DE-AC02-09CH11466 (PPPL).

Zircons reveal magma fluxes in the Earth's crust.

PubMed

Caricchi, Luca; Simpson, Guy; Schaltegger, Urs

2014-07-24

Magma fluxes regulate the planetary thermal budget, the growth of continents and the frequency and magnitude of volcanic eruptions, and play a part in the genesis and size of magmatic ore deposits. However, because a large fraction of the magma produced on the Earth does not erupt at the surface, determinations of magma fluxes are rare and this compromises our ability to establish a link between global heat transfer and large-scale geological processes. Here we show that age distributions of zircons, a mineral often present in crustal magmatic rocks, in combination with thermal modelling, provide an accurate means of retrieving magma fluxes. The characteristics of zircon age populations vary significantly and systematically as a function of the flux and total volume of magma accumulated in the Earth's crust. Our approach produces results that are consistent with independent determinations of magma fluxes and volumes of magmatic systems. Analysis of existing age population data sets using our method suggests that porphyry-type deposits, plutons and large eruptions each require magma input over different timescales at different characteristic average fluxes. We anticipate that more extensive and complete magma flux data sets will serve to clarify the control that the global heat flux exerts on the frequency of geological events such as volcanic eruptions, and to determine the main factors controlling the distribution of resources on our planet.

Tracking dust deposition around the North Pacific Gyre over the past 500kyr

NASA Astrophysics Data System (ADS)

Costa, K.; McManus, J. F.; Winckler, G.; Anderson, R. F.; Middleton, J. L.; Mukhopadhyay, S.

2017-12-01

Across the North Pacific, dust delivery and distribution depends on atmospheric transport and precipitation, and dust fluxes generally decrease with distance away from the Asian continent. While it is well established that dust fluxes vary on glacial-interglacial timescales, how the dust distribution from the source to the sediment may have evolved is poorly constrained, largely due to a lack of long dust flux records from this region. Here we reconstruct dust flux variability from six piston cores on the Juan de Fuca Ridge in the Northeastern Pacific over the past 500kyr using 232Th as a lithogenic tracer and 230Th normalization to calculate fluxes. Minimal spatial variability between the six cores allows the compilation of a single regional dust flux stack. Dust fluxes vary by a factor of two between glacial, high-dust flux, and interglacial, low-dust flux periods, consistent with global patterns. Interglacial periods MIS7 and MIS9 dust fluxes remain relatively high compared to the adjacent glacial periods MIS6 and MIS 8 so that dust fluxes are fairly constant (3.3±0.6 ug 232Th/cm2kyr) from 135-335ka, excepting the high-lithogenic feature at 272ka (turbidite). Dust fluxes may be highest in MIS10 (6.0 ug 232Th/cm2kyr) than more recent glacial periods, for example MIS2 (3.9 ug 232Th/cm2kyr). Five multicores add high-resolution data for the last 30kyr. We compare these new records from the Northeast Pacific with dust flux records from the Northwest Pacific and the Equatorial Pacific to better constrain how dust deposition varied at different locations around the North Pacific Gyre on glacial-interglacial timescales.

Metabolic analysis of adaptive evolution for in silico-designed lactate-producing strains.

PubMed

Hua, Qiang; Joyce, Andrew R; Fong, Stephen S; Palsson, Bernhard Ø

2006-12-05

Experimental evolution is now frequently applied to many biological systems to achieve desired objectives. To obtain optimized performance for metabolite production, a successful strategy has been recently developed that couples metabolic engineering techniques with laboratory evolution of microorganisms. Previously, we reported the growth characteristics of three lactate-producing, adaptively evolved Escherichia coli mutant strains designed by the OptKnock computational algorithm. Here, we describe the use of (13)C-labeled experiments and mass distribution measurements to study the evolutionary effects on the fluxome of these differently designed strains. Metabolic flux ratios and intracellular flux distributions as well as physiological data were used to elucidate metabolic responses over the course of adaptive evolution and metabolic differences among strains. The study of 3 unevolved and 12 evolved engineered strains as well as a wild-type strain suggests that evolution resulted in remarkable improvements in both substrate utilization rate and the proportion of glycolytic flux to total glucose utilization flux. Among three strain designs, the most significant increases in the fraction of glucose catabolized through glycolysis (>50%) and the glycolytic fluxes (>twofold) were observed in phosphotransacetylase and phosphofructokinase 1 (PFK1) double deletion (pta- pfkA) strains, which were likely attributed to the dramatic evolutionary increase in gene expression and catalytic activity of the minor PFK encoded by pfkB. These fluxomic studies also revealed the important role of acetate synthetic pathway in anaerobic lactate production. Moreover, flux analysis suggested that independent of genetic background, optimal relative flux distributions in cells could be achieved faster than physiological parameters such as nutrient utilization rate. (c) 2006 Wiley Periodicals, Inc.

Conservation of high-flux backbone in alternate optimal and near-optimal flux distributions of metabolic networks.

PubMed

Samal, Areejit

2008-12-01

Constraint-based flux balance analysis (FBA) has proven successful in predicting the flux distribution of metabolic networks in diverse environmental conditions. FBA finds one of the alternate optimal solutions that maximizes the biomass production rate. Almaas et al. have shown that the flux distribution follows a power law, and it is possible to associate with most metabolites two reactions which maximally produce and consume a given metabolite, respectively. This observation led to the concept of high-flux backbone (HFB) in metabolic networks. In previous work, the HFB has been computed using a particular optima obtained using FBA. In this paper, we investigate the conservation of HFB of a particular solution for a given medium across different alternate optima and near-optima in metabolic networks of E. coli and S. cerevisiae. Using flux variability analysis (FVA), we propose a method to determine reactions that are guaranteed to be in HFB regardless of alternate solutions. We find that the HFB of a particular optima is largely conserved across alternate optima in E. coli, while it is only moderately conserved in S. cerevisiae. However, the HFB of a particular near-optima shows a large variation across alternate near-optima in both organisms. We show that the conserved set of reactions in HFB across alternate near-optima has a large overlap with essential reactions and reactions which are both uniquely consuming (UC) and uniquely producing (UP). Our findings suggest that the structure of the metabolic network admits a high degree of redundancy and plasticity in near-optimal flow patterns enhancing system robustness for a given environmental condition.

Quantifying Carbon Flux Estimation Errors

NASA Astrophysics Data System (ADS)

Wesloh, D.

2017-12-01

Atmospheric Bayesian inversions have been used to estimate surface carbon dioxide (CO2) fluxes from global to sub-continental scales using atmospheric mixing ratio measurements. These inversions use an atmospheric transport model, coupled to a set of fluxes, in order to simulate mixing ratios that can then be compared to the observations. The comparison is then used to update the fluxes to better match the observations in a manner consistent with the uncertainties prescribed for each. However, inversion studies disagree with each other at continental scales, prompting further investigations to examine the causes of these differences. Inter-comparison studies have shown that the errors resulting from atmospheric transport inaccuracies are comparable to those from the errors in the prior fluxes. However, not as much effort has gone into studying the origins of the errors induced by errors in the transport as by errors in the prior distribution. This study uses a mesoscale transport model to evaluate the effects of representation errors in the observations and of incorrect descriptions of the transport. To obtain realizations of these errors, we performed an Observing System Simulation Experiments (OSSEs), with the transport model used for the inversion operating at two resolutions, one typical of a global inversion and the other of a mesoscale, and with various prior flux distributions to. Transport error covariances are inferred from an ensemble of perturbed mesoscale simulations while flux error covariances are computed using prescribed distributions and magnitudes. We examine how these errors can be diagnosed in the inversion process using aircraft, ground-based, and satellite observations of meteorological variables and CO2.

Leonid Storm Flux Analysis From One Leonid MAC Video AL50R

NASA Technical Reports Server (NTRS)

Gural, Peter S.; Jenniskens, Peter; DeVincenzi, Donald L. (Technical Monitor)

2000-01-01

A detailed meteor flux analysis is presented of a seventeen-minute portion of one videotape, collected on November 18, 1999, during the Leonid Multi-instrument Aircraft Campaign. The data was recorded around the peak of the Leonid meteor storm using an intensified CCD camera pointed towards the low southern horizon. Positions of meteors on the sky were measured. These measured meteor distributions were compared to a Monte Carlo simulation, which is a new approach to parameter estimation for mass ratio and flux. Comparison of simulated flux versus observed flux levels, seen between 1:50:00 and 2:06:41 UT, indicate a magnitude population index of r = 1.8 +/- 0.1 and mass ratio of s = 1.64 +/- 0.06. The average spatial density of the material contributing to the Leonid storm peak is measured at 0.82 +/- 0.19 particles per square kilometer per hour for particles of at least absolute visual magnitude +6.5. Clustering analysis of the arrival times of Leonids impacting the earth's atmosphere over the total observing interval shows no enhancement or clumping down to time scales of the video frame rate. This indicates a uniformly random temporal distribution of particles in the stream encountered during the 1999 epoch. Based on the observed distribution of meteors on the sky and the model distribution, recommendations am made for the optimal pointing directions for video camera meteor counts during future ground and airborne missions.

Global stability and exact solution of an arbitrary-solute nonlinear cellular mass transport system.

PubMed

Benson, James D

2014-12-01

The prediction of the cellular state as a function of extracellular concentrations and temperatures has been of interest to physiologists for nearly a century. One of the most widely used models in the field is one where mass flux is linearly proportional to the concentration difference across the membrane. These fluxes define a nonlinear differential equation system for the intracellular state, which when coupled with appropriate initial conditions, define the intracellular state as a function of the extracellular concentrations of both permeating and nonpermeating solutes. Here we take advantage of a reparametrization scheme to extend existing stability results to a more general setting and to a develop analytical solutions to this model for an arbitrary number of extracellular solutes. Copyright © 2014 Elsevier Inc. All rights reserved.

Real time PI-backstepping induction machine drive with efficiency optimization.

PubMed

Farhani, Fethi; Ben Regaya, Chiheb; Zaafouri, Abderrahmen; Chaari, Abdelkader

2017-09-01

This paper describes a robust and efficient speed control of a three phase induction machine (IM) subjected to load disturbances. First, a Multiple-Input Multiple-Output (MIMO) PI-Backstepping controller is proposed for a robust and highly accurate tracking of the mechanical speed and rotor flux. Asymptotic stability of the control scheme is proven by Lyapunov Stability Theory. Second, an active online optimization algorithm is used to optimize the efficiency of the drive system. The efficiency improvement approach consists of adjusting the rotor flux with respect to the load torque in order to minimize total losses in the IM. A dSPACE DS1104 R&D board is used to implement the proposed solution. The experimental results released on 3kW squirrel cage IM, show that the reference speed as well as the rotor flux are rapidly achieved with a fast transient response and without overshoot. A good load disturbances rejection response and IM parameters variation are fairly handled. The improvement of drive system efficiency reaches up to 180% at light load. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.

Numerical flux formulas for the Euler and Navier-Stokes equations. 2: Progress in flux-vector splitting

NASA Technical Reports Server (NTRS)

Coirier, William J.; Vanleer, Bram

1991-01-01

The accuracy of various numerical flux functions for the inviscid fluxes when used for Navier-Stokes computations is studied. The flux functions are benchmarked for solutions of the viscous, hypersonic flow past a 10 degree cone at zero angle of attack using first order, upwind spatial differencing. The Harten-Lax/Roe flux is found to give a good boundary layer representation, although its robustness is an issue. Some hybrid flux formulas, where the concepts of flux-vector and flux-difference splitting are combined, are shown to give unsatisfactory pressure distributions; there is still room for improvement. Investigations of low diffusion, pure flux-vector splittings indicate that a pure flux-vector splitting can be developed that eliminates spurious diffusion across the boundary layer. The resulting first-order scheme is marginally stable and not monotone.

On the intrinsic shape of the gamma-ray spectrum for Fermi blazars

NASA Astrophysics Data System (ADS)

Kang, Shi-Ju; Wu, Qingwen; Zheng, Yong-Gang; Yin, Yue; Song, Jia-Li; Zou, Hang; Feng, Jian-Chao; Dong, Ai-Jun; Wu, Zhong-Zu; Zhang, Zhi-Bin; Wu, Lin-Hui

2018-05-01

The curvature of the γ-ray spectrumin blazarsmay reflect the intrinsic distribution of emitting electrons, which will further give some information on the possible acceleration and cooling processes in the emitting region. The γ-ray spectra of Fermi blazars are normally fitted either by a single power-law (PL) or a log-normal (call Logarithmic Parabola, LP) form. The possible reason for this difference is not clear. We statistically explore this issue based on the different observational properties of 1419 Fermi blazars in the 3LAC Clean Sample.We find that the γ-ray flux (100MeV–100GeV) and variability index follow bimodal distributions for PL and LP blazars, where the γ-ray flux and variability index show a positive correlation. However, the distributions of γ-ray luminosity and redshift follow a unimodal distribution. Our results suggest that the bimodal distribution of γ-ray fluxes for LP and PL blazars may not be intrinsic and all blazars may have an intrinsically curved γ-ray spectrum, and the PL spectrum is just caused by the fitting effect due to less photons.

Geometrical correction factors for heat flux meters

NASA Technical Reports Server (NTRS)

Baumeister, K. J.; Papell, S. S.

1974-01-01

General formulas are derived for determining gage averaging errors of strip-type heat flux meters used in the measurement of one-dimensional heat flux distributions. The local averaging error e(x) is defined as the difference between the measured value of the heat flux and the local value which occurs at the center of the gage. In terms of e(x), a correction procedure is presented which allows a better estimate for the true value of the local heat flux. For many practical problems, it is possible to use relatively large gages to obtain acceptable heat flux measurements.

A single-stage flux-corrected transport algorithm for high-order finite-volume methods

DOE PAGES

Chaplin, Christopher; Colella, Phillip

2017-05-08

We present a new limiter method for solving the advection equation using a high-order, finite-volume discretization. The limiter is based on the flux-corrected transport algorithm. Here, we modify the classical algorithm by introducing a new computation for solution bounds at smooth extrema, as well as improving the preconstraint on the high-order fluxes. We compute the high-order fluxes via a method-of-lines approach with fourth-order Runge-Kutta as the time integrator. For computing low-order fluxes, we select the corner-transport upwind method due to its improved stability over donor-cell upwind. Several spatial differencing schemes are investigated for the high-order flux computation, including centered- differencemore » and upwind schemes. We show that the upwind schemes perform well on account of the dissipation of high-wavenumber components. The new limiter method retains high-order accuracy for smooth solutions and accurately captures fronts in discontinuous solutions. Further, we need only apply the limiter once per complete time step.« less

Carbon and energy fluxes from China's largest freshwater lake

NASA Astrophysics Data System (ADS)

Gan, G.; LIU, Y.

2017-12-01

Carbon and energy fluxes between lakes and the atmosphere are important aspects of hydrology, limnology, and ecology studies. China's largest freshwater lake, the Poyang lake experiences tremendous water-land transitions periodically throughout the year, which provides natural experimental settings for the study of carbon and energy fluxes. In this study, we use the eddy covariance technique to explore the seasonal and diurnal variation patterns of sensible and latent heat fluxes of Poyang lake during its high-water and low-water periods, when the lake is covered by water and mudflat, respectively. We also determine the annual NEE of Poyang lake and the variations of NEE's components: Gross Primary Productivity (GPP) and Ecosystem Respiration (Re). Controlling factors of seasonal and diurnal variations of carbon and energy fluxes are analyzed, and land cover impacts on the variation patterns are also studied. Finally, the coupling between the carbon and energy fluxes are analyzed under different atmospheric, boundary stability and land cover conditions.

Effects of variations of stage and flux at different frequencies on the estimates using river stage tomography

NASA Astrophysics Data System (ADS)

Wang, Y. L.; Yeh, T. C. J.; Wen, J. C.

2017-12-01

This study is to investigate the ability of river stage tomography to estimate the spatial distribution of hydraulic transmissivity (T), storage coefficient (S), and diffusivity (D) in groundwater basins using information of groundwater level variations induced by periodic variations of stream stage, and infiltrated flux from the stream boundary. In order to accomplish this objective, the sensitivity and correlation of groundwater heads with respect to the hydraulic properties is first conducted to investigate the spatial characteristics of groundwater level in response to the stream variations at different frequencies. Results of the analysis show that the spatial distributions of the sensitivity of heads at an observation well in response to periodic river stage variations are highly correlated despite different frequencies. On the other hand, the spatial patterns of the sensitivity of the observed head to river flux boundaries at different frequencies are different. Specifically, the observed head is highly correlated with T at the region between the stream and observation well when the high-frequency periodic flux is considered. On the other hand, it is highly correlated with T at the region between monitoring well and the boundary opposite to the stream when the low-frequency periodic flux is prescribed to the stream. We also find that the spatial distributions of the sensitivity of observed head to S variation are highly correlated with all frequencies in spite of heads or fluxes stream boundary. Subsequently, the differences of the spatial correlations of the observed heads to the hydraulic properties under the head and flux boundary conditions are further investigated by an inverse model (i.e., successive stochastic linear estimator). This investigation uses noise-free groundwater and stream data of a synthetic aquifer, where aquifer heterogeneity is known exactly. The ability of river stage tomography is then tested with these synthetic data sets to estimate T, S, and D distribution. The results reveal that boundary flux variations with different frequencies contain different information about the aquifer characteristics while the head boundary does not.

Low resolution ultraviolet and optical spectrophotometry of symbiotic stars

NASA Technical Reports Server (NTRS)

Slovak, M. H.

1982-01-01

Low resolution International Ultraviolet Explorer spectra combined with optical spectrophotometry provide absolute flux distributions for seven symbiotic variables from 1200 to 6450 A. For five stars (EG And, BF Cyg, CI Cyg, AG Peg, and Z And) the data are representative of the quiescent/out-of-eclipse energy distributions; for CH Cyg and AX Per, the observations were obtained following their atest outburst in 1977 and 1978, respectively. The de-reddened distributions reveal a remarkable diversity of both line spectra and continua. While the optical and near infrared regions lambda = 5500 A) are well represented by single component stellar models, multicomponent flux distributions are required to reproduce the ultraviolet continua.

Quasi-static and dynamic magnetic tension forces in arched, line-tied magnetic flux ropes

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

Myers, C. E.; Yamada, M.; Ji, H.

Solar eruptions are often driven by magnetohydrodynamic instabilities such as the torus and kink instabilities that act on line-tied magnetic flux ropes. We designed our recent laboratory experiments to study these eruptive instabilities which have demonstrated the key role of both dynamic (Myers et al 2015 Nature 528 526) and quasi-static (Myers et al 2016 Phys. Plasmas 23 112102) magnetic tension forces in contributing to the equilibrium and stability of line-tied magnetic flux ropes. In our paper, we synthesize these laboratory results and explore the relationship between the dynamic and quasi-static tension forces. And while the quasi-static tension force ismore » found to contribute to the flux rope equilibrium in a number of regimes, the dynamic tension force is substantial mostly in the so-called failed torus regime where magnetic self-organization events prevent the flux rope from erupting.« less

Quasi-static and dynamic magnetic tension forces in arched, line-tied magnetic flux ropes

DOE PAGES

Myers, C. E.; Yamada, M.; Ji, H.; ...

2016-11-22

Solar eruptions are often driven by magnetohydrodynamic instabilities such as the torus and kink instabilities that act on line-tied magnetic flux ropes. We designed our recent laboratory experiments to study these eruptive instabilities which have demonstrated the key role of both dynamic (Myers et al 2015 Nature 528 526) and quasi-static (Myers et al 2016 Phys. Plasmas 23 112102) magnetic tension forces in contributing to the equilibrium and stability of line-tied magnetic flux ropes. In our paper, we synthesize these laboratory results and explore the relationship between the dynamic and quasi-static tension forces. And while the quasi-static tension force ismore » found to contribute to the flux rope equilibrium in a number of regimes, the dynamic tension force is substantial mostly in the so-called failed torus regime where magnetic self-organization events prevent the flux rope from erupting.« less

A simplified computational fluid-dynamic approach to the oxidizer injector design in hybrid rockets

NASA Astrophysics Data System (ADS)

Di Martino, Giuseppe D.; Malgieri, Paolo; Carmicino, Carmine; Savino, Raffaele

2016-12-01

Fuel regression rate in hybrid rockets is non-negligibly affected by the oxidizer injection pattern. In this paper a simplified computational approach developed in an attempt to optimize the oxidizer injector design is discussed. Numerical simulations of the thermo-fluid-dynamic field in a hybrid rocket are carried out, with a commercial solver, to investigate into several injection configurations with the aim of increasing the fuel regression rate and minimizing the consumption unevenness, but still favoring the establishment of flow recirculation at the motor head end, which is generated with an axial nozzle injector and has been demonstrated to promote combustion stability, and both larger efficiency and regression rate. All the computations have been performed on the configuration of a lab-scale hybrid rocket motor available at the propulsion laboratory of the University of Naples with typical operating conditions. After a preliminary comparison between the two baseline limiting cases of an axial subsonic nozzle injector and a uniform injection through the prechamber, a parametric analysis has been carried out by varying the oxidizer jet flow divergence angle, as well as the grain port diameter and the oxidizer mass flux to study the effect of the flow divergence on heat transfer distribution over the fuel surface. Some experimental firing test data are presented, and, under the hypothesis that fuel regression rate and surface heat flux are proportional, the measured fuel consumption axial profiles are compared with the predicted surface heat flux showing fairly good agreement, which allowed validating the employed design approach. Finally an optimized injector design is proposed.

NIR-Driven Moist Upper Atmospheres of Synchronously Rotating Temperate Terrestrial Exoplanets

NASA Technical Reports Server (NTRS)

Fujii, Yuka; Del Genio, Anthony D.; Amundsen, David S.

2017-01-01

H2O is a key molecule in characterizing atmospheres of temperate terrestrial planets, and observations of transmission spectra are expected to play a primary role in detecting its signatures in the near future. The detectability of H2O absorption features in transmission spectra depends on the abundance of water vapor in the upper part of the atmosphere. We study the three-dimensional distribution of atmospheric H2O for synchronously rotating Earth-sized aquaplanets using the general circulation model (GCM) ROCKE-3D, and examine the effects of total incident flux and stellar spectral type. We observe a more gentle increase of the water vapor mixing ratio in response to increased incident flux than one-dimensional models suggest, in qualitative agreement with the climate-stabilizing effect of clouds around the substellar point previously observed in GCMs applied to synchronously rotating planets. However, the water vapor mixing ratio in the upper atmosphere starts to increase while the surface temperature is still moderate. This is explained by the circulation in the upper atmosphere being driven by the radiative heating due to absorption by water vapor and cloud particles, causing efficient vertical transport of water vapor. Consistently, the water vapor mixing ratio is found to be well-correlated with the near-infrared portion of the incident flux. We also simulate transmission spectra based on the GCM outputs, and show that for the more highly irradiated planets, the H2O signatures may be strengthened by a factor of a few, loosening the observational demands for a H2O detection.

Fine root mercury heterogeneity: metabolism of lower-order roots as an effective route for mercury removal.

PubMed

Wang, Jun-Jian; Guo, Ying-Ying; Guo, Da-Li; Yin, Sen-Lu; Kong, De-Liang; Liu, Yang-Sheng; Zeng, Hui

2012-01-17

Fine roots are critical components for plant mercury (Hg) uptake and removal, but the patterns of Hg distribution and turnover within the heterogeneous fine root components and their potential limiting factors are poorly understood. Based on root branching structure, we studied the total Hg (THg) and its cellular partitioning in fine roots in 6 Chinese subtropical trees species and the impacts of root morphological and stoichiometric traits on Hg partitioning. The THg concentration generally decreased with increasing root order, and was higher in cortex than in stele. This concentration significantly correlated with root length, diameter, specific root length, specific root area, and nitrogen concentration, whereas its cytosolic fraction (accounting for <10% of THg) correlated with root carbon and sulfur concentrations. The estimated Hg return flux from dead fine roots outweighed that from leaf litter, and ephemeral first-order roots that constituted 7.2-22.3% of total fine root biomass may have contributed most to this flux (39-71%, depending on tree species and environmental substrate). Our results highlight the high capacity of Hg stabilization and Hg return by lower-order roots and demonstrate that turnover of lower-order roots may be an effective strategy of detoxification in perennial tree species.

Sensitivity of the global submarine hydrate inventory to scenarios of future climate change

NASA Astrophysics Data System (ADS)

Hunter, S. J.; Goldobin, D. S.; Haywood, A. M.; Ridgwell, A.; Rees, J. G.

2013-04-01

The global submarine inventory of methane hydrate is thought to be considerable. The stability of marine hydrates is sensitive to changes in temperature and pressure and once destabilised, hydrates release methane into sediments and ocean and potentially into the atmosphere, creating a positive feedback with climate change. Here we present results from a multi-model study investigating how the methane hydrate inventory dynamically responds to different scenarios of future climate and sea level change. The results indicate that a warming-induced reduction is dominant even when assuming rather extreme rates of sea level rise (up to 20 mm yr-1) under moderate warming scenarios (RCP 4.5). Over the next century modelled hydrate dissociation is focussed in the top ˜100m of Arctic and Subarctic sediments beneath <500m water depth. Predicted dissociation rates are particularly sensitive to the modelled vertical hydrate distribution within sediments. Under the worst case business-as-usual scenario (RCP 8.5), upper estimates of resulting global sea-floor methane fluxes could exceed estimates of natural global fluxes by 2100 (>30-50TgCH4yr-1), although subsequent oxidation in the water column could reduce peak atmospheric release rates to 0.75-1.4 Tg CH4 yr-1.

On Heat Loading, Novel Divertors, and Fusion Reactors

NASA Astrophysics Data System (ADS)

Kotschenreuther, Mike

2006-10-01

A new magnetic divertor geometry has been proposed to solve reactor heat exhaust problems, which are far more severe for a reactor than for ITER. Using reactor-compatible coils to generate an extra X-point downstream from the main X-point, the new X-divertor (XD) is shown to greatly expand magnetic flux at the divertor plates. As a result, the heat is distributed over a larger area and the line length is greatly increased. The heat-flux limitations of a standard divertor (SD) force a high core radiation fraction (fRad) in most reactor designs that necessarily have a several times higher ratio of heating power to radius (P/R) than ITER. It is argued that such high values of fRad will probably have serious deleterious consequences on the core confinement and stability of a burning plasma. Operation with internal transport barriers (ITBs) does not appear to overcome this problem. By reducing the core fRad within an acceptable range, the X-divertor is shown to substantially lower the core confinement requirement for a fusion reactor. As a bonus, the XD also enables the use of liquid metals by reducing the MHD drag. A possible series of experiments for an efficient and attractive path to practical fusion power is suggested.

The New Face of FLUXNET: Redesigning the Web Site and Data Organization to Enhance the User Experience

NASA Astrophysics Data System (ADS)

Shanafield, Harold; Shamblin, Stephanie; Devarakonda, Ranjeet; McMurry, Ben; Walker Beaty, Tammy; Wilson, Bruce; Cook, Robert B.

2011-02-01

The FLUXNET global network of regional flux tower networks serves to coordinate the regional and global analysis of eddy covariance based CO2, water vapor and energy flux measurements taken at more than 500 sites in continuous long-term operation. The FLUXNET database presently contains information about the location, characteristics, and data availability of each of these sites. To facilitate the coordination and distribution of this information, we redesigned the underlying database and associated web site. We chose the PostgreSQL database as a platform based on its performance, stability and GIS extensions. PostreSQL allows us to enhance our search and presentation capabilities, which will in turn provide increased functionality for users seeking to understand the FLUXNET data. The redesigned database will also significantly decrease the burden of managing such highly varied data. The website is being developed using the Drupal content management system, which provides many community-developed modules and a robust framework for custom feature development. In parallel, we are working with the regional networks to ensure that the information in the FLUXNET database is identical to that in the regional networks. Going forward, we also plan to develop an automated way to synchronize information with the regional networks.

Studies of a subarctic coastal marsh. III. Modelling the subsurface water fluxes and chloride distribution

NASA Astrophysics Data System (ADS)

Price, Jonathan S.; Woo, Ming-Ko

1990-12-01

A two-dimensional advection dispersion model of solute transport is used to simulate the long-term changes in the chloride distribution of the young isostatically raised beach ridge and depression sequences in a James Bay coastal marsh. The USGS-SUTRA model reproduces the hydraulic conditions in the wetland, causing recharge of freshwater to the ridges and discharge of saline water to the inter-ridge depressions, demonstrating the importance of vertical water fluxes of water and chloride. Even though water velocities are very low, molecular diffusion alone cannot explain the observed chloride distribution. Imposing the characteristics of a frozen surface during winter eliminated the vertical fluxes, and doubled the time required for the simulated chloride distribution to match the field data. The model correctly predicts the observed pattern of suppressed salinity beneath the ridges and a general decrease of salinity with distance inland. The results are useful in understanding the processes which operate in the first 100 years of marsh development.

Experimental results for 2D magnetic resonance electrical impedance tomography (MR-EIT) using magnetic flux density in one direction.

PubMed

Birgül, Ozlem; Eyüboğlu, B Murat; Ider, Y Ziya

2003-11-07

Magnetic resonance electrical impedance tomography (MR-EIT) is an emerging imaging technique that reconstructs conductivity images using magnetic flux density measurements acquired employing MRI together with conventional EIT measurements. In this study, experimental MR-EIT images from phantoms with conducting and insulator objects are presented. The technique is implemented using the 0.15 T Middle East Technical University MRI system. The dc current method used in magnetic resonance current density imaging is adopted. A reconstruction algorithm based on the sensitivity matrix relation between conductivity and only one component of magnetic flux distribution is used. Therefore, the requirement for object rotation is eliminated. Once the relative conductivity distribution is found, it is scaled using the peripheral voltage measurements to obtain the absolute conductivity distribution. Images of several insulator and conductor objects in saline filled phantoms are reconstructed. The L2 norm of relative error in conductivity values is found to be 13%, 17% and 14% for three different conductivity distributions.

Lévy noise improves the electrical activity in a neuron under electromagnetic radiation.

PubMed

Wu, Juan; Xu, Yong; Ma, Jun

2017-01-01

As the fluctuations of the internal bioelectricity of nervous system is various and complex, the external electromagnetic radiation induced by magnet flux on membrane can be described by the non-Gaussian type distribution of Lévy noise. Thus, the electrical activities in an improved Hindmarsh-Rose model excited by the external electromagnetic radiation of Lévy noise are investigated and some interesting modes of the electrical activities are exhibited. The external electromagnetic radiation of Lévy noise leads to the mode transition of the electrical activities and spatial phase, such as from the rest state to the firing state, from the spiking state to the spiking state with more spikes, and from the spiking state to the bursting state. Then the time points of the firing state versus Lévy noise intensity are depicted. The increasing of Lévy noise intensity heightens the neuron firing. Also the stationary probability distribution functions of the membrane potential of the neuron induced by the external electromagnetic radiation of Lévy noise with different intensity, stability index and skewness papremeters are analyzed. Moreover, through the positive largest Lyapunov exponent, the parameter regions of chaotic electrical mode of the neuron induced by the external electromagnetic radiation of Lévy noise distribution are detected.

Lévy noise improves the electrical activity in a neuron under electromagnetic radiation

PubMed Central

Wu, Juan; Ma, Jun

2017-01-01

As the fluctuations of the internal bioelectricity of nervous system is various and complex, the external electromagnetic radiation induced by magnet flux on membrane can be described by the non-Gaussian type distribution of Lévy noise. Thus, the electrical activities in an improved Hindmarsh-Rose model excited by the external electromagnetic radiation of Lévy noise are investigated and some interesting modes of the electrical activities are exhibited. The external electromagnetic radiation of Lévy noise leads to the mode transition of the electrical activities and spatial phase, such as from the rest state to the firing state, from the spiking state to the spiking state with more spikes, and from the spiking state to the bursting state. Then the time points of the firing state versus Lévy noise intensity are depicted. The increasing of Lévy noise intensity heightens the neuron firing. Also the stationary probability distribution functions of the membrane potential of the neuron induced by the external electromagnetic radiation of Lévy noise with different intensity, stability index and skewness papremeters are analyzed. Moreover, through the positive largest Lyapunov exponent, the parameter regions of chaotic electrical mode of the neuron induced by the external electromagnetic radiation of Lévy noise distribution are detected. PMID:28358824

RELATIONSHIP BETWEEN DISTRIBUTION OF MAGNETIC DECAY INDEX AND FILAMENT ERUPTIONS

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

Li, H.; Liu, Y.; Elmhamdi, A.

2016-10-20

The decay index n of a horizontal magnetic field is considered to be an important parameter in judging the stability of a flux rope. However, the spatial distribution of this parameter has not been extensively explored so far. In this paper, we present a delineative study of the three-dimensional maps of n for two eruptive events, in which filaments underwent asymmetrical eruptions. The corresponding n -distributions are both found to show that the filaments tend to erupt at abnormal regions (dubbed ABN regions) of n . These ABN regions appear to be divided into two subregions, with larger and smallermore » n . Moreover, an analysis of the magnetic topological configuration of the ABN regions has been also performed. The results indicate that these ABN regions are associated with a kind of special quasi-separatrix layer across which the connectivity of magnetic field is discontinuous. The presented observations and analyses strongly suggest that the torus instability in ABN regions may play a crucial role for the triggering of an asymmetrical eruption. Additionally, our investigation can provide a way of forecasting how a filament might erupt, and predicting the location for an asymmetrically eruptive filament to be split through analyzing the spatial structure of n .« less

Auroral-particle precipitation and trapping caused by electrostatic double layers in the ionosphere.

PubMed

Albert, R D; Lindstrom, P J

1970-12-25

Interpretation of high-resolution angular distribution measurements of the primary auroral electron flux detected by a rocket probe launched into a visible aurora from Fort Churchill in the fall of 1966 leads to the following conclusions. The auroral electron flux is nearly monoenergetic and has a quasi-trapped as well as a precipitating component. The quasi-trapped flux appears to be limited to a region defined by magnetic-mirror points and multiple electrostatic double layers in the ionosphere. The electrostatic field of the double-layer distribution enhances the aurora by lowering the magnetic-mirror points and supplying energy to the primary auroral electrons.

Trapped particle stability for the kinetic stabilizer

NASA Astrophysics Data System (ADS)

Berk, H. L.; Pratt, J.

2011-08-01

A kinetically stabilized axially symmetric tandem mirror (KSTM) uses the momentum flux of low-energy, unconfined particles that sample only the outer end-regions of the mirror plugs, where large favourable field-line curvature exists. The window of operation is determined for achieving magnetohydrodynamic (MHD) stability with tolerable energy drain from the kinetic stabilizer. Then MHD stable systems are analysed for stability of the trapped particle mode. This mode is characterized by the detachment of the central-cell plasma from the kinetic-stabilizer region without inducing field-line bending. Stability of the trapped particle mode is sensitive to the electron connection between the stabilizer and the end plug. It is found that the stability condition for the trapped particle mode is more constraining than the stability condition for the MHD mode, and it is challenging to satisfy the required power constraint. Furthermore, a severe power drain may arise from the necessary connection of low-energy electrons in the kinetic stabilizer to the central region.

Stagnation point properties for non-continuum gaseous jet impinging at a flat plate surface from a planar exit

NASA Astrophysics Data System (ADS)

Cai, Chunpei

2013-10-01

In this paper, we investigate highly rarefied gaseous jet flows out of a planar exit and impinging at a normally set flat plate. Especially, we concentrate on the plate center stagnation point pressure and heat flux coefficients. For a specular reflective plate, the stagnation point pressure coefficient can be represented using two non-dimensional factors: the characteristic gas exit speed ratio S0 and the geometry ratio of H/L, where H is the planar exit semi-height and L is the center-to-center distance from the exit to the plate. For a diffuse reflective plate, the stagnation point pressure and heat flux coefficients involve an extra factor of T0/Tw, i.e., the ratio of exit gas temperature to the plate wall temperature. These results allow us to develop four diagrams, from which we can conveniently obtain the pressure and heat flux coefficients for the stagnation impingement point, at the collisionless flow limit. After normalization with these maximum coefficients, the pressure and heat flux coefficient distributions along the surface essentially degenerate to almost identical curves. As a result, with known plate surface pressure coefficient distributions and these diagrams, we can conveniently construct the heat flux coefficient distributions along the plate surface, and vice versa.

Simulating fluxes from heterogeneous land surfaces: Explicit subgrid method employing the biosphere-atmosphere transfer scheme (BATS)

NASA Technical Reports Server (NTRS)

Seth, Anji; Giorgi, Filippo; Dickinson, Robert E.

1994-01-01

A vectorized version of the biosphere-atmosphere transfer scheme (VBATS) is used to study moisture, energy, and momentum fluxes from heterogeneous land surfaces st the scale of an atmospheric model (AM) grid cells. To incorporate subgrid scale inhomogeneity, VBATS includes two important features: (1) characterization of the land surface (vegetation and soil parameters) at N subgrid points within an AM grid cell and (2) explicit distribution of climate forcing (precipitation, clouds, etc.) over the subgrid. In this study, VBATS is used in stand-alone mode to simulate a single AM grid cell and to evaluate the effects of subgrid scale vegetation and climate specification on the surface fluxes and hydrology. It is found that the partitioning of energy can be affected by up to 30%, runoff by 50%, and surface stress in excess of 60%. Distributing climate forcing over the AM grid cell increases the Bowen ratio, as a result of enhanced sensible heat flux and reduced latent heat flux. The combined effect of heterogeneous vegetation and distribution of climate is found to be dependent on the dominat vegetation class in the AM grid cell. Development of this method is part of a larger program to explore the importance of subgrid scale processes in regional and global climate simulations.

Squeezing of particle distributions by expanding magnetic turbulence and space weather variability

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

Ruffolo, D.; Seripienlert, A.; Tooprakai, P.

Among the space weather effects due to gradual solar storms, greatly enhanced high-energy ion fluxes contribute to radiation damage to satellites, spacecraft, and astronauts and dominate the hazards to air travelers, which motivates examination of the transport of high-energy solar ions to Earth's orbit. Ions of low kinetic energy (up to ∼2 MeV nucleon{sup –1}) from impulsive solar events exhibit abrupt changes due to filamentation of the magnetic connection from the Sun, indicating that anisotropic, field-aligned magnetic flux tubelike structures persist to Earth's orbit. By employing a corresponding spherical two-component model of Alfvénic (slab) and two-dimensional magnetic fluctuations to tracemore » simulated trajectories in the solar wind, we show that the distribution of high-energy (E ≥ 1 GeV) protons from gradual solar events is squeezed toward magnetic flux structures with a specific polarity because of the conical shape of the flux structures. Conical flux structures and the squeezing of energetic particle distributions should occur in any astrophysical wind or jet with expanding, magnetized, turbulent plasma. This transport phenomenon contributes to event-to-event variability in ground level enhancements of GeV-range ions from solar storms, presenting a fundamental uncertainty in space weather prediction.« less

The study of heat flux for disruption on experimental advanced superconducting tokamak

NASA Astrophysics Data System (ADS)

Yang, Zhendong; Fang, Jianan; Gong, Xianzu; Gan, Kaifu; Luo, Jiarong; Zhao, Hailin; Cui, Zhixue; Zhang, Bin; Chen, Meiwen

2016-05-01

Disruption of the plasma is one of the most dangerous instabilities in tokamak. During the disruption, most of the plasma thermal energy is lost, which causes damages to the plasma facing components. Infrared (IR) camera is an effective tool to detect the temperature distribution on the first wall, and the energy deposited on the first wall can be calculated from the surface temperature profile measured by the IR camera. This paper concentrates on the characteristics of heat flux distribution onto the first wall under different disruptions, including the minor disruption and the vertical displacement events (VDE) disruption. Several minor disruptions have been observed before the major disruption under the high plasma density in experimental advanced superconducting tokamak. During the minor disruption, the heat fluxes are mainly deposited on the upper/lower divertors. The magnetic configuration prior to the minor disruption is a lower single null with the radial distance between the two separatrices in the outer midplane dRsep = -2 cm, while it changes to upper single null (dRsep = 1.4 cm) during the minor disruption. As for the VDE disruption, the spatial distribution of heat flux exhibits strong toroidal and radial nonuniformity, and the maximum heat flux received on the dome plate can be up to 11 MW/m2.

Experimental determination of group flux control coefficients in metabolic networks

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

Simpson, T.W.; Shimizu, Hiroshi; Stephanopoulos, G.

1998-04-20

Grouping of reactions around key metabolite branch points can facilitate the study of metabolic control of complex metabolic networks. This top-down Metabolic Control Analysis is exemplified through the introduction of group control coefficients whose magnitudes provide a measure of the relative impact of each reaction group on the overall network flux, as well as on the overall network stability, following enzymatic amplification. In this article, the authors demonstrate the application of previously developed theory to the determination of group flux control coefficients. Experimental data for the changes in metabolic fluxes obtained in response to the introduction of six different environmentalmore » perturbations are used to determine the group flux control coefficients for three reaction groups formed around the phosphoenolpyruvate/pyruvate branch point. The consistency of the obtained group flux control coefficient estimates is systematically analyzed to ensure that all necessary conditions are satisfied. The magnitudes of the determined control coefficients suggest that the control of lysine production flux in Corynebacterium glutamicum cells at a growth base state resides within the lysine biosynthetic pathway that begins with the PEP/PYR carboxylation anaplorotic pathway.« less

Broadening of divertor heat flux profile with increasing number of ELM filaments in NSTX

DOE PAGES

Ahn, J. -W.; Maingi, R.; Canik, J. M.; ...

2014-11-13

Edge localized modes (ELMs) represent a challenge to future fusion devices, owing to cyclical high peak heat fluxes on divertor plasma facing surfaces. One ameliorating factor has been that the heat flux characteristic profile width has been observed to broaden with the size of the ELM, as compared with the inter-ELM heat flux profile. In contrast, the heat flux profile has been observed to narrow during ELMs under certain conditions in NSTX. Here we show that the ELM heat flux profile width increases with the number of filamentary striations observed, i.e., profile narrowing is observed with zero or very fewmore » striations. Because NSTX often lies on the long wavelength current-driven mode side of ideal MHD instabilities, few filamentary structures can be expected under many conditions. Lastly, ITER is also projected to lie on the current driven low-n stability boundary, and therefore detailed projections of the unstable modes expected in ITER and the heat flux driven in ensuing filamentary structures is needed.« less

Electric flux tube in a magnetic plasma

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

Liao Jinfeng; Shuryak, Edward

2008-06-15

In this paper we study a methodical problem related to the magnetic scenario recently suggested and initiated by Liao and Shuryak [Phys. Rev. C 75, 054907 (2007)] to understand the strongly coupled quark-gluon plasma (sQGP): the electric flux tube in a monopole plasma. A macroscopic approach, in which we interpolate between a Bose condensed (dual superconductor) medium and a classical gas medium, is developed first. Then we work out a microscopic approach based on detailed quantum mechanical calculations of the monopole scattering on the electric flux tube, evaluating induced currents for all partial waves. As expected, the flux tube losesmore » its stability when particles can penetrate it: We make this condition precise by calculating the critical value for the product of the flux tube size times the particle momentum, above which the flux tube dissolves. Lattice static potentials indicate that flux tubes seem to dissolve at T>T{sub dissolution}{approx_equal}1.3T{sub c}. Using our criterion one gets an estimate of the magnetic density n{approx_equal}4.4-6.6 fm{sup -3} at this temperature.« less

Ablative stabilization of Rayleigh-Taylor instabilities resulting from a laser-driven radiative shock

NASA Astrophysics Data System (ADS)

Huntington, C. M.; Shimony, A.; Trantham, M.; Kuranz, C. C.; Shvarts, D.; Di Stefano, C. A.; Doss, F. W.; Drake, R. P.; Flippo, K. A.; Kalantar, D. H.; Klein, S. R.; Kline, J. L.; MacLaren, S. A.; Malamud, G.; Miles, A. R.; Prisbrey, S. T.; Raman, K. S.; Remington, B. A.; Robey, H. F.; Wan, W. C.; Park, H.-S.

2018-05-01

The Rayleigh-Taylor (RT) instability is a common occurrence in nature, notably in astrophysical systems like supernovae, where it serves to mix the dense layers of the interior of an exploding star with the low-density stellar wind surrounding it, and in inertial confinement fusion experiments, where it mixes cooler materials with the central hot spot in an imploding capsule and stifles the desired nuclear reactions. In both of these examples, the radiative flux generated by strong shocks in the system may play a role in partially stabilizing RT instabilities. Here, we present experiments performed on the National Ignition Facility, designed to isolate and study the role of radiation and heat conduction from a shock front in the stabilization of hydrodynamic instabilities. By varying the laser power delivered to a shock-tube target with an embedded, unstable interface, the radiative fluxes generated at the shock front could be controlled. We observe decreased RT growth when the shock significantly heats the medium around it, in contrast to a system where the shock did not produce significant heating. Both systems are modeled with a modified set of buoyancy-drag equations accounting for ablative stabilization, and the experimental results are consistent with ablative stabilization when the shock is radiative. This result has important implications for our understanding of astrophysical radiative shocks and supernova radiative hydrodynamics [Kuranz et al., Nature Communications 9(1), 1564 (2018)].

Detection and Production of Methane Hydrate

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

George Hirasaki; Walter Chapman; Gerald Dickens

This project seeks to understand regional differences in gas hydrate systems from the perspective of as an energy resource, geohazard, and long-term climate influence. Specifically, the effort will: (1) collect data and conceptual models that targets causes of gas hydrate variance, (2) construct numerical models that explain and predict regional-scale gas hydrate differences in 2-dimensions with minimal 'free parameters', (3) simulate hydrocarbon production from various gas hydrate systems to establish promising resource characteristics, (4) perturb different gas hydrate systems to assess potential impacts of hot fluids on seafloor stability and well stability, and (5) develop geophysical approaches that enable remotemore » quantification of gas hydrate heterogeneities so that they can be characterized with minimal costly drilling. Our integrated program takes advantage of the fact that we have a close working team comprised of experts in distinct disciplines. The expected outcomes of this project are improved exploration and production technology for production of natural gas from methane hydrates and improved safety through understanding of seafloor and well bore stability in the presence of hydrates. The scope of this project was to more fully characterize, understand, and appreciate fundamental differences in the amount and distribution of gas hydrate and how this would affect the production potential of a hydrate accumulation in the marine environment. The effort combines existing information from locations in the ocean that are dominated by low permeability sediments with small amounts of high permeability sediments, one permafrost location where extensive hydrates exist in reservoir quality rocks and other locations deemed by mutual agreement of DOE and Rice to be appropriate. The initial ocean locations were Blake Ridge, Hydrate Ridge, Peru Margin and GOM. The permafrost location was Mallik. Although the ultimate goal of the project was to understand processes that control production potential of hydrates in marine settings, Mallik was included because of the extensive data collected in a producible hydrate accumulation. To date, such a location had not been studied in the oceanic environment. The project worked closely with ongoing projects (e.g. GOM JIP and offshore India) that are actively investigating potentially economic hydrate accumulations in marine settings. The overall approach was fivefold: (1) collect key data concerning hydrocarbon fluxes which is currently missing at all locations to be included in the study, (2) use this and existing data to build numerical models that can explain gas hydrate variance at all four locations, (3) simulate how natural gas could be produced from each location with different production strategies, (4) collect new sediment property data at these locations that are required for constraining fluxes, production simulations and assessing sediment stability, and (5) develop a method for remotely quantifying heterogeneities in gas hydrate and free gas distributions. While we generally restricted our efforts to the locations where key parameters can be measured or constrained, our ultimate aim was to make our efforts universally applicable to any hydrate accumulation.« less

Particle propagation, wave growth and energy dissipation in a flaring flux tube

NASA Technical Reports Server (NTRS)

White, S. M.; Melrose, D. B.; Dulk, G. A.

1986-01-01

Wave amplification by downgoing particles in a common flare model is investigated. The flare is assumed to occur at the top of a coronal magnetic flux loop, and results in the heating of plasma in the flaring region. The hot electrons propagate down the legs of the flux tube towards increasing magnetic field. It is simple to demonstrate that the velocity distributions which result in this model are unstable to both beam instabilities and cyclotron maser action. An explanation is presented for the propagation effects on the distribution, and the properties of the resulting amplified waves are explored, concentrating on cyclotron maser action, which has properties (emission in the z mode below the local gyrofrequency) quite different from maser action by other distributions considered in the context of solar flares. The z mode waves will be damped in the coronal plasma surrounding the flaring flux tube and lead to heating there. This process may be important in the overall energy budget of the flare. The downgoing maser is compared with the loss cone maser, which is more likely to produce observable bursts.

Exploring the Underlying Mechanisms of the Xenopus laevis Embryonic Cell Cycle.

PubMed

Zhang, Kun; Wang, Jin

2018-05-31

The cell cycle is an indispensable process in proliferation and development. Despite significant efforts, global quantification and physical understanding are still challenging. In this study, we explored the mechanisms of the Xenopus laevis embryonic cell cycle by quantifying the underlying landscape and flux. We uncovered the Mexican hat landscape of the Xenopus laevis embryonic cell cycle with several local basins and barriers on the oscillation path. The local basins characterize the different phases of the Xenopus laevis embryonic cell cycle, and the local barriers represent the checkpoints. The checkpoint mechanism of the cell cycle is revealed by the landscape basins and barriers. While landscape shape determines the stabilities of the states on the oscillation path, the curl flux force determines the stability of the cell cycle flow. Replication is fundamental for biology of living cells. We quantify the input energy (through the entropy production) as the thermodynamic requirement for initiation and sustainability of single cell life (cell cycle). Furthermore, we also quantify curl flux originated from the input energy as the dynamical requirement for the emergence of a new stable phase (cell cycle). This can provide a new quantitative insight for the origin of single cell life. In fact, the curl flux originated from the energy input or nutrition supply determines the speed and guarantees the progression of the cell cycle. The speed of the cell cycle is a hallmark of cancer. We characterized the quality of the cell cycle by the coherence time and found it is supported by the flux and energy cost. We are also able to quantify the degree of time irreversibility by the cross correlation function forward and backward in time from the stochastic traces in the simulation or experiments, providing a way for the quantification of the time irreversibility and the flux. Through global sensitivity analysis upon landscape and flux, we can identify the key elements for controlling the cell cycle speed. This can help to design an effective strategy for drug discovery against cancer.

Low-energy ion distribution functions on a magnetically quiet day at geostationary altitude /L = 7/

NASA Technical Reports Server (NTRS)

Singh, N.; Raitt, W. J.; Yasuhara, F.

1982-01-01

Ion energy and pitch angle distribution functions are examined for a magnetically quiet day using averaged data from ATS 6. For both field-aligned and perpendicular fluxes, the populations have a mixture of characteristic energies, and the distribution functions can be fairly well approximated by Maxwellian distributions over three different energy bands in the range 3-600 eV. Pitch angle distributions varying with local time, and energy distributions are used to compute total ion density. Pitch angle scattering mechanisms responsible for the observed transformation of pitch angle distribution are examined, and it is found that a magnetic noise of a certain power spectral density belonging to the electromagnetic ion cyclotron mode near the ion cyclotron frequency can be effective in trapping the field aligned fluxes by pitch angle scattering.

Air-Sea exchange of biogenic volatile organic compounds and the impact on aerosol particle size distributions

NASA Astrophysics Data System (ADS)

Kim, Michelle J.; Novak, Gordon A.; Zoerb, Matthew C.; Yang, Mingxi; Blomquist, Byron W.; Huebert, Barry J.; Cappa, Christopher D.; Bertram, Timothy H.

2017-04-01

We report simultaneous, underway eddy covariance measurements of the vertical flux of isoprene, total monoterpenes, and dimethyl sulfide (DMS) over the Northern Atlantic Ocean during fall. Mean isoprene and monoterpene sea-to-air vertical fluxes were significantly lower than mean DMS fluxes. While rare, intense monoterpene sea-to-air fluxes were observed, coincident with elevated monoterpene mixing ratios. A statistically significant correlation between isoprene vertical flux and short wave radiation was not observed, suggesting that photochemical processes in the surface microlayer did not enhance isoprene emissions in this study region. Calculations of secondary organic aerosol production rates (PSOA) for mean isoprene and monoterpene emission rates sampled here indicate that PSOA is on average <0.1 μg m-3 d-1. Despite modest PSOA, low particle number concentrations permit a sizable role for condensational growth of monoterpene oxidation products in altering particle size distributions and the concentration of cloud condensation nuclei during episodic monoterpene emission events from the ocean.

Determination of neutron flux distribution in an Am-Be irradiator using the MCNP.

PubMed

Shtejer-Diaz, K; Zamboni, C B; Zahn, G S; Zevallos-Chávez, J Y

2003-10-01

A neutron irradiator has been assembled at IPEN facilities to perform qualitative-quantitative analysis of many materials using thermal and fast neutrons outside the nuclear reactor premises. To establish the prototype specifications, the neutron flux distribution and the absorbed dose rates were calculated using the MCNP computer code. These theoretical predictions then allow one to discuss the optimum irradiator design and its performance.

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

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

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

1984-01-01

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 workmore » 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.« less

A preliminary assessment of the effects of heat flux distribution and penetration on the creep rupture of a reactor vessel lower head

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

Chu, T.Y.; Bentz, J.; Simpson, R.

1997-02-01

The objective of the Lower Head Failure (LHF) Experiment Program is to experimentally investigate and characterize the failure of the reactor vessel lower head due to thermal and pressure loads under severe accident conditions. The experiment is performed using 1/5-scale models of a typical PWR pressure vessel. Experiments are performed for various internal pressure and imposed heat flux distributions with and without instrumentation guide tube penetrations. The experimental program is complemented by a modest modeling program based on the application of vessel creep rupture codes developed in the TMI Vessel Investigation Project. The first three experiments under the LHF programmore » investigated the creep rupture of simulated reactor pressure vessels without penetrations. The heat flux distributions for the three experiments are uniform (LHF-1), center-peaked (LHF-2), and side-peaked (LHF-3), respectively. For all the experiments, appreciable vessel deformation was observed to initiate at vessel wall temperatures above 900K and the vessel typically failed at approximately 1000K. The size of failure was always observed to be smaller than the heated region. For experiments with non-uniform heat flux distributions, failure typically occurs in the region of peak temperature. A brief discussion of the effect of penetration is also presented.« less

Predicting watershed acidification under alternate rainfall conditions

USGS Publications Warehouse

Huntington, T.G.

1996-01-01

The effect of alternate rainfall scenarios on acidification of a forested watershed subjected to chronic acidic deposition was assessed using the model of acidification of groundwater in catchments (MAGIC). The model was calibrated at the Panola Mountain Research Watershed, near Atlanta, Georgia, U.S.A. using measured soil properties, wet and dry deposition, and modeled hydrologic routing. Model forecast simulations were evaluated to compare alternate temporal averaging of rainfall inputs and variations in rainfall amount and seasonal distribution. Soil water alkalinity was predicted to decrease to substantially lower concentrations under lower rainfall compared with current or higher rainfall conditions. Soil water alkalinity was also predicted to decrease to lower levels when the majority of rainfall occurred during the growing season compared with other rainfall distributions. Changes in rainfall distribution that result in decreases in net soil water flux will temporarily delay acidification. Ultimately, however, decreased soil water flux will result in larger increases in soil- adsorbed sulfur and soil-water sulfate concentrations and decreases in alkalinity when compared to higher water flux conditions. Potential climate change resulting in significant changes in rainfall amounts, seasonal distribution of rainfall, or evapotranspiration will change net soil water flux and, consequently, will affect the dynamics of the acidification response to continued sulfate loading.

Towards an explicit model of large field inflation

NASA Astrophysics Data System (ADS)

Dorronsoro, Juan Diaz; Schillo, Marjorie

2018-05-01

The unwinding inflation mechanism is studied in a type IIB flux compactification where all moduli are stabilized using flux, non-perturbative effects, and the leading α' corrections of the large volume scenario. We consider the backreaction on the geometry due to the presence of anti-D3 branes as well as the backreaction of inflation on the Kähler moduli, and compute the resulting corrections to the slow-roll potential. By taking large flux numbers, we are able to find inflationary epochs where backreaction effects are under control, the inflaton traverses a super-Planckian field range, and the resulting amplitude of scalar perturbations is consistent with observation.

Number concentration, size distribution and horizontal mass flux of Asian dust particles collected over free troposphere of Chinese desert region in calm weather condition using balloon borne measurements.

NASA Astrophysics Data System (ADS)

Habib, A.; Chen, B.

2017-12-01

Balloon borne measurements were carried out during calm weather conditions in Taklamakan Desert, which is considered as one of the major source areas of Asian dust (KOSA) particles. Vertical distribution of aerosols number concentration, size distribution, mass concentration and horizontal mass flux due to westerly wind was investigated .Vertical distribution of aerosol number concentration and size distribution at Dunhuang (40 °00'N, 94°30'E) China were observed by optical particle counter (OPC) on August 17, 2001, October 17, 2011, January 11, 2002, April 30, 2002. Five channels (0.3, 0.5, 0.8, 1.2 and 3.6 µm) were used in OPC for particle sizing measurements. Aerosol number concentration in winter season (January 11, 2002) at 3-5 km was very high. Variation of free tropospheric aerosols in April 30, 2002 was noticeable. Many inversions of temperature and aerosol concentration change are found at these inversion points. Super micron range was noticeable in size distribution of all balloon borne measurements. High values of estimated mass concentration of aerosols were observed at the ground atmosphere (1-2 km), and interestingly relatively high concentrations were frequently detected above about 2 km. Wind pattern observed by ERA-interim data sets at 500 and 850 hPa, shows that westerly winds were dominated in Taklamakan Desert during balloon borne observation period. Average horizontal mass flux of background Asian dust due to westerly wind was about in the range of 1219-58.5 μg/m³ tons/km2/day. Most of the profiles showed active transport of aerosols in the westerly dominated region, while, fluxes were found to be very low on January 11, 2002, compared with the other seasons. Vertical profiles of aerosols number concentration showed that significant transport of aerosols was dominated in westerly region (4-7 km). Low horizontal mass flux of aerosols was found in winter season

The photospheric magnetic flux budget

NASA Technical Reports Server (NTRS)

Schrijver, C. J.; Harvey, K. L.

1994-01-01

The ensemble of bipolar regions and the magnetic network both contain a substantial and strongly variable part of the photospheric magnetic flux at any phase in the solar cycle. The time-dependent distribution of the magnetic flux over and within these components reflects the action of the dynamo operating in the solar interior. We perform a quantitative comparison of the flux emerging in the ensemble of magnetic bipoles with the observed flux content of the solar photosphere. We discuss the photospheric flux budget in terms of flux appearance and disappearance, and argue that a nonlinear dependence exists between the flux present in the photosphere and the rate of flux appearance and disappearance. In this context, we discuss the problem of making quantitative statements about dynamos in cool stars other than the Sun.

Edge-based nonlinear diffusion for finite element approximations of convection-diffusion equations and its relation to algebraic flux-correction schemes.

PubMed

Barrenechea, Gabriel R; Burman, Erik; Karakatsani, Fotini

2017-01-01

For the case of approximation of convection-diffusion equations using piecewise affine continuous finite elements a new edge-based nonlinear diffusion operator is proposed that makes the scheme satisfy a discrete maximum principle. The diffusion operator is shown to be Lipschitz continuous and linearity preserving. Using these properties we provide a full stability and error analysis, which, in the diffusion dominated regime, shows existence, uniqueness and optimal convergence. Then the algebraic flux correction method is recalled and we show that the present method can be interpreted as an algebraic flux correction method for a particular definition of the flux limiters. The performance of the method is illustrated on some numerical test cases in two space dimensions.

Effect of fluxing treatment on the properties of Fe66Co15Mo1P7.5C5.5B2Si3 bulk metallic glass by water quenching

NASA Astrophysics Data System (ADS)

Li, Jin-Feng; Wang, Xin; Liu, Xue; Zhao, Shao-Fan; Yao, Ke-Fu

2018-01-01

The effect of fluxing treatment on the properties of Fe66Co15Mo1P7.5C5.5B2Si3bulk amorphous alloy (BAA) has been investigated. Prepared by a combination method of flux treatment and water quenching, the Fe66Co15Mo1P7.5C5.5B2Si3 BAA exhibits better glass-forming ability, thermal stability, soft magnetic properties and ductility than those of the one prepared by direct water quenching. This indicates that fluxing treatment can play a potential role in improving the properties of Fe-based BAA due to the effective elimination of the impurities within the alloy.

Fluctuations and intermittent poloidal transport in a simple toroidal plasma

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

Goud, T. S.; Ganesh, R.; Saxena, Y. C.

In a simple magnetized toroidal plasma, fluctuation induced poloidal flux is found to be significant in magnitude. The probability distribution function of the fluctuation induced poloidal flux is observed to be strongly non-Gaussian in nature; however, in some cases, the distribution shows good agreement with the analytical form [Carreras et al., Phys. Plasmas 3, 2664 (1996)], assuming a coupling between the near Gaussian density and poloidal velocity fluctuations. The observed non-Gaussian nature of the fluctuation induced poloidal flux and other plasma parameters such as density and fluctuating poloidal velocity in this device is due to intermittent and bursty nature ofmore » poloidal transport. In the simple magnetized torus used here, such an intermittent fluctuation induced poloidal flux is found to play a crucial role in generating the poloidal flow.« less

Simulation studies of wide and medium field of view earth radiation data analysis

NASA Technical Reports Server (NTRS)

Green, R. N.

1978-01-01

A parameter estimation technique is presented to estimate the radiative flux distribution over the earth from radiometer measurements at satellite altitude. The technique analyzes measurements from a wide field of view (WFOV), horizon to horizon, nadir pointing sensor with a mathematical technique to derive the radiative flux estimates at the top of the atmosphere for resolution elements smaller than the sensor field of view. A computer simulation of the data analysis technique is presented for both earth-emitted and reflected radiation. Zonal resolutions are considered as well as the global integration of plane flux. An estimate of the equator-to-pole gradient is obtained from the zonal estimates. Sensitivity studies of the derived flux distribution to directional model errors are also presented. In addition to the WFOV results, medium field of view results are presented.

Scanning micro-Hall probe mapping of magnetic flux distributions and current densities in YBa{sub 2}Cu{sub 3}O{sub 7}

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

Xing, W.; Heinrich, B.; Zhou, H.

1994-12-31

Mapping of the magnetic flux density B{sub z} (perpendicular to the film plane) for a YBa{sub 2}Cu{sub 3}O{sub 7} thin-film sample was carried out using a scanning micro-Hall probe. The sheet magnetization and sheet current densities were calculated from the B{sub z} distributions. From the known sheet magnetization, the tangential (B{sub x,y}) and normal components of the flux density B were calculated in the vicinity of the film. It was found that the sheet current density was mostly determined by 2B{sub x,y}/d, where d is the film thickness. The evolution of flux penetration as a function of applied field willmore » be shown.« less

A Summary of Biases in the BATSE Burst Trigger

NASA Technical Reports Server (NTRS)

Meegan, Charles A; Pendleton, Geoffrey N.; Mallozzi, Robert S.

1999-01-01

The BATSE threshold for triggering on a gamma-ray burst is generally expressed in units of peak flux between 50 and 300 keV averaged over 1024 milliseconds. The completeness of the sample is affected by several systematic and statistical affects. A study is currently underway to characterize two of these that have not yet been Included Abstract: in the BATSE trigger efficiency calculation. They are: 1) the effects of statistical fluctuations on the measurement of peak flux and, 2) the effect on the trigger threshold of "slow risers", In which some of the burst flux is Identified as background. Some other biases that have been identified are in fact Malmquist-type biases which relate to a volume limited, rather than peak flux limited, burst source distribution and which cannot be determined without knowledge of the burst luminosity distribution.

Modeled ground magnetic signatures of flux transfer events

NASA Technical Reports Server (NTRS)

Mchenry, Mark A.; Clauer, C. Robert

1987-01-01

The magnetic field on the ground due to a small (not greater than 200 km scale size) localized field-aligned current (FAC) system interacting with the ionosphere is calculated in terms of an integral over the ionospheric distribution of FAC. Two different candidate current systems for flux transfer events (FTEs) are considered: (1) a system which has current flowing down the center of a cylindrical flux tube with a return current uniformly distributed along the outside edge; and (2) a system which has upward current on one half of the perimeter of a cylindrical flux tube with downward current on the opposite half. The peak magnetic field on the ground is found to differ by a factor of 2 between the two systems, and the magnetic perturbations are in different directions depending on the observer's position.

Variability of CO2 concentrations and fluxes in and above an urban street canyon

NASA Astrophysics Data System (ADS)

Lietzke, Björn; Vogt, Roland

2013-08-01

The variability of CO2 concentrations and fluxes in dense urban environments is high due to the inherent heterogeneity of these complex areas and their spatio-temporally variable anthropogenic sources. With a focus on micro- to local-scale CO2-exchange processes, measurements were conducted in a street canyon in the city of Basel, Switzerland in 2010. CO2 fluxes were sampled at the top of the canyon (19 m) and at 39 m while vertical CO2 concentration profiles were measured in the center and at a wall of the canyon. CO2 concentration distributions in the street canyon and exchange processes with the layers above show, apart from expected general diurnal patterns due mixing layer heights, a strong dependence on wind direction relative to the canyon. As a consequence of the resulting corkscrew-like canyon vortex, accumulation of CO2 inside the canyon is modulated with distinct distribution patterns. The evaluation of diurnal traffic data provides good explanations for the vertical and horizontal differences in CO2-distribution inside the canyon. Diurnal flux characteristics at the top of the canyon can almost solely be explained with traffic density expressed by the strong linear dependence. Even the diurnal course of the flux at 39 m shows a remarkable relationship to traffic density for east wind conditions while, for west wind situations, a change toward source areas with lower emissions leads to a reduced flux.

Small impact craters in the lunar regolith - Their morphologies, relative ages, and rates of formation

USGS Publications Warehouse

Moore, H.J.; Boyce, J.M.; Hahn, D.A.

1980-01-01

Apparently, there are two types of size-frequency distributions of small lunar craters (???1-100 m across): (1) crater production distributions for which the cumulative frequency of craters is an inverse function of diameter to power near 2.8, and (2) steady-state distributions for which the cumulative frequency of craters is inversely proportional to the square of their diameters. According to theory, cumulative frequencies of craters in each morphologic category within the steady-state should also be an inverse function of the square of their diameters. Some data on frequency distribution of craters by morphologic types are approximately consistent with theory, whereas other data are inconsistent with theory. A flux of crater producing objects can be inferred from size-frequency distributions of small craters on the flanks and ejecta of craters of known age. Crater frequency distributions and data on the craters Tycho, North Ray, Cone, and South Ray, when compared with the flux of objects measured by the Apollo Passive Seismometer, suggest that the flux of objects has been relatively constant over the last 100 m.y. (within 1/3 to 3 times of the flux estimated for Tycho). Steady-state frequency distributions for craters in several morphologic categories formed the basis for estimating the relative ages of craters and surfaces in a system used during the Apollo landing site mapping program of the U.S. Geological Survey. The relative ages in this system are converted to model absolute ages that have a rather broad range of values. The range of values of the absolute ages are between about 1/3 to 3 times the assigned model absolute age. ?? 1980 D. Reidel Publishing Co.

Comparing Vertical Distributions of Water Vapor Flux within Two Landfalling Atmospheric Rivers

NASA Astrophysics Data System (ADS)

Rutz, J. J.; Lavers, D. A.

2015-12-01

The West Coast of North America is frequently impacted by atmospheric rivers (ARs), regions of intense horizontal water vapor transport that often produce heavy rain, flooding, and landslides when they interact with near-coastal mountains. Recently, studies have shown that ARs penetrate farther inland on many occasions, with indications that the vertical distribution of vapor transport within the ARs may play a key role in this penetration (Alexander et al. 2015; Rutz et al. 2015). We hypothesize that the amount of near-coastal precipitation and the likelihood of AR penetration farther inland may be inversely linked by vertical distributions of vapor fluxes before, during, and after landfall. To explore whether differing vertical distributions of transport explain differing precipitation and penetration outcomes, we compare two landfalling ARs that had very similar spatial extents and rates of vertically integrated (total) vapor transport, but which nonetheless produced very different amounts of precipitation over northern California. The vertical distribution of water vapor flux, specific humidity, and wind speed during these two ARs are examined along several transects using cross-sectional analyses of the Climate Forecast System Reanalysis with a horizontal resolution of ~0.5° (~63 km) and a sigma-pressure hybrid coordinate at 64 vertical levels. In addition, we pursue similar analyses of forecasts from the NCEP Global Ensemble Forecast System GEFS to assess whether numerical weather prediction models accurately represent these distributions. Finally, we calculate backward trajectories from within each AR to examine whether or not the origins of their respective air parcels play a role in the resulting vertical distribution of water vapor flux. The results have major implications for two problems in weather prediction: (1) the near-coastal precipitation associated with landfalling ARs and (2) the likelihood of AR penetration farther inland.

13C tracer experiments and metabolite balancing for metabolic flux analysis: comparing two approaches

PubMed

Schmidt; Marx; de Graaf AA; Wiechert; Sahm; Nielsen; Villadsen

1998-04-05

Conventional metabolic flux analysis uses the information gained from determination of measurable fluxes and a steady-state assumption for intracellular metabolites to calculate the metabolic fluxes in a given metabolic network. The determination of intracellular fluxes depends heavily on the correctness of the assumed stoichiometry including the presence of all reactions with a noticeable impact on the model metabolite balances. Determination of fluxes in complex metabolic networks often requires the inclusion of NADH and NADPH balances, which are subject to controversial debate. Transhydrogenation reactions that transfer reduction equivalents from NADH to NADPH or vice versa can usually not be included in the stoichiometric model, because they result in singularities in the stoichiometric matrix. However, it is the NADPH balance that, to a large extent, determines the calculated flux through the pentose phosphate pathway. Hence, wrong assumptions on the presence or activity of transhydrogenation reactions will result in wrong estimations of the intracellular flux distribution. Using 13C tracer experiments and NMR analysis, flux analysis can be performed on the basis of only well established stoichiometric equations and measurements of the labeling state of intracellular metabolites. Neither NADH/NADPH balancing nor assumptions on energy yields need to be included to determine the intracellular fluxes. Because metabolite balancing methods and the use of 13C labeling measurements are two different approaches to the determination of intracellular fluxes, both methods can be used to verify each other or to discuss the origin and significance of deviations in the results. Flux analysis based entirely on metabolite balancing and flux analysis, including labeling information, have been performed independently for a wild-type strain of Aspergillus oryzae producing alpha-amylase. Two different nitrogen sources, NH4+ and NO3-, have been used to investigate the influence of the NADPH requirements on the intracellular flux distribution. The two different approaches to the calculation of fluxes are compared and deviations in the results are discussed. Copyright 1998 John Wiley & Sons, Inc.

Simplified Calculation Of Solar Fluxes In Solar Receivers

NASA Technical Reports Server (NTRS)

Bhandari, Pradeep

1990-01-01

Simplified Calculation of Solar Flux Distribution on Side Wall of Cylindrical Cavity Solar Receivers computer program employs simple solar-flux-calculation algorithm for cylindrical-cavity-type solar receiver. Results compare favorably with those of more complicated programs. Applications include study of solar energy and transfer of heat, and space power/solar-dynamics engineering. Written in FORTRAN 77.

Objectified quantification of uncertainties in Bayesian atmospheric inversions

NASA Astrophysics Data System (ADS)

Berchet, A.; Pison, I.; Chevallier, F.; Bousquet, P.; Bonne, J.-L.; Paris, J.-D.

2015-05-01

Classical Bayesian atmospheric inversions process atmospheric observations and prior emissions, the two being connected by an observation operator picturing mainly the atmospheric transport. These inversions rely on prescribed errors in the observations, the prior emissions and the observation operator. When data pieces are sparse, inversion results are very sensitive to the prescribed error distributions, which are not accurately known. The classical Bayesian framework experiences difficulties in quantifying the impact of mis-specified error distributions on the optimized fluxes. In order to cope with this issue, we rely on recent research results to enhance the classical Bayesian inversion framework through a marginalization on a large set of plausible errors that can be prescribed in the system. The marginalization consists in computing inversions for all possible error distributions weighted by the probability of occurrence of the error distributions. The posterior distribution of the fluxes calculated by the marginalization is not explicitly describable. As a consequence, we carry out a Monte Carlo sampling based on an approximation of the probability of occurrence of the error distributions. This approximation is deduced from the well-tested method of the maximum likelihood estimation. Thus, the marginalized inversion relies on an automatic objectified diagnosis of the error statistics, without any prior knowledge about the matrices. It robustly accounts for the uncertainties on the error distributions, contrary to what is classically done with frozen expert-knowledge error statistics. Some expert knowledge is still used in the method for the choice of an emission aggregation pattern and of a sampling protocol in order to reduce the computation cost. The relevance and the robustness of the method is tested on a case study: the inversion of methane surface fluxes at the mesoscale with virtual observations on a realistic network in Eurasia. Observing system simulation experiments are carried out with different transport patterns, flux distributions and total prior amounts of emitted methane. The method proves to consistently reproduce the known "truth" in most cases, with satisfactory tolerance intervals. Additionally, the method explicitly provides influence scores and posterior correlation matrices. An in-depth interpretation of the inversion results is then possible. The more objective quantification of the influence of the observations on the fluxes proposed here allows us to evaluate the impact of the observation network on the characterization of the surface fluxes. The explicit correlations between emission aggregates reveal the mis-separated regions, hence the typical temporal and spatial scales the inversion can analyse. These scales are consistent with the chosen aggregation patterns.

Method for determining transport critical current densities and flux penetration depth in bulk superconductors

NASA Technical Reports Server (NTRS)

Israelsson, Ulf E. (Inventor); Strayer, Donald M. (Inventor)

1992-01-01

A contact-less method for determining transport critical current density and flux penetration depth in bulk superconductor material. A compressor having a hollow interior and a plunger for selectively reducing the free space area for distribution of the magnetic flux therein are formed of superconductor material. Analytical relationships, based upon the critical state model, Maxwell's equations and geometrical relationships define transport critical current density and flux penetration depth in terms of the initial trapped magnetic flux density and the ratio between initial and final magnetic flux densities whereby data may be reliably determined by means of the simple test apparatus for evaluating the current density and flux penetration depth.

Radiation−condensation instability in tokamaks with mixed impurities

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

Morozov, D. Kh.; Pshenov, A. A., E-mail: Pshenov.andrey@gmail.com

2015-08-15

Radiation−condensation instability (RCI) is one of the possible mechanisms behind the formation of microfaceted asymmetric radiation from the edge (MARFE) of a tokamak. It has been previously shown by the authors that RCI in carbon-seeded plasma can be stabilized using neon injection. Recently, beryllium- and tungsten-seeded plasmas became a subject of great interest. Therefore, in the present paper, RCI stability analysis of the edge plasma seeded with beryllium, tungsten, nitrogen, and carbon is performed. The influence of neutral hydrogen fluxes from the wall on the marginal stability limit is studied as well.

Role of surface heat fluxes underneath cold pools

PubMed Central

Garelli, Alix; Park, Seung‐Bu; Nie, Ji; Torri, Giuseppe; Kuang, Zhiming

2016-01-01

Abstract The role of surface heat fluxes underneath cold pools is investigated using cloud‐resolving simulations with either interactive or horizontally homogenous surface heat fluxes over an ocean and a simplified land surface. Over the ocean, there are limited changes in the distribution of the cold pool temperature, humidity, and gust front velocity, yet interactive heat fluxes induce more cold pools, which are smaller, and convection is then less organized. Correspondingly, the updraft mass flux and lateral entrainment are modified. Over the land surface, the heat fluxes underneath cold pools drastically impact the cold pool characteristics with more numerous and smaller pools, which are warmer and more humid and accompanied by smaller gust front velocities. The interactive fluxes also modify the updraft mass flux and reduce convective organization. These results emphasize the importance of interactive surface fluxes instead of prescribed flux boundary conditions, as well as the formulation of surface heat fluxes, when studying convection. PMID:27134320

On the Interaction between Marine Boundary Layer Cellular Cloudiness and Surface Heat Fluxes

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

Kazil, J.; Feingold, G.; Wang, Hailong

2014-01-02

The interaction between marine boundary layer cellular cloudiness and surface uxes of sensible and latent heat is investigated. The investigation focuses on the non-precipitating closed-cell state and the precipitating open-cell state at low geostrophic wind speed. The Advanced Research WRF model is used to conduct cloud-system-resolving simulations with interactive surface fluxes of sensible heat, latent heat, and of sea salt aerosol, and with a detailed representation of the interaction between aerosol particles and clouds. The mechanisms responsible for the temporal evolution and spatial distribution of the surface heat fluxes in the closed- and open-cell state are investigated and explained. Itmore » is found that the horizontal spatial structure of the closed-cell state determines, by entrainment of dry free tropospheric air, the spatial distribution of surface air temperature and water vapor, and, to a lesser degree, of the surface sensible and latent heat flux. The synchronized dynamics of the the open-cell state drives oscillations in surface air temperature, water vapor, and in the surface fluxes of sensible and latent heat, and of sea salt aerosol. Open-cell cloud formation, cloud optical depth and liquid water path, and cloud and rain water path are identified as good predictors of the spatial distribution of surface air temperature and sensible heat flux, but not of surface water vapor and latent heat flux. It is shown that by enhancing the surface sensible heat flux, the open-cell state creates conditions by which it is maintained. While the open-cell state under consideration is not depleted in aerosol, and is insensitive to variations in sea-salt fluxes, it also enhances the sea-salt flux relative to the closed-cell state. In aerosol-depleted conditions, this enhancement may replenish the aerosol needed for cloud formation, and hence contribute to the perpetuation of the open-cell state as well. Spatial homogenization of the surface fluxes is found to have only a small effect on cloud properties in the investigated cases. This indicates that sub-grid scale spatial variability in the surface flux of sensible and latent heat and of sea salt aerosol may not be required in large scale and global models to describe marine boundary layer cellular cloudiness.« less

Estimating the components of the sensible heat budget of a tall forest canopy in complex terrain

NASA Astrophysics Data System (ADS)

Moderow, U.; Feigenwinter, C.; Bernhofer, C.

2007-04-01

Ultrasonic wind measurements, sonic temperature and air temperature data at two heights in the advection experiment MORE II were used to establish a complete budget of sensible heat including vertical advection, horizontal advection and horizontal turbulent flux divergence. MORE II took place at the long-term Carbo-Europe IP site in Tharandt, Germany. During the growing period of 2003 three additional towers were established to measure all relevant parameters for an estimation of advective fluxes, primarily of CO2. Additionally, in relation to other advection experiments, a calculation of the horizontal turbulent flux divergence is proposed and the relation of this flux to atmospheric stability and friction velocity is discussed. In order to obtain a complete budget, different scaling heights for horizontal advection and horizontal turbulent flux divergence are tested. It is shown that neglecting advective fluxes may lead to incorrect results. If advective fluxes are taken into account, the sensible heat budget based upon vertical turbulent flux and storage change only, is reduced by approximately 30%. Additional consideration of horizontal turbulent flux divergence would in turn add 5 10% to this sum (i.e., the sum of vertical turbulent flux plus storage change plus horizontal and vertical advection). In comparison with available energy horizontal advection is important at night whilst horizontal turbulent flux divergence is rather insignificant. Obviously, advective fluxes typically improve poor nighttime energy budget closure and might change ecosystem respiration fluxes considerably.

Concerning neutral flux shielding in the U-3M torsatron

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

Dreval, N. B., E-mail: mdreval@kipt.kharkov.ua

2015-03-15

The volume of the torsatron U-3M vacuum chamber is about 70 m{sup 3}, whereas the plasma volume is about 0.3 m{sup 3}. The large buffer volume of the chamber serves as a source of a substantial neutral flux into the U-3M plasma. A fraction of this flux falls onto the torsatron helical coils located in front of the plasma, due to which the dynamics of neutral influx into the plasma modifies. The shielding of the molecular flux from the buffer volume into the plasma is estimated using numerical calculations. Only about 10% of the incident flux reaches the plasma volume.more » Estimates show that about 20% of atoms escape beyond the helical coils without colliding with them. Under these conditions, the helical coils substantially affect the neutral flux. A discharge regime with a hot low-density plasma produced by a frame antenna is considered. The spatial distribution of the molecular density produced in this regime by the molecular flux from the chamber buffer volume after it has passed between the helical coils is calculated. The contributions of the fluxes emerging from the side and inner surfaces of the helical coils are considered. The calculations show that the shape of the spatial distribution of the molecular density differs substantially from the shape of the magnetic surfaces.« less

Numerical Examination of Flux Correction for Solving the Navier-Stokes Equations on Unstructured Meshes

DTIC Science & Technology

2014-08-29

lends itself to parallelization due to it’s discontinuous nature [27]. It has well-established stability properties and is actively being researched...from considering Conservation of Mass , Conservation of Momentum, and Conservation of Energy. This well-known result, known as the Navier-Stokes...internal plus kinetic) per unit mass and h = e+ Pρ as the enthalpy. qj is the jth component of the heat flux vector. This can be related to temperature

Modelling total solar irradiance since 1878 from simulated magnetograms

NASA Astrophysics Data System (ADS)

Dasi-Espuig, M.; Jiang, J.; Krivova, N. A.; Solanki, S. K.

2014-10-01

Aims: We present a new model of total solar irradiance (TSI) based on magnetograms simulated with a surface flux transport model (SFTM) and the Spectral And Total Irradiance REconstructions (SATIRE) model. Our model provides daily maps of the distribution of the photospheric field and the TSI starting from 1878. Methods: The modelling is done in two main steps. We first calculate the magnetic flux on the solar surface emerging in active and ephemeral regions. The evolution of the magnetic flux in active regions (sunspots and faculae) is computed using a surface flux transport model fed with the observed record of sunspot group areas and positions. The magnetic flux in ephemeral regions is treated separately using the concept of overlapping cycles. We then use a version of the SATIRE model to compute the TSI. The area coverage and the distribution of different magnetic features as a function of time, which are required by SATIRE, are extracted from the simulated magnetograms and the modelled ephemeral region magnetic flux. Previously computed intensity spectra of the various types of magnetic features are employed. Results: Our model reproduces the PMOD composite of TSI measurements starting from 1978 at daily and rotational timescales more accurately than the previous version of the SATIRE model computing TSI over this period of time. The simulated magnetograms provide a more realistic representation of the evolution of the magnetic field on the photosphere and also allow us to make use of information on the spatial distribution of the magnetic fields before the times when observed magnetograms were available. We find that the secular increase in TSI since 1878 is fairly stable to modifications of the treatment of the ephemeral region magnetic flux.

First UAV Measurements of Entrainment Layer Fluxes with Coupled Cloud Property Measurements

NASA Astrophysics Data System (ADS)

Thomas, R. M.; Praveen, P. S.; Wilcox, E. M.; Pistone, K.; Bender, F.; Ramanathan, V.

2012-12-01

This study details entrainment flux measurements made from a lightweight unmanned aerial vehicle (UAV) containing turbulent water vapor flux instrumentation (Thomas et al., 2012). The system was flown for 26 flights during the Cloud, Aerosol, Radiative forcing, Dynamics EXperiment (CARDEX) in the Maldives in March 2012 to study interrelationships between entrainment, aerosols, water budget, cloud microphysics and radiative fluxes in a trade wind cumulus cloud regime. A major advantage of using this lightweight, precision autopiloted UAV system with scientific telemetry is the ability to target small-scale features in the boundary layer, such as an entrainment layer, with minimal aircraft induced disruption. Results are presented from two UAVs flown in stacked formation: one UAV situated in-cloud measuring cloud-droplet size distribution spectra and liquid water content, and another co-located 100m above measuring turbulent properties and entrainment latent heat flux (λEE). We also show latent heat flux and turbulence measurements routinely made at the entrainment layer base and altitudes from the surface up to 4kft. Ratios of λEE to corresponding surface tower values (λES) display a bimodal frequency distribution with ranges 0.22-0.53 and 0.79-1.5, with occasional events >7. Reasons for this distribution are discussed drawing upon boundary layer and free tropospheric dynamics and meteorology, turbulence length scales, surface conditions, and cloud interactions. Latent heat flux profiles are combined with in-cloud UAV Liquid Water Content (LWC) data and surface based Liquid Water Path (LWP) and Precipitable Water Vapor (PWV) measurements to produce observationally constrained vertical water budgets, providing insights into diurnal coupling of λEE and λES. Observed λEE, λES, water budgets, and cloud microphysical responses to entrainment are then contextualized with respect to measured aerosol loading profiles and airmass history.

Radial Flux Distribution of Low-Energy Neutrons.

ERIC Educational Resources Information Center

Higinbotham, J.

1979-01-01

Describes an experiment designed to illustrate the basic principle involved in the process of moderation of fast neutrons by water, and the monitoring of the low-energy neutron flux using indium as a probe. (GA)

Environmental controls on the distribution of living (stained) benthic foraminifera on the continental slope in the Campos Basin area (SW Atlantic)

NASA Astrophysics Data System (ADS)

Yamashita, Cintia; Mello e Sousa, Silvia Helena de; Vicente, Thaisa Marques; Martins, Maria Virgínia; Nagai, Renata Hanae; Frontalini, Fabrizio; Godoi, Sueli Susana; Napolitano, Dante; Burone, Letícia; Carreira, Renato; Figueira, Rubens Cesar Lopes; Taniguchi, Nancy Kazumi; Rezende, Carlos Eduardo de; Koutsoukos, Eduardo Apostolos Machado

2018-05-01

Living (stained) benthic foraminifera from deep-sea stations in the Campos Basin, southeastern Brazilian continental margin, were investigated to understand their distribution patterns and ecology, as well as the oceanographic processes that control foraminiferal distribution. Sediments were collected from 1050 m to 1950 m of water depth during the austral winter of 2003, below the Intermediate Western Boundary Current (IWBC) and the Deep Water Boundary Current (DWBC). Based on statistical analysis, vertical flux of particulate organic matter and the grain size of sediment seem to be the main factors controlling the spatial distribution of benthic foraminifera. The middle slope (1050 m deep) is characterized by relatively high foraminiferal density and a predominance of phytodetritus-feeding foraminifera such as Epistominella exigua and Globocassidulina subglobosa. The occurrence of these species seems to reflect the Brazil Current System (BCS). The above-mentioned currents are associated with the relatively high vertical flux of particulate organic matter and the prevalence of sandy sediments, respectively. The lower slope (between 1350 and 1950 m of water depth) is marked by low foraminiferal density and assemblages composed of Bolivina spp. and Brizalina spp., with low particulate organic matter flux values, muddy sediments, and more refractory organic matter. The distribution of this group seems to be related to episodic fluxes of food particles to the seafloor, which are influenced by the BCS at the surface and are deposited under low deep current activity (DWBC).

Modular decomposition of metabolic reaction networks based on flux analysis and pathway projection.

PubMed

Yoon, Jeongah; Si, Yaguang; Nolan, Ryan; Lee, Kyongbum

2007-09-15

The rational decomposition of biochemical networks into sub-structures has emerged as a useful approach to study the design of these complex systems. A biochemical network is characterized by an inhomogeneous connectivity distribution, which gives rise to several organizational features, including modularity. To what extent the connectivity-based modules reflect the functional organization of the network remains to be further explored. In this work, we examine the influence of physiological perturbations on the modular organization of cellular metabolism. Modules were characterized for two model systems, liver and adipocyte primary metabolism, by applying an algorithm for top-down partition of directed graphs with non-uniform edge weights. The weights were set by the engagement of the corresponding reactions as expressed by the flux distribution. For the base case of the fasted rat liver, three modules were found, carrying out the following biochemical transformations: ketone body production, glucose synthesis and transamination. This basic organization was further modified when different flux distributions were applied that describe the liver's metabolic response to whole body inflammation. For the fully mature adipocyte, only a single module was observed, integrating all of the major pathways needed for lipid storage. Weaker levels of integration between the pathways were found for the early stages of adipocyte differentiation. Our results underscore the inhomogeneous distribution of both connectivity and connection strengths, and suggest that global activity data such as the flux distribution can be used to study the organizational flexibility of cellular metabolism. Supplementary data are available at Bioinformatics online.

High resolution isotope data and ensemble modelling reveal ecohydrological controls on catchment storage-discharge relationships and flux travel time distributions

NASA Astrophysics Data System (ADS)

Soulsby, C.; Kuppel, S.; Smith, A.; Tetzlaff, D.

2017-12-01

The dynamics of water storage in a catchment provides a fundamental insight into the interlinkages between input and output fluxes, and how these are affected by environmental change. Such dynamics also mediate, and help us understand, the fundamental difference of the rapid celerity of the rainfall-runoff (minutes to hours) response of catchments and the much slower velocity of water particles (months to decades) as they are transported through catchment systems. In this contribution we report an intensive, long-term (>10year), multi-scale isotope study in the Scottish Highlands that has sought to better understand these issues. We have integrated empirical data collection with diverse modelling approaches to quantify the dynamics and residence times of storage in different compartments of the hydrological system (vegetation canopies, soils, ground waters etc.) and their relationship between the magnitude and travel time distributions of output fluxes (stream flow, transpiration and evaporation). Use of conceptual, physically-based and probabilistic modelling approaches give broadly consistent perspectives on the storage-discharge relationships and the preferential selection of younger waters in runoff, evaporation and transpiration; while older waters predominate in groundwater. The work also highlighted the importance role vegetation plays in regulating fluxes in evaporation and transpiration and how this contributes to the differential ageing of water in mobile and bulk waters in the soil compartment. A separate case study shows how land use change can affect storage distributions in a catchment and radically change travel time distributions in output fluxes.

Hardface coating systems and methods for metal alloys and other materials for wear and corrosion resistant applications

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

Seals, Roland D.

The present disclosure relates generally to hardface coating systems and methods for metal alloys and other materials for wear and corrosion resistant applications. More specifically, the present disclosure relates to hardface coatings that include a network of titanium monoboride (TiB) needles or whiskers in a matrix, which are formed from titanium (Ti) and titanium diboride (TiB.sub.2) precursors by reactions enabled by the inherent energy provided by the process heat associated with coating deposition and, optionally, coating post-heat treatment. These hardface coatings are pyrophoric, thereby generating further reaction energy internally, and may be applied in a functionally graded manner. The hardfacemore » coatings may be deposited in the presence of a number of fluxing agents, beta stabilizers, densification aids, diffusional aids, and multimode particle size distributions to further enhance their performance characteristics.« less

Switchable pH-responsive polymeric membranes prepared via block copolymer micelle assembly.

PubMed

Nunes, Suzana P; Behzad, Ali Reza; Hooghan, Bobby; Sougrat, Rachid; Karunakaran, Madhavan; Pradeep, Neelakanda; Vainio, Ulla; Peinemann, Klaus-Viktor

2011-05-24

A process is described to manufacture monodisperse asymmetric pH-responsive nanochannels with very high densities (pore density >2 × 10(14) pores per m(2)), reproducible in m(2) scale. Cylindric pores with diameters in the sub-10 nm range and lengths in the 400 nm range were formed by self-assembly of metal-block copolymer complexes and nonsolvent-induced phase separation. The film morphology was tailored by taking into account the stability constants for a series of metal-polymer complexes and confirmed by AFM. The distribution of metal-copolymer micelles was imaged by transmission electron microscopy tomography. The pH response of the polymer nanochannels is the strongest reported with synthetic pores in the nm range (reversible flux increase of more than 2 orders of magnitude when switching the pH from 2 to 8) and could be demonstrated by cryo-field emission scanning electron microscopy, SAXS, and ultra/nanofiltration experiments.

Construction of a High Temperature Teg Measurement System for the Evaluation of Thermoelectric Oxide Modules

NASA Astrophysics Data System (ADS)

Populoh, S.; Trottmann, M.; Brunko, O. C.; Thiel, P.; Weidenkaff, A.

2013-08-01

A dedicated test stand was developed and built to characterize the efficiency, power output and open circuit voltage of various thermoelectric generators (TEGs) based on tellurides, heusler compounds and thermoelectric oxides. The test stand allows measurements of TEGs of sizes up to 4 cm × 4 cm at hot side temperatures up to 1150 K in different atmospheres. Special care was taken about the heat flux measurement by precise measurement of the temperature distribution within the reference block. In order to demonstrate the functionality of the test stand thermoelectric oxide modules (TOM) were built from n-type perovskite-type manganates and p-type cuprates. The modules were tested regarding their stability, maximum power output and efficiency at temperatures up to 1100 K. The TOMs withstand large temperature gradients and operated in ambient air yielding high power densities.

Hardface coating systems and methods for metal alloys and other materials for wear and corrosion resistant applications

DOEpatents

Seals, Roland D.

2015-08-18

The present disclosure relates generally to hardface coating systems and methods for metal alloys and other materials for wear and corrosion resistant applications. More specifically, the present disclosure relates to hardface coatings that include a network of titanium monoboride (TiB) needles or whiskers in a matrix, which are formed from titanium (Ti) and titanium diboride (TiB.sub.2) precursors by reactions enabled by the inherent energy provided by the process heat associated with coating deposition and, optionally, coating post-heat treatment. These hardface coatings are pyrophoric, thereby generating further reaction energy internally, and may be applied in a functionally graded manner. The hardface coatings may be deposited in the presence of a number of fluxing agents, beta stabilizers, densification aids, diffusional aids, and multimode particle size distributions to further enhance their performance characteristics.

Bidirectional reaction steps in metabolic networks: I. Modeling and simulation of carbon isotope labeling experiments.

PubMed

Wiechert, W; de Graaf, A A

1997-07-05

The extension of metabolite balancing with carbon labeling experiments, as described by Marx et al. (Biotechnol. Bioeng. 49: 11-29), results in a much more detailed stationary metabolic flux analysis. As opposed to basic metabolite flux balancing alone, this method enables both flux directions of bidirectional reaction steps to be quantitated. However, the mathematical treatment of carbon labeling systems is much more complicated, because it requires the solution of numerous balance equations that are bilinear with respect to fluxes and fractional labeling. In this study, a universal modeling framework is presented for describing the metabolite and carbon atom flux in a metabolic network. Bidirectional reaction steps are extensively treated and their impact on the system's labeling state is investigated. Various kinds of modeling assumptions, as usually made for metabolic fluxes, are expressed by linear constraint equations. A numerical algorithm for the solution of the resulting linear constrained set of nonlinear equations is developed. The numerical stability problems caused by large bidirectional fluxes are solved by a specially developed transformation method. Finally, the simulation of carbon labeling experiments is facilitated by a flexible software tool for network synthesis. An illustrative simulation study on flux identifiability from available flux and labeling measurements in the cyclic pentose phosphate pathway of a recombinant strain of Zymomonas mobilis concludes this contribution.

Regional Carbon Dioxide and Water Vapor Exchange Over Heterogeneous Terrain

NASA Technical Reports Server (NTRS)

Mahrt, Larry J.

2005-01-01

In spite of setbacks due to forest fires, eviction after a change of landowners and unanticipated need to upgrade and replace much of the instrumentation, substantial progress has been made during the past three years, resulting in major new findings. Although most of the results are in manuscript form, three papers have been published and a fourth was recently submitted. The data has been subjected to extensive quality control. Extra attention has been devoted to the influence of tilt rotation and flux-calculation method, particularly with respect to nocturnal fluxes. Previous/standard methods for calculating nocturnal fluxes with moderate and strong stability are inadequate and lead to large random fluxes errors for individual records, due partly to inadvertent inclusion of mesoscale motions that strongly contaminant the estimation of fluxes by weak turbulence. Such large errors are serious for process studies requiring carbon dioxide fluxes for individual records, but are substantially reduced when averaging fluxes over longer periods as in calculation of annual NEE budgets. We have employed a superior method for estimating fluxes in stable conditions with a variable averaging width . Mesoscale fluxes are generally unimportant except for events and are generally not systematic or predictable. Mesoscale or regional models of our region are not able to reproduce important aspects of the diurnally varying wind field

Bed Surface Adjustments to Spatially Variable Flow in Low Relative Submergence Regimes

NASA Astrophysics Data System (ADS)

Monsalve, A.; Yager, E. M.

2017-11-01

In mountainous rivers, large relatively immobile grains partly control the local and reach-averaged flow hydraulics and sediment fluxes. When the flow depth is similar to the size of these grains (low relative submergence), heterogeneous flow structures and plunging flow cause spatial distributions of bed surface elevations, textures, and sedimentation rates. To explore how the bed surface responds to these flow variations we conducted a set of experiments in which we varied the relative submergence of staggered hemispheres (simulated large boulders) between runs. All experiments had the same average sediment transport capacity, upstream sediment supply, and initial bed thickness and grain size distribution. We combined our laboratory measurements with a 3-D flow model to obtain the detailed flow structure around the hemispheres. The local bed shear stress field displayed substantial variability and controlled the bed load transport rates and direction in which sediment moved. The divergence in bed shear stress caused by the hemispheres promoted size-selective bed load deposition, which formed patches of coarse sediment upstream of the hemisphere. Sediment deposition caused a decrease in local bed shear stress, which combined with the coarser grain size, enhanced the stability of this patch. The region downstream of the hemispheres was largely controlled by a recirculation zone and had little to no change in grain size, bed elevation, and bed shear stress. The formation, development, and stability of sediment patches in mountain streams is controlled by the bed shear stress divergence and magnitude and direction of the local bed shear stress field.

Gas hydrate exploration of Porangahau Ridge, East Coast, North Island, New Zealand

NASA Astrophysics Data System (ADS)

Pecher, I. A.; Henrys, S. A.; Crutchley, G.; Toulmin, S.; Gorman, A. R.; Wood, W. T.; Kukowski, N.; Greinert, J.; Faure, K.; Coffin, R. B.

2007-12-01

During June and July 2006 the R/V Tangaroa collected high-resolution seismic profiles, EM 300 swath bathymetry, 3.5 sub-bottom, as well as water column echosounder data across Porangahau Ridge east of the North Island. Piston cores were recovered for pore water chemistry, microbiology, and paleoceanographic analyses. We also acquired heatflow data, CTDs, and seawater samples for water-column chemistry. The seismic data show amplitude anomalies beneath the ridge. The anomalies develop along a prominent N-S fault-propagation anticline. We analyzed reflection coefficients and conclude that the anomalies are most likely caused by free gas within the regional gas hydrate stability field as defined by the depth of bottom simulating reflections. We suggest that local warming associated with fluid expulsion through faults keeps the temperature at the anomalies outside of the gas hydrate stability field. Based on the seismic amplitudes, we predict at least ~7% of the pore space to be saturated with gas if gas is evenly distributed. Gas saturation is predicted to be almost 70% for "patchy'' gas distribution. For the pressure-temperature conditions beneath the ridge, gas at a saturation of 7% would form gas hydrate at a saturation of ~10% of pore space. Should the localized heat flow anomaly weaken, e.g., because of sealing of the faults, the ridge could become an area with significant hydrate deposits. We speculate that the Porangahau Ridge constitutes a gas hydrate "sweet spot" in the process of formation. Pore water chemistry shows a shoaling of the base of the sulfate reduction zone across this feature, indicative of elevated methane flux through the hydrate stability field. There is a distinct thermal anomaly across the Porangahau Ridge, albeit with a complex signature. On the other hand, there are no indications of methane expulsion into the water column, neither in the echosounder records nor in the water chemistry profiles from CTDs.

Conceptualizing the self organization of cloud cells, cold pools and soil moisture

NASA Astrophysics Data System (ADS)

Henneberg, O.; Härter, J. O. M.

2017-12-01

Convective-type cloud is the cause of extreme, short-duration precipitation, challenging weather forecasting and climate modeling. Such extremes are ultimately tied to the uneven redistribution of water in the course of convective self organization and possibly the interaction between clouds [1]. Over land, moisture is organized through: cloud cells, cold pools, and the land surface. Each of these generally capture and release moisture at different rates, e.g. cold pools form quickly but dissipate slowly. Such distinct timescales have implications for the emergent dynamics.Incorporating such distinct time scales, we here present a conceptual model for the spatio-temporal self organization within the diurnal cycle of convection and describe the possible role of soil moisture memory in serving as a predisposition for extremes.We bolster our findings by high resolution, large eddy simulations: Sensible and latent heat fluxes, which are determined by the soil moisture content, can influence the stability of the atmosphere. The onset of initial precipitation is affected by such heat release, which in turn is modified by previous precipitation. Starting from static heat sources, we quantify how their spatial distribution affects the self organization and thus onset, duration and strength of precipitation events in an idealized model setup. Furthermore, an extended model setup with inhomogeneous, self organized distributions of latent and sensible heat fluxes is used to contrast how emergent soil moisture patterns impact on the selforganization structure of convection. Our findings may have implications for the role of land use changes regarding the development of extreme convective precipitation.Reference[1] Moseley et al. (2016) "Intensification of convective extremes driven by cloud-cloud interaction", Nature Geosc. , 9, 748-752

Could thermal sensitivity of mitochondria determine species distribution in a changing climate?

PubMed

Iftikar, Fathima I; MacDonald, Julia R; Baker, Daniel W; Renshaw, Gillian M C; Hickey, Anthony J R

2014-07-01

For many aquatic species, the upper thermal limit (Tmax) and the heart failure temperature (THF) are only a few degrees away from the species' current environmental temperatures. While the mechanisms mediating temperature-induced heart failure (HF) remain unresolved, energy flow and/or oxygen supply disruptions to cardiac mitochondria may be impacted by heat stress. Recent work using a New Zealand wrasse (Notolabrus celidotus) found that ATP synthesis capacity of cardiac mitochondria collapses prior to T(HF). However, whether this effect is limited to one species from one thermal habitat remains unknown. The present study confirmed that cardiac mitochondrial dysfunction contributes to heat stress-induced HF in two additional wrasses that occupy cold temperate (Notolabrus fucicola) and tropical (Thalassoma lunare) habitats. With exposure to heat stress, T. lunare had the least scope to maintain heart function with increasing temperature. Heat-exposed fish of all species showed elevated plasma succinate, and the heart mitochondria from the cold temperate N. fucicola showed decreased phosphorylation efficiencies (depressed respiratory control ratio, RCR), cytochrome c oxidase (CCO) flux and electron transport system (ETS) flux. In situ assays conducted across a range of temperatures using naive tissues showed depressed complex II (CII) and CCO capacity, limited ETS reserve capacities and lowered efficiencies of pyruvate uptake in T. lunare and N. celidotus. Notably, alterations of mitochondrial function were detectable at saturating oxygen levels, indicating that cardiac mitochondrial insufficiency can occur prior to HF without oxygen limitation. Our data support the view that species distribution may be related to the thermal limits of mitochondrial stability and function, which will be important as oceans continue to warm. © 2014. Published by The Company of Biologists Ltd.

Nicergoline inhibits human platelet Ca2+ signalling through triggering a microtubule‐dependent reorganization of the platelet ultrastructure

PubMed Central

Walford, T; Musa, F I

2015-01-01

Background and Purpose Recently, we demonstrated that a pericellular Ca2+ recycling system potentiates agonist‐evoked Ca2+ signalling and granule secretion in human platelets and hypothesized a role for the membrane complex (MC) in orchestrating the accumulation of Ca2+ in the pericellular region. Previous work has demonstrated that treatment with high concentrations of nicergoline may disrupt the MC through an ability to trigger a re‐organization of the dense tubular system. Experiments were therefore performed to assess whether nicergoline‐induced changes in platelet ultrastructure affects thrombin‐evoked Ca2+ fluxes and dense granule secretion. Experimental Approach Thrombin‐evoked Ca2+ fluxes were monitored in Fura‐2‐ or Fluo‐5N‐loaded human platelets, or using platelet suspensions containing Fluo‐4 or Rhod‐5N K+ salts. Fluorescence microscopy was utilized to monitor microtubule structure and intracellular Ca2+ store distribution in TubulinTracker‐ and Fluo‐5N‐loaded platelets respectively. Dense granule secretion was monitored using luciferin–luciferase. Key Results Nicergoline treatment inhibited thrombin‐evoked Ca2+ signalling and induced alterations in the microtubule structure and the distribution of intracellular Ca2+ stores in platelets. Nicergoline altered the generation and spreading of thrombin‐induced pericellular Ca2+ signals and almost completely prevented dense granule secretion. Stabilization of microtubules using taxol reversed most effects of nicergoline on platelet Ca2+ signalling and partially reversed its effects on dense granule secretion. Conclusions and Implications Nicergoline‐induced alterations to platelet ultrastructure disrupt platelet Ca2+ signalling in a manner that would be predicted if the MC had been disrupted. These data suggest that nicergoline may be a useful prototype for the discovery of novel MC‐disrupting anti‐thrombotics. PMID:26450366

Nicergoline inhibits human platelet Ca(2+) signalling through triggering a microtubule-dependent reorganization of the platelet ultrastructure.

PubMed

Walford, T; Musa, F I; Harper, A G S

2016-01-01

Recently, we demonstrated that a pericellular Ca(2+) recycling system potentiates agonist-evoked Ca(2+) signalling and granule secretion in human platelets and hypothesized a role for the membrane complex (MC) in orchestrating the accumulation of Ca(2+) in the pericellular region. Previous work has demonstrated that treatment with high concentrations of nicergoline may disrupt the MC through an ability to trigger a re-organization of the dense tubular system. Experiments were therefore performed to assess whether nicergoline-induced changes in platelet ultrastructure affects thrombin-evoked Ca(2+) fluxes and dense granule secretion. Thrombin-evoked Ca(2+) fluxes were monitored in Fura-2- or Fluo-5N-loaded human platelets, or using platelet suspensions containing Fluo-4 or Rhod-5N K(+) salts. Fluorescence microscopy was utilized to monitor microtubule structure and intracellular Ca(2+) store distribution in TubulinTracker- and Fluo-5N-loaded platelets respectively. Dense granule secretion was monitored using luciferin-luciferase. Nicergoline treatment inhibited thrombin-evoked Ca(2+) signalling and induced alterations in the microtubule structure and the distribution of intracellular Ca(2+) stores in platelets. Nicergoline altered the generation and spreading of thrombin-induced pericellular Ca(2+) signals and almost completely prevented dense granule secretion. Stabilization of microtubules using taxol reversed most effects of nicergoline on platelet Ca(2+) signalling and partially reversed its effects on dense granule secretion. Nicergoline-induced alterations to platelet ultrastructure disrupt platelet Ca(2+) signalling in a manner that would be predicted if the MC had been disrupted. These data suggest that nicergoline may be a useful prototype for the discovery of novel MC-disrupting anti-thrombotics. © 2015 The British Pharmacological Society.

Initial Stability Assessment of S-NPP VIIRS Reflective Solar Band Calibration Using Invariant Desert and Deep Convective Cloud Targets

NASA Technical Reports Server (NTRS)

Bhatt, Rajendra; Doelling, David R.; Wu, Aisheng; Xiong, Xiaoxiong (Jack); Scarino, Benjamin R.; Haney, Conor O.; Gopalan, Arun

2014-01-01

The latest CERES FM-5 instrument launched onboard the S-NPP spacecraft will use the VIIRS visible radiances from the NASA Land Product Evaluation and Analysis Tool Elements (PEATE) product for retrieving the cloud properties associated with its TOA flux measurement. In order for CERES to provide climate quality TOA flux datasets, the retrieved cloud properties must be consistent throughout the record, which is dependent on the calibration stability of the VIIRS imager. This paper assesses the NASA calibration stability of the VIIRS reflective solar bands using the Libya-4 desert and deep convective clouds (DCC). The invariant targets are first evaluated for temporal natural variability. It is found for visible (VIS) bands that DCC targets have half of the variability of Libya-4. For the shortwave infrared (SWIR) bands, the desert has less variability. The brief VIIRS record and target variability inhibits high confidence in identifying any trends that are less than 0.6yr for most VIS bands, and 2.5yr for SWIR bands. None of the observed invariant target reflective solar band trends exceeded these trend thresholds. Initial assessment results show that the VIIRS data have been consistently calibrated and that the VIIRS instrument stability is similar to or better than the MODIS instrument.

Urban surface energy fluxes based on remotely-sensed data and micrometeorological measurements over the Kansai area, Japan

NASA Astrophysics Data System (ADS)

Sukeyasu, T.; Ueyama, M.; Ando, T.; Kosugi, Y.; Kominami, Y.

2017-12-01

The urban heat island is associated with land cover changes and increases in anthropogenic heat fluxes. Clear understanding of the surface energy budget at urban area is the most important for evaluating the urban heat island. In this study, we develop a model based on remotely-sensed data for the Kansai area in Japan and clarify temporal transitions and spatial distributions of the surface energy flux from 2000 to 2016. The model calculated the surface energy fluxes based on various satellite and GIS products. The model used land surface temperature, surface emissivity, air temperature, albedo, downward shortwave radiation and land cover/use type from the moderate resolution imaging spectroradiometer (MODIS) under cloud free skies from 2000 to 2016 over the Kansai area in Japan (34 to 35 ° N, 135 to 136 ° E). Net radiation was estimated by a radiation budget of upward/downward shortwave and longwave radiation. Sensible heat flux was estimated by a bulk aerodynamic method. Anthropogenic heat flux was estimated by the inventory data. Latent heat flux was examined with residues of the energy budget and parameterization of bulk transfer coefficients. We validated the model using observed fluxes from five eddy-covariance measurement sites: three urban sites and two forested sites. The estimated net radiation roughly agreed with the observations, but the sensible heat flux were underestimated. Based on the modeled spatial distributions of the fluxes, the daytime net radiation in the forested area was larger than those in the urban area, owing to higher albedo and land surface temperatures in the urban area than the forested area. The estimated anthropogenic heat flux was high in the summer and winter periods due to increases in energy-requirements.

Sampling with poling-based flux balance analysis: optimal versus sub-optimal flux space analysis of Actinobacillus succinogenes.

PubMed

Binns, Michael; de Atauri, Pedro; Vlysidis, Anestis; Cascante, Marta; Theodoropoulos, Constantinos

2015-02-18

Flux balance analysis is traditionally implemented to identify the maximum theoretical flux for some specified reaction and a single distribution of flux values for all the reactions present which achieve this maximum value. However it is well known that the uncertainty in reaction networks due to branches, cycles and experimental errors results in a large number of combinations of internal reaction fluxes which can achieve the same optimal flux value. In this work, we have modified the applied linear objective of flux balance analysis to include a poling penalty function, which pushes each new set of reaction fluxes away from previous solutions generated. Repeated poling-based flux balance analysis generates a sample of different solutions (a characteristic set), which represents all the possible functionality of the reaction network. Compared to existing sampling methods, for the purpose of generating a relatively "small" characteristic set, our new method is shown to obtain a higher coverage than competing methods under most conditions. The influence of the linear objective function on the sampling (the linear bias) constrains optimisation results to a subspace of optimal solutions all producing the same maximal fluxes. Visualisation of reaction fluxes plotted against each other in 2 dimensions with and without the linear bias indicates the existence of correlations between fluxes. This method of sampling is applied to the organism Actinobacillus succinogenes for the production of succinic acid from glycerol. A new method of sampling for the generation of different flux distributions (sets of individual fluxes satisfying constraints on the steady-state mass balances of intermediates) has been developed using a relatively simple modification of flux balance analysis to include a poling penalty function inside the resulting optimisation objective function. This new methodology can achieve a high coverage of the possible flux space and can be used with and without linear bias to show optimal versus sub-optimal solution spaces. Basic analysis of the Actinobacillus succinogenes system using sampling shows that in order to achieve the maximal succinic acid production CO₂ must be taken into the system. Solutions involving release of CO₂ all give sub-optimal succinic acid production.

Morphology and magnetic flux distribution in superparamagnetic, single-crystalline Fe3O4 nanoparticle rings.

PubMed

Takeno, Yumu; Murakami, Yasukazu; Sato, Takeshi; Tanigaki, Toshiaki; Park, Hyun Soon; Shindo, Daisuke; Ferguson, R Matthew; Krishnan, Kannan M

2014-11-03

This study reports on the correlation between crystal orientation and magnetic flux distribution of Fe 3 O 4 nanoparticles in the form of self-assembled rings. High-resolution transmission electron microscopy demonstrated that the nanoparticles were single-crystalline, highly monodispersed, (25 nm average diameter), and showed no appreciable lattice imperfections such as twins or stacking faults. Electron holography studies of these superparamagnetic nanoparticle rings indicated significant fluctuations in the magnetic flux lines, consistent with variations in the magnetocrystalline anisotropy of the nanoparticles. The observations provide useful information for a deeper understanding of the micromagnetics of ultrasmall nanoparticles, where the magnetic dipolar interaction competes with the magnetic anisotropy.

Integrated cosmic muon flux in the zenith angle range 0 < cosθ < 0.37 for momentum threshold up to 11.6 GeV/c

NASA Astrophysics Data System (ADS)

Fujii, Hirofumi; Hara, Kazuhiko; Hayashi, Kohei; Kakuno, Hidekazu; Kodama, Hideyo; Nagamine, Kanetada; Sato, Kazuyuki; Sato, Kotaro; Kim, Shin-Hong; Suzuki, Atsuto; Takahashi, Kazuki; Takasaki, Fumihiko

2017-12-01

We have measured the cosmic muon flux in the zenith angle range {<} cos θ {<} 0.37 with a detector comprising planes of scintillator hodoscope bars and iron blocks inserted between them. The muon ranges for up to 9.5 m-thick iron blocks allow the provision of muon flux data integrated over corresponding threshold momenta up to 11.6 GeV/c. Such a dataset covering the horizontal direction is extremely useful for a technique called muon radiography, where the mass distribution inside a large object is investigated from the cosmic muon distribution measured behind the object.

Numerical investigation on properties of attack angle for an opposing jet thermal protection system

NASA Astrophysics Data System (ADS)

Lu, Hai-Bo; Liu, Wei-Qiang

2012-08-01

The three-dimensional Navier—Stokes equation and the k-in viscous model are used to simulate the attack angle characteristics of a hemisphere nose-tip with an opposing jet thermal protection system in supersonic flow conditions. The numerical method is validated by the relevant experiment. The flow field parameters, aerodynamic forces, and surface heat flux distributions for attack angles of 0°, 2°, 5°, 7°, and 10° are obtained. The detailed numerical results show that the cruise attack angle has a great influence on the flow field parameters, aerodynamic force, and surface heat flux distribution of the supersonic vehicle nose-tip with an opposing jet thermal protection system. When the attack angle reaches 10°, the heat flux on the windward generatrix is close to the maximal heat flux on the wall surface of the nose-tip without thermal protection system, thus the thermal protection has failed.

Computational Platform for Flux Analysis Using 13C-Label Tracing- Phase I SBIR Final Report

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

Van Dien, Stephen J.

Isotopic label tracing is a powerful experimental technique that can be combined with metabolic models to quantify metabolic fluxes in an organism under a particular set of growth conditions. In this work we constructed a genome-scale metabolic model of Methylobacterium extorquens, a facultative methylotroph with potential application in the production of useful chemicals from methanol. A series of labeling experiments were performed using 13C-methanol, and the resulting distribution of labeled carbon in the proteinogenic amino acids was determined by mass spectrometry. Algorithms were developed to analyze this data in context of the metabolic model, yielding flux distributions for wild-type andmore » several engineered strains of M. extorquens. These fluxes were compared to those predicted by model simulation alone, and also integrated with microarray data to give an improved understanding of the metabolic physiology of this organism.« less

Biogeochemistry in highly reduced mussel farm sediments during macrofaunal recolonization by Amphiura filiformis and Nephtys sp.

PubMed

Lindqvist, Stina; Norling, Karl; Hulth, Stefan

2009-04-01

Mussel farming is considered a viable means for reducing coastal eutrophication. This study assessed the importance of bioturbation by recolonizing fauna for benthic solute fluxes and porewater distributions in manipulated mussel farm sediments. Three consecutive time-series flux incubations were performed during an experimental period of three weeks in sieved farm sediment treated with the brittle star Amphiura filiformis and the polychaete Nephtys sp. The functional behavior of Nephtys sp. and interactions between Nephtys sp. and the spontaneously colonizing spionid Malacoceros fuliginosus determined the biogeochemical response in the Nephtys sp. treatment. For example, the oxic zone was restricted and benthic nitrate and silicate fluxes were reduced compared to the brittle star treatment. A. filiformis seemed to enhance the bioadvective solute transport, although an increased supply of oxygen was due to the highly reducing conditions of the sediment mainly seen as secondary effects related to porewater distributions and benthic nutrient fluxes.

Sonar gas flux estimation by bubble insonification: application to methane bubble flux from seep areas in the outer Laptev Sea

NASA Astrophysics Data System (ADS)

Leifer, Ira; Chernykh, Denis; Shakhova, Natalia; Semiletov, Igor

2017-06-01

Sonar surveys provide an effective mechanism for mapping seabed methane flux emissions, with Arctic submerged permafrost seepage having great potential to significantly affect climate. We created in situ engineered bubble plumes from 40 m depth with fluxes spanning 0.019 to 1.1 L s-1 to derive the in situ calibration curve (Q(σ)). These nonlinear curves related flux (Q) to sonar return (σ) for a multibeam echosounder (MBES) and a single-beam echosounder (SBES) for a range of depths. The analysis demonstrated significant multiple bubble acoustic scattering - precluding the use of a theoretical approach to derive Q(σ) from the product of the bubble σ(r) and the bubble size distribution where r is bubble radius. The bubble plume σ occurrence probability distribution function (Ψ(σ)) with respect to Q found Ψ(σ) for weak σ well described by a power law that likely correlated with small-bubble dispersion and was strongly depth dependent. Ψ(σ) for strong σ was largely depth independent, consistent with bubble plume behavior where large bubbles in a plume remain in a focused core. Ψ(σ) was bimodal for all but the weakest plumes. Q(σ) was applied to sonar observations of natural arctic Laptev Sea seepage after accounting for volumetric change with numerical bubble plume simulations. Simulations addressed different depths and gases between calibration and seep plumes. Total mass fluxes (Qm) were 5.56, 42.73, and 4.88 mmol s-1 for MBES data with good to reasonable agreement (4-37 %) between the SBES and MBES systems. The seepage flux occurrence probability distribution function (Ψ(Q)) was bimodal, with weak Ψ(Q) in each seep area well described by a power law, suggesting primarily minor bubble plumes. The seepage-mapped spatial patterns suggested subsurface geologic control attributing methane fluxes to the current state of subsea permafrost.

Local time variations of high-energy plasmaspheric ion pitch angle distributions

DOE PAGES

Sarno-Smith, Lois K.; Liemohn, Michael W.; Skoug, Ruth M.; ...

2016-07-01

Recent observations from the Van Allen Probes Helium Oxygen Proton Electron (HOPE) instrument revealed a persistent depletion in the 1–10 eV ion population in the postmidnight sector during quiet times in the 2 < L < 3 region. This study explores the source of this ion depletion by developing an algorithm to classify 26 months of pitch angle distributions measured by the HOPE instrument. We correct the HOPE low energy fluxes for spacecraft potential using measurements from the Electric Field and Waves (EFW) instrument. A high percentage of low count pitch angle distributions is found in the postmidnight sector coupledmore » with a low percentage of ion distributions peaked perpendicular to the field line. A peak in loss cone distributions in the dusk sector is also observed. Here, these results characterize the nature of the dearth of the near 90° pitch angle 1–10 eV ion population in the near-Earth postmidnight sector. This study also shows, for the first time, low-energy HOPE differential number fluxes corrected for spacecraft potential and 1–10 eV H + fluxes at different levels of geomagnetic activity.« less

A maximum entropy principle for inferring the distribution of 3D plasmoids

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

Lingam, Manasvi; Comisso, Luca

The principle of maximum entropy, a powerful and general method for inferring the distribution function given a set of constraints, is applied to deduce the overall distribution of 3D plasmoids (flux ropes/tubes) for systems where resistive MHD is applicable and large numbers of plasmoids are produced. The analysis is undertaken for the 3D case, with mass, total flux, and velocity serving as the variables of interest, on account of their physical and observational relevance. The distribution functions for the mass, width, total flux, and helicity exhibit a power-law behavior with exponents of -4/3, -2, -3, and -2, respectively, for smallmore » values, whilst all of them display an exponential falloff for large values. In contrast, the velocity distribution, as a function of v=|v|, is shown to be flat for v→0, and becomes a power law with an exponent of -7/3 for v→∞. Most of these results are nearly independent of the free parameters involved in this specific problem. In conclusion, a preliminary comparison of our results with the observational evidence is presented, and some of the ensuing space and astrophysical implications are briefly discussed.« less

A maximum entropy principle for inferring the distribution of 3D plasmoids

DOE PAGES

Lingam, Manasvi; Comisso, Luca

2018-01-18

The principle of maximum entropy, a powerful and general method for inferring the distribution function given a set of constraints, is applied to deduce the overall distribution of 3D plasmoids (flux ropes/tubes) for systems where resistive MHD is applicable and large numbers of plasmoids are produced. The analysis is undertaken for the 3D case, with mass, total flux, and velocity serving as the variables of interest, on account of their physical and observational relevance. The distribution functions for the mass, width, total flux, and helicity exhibit a power-law behavior with exponents of -4/3, -2, -3, and -2, respectively, for smallmore » values, whilst all of them display an exponential falloff for large values. In contrast, the velocity distribution, as a function of v=|v|, is shown to be flat for v→0, and becomes a power law with an exponent of -7/3 for v→∞. Most of these results are nearly independent of the free parameters involved in this specific problem. In conclusion, a preliminary comparison of our results with the observational evidence is presented, and some of the ensuing space and astrophysical implications are briefly discussed.« less

Superenergy flux of Einstein-Rosen waves

NASA Astrophysics Data System (ADS)

Domínguez, P. J.; Gallegos, A.; Macías-Díaz, J. E.; Vargas-Rodríguez, H.

In this work, we consider the propagation speed of the superenergy flux associated to the Einstein-Rosen cylindrical waves propagating in vacuum and over the background of the gravitational field of an infinitely long mass line distribution. The velocity of the flux is determined considering the reference frame in which the super-Poynting vector vanishes. This reference frame is then considered as comoving with the flux. The explicit expressions for the velocities are given with respect to a reference frame at rest with the symmetry axis.

Effect of gage size on the measurement of local heat flux. [formulas for determining gage averaging errors

NASA Technical Reports Server (NTRS)

Baumeister, K. J.; Papell, S. S.

1973-01-01

General formulas are derived for determining gage averaging errors of strip-type heat flux meters used in the measurement of one-dimensional heat flux distributions. In addition, a correction procedure is presented which allows a better estimate for the true value of the local heat flux. As an example of the technique, the formulas are applied to the cases of heat transfer to air slot jets impinging on flat and concave surfaces. It is shown that for many practical problems, the use of very small heat flux gages is often unnecessary.

The study of heat flux for disruption on experimental advanced superconducting tokamak

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

Yang, Zhendong, E-mail: dongyz@ipp.ac.cn, E-mail: jafang@dhu.edu.cn; Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031; Fang, Jianan, E-mail: dongyz@ipp.ac.cn, E-mail: jafang@dhu.edu.cn

Disruption of the plasma is one of the most dangerous instabilities in tokamak. During the disruption, most of the plasma thermal energy is lost, which causes damages to the plasma facing components. Infrared (IR) camera is an effective tool to detect the temperature distribution on the first wall, and the energy deposited on the first wall can be calculated from the surface temperature profile measured by the IR camera. This paper concentrates on the characteristics of heat flux distribution onto the first wall under different disruptions, including the minor disruption and the vertical displacement events (VDE) disruption. Several minor disruptionsmore » have been observed before the major disruption under the high plasma density in experimental advanced superconducting tokamak. During the minor disruption, the heat fluxes are mainly deposited on the upper/lower divertors. The magnetic configuration prior to the minor disruption is a lower single null with the radial distance between the two separatrices in the outer midplane dR{sub sep} = −2 cm, while it changes to upper single null (dR{sub sep} = 1.4 cm) during the minor disruption. As for the VDE disruption, the spatial distribution of heat flux exhibits strong toroidal and radial nonuniformity, and the maximum heat flux received on the dome plate can be up to 11 MW/m{sup 2}.« less

The truth is out there: measured, calculated and modelled benthic fluxes.

NASA Astrophysics Data System (ADS)

Pakhomova, Svetlana; Protsenko, Elizaveta

2016-04-01

In a modern Earth science there is a great importance of understanding the processes, forming the benthic fluxes as one of element sources or sinks to or from the water body, which affects the elements balance in the water system. There are several ways to assess benthic fluxes and here we try to compare the results obtained by chamber experiments, calculated from porewater distributions and simulated with model. Benthic fluxes of dissolved elements (oxygen, nitrogen species, phosphate, silicate, alkalinity, iron and manganese species) were studied in the Baltic and Black Seas from 2000 to 2005. Fluxes were measured in situ using chamber incubations (Jch) and at the same time sediment cores were collected to assess the porewater distribution at different depths to calculate diffusive fluxes (Jpw). Model study was carried out with benthic-pelagic biogeochemical model BROM (O-N-P-Si-C-S-Mn-Fe redox model). It was applied to simulate biogeochemical structure of the water column and upper sediment and to assess the vertical fluxes (Jmd). By the behaviour at the water-sediment interface all studied elements can be divided into three groups: (1) elements which benthic fluxes are determined by the concentrations gradient only (Si, Mn), (2) elements which fluxes depend on redox conditions in the bottom water (Fe, PO4, NH4), and (3) elements which fluxes are strongly connected with organic matter fate (O2, Alk, NH4). For the first group it was found that measured fluxes are always higher than calculated diffusive fluxes (1.5

Electromagnetic Properties Analysis on Hybrid-driven System of Electromagnetic Motor

NASA Astrophysics Data System (ADS)

Zhao, Jingbo; Han, Bingyuan; Bei, Shaoyi

2018-01-01

The hybrid-driven system made of permanent-and electromagnets applied in the electromagnetic motor was analyzed, equivalent magnetic circuit was used to establish the mathematical models of hybrid-driven system, based on the models of hybrid-driven system, the air gap flux, air-gap magnetic flux density, electromagnetic force was proposed. Taking the air-gap magnetic flux density and electromagnetic force as main research object, the hybrid-driven system was researched. Electromagnetic properties of hybrid-driven system with different working current modes is studied preliminary. The results shown that analysis based on hybrid-driven system can improve the air-gap magnetic flux density and electromagnetic force more effectively and can also guarantee the output stability, the effectiveness and feasibility of the hybrid-driven system are verified, which proved theoretical basis for the design of hybrid-driven system.

Mitigation of methane emissions in a pilot-scale biocover system at the AV Miljø Landfill, Denmark: 1. System design and gas distribution.

PubMed

Cassini, Filippo; Scheutz, Charlotte; Skov, Bent H; Mou, Zishen; Kjeldsen, Peter

2017-05-01

Greenhouse gas mitigation at landfills by methane oxidation in engineered biocover systems is believed to be a cost effective technology, but so far a full quantitative evaluation of the efficiency of the technology in full scale has only been carried out in a few cases. A third generation semi-passive biocover system was constructed at the AV Miljø Landfill, Denmark. The biocover system was fed by landfill gas pumped out of three leachate collection wells. An innovative gas distribution system was used to overcome the commonly observed surface emission hot spot areas resulting from an uneven gas distribution to the active methane oxidation layer, leading to areas with methane overloading. Performed screening of methane and carbon dioxide surface concentrations, as well as flux measurement using a flux chamber at the surface of the biocover, showed homogenous distributions indicating an even gas distribution. This was supported by results from a tracer gas test where the compound HFC-134a was added to the gas inlet over an adequately long time period to obtain tracer gas stationarity in the whole biocover system. Studies of the tracer gas movement within the biocover system showed a very even gas distribution in gas probes installed in the gas distribution layer. Also the flux of tracer gas out of the biocover surface, as measured by flux chamber technique, showed a spatially even distribution. Installed probes logging the temperature and moisture content of the methane oxidation layer at different depths showed elevated temperatures in the layer with temperature differences to the ambient temperature in the range of 25-50°C at the deepest measuring point due to the microbial processes occurring in the layer. The moisture measurements showed that infiltrating precipitation was efficiently drained away from the methane oxidation layer. Copyright © 2017 Elsevier Ltd. All rights reserved.

Local and global stability for Lotka-Volterra systems with distributed delays and instantaneous negative feedbacks

NASA Astrophysics Data System (ADS)

Faria, Teresa; Oliveira, José J.

This paper addresses the local and global stability of n-dimensional Lotka-Volterra systems with distributed delays and instantaneous negative feedbacks. Necessary and sufficient conditions for local stability independent of the choice of the delay functions are given, by imposing a weak nondelayed diagonal dominance which cancels the delayed competition effect. The global asymptotic stability of positive equilibria is established under conditions slightly stronger than the ones required for the linear stability. For the case of monotone interactions, however, sharper conditions are presented. This paper generalizes known results for discrete delays to systems with distributed delays. Several applications illustrate the results.

Constraining the Surface Energy Balance of Snow in Complex Terrain

NASA Astrophysics Data System (ADS)

Lapo, Karl E.

Physically-based snow models form the basis of our understanding of current and future water and energy cycles, especially in mountainous terrain. These models are poorly constrained and widely diverge from each other, demonstrating a poor understanding of the surface energy balance. This research aims to improve our understanding of the surface energy balance in regions of complex terrain by improving our confidence in existing observations and improving our knowledge of remotely sensed irradiances (Chapter 1), critically analyzing the representation of boundary layer physics within land models (Chapter 2), and utilizing relatively novel observations to in the diagnoses of model performance (Chapter 3). This research has improved the understanding of the literal and metaphorical boundary between the atmosphere and land surface. Solar irradiances are difficult to observe in regions of complex terrain, as observations are subject to harsh conditions not found in other environments. Quality control methods were developed to handle these unique conditions. These quality control methods facilitated an analysis of estimated solar irradiances over mountainous environments. Errors in the estimated solar irradiance are caused by misrepresenting the effect of clouds over regions of topography and regularly exceed the range of observational uncertainty (up to 80Wm -2) in all regions examined. Uncertainty in the solar irradiance estimates were especially pronounced when averaging over high-elevation basins, with monthly differences between estimates up to 80Wm-2. These findings can inform the selection of a method for estimating the solar irradiance and suggest several avenues of future research for improving existing methods. Further research probed the relationship between the land surface and atmosphere as it pertains to the stable boundary layers that commonly form over snow-covered surfaces. Stable conditions are difficult to represent, especially for low wind speed values and coupled land-atmosphere models have difficulty representing these processes. We developed a new method analyzing turbulent fluxes at the land surface that relies on using the observed surface temperature, which we called the offline turbulence method. We used this method to test a number of stability schemes as they are implemented within land models. Stability schemes can cause small biases in the simulated sensible heat flux, but these are caused by compensating errors, as no single method was able to accurately reproduce the observed distribution of the sensible heat flux. We described how these turbulence schemes perform within different turbulence regimes, particularly noting the difficulty representing turbulence during conditions with faster wind speeds and the transition between weak and strong wind turbulence regimes. Heterogeneity in the horizontal distribution of surface temperature associated with different land surface types likely explains some of the missing physics within land models and is manifested as counter-gradient fluxes in observations. The coupling of land and atmospheric models needs further attention, as we highlight processes that are missing. Expanding on the utility of surface temperature, Ts, in model evaluations, we demonstrated the utility of using surface temperature in snow models evaluations. Ts is the diagnostic variable of the modeled surface energy balance within physically-based models and is an ideal supplement to traditional evaluation techniques. We demonstrated how modeling decisions affect Ts, specifically testing the impact of vertical layer structure, thermal conductivity, and stability corrections in addition to the effect of uncertainty in forcing data on simulated Ts. The internal modeling decisions had minimal impacts relative to uncertainty in the forcing data. Uncertainty in downwelling longwave was found to have the largest impact on simulated Ts. Using Ts, we demonstrated how various errors in the forcing data can be identified, noting that uncertainty in downwelling longwave and wind are the easiest to identify due to their effect on night time minimum Ts.

Dual-keel electrodynamic maglev system

DOEpatents

He, Jianliang; Wang, Zian; Rote, Donald M.; Coffey, Howard T.; Hull, John R.; Mulcahy, Thomas M.; Cal, Yigang

1996-01-01

A propulsion and stabilization system with a plurality of superconducting magnetic devices affixed to the dual-keels of a vehicle, where the superconducting magnetic devices produce a magnetic field when energized. The system also includes a plurality of figure-eight shaped null-flux coils affixed to opposing vertical sides of slots in a guideway. The figure-eight shaped null-flux coils are vertically oriented, laterally cross-connected in parallel, longitudinally connected in series, and continue the length of the vertical slots providing levitation and guidance force. An external power source energizes the figure-eight shaped null-flux coils to create a magnetic traveling wave that interacts with the magnetic field produced by the superconducting magnets to impart motion to the vehicle.

An improved flux-split algorithm applied to hypersonic flows in chemical equilibrium

NASA Technical Reports Server (NTRS)

Palmer, Grant

1988-01-01

An explicit, finite-difference, shock-capturing numerical algorithm is presented and applied to hypersonic flows assumed to be in thermochemical equilibrium. Real-gas chemistry is either loosely coupled to the gasdynamics by way of a Gibbs free energy minimization package or fully coupled using species mass conservation equations with finite-rate chemical reactions. A scheme is developed that maintains stability in the explicit, finite-rate formulation while allowing relatively high time steps. The codes use flux vector splitting to difference the inviscid fluxes and employ real-gas corrections to viscosity and thermal conductivity. Numerical results are compared against existing ballistic range and flight data. Flows about complex geometries are also computed.

Mechanisms of heat and mass transfer across a double-diffusive interface

NASA Astrophysics Data System (ADS)

Ko, B. H.; Smith, K. A.

1984-06-01

Flux measurements in an aqueous two-layer double-diffusive system using heat and NaCl confirmed the existence of a regime in which the ratio of the buoyancy fluxes (BFR) of salt and heat is independent of the stability ratio (R = beta(delta C)/alpha(delta T)). Linear analysis showed that the quiescent system can become unstable to small perturbations even when the lower layer is denser than the upper. If R is large, the most unstable mode presents as an oscillatory, antisymmetric pattern.

Hydrological patterns in warming permafrost: comparing results from a control and drained site on a floodplain tundra near Chersky, Northeast Siberia

NASA Astrophysics Data System (ADS)

Boelck, Sandra; Goeckede, Mathias; Hildebrandt, Anke; Vonk, Jorien; Heimann, Martin

2017-04-01

Permafrost areas represent a major reservoir for organic carbon. At the same time, permafrost ecosystems are very susceptible to changing climate conditions. The stability of this reservoir, i.e. changes in lateral and vertical carbon fluxes in permafrost ecosystems, largely depends on groundwater level, temperature and vegetation community. Particularly during summer when the soil thaws and a so-called active layer develops, fluctuations in carbon flux rates are often dominantly driven by water availability. Such dry soil conditions are expected to become more frequent in the future due to deepening active layers as a consequence of climate change. This could result in degradation of polygonal tundra landscape properties with channelled water transport pathways. Therefore, water table depth and the associated groundwater fluxes are crucial to understand transport patterns and to quantify the lateral export of carbon through an aquatic system. Consequently, a fundamental understanding of hydrological patterns on ecosystem structure and function is required to close the carbon balance of permafrost ecosystems. This study focuses on small-scale hydrological patterns and its influencing factors, such as topography and precipitation events. Near Chersky, Northeast Siberia, we monitored (i) a control site of floodplain tundra, and (ii) a drained site, characterised by a drainage ring which was constructed in 2004, to study the effects of water availability on the carbon cycle. This experimental disturbance simulates drainage effects following the degradation of ice-rich permafrost ecosystems under future climate change. Continuous monitoring of water table depth in drained and control areas revealed small-scale water table variations. At several key locations, we collected water samples to determine the isotopic composition (δ18O, δD) of surface water, suprapermafrost groundwater and precipitation. Furthermore, a weir at the drainage ditch was constructed to directly measure the discharge of the drained system. This hydrological sampling programme was complemented by continuous monitoring of atmospheric vertical turbulent carbon fluxes and meteorological conditions by two eddy-covariance towers on each site. Our results from the hydrological sampling campaign of summer 2016 indicate that total discharge through the drained system was mainly driven by precipitation events as well as modified evaporative loss due to temperature changes. The distributed network of groundwater gauges allows deriving lateral, local scale groundwater flow direction and its spatial variability, as well as the response to precipitation events within different parts of this ecosystem. Isotopic analysis of water samples showed the contribution of specific end member water sources, and how these vary across the season while the active layer deepens. Future research will focus on carbon fluxes, distribution and sources in relation to hydrological patterns.

Methane fluxes during the cold season: distribution and mass transfer in the snow cover of bogs

NASA Astrophysics Data System (ADS)

Smagin, A. V.; Shnyrev, N. A.

2015-08-01

Fluxes and profile distribution of methane in the snow cover and different landscape elements of an oligotrophic West-Siberian bog (Mukhrino Research Station, Khanty-Mansiisk autonomous district) have been studied during a cold season. Simple models have been proposed for the description of methane distribution in the inert snow layer, which combine the transport of the gas and a source of constant intensity on the soil surface. The formation rates of stationary methane profiles in the snow cover have been estimated (characteristic time of 24 h). Theoretical equations have been derived for the calculation of small emission fluxes from bogs to the atmosphere on the basis of the stationary profile distribution parameters, the snow porosity, and the effective methane diffusion coefficient in the snow layer. The calculated values of methane emission significantly (by 2-3 to several tens of times) have exceeded the values measured under field conditions by the closed chamber method (0.008-0.25 mg C/(m2 h)), which indicates the possibility of underestimating the contribution of the cold period to the annual emission cycle of bog methane.

The global distribution of magnetic helicity in the solar corona

NASA Astrophysics Data System (ADS)

Yeates, A. R.; Hornig, G.

2016-10-01

By defining an appropriate field line helicity, we apply the powerful concept of magnetic helicity to the problem of global magnetic field evolution in the Sun's corona. As an ideal-magnetohydrodynamic invariant, the field line helicity is a meaningful measure of how magnetic helicity is distributed within the coronal volume. It may be interpreted, for each magnetic field line, as a magnetic flux linking with that field line. Using magneto-frictional simulations, we investigate how field line helicity evolves in the non-potential corona as a result of shearing by large-scale motions on the solar surface. On open magnetic field lines, the helicity injected by the Sun is largely output to the solar wind, provided that the coronal relaxation is sufficiently fast. But on closed magnetic field lines, helicity is able to build up. We find that the field line helicity is non-uniformly distributed, and is highly concentrated in twisted magnetic flux ropes. Eruption of these flux ropes is shown to lead to sudden bursts of helicity output, in contrast to the steady flux along the open magnetic field lines. Movies are available at http://www.aanda.org

Atmospheric stability analysis over statically and dynamically rough surfaces

NASA Astrophysics Data System (ADS)

Maric, Emina; Metzger, Meredith; Singha, Arindam; Sadr, Reza

2011-11-01

The ratio of buoyancy flux to turbulent kinetic energy production in the atmospheric surface layer is investigated experimentally for air flow over two types of surfaces characterized by static and dynamic roughness. In this study, ``static'' refers to the time-invariant nature of naturally-occurring roughness over a mud/salt playa; while, ``dynamic'' refers to the behavior of water waves along an air-water interface. In both cases, time-resolved measurements of the momentum and heat fluxes were acquired from synchronized 3D sonic anemometers mounted on a vertical tower. Field campaigns were conducted at two sites, representing the ``statically'' and ``dynamically'' rough surfaces, respectively: (1) the SLTEST facility in Utah's western desert, and (2) the new Doha airport in Qatar under construction along the coast of the Persian Gulf. Note, at site 2, anemometers were located directly above the water by extension from a tower secured to the end of a 1 km-long pier. Comparisons of the Monin-Obukhov length, flux Richardson number, and gradient Richardson number are presented, and discussed in the context of the observed evolution of the turbulent spectra in response to diurnal variations of atmospheric stability. Supported by the Qatar National Research Fund.

The effect of heat treatment on the stability of Nb 3Sn RRP-150/169 strands

DOE PAGES

Li, Pei; Turrioni, Daniele; Barzi, Emanuela; ...

2017-02-17

Here, the magnetic stability of superconductor strands and cables is a key issue in the successful building and operation of high-field accelerator magnets. In this paper, we report the study of a state-of-the-art 0.7 mm Nb 3Sn restacked-rod-process strand manufactured by Oxford Instrument Superconductor Technology. This conductor will be used in Rutherford cable for a 15-T Nb 3Sn dipole demonstrator being built at Fermi National Accelerator Laboratory. Particularly, this study focuses on the impact of varying heat treatment conditions on the stability of the strand. Both the stability against internal flux jumps and external thermal perturbations are studied.

The effect of heat treatment on the stability of Nb 3Sn RRP-150/169 strands

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

Li, Pei; Turrioni, Daniele; Barzi, Emanuela

Here, the magnetic stability of superconductor strands and cables is a key issue in the successful building and operation of high-field accelerator magnets. In this paper, we report the study of a state-of-the-art 0.7 mm Nb 3Sn restacked-rod-process strand manufactured by Oxford Instrument Superconductor Technology. This conductor will be used in Rutherford cable for a 15-T Nb 3Sn dipole demonstrator being built at Fermi National Accelerator Laboratory. Particularly, this study focuses on the impact of varying heat treatment conditions on the stability of the strand. Both the stability against internal flux jumps and external thermal perturbations are studied.

Local bounds preserving stabilization for continuous Galerkin discretization of hyperbolic systems

NASA Astrophysics Data System (ADS)

Mabuza, Sibusiso; Shadid, John N.; Kuzmin, Dmitri

2018-05-01

The objective of this paper is to present a local bounds preserving stabilized finite element scheme for hyperbolic systems on unstructured meshes based on continuous Galerkin (CG) discretization in space. A CG semi-discrete scheme with low order artificial dissipation that satisfies the local extremum diminishing (LED) condition for systems is used to discretize a system of conservation equations in space. The low order artificial diffusion is based on approximate Riemann solvers for hyperbolic conservation laws. In this case we consider both Rusanov and Roe artificial diffusion operators. In the Rusanov case, two designs are considered, a nodal based diffusion operator and a local projection stabilization operator. The result is a discretization that is LED and has first order convergence behavior. To achieve high resolution, limited antidiffusion is added back to the semi-discrete form where the limiter is constructed from a linearity preserving local projection stabilization operator. The procedure follows the algebraic flux correction procedure usually used in flux corrected transport algorithms. To further deal with phase errors (or terracing) common in FCT type methods, high order background dissipation is added to the antidiffusive correction. The resulting stabilized semi-discrete scheme can be discretized in time using a wide variety of time integrators. Numerical examples involving nonlinear scalar Burgers equation, and several shock hydrodynamics simulations for the Euler system are considered to demonstrate the performance of the method. For time discretization, Crank-Nicolson scheme and backward Euler scheme are utilized.

Confined Rayleigh-Bénard, Rotating Rayleigh-Bénard, and Double Diffusive Convection: A Unifying View on Turbulent Transport Enhancement through Coherent Structure Manipulation

NASA Astrophysics Data System (ADS)

Chong, Kai Leong; Yang, Yantao; Huang, Shi-Di; Zhong, Jin-Qiang; Stevens, Richard J. A. M.; Verzicco, Roberto; Lohse, Detlef; Xia, Ke-Qing

2017-08-01

Many natural and engineering systems are simultaneously subjected to a driving force and a stabilizing force. The interplay between the two forces, especially for highly nonlinear systems such as fluid flow, often results in surprising features. Here we reveal such features in three different types of Rayleigh-Bénard (RB) convection, i.e., buoyancy-driven flow with the fluid density being affected by a scalar field. In the three cases different stabilizing forces are considered, namely (i) horizontal confinement, (ii) rotation around a vertical axis, and (iii) a second stabilizing scalar field. Despite the very different nature of the stabilizing forces and the corresponding equations of motion, at moderate strength we counterintuitively but consistently observe an enhancement in the flux, even though the flow motion is weaker than the original RB flow. The flux enhancement occurs in an intermediate regime in which the stabilizing force is strong enough to alter the flow structures in the bulk to a more organized morphology, yet not too strong to severely suppress the flow motions. Near the optimal transport enhancements all three systems exhibit a transition from a state in which the thermal boundary layer (BL) is nested inside the momentum BL to the one with the thermal BL being thicker than the momentum BL. The observed optimal transport enhancement is explained through an optimal coupling between the suction of hot or fresh fluid and the corresponding scalar fluctuations.

Subglacial sedimentary basin characterization of Wilkes Land, East Antarctica via applied aerogeophysical inverse methods

NASA Astrophysics Data System (ADS)

Frederick, B. C.; Gooch, B. T.; Richter, T.; Young, D. A.; Blankenship, D. D.; Aitken, A.; Siegert, M. J.

2013-12-01

Topography, sediment distribution and heat flux are all key boundary conditions governing the stability of the East Antarctic ice sheet (EAIS). Recent scientific scrutiny has been focused on several large, deep, interior EAIS basins including the submarine basal topography characterizing the Aurora Subglacial Basin (ASB). Numerical ice sheet models require accurate deformable sediment distribution and lithologic character constraints to estimate overall flow velocities and potential instability. To date, such estimates across the ASB have been derived from low-resolution satellite data or historic aerogeophysical surveys conducted prior to the advent of GPS. These rough basal condition estimates have led to poorly-constrained ice sheet stability models for this remote 200,000 sq km expanse of the ASB. Here we present a significantly improved quantitative model characterizing the subglacial lithology and sediment in the ASB region. The product of comprehensive ICECAP (2008-2013) aerogeophysical data processing, this sedimentary basin model details the expanse and thickness of probable Wilkes Land subglacial sedimentary deposits and density contrast boundaries indicative of distinct subglacial lithologic units. As part of the process, BEDMAP2 subglacial topographic results were improved through the additional incorporation of ice-penetrating radar data collected during ICECAP field seasons 2010-2013. Detailed potential field data pre-processing was completed as well as a comprehensive evaluation of crustal density contrasts based on the gravity power spectrum, a subsequent high pass data filter was also applied to remove longer crustal wavelengths from the gravity dataset prior to inversion. Gridded BEDMAP2+ ice and bed radar surfaces were then utilized to establish bounding density models for the 3D gravity inversion process to yield probable sedimentary basin anomalies. Gravity inversion results were iteratively evaluated against radar along-track RMS deviation and gravity and magnetic depth to basement results. This geophysical data processing methodology provides a substantial improvement over prior Wilkes Land sedimentary basin estimates yielding a higher resolution model based upon iteration of several aerogeophysical datasets concurrently. This more detailed subglacial sedimentary basin model for Wilkes Land, East Antarctica will not only contribute to vast improvements on EAIS ice sheet model constraints, but will also provide significant quantifiable controls for subglacial hydrologic and geothermal flux estimates that are also sizable contributors to the cold-based, deep interior basal ice dynamics dominant in the Wilkes Land region.

The Role of Self-Organized Criticality in the Substorm Phenomenon and its Relation to Localized Reconnection in the Magnetospheric Plasma Sheet

NASA Technical Reports Server (NTRS)

Klimas, Alex J.; Valdivia, J. A.; Vassiliadis, D.; Baker, D. N.; Hesse, M.; Takalo, J.

1999-01-01

Evidence is presented that suggests there is a significant self-organized criticality (SOC) component in the dynamics of substorms in the magnetosphere. Observations of BBFs, fast flows, localized dipolarizations, plasma turbulence, etc. are taken to show that multiple localized reconnection sites provide the basic avalanche phenomenon in the establishment of SOC in the plasma sheet. First results are presented from a continuing plasma physical study of this avalanche process. A one-dimensional resistive MHD model of a magnetic field reversal is discussed. Resistivity, in this model, is self-consistently generated in response to the excitation of an idealized current-driven instability. When forced by convection of magnetic flux into the field reversal region, the model yields rapid magnetic field annihilation through a dynamic behavior that is shown to exhibit many of the characteristics of SOC. Over a large range of forcing strengths, the annihilation rate is shown to self-adjust to balance the rate at which flux is convected into the reversal region. Several analogies to magnetotail dynamics are discussed: (1) It is shown that the presence of a localized criticality in the model produces a remarkable stability in the global configuration of the field reversal while simultaneously exciting extraordinarily dynamic internal evolution. (2) Under steady forcing, it is shown that a loading-unloading cycle may arise that, as a consequence of the global stability, is quasi-periodic and, therefore, predictable despite the presence of internal turbulence in the field distribution. Indeed, it is shown that the global loading-unloading cycle is a consequence of the internal turbulence. (3) It is shown that, under steady, strong forcing the loading-unloading cycle vanishes. Instead, a recovery from a single unloading persists indefinitely. The field reversal is globally very steady while internally it is very dynamic as field annihilation goes on at the rate necessary to match the strong forcing. From this result we speculate that steady magnetospheric convection events result when the plasma sheet has been driven close to criticality over an extended spatial domain. During these events, we would expect to find localized reconnection sites distributed over the spatial domain of near criticality and we would expect to find plasma sheet transport in that domain to be closely related to that of BBF and fast flow events.

Polarized neutron imaging and three-dimensional calculation of magnetic flux trapping in bulk of superconductors

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

Treimer, Wolfgang; Ebrahimi, Omid; Karakas, Nursel

Polarized neutron radiography was used to study the three-dimensional magnetic flux distribution inside of single-crystal and polycrystalline Pb cylinders with large (cm3) volume and virtually zero demagnetization. Experiments with single crystals being in the Meissner phase (T

Derivation of regularized Grad's moment system from kinetic equations: modes, ghosts and non-Markov fluxes

NASA Astrophysics Data System (ADS)

Karlin, Ilya

2018-04-01

Derivation of the dynamic correction to Grad's moment system from kinetic equations (regularized Grad's 13 moment system, or R13) is revisited. The R13 distribution function is found as a superposition of eight modes. Three primary modes, known from the previous derivation (Karlin et al. 1998 Phys. Rev. E 57, 1668-1672. (doi:10.1103/PhysRevE.57.1668)), are extended into the nonlinear parameter domain. Three essentially nonlinear modes are identified, and two ghost modes which do not contribute to the R13 fluxes are revealed. The eight-mode structure of the R13 distribution function implies partition of R13 fluxes into two types of contributions: dissipative fluxes (both linear and nonlinear) and nonlinear streamline convective fluxes. Physical interpretation of the latter non-dissipative and non-local in time effect is discussed. A non-perturbative R13-type solution is demonstrated for a simple Lorentz scattering kinetic model. The results of this study clarify the intrinsic structure of the R13 system. This article is part of the theme issue `Hilbert's sixth problem'.

Heat transfer experiments with a central receiver tube subjected to unsteady and non-uniform heat flux

NASA Astrophysics Data System (ADS)

Fernández-Torrijos, María; Marugán-Cruz, Carolina; Sobrino, Celia; Santana, Domingo

2017-06-01

In this work, a molten salt test loop to study the heat transfer process in external molten salt receivers is described. The experimental installation is formed by a cylindrical molten salt tank, a pump, a flow meter, and an induction heater to generate the heat flux, which is applied in a small rectangular region of the tube surface. In central tower plants, the external receiver pipe is considered to be under unilateral concentrated solar radiation, because only one side of the pipe receives high heat flux. The main advantage of using an induction heater is the control of heating in different areas of the tube. In order to measure the effects of a non-homogenous and unsteady heat flux on the wall temperature distribution a series of experiments have been carried out. 4 K-type thermocouples have been welded at different axial and azimuthal positions of the pipe to obtain the wall temperature distribution. Different temperature measurements have been made varying the heat flux and water velocity to study their effects on the heat transfer process.

HOPE Survey of the Near-Equatorial Magnetosphere Plasma Environment

NASA Astrophysics Data System (ADS)

Fernandes, P. A.; Larsen, B.; Skoug, R. M.; Reeves, G. D.; Denton, M.; Thomsen, M. F.; Funsten, H. O.; Jahn, J. M.; MacDonald, E.

2016-12-01

The twin Van Allen Probes spacecraft have completed over four years on-orbit resulting in more than 2 full precessions in local time. We present for the first time a summary of the plasma environment at the near-equatorial magnetosphere inside geostationary orbit from the HOPE (Helium-Oxygen-Proton-Electron) spectrometer. This rich data set is comprised of 48 months of release 3 particle data for electrons, protons, helium ions, and oxygen ions for energies from 15 eV to 50 keV. For each species we calculate median fluxes and flux distributions over the instrument energy range. We present the L and MLT (magnetic local time) distributions of these fluxes, percentiles, and flux ratios. This full-coverage survey, over an extended duration and range of energies and L-shells, examines the ion and electron fluxes and their ratios as a function of solar and geomagnetic activity. This detailed observation of the near-equatorial plasma environment reproduces well-known phenomenology in the energy ranges of overlap, and interpretation focuses on the structure, composition, and dynamics of the inner magnetosphere for various degrees of geomagnetic activity.

Dimethyl sulfide in the surface ocean and the marine atmosphere: a global view.

PubMed

Andreae, M O; Raemdonck, H

1983-08-19

Dimethyl sulfide (DMS) has been identified as the major volatile sulfur compound in 628 samples of surface seawater representing most of the major oceanic ecozones. In at least three respects, its vertical distribution, its local patchiness, and its distribution in oceanic ecozones, the concentration of DMS in the sea exhibits a pattern similar to that of primary production. The global weightedaverage concentration of DMS in surface seawater is 102 nanograms of sulfur (DMS) per liter, corresponding to a global sea-to-air flux of 39 x 10(12) grams of sulfur per year. When the biogenic sulfur contributions from the land surface are added, the biogenic sulfur gas flux is approximately equal to the anthropogenic flux of sulfur dioxide. The DMS concentration in air over the equatorial Pacific varies diurnally between 120 and 200 nanograms of sulfur (DMS) per cubic meter, in agreement with the predictions of photochemical models. The estimated source flux of DMS from the oceans to the marine atmosphere is in agreement with independently obtained estimates of the removal fluxes of DMS and its oxidation products from the atmosphere.

Dimethyl Sulfide in the Surface Ocean and the Marine Atmosphere: A Global View

NASA Astrophysics Data System (ADS)

Andreae, Meinrat O.; Raemdonck, Hans

1983-08-01

Dimethyl sulfide (DMS) has been identified as the major volatile sulfur compound in 628 samples of surface seawater representing most of the major oceanic ecozones. In at least three respects, its vertical distribution, its local patchiness, and its distribution in oceanic ecozones, the concentration of DMS in the sea exhibits a pattern similar to that of primary production. The global weighted-average concentration of DMS in surface seawater is 102 nanograms of sulfur (DMS) per liter, corresponding to a global sea-to-air flux of 39 × 1012 grams of sulfur per year. When the biogenic sulfur contributions from the land surface are added, the biogenic sulfur gas flux is approximately equal to the anthropogenic flux of sulfur dioxide. The DMS concentration in air over the equatorial Pacific varies diurnally between 120 and 200 nanograms of sulfur (DMS) per cubic meter, in agreement with the predictions of photochemical models. The estimated source flux of DMS from the oceans to the marine atmosphere is in agreement with independently obtained estimates of the removal fluxes of DMS and its oxidation products from the atmosphere.

Additional flux of particles and albedo-electrons in upper atmosphere

NASA Technical Reports Server (NTRS)

Aitbaev, F. B.; Dyuisembaev, B. M.; Kolomeets, E. V.

1985-01-01

The results are presented of the Monte Carlo simulation of albedo flux from the dense layers of the Earth's atmosphere and the dependence of angular distribution on the rigidity of geomagnetic cut off and additional flux of particles at the depth in the atmosphere 15-20 g/sq sm. Influence of geomagnetic field on the propagation of charged particles was not taken into account.

Space shuttle cavity assessment test program

NASA Technical Reports Server (NTRS)

Scheps, P. B.

1976-01-01

In order to obtain basic radiation properties of the radiator/payload bay door cavity, three tests were conducted on a full-size structural simulator of the cavity. There were three tests conducted: (1) CATA used for determination of exchange factors, absorbed solar flux, and door covering influences, (2) quartz lamp array calibrated to provide IR flux distribution on CATA, and (3) retest with radiometer array for background flux measurement.

Wind-tunnel experiments of scalar transport in aligned and staggered wind farms

NASA Astrophysics Data System (ADS)

Zhang, W.; Markfort, C. D.; Porté-Agel, F.

2012-04-01

Wind energy is the fastest growing renewable energy worldwide, and it is expected that many more large-scale wind farms will be built and will cover a significant portion of land and ocean surfaces. By extracting kinetic energy from the atmospheric boundary layer, wind farms may affect the exchange/transport of momentum, heat and moisture between the atmosphere and land surface. To ensure the long-term sustainability of wind energy, it is important to understand the influence of large-scale wind farms on land-atmosphere interaction. Knowledge of this impact will also be useful to improve parameterizations of wind farms in numerical prediction tools, such as large-scale weather models and large-eddy simulation. Here, we present wind-tunnel measurements of the surface scalar (heat) flux from model wind farms, consisting of more than 10 rows of wind turbines, in a turbulent boundary layer with a surface heat source. Spatially distributed surface heat flux was obtained in idealized aligned and staggered wind farm layouts, having the same turbine distribution density. Measurements, using surface-mounted heat flux sensors, were taken at the 11th out of 12 rows of wind turbines, where the mean flow achieves a quasi-equilibrium state. In the aligned farm, there exist two distinct regions of increased and decreased surface heat flux on either side of turbine columns. The regions are correlated with coherent wake rotation in the turbine-array. On the upwelling side there is decreased flux, while on the downwelling side cool air moves towards the surface causing increased flux. For the staggered farm, the surface heat flux exhibits a relatively uniform distribution and an overall reduction with respect to the boundary layer flow, except in the vicinity of the turbine tower. This observation is also supported by near-surface temperature and turbulent heat flux measured using a customized x-wire/cold-wire. The overall surface heat flux, relative to that of the boundary layer flow without wind turbines, is reduced by approximately 4% in the staggered wind farm and remains nearly the same in the aligned wind farm.

Reconstruction and flux analysis of coupling between metabolic pathways of astrocytes and neurons: application to cerebral hypoxia

PubMed Central

Çakιr, Tunahan; Alsan, Selma; Saybaşιlι, Hale; Akιn, Ata; Ülgen, Kutlu Ö

2007-01-01

Background It is a daunting task to identify all the metabolic pathways of brain energy metabolism and develop a dynamic simulation environment that will cover a time scale ranging from seconds to hours. To simplify this task and make it more practicable, we undertook stoichiometric modeling of brain energy metabolism with the major aim of including the main interacting pathways in and between astrocytes and neurons. Model The constructed model includes central metabolism (glycolysis, pentose phosphate pathway, TCA cycle), lipid metabolism, reactive oxygen species (ROS) detoxification, amino acid metabolism (synthesis and catabolism), the well-known glutamate-glutamine cycle, other coupling reactions between astrocytes and neurons, and neurotransmitter metabolism. This is, to our knowledge, the most comprehensive attempt at stoichiometric modeling of brain metabolism to date in terms of its coverage of a wide range of metabolic pathways. We then attempted to model the basal physiological behaviour and hypoxic behaviour of the brain cells where astrocytes and neurons are tightly coupled. Results The reconstructed stoichiometric reaction model included 217 reactions (184 internal, 33 exchange) and 216 metabolites (183 internal, 33 external) distributed in and between astrocytes and neurons. Flux balance analysis (FBA) techniques were applied to the reconstructed model to elucidate the underlying cellular principles of neuron-astrocyte coupling. Simulation of resting conditions under the constraints of maximization of glutamate/glutamine/GABA cycle fluxes between the two cell types with subsequent minimization of Euclidean norm of fluxes resulted in a flux distribution in accordance with literature-based findings. As a further validation of our model, the effect of oxygen deprivation (hypoxia) on fluxes was simulated using an FBA-derivative approach, known as minimization of metabolic adjustment (MOMA). The results show the power of the constructed model to simulate disease behaviour on the flux level, and its potential to analyze cellular metabolic behaviour in silico. Conclusion The predictive power of the constructed model for the key flux distributions, especially central carbon metabolism and glutamate-glutamine cycle fluxes, and its application to hypoxia is promising. The resultant acceptable predictions strengthen the power of such stoichiometric models in the analysis of mammalian cell metabolism. PMID:18070347

Role of surface heat fluxes underneath cold pools

DOE PAGES

Gentine, Pierre; Garelli, Alix; Park, Seung -Bu; ...

2016-01-05

In this paper, the role of surface heat fluxes underneath cold pools is investigated using cloud–resolving simulations with either interactive or horizontally homogenous surface heat fluxes over an ocean and a simplified land surface. Over the ocean, there are limited changes in the distribution of the cold pool temperature, humidity, and gust front velocity, yet interactive heat fluxes induce more cold pools, which are smaller, and convection is then less organized. Correspondingly, the updraft mass flux and lateral entrainment are modified. Over the land surface, the heat fluxes underneath cold pools drastically impact the cold pool characteristics with more numerousmore » and smaller pools, which are warmer and more humid and accompanied by smaller gust front velocities. The interactive fluxes also modify the updraft mass flux and reduce convective organization. These results emphasize the importance of interactive surface fluxes instead of prescribed flux boundary conditions, as well as the formulation of surface heat fluxes, when studying convection.« less

Viscous hydrodynamic instability theory of the peak and minimum pool boiling heat fluxes

NASA Technical Reports Server (NTRS)

Dhir, V. K.

1972-01-01

Liquid viscosity was included in the Bellman-Pennington theory of the Taylor wave in a liquid vapor interface. Predictions of the most susceptible wavelength, and of the wave frequency, were made as a function of a liquid viscosity parameter and the Bond number. The stability of a gas jet in a viscous liquid was studied and the result is used to predict the peak heat flux on large horizontal heaters. Experimental measurements of the dominant Taylor wave and its growth rate were made during the film boiling of cyclohexanol on cylindrical heaters. The results bear out the predictions quite well. The thickness of the vapor blanket surrounding a cylindrical heater was measured and a correlation suggested. The effect of large fluxes of vapor volume on the dominant wavelength was also noted. Theoretical results of the peak heat flux are compared with the experimental data, and the effect of finite geometry of flat plate heaters on the peak heat flux is also discussed.

Trace Gas and Carbon Sequestration Dynamics in Temperate Croplands and Successional Ecosystems: A Full-Cost Accounting

NASA Astrophysics Data System (ADS)

Robertson, G. P.; McSwiney, C. P.

2003-12-01

Agriculture is responsible for 21-25% of the global anthropic CO2 flux, 55-60% of the anthropic CH4 flux, and 65-80% of the anthopic flux of N2O. A number of CO2 stabilization strategies target agricultural production practices, and the potential for simultaneously abating fluxes of the non-CO2 greenhouse gases is substantial. But so is the potential for creating greenhouse gas (GHG) liabilities, the unintentional increase in one or more GHGs by activities that mitigate another. Whole-system accounting provides a means for including all GHG-contributing processes in the same cropping system analysis in order to illuminate major liabilities and synergies. We contrast a field crop system in the upper U.S. midwest with unmanaged successional ecosystems in the same landscape, and provide evidence that N2O flux - the major contributor to radiative forcing in row-crop systems - can be abated with little loss of crop productivity.

High-order flux correction/finite difference schemes for strand grids

NASA Astrophysics Data System (ADS)

Katz, Aaron; Work, Dalon

2015-02-01

A novel high-order method combining unstructured flux correction along body surfaces and high-order finite differences normal to surfaces is formulated for unsteady viscous flows on strand grids. The flux correction algorithm is applied in each unstructured layer of the strand grid, and the layers are then coupled together via a source term containing derivatives in the strand direction. Strand-direction derivatives are approximated to high-order via summation-by-parts operators for first derivatives and second derivatives with variable coefficients. We show how this procedure allows for the proper truncation error canceling properties required for the flux correction scheme. The resulting scheme possesses third-order design accuracy, but often exhibits fourth-order accuracy when higher-order derivatives are employed in the strand direction, especially for highly viscous flows. We prove discrete conservation for the new scheme and time stability in the absence of the flux correction terms. Results in two dimensions are presented that demonstrate improvements in accuracy with minimal computational and algorithmic overhead over traditional second-order algorithms.

A scheme for computing surface layer turbulent fluxes from mean flow surface observations

NASA Technical Reports Server (NTRS)

Hoffert, M. I.; Storch, J.

1978-01-01

A physical model and computational scheme are developed for generating turbulent surface stress, sensible heat flux and humidity flux from mean velocity, temperature and humidity at some fixed height in the atmospheric surface layer, where conditions at this reference level are presumed known from observations or the evolving state of a numerical atmospheric circulation model. The method is based on coupling the Monin-Obukov surface layer similarity profiles which include buoyant stability effects on mean velocity, temperature and humidity to a force-restore formulation for the evolution of surface soil temperature to yield the local values of shear stress, heat flux and surface temperature. A self-contained formulation is presented including parameterizations for solar and infrared radiant fluxes at the surface. Additional parameters needed to implement the scheme are the thermal heat capacity of the soil per unit surface area, surface aerodynamic roughness, latitude, solar declination, surface albedo, surface emissivity and atmospheric transmissivity to solar radiation.

Advanced Tokamak Stability Theory

NASA Astrophysics Data System (ADS)

Zheng, Linjin

2015-03-01

The intention of this book is to introduce advanced tokamak stability theory. We start with the derivation of the Grad-Shafranov equation and the construction of various toroidal flux coordinates. An analytical tokamak equilibrium theory is presented to demonstrate the Shafranov shift and how the toroidal hoop force can be balanced by the application of a vertical magnetic field in tokamaks. In addition to advanced theories, this book also discusses the intuitive physics pictures for various experimentally observed phenomena.

Progress Report on Rotating Liquid Liner Implosion Experiment, 1 June to 31 December 1975.

DTIC Science & Technology

A critical question in the use of imploding liner flux compression for controlled fusion has been the stability of the inner surface of the liner ...To study the problem experimentally, the existing NRL Imploding Liner Facility was modified to allow the implosion of rotating liquid metal liners ...Rotational stabilization of lthe inner surface of a decelerating liquid sodium-potassium liner has been demonstrated, with excellent circularity of the

Using metabolic flux data to further constrain the metabolic solution space and predict internal flux patterns: the Escherichia coli spectrum.

PubMed

Wiback, Sharon J; Mahadevan, Radhakrishnan; Palsson, Bernhard Ø

2004-05-05

Constraint-based metabolic modeling has been used to capture the genome-scale, systems properties of an organism's metabolism. The first generation of these models has been built on annotated gene sequence. To further this field, we now need to develop methods to incorporate additional "omic" data types including transcriptomics, metabolomics, and fluxomics to further facilitate the construction, validation, and predictive capabilities of these models. The work herein combines metabolic flux data with an in silico model of central metabolism of Escherichia coli for model centric integration of the flux data. The extreme pathways for this network, which define the allowable solution space for all possible flux distributions, are analyzed using the alpha-spectrum. The alpha-spectrum determines which extreme pathways can and cannot contribute to the metabolic flux distribution for a given condition and gives the allowable range of weightings on each extreme pathway that can contribute. Since many extreme pathways cannot be used under certain conditions, the result is a "condition-specific" solution space that is a subset of the original solution space. The alpha-spectrum results are used to create a "condition-specific" extreme pathway matrix that can be analyzed using singular value decomposition (SVD). The first mode of the SVD analysis characterizes the solution space for a given condition. We show that SVD analysis of the alpha-spectrum extreme pathway matrix that incorporates measured uptake and byproduct secretion rates, can predict internal flux trends for different experimental conditions. These predicted internal flux trends are, in general, consistent with the flux trends measured using experimental metabolic flux analysis techniques. Copyright 2004 Wiley Periodicals, Inc.

Estimates of Oceanic Eddy Heat and Salt Transports from Satellite Altimetry and Argo Profile Data.

NASA Astrophysics Data System (ADS)

Amores Maimo, A. M.; Melnichenko, O.; Maximenko, N. A.

2016-12-01

Horizontal heat and salt fluxes by mesoscale eddies are estimated in the near-global ocean (10°-60° N and 10°-60° S) by combining historical records of Argo temperature/salinity profiles and satellite sea level anomaly data in the framework of the eddy tracking technique. The eddy fluxes are expectedly strong in the western boundary currents and in the Southern Ocean along the Antarctic Circumpolar Current (ACC). The fluxes are generally weak, but not negligible in gyre interiors. In the vertical, the eddy heat and salt fluxes are surface-intensified and confined mainly to the upper 600m layer, but their distribution with depth is not homogeneous throughout the ocean. In the Kuroshio Extension (KE) region, for example, the heat flux is poleward everywhere in the surface layer above the thermocline, but oppositely signed relative to the jet's axis in a deeper layer between approximately 300-800 m, where the flux is poleward on the northern side of the jet and equatorward on its southern side. Relatively strong fluxes at depth are also observed in the ACC, particularly in the Indian sector, and in the subtropical North Atlantic at the level of the Mediterranean Water (MW) at around 1000 m depth. The latter exemplifies the role of eddies in MW spreading. These and other features of the longitude-latitude-depth distributions of the eddy heat and salt fluxes, constructed for the first time from observational data, are presented and discussed.

Numerical Study of Nonlinear Structures of Locally Excited Marangoni Convection in the Long-Wave Approximation

NASA Astrophysics Data System (ADS)

Wertgeim, Igor I.

2018-02-01

We investigate stationary and non-stationary solutions of nonlinear equations of the long-wave approximation for the Marangoni convection caused by a localized source of heat or a surface active impurity (surfactant) in a thin horizontal layer of a viscous incompressible fluid with a free surface. The distribution of heat or concentration flux is determined by the uniform vertical gradient of temperature or impurity concentration, distorted by the imposition of a slightly inhomogeneous heating or of surfactant, localized in the horizontal plane. The lower boundary of the layer is considered thermally insulated or impermeable, whereas the upper boundary is free and deformable. The equations obtained in the long-wave approximation are formulated in terms of the amplitudes of the temperature distribution or impurity concentration, deformation of the surface, and vorticity. For a simplification of the problem, a sequence of nonlinear equations is obtained, which in the simplest form leads to a nonlinear Schrödinger equation with a localized potential. The basic state of the system, its dependence on the parameters and stability are investigated. For stationary solutions localized in the region of the surface tension inhomogeneity, domains of parameters corresponding to different spatial patterns are delineated.

Production of Concentrated Pickering Emulsions with Narrow Size Distributions Using Stirred Cell Membrane Emulsification.

PubMed

Manga, Mohamed S; York, David W

2017-09-12

Stirred cell membrane emulsification (SCME) has been employed to prepare concentrated Pickering oil in water emulsions solely stabilized by fumed silica nanoparticles. The optimal conditions under which highly stable and low-polydispersity concentrated emulsions using the SCME approach are highlighted. Optimization of the oil flux rates and the paddle stirrer speeds are critical to achieving control over the droplet size and size distribution. Investigating the influence of oil volume fraction highlights the criticality of the initial particle loading in the continuous phase on the final droplet size and polydispersity. At a particle loading of 4 wt %, both the droplet size and polydispersity increase with increasing of the oil volume fraction above 50%. As more interfacial area is produced, the number of particles available in the continuous phase diminishes, and coincidently a reduction in the kinetics of particle adsorption to the interface resulting in larger polydisperse droplets occurs. Increasing the particle loading to 10 wt % leads to significant improvements in both size and polydispersity with oil volume fractions as high as 70% produced with coefficient of variation values as low as ∼30% compared to ∼75% using conventional homogenization techniques.

An MHD variational principle that admits reconnection

NASA Technical Reports Server (NTRS)

Rilee, M. L.; Sudan, R. N.; Pfirsch, D.

1997-01-01

The variational approach of Pfirsch and Sudan's averaged magnetohydrodynamics (MHD) to the stability of a line-tied current layer is summarized. The effect of line-tying on current sheets that might arise in line-tied magnetic flux tubes by estimating the growth rates of a resistive instability using a variational method. The results show that this method provides a potentially new technique to gauge the stability of nearly ideal magnetohydrodynamic systems. The primary implication for the stability of solar coronal structures is that tearing modes are probably constant at work removing magnetic shear from the solar corona.

Divertor heat flux mitigation in the National Spherical Torus Experimenta)

NASA Astrophysics Data System (ADS)

Soukhanovskii, V. A.; Maingi, R.; Gates, D. A.; Menard, J. E.; Paul, S. F.; Raman, R.; Roquemore, A. L.; Bell, M. G.; Bell, R. E.; Boedo, J. A.; Bush, C. E.; Kaita, R.; Kugel, H. W.; Leblanc, B. P.; Mueller, D.; NSTX Team

2009-02-01

Steady-state handling of divertor heat flux is a critical issue for both ITER and spherical torus-based devices with compact high power density divertors. Significant reduction of heat flux to the divertor plate has been achieved simultaneously with favorable core and pedestal confinement and stability properties in a highly shaped lower single null configuration in the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 2000] using high magnetic flux expansion at the divertor strike point and the radiative divertor technique. A partial detachment of the outer strike point was achieved with divertor deuterium injection leading to peak flux reduction from 4-6MWm-2to0.5-2MWm-2 in small-ELM 0.8-1.0MA, 4-6MW neutral beam injection-heated H-mode discharges. A self-consistent picture of the outer strike point partial detachment was evident from divertor heat flux profiles and recombination, particle flux and neutral pressure measurements. Analytic scrape-off layer parallel transport models were used for interpretation of NSTX detachment experiments. The modeling showed that the observed peak heat flux reduction and detachment are possible with high radiated power and momentum loss fractions, achievable with divertor gas injection, and nearly impossible to achieve with main electron density, divertor neutral density or recombination increases alone.

Why Gas Hydrate Occurrenced Over Topographic Highs in Shenhu Area Northern South China Sea？

NASA Astrophysics Data System (ADS)

Liao, J.

2015-12-01

Methane gas hydrate has been drilled by China Geological Survey in shenhu area northern south china sea in 2007 .Shenhu area is located in the middle-lower continental slope and 17 submarine canyons are incised into the shelf,gas hydrtae was observed in boreholes over topographic highs,but origin of the hydrate is controversial.Accumulation of gas hydrate is depending on temperature-pressure field and supply quantities of methane and some other factors,in the same depth of the shallow sediments there is the same press,so temperature field and supply quantities of methane become the most important factors.Lachenbruch(1968) calculated the topographic disturbance to geothermal gradients,in shenhu area consistent local variations were observed, notably low heat flow values over prominent topographic highs and high heat flow values over the flanks of the topographic highs. At some localities over a horizontal distance of 2.5 km, heat flow increased by as much as 50%, from typical values of 65 to 100 mW/m2 .Some vertical fractures were observed beneath topographic highs in previous studies.Based on the profile across borehole SH7,we designed four experiments:A,uniform distribution of heat flux with no vertical fractures；B,Uniform distribution of heat flux with vertical fractures beneath geographic highs;C,uneven distribution of heat flux with no vertical fractures;D,uneven distribution of heat flux with vertical fractures beneath geographic highs.According to previous studies,we restored Palaeobathymetry,abundance of organic matters, sandstone-madstone ratio ,porosity and permeability of each,and parameters of vertical fractures.The result of experiment D shows the similar distribution characteristic with the drilling result,so We believe that low heat flux and Vertical fractures are the most important factors . This work was supported by the National Science Foundation of China(grant no. 41406080).

Use of Radon for Evaluation of Atmospheric Transport Models: Sensitivity to Emissions

NASA Technical Reports Server (NTRS)

Gupta, Mohan L.; Douglass, Anne R.; Kawa, S. Randolph; Pawson, Steven

2004-01-01

This paper presents comparative analyses of atmospheric radon (Rn) distributions simulated using different emission scenarios and the observations. Results indicate that the model generally reproduces observed distributions of Rn but there are some biases in the model related to differences in large-scale and convective transport. Simulations presented here use an off-line three-dimensional chemical transport model driven by assimilated winds and two scenarios of Rn fluxes (atom/cm s) from ice-free land surfaces: (A) globally uniform flux of 1.0, and (B) uniform flux of 1.0 between 60 deg. S and 30 deg. N followed by a sharp linear decrease to 0.2 at 70 deg. N. We considered an additional scenario (C) where Rn emissions for case A were uniformly reduced by 28%. Results show that case A overpredicts observed Rn distributions in both hemispheres. Simulated northern hemispheric (NH) Rn distributions from cases B and C compare better with the observations, but are not discernible from each other. In the southern hemisphere, surface Rn distributions from case C compare better with the observations. We performed a synoptic scale source-receptor analysis for surface Rn to locate regions with ratios B/A and B/C less than 0.5. Considering an uncertainty in regional Rn emissions of a factor of two, our analysis indicates that additional measurements of surface Rn particularly during April-October and north of 50 deg. N over the Pacific as well as Atlantic regions would make it possible to determine if the proposed latitude gradient in Rn emissions is superior to a uniform flux scenario.

Performance of 'energy efficient' compact fluorescent lamps.

PubMed

Yuen, Gloria S-C; Sproul, Alistair B; Dain, Stephen J

2010-03-01

Compact fluorescent lamps (CFLs) have been heralded as highly energy efficient replacements for incandescent light globes, however, there is some public dissatisfaction with the light output and colour of CFLs. Independent examination of the claims made has not been made. Compliance with the interim Australian/New Zealand Standard has not been established by any independent authority. While the total light output (luminous flux) may meet certain standards, luminous intensity distributions of some designs do differ significantly from the incandescent sources that they are intended to replace. Luminous intensity distribution, luminous flux and spectral energy distribution of CFLs claimed to be equivalent to 75 W incandescent globes and 75 W incandescent globes (pearl and clear) were measured. Luminous flux, luminous efficacy, colour rendering index, correlated colour temperature, wattage and power factor were then calculated and compared with claims made by manufacturers and requirements of the standards. The sources generally complied with the requirements for luminous flux, luminous efficacy, colour rendering index and correlated colour temperature. The claim of 75 W equivalence, which is not regulated in Australia and New Zealand, is justified less than half the time. Luminous intensity distributions of biaxial CFLs are distinctly different from the incandescent lamps they purport to replace. CFLs generally comply with the standards set. The basis on which equivalent wattages are claimed needs to be included in the Australian and New Zealand standard because this is the measure most likely to be relied on by the public. Due to the differences in luminous intensity distribution, CFLs may not necessarily be a direct replacement for incandescent sources without some consideration.

Predicted Water and Carbon Fluxes as well as Vegetation Distribution on the Korean Peninsula in the Future with the Ecosystem Demography Model version 2

NASA Astrophysics Data System (ADS)

Kim, J. B.; Kim, Y.

2017-12-01

This study investigates how the water and carbon fluxes as well as vegetation distribution on the Korean peninsula would vary with climate change. Ecosystem Demography (ED) Model version 2 (ED2) is used in this study, which is an integrated terrestrial biosphere model that can utilize a set of size- and age- structured partial differential equations that track the changing structure and composition of the plant canopy. With using the vegetation distribution data of Jeju Island, located at the southern part of the Korean Peninsula, ED2 is setup and driven for the past 10 years. Then the results of ED2 are evaluated and adjusted with observed forestry data, i.e., growth and mortality, and the flux tower and MODIS satellite data, i.e., evapotranspiration (ET) and gross primary production (GPP). This adjusted ED2 are used to simulate the water and carbon fluxes as well as vegetation dynamics in the Korean Peninsula for the historical period with evaluating the model against the MODIS satellite data. Finally, the climate scenarios of RCP 2.6 and 6.0 are used to predict the fluxes and vegetation distribution of the Korean Peninsula in the future. With using the state-of-art terrestrial ecosystem model, this study would provide us better understanding of the future ecosystem vulnerability of the Korean Peninsula. AcknowledgementsThis work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (2015R1C1A2A01054800) and by the Korea Meteorological Administration R&D Program under Grant KMIPA 2015-6180. This work was also supported by the Yonsei University Future-leading Research Initiative of 2015(2016-22-0061).

Temperature-dependant shifts in a wet tropical Hawaiian forest ecosystem: impact on belowground carbon stocks, dynamics, and processes

NASA Astrophysics Data System (ADS)

Crow, S. E.; Litton, C. M.; Giardina, C. P.

2009-12-01

Global patterns suggest a positive correlation between temperature and total belowground carbon (C) flux and partitioning in temperate and tropical regions, but these relationships have yet to be tested within a given ecosystem type. We established a transect of nine permanent forest plots along an elevation gradient (800-1600 m) in native-dominated Metrosideros polymorpha / Acacia koa rainforest developed in volcanic ash soils along the windward slope of Mauna Kea, Hawaii. Along the transect parent material, bedrock age, species composition, and plant available water are nearly constant and only mean annual temperature (MAT) varies substantially (13°C-18°C). We hypothesized that warmer temperatures at lower elevations would drive greater C flux and partitioning to belowground, which represents a direct input of C into belowground stocks. Roots are often sources of stabilized soil organic matter, thus we expected that increased belowground flux and partitioning of C at higher MATs would increase soil C stocks within recalcitrant C pools, even if bulk soil C stock decreases overall. In fact, our data suggest non-linear relationships between temperature and the distribution of C among soil pools based on sequential density fractionation at 1.6 and 2.4 g mL-1, and radiocarbon-based estimates of mean residence time. The proportion of C recovered within the mineral-associated heavy fraction (>2.4 g mL-1) was greatest at the highest MAT (nearly 30% of total soil C), initially declined at the mid-MAT plots (~10% of total soil C), but then increased again at the lowest MAT plots (~25%). Although the proportion of soil C within the heavy fraction was lowest at the mid-MAT plots, the mean residence time of heavy fraction C was greatest in these plots (570-663 yr for the mid-MAT plots versus 120-220 yr for the highest MAT plots and 64-308 for the lowest MAT plots), suggesting that the mineral-associated C in the mid-MAT plots was the most stabilized. In contrast, the proportion of C recovered within the rapidly cycling light fraction (<1.6 g mL-1) initially increased as MAT decreased, from <10% to a peak of nearly 50% of total soil C in the mid-MAT plots, but then decreased again in the plots with lowest MAT. High temperature both directly and indirectly stimulates weathering in these soils-which are thought to be within the phase of maximum nutrient availability, productivity, and potential SOM stabilization during ecosystem development-through increased belowground activity. However, complex feedbacks between temperature, resource allocation, weathering rate, and carbon storage may be driving non-linear relationships between temperature and soil processes.

Design, construction, and testing of the direct absorption receiver panel research experiment

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

Chavez, J.M.; Rush, E.E.; Matthews, C.W.

1990-01-01

A panel research experiment (PRE) was designed, built, and tested as a scaled-down model of a direct absorption receiver (DAR). The PRE is a 3-MW{sub t}DAR experiment that will allow flow testing with molten nitrate salt and provide a test bed for DAR testing with actual solar heating. In a solar central receiver system DAR, the heat absorbing fluid (a blackened molten nitrate salt) flows in a thin film down a vertical panel (rather than through tubes as in conventional receiver designs) and absorbs the concentrated solar flux directly. The ability of the flowing salt film to absorb flux directly.more » The ability of the flowing salt film to absorb the incident solar flux depends on the panel design, hydraulic and thermal fluid flow characteristics, and fluid blackener properties. Testing of the PRE is being conducted to demonstrate the engineering feasibility of the DAR concept. The DAR concept is being investigated because it offers numerous potential performance and economic advantages for production of electricity when compared to other solar receiver designs. The PRE utilized a 1-m wide by 6-m long absorber panel. The salt flow tests are being used to investigate component performance, panel deformations, and fluid stability. Salt flow testing has demonstrated that all the DAR components work as designed and that there are fluid stability issues that need to be addressed. Future solar testing will include steady-state and transient experiments, thermal loss measurements, responses to severe flux and temperature gradients and determination of peak flux capability, and optimized operation. In this paper, we describe the design, construction, and some preliminary flow test results of the Panel Research Experiment. 11 refs., 8 figs., 2 tabs.« less

Photoneutron Flux Measurement via Neutron Activation Analysis in a Radiotherapy Bunker with an 18 MV Linear Accelerator

NASA Astrophysics Data System (ADS)

Çeçen, Yiğit; Gülümser, Tuğçe; Yazgan, Çağrı; Dapo, Haris; Üstün, Mahmut; Boztosun, Ismail

2017-09-01

In cancer treatment, high energy X-rays are used which are produced by linear accelerators (LINACs). If the energy of these beams is over 8 MeV, photonuclear reactions occur between the bremsstrahlung photons and the metallic parts of the LINAC. As a result of these interactions, neutrons are also produced as secondary radiation products (γ,n) which are called photoneutrons. The study aims to map the photoneutron flux distribution within the LINAC bunker via neutron activation analysis (NAA) using indium-cadmium foils. Irradiations made at different gantry angles (0°, 90°, 180° and 270°) with a total of 91 positions in the Philips SLI-25 linear accelerator treatment room and location-based distribution of thermal neutron flux was obtained. Gamma spectrum analysis was carried out with high purity germanium (HPGe) detector. Results of the analysis showed that the maximum neutron flux in the room occurred at just above of the LINAC head (1.2x105 neutrons/cm2.s) which is compatible with an americium-beryllium (Am-Be) neutron source. There was a 90% decrease of flux at the walls and at the start of the maze with respect to the maximum neutron flux. And, just in front of the LINAC door, inside the room, neutron flux was measured less than 1% of the maximum.

Water Vapor Transport Over the Tropical Oceans During ENSO as Diagnosed from TRMM and SSM/I Data

NASA Technical Reports Server (NTRS)

Robertson, Franklin R.; Smith, Eric A.; Sohn, Byung-Ju

2000-01-01

Traditionally, large-scale water vapor transport [div Q] has been derived directly from circulation statistics in which transport processes are often depicted by mean and eddy motions. Thus detailed and accurate calculations of moisture transport terms over the globe are required. Notably, the lack of systematically spaced conventional measurements of meteorological variables over oceans has hindered understanding of the distribution and transport of water vapor. This motivates the use of indirect calculation methods in which horizontal divergence of water vapor is balanced by the evaporation minus precipitation, assuming the rate of changes of precipitable water and condensates is small over a sufficiently long time period. In order to obtain the water vapor transport, we need evaporation rate minus precipitation (E-P). Focussing on the differences in water vapor transport between El Nino and La Nina periods and their influences on atmospheric circulations, we study January, February, and March of 1998 and 1999 periods which represent El Nino and La Nina respectively. SSM/I-derived precipitation and evaporation rate from SSM/I wind and total precipitable water, in conjunction with NCEP SST and surface air temperature, are used for the calculation of the transport potential function. For the retrieval of evaporation we use a stability-dependent aerodynamic bulk scheme developed by Chou (1993). It was tested against aircraft covariance fluxes measured during cold air outbreaks over the North Atlantic Ocean. Chou et al. (1997) reported that the SSM/I retrieved latent heat flux over the western Pacific warm pool area were found to be comparable with daily mean fluxes of a ship measurements during TOGA/COARE.

Physical mechanism of mind changes and tradeoffs among speed, accuracy, and energy cost in brain decision making: Landscape, flux, and path perspectives

NASA Astrophysics Data System (ADS)

Han, Yan; Kun, Zhang; Jin, Wang

2016-07-01

Cognitive behaviors are determined by underlying neural networks. Many brain functions, such as learning and memory, have been successfully described by attractor dynamics. For decision making in the brain, a quantitative description of global attractor landscapes has not yet been completely given. Here, we developed a theoretical framework to quantify the landscape associated with the steady state probability distributions and associated steady state curl flux, measuring the degree of non-equilibrium through the degree of detailed balance breaking for decision making. We quantified the decision-making processes with optimal paths from the undecided attractor states to the decided attractor states, which are identified as basins of attractions, on the landscape. Both landscape and flux determine the kinetic paths and speed. The kinetics and global stability of decision making are explored by quantifying the landscape topography through the barrier heights and the mean first passage time. Our theoretical predictions are in agreement with experimental observations: more errors occur under time pressure. We quantitatively explored two mechanisms of the speed-accuracy tradeoff with speed emphasis and further uncovered the tradeoffs among speed, accuracy, and energy cost. Our results imply that there is an optimal balance among speed, accuracy, and the energy cost in decision making. We uncovered the possible mechanisms of changes of mind and how mind changes improve performance in decision processes. Our landscape approach can help facilitate an understanding of the underlying physical mechanisms of cognitive processes and identify the key factors in the corresponding neural networks. Project supported by the National Natural Science Foundation of China (Grant Nos. 21190040, 91430217, and 11305176).

Conduit Stability and Collapse in Explosive Volcanic Eruptions: Coupling Conduit Flow and Failure Models

NASA Astrophysics Data System (ADS)

Mullet, B.; Segall, P.

2017-12-01

Explosive volcanic eruptions can exhibit abrupt changes in physical behavior. In the most extreme cases, high rates of mass discharge are interspaced by dramatic drops in activity and periods of quiescence. Simple models predict exponential decay in magma chamber pressure, leading to a gradual tapering of eruptive flux. Abrupt changes in eruptive flux therefore indicate that relief of chamber pressure cannot be the only control of the evolution of such eruptions. We present a simplified physics-based model of conduit flow during an explosive volcanic eruption that attempts to predict stress-induced conduit collapse linked to co-eruptive pressure loss. The model couples a simple two phase (gas-melt) 1-D conduit solution of the continuity and momentum equations with a Mohr-Coulomb failure condition for the conduit wall rock. First order models of volatile exsolution (i.e. phase mass transfer) and fragmentation are incorporated. The interphase interaction force changes dramatically between flow regimes, so smoothing of this force is critical for realistic results. Reductions in the interphase force lead to significant relative phase velocities, highlighting the deficiency of homogenous flow models. Lateral gas loss through conduit walls is incorporated using a membrane-diffusion model with depth dependent wall rock permeability. Rapid eruptive flux results in a decrease of chamber and conduit pressure, which leads to a critical deviatoric stress condition at the conduit wall. Analogous stress distributions have been analyzed for wellbores, where much work has been directed at determining conditions that lead to wellbore failure using Mohr-Coulomb failure theory. We extend this framework to cylindrical volcanic conduits, where large deviatoric stresses can develop co-eruptively leading to multiple distinct failure regimes depending on principal stress orientations. These failure regimes are categorized and possible implications for conduit flow are discussed, including cessation of eruption.

NIR-driven Moist Upper Atmospheres of Synchronously Rotating Temperate Terrestrial Exoplanets

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

Fujii, Yuka; Del Genio, Anthony D.; Amundsen, David S.

H{sub 2}O is a key molecule in characterizing atmospheres of temperate terrestrial planets, and observations of transmission spectra are expected to play a primary role in detecting its signatures in the near future. The detectability of H{sub 2}O absorption features in transmission spectra depends on the abundance of water vapor in the upper part of the atmosphere. We study the three-dimensional distribution of atmospheric H{sub 2}O for synchronously rotating Earth-sized aquaplanets using the general circulation model (GCM) ROCKE-3D, and examine the effects of total incident flux and stellar spectral type. We observe a more gentle increase of the water vapormore » mixing ratio in response to increased incident flux than one-dimensional models suggest, in qualitative agreement with the climate-stabilizing effect of clouds around the substellar point previously observed in GCMs applied to synchronously rotating planets. However, the water vapor mixing ratio in the upper atmosphere starts to increase while the surface temperature is still moderate. This is explained by the circulation in the upper atmosphere being driven by the radiative heating due to absorption by water vapor and cloud particles, causing efficient vertical transport of water vapor. Consistently, the water vapor mixing ratio is found to be well-correlated with the near-infrared portion of the incident flux. We also simulate transmission spectra based on the GCM outputs, and show that for the more highly irradiated planets, the H{sub 2}O signatures may be strengthened by a factor of a few, loosening the observational demands for a H{sub 2}O detection.« less