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NASA NTRS1998

An Atmospheric General Circulation Model with Chemistry for the CRAY T3E: Design, Performance Optimization and Coupling to an Ocean Model

The design, implementation and performance optimization on the CRAY T3E of an atmospheric general circulation model (AGCM) which includes the transport of, and chemical reactions among, an arbitrary number of constituents is reviewed. The parallel implementation is based on a two-dimensional (longitude and latitude) data domain decomposition. Initial optimization efforts centered on minimizing the impact of substantial static and weakly-dynamic load imbalances among processors through load redistribution schemes. Recent optimization efforts have centered on single-node optimization. Strategies employed include loop unrolling, both manually and through the compiler, the use of an optimized assembler-code library for special function calls, and restructuring of parts of the code to improve data locality. Data exchanges and synchronizations involved in coupling different data-distributed models can account for a significant fraction of the running time. Therefore, the required scattering and gathering of data must be optimized. In systems such as the T3E, there is much more aggregate bandwidth in the total system than in any particular processor. This suggests a distributed design. The design and implementation of a such distributed 'Data Broker' as a means to efficiently couple the components of our climate system model is described.

Farrara, John D.↗

NASA NTRS1996

Adaptation of Motility Analysis Apparatus for Space Science and Microgravity Ground-Based Experiments

Previous space flight studies have described unfavorable effects of microgravity on testicular morphology and spermatogenesis (Cosmos 1887 Biosputnik flight, 9/29/87 - 10/12/87). The flight animals demonstrated small reductions in testicular and epididymal size, the phenomenon explained as resulting water loss. Yet, light microscopic histological preparations revealed few spermatozoa in the rete testis of the flight males compared to control animals. The cause for this finding was subjectively assessed to be due to "the anatomical dislocation of the organs... and a disturbance in testicular blood supply". Unfortunately, the reported effects of microgravity on the reproductive processes (particularly within males) are few and divergent. If habitation in space is a futuristic goal, more objective testing (of male and female gametes) in a microgravity environment will provide insight to the developmental potential of these reproductive cells. As part of the Marshall Space Flight Centers' Summer Faculty Fellowship Program within the Biophysics Branch, a key component of the research investigation was to develop a test to evaluate individual cell motility and orientation in varying gravitational environments, using computerized assessment of sperm cell concentration, morphology and motility to provide objective, quantitative experimental control. In previous work performed jointly by the author and a NASA colleague, it has been shown that macroscopic motile aggregates of spermatozoa were not altered by the absence of microgravity. Variations in the number of normal versus abnormal sperm due to microgravity influences have yet to be established. It is therefore of interest to monitor the cytoskeletal matrix (microtubulin) of these organisms as a possible indicator of cell viability and/or function.

Johnson, Jacqueline U.↗

NASA NTRS1996

Synthesis and Characterization of a Chitosan Derivative for Electro-Optical Applications

Chitin is a naturally occurring polymer of alpha(1-4) poly N-acetylglucosamine found primarily in the shells of crustaceans and insects. This polymer is chemically and thermally stable and physically durable as a consequence of hydrogen bonding which causes the alignment and ordering of the polymer chains into microcrystals which aggregate into sheets with chiral nematic order. Industry has attempted to take advantage of chitin's properties and low cost (chitin is a waste product of the shellfish industry) to produce durable fibers and other products. This has been largely unsuccessful because of chitin's non reactivity and insolubility. Chitosan is the deacetylation product of chitin and retains many of the structural properties of chitin. Unlike chitin, chitosan is soluble in aqueous solution at reduced pH making it easier to be processed into fibers and films than chitin. Chitosan and its derivatives are now used in such commercial applications as wound dressings, waste water treatment, and in pharmaceuticals. In this study, we have synthesized a chitosan derivative, N-para-nitrophenyl chitosan (NPNPC), as a model material with potential applications in electro optics.

Prastofer, Thomas↗

NASA NTRS1998

Ground Based Program for the Physical Analysis of Macromolecular Crystal Growth

During the past year we have focused on application of in situ Atomic Force Microscopy (AFM) for studies of the growth mechanisms and kinetics of crystallization for different macromolecular systems. Mechanisms of macrostep formation and their decay, which are important in understanding of defect formation, were studied on the surfaces of thaumatin, catalase, canavalin and lysozyme crystals. Experiments revealed that step bunching on crystalline surfaces occurred either due to two- or three-dimensional nucleation on the terraces of vicinal slopes or as a result of uneven step generation by complex dislocation sources. No step bunching arising from interaction of individual steps in the course of the experiment was observed. The molecular structure of the growth steps for thaumatin and lipase crystals were deduced. It was further shown that growth step advance occurs by incorporation of single protein molecules. In singular directions growth steps move by one-dimensional nucleation on step edges followed by lateral growth. One-dimensional nuclei have different sizes, less then a single unit cell, varying for different directions of step movement. There is no roughness due to thermal fluctuations, and each protein molecule which incorporated into the step remained. Growth kinetics for catalase crystals was investigated over wide supersaturation ranges. Strong directional kinetic anisotropy in the tangential step growth rates in different directions was seen. The influence of impurities on growth kinetics and cessation of macromolecular crystals was studied. Thus, for catalase, in addition to pronounced impurity effects on the kinetics of crystallization, we were also able to directly observe adsorption of some impurities. At low supersaturation we repeatedly observed filaments which formed from impurity molecules sedimenting on the surfaces. Similar filaments were observed on the surfaces of thaumatin, canavalin and STMV crystals as well, but the frequency was low compared with catalase crystallization. Cessation of growth of xylanase and lysozyme crystals was also observed and appeared to be a consequence of the formation of dense impurity adsorption layers. Attachment: "An in situ AFM investigation of catalase crystallization", "Atomic force microscopy studies of living cells: visualization of motility, division, aggregation, transformation, and apoptosis", AFM studies on mechanisms of nucleation and growth of macromolecular crystals", and "In situ atomic force microscopy studies of surface morphology, growth kinetics, defect structure and dissolution in macromolecular crystallization".

Malkin, Alexander J.↗

NASA NTRS1994

Multicomponent Gas Diffusion and an Appropriate Momentum Boundary Condition

Multicomponent gas diffusion is reviewed with particular emphasis on gas flows near solid boundaries-the so-called Kramers-Kistemaker effect. The aim is to derive an appropriate momentum boundary condition which governs many gaseous species diffusing together. The many species' generalization of the traditional single gas condition, either as slip or stick (no-slip), is not obvious, particularly for technologically important cases of lower gas pressures and very dissimilar molecular weight gases. No convincing theoretical case exists for why two gases should interact with solid boundaries equally but in opposite flow directions, such that the total gas flow exactly vanishes. ln this way, the multicomponent no-slip boundary requires careful treatment The approaches discussed here generally adopt a microscopic model for gas-solid contact. The method has the advantage that the mathematics remain tractable and hence experimentally testable. Two new proposals are put forward, the first building in some molecular collision physics, the second drawing on a detailed view of surface diffusion which does not unphysically extrapolate bulk gas properties to govern the adsorbed molecules. The outcome is a better accounting of previously anomalous experiments. Models predict novel slip conditions appearing even for the case of equal molecular weight components. These approaches become particularly significant in view of a conceptual contradiction found to arise in previous derivations of the appropriate boundary conditions. The analogous case of three gases, one of which is uniformly distributed and hence non-diffusing, presents a further refinement which gives unexpected flow reversals near solid boundaries. This case is investigated alone and for aggregating gas species near their condensation point. In addition to predicting new physics, this investigation carries practical implications for controlling vapor diffusion in the growth of crystals used in medical diagnosis (e.g. mercuric iodide) and semiconductors.

Noever, David A.↗

NASA NTRS1997

Colloids and Nucleation

The objectives of the work funded under this grant were to develop a microphotographic technique and use it to monitor the nucleation and growth of crystals of hard colloidal spheres. Special attention is given to the possible need for microgravity studies in future experiments. A number of persons have been involved in this work. A masters student, Keith Davis, began the project and developed a sheet illumination apparatus and an image processing system for detection and analysis. His work on a segmentation program for image processing was sufficient for his master's research and has been published. A post doctoral student Bernie Olivier and a graduate student Yueming He, who originally suggested the sheet illumination, were funded by another source but along with Keith made photographic series of several samples (that had been made by Keith Davis). Data extraction has been done by Keith, Bernie, Yueming and two undergraduates employed on the grant. Results are published in Langmuir. These results describe the sheet lighting technique as one which illuminates not only the Bragg scattering crystal, but all the crystals. Thus, accurate crystal counts can be made for nucleation rate measurements. The strange crystal length scale reduction, observed in small angle light scattering (SALS) studies, following the initial nucleation and growth period, has been observed directly. The Bragg scattering (and dark) crystal size decreases in the crossover region. This could be an effect due to gravitational forces or due to over- compression of the crystal during growth. Direct observations indicate a complex morphology for the resulting hard sphere crystals. The crystal edges are fairly sharp but the crystals have a large degree of internal structure. This structure is a result of (unstable) growth and not aggregation. As yet unpublished work compares growth exponents data with data obtained by SALS. The nucleation rate density is determined over a broad volume fraction range (0.505 to 0.575) and compared to classical nucleation rate calculations. The experimental nucleation rate density varies with volume fraction more slowly than expected theoretically. Gravity may influence nucleation because crystal nuclei are more dense than the surrounding fluid and may be gravitationally convected. The largest observed crystal size was near volume fraction 0.52. Near the freezing point, crystals should grow to large size because nuclei are sparse and there is plenty of room to grow without contacting other crystals. Near melting the opposite is true, with crystals growing into one another shortly after nucleation. The maximum crystal size seen near 0.52 volume fraction suggests that gravitational stresses are limiting crystal growth near freezing.

Ackerson, Bruce↗

NASA NTRS1998

Scale in Remote Sensing and GIS: An Advancement in Methods Towards a Science of Scale

The term "scale", both in space and time, is central to remote sensing and Geographic Information Systems (GIS). The emergence and widespread use of GIS technologies, including remote sensing, has generated significant interest in addressing scale as a generic topic, and in the development and implementation of techniques for dealing explicitly with the vicissitudes of scale as a multidisciplinary issue. As science becomes more complex and utilizes databases that are capable of performing complex space-time data analyses, it becomes paramount that we develop the tools and techniques needed to operate at multiple scales, to work with data whose scales are not necessarily ideal, and to produce results that can be aggregated or disaggregated ways that suit the decision-making process. Contemporary science is constantly coping with compromises, and the data available for a particular study rarely fit perfectly with the scales at which the processes being investigated operate, or the scales that policy-makers require to make sound, rational decisions. This presentation discusses some of the problems associated with scale as related to remote sensing and GIS, and describes some of the questions that need to be addressed in approaching the development of a multidisciplinary "science of scale". Techniques for dealing with multiple scaled data that have been developed or explored recently are described as a means for recognizing scale as a generic issue, along with associated theory and tools that can be of simultaneous value to a large number of disciplines. These can be used to seek answers to a host of interrelated questions in the interest of providing a formal structure for the management and manipulation of scale and its universality as a key concept from a multidisciplinary perspective.

Quattrochi, D. A.↗

NASA NTRS1998

Locations of Halide Ions in Tetragonal Lysozyme Crystals

Anions play an important role in the crystallization of lysozyme, and are known to bind to the crystalline protein. Previous studies employing X-ray crystallography had found one chloride ion binding site in the tetragonal crystal form of the protein and four nitrate ion binding sites in the monoclinic form. Studies using other approaches have reported more chloride ion binding sites, but their locations were not known. Knowing the precise location of these anions is also useful in determining the correct electrostatic fields surrounding the protein. In the first part of this study the anion positions in the tetragonal form were determined from the difference Fourier map obtained from the lysozyme crystals grown in bromide and chloride solutions under identical conditions. The anion locations were then obtained from standard crystallographic methods and five possible anion binding sites were found in this manner. The sole chloride ion binding site found in previous studies was confirmed. The remaining four sites were new ones for tetragonal lysozyme crystals. However, three of these new sites and the previously found one corresponded to the four unique binding sites found for nitrate ions in monoclinic crystals. This suggests that most of the anion binding sites in lysozyme remain unchanged, even when different anions and different crystal forms of lysozyme are employed. It is unlikely that there are many more anions in the tetragonal lysozyme crystal structure. Assuming osmotic equilibrium it can be shown that there are at most three more anions in the crystal channels. Some of the new anion binding sites found in this study were, as expected, in pockets containing basic residues. However, some of them were near neutral, but polar, residues. Thus, the study also showed the importance of uncharged, but polar groups, on the protein surface in determining its electrostatic field. This was important for the second part of this study where the electrostatic field surrounding the protein was accurately determined. This was achieved by solving the linearized version of the Poisson-Boltzmann equation for the protein in solution. The solution was computed employing the commercial code Delphi which uses a finite difference technique. This has recently become available as a module in the general protein visualization code Insight II. Partial charges were assigned to the polar groups of lysozyme for the calculations done here. The calculations showed the complexity of the electrostatic field surrounding the protein. Although most of the region near the protein surface had a positive field strength, the active site cleft was negatively charged and this was projected a considerable distance. This might explain the occurrence of "head-to-side" interactions in the formation of lysozyme aggregates in solution. Pockets of high positive field strength were also found in the vicinity of the anion locations obtained from the crystallographic part of this study, confirming the validity of these calculations. This study clearly shows not only the importance of determining the counterion locations in protein crystals and the electrostatic fields surrounding the protein, but also the advantage of performing them together.

Lim, Kap↗

NASA NTRS1998

Determining the Molecular Growth Mechanisms of Tetragonal Lysozyme Crystals

Studies of the growth of tetragonal lysozyme crystals employing atomic force microscopy (AFM) have shown the advantages of this technique in investigating the growth mechanisms of protein crystals [1]. The resolution of these studies was in the micron range, which revealed surface features such as the occurrence of dislocations and 2D nucleation islands, similar to those found in inorganic systems. They clearly showed that the crystals grew by these surface growth mechanisms. However, the studies also revealed some surprising features, such as bimolecular growth step heights and pronounced growth anisotropies on the (110) face, which could not be explained. In previous studies we employed Periodic Bond Chain (PBC) theory to tetragonal lysozyme crystal growth and found that the crystals were constructed by strongly bonded molecular chains forming helices about the 43 axes [2,3]. The helices were connected to each other with weaker bonds. The growth process was shown to proceed by the formation of these 43 helices, resulting in bimolecular growth steps on the (110) face. It was also shown to explain many other observations on tetragonal lysozyme crystal growth. Although PBC analysis is not a new technique [4], it has not been widely used as the mechanisms predicted from it could not be experimentally verified. In this study the growth process of these crystals was investigated, particularly for the (110) face, employing some newly developed high resolution AFM techniques. These techniques allowed individual lysozyme molecules on the crystal faces to be resolved and predictions from PBC analyses to be tested. The analyses had shown that of the two possible packing arrangements on (110) faces, only one would actually occur. Employing the first of the newly developed techniques, these faces were scanned by high resolution AFM. The resulting images were then compared with the theoretically constructed images for the two possible packing arrangements on the (110) face. The theoretical images were constructed by convolution of the crystal surface shape obtained from crystallographic data with the AFM tip shape. The comparison confirmed the prediction that the molecular packing arrangement of these faces corresponded to that for complete 43 helices. The second AFM technique that was developed was used to follow the growth process by measuring the dimensions of individual growth units on the (110) face. Linescans across a growth step, performed near the saturation limit of the crystals, allowed the growth unit dimensions to be measured. These measurements showed that growth on the (110) face proceeded by the formation of new 43 helices from the addition of at least tetramer units in the [110] direction. In the [001] direction growth proceeded by the addition of various aggregate units corresponding to the 4(sub 3) helices.

Li, Huayu↗

NASA NTRS1998

Tetragonal Lysozyme Interactions Studied by Site Directed Mutagenesis

A number of recent experimental and theoretical studies have indicated that tetragonal lysozyme crystal growth proceeds by the addition of aggregates, formed by reversible self association of the solute molecules in the bulk'solution. Periodic bond chain and atomic force microscopy studies have indicated that the probable growth unit is at minimum a 43 tetramer, and most likely an octamer composed of two complete turns about the 4(sub 3) axis. If these results are correct, then there are intermolecular interactions which are only formed in the solution and others only formed at the joining of the growth unit to the crystal surface. We have set out to study these interactions, and the correctness of this hypothesis, using site directed mutagenesis of specific amino acid residues involved in the different bonds. We had initially expressed wild type lysozyme in S. cervasiae with yields of approximately 5 mg/L, which were eventually raised to approximately 40 mg/L. We are now moving the expression to the Pichia system, with anticipated yields of 300 to greater than 500 mg/L, comparable to what can be obtained from egg whites. An additional advantage of using recombinant protein is the greater genetic homogeneity of the material obtained and the absence of any other contaminating egg proteins. The first mutation experiments are TYR 23 yields PHE or ALA and ASN 113 yields ALA or ASP. Both TYR 23 and ASN 113 form part of the postulated dimerization intermolecular binding site which lead to the formation of the 4(sub 3) helix. Tyrosine also participates in an intermolecular hydrogen bond with ARG 114. The results of these and subsequent experiments will be discussed.

Crawford, Lisa↗

NASA NTRS1998

New AFM Techniques for Investigating Molecular Growth Mechanisms of Protein Crystals

Atomic Force Microscopy (AFM) has emerged as a powerful technique for investigating protein crystal growth. Earlier AFM studies were among the first to demonstrate that these crystals grew by dislocation and 2D nucleation growth mechanisms [1]. These investigations were restricted to the micron range where only surface features, such as dislocation hillocks and 2D islands are visible. Most AFM instruments can scan at higher resolutions and have the potential to resolve individual protein molecules at nanometer ranges. Such scans are essential for determining the molecular packing arrangements on crystal faces and for probing the growth process at the molecular level. However, at this resolution the AFM tip influences the image produced, with the resulting image being a convolution of the tip shape and the surface morphology [2]. In most studies this problem is resolved by deconvoluting the image to obtain the true surface morphology. Although deconvolution routines work reasonably well for simple one- dimensional shapes, for complex surfaces this approach does not produce accurate results. In this study we devised a new approach which takes advantage of the precise molecular order of crystal surfaces, combined with the knowledge of individual molecular shapes from the crystallographic data of the protein and the AFM tip shape. This information is used to construct expected theoretical AFM images by convoluting the tip shape with the constructed crystal surface shape for a given surface packing arrangement. By comparing the images from actual AFM scans with the constructed ones for different possible surface packing arrangements, the correct packing arrangement can be conclusively determined. This approach was used in this study to determine the correct one from two possible packing arrangements on (I 10) faces of tetragonal lysozyme crystals. Another novel AFM technique was also devised to measure the dimension of individual growth units of the crystal faces. Measuring these units was not attempted before and most studies have assumed that the growth unit consisted of individual protein molecules. The linescan mode of AFM instruments allows the crystal surface to be scanned along a single line. By scanning across a growth step an image showing the motion of the step is obtained. Normally such an image shows a straight line for continuous and constant step velocity. In this study by increasing the scan rate and by decreasing the step velocity (by decreasing the supersaturation), we were able to capture images of individual growth events, shown by jump discontinuities in the step line. By suitable integration of the image the growth unit dimension in the scanned direction can be obtained. Since multiple units can be involved in the growth process it is necessary to collect a statistically relevant sample before drawing conclusions about the growth mechanism. This technique was successfully employed to obtain the dimensions of growth units for the (110) face, showing that they consisted of various aggregates corresponding to the 43 helices in the crystal structure.

Li, Huayu↗

NASA NTRS1998

An Object-Oriented Interface to the CCSDS Ground Telecommand Services

The Telecommand Data Routing and Channel Services defined by the Consultative Committee for Space Data Systems (CCSDS) are flexible enough to support a myriad of commanding models. Because the standard is so broad, the traditional approach has been to implement only the portion of the standard needed by the particular spacecraft being tested/operated. Tasked with providing Telecommand Services for an entire class of spacecraft, where each spacecraft may choose any valid CCSDS commanding model, NASA Code 584 designed a common architecture capable of handling the full CCSDS protocol. The solution uses another CCSDS standard - the Standard Formatted Data Unit (SFDU) as the interface to the Telecommand Services. SFDUs provide a consistent way of labelling data objects, as well as allowing data objects to encapsulate other data objects. The resulting interface is: - Flexible: The full Data Routing and Channel Services are available via a single interface. The client (i.e. the command source) may enter commands at any layer within the protocol stack, specify any of the data aggregation or segmentation methods, and dynamically set any configuration parameter defined in the standard. - Object-oriented: Each object specifies both the data and the actions to be performed with the data. An object may contain other objects. - Expandable: New capabilities are added by defining new objects. Objects pass thru the protocol layers until they reach the applicable layer. The resulting design is: - Modular: The logic for each protocol layer is contained in a separate Application Program Interface (API). The objects used for the external interface are also used for communication between layers. - Distributable: The design can be split along any layer boundary for distribution across multiple machines. The objects ensure data consistency across platforms. This paper describes the SFDU-based interface and the resulting protocol implementation. The implementation is currently used by NASA (National Aeronautics and Space Administration) for integration & test of the microwave Anisotropy Probe (MAP) and Earth observer-I (EO-l) spacecraft. It will be used for post-launch operations of these spacecraft as well as the Imager for Magnetopause to Aurora Global Exploration (IMAGE) spacecraft.

Ray, Timothy Joseph↗

NASA NTRS1996

Transient Creep of a Composite Lower Crust: Constitutive Theory - 1

A composite model is proposed to describe the time-dependent response of the Earth's lower crust. The motivation for such it model is twofold: First, new observations of widespread postseismic deformation indicate that the deep continental crust responds viscoelastically, having both long-and short-term decay times. Second, by any number of observationally based rationales, the lower crust is compositionally and structurally heterogeneous over many length scales. For heterogeneities that have much smaller characteristic lengths than the minimum deformation wavelength of interest, the aggregate rheology can be described by composite media theory. For wavelengths of the order of the thickness of the lower crust (approx. = 25-40 km) and larger, composite theory may be applied to heterogeneities that are smaller than about several hundred meters, or equivalent to the vertical extent of a thick lower crustal mylonitic shear zone. The composite media theory developed here is constructed using both Eshelhy-Mori-Tanaka theory for aligned generalized spheroidal inclusions and a generalized self-consistent method. The inclusions and matrix are considered to be Maxwellian viscoelastic: a rheology that is consistent with past homogeneous models of postseismic stress relaxation. The composite theory presented here introduces a transient response to a suddenly imposed stress field which does not appear in homogeneous Maxwell models. Analytic expressions for the amplitude and duration of the transient and for the effective long-and short-term viscosities of the composite are given which describe the sensitivity to inclusion concentration (phi), to shape, and to ratio of inclusion-to-matrix viscosity (R).

Ivins, Erik R.↗

NASA NTRS1998

Media Compositions for Three-Dimensional Mammalian Tissue Growth under Microgravity Culture Conditions

Normal mammalian tissue and the culturing process has been developed for the three groups of organ, structural and blood tissue.The cells are grown in vitro under microgravity culture conditions and form three dimensional cells aggregates with normal cell function. The microgravity culture conditions may be microgravity or simulated microgravity created in a horizontal rotating wall culture vessel.

Goodwin, Thomas J.↗

NASA NTRS1998

Comparative Soot Diagnostics: 1 Year Report

The motivation for the Comparative Soot Diagnostics (CSD) experiment lies in the broad practical importance of understanding combustion generated particulate. Depending upon the circumstances, particulate matter can affect the durability and performance of combustion equipment, can be a pollutant, can be used to detect fires and, in the form of soot, can be the dominant source of radiant energy from flames. Bright sooty fires are desirable for efficient energy extraction in furnaces and power equipment. In contrast, soot-enhanced radiation is undesirable in many propulsion systems (e.g. jet engines). The non-buoyant structure of most flames of practical interest (turbulent) makes understanding of soot processes in low gravity flames important to our ability to predict fire behavior on earth. These studies also have direct applications to fire safety in human-crew spacecraft, since smoke is the indicator used for automated detection in current spacecraft. In addition, recent tests conducted on MIR showed that a candle in a truly quiescent spacecraft environment can burn for tens of minutes. Consequently, this test and many earlier tests have demonstrated that fires in spacecraft can be considered a credible risk. In anticipation of this risk, NASA has included fire detectors on Skylab, smoke detectors on the Space Shuttle (STS), and smoke detectors in the design for the International Space Station (ISS). In the CSD experiment, these smoke detectors were tested using, quasi-steady, low-gravity, particulate generating materials. Samples of the particulate were also obtained from these low-gravity sources. This experiment provides the first such measurements aimed toward understanding of soot processes here on earth and for the testing and design of advanced spacecraft smoke detection systems. This paper describes the operation and preliminary results of the CSD experiment which was was conducted in the Middeck Glovebox Facility (MGBX) on USMP-3. The objectives of CSD are to examine the particulate emission from a variety of pyrolyzing and combusting sources and to quantify the performance of several particulate-sensing diagnostic techniques. This paper presents the results of the microgravity portion of the CSD experiment. The results include the temporal response of the detectors and average sizes of the primary and aggregate particles captured on the thermophoretic probes. Complete assessment of the microgravity data and its combination with the normal-gravity data are still in process.

Urban, David L.↗

NASA NTRS1995

The Experience Factory: Strategy and Practice

The quality movement, that has had in recent years a dramatic impact on all industrial sectors, has recently reached the system and software industry. Although some concepts of quality management, originally developed for other product types, can be applied to software, its specificity as a product which is developed and not produced requires a special approach. This paper introduces a quality paradigm specifically tailored on the problem of the systems and software industry. Reuse of products, processes and experiences originating from the system life cycle is seen today as a feasible solution to the problem of developing higher quality systems at a lower cost. In fact, quality improvement is very often achieved by defining and developing an appropriate set of strategic capabilities and core competencies to support them. A strategic capability is, in this context, a corporate goal defined by the business position of the organization and implemented by key business processes. Strategic capabilities are supported by core competencies, which are aggregate technologies tailored to the specific needs of the organization in performing the needed business processes. Core competencies are non-transitional, have a consistent evolution, and are typically fueled by multiple technologies. Their selection and development requires commitment, investment and leadership. The paradigm introduced in this paper for developing core competencies is the Quality Improvement Paradigm which consists of six steps: (1) Characterize the environment, (2) Set the goals, (3) Choose the process, (4) Execute the process, (5) Analyze the process data, and (6) Package experience. The process must be supported by a goal oriented approach to measurement and control, and an organizational infrastructure, called Experience Factory. The Experience Factory is a logical and physical organization distinct from the project organizations it supports. Its goal is development and support of core competencies through capitalization and reuse of its cycle experience and products. The paper introduces the major concepts of the proposed approach, discusses their relationship with other approaches used in the industry, and presents a case in which those concepts have been successfully applied.

Basili, Victor R.↗

NASA NTRS1998

Use of NASA Bioreactor in Engineering Tissue for Bone Repair

This study was proposed in search for a new alternative for bone replacement or repair. Because the systems commonly used in repair of bony defects form bone by going through a cartilaginous phase, implantation of a piece of cartilage could enhance the healing process by having a more advanced starting point. However, cartilage has seldom been used to replace bone due, in part, to the limitations in conventional culture systems that did not allow production of enough tissue for implants. The NASA-developed bioreactors known as STLV (Slow Turning Lateral Vessel) provide homogeneous distribution of cells, nutrients, and waste products, with less damaging turbulence and shear forces than conventional systems. Cultures under these conditions have higher growth rates, viability, and longevity, allowing larger "tissue-like" aggregates to form, thus opening the possibilities of producing enough tissue for implantation, along with the inherent advantages of in vitro manipulations. To assure large numbers of cells and to eliminate the use of timed embryos, we proposed to use an immortalized mouse limb bud cell line as the source of cells.

Duke, Pauline↗

NASA NTRS1998

Rotaing Systems Used as Microgravity Simulators for Studies of Cartilage Differentiation

Just as Studies of abnormal chondrogenesis produced by mutation or teratogen add to our understanding of the normal chondrogenic process, studying chondrogenesis in space may assist in 1 g studies of chondrogenic defects. Opportunities to study cartilage differentiation in space, however, are limited, so systems have been developed which can be used at 1 g to simulate microgravity. One model used to mimic effects of microgravity is the clinostat a rotating system which converts gravity from a vector quantity to a scalar quantity. In slow rotating clitiostat systems, cells are attached to a substrate as at 1 g, and rotated with the plane of the culture perpendicular to the gravitational field. Another rotating system used as a microgravity simulator is the Slow Turning Lateral Vessel (STLV) which uses a rotating cylindrical vessel, completely filled with medium to culture cells in suspension without subjecting them to damaging shear forces. Embronic limb cells cultured in the slow rotating clinostat, the STLV, and in space exhibit changes in chondrogenesis related to the stage at which the cells are exposed. Clinorotation decreases the number of nodules in micromass cultures, showing an effect on the condensation process. In micromass cultures flown in space, condensation occurred preflight, so the primary effect of microgravity exposure was on matrix production. In chondrocytes in the STLV, as in growth plates of spaceflown rats, hypertrophy was decreased. Future clinostat and spaceflight experiments will examine the effect on adhesive molecules and on cytoskeletal organization because of their involvement in the processes that are affected. The mechanisms by which micro-gravity alters phenotype modulation, matrix production and aggregation, and chondrocyte hypertrophy after the cartilage phenotype is established must also be elucidated. The mechanisms resulting in cartilage defects are to a large extent unknown, and microgravitv may provide a way to identify them.

Duke, Pauline Jackie↗