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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 NTRS2001

Virtual Antiparticle Pairs, the Unit of Charge Epsilon and the QCD Coupling Alpha(sub s)

New semi-classical models of virtual antiparticle pairs are used to compute the pair lifetimes, and good agreement with the Heisenberg lifetimes from quantum field theory (QFT) is found. When the results of the new models and QFT are combined, formulae for e and alpha(sub s)(q) are derived in terms of only h and c. The modeling method applies to both the electromagnetic and color forces. Evaluation of the action integral of potential field fluctuation for each interaction potential yields approx. = h/2 for both electromagnetic and color fluctuations, in agreement with QFT. Thus each model is a quantized semiclassical representation for such virtual antiparticle pairs, to good approximation. This work reduces the number of arbitrary parameters of the Standard Model by two from 18 to 16. These are remarkable, unexpected results from a basically classical method.

Batchelor, David↗
NASA NTRS2001

Semiclassical Models for Virtual Antiparticle Pairs, the Unit of Charge e, and the QCD Coupling alpha(sub s)

New semiclassical models of virtual antiparticle pairs are used to compute the pair lifetimes, and good agreement with the Heisenberg lifetimes from quantum field theory (QFT) is found. The modeling method applies to both the electromagnetic and color forces. Evaluation of the action integral of potential field fluctuation for each interaction potential yields approximately Planck's constant/2 for both electromagnetic and color fluctuations, in agreement with QFT. Thus each model is a quantized semiclassical representation for such virtual antiparticle pairs, to good approximation. When the results of the new models and QFT are combined, formulae for e and alpha(sub s)(q) are derived in terms of only Planck's constant and c.

Batchelor, David↗
NASA NTRS1977

Industrial ion source technology

Plasma probe surveys were conducted in a 30-cm source to verify that the uniformity in the ion beam is the result of a corresponding uniformity in the discharge-chamber plasma. A 15 cm permanent magnet multipole ion source was designed, fabricated, and demonstrated. Procedures were investigated for texturing a variety of seed and surface materials for controlling secondary electron emission, increasing electron absorption of light, and improved attachment of biological tissue for medical implants using argon and tetrafluoromethane as the working gases. The cross section for argon-argon elastic collisions in the ion-beam energy range was calculated from interaction potentials and permits calculation of beam interaction effects that can determine system pumping requirements. The data also indicate that different optimizations of ion-beam machines will be advantageous for long and short runs, with 1 mA-hr/cm being the rough dividing line for run length. The capacity to simultaneously optimize components in an ion-beam machine for a single application, a capacity that is not evident in competitive approaches such as diode sputtering is emphasized.

Kaufman, H. R.↗
NASA NTRS1974

Intermolecular potentials from shock structure experiments

Ground-state intermolecular interaction potentials determined from shock structure experiments with four monatomic gases are reported. These potentials are assessed for self-consistency, using the law of corresponding states, and their suitability for engineering applications in rarefied gas dynamics is discussed.

Sturtevant, B.↗
NASA NTRS2022

Thresholds of Temperature and Time for Mars Sample Return: Final Report of The Mars Sample Return Temperature-Time Tiger Team

The time-temperature tiger team (T4) was chartered by NASA and ESA to evaluate the risks to the scientific return of the MSR samples if they are exposed to temperatures between +30 and +60 ⁰C for different amounts of time. This team consists of 13 scientists, who were selected based on their scientific background to represent the scientific disciplines that are expected to be the ones that will be the most affected if such heating were to happen. The expertise of the team will help to understand whether exposing the MSR samples to temperatures between +30 and +60 ⁰C will pose any risk to the sample integrity and therefore, to future scientific investigations. Key processes identified by the T4 were: the release of volatiles by desorption and sublimation and release from condensed phases (interiors, decomposition, dehydration); chemical reactions including gas-gas and gas-solid; deliquescence of hygroscopic salts; acid/base interactions (potential for extreme pH conditions); aqueous redox reactions, isotopic exchange (aqueous phases, minerals, gasses, organic phases); condensation and freezing (in the after-heating cooling phase) and interactions with the sample tube materials. There is potential for multiple interactions and overlapping effects. For inorganic materials and the records they represent, over both long time scales (hours to days) and short time scales (minutes to hours) no temperature excursion above +30 °C could be accommodated without loss of science (Figure 1.1). While there will be some robust constituents (feldspars, quartz, pyroxenes, etc.) that are unaffected, there will also be some less robust constituents (salts, phyllosilicates, radicals, etc.) that are affected across all temperature ranges ≤60 °C. For organic materials, in particular organic biosignatures, the risks reflect that preservation is reliant on a number of processes, and a change in one component within a sample tube can affect another. For organic materials, over long timescales of hours to days no temperature excursion above +30 °C could be accommodated without loss of science, but over shorter time scales (minutes to hours), raising the temperature to 40 °C could be manageable without major disruption to science, whereas temperatures above 40 °C would lead to significant losses. The consideration of these findings by the MSR team will help to maintain the fidelity of samples returned from Mars in the future and maximize scientific return when analyzed in Earth laboratories.

Mark A Sephton↗
NASA NTRS1998

Compressibility and Turbulence Effects Due to Airfoil Clocking in Axial Compressors

Axial compressors have inherently unsteady flow fields because of relative motion between rotor and stator airfoils. This relative motion leads to viscous and inviscid (potential) interactions between blade rows. As the number of stages increases in a turbomachine, the buildup of convected wakes can lead to progressively more complex wake/wake and wake/airfoil interactions. Variations in the relative circumferential positions of stators or rotors can change these interactions, leading to different unsteady forcing functions on airfoils and different compressor efficiencies. In addition, as the Mach number increases the interaction between blade rows is intensified due to potential effects. The current study uses an unsteady, two-dimensional Navier-Stokes approach to investigate the unsteady aerodynamics of stator clocking in a 1-1/2 stage compressor, typical of high-pressure compressors used in advanced commercial jet engines. The effects of turbulence are modeled with both algebraic and two-equation models. Results include surface pressures, efficiencies, boundary layer quantities and turbulence quantities. In addition, the growth of turbulence and the effects of compressibility on airfoil are discussed.

Dorney, Daniel J.↗
NASA NTRS1983

A potential energy scaling Monte Carlo simulation of thin film nucleation and growth

The initial growth of thin Ge fims on the (100) surface of an Fe substrate is investigated theoretically by means of Monte Carlo simulations based on a potential-energy-scaling technique. The substrate is modeled as a 20 x 20-square array with periodic boundary conditions, as described by Heinbockel et al. (1983), and the movement of surface atoms under the influence of the substrate interaction potential and the lateral interaction of neighboring atoms is explored via continuous updating (on the time scale of single events) of the potential energy at each site in the array. Results for the clustering of nine dispersed atoms over 1.0 s at 600 K and for deposition at 5 x 10 to the -14th/sq cm s over 2.0 s at 500 K are presented graphically.

Outlaw, R. A.↗
NASA NTRS1974

A constructive model potential method for atomic interactions

A model potential method is presented that can be applied to many electron single centre and two centre systems. The development leads to a Hamiltonian with terms arising from core polarization that depend parametrically upon the positions of the valence electrons. Some of the terms have been introduced empirically in previous studies. Their significance is clarified by an analysis of a similar model in classical electrostatics. The explicit forms of the expectation values of operators at large separations of two atoms given by the model potential method are shown to be equivalent to the exact forms when the assumption is made that the energy level differences of one atom are negligible compared to those of the other.

Bottcher, C.↗
NASA NTRS2024

Lunar Dust Considerations for Vertical Solar Arrays Volume 1: Lunar Environment and Dust Interactions

Lunar dust can complicate nearly every aspect of operations on the lunar surface. Jagged surface asperities, electrostatic charge, chemical reactivity, and interactions resulting in high-velocity motion enable a myriad of potential interaction pathways for lunar dust to adversely affect any exposed surface. Optimization of solar array energy collection efficiency, which will be important for a sustained lunar presence, will require overcoming many challenges presented by lunar dust. In this work, the fundamental properties of lunar dust, natural aspects of the lunar environment that influence the properties of lunar dust, and lunar exploration activities that will contribute to problems associated with lunar dust exposure are discussed. Aspects of the lunar environment that could contribute to reducing the operational efficiency of vertical solar arrays, which will be required for the lunar south pole region, are also identified.

vertical solar array technology↗
NASA NTRS1993

Calculation of molecular excitation rates

State-to-state collisional excitation rates for interstellar molecules observed by radio astronomers continue to be required to interpret observed line intensities in terms of local temperatures and densities. A problem of particular interest is collisional excitation of water which is important for modeling the observed interstellar masers. In earlier work supported by a different NASA Grant, excitation of water in collisions with He atoms was studied; after many years of successively more refined calculations that problem now seems to be well understood, and discrepancies with earlier experimental data for related (pressure broadening) phenomena are believed to reflect experimental errors. Because of interstellar abundances, excitation by H2, the dominant interstellar species, is much more important than excitation by He, although it has been argued that rates for excitation by these are similar. Under the current grant theoretical study of this problem has begun which is greatly complicated by the additional degrees of freedom which must be included both in determining the interaction potential and also in the molecular scattering calculation. We have now computed the interaction forces for nearly a thousand molecular geometries and are close to having an acceptable global fit to these points which is necessary for the molecular dynamics calculations. Also, extensive modifications have been made to the molecular scattering code, MOLSCAT. These included coding the rotational basis sets and coupling matrix elements required for collisions of an asymmetric top with a linear rotor. A new method for numerical solution of the coupled equations has been incorporated. Because of the long-ranged nature of the water-hydrogen interaction it is necessary to integrate the equations to rather large intermolecular separations, and the integration methods previously available in MOLSCAT are not ideal for such cases. However, the method used by Alexander in his HIBRIDON code is particularly suited for such cases. We have obtained this code and incorporated that part which solves the coupled differential equations as an option in the MOLSCAT program.

Flynn, George↗
NASA NTRS1983

Transport properties of ground state nitrogen atoms

In view of the dependence of the transport properties of dilute monatomic gases on the two-body, atom-atom interaction potential, any one of four potential energy curves corresponding to the N2 molecule can be followed when two ground state N atoms interact. Transport collision integrals for the 1Sigma(+)g and 3Sigma(+)u states have been calculated by representing their potentials with the Hulburt-Hirschfelder (1941, 1961) potential. The 5Sigma(+)g state has a large local maximum requiring changes in a previously used computational procedure, and its potential has also been represented by a Hulburt-Hirschfelder potential. Collision integrals for the 7Sigma(+)u state have been obtained through the direct use of a recently proposed theoretical potential for this state. The collision integrals are compared with results gathered from previous studies.

Rainwater, J. C.↗
NASA NTRS1979

Effects of Impurities and Processing on Silicon Solar Cells, Phase 3

Results of the 14th quarterly report are presented for a program designed to assess the effects of impurities, thermochemical processes and any impurity process interactions on the performance of terrestrial silicon solar cells. The Phase 3 effort encompasses: (1) potential interactions between impurities and thermochemical processing of silicon; (2) impurity-cell performance relationships in n-base silicon; (3) effect of contaminants introduced during silicon production, refining or crystal growth on cell performance; (4) effects of nonuniform impurity distributions in large area silicon wafers; and (5) a preliminary study of the permanence of impurity effects in silicon solar cells.

Hopkins, R. H.↗
NASA NTRS1983

Transport properties for the nitrogen system - N2, N, N(+) and E

The transport properties of the 'nitrogen system' (N2, N, N(+), and e) are important in a variety of applications, including atmospheric entry of the Shuttle and other re-entry vehicles. The kinetic theory of gases has been used to calculate the conductive transport properties for this system. The best available two-body interaction potentials have been used to calculate the transport collision integrals for each of the ten interactions which can occur in this system. Results are presented for the pure species and for the gas mixture from 600K-14000K.

Biolsi, L.↗
NASA NTRS1984

Laboratory Investigations

The primary objectives were to examine the site-specific physical, chemical, and biological factors that impact construction, durability and performance of the proposed 5-MW (sub e) solar pond system at the Salton Sea. The interactions of the water, salt, and soil of the site and on material compatibility were examined. Potential interactions of the water/brine and soil are particularly important because the pond will utilize the naturally occurring clays as a bottom seal. Although there is a considerable and growing solar pond literature, little written information deals with the important site-specific investigations of water, salt, and soil. Therefore, technical effort was directed toward identifying the factors that should be investigated and determining methods of investigation. As a result, a by-product was the development of an approach for site-specific investigations and some specific methodologies. This development should continue in order to establish a generic approach for evaluating the suitability of any site for the construction of large-scale solar ponds.

Source record↗
NASA NTRS1995

Potential energy curves and collision integrals of air components

Collision integrals are fundamental quantities required to determine the transport properties of the environment surrounding aerospace vehicles in the upper atmosphere. These collision integrals can be determined as a function of temperature from the potential energy curves describing the atomic and molecular collisions. Ab initio calculations provide a practical method of computing the required interaction potentials. In this work we will discuss recent advances with an emphasis on the accuracy that is obtainable. Results for interactions, e.g. N+N, N+O, O+O, and H+N2 will be reviewed and their application to the determination of transport properties, such as diffusion and viscosity coefficients, will be examined.

Partridge, Harry↗
NASA NTRS1991

Theoretical molecular studies of astrophysical interest

When work under this grant began in 1974 there was a great need for state-to-state collisional excitation rates for interstellar molecules observed by radio astronomers. These were required to interpret observed line intensities in terms of local temperatures and densities, but, owing to lack of experimental or theoretical values, estimates then being used for this purpose ranged over several orders of magnitude. A problem of particular interest was collisional excitation of formaldehyde; Townes and Cheung had suggested that the relative size of different state-to-state rates (propensity rules) was responsible for the anomalous absorption observed for this species. We believed that numerical molecular scattering techniques (in particular the close coupling or coupled channel method) could be used to obtain accurate results, and that these would be computationally feasible since only a few molecular rotational levels are populated at the low temperatures thought to prevail in the observed regions. Such calculations also require detailed knowledge of the intermolecular forces, but we thought that those could also be obtained with sufficient accuracy by theoretical (quantum chemical) techniques. Others, notably Roy Gordon at Harvard, had made progress in solving the molecular scattering equations, generally using semi-empirical intermolecular potentials. Work done under this grant generalized Gordon's scattering code, and introduced the use of theoretical interaction potentials obtained by solving the molecular Schroedinger equation. Earlier work had considered only the excitation of a diatomic molecule by collisions with an atom, and we extended the formalism to include excitation of more general molecular rotors (e.g., H2CO, NH2, and H2O) and also collisions of two rotors (e.g., H2-H2).

Flynn, George↗