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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Absorption by H2O and H2O-N2 mixtures at 153 GHz

New experimental data on and a theoretical analysis of the absorption coefficient at 153 GHz are presented for pure water vapor and water vapor-nitrogen mixtures. This frequency is 30 GHz lower than the resonant frequency of the nearest strong water line (183 GHz) and complements our previous measurements at 213 GHz. The pressure dependence is observed to be quadratic in the case of pure water vapor, while in the case of mixtures there are both linear and quadratic density components. By fitting our experimental data taken at several temperatures we have obtained the temperature dependence of the absorption. Our experimental data are compared to several theoretical models with and without a continuum contribution, and we find that none of the models is in very good agreement with the data; in the case of pure water vapor, the continuum contribution calculated using the recent theoretical absorption gives the best results. In general, the agreement between the data and the various models is less satisfactory than found previously in the high-frequency wing. The anisotropy in the observed absorption differs from that currently used in atmospheric models.

Bauer, A.↗
NASA NTRS1998

Air- and N2-Broadening Coefficients and Pressure-Shift Coefficients in the C-12(O2-16) Laser Bands

In this paper we report the pressure broadening and the pressure-induced line shift coefficients for 46 individual rovibrational lines in both the (12)C(16)O2, 00(sup 0)1-(10(sup 0)0-02(sup 0)0)I, and 00(sup 0)1-(10(sup 0)0-02(sup 0)0)II, laser bands (laser band I centered at 960.959/cm and laser band II centered at 1063.735/cm) determined from spectra recorded with the McMath-Pierce Fourier transform spectrometer. The results were obtained from analysis of 10 long-path laboratory absorption spectra recorded at room temperature using a multispectrum nonlinear least-squares technique. Pressure effects caused by both air and nitrogen have been investigated. The air-broadening coefficients determined in this study agree well with the values in the 1996 HITRAN database; ratios and standard deviations of the ratios of the present air-broadening measurements to the 1996 HITRAN values for the two laser bands are: 1.005(15) for laser band I and 1.005(14) for laser band II. Broadening by nitrogen is 3 to 4% larger than that of air. The pressure-induced line shift coefficients are found to be transition dependent and different for the P- and R-branch lines with same J" value. No noticeable differences in the shift coefficients caused by air and nitrogen were found. The results obtained are compared with available values previously reported in the literature.

Devi, V. Malathy↗
NASA NTRS2001

The Effect of O2, H2O, and N2 on the Fatigue Crack Growth Behavior of an Alpha + Beta Titanium Alloy at 24 C and 177 C

To study the effects of atmospheric species on the fatigue crack growth behavior of an a+B titanium alloy (Ti 6-2-2-2-2) at room temperature and 177 C, fatigue tests were performed in laboratory air, ultrahigh vacuum, and high purity water vapor, oxygen, nitrogen and helium at various partial pressures. Accelerated fatigue crack growth rates in laboratory air compared to ultrahigh vacuum are linked to the damaging effects of both water vapor and oxygen. Observations of the fatigue crack growth behavior in ultrahigh purity environments, along with surface film analysis using X-ray photoelectron spectroscopy (XPS), suggest that multiple crack-tip processes govern the damaging effects of air. Three possible mechanisms are proposed: 1) at low pressure (less than 10(exp -1) Pa), accelerated da/dN is likely due to monolayer adsorption on crack-tip surfaces presumably resulting in decreased bond strengths at the fatigue crack tip, 2) for pressures greater than 10(exp -1) Pa, accelerated da/dN in oxygen may result from oxidation at the crack tip limiting reversible slip, and 3) in water vapor, absorption of atomic hydrogen at the reactive crack tip resulting in process zone embrittlement.

Smith, Stephen W.↗
NASA NTRS1997

Changes in soluble sugar, starch, and alcohol dehydrogenase in Arabidopsis thaliana exposed to N2 diluted atmospheres

Proper exchange of atmospheric gases is important for normal root and shoot metabolism in plants. This study was conducted to determine how restricted air supply affects foliar carbohydrates, while using the marker enzyme alcohol dehydrogenase (ADH) to report on the oxygenation status of the rootzone. Fourteen-day-old Arabidopsis thaliana (L.) Heynh. plants grown singly in 7-ml tubes containing agarified nutrient medium were placed in coupled Magenta vessels and exposed for six days to either ambient air or one of six different air/nitrogen dilutions. Redox potential of the agar medium was measured immediately after harvesting and freezing leaf tissue, and then root systems were quickly extracted from the agar and frozen for subsequent analyses. Redox potential measurements indicated that this series of gas mixtures produced a transition from hypoxia to anoxia in the root zones. Root ADH activity increased at higher rates as the redox potential neared anoxic levels. In contrast, ADH mRNA expression quickly neared its maximum as the medium became hypoxic and showed little further increase as it became anoxic. Foliar carbohydrate levels increased 1.5- to 2-fold with decreased availability of metabolic gases, with starch increasing at higher concentrations of air than soluble carbohydrate. The results serve as a model for plant performance under microgravity conditions, where absence of convective air movement prevents replenishment of metabolic gases.

NASA Discipline Plant Biology↗
NASA NTRS1996

Absolute Inelastic Differential Electron Scattering Cross Sections for He, Xe, N2, and CO at Near Threshold Impact Energies for 90(deg) Scattering Angle

There is a great deal of need for accurate differential cross sections (DCSs) associated with electron impact excitation of various atomic and molecular species. These cross sections are needed for modeling of various plasma systems (ranging from lasers and material processing plasmas to planetary and astrophysical plasmas) and for guiding development of theoretical and computational schemes.

DCS beam scattering beam-beam scattering↗
NASA NTRS2016

Comparison of Quantum Mechanical and Empirical Potential Energy Surfaces and Computed Rate Coefficients for N2 Dissociation

Physics-based modeling of hypersonic flows is predicated on the availability of chemical reaction rate coefficients and cross sections for the collisional processes. This approach has been built around the use of quantum mechanical calculations to describe the interaction between the colliding particles. In this approach a potential energy surface (PES) is computed by solving the electronic Schrödinger equation and collision cross sections are determined for that PES using classical, semiclassical or quantum mechanical scattering methods. The rate coefficients are computed by integrating the thermally weighted cross sections. State-to-state rate coefficients are determined by only integrating over a thermal distribution of collisional energies. Finally, thermal rate coefficients are determined by summation of the state-to-state rate coefficients for reactions of molecules in all relevant ro-vibrational energy levels. If the flow is in thermal non-equilibrium, the translational, vibrational and rotational energy modes can be represented in different ways: three unique temperatures can be used to describe the distributions, the populations of individual ro-vibrational energy levels can be determined by solving the Master Equation, or through the use of direct simulation in particle-based Monte Carlo sampling. The PES-to-rate coefficient approach had been proposed and attempted in the early days of digital computing, but it is only in the last 15 years that computer hardware and software have been up to the task of calculating accurate interatomic and intermolecular potentials.

Jaffe, Richard L.↗
NASA NTRS2019

N2 and H2 Broadened Isobutane Infrared Absorption Cross Sections and Butane Upper Limits on Titan

High resolution infrared absorption cross sections of isobutane, (CH3)3CH, were measured in the 1050-1900 cm-1spectral range by Fourier transform spectroscopy. Four sample temperatures (210, 234, 265 and 296 K) were used with three pressures (10, 30 and 100 Torr) of N2and H2broadening gas. Spectra of pure isobutane samples were also recorded. These cross sections are useful for the interpretation of infrared spectra of the Giant Planets and Titan. The isobutane cross sections give an upper limit of 3.91e-8for its fractional abundance on Titan based on CIRS/Cassini infrared spectra. Using n-butane, CH3(CH2)2CH3, cross sections from the literature, we obtain an upper limit of 5.13e-7for its abundance on Titan. The combined upper limit for both isomers of butane, C4H10, on Titan of 5.52e-7is consistent with the lower limit of recent model predictions

Dan Hewett↗
NASA NTRS1995

High Resolution UV Spectroscopy of H2 and N2 Applied to Observations of the Planets by Spacecraft

The next generation of high resolution UV imaging Spacecraft are being prepared for studying the airglow and aurora of the Earth, the other terrestrial planets and the Jovian planets. To keep pace with these technological improvements we have developed a laboratory program to provide electron impact collision cross sections of the major molecular planetary gases. This program is described in detail.

Spectroscopy↗
NASA NTRS2022

Anisotropy Measurements from the Near-Threshold Photodissociation of the N2−NO Complex

We have used velocity map ion imaging to measure the angular anisotropy of the NO (A) products from the photodissociation of the N 2 −NO complex. Our experiment ranged from 108 to 758 cm −1 above the threshold energy to form NO (A)+N 2 (X) products, and these measurements reveal, for the first time, a strong angular anisotropy from photodissociation. At 108 cm −1 above the photodissociation threshold, we observed NO (A) photoproducts recoil preferentially perpendicular to the laser polarization axis with an average anisotropy parameter, β = −0.25; however, as the available energy was increased, the anisotropy increased, and at 758 cm −1 above the threshold energy, we found an average β = +0.28. The observed changes in the angular anisotropy of the NO (A) photoproduct are qualitatively similar to those observed for the photodissociation of the Ar−NO complex and likely result from changes in the region of the excited state potential energy surface accessed during the electronic excitation. At the lowest available energy, we also noted a large contribution from hot band excitation; however, this contribution decreased as the available energy increased. The outsized contribution at the lowest available energy may result from hot bands having better Franck−Condon overlap with the excited electronic state near threshold. Finally, we contrast the experimental center of mass translational energy distribution with a statistical energy distribution determined from phase space theory. The experimental and statistical distributions show pronounced disagreement, particularly at low kinetic energies, with the experimental one showing less dissociation resulting in high rotational levels of the fragments.

Energy↗
DOE OSTI2020

Materials Data on MgH18C4SN8O9 by Materials Project

MgC4N8H18SO9 is beta Np structured and crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four MgC4N8H18SO9 clusters. Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share a cornercorner with one SO4 tetrahedra. There are a spread of Mg–O bond distances ranging from 2.08–2.16 Å. There are four inequivalent C4+ sites. In the first C4+ site, C4+ is bonded in a trigonal planar geometry to two N2- and one O2- atom. There is one shorter (1.34 Å) and one longer (1.37 Å) C–N bond length. The C–O bond length is 1.27 Å. In the second C4+ site, C4+ is bonded in a trigonal planar geometry to two N2- and one O2- atom. Both C–N bond lengths are 1.35 Å. The C–O bond length is 1.28 Å. In the third C4+ site, C4+ is bonded in a trigonal planar geometry to two N2- and one O2- atom. Both C–N bond lengths are 1.35 Å. The C–O bond length is 1.28 Å. In the fourth C4+ site, C4+ is bonded in a trigonal planar geometry to two N2- and one O2- atom. There is one shorter (1.35 Å) and one longer (1.36 Å) C–N bond length. The C–O bond length is 1.27 Å. There are eight inequivalent N2- sites. In the first N2- site, N2- is bonded in a distorted trigonal non-coplanar geometry to one C4+ and two H1+ atoms. Both N–H bond lengths are 1.02 Å. In the second N2- site, N2- is bonded in a trigonal planar geometry to one C4+ and two H1+ atoms. Both N–H bond lengths are 1.02 Å. In the third N2- site, N2- is bonded in a trigonal planar geometry to one C4+ and two H1+ atoms. Both N–H bond lengths are 1.02 Å. In the fourth N2- site, N2- is bonded in a trigonal planar geometry to one C4+ and two H1+ atoms. There is one shorter (1.01 Å) and one longer (1.02 Å) N–H bond length. In the fifth N2- site, N2- is bonded in a trigonal planar geometry to one C4+ and two H1+ atoms. Both N–H bond lengths are 1.02 Å. In the sixth N2- site, N2- is bonded in a trigonal planar geometry to one C4+ and two H1+ atoms. Both N–H bond lengths are 1.02 Å. In the seventh N2- site, N2- is bonded in a trigonal planar geometry to one C4+ and two H1+ atoms. Both N–H bond lengths are 1.02 Å. In the eighth N2- site, N2- is bonded in a trigonal planar geometry to one C4+ and two H1+ atoms. There is one shorter (1.01 Å) and one longer (1.02 Å) N–H bond length. There are eighteen inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the third H1+ site, H1+ is bonded in a single-bond geometry to one N2- atom. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one N2- atom. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one N2- atom. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one N2- atom. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one N2- atom. In the eighth H1+ site, H1+ is bonded in a single-bond geometry to one N2- atom. In the ninth H1+ site, H1+ is bonded in a single-bond geometry to one N2- atom. In the tenth H1+ site, H1+ is bonded in a single-bond geometry to one N2- atom. In the eleventh H1+ site, H1+ is bonded in a single-bond geometry to one N2- atom. In the twelfth H1+ site, H1+ is bonded in a single-bond geometry to one N2- atom. In the thirteenth H1+ site, H1+ is bonded in a single-bond geometry to one N2- atom. In the fourteenth H1+ site, H1+ is bonded in a single-bond geometry to one N2- atom. In the fifteenth H1+ site, H1+ is bonded in a single-bond geometry to one N2- atom. In the sixteenth H1+ site, H1+ is bonded in a single-bond geometry to one N2- atom. In the seventeenth H1+ site, H1+ is bonded in a single-bond geometry to one N2- atom. In the eighteenth H1+ site, H1+ is bonded in a single-bond geometry to one N2- atom. S2- is bonded to four O2- atoms to form SO4 tetrahedra that share a cornercorner with one MgO6 octahedra. The corner-sharing octahedral tilt angles are 42°. There are a spread of S–O bond distances ranging from 1.48–1.50 Å. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one S2- atom. In the second O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Mg2+ and one S2- atom. In the third O2- site, O2- is bonded in a single-bond geometry to one S2- atom. In the fourth O2- site, O2- is bonded in a single-bond geometry to one S2- atom. In the fifth O2- site, O2- is bonded in a distorted water-like geometry to one Mg2+ and two H1+ atoms. In the sixth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Mg2+ and one C4+ atom. In the seventh O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Mg2+ and one C4+ atom. In the eighth O2- site, O2- is bonded in a bent 150 degrees geometry to one Mg2+ and one C4+ atom. In the ninth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Mg2+ and one C4+ atom.

36 MATERIALS SCIENCE↗