ALBERT

Description: The objectives of this report was to develop a methodology to predict the time-dependent reliability (probability of failure) of brittle material components subjected to transient thermomechanical loading, taking into account the change in material response with time. This methodology for computing the transient reliability in ceramic components subjected to fluctuation thermomechanical loading was developed, assuming SCG (Slow Crack Growth) as the delayed mode of failure. It takes into account the effect of varying Weibull modulus and materials with time. It was also coded into a beta version of NASA's CARES/Life code, and an example demonstrating its viability was presented.

Description: 'NASA is preparing to launch the Next Generation Space Telescope (NGST). This telescope will be larger than the Hubble Space Telescope, be launched on an Atlas missile rather than the Space Shuttle, have a segmented primary mirror, and be placed in a higher orbit. All these differences pose significant challenges.' This effort addresses the challenge of implementing an algorithm for aligning the segments of the primary mirror during the initial deployment that was designed by Philip Olivier and members of SOMTC (Space Optics Manufacturing Technology Center). The implementation was to be performed on the SIBOA (Systematic Image Based Optical Alignment) test bed. Unfortunately, hardware/software aspect concerning SIBOA and an extended time period for algorithm development prevented testing before the end of the study period. Properties of the digital camera were studied and understood, resulting in the current ability of selecting optimal settings regarding saturation. The study was successful in manually capturing several images of two stacked segments with various relative phases. These images can be used to calibrate the algorithm for future implementation. Currently the system is ready for testing.

Description: At the end of World War II Duane Deming, an internationally known economist enunciated what later came to be called "Total Quality Management" (TQM). The basic thrust of this economic theory called for companies and governments to identify their customers and to do whatever was necessary to meet their demands and to keep them satisfied. It also called for companies to compete internally. That is, they were to build products that competed with their own so that they were always improving. Unfortunately most U.S. corporations failed to heed this advice. Consequently, the Japanese who actively sought Deming's advice and instituted it in their corporate planning, built an economy that outstripped that of the U.S. for the next three to four decades. Only after U.S. corporations reorganized and fashioned joint ventures which incorporated the tenets of TQM with their Japanese competitors did they start to catch up. Other institutions such as the U.S. government and its agencies and schools face the same problem. While the power of the U.S. government is in no danger of being usurped, its agencies and schools face real problems which can be traced back to not heeding Deming's advice. For example, the public schools are facing real pressure from private schools and home school families because they are not meeting the needs of the general public, Likewise, NASA and other government agencies find themselves shortchanged in funding because they have failed to convince the general public that their missions are important. In an attempt to convince the general public that its science mission is both interesting and important, in 1998 the Science Directorate at NASA's Marshall Space Flight Center (MSFC) instituted a new outreach effort using the interact to reach the general public as well as the students. They have called it 'Science@NASA'.

Description: This report summarizes the technical parameters and the technical staff of the VLBI system at GGAO. It also gives an overview of VLBI activities during the previous year. The outlook lists the tasks planned for 1999.

Description: Seal technology development is an important part of the Air Force's participation in the Integrated High Performance Turbine Engine Technology (IHPTET) initiative, the joint DOD, NASA, ARPA, and industry endeavor to double turbine engine capabilities by the turn of the century. Significant performance and efficiency improvements can be obtained through reducing internal flow system leakage, but seal environment requirements continue to become more extreme as the engine thermodynamic cycles advance towards these IHPTET goals. Seal technology continues to be pursued by the Air Force to control leakage at the required conditions. This presentation briefly describes current seal research and development programs and gives a summary of seal applications in demonstrator and developmental engines.

Description: Designers and customers are demanding higher performance turbomachine systems that have long life between overhauls and satisfy the more restrictive environmental constraints. This overview provides sources of design data, numerical, and experimental results along with selected new seal configurations and static sealing challenges such as in the combustors. The following categories are presented: (1) Seal Rotordynamic Data Base (experimental analytical program at Texas A&M); (2) Secondary Flow Interactions (validation studies at CFDRC, Huntsville AL); (3) Contact Sealing (selected types with finger seal model); and (4) Environmental Constraints (emphasis on combustors).

Description: This effort is to develop large diameter (22 - 36 inch) Aspirating Seals for application in aircraft engines. Stein Seal Co. will be fabricating the 36-inch seal(s) for testing. GE's task is to establish a thorough understanding of the operation of Aspirating Seals through analytical modeling and full-scale testing. The two primary objectives of this project are to develop the analytical models of the aspirating seal system, to upgrade using GE's funds, GE's 50-inch seal test rig for testing the Aspirating Seal (back-to-back with a corresponding brush seal), test the aspirating seal(s) for seal closure, tracking and maneuver transients (tilt) at operating pressures and temperatures, and validate the analytical model. The objective of the analytical model development is to evaluate the transient and steady-state dynamic performance characteristics of the seal designed by Stein. The transient dynamic model uses a multi-body system approach: the Stator, Seal face and the rotor are treated as individual bodies with relative degrees of freedom. Initially, the thirty-six springs are represented as a single one trying to keep open the aspirating face. Stops (Contact elements) are provided between the stator and the seal (to compensate the preload in the fully-open position) and between the rotor face and Seal face (to detect rub). The secondary seal is considered as part of the stator. The film's load, damping and stiffness characteristics as functions of pressure and clearance are evaluated using a separate (NASA) code GFACE. Initially, a laminar flow theory is used. Special two-dimensional interpolation routines are written to establish exact film load and damping values at each integration time step. Additionally, other user-routines are written to read-in actual pressure, rpm, stator-growth and rotor growth data and, later, to transfer these as appropriate loads/motions in the system-dynamic model. The transient dynamic model evaluates the various motions, clearances and forces as the seals are subjected to different aircraft maneuvers: Windmilling restart; start-ground idle; ground idle-takeoff; takeoff-burst chop, etc. Results of this model show that the seal closes appropriately and does not ram into the rotor for all of the conditions analyzed. The rig upgrade design for testing Aspirating Seals has been completed. Long lead-time items (forgings, etc.) have been ordered.

Description: The Mayak Production Association was the first Russian site for the production and separation of plutonium. The extensive increase in plutonium production during 1948-1955, as well as the absence of reliable waste-management technology, resulted in significant releases of liquid radioactive effluent into the rather small Techa River. This resulted in chronic external and internal exposure of about 30,000 residents of riverside communities; these residents form the cohort of an epidemiologic investigation. Analysis of the available historical monitoring data indicates that the following reliable data sets can be used for reconstruction of doses received during the early periods of operation of the Mayak Production Association: Temporal pattern of specific beta activity of river water for several sites in the upper Techa region since July 1951; average annual values of specific beta activity of river water and bottom sediments as a function of downstream distance for the whole river since 1951; external gamma-exposure rates near the shoreline as a function of downstream distance for the whole Techa River since 1952; and external gamma-exposure rate as a function of distance from the shoreline for several sites in the upper and middle Techa since 1951.

Description: Processed ball clay samples used in the production of ceramics and samples of the ceramic products were collected and analyzed for the presence and concentration of the 2,3,7,8-Cl substituted polychlorinated dibenzo-p-dioxins and -furans (PCDDs/PCDFs). The processed ball clay had average PCDD concentrations of 3.2 ng/g toxic equivalents, a congener profile, and isomer distribution consistent with those found previously in raw ball clay. The PCDF concentrations were below the average limit of detection (LOD) of 0.5 pg/g. The final fired ceramic products were found to be free of PCDDs/PCDFs at the LODs. A consideration of the conditions involved in the firing process suggests that the PCDDs, if not destroyed, may be released to the atmosphere and could represent an as yet unidentified source of dioxins to the environment. In addition, the PCDDs in clay dust generated during manufacturing operations may represent a potential occupational exposure.

Description: Age and sex features of strontium metabolism have been analyzed on studies of the population residing on the banks of the Techa river which was contaminated by fission products during the years 1949-1956. Measurements of 90Sr body burden have been performed since 1974 using a whole-body counter, and these have made it possible to estimate age-specific long-term retention and elimination rates for men and women. Regarding the retention that correlated with the respective maturation ages, distinct sex differences have been observed for adolescents, whereas only postmenopausal women showed a sharp increase of their elimination rates. There were no differences concerning the reproductive ages. Our experimental findings have a clear physiological interpretation and can be used to develop metabolic models for bone-seeking radionuclides.

Description: The sampling capability of Tenax-TA tubes, used in the National Aeronautics and Space Administration's solid sorbent air sampler to trap and concentrate contaminants from air aboard spacecraft, was improved by incorporating two sorbents within the tubes. Existing tubes containing only Tenax-TA allowed highly volatile compounds to "break through" during collection of a 1.5 L air sample. First the carbon molecular sieve-type sorbents Carboxen 569 and Carbosieve S-III were tested for their ability to quantitatively trap the highly volatile compounds. Breakthrough volumes were determined with the direct method, whereby low ppm levels of methanol or Freon 12 in nitrogen were flowed through the sorbent tubes at 30 mL/min, and breakthrough was detected by gas chromatography. Breakthrough volumes for methanol were about 9 L/g on Carboxen 569 and 11 L/g on Carbosieve S-III; breakthrough volumes for Freon 12 were about 7 L/g on Carboxen 569 and 〉 26 L/g on Carbosieve S-III. Next, dual-bed tubes containing either Tenax-TA/Carbosieve S-III, Tenax-TA/Carboxen 569, or Carbotrap/Carboxen 569 to a 10-component gas mixture were exposed, in dry and in humidified air (50% relative humidity), and percentage recoveries of each compound were determined. The Tenax-TA/Carboxen 569 combination gave the best overall recoveries (75-114% for the 10 compounds). Acetaldehyde had the lowest recovery (75%) of the 10 compounds, but this value was still an improvement over either the other two sorbent combinations or the original single-sorbent tubes.

Description: Ferrihydrite, which is known to form in the presence of oxygen and to be stabilized by the adsorption of Si, PO4 and SO4, is ubiquitous in the fine-grained fractions of permeable reactive barrier (PRB) samples from the U.S. Coast Guard Support Center (Elizabeth City, NC) and the Denver Federal Center (Lakewood, CO) studied by high-resolution transmission electron microscopy and selected area electron diffraction. The concurrent energy-dispersive X-ray data indicate a strong association between ferrihydrite and metals such as Si, Ca, and Cr. Magnetite, green rust 1, aragonite, calcite, mackinawite, greigite and lepidocrocite were also present, indicative of a geochemical environment that is temporally and spatially heterogeneous. Whereas magnetite, which is known to form due to anaerobic Fe0 corrosion, passivates the Fe0 surface, ferrihydrite precipitation occurs away from the immediate Fe0 surface, forming small (〈0.1 microm) discrete clusters. Consequently, Fe0-PRBs may remain effective for a longer period of time in slightly oxidized groundwater systems where ferrihydrite formation occurs compared to oxygen-depleted systems where magnetite passivation occurs. The ubiquitous presence of ferrihydrite suggests that the use of Fe0-PRBs may be extended to applications that require contaminant adsorption rather than, or in addition to, redox-promoted contaminant degradation.

Description: Recent advances in room-temperature, near-IR and visible diode laser sources for tele-communication, high-speed computer networks, and optical data storage applications are enabling a new generation of gas-dynamic and combustion-flow sensors based on laser absorption spectroscopy. In addition to conventional species concentration and density measurements, spectroscopic techniques for temperature, velocity, pressure and mass flux have been demonstrated in laboratory, industrial and technical flows. Combined with fibreoptic distribution networks and ultrasensitive detection strategies, compact and portable sensors are now appearing for a variety of applications. In many cases, the superior spectroscopic quality of the new laser sources compared with earlier cryogenic, mid-IR devices is allowing increased sensitivity of trace species measurements, high-precision spectroscopy of major gas constituents, and stable, autonomous measurement systems. The purpose of this article is to review recent progress in this field and suggest likely directions for future research and development. The various laser-source technologies are briefly reviewed as they relate to sensor applications. Basic theory for laser absorption measurements of gas-dynamic properties is reviewed and special detection strategies for the weak near-IR and visible absorption spectra are described. Typical sensor configurations are described and compared for various application scenarios, ranging from laboratory research to automated field and airborne packages. Recent applications of gas-dynamic sensors for air flows and fluxes of trace atmospheric species are presented. Applications of gas-dynamic and combustion sensors to research and development of high-speed flows aeropropulsion engines, and combustion emissions monitoring are presented in detail, along with emerging flow control systems based on these new sensors. Finally, technology in nonlinear frequency conversion, UV laser materials, room-temperature mid-IR materials and broadly tunable multisection devices is reviewed to suggest new sensor possibilities.

Description: Polar stratospheric clouds (PSC's) provide surfaces for heterogeneous processes which can dramatically alter the normal partitioning of odd nitrogen and chlorine families in the winter polar stratospheres, setting up conditions for significant ozone depletion as manifested in the springtime Antarctic ozone hole. The spatial and temporal distribution of PSC's is important for parameterizing PSC occurrence in multidimensional photochemical models whose use is essential for fully understanding observed Antarctic ozone losses as well as for accessing the possibility of a similar phemonenon occurring in the future in the Arctic. The Stratospheric Aerosol Measurement (SAM) 2 sensor, a single-channel (1mu m) photometer launched into a Sun-synchronous orbit aboard the Nimbus 7 satellite in October 1978, provided a unique database to establish the climatology of PSC's. Poole and Pitts (1994) used the record of high-latitude aerosol extinction obtained by SAM II from 1979-1989 to establish the climatology of PSC occurrences in the Arctic and Antarctic. Unfortunately, little information about PSC composition or type was detectable from the single-wavelength SAM II data.

Description: Urban metabolism measures quantitatively a city's load on the natural environment. We update the Newcombe et al. (3) pioneering study of Hong Kong's urban metabolism in 1971, highlighting trends in resource consumption and waste generation. Per capita food, water and materials consumption have surged since the early 1970s by 20%, 40%, and 149%, respectively. Tremendous pollution has accompanied this growing affluence and materialism, and total air emissions, CO2 outputs, municipal solid wastes, and sewage discharges have risen by 30%, 250%, 245%, and 153%. As a result, systemic overload of land, atmospheric and water systems has occurred. While some strategies to tackle deteriorating environmental quality have succeeded, greater and more far-reaching changes in consumer behavior and government policy are needed if Hong Kong is to achieve its stated goal of becoming "a truly sustainable city" in the 21st century.

Description: The Techa River (Southern Urals, Russia) was contaminated in 1949-1956 by liquid radioactive wastes from the Mayak complex, the first Russian facility for the production of plutonium. The measurements of environmental contamination were started in 1951. A simple model describing radionuclide transport along the free-flowing river and the accumulation of radionuclides by bottom sediments is presented. This model successfully correlates the rates of radionuclide releases as reconstructed by the Mayak experts, hydrological data, and available environmental monitoring data for the early period of contamination (1949-1951). The model was developed to reconstruct doses for people who lived in the riverside communities during the period of the releases and who were chronically exposed to external and internal irradiation. The model fills the data gaps and permits reconstruction of external gamma-exposure rates in air on the river bank and radionuclide concentrations in river water used for drinking and other household needs in 1949-1951.

Description: The spectrum and light curve of the bright X-ray source CG X-1 in the field of the Circinus galaxy are reexamined. Previous analyses have concluded that the source is an accreting black hole of mass 〉 or approx. 50 solar masses although it has been noted that the light curve resembles that of an AM Herculis system. Here we show that the short period and an assumed main-sequence companion constrain the mass of the companion to less than 1 solar mass. Furthermore, a possible eclipse seen during one of the Chandra observations and a subsequent XMM-Newton observation constrain the mass of the compact object to less than 60 solar masses. If such a system lies in the Circinus galaxy, then the accreting object must either radiate anisotropically or strongly violate the Eddington limit. Even if the emission is beamed, then the companion star that intercepts this flux during eclipse will be driven out of thermal equilibrium and evaporate within approx. 10(exp 3) yr. We find that the observations cannot rule out an AM Herculis system in the Milky Way and that such a system can account for the variations seen in the light curve.

Description: The next generation of high resolution UV imaging spacecraft are being prepared for studying the airglow and aurora of the Earth, the other terrestrial planets and the Jovian planets. To keep pace with these technological improvements we have developed a laboratory program to provide electron impact collision cross sections of the major molecular planetary gases (H2, N2, CO2, O2, and CO). Spectra under optically thin conditions have been measured with a high resolution (lambda/delta(lambda) = 50000) UV spectrometer in tandem with electron impact collision chamber. High resolution spectra of the Lyman and Wemer band systems of H2 have been obtained and modeled. Synthetic spectral intensities based on the J-dependent transition probabilities that include ro-vibronic perturbations are in very good agreement with experimental intensities. The kinetic energy distribution of H(2p,3p) atoms resulting from electron impact dissociation of H2 has been measured. The distribution is based on the first measurement of the H Lyman-alpha (H L(alpha)) and H Lyman-beta (H L(beta)) emission line Doppler profiles. Electron impact dissociation of H2 is believed to be one of the major mechanisms leading to the observed wide profile of H L-alpha from Jupiter aurora by the Hubble Space Telescope (HST). Analysis of the deconvolved line profile of H L-alpha reveals the existence of a narrow line peak (40 mA FWHM) and a broad pedestal base (240 mA FWHM). The band strengths of the electron excited N2 (C(sup 3) Pi(sub(upsilon) - B(sup 3)Pi(sub g)) second positive system have been measured in the middle ultraviolet. We report a quantitative measurement of the predissociation fraction 0.15 +/- 01(sup .045, sub .01) at 300 K in the N2 c'(sub )4 (1)sigma(sup +, sub g) - x(1)sigma(sup +, sub g)(00) band, with an experimental determination of rotational line strengths to be used to understand N2 EUV emission from Titan, Triton and the Earth.

Description: NASA personnel at Kennedy Space Center's Material Science Laboratory have developed new environmentally sound precision cleaning and verification techniques for systems and components found at the center. This technology is required to replace existing methods traditionally employing CFC-113. The new patent-pending technique of precision cleaning verification is for large components of cryogenic fluid systems. These are stainless steel, sand cast valve bodies with internal surface areas ranging from 0.2 to 0.9 m(exp 2). Extrapolation of this technique to components of even larger sizes (by orders of magnitude) is planned. Currently, the verification process is completely manual. In the new technique, a high velocity, low volume water stream impacts the part to be verified. This process is referred to as Breathing Air/Water Impingement and forms the basis for the Impingement Verification System (IVS). The system is unique in that a gas stream is used to accelerate the water droplets to high speeds. Water is injected into the gas stream in a small, continuous amount. The air/water mixture is then passed through a converging-diverging nozzle where the gas is accelerated to supersonic velocities. These droplets impart sufficient energy to the precision cleaned surface to place non-volatile residue (NVR) contaminants into suspension in the water. The sample water is collected and its NVR level is determined by total organic carbon (TOC) analysis at 880 C. The TOC, in ppm carbon, is used to establish the NVR level. A correlation between the present gravimetric CFC-113 NVR and the IVS NVR is found from experimental sensitivity factors measured for various contaminants. The sensitivity has the units of ppm of carbon per mg-ft(exp 2) of contaminant. In this paper, the equipment is described and data are presented showing the development of the sensitivity factors from a test set including four NVR's impinged from witness plates of 0.05 to 0.75 m(exp 2).

Description: The NASA White Sands Test Facility (WSTF) is developing cleaning and verification processes to replace currently used chlorofluorocarbon-113- (CFC-113-) based processes. The processes being evaluated include both aqueous- and solvent-based techniques. The presentation will include the findings of investigations of aqueous cleaning and verification processes that are based on a draft of a proposed NASA Kennedy Space Center (KSC) cleaning procedure. Verification testing with known contaminants, such as hydraulic fluid and commonly used oils, established correlations between nonvolatile residue and CFC-113. Recoveries ranged from 35 to 60 percent of theoretical. WSTF is also investigating enhancements to aqueous sampling for organics and particulates. Although aqueous alternatives have been identified for several processes, a need still exists for nonaqueous solvent cleaning, such as the cleaning and cleanliness verification of gauges used for oxygen service. The cleaning effectiveness of tetrachloroethylene (PCE), trichloroethylene (TCE), ethanol, hydrochlorofluorocarbon-225 (HCFC-225), tert-butylmethylether, and n-Hexane was evaluated using aerospace gauges and precision instruments and then compared to the cleaning effectiveness of CFC-113. Solvents considered for use in oxygen systems were also tested for oxygen compatibility using high-pressure oxygen autoignition and liquid oxygen mechanical impact testing.

Description: Solid-waste treatment in space for Advanced Life Support, ALS, applications requires that the material can be safely processed and stored in a confined environment. Many solid-wastes are not stable because they are wet (40-90% moisture) and contain levels of soluble organic compounds that can contribute to the growth of undesirable microorganisms with concomitant production of noxious odors. In the absence of integrated Advanced Life Support systems on orbit, permanent gas, trace volatile organic and microbiological analyses were performed on crew refuse returned from the volume F "wet" trash of three consecutive Shuttle missions (STS-105, 109, and 110). These analyses were designed to characterize the short-term biological stability of the material and assess potential crew risks resulting from microbial decay processes during storage. Waste samples were collected post-orbiter landing and sorted into packaging material, food waste, toilet waste, and bulk liquid fractions deposited during flight in the volume F container. Aerobic and anaerobic microbial loads were determined in each fraction by cultivation on R2A and by acridine orange direct count (AODC). Dry and ash weights were performed to determine both water and organic content of the materials. Experiments to determine the aerobic and anaerobic biostability of refuse stored for varying periods of time were performed by on-line monitoring of CO2 and laboratory analysis for production of hydrogen sulfide and methane. Volatile organic compounds and permanent gases were analyzed using EPA Method TO15 by USEPA et al. [EPA Method TO15, The Determination of Volatile Organic Compounds (VOCs) in Ambient Air using SUMMA, Passivated Canister Sampling and Gas Chromatographic Analysis,1999] with gas chromatography/mass spectrometry and by gas chromatography with selective detectors. These baseline measures of waste stream content, labile organics, and microbial load in the volume F Shuttle trash provide data for waste subsystem analysis and atmospheric management within the ALS Project. Published by Elsevier Ltd on behalf of COSPAR.

Description: Drinking water and condensate samples collected from the US Space Shuttle and the Russian Mir Space Station are analyzed routinely at the NASA-Johnson Space Center as part of an ongoing effort to verify water quality and monitor the environment of the spacecraft. Water quality monitoring is particularly important for the Mir water supply because approximately half of the water consumed is recovered from humidity condensate. Drinking water on Shuttle is derived from the fuel cells. Because there is little equipment on board the spacecraft for monitoring the water quality, samples collected by the crew are transported to Earth on Shuttle or Soyuz vehicles, and analyzed exhaustively. As part of the test battery, anions and cations are measured by ion chromatography, and carboxylates and amines by capillary electrophoresis. Analytical data from Shuttle water samples collected before and after several missions, and Mir condensate and potable recovered water samples representing several recent missions are presented and discussed. Results show that Shuttle water is of distilled quality, and Mir recovered water contains various levels of minerals imparted during the recovery processes as designed. Organic ions are rarely detected in potable water samples, but were present in humidity condensate samples.

Description: Rejection characteristics of nitrogen compounds were examined for reverse osmosis, nanofiltration, and low-pressure reverse osmosis membranes. The rejection of nitrogen compounds is explained by integrating experimental results with calculations using the extended Nernst-Planck model coupled with a steric hindrance model. The molecular weight and chemical structure of nitrogen compounds appear to be less important in determining rejection than electrostatic properties. The rejection is greatest when the Donnan potential exceeds 0.05 V or when the ratio of the solute radius to the pore radius is greater than 0.8. The transport of solute in the pore is dominated by diffusion, although convective transport is significant for organic nitrogen compounds. Electromigration contributes negligibly to the overall solute transport in the membrane. Urea, a small organic compound, has lower rejection than ionic compounds such as ammonium, nitrate, and nitrite, indicating the critical role of electrostatic interaction in rejection. This suggests that better treatment efficiency for organic nitrogen compounds can be obtained after ammonification of urea.

Description: Various aspects of the Continuous Observations of the Rotation of the Earth (CORE) program are presented, including the science goals, validation strategy, and evolutionary plan.

Description: Digital Particle Imaging Velocimetry (DPIV) is a powerful measurement technique, which can be used as an alternative or complementary approach to Laser Doppler Velocimetry (LDV) in a wide range of research applications. The instantaneous planar velocity measurements obtained with PIV make it an attractive technique for use in the study of the complex flow fields encountered in turbomachinery. Many of the same issues encountered in the application of LDV to rotating machinery apply in the application of PIV. Techniques for optical access, light sheet delivery, CCD camera technology and particulate seeding are discussed. Results from the successful application of the PIV technique to both the blade passage region of a transonic axial compressor and the diffuser region of a high speed centrifugal compressor are presented. Both instantaneous and time-averaged flow fields were obtained. The 95% confidence intervals for the time-averaged velocity estimates were also determined. Results from the use of PIV to study surge in a centrifugal compressor are discussed. In addition, combined correlation/particle tracking results yielding super-resolution velocity measurements are presented.

Description: This presentation discusses the problem of local air quality as it is affected by modern aircraft engine exhaust and the objective of this workshop. It begins with a discussion on the nature and sources of particulates and aerosols. The problems, and the technical considerations of how to regulate the aircraft emissions, are reviewed. There is no local (i.e., state or county) regulations of the aircraft operations. Amongst the conclusions are: (1) there is an inadequate database of information regarding the emittants from aircrafts. (2) That data which does exist represents older engines and aircraft, it is not representative of the advanced and future fleet.

Description: The aerosol retrieval algorithms used by the Moderate-Resolution Imaging Spectroradiometer (MODIS) and Multi-Angle Imaging SpectroRadiometer (MISR) sensors on the Earth Observing Satellite (EOS) AM-1 platform operate by comparing measured radiances with tabulated radiances that have been computed for specific aerosol models. These aerosol models are based almost entirely on surface and/or column averaged measurements and so may not accurately represent the ambient aerosol properties. Therefore, to validate these EOS algorithms and to determine the effects of aerosols on the clear-sky radiative flux, we have begun to evaluate the vertical variability of ambient aerosol properties using the aerosol backscattering and extinction profiles measured by the Cloud and Radiation Testbed (CART) and NASA Goddard Space Flight Center (GSFC) Raman Lidars. Using the procedures developed for the GSFC Scanning Raman Lidar (SRL), we have developed and have begun to implement algorithms for the CART Raman Lidar to routinely provide profiles of aerosol extinction and backscattering during both nighttime and ,daytime operations. Aerosol backscattering and extinction profiles are computed for both lidar systems using data acquired during the 1996 and 1997 Water Vapor Intensive Operating Periods (IOPs). By integrating these aerosol extinction profiles, we derive measurements of aerosol optical thickness and compare these with coincident sun photometer measurements. We also use these measurements to measure the aerosol extinction/backscatter ratio S(sub a) (i.e. 'lidar ratio'). Furthermore, we use the simultaneous water vapor measurements acquired by these Raman lidars to investigate the effects of water vapor on aerosol optical properties.

Description: The scientific requirements and implications for the instruments and telescope design for the Next Generation Space Telescope (NGST) are described. A candidate concept is a deployable, 8 m diameter telescope, optimized for the near infrared region, but featuring instruments capable of observing up to 30 micrometers. The observatory is radiatively cooled to approximately 30 K.

Description: New technological advances have made possible new active remote sensing capabilities from space. Utilizing these technologies, the Ozone Research with Advanced Cooperative Lidar Experiment (ORACLE) will provide high spatial resolution measurements of ozone, clouds and aerosols in the stratosphere and lower troposphere. Simultaneous measurements of ozone, clouds and aerosols will assist in the understanding of global change, atmospheric chemistry and meteorology.

Description: This paper will describe the planned 3-year Pathfinder Instruments for Cloud and Aerosol Spaceborne Observations (PICASSO) mission, its instrumentation and implementation. It will use LITE and other data, plus analyses, to show the feasibility of such a mission. PICASSO is being proposed for NASA's Earth System Science Pathfinder (ESSP) program with launch predicted in 2003.

Description: Detailed understanding of the properties of the point-spread function (PSF) of Space Telescope Imaging Spectrograph (STIS) imaging modes is necessary to separate real effects of geometrically complex astronomical sources, such as protoplanetary disks surrounding bright stars, from instrumental effects, such as scattering and diffraction. In order to investigate STIS imaging properties we have numerically simulated broadband stellar PSFs generated by STIS in CCD clear imaging mode, including the effects of the Lyot stop and the coronagraphic wedges. The input spectrum is a stellar model atmosphere of the appropriate spectral type, convolved with the pre-flight STIS CCD response function. The PSF modeler generates broadband PSFs by co-adding weighted monochromatic PSFs across the waveband.

Description: Using the Early Release Observation of 9 Comae, we demonstrate an iterative method for correcting Space Telescope Imaging Spectrograph (STIS) echelle spectra for the effects of the echelle ripple. This analytic approach allows the actual spectrum of interest to be used in the determination of its calibration. The late F star 9 Comae is not an ideal candidate for this method, due to the many absorption lines present in its E230M spectrum, yet, given this difficulty, the method still works quite well.

Description: The installation of the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) allows for the first time two-dimensional optical and ultraviolet slitless spectroscopy of faint objects from space. The STIS Parallel Survey (SPS) routinely obtains broad band images and slitless spectra of random fields in parallel with HST observations using other instruments. The SPS is designed to study a wide variety of astrophysical phenomena, including the rate of star formation in galaxies at intermediate to high redshift through the detection of emission-line galaxies. We present the first results of the SPS, which demonstrate the capability of STIS slitless spectroscopy to detect and identify high-redshift galaxies.

Description: An analysis of the fine pointing errors of the Hubble Space Telescope (HST), in the range from 1 to 15 milliarcsecs, is reported on. The emphasis is on the study of the performance characteristics of the pointing control system, fine guidance sensors and the optical telescope assembly, which produce relative attitude and astrometric measurement errors. Since the first servicing mission in December 1993, the HST relative short term position stability is of the order of 3 milliarcsecs RMS when averaged over 1 min intervals. At this level of accuracy, longer term systematic attitude errors in this range can have a noticeable impact on the telescope's observations. The various error sources are described, including: internal temperature effects; spacecraft structure temperature effects; calibration procedures, and computational inaccuracies.

Description: The prospects for global astrometric measurements with the space interferometry mission (SIM) are discussed. The SIM mission will perform four microarcsec astrometric measurements on objects as faint as 20 mag using the optical interferometry technique with a 10 m baseline. The SIM satellite will perform narrow angle astrometry and global astrometry by means of an astrometric grid. The sensitivities of the SIM global astrometric performance and the grid accuracy versus instrumental parameters and sky coverage schemes are reported on. The problems in finding suitable astrometric grid objects to support microarcsec astrometry, and related ground-based observation programs are discussed.

Description: The space interferometry mission (SIM), for launch in 2004, is expected to determine the positions of point sources to a global accuracy of 4 microarcsec, and an accuracy of 1 microarcsec over small angles. The instrument will reach 200 mag in 3 x 10(exp 4) s and has a nominal lifetime of five years. A nulling capability will be provided and synthesis imaging and near-infrared capabilities are being considered. These capabilities will extend those of the Hipparcos mission by almost three orders of magnitude in every sense. The NASA's expectation for the scientific return from the SIM mission is outlined in terms of the areas of stellar physics, galactic structure and extragalactic astrophysics, including the distance scale problem.

Description: The burst and transient source experiment (BATSE) survey of the high energy emission from supernova remnants is reported on. The ability of BATSE to continuously monitor the entire sky in the 20 keV to 2 MeV energy range enables a large group of remnants to by studied at high energies. Preliminary analysis indicates the likely detection of several supernova remnants other than the Crab nebula. Among these are MSH 15-52, Vela, Cas A and possibly HB 9. The techniques employed are discussed together with the status of the survey and its limitations.

Description: The progress, results and future plans for the following objectives are presented: (1) To compare the types, rates, and magnitudes of surficial modification processes that have operated in Northwest China and the Southwestern U.S.; (2) To quantify and understand the basis of the remote sensing signatures of these processes to allow extrapolation from field sites to regional maps and to allow comparisons between widely separated arid regions; (3) To use the resulting chronologies to help define the temporal and spatial distribution of continental climate changes; and (4) Determine the ages of movements on some of the active faults in Northwestern China.

Description: In response to the elimination of production of several Ozone Depleting Chemicals (ODCs) which have been widely used in successful space flight mechanism cleaning and lubricating procedures, GSFC developed and implemented an overall philosophy of mitigating the risks to flight hardware during the transition phase to ODC-Free cleaning procedures. One leg of that philosophy is the initiation of a several tier testing program which will deliver increasing amounts of information over the next few years, starting with original surface analysis comparisons between ODC and various ODC-Free cleaning technologies. The other leg is the stockpiling of an appropriate amount of ODC solvents such that all short term GSFC missions will be able to stay with or revert to heritage cleaning and lubricating procedures in the face of life issues. While tribological testing, mechanism life testing and space-flight experience will ultimately bring us into the 21st century with environmentally friendly means of cleaning long-life precision mechanism components, many satellites will be launched over the next few years with a number of important tribological questions unanswered. In order to prepare for this challenge, the Materials Engineering Branch in cooperation with the Electromechanical Branch launched an intensive review of all ongoing missions. The failure risk was determined for each long-life mechanism based on a number of parameters, including a comparison of flight solvents used to clean the heritage/life test hardware. Also studied was the ability of the mechanism manufacturers to stockpile ODCs based on state laws and company policies. A stockpiling strategy was constructed based on this information and subsequently implemented. This paper provides an overview of the GSFC ODC elimination risk mitigation philosophy as well as a detailed examination of the development of the ODC stockpiling plan.

Description: Data from the transient gamma ray germanium detector taken during 1995 provide a limited ability to study the high resolution spectrum of the X-ray transient GRO J1655-40. During a two-day period around the peak intensity, the soft spectrum was measured and found to be consistent with a power law spectrum with photon index -3.0 +/- 0.2. No evidence was found for narrow spectral features in the 50 to 100 keV band or around 511 keV. The 3 sigma upper limit for a narrow emission line at 511 keV is 1.2 x 10(exp -2) phot/cu cm s.

Description: The broad line radio galaxy 3C 390.3 was observed in a multiwavelength monitoring campaign by the Rosat high resolution imager (HRI), the International Ultraviolet Explorer and ground-based optical, infrared and and radio observations. The preliminary results from the campaign are reported, with emphasis on the X-ray observations. A large amplitude variability is observed. The light curve is dominated by a flare near JD 2449800, characterized by a doubling time scale of 9 days and a general increase in flux after the flare. The optical R and I band light curves show a general increase in flux. Spectra from the Advanced Satellite for Cosmology and Astrophysics (ASCA) obtained before and after the flare can be described by an absorbed power law.

Description: The results of four simultaneous observations of Cygnus X-1 by Ginga and the orientated scintillation spectrometer experiment (OSSE) are presented. The X-ray/gamma ray spectra can be described by an intrinsic continuum and a component due to Compton reflection including an iron K alpha line. The intrinsic spectrum at X-ray energies is a power law with a photon spectral index of Gamma = 1.6. The intrinsic gamma ray spectrum can be phenomenologically described by either a power law without cutoff up to 150 keV and an exponential cutoff above this energy, or by an expoential cutoff power law and a second hard component.

Description: To show that robust vortices can exist in the solar nebula, a pseudospectral model has been developed to examine the evolution of the vortex in a Keplerian shear. Calculations show that a vortex can exist for 10(exp 4)yr at Jupiter's radius.

Description: The time evolution of dust particles in circumstellar disk-like structures around protostars and young stellar objects is discussed. In particular, we consider the coagulation of grains due to collisional aggregation. The coagulation of the particles is calculated by solving numerically the non-linear Smoluchowski equation. The different physical processes leading to relative velocities between the grains are investigated. The relative velocities may be induced by Brownian motion, turbulence and drift motion. Starting from different regimes which can be identified during the grain growth we also discuss the evolution of dust opacities. These opacities are important for both the derivation of the circumstellar dust mass from submillimeter/millimeter continuum observations and the dynamical behavior of the disks. We present results of our numerical studies of the coagulation of dust grains in a turbulent protoplanetary accretion disk described by a time-dependent one-dimensional (radial) alpha-model. For several periods and disk radii, mass distributions of coagulated grains have been calculated. From these mass spectra, we determined the corresponding Rosseland mean dust opacities. The influence of grain opacity changes due to dust coagulation on the dynamical evolution of a protostellar disk is considered. Significant changes in the thermal structure of the protoplanetary nebula are observed. A 'gap' in the accretion disk forms at the very frontier of the coagulation, i.e., behind the sublimation boundary in the region between 1 and 5 AU.

Description: We present OVRO interferometric observations of linearly polarized emission from magnetically aligned dust grains which allow the magnetic field geometry in nearby star formation regions to be probed on scales ranging from 100 to 3000 AU. Current results include observations of the young stellar objects NGC1333/IRAS 4A, IRAS 16293-2422 and Orion IRc2-KL.

Description: The emission from polycyclic aromatic hydrocarbons (PAH's) in the Orion Bar region is investigated using a combination of narrow-band imaging and long-slit spectroscopy. The goal was to study how the strength of the PAH bands vary with spatial position in this edge-on photo-dissociation region. The specific focus here is how these variations constrain the carrier of the 3.4 micron band.

Description: Carbon-rich Asymptotic Giant Branch stars are sites of dust formation and undergo mass loss at rates ranging from 10(exp -7) to 10(exp -4) solar mass/yr. The state-of-the-art in modeling these processes is time-dependent models which simultaneously solve the grain formation and gas dynamics problem. We present results from such a model, which also includes an exact solution of the radiative transfer within the system.

Description: Silicon carbide (SiC) is known to form in circumstellar shells around carbon stars. SiC can come in two basic types - hexagonal alpha-SiC or cubic beta-SiC. Laboratory studies have shown that both types of SiC exhibit an emission feature in the 11-11.5 micron region, the size and shape of the feature varying with type, size and shape of the SiC grains. Such a feature can be seen in the spectra of carbon stars. Silicon carbide grains have also been found in meteorites. The aim of the current work is to identity the type(s) of SiC found in circumstellar shells and how they might relate to meteoritic SiC samples. We have used the CGS3 spectrometer at the 3.8 m UKIRT to obtain 7.5-13.5 micron spectra of 31 definite or proposed carbon stars. After flux-calibration, each spectrum was fitted using a chi(exp 2)-minimisation routine equipped with the published laboratory optical constants of six different samples of small SiC particles, together with the ability to fit the underlying continuum using a range of grain emissivity laws. It was found that the majority of observed SiC emission features could only be fitted by alpha-SiC grains. The lack of beta-SiC is surprising, as this is the form most commonly found in meteorites. Included in the sample were four sources, all of which have been proposed to be carbon stars, that appear to show the SiC feature in absorption.

Description: The photometric behavior of the Herbig Ae star V351 Ori was investigated combining data from the literature with new photometry. It is shown that this object changed from a Herbig Ae star with strong photometric variations, due to extinction by circumstellar dust clouds, to that of an almost non-variable star. Such a behavior is not unique; it has been found also in the star BN Ori. This suggests that such transitions as well as the opposite must occur quite often during the evolution of these intermediate mass stars towards the main-sequence. A provisional model to explain V351 Ori's behavior, in which it is assumed that a temporarily strong accretion of matter onto the star took place, is proposed.

Description: The pre-main sequence star V536 Aql, classified as a K7 classical T Tauri star by Cohen & Kuhi has been resolved, by high angular resolution near-infrared speckle observations, as a close binary (0.52 sec separation at 17 deg) surrounded by extended structures. These structures seen, both in the July 1993 and April 1994 observations, are not at the same position in the reconstructed image and do not present exactly the same shape at both times. Although it is unlikely that the presence of these structures is due to seeing calibration problems, the exact shape might be affected by it. We cannot presently make a final interpretation of the observations but can formulate different possibilities: the 'circumstellar' material seen in our images can be an independent cloud, or simply gas or dust, in front of the system on our line of sight, but close enough to still be illuminated by the binary; this material may be 'by chance' there or be a remnant of the material in which the star was born. We propose a model to explain the position variation of the extended structures. New observations are under reduction and should help to determine the exact value of this motion. At their distance from the star, motions of the extended matter would correspond to velocities much higher than the Kepler velocities. To explain this, we have developed a model based on a 'torch-light' effect. The possibility that the observed elongated structures belong to a circumstellar or circumbinary disk are discussed.

Description: The next generation of subsonic engines can be expected to continue the historical trend towards increased thrust to weight (T/W) and decreased specific fuel consumption (SFC). Development programs currently underway throughout the gas turbine industry such as DOD's Integrated High Performance Turbine Engine Technology (IHPTET), and more recently NASA's Advanced Subsonic Transport (AST) programs, have altered these trends in both pace and magnitude. Advanced seals and sealing technologies have become a prominent part of these efforts due to the large potential performance gains which can be realized. Allison has recently completed a study for NASA the goal of which was to quantize the potential performance benefits which might accrue through the use of advanced seals in future subsonic gas turbine engines. For the study, two engines where analyzed, a small turboshaft and a larger turbofan engine to help assess the effect of engine size on the results. Engines were analyzed stage by stage with the most sensitive areas highlighted. Leakage characteristics for advanced seals were then substituted into secondary airflow models, and the leakage reductions documented. These leakage reductions were then converted to changes in performance, i.e. increased range, decreased takeoff gross weight, etc. and presented. It was found that the development and use of a realtively few advanced seals, less than 5, could for example reduce SFC by 10% or more.

Description: Thermal analysis in both simple and complex models can require calculating the propagation of radiant energy to and from multiple surfaces. This can be accomplished through simple estimation techniques or complex computationally intense computer modeling simulations. Currently there are a variety of computer analysis techniques used to simulate the propagation of radiant energy, each having advantages and disadvantages. The major objective of this effort was to compare two ray tracing radiation propagation analysis programs (NEVADA and TSS) Net Energy Verification and Determination Analyzer and Thermal Synthesizer System with experimental data. Results from a non-flowing, electrically heated test rig was used to verify the calculated radiant energy propagation from a nozzle geometry that represents an aircraft propulsion nozzle system. In general the programs produced comparable overall results, and results slightly higher then the experimental data. Upon inspection of individual radiation interchange factors, differences were evident and would have been magnified if a more radical model temperature profile was analyzed. Bidirectional reflectivity data (BRDF) was not used do to modeling limitations in TSS. For code comparison purposes, this nozzle geometry represents only one case for one set of analysis conditions. Since each computer code has advantages and disadvantages bases on scope, requirements, and desired accuracy, the usefulness of this single case study may be limiting.

Description: The assignments and charges to the three workgroups are discussed. The three workgroups were: (1) Trace Chemistry, (2) Instrumentation, (3) Venues and procedures.

Description: We presented results from the SASS Near-Field Interactions Flight (SNIF-III) Experiment which was conducted during May and June 1997 in collaboration with the Vermont and New Jersey Air National Guard Units. The project objectives were to quantify the fraction of fuel sulfur converted to S(VI) species by jet engines and to gain a better understanding of particle formation and growth processes within aircraft wakes. Size and volatility segregated aerosol measurements along with sulfur species measurements were recorded in the exhaust of F-16 aircraft equipped with F-100 engines burning fuels with a range of fuel S concentrations at different altitudes and engine power settings. A total of 10 missions were flown in which F-16 exhaust plumes were sampled by an instrumented T-39 Sabreliner aircraft. On six of the flights, measurements were obtained behind the same two aircraft, one burning standard JP-8 fuel and the other either approximately 28 ppm or 1100 ppm S fuel or an equal mixture of the two (approximately 560 ppm S). A pair of flights was conducted for each fuel mixture, one at 30,000 ft altitude and the other starting at 35,000 ft and climbing to higher altitudes if contrail conditions were not encountered at the initial flight level. In each flight, the F-16s were operated at two power settings, approx. 80% and full military power. Exhaust emissions were sampled behind both aircraft at each flight level, power setting, and fuel S concentration at an initial aircraft separation of 30 m, gradually widening to about 3 km. Analyses of the aerosol data in the cases where fuel S was varied suggest results were consistent with observations from project SUCCESS, i.e., a significant fraction of the fuel S was oxidized to form S(VI) species and volatile particle emission indices (EIs) in comparably aged plumes exhibited a nonlinear dependence upon the fuel S concentration. For the high sulfur fuel, volatile particle EIs in 10-second-old-plumes were 2 to 3 x 10 (exp 17) / kg of fuel burned and exhibited no obvious trend with engine power setting or flight altitude. In contrast, about 8-fold fewer particles were observed in similarly aged plumes from the same aircraft burning fuel with 560 ppm S content and EIs of 1 x 10(exp 15)/ kg of fuel burned were observed in the 28 ppm S fuel case. Moreover, data recorded as a function of plume age indicates that formation and growth of the volatile particles proceeds more slowly as the fuel S level is reduced. For example, ultrafine particle concentrations appear to stabilize within 5 seconds after emission in the 1100 ppm S cases but are still increasing in 20-second old plumes produced from burning the 560 ppm S fuel.

Description: The overall focus of our research is to document long-term elevation change of the Greenland ice sheet using satellite altimeter data. In addition, we are investigating seasonal and interannual variations in the ice-sheet elevations to place the long-term measurements in context. Specific objectives of this research include: 1) Developing new techniques to significantly improve the accuracy of elevation-change estimates derived from satellite altimetry. 2) Measuring the elevation change of the Greenland ice sheet over a 10-year time period using Seasat (1978) and Geosat GM (1985-86) and Geosat ERM (1986-88) altimeter data. 3) Quantifying seasonal/interannual variations in the elevation-change estimates using the continuous time series of surface elevations from the Geosat GM and ERM datasets. 4) Extending the long-term elevation change analysis to two decades by incorporating data from the ERS-1/2 missions (1991-99) and, if available, the Geosat-Follow On (GFO) mission (1998-??).

Description: The Vulcan Photometric Planet Search is the ground-based counterpart of Kepler Mission Proposal. The Kepler Proposal calls for the launch of telescope to look intently at a small patch of sky for four year. The mission is designed to look for extra-solar planets that transit sun-like stars. The Kepler Mission should be able to detect Earth-size planets. This goal requires an instrument and software capable of detecting photometric changes of several parts per hundred thousand in the flux of a star. The goal also requires the continuous monitoring of about a hundred thousand stars. The Kepler Mission is a NASA Discovery Class proposal similar in cost to the Lunar Prospector. The Vulcan Search is also a NASA project but based at Lick Observatory. A small wide-field telescope monitors various star fields successively during the year. Dozens of images, each containing tens of thousands of stars, are taken any night that weather permits. The images are then monitored for photometric changes of the order of one part in a thousand. These changes would reveal the transit of an inner-orbit Jupiter-size planet similar to those discovered recently in spectroscopic searches. In order to achieve a one part in one thousand photometric precision even the choice of a filter used in taking an exposure can be critical. The ultimate purpose of an filter is to increase the signal-to-noise ratio (S/N) of one's observation. Ideally, filters reduce the sky glow cause by street lights and, thereby, make the star images more distinct. The higher the S/N, the higher is the chance to observe a transit signal that indicates the presence of a new planet. It is, therefore, important to select the filter that maximizes the S/N.

Description: Through the NASA/Industry Cooperative Effort (NICE) agreement, NASA Lewis and industry partners are developing a new engine simulation, called the National Cycle Program (NCP), which is the initial framework of NPSS. NCP is the first phase toward achieving the goal of NPSS. This new software supports the aerothermodynamic system simulation process for the full life cycle of an engine. The National Cycle Program (NCP) was written following the Object Oriented Paradigm (C++, CORBA). The software development process used was also based on the Object Oriented paradigm. Software reviews, configuration management, test plans, requirements, design were all apart of the process used in developing NCP. Due to the many contributors to NCP, the stated software process was mandatory for building a common tool intended for use by so many organizations. The U.S. aircraft and airframe companies recognize NCP as the future industry standard for propulsion system modeling.

Description: The effect of clouds and aerosol on the atmospheric energy balance is a key global change problem. Full knowledge of aerosol distributions is difficult to obtain by passive sensing alone. Aerosol and cloud retrievals in several important areas can be significantly improved with active remote sensing by lidar. Micro Pulse Lidar (MPL) is an aerosol and cloud profilometer that provides a detailed picture of the vertical structure of boundary layer and elevated dust or smoke plume aerosols. MPL is a compact, fully eyesafe, ground-based, zenith pointing instrument capable of full-time, long-term unattended operation at 523 nm. In October of 1993, MPL began taking full-time measurements for the Atmospheric Radiation Measurement (ARM) program at its Southern Great Plains (SGP) site and has since expanded to ARM sites in the Tropical West Pacific (TWP) and the North Slope of Alaska (NSA). Other MPL's are moving out to some of the 60 world-wide Aerosol Robotic Network (AERONET) sites which are already equipped with automatic sun-sky scanning spectral radiometers providing total column optical depth measurements. Twelve additional MPL's have been purchased by NASA to add to the aerosol and cloud database of the EOS ground validation network. The original MPL vertical resolution was 300 meters but the newer versions have a vertical resolution of 30 meters. These expanding data sets offer a significant new resource for atmospheric radiation analysis. Under the direction of Jim Spinhirne, the MPL analysis team at NASA/GSFC has developed instrument correction and backscatter analysis techniques for ARM to detect cloud boundaries and analyze vertical aerosol structures. A summary of MPL applications is found in Hlavka (1997). With the aid of independent total column optical depth instruments such as the Multifilter Rotating Shadowband Radiometer (MFRSR) at the ARM sites or sun photometers at the AERONET sites, the MPL data can be calibrated, and time-resolved vertical profiles of aerosol optical depth as well as aerosol extinction can be calculated. The techniques used to calibrate the lidar, calculate the aerosol extinction-to-backscatter ratio, and produce profiles of aerosol extinction and aerosol optical depths, will be described. Results using these techniques will be presented for case studies at the ARM site in the Tropical West Pacific and later in the Southern Great Plains.

Description: In November of 1998 (or in 1999 with about equal probability) will be our one chance in a lifetime to anticipate with some certainty the occurrence of a meteor storm. For a period of up to 2 hours, rates are expected to increase above 1 meteor per second for a naked eye observer. At that time, Earth passes through the outer regimes of the dust trail of comet 55P/Tempel-Tuttle. The high meteor flux offers unprecedented precision in characterizing the dust trail in terms of spatial and particle size distributions of dust grains and allows the measurement of composition, morphology and orbits of individual cometary grains relatively soon after ejection from the comet. By using the Earth's atmosphere as a detector for the dust trains, grains are sampled over a wide mass range, from the typical grain size of zodiacal dust (40 - 200 micron) up until the rare boulders that can still be lifted off the comet nucleus.

Description: This overview discusses three interferometers for characterization of exozodiacal dust: Keck Interferometer, the Very Large Telescope Interferometer (VLTI), and the Space Interferometry Mission (SIM). The emphasis will be toward the Keck Interferometer, as exozodiacal dust characterization is one of its science requirements.

Description: WIRE, SOFIA and SIRTF are three planned NASA missions for infrared astronomy. Each will make significant contributions to the study of exo-zodiacal dust, planetary debris disks, and/or the zodiacal material within our own solar system. These missions and their measurement and scientific capabilities are synopsized. The principal contribution of these missions to this field of study will be to establish and strengthen its intellectual foundations rather than to pinpoint specific targets for planetary searches. This is consistent with their relatively near-term availability. Moreover, this intellectual understanding can assure that subsequent missions approach this subject from a sound scientific perspective which will yield valuable results independent of the success of a particular planet finding strategy. Each of these missions - most urgently WIRE with its Fall, 1998 launch date - would make good use of a list of candidate target stars for exo-zodiacal/planet-finding studies. The preparation of such a list was one of the recommendations of the exo-zodiacal workshop.

Description: In Situ experiments on space craft yield information about dust parameters such as velocity, flux and size, and mass of particles. In Situ experiments as well as brightness measurements in the inner solar system have been made with Helios from .3 to 1 AU in the ecliptic plane which reveal two different dust populations with different bulk densities and relative velocities to the spacecraft. Zodiacal light measurements from Helios 1 and 2 reveal a radial brightness gradient proportional to R(exp -2.3). Measurements of dust particles in the outer solar system have been made onboard the Pioneer 10 and 11 spacecraft and for the high latitude region with Ulysses. Pioneer 10 and 11 also carried a spin-scan photopolarimeter that was used to map the zodiacal light and background starlight during the cruise to Jupiter in two broad bandpasses centered at .44 and .64 micron. Details of these measurements are briefly discussed.

Description: We describe the STIS autonomous target acquisition capabilities. We also present the results of dedicated tests executed as part of Cycle 7 calibration, following post-launch improvements to the Space Telescope Imaging Spectrograph (STIS) flight software. The residual pointing error from the acquisitions are 〈 0.5 CCD pixels, which is better than preflight estimates. Execution of peakups show clear improvement of target centering for slits of width 0.1 sec or smaller. These results may be used by Guest Observers in planning target acquisitions for their STIS programs.

Description: An intercomparison campaign for Lidar measurements of stratospheric ozone and aerosol has been conducted at the Primary Station of the Network for the Detection of Stratospheric Change (NDSC) in Ny-Alesund/Spitsbergen during January-February 1998. In addition to local instrumentation, the NDSC mobile ozone lidar from NASA/GSFC and the mobile aerosol lidar from Alfred Wegener Institute (AWI) participated. The aim is the validation of stratospheric ozone and aerosol profile measurements according to NDSC guidelines. This paper briefly presents the employed instruments and outlines the campaign. Results of the blind intercomparison of ozone profiles are given in a companion paper and temperature measurements are described in this issue.

Description: Lidar Atmospheric Sensing Experiment (LASE) is the first fully engineered, autonomous airborne DIAL (Differentials Absorption Lidar) system to measure water vapor, aerosols, and clouds throughout the troposphere. This system uses a double-pulsed Ti:sapphire laser, which is pumped by a frequency-doubled flashlamp-pumped Nd: YAG laser, to transmit light in the 815 mn absorption band of water vapor. LASE operates by locking to a strong water vapor line and electronically tuning to any spectral position on the absorption line to choose the suitable absorption cross-section for optimum measurements over a range of concentrations in the atmosphere. During the LASE Validation Experiment, which was conducted over Wallops Island during September, 1995, LASE operated on either the strong water line for measurements in middle to upper troposphere, or on the weak water line for measurements made in the middle to lower troposphere including the boundary layer. Comparisons with water vapor measurements made by airborne dew point and frost point hygrometers, NASA/GSFC (Goddard Space Flight Center) Raman Lidar, and radiosondes showed the LASE water vapor mixing ratio measurements to have an accuracy of better than 6% or 0.01 g/kg, whichever is larger, throughout the troposphere. In addition to measuring water vapor mixing ratio profiles, LASE simultaneously measures aerosol backscattering profiles at the off-line wavelength near 815 nm from which atmospheric scattering ratio (ASR) profiles are calculated. ASR is defined as the ratio of total (aerosol + molecular) atmospheric scattering to molecular scattering. Assuming a region with very low aerosol loading can be identified, such as that typically found just below the tropopause, then the ASR can be determined. The ASR profiles are calculated by normalizing the scattering in the region containing enhanced aerosols to the expected scattering by the "clean" atmosphere at that altitude. Images of the total ASR clearly depict cloud regions, including multiple cloud layers, thin upper level cirrus, etc., throughout the troposphere. New data products that are being derived from the LASE aerosol and water measurements include: 1) aerosol extinction coefficient, 2) aerosol optical thickness, 3) precipitable water vapor, and 4) relative humidity (RH). These products can be compared with airborne in-situ, and ground and satellite remote sensing measurements,. This paper presents a preliminary examination of RH profiles in the middle to upper troposphere that are generated from LASE measured water vapor mixing ratio profiles coupled with rawinsonde profiles of temperature and pressure.

Description: During January and February, 1998, a measurements campaign was held at the Network for the Detection of Stratospheric Change (NDSC) Arctic site at Ny-Alesund (78.9N). Lidar measurements of ozone, temperature and aerosol parameters were made along with balloon sonde and microwave measurements of ozone. Atmospheric temperatures were measured between 10 and 70 km. During the time of the campaign an strong warming occurred at the stratopause, elevating the measured temperature by as much as 80 K. The height of the stratopause descended at this time to below 40 km.

Description: The temperature structure of the middle atmosphere has been studied for several decades using a variety of techniques. However, temperature profiles derived from lidar measurements can provide improved vertical resolution and accuracy. Lidars can also provide long-term data series relatively absent of instrumental drift, and integration of the measurements over several hours removes most of the gravity wave-like short-scale disturbances. This paper describes a seasonal climatology of the middle atmosphere temperature derived from lidar measurements obtained at several mid- and low-latitude locations. Results from the following lidars, which have all obtained a long-term measurement record, were used in this study: the two Rayleigh lidars of the Service d'Aeronomie du CNRS, France, located at the Observatoire de Haute Provence (OHP, 44.0 deg N) and at the Centre d'Essais des Landes (CEL, 44.0 deg N), the two Rayleigh/Raman lidars of the Jet Propulsion Laboratory, USA, located at Table Mountain, California (TMF, 34.4 deg N) and at Mauna Loa, Hawaii (MLO, 19.5 deg N), and the Colorado State University, USA, sodium lidar located at Fort Collins, Colorado (CSU, 40.6 deg N). The overall data set extends from 1978 to 1997 with different periods of measurements depending on the instrument. Three of the instruments are located at primary or complementary stations (OHP, TMF, MLO) within the Network for Detection of Stratospheric Change (NDSC). Several aspects of the temperature climatology obtained by lidar in the middle atmosphere are presented, including the climatological temperature average through the year; the annual and semi-annual components, and the differences compared to the CIRA-86 climatological model.

Description: During early August 1997, the ozone column density measured over Lauder was unusually low, with a minimum value of 222 Dobson Units (DU) at August 10. These observations are striking since in August, during the Austral winter, the ozone column density should be heading towards its yearly maximum; The August mean ozone column density measured over Lauder between 1987 and 1996 was 348(+/-28) DU, the lowest monthly average in these ten years was 255 DU. Regular altitude profile measurements of ozone, performed at Network for the Detection of Stratospheric Change (NDSC) station Lauder, make it possible to do a detailed, altitude-resolved, study of the low ozone observations. The measurements show ozone poor air in two altitude regions of the stratosphere: A 'high region', extending from the 600 K to the 1050 K isentrope (25 to 34 km), and a 'low region', below about 550 K (22 km). High resolution reverse trajectory maps of potential vorticity (PV) and ozone mixing ratio, based on the assumption of passive advection by the large-scale three-dimensional winds, show that in the 'high region' the ozone poor air was part of the polar vortex, which was centered off the pole and extended over Lauder for several days, while in the 'low region' the ozone poor air was mixed in from low latitudes. A rapid recovery of the ozone column density, by more than 110 DU within 24 hours, was observed when in the low region an ozone rich filament of the polar vortex moved over Lauder, while in the high region the (ozone poor) high part of the vortex moved away.

Description: Airborne lidar measurements of aerosol and ozone distributions from the surface to above the tropopause over the South Pacific Ocean are presented. The measurements illustrate large-scale features of the region, and are used to quantify the relative contributions of different ozone sources to the tropospheric ozone budget in this remote region.

Description: A Kalman filter for the assimilation of long-lived atmospheric chemical constituents has been developed for two-dimensional transport models on isentropic surfaces over the globe. An important attribute of the Kalman filter is that it calculates error covariances of the constituent fields using the tracer dynamics. Consequently, the current Kalman-filter assimilation is a five-dimensional problem (coordinates of two points and time), and it can only be handled on computers with large memory and high floating point speed. In this paper, an implementation of the Kalman filter for distributed-memory, message-passing parallel computers is discussed. Two approaches were studied: an operator decomposition and a covariance decomposition. The latter was found to be more scalable than the former, and it possesses the property that the dynamical model does not need to be parallelized, which is of considerable practical advantage. This code is currently used to assimilate constituent data retrieved by limb sounders on the Upper Atmosphere Research Satellite. Tests of the code examined the variance transport and observability properties. Aspects of the parallel implementation, some timing results, and a brief discussion of the physical results will be presented.

Description: Various tests have been done of the Space Telescope Imaging Spectrograph (STIS) using internal wavecals to measure thermal motion of the spectral format on the detectors. In most cases, the spectral format moves less than the specification not to exceed 0.2 pixels per hour. Primary causes of the motion are (1) changes to the thermal design dictated by the warmer Aft Shroud environment and (2) on-orbit power cycling of Multi-Anode Microchannel Arrays (MAMA) electronics to minimize the effects of radiation hits on the MAMA detectors. The rear portion of the STIS optical bench is too warm to be held at a constant temperature by internal heaters. Electronics swing in temperature with an orbital and daily frequency. The thermal drift of the optical formats is not negligible, but is well behaved in most circumstances. The observer is advised to examine the trade-off between the most accurate wavelengths with best spectral/spatial resolutions versus increased overheads that directly affect the observing times. A long term concern is that the Aft Shroud thermal environment is predicted to heat up as much as one Centigrade degree per year. Progressively more of the bench would move out of thermal control. Thus the external cooler for STIS, being considered for the Third Servicing Mission is of major importance to the long term operation of STIS.

Description: The astrophysical implications of the large width of the 1809 keV gamma ray line from the decay of radioactive Al-26, recently observed with the gamma ray imaging spectrometer (GRIS), are discussed. While there may be no apparent single mechanism that can explain the observed broadening, high speed dust grains, extremely hot superbubbles and a large, low density gaseous halo were identified in the Galactic center region as the possible origins. The implications of these observations on the hot gas content in the interstellar medium are discussed.

Description: The phenomenon of broad gamma ray line splitting is discussed, together with a scenario for the suppression of the blue wings of these broad lines due to the geometry of the accelerated particle interaction region. The broad and narrow gamma ray line emissions are compared taking into account the line splitting effect. It is concluded that the observed gamma ray lines from Orion are most likely broad, implying that the low energy cosmic rays which produce this line emission consist mostly of C and heavier ions. The suppression of the proton and alpha particle abundances requires acceleration conditions such as the acceleration of the ejecta of the supernovae before mixing with the interstellar medium. Similar conditions are implied by observations of the B and Be in low metallicity stars formed during the first Gyr of galactic evolution.

Description: The spectral and timing characteristics from a sample, of 91 objects, of the variable sources obtained using the Kolmogorov-Smirnov test technique are presented. The data were extracted from the catalog constructed by White, Giommi and Angelini, the WGACAT, based on the pointed observations from the Rosat missions. The application of the test revealed more than 2400 individual variable candidates, with 'sq chi' greater than 12. The sample of these variable sources, mostly unidentified, probably contains many flare stars, a few cataclysmic variables and a possible transient source.

Description: The wide angle Rosat pointed survey (WARPS) of clusters is based on the Rosat position sensitive proportional counter (PSPC) archive of pointed observations. It includes extended X-ray sources and point-like X-ray sources with non-stellar optical counterparts. It was designed to minimize the selection effects while covering a large area of the sky. The purposes of the survey were to measure the low luminosity, high redshift, X-ray luminosity function of clusters and groups and to investigate cluster morphologies and unusual systems.

Description: The results of the three Rosat position sensitive proportional counter (PSPC) observations of the supernova remnant W28 are discussed. The X-ray emission of W28 is centrally concentrated, while the radio emission has a shell-like morphology. The structure is likely to be due to a large H I or molecular cloud in the north of the remnant, which is consistent with the OH maser detection along the inner shell. The spectra are well modeled by a one temperature thermal model. The origin of the central emission and the effects of the reflected shock from the large scale H I and the molecular gas on the X-ray and radio morphologies are discussed.

Description: Narrow band X-ray images of Tycho's supernova remnant, acquired with the solid-state spectrometer onboard the Advanced Satellite for Cosmology and Astrophysics (ASCA), are presented. The remnant is mapped in several prominent emission lines and in the 1.4 keV to 1.7 keV and 4 keV to 6 keV continua. A spatial resolution of approximately 0.5 min was obtained. No significant correlation was found for Tycho between the X-ray 4 keV to 6 keV continuum and the radio morphology.

Description: The combined spectral and imaging capabilities of the Advanced Satellite for Cosmology and Astrophysics (ASCA) provides new possibilities for studying supernova remnants. The most powerful of these are spatially resolved, moderate resolution spectroscopy and narrowband spectral imaging. The use of these techniques yielded a number of results that challenge the currently held views on X-ray emission processes in supernova remnants. Evidence was found for the plasmas in which a different ionization timescale must be used to characterize each metal. Some recent findings from supernova remnant surveys conducted using ASCA are presented.

Description: The comparison of five X-ray observations of FO Aqr reveals that the morphology of the X-ray light curve changes considerably with time. Power spectra from 1988 and 1993 reveal a sideband component, while power spectra from 1990 do not. This suggests that the amount of disk overflow accretion varies as a function of time. From structured spin folded light curves, the presence of complex, multicomponent emitting regions near the white dwarf's surface can be inferred.

Description: Recent Rosat position sensitive proportional counter (PSPC) observations demonstrate the presence of a compact source of hard X-ray emission centers on the peculiar star, eta Carinae. These observations show a change in the hard band counting rate of a factor of 2 in a 4-month interval. The Rosat high resolution imager (HRI) observations which span the PSPC observations also reveal a variable source of X-ray emission centered in eta Carinae. Therefore, the strong variability which is a characteristic of eta Carinae in radio, infrared and visible wavebands is also observed at X-ray energies. The X-ray light curve of eta Carinae is examined using data from various astronomical data bases.

Description: Cometary interactions with the solar wind allow us to use comets as probes of the inner regions of the heliosphere. During their close passage to the Sun, comets are exposed to different environments depending on their latitude. Until recently, characterizing these environments has been difficult because most spacecraft studying the sun have been confined to studying its mid-latitudes. A valuable source of information about the differing regimes of the solar wind is the joint ESA/NASA ULYSSES mission, which is the first spacecraft to explore the polar regions of the heliosphere. In 1995, ULYSSES' orbit covered a range of solar latitudes from -80 degrees to +80 degrees - an interval referred to as the 'fast latitude scan.' The Ulysses Comet Watch incorporates in-situ measurements during these periods by the ULYSSES spacecraft with images contributed by a world-wide network of observers (both amateur and professional). Bright comets whose paths come within 20 degrees solar latitude of the spacecraft are considered especially good targets for correlation between spacecraft data and plasma tail activity. Ulysses findings of interest to cometary plasma research are: Verification of global differences in solar wind properties (speed and density) at different solar latitudes. At polar latitudes - ranging from roughly +/-30 degrees to +/-80 degrees - the solar wind speed is about 750 kilometers/sec, and has a proton density (1 AU) around 3 cm(exp -3). Changes in properties are small and the heliospheric current sheet (HCS) is not seen. In the equatorial latitudes (roughly +30 to -30 degrees), the average solar wind speed is about 450 kilometers/sec, with an average proton density (at 1 AU) around 9 cm(exp -3). The HCS is seen and changes in properties can be large. An object, spacecraft or comet, at a given latitude, can be entirely in the polar, entirely in the equatorial, or can experience both - sort of a transition region.

Description: The usual theory of planetesimal formation is untenable because turbulence inhibits gravitational instability. However, turbulence can actually concentrate chondrule-sized particles by factors up to a million near stagnation points. The implications for accretion may be profound.

Description: A multi-component method for the description of the evolution of the grain size distribution in consideration of a size dependent grain drift and growth rate is applied in order to model dust driven winds around cool C-stars. Grain drift introduces several modifications concerning dust growth: on one hand the residence time in the region of efficient growth is reduced, on the other hand the growth efficiency is higher due to an increased collisional rate. For carbon grains the surface density of radical sites is increased, but on the other hand there is a reduction of the sticking efficiency of the growth species for drift velocities larger than a few km/s. It is found that the consideration of drift results in a considerable distortion of the size distribution as compared to the case of zero drift velocity. Generally, there are less, but larger grains if drift is included.

Description: We present results from an ongoing effort to classify the infrared spectra produced by circumstellar dust shells. Earlier efforts concentrated on oxygen-rich dust shells from sources associated with the asymptotic giant branch (AGB). Here, we describe the expansion of our classification to include S stars, supergiants, and carbon stars.

Description: Master equation gives a more fundamental description of stochastic coagulation processes rather than popular Smoluchowski's equation. In order to examine the effect of the dynamics on the geometry of resulting aggregates, we study Master equation with a rigorous Monte Carlo algorithm. It is found that Cluster-Cluster aggregation model is a good approximation of orderly growth and the aggregates have fluffy structures with a fractal dimension approx. 2. A scaling analysis of Smoluchowski's equation also supports this conclusion.

Description: Recent progress in the modeling of the radiative transfer in star forming regions has lead to improved dusty envelope models. Such models can now explain in great detail the observed infrared spectrum. The success of such models suggests that input parameters correspond to the true physical situation of the environment of the young stellar object. However, so far only minor attention has been given to models which include the spectroscopic signature of ice bands. Such models are applied to the Herbig-Haro energy source HH100 IRS. Calculations have been performed to interpret the spectral energy distribution as a function of dust parameters such as the grain size, the ice volume fraction, and the 'fluffiness' of the particles. The infrared spectrum together with the strength of the water ice band of HH 100 IRS is successfully reproduced if an upper limit of the grain size below 1 micron is used. Comet-like grains, with sizes above 1 micron, result in a poor fit of the observations.

Description: We present here UV-visible spectra of carbon grains produced by direct condensation of the carbon vapors in partially hydrogenated atmospheres. The freshly formed grains exhibit an extinction peak in the wavelength range 200-240 nm whose exact position depends on the hydrogen abundance. The results are discussed in terms of formation and evolution of circumstellar and interstellar cosmic dust.

Description: Models are presented of four Vega-like stars: main-sequence stars with infrared emission from circumstellar dust. The dusty environments of the four stars are rather diverse, as shown by their spectral energy distributions. Good fits to the observations were obtained for all four stars.

Description: One of the environmental issues affecting the development of a second-generation supersonic commercial transport is the impact of sonic booms on people. Aircraft designers are attempting to design the transport to produce sonic boom signatures that will have minimum impact on the public. Current supersonic commercial aircraft produce an 'N-wave' sonic boom pressure signature that is considered unacceptable by the public. This has resulted in first-generation supersonic transports being banned from flying supersonic over land in the United States, a severe economic constraint. By tailoring aircraft volume and lift distributions, designers hope to produce sonic boom signatures having specific shapes other than 'N-wave' that may be more acceptable to the public. As part of the effort to develop a second-generation supersonic commercial transport, Langley Research Center is conducting research to study people's subjective response to sonic booms. As part of that research, a system was developed for performing studies of the subjective response of people to the occurrence of simulated sonic booms in their homes. The In-Home Noise Generation/Response System (IHONORS) provides a degree of situational realism not available in the laboratory and a degree of control over the noise exposure not found in community surveys. The computer-controlled audio system generates the simulated sonic booms, measures the noise levels, and records the subjects' ratings and can be placed and operated in individual homes for extended periods of time. The system was used to conduct an in-home study of subjective response to simulated sonic booms. The primary objective of the study was to determine the effect on annoyance of the number of sonic boom occurrences in a realistic environment. The effects on annoyance of several other parameters were also examined. Initially, data analyses were based on all the data collected. However, further analyser found that test subjects adapted to the sonic booms during the first few days of exposure. The first eight days of each testing period consisted of eight introductory exposures that were repeated on randomly selected days later in the testing period. Comparison of the introductory exposures with their repeats indicated that the test subjects adapted to the new sonic boom noise environment during the first days of the testing period. Because of the adaptation occurring, the introductory days were deleted from the ds set and the analyses redone. This paper presents the updated analyses. Elimination of the introductory days did not significantly affect the results and conclusions of the initial analyses. This paper also presents analyses of the effects on annoyance of additional factors in the study not previously examined.

Description: The latest CHABA Working Group to have reviewed published information about the effects of high energy impulsive sounds (such as sonic booms) on communities has recommended abandonment of the dosage-response relationship identified by its predecessor in favor of two alternate prediction method. Both of the new assessment methods continue to rely on C-weighted measurements of impulsive sounds One of the two assessment methods retains the standard assumptions of the 'equal energy hypothesis' (the notion that annoyance is governed simply by the product of level, duration, and number noise events), and further assumes that the rate of growth of the prevalence of annoyance is proportional to the rate of growth of loudness with level. The other assessment method, however, assumes a level dependent (non-equal energy) summation of the C-weighted sound exposure levels of individual impulsive events. Since predictions of the second method are distribution-dependent, they are not readily represents graphically in the form of a single dosage-response function. The effects on annoyance predictions of variance in distributions of CSEL values of impulsive sounds are explored in this presentation.

Description: Cycle studies have shown the benefits of increasing engine pressure ratios and cycle temperatures to decrease engine weight and improve performance of commercial turbine engines. NASA is working with industry to define technology requirements of advanced engines and engine technology to meet the goals of NASA's Advanced Subsonic Technology Initiative. As engine operating conditions become more severe and customers demand lower operating costs, NASA and engine manufacturers are investigating methods of improving engine efficiency and reducing operating costs. A number of new technologies are being examined that will allow next generations engines to operate at higher pressures and temperatures. Improving seal performance - reducing leakage and increasing service life while operating under more demanding conditions - will play an important role in meeting overall program goals of reducing specific fuel consumption and ultimately reducing direct operating costs. This paper provides an overview of the Advanced Subsonic Technology Program goals discusses the motivation for advanced seal development, and highlights seal technology requirements to meet future engine performance goals.

Description: Work this summer in the Office of Safety, Environment, and Mission Assurance began with a review of current initiatives and environmental projects at the Langley Research Center (LaRC). This involved researching many of the documents on file which detail problems which have occurred as well as various approaches which have been used to address these problems. A large portion of the time was spent interviewing and working with each of the engineers, industrial hygienists and other professionals connected with the Office of Environmental Engineering. A few of the projects I worked on include: Researching environmental compliance, and pollution prevention efforts; touring many of the facilities at LaRC to observe the environmental efforts in the work place; researching equipment needs for the recycling/reclamation center; writing scripts for in-house training videos; working with the video production department to produce a training video; developing e-mail distribution list; developing environmental coordinator's database; and working with others to research logistics of recycling and waste minimization efforts.

Description: Ozone is a relatively unstable molecule found in Earth's atmosphere. An ozone molecule is made up of three atoms of oxygen. Depending on where ozone resides, it can protect or harm life on Earth. High in the atmosphere, about 15 miles up, ozone acts as a shield to protect Earth's surface from the sun's harmful ultraviolet radiation. Without this shield, we would be more susceptible to skin cancer, cataracts, and impaired immune systems. Closer to Earth, in the air we breathe, ozone is a harmful pollutant that causes damage to lung tissue and plants. Since the early 1980's, airborne lidar systems have been used for making measurements of ozone. The differential absorption lidar (DIAL) technique is used in the remote measurement of O3. This system allows the O3 to be measured as function of the range in the atmosphere. Two frequency-doubled Nd:YAG lasers are used to pump tunable dye lasers. The lasers are operating at 289 nm for the DIAL on-line wavelength of O3, and the other one is operated at 300 nm for the off-line wavelength. The DIAL wavelengths are produced in sequential laser pulses with a time separation of 300 micro s. The backscattered laser energy is collected by telescopes and measured using photon counting systems. The photon counting system measures the light signal by making use of the photon nature of light. The output pulse from the Photo-Multiplier Tube (PE), caused by a photon striking the PMT photo-cathode, is amplified and passed to a pulse height discriminator. The peak value of the pulse is compared to a reference voltage (discrimination level). If the pulse amplitude exceeds the discrimination level, the discriminator generates a standard pulse which is counted by the digital counter. Non-linearity in the system is caused by the overlapping of pulses and the finite response time of the electronics. At low count rates one expects the system to register one event for each output pulse from the PMT corresponding to a photon incident upon the photocathode, however, at higher rates the limitations of the discrimination/counting system will cause the observed count rate to be non-linear with respect to the true count rate. Depending on the pulse height distribution and the discriminator level, the overlapping of pulses (pulse pile-up) can cause count loss or even an additional apparent count gain as the signal levels increase. Characterization of the system, including the pulse height distribution, the signal to noise ratio, and the effect of the discriminator threshold level, is critical in maximizing the linear operating region of the system, thus greatly increasing the useful dynamic range of the system.

Description: The Second Workshop on Stratospheric Models and Measurements Workshop (M&M II) is the continuation of the effort previously started in the first Workshop (M&M I, Prather and Remsberg [1993]) held in 1992. As originally stated, the aim of M&M is to provide a foundation for establishing the credibility of stratospheric models used in environmental assessments of the ozone response to chlorofluorocarbons, aircraft emissions, and other climate-chemistry interactions. To accomplish this, a set of measurements of the present day atmosphere was selected. The intent was that successful simulations of the set of measurements should become the prerequisite for the acceptance of these models as having a reliable prediction for future ozone behavior. This section is divided into two: model experiment and model descriptions. In the model experiment, participant were given the charge to design a number of experiments that would use observations to test whether models are using the correct mechanisms to simulate the distributions of ozone and other trace gases in the atmosphere. The purpose is closely tied to the needs to reduce the uncertainties in the model predicted responses of stratospheric ozone to perturbations. The specifications for the experiments were sent out to the modeling community in June 1997. Twenty eight modeling groups responded to the requests for input. The first part of this section discusses the different modeling group, along with the experiments performed. Part two of this section, gives brief descriptions of each model as provided by the individual modeling groups.

Description: The crack propagation life of tested specimens has been repeatedly shown to strongly depend on the loading history. Overloads and extended stress holds at temperature can either retard or accelerate the crack growth rate. Therefore, to accurately predict the crack propagation life of an actual component, it is essential to approximate the true loading history. In military rotorcraft engine applications, the loading profile (stress amplitudes, temperature, and number of excursions) can vary significantly depending on the type of mission flown. To accurately assess the durability of a fleet of engines, the crack propagation life distribution of a specific component should account for the variability in the missions performed (proportion of missions flown and sequence). In this report, analytical and experimental studies are described that calibrate/validate the crack propagation prediction capability for a disk alloy under variable amplitude loading. A crack closure based model was adopted to analytically predict the load interaction effects. Furthermore, a methodology has been developed to realistically simulate the actual mission mix loading on a fleet of engines over their lifetime. A sequence of missions is randomly selected and the number of repeats of each mission in the sequence is determined assuming a Poisson distributed random variable with a given mean occurrence rate. Multiple realizations of random mission histories are generated in this manner and are used to produce stress, temperature, and time points for fracture mechanics calculations. The result is a cumulative distribution of crack propagation lives for a given, life limiting, component location. This information can be used to determine a safe retirement life or inspection interval for the given location.

Description: Solid (soot) and liquid (presumed sulfate) particle emissions from aircraft engines may have serious impacts on the atmosphere. While the direct radiative impact of these particles is expected to be small relative to those from natural sources (Atmospheric Effects of Subsonic Aircraft: Interim Assessment of the Advanced Subsonic Technology Program, NASA Ref. Pub. 1400, 1997), their indirect effects on atmospheric chemistry and cloud formation may have a significant impact. The potential impacts of primary concern are the increase of sulfate surface area and accelerated heterogeneous chemical reactions, and the potential for either modified soot or sulfate particles to serve as cloud nuclei which would change the frequency or radiative characteristics of clouds. Volatile (sulfate) particle concentrations measured behind the Concorde aircraft in flight in the stratosphere were much higher than expected from near-field model calculations of particle formation and growth. Global model calculations constrained by these data calculate a greater level of stratospheric ozone depletion from the proposed High speed Civil Transport (HSCT) fleet than those without particle emission. Soot particles have also been proposed as important in heterogeneous chemistry but this remains to be substantiated. Aircraft volatile particle production in the troposphere has been shown by measurements to depend strongly on fuel sulfur content. Sulfate particles of sufficient size are known to provide a good nucleating surface for cloud growth. Although pure carbon soot is hydrophobic, the solid particle surface may incorporate more suitable nucleating sites. The non-volatile (soot) particles also tend to occupy the large end of aircraft particle size spectra. Quantitative connection between aircraft particle emissions and cloud modification has not been established yet, however, even small changes in cloud amount or properties could have a significant effect on the radiative balance of the atmosphere.

Description: The objectives of this work are to measure the ice discharge of the Greenland Ice Sheet close to the grounding line and/or calving front, and compare the results with mass accumulation and ablation in the interior to estimate the ice sheet mass balance.

Description: In calculating the position vector of the Moon in on-board flight software, one often begins by using a series expansion to calculate the ecliptic latitude and longitude of the Moon, referred to the mean ecliptic and equinox of date. One then performs a reduction for precession, followed by a rotation of the position vector from the ecliptic plane to the equator, and a transformation from spherical to Cartesian coordinates before finally arriving at the desired result: equatorial J2000 Cartesian components of the lunar position vector. An alternative method is developed here in which the equatorial J2000 Cartesian components of the lunar position vector are calculated directly by a series expansion, saving valuable onboard computer resources.

Description: The Urban Environment Initiative (UEI), has been established as part of a Cooperative Agreement with the National Aeronautics and Space Administration (NASA). The UEI is part of NASA's overall High Performance Computing and Communications (HPCC) and the Information Infrastructure Technology Applications (IITA) programs. The goal of the UEI is to provide public access to Earth Science information and promote its use with a focus on the environment of urban areas. This goal will be accomplished through collaborative efforts of the UEI team with both community-based and local/regional governmental organizations. The UEI team is comprised of four organizations representing private industry, NASA, and universities: Prime Technologies Service Corporation, NASA's Minority University Space Interdisciplinary Network (MU-SPIN) California State University, at Los Angeles, and Central State University (Wilberforce, OH). "Urban Environment" refers to the web of environmental, economic, and social factors that combine to create the urban world in which we live. Examples of these factors are population distribution, neighborhood demographic profiles, economic resources, business activities, location and concentration of environmental hazards and various pollutants, proximity and level of urban services, which form the basis of the urban environment and ultimately affect our lives and experiences. The use of Geographic Information Systems (GIS) and remote sensing allows data to be visualized in the forms of maps and spatial images. The use of these tools allow analysis of information about urban environments. Also included are descriptions of the four query types which will assist in understanding the maps.

Description: The Smoke, Clouds, Aerosol, and Radiation Brazil(SCAR-B) field campaign was conducted to study the effects that widespread and persistent biomass burning have upon radiative and chemical processes in the atmosphere. The radiative transfer characteristics of the atmosphere are altered by the introduction of particulate and gaseous materials which are the products of the combustion of vegetative material at ground level. These substances are transported and distributed horizontally and vertically by atmospheric dynamical processes which may be perturbed by the heat energy from the fires. As the pollutants disperse, their physical and chemical properties change substantially. A complete description of the effects of smoke requires that the evolution back to the natural situation be fully examined. A most important component of smoke haze investigation is finding its vertical and horizontal distribution in relation to the driving factors of dynamics and the related horizontal transport. In this presentation, we employ data from the Cloud Lidar System(CLS), carried aboard the NASA ER-2 aircraft, to provide a unique view of the particulate or aerosol loading produced by fires, especially with regard to the geometrical distribution of the aerosols in the vertical plane. The lidar has the ability to measure aerosol optical properties in a continuous fashion at quite fine vertical and horizontal resolution. The results from the lidar provide measurements that are largely independent of influences that corrupt passive instruments and thus it can serve to corroborate their results. The extended horizontal and vertical range of lidar results can also augment ground based and airborne in situ measurements which have limited horizontal and vertical scope. We present the results of our analysis of CLS observations taken during the SCAR-B field campaign. Observations of the the aerosol optical thickness from the Aerosol Robotic Network(AERONET) of solar photometers are employed in conjunction with CLS data to derive extinction to backscatter ratio values which are used to convert the lidar backscatter coefficient into extinction coefficient. The extinction coefficient is integrated vertically to find aerosol optical thickness along ER-2 flight tracks. We use images of the CLS derived extinction coefficient to depict its horizontal and vertical distribution. Multispectral photometer optical thickness is used to compute the Angstrom exponent. With these, we examine the hypothesis that the values of extinction to backscatter ratio can be related to the Anstrom coefficient since both of these would be a function of the refractive index and size distribution of the aerosols.