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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Biochemical Kinetics Model of DSB Repair and GammaH2AX FOCI by Non-homologous End Joining

We developed a biochemical kinetics approach to describe the repair of double strand breaks (DSB) produced by low LET radiation by modeling molecular events associated with the mechanisms of non-homologous end-joining (NHEJ). A system of coupled non-linear ordinary differential equations describes the induction of DSB and activation pathways for major NHEJ components including Ku(sub 70/80), DNA-PK(sub cs), and the Ligase IV-XRCC4 hetero-dimer. The autophosphorylation of DNA-PK(sub cs and subsequent induction of gamma-H2AX foci observed after ionizing radiation exposure were modeled. A two-step model of DNA-PK(sub cs) regulation of repair was developed with the initial step allowing access of other NHEJ components to breaks, and a second step limiting access to Ligase IV-XRCC4. Our model assumes that the transition from the first to second-step depends on DSB complexity, with a much slower-rate for complex DSB. The model faithfully reproduced several experimental data sets, including DSB rejoining as measured by pulsed-field electrophoresis (PFGE), quantification of the induction of gamma-H2AX foci, and live cell imaging of the induction of Ku(sub 70/80). Predictions are made for the behaviors of NHEJ components at low doses and dose-rates, where a steady-state is found at dose-rates of 0.1 Gy/hr or lower.

Cucinotta, Francis, A.↗
NASA NTRS1985

The cleft ion fountain - A two-dimensional kinetic model

The transport of ionospheric ions from a source in the polar cleft ionosphere through the polar magnetosphere is investigated using a two-dimensional, kinetic, trajectory-based code. The transport model includes the effects of gravitation, longitudinal magnetic gradient force, convection electric fields, and parallel electric fields. Individual ion trajectories as well as distribution functions and resulting bulk parameters of density, parallel average energy, and parallel flux for a presumed cleft ionosphere source distribution are presented for various conditions to illustrate parametrically the dependences on source energies, convection electric field strengths, ion masses, and parallel electric field strengths. The essential features of the model are consistent with the concept of a cleft-based ion fountain supplying ionospheric ions to the polar magnetosphere, and the resulting plasma distributions and parameters are in general agreement with recent low-energy ion measurements from the DE 1 satellite.

Horwitz, J. L.↗
NASA NTRS1996

On Kinetics Modeling of Vibrational Energy Transfer

Two models of vibrational energy exchange are compared at equilibrium to the elementary vibrational exchange reaction for a binary mixture. The first model, non-linear in the species vibrational energies, was derived by Schwartz, Slawsky, and Herzfeld (SSH) by considering the detailed kinetics of vibrational energy levels. This model recovers the result demanded at equilibrium by the elementary reaction. The second model is more recent, and is gaining use in certain areas of computational fluid dynamics. This model, linear in the species vibrational energies, is shown not to recover the required equilibrium result. Further, this more recent model is inconsistent with its suggested rate constants in that those rate constants were inferred from measurements by using the SSH model to reduce the data. The non-linear versus linear nature of these two models can lead to significant differences in vibrational energy coupling. Use of the contemporary model may lead to significant misconceptions, especially when integrated in computer codes considering multiple energy coupling mechanisms.

Gilmore, John O.↗
NASA NTRS2011

Merging for Particle-Mesh Complex Particle Kinetic Modeling of the Multiple Plasma Beams

We suggest a merging procedure for the Particle-Mesh Complex Particle Kinetic (PMCPK) method in case of inter-penetrating flow (multiple plasma beams). We examine the standard particle-in-cell (PIC) and the PMCPK methods in the case of particle acceleration by shock surfing for a wide range of the control numerical parameters. The plasma dynamics is described by a hybrid (particle-ion-fluid-electron) model. Note that one may need a mesh if modeling with the computation of an electromagnetic field. Our calculations use specified, time-independent electromagnetic fields for the shock, rather than self-consistently generated fields. While a particle-mesh method is a well-verified approach, the CPK method seems to be a good approach for multiscale modeling that includes multiple regions with various particle/fluid plasma behavior. However, the CPK method is still in need of a verification for studying the basic plasma phenomena: particle heating and acceleration by collisionless shocks, magnetic field reconnection, beam dynamics, etc.

Lipatov, Alexander S.↗
NASA NTRS2000

Detailed Chemical Kinetic Modeling of Hydrazine Decomposition

The purpose of this research project is to develop and validate a detailed chemical kinetic mechanism for gas-phase hydrazine decomposition. Hydrazine is used extensively in aerospace propulsion, and although liquid hydrazine is not considered detonable, many fuel handling systems create multiphase mixtures of fuels and fuel vapors during their operation. Therefore, a thorough knowledge of the decomposition chemistry of hydrazine under a variety of conditions can be of value in assessing potential operational hazards in hydrazine fuel systems. To gain such knowledge, a reasonable starting point is the development and validation of a detailed chemical kinetic mechanism for gas-phase hydrazine decomposition. A reasonably complete mechanism was published in 1996, however, many of the elementary steps included had outdated rate expressions and a thorough investigation of the behavior of the mechanism under a variety of conditions was not presented. The current work has included substantial revision of the previously published mechanism, along with a more extensive examination of the decomposition behavior of hydrazine. An attempt to validate the mechanism against the limited experimental data available has been made and was moderately successful. Further computational and experimental research into the chemistry of this fuel needs to be completed.

Meagher, Nancy E.↗
NASA NTRS2009

A Cell Kinetic Model of Granulocytopoiesis Under Radiation Exposure: Extension from Murines to Canines and Humans

Space radiation poses significant challenges to space travel, and it is essential to understand the possible adverse effects from space radiation exposure to the radiosensitive organ systems that are important for immediate survival of human, e.g., the hematopoietic system. In this presentation a biomathematical model of granulocytopoiesis is described and used to analyze the blood granulocyte changes seen in the blood of mammalians under continuous and acute radiation exposure. This is one of a set of hematopoietic models that have been successfully utilized to simulate and interpret the experimental data of acute and chronic radiation on rodents. We discuss the underlying implicit regulation mechanism and the biological relevance of the kinetic parameters estimation method. Extension of the model to predictions in dogs and humans systems indicates that the modeling results are consistent with the cumulative experimental and empirical data from various sources. This implies the potential to integrate the models into one united system for monitoring the hematopoietic response of various species under irradiation. Based on the evidence of threshold responses of dogs to extended periods of low daily dose exposures, we discuss the potential health risks of the space traveler under chronic stress of low-dose irradiation and the possibly encountered Solar Particle Events.

Hu, Shaowen↗
NASA NTRSDate not supplied

Kinetic Model Development of the Carbon Vapor Deposition Reactor to Predict Performance Versus Design

To enable complete closure of a Sabatier-based atmosphere revitalization system where oxygen recovery is predicated by carbon dioxide reduction to methane and water, there must be a means of recovering the hydrogen from the byproduct methane. Honeywell’s carbon vapor deposition (CVD) reactor is a potential technology that provides a thermochemical means by which methane decomposes at high temperatures (> 1,000 °C) into hydrogen, solid carbon, and a small percentage of hydrocarbons. This advanced methane pyrolysis reactor utilizes a carbon fiber substrate to capture and immobilize the solid pyrolytic carbon rather than allowing continuation toward undesirable soot. The CVD reactor is a highly dynamic system whose characteristic geometry changes while operating. The reactor model was developed to provide predictive performance assessment capabilities at different operating conditions, geometries, and configurations to aid in technology development. Modeling of the CVD reactor considered the multitude of simultaneous and interdependent physicochemical processes that are entailed, including: (1) the homogeneous gas-phase pyrolysis reactions, (2) the heterogeneous deposition reactions, and (3) the transport of gaseous species in the reactor domains. A 1-D CVD reactor model was developed based on a general packed-bed, axial-dispersion plug flow reactor model with a solid substrate balance to account for carbon deposition. The model includes 59 species and 243 reactions constituting the methane pyrolysis reaction network, carbon deposition, and interconversions of oxygenate species. The reactor model was compared to brassboard test data, where it was shown to be able to capture the pertinent physicochemical phenomena as evidenced by its agreement with short-duration run data (i.e., looking at different temperature and flow rate conditions), as well as trend agreement with the brassboard reactor’s long-duration test data. Recommendations are provided on further model development steps as well as its use cases.

Air Revitalization↗
NASA NTRS1978

Kinetic model of turbulence in an incompressible fluid

A statistical description of turbulence in an incompressible fluid obeying the Navier-Stokes equations is proposed, where pressure is regarded as a potential for the interaction between fluid elements. A scaling procedure divides a fluctuation into three ranks representing the three transport processes of macroscopic evolution, transport property, and relaxation. Closure is obtained by relaxation, and a kinetic equation is obtained for the fluctuation of the macroscopic rank of the distribution function. The solution gives the transfer function and eddy viscosity. When applied to the inertia subrange of the energy spectrum the analysis recovers the Kolmogorov law and its numerical coefficient.

Tchen, C. M.↗
NASA NTRS1977

Chemical kinetic modeling of propane oxidation behind shock waves

The stoichiometric combustion of propane behind incident shock waves was studied experimentally and analytically over a temperature range from 1700 K to 2600 K and a pressure range from 1.2 to 1.9 atm. Measurements of the concentrations of carbon monoxide (CO) and carbon dioxide (CO2) and the product of the oxygen atom and carbon dioxide concentrations (O)(CO) were made after passage of the incident shock wave. A kinetic mechanism was developed which, when used in a computer program for a flowing, reacting gas behind an incident shock wave predicted experimentally measured results quite well. Ignition delay times from the literature were also predicted quite well. The kinetic mechanism consisted of 59 individual kinetic steps.

Mclain, A. G.↗
NASA NTRS1979

Chemical kinetic modeling of benzene and toluene oxidation behind shock waves

The oxidation of stoichiometric mixtures of benzene and toluene behind incident shock waves was studied for a temperature range from 1700 to 2800 K and a pressure range from 1.1 to 1.7 atm. The concentration of CO and CO2 produced were measured as well as the product of the oxygen atom and carbon monoxide concentrations. Comparisons between the benzene experimental data and results calculated by use of a reaction mechanism published in the open literature were carried out. With some additional reactions and changes in rate constants to reflect the pressure-temperature range of the experimental data, a good agreement was achieved between computed and experimental results. A reaction mechanism was developed for toluene oxidation based on analogous rate steps from the benzene mechanism. Measurements of NOx levels in an actual flame device, a jet-stirred combustor, were reproduced successfully by use of the reaction mechanism developed from the shock-tube experiments on toluene. These experimental measurements of NOx levels were reproduced from a computer simulation of a jet-stirred combustor.

Mclain, A. G.↗
NASA NTRS1979

A unified kinetic model of the tangential magnetopause structure

In the self-consistent model of the tangential magnetopause, formulated in the present paper on the basis of the Vlasov-Maxwell equations, the plasmas on both sides are magnetized and the magnetic field is everywhere parallel to the magnetopause (i.e., the normal field component is zero) and rotates through an arbitrary angle across the magnetopause. It is shown that the thickness of the magnetopause is greater than the gyroradius of the plasma ions. The presence of a trapped particle population within the magnetopause is shown to be required to allow the magnetic field to rotate more than a certain critical angle (-90 degrees). The model proposed can reproduce the observed features of the tangential magnetopause structure by specifying boundary conditions on both sides of the magnetopause.

Lee, L. C.↗
NASA NTRS1980

Chemical kinetic models for combustion of hydrocarbons and formation of nitric oxide

The formation of nitrogen oxides NOx during combustion of methane, propane, and a jet fuel, JP-4, was investigated in a jet stirred combustor. The results of the experiments were interpreted using reaction models in which the nitric oxide (NO) forming reactions were coupled to the appropriate hydrocarbon combustion reaction mechanisms. Comparison between the experimental data and the model predictions reveals that the CH + N2 reaction process has a significant effect on NO formation especially in stoichiometric and fuel rich mixtures. Reaction models were assembled that predicted nitric oxide levels that were in reasonable agreement with the jet stirred combustor data and with data obtained from a high pressure (5.9 atm (0.6 MPa)), prevaporized, premixed, flame tube type combustor. The results also suggested that the behavior of hydrocarbon mixtures, like JP-4, may not be significantly different from that of pure hydrocarbons. Application of the propane combustion and nitric oxide formation model to the analysis of NOx emission data reported for various aircraft gas turbines showed the contribution of the various nitric oxide forming processes to the total NOx formed.

Jachimowski, C. J.↗
NASA NTRS1984

Systematic optimization of a detailed kinetic model using a methane ignition example

An approach to the systematic optimization of a large-scale dynamic model is proposed which consists in parameterization of simulation results as response surfaces. The optimization procedure is carried out using a second-order orthogonal design. The approach proposed here is demonstrated by an example involving the shock-initiated ignition of methane.

Frenklach, M.↗
NASA NTRS1986

Assessment of two-temperature kinetic model for dissociating and weakly-ionizing nitrogen

The validity of the author's two-temperature, chemical/kinetic model which the author has recently improved is assessed by comparing the calculated results with the existing experimental data for nitrogen in the dissociating and weakly ionizing regime produced behind a normal shock wave. The computer program Shock Tube Radiation Program (STRAP) based on the two-temperature model is used in calculating the flow properties behind the shock wave and the Nonequilibrium Air Radiation (NEQAIR) program, in determining the radiative characteristics of the flow. Both programs were developed earlier. Comparison is made between the calculated and the existing shock tube data on (1) spectra in the equilibrium region, (2) rotational temperature of the N2(+) B state, (3) vibrational temperature of the N2(+) B state, (4) electronic excitation temperature of the N2 B state, (5) the shape of time-variation of radiation intensities, (6) the times to reach the peak in radiation intensity and equilibrium, and (7) the ratio of nonequilibrium to equilibrium radiative heat fluxes. Good agreement is seen between the experimental data and the present calculation except for the vibrational temperature. A possible reason for the discrepancy is given.

Park, C.↗