Results for “Exchange interactions” — Page 4

NASA NTRS1992

CAGI: Computer Aided Grid Interface. A work in progress

Progress realized in the development of a Computer Aided Grid Interface (CAGI) software system in integrating CAD/CAM geometric system output and/or Interactive Graphics Exchange Standard (IGES) files, geometry manipulations associated with grid generation, and robust grid generation methodologies is presented. CAGI is being developed in a modular fashion and will offer fast, efficient and economical response to geometry/grid preparation, allowing the ability to upgrade basic geometry in a step-by-step fashion interactively and under permanent visual control along with minimizing the differences between the actual hardware surface descriptions and corresponding numerical analog. The computer code GENIE is used as a basis. The Non-Uniform Rational B-Splines (NURBS) representation of sculptured surfaces is utilized for surface grid redistribution. The computer aided analysis system, PATRAN, is adapted as a CAD/CAM system. The progress realized in NURBS surface grid generation, the development of IGES transformer, and geometry adaption using PATRAN will be presented along with their applicability to grid generation associated with rocket propulsion applications.

Soni, Bharat K.↗

NASA NTRS1988

Evaporation, ignition and combustion of nondilute clusters of drops

A theory of evaporation, ignition, and burning of moderately dense spherical drop clusters has been developed. The theory takes into account burning of premixed air and fuel internal to the cluster at ignition and subsequent burning of fuel emitted from the cluster by a flame sheet surrounding it. The model considers interdrop interaction, momentum exchange between drops and gas, and turbulent exchange processes between the cluster and its surroundings. Calcualtions are performed for varying initial air to fuel mass ratios, initial cluster radii, ambient gas temperatures, and initial drop temperatures. Results are presented for fuel burn fractions at ignition and at the moment of drop disappearance, as well as jump conditions at ignition.

Bellan, J.↗

NASA NTRS1990

Evaporation, ignition, and combustion of nondilute clusters of drops

A theory of evaporation, ignition, and burning of moderately dense spherical drop clusters has been developed. The theory takes into account burning of premixed air and fuel internal to the cluster at ignition and subsequent burning of fuel emitted from the cluster by a flame sheet surrounding it. The model considers interdrop interaction, momentum exchange between drops and gas, and turbulent exchange processes between the cluster and its surroundings. Calculations are performed for varying initial air-to-fuel-mass ratios, initial cluster radii, ambient gas temperatures and initial drop temperatures. Results are presented for ratios of fuel mass burned to fuel mass lost from the cluster between drop ignition and drop disappearance, fuel burned fractions at ignition and at the moment of drop disappearance, and jump conditions at ignition.

Bellan, J.↗

NASA NTRS1990

TEJAS

The Telerobotics/EVA Joint Analysis System (TEJAS) is a hypermedia information system that provides a clear, consistent, repeatable, interactive, and exchangeable multilevel mechanism for telerobotics technology development planning, based on a realistic understanding of the following: (1) Task description, assumptions, and open issues; (2) Specific task primitives (derived from generic primitives); (3) Technologies required to perform on-orbit telerobotics; (4) Planned telerobotics systems' use of those technologies; and (5) Forecast for each technology in terms of time and money. TEJAS was created in HyperCard on a Macintosh 2 personal workstation, with HyperTalk scripts providing action and relational capability. Version 1.0, consisting of more than a dozen interrelated files, will be released in Jan. 1990.

Drews, Michael↗

NASA NTRS2004

Using Ontologies to Formalize Services Specifications in Multi-Agent Systems

One key issue in multi-agent systems (MAS) is their ability to interact and exchange information autonomously across applications. To secure agent interoperability, designers must rely on a communication protocol that allows software agents to exchange meaningful information. In this paper we propose using ontologies as such communication protocol. Ontologies capture the semantics of the operations and services provided by agents, allowing interoperability and information exchange in a MAS. Ontologies are a formal, machine processable, representation that allows to capture the semantics of a domain and, to derive meaningful information by way of logical inference. In our proposal we use a formal knowledge representation language (OWL) that translates into Description Logics (a subset of first order logic), thus eliminating ambiguities and providing a solid base for machine based inference. The main contribution of this approach is to make the requirements explicit, centralize the specification in a single document (the ontology itself), at the same that it provides a formal, unambiguous representation that can be processed by automated inference machines.

Breitman, Karin Koogan↗

NASA NTRS2005

Workshop on Radical Agent Concepts (WRAC)

Agent technology, along with autonomous and autonomic computing, has emerged as a major field in computing, and will greatly influence the future development of complex computer-based systems. The area of research is strongly influenced by the Autonomic Computing initiative as well as by developments in biologically-inspired computing, and involves interdisciplinary interaction from those involved in research in social intelligence, psychology, arts, biology, computer science, computer communications and philosophy. This volume includes revised versions of papers presented at the workshop. The workshop was structured so as to allow adequate time for discussion and interaction, to exchange ideas and reflect on the motivations, scientific grounds and practical consequences of the concepts presented. Many of the ideas are truly "radical", and so authors were given time to revise their papers to reflect further thoughts on the ideas presented, and to reflect feedback received at the workshop.

Hinchey, Michael G.↗

NASA NTRS2008

Virtual Satellite

Virtual Satellite (VirtualSat) is a computer program that creates an environment that facilitates the development, verification, and validation of flight software for a single spacecraft or for multiple spacecraft flying in formation. In this environment, enhanced functionality and autonomy of navigation, guidance, and control systems of a spacecraft are provided by a virtual satellite that is, a computational model that simulates the dynamic behavior of the spacecraft. Within this environment, it is possible to execute any associated software, the development of which could benefit from knowledge of, and possible interaction (typically, exchange of data) with, the virtual satellite. Examples of associated software include programs for simulating spacecraft power and thermal- management systems. This environment is independent of the flight hardware that will eventually host the flight software, making it possible to develop the software simultaneously with, or even before, the hardware is delivered. Optionally, by use of interfaces included in VirtualSat, hardware can be used instead of simulated. The flight software, coded in the C or C++ programming language, is compilable and loadable into VirtualSat without any special modifications. Thus, VirtualSat can serve as a relatively inexpensive software test-bed for development test, integration, and post-launch maintenance of spacecraft flight software.

Hammrs, Stephan R.↗

NASA NTRS2010

Requirements of an Integrated Formal Method for Intelligent Swarms

NASA is investigating new paradigms for future space exploration, heavily focused on the (still) emerging technologies of autonomous and autonomic systems [47, 48, 49]. Missions that rely on multiple, smaller, collaborating spacecraft, analogous to swarms in nature, are being investigated to supplement and complement traditional missions that rely on one large spacecraft [16]. The small spacecraft in such missions would each be able to operate on their own to accomplish a part of a mission, but would need to interact and exchange information with the other spacecraft to successfully execute the mission.

Hinchey, M. G.↗

NASA NTRS2019

Grossite-Rich Refractory Inclusions in Carbonaceous Chondrites: Evidence for Early Generation of Different O-Isotope Reservoirs in the Protoplanetary Disk and O-Isotope Exchange During Fluid-Rock Interaction

The oxygen isotopic composition of the Sun inferred from the measurements of the solar wind returned by the Genesis spacecraft is O-16-enriched (△O-17 = -28.4±3.6‰) relative to the whole-rock O-isotope compositions of chondrites and achondrites, and chondrule phenocrysts, which all plot close to the terrestrial fractionation line (△O-17 ∼ ±5‰). Vast majority of refractory inclusions (CAIs and AOAs) in carbonaceous chondrites of petrologic types 2-3.0 are iso-topically uniform and have solar-like △O-17. In contrast, CAIs and AOAs in metamorphosed CV and CO chondrites are isotopically heterogeneous with melilite, anorthite, perovskite, Zr- and Sc-rich oxides and silicates, and occasionally Al, Ti-diopside being O-16-depleted relative to hibonite, spinel, Al-diopside, and forsterite. The timing of generation of different O-isotope reservoirs and the nature of O-isotope heterogeneity in refractory inclusions in CO3 and CV3 chondrites are poorly known. Grossite (CaAl4O7) is one of the first minerals predicted to condense from a gas of solar composition and therefore it could have recorded isotopic compositions of reservoirs during the earliest stages of the Solar System evolution. Here we report on O-isotope compositions of grossite-rich CAIs in CH3 and CO3 chondrites measured in situ with the UH Cameca ims-1280. For analytical procedures see [9].

A N Krot↗

NASA NTRS1985

Global transport of atmospheric smoke following a major nuclear exchange

A fully interactive zonally symmetric general circulation model is used to simulate the transport and evolution of a massive smoke cloud that is likely to form in the atmosphere following a major nuclear war. The presence of such a cloud significantly alters the simulated circulation and the subsequent transport of the smoke particles themselves. While the model indicates a tendency for interhemispheric exchange, the most immediate effect is that the radiatively active particles are carried into the stratosphere by the generation of strong vertical motions and intense convection regardless of their initial injection altitudes.

Haberle, R. M.↗

NASA NTRS1983

Charge exchange in solar wind-cometary interactions

A simple model of a cometary spherically symmetrical atmosphere and ionosphere is considered. An analytic solution of the governing equations describing the radial distribution of the neutral and ion densities is found. The new solution is compared to the well-known solution of the equations containing only ionization terms. Neglecting recombination causes a significant overestimate of the ion density in the vicinity of the comet. An axisymmetric model of the solar wind-cometary interaction is considered, taking into account the loss of solar wind ions due to charge exchange. The calculations predict that for active comets, solar wind absorption due to charge exchange becomes important at a few thousand kilometers from the nucleus, and a surface separating the shocked solar wind from the cometary ionosphere develops in this region. These calculations are in reasonable agreement with the few observations available for the ionopause location at comets.

Gombosi, T. I.↗

NASA NTRSDate not supplied

Process Drivers, Inter-model Spread, and a Path Forward: What Do We Know About Arctic Amplification?

Over the recent decades, rapid changes have been observed in the Arctic resulting from enhanced surface warming in the Arctic relative to the rest of the globe, a phenomenon called Arctic Amplification. While surface-based amplification of Arctic warming in response to increased CO2 has been established. The driving mechanisms, relevant processes, and the relative roles of local and remote mechanisms to Arctic Amplification remain unclear. Research over the last decade has made it clear that coupling between the atmosphere, sea ice, and ocean play a key role in Arctic Amplification. This presentation summarizes recent research on the fundamental role that atmosphere-sea ice-ocean interactions and energy exchanges play in driving Arctic Amplification, how these interactions manifest as radiative climate feedbacks, and how these processes influence the differences in the projected Arctic climate change across CMIP5 and 6. We hypothesize that models that simulate larger warming do so by generating a larger local atmospheric circulation response that more effectively redistributes energy drawn from the ocean in sea ice retreat regions Arctic-wide and contributing to a larger increase in downwelling long wave radiation. This process is also fundamentally tied to the Arctic lapse rate feedback.

Patrick Charles Taylor↗

NASA NTRSDate not supplied

Process drivers, inter-model spread, and a path forward: What do we know about Arctic Amplification?

Over the recent decades, rapid changes have been observed in the Arctic resulting from enhanced surface warming in the Arctic relative to the rest of the globe, a phenomenon called Arctic Amplification. While surface-based amplification of Arctic warming in response to increased CO2 has been established. The driving mechanisms, relevant processes, and the relative roles of local and remote mechanisms to Arctic Amplification remain unclear. Research over the last decade has made it clear that coupling between the atmosphere, sea ice, and ocean play a key role in Arctic Amplification. This presentation summarizes recent research on the fundamental role that atmosphere-sea ice-ocean interactions and energy exchanges play in driving Arctic Amplification, how these interactions manifest as radiative climate feedbacks, and how these processes influence the differences in the projected Arctic climate change across CMIP5 and 6. We hypothesize that models that simulate larger warming do so by generating a larger local atmospheric circulation response that more effectively redistributes energy drawn from the ocean in sea ice retreat regions Arctic-wide and contributing to a larger increase in downwelling long wave radiation. This process is also fundamentally tied to the Arctic lapse rate feedback.

Arctic amplification↗

NASA NTRSDate not supplied

Process drivers, inter-model spread, and a path forward: What do we know about Arctic Amplification?

Over the recent decades, rapid changes have been observed in the Arctic resulting from enhanced surface warming in the Arctic relative to the rest of the globe, a phenomenon called Arctic Amplification. While surface-based amplification of Arctic warming in response to increased CO2 has been established. The driving mechanisms, relevant processes, and the relative roles of local and remote mechanisms to Arctic Amplification remain unclear. Research over the last decade has made it clear that coupling between the atmosphere, sea ice, and ocean play a key role in Arctic Amplification. This presentation summarizes recent research on the fundamental role that atmosphere-sea ice-ocean interactions and energy exchanges play in driving Arctic Amplification, how these interactions manifest as radiative climate feedbacks, and how these processes influence the differences in the projected Arctic climate change across CMIP5 and 6. We hypothesize that models that simulate larger warming do so by generating a larger local atmospheric circulation response that more effectively redistributes energy drawn from the ocean in sea ice retreat regions Arctic-wide and contributing to a larger increase in downwelling long wave radiation. This process is also fundamentally tied to the Arctic lapse rate feedback.

Patrick C. Taylor↗

NASA NTRS1981

Elastic scattering and rotational excitation of a polyatomic molecule by electron impact - Acetylene

Differential, integral, momentum transfer, and partial cross sections have been calculated for elastic scattering and rotational excitation of C2H2 by 10-eV electrons. The effective potential includes static, exchange, and polarization interactions calculated by the INDOX/1s method and the semiclassical exchange approximation with adiabatic polarization at large electron-molecule distances. The scattering is treated by well converged rotational close coupling using the centrifugal dominant scheme to select the channels included and including up to 32 coupled channels for a given total angular momentum. The calculated integral cross sections for pure elastic scattering and rotation excitation are 54.5 and 41.4 a(0)squared, respectively. These are much larger than the values (34.4 and 18.6 a(0)squared) previously (Onda and Truhlar, 1979) calculated for the isoelectronic molecule N2, at this energy. This illustrates how the greater spatial extent of C2H2 greatly increases the cross sections for pure elastic and rotationally inelastic scattering.

Thirumalai, D.↗

NASA NTRS1975

Two-electron bond-orbital model. I

The one-electron bond-orbital model of Harrison (1973) for tetrahedrally coordinated solids is modified to a two-electron model using a generalization of Falicov and Harris' (1969) method for treating the hydrogen molecule. Expressions for nuclear-exchange and pseudodipolar interactions are obtained in terms of bond-orbital model parameters. The eigenfunctions and eigenvalues of the Hamiltonian are employed along with standard perturbation theory to calculate the energy shifts resulting from the application of an external electric field and induced by the magnetic interaction between the nuclear spins and the bond-electron spins. The quantitative predictions of the derived formulas are examined for real semiconductors involving elements and compounds from periodic groups III, IV, and V. It is concluded that the present two-electron model makes it possible to assess the quantitative effects of electron correlation in the anion-cation bond for both nonmagnetic properties (electric susceptibility, dielectric constant) and magnetic properties (nuclear-exchange and pseudodipolar interactions) of various materials.

Huang, C.↗

NASA NTRS1995

Simultaneous concentration and purification through gradient deformation chromatography

Mobile-phase additives, commonly used to modulate absorbate retention in gradient elution chromatography, are usually assumed to be either linearly retained or unretained. Previous theoretical work from our laboratory has shown that these modulators, such as salts in ion-exchange and hydrophobic interaction chromatography and organic modifiers in reversed-phase chromatography, can absorb nonlinearly, giving rise to gradient deformation. Consequently, adsorbate peaks that elute in the vicinity of the head of the deformed gradient may exhibit unusual shapes, form shoulders, and/or be concentrated. These effects for a reversed-phase sorbent with aqueous acetonitrile (ACN) as the modulator are verified experimentally. Gradient deformation is demonstrated experimentally and agrees with simulations based on ACN isotherm parameters that are independently determined from batch equilibrium studies using the layer model. Unusual absorbate peak shapes were found experimentally for single-component injections of phenylalanine, similar to those calculated by the simulations. A binary mixture of tryptophan and phenylalanine is used to demonstrate simultaneous concentration and separation, again in agreement with simulations. The possibility of gradient deformation in ion-exchange and hydrophobic interaction chromatography is discussed.

NASA Discipline Number 93-10↗

NASA NTRS1996

Ab initio Potential-Energy Surfaces and Electron-Spin-Exchange Cross Sections for H-O2 Interactions

Accurate quartet- and doublet-state potential-energy surfaces for the interaction of a hydrogen atom and an oxygen molecule in their ground states have been determined from an ab initio calculation using large-basis sets and the internally contracted multireference configuration interaction method. These potential surfaces have been used to calculate the H-O2 electron-spin-exchange cross section; the square root of the cross section (in a(sub 0)), not taking into account inelastic effects, can be obtained approximately from the expressions 2.390E(sup -1/6) and 5.266-0.708 log10(E) at low and high collision energies E (in E(sub h)), respectively. These functional forms, as well as the oscillatory structure of the cross section found at high energies, are expected from the nature of the interaction energy. The mean cross section (the cross section averaged over a Maxwellian velocity distribution) agrees reasonably well with the results of measurements.

Stallcop, James R.↗