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At least 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

A second-order analytic analysis for frozen orbits

An analytical method for studying characteristics of frozen orbits using mean orbital elements is presented. By removing some of the approximations of Brouwer and Kosai (1959) and using the method of integration by parts, an analytic solution is obtained accurate to the second order in the sense of expansion of the perturbing potential of an aspherical approximation. The solution applies to orbits at and near the critical inclination as well as to frozen orbits and, of course, to unfrozen orbits. The analysis reveals that a frozen orbit can be interpreted as an orbit in which movements of the long-periodic part of the rate of change of periapsis cancels the secular part exactly at any time.

Tang, Charles C. H.↗
DOE OSTI2021

Solving puzzles in deformed JT gravity: phase transitions and non-perturbative effects

Recent work has shown that certain deformations of the scalar potential in Jackiw-Teitelboim gravity can be written as double-scaled matrix models. However, some of the deformations exhibit an apparent breakdown of unitarity in the form of a negative spectral density at disc order. We show here that the source of the problem is the presence of a multi-valued solution of the leading order matrix model string equation. While for a class of deformations we fix the problem by identifying a first order phase transition, for others we show that the theory is both perturbatively and non-perturbatively inconsistent. Aspects of the phase structure of the deformations are mapped out, using methods known to supply a non-perturbative definition of undeformed JT gravity. Some features are in qualitative agreement with a semi-classical analysis of the phase structure of two-dimensional black holes in these deformed theories.

2D gravity↗
DOE OSTI2022

Line coupling and line mixing effects on calculated widths of symmetric-top molecules with the k-degeneracy: A theoretical study of N 2 -, O 2 -, and air-broadened lines of CH 3 I

Calculations of the N 2 -, O 2 -, and air-broadened widths, together with their temperature dependence exponents have been made for transitions of CH 3 I in the ν 5 and ν 6 bands. The calculations are based on a semi-classical line shape formalism developed by the current authors through modifying and refining the Robert-Bonamy formalism. In recent years, we have applied this formalism for linear molecules, symmetric-top molecules with inversion symmetry, and asymmetric-top molecules. For symmetric-top molecules with the k degeneracy such as CH 3 I, the formalism has a new feature. In this case, one should consider each of the CH 3 I transitions labeled by k i or f ≠ 0 as a doublet. Then, one needs to consider the effects of the line mixing process between these two components. Furthermore, comparisons of our theoretical predictions with some data available demonstrate a very reasonable agreement. Finally, we propose new experiments at higher perturber pressures that would enable one to check the theoretically calculated relaxation matrices and to extend the analysis to the inter-doublet mixing effects.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1974

The chemistry and diffusion of aircraft exhausts in the lower stratosphere during the first few hours after fly-by

An analysis of the hydrogen-nitrogen-oxygen reaction systems in the lower stratosphere as they are initially perturbed by individual aircraft engine exhaust plumes was conducted in order to determine whether any significant chemical reactions occur, either among exhaust chemical species, or between these species and the environmental ozone, while the exhaust products are confined to intact plume segments at relatively high concentrations. The joint effects of diffusive mixing and chemical kinetics on the reactions were also studied, using the techniques of second-order closure diffusion/chemistry models. The focus of the study was on the larger problem of the potential depletion of ozone by supersonic transport aircraft exhaust materials emitted into the lower stratosphere.

Hilst, G. R.↗
NASA NTRS1985

Analysis of buoyancy effect on fully developed laminar heat transfer in a rotating tube

Laminar heat transfer is analyzed in a tube rotating about an axis perpendicular to the tube axis. The solution applies for flow that is either radially outward from the axis of rotation, or radially inward toward the axis of rotation. The conditions are fully developed, and there is uniform heat addition at the tube wall. The analysis is performed by expanding velocities and temperature in power series using the Taylor number as a perturbation parameter. Coriolis and buoyancy forces caused by tube rotation are included, and the solution is calculated through second-order terms. The secondary flow induced by the Coriolis terms always tends to increase the heat transfer coefficient; this effect can dominate for small wall heating. For radial inflow, buoyancy also tends to improve heat transfer. For radial outflow, however, buoyancy tends to reduce heat transfer; for large wall heating this effect can dominate, and there is a net reduction in heat transfer coefficient.

Siegel, R.↗
NASA NTRS1986

Features of stratospheric aerosol lidar observations at Mauna Loa, 1974 - 1985

Lidar observations of the stratospheric aerosol over Mauna Loa were begun in the fall of 1974 and have continued to the present. An analysis of these observations has yielded interesting features of the stratospheric aerosol profile that change according to perturbed (from volcanic activity) and quiescent conditions. In the Mauna Loa lidar record there are two major perturbations that are contrasted, Fuego and El Chichon. The variations in relative aerosol cloud thickness, altitude of the maximum concentration and nonsymmetry are compared for the quiescent and perturbed time periods. Also, a climatology of annual average aerosol profiles is descrbied. A brief description will be given of procedures used to validate the lidar optical thickness information.

Delusi, J. J.↗
NASA NTRS1987

Dynamic characteristics of a vibrating beam with periodic variation in bending stiffness

A detailed dynamic analysis is performed of a vibrating beam with bending stiffness periodic in the spatial coordinate. Using a perturbation expansion technique the free vibration solution is obtained in a closed-form, and the effects of system parameters on beam response are explored. It is found that periodic stiffness acts to modulate the modal displacements from the characteristic shape of a simple sine wave. The results are verified by a finite element solution and through experimental testing.

Townsend, John S.↗
NASA NTRS1994

Observed solar UV irradiance variations of importance to middle atmosphere energetics and photochemistry

Absorption of solar UV irradiance in the spectral interval 120-420 nm is chiefly responsible for radiative heating and photodissociation of important atmospheric constituents (e.g., O2, O3, H2O, NO2, etc.) in the stratosphere, mesosphere, and lower thermosphere. Thus, the absolute value and time perturbations of the UV irradiance could significantly affect the energetics, photochemistry, and subsequent dynamics of these regions. Analysis of preliminary data from the SOLSTICE (UARS) observations for a period of 244 days (3 Oct 1991-2 Jun 1992) is discussed in this paper. The data provide mean daily values of the spectral distribution of the observed irradiances at 1-nm resolution and their solar rotation and semirotation variations. The average amplitudes of the 27-day irradiance oscillations for the 244-day data period were 5.7% at Lyman-alpha (121 nm), 1% at 200 nm, 0.5% at 210 nm, and generally less than 0.2% at wavelengths longer than 280 nm. The average amplitudes of 13.5-day oscillations were, by and large, about half of these values. Solar irradiance variations at 10.7 cm are highly correlated with those at Ly-alpha and other chromospheric emission lines (r = 0.7 to 0.8) and only moderately correlated with irradiances at wavelengths of 180-208 nm (r = 0.5). The correlation decreases as the source region of the irradiance gets closer to the base of the photosphere. At the 2-nm interval 279-281 nm, however, which contains the cores of the Mg II h and k lines, the correlation is again approximately 0.8.

London, Julius↗
NASA NTRS2016

Trajectory Design Tools for Libration and Cis-Lunar Environments

Innovative trajectory design tools are required to support challenging multi-body regimes with complex dynamics, uncertain perturbations, and the integration of propulsion influences. Two distinctive tools, Adaptive Trajectory Design and the General Mission Analysis Tool have been developed and certified to provide the astrodynamics community with the ability to design multi-body trajectories. In this paper we discuss the multi-body design process and the capabilities of both tools. Demonstrable applications to confirmed missions, the Lunar IceCube Cubesat lunar mission and the Wide-Field Infrared Survey Telescope (WFIRST) Sun-Earth L2 mission, are presented.

Earth-Moon↗
NASA NTRS2022

Line Coupling and Line Mixing Effects on Calculated Widths of Symmetric-Top Molecules With the k-Degeneracy: A Theoretical Study of N 2 -, O 2 -, and Air-Broadened Lines of CH 3 I

Calculations of the N 2 -, O 2 - and air-broadened widths, together with their temperature dependence exponents have been made for transitions of CH 3 I in the v 5 and v 6 bands. The calculations are based on a semi-classical line shape formalism developed by the current authors through modifying and refining the Robert-Bonamy formalism. In recent years, we have applied this formalism for linear molecules, symmetric-top molecules with inversion symmetry, and asymmetric-top molecules. For symmetric-top molecules with the k degeneracy such as CH 3 I, the formalism has a new feature. In this case, one should consider each of the CH 3 I transitions labeled by k i or ƒ ≠ 0 as a doublet. Then, one needs to consider the effects of the line mixing process between these two components. Comparisons of our theoretical predictions with some data available demonstrate a very reasonable agreement. Finally we propose new experiments at higher perturber pressures that would enable one to check the theoretically calculated relaxation matrices and to extend the analysis to the interdoublet mixing effects.

Line coupling↗
NASA NTRSDate not supplied

Thermomechanical Relaxation of Vibrationally Excited NO in a Hypersonic Turbulent Boundary Layer

The effects of thermal nonequilibrium are studied using a DC glow discharge plasma to selectively modify the vibrational temperature of an otherwise cold flow. These experiments were performed at 𝑴=5.7and 𝑹𝒆=6×10 6 /m in the Actively Controlled Expansion tunnel at Texas A&M University on a canonical 2.75° half-angle wedge test article. A∼47 W plasma was generated across spanwise electrodes, and removable trips produced either a laminar or turbulent boundary layer. NO planar laser-induced fluorescence (PLIF) quantified the extent of the NO 𝑿 2 𝚷 (𝒗=1) vibrational perturbation due to the plasma and its subsequent interplay with the boundary layer, the first such data of which the authors are aware. NOPLIF measurements were taken at three locations along the test article, and quasi-temperature measurements are reported at each. Despite not quantifiably perturbing the boundary layer, the plasma was shown to alter the NO vibrational temperature profile therein. Independent analysis of the thermodynamics and fluid mechanics of the system suggests each set of physics could explain the results observed near and far from the wall, respectively.

Casey J. Broslawski↗
NASA NTRSDate not supplied

Thermomechanical Relaxation of Vibrationally Excited NO in a Hypersonic Turbulent Boundary Layer

The effects of thermal nonequilibrium are studied using a DC glow discharge plasma to selectively modify the vibrational temperature of an otherwise cold flow. These experiments were performed at 𝑴=5.7and 𝑹𝒆=6×10 6 /m in the Actively Controlled Expansion tunnel at Texas A&M University on a canonical 2.75° half-angle wedge test article. A∼47 W plasma was generated across spanwise electrodes, and removable trips produced either a laminar or turbulent boundary layer. NO planar laser-induced fluorescence (PLIF) quantified the extent of the NO 𝑿 2 𝚷 (𝒗=1) vibrational perturbation due to the plasma and its subsequent interplay with the boundary layer, the first such data of which the authors are aware. NOPLIF measurements were taken at three locations along the test article, and quasi-temperature measurements are reported at each. Despite not quantifiably perturbing the boundary layer, the plasma was shown to alter the NO vibrational temperature profile therein. Independent analysis of the thermodynamics and fluid mechanics of the system suggests each set of physics could explain the results observed near and far from the wall, respectively.

Casey J. Broslawski↗
NASA NTRS1984

Methodology for predictive testing of fuel cells

A perturbation testing method has been developed and tested for predictive testing of fuel cells. This method involves application of small changes to the operating conditions of the cell in a predetermined sequence. The resultant response of the cell is then measured and statistically correlated with the corresponding test conditions. This method has been applied to the phosphoric acid fuel cell, and the effect of operating and cell-component variables on cell-performance degradation has been studied. A strong effect of the cell temperature and cathode potential on fuel-cell-performance degradation has been observed. A cell-performance degradation model has been formulated, and the unknown parameters in the model have been estimated by a regression analysis of the experimental data. A reasonable agreement between the fuel cell performance predicted by this model (derived from the perturbation experiments) and the unperturbed test data supports fthe applicability of the perturbation method.

Patel, D. N.↗
NASA NTRS1980

Properties of African squall lines inferred from time-lapse satellite imagery

Analysis of 48 h of time-lapse satellite imagery of a family of squall lines in Africa links the phenomena with a characteristic cloud cluster and with a wind field perturbation which is enhanced in passing through an African easterly wave trough. A thin 'arc line' of low-level developing cumulus, a salient feature of the squall lines on the imagery, is shown to occur at the front boundary of the mesoscale/convective scale subsidence. Analysis of the wind field indicates that a squall line is associated with a vorticity center in the mid-level easterly flow which accompanies the mesoscale subsidence which, in turn, contributes to further forced ascent of subcloud air along the front of the squall line into convective towers which merge into an extensive anvil. The squall lines evolved through a life cycle of 6 to 12 h while the larger cloud cluster and wind perturbation lasted over 48 h. The magnitude of the vertical mass exchange suggests that squall-line families contribute significantly to the tropical energy balance.

Fortune, M.↗
NASA NTRS1986

Physical optics analysis of a four-reflector antenna, part 1

Concern has been raised for the 64-m to 70-m antenna upgrade project that the 70-m system may experience greater S-band beam-pointing perturbations than the 64-m system. The S-band perturbations are due to minor (higher order) mode generation, causing subtle cross-polarization fields affecting beam pointing direction, as described herein. For the antennas in their present configuration (64 m), a slight S-band gain degradation of about 0.05 dB can be attributed to these effects. Therefore, a full physical optics analysis was performed for the present-day 64-m system, as described herein. The results were compared with past analyses and experimental observations in order to verify the algebra and computer code with the intent of deriving a valid analysis method for accurately analyzing the 70-m shaped dual reflector Cassegrainian antenna. The results of the new analysis appear to be in excellent agreement with previous analyses and experimental data.

Cha, A. G.↗
NASA NTRS1980

Determination of the total grain size distribution in a vulcanian eruption column, and its implications to stratospheric aerosol perturbation

The total grain distribution of tephra from the eruption by the Fuego volcano in Guatemala on Oct. 14, 1974 was determined by grain size analysis. The region within each isopach has a grain distribution which was weighted proportionally to its percentage volume; the total distribution had a median grain size of 0.6 mm and a sorting coefficient of 2.3. The ash composed of fine particles did not fall in the volcano area as part of the recognizable tephra blanket; the eruption column reached well into the stratosphere to the height of 10-12 km above sea level, with mass flux rate estimated altitudes of 18-23 km

Murrow, P. J.↗
NASA NTRS1985

Linear analysis of an axially grooved rectangular gyrotron for harmonic operation

In an axially grooved rectangular waveguide the linearized Vlasov equation is solved to find the perturbed distribution function resulting from the electromagnetic forces on the electrons. The resulting beam current and the propagating electromagnetic waves of the cold tube are used in the inhomogeneous Maxwell's equation to derive the general dispersion equation. This equation is then transformed into the electron beam frame and the resulting linear growth rate of amplification is calculated. By maximizing the linear growth rate, the operational parameters of the gyrotron are then optimized.

Ferendeci, A. M.↗