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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Parallel characterization of anaerobic toluene- and ethylbenzene-degrading microbial consortia by PCR-denaturing gradient gel electrophoresis, RNA-DNA membrane hybridization, and DNA microarray technology

A mesophilic toluene-degrading consortium (TDC) and an ethylbenzene-degrading consortium (EDC) were established under sulfate-reducing conditions. These consortia were first characterized by denaturing gradient gel electrophoresis (DGGE) fingerprinting of PCR-amplified 16S rRNA gene fragments, followed by sequencing. The sequences of the major bands (T-1 and E-2) belonging to TDC and EDC, respectively, were affiliated with the family Desulfobacteriaceae. Another major band from EDC (E-1) was related to an uncultured non-sulfate-reducing soil bacterium. Oligonucleotide probes specific for the 16S rRNAs of target organisms corresponding to T-1, E-1, and E-2 were designed, and hybridization conditions were optimized for two analytical formats, membrane and DNA microarray hybridization. Both formats were used to characterize the TDC and EDC, and the results of both were consistent with DGGE analysis. In order to assess the utility of the microarray format for analysis of environmental samples, oil-contaminated sediments from the coast of Kuwait were analyzed. The DNA microarray successfully detected bacterial nucleic acids from these samples, but probes targeting specific groups of sulfate-reducing bacteria did not give positive signals. The results of this study demonstrate the limitations and the potential utility of DNA microarrays for microbial community analysis.

Non-NASA Center↗
NASA NTRS1987

Isolation and characterization of esters of indole-3-acetic acid from the liquid endosperm of the horse chestnut (Aesculus species)

Esters of indole-3-acetic acid were extracted and purified from the liquid endosperm of immature fruits of various species of the horse chestnut (Aesculus parviflora, A. baumanni, A. pavia rubra, and A. pavia humulis). The liquid endosperm contained, at least 12 chromatographically distinct esters. One of these compounds was purified and characterized as an ester of indole-3-acetic acid and myo-inositol. A second compound was found to be an ester of indole-3-acetic acid and the disaccharide rutinose (glucosyl-rhamnose). A third compound was partially characterized as an ester of indole-3-acetic acid and a desoxyaminohexose.

NASA Discipline Number 40-10↗
NASA NTRS1990

Characterization and effect of light on the plasma membrane H(+) -ATPase of bean leaves

Proton excretion from bean (Phaseolus vulgaris L.) leaf cells is increased by bright white light. To test whether this could be due, at least in part, to an increase in plasma membrane (PM) ATPase activity, PM vesicles were isolated from primary leaves by phase partitioning and used to characterize PM ATPase activity and changes in response to light. ATPase activity was characterized as magnesium ion dependent, vanadate sensitive, and slightly stimulated by potassium chloride. The pH optimum was 6.5, the Km was approximately 0.30 millimolar ATP, and the activity was about 60% latent. PM vesicles were prepared from leaves of plants grown for 11 days in dim red light (growing slowly) or grown for 10 days in dim red light and then transferred to bright white-light for 1 day (growing rapidly). For both light treatments, ATPase specific activity was approximately 600 to 700 nanomoles per milligram protein per minute, and the latency, Km, and sensitivity to potassium chloride were also similar. PM vesicles from plants grown in complete darkness, however, exhibited a twofold greater specific activity. We conclude that the promotion of leaf growth and proton excretion by bright white light is not due to an increase in ATPase specific activity. Light does influence ATPase activity, however; both dim red light and bright white light decreased the ATPase specific activity by nearly 50% as compared with dark-grown leaves.

NASA Program Space Biology↗
NASA NTRS2004

Goals and Progress for Mil Handbook 17, Vol. 5 on Ceramic Matrix Composites: Testing and Characterization

The initial edition of the Mil Handbook 17, Vol. 5 on ceramic matrix composites (CMCs) was recently published. Part C of this CMC volume describes procedures for characterization of the thermal, physical, and mechanical properties of CMCs and subsequent data analysis procedures. As is the case for entire CMC volume, this chapter is a "work in progress" with sections on recommended test plans and matrices, data reduction, and test methods. This presentation will describe the current status in development of this section of the CMC volume and will highlight examples of critical issues that will be addressed in this volume. CMC systems are a different class of material than metals or polymer matrix composite with different mechanical response and failure modes, design rules, test methods, and characterization techniques. The CMC test protocols need to include guidance on how to generate enough reliable data in order to estimate, with reasonable confidence, the lower bounds of performance properties, such as strength and life. Strength data sets on two material systems, C/SiC and Nicalon/SiNC, and a creep rupture data set on C/SiC, will be presented to highlight this issue. The structural properties of CMC parts can sometimes be significantly different than those obtained from flat panels because of changes in fiber architecture often required to make shapes and spatial and lot-to-lot variations in processing conditions. To illustrate an example, the hoop tensile properties of SiC/SiC cylinders will be compared to properties obtained from flat panels fabricated from the same composites. These CMC testing-design issues are being defined and documented in the Mil Handbook 17 CMC volume.

Verrilli, Michael J.↗
NASA NTRS2004

Development Status for the Stennis Space Center LIDAR Product Characterization Range

The presentation describes efforts to develop a LIDAR in-flight product characterization range at Stennis Space Center as the next phase of the NASA Verification and Validation activities. It describes the status of surveying efforts on targets of interest to LIDAR vendors as well as the potential guidelines that will be used for product characterization.

Zanoni, Vicki↗
NASA NTRS1999

Characterization of ionic currents of cells of the subfornical organ that project to the supraoptic nuclei

The subfornical organ (SFO) is a forebrain structure that converts peripheral blood-borne signals reflecting the hydrational state of the body to neural signals and then through efferent fibers conveys this information to several central nervous system structures. One of the forebrain areas receiving input from the SFO is the supraoptic nucleus (SON), a source of vasopressin synthesis and control of release from the posterior pituitary. Little is known of the transduction and transmission processes by which this conversion of systemic information to brain input occurs. As a step in elucidating these mechanisms, the present study characterized the ionic currents of dissociated cells of the SFO that were identified as neurons that send efferents to the SON. A retrograde tracer was injected into the SON area in eleven-day-old rats. After three days for retrograde transport of the label, the SFOs of these animals were dissociated and plated for tissue culture. The retrograde tracer was used to identify the soma of SFO cells projecting to the SON so that voltage-dependent ionic currents using whole-cell voltage clamp methods could be studied. The three types of currents in labeled SFO neurons were characterized as a 1) rapid, transient inward current that can be blocked by tetrodotoxin (TTX) characteristic of a sodium current; 2) slow-onset sustained outward current that can be blocked by tetraethylammonium (TEA) characteristic of a delayed rectifier potassium current; and 3) remaining outward current that has a rapid-onset and transient characteristic of a potassium A-type current. Copyright 1999 Elsevier Science B.V.

Non-NASA Center↗
NASA NTRS2004

Characterization of Space Shuttle External Tank Thermal Protection System (TPS) Materials in Support of the Columbia Accident Investigation

NASA suffered the loss of the seven-member crew of the Space Shuttle Columbia on February 1, 2003 when the vehicle broke apart upon re-entry to the Earth's atmosphere. The final report of the Columbia Accident Investigation Board (CAIB) determined that the accident was caused by a launch ascent incident-a suitcase-sized chunk of insulating foam on the Shuttle's External Tank (ET) broke off, and moving at almost 500 mph, struck an area of the leading edge of the Shuttle s left wing. As a result, one or more of the protective Reinforced Carbon-Carbon (RCC) panels on the wing leading edge were damaged. Upon re-entry, superheated air approaching 3,000 F breached the wing damage and caused the vehicle breakup and loss of crew. The large chunk of insulating foam that broke off during the Columbia launch was determined to come from the so-called bipod ramp area where the Shuttle s orbiter (containing crew) is attached to the ET. Underneath the foam in the bipod ramp area is a layer of TPS that is a cork-filled silicone rubber composite. In March 2003, the NASA Marshall Space Flight Center (MSFC) in Huntsville, Alabama received cured samples of the foam and composite for testing from the Michoud Assembly Facility (MAF) in New Orleans, Louisiana. The MAF is where the Shuttle's ET is manufactured. The foam and composite TPS materials for the ET have been well characterized for mechanical property data at the super-cold temperatures of the liquid oxygen and hydrogen fuels used in the ET. However, modulus data on these materials is not as well characterized. The TA Instruments 2980 Dynamic Mechanical Analyzer (DMA) was used to determine the modulus of the two TPS materials over a range of -145 to 95 C in the dual cantilever bending mode. Multi-strain, fixed frequency DMA tests were followed by multi-frequency, fixed strain tests to determine the approximate bounds of linear viscoelastic behavior for the two materials. Additional information is included in the original extended abstract.

Wingard, Charles D.↗
NASA NTRS1989

Laboratory Calibration and Characterization of Video Cameras

Some techniques for laboratory calibration and characterization of video cameras used with frame grabber boards are presented. A laser-illuminated displaced reticle technique (with camera lens removed) is used to determine the camera/grabber effective horizontal and vertical pixel spacing as well as the angle of non-perpendicularity of the axes. The principal point of autocollimation and point of symmetry are found by illuminating the camera with an unexpanded laser beam, either aligned with the sensor or lens. Lens distortion and the principal distance are determined from images of a calibration plate suitable aligned with the camera. Calibration and characterization results for several video cameras are presented. Differences between these laboratory techniques and test range and plumb line calibration are noted.

Burner, A. W.↗
NASA NTRS2004

Characterizing the Energy Scale of the XRS on Astro-E2

The XRS on Astro-E2 consists of a microcalorimeter array with 31 active pixels. The XRS energy scale, which converts the measured pulse heights to the energies of the photons incident on the array, is a non-linear function of the thermal properties of the pixels and the power and noise conditions on the array. Each of the pixels operates independently and requires an individual energy scale. Analytic models of the XRS pulses are currently being developed that will be used to model the energy scale. However, because of the inherent complexity, a full empirical calibration of the energy scale is being conducted. The XRS energy scale has been calibrated for a range of operating conditions including variations in the detector temperature, bath temperatures, and photon flux. This allows us to characterize the functional dependence of the energy scale on these variables and to then generate a semi-empirical model that can be used to account for variations in operating conditions in space. We will present the results of the empirical characterization and comparisons to the analytic models.

Cottam, J.↗
NASA NTRS2004

Preform Characterization in VARTM Process Model Development

Vacuum-Assisted Resin Transfer Molding (VARTM) is a Liquid Composite Molding (LCM) process where both resin injection and fiber compaction are achieved under pressures of 101.3 kPa or less. Originally developed over a decade ago for marine composite fabrication, VARTM is now considered a viable process for the fabrication of aerospace composites (1,2). In order to optimize and further improve the process, a finite element analysis (FEA) process model is being developed to include the coupled phenomenon of resin flow, preform compaction and resin cure. The model input parameters are obtained from resin and fiber-preform characterization tests. In this study, the compaction behavior and the Darcy permeability of a commercially available carbon fabric are characterized. The resulting empirical model equations are input to the 3- Dimensional Infiltration, version 5 (3DINFILv.5) process model to simulate infiltration of a composite panel.

Grimsley, Brian W.↗
NASA NTRS1995

Respiratory sinus arrhythmia: time domain characterization using autoregressive moving average analysis

Fourier-based techniques are mathematically noncausal and are therefore limited in their application to feedback-containing systems, such as the cardiovascular system. In this study, a mathematically causal time domain technique, autoregressive moving average (ARMA) analysis, was used to parameterize the relations of respiration and arterial blood pressure to heart rate in eight humans before and during total cardiac autonomic blockade. Impulse-response curves thus generated showed the relation of respiration to heart rate to be characterized by an immediate increase in heart rate of 9.1 +/- 1.8 beats.min-1.l-1, followed by a transient mild decrease in heart rate to -1.2 +/- 0.5 beats.min-1.l-1 below baseline. The relation of blood pressure to heart rate was characterized by a slower decrease in heart rate of -0.5 +/- 0.1 beats.min-1.mmHg-1, followed by a gradual return to baseline. Both of these relations nearly disappeared after autonomic blockade, indicating autonomic mediation. Maximum values obtained from the respiration to heart rate impulse responses were also well correlated with frequency domain measures of high-frequency "vagal" heart rate control (r = 0.88). ARMA analysis may be useful as a time domain representation of autonomic heart rate control for cardiovascular modeling.

NASA Discipline Regulatory Physiology↗
NASA NTRS1993

Characterization of atrial natriuretic peptide degradation by cell-surface peptidase activity on endothelial cells

Atrial natriuretic peptide (ANP) is a fluid-regulating peptide hormone that promotes vasorelaxation, natriuresis, and diuresis. The mechanisms for the release of ANP and for its clearance from the circulation play important roles in modulating its biological effects. Recently, we have reported that the cell surface of an endothelial cell line, CPA47, could degrade 125I-ANP in the presence of EDTA. In this study, we have characterized this degradation of 125I-ANP. The kinetics of ANP degradation by the surface of CPA47 cells were first order, with a Km of 320 +/- 60 nM and Vmax of 35 +/- 14 pmol of ANP degraded/10 min/10(5) cells at pH 7.4. ANP is degraded by the surface of CPA47 cells over a broad pH range from 7.0-8.5. Potato carboxypeptidase inhibitor and bestatin inhibited 125I-ANP degradation, suggesting that this degradative activity on the surface of CPA47 cells has exopeptidase characteristics. The selectivity of CPA47 cell-surface degradation of ANP was demonstrated when 125I-ANP degradation was inhibited in the presence of neuropeptide Y and angiotensin I and II but not bradykinin, bombesin, endothelin-1, or substance P. The C-terminal amino acids phe26 and tyr28 were deduced to be important for ANP interaction with the cell-surface peptidase(s) based on comparison of the IC50 of various ANP analogues and other natriuretic peptides for the inhibition of ANP degradation. These data suggest that a newly characterized divalent cation-independent exopeptidase(s) that selectively recognizes ANP and some other vasoactive peptides exists on the surface of endothelial cells.

NASA Discipline Regulatory Physiology↗
NASA NTRS2005

Synthesis, Characterization and Decomposition Studies of Tris(N,N-dibenzyldithiocarbamato) Indium(III): Chemical Spray Deposition of Polycrystalline CuInS2 on Copper Films

Tris(bis(phenylmethyl)carbamodithioato-S,S ), commonly referred to as tris(N,Ndibenzyldithiocarbamato) indium(III), In(S2CNBz2)3, was synthesized and characterized by single crystal X-ray crystallography. The compound crystallizes in the triclinic space group P1 bar with two molecules per unit cell. The material was further characterized using a novel analytical system employing the combined powers of thermogravimetric analysis, gas chromatography/mass spectrometry and Fourier-Transform infrared spectroscopy to investigate its potential use as a precursor for the chemical vapor deposition (CVD) of thin film materials for photovoltaic applications. Upon heating, the material thermally decomposes to release CS2 and benzyl moieties in to the gas phase, resulting in bulk In2S3. Preliminary spray CVD experiments indicate that In(S2CNBz2)3 decomposed on a Cu substrate reacts to produce stoichiometric CuInS2 films.

Hehemann, David G.↗
NASA NTRS2004

Characterizing Oscillatory Bursts in Single-Trial EEG Data

Oscillatory bursts in numerous bands ranging from low (theta) to high frequencies (e.g., gamma) undoubtedly play an important role in cortical dynamics. Largely because of the inadequacy of existing analytic techniques. however, oscillatory bursts and their role in cortical processing remains poorly understood. To study oscillatory bursts effectively one must be able to isolate them and characterize them in the single trial. We describe a series of straightforward analysis techniques that produce useful indices of burst characteristics. First, stimulus-evoked responses are estimated using Differentially Variable Component Analysis (dVCA), and are subtracted from the single-trial. The single-trial characteristics of the evoked responses are stored to identify possible correlations with burst activity. Time-frequency (T-F), or wavelet, analyses are then applied to the single trial residuals. While T-F plots have been used in recent studies to identify and isolate bursts, we go further by fitting each burst in the T-F plot with a two-dimensional Gaussian. This provides a set of burst characteristics, such as, center time. burst duration, center frequency. frequency dispersion. and amplitude, all of which contribute to the accurate characterization of the individual burst. The burst phase can also be estimated. Burst characteristics can be quantified with several standard techniques (e.g.. histogramming and clustering), as well as Bayesian techniques (e.g., blocking) to allow a more parametric description analysis of the characteristics of oscillatory bursts, and the relationships of specific parameters to cortical excitability and stimulus integration.

Knuth, K. H.↗
NASA NTRS2005

Characterization Strategies and Requirements for Lunar Regolith Simulant Materials

Lunar samples returned from the Apollo missions represent a wide range of geological materials and processes, and have been studied in considerable detail using a wide range of characterization techniques. In contrast, lunar regolith simulant materials lag far behind in source material matching, and generally have been utilized as engineering test materials with secondary emphasis on extensive supporting chemical and mineralogical analysis. Presented here is a brief roadmap of analytical characterization approaches coupled with a breakdown of lunar simulant requirements developed in the past and anticipated in support of upcoming NASA missions.

Carpenter, Paul K.↗
NASA NTRS2005

Scanning Backscatter Lidar Observations for Characterizing 4-D Cloud and Aerosol Fields to Improve Radiative Transfer Parameterizations

Clouds have a powerful influence on atmospheric radiative transfer and hence are crucial to understanding and interpreting the exchange of radiation between the Earth's surface, the atmosphere, and space. Because clouds are highly variable in space, time and physical makeup, it is important to be able to observe them in three dimensions (3-D) with sufficient resolution that the data can be used to generate and validate parameterizations of cloud fields at the resolution scale of global climate models (GCMs). Simulation of photon transport in three dimensionally inhomogeneous cloud fields show that spatial inhomogeneities tend to decrease cloud reflection and absorption and increase direct and diffuse transmission, Therefore it is an important task to characterize cloud spatial structures in three dimensions on the scale of GCM grid elements. In order to validate cloud parameterizations that represent the ensemble, or mean and variance of cloud properties within a GCM grid element, measurements of the parameters must be obtained on a much finer scale so that the statistics on those measurements are truly representative. High spatial sampling resolution is required, on the order of 1 km or less. Since the radiation fields respond almost instantaneously to changes in the cloud field, and clouds changes occur on scales of seconds and less when viewed on scales of approximately 100m, the temporal resolution of cloud properties should be measured and characterized on second time scales. GCM time steps are typically on the order of an hour, but in order to obtain sufficient statistical representations of cloud properties in the parameterizations that are used as model inputs, averaged values of cloud properties should be calculated on time scales on the order of 10-100 s. The Holographic Airborne Rotating Lidar Instrument Experiment (HARLIE) provides exceptional temporal (100 ms) and spatial (30 m) resolution measurements of aerosol and cloud backscatter in three dimensions. HARLIE was used in a ground-based configuration in several recent field campaigns. Principal data products include aerosol backscatter profiles, boundary layer heights, entrainment zone thickness, cloud fraction as a function of altitude and horizontal wind vector profiles based on correlating the motions of clouds and aerosol structures across portions of the scan. Comparisons will be made between various cloud detecting instruments to develop a baseline performance metric.

Schwemmer, Geary K.↗
NASA NTRS2005

Calibration and Characterization of the NASA EOS Terra and Aqua MODIS Instruments

The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument is operating on both of the Terra and Aqua missions within the NASA Earth Observing System (EOS). The Terra MODIS instrument began taking observations in February 2000 and the Aqua MODIS instrument began taking observations in June of 2002 and both continue to operate successfully up to the present time. The MODIS instrument scans the entire Earth every 24 hours at nominal spatial resolutions between 250 and 1000 meters. It has 36 spectral bands spanning the electromagnetic spectrum from the visible wavelengths mar 400 micrometers to the emissive thermal infrared wavelengths at 15 micrometers. The MODIS instruments produce approximately 40 geophysical products devoted to observing land, ocean, and atmospheric processes and trends. To meet the scientific objectives associated with the NASA Earth sciences efforts the MODIS instruments must be and have been carefully calibrated and the performance characterized to meet specifications and goals such as five percent radiance and two percent relative to the sun accuracy in the twenty bands providing reflected solar radiation observations and one percent radiance accuracy in the sixteen bands observing in the thermal infrared. Over the time spanning instrument development and the pre-launch calibration and characterization of the instrument through the years of operation in space, the performance of the MODIS instruments have changed in multiple ways and appropriate adjustments made in relevant algorithms and look-up tables necessary to produce observations that meet the scientific objectives and requirements. The changes have been quantified and accounted for through careful use of on-board calibration devices such as the Spectro-Radiometric Calibration Assembly (SRCA), the Solar Diffuser (SD) and its companion Solar Diffuser Stability Monitor (SDSM), deep-space and lunar observations, and calibration targets on the Earth's surface. The strictest and most difficult challenges have come in trying to meet the requirements for observing Ocean color and related ocean biology processes over time and space. Overall the MODIS observations have been very successful in providing valuable scientific and applications results. The essential capabilities of MODIS are to be provided in the future by the Visible and Infrared Imaging Radiometer Suite (VIIRS) on the National Polar Orbiting Environmental Satellite Series (NPOESS).

Salomonson, Vincent V.↗
NASA NTRS2005

Detailed Mineralogical Characterizations of Four S-Asteroids: 138 Tolosa, 306 Unitas, 346 Hermentaria, and 480 Hansa

The S-asteroid taxonomic class is the second largest grouping of main-belt asteroids that are primarily located in the inner main belt (a < 3.0 AU) [1]. These asteroids have historically been the subject of interest within the asteroid community for several reasons. Continuing discussions about the nature of the S-asteroids (ordinary chondrite-like or thermally-evolved) and the putative space weathering effect on S-asteroids serve as examples of issues currently unresolved within the community [2,3]. Despite this general interest, detailed mineralogical investigations of individual S-asteroids has been relatively rare. A few workers have studied individual, or small groups of, S-asteroids [4,5,6,7]. Gaffey et al. [2] published their S-asteroid survey in 1993 that characterized 39 of the 144 then-classified S-asteroids. Despite the work already accomplished, the need exists to rigorously characterize the remaining S-asteroid population to gain a better understanding of these asteroids origin, nature, and physical characteristics.

Hardersen, P. S.↗