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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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9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Fundamental Optical Functions and Fine-Structure Parameters of Strontium–Selenide Crystal Transition Bands in the 0–40 eV Range

The spectral complex of fundamental optical functions of strontium-selenide (SrSe) crystal in the range 0–40 eV was determined. Spectra of the imaginary parts of three functions [transverse dielectric permittivity ε{sub 2}(E) and longitudinal volume –Im ε{sup –1} and surface –Im (1 + ε){sup –1} characteristic electron energy losses] of SrSe crystal were deconvoluted into 36 elementary bands. Energies of maxima E{sub i}, half-widths H{sub i}, amplitudes I{sub i}, areas S{sub i}, and oscillator strengths f{sub i} were determined for every band of the three spectra. The main spectral features of the optical functions and 36 elementary bands of SrSe in the range 3–35 eV due to excitons and transverse and longitudinal interband transitions were established. The calculations were based on experimental reflectance spectra and used the Kramers–Kronig integral relations, a modified combined Argand diagram method, and a number of computer programs.

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

On the complex structure of the optical spectra of a tetragonal calomel single crystal in a wide energy range

The spectral complex of optical functions of the calomel Hg{sub 2}Cl{sub 2} single crystal is determined in the range 0–20 eV at 300 K in unpolarized light. The spectra of the imaginary part of the permittivity ε{sub 2}(E), the bulk–Imε{sup –1} and the surface–Im(1 + ε){sup –1} electron energy losses are decomposed into elementary bands. Their main parameters, including energies and oscillator strengths of the transition bands are determined. Calculations are performed on the basis of the experimental reflectance spectrum of the crystal cleavage. Computer programs based on Kramers–Kronig relations, analytical formulas, and the advanced parameterfree method of combined Argand diagrams are used. The main features of the spectral set of optical functions and the parameters of expansion band components ε{sub 2}(E),–Imε{sup –1}, and–Im(1 + ε){sup –1} are determined.

36 MATERIALS SCIENCE↗
DOE OSTI2010

No indication of f{sub 0}(1370) in {pi}{pi} phase shift analyses

The scalar meson f{sub 0}(1370) - indicated in particular in the low energy pp-bar{yields}3 body reactions - is a crucial element in certain schemes of the scalar meson spectroscopy including glueballs. The most definitive results can be obtained from elastic and inelastic {pi}{pi} phase shift analyses using the constraints from unitarity where the discrete ambiguities can be identified and resolved. We reconsider the phase shift analyses for {pi}{sup +{pi}-{yields}{pi}+{pi}-}, {pi}{sup 0{pi}0}, KK-bar, {eta}{eta}. While a clear resonance signal for f{sub 0}(1500) in the resp. Argand diagrams is seen in all channels above a large 'background' from f{sub 0}(600) there is no clear signal of a second resonance 'f{sub 0}(1370)' in this mass range in any reaction, at the level of {approx}10% branching ratio into {pi}{pi}.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Properties of the Fundamental Optical Functions of Magnesium Silicide

The spectra of 16 optical Mg{sub 2}Si functions in the range from 0 to 11 eV at 77 K are determined. They contain five maxima and shoulders due to interband transitions and metastable excitons, as well as the maxima of bulk and surface plasmons at ~9.56 and ~7.30 eV. Their peculiarities and general patterns of behavior are established. Calculations were performed based on a well-known experimental reflection spectrum in the range from 0 to 11 eV at 77 K. The integral spectra of the imaginary parts of the permittivity ε{sub 2}(E), characteristic bulk (–Im ε{sup –1}), and surface (–Im (1 + ε){sup –1}) energy losses of electrons are expanded into elementary components in the region from 2 to 5 eV. The main parameters of the transition components were determined, including the energies of their maxima and oscillator strengths. Calculations were carried out using computer programs based on the Kramers–Kronig relations and known analytical formulas for the correlation between optical functions, as well as an improved nonparametric method of combined Argand diagrams taking into account the effective number of valence electrons participating in the formation of individual bands. Instead of five maxima and shoulders of the integral spectra, 17 elementary bands with oscillator strengths in the range from 0.0003 to 1.92 were established. They are due to transverse and longitudinal type excitonic and interband transitions. Based on known theoretical calculations, we propose herein the localization and assumed nature of the optical transition bands.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Optical Transitions from Core d Levels of Gallium Arsenide

An improved parameter-free method of joint Argand diagrams was used to expand the permittivity spectrum of gallium arsenide in a region of 19–26 eV into 12 bands of optical transitions with determining their maximum and half-width energies, as well as the oscillator strengths. The values of oscillator strengths of the obtained bands lie within an interval from 0.0009 to 0.06. In the regions of 19.2–21.3 and 24–26 eV, the permittivity spectrum was preliminarily calculated on the basis of experimental reflectance spectra with the use of the Kramers–Kronig integral relation method. The nature of the obtained transition bands is suggested in terms of the band-to-band and exciton transitions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Impact of reduced dimensionality on the correlation length and magnetization dynamics of the spin chain cobaltite Ca 3 Co 2 O 6

We have recently applied the magnetic field and temperature dependence of magnetic entropy change as a probe of the magnetic states of a single crystal of Ca 3 Co 2 O 6 to establish a more comprehensive magnetic phase diagram for this exotic system. The results are consistent with the spin-density wave description of the ground state and indicate the suppression of the modulated state in favor of a ferrimagnetic up-up-down arrangement of the spin chains with the application of a moderate field. We demonstrate, in this study, that the features of the static magnetic phase diagram are preserved when the grain size of Ca 3 Co 2 O 6 is reduced to 440 nm (below the maximum c-axis correlation length of ~550 nm in Ca 3 Co 2 O 6 ), although the polycrystalline materials show a non-saturating behavior, rounded steps, and reduced magnetization when compared to the single crystal. Our new finding of the multiple low-temperature magnetization steps in the 440 nm sample, together with conflicting reports concerning such steps in nanostructured samples, suggests that correlations in the ab plane are more important than correlations along the c-axis in the appearance of the plateaus. The relaxation processes in the system are studied through the decay of remanent magnetization, ac susceptibility, and Argand diagrams. The introduction of grain boundaries in Ca 3 Co 2 O 6 weakens the slow-dynamic state, widens the low-temperature distribution of relaxation times, and lowers activation energies within the Arrhenius-like relaxation regime.

36 MATERIALS SCIENCE↗
NASA NTRS1989

Spectroscopic analysis of transition state energy levels - Bending-rotational spectrum and lifetime analysis of H3 quasibound states

Converged quantum mechanical calculations of scattering matrices and transition probabilities are reported for the reaction of H with H2 with total angular momentum 0, 1, and 4 as functions of total energy in the range 0.85-1.15 eV on an accurate potential energy surface. The resonance structure is illustrated with Argand diagrams. State-to-state reactive collision delay times and lifetimes are presented. For J = 0, 1, and 4, the lowest-energy H3 resonance is at total energies of 0.983, 0.985, and 1.01 eV, respectively, with lifetimes of about 16-17 fs. For J = 1 and 4 there is a higher-energy resonance at 1.10-1.11 eV. For J = 1 the lifetime is about 4 fs and for J = 4 it is about 1 fs.

Zhao, Meishan↗
DOE OSTI2018

Fundamental Optical Functions and Parameters of Elementary Bands Corresponding to Transitions of the Mg{sub 2}Ge Crystal

Spectra of sixteen optical functions of Mg{sub 2}Ge at 77 K in the energy interval 0–11 eV are determined. The main features and the general patterns of behavior of the optical functions are established. They contain six maxima and shoulders caused by interband transitions and metastable excitons. The integral spectrum of the dielectric permittivity ε{sub 2}(E) at 77 K in the energy interval 2–5 eV comprising six maxima and shoulders is decomposed into sixteen elementary transition bands caused by exciton and interband transitions of transverse and longitudinal types. The supposed nature and the localization of transition bands in the optical spectra of magnesium germanide is proposed proceeding from the known results of theoretical calculations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2010

Quantum interference within the complex quantum Hamilton-Jacobi formalism

Quantum interference is investigated within the complex quantum Hamilton-Jacobi formalism. As shown in a previous work [Phys. Rev. Lett. 102 (2009) 250401], complex quantum trajectories display helical wrapping around stagnation tubes and hyperbolic deflection near vortical tubes, these structures being prominent features of quantum caves in space-time Argand plots. Here, we further analyze the divergence and vorticity of the quantum momentum function along streamlines near poles, showing the intricacy of the complex dynamics. Nevertheless, despite this behavior, we show that the appearance of the well-known interference features (on the real axis) can be easily understood in terms of the rotation of the nodal line in the complex plane. This offers a unified description of interference as well as an elegant and practical method to compute the lifetime for interference features, defined in terms of the average wrapping time, i.e., considering such features as a resonant process.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗