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NASA NTRS1992

Perspectives on integrated modeling of transport processes in semiconductor crystal growth

The wide range of length and time scales involved in industrial scale solidification processes is demonstrated here by considering the Czochralski process for the growth of large diameter silicon crystals that become the substrate material for modern microelectronic devices. The scales range in time from microseconds to thousands of seconds and in space from microns to meters. The physics and chemistry needed to model processes on these different length scales are reviewed.

Brown, Robert A.↗

NASA NTRS1994

An integrated strategy for the planetary sciences: 1995 - 2010

In 1992, the National Research Council's Space Studies Board charged its Committee on Planetary and Lunar Exploration (COMPLEX) to: (1) summarize current understanding of the planets and the solar system; (2) pose the most significant scientific questions that remain; and (3) establish the priorities for scientific exploration of the planets for the period from 1995 to 2010. The broad scientific goals of solar system exploration include: (1) understanding how physical and chemical processes determine the major characteristics of the planets, and thereby help us to understand the operation of Earth; (2) learning about how planetary systems originate and evolve; (3) determining how life developed in the solar system, particularly on Earth, and in what ways life modifies planetary environments; and (4) discovering how relatively simple, basic laws of physics and chemistry can lead to the diverse phenomena observed in complex systems. COMPLEX maintains that the most useful new programs to emphasize in the period from 1995 to 2010 are detailed investigations of comets, Mars, and Jupiter and an intensive search for, and characterization of, extrasolar planets.

Source record↗

NASA NTRS1994

Some considerations on velocity vector accuracy in dust trajectory analysis

The relative contributions of comets and asteroids to the reservoir of dust in the interplanetary medium is not known. There are direct observations of dust released from comets and there is evidence to associate the IRAS dust bands with possible collisions of asteroids in the main belt. A means towards sorting out the parent sources has been proposed in the establishment of a dust collector in orbit about the Earth. The purpose of such a facility would be to collect not only cosmic dust particles intact but also the state vectors, as they arrive at the detector, the idea being that one may combine analytical laboratory analysis of the physics and chemistry of the captured particles with orbital data in order to help distinguish between bodies and identify parent bodies. The theoretical study of dust particle orbits in the solar system takes on greatly more importance if we use collected trajectory data. The orbital motion of dust when radiation and forces alone are acting is well understood. When gravitational forces due to the planets are included, the motion can become quite complex. In order to characterize the orbits of particles as they crossed the Earth's orbits, a study of the long-time dust orbital evolution was undertaken. We have considered various parameters associated with these dust orbits to see if one may in a general way discriminate between particles evolved from comets and asteroids. We proceed in this study as we have done previously. That is, we considered the dust particles as ideal black bodies, of density 1 gm/cc, spherical, with radii 10-100 microns. Particles of this size are affected by radiation forces, photon pressure, and Poynting-Robertson drag. Account was also taken of solar wind drag, which amounts to about 30 percent of the Poynting-Robertson drag negligible. The gravitational forces due to the planets are included, unlike in our previous study; the planetary orbits are those of true n-body interaction so that the possibility of secular resonance is included. Our method was to calculate explicitly by a numerical procedure the orbits of dust particles after they left their parent bodies. The motion is determined numerically with the implicit Runge-Kutta integrator using Gauss-Radau spacings.

Jackson, A. A.↗

NASA NTRS1995

High latitude ion composition

A data base comprised of all available ionosphere satellite ion composition measurements - the Goddard Comprehensive Ionosphere Data Base (GCID) - has been set upon optical disks for convenient merging and accessing of data from different satellites. This data has recentely been expanded to include all accessible satellite electron density and plasma temperature measurements. This paper demonstrates with a couple examples, the potential of GCID as an alternative to empirical models for undertanding ionsophere physics and chemistry. Through binning techniques GCID provdes a tool that complements and improves on the International Reference Ionosphere model (IRI) in delineating the topology of high latitude ion composition. GCID provides at a glance a measure of the local statistical variabilty of the ion compostions that is not in empirical models such as IRI. Furthermusing the data to determine the spatial and geophysical parameter range over which the minor ion species are approximately in chemical equilibrium, the number of data points available for empirical ion composition models can be increased by using the statiscally more reliable neutral and electron empirical models to derive ions composition. Currently available empirical models are not capable of adequately defining the comples high latitude distribution - a measure of the variablity is needed.

Grebowsky, J. M.↗

NASA NTRS1995

An innovative approach to the development of a portable unit for analytical flame characterization in a microgravity environment

The availability of manned laboratory facilities in space offers wonderful opportunities and challenges in microgravity combustion science and technology. In turn, the fundamentals of microgravity combustion science can be studied via spectroscopic characterization of free radicals generated in flames. The laser-induced fluorescence (LIF) technique is a noninvasive method of considerable utility in combustion physics and chemistry suitable for monitoring not only specific species and their kinetics, but it is also important for imaging of flames. This makes LIF one of the most important tools for microgravity combustion science. Flame characterization under microgravity conditions using LIF is expected to be more informative than other methods aimed at searching for effects like pumping phenomenon that can be modeled via ground level experiments. A primary goal of our work consisted in working out an innovative approach to devising an LIF-based analytical unit suitable for in-space flame characterization. It was decided to follow two approaches in tandem: (1) use the existing laboratory (non-portable) equipment and determine the optimal set of parameters for flames that can be used as analytical criteria for flame characterization under microgravity conditions; and (2) use state-of-the-art developments in laser technology and concentrate some effort in devising a layout for the portable analytical equipment. This paper presents an up-to-date summary of the results of our experiments aimed at the creation of the portable device for combustion studies in a microgravity environment, which is based on a portable UV tunable solid-state laser for excitation of free radicals normally present in flames in detectable amounts. A systematic approach has allowed us to make a convenient choice of species under investigation, as well as the proper tunable laser system, and also enabled us to carry out LIF experiments on free radicals using a solid-state laser tunable in the UV.

Dubinskiy, Mark A.↗

NASA NTRS1995

Technical Reports: Langley Aerospace Research Summer Scholars

The Langley Aerospace Research Summer Scholars (LARSS) Program was established by Dr. Samuel E. Massenberg in 1986. The program has increased from 20 participants in 1986 to 114 participants in 1995. The program is LaRC-unique and is administered by Hampton University. The program was established for the benefit of undergraduate juniors and seniors and first-year graduate students who are pursuing degrees in aeronautical engineering, mechanical engineering, electrical engineering, material science, computer science, atmospheric science, astrophysics, physics, and chemistry. Two primary elements of the LARSS Program are: (1) a research project to be completed by each participant under the supervision of a researcher who will assume the role of a mentor for the summer, and (2) technical lectures by prominent engineers and scientists. Additional elements of this program include tours of LARC wind tunnels, computational facilities, and laboratories. Library and computer facilities will be available for use by the participants.

Schwan, Rafaela↗

NASA NTRS1995

Langley Aerospace Research Summer Scholars

Schwan, Rafaela↗

NASA NTRS1995

The Schwinger Variational Method

Variational methods have proven invaluable in theoretical physics and chemistry, both for bound state problems and for the study of collision phenomena. The application of the Schwinger variational (SV) method to e-molecule collisions and molecular photoionization has been reviewed previously. The present chapter discusses the implementation of the SV method as applied to e-molecule collisions. Since this is not a review of cross section data, cross sections are presented only to server as illustrative examples. In the SV method, the correct boundary condition is automatically incorporated through the use of Green's function. Thus SV calculations can employ basis functions with arbitrary boundary conditions. The iterative Schwinger method has been used extensively to study molecular photoionization. For e-molecule collisions, it is used at the static exchange level to study elastic scattering and coupled with the distorted wave approximation to study electronically inelastic scattering.

Huo, Winifred M.↗

NASA NTRS1995

The Schwinger Variational Method

Variational methods have proven invaluable in theoretical physics and chemistry, both for bound state problems and for the study of collision phenomena. For collisional problems they can be grouped into two types: those based on the Schroedinger equation and those based on the Lippmann-Schwinger equation. The application of the Schwinger variational (SV) method to e-molecule collisions and photoionization has been reviewed previously. The present chapter discusses the implementation of the SV method as applied to e-molecule collisions.

Huo, Winifred M.↗

NASA NTRS1999

The Effects of Gravity on Combustion and Structure Formation During Synthesis of Advanced Materials

Combustion in a variety of heterogeneous systems, leading to the synthesis of advanced materials, is characterized by high temperatures (2000-3500 K) and heating rates (up to 10(exp 6) K/s) at and ahead of the reaction front. These high temperatures generate liquids and gases which are subject to gravity-driven flow. The removal of such gravitational effects is likely to provide increased control of the reaction front, with a consequent improvement in control of the microstructure of the synthesized products. Thus, microgravity experiments can lead to major advances in the understanding of fundamental aspects of combustion and structure formation under the extreme conditions of the combustion synthesis wave. In addition, the specific features of microgravity environment allow one to produce unique materials, which cannot be obtained under terrestrial conditions. The general goals of the current research are: 1) to improve the understanding of fundamental phenomena taking place during combustion of heterogeneous systems, 2) to use low-gravity experiments for insight into the physics and chemistry of materials synthesis processes, and 3) based on the obtained knowledge, to optimize processing conditions for synthesis of advanced materials with desired microstructures and properties. This research follows logically from the results of investigations we have conducted in the framework of our previous grant on gravity influence on combustion synthesis (CS) of gasless systems. Prior work, by others and by us, has clearly demonstrated that gravity plays an important role during combustion synthesis of materials. The immediate tasks for the future are to quantitatively identify the nature of observed effects, and to create accurate local kinetic models of the processes, which can lead to a control of the microstructure and properties of the synthesized materials. In summary, this is the value of the proposed research. Based on our prior work, we focus on the fundamental aspects of combustion and structure formation under the unique condition of microgravity.

Varma, A.↗

NASA NTRS1999

Aerosol Retrievals Using Channel 1 and 2 AVHRR Data

The effect of tropospheric aerosols on global climate via the direct and indirect radiative forcings is one of the largest remaining uncertainties in climate change studies. Current assessments of the direct aerosol radiative effect mainly focus on sulfate aerosols. It has become clear, however, that other aerosol types like soil dust and smoke from biomass burning are also likely to be important climate forcing factors. The magnitude and even the sign of the climate forcing caused by these aerosol types is still unknown. General circulation models (GCMs) can be used to estimate the climatic effect of the direct radiative forcing by tropospheric and stratospheric aerosols. Aerosol optical properties are already parameterized in the Goddard Institute for Space Studies GCM. Once the global distribution of aerosol properties (optical thickness, size distribution, and chemical composition) is available, the calculation of the direct aerosol forcing is rather straighfforward. However, estimates of the indirect aerosol effect require additional knowledge of the physics and chemistry of aerosol-cloud interactions which are still poorly understood. One of the main objectives of the Global Aerosol Climatology Project, established in 1998 as a joint initiative of NASA's Radiation Science Program and GEWEX, is to infer the global distribution of aerosols, their properties, and their seasonal and interannual variations for the full period of available satellite data. This will be accomplished primarily through a systematic application of multichannel aerosol retrieval algorithms to existing satellite data and advanced 3-dimensional aerosol chemistry/transport models. In this paper we outline the methodology of analyzing channel 1 and 2 AVHRR radiance data over the oceans and describe preliminary retrieval results.

Mishchenko, Michael I.↗

NASA NTRS1998

Pulsations, Shocks, and Mass Loss

This grant provided long-term support for my investigation of the outflows powered by young stars. Several major research results emerged during the course of this research, including: (1) The discovery of giant Herbig-Haro outflows from young stars that can extend for many parsecs from their sources. The first parsec-scale outflow to be recognized led to the realization that Herbig-Haro outflows, even those produced by low mass young stellar objects, can extend orders of magnitude farther from their sources than previously thought. Our preconceptions were to a large extent driven by the narrow fields-of-view then provided by CCD detectors. With the recent advent of large format CCDs and CCD mosaics, we have come to realize that most outflows attain parsec-scale dimensions. Even at the distance of the Orion star forming clouds, such flows can subtend a degree on the sky. Our work has led to the recognition of over two dozen giant. (2) The discovery that outflows are highly clustered. Even regions of relatively isolated star formation such as those in Taurus frequently produce multiple outflows. (3) The discovery of a new family of externally irradiated jets. During the last year of support from this grant, we made the startling discovery that there is a class of jets from young stars that are illuminated by the ionizing radiation field of nearby massive stars. The first four examples were discovered in the vicinity of the a Orionis sub-group of the Orion OB Association which is believed to be at least 2 million years old. Since the jets are photo-ionized, their densities can be reliably estimated. Most HH jets are shock excited, and are therefore notoriously difficult to characterize since their visibility and observed properties depend on the complex and highly non-linear processes associated with shocks. Furthermore, many irradiated jets are one sided rather than bipolar. Thus, irradiated jets may for the first time be used to accurately diagnose jet densities and mass loss rates, and to probe the physics of jet collimation, and may indicate that the jet production phase of certain young stars may last more than a million years. These three discoveries provide us with fundamental new insights into the star formation process, into the physical conditions inside and near star forming clouds, and into new ways to probe the physics and chemistry of such clouds.

Bally, John↗

NASA NTRS1999

A Global Data Assimilation System for Atmospheric Aerosol

We will give an overview of an aerosol data assimilation system which combines advances in remote sensing of atmospheric aerosols, aerosol modeling and data assimilation methodology to produce high spatial and temporal resolution 3D aerosol fields. Initially, the Goddard Aerosol Assimilation System (GAAS) will assimilate TOMS, AVHRR and AERONET observations; later we will include MODIS and MISR. This data assimilation capability will allows us to integrate complementing aerosol observations from these platforms, enabling the development of an assimilated aerosol climatology as well as a global aerosol forecasting system in support of field campaigns. Furthermore, this system provides an interactive retrieval framework for each aerosol observing satellites, in particular TOMS and AVHRR. The Goddard Aerosol Assimilation System (GAAS) takes advantage of recent advances in constituent data assimilation at DAO, including flow dependent parameterizations of error covariances and the proper consideration of model bias. For its prognostic transport model, GAAS will utilize the Goddard Ozone, Chemistry, Aerosol, Radiation and Transport (GOCART) model developed at NASA/GSFC Codes 916 and 910.3. GOCART includes the Lin-Rood flux-form, semi-Langrangian transport model with parameterized aerosol chemistry and physical processes for absorbing (dust and black carbon) and non-absorbing aerosols (sulfate and organic carbon). Observations and model fields are combined using a constituent version of DAO's Physical-space Statistical Analysis System (PSAS), including its adaptive quality control system. In this talk we describe the main components of this assimilation system and present preliminary results obtained by assimilating TOMS data.

daSilva, Arlindo↗

NASA NTRS1999

Mars 2001 Lander Mission: Measurement Synergy Through Coordinated Operations Planning And Implementation

The 2001 Mars Surveyor Program Mission includes an orbiter with a gamma ray spectrometer and a multispectral thermal imager, and a lander with an extensive set of instrumentation, a robotic arm, and the Marie Curie Rover. The Mars 2001 Science Operations Working Group (SOWG) is a subgroup of the Project Science Group that has been formed to provide coordinated planning and implementation of scientific observations, particularly for the landed portion of the mission. The SOWG will be responsible for delivery of a science plan and, during operations, generation and delivery of conflict-free sequences. This group will also develop an archive plan that is compliant with Planetary Data System (PDS) standards, and will oversee generation, validation, and delivery of integrated archives to the PDS. In this report we cover one element of the SOWG planning activities, the development of a plan that maximizes the scientific return from lander-based observations by treating the instrument packages as an integrated payload. Scientific objectives for the lander mission have been defined. They include observations focused on determining the bedrock geology of the site through analyses of rocks and also local materials found in the soils, and the surficial geology of the site, including windblown deposits and the nature and history of formation of indurated sediments such as duricrust. Of particular interest is the identification and quantification of processes related to early warm, wet conditions and the presence of hydrologic or hydrothermal cycles. Determining the nature and origin of duricrust and associated salts is -very important in this regard. Specifically, did these deposits form in the vadose zone as pore water evaporated from soils or did they form by other processes, such as deposition of volcanic aerosols? Basic information needed to address these questions includes the morphology, topography, and geologic context of landforms and materials exposed at the site, together with quantitative information on material mineralogy, chemistry, and physical properties (rock textures; soil grain size and shape distributions; degree and nature of soil induration; soil magnetic properties). The calibration targets provide radiometric and mineralogical control surfaces. The magnets allow observations of magnetic phases. Patch plates are imaged to determine adhesive and abrasive properties of soils. Coordinated mission planning is crucial for optimizing the measurement synergy among the packages included on the lander. This planning has already begun through generation of multi-sol detailed operations activities. One focus has been to develop a scenario to use the arm to dig a soil trench to a depth of tens of centimeters. The activity will be monitored through use of Pancam and RAC to ensure nominal operations and to acquire data to determine subsurface physical properties (e.g., angle of repose of trench walls). Pancam and Mini-TES observations would also provide constraints on mineralogy and texture for the walls and bottom of the trench during excavation. If desired, soils excavated at depth could be deposited on the surface and Mossbauer and APXS measurements could be acquired for these materials. Soil samples from various depths would be delivered to MECA for characterization of aqueous geochemistry and physical properties of soil grains, particularly size, shape, and hardness. These physical properties would be determined by optical and atomic force microscopy. When completed, detailed information of soil properties as a function of depth would be obtained. These various data sets would constrain our understanding of whether or not there are systematic variations in soil characteristics as a function of depth. These variations might be related, for example, to evaporative moisture losses and formation of salt deposits, thereby indicating water transport processes occurred fairly recently. Many other value-added measurement scenarios are being developed. For example, characterizing the nature and dynamics of dust deposition will be done using MIP/DART to provide deposition rates, Pancam and RAC imaging of lander and rover surfaces to extrapolate these measurements to other areas, and a variety of measurements to determine if the bulk loose soil has the same characteristics as dust that accumulates during the mission. Bedrock geology of the site is primarily an APEX-focus setting, mineralogy, and texture, and APXS data to be we interest will be to determine the extent to which rock hydrothermal processes, given that APEX is the precursor 4 and 2005 rover missions. Additional information is contained in the original.

Arvidson, R.↗

NASA NTRS1998

Improving Student Achievement in Math and Science

As the new millennium approaches, a long anticipated reckoning for the education system of the United States is forthcoming, Years of school reform initiatives have not yielded the anticipated results. A particularly perplexing problem involves the lack of significant improvement of student achievement in math and science. Three "Partnership" projects represent collaborative efforts between Xavier University (XU) of Louisiana, Southern University of New Orleans (SUNO), Mississippi Valley State University (MVSU), and the National Aeronautics and Space Administration (NASA), Stennis Space Center (SSC), to enhance student achievement in math and science. These "Partnerships" are focused on students and teachers in federally designated rural and urban empowerment zones and enterprise communities. The major goals of the "Partnerships" include: (1) The identification and dissemination of key indices of success that account for high performance in math and science; (2) The education of pre-service and in-service secondary teachers in knowledge, skills, and competencies that enhance the instruction of high school math and science; (3) The development of faculty to enhance the quality of math and science courses in institutions of higher education; and (4) The incorporation of technology-based instruction in institutions of higher education. These goals will be achieved by the accomplishment of the following objectives: (1) Delineate significant ?best practices? that are responsible for enhancing student outcomes in math and science; (2) Recruit and retain pre-service teachers with undergraduate degrees in Biology, Math, Chemistry, or Physics in a graduate program, culminating with a Master of Arts in Curriculum and Instruction; (3) Provide faculty workshops and opportunities for travel to professional meetings for dissemination of NASA resources information; (4) Implement methodologies and assessment procedures utilizing performance-based applications of higher order thinking via the incorporation of Global Learning Observations To Benefit the Environment (GLOBE), Mission to Planet Earth and the use of Geographic Imaging Systems into the K-12th grade curriculum.

Sullivan, Nancy G.↗

NASA NTRS1999

Physical and Chemical Study of Minerals and Rocks Containing Low-Z Compounds of Interest to Astrobiology and Origin of Life

Understanding the origins of Life requires a good understanding of the physics and chemistry of biogenic low-z elements H, C, N, O, P, S in terrestrial environments, on Mars, on extraterrestrial bodies such as meteorite parent bodies and comets, and in interstellar space. In this Proposal five Tasks form a coherent program aimed at elucidating various aspects of low-z element geo- and cosmochemistry with special reference to the origin of Life on Earth and to the search for life on Mars, extant or extinct. (i) Formation of organic molecules, in particular oxygenated H-C-0 molecules or precursors thereof of the composition H(x)C(y)O(z)(n-), inside the hard matrix of structurally dense magmatic minerals; (ii) Formation of organic molecules inside the soft matrix of amorphous and crystalline water ice; (iii) Preservation of organic molecules in cherts and other siliceous rocks formed in hot spring or submarine hydrothermal vent environments; (iv) The nature of the elusive Martian soil oxidant; and (v) Prototype development of an XRD instrument, using a new patented XRD camera concept that utilizes a Charge Coupled Device (CCD) as a camera and as a energy-dispersive analyzer.

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NASA NTRS1999

Membrane-Based Functions in the Origin of Cellular Life

Our objective is to help explain how the earliest ancestors of contemporary cells (protocells) performed their essential functions employing only the molecules available in the protobiological milieu. Our hypothesis is that vesicles, built of amphiphilic, membrane-forming materials, emerged early in protobiological evolution and served as precursors to protocells. We further assume that the cellular functions associated with contemporary membranes, such as capturing and, transducing of energy, signaling, or sequestering organic molecules and ions, evolved in these membrane environments. An alternative hypothesis is that these functions evolved in different environments and were incorporated into membrane-bound structures at some later stage of evolution. We focus on the application of the fundamental principles of physics and chemistry to determine how they apply to the formation of a primitive, functional cell. Rather than attempting to develop specific models for cellular functions and to identify the origin of the molecules which perform these functions, our goal is to define the structural and energetic conditions that any successful model must fulfill, therefore providing physico-chemical boundaries for these models. We do this by carrying out large-scale, molecular level computer simulations on systems of interest.

Chipot, Christophe↗

NASA NTRS2001

Plasma Reactor Modeling and Validation Experiments

Plasma processing is a key processing stop in integrated circuit manufacturing. Low pressure, high density plum reactors are widely used for etching and deposition. Inductively coupled plasma (ICP) source has become popular recently in many processing applications. In order to accelerate equipment and process design, an understanding of the physics and chemistry, particularly, plasma power coupling, plasma and processing uniformity and mechanism is important. This understanding is facilitated by comprehensive modeling and simulation as well as plasma diagnostics to provide the necessary data for model validation which are addressed in this presentation. We have developed a complete code for simulating an ICP reactor and the model consists of transport of electrons, ions, and neutrals, Poisson's equation, and Maxwell's equation along with gas flow and energy equations. Results will be presented for chlorine and fluorocarbon plasmas and compared with data from Langmuir probe, mass spectrometry and FTIR.

Meyyappan, M.↗