Spatiotemporal characteristics of deep convection initiation in the Central United States
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Stephen A. Shield↗
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Results for “initial state”
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Effects of transient pressure environments on heat transfer in one-dimensional composite slabs with contact resistance.
Transient temperature distribution in two layer one dimensional slab with initially steady state heat transfer and suddenly changed thermal contact resistances
Blum, H. A.↗
Experimental Investigation of the Mechanical Behavior of a Filled Elastomer at Pressures Below 10 to the -6th Power Torr
The mechanical behavior of a filled elastomer was studied with emphasis on understanding the vacuum-material interactions occurring, and to develop analytical techniques for predicting the vacuum behavior. The test results indicate that two separate mechanisms are involved in the observed property changes: the first controls the time response to applied stress; the second determines the initial internal state of the materials as the result of stresses. It is concluded that the mechanical property changes are attributable to changes in the relaxation processes occurring in the material. These changes are brought about by outgassing of water. Recommendations for future investigations are included.
Gregory, G. L.↗
Molecular dynamics - The dissociation of H2 by He.
The dissociation of molecular hydrogen by helium was studied at 5500 deg K using the quasiclassical approximation. The temperature-dependent reaction cross sections were very dependent on the initial quantum states of the molecule. A rate constant was estimated for the dissociation reaction, and agreement between theory and experiment was satisfactory.
Brown, N. J.↗
Pilot's manual for automated 4D guidance system
Operational procedures and modes of an experimental 4D guidance system are described from the pilot's point of view. The system consists of the experimental avionics equipment referred to as STOLAND and a specially developed software package for the STOLAND digital computer. A capture mode of the system provides arrival time control and automatic tracking of the 4D flight path from any feasible initial aircraft state to any waypoint. Precise arrival time at a waypoint is achieved by means of speed control or, if large delays are required, by path stretching. Continuous recomputation and display of the capture flight path prior to engaging the system permits the pilot to determine the exact moment for terminating a holding or path stretching maneuver in order to achieve a specified arrival time.
Erzberger, H.↗
Display requirements for the final approach and landing phase of an RPV mission
A two part investigation was conducted to determine the display requirements for the final approach and landing phase of a remotely piloted vehicle (RPV) mission, and to assess the relative merits of several possible display configurations. The objective of the first part of the investigation was to obtain subjective assessments of several display configurations, and to select the most promising display concepts for subsequent evaluation in terms of performance measures. A basic display consisting of a perspective image of terrain and runway, a horizon bar and an aircraft symbol was used, and guidance symbology was added to the basic displaying selected state variables. Initial results suggested that as guidance symbology is added to the basic display, pilot acceptance tends to increase. A point of diminishing returns is eventually reached, however, when additional information produces too much clutter, and makes it difficult for the pilot to process the displayed information.
Howard, J. C.↗
Numerical simulation of small-scale thermal convection in the atmosphere
A Boussinesq system is integrated numerically in three dimensions and time in a study of nonhydrostatic convection in the atmosphere. Simulation of cloud convection is achieved by the inclusion of parametrized effects of latent heat and small-scale turbulence. The results are compared with the cell structure observed in Rayleigh-Benard laboratory conversion experiments in air. At a Rayleigh number of 4000, the numerical model adequately simulates the experimentally observed evolution, including some prominent transients of a flow from a randomly perturbed initial conductive state into the final state of steady large-amplitude two-dimensional rolls. At Rayleigh number 9000, the model reproduces the experimentally observed unsteady equilibrium of vertically coherent oscillatory waves superimposed on rolls.
Somerville, R. C. J.↗
Experiments leading to the production of new glasses in space
A number of oxide compositions were prepared as ceramic rods which were melted in a CO2 laser beam while spinning. The molten droplets which were spun off the rods were allowed to free-fall cool. Many of the compositions selected were obtained as glasses of never-before-reported composition. It can be concluded that it is possible to obtain spherules of glasses from oxide compositions that have never before been obtained in the 'glassy state.' These initial experiments encourage future attempts to prepare larger sized glass boules by containerless melting and cooling in space or in appropriately simulated space.
Happe, R. A.↗
Ion-molecule reactions and vibrational deactivation of H2/+/ ions in mixtures of hydrogen and helium
Use of ion cyclotron resonance methods to measure the thermal energy rate constants for a number of ion-molecule reactions involving hydrogen and hydrogen-helium mixtures. Assuming that the distribution of initial vibrational states in the H2(+) ion is a near-Franck-Condon distribution, the occurrence of collisional deactivation of vibrationally excited H2(+) ions by He atoms is identified, and an approximate rate constant for the deactivation process and its dependence on vibrational energy are given.
Theard, L. P.↗
Atmospheric response to variations in sea surface temperature
An extended range prediction experiment was performed with the GISS atmospheric model on a global data to test the sensitivity of the model to sea surface temperature (SST) variation over a two-week forecast period. The use of an initial observed SST field in place of the climatological monthly mean sea temperatures for surface flux calculations in the model was found to have a significant effect on the predicted precipitation over the ocean, with enhanced convection computed over areas where moderately large warm SST anomalies are found. However, there was no detectable positive effect of the SST anomaly field on forecast quality. The influence of the SST anomalies on the daily predicted fields of pressure and geopotential is relatively insignificant up to about one week compared with the growth of prediction error, and is no greater over a two-week period than that resulting from random errors in the initial meteorological state. The 14-day average fields of sea level pressure and 500-mb height predicted by the model, appear to be similarly insensitive to anomalies of sea surface temperature.
Spar, J.↗
Thermoelastic constitutive equations for chemically hardening materials
Thermoelastic constitutive equations are derived for a material undergoing solidification or hardening as the result of a chemical reaction. The derivation is based upon a two component model whose composition is determined by the degree of hardening, and makes use of strain-energy considerations. Constitutive equations take the form of stress rate-strain rate relations, in which the coefficients are time-dependent functions of the composition. Specific results are developed for the case of a material of constant bulk modulus which undergoes a transition from an initial liquidlike state into an isotropic elastic solid. Potential applications are discussed.
Shaffer, B. W.↗
Atmospheric response to variations in sea-surface temperature
A two-week prediction experiment was performed with the GISS atmospheric model on a global data set beginning 20 December 1972 to test the sensitivity of the model to sea-surface temperature (SST) variations. Use of observed SST's in place of climatological monthly mean sea temperatures for surface flux calculations in the model was found to have a marked local effect on predicted precipitation over the ocean, with enhanced convection over warm SST anomalies. However, use of observed SST's did not lead to any detectable general improvement in forecast skill. The influence of the SST anomalies on daily predicted fields of pressure and geopotential was small up to about one week compared with the growth of prediction error, and no greater over a two-week period than that resulting from random errors in the initial meteorological state. The 14-day average fields of sea-level pressure and 500 mb height predicted by the model were similarly insensitive to the SST anomalies.
Spar, J.↗
Minima in generalized oscillator strengths for initially excited hydrogen-like atoms
Generalized oscillator strengths for transitions from an initially excited state of a hydrogenic atom to final states (either discrete or continuum) have complicated structures, including minima and shoulders, as functions of the momentum transfer. Extensive calculations carried out in the present work have revealed certain systematics of these structures. Some implications of the minima to the energy dependence of the inner-shell ionization cross section of heavy atoms by proton impact are discussed.
Matsuzawa, M.↗
Laser-induced fluorescence of CN/X2 Sigma +/ produced by photolysis of C2N2 at 160 nm
The paper reports laser-induced fluorescence measurements of the initial product state distributions of CN(X2 Sigma +) produced during the photolysis of C2N2 at a wavelength of 160 nm. The parent molecules were photodissociated by an argon flash lamp, and saturated solutions of BBD in p-dioxane were used as a laser dye to produce radiation that excited CN radicals in the (upsilon-double-prime, N-prime) vibrational-rotational sublevels of the X state to the B-state sublevels. Spectral-line identification is discussed along with the observed rotational, electronic, and vibrational energy partitionings. The effect of added buffer gas (N2 or He) on the observed product state distributions is examined in order to monitor collisional energy transfer from CN(A2 Pi, upsilon = 0) to CN(X2 Sigma +, upsilon-double-prime = 4). It is found that both buffer gases produce population inversion between the upsilon-double-prime = 4 and upsilon-double-prime = 3 levels of the X state.
Cody, R. J.↗
Accretion of rotating fluids by barytropes - Numerical results for white-dwarf models
Numerical sequences of rotating axisymmetric nonmagnetic equilibrium models are constructed which represent the evolution of a barytropic star as it accretes material from a rotating medium. Two accretion geometries are considered - one approximating accretion from a rotating cloud and the other, accretion from a Keplerian disk. It is assumed that some process, such as Ekman spin-up or nonequilibrium oscillations, maintains nearly constant angular velocity along cylinders about the rotation axis. Transport of angular momentum in the cylindrically radial direction by viscosity is included. Fluid instabilities and other physical processes leading to enhancement of this transport are discussed. Particular application is made to zero-temperature white-dwarf models, using the degenerate electron equation of state. An initially nonrotating 0.566-solar-mass white dwarf is followed during the accretion of more than one solar mass of material. Applications to degenerate stellar cores, to mass-transfer binary systems containing white dwarfs, such as novae and dwarf novae, to Type I supernovae, and to galactic X-ray sources are considered.
Durisen, R. H.↗
Charging rates of metal-dielectric structures
Metal plates partially covered by 0.01-centimeter-thick fluorinated ethylene-propylene (FEP) Teflon were charged in the Lewis Research Center's geomagnetic substorm simulation facility using 5-, 8-, 10-, and 12-kilovolt electron beams. Surface voltage as a function of time was measured for various initial conditions (Teflon discharged or precharged) with the metal plate grounded or floating. Results indicate that both the charging rates and the levels to which the samples become charged are influenced by the geometry and initial charge state of the insulating surfaces. The experiments are described and the results are presented and discussed. NASA charging analyzer program (NASCAP) models of the experiments have been generated, and the predictions obtained are described. Implications of the study results for spacecraft are discussed.
Purvis, C. K.↗
Uncontrolled dynamics of the Skylab vehicle - Comparison of simulation, theory and flight data
When the final Skylab mission was completed in 1974, the onboard systems were used to maneuver the vehicle to a gravity gradient equilibrium attitude and were then shut down. Parked in this storage attitude, the vehicle was left undisturbed until March 1978 when contact was reestablished and the control systems were reactivated. During the intervening four years, the vehicle was subjected to subtle environmental torques which caused the vehicle to gradually progress from its initial stable state to a very dynamic condition just prior to the resumption of control. The paper deals with the dynamics of this process, including the analyses and simulations which were made to explain the motion and enable the planning of the reactivation process. The complementary roles of both numerical integration and closed-form analysis are demonstrated. Flight data obtained in the spring of 1978 are presented which support the analytical and simulation results.
Buchanan, H. J.↗
Whole planet cooling and the radiogenic heat source contents of the earth and moon
Thermal evolution models based on subsolidus whole mantle convection which indicate that the surface heat flows of the earth and the moon do not necessarily provide good measures of the total amounts of radioactives in these bodies have been constructed. These models assume an initially hot state, but with a wide variety of choices for the parameters characterizing the rheology and convective vigor. All models are constrained to be consistent with present-day surface heat fluxes, and many of the terrestrial models are consistent with the mantle viscosities indicated by postglacial rebound. In the lunar models, heat generation is typically only 70-80% of the surface heat flow, even with allowance for the strong near-surface enhancement of radioactives. Despite the simplicity of these models, the persistence of a significant difference between heat generation and heat output indicates that this difference is real and should be incorporated in geochemical modeling of planets.
Schubert, G.↗