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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Gravitational waves from breaking of an extra U (1) in SO (10) grand unification

Abstract In a class of gauged $U(1)$ extended Standard Models (SMs), the breaking of the $U(1)$ symmetry is not only a source for Majorana masses of right-handed (RH) neutrinos crucial for the seesaw mechanism, but also a source of stochastic gravitational wave (GW) background. Such $U(1)$ extended models are well-motivated from the viewpoint of grand unification. In this paper, we discuss a successful ultraviolet completion of a $U(1)$ extended SM by an $SO(10)$ grand unified model through an intermediate step of $SU(5) \times U(1)$ unification. With a parameter set that is compatible with the $SO(10)$ grand unification, we find that a first-order phase transition associated with the $U(1)$ symmetry breaking can be strong enough to generate GWs with a detectable size of amplitude. We also find that the resultant GW amplitude reduces and its peak frequency becomes higher as the RH neutrino masses increase.

Physics↗
DOE OSTI2020

Unconventional domain-wall pairs and interacting Bloch lines in a Dzyaloshinskii-Moriya multilayer thin film

Bloch-lines (BLs) play a key role in determining the static and dynamic behavior of chiral domain walls and skyrmions in multilayer films with a significant Dzyaloshinskii-Moriya interaction (DMI). Here, using in-situ Lorentz phase microscopy, we reveal a new type of spin texture, termed a type-II domain wall pair (DWP), stabilized in DMI multilayer thin films with BLs. For a type-II DWP, the Bloch components of each complementary domain wall are parallel, implying opposite chirality. Additionally, we find that type-II DWPs preferentially form through bifurcation of a type-I DWP and require the formation of at least two BLs. We demonstrate a distinct phase jump associated with type-II DWPs, and further reveal the role they play in the formation of mixed-character skyrmions where the Bloch component that can be of either left- or right-handed chirality.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Nearly hyperuniform, nonhyperuniform, and antihyperuniform density fluctuations in two-dimensional transition metal dichalcogenides with defects

Hyperuniform many-body systems in d-dimensional Euclidean space R d are characterized by completely suppressed (normalized) infinite-wavelength density fluctuations, and appear to be endowed with novel exotic physical properties. Recently, hyperuniform systems of disordered varieties have been observed in the context of various atomic-scale two-dimensional (2D) materials. Here, we analyze the effects of localized defects on the density fluctuations across length scales and on the hyperuniformity property of experimental samples of two-dimensional transition metal dichalcogenides. In particular, we extract atomic coordinates from time series annular dark field-scanning transmission electron microscopy (ADF-STEM) imaging data of 2D tungsten chalcogenides with the 2H structure (Te-doped 2H-WSe 2 ) showing continuous development and evolution of electron-beam induced defects, and construct the corresponding chemical-bonding informed coordination networks between the atoms. We then compute a variety of pair statistics and bond-orientational statistics to characterize the samples. At low defect concentrations, the corresponding materials are nearly hyperuniform, characterized by significantly suppressed scattering at the zero wave-number limit (omitting forward/ballistic scattering). As more defects are introduced, the (approximate) hyperuniformity of the materials is gradually destroyed, and the system becomes non-hyperuniform even when the material still contains a significant amount of crystalline regions. At high defect concentrations, the structures become antihyperuniform with diverging (normalized) large-scale density fluctuations, mimicking those typically observed at the thermal critical points associated with phase transitions. Overall, the defected materials possess varying degrees of orientation order, and there is apparently no intermediate hexatic phase emerging. To understand the observed nearly hyperuniform density fluctuations in the slightly defected materials, we construct a minimalist structural model and demonstrate that the experimental samples can be essentially viewed as perturbed honeycomb crystals with small correlated displacements and double chalcogen vacancies. Moreover, the small correlated displacements alone can significantly degrade hyperuniformity of the perfect honeycomb structure. Therefore, even a small amount of vacancies, when coupled with correlated displacements, can completely destroy hyperuniformity of the system.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Strongly correlated itinerant magnetism near superconductivity in NiTa 4 Se 8

Metallic ferromagnets with strongly interacting electrons often exhibit remarkable electronic phases such as ferromagnetic superconductivity, complex spin textures, and nontrivial topology. Here, in this report, we discuss the synthesis of a layered magnetic metal NiTa 4 Se 8 (or Ni 1/4 TaSe 2 ) with a Curie temperature of 58 Kelvin. Magnetization data and density functional theory calculations indicate that the nickel atoms host uniaxial ferromagnetic order of about 0.7µ B per atom, while an even smaller moment is generated in the itinerant tantalum conduction electrons. Strong correlations are evident in flat bands near the Fermi level, a high heat capacity coefficient, and a high Kadowaki-Woods ratio. Density functional theory calculations suggest that electron and hole Fermi surfaces in the ferromagnetic phase are associated with opposite spin polarization. When the system is diluted of magnetic ions, the samples become superconducting below about 2 Kelvin. We discuss possible mechanisms for superconductivity in this family.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2024

Gravitational wave spectrum of chain inflation

Chain inflation is an alternative to slow-roll inflation in which the inflaton tunnels along a large number of consecutive minima in its potential. In this work we perform the first comprehensive calculation of the gravitational wave (GW) spectrum of chain inflation. In contrast to slow-roll inflation the latter does not stem from quantum fluctuations of the gravitational field during inflation, but rather from the bubble collisions during the first-order phase transitions associated with vacuum tunneling. Our calculation is performed within an effective theory of chain inflation which builds on an expansion of the tunneling rate capturing most of the available model space. The effective theory can be seen as chain inflation’s analog of the slow-roll expansion in rolling models of inflation. The near scale-invariance of the scalar power spectrum translates to a quasiperiodic shape of the inflaton potential in chain inflation, with the tunneling rate changing very slowly during the e-folds leading to cosmic microwave background observables. We show that chain inflation produces a very characteristic double-peak GW spectrum: a faint high-frequency peak associated with the gravitational radiation emitted during inflation, and a strong low-frequency peak associated with the graceful exit from chain inflation (marking the transition to the radiation-dominated epoch). There exist very exciting prospects to test the gravitational wave signal from chain inflation at the aLIGO-aVIRGO-KAGRA network, at LISA and /or at pulsar timing array experiments. A particularly intriguing possibility we point out is that chain inflation could be the source of the stochastic gravitational wave background recently detected by NANOGrav, PPTA, EPTA, and CPTA. We also show that the gravitational wave signal of chain inflation is often accompanied by running/ higher running of the scalar spectral index to be tested at future cosmic microwave background experiments. Published by the American Physical Society 2024

Freese, Katherine↗
DOE OSTI2020

A Thermosensitive, Phase-Variable Epigenetic Switch: pap Revisited

It has been more than a decade since the last comprehensive review of the phase-variable uropathogen-associated pyelonephritis-associated pilus (pap) genetic switch. Since then, important data have come to light, including additional factors that regulate pap expression, better characterization of H-NS regulation, the structure of the Lrp octamer in complex with pap regulatory DNA, the temperature-insensitive phenotype of a mutant lacking the acetyltransferase RimJ, evidence that key components of the regulatory machinery are acetylated, and new insights into the role of DNA binding by key regulators in shaping both the physical structure and regulatory state of the papI and papBA promoters. This review revisits pap, integrating these newer observations with older ones to produce a new model for the concerted behavior of this virulence-regulatory region.

gene silencing↗
DOE OSTI2024

Lattice regularization of reduced Kähler-Dirac fermions and connections to chiral fermions

We show how a path integral for reduced Kähler-Dirac fermions suffers from a phase ambiguity associated with the fermion measure that is an analog of the measure problem seen for chiral fermions. However, unlike the case of chiral symmetry, a doubler free lattice action exists which is invariant under the corresponding onsite symmetry. This allows for a clear diagnosis and solution to the problem using mirror fermions resulting in a unique gauge invariant measure. By introducing an appropriate set of Yukawa interactions which are consistent with ’t Hooft anomaly cancellation we conjecture the mirrors can be decoupled from low energy physics. Moreover, the minimal such Kähler-Dirac mirror model yields a light sector which corresponds, in the flat space continuum limit, to the Pati-Salam GUT model.

Physics↗
DOE OSTI2021

Dose Rate Analysis of the WCS Consolidated Interim Storage Facility

This report describes a confirmatory calculation for a proposed consolidated interim storage facility (CISF) to support the US Nuclear Regulatory Commission’s review of the license application submitted by the Interim Storage Partners. The scope of this report is limited to an assessment of the annual dose from direct radiation associated with Phase 1 of the Waste Control Specialists (WCS) CISF and the determination of the minimum controlled area boundary based on the 10 CFR 72.104 limit of 25 mrem annual dose to the whole body. The confirmatory dose rate calculations used the source term and shielding calculation capabilities of the SCALE 6.2.3 computer code system. The calculation method employed in the confirmatory calculations uses a detailed Monte Carlo radiation transport simulation from source to dose rate. This method differs from the two-step method used in the safety analysis report (SAR), which requires determination of the photon and neutron energy and angular distributions on the cask external surface and then the use of this surface source in a new radiation transport calculation to determine dose rate as a function of distance from the storage facility. A simulation was made using the complete site geometry (all casks present) but with only one cask containing source, and a total of 467 independent calculations were performed to obtain the dose rate maps produced by each storage cask. Basic input data and assumptions used in the SAR (e.g., cask design parameters and design basis assembly characteristics) were used in this confirmatory calculation for consistency with the SAR. Local atmospheric conditions for skyshine calculations were simulated using US standard atmosphere data, which describe average air temperature, pressure, and density as a function of altitude. The determined minimum required distances from the WCS Phase 1 CISF to a contour defined by the 25 mrem annual dose limit were approximately 623 m (0.387 miles) in the N-NE direction, 594 m (0.369 miles) in the SSW direction, and 533 m (0.331 miles) in the E-SE direction and the W-NW direction. The annual dose results of the confirmatory calculation are in relatively good agreement with the annual dose values presented in the WCS SAR. The annual dose produced by the Phase 1 CISF at the nearest site boundary, 0.75 miles away from the CISF, was estimated by this study to be approximately 6.02E-02 ± 2.0E-04 mrem, which is significantly smaller than the 25 mrem annual dose limit provided in 10 CFR 72.104. The SAR annual dose rate value for the nearest site boundary was 7.52E-2 mrem, which included 7.73E-03 mrem due to postulated leakage of the FO-, FC-, and FF-canisters. A comparison with the dose rate values reported in the SAR for 16 detector locations, D1 through D16, on the protected area boundary is also included in this report. This comparison shows that the SAR determined higher annual dose values for detectors D1 through D14 by 12% to 45% and lower annual dose values for detectors D15 and D16 by 18% and 8%, respectively, as compared with this ORNL confirmatory calculation. Sensitivity studies have been performed to support a comprehensive review of the application. In these studies, the effects on dose rate of the modeled air volume, density, and humidity were analyzed. The sensitivity calculations showed that the air volume used in the Monte Carlo simulations was adequate and that a larger air volume would not further increase the dose rate due to skyshine contributions. The sensitivity analysis showed that simulation of local atmospheric conditions is important for the accuracy of dose rate estimates at large distances from the facility. Air humidity was demonstrated to have negligible effects on dose rate values for the simulated local atmospheric conditions.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2025

Enhancing chemical bioproduction with rational control of bacterial post-translational modifications

Efficient conversion of inexpensive feedstocks to valuable chemicals by microbes is critical for a robust bioeconomy, but the ability to rationally design bacteria is hampered by insufficient knowledge of how post translational modifications (PTMs) control bacterial protein function and thus bioproduction phenotypes. Our study will focus on the lysine acetylation, a ubiquitous bacterial PTM that can affect the function of enzymes in central metabolism that are often critical for bioproduction processes, disrupt transcriptional regulation, and reduce translation. However, most lysine acetylation data is observational, which means that we do not know when, how, and what specific acetylated residues affect protein function and bacterial physiology. For our model host, we will use a Pseudomonas putida strain that we previously engineered to convert lignocellulosic feedstocks into chemicals such as itaconic acid (ITA). With this strain, we use a dynamic two-stage bioproduction process in which ITA is produced during a non-growth associated production phase. Production is highest during growth stages when lysine acetylation is low in other organisms (early stationary phase) and stalls in conditions where acetylation is highest (late stationary phase). The switch from high to stalled ITA production is also correlated with an unexpected increase in acetate levels – the precursor to non-enzymatic lysine acetylation. As such, we predict that lysine acetylation plays a substantial role in regulating the metabolic pathways required for ITA production. We will develop a generalizable approach that combines high-throughput genetic screens and cutting-edge genome engineering with state-of-the-art proteomics, metabolomics, and genetic code expansion methods to identify and modulate lysine acetylation patterns in bacteria. Ultimately, these strategies aim to manipulate protein expression and acetylation patterns to enhance bioproduction phenotypes (e.g., sustained ITA production in late stationary phase).

60 APPLIED LIFE SCIENCES↗
NASA NTRS1975

Heavy element affinities in Apollo 17 samples

Pb-204, Bi, Tl, and Zn in samples from the Apollo 17 site exhibit relationships not found in samples from other sites. Pb-204, Tl, and Zn in residues remaining after dilute acid leaching are correlated with one another. Orange soil 74220, which is enriched in Pb-204, Tl, and Zn, is included in these relationships. In addition, the submicron metallic phase generally associated with agglutinate formation is correlated with all three of these elements; this relationship has already been reported for Pb-204 in other samples. Thus, orange soil and agglutinates appear to be involved in concentrating heavy volatile metals. A process other than mixing is required to account for this. As a consequence of the isolation of the landing site by the surrounding massifs, local supply and recycling of volatile trace elements in soils may account for some of the interelement relations.

Allen, R. O., Jr.↗
NASA NTRS1982

An analytical approach to thermal modeling of Bridgman-type crystal growth. I - One-dimensional analysis

A relatively simple one-dimensional thermal model of the Bridgman growth process has been developed which is applicable to the growth of small diameter samples with conductivities similar to those of metallic alloys. The heat flow in a translating rod is analyzed in a way that is applicable to Biot numbers less than unity. The model accommodates an adiabatic zone, different heat transfer coefficients in the hot and cold zones, and changes in sample material properties associated with phase change. The analysis is applied to several simplified cases. The effect of the rod's motion is studied in a three-zone furnace for a rod sufficiently long that end effects can be neglected; end effects are then investigated for a motionless rod. Finally, the addition of a fourth zone, an independently controlled booster heater between the main heater and the adiabatic zone, is evaluated for its ability to increase the gradient in the sample at the melt interface and to control the position of the interface.

Naumann, R. J.↗
NASA NTRS1984

Gravitational effects on the extinction conditions for premixed flames

The four particular classes of premixed flames which are of special interest include freely propagating gaseous flames, burner stabilized premixed gaseous flames, freely propagating particle-cloud flames, and burner stabilized two-phase flames. Associated gravitational effects are related to upward flame propagation, downward flame propagation, and flame propagation in microgravity. The results of theoretical and experimental studies suggest that a comprehensive approach to representation of extinction limits must deal with the full range of existence limits observed for flames. Issues awaiting solution are related to the flammability limits, extinction limit relations, and flame theories for g = 0. Attention is given to theoretical considerations, nonadiabatic features of premixed lycopodium-air flames, and general comments on the extinction conditions for premixed flames.

Berlad, A. L.↗
NASA NTRS1987

Effect of high temperature annealing on the thermoelectric properties of GaP doped SiGe

Silicon-germanium alloys doped with GaP are used for thermoelectric energy conversion in the temperature range 300-1000 C. The conversion efficiency depends on Z = S-squared/rho lambda, a material's parameter (the figure of merit), where S is the Seebeck coefficient, rho is the electrical resistivity and lambda is the thermal conductivity. The annealing of several samples in the temperature range of 1100-1300 C resulted in the power factor P (= S-squared/rho) increasing with increased annealing temperature. This increase in P was due to a decrease in rho which was not completely offset by a drop in S-squared suggesting that other changes besides that in the carrier concentration took place. SEM and EDX analysis of the samples indicated the formation of a Ga-P-Ge rich phase as a result of the annealing. It is speculated that this phase is associated with the improved properties. Several reasons which could account for the improvement in the power factor of annealed GaP doped SiGe are given.

Vandersande, Jan W.↗
NASA NTRS1989

Theoretical studies in support of the 3M-vapor transport (PVTOS-) experiments

Results are reported for a preliminary theoretical study of the coupled mass-, momentum-, and heat-transfer conditions expected within small ampoules used to grow oriented organic solid (OS-) films, by physical vapor transport (PVT) in microgravity environments. It is show that previous studies made restrictive assumptions (e.g., smallness of delta T/T, equality of molecular diffusivities) not valid under PVTOS conditions, whereas the important phenomena of sidewall gas creep, Soret transport of the organic vapor, and large vapor phase supersaturations associated with the large prevailing temperature gradients were not previously considered. Rational estimates are made of the molecular transport properties relevant to copper-phthalocyanine monomeric vapor in a gas mixture containing H2(g) and Xe(g). Efficient numerical methods have been developed and are outlined/illustrated here to making steady axisymmetric gas flow calculations within such ampoules, allowing for realistic realistic delta T/T(sub)w-values, and even corrections to Navier-Stokes-Fourier 'closure' for the governing continuum differential equations. High priority follow-on studies are outlined based on these new results.

Rosner, Daniel E.↗
NASA NTRS1989

Surface studies relevant to silicon carbide chemical vapor deposition

Reactions of C2H4, C3H8, and CH4 on the Si(111) surface and C2H4 on the Si(100) surface were investigated for surface temperatures in the range of 1062-1495 K. Results led to the identification of the reaction products, a characterization of the solid-state transport process, a determination of the nucleation mechanism and growth kinetics, and an assessment of orientation effects. Based on these results and on the modeling studies of Stinespring and Wormhoudt (1988) on the associated gas phase chemistry, a physical model for the two-step beta-SiC CVD process is proposed.

Stinespring, C. D.↗
NASA NTRS1989

An ion microprobe study of the intra-crystalline behavior of REE and selected trace elements in pyroxene from mare basalts with different cooling and crystallization histories

The effects of crystallization interaction on the trace element zoning characteristics of pyroxenes are analyzed using electron and ion microprobe techniques. Four pigeonite basalts with similar isochemical composition, but different cooling rates and crystallization histories are studied. Pyroxene quadrilaterals displaying crystallization trends are presented. The crystal chemical rationalization of REE zoning, pattern shapes, and abundances are examined. The data reveal that the trace element zoning characteristics in pyroxene and the partitioning of trace elements between pyroxene and the melt are related to the interaction between the efficiency of the crystallization process, the kinetics at the crystal-melt interface, the kinetics of plagioclase nucleation and the characteristics of the crystal chemical substitutions in the pyroxene and the associated crystallizing phase.

Shearer, C. K.↗
NASA NTRS1990

Interpretation of satellite-measured bidirectional reflectance from Cirrus cloudy atmospheres

The interpretation of the observed bidirectional reflectance from cirrus cloudy atmospheres is presented. A theoretical model was developed for the computation of the transfer of solar radiation in an anisotropic medium with particular applications to oriented ice crystals in cirrus clouds. In this model, the adding principle for radiative transfer was used with modifications to account for the anisotropy of scattering particles and the associated scattering phase matrix. The single-scattering properties, including the phase function, single-scattering albedo, and extinction cross sections, were used for randomly and horizontally oriented hexagonal ice crystals in radiative transfer computations. The radiative transfer model developed for the cirrus clouds was modified to account for the scattering contributions from the atmosphere and the surface. In order to test the relevance and significance of the ice crystal model for the interpretation of observed bidirectional reflectance from satellites, visible radiances collected on the half hour by the GOES series were selected. The data are calibrated and corrected with the proper filter functions, then navigated to match selected landmark data. A number of clear and cloudy cases during the cirrus IFO of the Fire experiment were chosen for theoretical analyses. The cloud particle shape and size distributions that were taken during satellite overpasses are used in radiative transfer calculations. The sensitivities of the shape, orientation, and size distribution of ice crystals on the reflected intensities at the top of the atmosphere are investigated. Finally, the relative importance of these cloud microphysical properties in the interpretation of satellite bidirectional reflectance are assessed and presented.

Takano, Y.↗