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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 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Checking the statistical theory of liquids by ultraacoustic measurements

The manner of theoretically obtaining radial distribution functions 9(r) for n-hexane as a function of temperature is described. With the aid of function g(r) the coefficient of dynamic viscosity and the coefficient of volumetric viscosity for temperatures ranging from 213 K to 273 K were calculated. With the aid of the two coefficients of viscosity the coefficient of absorption of ultrasounds in n-hexane referred to the square of the frequency was determined. The same values were measured experimentally. Comparison of theory with experiments resulted in satisfactory agreement.

Dima, V. N.↗
NASA NTRS1978

Search for X-ray emission from AO0235+164

Limits to the first-order Compton scattering, brightness temperature, and angular size of the compact radio source AO0235+164 were calculated on the basis of a flux density of less than about 1 microJy at 10 to the 18th Hz calculated from observations of the source with the rotating modulation collimator aboard the SAS 3 X-ray observatory. It was found that the maximum brightness temperature at this frequency is less than 2.4 times 10 to the 11th K, corresponding to a minimum angular size of 0.38 msec of arc, assuming the synchrotron self-absorption turnover coefficient is 0.5. On the basis of the distance implied by the largest redshift present, the energy contained in relativistic particles and the magnetic field are calculated, and the ratio of particle to magnetic energy is greater than 10, so the dynamics must be particle dominated. This indicates relativistic expansion if the mean energy per particle is comparable to or greater than the rest of those particles that neutralize the electron plasma.

Dennison, B.↗
NASA NTRS1980

Advanced methods for preparation and characterization of infrared detector materials

Mercury cadmium telluride crystals were prepared by the Bridgman method with a wide range of crystal growth rates and temperature gradients adequate to prevent constitutional supercooling under diffusion-limited, steady state, growth conditions. The longitudinal compositional gradients for different growth conditions and alloy compositions were calculated and compared with experimental data to develop a quantitative model of the crystal growth kinetics for the Hg(i-x)CdxTe alloys, and measurements were performed to ascertain the effect of growth conditions on radial compositional gradients. The pseudobinary HgTe-CdTe constitutional phase diagram was determined by precision differential thermal analysis measurements and used to calculate the segregation coefficient of Cd as a function of x and interface temperature. Computer algorithms specific to Hg(1-x)CdxTe were developed for calculations of the charge carrier concentrations, charge carrier mobilities, Hall coefficient, optical absorptance, and Fermi energy as functions of x, temperature, ionized donor and acceptor concentrations, and neutral defect concentrations.

Lehoczky, S. L.↗
NASA NTRS1982

Direct observation of interface instability during crystal growth

The general aim of this investigation was to study interface stability and solute segregation phenomena during crystallization of a model system. Emphasis was to be placed on direct observational studies partly because this offered the possibility at a later stage of performing related experiments under substantially convection-free conditions in the space shuttle. The major achievements described in this report are: (1) the development of a new model system for fundamental studies of crystal growth from the melt and the measurement of a range of material parameters necessary for comparison of experiment with theory. (2) The introduction of a new method of measuring segregation coefficient using absorption of a laser beam by the liquid phase. (3) The comparison of segregation in crystals grown by gradient freezing and by pulling from the melt. (4) The introduction into the theory of solute segregation of an interface field term and comparison with experiment. (5) The introduction of the interface field term into the theories of constitutional supercooling and morphological stability and assessment of its importance.

Tiller, W. A.↗
NASA NTRS2017

Relaxation Matrix for Symmetric Tops with Inversion Symmetry: Line Coupling and Line Mixing Effects on NH3 Lines in the V4 Band

Line shape parameters including the half-widths and the off-diagonal elements of the relaxation matrix have been calculated for self-broadened NH3 lines in the perpendicular v4 band. As in the pure rotational and the parallel v1 bands, the small inversion splitting in this band causes a complete failure of the isolated line approximation. As a result, one has to use formalisms not relying on this approximation. However, due to differences between parallel and perpendicular bands of NH3, the applicability of the formalism used in our previous studies of the v1 band and other parallel bands must be carefully verified. We have found that, as long as potential models only contain components with K1 equals K2 equals 0, whose matrix elements require the selection rule delta k equals 0, the formalism is applicable for the v4 band with some minor adjustments. Based on both theoretical considerations and results from numerical calculations, the non-diagonality of the relaxation matrices in all the PP, RP, PQ, RQ, PR, and RR branches is discussed. Theoretically calculated self-broadened half-widths are compared with measurements and the values listed in HITRAN 2012. With respect to line coupling effects, we have compared our calculated intra-doublet off-diagonal elements of the relaxation matrix with reliable measurements carried out in the PP branch where the spectral environment is favorable. The agreement is rather good since our results do well reproduce the observed k and j dependences of these elements, thus validating our formalism.

Absorption coefficient↗
DOE OSTI2014

Model-based dose calculations for COMS eye plaque brachytherapy using an anatomically realistic eye phantom

Purpose : To investigate the effects of the composition and geometry of ocular media and tissues surrounding the eye on dose distributions for COMS eye plaque brachytherapy with{sup 125}I, {sup 103}Pd, or {sup 131}Cs seeds, and to investigate doses to ocular structures. Methods : An anatomically and compositionally realistic voxelized eye model with a medial tumor is developed based on a literature review. Mass energy absorption and attenuation coefficients for ocular media are calculated. Radiation transport and dose deposition are simulated using the EGSnrc Monte Carlo user-code BrachyDose for a fully loaded COMS eye plaque within a water phantom and our full eye model for the three radionuclides. A TG-43 simulation with the same seed configuration in a water phantom neglecting the plaque and interseed effects is also performed. The impact on dose distributions of varying tumor position, as well as tumor and surrounding tissue media is investigated. Each simulation and radionuclide is compared using isodose contours, dose volume histograms for the lens and tumor, maximum, minimum, and average doses to structures of interest, and doses to voxels of interest within the eye. Results : Mass energy absorption and attenuation coefficients of the ocular media differ from those of water by as much as 12% within the 20–30 keV photon energy range. For all radionuclides studied, average doses to the tumor and lens regions in the full eye model differ from those for the plaque in water by 8%–10% and 13%–14%, respectively; the average doses to the tumor and lens regions differ between the full eye model and the TG-43 simulation by 2%–17% and 29%–34%, respectively. Replacing the surrounding tissues in the eye model with water increases the maximum and average doses to the lens by 2% and 3%, respectively. Substituting the tumor medium in the eye model for water, soft tissue, or an alternate melanoma composition affects tumor dose compared to the default eye model simulation by up to 16%. In the full eye model simulations, the average dose to the lens is larger by 7%–9% than the dose to the center of the lens, and the maximum dose to the optic nerve is 17%–22% higher than the dose to the optic disk for all radionuclides. In general, when normalized to the same prescription dose at the tumor apex, doses delivered to all structures of interest in the full eye model are lowest for{sup 103}Pd and highest for {sup 131}Cs, except for the tumor where the average dose is highest for {sup 103}Pd and lowest for {sup 131}Cs. Conclusions : The eye is not radiologically water-equivalent, as doses from simulations of the plaque in the full eye model differ considerably from doses for the plaque in a water phantom and from simulated TG-43 calculated doses. This demonstrates the importance of model-based dose calculations for eye plaque brachytherapy, for which accurate elemental compositions of ocular media are necessary.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2024

The Role of Spin–Orbit Coupling in the Linear Absorption Spectrum and Intersystem Crossing Rate Coefficients of Ruthenium Polypyridyl Dyes

The successful use of molecular dyes for solar energy conversion requires efficient charge injection, which in turn requires the formation of states with sufficiently long lifetimes (e.g., triplets). The molecular structure elements that confer this property can be found empirically, however computational predictions using ab initio electronic structure methods are invaluable to identify structure-property relations for dye sensitizers. The primary challenge for simulations to elucidate the electronic and nuclear origins of these properties is a spin-orbit interaction which drives transitions between electronic states. Here, in this work, we present a computational analysis of the spin-orbit corrected linear absorption cross sections and intersystem crossing rate coefficients for a derivative set of phosphonated tris(2,2'-bipyridine)ruthenium(2+) dye molecules. After sampling the ground state vibrational distributions, the predicted linear absorption cross sections indicate that the mixture between singlet and triplet states plays a crucial role in defining the line shape of the metal-to-ligand charge transfer bands in these derivatives. Additionally, an analysis of the intersystem crossing rate coefficients suggests that transitions from the singlet into the triplet manifolds are ultrafast with rate coefficients on the order of 10 13 s -1 for each dye molecule.

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

Influence of electrically induced refraction and absorption on the measurement of spin current by pockels effect in GaAs

The pockels effect could be utilized to measure spin current in semiconductors for linear electro-optic coefficient can be induced by spin current. When dc electric field is applied, the carriers will shift in k space, which could lead to the change of refraction and absorption coefficients. In this paper, we investigate the influence of the induced change of the refraction and absorption coefficients on the measurement of spin current by pockels effect in GaAs.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2002

Coastal Atmosphere and Sea Time Series (CoASTS)

In this document, the first three years of a time series of bio-optical marine and atmospheric measurements are presented and analyzed. These measurements were performed from an oceanographic tower in the northern Adriatic Sea within the framework of the Coastal Atmosphere and Sea Time Series (CoASTS) project, an ocean color calibration and validation activity. The data set collected includes spectral measurements of the in-water apparent (diffuse attenuation coefficient, reflectance, Q-factor, etc.) and inherent (absorption and scattering coefficients) optical properties, as well as the concentrations of the main optical components (pigment and suspended matter concentrations). Clear seasonal patterns are exhibited by the marine quantities on which an appreciable short-term variability (on the order of a half day to one day) is superimposed. This short-term variability is well correlated with the changes in salinity at the surface resulting from the southward transport of freshwater coming from the northern rivers. Concentrations of chlorophyll alpha and total suspended matter span more than two orders of magnitude. The bio-optical characteristics of the measurement site pertain to both Case-I (about 64%) and Case-II (about 36%) waters, based on a relationship between the beam attenuation coefficient at 660nm and the chlorophyll alpha concentration. Empirical algorithms relating in-water remote sensing reflectance ratios and optical components or properties of interest (chlorophyll alpha, total suspended matter, and the diffuse attenuation coefficient) are presented.

Hooker, Stanford B.↗