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Results for “Kinetic parameters”

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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Introductory study of the chemical behavior of jet emissions in photochemical smog

Jet aircraft emissions data from the literature were used as initial conditions for a series of computer simulations of photochemical smog formation in static air. The chemical kinetics mechanism used in these simulations was an updated version which contains certain parameters designed to account for hydrocarbon reactivity. These parameters were varied to simulate the reaction rate constants and average carbon numbers associated with the jet emissions. The roles of surface effects, variable light sources, NO/NO2 ratio, continuous emissions, and untested mechanistic parameters were also assessed. The results of these calculations indicate that the present jet emissions are capable of producing oxidant by themselves. The hydrocarbon/nitrous oxides ratio of present jet aircraft emissions is much higher than that of automobiles. These two ratios appear to bracket the hydrocarbon/nitrous oxides ratio that maximizes ozone production. Hence an enhanced effect is seen in the simulation when jet exhaust emissions are mixed with automobile emissions.

Whitten, G. Z.↗
NASA NTRS1990

Growth morphology with anisotropic surface kinetics

The morphological evolution of crystals growing from an incongruent vapor phase is studied using a Monte Carlo model, and the full range of growth morphologies is recovered. The diffusion in the bulk nutrient and the anisotropy in the interface kinetics are morphologically destabilizing and stabilizing, respectively. For a given set of simulation parameters and lattice symmetries there is a critical size, which scales linearly with the mean free path in the vapor, beyond which a crystal cannot retain its stable, macroscopically faceted growth shape. Surface diffusion stabilizes faceted growth on the shorter scale of the mean surface diffusion length. In simulations with a uniform drift superimposed on the random walk nutrient transport, crystal faces oriented toward the drift show enhanced morphological stability compared to the purely diffusive situation. Rotational drifts with periodic reversal of direction are morphologically stabilizing for all crystal facets.

Xiao, Rong-Fu↗
NASA NTRS1991

Kinetic friction attributed to enhanced radiation by cyclotron maser instability

Along the auroral field lines, a fraction of the energetic electrons injected from the magnetotail is reflected by the earth's convergent geomagnetic field. The reflected loss-cone electrons are unstable with respect to the cyclotron maser instability, resulting in the auroral kilometric radiation. This paper investigates the kinetic friction force exerted on the energetic electrons by the enhanced radiation field. It is found that the enhanced radiation results in a deceleration of reflected electrons, thereby providing an effective resistivity. In addition, the rate of decrease (increase) of effective perpendicular (parallel) kinetic temperatures is also evaluated. The analysis is carried out over various physical parameters such as the degree of loss cone, average particle energy, and the ratio of plasma frequency to cyclotron frequency.

Yoon, Peter H.↗
NASA NTRS1957

Analysis of efficiency characteristics of a single-stage turbine with downstream stators in terms of work and speed requirements

One-dimensional mean-section flow and blade specific losses proportional to average specific kinetic energy are assumed in the analysis. Range of the work-speed parameter lambda considered includes low to moderate blade speeds with high specific work outputs, where critical turbojet, turbopump, and accessory-drive turbines are encountered. A diffusion factor of 0.5 limits the loading on the downstream stators. Turbine efficiences considered are total or aerodynamic, rating, and static. Efficiences of velocity-diagram types at impulse and that corresponding to values of maximum efficiency are presented and compared to indicate in what range of lambda downstream stators are beneficial as well as the attending improvements in efficiency.

Wintucky, William T↗
NASA NTRS1994

Assessment of velocity/trajectory measurement technologies during a particle capture event

Since the early 1960s, the means to measure the time of flight (TOF) of dust grain within a mechanical detection array has existed, first in the laboratory and then in space experiments. Laboratory hypervelocity dust particle accelerators have used electrostatic detection of charge on accelerated particles for TOF and particle mass detections. These laboratory studies have led to the development of ultra-thin-film sensors that have been used for TOF measurements in dust particle space experiments. The prototypes for such devices were ultra-thin-film capacitors that were used in the OGO series of satellites. The main goal of the experimental work to be described is the development of the capability to determine the velocity vector or trajectory of a dust grain traversing an integrated dust detection array. The results of these studies have shown that the capability of detecting the charge liberated by hypervelocity dust grains with diameters in the micrometer range can be detected. Based on these results, detection systems have been designed to provide a precise analysis of the physical and dynamic properties of micrometer and submicrometer dust grains, namely the design verification unit (DVU). Through unique combinations of in situ detection systems, direct measurements of particle surface charge, velocity, momentum, kinetic energy, and trajectory have been achieved. From these measurements, the remaining physical parameters of mass, size, and density can be determined.

Tanner, William G.↗
NASA NTRS1997

Physiological Response of Plants Grown on Porous Ceramic Tubes

This research involves the manipulation of the root-zone water potential for the purposes of discriminating the rate limiting step in the inorganic nutrient uptake mechanism utilized by higher plants. This reaction sequence includes the pathways controlled by the root-zone conditions such as water tension and gradient concentrations. Furthermore, plant based control mechanisms dictated by various protein productions are differentiated as well. For the nutrients limited by the environmental availability, the kinetics were modeled using convection and diffusion equations. Alternatively, for the nutrients dependent upon enzyme manipulations, the uptakes are modeled using Michaelis-Menten kinetics. In order to differentiate between these various mechanistic steps, an experimental apparatus known as the Porous Ceramic Tube - Nutrient Delivery System (PCT-NDS) was used. Manipulation of the applied suction pressure circulating a nutrient solution through this system imposes a change in the matric component of the water potential. This compensates for the different osmotic components of water potential dictated by nutrient concentration. By maintaining this control over the root-zone conditions, the rate limiting steps in the uptake of the essential nutrients into tomato plants (Lycopersicon esculentum cv. Cherry Elite) were differentiated. Results showed that the uptake of some nutrients were mass transfer limited while others were limited by the enzyme kinetics. Each of these were adequately modeled with calculations and discussions of the parameter estimations provided.

Tsao, David↗
NASA NTRS2017

Spacecraft Mission Design for the Mitigation of the 2017 PDC Hypothetical Asteroid Threat

This paper presents a detailed mission design analysis results for the 2017 Planetary Defense Conference (PDC) Hypothetical Asteroid Impact Scenario, documented at https://cneos.jpl.nasa.gov/ pd/cs/pdc17/. The mission design includes campaigns for both reconnaissance (flyby or rendezvous) of the asteroid (to characterize it and the nature of the threat it poses to Earth) and mitigation of the asteroid, via kinetic impactor deflection, nuclear explosive device (NED) deflection, or NED disruption. Relevant scenario parameters are varied to assess the sensitivity of the design outcome, such as asteroid bulk density, asteroid diameter, momentum enhancement factor, spacecraft launch vehicle, and mitigation system type. Different trajectory types are evaluated in the mission design process from purely ballistic to those involving optimal midcourse maneuvers, planetary gravity assists, and/or lowthrust solar electric propulsion. The trajectory optimization is targeted around peak deflection points that were found through a novel linear numerical technique method. The optimization process includes constrain parameters, such as Earth departure date, launch declination, spacecraft/asteroid relative velocity and solar phase angle, spacecraft dry mass, minimum/maximum spacecraft distances from Sun and Earth, and Earth/spacecraft communications line of sight. Results show that one of the best options for the 2017 PDC deflection is solar electric propelled rendezvous mission with a single spacecraft using NED for the deflection

Barbee, Brent W.↗
NASA NTRS2017

Spacecraft Mission Design for the Mitigation of the 2017 PDC Hypothetical Asteroid Threat

This paper presents a detailed mission design analysis results for the 2017 Planetary Defense Conference (PDC) Hypothetical Asteroid Impact Scenario, documented at https:cneos.jpl.nasa.govpdcspdc17. The mission design includes campaigns for both reconnaissance (flyby or rendezvous) of the asteroid (to characterize it and the nature of the threat it poses to Earth) and mitigation of the asteroid, via kinetic impactor deflection, nuclear explosive device (NED) deflection, or NED disruption. Relevant scenario parameters are varied to assess the sensitivity of the design outcome, such as asteroid bulk density, asteroid diameter, momentum enhancement factor, spacecraft launch vehicle, and mitigation system type. Different trajectory types are evaluated in the mission design process from purely ballistic to those involving optimal midcourse maneuvers, planetary gravity assists, and/or low-thrust solar electric propulsion. The trajectory optimization is targeted around peak deflection points that were found through a novel linear numerical technique method. The optimization process includes constrain parameters, such as Earth departure date, launch declination, spacecraft, asteroid relative velocity and solar phase angle, spacecraft dry mass, minimum/maximum spacecraft distances from Sun and Earth, and Earth-spacecraft communications line of sight. Results show that one of the best options for the 2017 PDC deflection is solar electric propelled rendezvous mission with a single spacecraft using NED for the deflection.

Barbee, Brent W.↗
NASA NTRS1989

Nonlinear evolution of the auroral electron beam

The nonlinear spatial evolution, from the source to the atmosphere, of the auroral electron beam and the beam-generated electrostatic whistler noise was studied, calculating changes in beam parameters from equations for the conservation of total particle and wave energy and momentum flux density. Wave power fluxes were calculated by numerically integrating the wave kinetic equations, and the levels of beam-generated noise were determined by using thermal levels of Cerenkov radiation as a source. It was found that beam parameters evolve on ionospheric scale lengths, and their positive slope feature in velocity space is maintained over altitudes measured in thousands of kilometers of altitude, even though they can generate wave energy density fluxes sufficient to modify the ionospheric density profile.

Maggs, James E.↗
NASA NTRS1972

Real-air data reduction procedures based on flow parameters measured in the test section of supersonic and hypersonic facilities

Data-reduction procedures for determining free stream and post-normal shock kinetic and thermodynamic quantities are derived. These procedures are applicable to imperfect real air flows in thermochemical equilibrium for temperatures to 15 000 K and a range of pressures from 0.25 N/sq m to 1 GN/sq m. Although derived primarily to meet the immediate needs of the 6-inch expansion tube, these procedures are applicable to any supersonic or hypersonic test facility where combinations of three of the following flow parameters are measured in the test section: (1) Stagnation pressure behind normal shock; (2) freestream static pressure; (3) stagnation point heat transfer rate; (4) free stream velocity; (5) stagnation density behind normal shock; and (6) free stream density. Limitations of the nine procedures and uncertainties in calculated flow quantities corresponding to uncertainties in measured input data are discussed. A listing of the computer program is presented, along with a description of the inputs required and a sample of the data printout.

Miller, C. G., III↗
NASA NTRS1982

The isotopes of H through C in galactic cosmic rays

The charge, energy spectra, and isotopic composition of hydrogen through nitrogen have been studied with the GSFC/UNH cosmic ray experiments on board the Pioneer 10 and 11 spacecraft. Good charge and mass resolution have been obtained by utilizing three parameter analysis (i.e., two measurements of delta E and a measurement of the residual kinetic energy of stopping particles). This method allows isotopic resolution for the High Energy Telescope (HET) which operates over a typical energy range of 30-56-MeV/nuc for He. The observations will be over solar quiet times from September 1976-September 1977. The resolution, methods of analysis, spectra, and isotopic composition will be presented and discussed where the statistical significance of H to C isotopes is meaningful.

Smith, B.↗
NASA NTRS1983

The molten carbonate carbon dioxide concentrator - Cathode performance at high CO2 utilization

An experimental study of the cathode performance of the molten carbonate carbon dioxide concentrator (MCCDC) at typical gas concentrations is reported, and the behavior is described in terms of standard electrochemical kinetic analysis. Theoretical aspects of the MCCDC are discussed, including the current-generating processes, the overpotential, and the reaction kinetics. A final working equation is derived, and the electrochemical cell is described. The parameters determined by the experiments include cathode overpotentials and removal and current efficiency as a function of current density, as well as carbon dioxide removal rate as a function of flow rate. The results are compared with data for other cells; the agreement with data for the molten carbonate fuel cell suggests that the major difference between the two cells is in the wetting characteristics. The MCCDC achieves high removal efficiencies at high current efficiencies. The lowest current efficiency recorded was 80 percent, and at most current densities, current efficiencies were above 100 percent.

Weaver, J. L.↗
NASA NTRS1993

Electromagnetically driven relativistic jets - A class of self-consistent numerical solutions

We explore the generalized Grad-Shafranov (GS) equation (Lovelace et al. 1986), which describes the cross-field balance of the magnetic flux surfaces in a stationary, axisymmetric, cold relativistic MHD wind. We construct a family of self-consistent, jet-type, non-self-similar solutions in which flux surfaces thread the equatorial plane vertically and are eventually collimated into nested cylinders. These solutions conserve the total energy and angular momentum along each flux surface and satisfy the relativistic GS equation in the cross-field direction. We find that the total specific energy in the flow depends primarily on a dimensionless combination of the poloidal magnetic flux, the rotation, and the mass loading rate, which reduces to Michel's (1969) magnetization parameter for radial winds. The final width of the flow and its ratio of kinetic energy flux to Poynting flux depend sensitively on the pressure distribution of the ambient medium, which is required to contain the jet at its outer edge when no jet-confirming external toroidal magnetic field is present. Furthermore, we show that the magnetic pressure in the flow can be much higher near the axis than close to the edge, reflecting the 'pinching' effect of the toroidal magnetic field.

Li, Zhi-Yun↗
NASA NTRS2000

DyFK Simulation of Field-Aligned Ion Flows Observed by POLAR within Convecting Flux Over the Polar Ionosphere

Ion (O+ and H+) parallel flows along antisunward convecting flux tubes across the polar ionosphere from day to night side are simulated by an extended Dynamic Fluid semiKinetic (DyFK) model. The collision dominated portion of the flux tubes is treated with a moment-based fluid model for altitudes from 120 ?1100 km, while the generalized semikinetic model is used for the topside through 3 RE region. The effects of cleft/auroral soft electron precipitation and wave-driven transverse ion heating are incorporated into the generalized semi-kinetic treatment of topside ionosphere. The simulated evolution of field-aligned ion flow parameters is compared with observations made by the Thermal Ion Dynamics Experiment (TIDE) on board the POLAR satellite near 5000 km altitude over the southern hemisphere polar ionosphere.

Tu, J.-N.↗
NASA NTRS2003

Many-Body Effects in Quantum-Well Intersubband Transitions

Intersubband polarization couples to collective excitations of the interacting electron gas confined in a semiconductor quantum well (Qw) structure. Such excitations include correlated pair excitations (repellons) and intersubband plasmons (ISPs). The oscillator strength of intersubband transitions (ISBTs) strongly varies with QW parameters and electron density because of this coupling. We have developed a set of kinetic equations, termed the intersubband semiconductor Bloch equations (ISBEs), from density matrix theory with the Hartree-Fock approximation, that enables a consistent description of these many-body effects. Using the ISBEs for a two-conduction-subband model, various many-body effects in intersubband transitions are studied in this work. We find interesting spectral changes of intersubband absorption coefficient due to interplay of the Fermi-edge singularity, subband renormalization, intersubband plasmon oscillation, and nonparabolicity of bandstructure. Our results uncover a new perspective for ISBTs and indicate the necessity of proper many-body theoretical treatment in order for modeling and prediction of ISBT line shape.

Li, Jian-Zhong↗
NASA NTRS2013

Athermal Energy Loss from X-rays Deposited in Thin Superconducting Films on Solid Substrates

When energy is deposited in a thin-film cryogenic detector, such as from the absorption of an X-ray, an important feature that determines the energy resolution is the amount of athermal energy that can be lost to the heat bath prior to the elementary excitation systems coming into thermal equilibrium. This form of energy loss will be position-dependent and therefore can limit the detector energy resolution. An understanding of the physical processes that occur when elementary excitations are generated in metal films on dielectric substrates is important for the design and optimization of a number of different types of low temperature detector. We have measured the total energy loss in one relatively simple geometry that allows us to study these processes and compare measurements with calculation based upon a model for the various di.erent processes. We have modeled the athermal phonon energy loss in this device by finding an evolving phonon distribution function that solves the system of kinetic equations for the interacting system of electrons and phonons. Using measurements of device parameters such as the Debye energy and the thermal di.usivity we have calculated the expected energy loss from this detector geometry, and also the position-dependent variation of this loss. We have also calculated the predicted impact on measured spectral line-shapes, and shown that they agree well with measurements. In addition, we have tested this model by using it to predict the performance of a number of other types of detector with di.erent geometries, where good agreement is also found.

Kozorezov, Alexander G.↗
NASA NTRS1986

The role of impulse parameters in force variability

One of the principle limitations of the human motor system is the ability to produce consistent motor responses. When asked to repeatedly make the same movement, performance outcomes are characterized by a considerable amount of variability. This occurs whether variability is expressed in terms of kinetics or kinematics. Variability in performance is of considerable importance because for tasks requiring accuracy it is a critical variable in determining the skill of the performer. What has long been sought is a description of the parameter or parameters that determine the degree of variability. Two general experimental protocals were used. One protocal is to use dynamic actions and record variability in kinematic parameters such as spatial or temporal error. A second strategy was to use isometric actions and record kinetic variables such as peak force produced. What might be the important force related factors affecting variability is examined and an experimental approach to examine the influence of each of these variables is provided.

Carlton, L. G.↗