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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Influence of site and soil properties on the DRIFT spectra of northern cold-region soils [Influence of site and soil properties on the mid-infrared spectra of northern cold-region soils]

Here, we investigated the influence of site characteristics and soil properties on the chemical composition of organic matter in soils collected from a latitudinal transect across Alaska through analysis of diffuse reflectance Fourier transform mid infrared (MidIR) spectra of bulk soils. The study included 119 soil samples collected from 28 sites including tundra, boreal forest, and grassland ecosystems. Organic, mineral, and cryoturbated soil horizons, both seasonally and perennially frozen, from a variety of depths and edaphic conditions were examined. The amount and chemical composition of organic matter as well as site and soil properties exerted a strong influence on the MidIR spectra. The spectra were highly sensitive to the extent of organic matter decomposition, enabling the ordination of Oi, Oe and Oa organic horizons. Differences in absorbance intensity for several spectral bands indicated that Oi horizons contained greater abundance of relatively fresh residues, phenolic-OH compounds, aliphatic compounds (waxes, lipids and fats), and carbohydrates. In contrast, Oa horizons had a greater presence of amide groups (possibly from microbial residues), aromatics, C=C bonds, carboxylates and carboxylic acids. Another significant factor differentiating these horizons was the incorporation of clays and silicates into the decomposing organic matter of Oa horizons. Calculated height peak ratios showed a clear trend to greater decomposition among Oi, Oe and Oa. The MidIR spectra were related to many site/soil attributes including land cover type, parent material, and associated factors, such as permafrost presence/absence, soil drainage, horizon depth, bulk density, cation exchange capacity, and pH. Single MidIR spectral bands were identified that might be used in future studies to quickly estimate the organic and inorganic carbon, total nitrogen, and carbon:nitrogen ratios of soils from northern latitudes. Lastly, our results demonstrate that the information contained in MidIR spectra of bulk soil integrates the quantity and chemical composition of soil organic matter with soil forming factors and highlights the potential for using this information to assess the degradation state of organic matter stored in northern cold-region soils.

58 GEOSCIENCES↗
DOE OSTI2021

Accurate numerical, integral methods for computing drift-kinetic Trubnikov-Rosenbluth potentials

A novel numerical method is employed to compute the integral form of the axi-symmetric Trubnikov-Rosenbluth potentials. Two methods for quadrature in pitch-angle are described and their convergence properties are studied. Careful attention is given to quadrature over a singular Green's function. Here it is shown that an infinite series representation of the Green's function can be used more efficiently than its closed form involving complete elliptic integrals. Then a collocation method in speed, with its associated quadrature scheme, is laid out and its convergence properties are studied. Using the proposed scheme, accurate low-order moments of the field collision operator are obtained using relatively few velocity space degrees of freedom. The scheme is showcased by solving for the equilibrium, axi-symmetric bootstrap current in tokamaks. A C 0 Gauss-Lobatto-Legendre finite element pitch-angle basis with vertex nodes at the trapped/passing boundary is shown, in the context of the integral methods used, to be much more efficient than the more common Legendre polynomial expansion.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Correcting nonlinear drift distortion of scanning probe and scanning transmission electron microscopies from image pairs with orthogonal scan directions

Unwanted motion of the probe with respect to the sample is a ubiquitous problem in scanning probe and scanning transmission electron microscopies, causing both linear and nonlinear artifacts in experimental images. We have designed a procedure to correct these artifacts by using orthogonal scan pairs to align each measurement line-by-line along the slow scan direction, by fitting contrast variation along the lines. We demonstrate the accuracy of our algorithm on both synthetic and experimental data and provide an implementation of our method.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Comparison of Edge and Internal Transport Barriers in Drift Wave Predictive Simulations

We have simulated the formation of an internal transport barrier on JET including a self-consistent treatment of ion and electron temperatures and poloidal and toroidal momentum.Similar simulations of edge transport barriers, including the L-H transition have also been made. However, here only poloidal momentum and the temperatures were simulated. The internal barrier included an anomalous spinup of poloidal momentum similar to that in the experiment. Also the edge barrier was accompanied by a spinup of poloidal momentum. The experimental density (with no barrier) was used and kept fixed for the internal barrier. For the edge barrier the edge density was varied and it turned out that a lower edge density gave a stronger barrier. Electromagnetic and nonlocal effects were important for both types of barriers.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Electromagnetic fluctuations and normal modes of a drifting relativistic plasma

We present an exact calculation of the power spectrum of the electromagnetic fluctuations in a relativistic equilibrium plasma described by Maxwell-Jüttner distribution functions. We consider the cases of wave vectors parallel or normal to the plasma mean velocity. The relative contributions of the subluminal and supraluminal fluctuations are evaluated. Analytical expressions of the spatial fluctuation spectra are derived in each case. These theoretical results are compared to particle-in-cell simulations, showing a good reproduction of the subluminal fluctuation spectra.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Effect of fast drifting electrons on electron temperature measurement with a triple Langmuir probe

Triple Langmuir Probe (TLP) is a widely used diagnostics for instantaneous measurement of electron temperature and density in low temperature laboratory plasmas as well as in edge region of fusion plasma devices. Presence of a moderately energetic flowing electron component, constituting only a small fraction of the bulk electrons, is also a generally observed scenario in plasma devices, where plasmas are produced by electron impact ionization of neutrals. A theoretical analysis of its effect on interpretation of the TLP data for bulk electron temperature measurement is presented here assuming electron velocity distribution is not deviating substantially from a Maxwellian. The study predicts conventional expression from standard TLP theory to give overestimated value of bulk electron temperature. Correction factor is significant and largely depends on population density, temperature, and energy of the fast component. Experimental verification of theoretical results is obtained in the magnetized plasma linear experimental device of Saha Institute of Nuclear Physics where plasma is produced by an electron cyclotron resonance method and known to have a fast flowing electron component.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Energy exchange in strongly coupled plasmas with electron drift

In this paper, the generalized viscoelastic collisional quantum hydrodynamic model is employed in order to investigate the linear dielectric response of a quantum plasma in the presence of strong electron-beam plasma interactions. The generalized Chandrasekhar's relativistic degeneracy pressure together with the electron-exchange and Coulomb interaction effects are taken into account in order to extend current research to a wide range of plasma number density relevant to big planetary cores and astrophysical compact objects. The previously calculated shear viscosity and the electron-ion collision frequencies are used for strongly coupled ion fluid. The effect of the electron-beam velocity on complex linear dielectric function is found to be profound. This effect is clearly interpreted in terms of the wave-particle interactions and their energy-exchange according to the sign of the imaginary dielectric function, which is closely related to the wave attenuation coefficient in plasmas. Such kinetic effect is also shown to be in close connection with the stopping power of a charged-particle beam in a quantum plasma. The effect of many independent plasma parameters, such as the ion charge-state, electron beam-velocity, and relativistic degeneracy, is shown to be significant on the growing/damping of plasma instability or energy loss/gain of the electron-beam.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Coordinate detectors based on thin-wall drift tubes

Design features and basic parameters of the detectors based on straw trackers are reviewed using the example of the studies and development of trackers in a number of operating and proposed accelerator experimental facilities. The results of methodological studies aimed at qualitatively improving the spatial/time resolution and high rate capability of the detector and enhancing the performance capabilities of such detectors used for particle detection in a high multiplicity environment (and in high-luminosity experiments) are presented.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Epigenetic drift underlies epigenetic clock signals, but displays distinct responses to lifespan interventions, development, and cellular dedifferentiation

Changes in DNA methylation with age are observed across the tree of life. The stereotypical nature of these changes can be modeled to produce epigenetic clocks capable of predicting chronological age with unprecedented accuracy. Despite the predictive ability of epigenetic clocks and their utility as biomarkers in clinical applications, the underlying processes that produce clock signals are not fully resolved, which limits their interpretability. Here, we develop a computational approach to spatially resolve the within read variability or “disorder” in DNA methylation patterns and test if age-associated changes in DNA methylation disorder underlie signals comprising epigenetic clocks. We find that epigenetic clock loci are enriched in regions that both accumulate and lose disorder with age, suggesting a link between DNA methylation disorder and epigenetic clocks. We then develop epigenetic clocks that are based on regional disorder of DNA methylation patterns and compare their performance to other epigenetic clocks by investigating the influences of development, lifespan interventions, and cellular dedifferentiation. We identify common responses as well as critical differences between canonical epigenetic clocks and those based on regional disorder, demonstrating a fundamental decoupling of epigenetic aging processes. Collectively, we identify key linkages between epigenetic disorder and epigenetic clocks and demonstrate the multifaceted nature of epigenetic aging in which stochastic processes occurring at non-random loci produce predictable outcomes.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2012

Gyrokinetic studies of the effect of β on drift-wave stability in NCSX

The gyrokinetic turbulence code GS2 was used to investigate the effects of plasma β on linear, collisionless ion temperature gradient (ITG) modes and trapped electron modes (TEM) in National Compact Stellarator Experiment (NCSX) geometry. Plasma β affects stability in two ways: through the equilibrium and through magnetic fluctuations. The first was studied here by comparing ITG and TEM stability in two NCSX equilibria of differing β values, revealing that the high β equilibrium was marginally more stable than the low β equilibrium in the adiabatic-electron ITG mode case. However, the high β case had a lower kinetic-electron ITG mode critical gradient. Electrostatic and electromagnetic ITG and TEM mode growth rate dependencies on temperature gradient and density gradient were qualitatively similar. The second β effect is demonstrated via electromagnetic ITG growth rates' dependency on GS2's β input parameter. A linear benchmark with gyrokinetic codes GENE and GKV-X is also presented.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Theoretical Studies of Drift-Alfven and Energetic Particle Physics

The research program supported by this DOE grant has been rather successful and productive in terms of both scientific investigations as well as human resources development; as demonstrated by the large number (60) of journal articles, 6 doctoral degrees, and 3 postdocs. This PI is particularly grateful to the generous support and flexible management of the DOE–SC-OFES Program. He has received three award/prize (APS Excellence in Plasma Physics Research Award, 2004; EPS Alfven Prize, 2008; APS Maxwell Prize, 2012) as the results of research accomplishments supported by this grant. Our research results have made important impacts not only on fusion plasma physics, but also on space as well as basic plasma physics. While the details of the results can be found in the attached more extensive list of publications, we should present here some of the highlights.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1993

Influence of drift flow turbulence on surface gravity wave propagation

The theory of surface gravity waves scattering at vortex flows in the ocean is developed in this paper. A scattering amplitude is found in the Born approximation as a function of Vorticity that appears very convenient for investigation of scattering at simple localized flows.

drift flow turbulence↗