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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Stabilizing homogeneous CaMn6Sn6via oscillatory crystal growth: structural complexity in a kagome metal

CaMn6Sn6 is a member of the large family of Mn-based kagome metals derived by filling voids of the prototypical CoSn structure. We observed Ca-deficiency and structural complexity, with approximately 10% deficiency of calcium relative to the ideal 166 stoichiometry. These features are common in related Ca-based materials. We find that growth conditions stabilize different phases with varying Curie temperatures. Diffraction and magnetization measurements reveal that conventional growth profiles yield inhomogeneity both within and between crystals in a given batch, whereas an oscillatory temperature profile promotes homogeneous crystals that adopt a superstructure beyond the parent hexagonal structure type. We present the physical properties of crystals grown using the oscillatory approach. The crystals are highly conductive, with a c-axis residual resistivity ratio ρ(300 K)/ρ(2 K) exceeding 100 and a positive, linear magnetoresistance at base temperature. Magnetically, the crystals are quite similar to MgMn6Sn6, with easy-plane ferromagnetic behavior and a Curie temperature of TC ≈ 237 K. These results highlight the critical role of growth conditions in stabilizing homogeneous crystals of complex phases such as Ca0.9Mn6Sn6. The oscillatory growth approach provides an effective route for accessing the intrinsic properties of this complex material and may be broadly useful for the growth of related kagome systems.

May, Andrew [ORNL] (ORCID:0000000307778539)↗
DOE OSTI2024

Performance of three hydrophone flow shields in a tidal channel

Pseudosound caused by turbulent pressure fluctuations in fluid flow past a hydrophone, referred to as flow noise, can mask propagating sounds of interest. Flow shields can mitigate flow noise by reducing non-acoustic pressure fluctuations sensed by a hydrophone. We evaluate the performance of three hydrophone flow shields (two nylon fabrics and an oil-filled enclosure) in a tidal channel with peak current speed of 1.3 m s−1. All three flow shields reduced flow noise without attenuating propagating sound below 20 kHz. The oil-filled enclosure performed best, reducing flow noise by over 30 dB at frequencies below 40 Hz.

47 OTHER INSTRUMENTATION↗
NASA NTRS1995

HST observations of the ring around SN 1987A

Hubble Space Telescope observations of SN 1987A show that the circumstellar material near the supernova forms a clumpy elliptical ring. We analyze six epochs of images made with the Faint Object Camera (FOC) imaging the lines of (O III) and H beta over the interval 1990 August-1993 October, and three epochs of observations with the Planetary Camera in the continuum and (N II) line over the interval 1992 April-1993 May. The elliptical ring in the (O III) images has a semimajor axis of 858 +/- 11 milliarcsec and a semiminor axis of 621 +/- 11 milliarsce (6.4 x 10(exp 17) and 4.6 x 10(exp 17) +/- 8.1 x 10(exp 15) cm, respectively, for a distance of 50 kpc), which implies an inclination angle of 44 +/- 1, if the ring is a circle inclined to our line of sight. The apparent width of the ring in (O III) is 121 +/- 22 milliarcsec (9.0 x 10(exp 16) +/- 1.6 x 10(exp 16) cm) based on our deconvolved image, which represents an upper limit to the width of the of the ring. The position angle of the major axis on the sky is 89 deg +/- 3 deg. One of the 'clumps' on the ring is a superposed star, whose energy distribution is consistent with an A-type dwarf (V = 20.2 mag) in the Large Magellanic Cloud (LMC) The radial profile of the ring is not symmetric, with the inner boundary sharper than the outer. Based on the radial profiles and the flux interior to the ring, we conclude that the ring is indeed a tilted ring, and not a spheroidal shell. While the observed width of the ring is approximately 10(exp 17) cm, we find that the average path length through the emitting gas is approximately 4 x 10(exp 15) cm, so the filling factor is small. The ring has faded by a factor of approximately equals 3.7 in (O III) from 1990 August to 1993 October. The characteristic electron density from the (O III) lambda 5007 emission line averages 1.2 x 10exp 4)/cu cm, based on recombination models of the emission. Because the fading rate is uncorrelated with the surface brightness, the density appears to be independent of the brightness, which implies significant path length differences through the ring. By assuming the current structure observed in optical lines applies to the early structure in ultraviolet lines, we construct light curve models to compare with early IUE observations. The clumpy structure of the ring has relatively little effect on the light curves. The (O III) images show faint arclike nebulosity probably associated with the bipolar nebula around SN 1987A and projected inside the ring, which may have affected previous observations of the ring. Finally, we find that the fading rate provides evidence, though weak, favoring an expanding ring over a contracting one.

Plait, Philip C.↗
DOE OSTI2021

Cost-Performance Trade-off in thermoelectric air conditioning system with graded and constant material properties

Thermoelectric (TE) air cooling is a solid-state technology that has the potential to replace conventional vapor compression-based air conditioning. In this paper, we present a detailed system-level modeling for thermoelectric air conditioning system with position-dependent (graded) and constant material properties. Strategies for design optimization of the system are provided in terms of cost-performance trade-off. Realistic convection heat transfer at both sides of the system are taken into account in our modeling. Here, the effects of convection heat transfer coefficients, air flowrate, and thermoelectric material properties are investigated with varying key parameters such as TE leg thickness, module fill factor, and input current. Both constant material properties and graded properties are considered for the TE materials, and they are compared in terms of the degree of cooling, coefficient of performance (COP), and power consumption. For graded materials, we employ one-dimensional finite element methods to solve the coupled electrical and thermal current equations with arbitrary profile of material properties varying with position along the TE legs. We find that graded materials can enhance the degree of cooling, but only at the expense of COP, compared to the case of constant property materials. With constant material properties of ZT = 1 and relatively low electric current, the power consumption of TE coolers can be lower than those of conventional air conditioners at an equivalent cooling capacity. Considering additional advantages such as demand-flexible operation, low noise, and high scalability, thermoelectric cooling could be a competitive technology for future air conditioning applications.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
NASA NTRS1986

Focusing anisotropy of solar cosmic rays

Analysis of 50-MeV particle data from ICE and 1-GeV data from eight high-latitude neutron monitors of the February 16, 1984 solar cosmic ray event indicates that an exponential with scattering mean free path of greater than 2 AU and with index in the 1.3-1.7 range provides a better description of particle anisotropies than the first-order form, confirming the prediction from cosmic ray transport theories which incorporate the effect of adiabatic focusing into the usual pitch angle scattering formalism. The time profile of the event is largely a reflection of coronal transport processes, with good fits provided by a coronal diffusion coefficient of about 10 to the 18th sq cm/s and with velocity-dependent escape. The simple method of predicting the interplanetary scattering parameters has application where particle injection is nearly continuous, but where previously accelerated particles have filled the heliosphere with a large omnidirectional background.

Bieber, J. W.↗
NASA NTRS1978

Volcanism in the cratered terrain hemisphere of Mars

Four kinds of Martian volcanoes and their prevalences in the cratered terrain hemisphere (generally the southern hemisphere) are described. Patera, which are large low-profile volcanic structures, appear to be either older shield volcanoes or a unique type of volcano. 'Plains' volcanics represent low-volume eruptions that formed cones, low shields, and other small-scale structures. Flood volcanics are produced by high-volume eruptions, post-date the older and more degraded plateau plains, and occur mostly as basin-fill materials. Plateau plains, the Martian intercrater plains, contain many wrinkle ridges and floor-fractured craters. It is suggested that volcanic processes as well as erosional processes have been important in obliterating small Martian craters and that volcanic products may constitute a significant fraction (up to 44%) of the surface rocks in the cratered terrain

Greeley, R.↗
NASA NTRS1992

Spatially extended measurements of magnetic field strength in solar plages

The study determines magnetic field strengths along one spatial dimension of a plage region from circularly polarized (Stokes V) spectra of a highly Zeeman-sensitive iron line at 6388.6/cm (1.565 micron). The measured fields are found to lie primarily in the range 1200-1700 G. The mean formal precision for a single determination is +/-65 G. More than 90 percent of the magnetic flux is kilogauss-strength fields. The field strength is coherently organized on spatial scales from 1 arcmin to the limit of angular resolution (2 arcsec). It is inferred from the amplitude of the V signal that the spatial filling factor of the strong-field elements can approach 0.5 within a 2-arcsec resolution element. Magnetic field strength and amplitude are correlated in the sense that locations with stronger mean fields have larger V amplitudes, but the relationship shows more scatter than can be explained by errors in measurement. The individual sigma-components of the V profile are broader than an average quiet-sun line profile would produce by an amount corresponding to 625 G or 4.1 km/s; Zeeman broadening due to a range of magnetic field strength within the resolution element is proposed as the likely explanation.

Rabin, Douglas↗
DOE OSTI2025

Quantifying UAS Observation Error Variance Used in Data Assimilation Systems and Its Impact on Predictive Skill

Observation error determines the weights of the observations and background state used in data assimilation to generate analyses. Quantifying observation error is critical for the optimal assimilation of observational data sets. Uncrewed Aircraft System (UAS) observations have shown potential benefits in filling observational gaps in the lower atmosphere; however, characterization of their error characteristics has been limited. To optimize the use of UAS observations in numerical weather prediction, UAS observation error is estimated based on the 3‐cornered hat diagnostic approach which uses three independent estimates of the atmospheric state. This approach is applied to data from the 2018 Lower Atmospheric Profiling Studies at Elevation‐a Remotely‐piloted Aircraft Team Experiment field campaign using collocated UAS and rawinsonde observations along with output from a set of convection‐permitting model simulations. The estimated observation error values for UAS temperature, wind, and relative humidity measurements were found to be only weakly dependent on height AGL with mean values equal to 0.5°C, 0.8 m s −1 , and 3%, respectively. Only the newly estimated observation error for temperature differed from that previously used to assimilate commercial aircraft observations into global models (1.0°C). However, using this reduced temperature observation error produced more accurate mesoscale analyses and forecasts of both terrain‐driven flows and convection initiation generated by colliding outflow boundaries within the San Luis Valley of Colorado.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1994

Adjustable Reeds For Weaving

Local characteristics of fabrics varied to suit special applications. Adjustable reed machinery proposed for use in weaving fabrics in various net shapes, widths, yarn spacings, and yarn angles. Locations of edges of fabric and configuration of warp and filling yarns varied along fabric to obtain specified properties. In machinery, reed wires mounted in groups on sliders, mounted on lengthwise rails in reed frame. Mechanisms incorporated to move sliders lengthwise, parallel to warp yarns, by sliding them along rails; move sliders crosswise by translating reed frame rails perpendicular to warp yarns; and crosswise by spreading reed rails within group. Profile of reed wires in group on each slider changed.

Farley, Gary L.↗
NASA NTRS1977

Modification of os calcis bone mineral profiles during bedrest

The mineral content of the left central os calcis was determined using the photon absorptiometric technique modified for the space missions to permit area scanning, and was compared with total body calcium balance changes. The instrument consists of a rectilinear scanner that is programmed by a specially designed control module to move a low energy X-ray emitting radionuclide placed in opposition to a detector to scan the foot which is places between them. The foot is placed in a plexiglas box filled with water to provide tissue equivalence and to compensate for irregularities in thickness of tissue cover that surrounds the bone. The mineral content is obtained from basic attenuation equation.

Vogel, J. M.↗
DOE OSTI2025

Direct Evidence of Multispecies Hydrodynamics in Ignition-Scale Hohlraums

A targeted experiment at the National Ignition Facility (NIF) confirms the presence of multispecies hydrodynamics in inertial confinement fusion hohlraums relevant to ignition. Here, the effects are identified by filling the gold hohlraum with a deuterium-tritium (DT) gas mixture instead of helium. As the hohlraum is heated by the NIF lasers, it implodes inward, compressing and heating the DT, which leads to fusion. The resulting DT-fusion neutrons are measured in space, time, yield, angle, and energy. A distinct, peaked, triangular shape in the radial neutron emission profile provides evidence of a “leaky piston” effect caused by the interpenetration of DT into the expanding gold. This process reduces the reversibility of DT compression and decreases neutron generation on the temporal trailing edge compared to the leading edge. These results are well described by multispecies hydrodynamics simulations, which reproduce the observed spatial and temporal features, as well as the total neutron yield and angularly resolved energy spectra. In contrast, conventional simulations that use only single-species physics fail to match the experimental data. They overpredict the neutron yield, produce a flatter-than-observed spatial profile, and show excessive emission at late times compared to the experimental measurements.

Higginson, Drew P. [Lawrence Livermore National La↗
DOE OSTI2022

Metastability and Degradation of CdTe Solar Cells Investigated by nm-Scale Electrical Potential Imaging

We report on investigations of reversible metastability and irreversible degradation of MZO/CdSeTe/CdTe devices from the perspective of electric field across the device using Kelvin probe force microscopy (KPFM). The device showed reversible transitions between the light-soak state (LSS) with the best device efficiency and the dark-soak state (DSS) with an inferior efficiency. However, it showed an irreversible degradation state (DgS) driven by long-hour light soaking at an elevated temperature. The nm-scale KPFM electric field imaging on cross-sections of the devices revealed different anomalous electric field profiles. The electric field at the LSS exhibits a main peak inside the CdSeTe layer but not at the MZO/CdSeTe heterointerface, demonstrating that working junction of the device is a buried homojunction (BHJ). At the DSS, a second electric field peak was observed at the MZO/CdSeTe interface with a similar strength to the main BHJ, which probably caused the decrease in fill factor at the DSS. At the DgS, the electric field peak at the MZO/CdSeTe interface increased significantly and a third electric field was measured at the back contact of the device. Device modeling using COMSOL and in alignment with both the electric field and device current-voltage curves suggest that a slightly low n-doped CdSeTe in the region near the MZO/CdSeTe interface caused the BHJ, and that either a loss of MZO doping or increase of the conduction band offset spike due to long-term stress caused the fill factor-dominated degradation and the increased electric field near the MZO/CdSeTe interface at the DgS. The former, MZO doping decrease, is more plausible by referring the related literature.

BHJ↗
NASA NTRS2010

Shape Bonding method

The present invention is directed to a method of bonding at least two surfaces together. The methods step of the present invention include applying a strip of adhesive to a first surface along a predefined outer boundary of a bond area and thereby defining a remaining open area there within. A second surface, or gusset plate, is affixed onto the adhesive before the adhesive cures. The strip of adhesive is allowed to cure and then a second amount of adhesive is applied to cover the remaining open area and substantially fill a void between said first and second surfaces about said bond area. A stencil may be used to precisely apply the strip of adhesive. When the strip cures, it acts as a dam to prevent overflow of the subsequent application of adhesive to undesired areas. The method results in a precise bond area free of undesired shapes and of a preferred profile which eliminate the drawbacks of the prior art bonds.

Pontius, James T.↗
NASA NTRS2017

The Next Generation of Spaceborne Radars for Cloud and Precipitation Measurements

NASA’s Earth Science Technology Office (ESTO) is currently developing advanced instrument concepts and technologies for the next generation of spaceborne atmospheric radars for clouds and precipitation measurements. Two representative examples are the Radar in a CubeSat (RainCube) – a miniaturized Ka-band precipitation intensity profiling radar for operation on a 6U CubeSat bus; and the Multi-Application Smallsat Tri-band Radar (MASTR) – a Ku/Ka/W band, electronic scanning, and Doppler atmospheric radar. These radar concepts will be capable of providing information on both the state and the process of the atmospheric water (as opposed to just the state information provided by existing spaceborne radars) to fill the current observational gaps in the advancement of weather and climate models.

Im, Eastwood↗
DOE OSTI2021

Trap-Assisted Dopant Compensation Prevents Shunting in Poly-Si Passivating Interdigitated Back Contact Silicon Solar Cells

Using a trap-assisted compensation model, we explain why polycrystalline Si (poly-Si) passivating contacts are able to achieve low leakage current between the doped fingers of interdigitated back contact (IBC) monocrystalline Si solar cells despite mixing of boron and phosphorus dopants in the isolation region. The fill factor of IBC solar cells is strongly affected by the electrical isolation region between n- and p-type fingers, as this region is critical in minimizing shunting losses. During fabrication of monocrystalline Si solar cells with poly-Si passivating contacts, the intrinsic poly-Si isolation region inevitably gets contaminated with both p- and n-type dopants. Using dopant profiles measured with time-of-flight secondary ion mass spectrometry and scanning probe measurements of the isolation region, we demonstrate that despite the dopant spreading during cell processing, a well-compensated region between the doped fingers exists that prevents shunting. The trap-assisted dopant compensation mechanism significantly widens the compensated region to tens of microns, where the residual dopant densities are below the trap density. This enables a high-resistivity region, resulting in low shunt current. Using one-dimensional (1-D) finite element diode simulations, we identify the design parameters and experimental conditions under which a sufficiently resistive region can form. Furthermore, our measurements of 2-D local resistivity and work function maps across the isolation region using scanning spreading resistance microscopy and Kelvin probe force microscopy demonstrate the existence of a highly resistive, wide compensated region and confirm our proposed compensation mechanism. For our structures, this region is ~25 µm in width within a ~150 µm wide finger isolation region with nearly 3 orders of magnitude higher resistivity than the regions dominated by a single type of dopant.

14 SOLAR ENERGY↗
DOE OSTI2022

A Meteorology and Snow Data Set From Adjacent Forested and Meadow Sites at Crested Butte, CO, USA

We present meteorology and snow observation data collected at sites in the southwestern Colorado Rocky Mountains (USA) over three consecutive water years with different amounts of snow water equivalent (SWE) accumulation: A year with above average SWE (2019), a year with average SWE (2020), and a year with below average SWE (2021). This data set is distinguished by its emphasis on paired open-forest sites in a continental snow climate. Approximately once a month during February–May, we collected data from 15 to 20 snow pits and took 8 to 19 snow depth transects. Our sampling sites were in open and adjacent forested areas at 3,100 m and in a lower elevation aspen (3,035 m) and higher elevation conifer stand (3,395 m). In total, we recorded 270 individual snow pit density and temperature profiles and over 4,000 snow depth measurements. These data are complimented by continuous meteorological measurements from two weather stations: One in the open and one in the adjacent forest. Meteorology data—including incoming shortwave and longwave radiation, outgoing shortwave radiation, relative humidity, wind speed, snow depth, and air and infrared surface temperature—were quality controlled and the forcing data were gap-filled. These data are available to download from Bonner, Smyth, et al. at three levels of processing, including a level with downscaled, adjusted precipitation based on data assimilation using observed snow depth and a process-based snow model. We demonstrate the utility of these data with a modeling experiment that explores open-forest differences and identifies opportunities for improvements in model representation.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2026

New approaches to Bayesian uncertainty quantification for Nuclear Science (Final Technical Report)

Inverse problems play a central role in experimentation and theory/data comparisons for many areas of modern Nuclear Physics (NP) and High-Energy Physics (HEP). Bayes’s Theorem is a powerful tool for solving Inverse Problems, providing conceptually transparent and unbiased constraints on theoretical parameters and their uncertainties (“Bayesian Inference”) and enabling the quantification of agreement or tension between models and data. However, analyses based on Bayesian Inference are often challenging for NP and HEP applications, either because of the large number of parameters in the problem, the high computational cost, or both. We propose a multi-institutional collaboration to develop and deploy novel Bayesian analysis tools that advance the scientific scope of a broad range of current and future NP experiments. This project brings together NP domain scientists working on several high-profile NP projects for which new, high-performance Bayesian Uncertainty Quantification (“Bayesian UQ”) methods are essential to carry out the science, and data scientists who are developing state-of-the-art methods applicable to these problems. The NP projects in this proposal comprise measurements of the mass and fundamental nature of the neutrino; study of the Quark-Gluon Plasma that filled the early universe; and mapping of natural and anthropogenic radiation environments. While these NP projects have very different scientific goals, with datasets and analysis approaches that differ significantly, they share common requirements for improving computationally intensive Bayesian analyses using advanced Machine Learning algorithms and will benefit strongly from a coherent effort to develop general solutions. This proposal brings together these projects and forefront ML-based data science algorithms to develop such general solutions. The methods developed in this project will also be more widely applicable, thereby advancing science in the larger Nuclear Physics portfolio.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1995

Molecular dynamics simulation of a piston driven shock wave in a hard sphere gas

Molecular dynamics simulation is used to study the piston driven shock wave at Mach 1.5, 3, and 10. A shock tube, whose shape is a circular cylinder, is filled with hard sphere molecules having a Maxwellian thermal velocity distribution and zero mean velocity. The piston moves and a shock wave is generated. All collisions are specular, including those between the molecules and the computational boundaries, so that the shock development is entirely causal, with no imposed statistics. The structure of the generated shock is examined in detail, and the wave speed; profiles of density, velocity, and temperature; and shock thickness are determined. The results are compared with published results of other methods, especially the direct simulation Monte-Carlo method. Property profiles are similar to those generated by direct simulation Monte-Carlo method. The shock wave thicknesses are smaller than the direct simulation Monte-Carlo results, but larger than those of the other methods. Simulation of a shock wave, which is one-dimensional, is a severe test of the molecular dynamics method, which is always three-dimensional. A major challenge of the thesis is to examine the capability of the molecular dynamics methods by choosing a difficult task.

Woo, Myeung-Jouh↗