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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 1,333 records · Page 74
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Cascade morphology transition in bcc metals

Energetic atom collisions in solids induce shockwaves with complex morphologies. In this paper, we establish the existence of a morphological transition in such cascades. The order parameter of the morphology is defined as the exponent, $b$, in the defect production curve as a function of cascade energy ($N_F$$ \sim$$E_{MD}^b$). Response of different bcc metals can be compared in a consistent energy domain when the energy is normalized by the transition energy, $\mu$, between the high- and the low-energy regime. Using Cr, Fe, Mo and W data, an empirical formula of $\mu$ as a function of displacement threshold energy, $E_d$, is presented for bcc metals.

cascade morphology↗
DOE OSTI2025

Including the vacuum energy in stellarator coil design

Being three-dimensional, stellarators have the advantage that plasma currents are not essential for creating rotational-transform; however, the external current-carrying coils in stellarators can have strong geometrical shaping, which can complicate the construction. Reducing the inter-coil electromagnetic forces acting on strongly shaped 3D coils and the stress on the support structure while preserving the favorable properties of the magnetic field is a design challenge. In this work, we recognize that the inter-coil forces are the gradient of the vacuum magnetic energy. We introduce an objective functional built on the usual quadratic flux on a prescribed target surface together with a weighed penalty on the vacuum energy. The Euler–Lagrange equation for stationary states is derived, and numerical illustrations are computed using a modern stellarator optimization framework. A study of the effect of the energy functional on the inter-coil forces is conducted and the energy is shown to be a promising quantity in producing coils with low forces.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1981

Theoretical studies of solar-pumped lasers

Estimates of the absorption and emission characteristics of molecules required to develop materials for solar-pumped lasers are addressed. These characteristics are described in terms of the Franck Condon factors, which are calculated from the molecular wave functions. Wave functions for vibrational levels in the lower and upper electronic states of I2 and NSe are calculated numerically and methods of checking errors discussed. Errors arise when the vibrational quantum numbers are high; but, using a calculated rather than measured value of the dissociation energy, wave functions up to the fiftieth vibrational level are obtained. A numerical method of evaluating the wave functions is given, which should be more accurate in the region of electronic transitions during absorption. Franck Condon factors, plotted versus the wavelength of the absorbed photons, are shown, and a check on the Franck Condon factors is made using the vibrational sum rule.

Harries, W. L.↗
DOE OSTI2017

Functional photosystem I maintains proper energy balance during nitrogen depletion in Chlamydomonas reinhardtii, promoting triacylglycerol accumulation

Nutrient deprivation causes significant stress to the unicellular microalga, Chlamydomonas reinhardtii, which responds by significantly altering its metabolic program. In following N deprivation, the accumulation of starch and triacylglycerols (TAGs) is significantly altered following massive reprogramming of cellular metabolism. One protein that was found to change dramatically and early to this stress was TAB2, a photosystem I (PSI) translation initiation factor, whose transcript and protein levels increased significantly after only 30 min of N deprivation. A detailed physiological and omics-based analysis of an insertional mutant of Chlamydomonas with reduced TAB2 function was conducted to determine what role the functional PSI plays in regulating the cellular response to N deprivation. The tab2 mutant displayed increased acetate assimilation and elevated starch levels during the first 6 h of N deprivation, followed by a shift toward altered amino acid synthesis, reduced TAG content and altered fatty acid profiles. Our results suggested a central role for PSI in controlling cellular metabolism and its implication in regulation of lipid/starch partitioning. Time course analyses of the tab2 mutant versus wild type under N-deprived versus N replete conditions revealed changes in the ATP/NADPH ratio and suggested that TAG biosynthesis may be associated with maintaining the redox state of the cell during N deprivation. The loss of ability to accumulate TAG in the tab2 mutant co-occurred with an up-regulation of photo-protective mechanisms, suggesting that the synthesis of TAG in the wild type occurs not only as a temporal energy sink, but also as a protective electron sink. By exploiting the tab2 mutation in the cells of C. reinhardtii cultured under autotrophic, mixotrophic, and heterotrophic conditions during nitrogen replete growth and for the first 8 days of nitrogen deprivation, we showed that TAG accumulation and lipid/starch partitioning are dynamically regulated by alterations in PSI function, which concomitantly alters the immediate ATP/NADPH demand. This occurs even without removal of nitrogen from the medium, but sufficient external carbon must nevertheless be available. Our efforts to increase lipid accumulation in algae such as Chlamydomonas need to consider carefully how the energy balance of the cell is involved in or affected by such efforts and that numerous layers of metabolic and genetic regulatory control are likely to interfere with such efforts to control oil biosynthesis. Such knowledge will enable synthetic biology approaches to alter the response to the N depletion stress, leading to rewiring of the regulatory networks so that lipid accumulation could be turned on in the absence of N deprivation, allowing for the development of algal production strains with highly enhanced lipid accumulation profiles.

09 BIOMASS FUELS↗
DOE OSTI2015

A STUDY OF VARIABILITY IN THE FREQUENCY DISTRIBUTIONS OF THE SUPERFLARES OF G-TYPE STARS OBSERVED BY THE KEPLER MISSION

The energy and time profiles of 4944 superflares from 77 G-type stars with well-defined light curve periodicities from the Kepler measurements have been analyzed in detail. The total value of the power-law index of the flare frequency distribution as a function of energy (dN/dE ∝ E {sup –γ}) between 5 × 10{sup 34} and 10{sup 36} erg is on average γ = 2.04 ± 0.17, which is in agreement with previous results. The γ values of eight stars with frequent flaring activity vary between 1.59 ± 0.06 and 2.11 ± 0.19, suggesting a possible diversity of energy release effects. In general, stars with shorter rotation periods tend to have larger γ values. There is an indication that the flare energy is saturated at about 2 × 10{sup 37} erg. For a few large superflares of this energy range, it is found that their temporal behaviors could be characterized by a transition from single impulsive flares to long-duration flares composed of several flares.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1979

Application of the trap-plus-precipitation hard X-ray burst model to the flare of August 4, 1972

The theory of Melrose and Brown (1976) concerning the X-ray spectrum resulting from combined precipitation and in-trap acceleration of nonthermal electrons is applied to a large solar flare on the basis of high-time-resolution hard X-ray data. The time behavior of the electron source function is inferred as a function of energy and mean ambient trap density. The results are interpreted in the context of a purely thick-target model, a static trap with continuous injection of fresh electrons, and a dynamic trap with continuous redistribution of electron energies. It is concluded that: (1) a minimum trap density exists below which the static-trap description cannot be valid; (2) a mean ambient trap density less than the cited minimum is possible if a dynamic trap is invoked; and (3) the electron source function at a given instant in such low-density dynamic traps may bear little or no resemblance to a power-law spectrum despite its production, via nonthermal bremsstrahlung, of a power-law X-ray spectrum.

Emslie, A. G.↗
DOE OSTI2016

Ion recombination correction in carbon ion beams

Purpose: In this work, ion recombination is studied as a function of energy and depth in carbon ion beams. Methods: Measurements were performed in three different passively scattered carbon ion beams with energies of 62 MeV/n, 135 MeV/n, and 290 MeV/n using various types of plane-parallel ionization chambers. Experimental results were compared with two analytical models for initial recombination. One model is generally used for photon beams and the other model, developed by Jaffé, takes into account the ionization density along the ion track. An investigation was carried out to ascertain the effect on the ion recombination correction with varying ionization chamber orientation with respect to the direction of the ion tracks. The variation of the ion recombination correction factors as a function of depth was studied for a Markus ionization chamber in the 62 MeV/n nonmodulated carbon ion beam. This variation can be related to the depth distribution of linear energy transfer. Results: Results show that the theory for photon beams is not applicable to carbon ion beams. On the other hand, by optimizing the value of the ionization density and the initial mean-square radius, good agreement is found between Jaffé’s theory and the experimental results. As predicted by Jaffé’s theory, the results confirm that ion recombination corrections strongly decrease with an increasing angle between the ion tracks and the electric field lines. For the Markus ionization chamber, the variation of the ion recombination correction factor with depth was modeled adequately by a sigmoid function, which is approximately constant in the plateau and strongly increasing in the Bragg peak region to values of up to 1.06. Except in the distal edge region, all experimental results are accurately described by Jaffé’s theory. Conclusions: Experimental results confirm that ion recombination in the investigated carbon ion beams is dominated by initial recombination. Ion recombination corrections are found to be significant and cannot be neglected for reference dosimetry and for the determination of depth dose curves in carbon ion beams.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Extending a 10‐node composite tetrahedral finite element for solid mechanics

Abstract We propose to extend the composite tetrahedral finite element first introduced by Thoutireddy et al. (2002) and recently reformulated by Ostien et al. (2016). We generalize the gradient operator and mass matrix to curved domains through analytical expressions weighted by subtetrahedra Jacobians. Optimal integration weights are constructed to increase the accuracy of Gaussian quadrature. We preserve the variational structure of the formulation through a new five‐field functional with additional, independent fields for the Jacobian and the pressure. This approach not only obviates volumetric locking but also yields symmetry. A deleterious soft mode, common to both the quadratic and composite tetrahedral element with constant pressure formulations is effectively stabilized through a novel convex energy penalty function. Numerous numerical examples spanning a patch test to the impact of a Taylor bar demonstrate the accuracy, robustness, and convergence of the extended composite tetrahedral element for application to structural metals.

Foulk III, James W.↗
DOE OSTI2020

A Pd III Sulfate Dimer Initiates Rapid Methane Monofunctionalization by H Atom Abstraction

An electrogenerated Pd III 2 species in fuming sulfuric acid is competent for rapid and concurrent methane monohydroxylation to methyl bisulfate (CH 3 OSO 3 H) and methane sulfonation to methanesulfonic acid (CH 3 SO 3 H). In situ NMR at 50 °C is used to track methane transformation exclusively to CH 3 OSO 3 H and CH 3 SO 3 H at high conversions. Integrating a set of kinetic and computational studies, the mechanism of methane monofunctionalization by Pd III 2 is examined. Here, experimental rate laws and common kinetic isotope effects for CH 3 OSO 3 H and CH 3 SO 3 H formation suggest that both transformations proceed via a common rate-limiting C-H activation step. Introduction of O 2 or Pd II,III 2 suppresses CH 3 SO 3 H generation, indicating a radical chain sequence. Although the metal-metal bonded Pd III 2 complex is a net two-electron oxidant, our aggregate kinetic data point to a mechanistic model that features rate-limiting H atom abstraction by the Pd III 2 complex to generate a methyl radical intermediate. The CH 3 • intermediate then recombines with Pd II,III 2 to furnish a CH 3 Pd III 2 intermediate that reductively eliminates CH 3 OSO 3 H. Alternatively, the CH 3 intermediate can enter a chain reaction with SO 3 to generate CH 3 SO 3 H. DFT computations support the radical-based C-H activation by Pd III 2 and delineate H atom abstraction pathways with computed reaction barriers and kinetic isotope effects (KIEs) that are consistent with experimental data. These mechanistic investigations challenge the paradigm of electrophilic C-H activation and highlight H atom abstraction as a potent pathway for selective methane C-H oxidative functionalization at high reaction rates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Sensitivity of the electric dipole polarizability to the neutron skin thickness in {sup 208}Pb

The static dipole polarizability, {alpha}{sub D}, in {sup 208}Pb has been recently measured with highresolution via proton inelastic scattering at the Research Center for Nuclear Physics (RCNP) [1]. This observable is thought to be intimately connected with the neutron skin thickness, r{sub skin}, of the same nucleus and, more fundamentally, it is believed to be associated with the density dependence of the nuclear symmetry energy. The impact of r{sub skin} on {alpha}{sub D} in {sup 208}Pb is investigated and discussed on the basis of a large and representative set of relativistic and non-relativistic nuclear energy density functionals (EDF) [2].

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

External circuit integration with electromagnetic particle in cell modeling of plasma focus devices

The pinch performance of a plasma focus (PF) device is sensitive to the physical conditions of the breakdown phase. It is therefore essential to model and study the initial phase in order to optimize device performance. An external circuit is self consistently coupled to the electromagnetic particle in cell code to model the breakdown and initial lift phase of the United Nations University/International Centre for Theoretical Physics (UNU-ICTP) plasma focus device. Gas breakdown during the breakdown phase is simulated successfully, following a drop in the applied voltage across the device and a concurrent substantial rise in the circuit current. As a result, the plasma becomes magnetized, with the growing value of the magnetic field over time leading to the gradual lift off of the well formed current sheath into the axial acceleration phase. This lifting off, with simultaneous outward sheath motion along the anode and vertical cathode, and the strong magnetic fields in the current sheath region, was demonstrated in this work, and hence validates our method of coupling the external circuit to PF devices. Our method produces voltage waveforms that are qualitatively similar to the observed experimental voltage profiles of the UNU-ICTP device. Values of the mean electron energy before and after voltage breakdown turned out to be different, with the values after breakdown being much lower. In both cases, the electron energy density function turned out to be non-Maxwellian.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

GRAVITATIONAL ENCOUNTERS AND THE EVOLUTION OF GALACTIC NUCLEI. I. METHOD

An algorithm is described for evolving the phase-space density of stars or compact objects around a massive black hole at the center of a galaxy. The technique is based on numerical integration of the Fokker–Planck equation in energy-angular momentum space, f(E, L, t), and includes, for the first time, diffusion coefficients that describe the effects of both random and correlated encounters (“resonant relaxation”), as well as energy loss due to emission of gravitational waves. Destruction or loss of stars into the black hole is treated by means of a detailed boundary-layer analysis. Performance of the algorithm is illustrated by calculating two-dimensional, time-dependent, and steady-state distribution functions and their corresponding loss rates.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Structure of superheavy nuclei along decay chains of element 115

A recent high-resolution $α$, X -ray, and $γ$-ray coincidence-spectroscopy experiment offered first glimpse of excitation schemes of isotopes along $α$-decay chains of $Z=115$. To understand these observations and to make predictions about shell structure of superheavy nuclei below $^{288}115$, we employ two complementary mean-field models: self-consistent Skyrme Energy Density Functional approach and the macroscopic-microscopic Nilsson model. We discuss the spectroscopic information carried by the new data. In particular, candidates for the experimentally observed $E1$ transitions in $\mathrm{^{276}Mt}$ are proposed. In this study, we find that the presence and nature of low-energy $E1$ transitions in well-deformed nuclei around $Z=110,N=168$ strongly depends on the strength of the spin-orbit coupling; hence, it provides an excellent constraint on theoretical models of superheavy nuclei. To clarify competing theoretical scenarios, an experimental search for $E1$ transitions in odd-$A$ systems $\mathrm{^{277}Mt, ^{275}Hs}$, and $\mathrm{^{277}Ds}$ is strongly recommended.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Thorium-doped CsI: Implications for the thorium nuclear clock transition

For 229m Th isomer nucleus with an anomalously low nuclear excitation energy, E$\star$ (currently accepted value of 7.8 ± 0.5 eV), the bound internal conversion (BIC) decay process is caused by the excitation of a valence electron that is sensitive to the electronic structure of the atomic-sized neighborhood. For this, we analyze an experiment where an impacting Th ion is neutralized by a negatively charged ion-receiving cesium iodide (CsI) surface, to obtain the minimal nuclear excitation energy E$\star\atop{min}$ necessary for BIC promotion of a Th-impurity valence electron in a CsI matrix. We analyze two cases: CsI with Th deposited into the bulk and with Th deposited on the CsI surface. In the bulk we consider band gap effects while on the surface we consider the work function. The energy to pull the electron to the surface is 1.5 – 2.2 eV depending on the surface plane, while to promote to the conduction band in the bulk it is 1.5 eV. Therefore we conclude that the Th-surface interaction can significantly reduce the lower E$\star$ bound of 6.3 eV, as estimated from the direct observation of the Th-clock transition [von der Wense et al., Nature (London) 533, 47 (2016)]. We suggest coating the multichannel plate with differing materials leading to different Th-impurity gaps and work functions can further narrow the E$\star$ uncertainty interval.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Energy dependence of polarized 𝛾⁢𝛾 → 𝑒 + ⁢ 𝑒− in peripheral Au+Au collisions at $\sqrt{s_{NN}}$ = 54.4 and 200 GeV with the STAR experiment at RHIC

We report the differential yields at mid-rapidity of the Breit-Wheeler process (𝛾⁢𝛾 → 𝑒 + ⁢𝑒 − ) in peripheral Au+Aucollisions at $\sqrt{s_{NN}}$ = 54.4 and 200 GeV with the STAR experiment at the Relativistic Heavy Ion Collider (RHIC), as a function of energy $\sqrt{s_{NN}}$, 𝑒 + ⁢𝑒 − transverse momentum 𝑝 T , 𝑝$^{2}_{T}$, invariant mass 𝑀 𝑒⁢𝑒 , and azimuthal angle. In the invariant mass range of 0.4 < 𝑀 𝑒⁢𝑒 < 2.6GeV/𝑐 2 at low transverse momentum (𝑝 T < 0.15GeV/𝑐), the yields increase while the pair √⟨𝑝$^{2}_{T}$⟩ decreases with increasing $\sqrt{s_{NN}}$, a feature that is correctly predicted by the QED calculation. Here, the energy dependencies of the measured quantities are sensitive to the nuclear form factor, infrared divergence and photon polarization. The data are compiled and used to extract the charge radius of the Au nucleus.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Plasma diagnostics and modeling of lithium-containing plasmas

Thin-film deposition from chemically reactive multi-component plasmas is complex, and the lack of electron collision cross-sections for even the most common metalorganic precursors and their fragments complicates their modeling based on fundamental plasma physics. This study focuses on understanding the plasma physics and chemistry in argon (Ar) plasmas containing lithium bis (trimethylsilyl) amide used to deposit Li x Si y thin films. These films are emerging as potential solid electrolytes for lithium-ion batteries, and the Li-to-Si ratio is a crucial parameter to enhance their ionic conductivity. We deposited Li x Si y films in an axial flow-through plasma reactor and studied the factors that determine the variation of the Li-to-Si ratio in films deposited at various points on a substrate spanning the entire reactor axis. While the Li-to-Si ratio is 1:2 in the precursor, the Li-to-Si ratio is as high as 3:1 in films deposited near the plasma entrance and decreases to 1:1 for films deposited downstream. Optical emission from the plasma is dominated by Li emission near the entrance, but Li emission disappears downstream, which we attribute to the complete consumption of the precursor. We hypothesized that the axially decreasing precursor concentration affects the electron energy distribution function in a way that causes different dissociation efficiencies for the production of Li and Si. We used Li line intensities to estimate the local precursor concentration and Ar line ratios to estimate the local reduced electric field to test this hypothesis. This analysis suggests that the mean electron energy increases along the reactor axis with decreasing precursor concentration. As a result, the decreasing Li-to-Si ratio with axially decreasing precursor concentration may be explained by Li release from the precursor having lower threshold energy than Si release.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1977

The signature of parallel electric fields in a collisionless plasma

The presence of a parallel electric field in the magnetosphere should be apparent through its effect on particles. An analysis is made of particle trajectories in phase space for a steady state collisionless plasma. The analysis utilizes the concepts of distribution function, total energy, and magnetic moment because all three quantities are conserved in a steady state situation in the absence of collisions. Two methods are presented for using particle data to gain information on the potential distribution. The first method involves the use of measurements of both ion and electron distribution functions and invokes the principle of quasi-neutrality. The second method involves the observation of discontinuities in velocity space which can be interpreted in terms of the effect of the electric field on the apparent loss or source cone.

Whipple, E. C., Jr.↗