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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Atomic Data and Spectral Line Intensities for Ni XXI

Electron impact collision strengths, energy levels, oscillator strengths and spontaneous radiative decay rates are calculated for Ni XXI. The configurations used are 2s(sup 2)2p(sup 4), 2s2p(sup 5), 2p(sup 6), 2s(sup 2)2p(sup 3)3s, and 2s(sup 2)3p(sup 3)3d giving rise to 58 fine-structure levels in intermediate coupling. Collision strengths are calculated at five incident energies, 85, 170, 255, 340, and 425 Ry. Excitation rate coefficients are calculated by assuming a Maxwellian electron velocity distribution at an electron temperature of log T(sub e)(K)=6.9, corresponding to maximum abundance of Ni XXI. Using the excitation rate coefficients and the radiative transition rates, statistical equilibrium equations for level populations are solved at electron densities 10(exp 8)-10(exp 14) per cubic centimeter. Relative spectral line intensities are calculated. Proton excitation rates between the lowest three levels have been included in the statistical equilibrium equations. The predicted intensity ratios are compared with available observations.

Bhatia, A. K.↗
NASA NTRS1975

K-alpha X-rays from cosmic ray oxygen

Equilibrium charge fractions are calculated for subrelativistic cosmic ray oxygen ions in the interstellar medium. These are used to determine the expected flux of K-alpha rays arising from atomic processes for a number of different postulated interstellar oxygen spectra. Relating these results to the diffuse X-ray background measured at the appropriate energy level suggests an observable line feature. If the flux of low energy cosmic ray oxygen is sufficiently large, K-alpha X-ray line emission from these nuclei will comprise a significant fraction of the total diffuse flux at approximately 0.6 keV. A satellite borne detector with a resolution greater than 30 percent could observe this feature if the subrelativistic interstellar cosmic ray oxygen spectrum is as large as certain theoretical estimates expressed in the text.

Pravdo, S. H.↗
NASA NTRS1993

Predissociation linewidths in O2 B3Sigma-sub-u(-) (v = 0,2)

Results are presented of measurements of the rotational and fine-structure level-specific linewidths in v = 0 and v = 2 of the O2 B3Sigma-sub-u(-) state, which were carried out using laser-induced fluorescence techniques applied to Schumann-Runge absorption transitions from vibrationally excited O2 X3Sigma-sub-g(-) system. These linewidths represent the first measurements reflecting relative predissociation rates among the B-state levels. The linewidths were found to vary considerably among the various energy levels.

Cosby, P. C.↗
NASA NTRS2000

Consensus Assignments for Water Vapor Lines Not Assigned on the HITRAN Database: 13,200 to 16,500/cm

There are nearly 800 water Vapor-lines in the 13,200-16,500/cm region that do not have rovibrational assignments in the HITRAN database. The positions and intensities in the database were determined by Mandin et al., but assignments could not be determined at that time. Polyansky, et al. have now assigned over 600 of the unassigned lines in the 11,200-16,500/cm region. Schwenke has also given rovibrational assignments to many of these unassigned lines throughout the visible and near-infrared. Both articles changed the assignments of some HITRAN lines. Carleer et al. extend assignments to some weaker lines measured by them on new spectra with excellent signal/noise. However, some lines measured by Mandin et al. were omitted by Carleer, et al. because of blends due to lower spectral resolution. The rovibrational assignments of Polyansky et al. completely agree with those in Schwenke's article for only about 200 lines. However, Schwenke's ab initio line list is available on his internet site (http://ccf.arc.nasa.gov/-dschwenke). A detailed comparison of the Polyansky et al.line list, the Carleer et al.line list, and Schwenke's ab initio line list shows a larger number of agreements. In many cases the disagreement is only about the vibrational and/or rotational upper level, while there is agreement on the lower state assignment and energy level, "E", which is of primary importance for atmospheric applications. We will present a line list of "consensus" assignments in the 13,200-16,500/cm region for consideration of inclusion on the HITRAN and GEISA databases. This will substantially reduce the number of unassigned lines on the databases in this spectral region.

Giver, Lawerence P.↗
NASA NTRS2020

Exploring the Limits of the Data-Model-Theory Synergy: “Hot” MW Transitions for Rovibrational IR Studies

In order to further improve the accuracy of rovibrational IR line lists generated from the “Best Theory +Reliable High-resolution Experiment” (BTRHE) strategy from 0.01-0.05 cm-1, or 300-1500 MHz, to ~10 MHz, we explore the current limits of the Data-Model-Theory synergy by examining the accuracy and consistency of existing data, then propose that “hot” bands in microwave (MW) spectra is the solution we need for future enhancements. The Ames SO2 J=0-20 rovibrational energy levels computed on the semi-empirically refined Ames-2 potential energy surface (PES) are fit to the Effective Hamiltonian (EH) model regularly used in the experimental infrared (IR) analysis for SO2 isotopologues. In the fitted EH(Ames) model, the rotational constants A/B/C and all 5 quartic centrifugal distortion constants display clear, systematic, and consistent patterns along the vibrational state energy or quanta. Such consistent patterns may facilitate the vibrational assignments for MW hot bands and extract more information from high temperature MW spectra. Some EH(Expt) analyses were carried out with the lowest order Coriolis Coupling term, C1. Their constants should not be directly compared with other EH(Expt) and EH(Ames) results. After excluding them, our  = EH(Ames)- EH(Expt) analyses for 5 isotopologues (626, 636, 646, 628 and 828) indicates some loss of accuracy and consistency starting from vibrational states as low as 22 or 1000 cm-1. Some EH parameters, e.g. K, may have relative deviations as large as 50-100% and totally lose any recognizable patterns. This simply means that current EH(Expt) models do not have the system-wide consistency we need to further refine the EH(Ames) and Ames rovibrational IR line lists. A large part of such defects are probably inherited from the limited precision of experimental line positions, i.e. 1E-3 ~ 1E-4 cm-1, or 3-30 MHz. This is confirmed in a series of truncation tests using the Ames data. Although the EH(Ames) consistency may help identify unreliable rovibrational EH(Expt) parameters, and make reliable predictions for minor isotopologues and unobserved vibrational bands, we believe only the highly accurate “hot” MW transitions can provide real enhancements for EH(Expt) accuracy and consistency. “Hot” MW spectra should play a more significant role in the future synergy of Data, Model, and Theory in the field of rovibrational IR studies.

Xinchuan Huang↗
NASA NTRS1994

The Infrared Spectrum of H2S From 1 to 5 Microns

The absorption spectra of H2S from 2000 to 11,147 cm(exp -1) have been obtained with spectral resolutions of 0.006, 0.012, and 0.021 cm(exp -1) using the Fourier transform spectrometer at Kitt Peak National Observatory. The transitions of 21 bands have been assigned for the first time and 9 others reanalyzed so that accurate energy levels, band origins, and rotational parameters could be determined. The analysis of these data revealed some remarkable features in the energy spectrum, e.g., fourfold clustering of rotational levels belonging to the symmetric and asymmetric components of local mode manifolds at a high degree of stretching excitation. This paper reports fitted vibrational parameters and predicted band origins of H2S-32 up to 12,735 cm(exp -1). It also presents the degenerate rotational constants and upper state energies of (301)-(202) and (311)-(212) at 1 micron as illustrations of clustering in the local mode limit.

Alexander D. Bykov↗
NASA NTRS2003

Atomic Data and Emission Line Intensities for CA VII

In the present work we calculate energy levels, transition probabilities and electron-ion collisional excitation rates for the 3s(sup 2)3p(sup 2), 3s3p(sup 3) and 3s(sup 2)3p3d configurations of the silicon-like ion Ca VII. The total number of intermediate coupling levels considered is 27. Collision strengths are calculated at seven incident electron energies: 8, 10, 15, 20, 30,40 and 60 Ry, using the Distorted Wave approximation and a 5-configuration model. Excitation rate coefficients are calculated by assuming a Maxwellian distribution of velocities and are used to calculate level populations and line emissivities under the assumption of statistical equilibrium. Line intensity ratios are calculated and compared with observed values measured from SERTS and SOHO/CDS spectra. The diagnostic potential of Ca VII is demonstrated, with particular emphasis on the possibility to measure the Ne/Ca relative abundance through simultaneous observations of Ca VII and N VI lines. Ca VII proves to be an excellent tool for the study of the FIP effect in the solar transition region.

Landi, E.↗
NASA NTRS1977

Molecular cluster theory of CO chemisorption on a nickel /100/ surface

Self-consistent Hartree-Fock-Slater molecular cluster models for the chemisorption of carbon monoxide on a (100) transition metal surface are presented. Energy levels and charge distribution for the CO:Ni5 cluster in C sub 4v symmetry are obtained, and the variation of binding energies with height of the CO molecule above the surface of nickel is studied in detail. Comparison is made with experimental binding energy spectra and with the multiple-scattering results of Batra and Bagus. The redistribution in energy of free-atom valence levels is studied by means of local-densities-of-states diagrams.

Ellis, D. E.↗
NASA NTRS1981

Collisional excitation of electron Landau levels in strong magnetic fields

The cross sections for the excitation and deexcitation of the quantized transverse energy levels of an electron in a magnetic field are calculated for electron-proton and electron-electron collisions in light of the importance of the cross sections for studies of X-ray pulsar emission. First-order matrix elements are calculated using the Dirac theory of the electron, thus taking into account relativistic effects, which are believed to be important in accreting neutron stars. Results for the collisional excitation of ground state electrons by protons are presented which demonstrate the importance of proton recoil and relativistic effects, and it is shown that electron-electron excitations may contribute 10 to 20% of the excitation rate from electron-proton scattering in a Maxwellian plasma. Finally, calculations of the cross section for electron-proton small-angle scattering are presented which lead to relaxation rates for the electron velocity distribution which are modified by the magnetic field, and to a possible increase in the value of the Coulomb logarithm.

Langer, S. H.↗
NASA NTRS1983

Analysis of the economics of photovoltaic-diesel-battery energy systems for remote applications

Computer simulations were conducted to analyze the performance and operating cost of a photovoltaic energy source combined with a diesel generator system and battery storage. The simulations were based on the load demand profiles used for the design of an all photovoltaic energy system installed in the remote Papago Indian Village of Schuchuli, Arizona. Twenty year simulations were run using solar insolation data from Phoenix SOLMET tapes. Total energy produced, energy consumed, operation and maintenance costs were calculated. The life cycle and levelized energy costs were determined for a variety of system configurations (i.e., varying amounts of photovoltaic array and battery storage).

Brainard, W. A.↗
NASA NTRS1986

Cell performance and defect behavior in proton-irradiated lithium-counterdoped n(+)p silicon solar cells

Lithium-counterdoped n(+)p silicon solar cells were irradiated by 10-MeV protons, and their performance was determined as a function of fluence. It was found that the cell with the highest lithium concentration exhibited the higher radiation resistance. Deep-level transient spectroscopy studies of deep-level defects were used to identify two lithium-related defects. Defect energy levels obtained after the present 10-MeV irradiations were found to be markedly different than those observed after previous 1-MeV electron irradiations. However, the present DLTS data are consistent with previous suggestion by Weinberg et al. (1984) of a lithium-oxygen interaction which tends to inhibit formation of an interstitial boron-oxygen defect.

Weinberg, I.↗
NASA NTRS1997

A Study of the Use of Contact Loading to Simulate Low Velocity Impact

Although numerous studies on the impact response of laminated composites have been conducted, there is as yet no agreement within the composites community on what parameter or parameters are adequate for quantifying the severity of an impact event. One of the more interesting approaches that has been proposed uses the maximum contact force during impact to "quantify" the severity of the impact event, provided that the impact velocity is sufficiently low. A significant advantage of this approach, should it prove to be reliable, is that quasi-static contact loading could be used to simulate low velocity impact. In principle, a single specimen, loaded quasi-statically to successively increasing contact loads could be used to map the entire spectrum of damage as a function of maximum contact force. The present study had as its objective assessing whether or not the maximum contact force during impact is a suitable parameter for characterizing an impact. The response of [+/-60/0(sub 4)/+/-60/0(sub 2)](sub s) laminates fabricated from Fiberite T300/934 graphite epoxy and subjected to quasi-static contact loading and to low velocity impact was studied. Three quasi-static contact load levels - 525 lb., 600 lb., and 675 lb. - were selected. Three impact energy levels - 1.14 ft.-lb., 2.0 ft.-lb., and 2.60 ft.-lb. - were chosen in an effort to produce impact events in which the maximum contact forces during the impact events were 525 lb., 600 lb., and 625 lb., respectively. Damage development was documented using dye-penetrant enhanced x-ray radiography. A digital image processing technique was used to obtain quantitative information about the damage zone. Although it was intended that the impact load levels produce maximum contact forces equal to those used in the quasi-static contact experiments, larger contact forces were developed during impact loading. In spite of this, the damage zones developed in impacted specimens were smaller than the damage zones developed in specimens subjected to the corresponding quasi-static contact loading. The impacted specimens may have a greater tendency to develop fiber fracture, but, at present, a quantitative assessment of fiber fracture is not available. In addressing whether or not contact force is an adequate metric for describing the severity of an impact event, the results of this study suggest that it is not. In cases where the quasi-static load level and the maximum contact force during impact were comparable, the quasi-statically loaded specimens consistently developed larger damage zones. It should be noted, however, that using quasi-static damage data to forecast the behavior of impacted material may give conservative estimates of the residual strength of impacted composites.

Highsmith, Alton L.↗
NASA NTRS2005

Calculating the X-Ray Fluorescence from the Planet Mercury Due to High-Energy Electrons

The least-studied terrestrial planet is Mercury due to its proximity to the Sun, which makes telescopic observations and spacecraft encounters difficult. Our lack of knowledge about Mercury should change in the near future due to the recent launching of MESSENGER, a Mercury orbiter. Another mission (BepiColombo) is currently being planned. The x-ray spectrometer on MESSENGER (and planned for BepiColombo) can characterize the elemental composition of a planetary surface by measuring emitted fluorescent x-rays. If electrons are ejected from an atom s inner shell by interaction with energetic particles such as photons, electrons, or ions, electrons from an outer shell can transfer to the inner shell. Characteristic x-rays are then emitted with energies that are the difference between the binding energy of the ion in its excited state and that of the ion in its ground state. Because each element has a unique set of energy levels, each element emits x-rays at a unique set of energies. Electrons and ions usually do not have the needed flux at high energies to cause significant x-ray fluorescence on most planetary bodies. This is not the case for Mercury where high-energy particles were detected during the Mariner 10 flybys. Mercury has an intrinsic magnetic field that deflects the solar wind, resulting in a bow shock in the solar wind and a magnetospheric cavity. Electrons and ions accelerated in the magnetosphere tend to follow its magnetic field lines and can impact the surface on Mercury s dark side Modeling has been done to determine if x-ray fluorescence resulting from the impact of high-energy electrons accelerated in Mercury's magnetosphere can be detected by MESSENGER. Our goal is to understand how much bulk chemical information can be obtained from x-ray fluorescence measurements on the dark side of Mercury.

Burbine, T. H.↗
NASA NTRS2016

Exergy Based Analysis for the Environmental Control and Life Support Systems of the International Space Station

When optimizing the performance of complex systems, a logical area for concern is improving the efficiency of useful energy. The energy available for a system to perform work is defined as a system's energy content. Interactions between a system's subsystems and the surrounding environment can be accounted for by understanding various subsystem energy efficiencies. Energy balance of reactants and products, and enthalpies and entropies, can be used to represent a chemical process. Heat transfer energy represents heat loads, and flow energy represents system flows and filters. These elements allow for a system level energy balance. The energy balance equations are developed for the subsystems of the Environmental Control and Life Support (ECLS) system aboard the International Space Station (ISS). The use of these equations with system information would allow for the calculation of the energy efficiency of the system, enabling comparisons of the ISS ECLS system to other systems as well as allows for an integrated systems analysis for system optimization.

Clem, Kirk A.↗
NASA NTRS1976

Argon hydrochloride, Ar.HCl, bond energy by infrared spectroscopy

The infrared absorption of argon (200 to 760 torr) and hydrogen chloride (2 to 6 torr) mixtures is reexamined in the missing Q branch region (spectral region between 2860 and 3010 wavelength/cm) at temperatures ranging from 195 to 298 K. The temperature dependence of two absorption features of the argon hydrogen chloride complex, at 2887 and 2879 wavelength/cm, leads to a bond energy estimate that depends on the assumptions made about the internal degrees of freedom of the complex. It is shown that agreement with experiment can be reached for well depths near 1.2 kcal/mole. This result is relatively insensitive to the choice of the vibrational frequencies and anharmonicities, but does depend on the extent to which the energy level manifolds are truncated to avoid molecular excitation in excess of the bond energy. The bond energy is found to deviate from the commonly accepted value of 0.4 kcal/mole. Possible causes for the discrepancy are considered.

Miziolek, A. W.↗
NASA NTRS1994

Ab Initio Vibrational Levels For HO2 and Vibrational Splittings for Hydrogen Atom Transfer

We calculate vibrational levels and wave functions for HO2 using the recently reported ab initio potential energy surface of Walch and Duchovic. There is intramolecular hydrogen atom transfer when the hydrogen atom tunnels through a T-shaped saddle point separating two equivalent equilibrium geometries, and correspondingly, the energy levels are split. We focus on vibrational levels and wave functions with significant splitting. The first three vibrational levels with splitting greater than 2/cm are (15 0), (0 7 1) and (0 8 0) where V(sub 2) is the O-O-H bend quantum number. We discuss the dynamics of hydrogen atom transfer; in particular, the O-O distances at which hydrogen atom transfer is most probable for these vibrational levels. The material of the proposed presentation was reviewed and the technical content will not reveal any information not already in the public domain and will not give any foreign industry or government a competitive advantage.

Barclay, V. J.↗
NASA NTRS1979

Energy and cost saving results for advanced technology systems from the Cogeneration Technology Alternatives Study (CTAS)

An overview of the organization and methodology of the Cogeneration Technology Alternatives Study is presented. The objectives of the study were to identify the most attractive advanced energy conversion systems for industrial cogeneration applications in the future and to assess the advantages of advanced technology systems compared to those systems commercially available today. Advanced systems studied include steam turbines, open and closed cycle gas turbines, combined cycles, diesel engines, Stirling engines, phosphoric acid and molten carbonate fuel cells and thermionics. Steam turbines, open cycle gas turbines, combined cycles, and diesel engines were also analyzed in versions typical of today's commercially available technology to provide a base against which to measure the advanced systems. Cogeneration applications in the major energy consuming manufacturing industries were considered. Results of the study in terms of plant level energy savings, annual energy cost savings and economic attractiveness are presented for the various energy conversion systems considered.

Sagerman, G. D.↗
NASA NTRS1993

Electronic characterization of defects in narrow gap semiconductors

The study of point defects in semiconductors has a long and honorable history. In particular, the detailed understanding of shallow defects in common semiconductors traces back to the classic work of Kohn and Luttinger. However, the study of defects in narrow gap semiconductors represents a much less clear story. Here, both shallow defects (caused by long range potentials) and deep defects (from short range potentials) are far from being completely understood. In this study, all results are calculational and our focus is on the chemical trend of deep levels in narrow gap semiconductors. We study substitutional (including antisite), interstitial and ideal vacancy defects. For substitutional and interstitial impurities, the efects of relaxation are included. For materials like Hg(1-x)Cd(x)Te, we study how the deep levels vary with x, of particular interest is what substitutional and interstitial atoms yield energy levels in the gap i.e. actually produce deep ionized levels. Also, since the main technique utilized is Green's functions, we include some summary of that method.

Patterson, James D.↗