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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

The Synchrotron Low-energy Spectrum Arising from the Cooling of Electrons in Gamma-Ray Bursts

This work is a continuation of a previous effort (Panaitescu) to study the cooling of relativistic electrons through radiation (synchrotron and self-Compton) emission and adiabatic losses, with application to the spectra and light curves of the synchrotron gamma-ray burst (GRB) produced by such cooling electrons. Here, we derive the low-energy slope β LE of a GRB pulse-integrated spectrum and quantify the implications of the measured distribution of β LE . Radiative processes that produce soft integrated spectra can accommodate the harder slopes measured by CGRO/BATSE and Fermi/GBM only if the magnetic field lifetime t B is shorter than the time during which the typical GRB electrons cool to radiate below 1–10 keV, which is less than (at most) 10 radiative cooling timescales t rad of the typical GRB electron. In this case, there is a one-to-one correspondence between t B and β LE . To account for low-energy slopes β LE > -3/4, the adiabatic electron-cooling requires a similar restriction on t B . In this case, the diversity of slopes arises mostly from how the electron-injection rate varies with time (temporal power-law injection rates yield power-law low-energy GRB spectra) and not from the magnetic field timescale.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1974

Birefringing arising from the reorientation of the polarizability anisotropy of molecules in collisionless gases

The refractive index change in a collisionless gas is evaluated from the Stark shifts of the rotational energy levels that arise from the polarizability anisotropy. For the limit of an extremely short-duration excitation, a multilevel coherent effect resulted in delayed refractive index bursts. Both stationary and transient responses of this birefringence to an optical field were considered for symmetric top molecules, with particular emphasis on the special case of linear molecules.

Lin, C. H.↗
NASA NTRS1975

Fate in humans of the plasticizer, DI (2-ethylhexyl) phthalate, arising from transfusion of platelets stored in vinyl plastic bags

Platelet concentrates were shown to contain 18-38 mg/100 ml of a phthalate plasticizer (DEHP) which arose by migration from the vinyl plastic packs in which the plateletes were prepared and stored. Transfusion of these platelets into 6 adult patients with leukemia resulted in peak blood plasma levels of DEHP ranging from 0.34 - 0.83 mg/100 ml. The blood levels fell mono-exponentially with a mean rate of 2.83 percent per minute and a half-life of 28.0 minutes. Urine was assayed by a method that would measure unchanged DEHP as well as all phthalic acid-containing metabolities. In two patients, at most 60 and 90% of the infused dose, respectively, was excreted in the urine collected for 24 hours post-transfusion. These estimates, however, could be high due to the simultaneous excretion of DEHP remaining from previous transfusions or arising from uncontrolled environmental exposures.

Rubin, R. J.↗
NASA NTRS1976

Birefringence arising from the reorientation of the polarizability anisotropy of molecules in collisionless gases

The refractive-index change in a collisionless gas is evaluated from the Stark shifts of the rotational energy levels that arise from the polarizability anisotropy. In the limit of an extremely-short-duration excitation, a multilevel coherent effect results in delayed refractive-index bursts. Both stationary and transient responses of this birefringence to an optical field are considered for symmetric-top molecules, with particular emphasis on the special case of linear molecules.

Lin, C. H.↗
NASA NTRS1978

Numerical solution of a class of integral equations arising in two-dimensional aerodynamics

We consider the numerical solution of a class of integral equations arising in the determination of the compressible flow about a thin airfoil in a ventilated wind tunnel. The integral equations are of the first kind with kernels having a Cauchy singularity. Using appropriately chosen Hilbert spaces, it is shown that the kernel gives rise to a mapping which is the sum of a unitary operator and a compact operator. This allows the problem to be studied in terms of an equivalent integral equation of the second kind. A convergent numerical algorithm for its solution is derived by using Galerkin's method. It is shown that this algorithm is numerically equivalent to Bland's collocation method, which is then used as the method of computation. Extensive numerical calculations are presented establishing the validity of the theory.

Fromme, J.↗
NASA NTRS1980

An assessment of the risk arising from electrical effects associated with carbon fibers released from commercial aircraft fires

The risks associated with electrical effects arising from carbon fibers released from commercial aviation aircraft fires were estimated for 1993. The expected annual losses were estimated to be about $470 (1977 dollars) in 1993. The chances of total losses from electrical effects exceeding $100,000 (1977 dollars) in 1993 were established to be about one in ten thousand.

Kalelkar, A. S.↗
NASA NTRS1984

On the X-ray spectrum of the volume emissivity arising from Abell clusters

HEAO 1 A-2 X-ray spectra (2-15 keV) for an optically selected sample of Abell clusters of galaxies with z less than 0.1 have been analyzed to determine the energy dependence of the cosmological X-ray volume emissivity arising from such clusters. This spectrum is well fitted by an isothermal-bremsstrahlung model with kT = 7.4 + or - 1.5 KeV. This result is a test of the isothermal-volume-emissivity spectrum to be inferred from the conjecture that all contributing clusters may be characterized by kT = 7 keV, as assumed by McKee et al. (1980) in estimating the underlying luminosity function for the same sample. Although satisfied at the statistical level indicated, the analysis of a low-luminosity subsample suggests that this assumption of identical isothermal spectra would lead to a systematic error for a more statistically precise determination of the luminosity function's form.

Stottlemyer, A. R.↗
NASA NTRS1987

Numerical methods for one-dimensional reaction-diffusion equations arising in combustion theory

A review of numerical methods for one-dimensional reaction-diffusion equations arising in combustion theory is presented. The methods reviewed include explicit, implicit, quasi-linearization, time linearization, operator-splitting, random walk and finite-element techniques and methods of lines. Adaptive and nonadaptive procedures are also reviewed. These techniques are applied first to solve two model problems which have exact traveling wave solutions with which the numerical results can be compared. This comparison is performed in terms of both the wave profile and computed wave speed. It is shown that the computed wave speed is not a good indicator of the accuracy of a particular method. A fourth-order time-linearized, Hermitian compact operator technique is found to be the most accurate method for a variety of time and space sizes.

Ramos, J. I.↗
NASA NTRS1988

Boundary identification for 2-D parabolic problems arising in thermal testing of materials

Problems on the identification of two-dimensional spatial domains arising in the detection and characterization of structural flaws in materials are considered. For a thermal diffusion system with external boundary input, observations of the temperature on the surface are used in an output least square approach. Parameter estimation techniques based on the method of mappings are discussed, and approximation schemes are developed based on a finite-element Galerkin approach. Theoretical convergence results for computational techniques are given, and the results are applied to the identification of two kinds of boundary shapes.

Banks, H. T.↗
NASA NTRS1989

Boundary estimation problems arising in thermal tomography

Problems on the identification of two-dimensional spatial domains arising in the detection and characterization of structural flaws in materials are considered. For a thermal diffusion system with external boundary input, observations of the temperature on the surface are used in a output least squares approach. Parameter estimation techniques based on the method of mappings are discussed and approximation schemes are developed based on a finite element Galerkin approach. Theoretical convergence results for computational techniques are given and the results are applied to experimental data for the identification of flaws in the thermal testing of materials.

Banks, H. T.↗
NASA NTRS1991

Optical glow spectra arising from low-energy N2, N2(+) and electron bombardment of MgF2 surfaces

Photon emission spectra resulting from the impact of N2, N2(+), and electron beams on magnesium fluoride in an ultrahigh vacuum environment were measured and compared for beam energies in the range 200-2000 eV. Unexpectedly, only the ion- and electron-induced spectra exhibited broad fluorescence. The observed data suggest that the broad fluorescence arising from low-energy ion bombardment is due primarily to the transfer of electronic energy to the surface by resonance or Auger neutralization. Since molecular nitrogen is a major constituent of the atmosphere at orbital altitudes, these measurements bear directly on radiation-induced glow and erosion processes on surfaces of spacecraft in low-earth orbit.

Qi, J.↗