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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Molecular dynamics discovery of an extraordinary ionic migration mechanism in dislocation-containing TlBr crystals

TlBr can surpass CZT as the leading semiconductor for γ- and X-radiation detection. Unfortunately, the optimum properties of TlBr quickly decay when an operating electrical field is applied. Quantum mechanical studies indicated that if this property degradation comes from the conventional mechanism of ionic migration of vacancies, then an unrealistically high vacancy concentration is required to account for the rapid aging of TlBr seen in experiments. Here, we have applied large scale molecular dynamics simulations to study the effects of dislocations on ionic migration of TlBr crystals under electrical fields. We found that electrical fields can drive the motion of edge dislocations in both slip and climb directions. These combined motions eject enormous vacancies in the dislocation trail. Both dislocation motion and a high vacancy concentration can account for the rapid aging of the TlBr detectors. These findings suggest that strengthening methods to pin dislocations should be explored to increase the lifetimes of TlBr crystals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Multi-time Schrödinger equations cannot contain interaction potentials

Multi-time wave functions are wave functions that have a time variable for every particle, such as ϕ(t{sub 1},x{sub 1},...,t{sub N},x{sub N}). They arise as a relativistic analog of the wave functions of quantum mechanics but can be applied also in quantum field theory. The evolution of a wave function with N time variables is governed by N Schrödinger equations, one for each time variable. These Schrödinger equations can be inconsistent with each other, i.e., they can fail to possess a joint solution for every initial condition; in fact, the N Hamiltonians need to satisfy a certain commutator condition in order to be consistent. While this condition is automatically satisfied for non-interacting particles, it is a challenge to set up consistent multi-time equations with interaction. We prove for a wide class of multi-time Schrödinger equations that the presence of interaction potentials (given by multiplication operators) leads to inconsistency. We conclude that interaction has to be implemented instead by creation and annihilation of particles, which, in fact, can be done consistently [S. Petrat and R. Tumulka, “Multi-time wave functions for quantum field theory,” Ann. Physics (to be published)]. We also prove the following result: When a cut-off length δ > 0 is introduced (in the sense that the multi-time wave function is defined only on a certain set of spacelike configurations, thereby breaking Lorentz invariance), then the multi-time Schrödinger equations with interaction potentials of range δ are consistent; however, in the desired limit δ → 0 of removing the cut-off, the resulting multi-time equations are interaction-free, which supports the conclusion expressed in the title.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Composite thermochemistry of gas phase U(VI)-containing molecules

Reaction energies have been calculated for a series of reactions involving UF{sub 6}, UO{sub 3}, UO{sub 2}(OH){sub 2}, and UO{sub 2}F{sub 2} using coupled cluster singles and doubles with perturbative triples, CCSD(T), with a series of correlation consistent basis sets, including newly developed pseudopotential (PP)- and all-electron (AE) Douglas-Kroll-Hess-based sets for the U atom. The energies were calculated using a Feller-Peterson-Dixon composite approach in which CCSD(T) complete basis set (CBS) limits were combined with a series of additive contributions for spin-orbit coupling, outer-core correlation, and quantum electrodynamics effects. The calculated reaction enthalpies (both PP and AE) were combined with the accurately known heat of formation of UF{sub 6} to determine the enthalpies of formation of UO{sub 3}, UO{sub 2}(OH){sub 2}, and UO{sub 2}F{sub 2}. The contribution to the reaction enthalpies due to correlation of the 5s5p5d electrons of U was observed to be very slowly convergent with basis set and at the CBS limit their impact on the final enthalpies was on the order of 1 kcal/mol or less. For these closed shell molecules, spin-orbit effects contributed about 1 kcal/mol to the final enthalpies. Interestingly, the PP and AE approaches yielded quite different spin-orbit contributions (similar magnitude but opposite in sign), but the total scalar plus spin-orbit results from the two approaches agreed to within ∼1 kcal/mol of each other. The final composite heat of formation for UO{sub 2}F{sub 2} was in excellent agreement with experiment, while the two results obtained for UO{sub 3} were just outside the ±2.4 kcal/mol error bars of the currently recommended experimental value. An improved enthalpy of formation (298 K) for UO{sub 2}(OH){sub 2} is predicted from this work to be −288.7 ± 3 kcal/mol, compared to the currently accepted experimental value of −292.7 ± 6 kcal/mol.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Deformation of a Ti-Nb alloy containing α"-martensite and omega phases

Microscopic deformation of a Ti-17at. %Nb alloy with high fractions of α"-martensite and ω phases was studied by in-situ synchrotron X-ray diffraction. Textures, phase fractions, individual lattice strains, and peak intensities during deformation were studied. It is found that, to accommodate the external tensile strain, some of the α" and ω grains were first transformed to the β-phase, which then continuously transformed to the α"-phase with chosen variants that effectively accommodate the deformation strain. Here, a strong (010)α" fiber texture was formed at the expense of the (001)α" and (111)α" fiber textures. Above 400 MPa applied stress, (110)α" deformation twinning was triggered with a simultaneous stress relaxation in the (110)α" family and a slight increase in its texture strength in the loading direction.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Simulation of magnetic hysteresis loops and magnetic Barkhausen noise of α-iron containing nonmagnetic particles

Here, the magnetic hysteresis loops and Barkhausen noise of a single α-iron with nonmagnetic particles are simulated to investigate into the magnetic hardening due to Cu-rich precipitates in irradiated reactor pressure vessel (RPV) steels. Phase field method basing Landau-Lifshitz-Gilbert (LLG) equation is used for this simulation. The results show that the presence of the nonmagnetic particle could result in magnetic hardening by making the nucleation of reversed domains difficult. The coercive field is found to increase, while the intensity of Barkhausen noise voltage is decreased when the nonmagnetic particle is introduced. Simulations demonstrate the impact of nucleation field of reversed domains on the magnetization reversal behavior and the magnetic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Density functional study of the electronic structure of dye-functionalized fullerenes and their model donor-acceptor complexes containing P3HT

We study the electronic structure of C{sub 60} fullerenes functionalized with a thiophene-diketo-pyrrolopyrrole-thiophene based chromophore using density functional theory combined with large polarized basis sets. As the attached chromophore has electron donor character, the functionalization of the fullerene leads to a donor-acceptor (DA) system. We examine in detail the effect of the linker and the addition site on the electronic structure of the functionalized fullerenes. We further study the electronic structure of these DA complexes with a focus on the charge transfer excitations. Finally, we examine the interface of the functionalized fullerenes with the widely used poly(3-hexylthiophene-2,5-diyl) (P3HT) donor. Our results show that all functionalized fullerenes with an exception of the C{sub 60}-pyrrolidine [6,6], where the pyrrolidine is attached at a [6,6] site, have larger electron affinities relative to the pristine C{sub 60} fullerene. We also estimate the quasi-particle gap, lowest charge transfer excitation energy, and the exciton binding energies of the functionalized fullerene-P3MT model systems. Results show that the exciton binding energies in these model complexes are slightly smaller compared to a similarly prepared phenyl-C{sub 61}-butyric acid methyl ester (PCBM)-P3MT complex.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Mapping compound cosmic telescopes containing multiple projected cluster-scale halos

Lines of sight with multiple projected cluster-scale gravitational lenses have high total masses and complex lens plane interactions that can boost the area of magnification, or étendue, making detection of faint background sources more likely than elsewhere. To identify these new 'compound' cosmic telescopes, we have found directions in the sky with the highest integrated mass densities, as traced by the projected concentrations of luminous red galaxies (LRGs). We use new galaxy spectroscopy to derive preliminary magnification maps for two such lines of sight with total mass exceeding ∼3 × 10{sup 15} M {sub ☉}. From 1151 MMT Hectospec spectra of galaxies down to i {sub AB} = 21.2, we identify two to three group- and cluster-scale halos in each beam. These are well traced by LRGs. The majority of the mass in beam J085007.6+360428 (0850) is contributed by Zwicky 1953, a massive cluster at z = 0.3774, whereas beam J130657.5+463219 (1306) is composed of three halos with virial masses of 6 × 10{sup 14}-2 × 10{sup 15} M {sub ☉}, one of which is A1682. The magnification maps derived from our mass models based on spectroscopy and Sloan Digital Sky Survey photometry alone display substantial étendue: the 68% confidence bands on the lens plane area with magnification exceeding 10 for a source plane of z{sub s} = 10 are [1.2, 3.8] arcmin{sup 2} for 0850 and [2.3, 6.7] arcmin{sup 2} for 1306. In deep Subaru Suprime-Cam imaging of beam 0850, we serendipitously discover a candidate multiply imaged V-dropout source at z {sub phot} = 5.03. The location of the candidate multiply imaged arcs is consistent with the critical curves for a source plane of z = 5.03 predicted by our mass model. Incorporating the position of the candidate multiply imaged galaxy as a constraint on the critical curve location in 0850 narrows the 68% confidence band on the lens plane area with μ > 10 and z{sub s} = 10 to [1.8, 4.2] arcmin{sup 2}, an étendue range comparable to that of MACS 0717+3745 and El Gordo, two of the most powerful single cluster lenses known. The significant lensing power of our beams makes them powerful probes of reionization and galaxy formation in the early universe.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Free-moving artificial eggs containing temperature loggers reveal remarkable within-clutch variance in incubation temperature

Incubation is a crucial aspect of avian parental care and measuring incubation temperature in the wild can improve our understanding of life history tradeoffs and inform conservation efforts. However, there are challenges associated with measuring the temperature of eggs in natural nests. Most studies to date have measured incubation temperature by using a single, stationary logger in each nest. However, real eggs are rotated and moved throughout the nest by the parent during the incubation period, and thus, a stationary logger may not accurately represent the temperature experienced by individual eggs within the entire clutch. We recorded incubation temperature in nests by using multiple, mobile artificial egg temperature loggers. We installed six mobile loggers and one stationary logger in wood duck Aix sponsa nests to compare the two logger types in the field. We found that at a given ambient temperature, mobile loggers recorded lower average and more variable temperatures than stationary loggers. Further, temperatures recorded by stationary loggers showed no relationship with clutch size, while mobile loggers captured temperatures that were lower and more variable as clutch size increased. Also, the multiple mobile loggers revealed that eggs within a nest experienced a substantial range of temperatures throughout the incubation period. Here, we discuss potential limitations of this method, but believe that it is a promising way to collect biologically-relevant incubation temperature data and provides an opportunity to advance our understanding of incubation temperature as a parental effect.

59 BASIC BIOLOGICAL SCIENCES↗