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At least 721 records · Page 40

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DOE OSTI2022

A comparison between the one- and two-step spin-orbit coupling approaches based on the ab initio Density Matrix Renormalization Group

The efficient and reliable treatment of both spin-orbit coupling (SOC) and electron correlation is essential for understanding f-element chemistry. Here, we analyze two approaches to the problem, the one-step approach where both effects are treated simultaneously, and the two-step state interaction approach. We report an implementation of the ab initio density matrix renormalization group(DMRG) with a one-step treatment of the SOC effect which can be compared to prior two-step treatments on an equal footing. Using a dysprosium octahedral complex and bridged dimer as benchmark systems, we identify characteristics of problems where the one-step approach is beneficial for obtaining the low-energy spectrum.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Magnetisation and magneto-transport measurements on CeBi single crystals

In this study, we report the synthesis of CeBi single crystals out of Bi self-flux and a systematic study of the magnetic and transport properties with varying temperature and applied magnetic fields. From these R(T, H) and M(T, H) data, we could assemble the field-temperature (H⁻T) phase diagram for CeBi and visualise the three-dimensional M⁻T⁻H surface. In the phase diagram, we identify regions with well-defined magnetisation values and identify a new phase region. The magnetoresistance (MR) in the low-temperature regime shows, above 6T a power-law, non-saturated behaviour with large MR (~3 × 10 5 % at 2K and 13.95T), along with Shubnikov–de Haas oscillations. With increasing temperatures, MR decreases, and then becomes negative for T ⪆10 K . This crossover in MR seems to be unrelated to any specific magnetic or metamagnetic transitions, but rather is associated with changing from a low-temperature normal metal regime with little or no scattering from the Ce 3 + moments and an anomalously large MR, to increased scattering from local Ce moments and a negative MR as temperature increases.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2023

The first two chromosome‐scale genome assemblies of American hazelnut enable comparative genomic analysis of the genus Corylus

Summary The native, perennial shrub American hazelnut ( Corylus americana ) is cultivated in the Midwestern United States for its significant ecological benefits, as well as its high‐value nut crop. Implementation of modern breeding methods and quantitative genetic analyses of C. americana requires high‐quality reference genomes, a resource that is currently lacking. We therefore developed the first chromosome‐scale assemblies for this species using the accessions ‘Rush’ and ‘Winkler’. Genomes were assembled using HiFi PacBio reads and Arima Hi‐C data, and Oxford Nanopore reads and a high‐density genetic map were used to perform error correction. N50 scores are 31.9 Mb and 35.3 Mb, with 90.2% and 97.1% of the total genome assembled into the 11 pseudomolecules, for ‘Rush’ and ‘Winkler’, respectively. Gene prediction was performed using custom RNAseq libraries and protein homology data. ‘Rush’ has a BUSCO score of 99.0 for its assembly and 99.0 for its annotation, while ‘Winkler’ had corresponding scores of 96.9 and 96.5, indicating high‐quality assemblies. These two independent assemblies enable unbiased assessment of structural variation within C. americana , as well as patterns of syntenic relationships across the Corylus genus. Furthermore, we identified high‐density SNP marker sets from genotyping‐by‐sequencing data using 1343 C. americana , C. avellana and C. americana × C. avellana hybrids, in order to assess population structure in natural and breeding populations. Finally, the transcriptomes of these assemblies, as well as several other recently published Corylus genomes, were utilized to perform phylogenetic analysis of sporophytic self‐incompatibility (SSI) in hazelnut, providing evidence of unique molecular pathways governing self‐incompatibility in Corylus .

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS1984

A comparison between active and passive sensing of soil moisture from vegetated terrains

A comparison between active and passive sensing of soil moisture over vegetated areas is studied via scattering models. In active sensing three contributing terms to radar backscattering can be identified: (1) the ground surface scatter term; (2) the volume scatter term representing scattering from the vegetation layer; and (3) the surface volume scatter term accounting for scattering from both surface and volume. In emission three sources of contribution can also be identified: (1) surface emission; (2) upward volume emission from the vegetation layer; and (3) downward volume emission scattered upward by the ground surface. As ground moisture increases, terms (1) and (3) increase due to increase in permittivity in the active case. However, in passive sensing, term (1) decreases but term (3) increases for the same reason. This self conpensating effect produces a loss in sensitivity to change in ground moisture. Furthermore, emission from vegetation may be larger than that from the ground. Hence, the presence of vegetation layer causes a much greater loss of sensitivity to passive than active sensing of soil moisture.

Fung, A. K.↗

NASA NTRS1985

A comparison between active and passive sensing of soil moisture from vegetated terrains

A comparison between active and passive sensing of soil moisture over vegetated areas is studied via scattering models. In active sensing three contributing terms to radar backscattering can be identified: (1) the ground surface scatter term; (2) the volume scatter term representing scattering from the vegetation layer; and (3) the surface volume scatter term accounting for scattering from both surface and volume. In emission three sources of contribution can also be identified: (1) surface emission; (2) upward volume emission from the vegetation layer; and (3) downward volume emission scattered upward by the ground surface. As ground moisture increases, terms (1) and (3) increase due to increase in permittivity in the active case. However, in passive sensing, term (1) decreases but term (3) increases for the same reason. This self compensating effect produces a loss in sensitivity to change in ground moisture. Furthermore, emission from vegetation may be larger than that from the ground. Hence, the presence of vegetation layer causes a much greater loss of sensitivity to passive than active sensing of soil moisture.

Fung, A. K.↗

NASA NTRS1993

Gas-rich dwarf galaxies in dense and sparse environments

Dwarf irregular galaxies (generically labelled Im for the present purposes) pose an enigma to students of galaxy evolution. In nearby groups and the Virgo cluster, Im galaxies are at least as abundant as spiral galaxies, and their low surface brightnesses and high gas-to-stars ratios suggest that (at least in the stochastic self-propagating star formation scenario) there should be significant numbers of HI clouds with masses approaching 10(exp 8) solar mass which have undergone very little or no star formation. To date, however, no clouds with so little star formation that they would not be recognized as Im galaxies on high-quality photographic plates have been identified. There have been suggestions that such dwarfs may be tidally disrupted in regions of high galactic density, but may be prevalent in low density regions. We offer data from three parallel programs relevant to this issue. (1) A large number of Im galaxies throughout the Local Supercluster have been mapped in the HI spectral line using the Arecibo Radiotelescope, and we can establish the frequency with which HI disks much more extended than their optically visible portions are found. (2) Our extensive mapping of spiral and dwarf galaxies in the Virgo cluster allows us to set stringent limits on the density of star-free Hi clouds in that cluster. (3) We have conducted a sampling of the void in the distribution of galaxies toward the super galactic pole, optimized for finding low-mass HI clouds at redshifts out to approximately 2000 km/s.

Hoffman, G. Lyle↗

NASA NTRS2000

Treatability Study of Pentaborane(9)

Procedures for the safe destruction of liquid pentaborane(9), B5H9, by solvolysis were investigated. The objective of the study was to establish the optimum conditions for a pilot plant operation that would use water, or alcohol, or water-alcohol mixtures as the solvolysis reagent. Small amounts of B5H9 sprayed from a syringe will not necessarily enflame, nor will a small pool on a spot plate. Therefore, a procedure was developed to reproducibly demonstrate the flammability of B5H9. In these tests every sample of neat B5H9 ignited and burned with a very sooty flame till the sample was consumed. The spontaneous self-ignition of B5H9 was quenched by the addition of small concentrations of ethers THF (tetrahydrofuran) or DME (1,2-dimethoxy ethane). It was found that ten percent (volume) of either provided total quenching with a large margin of safety. When these stabilized solutions were exposed to air, they decomposed and evaporated leaving a residue that was identified by nuclear magnetic resonance (NMR) analysis as boric acid. Most of the laboratory solvolysis experiments used the 90 percent B5H9, 10 percent THF solution. This mixture was safer to handle and its solvolysis reactivity was virtually identical to that of 100 percent B5H9. Reaction rates were analyzed by measurement of hydrogen evolved during the solvolysis reactions. In terms of the minimum overall complete reaction time, the data indicate that 50/50 alcohol/water is the optimum solvolysis reagent. This reaction produced a mixture of boric acid, B(OH)3, and triethoxyborane, B(OEt)3[Et = C2H5], and mixed exchange derivatives thereof.

McDonald, Joseph K.↗

NASA NTRS2000

Treatability Study of Pentaborane(9)

Procedures for the safe destruction of liquid pentaborane(9), B5H9, by solvolysis were investigated. The objective of the study was to establish the optimum conditions for a pilot plant operation that would use water, or alcohol, or water-alcohol mixtures as the solvolysis reagent Small amounts of B5H9 sprayed from a syringe will not necessarily enflame, nor will a small pool on a spot plate. Therefore, a procedure was developed to reproducibly demonstrate the flammability of B5H9 In these tests every sample of neat B5H9 ignited and burned with a very sooty flame till the sample was consumed. The spontaneous self-ignition of B5H9 was quenched by the addition of small concentrations of the ethers THF (tetrahydrofuran) or DME (1,2-dimethoxy ethane). It was found that 10% (volume) of either provided total quenching with a large margin of safety. When these stabilized solutions were exposed to air, they decomposed and evaporated leaving a residue that was identified by NMR analysis as boric acid. Most of the laboratory solvolysis experiments used the 90% B5H9, 10% THF solution. This mixture was safer to handle and its solvolysis reactivity was virtually identical to that of 100% B5H9. Reaction rates were analyzed by measurement of hydrogen evolved during the solvolysis reactions. In terms of the minimum overall complete reaction time, the data indicate that 50150 alcohol/water is the optimum solvolysis reagent. This reaction produced a mixture of boric acid, B(OH)3, and triethoxyborane, B(OEt)3 [Et = C2H5], and mixed exchange derivatives thereof.

McDonald, Joseph K.↗

NASA NTRSDate not supplied

Limitations on the Use of Eye-Tracking Data to Understand Operator Awareness

In the last 20 years, a number of accidents and incidents in commercial aviation have pointed to poor flight crew awareness of basic flight path parameters (e.g., airspeed, bank, pitch). As a result, there is a desire to improve pilot situation awareness and how attention is allocated. Eye-tracking has been a commonly used measure of awareness; it can aid in understanding whether specific indications were fixated, and perhaps how a pilot gathered information (that is, which indications in which sequence). In this paper, we discuss limitations on what eye-tracking data can reveal about pilot awareness and understanding. First, previous studies (e.g., Sarter et al., 2007) have shown that fixation on an indication may not ensure awareness or understanding. Further, an operator may have awareness of information not fixated. Additional measures—such as self-report or control inputs—can help to better establish the extent of pilot awareness and understanding. Second, sequences of fixations (scan patterns) have also become a performance measure. While a small number of recognized scan patterns have been validated for a small set of parameters on the Primary Flight Display (PFD), scan patterns have not been identified to support the broader context of flight path management or flight operations. More important is to understand the full set of drivers underlying the larger pattern of eye fixations; this approach moves away from the idea of well-established scan patterns as a marker of skilled performance and gives a larger role to pilot cognition. Pilots have various reasons to direct attention to specific elements on the interface, such as: - feedback tied to control inputs - a check on compliance with flight path targets - a reaction to an alert or a call out - attempt to understand an unexpected indication - assess progress toward a flight path target The importance of cognition is further implicated in the finding that pilot interviews show that fixating typically is accompanied by expectation; generally, pilots have a strong expectation of what value or indication they will see, which allows more efficient integration of information and an ability to identify indications that suggest an alternative account of the current system state. We will describe a range of eye-tracking measures and how they should and should not be used.

aviation↗

NASA NTRSDate not supplied

Development of Head-Trunk Coordination Measures for Monitoring Postflight Sensorimotor Readaptation Strategies

During exploration missions, individual health assessments will be required to account for variability in neurosensory adaptation and task readiness for the initial extravehicular activities (EVAs). Previous research has identified postflight vestibular alterations and disruptions in head-trunk coordination after both short and long duration spaceflight missions. Astronauts were found to minimize head angular displacement and utilize a consistent forward head tilt theorized as a compensatory approach to stabilize the cephalic system and reduce motion sickness during readaptation to Earth’s gravity. Further, anecdotal self-reports from Shuttle crewmembers stated that pitch and side-to-side head movements immediately post-landing typically resulted in perceived angular self-motion. Notable disruptions also occur upon arrival in orbit, with astronauts choosing waist rotation rather than head movements during dynamic tasks. It is thought that the underlying sensorimotor disruptions may contribute to motion sickness in space and upon landing, postflight gait dysfunction, and inaccurate spatial orientation when performing daily tasks. To better characterize microgravity-induced sensorimotor adaptations, it is important to develop measures and monitoring tools that have high sensitivity in detecting changes in head-trunk coordination.

H M Weiss↗

DOE OSTI2026

Local Spin Density Approximation Strongly Improved by a Better-Informed Local Scaling of Its Self-Interaction Correction

The Perdew−Zunger self-interaction correction (PZSIC) makes density functional approximations (DFAs) exact for all one-electron densities. However, it overcorrects in manyelectron regions, introducing errors for the uniform-density limit, where uncorrected DFAs are exact. The locally scaled PZSIC (LSIC), based on the iso-orbital indicator zσ [which distinguishes single-orbital and slowly varying density regions and is used with the local spin density approximation (LSDA)], restores the uniform-density limit and significantly improves results for many properties, including chemical reaction barrier heights, atomization energies, and ionization potentials. Yet, LSIC performs poorly for weakly bonded systems, leaving many unbound, due to limitations of its iso-orbital indicator. To correct this, in this work we propose a new local scaling, LSIC-α, based on the iso-orbital indicator ασ (which additionally identifies regions of overlapping density tails). A two-parameter scaling function of ασ is fitted to a subset of the nonbonded appropriate norms for the SCAN and r2SCAN meta- GGAs, and tested on many properties of main-group atoms, molecules, and molecular complexes. LSIC-α greatly improves the interaction energies of weakly bonded systems in the S22 data set while retaining LSIC’s accuracy for other properties. This work shows that the errors of LSDA (and presumably of higher-level DFAs) can be largely but not entirely repaired by a proper “do no harm” self-interaction correction.

Approximation↗

NASA NTRS1982

Measurements of self-excited rotor-blade vibrations using optical dispacements

The characteristics of optical displacement spectra and their role of monitoring rotor blade vibrations are discussed. During the operation of a turbofan engine at part speed, near stall, and elevated inlet pressure and temperature, several vibratory instabilities were excited simultaneously on the first fan rotor. The torsional and bending contributions to the main flutter mode were resolved by using casing-mounted optical displacement sensors. Other instabilities in the blade deflection spectra were identified.

Kurkov, A. P.↗

NASA NTRS1984

Measurements of self-excited rotor-blade vibrations using optical displacements

Kurkov, A. P.↗

DOE OSTI2020

Conscientious vaccination exemptions in kindergarten to eighth-grade children across Texas schools from 2012 to 2018: A regression analysis

Background: As conscientious vaccination exemption (CVE) percentages rise across the United States, so does the risk and occurrence of outbreaks of vaccine-preventable diseases such as measles. In the state of Texas, the median CVE percentage across school systems more than doubled between 2012 and 2018. During this period, the proportion of schools surpassing a CVE percentage of 3% rose from 2% to 6% for public schools, 20% to 26% for private schools, and 17% to 22% for charter schools. The aim of this study was to investigate this phenomenon at a fine scale. Methods and findings: Here, we use beta regression models to study the socioeconomic and geographic drivers of CVE trends in Texas. Using annual counts of CVEs at the school system level from the 2012–2013 to the 2017–2018 school year, we identified county-level predictors of median CVE percentage among public, private, and charter schools, the proportion of schools below a high-risk threshold for vaccination coverage, and five-year trends in CVEs. Since the 2012–2013 school year, CVE percentages have increased in 41 out of 46 counties in the top 10 metropolitan areas of Texas. We find that 77.6% of the variation in CVE percentages across metropolitan counties is explained by median income, the proportion of the population that holds a bachelor's degree, the proportion of the population that self-reports as ethnically white, the proportion of the population that is English speaking, and the proportion of the population that is under the age of five years old. Across the 10 top metropolitan areas in Texas, counties vary considerably in the proportion of school systems reporting CVE percentages above 3%. Sixty-six percent of that variation is explained by the proportion of the population that holds a bachelor’s degree and the proportion of the population affiliated with a religious congregation. Three of the largest metropolitan areas—Austin, Dallas–Fort Worth, and Houston—are potential vaccination exemption "hotspots," with over 13% of local school systems above this risk threshold. The major limitations of this study are inconsistent school-system-level CVE reporting during the study period and a lack of geographic and socioeconomic data for individual private schools. Conclusions: In this study, we have identified high-risk communities that are typically obscured in county-level risk assessments and found that public schools, like private schools, are exhibiting predictable increases in vaccination exemption percentages. As public health agencies confront the reemerging threat of measles and other vaccine-preventable diseases, findings such as ours can guide targeted interventions and surveillance within schools, cities, counties, and sociodemographic subgroups.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2026

Dara: Automated Multiple-Hypothesis Phase Identification and Refinement from Powder X-ray Diffraction

Powder X-ray diffraction (XRD) is a foundational technique for characterizing crystalline materials. However, the reliable interpretation of XRD patterns, particularly in multiphase systems, remains a manual and expertise-demanding task. As a characterization method that only provides structural information, multiple reference phases can often be fit to a single pattern, leading to potential misinterpretation when alternative solutions are overlooked. To ease humans’ efforts and address the challenge, we introduce Dara (data-driven automated Rietveld analysis), a framework designed to automate the robust identification and refinement of multiple phases from powder XRD data. Dara performs an exhaustive tree search over all plausible phase combinations within a given chemical space and validates each hypothesis using the BGMN Rietveld refinement routine. Key features include structural database filtering, automatic clustering of isostructural phases during tree expansion, and peak-matching-based scoring to identify promising phases for refinement. When ambiguity exists, Dara generates multiple hypothesis which can then be decided between by human experts or with further characterization tools. By enhancing the reliability and accuracy of phase identification, Dara enables scalable analysis of realistic complex XRD patterns and provides a foundation for integration into multimodal characterization workflows, moving toward fully self-driving materials discovery.

Biological databases↗

DOE OSTI2023

Octahedral Distortion and Excitonic Behavior of Cs 3 Bi 2 Br 9 Halide Perovskite at Low Temperature

The metal halide ionic octahedron, represented as [MX 6 ] $n$- (M = metal cation, X = halide anion), serves as the basic structural unit in halide perovskites and plays a crucial role in determining their optoelectronic and chemical properties. Thus, it is possible to correlate the responses of metal halide perovskites to various environmental stimuli with the dynamic behaviors of the [MX 6 ] $n$- octahedra. In this study, with the temperature-dependent single-crystal X ray diffraction (SCXRD) measurements on Cs 3 Bi 2 Br 9 2D halide perovskites, we can identify two classes of distortions through the lowering of temperature: intraoctahedral distortion, which is the off-centering of Bi 3+ cation within a [BiBr 6 ] 3– octahedron due to the Bi 3+ 6s 2 lone pair electrons, and interoctahedral distortion, which is the collective misalignments among the [BiBr 6 ] 3– building blocks. Free exciton (FE) and self-trapped exciton (STE) models are used to study the relationship between the distortion of octahedra in Cs 3 Bi 2 Br 9 and the corresponding changes in its optoelectronic properties, which transform from dominating blue emission above 100 K to red emission at 4 K. In conclusion, this work provides new insights into the excitonic behaviors of perovskites and suggests a possibility that we can design and rationalize the optical properties of halide perovskites by regulating the environmental stimuli based on the knowledge of behaviors of the individual [MX 6 ] $n$- building blocks.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Observation of Kolmogorov turbulence due to multiscale vortices in dusty plasma experiments

We report the experimental observation of fully developed Kolmogorov turbulence originating from self-excited vortex flows in a three-dimensional (3D) dust cloud. The characteristic -5/3 scaling of 3D Kolmogorov turbulence is consistent in both the spatial and temporal energy spectra within a statistical variation of experimental data. Additionally, the 2/3 scaling in the second-order structure function further supports the presence of Kolmogorov turbulence. We also identified a slight deviation in the tails of the probability distribution functions for velocity gradients, a reflection of intermittency. The experiment showed the formation of a dust cloud in the diffused plasma region away from the electrodes. The dust rotation was observed in multiple experimental campaigns under different discharge conditions at different spatial locations and background plasma environments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Transport characterization and pinning analysis of BaFe 1.9 Ni 0.1 As 2.05 thin films

In this paper, we report on the vortex-glass transition and superconducting performance of BaFe 1.9 Ni 0.1 As 2.05 thin films with T c = 17.8 K on CaF 2 (00 l ) single crystals by pulsed laser deposition. Atomic force microscopy characterization indicates the volumes of droplets appearing on the film surface increase with thickness and Magneto-optical imaging proves slight inhomogeneities in the current flow within the ab -plane of thin film. The thin films show a transport current density J c of ~1.14 MA cm –2 in self-field, and 0.34 and 0.28 MA cm –2 for H // c and H // ab up to 9 T at 4.2 K. Pinning mechanism associated with the fluctuations in the mean free path of the charge carries is found to be dominant in the thin films. The vortex-glass (VG) to vortex-liquid phase transition is identified in terms of the plots of the logarithmic derivative of the resistivity curves under different fields, allowing us to deduce the values of the VG transition temperature T g , and the critical exponent s . The ρ – T curves are well scaled by VG theory. A phase diagram combining the VG transition temperature, irreversibility field and upper critical field is constructed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗