Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “DE”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,567 records · Page 87
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Modeling of the Coupled Magnetospheric and Neutral Wind Dynamos

Over the past four years of funding, SRI, in collaboration with the University of Texas at Dallas, has been involved in assessing the influence of thermospheric neutral winds on the electric field and current systems at high latitudes. The initial direction of the project was to perform a set of numerical experiments concerning the contribution of the magnetospheric and neutral wind dynamo processes, under specific boundary conditions, to the polarization electric field and/or the field-aligned current distribution at high latitudes. To facilitate these numerical experiments we developed a numerical scheme that relied on using output from the NCAR Thermosphere-Ionosphere General Circulation Model (NCAR-TIGCM), expanding them in the form of spherical harmonics and solving the dynamo equations spectrally. Once initial calculations were completed, it was recognized that the neutral wind contribution could be significant but its actual contribution to the electric field or currents depended strongly on the generator properties of the magnetosphere. Solutions to this problem are not unique because of the unknown characteristics of the magnetospheric generator, therefore the focus was on two limiting cases. One limiting case was to consider the magnetosphere as a voltage generator delivering a fixed voltage to the high-latitude ionosphere and allowing for the neutral wind dynamo to contribute only to the current system. The second limiting case was to consider the magnetosphere as a current generator and allowing for the neutral wind dynamo to contribute only to the generation of polarization electric fields. This work was completed and presented at the l994 Fall AGU meeting. The direction of the project then shifted to applying the Poynting flux concept to the high-latitude ionosphere. This concept was more attractive as it evaluated the influence of neutral winds on the high-latitude electrodynamics without actually having to determine the generator characteristics of the magnetosphere. The influence of the neutral wind was then determined not by estimating how much electric potential or current density it provides, but by determining the contribution of the neutral wind to the net electromagnetic energy transferred between the ionosphere and magnetosphere. The estimate of the net electromagnetic energy transfer and the role of the neutral winds proves to be a more fundamental quantity in studies of magnetosphere- ionosphere coupling also showed that by using electric and magnetic field measurements from the HILAT satellite, the Poynting flux could be a measurable quantity from polar-orbiting, low- altitude spacecraft. Through collaboration with Dr. Heelis and others at UTD and their expertise of the electric field measurements on the DE-B satellite, an extensive analysis was planned to determine the Poynting flux from the DE-B measurements in combination with a modeling effort to help interpret the observations taking into account the coupled magnetosphere-ionosphere.

Thayer, Jeffrey P.↗
NASA NTRS1995

Adaptive Identification and Characterization of Polar Ionization Patches

Dynamics Explorer 2 (DE 2) spacecraft data are used to detect and characterize polar cap 'ionization patches' loosely defined as large-scale (greater than 100 km) regions where the F region plasma density is significantly enhanced (approx greater than 100%) above the background level. These patches are generally believed to develop in or equatorward of the dayside cusp region and then drift in an antisunward direction over the polar cap. We have developed a flexible algorithm for the identification and characterization of these structures, as a function of scale-size and density enhancement, using data from the retarding potential analyzer, the ion drift meter, and the langmuir probe on board the DE 2 satellite. This algorithm was used to study the structure and evolution of ionization patches as they cross the polar cap. The results indicate that in the altitude region from 240 to 950 km ion density enhancements greater than a factor of 3 above the background level are relatively rare. Further, the ionization patches show a preferred horizontal scale size of 300-400 km. There exists a clear seasonal and universal time dependence to the occurrence frequency of patches with a northern hemisphere maximum centered on the winter solstice and the 1200-2000 UT interval.

Coley, W. R.↗
NASA NTRS1996

Results of Detailed Modeling of the Narrow-Line Region of Seyfert Galaxies

We present model line profiles of [O II] lambda3727, [Ne III] lambda3869, [O I] lambda5007, [Fe VII] lambda6087, [Fe X] lambda6374, [O I] lambda6300, H(alpha) lambda6563, and [S 2] lambda6731. The profiles presented here illustrate explicitly the pronounced effects that collisional de-excitation, and that spatial variations in both the ionization parameter and cloud column density, have on Narrow-Line Region (NLR) model profiles. The above effects were included only qualitatively in a previous analytical treatment by Moore and Cohen. By making a direct correspondence between these model profiles and the analytical model profiles of Moore and Cohen, and by comparing with the observed profiles presented in a companion paper and also with those presented elsewhere in the literature, we strengthen some of the conclusions of Moore and Cohen. Most notably, we argue for constant ionization parameter, uniformly accelerated outflow of clouds that are individually stratified in ionization, and the interpretation of emission-line width correlations with ionization potential as a column density effect. For comparison with previous observational studies, such as our own in a companion paper, we also calculate profile parameters for some of the models, and we present and discuss the resulting line width correlations with critical density (n(sub cr)) and Ionization Potential (IP). Because the models we favor are those that produce extended profile wings as observed in high spectral resolution studies, the line width correlations of our favoured models are of particular interest. Line width correlations with n(sub cr) and/or IP result only if the width parameter is more sensitive to extended profile wings than is the Full Width at Half-Maximum (FWHM). Correlations between FWHM and n(sub cr) and/or IP result only after convolving the model profiles with a broad instrumental profile that simulates the lower spectral resolution used in early observational studies. The model in agreement with the greatest number of observational considerations has electron density decreasing outward from n(sub e) approx. equals 10(exp 6)/cu cm to n(sub e) approx. equals 10(exp 2)/cu cm and, due to collisional de-excitation effects in the lowest velocity clouds, it generates broad flat-topped profile peaks in the lines of lowest critical density (e.g., [O II] lambda3727 and [S II] lambda(lambda)6716, 6731). Because the observed profile peaks of both low and high critical density lines are often very similar, our favored model requires a contribution to NLR emission-line spectra from low-velocity, low-density, and low-ionization gas not included in the model NLR.

Moore, David↗
NASA NTRS1995

Large Enhancements in the O/N2 Ratio in the Evening Sector of the Winter Hemisphere During Geomagnetic Storms

In this paper, we have looked for enhancements of the O/N2 ratio in data measured by the Dynamics Explorer 2 (DE 2) satellite in the middle latitudes of the winter hemisphere, based on a prediction that was made by the National Center for Atmospheric Research thermosphere/tonosphere general circulation model (NCAR-TIGCM) that such increases occur. The NCAR-TIGCM predicts that these enhancements should be seen throughout the low latitude region and in many middle latitude locations, but that the enhancements in O/N2 are particularly strong in the middle-latitude, evening-to-midnight sector of the winter hemisphere. When this prediction was used to look for these effects in DE 2 NACS (neutral atmosphere composition spectrometer) data, large enhancements in the O/N2 ratio (approx. 50 to 90%) were seen. These enhancements were observed during the main phase of a storm that occurred on November 24, 1982, and were seen in the same region of the winter hemisphere predicted by the NCAR-TIGCM. They are partially the result of the depletion of N2 and, as electron loss is dependent on dissociative recombination at F(sub 2) altitudes, they have implications for electron densities in this area. Parcel trajectories, which have been followed through the NCAR-TIGCM history file for this event, show that large O/N2 enhancements occur in this limited region in the winter hemisphere for two reasons. First, these parcels of air are decelerated by the antisunward edge of the ion convection pattern; individual parcels converge and subsidence occurs. Thus molecular-nitrogen-poor air is brought from higher to lower heights. Because neutral parcels that are found a little poleward of the equatorial edge of the eveningside convection pattern are swept inward toward the center of the auroral oval, the enhancements occur only in a very limited range of latitudes. Second, nitrogen-poor air is transported from regions close to the magnetic pole in the winter hemisphere. During geomagnetic storms, enhanced meridional winds are driven by the increased pressure-gradient force that is associated with intensified Joule heating in the auroral oval. These pressure-driven winds decrease rapidly on the dayside beyond the auroral oval where the parcels originate, limiting the region into which the parcels can be transported. Thus these two processes drive values of O/N2 in a limited region of the winter hemisphere, and reinforce only in the evening sector, causing large changes in this region.

Burns, A. G.↗
NASA NTRS1997

Electric Propulsion for Low Earth Orbit Communication Satellites

Electric propulsion was evaluated for orbit insertion, satellite positioning and de-orbit applications on big (hundreds of kilograms) and little (tens of kilograms) low earth orbit communication satellite constellations. A simple, constant circumferential thrusting method was used. This technique eliminates the complex guidance and control required when shading of the solar arrays must be considered. Power for propulsion was assumed to come from the existing payload power. Since the low masses of these satellites enable multiple spacecraft per launch, the ability to add spacecraft to a given launch was used as a figure of merit. When compared to chemical propulsion ammonia resistojets, ion, Hall, and pulsed plasma thrusters allowed an additional spacecraft per launch Typical orbit insertion and de-orbit times were found to range from a few days to a few months.

Oleson, Steven R.↗
NASA NTRS1997

Radiation Near 2f(sub p) and Intensified Emissions Near f(sub p) in the Dayside and Nightside Auroral Region and Polar Cap

This paper reports the discovery in the DE 1 data of propagating radiation near 2f(sub p) (the H component) and relatively intense electromagnetic waves near f(sub p) with fields typically less than or approximately equal to 1 mV/m (the PF or plasma frequency component) on both the dayside and the nightside of Earth. These emissions are observed at auroral and polar cap latitudes for radial distances ranging from 2.5 to 4.5 R(sub E). The H component is unique in that no other 2f(sub p) emissions are known to be generated where the electron gyrofrequency f(sub g) exceeds 2f(sub p). Since existing theories for 2f(sub p) radiation assume f(sub g)/f(sub p) less than 1, new theories will be required to explain the H component. The PF waves near f(sub p) are electromagnetic, but with large ratios E/cB approximately 20. On the basis of cold plasma theory, the wave frequencies and the ratios E/cB, the PF component plausibly consists of zeta-mode and/or whistler mode waves near f(sub p), presumably driven by an electron instability. The H emissions have modest bandwidths of approximately 50% at frequencies ranging from 5 to 20 kHz. Grounds for interpreting the H component as emissions generated near 2f(sub p) are provided by the very good frequency tracking of the PF and H components and typical frequency ratios near 2.0. Strong evidence exists that part of the H component is propagating, electromagnetic radiation, based on propagation effects and spin modulation patterns. However, no magnetic signals have yet been detected for the H component, so that it could be partly electrostatic. Cold plasma theory and the observed wave characteristics favor interpreting the H component as composed of omicron mode and/or zeta mode signals. Combining the DE 1 observations with rocket observations, it is predicted that the much more intense Langmuir-like fields observed in the low altitude auroral zones should also generate observable 2f(sub p) radiation. This prediction should be testable using Polar and future rocket flights. Directions for future research are also described.

Cairns, Iver H.↗
NASA NTRS1997

Modeling a simple coronal streamer during whole sun month

The solar minimum streamer structure observed during the whole sun month was modeled. The Van de Hulst inversion was used in order to determine the coronal electron density profiles and scale-height temperature profiles. The axisymmetric magnetostatic model of Gibson, Bagenal and Low was also used. The density, temperature, and magnetic field distribution were quantified using both coronal white light data and photospheric magnetic field data from the Wilcox Solar Observatory. The densities and temperatures obtained by the Van de Hulst and magnetostatic models are compared to the magnetic field predicted by the magnetostatic model to a potential field extrapolated from the photosphere.

Gibson, S. E.↗
NASA NTRS1999

Evolution of Plasmaspheric Refilling: A Comparison of Measurements with an Interhemispheric Plasmasphere Model

The evolution of plasmasphere is closely coupled to processes governing flux tube refilling and transport. In this study we follow this evolution through a series of sequential ion observations made by RIMS on the DE 1 satellite and with the intervening time intervals filled by simulations made with the FLIP model. The FLIP model solves the continuity and momentum equations for the major ion species as well as the energy equations for ions and electrons along entire flux tubes rom 100 k altitude in both hemispheres. Convection has recently been included, driven a dawn-dusk electric field model. Since the observations are necessarily restricted to two local time passes through the plasmasphere per orbit, the FLIP code will follow the observed flux tubes as they corotate and convect through the other local times. The period of DE 1 is such that nearly the same flux tubes are observed every second day or every sixth orbit. The composite of observations and simulations allows assessment of the degree to which the degree to which the FLIP simulations accurately describe the processes which govern flux tube refilling over the two-day period between observations of the same flux tubes.

Comfort, Richard H.↗
NASA NTRS1999

Detecting 1mm/Year Signals in Altimetric Global Sea Level: Effect of Atmospheric Water Vapor and Precipitation

Several research efforts exist to use Topography Experiment (TOPEX)/ Projet d'Observatorie de Surveillance et d'Etudes Integrees de la Dynamique des Oceans (Poseidon) (T/P) to detect changes in global sea level possibly associated with climate change. This requires much better than 1 mm/yr accuracy, something that none of the instruments in T/P [or the European Remote Sensing (ERS-2) satellite, or the U.S. Navy's Geosat Follow-On (GFO) satellite] were designed for. This work focuses on the ability of the T/P microwave radiometer (TMR) to retrieve the path delay due to atmospheric water vapor along the altimeter's path with accuracy in the time changes below 1 mm/yr on global average. In collaboration with Stephen Keihm of JPL and Christopher Ruf of Pennsylvania State University, we compared TMR path delay (PD) estimates with atmospheric precipitable water (PW) from the Special Sensor Microwave Imager (SSMI) aboard the Defense Meteorological Satellite Program (DMSP) series of satellites for 1992-1998 to selected radiosondes, and we also looked at the brightness temperatures measured by TMR in the lowest 1% of the histogram. The conclusion is that TMR had a slow instrumental drift, associated with the 18-GHz channel, which causes an approximate underestimation of water vapor at a rate equivalent to 1.2 mm/yr in path delay between 1992 and 1996; this effect stopped and no drift is detected in 1997. The same study concluded that there is no detectable scale error (one which is proportional to measured vapor) in TMR. In related work, carried out with graduate student Damien Cailliau, we investigated the relative abilities of TMR, SSMI and the UP dual-frequency radar altimeter to detect rain, relative to a climatology of shipborne observations. Rain is a crucial but poorly measured variable in studies of the climate system, and a dedicated mission, Tropical Rainfall Measuring Mission (TRMM), was recently launched to measure it. However, the climatologies built over the past 10 years used passive radiometers, such as SSMI, or infrared observation from National Oceanic and Atmospheric Administration (NOAA) geostationary satellites. We concluded that the dual-frequency altimeter does an excellent job at retrieving rain on scales much smaller than the passive radiometer, and a better job at retrieving total precipitation (rain as well as snow) at high latitudes. This work improves the sea level observations by allowing better flagging of observations contaminated by rain, and more importantly, provides an alternative way to measure rainfall over the oceans.

Zlotnicki, Victor↗
NASA NTRS2000

The DORIS Data Center at the CDDIS

The DORIS system (Doppler Orbitography and Radio positioning Integrated by Satellite) was designed and developed by CNES, the National Geographic Institute, IGN (Institut G6ographique National), and the Space Geodesy Research Group, GRGS (Groupe de Recherches de Geodesie Spatiale - CNES/CNRS/Universite Paul Sabatier) to meet new needs for the precise determination of satellite positions on their orbits and for precise positioning of terrestrial beacons. This system has been carried since 1990 on the French SPOT 2 satellite, since 1992 on the French/American satellite TOPEX/POSEIDON, and since 1998 on the French SPOT 4 satellite. It will be part of the JASON (CNES/NASA) and ENVISAT (ESA) altimetric missions and also the SPOT follow-on Earth observation missions. DORIS is a radio-electrical system which takes Doppler measurements between a satellite in low orbit and a permanent global network for the purpose, on the one hand, of determining the satellite's position in orbit, and on the other hand, of locating ground beacons with a high degree of precision.

Noll, Carey E.↗
NASA NTRS1997

Low Temperature Operation of a Switching Power Converter

The low temperature operation of a 48 W, 50 kHz, 36/12 V pulse width modulated (PWM) buck de-de power converter designed with standard commercially available components and devices is reported. The efficiency of the converter increased from 85.6% at room temperature (300 K) to 92.0% at liquid nitrogen temperature (77 K). The variation of power MOSFET, diode rectifier, and output filter inductor loss with temperature is discussed. Relevant current, voltage. and power waveforms are also included.

Anglada-Sanchez, Carlos R.↗
NASA NTRS2000

Renewable Energy SCADA/Training Using NASA's Advanced Technology Communication Satellite

The lack of electrical energy in the rural communities of developing countries is well known, as is the economic unfeasibility of providing much needed energy to these regions via electric grids. Renewable energy (RE) can provide an economic advantage over conventional forms in meeting some of these energy needs. The use of a Supervisory Control and Data Acquisition (SCADA) arrangement via satellite could enable experts at remote locations to provide technical assistance to local trainees while they acquire a measure of proficiency with a newly installed RE system through hands-on training programs using the same communications link. Upon full mastery of the technologies, indigenous personnel could also employ similar SCADA arrangements to remotely monitor and control their constellation of RE systems. Two separate ACTS technology verification experiments (TVEs) have demonstrated that the portability of the Ultra Small Aperture Terminal (USAT) and the versatility of NASA's Advanced Communications Technology Satellite (ACTS), as well as the advantages of Ka band satellites, can be invaluable in providing energy training via distance education (DE), and for implementing renewable energy system SCADA. What has not been tested is the capabilities of these technologies for a simultaneous implementation of renewable energy DE and SCADA. Such concurrent implementations will be useful for preparing trainees in developing countries for their eventual SCADA operations. The project described in this correspondence is the first effort, to our knowledge, in this specific TVE. The setup for this experiment consists of a one-Watt USAT located at Florida Solar Energy Center (FSEC) connected to two satellite modems tuned to different frequencies to establish two duplex ACTS Ka-band communication channels. A short training program on operation and maintenance of the system will be delivered while simultaneously monitoring and controlling the hybrid using the same satellite communications link. The trainees will include faculty and students from Savannah State University, and staff from FSEC. An interactive internet link will be used to allow faculty from the University of West Indies to participate in the training session.

Kalu, A.↗
NASA NTRS2001

Comparison of z-known GRBs with the Main Groups of Bright BATSE Events

The small reference sample of six BATSE gamma-ray bursts with known redshifts from optical afterglows is compared with a comparison group of the 218 brightest BATSE bursts. These two groups are shown to be consistent both with respect to the distributions of the spectral peak parameter in the observer's frame and also with respect to the distributions of the frame-independent cosmological invariant parameter (CIP). Using the known values of the redshifts z for the reference sample, the rest-frame distribution of spectral parameters is built. The de-redshifted distribution of the spectral parameters of the reference sample is compared with distribution of these parameters for the comparison group after de-redshifting by the factor 1/(1+z), with z a free parameter. Requiring consistency between these two distributions produces a collective estimation of the best fitting redshifts z for the comparison group, z=1.8--3.6. These values can be considered as the average cosmological redshift of the sources of the brightest BATSE bursts. The most probable value of the peak energy of the spectrum in the rest frame is 920 keV, close to the rest mass of an electron-positron pair.

Mitrofanov, Igor G.↗
NASA NTRS2001

Pick-Up Ion Instabilities at Planetary Magnetospheres

This effort involved the analysis of low frequency waves as observed by the Galileo spacecraft near the Galilean moon, Io. Io is a significant source of material, especially SO2, and various products of dissociation, and further these atoms and molecules are readily ionized. The initial velocity of the ions is essentially that of the neutral species, i.e., the Keplerian velocity. The plasma, on the other hand is co-rotating, and there is a differential flow of the order 57 km/s between the plasma and the neutral particles. Thus pick-up ion instabilities are Rely to occur within the Jovian magnetosphere. Indeed, magnetometer observations from the Galileo spacecraft clearly show ion cyclotron waves that have been identified with a large variety of plasma species, such as O+, S++ (which has the same gyro-frequency as O+), S+, and SO2+. Typically, however, the dominant frequency is near the SO2+ gyro-frequency. The research effort was originally planned to be a team effort between Robert J. Strangeway as the Principal Investigator, and Debbie Huddleston, who was an Assistant Research Geophysicist at UCLA. Unfortunately, Dr. Huddleston took a position within Industry. The effort was therefore descoped, and Dr. Strangeway instead pursued a collaboration with Dr. Xochitl Blanco-Cano, of the Instituto de Geofisica, Universidad Nacional Autonoma de Mexico. This has proved to be a productive collaboration, with several papers and publications arising out of the effort. The magnetic field oscillations near lo generally fall into two types: ion cyclotron waves, with frequencies near an ion gyro-frequency, and lower frequency mirror-mode waves. The ion cyclotron waves are mainly transverse, and frequently propagate along the ambient magnetic field. The mirror-mode waves are compressional waves, and they have essentially zero frequency in the plasma rest frame. One of the purposes of our investigation is to understand what controls the types of wave modes that occur, since both wave modes can be drive unstable by the pressure anisotropy associated with the pick up ions. The pick ion velocity is perpendicular to the ambient magnetic field, and is generally much larger than the thermal velocity, at least initially. At its simplest, we found that the ion cyclotron waves are controlled by the parameters of the species in gyro-resonance with the wave. Thus, while the growth rates for the lower mass (higher gyro-frequency) pick-up ions are generally larger, we found that the heavier SO2+ ion cyclotron waves are generally preferred. This is because one of the effects of the wave instability is to diffuse the ions in pitch angle and energy. The lower mass ions therefore consist of both a ring of recently created pick-up ions, and a thermal background. This thermal background quenches the ion cyclotron instability. SO2+ is different, however. Being a molecule, the species can also dissociate. Our analysis suggests that the dissociation acts on a time scale comparable to or faster than the velocity space diffusion time scale. There are consequently no thermal SO2+ ions to quench the instability. We have also investigated the mirror-mode. This mode can at times grow more rapidly than the individual ion cyclotron waves. This is mainly because the mirror-mode can grow off the pressure anisotropy of the individual species with which the waves are in resonance. Lastly, as part of this effort we have begun to investigate the instability for obliquely propagating modes. Galileo observations show that at times the ion cyclotron waves are significantly elliptically polarized, and further the wave vector is at a large angle to the field, significant growth can occur for oblique propagation. Depending on the group velocity of the waves, it is possible that obliquely propagating modes have higher advective growth rate, but this has yet to be determined.

Strangeway, Robert J.↗
NASA NTRS2001

Ecophysiological Changes in Microbial Mats Incubated in a Greenhouse Collaboratory

Microbial mats are modern examples of the earliest microbial communities known. Among the best studied are microbial mats growing in hypersaline ponds managed for the production of salt by Exportadora de Sal, S.A. de C.V., Guerrero Negro, Baja California Sur, Mexico. In May, 2001, we collected mats from Ponds 4 and 5 in this system and returned them to Ames Research Center, where they have been maintained for a period of over nine months. We report here on both the ecophysiological changes occurring in the mats over that period of time as well as the facility in which they were incubated. Mats (approximately 1 sq. meter total area) were incubated in a greenhouse facility modified to provide the mats with natural levels of visible and ultraviolet radiation as well as constantly flowing, temperature-controlled water. Two replicated treatments were maintained, a 'high salinity' treatment (about 120 ppt) and a 'low salinity' treatment (about 90 ppt). Rates of net biological activity (e.g., photosynthesis, respiration, trace gas production) in the mats were relatively constant over the several months, and were similar to rates of activity measured in the field. However, over the course of the incubation, mats in both treatments changed in physical appearance. The most obvious change was that mats in the higher salinity treatments developed a higher proportion of carotenoid pigments (relative to chlorophyll), resulting in a noticeably orange color in the high salinity mats. This trend is also seen in the natural salinity gradient present at the field site. Changes in the community composition of the mats, as assayed by denaturing gradient gel electrophoresis (DGGE), as well as biomarker compounds produced in the mats were also monitored. The degree to which the mats kept in the greenhouse changed from the originally collected mats, as well as differences between high and low salinity mats will be discussed. Additional information is contained in the original extended abstract.

Bebout, Brad↗
NASA NTRS1995

Rotational And Rovibrational Energy Transfer In Electron Collisions With Molecules

Air flows around a hypervelocity reentry vehicle undergo dissociation, rovibrational excitation and ionization. More specifically the air, initially 80% N2 and 20% O2, in the shock layer consists of species such as N, O, N2, O2, NO, N+, O+, N+, O+, NO+ and 2 free electrons. It was pointed out in multi temperature models'' that the temperature of the rotational energy modes and the gas-kinetic translational temperature are quickly equilibrated by a few collisions and rise rapidly to high temperatures as 50000K before falling off to equilibrium value of 10000K. Contrary, the electronic and vibrational temperatures state energy distributions remain low (less than 15000K) because of the slow equilibration. Electron vibrational energy transfer is thought to play a crucial role in such a ionizing flow regime since chemical reaction rates and dissociation depend strongly on the vibrational temperatures. Modeling of these flowfields in principle require the rovibrational excitation and de-excitation cross section data for average electron energies from threshold up to several eV (leV=11605.4 K). In this lecture we focus on theoretical description of rotational effects i.e. energy transfer of electrons to molecules such that the molecular rotational (vojo goes to voj) or vibrational and rotational (v(sub 0)j(sub 0) goes to vj) states are changed. Excitation and de-excitation of electronic states was discussed in a previous talk at this conference.

Thuemmel, Helmar T.↗
NASA NTRS1997

Etch Profile Simulation Using Level Set Methods

Etching and deposition of materials are critical steps in semiconductor processing for device manufacturing. Both etching and deposition may have isotropic and anisotropic components, due to directional sputtering and redeposition of materials, for example. Previous attempts at modeling profile evolution have used so-called "string theory" to simulate the moving solid-gas interface between the semiconductor and the plasma. One complication of this method is that extensive de-looping schemes are required at the profile corners. We will present a 2D profile evolution simulation using level set theory to model the surface. (1) By embedding the location of the interface in a field variable, the need for de-looping schemes is eliminated and profile corners are more accurately modeled. This level set profile evolution model will calculate both isotropic and anisotropic etch and deposition rates of a substrate in low pressure (10s mTorr) plasmas, considering the incident ion energy angular distribution functions and neutral fluxes. We will present etching profiles of Si substrates in Ar/Cl2 discharges for various incident ion energies and trench geometries.

Hwang, Helen H.↗
NASA NTRS2002

PCS: The First Fluid Physics Payload on ISS

The Physics of Colloids in Space (PCS) experiment was accommodated within International Space Station (ISS) EXpedite the PRocessing of Experiments to Space Station (EXPRESS) Rack 2 and was remotely operated from early June 2001 until February 2002 from NASA Glenn Research Center's Telescience Support Center in Cleveland, Ohio and from a remote site at Harvard University in Cambridge, Massachusetts. PCS is an experiment conceived by Professor David A. Weitz of Harvard University (the Principal Investigator), focusing on the behavior of three different classes of colloid mixtures. The sophisticated light scattering instrumentation comprising PCS is capable of color imaging, and dynamic and static light scattering from 11 to 169 degrees, Bragg scattering over the range from 10 to 60 degrees, and laser light scattering at low angles from 0.3 to 6.0 degrees. The PCS instrumentation performed remarkably well, demonstrating a flexibility that enabled experiments to be performed that had not been envisioned prior to launch. While on-orbit, PCS accomplished 2400 hours of science operations, and was declared a resounding success. Each of the eight sample cells worked well and produced interesting and important results. Crystal nucleation and growth and the resulting structures of two binary colloidal crystal alloys were studied, with the long duration microgravity environment of the ISS facilitating extended studies on the growth and coarsening characteristics of the crystals. In another experiment run, the de-mixing of the colloid-polymer critical-point sample was studied as it phase-separates into two phases, one that resembles a gas and one that resembles a liquid. This process was studied over four decades of length scale, from 1 micron to 1 centimeter, behavior that cannot be observed in this sample on Earth because sedimentation would cause the colloids to fall to the bottom of the cell faster than the de-mixing process could occur. Similarly, the study of gelation and aging of another colloid-polymer sample, the colloid-polymer gel, also provided valuable information on gelation mechanisms, as did investigations on the extremely the low concentration silica and polystyrene fractal gel samples.

Doherty, M.↗