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All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Interaction and Aggregation of Colloidal Biological Particles and Droplets in Electrically-Driven Flows

The primary objective of this research was to develop a fundamental understanding of aggregation and coalescence processes during electrically-driven migration of cells, particles and droplets. The process by which charged cells, particles, molecules, or drops migrate in a weak electric field is known as electrophoresis. If the migrating species have different charges or surface potentials, they will migrate at different speeds and thus may collide and aggregate or coalesce. Aggregation and coalescence are undesirable, if the goal is to separate the different species on the basis of their different electrophoretic mobilities.

Davis, Robert H.↗
DOE OSTI2024

Multilevel well modeling in aggregation-based nonlinear multigrid for multiphase flow in porous media

A full approximation scheme (FAS) nonlinear multigrid solver for two-phase flow and transport problems driven by wells with multiple perforations is developed here. It is an extension to our previous work on FAS solvers for diffusion and transport problems. The solver is applicable to discrete problems defined on unstructured grids as the coarsening algorithm is aggregation-based and algebraic. To construct coarse basis that can better capture the radial flow near wells, coarse grids in which perforated well cells are not near the coarse-element interface are desired. This is achieved by an aggregation algorithm proposed in this paper that makes use of the location of well cells in the cell-connectivity graph. Numerical examples in which the FAS solver is compared against Newton's method on benchmark problems are given. In particular, for a refined version of the SAIGUP model, the FAS solver is at least 35% faster than Newton's method for time steps with a CFL number greater than 10.

58 GEOSCIENCES↗
NASA NTRS2004

Comparison of Genotoxic Damage in Monolayer Cell Cultures and Three-Dimensional Tissue-Like Cell Assemblies

Assessing the biological risks associated with exposure to the high-energy charged particles encountered in space is essential for the success of long-term space exploration. Although prokaryotic and eukaryotic cell models developed in our laboratory and others have advanced our understanding of many aspects of genotoxicity, in vitro models are needed to assess the risk to humans from space radiation insults. Such models must be representative of the cellular interactions present in tissues and capable of quantifying I genotoxic damage. Toward this overall goal, the objectives of this study were to examine the effect of the localized microenvironment of cells, cultured as either 2-dimensional (2D) monolayers or 3-dimensional (3D) aggregates, on the rate and type of genotoxic damage resulting from exposure to iron charged particles, a significant portion of space radiation. We used rodent transgenic cell lines containing 50-70 copies of a LacI transgene to provide the enhanced sensitivity required to quantify mutational frequency and type in the 1,100-bp LacI target as well as assessment of DNA,damage to the entire 45-kbp construct. Cultured cells were exposed to high-ener~ir on charged particles at Brookhaven National Laboratory s Alternating Gradient Synchrotron facility for a total dose of 0, 0.1, 0.25,0.5, 1.0, or 2.0 Gy and allowed to recover for 0, 1, or 7 days, after which mutational type and frequency were evaluated. The mutational frequency was found to be higher in 3D samples than in 2D samples at all radiation doses. Mutational frequency also was higher at 7 days after irradiation than immediately after exposure. DNA sequencing of the mutant targets revealed that deletional mutations contributed an increasingly high percentage (up to 27%) of all mutations in cells as the dose was increased from 0.5 to 2 Gy. Several mutants also showed large and complex deletions in multiple locations within the Lac1 target. However, no differences in mutational type were found between the 2D and the 3D samples. These 3D tissue-like model systems can reduce the uncertainty involved in extrapolating risk between in vitro cellular and in vivo models.

Behravesh, E.↗
NASA NTRS2016

Impact of Spatial Sampling on Continuity of MODIS-VIIRS Land Surface Reflectance Products: A Simulation Approach

With the increasing need to construct long-term climate-quality data records to understand, monitor, and predict climate variability and change, it is vital to continue systematic satellite measurements along with the development of new technology for more quantitative and accurate observations. The Suomi National Polar-orbiting Partnership mission provides continuity in monitoring the Earths surface and its atmosphere in a similar fashion as the heritage MODIS instruments onboard the National Aeronautics and Space Administrations Terra and Aqua satellites. In this paper, we aim at quantifying the consistency of Aqua MODIS and Suomi-NPP Visible Infrared Imaging Radiometer Suite (VIIRS) Land Surface Reflectance (LSR) and NDVI products as related to their inherent spatial sampling characteristics. To avoid interferences from sources of measurement and/or processing errors other than spatial sampling, including calibration, atmospheric correction, and the effects of the bidirectional reflectance distribution function, the MODIS and VIIRSLSR products were simulated using the Landsat-8s Operational Land Imager (OLI) LSR products. The simulations were performed using the instruments point spread functions on a daily basis for various OLI scenes over a 16-day orbit cycle. It was found that the daily mean differences due to discrepancies in spatial sampling remain below 0.0015 (1) in absolute surface reflectance at subgranule scale (i.e., OLI scene size).We also found that the MODISVIIRS product intercomparisons appear to be minimally impacted when differences in the corresponding view zenith angles (VZAs) are within the range of -15deg to -35deg (VZA(sub v) - VZA(sub m)), where VIIRS and MODIS footprints resemble in size. In general, depending on the spatial heterogeneity of the OLI scene contents, per-grid-cell differences can reach up to 20.Further spatial analysis of the simulated NDVI and LSR products revealed that, depending on the user accuracy requirements for product intercomparisons, spatial aggregations may be used. It was found that if per-grid-cell differences on the order of 10(in LSR or NDVI) are tolerated, the product intercomparisons are expected to be immune from differences in spatial sampling.

VIIRS↗
DOE OSTI2025

Integrated GW Farm ABM

This Data Repository includes data used for the integrated groundwater- farm ABM model, raw model output from scenario ensemble, and processed outputs that isolate the groundwater storage depletion outcomes for the 35,000 farm cells. Model Inputs: Farm ABM Inputs: This folder contains the input data used by the integrated groundwater - farm ABM modelling script (Python file) used for the high performance computing (HPC) experiments. The sub-folder "data inputs" contains all of the farm attribute data, while the three files in the folder have the hydrogeological data lookup table (NLDAS Cost Curve Attributes.csv), a lookup table (Theis well function table.csv) for the groundwater cost curve function, and the farm indexes and corresponding NLDAS ids for all of the cells run in this experiment (nldas farms subset final.csv). NLDAS Cost curve hydrogeological data: Hydrogeological data aggregated to 1/8 degree resolution and aligned with the NLDAS grid. Parameters include: water depth below ground surface [meters], subsurface porosity [unitless], aquifer depth from ground surface to aquifer bottom [meters], annual average recharge (USGS: mm, Doll: meters), and three different hydraulic conductivity (K) values (meters/day). The three K values represent the mean value from Gleeson et al. (2018), one standard deviation above the mean from Gleeson et al. (2018), and the de Graaf et al. 2020 modifications to certain lithologies. Additional information about these datasets and their processing are documented in the supplement to Yoon et al. 2025 (in review). Output: Raw outputs: This folder contains a .zip file that has model outputs for the entire scenario ensemble. There is one csv for each farm id, using the format "farm farmid cases.csv". The relationship between the farm id and NLDAS id is defined by the "nldas farms subset final.csv" located in the Farm ABM Inputs folder. Each csv has 625 rows, corresponding to 625 combinations of different scenario parameter values. Each row (scenario) represents the outcome of a 100 year simulation. Columns define scenario settings and summary statistics for each scenario. The first four columns define the scenario settings: "hydro ratio," "econ ratio," "K scenario," and "gamma scenario." The hydro and econ ratios are values passed to the modeling script that influence multipliers for other model parameters, as documented in the supplement to Yoon et al. 2025 (in review). The gamma multiplier is a coefficient multiplier applied to the baseline gamma values (values below 1 represent lower unobserved costs compared to baseline, values above 1 represent higher costs). The K scenario names represent K values of: "low": 0.5 m/d, "int 1": 2.5 m/d, "int 2": 10 m/d, "high": 50 m/d, and "gleeson": mean Gleeson K value. "Perc vol depleted" is the fraction of groundwater depleted at the end of the 100 simulation. Processed Output: Derived depletion outcomes from raw outputs: All of the individual csv files from the Raw outputs were aggregated into a single file that has the scenario settings and fraction depletion "Perc vol depleted" for every farm cell, for every scenario. The other two files define relationships between the farm id, NLDAS id, and local and major aquifer units, used for aquifer-level depletion analysis.

Agent based modeling↗
DOE OSTI2025

A Solvatochromic Near Infrared Fluorophore Sensitive to the Full Amyloid Beta Aggregation Pathway

Alzheimer's disease has long been associated with the aggregation of amyloid beta peptides (Aβ42) into macroscale plaques, although specific neurodegenerative agents have not been definitively identified. Much evidence has pointed to the soluble nanoscale oligomers that form early in the Aβ42 aggregation pathway, but there is little understanding of these structures, their mechanisms of formation, or how they grow into plaques. Here, we show that a solvatochromic fluorophore with near-infrared (NIR) emission can track synthetic Aβ42 aggregation through environment-sensitive spectral shifts from the earliest time points through plaque formation. This azide-functionalized phosphine oxide azetidine rhodol (Phazr-N3) shows large polarity-dependent changes in fluorescence emission, with maxima shifting from 630 nm in toluene to 703 nm in aqueous buffer, and a maximum quantum yield of 62%. Upon induction of Aβ42 aggregation, we observe immediate solvatochromic changes in Phazr-N3 fluorescence, with multiple apparent phases over 12 h, and which culminate before the onset of any major fluorescence changes of conformation-specific aggregation fluorophore thioflavin T. Solution anisotropy measurements show a low micromolar affinity of Phazr-N3 for disordered, free Aβ42 in solution, and real-time measurements are consistent with rapid liquid-liquid phase separation and slow dehydration of the growing aggregate. Spectral imaging of synthetic plaques stained in the presence of live cells and lipid-binding protein albumin shows over 4000-fold Phazr-N3 fluorescence intensity above background under no-wash conditions, and over 100-fold intensity above coplated microglial cells or a large excess of albumin. This use of a solvatochromic probe with structure-independent binding to free Aβ42 offers real-time, minimally invasive insight into the full Aβ42 aggregation pathway.

Wang, Zeming↗
DOE OSTI2024

Tackling P3HT:Y‐Series Miscibility Through Advanced Processing for Tunable Aggregation

Abstract Polymer and small molecule blend thin films are of strong interest for organic electronics and particularly organic solar cells. The high miscibility in blends of ordinary P3HT and state‐of‐the‐art Y‐series non‐fullerene acceptors (NFAs) suppresses phase separation and aggregation challenging successful charge separation and transport. In a recent work, current‐induced doping (CID) is introduced, a method to precisely control the aggregation of Poly(3‐hexylthiophene) (P3HT) in solution. The highly ordered pre‐aggregation in solution is used here to control the P3HT aggregation in neat films and blends with Y12 (BTP‐4F‐12). This results in a 25‐fold increase in hole mobility in P3HT organic field‐effect transistor (OFET) devices and tunability of the P3HT aggregate quality in the presence of Y12 over large ranges. At the same time, particularly the Y12 long‐range ordering is heavily suppressed by increasing P3HT aggregation. However, solvent vapor annealing (SVA) leads to an extraordinarily high Y12 ordering, changes in the crystal orientation of Y12, and a further improvement of P3HT aggregation. A broad range of different degrees of aggregation of both materials can therefore be obtained in the final thin films solely by changing processing parameters without changing the composition of the material system.

Chemistry↗
NASA NTRS1994

Neonatal rat heart cells cultured in simulated microgravity

In vitro characteristics of cardiac cells cultured in simulated microgravity are reported. Tissue culture methods performed at unit gravity constrain cells to propagate, differentiate, and interact in a two dimensional (2D) plane. Neonatal rat cardiac cells in 2D culture organize predominantly as bundles of cardiomyocytes with the intervening areas filled by non-myocyte cell types. Such cardiac cell cultures respond predictably to the addition of exogenous compounds, and in many ways they represent an excellent in vitro model system. The gravity-induced 2D organization of the cells, however, does not accurately reflect the distribution of cells in the intact tissue. We have begun characterizations of a three-dimensional (3D) culturing system designed to mimic microgravity. The NASA designed High-Aspect-Ratio-Vessel (HARV) bioreactors provide a low shear environment which allows cells to be cultured in static suspension. HARV-3D cultures were prepared on microcarrier beads and compared to control-2D cultures using a combination of microscopic and biochemical techniques. Both systems were uniformly inoculated and medium exchanged at standard intervals. Cells in control cultures adhered to the polystyrene surface of the tissue culture dishes and exhibited typical 2D organization. Cells in cultured in HARV's adhered to microcarrier beads, the beads aggregated into defined clusters containing 8 to 15 beads per cluster, and the clusters exhibited distinct 3D layers: myocytes and fibroblasts appeared attached to the surfaces of beads and were overlaid by an outer cell type. In addition, cultures prepared in HARV's using alternative support matrices also displayed morphological formations not seen in control cultures. Generally, the cells prepared in HARV and control cultures were similar, however, the dramatic alterations in 3D organization recommend the HARV as an ideal vessel for the generation of tissue-like organizations of cardiac cells in simulated microgravity.

Akins, Robert E.↗
DOE OSTI2024

Getting to the root of the problem: Soil carbon and microbial responses to root inputs within a buried paleosol along an eroding hillslope in southwestern Nebraska, USA

Large quantities of soil carbon (C) can persist within paleosols for millennia due to burial and subsequent isolation from plant-derived inputs, atmospheric conditions, and microbial activity at the modern surface. Erosion exposes buried soils to modern root-derived C influx via root exudation and root turnover, thus stimulating microbial activity leading to SOC decomposition and accumulation through organo-mineral stabilization of modern C. With this study we aim to quantify how modern root-derived C inputs impact paleosol C decomposition and stabilization across varying degrees of isolation from modern surface conditions in southwestern Nebraska, USA, where hillslope erosion is bringing a buried Late-Pleistocene-early Holocene paleosol (the “Brady Soil”) closer to the modern surface. We collected Brady Soil samples from 0.2m, 0.4m, and 1.2m below the modern surface and conducted two lab-based incubations. Soils were amended with either (1) a lab-synthesized mixture of low molecular weight compounds (12 atom% 13 C), or (2) 13 C enriched root residues (92 atom% 13 C), in 30-day and 240-day incubation experiments, respectively. Here we determined microbial responses to synthetic root exudates and residues by partitioning the 13 C label from Brady Soil C, including measurements of total, root, and primed C respiration, microbial biomass C (MBC), microbial C use efficiency (CUE). To assess the capacity of isolated paleosols to accrue modern plant C, we used Nano-scale Secondary Ion Mass Spectrometry imaging. We found that: (1) adding root-derived C inputs primed Brady Soil C across all depths, and was mediated by depth and composition of root additions; (2) root-derived C inputs stimulated microbial biomass C (MBC) growth similarly across depths, but the magnitude of CUE and MBC varied by chemistry of root-derived additions; (3) new particulate organic matter was incorporated into mineral-associated pools over time; (4) material from the added root residues was found in association with bacterial cells and fungal hyphae as well as with soil aggregate and mineral surfaces. Our study shows that paleosols defy expectations of C content and reactivity with depth, and changes in land cover and climate will expose buried paleosols to modern surface conditions, increasing respired C. This work highlights the importance of evaluating the role resurfacing buried soils through landscape change plays in C cycle feedbacks to the climate system.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1994

Induction of carcinoembryonic antigen expression in a three-dimensional culture system

MIP-101 is a poorly differentiated human colon carcinoma cell line established from ascites that produces minimal amounts of carcinoembryonic antigen (CEA), a 180 kDa glycoprotein tumor marker, and nonspecific cross-reacting antigen (NCA), a related protein that has 50 and 90 kDa isoforms, in vitro in monolayer culture. MIP-101 produces CEA when implanted into the peritoneum of nude mice but not when implanted into subcutaneous tissue. We tested whether MIP-101 cells may be induced to express CEA when cultured on microcarrier beads in three-dimensional cultures, either in static cultures as non-adherent aggregates or under dynamic conditions in a NASA-designed low shear stress bioreactor. MIP- 101 cells proliferated well under all three conditions and increased CEA and NCA production 3 - 4 fold when grown in three-dimensional cultures compared to MIP-101 cells growing logarithmically in monolayers. These results suggest that three-dimensional growth in vitro simulates tumor function in vivo and that three-dimensional growth by itself may enhance production of molecules that are associated with the metastatic process.

Jessup, J. M.↗
NASA NTRS2000

BOREAS AFM-12 1-km AVHRR Seasonal Land Cover Classification

The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-12 team's efforts focused on regional scale Surface Vegetation and Atmosphere (SVAT) modeling to improve parameterization of the heterogeneous BOREAS landscape for use in larger scale Global Circulation Models (GCMs). This regional land cover data set was developed as part of a multitemporal one-kilometer Advanced Very High Resolution Radiometer (AVHRR) land cover analysis approach that was used as the basis for regional land cover mapping, fire disturbance-regeneration, and multiresolution land cover scaling studies in the boreal forest ecosystem of central Canada. This land cover classification was derived by using regional field observations from ground and low-level aircraft transits to analyze spectral-temporal clusters that were derived from an unsupervised cluster analysis of monthly Normalized Difference Vegetation Index (NDVI) image composites (April-September 1992). This regional data set was developed for use by BOREAS investigators, especially those involved in simulation modeling, remote sensing algorithm development, and aircraft flux studies. Based on regional field data verification, this multitemporal one-kilometer AVHRR land cover mapping approach was effective in characterizing the biome-level land cover structure, embedded spatially heterogeneous landscape patterns, and other types of key land cover information of interest to BOREAS modelers.The land cover mosaics in this classification include: (1) wet conifer mosaic (low, medium, and high tree stand density), (2) mixed coniferous-deciduous forest (80% coniferous, codominant, and 80% deciduous), (3) recent visible bum, vegetation regeneration, or rock outcrops-bare ground-sparsely vegetated slow regeneration bum (four classes), (4) open water and grassland marshes, and (5) general agricultural land use/ grasslands (three classes). This land cover mapping approach did not detect small subpixel-scale landscape features such as fens, bogs, and small water bodies. Field observations and comparisons with Landsat Thematic Mapper (TM) suggest a minimum effective resolution of these land cover classes in the range of three to four kilometers, in part, because of the daily to monthly compositing process. In general, potential accuracy limitations are mitigated by the use of conservative parameterization rules such as aggregation of predominant land cover classes within minimum horizontal grid cell sizes of ten kilometers. The AFM-12 one-kilometer AVHRR seasonal land cover classification data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

Steyaert, Lou↗
NASA NTRS2004

Immunofluorescent Detection of DNA Double Strand Breaks induced by High-LET Radiation

Within cell nuclei, traversing charged heavy ion particles lead to the accumulation of proteins related to DNA lesions and repair along the ion trajectories. Irradiation using a standard geometric setup with the beam path perpendicular to the cell monolayer generates discrete foci of several proteins known to localize at sites of DNA double strand breaks (DSBs). One such molecule is the histone protein H2AX (gamma-H2AX), which gets rapidly phosphorylated in response to ionizing radiation. Here we present data obtained with a modified irradiation geometry characterized by a beam path parallel to a monolayer of human fibroblast cells. This new irradiation geometry leads to the formation of gamma-H2AX aggregates in the shape of streaks stretching over several micrometers in the x/y plane, thus enabling the analysis of the fluorescence distributions along the particle trajectories. Qualitative analysis of these distributions presented insights into the DNA repair kinetics along the primary track structure and visualization of possible chromatin movement. We also present evidence of colocalization of gamma-H2AX with several other proteins in responses to ionizing radiation exposure. Analysis of gamma-H2AX has the potential to provide useful information on human cell responses to high LET radiation after exposure to space-like radiation.

Cucinotta, Francis A.↗
NASA NTRS2004

"Smart" Magnetic Fluids Experiment Operated on the International Space Station

InSPACE is a microgravity fluid physics experiment that was operated on the International Space Station (ISS) in the Microgravity Science Glovebox from late March 2003 through early July 2003. (InSPACE is an acronym for Investigating the Structure of Paramagnetic Aggregates From Colloidal Emulsions.) The purpose of the experiment is to obtain fundamental data of the complex properties of an exciting class of smart materials termed magnetorheological (MR) fluids. MR fluids are suspensions, or colloids, comprised of small (micrometer-sized) superparamagnetic particles in a nonmagnetic medium. Colloids are suspensions of very small particles suspended in a liquid. (Examples of other colloids are blood, milk, and paint.) These controllable fluids can quickly transition into a nearly solid state when exposed to a magnetic field and return to their original liquid state when the magnetic field is removed. Controlling the strength of the magnetic field can control the relative stiffness of these fluids. MR fluids can be used to improve or develop new seat suspensions, robotics, clutches, airplane landing gear, and vibration damping systems. The principal investigator for InSPACE is Professor Alice P. Gast of the Massachusetts Institute of Technology (MIT). The InSPACE hardware was developed at the NASA Glenn Research Center. The InSPACE samples were delivered to the ISS in November 2002, on the Space Shuttle Endeavour, on Space Station Utilization Flight UF-2/STS113. Operations began on March 31, 2003, with the processing of three different particle size samples at multiple test parameters. This investigation focused on determining the structural organization of MR colloidal aggregates when exposed to a pulsing magnetic field. On Earth, the aggregates take the shape of footballs with spiky tips. This characteristic shape may be influenced by the pull of gravity, which causes most particles initially suspended in the fluid to sediment, (i.e., settle and collect at the bottom of the cell). In the absence of sedimentation effects on the ISS, the behavior and shape of these MR aggregate structures are dominated exclusively by magnetic and surface tension forces. The microscopic detail of these structures was imaged under two orthogonal camera views. The video was downlinked to the InSPACE team at Glenn's Telescience Support Center and to MIT and also recorded onboard the ISS on videotapes that will be brought back to the ground by the space shuttles. The study examined the effect on the structure formation by varying the magnetic field strength and pulse frequency, and particle size. Fundamental data that characterized the structure formation were obtained. InSPACE completed its last planned test run on July 2, 2003. Operations occurred on 21 days over approximately a 3-month period. Forty-one test points were completed during 26 test runs. During the initial testing, the procedures followed by the crew were modified to maximize the observation of some unexpected and interesting aggregate behavior. As a result Dr. Gast has reported on the formation of aggregate shapes that are more extended and diverse than those observed on the ground. Sheets of magnetic material folded over in a labyrinth pattern and large columnar aggregates with complex interfaces with the surrounding fluid are examples of the interesting structures that have been observed on the ISS. In light of these early findings, the understanding of the fundamental properties of MR fluids on the basis of ground-based observations may need to be reconsidered.The experiments on the ISS have provided a vast amount of video data for analysis. While this analysis is ongoing, plans are being made for additional experimental runs. For this purpose, additional hardware and cells containing samples of different magnetic particles and sizes are being fabricated for a future launch to the ISS. The InSPACE hardware will remain on orbit until this testing is completed.

Agui, Juan H.↗
NASA NTRS2003

Physiological and Molecular Genetic Effects of Time-Varying Electromagnetic Fields on Human Neuronal Cells

The present investigation details the development of model systems for growing two- and three-dimensional human neural progenitor cells within a culture medium facilitated by a time-varying electromagnetic field (TVEMF). The cells and culture medium are contained within a two- or three-dimensional culture vessel, and the electromagnetic field is emitted from an electrode or coil. These studies further provide methods to promote neural tissue regeneration by means of culturing the neural cells in either configuration. Grown in two dimensions, neuronal cells extended longitudinally, forming tissue strands extending axially along and within electrodes comprising electrically conductive channels or guides through which a time-varying electrical current was conducted. In the three-dimensional aspect, exposure to TVEMF resulted in the development of three-dimensional aggregates, which emulated organized neural tissues. In both experimental configurations, the proliferation rate of the TVEMF cells was 2.5 to 4.0 times the rate of the non-waveform cells. Each of the experimental embodiments resulted in similar molecular genetic changes regarding the growth potential of the tissues as measured by gene chip analyses, which measured more than 10,000 human genes simultaneously.

Goodwin, Thomas J.↗
NASA NTRS1985

Oxygen and carbon in silicon

The properties of the early transistors were determined by the minority-carrier lifetime, as is the silicon photovoltaic solar cell. Most of the devices on the modern integrated circuits are majority carrier devices, in part to avoid this lifetime dependence. The micro-electronics industry typically starts with wafers with a minority-carrier lifetime of 1000 micro-seconds, but during device fabrication this lifetime is reduced to beflow 1 micro-second, in spite of extraordinary cleanliness and precautions. Process-induced defects (PID) include point defects, defect complexes, line defects, and bulk precipitates. One of the aspects that needs to be better understood is the nature of minority carrier recombination at line defects and at precipitates. Some of the PIDs are known to be related to the fast-diffusers of the iron-series transition elements. One of the common techniques of dealing with these elements is intrinsic gettering by the oxygen precipitates. But even in the gettered state, there may be a residual effect on the lifetime. Oxygen is an almost ubiquitous impurity in silicon and plays an important role in both integrated circuits and solar cells. The isolated oxygen interstitial is electrically inactive, but in its various aggregated forms it has a variety of electrical activities. The agglomeration and precipitation of oxygen, including impurity gettering and the complicating role of carbon, is discussed.

Corbett, J. W.↗
NASA NTRS1988

Does vector-free gravity simulate microgravity? Functional and morphologic attributes of clinorotated nerve and muscle grown in cell culture

Cocultured Xenopus neurons and myocytes were subjected to non-vectorial gravity by clinostat rotation to determine if microgravity, during space flights, may affect cell development and communications. Clinorotated cells showed changes consistent with the hypothesis that cell differentiation, in microgravity, is altered by interference with cytoskeleton-related mechanisms. We found: increases in the myocyte and its nuclear area, "fragmentation" of nucleoli, appearance of neuritic "aneurysms", decreased growth in the presence of "trophic" factors, and decreased yolk utilization. The effects were most notable at 1-10 rpm and depended on the onset and duration of rotation. Some parameters returned to near control values within 48 hrs after cessation of rotation. Cells from cultures rotated at higher speeds (>50 rpm) appeared comparable to controls. Compensation by centrifugal forces may account for this finding. Our data are consistent, in principle, with effects on other, flighted cells and suggest that "vector-free" gravity may simulate certain aspects of microgravity. The distribution of acetylcholine receptor aggregates, on myocytes, was also altered. This indicates that brain development, in microgravity, may also be affected.

NASA Discipline Cell Biology↗
NASA NTRS2000

Thermocapillary Flow and Aggregation of Bubbles on a Solid Wall

During the electrolytic evolution of oxygen bubbles forming on a vertically oriented transparent tin oxide electrode, bubbles were found to be mutually attractive. The mechanism of the aggregation had never been explained satisfactorily until Guelcher et al. attributed it to thermocapillary flow. The gradient of surface tension of the liquid at the bubble's surface, which was established because of reaction heat and ohmic heat loss at the electrode wall, drives flow of the liquid adjacent to each bubble; the bubble "pumps" fluid along its surface away from the wall. Fluid flows toward the bubble to conserve mass and entrains nearby bubbles in the flow pattern. The same logic would apply when two bubbles of equal size are adjacent to each other on a warm wall. Each bubble drives thermocapillary flow and hence entrains the other in its flow pattern, which drives the aggregation. Our objective here is to perform experiments where the temperature gradient at the wall is well known and controlled. The theory can be quantitatively tested by studying aggregation of bubble pairs of equal size, and by varying system parameters such as temperature gradient, bubble size and fluid viscosity. The results are then compared with the theory in a quantitatively rigorous manner. We demonstrate that the theory without adjustable parameters is capable of quantitatively modeling the rate of aggregation of two bubbles. The equations governing the thermocapillary flow around a single stationary bubble on a heated or cooled wall in a semi-infinite domain were solved. Both Reynolds number and Marangoni number were much less than unity. The critical result is that liquid in the vicinity of a warm wall flows toward a stationary collector bubble. Consequently the thermocapillary flow around the stationary bubble entrains another bubble toward itself. The bubbles undergo hindered translation parallel to the wall with velocity U while the fluid flow field is described with u. Two velocities were equated by using a wall hindrance parameter q: U = qu [1] which shows the velocity of bubble is proportional to the entraining velocity. The hindrance parameter q can experimentally be measured independently. q can also be calculated by solving the equations of motion for a bubble translating parallel to a solid wall. The experimental cell is cylindrical with an ID of 10 cm and consists of a 1 cm deep main cell filled with silicone oil and flanked by two thermal reservoirs. The upper thermal reservoir was heated and the lower thermal reservoir was cooled so that the bubbles aggregate. Two types of silicone oil (eta = 0.02 and 0.50 Pa s) were used. Two equal sized air bubbles were injected into the cell with a syringe. The center-to-center distance of bubbles was observed through a microscope. Bubble radius ranged from 0.40 mm to 0.65 mm and the temperature gradients along with the cell ranged from 1400 to 5000 K/m. The bubbles aggregated when heat flows from the wall to the fluid. The velocities of bubbles were in the range of 1 - 10 microns/s. The separation r decreased more quickly when the temperature gradient was higher, bubble size was larger, and the oil viscosity was lower. r decreased more rapidly as the bubbles approached each other. Dimensionless time was arbitrarily set to be zero when the dimensionless center-to-center distance between the bubbles was 4. All the bubble trajectories fall onto one line, especially in the range of dimensionless distance from 4 to 3. This means the relative movement of the bubble pair is proportional to the temperature gradient and bubble size and it is inversely proportional to the viscosity of the oil. This result strongly suggests that the thermocapillary flow-based aggregation mechanism is correct. A value of q can be estimated by fitting the scaled data to Eq. [1]. A best fit value of q was obtained as q = 0.26 with a standard deviation of 0.03. Independent experimental results for q for a 0.5 mm radius bubble, give values of q in the range 0.11 to 0.23. The value of q obtained from solving the equations of motion reveals q has values in the range 0.23 - 0.30. Since the full scale of possible values of q is zero to one, the maximum deviation of independently determined values of q from the best fit value was 15% of this full scale. Thus reasonable quantitative agreement between theory and experiment has been obtained.

Kasumi, Hiroki↗
NASA NTRS1999

Induction of three-dimensional assembly of human liver cells by simulated microgravity

The establishment of long-term cultures of functional primary human liver cells (PHLC) is formidable. Developed at NASA, the Rotary Cell Culture System (RCCS) allows the creation of the unique microgravity environment of low shear force, high-mass transfer, and 3-dimensional cell culture of dissimilar cell types. The aim of our study was to establish long-term hepatocyte cultures in simulated microgravity. PHLC were harvested from human livers by collagenase perfusion and were cultured in RCCS. PHLC aggregates were readily formed and increased up to 1 cm long. The expansion of PHLC in bioreactors was further evaluated with microcarriers and biodegradable scaffolds. While microcarriers were not conducive to formation of spheroids, PHLC cultured with biodegradable scaffolds formed aggregates up to 3 cm long. Analyses of PHLC spheroids revealed tissue-like structures composed of hepatocytes, biliary epithelial cells, and/or progenitor liver cells that were arranged as bile duct-like structures along nascent vascular sprouts. Electron microscopy revealed groups of cohesive hepatocytes surrounded by complex stromal structures and reticulin fibers, bile canaliculi with multiple microvilli, and tight cellular junctions. Albumin mRNA was expressed throughout the 60-d culture. A simulated microgravity environment is conducive to maintaining long-term cultures of functional hepatocytes. This model system will assist in developing improved protocols for autologous hepatocyte transplantation, gene therapy, and liver assist devices, and facilitate studies of liver regeneration and cell-to-cell interactions that occur in vivo.

NASA Center JSC↗