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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Metastable tetragonal structure of Fe{sub 100-x}Ga{sub x} epitaxial thin films on ZnSe/GaAs(001) substrate

We investigated by x-ray diffraction the Ga concentration dependences of the structural properties of Fe{sub 100-x}Ga{sub x} (galfenol) thin films grown on a ZnSe/GaAs(001) substrate, a material known for its high magnetostriction. By molecular beam epitaxy (MBE) we grew a series of (001)-oriented layers without in-plane misorientation, ranging from pure Fe up to x=29.4% Ga. We find a strong Ga-induced tetragonal distortion that conserves the pristine Fe in-plane lattice parameters for all Ga compositions. Supported by theoretical predictions [R. Wu, J. Appl. Phys. 91, 7358 (2002)], we attribute this unusual tetragonal distortion to short-range ordering of Ga-Ga pairs along the [001]-growth direction. The low-temperature and out-of-equilibrium MBE growth regime tends to stabilize a strong deformed tetragonal phase (up to c/a{approx}1.05 for x{approx}29%). This tetragonal structure is fully released by postgrowth annealing.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Structures, phase transitions, and magnetic properties of C o 3 Si from first-principles calculations

Co 3 Si was recently reported to exhibit remarkable magnetic properties in the nanoparticle form [Appl. Phys. Lett. 108, 152406 (2016)], yet better understanding of this material is to be promoted. Here we report a study on the crystal structures of Co 3 Si using adaptive genetic algorithm, and discuss its electronic and magnetic properties from first-principles calculations. Several competing phases of Co 3 Si have been revealed from our calculations. We show that the hexagonal Co 3 Si structure reported in experiments has lower energy in non-magnetic state than ferromagnetic state at zero temperature. The ferromagnetic state of the hexagonal structure is dynamically unstable with imaginary phonon modes and transforms to a new orthorhombic structure, which is confirmed by our structure searches to have the lowest energy for both Co 3 Si and Co 3 Ge. Magnetic properties of the experimental hexagonal structure and the lowest-energy structures obtained from our structure searches are investigated in detail.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Direct determination of the La 138 β -decay Q value using Penning trap mass spectrometry

Background: The understanding and description of forbidden decays provides interesting challenges for nuclear theory. These calculations could help to test underlying nuclear models and interpret experimental data. Purpose: Compare a direct measurement of the 138 La $\beta$-decay $Q$ value with the beta-decay spectrum end-point energy measured by Quarati et al. using LaBr 3 detectors [Appl. Radiat. Isot. 108, 30 (2016)]. Use new precise measurements of the 138 La $\beta$-decay and electron capture (EC) $Q$ values to improve theoretical calculations of the $\beta$-decay spectrum and EC probabilities. Method: High-precision Penning trap mass spectrometry was used to measure cyclotron frequency ratios of 138 La, 138 Ce and 138 Ba ions from which beta-decay and EC Q values for 138 La were obtained.Results: The 138 La beta-decay and EC Q values were measured to be Q$_\beta$ = 1052.42(41) keV and $Q_{EC}$ = 1748.41(34) keV, improving the precision compared to the values obtained in the most recent atomic mass evaluation [Wang, et al., Chin. Phys. C 41, 030003 (2017)] by an order of magnitude. These results are used for improved calculations of the 138 La $\beta$-decay shape factor and EC probabilities. New determinations for the 138 Ce 2EC $Q$ value and the atomic masses of 138 La, 138 Ce, and 138 Ba are also reported. Conclusion: The 138 La $\beta$-decay Q value measured by Quarati et al. is in excellent agreement with our new result, which is an order of magnitude more precise. Uncertainties in the shape factor calculations for 138 La $\beta$-decay using our new $Q$ value are reduced by an order of magnitude. Uncertainties in the EC probability ratios are also reduced and show improved agreement with experimental data.

138La↗
DOE OSTI2016

Viscous Rayleigh-Taylor instability in spherical geometry

We consider viscous fluids in spherical geometry, a lighter fluid supporting a heavier one. Chandrasekhar [Q. J. Mech. Appl. Math. 8, 1 (1955)] analyzed this unstable configuration providing the equations needed to find, numerically, the exact growth rates for the ensuing Rayleigh-Taylor instability. He also derived an analytic but approximate solution. We point out a weakness in his approximate dispersion relation (DR) and offer one that is to some extent improved.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Generation of anisotropy in turbulent flows subjected to rapid distortion

A computational tool for the anisotropic time-evolution of the spectral velocity correlation tensor is presented. We operate in the linear, rapid distortion limit of the mean-field-coupled equations. Each term of the equations is written in the form of an expansion to arbitrary order in the basis of irreducible representations of the SO(3) symmetry group. The computational algorithm for this calculation solves a system of coupled equations for the scalar weights of each generated anisotropic mode. The analysis demonstrates that rapid distortion rapidly but systematically generates higher-order anisotropic modes. To maintain a tractable computation, the maximum number of rotational modes to be used in a given calculation is specified a priori . The computed Reynolds stress converges to the theoretical result derived by Batchelor and Proudman [Quart. J. Mech. Appl. Math. 7, 83 (1954)] if a sufficiently large maximum number of rotational modes is utilized; more modes are required to recover the solution at later times. In conclusion, the emergence and evolution of the underlying multidimensional space of functions is presented here using a 64-mode calculation. Alternative implications for modeling strategies are discussed.

42 ENGINEERING↗
DOE OSTI2014

Control of the polarization of a vacuum-ultraviolet, high-gain, free-electron laser

The two single-pass, externally seeded free-electron lasers (FELs) of the FERMI user facility are designed around Apple-II-type undulators that can operate at arbitrary polarization in the vacuum ultraviolet-to-soft x-ray spectral range. Furthermore, within each FEL tuning range, any output wavelength and polarization can be set in less than a minute of routine operations. We report the first demonstration of the full output polarization capabilities of FERMI FEL-1 in a campaign of experiments where the wavelength and nominal polarization are set to a series of representative values, and the polarization of the emitted intense pulses is thoroughly characterized by three independent instruments and methods, expressly developed for the task. The measured radiation polarization is consistently >90% and is not significantly spoiled by the transport optics; differing, relative transport losses for horizontal and vertical polarization become more prominent at longer wavelengths and lead to a non-negligible ellipticity for an originally circularly polarized state. The results from the different polarimeter setups validate each other, allow a cross-calibration of the instruments, and constitute a benchmark for user experiments.

42 ENGINEERING↗
DOE OSTI2020

Seasonal Zinc Storage and a Strategy for Its Use in Buds of Fruit Trees

Bud dormancy allows deciduous perennial plants to rapidly grow following seasonal cold conditions. Although many studies have examined the hormonal regulation of bud growth, the role of nutrients remains unclear. Insufficient accumulation of the key micronutrient zinc (Zn) in dormant buds affects the vegetative and reproductive growth of perennial plants during the subsequent year, requiring the application of Zn fertilizers in orchard management to avoid growth defects in fruit trees. However, the mechanisms of seasonal Zn homeostasis in perennial plants remain poorly understood. Here, we provide new insights into Zn distribution and speciation within reproductive and vegetative buds of apple (Malus domestica) and four other deciduous fruit trees (peach [Amygdalus persica], grape [Vitis vinifera], pistachio [Pistacia vera], and blueberry [Vaccinium spp.]) using microscopic and spectroscopic characterization techniques comprising synchrotron-based x-ray fluorescence and x-ray absorption near-edge-structure analyses. By establishing a link between bud development and Zn distribution, we identified the following important steps of Zn storage and use in deciduous plants: Zn is preferentially deposited in the stem nodes subtending apical and axillary buds; Zn may then be sequestered as Zn-phytate prior to dormancy; in spring, Zn effectively releases for use during budbreak and subsequent meristematic growth. The mechanisms of Zn homeostasis during the seasonal cycles of plant growth and dormancy described here will contribute to improving orchard management, and to selection and breeding of deciduous perennial species.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2011

iotbx.cif : a comprehensive CIF toolbox

iotbx.cif is a new software module for the development of applications that make use of the CIF format. Comprehensive tools are provided for input, output and validation of CIFs, as well as for interconversion with high-level cctbx [Grosse-Kunstleve, Sauter, Moriarty & Adams (2002). J. Appl. Cryst. 35, 126–136] crystallographic objects. The interface to the library is written in Python, whilst parsing is carried out using a compiled parser, combining the performance of a compiled language (C++) with the benefits of using an interpreted language.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Analyzing diffuse scattering with supercomputers. Corrigendum

The study by Michels-Clark et al. (2013 [Michels-Clark, T. M., Lynch, V. E., Hoffmann, C. M., Hauser, J., Weber, T., Harrison, R. & Bürgi, H. B. (2013). J. Appl. Cryst. 46, 1616-1625.]) contains misleading errors which are corrected here. The numerical results reported in that paper and the conclusions given there are not affected and remain unchanged. The transition probabilities in Table 1 (rows 4, 5, 7, 8) and Fig. 2 (rows 1 and 2) of the original paper were different from those used in the numerical calculations. Corrected transition probabilities as used in the computations are given in Table 1 and Fig. 1 of this article. The Δ parameter in the stacking model expresses the preference for the fifth layer in a five-layer stack to be eclipsed with respect to the first layer. This statement corrects the original text on p. 1622, lines 4–7. In the original Fig. 2 the helicity of the layer stacks b L and b R in rows 3 and 4 had been given as opposite to those in rows 1, 2 and 5. Fig. 1 of this article shows rows 3 and 4 corrected to correspond to rows 1, 2 and 5.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

WavePropaGator : interactive framework for X-ray free-electron laser optics design and simulations

This article describes the WavePropaGator (WPG) package, a new interactive software framework for coherent and partially coherent X-ray wavefront propagation simulations. The package has been developed at European XFEL for users at the existing and emerging free-electron laser (FEL) facilities, as well as at the third-generation synchrotron sources and future diffraction-limited storage rings. The WPG addresses the needs of beamline scientists and user groups to facilitate the design, optimization and improvement of X-ray optics to meet their experimental requirements. The package uses the Synchrotron Radiation Workshop (SRW) C/C++ library and its Python binding for numerical wavefront propagation simulations. The framework runs reliably under Linux, Microsoft Windows 7 and Apple Mac OS X and is distributed under an open-source license. The available tools allow for varying source parameters and optics layouts and visualizing the results interactively. The wavefront history structure can be used for tracking changes in every particular wavefront during propagation. The batch propagation mode enables processing of multiple wavefronts in workflow mode. The paper presents a general description of the package and gives some recent application examples, including modeling of full X-ray FEL beamlines and start-to-end simulation of experiments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

WinPSSP : a revamp of the computer program PSSP and its performance solving the crystal structures of small organic compounds and solids of biological and pharmaceutical interest

The direct-space methods software Powder Structure Solution Program ( PSSP ) [Pagola & Stephens (2010). J. Appl. Cryst. 43 , 370–376] has been migrated to the Windows OS and the code has been optimized for fast runs. WinPSSP is a user-friendly graphical user interface that allows the input of preliminary crystal structure information, integrated intensities of the reflections and FWHM, the definition of structural parameters and a simulated annealing schedule, and the visualization of the calculated and experimental diffraction data overlaid for each individual solution. The solutions are reported as filename.cif files, which can be used to analyze packing motifs and chemical bonding, and to input the atomic coordinates into the Rietveld analysis software GSAS. WinPSSP performance in straightforward crystal structure determinations has been evaluated using 18 molecular solids with 6–20 degrees of freedom. The free-distribution program as well as multimedia tutorials can be accessed at http://users.uoi.gr/nkourkou/winpssp/.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Expected values and variances of Bragg peak intensities measured in a nanocrystalline powder diffraction experiment

A rigorous study of sampling and intensity statistics applicable for a powder diffraction experiment as a function of crystallite size is presented. Our analysis yields approximate equations for the expected value, variance and standard deviations for both the number of diffracting grains and the corresponding diffracted intensity for a given Bragg peak. The classical formalism published in 1948 by Alexander, Klug & Kummer [ J. Appl. Phys. (1948), 19 , 742–753] appears as a special case, limited to large crystallite sizes, here. It is observed that both the Lorentz probability expression and the statistics equations used in the classical formalism are inapplicable for nanocrystalline powder samples.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Angle calculations using two detector circles and wavelength

Here, a `2D + λ' mode using two detector angles and wavelength is added to the modes of operation of a six-circle diffractometer, i.e. `4S + 2D' diffractometer [You (1999). J. Appl. Cryst. 32, 614–623]. In synchrotron sources, the X-ray energy, and hence the wavelength, can be a degree of freedom for angle calculations. For diffractometers with two detector circles, therefore, the variable X-ray energy can be the third degree of freedom, sufficient for accessing reciprocal space without rotating the sample. This mode is useful for limited sample rotations or X-ray beams focused smaller than the diffractometer circle of confusion.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Effects of surface undulations on asymmetric X-ray diffraction: a rocking-curve topography study

The results are reported of an X-ray diffraction study of an Si crystal designed and fabricated for very asymmetric diffraction from the 333 reflection for X-ray energies of 8.100 and 8.200 keV. A crystal with an asymmetry angle of 46 ± 0.1° between the surface and the (111) planes was studied. The grazing angles of incidence were near 1.08 and 0.33° for these two energies, respectively. Features arising from surface undulations were not observed at 8.100 keV, but were observed at 8.200 keV. The results at 8.100 keV allow an alternative explanation based on strain near the surface to be ruled out. Topographic images were obtained as a function of rocking angle, and in the case of 8.200 keV the surface morphology is evident. Finally, the results are found to be in agreement with dynamical X-ray diffraction calculations made with the Takagi–Taupin equations specialized to a surface having convex or concave features, as reported in the accompanying paper [Macrander (2020). J. Appl. Cryst. 53 , 793–799].

36 MATERIALS SCIENCE↗
DOE OSTI2020

Takagi–Taupin dynamical X-ray diffraction simulations of asymmetric X-ray diffraction from crystals: the effects of surface undulations

Dynamical X-ray diffraction simulations from crystals with surface undulations are reported. The Takagi–Taupin equations are applied and used to derive results in good agreement with experimental data reported in a separate paper [Macrander, Pereira, Huang, Kasman, Qian, Wojcik & Assoufid (2020). J. Appl. Cryst. 53, 789–792]. The development of Uragami [J. Phys. Soc. Jpn, (1969), 27, 147–154] is followed. Although previous work by Olekhnovich & Olekhnovich [Acta. Cryst. (1980), A36, 22–27] treated a crystal in the shape of a round cylinder, there do not seem to be any reports of previous dynamical X-ray diffraction treatments specifically for surface undulations. The significance of the present work is that it bridges the diffraction treatment of more classical dynamical diffraction theory, which assumes a flat surface, and the simple kinematic diffraction theory. Finally, the kinematic theory has, to date, been the primary means of simulating X-ray diffraction from surfaces.

36 MATERIALS SCIENCE↗