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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Code for Value Decomposition Graph Network and environment for AMR on linear advection

This is the code for the paper [Multi-Agent Reinforcement Learning for Adaptive Mesh Refinement](https://arxiv.org/abs/2211.00801), published at AAMAS 2023. It contains the implementation of a new algorithm, called Value Decomposition Graph Network (VDGN), for applying multi-agent reinforcement learning to the problem of adaptive mesh refinement (AMR). It also contains the implementation of a multi-agent environment for AMR on a linear advection problem. VDGN is the first learning algorithm to display anticipatory refinement behavior in AMR, and it outperforms local error threshold-based heuristic strategies.

Yang, Jiachen↗
NASA NTRS2005

Global Admittance Estimates of Elastic and Crustal Thickness of Venus: Results from Top, Hot Spot, and Bottom Loading Models

We have calculated admittance spectra using the spatio-spectral method [14] for Venus by moving the central location of the spectrum over a 1 grid, create 360x180 admittance spectra. We invert the observed admittance using top-loading (TL), hot spot (HS), and bottom loading (BL) models, resulting in elastic, crustal, and lithospheric thickness estimates (Te, Zc, and Zl) [0]. The result is a global map for interpreting subsurface structure. Estimated values of Te and Zc concur with previous TL local admittance results, but BL estimates indicate larger values than previously suspected.

Smrekar, S. E.↗
DOE OSTI2025

Relaxation time approximation for a multispecies relativistic gas

We generalize a recent prescription for the relaxation time approximation for the relativistic Boltzmann equation for systems with multiple particle species at finite temperature. This is performed by adding counter-terms to the traditional Anderson-Witting ansatz for each particle species. Our approach allows for the use of momentum-dependent relaxation times and the obedience of local conservation laws regardless of the definition of the local equilibrium state. As an application, we derive the first order Chapman-Enskog corrections to the equilibrium distribution and display results for the hadron-resonance gas. We also demonstrate that our collision term ansatz obeys the second law of thermodynamics.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1975

Application of satellite remote-sensing data to land selection and management

A pilot project conducted to demonstrate the utility and economy of satellite data in preparing thematic maps of a wilderness area emphasizing those resources of greatest interest to the potential owner is described. Vegetation maps delineating potential commercial timber and maps of suggested mineral prospecting areas of seven scattered regions were prepared by interpretation of LANDSAT images, coupled with a limited amount of ground truth. Images acquired both in winter and summer seasons were registered to township maps and used in making interpretations of the areal extent of commercial timber potentials. The amount of snow cover visible through the forest canopies was found to be a useful indicator of timber potentials. Identification was made of characteristic topographic features which are typical of flood plain deposits or of the well developed trellis drainage patterns which can indicate the strike of structural grain of underlying Cretaceous sedimentary rocks. The presence of igneous and mixed igneous and metamorphic rocks were indicated by combinations of spectral differences and anomalous interruptions of local radial drainage patterns.

Stringer, W. J.↗
NASA NTRS1979

Copernicus observations of neutral hydrogen and deuterium in the direction of HR 1099

High-resolution Copernicus U1 scans were obtained of the bright RS CVn binary HR 1099 (d = 33 pc, galactic longitude = 185 deg, galactic latitude = -41 deg) in October 1977. Strong emission at L-alpha was detected. The interstellar L-alpha absorption features of H I and D I were also observed. Analyses of these interstellar lines are reported in this paper. The average density of neutral H in the direction of this system is found to be 0.006-0.012 per cu cm, which, because the local density is higher, requires a marked inhomogeneity along this line of sight. This result, when combined with other recent studies of the local interstellar medium, suggests the sun is located within a moderate-density H I region.

Anderson, R. C.↗
NASA NTRS1985

Inference of equatorial field-line-integrated electron density values using whistlers

The nighttime electron density integrated along a magnetic field line at very small L-values (about 1.06) is inferred by comparing whistler dispersions, measured from a sounding rocket, with model ionospheric calculations. At a local time of 0500 LT, the electron density in the F-layer valley was found to be about 1000 per cu cm. It is suggested that this technique can be applied to earlier times in the local evening to determine ionospheric conditions which benefit the growth of low-latitude plasma instabilities.

Anderson, D. N.↗
NASA NTRS1991

The role of the ionosphere in coupling upstream ULF wave power into the dayside magnetosphere

A series of recent studies of Pc 3 magnetic pulsations in the dayside outer magnetosphere has given new insights into the possible mechanisms of entry of ULF wave power into the magnetosphere from a bow shock-related upstream source. A comparison is made of data from two 10-hour intervals on successive days in April 1986 and then a possible model for transmission of pulsation signals from the magnetosheath into the dayside magnetosphere is presented. Clear interplanetary magnetic field magnitude control of dayside resonant harmonic pulsations and band-limited very high latitude pulsations, as well as pulsation-modulated precipitation of what appear to be magnetosheath/boundary layer electrons are shown. It is believed that this modulated precipitation may be responsible for the propagation of upstream wave power in the Pc 3 frequency band into the high-latitude ionosphere, from whence it may be transported throughout the dayside outer magnetosphere by means of an 'ionospheric transistor'. In this model, modulations in ionospheric conductivity caused by cusp/cleft precipitation cause varying ionospheric currents with frequency spectra determined by the upstream waves; these modulations will be superimposed on the Birkeland currents, which close via these ionospheric currents. Modulated region 2 Birkeland currents will in turn provide a narrow-band source of wave energy to a wide range of dayside local times in the outer magnetosphere.

Engebretson, M. J.↗
NASA NTRS1993

Electron generation of electrostatic waves in the plasma sheet boundary layer

Broadband electrostatic noise (BEN) has been shown to occur in conjunction with ion beams; extensive investigations of possible ion beam-related instabilities that could generate the observed wave spectra have been conducted. It has also been demonstrated that unstable electron distribution functions are sometimes measured in the plasma sheet boundary layer. We present simultaneous observations of ion and electron distribution functions and electric field wave spectra measured by ISEE 1 and ISEE 2 in the Earth's magnetotail. As the spacecraft moved from the tail lobe toward the plasma sheet, the fast indication of boundary layer plasma was seen in the electron distributions, followed some minutes later by the detection of boundary layer ions. The onset of large-amplitude electrostatic waves at frequencies up to the electron plasma frequency was coincident with the onset of the boundary layer electrons, suggesting that broadband electrostatic waves may often be generated by unstable electron distributions in the plasma sheet boundary layer, particularly the higher frequency portion of the wave spectrum. The observed changes in the electron distribution functions indicate that the plasma was not heated locally by the waves.

Onsager, T. G.↗
NASA NTRS2000

Preliminary Admittance Estimates for the Valles Marineris, Mars

We use the gravity and topography fields derived from Mars Global Surveyor in conjunction with a multi-resolution localization admittance technique to constrain lithospheric structure for the trough system of Valles Marineris on Mars.

Anderson, F. Scott↗
NASA NTRS2012

Team LunaCY Outreach Paper

Iowa State University's Lunabotics Club, Team LunaCY, has worked hard to generate enthusiasm for robotics, engineering, and lunar activities. Team LunaCY participated in a variety of different outreach events making a strong impression on Iowa youth. These events led the chair of the mechanical engineering department, Dr. Ted Heindel, to refer to the club's outreach program as "the model that all other engineering clubs should follow." Team LunaCY's outreach activities totaled over 200 hours and captivated over 3000 students and adults throughout the course of this acaden1ic year, reaching out to people all over Iowa and to several special guests. These guests included Vice-President Joe Biden, during a visit to Iowa State University in March 2012, and astronaut Clayton Anderson, during a visit to Iowa State's campus in the fall 2011. Team LunaCY's outreach events created hands on learning opportunities for local youth ranging in age from elementary school children to high school students. The team strove to make a positive impression on Iowa youth and to encourage interest and involvement in scientific fields. The full list of events is shown in Table 1. Three of the major outreach events the team participated in were the FIRST LEGO League, Science Bound, and iExplore STEM Festival.

Heise, James↗
DOE OSTI2026

Challenges and Considerations for Rural Transportation: Stakeholder Perspectives

This fact sheet presents key findings and challenges identified by stakeholders through an initiative supported by the U.S. Department of Energy's Communities Local Energy Action Program (Communities LEAP). The project engaged community stakeholders, fleet operators, and local officials across ten rural counties in western Alabama to explore opportunities for expanding access to alternative transportation fuels. Guided by a regional coalition and supported by the National Laboratory of the Rockies (NLR), the effort emphasized challenges and related potential technical solutions. The fact sheet highlights transportation priorities identified by participants, outlines barriers unique to rural contexts, and summarizes resources developed by NLR subject matter experts to help local entities address these challenges.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2024

Anderson impurity mechanism for a multi-level model in δ-Pu

Abstract Electronic correlations and spin–orbit interactions in plutonium create variations in the bonding behavior of each of its allotropes. In δ -Pu, the 5f electrons lie at the tipping point between itinerant and localized behavior which has made the use of mixed-level models successful in describing its mechanical properties. The mechanism for the emergence of a mixed-level model has not yet been understood. We use a series of density functional theory approximations to understand the interactions that create a mixed-level description of δ -Pu which leads to accurate physical properties. With the intersite interactions present in the hybrid functional, we show that a single 5f electron engages in orbital-selective bonding that can be understood with an Anderson impurity picture. The Anderson model gives us a mechanism to understand how the bonding in δ -Pu evolves as a function of the interactions in the material such that we obtain both the accuracy and physics of the multi-level models from ab initio theory.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2021

Localization dynamics in a centrally coupled system

In systems in which interactions couple a central degree of freedom and a bath, one would expect signatures of the bath's phase to be reflected in the dynamics of the central degree of freedom. This has been recently explored in connection with many-body localized baths coupled with a central qubit or a single-cavity mode - systems with growing experimental relevance in various platforms. Such models also have an interesting connection with Floquet many-body localization via quantizing the external drive, although this has been relatively unexplored. Here we adapt the multilayer multiconfigurational time-dependent Hartree (ML-MCTDH) method, a well-known tree tensor network algorithm, to numerically simulate the dynamics of a central degree of freedom, represented by a d-level system (qudit), coupled to a disordered interacting one-dimensional spin bath. ML-MCTDH allows us to reach ≈10 2 lattice sites, a far larger system size than what is feasible with exact diagonalization or kernel polynomial methods. From the intermediate time dynamics, we find a well-defined thermodynamic limit for the qudit dynamics upon appropriate rescaling of the system-bath coupling. The spin system shows similar scaling collapse in the Edward-Anderson spin-glass order parameter or entanglement entropy at relatively short times. At longer timescales, we see slow growth of the entanglement, which may arise from dephasing mechanisms in the localized system or long-range interactions mediated by the central degree of freedom. Similar signs of localization are shown to appear as well with unscaled system-bath coupling.

1-dimensional spin chains↗
NASA NTRS1981

Observations of the interaction of ozone and dynamics

Data on the global distribution of temperature and ozone obtained with the Limb Radiance Inversion Radiometer which flew on the Nimbus 6 spacecraft are analyzed within the conceptual framework of Hartmann and Garcia (1979). The analysis supports the conclusion that ozone perturbations are dynamically controlled when the photochemical time constant is much greater than the dynamical time constant; when the photochemical constant is much less than the dynamical constant, ozone perturbations are photochemically controlled. It is also shown that the transports of planetary waves, or eddy transports, appear to be strongly localized in the region between the regimes in which dynamical and photochemical controls operate.

Gille, J. C.↗
NASA NTRS1980

Grid evolution in time asymptotic problems

A technique for generating systems of coordinates for solving time asymptotic problems is described which provides a simple way of moving the mesh points in physical space and reduces the error in the solution relative to that obtained using a fixed mesh. First order partial differential equations are formulated for the grid point velocity in transient problems. Local flow information and boundary motion are used to determine the interior grid point motion.

Rai, M. M.↗
DOE OSTI2022

Evidence for a spinon Kondo effect in cobalt atoms on single-layer 1T-TaSe 2

Quantum spin liquids are highly entangled, disordered magnetic states that are expected to arise in frustrated Mott insulators and to exhibit exotic fractional excitations such as spinons and chargons. Despite being electrical insulators, some quantum spin liquids are predicted to exhibit gapless itinerant spinons that yield metallic behaviour in the charge-neutral spin channel. For this study, we deposited isolated magnetic atoms onto single-layer 1T-TaSe 2 , a candidate gapless spin liquid, to probe how itinerant spinons couple to impurity spin centres. Using scanning tunnelling spectroscopy, we observe the emergence of new, impurity-induced resonance peaks at the 1T-TaSe 2 Hubbard band edges when cobalt adatoms are positioned to have maximal spatial overlap with the local charge distribution. These resonance peaks disappear when the spatial overlap is reduced or when the magnetic impurities are replaced with nonmagnetic impurities. Theoretical simulations of a modified Anderson impurity model show that the observed peaks are consistent with a Kondo resonance induced by spinons combined with spin-charge binding effects that arise due to fluctuations of an emergent gauge field.

36 MATERIALS SCIENCE↗
NASA NTRS1989

IR emission and UV extinction in two open clusters

Recent models of interstellar extinction have shown the importance of understanding both the UV and IR properties of interstellar dust grains. IRAS data have shown variations in 60 and 100 micron emissions presumably due to the presence of IR cirrus, while recent observations in the UV by Fitzpatrick and Massa have identified components in the UV extinction curve which vary in different star regions. A Draine and Anderson model connects these results by proposing that different size variations in interstellar grains would cause distinct changes in both the IR emission and the UV extinction. In order to test this model it is necessary to make observations in well defined locations away from peculiar extinction regions. In the infrared this means looking away from the galactic plane so as to limit non-local sources of IR radiation. Two open clusters that are out of the galactic plane and which contain a number of late B and early A stars suitable for UV extinction studies, and whose IRAS data show variations in the 60/100 micron ratio were studied. Based on the Drain and Anderson model, variations were expected in their UV extinction curves that correlate with the IR cirrus emission.

Hackwell, James A.↗