Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “absorption coefficient”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Temperature dependence of HNO3 absorption in the 11.3-micron region

Laboratory spectra have been obtained for HNO3 with a Michelson-type Fourier transform interferometer using absorption cells with path lengths of 10.3, 25.5, and 49.8 cm at temperatures of 240, 248, 283, and 294 K. The measurements lead to a total band intensity value of 642 plus or minus 5% per sq cm amagat, which is a temperature independent value after the gas density correction has been made. However, the temperature dependence of the spectral absorption coefficients is apparent in the 885 kayser region.

Goldman, A.↗
NASA NTRS1981

Polarized radiation from hot plasmas and applications to AM Herculis binaries

Absorption coefficients for the ordinary and extraordinary modes are calculated for cyclotron radiation from hot plasmas with temperatures between 0.2 and 20 keV. The results are applied to the accretion columns of the AM Herculis binaries. The linear and circular polarization properties of the observed polarized light can be understood if the emission is at approximately the fifth harmonic of the cyclotron frequency. The magnetic fields in these systems is deduced to be roughly 4 x 10 to the 7th gauss.

Chanmugam, G.↗
NASA NTRS1982

Microwave rotational spectroscopy

The region of planetary atmospheres upward of 1 millimeter is considered. The applications of this region, how microwave, millimeter, and submillimeter spectra (the so called rotational spectra) can fruitfully interact with infrared spectral measurements are described. Both the rotational bands and vibrational bands of molecules are considered. A typical rotational absorption coefficient for a linear molecule in a low J state with a dipole moment of about one Debye is plotted and evaluated. A vibrational case was chosen similarly: the transition dipole moment used for the vibrational case is typical of CO at the peak of its rotational distribution. Information on high altitude parameters that often cannot be obtained from higher frequency spectra, which can be provided by rotational spectra is discussed.

Pickett, H.↗
NASA NTRS1982

Current band model studies of CH4 at wavelengths less than 2.5 microns

Band model theories are used to calculate the transmission of the methane spectrum. In a band model the monochromatic absorption coefficient over a small wavelength interval is replaced, and an average pressure coefficient is introduced. Two main types of band models were developed. The first is the 'regular' band model, in which the lines in a band are presumed evenly spaced; this is also called the Elsasser band model. In the second type of band model, the lines are randomly spaced; this is often referred to as the Mayor-Goody band model. The methane spectrum is sufficiently irregular that the second band model, the irregular band model, should apply.

Fink, U.↗
NASA NTRS1982

Ion beam sputter deposited diamond like films

A single argon ion beam source was used to sputter deposit carbon films on fused silica, copper, and tantalum substrates under conditions of sputter deposition alone and sputter deposition combined with simultaneous argon ion bombardment. Simultaneously deposited and ion bombarded carbon films were prepared under conditions of carbon atom removal to arrival ratios of 0, 0.036, and 0.71. Deposition and etch rates were measured for films on fused silica substrates. Resulting characteristics of the deposited films are: electrical resistivity of densities of 2.1 gm/cu cm for sputter deposited films and 2.2 gm/cu cm for simultaneously sputter deposited and Ar ion bombarded films. For films approximately 1700 A thick deposited by either process and at 5550 A wavelength light the reflectance was 0.2, the absorptance was 0.7, the absorption coefficient was 67,000 cm to the -1 and the transmittance was 0.1.

Banks, B. A.↗
NASA NTRS1980

User's guide for the computer code COLTS for calculating the coupled laminar and turbulent flow over a Jovian entry probe

A user's guide for a computer code 'COLTS' (Coupled Laminar and Turbulent Solutions) is provided which calculates the laminar and turbulent hypersonic flows with radiation and coupled ablation injection past a Jovian entry probe. Time-dependent viscous-shock-layer equations are used to describe the flow field. These equations are solved by an explicit, two-step, time-asymptotic finite-difference method. Eddy viscosity in the turbulent flow is approximated by a two-layer model. In all, 19 chemical species are used to describe the injection of carbon-phenolic ablator in the hydrogen-helium gas mixture. The equilibrium composition of the mixture is determined by a free-energy minimization technique. A detailed frequency dependence of the absorption coefficient for various species is considered to obtain the radiative flux. The code is written for a CDC-CYBER-203 computer and is capable of providing solutions for ablated probe shapes also.

Kumar, A.↗
NASA NTRS1982

Emission, absorption and polarization of gyrosynchrotron radiation of mildly relativistic paricles

Approximate analytic expressions for the emissivity and absorption coefficient of synchrotron radiation of mildly relativistic particles with an arbitrary energy spectrum and pitch angle distribution are given. From these, an expression for the degree of polarization is derived. To accomplish this, previously developed methods of integration are used. The analytic results are compared with numerical results for both thermal and non-thermal (power law) distributions of particles.

Petrosian, V.↗
NASA NTRS1981

The helium abundance of Jupiter from Voyager

The helium abundance in the Jovian atmosphere is derived from Voyager 1 data by two methods. The first method uses only infrared spectra from selected locations on the planet while the second method uses a thermal profile independently derived from radio occultation measurements and infrared spectra recorded near the occultation point. A hydrogen mole fraction of 0.897 plus or minus 0.030 is obtained from the first method, while the second method gives 0.880 plus or minus 0.036, corresponding to helium mass fractions of 0.19 plus or minus 0.05 and 0.21 plus or minus 0.06, respectively. The estimated errors for the first method are primarily due to systematic uncertainties in the H2 and He absorption coefficients, while those for the second method result mainly from errors in the radio occultation profile and are less well known. Random errors in the measured infrared spectra are found to be negligible in both cases. The results are consistent with a uniform mix of hydrogen and helium within Jupiter's interior, but a modest amount of helium depletion (Delta Y equal to or less than 0.05) cannot be excluded.

Gautier, D.↗
NASA NTRS1982

A two-dimensional model of the hydrogen plasma for a laser powered rocket

A two-dimensional, closed-form model originally developed by Batteh and Keefer (1974) is modified and applied to the absorption of laser radiation by a hydrogen plasma. The model is used to predict the power absorbed by plasmas at one- and ten-atmosphere pressure as a function of laser beam radius. Predicted isotherms are given for one- and ten-atmosphere plasmas, together with thermal loading of the absorption chamber wall. The model is also used in predicting the laser power required to sustain a hydrogen plasma as a function of the absorption coefficient.

Keefer, D.↗
NASA NTRS1982

Atmospheric ozone profiles from high resolution UV spectra obtained with a balloon-borne spectrometer

High resolution solar spectra at high and low sun angles are analyzed by a layer-by-layer three-wavelength differential absorption method. Ozone amounts are derived from the ratio of a low sun angle scan through a long atmosphere path to a high sun angle scan through a negligible atmosphere path. Ozone volume-mixing ratio profiles are derived and agree with standard profiles. The accuracy of the ozone profiles is found to be limited mostly by the accuracy of the ozone absorption coefficients, and suggestions are made for improving the accuracy of the results in future measurements.

Gillis, J. R.↗
NASA NTRS1982

Application of Kubelka-Munk theory of diffuse reflectance to geologic problems - The role of scattering

An understanding of the reflectance spectra of scattering media is vital for the appropriate interpretation of the reflectance spectra of planetary surfaces. When the absorption coefficient (k) and the mean size of the scattering centers are small, the Kubelka-Munk (K-M) theory of diffuse reflectance is valid. Since small values of k are characteristic of a wide variety of geologically important materials over a significant range of wavelength, the K-M theory should be applicable to appropriate portions of the reflectance spectra of these media if the dimensions of the scattering centers are sufficiently small. To test the utility of the K-M theory, a comparison is conducted of a set of theoretically generated spectra with a set of independently measured experimental spectra. The similarities found in the behavior of the two sets of spectra demonstrate the applicability of the K-M theory to the understanding of physical phenomena. Aspects of wavelength-dependent scattering are investigated.

Morris, R. V.↗
NASA NTRS1982

Effective temperatures of A and F stars

Effective temperatures of late A and early F stars are determined from the observed fluxes in the visual at 1900 A and 1420 A. The observed ratios are compared with those calculated by Kurucz (1979). A correction of the theoretical fluxes at 1900 A brings the effective temperatures obtained from different ratios into reasonable agreement. The effective temperatures determined in this way for late A stars agree well with those obtained from the optical region. For F stars, however, the effective temperatures obtained from the UV are found to be higher than those obtained from the optical region if radiative equilibrium models are used for the comparison. It is thought that this discrepancy may derive from the effects of temperature, pressure, and absorption coefficient inhomogeneities caused by convection.

Boehm-Vitense, E.↗
NASA NTRS1982

Absorptivity of water vapor for 10.6 micron radiation

Attention is called to recent measurements of the absorptivity of water vapor to 10.6-micron laser radiation made using shock-heated H2O/H2 and H2O/Ar mixtures and a probe CO2 laser. It is noted that these measurements give values about a factor of 2 lower than Ludwig's (1971) low resolution values. It is also argued that Fowler's (1981) high values are not likely to be caused by excited water molecules. It is shown that very intense laser radiation would be required to obtain any appreciable vibrational nonequilibrium. Within the narrow spectral range of 944-948/cm, no significant variation in absorption coefficient (suitably normalized) is observed as a function of laser line, water vapor concentration, total pressure, or diluent gas.

Pugh, E. R.↗
NASA NTRS1982

Effect of differential spectral reflectance on DIAL measurements using topographic targets

Differential absorption lidar (DIAL) measurements of atmospheric gases and temperature made using topographic targets to provide the backscattered signal are subject to errors from the differential spectral reflectance of the target materials. The magnitude of this effect is estimated for a number of DIAL measurements reported in the literature. Calculations are presented for several topographic targets. In general the effect on a DIAL measurement increases directly with increasing wavelength and laser line separation, and inversely with differential absorption coefficient and distance to the target. The effect can be minimized by using tunable or isotope lasers to reduce the laser line separation or by using additional reference wavelengths to determine the surface differential spectral reflectance.

Grant, W. B.↗
NASA NTRS1982

The vacuum ultraviolet spectra of HCN, C2N2, and CH3CN

Quantitative vacuum ultraviolet absorption spectra for HCN, C2N2, and CH3CN have been obtained over the wavelength range 60-160 nm. Where comparison is possible, the measurements of the absorption coefficients for HCN and C2N2 are consistent with previous studies. Because of the superior resolution of this work (0.05 nm), vibrational assignments in the valence and Rydberg transitions of HCN have been extended while higher members of the Rydberg series in CH3CN have been identified.

Nuth, J. A.↗
NASA NTRS1982

On redistribution and the equations for radiative transfer

The derivation of the equations of statistical equilibrium are outlined, starting from the quantum density-matrix equations, drawing particular attention to the approximations and assumptions used in the development of tractable expressions. Then, using the quantum-fluctuation-regression theorem, emission and absorption coefficients are obtained for multilevel atomic systems which are nondegenerate except for m-substates. These coefficients are valid to first order in the incident intensity. Possible extensions to higher intensity broadband incoherent fields are suggested.

Cooper, J.↗
NASA NTRS1982

Thickness dependences of solar cell performance

The significance of including factors such as the base resistivity loss for solar cells thicker than 100 microns and emitter and BSF layer recombination for thin cells in predicting the fill factor and efficiency of solar cells is demonstrated analytically. A model for a solar cell is devised with the inclusion of the dopant impurity concentration profile, variation of the electron and hole mobility with dopant concentration, the concentration and thermal capture and emission rates of the recombination center, device temperature, the AM1 spectra and the Si absorption coefficient. Device equations were solved by means of the transmission line technique. The analytical results were compared with those of low-level theory for cell performance. Significant differences in predictions of the fill factor resulted, and inaccuracies in the low-level approximations are discussed.

Sah, C. T.↗
NASA NTRS1983

Emission, absorption and polarization of gyrosynchrotron radiation of mildly relativistic particles

Approximate analytic expressions are presented for the emissivity and absorption coefficient of synchrotron radiation of mildly relativistic particles with an arbitrary energy spectrum and pitch angle distribution. From these, an expression for the degree of polarization is derived. The analytic results are compared with numerical results for both thermal and non-thermal (power law) distributions of particles.

Petrosian, V.↗