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  • Articles
  • Other Sources  (1,672)
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  • 2000-2004  (1,672)
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  • 2001  (1,672)
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  • Articles
  • Other Sources  (1,672)
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  • 2000-2004  (1,672)
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  • 1
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    A proposal to extend the ICRF to multiple frequencies (2001)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Type: 33rd Annual Meeting of the Division for Planetary Sciences; New Orleans, LA; United States
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  • 2
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    Low Temperature Ohmic Contact Formation of Ni2Si on N-type 4H-SiC and 6H-SiC (2001)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: Nickel Silicide (Ni2Si) is investigated as possible ohmic contact to heavily nitrogen-doped N-type 4H-SiC and 6H-SiC. Nickel Silicide was deposited via electron gun with various thicknesses on both Si and C faces of the SiC substrates. The Ni2Si contacts were formed at room temperature as well as at elevated temperatures (400 to 1000 K). Contact resistivities and I-V characteristics were measured at temperatures between 100 and 700 C. To investigate the electric properties, I-V characteristics were studied and the Transmission Line Method (TLM) was used to determine the specific contact resistance for the samples at each annealing temperature. Both Rutherford Backscattering Spectroscopy (RBS) and Auger Electron Spectroscopy (AES) were used for depth profiling of the Ni2Si, Si, and C. X-ray Photoemission Spectroscopy (XPS) was used to study the chemical structure of the Ni2Si/SiC interface.
    Keywords: Solid-State Physics
    Type: P1 , HBCUs/OMUs Research Conference Agenda and Abstracts; 9; NASA/TM-2001-211289
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  • 3
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    Precise Orbit Determination for GEOSAT Follow-On Using Satellite Laser Ranging Data and Intermission Altimeter Crossovers (2001)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: The U.S. Navy's GEOSAT Follow-On Spacecraft was launched on February 10, 1998 and the primary objective of the mission was to map the oceans using a radar altimeter. Following an extensive set of calibration campaigns in 1999 and 2000, the US Navy formally accepted delivery of the satellite on November 29, 2000. The spacecraft is tracked by satellite laser ranging (SLR) and Doppler (Tranet-style) beacons. Although a limited amount of GPS data were obtained, the primary mode of tracking remains satellite laser ranging. In this paper, we report on progress in orbit determination for GFO using GFO/GFO and TOPEX/GFO altimeter crossovers. We have tuned the nonconservative force model for GFO and the gravity model using SLR, Doppler and altimeter crossover data spanning over one year. Preliminary results show that the predicted radial orbit error from the gravity field covariance to 70x70 on GEOSAT was reduced from 2.6 cm in EGM96 to 1.9 cm with the addition of only five months of the GFO SLR and GFO/GFO crossover data. Further progress is possible with the addition of more data, particularly the TOPEX/GFO crossovers. We will evaluate the tuned GFO gravity model (a derivative of EGM96) using altimeter data from the GEOSAT mission. In January 2000, a limited quantity of GPS data were obtained. We will use these GPS data in conjunction with the SLR and altimeter crossover data obtained over the same time span to compute quasi-reduced dynamic orbits which will also aid in the evaluation of the tuned GFO geopotential model.
    Keywords: Space Communications, Spacecraft Communications, Command and Tracking
    Type: European Geophysical Society (EGS)36th General Assembly; Mar 25, 2001 - Mar 30, 2001; Nice; France
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  • 4
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    The release of alginate lyase from growing Pseudomonas syringae pathovar phaseolicola (2001)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Pseudomonas syringae pathovar phaseolicola, which produces alginate during stationary growth phase, displayed elevated extracellular alginate lyase activity during both mid-exponential and late-stationary growth phases of batch growth. Intracellular activity remained below 22% of the total activity during exponential growth, suggesting that alginate lyase has an extracellular function for this organism. Extracellular enzyme activity in continuous cultures, grown in either nutrient broth or glucose-simple salts medium, peaked at 60% of the washout rate, although nutrient broth-grown cultures displayed more than twice the activity per gram of cell mass. These results imply that growth rate, nutritional composition, or both initiate a release of alginate lyase from viable P. syringae pv. phaseolicola, which could modify its entrapping biofilm.
    Keywords: Life Sciences (General)
    Type: Current microbiology (ISSN 0343-8651); Volume 42; 2; 78-81
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  • 5
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    Localization of needle tip with color doppler during pericardiocentesis: In vitro validation and initial clinical application (2001)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: This study evaluates a new device that uses color Doppler ultrasonography to enable real-time image guidance of the aspirating needle, which has not been possible until now. The ColorMark device (EchoCath Inc, Princeton, NJ) induces high-frequency, low-amplitude vibrations in the needle to enable localization with color Doppler. We studied this technique in 25 consecutive patients undergoing pericardiocentesis, and in vitro, in a urethane phantom with which the accuracy of color Doppler localization of the needle tip was compared with that obtained by direct measurement. Tip localization was excellent in vitro; errors axial to the ultrasound beam (velocity Doppler -0.13 +/- 0.90 mm, power Doppler -0.05 +/- 1.7 mm) were less than lateral errors (velocity -0.36 +/- 1.8 mm, power -0.02 +/- 2.8 mm). In 18 of 25 patients, the needle was identified and guided into the pericardial space with the ColorMark technique, and it allowed successful, uncomplicated drainage of fluid. Initial failures were the result of incorrect settings on the echocardiographic machine and inappropriate combinations of the needle puncture site and imaging window. This study demonstrates a novel color Doppler technique that is highly accurate at localizing a needle tip. The technique is feasible for guiding pericardiocentesis. Further clinical validation of this technique is required.
    Keywords: Life Sciences (General)
    Type: Journal of the American Society of Echocardiography : official publication of the American Society of Echocardiography (ISSN 0894-7317); Volume 14; 1; 29-37
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  • 6
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    Effects of spaceflight on human calf hemodynamics (2001)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Chronic microgravity may modify adaptations of the leg circulation to gravitational pressures. We measured resting calf compliance and blood flow with venous occlusion plethysmography, and arterial blood pressure with sphygmomanometry, in seven subjects before, during, and after spaceflight. Calf vascular resistance equaled mean arterial pressure divided by calf flow. Compliance equaled the slope of the calf volume change and venous occlusion pressure relationship for thigh cuff pressures of 20, 40, 60, and 80 mmHg held for 1, 2, 3, and 4 min, respectively, with 1-min breaks between occlusions. Calf blood flow decreased 41% in microgravity (to 1.15 +/- 0.16 ml x 100 ml(-1) x min(-1)) relative to 1-G supine conditions (1.94 +/- 0.19 ml x 100 ml(-1) x min(-1), P = 0.01), and arterial pressure tended to increase (P = 0.05), such that calf vascular resistance doubled in microgravity (preflight: 43 +/- 4 units; in-flight: 83 +/- 13 units; P 〈 0.001) yet returned to preflight levels after flight. Calf compliance remained unchanged in microgravity but tended to increase during the first week postflight (P 〉 0.2). Calf vasoconstriction in microgravity qualitatively agrees with the "upright set-point" hypothesis: the circulation seeks conditions approximating upright posture on Earth. No calf hemodynamic result exhibited obvious mechanistic implications for postflight orthostatic intolerance.
    Keywords: Life Sciences (General)
    Type: Journal of applied physiology (Bethesda, Md. : 1985) (ISSN 8750-7587); Volume 90; 4; 1552-8
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  • 7
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    Amyloplasts that sediment in protonemata of the moss Ceratodon purpureus are nonrandomly distributed in microgravity (2001)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Little is known about whether or how plant cells regulate the position of heavy organelles that sediment toward gravity. Dark-grown protonemata of the moss Ceratodon purpureus displays a complex plastid zonation in that only some amyloplasts sediment along the length of the tip cell. If gravity is the major force determining the position of amyloplasts that sediment, then these plastids should be randomly distributed in space. Instead, amyloplasts were clustered in the subapical region in microgravity. Cells rotated on a clinostat on earth had a roughly similar non-random plastid distribution. Subapical clusters were also found in ground controls that were inverted and kept stationary, but the distribution profile differed considerably due to amyloplast sedimentation. These findings indicate the existence of as yet unknown endogenous forces and mechanisms that influence amyloplast position and that are normally masked in stationary cells grown on earth. It is hypothesized that a microtubule-based mechanism normally compensates for g-induced drag while still allowing for regulated amyloplast sedimentation.
    Keywords: Life Sciences (General)
    Type: Plant physiology (ISSN 0032-0889); Volume 125; 4; 2085-94
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  • 8
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    Characteristics of human dendritic cells generated in a microgravity analog culture system (2001)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Generation of an effective immune response requires that antigens be processed and presented to T lymphocytes by antigen-presenting cells, the most efficient of which are dendritic cells (DC). Because of their influence on both the innate and the acquired arms of immunity, a defect in DC would be expected to result in a broad impairment of immune function, not unlike that observed in astronauts during or after space flight. In the study reported here, we investigated whether DC generation and function are altered in a culture environment that models microgravity, i.e., the rotary-cell culture system (RCCS). We observed that RCCS supported the generation of DC identified by morphology, phenotype (HLA-DR+ and lacking lineage-associated markers), and function (high allostimulatory activity). However, the yield of DC from RCCS was significantly lower than that from static cultures. RCCS-generated DC were less able to phagocytose Aspergillus fumigatus conidia and expressed a lower density of surface HLA-DR. The proportion of DC expressing CD80 was also significantly reduced in RCCS compared to static cultures. When exposed to fungal antigens, RCCS-generated DC produced lower levels of interleukin-12 and failed to upregulate some costimulatory/adhesion molecules involved in antigen presentation. These data suggest that DC generation, and some functions needed to mount an effective immune response to pathogens, may be disturbed in the microgravity environment of space.
    Keywords: Life Sciences (General)
    Type: In vitro cellular & developmental biology. Animal (ISSN 1071-2690); Volume 37; 4; 216-22
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  • 9
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    First Astronomical Use Of Multiplexed Transition Edge Bolometers (2001)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: We present performance results based on the first astronomical use of multiplexed superconducting bolometers. The Fabry-Perot Interferometer Bolometer Research Experiment (FIBRE) is a broadband submillimeter spectrometer that achieved first light in June 2001 at the Caltech Submillimeter Observatory (CSO). FIBRE's detectors are superconducting transition edge sensor (TES) bolometers read out by a SQUID multiplexer. The Fabry-Perot uses a low resolution grating to order sort the incoming light. A linear bolometer array consisting of 16 elements detects this dispersed light, capturing five orders simultaneously from one position on the sky. With tuning of the Fabry-Perot over one free spectral range, a spectrum covering delta-lamda/lamda = 1/7 at a resolution of delta-lamda/lamda = 1/1200 can be acquired. This spectral resolution is sufficient to resolve doppler broadened line emission from external galaxies. FIBRE operates in the 350 micrometer and 450 micrometer bands. These bands cover line emission from the important PDR tracers neutral carbon [CI] and carbon monoxide (CO). We have verified that the multiplexed bolometers are photon noise limited even with the low power present in moderate resolution spectrometry.
    Keywords: Optics
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  • 10
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    The Effect of Microgravity on the Growth of Silica Nanostructures (2001)
    In:  CASI
    Details
    Publication Date: 2017-09-27
    Description: The process of the formation of structures from coagulating ensembles is fundamentally important since the collective behavior of the constituents often results in dramatically improved or unusual mechanical, thermal, chemical, and optical properties. In this study we examine the effect of microgravity on the formation of silica structures, specifically particles and gels.
    Keywords: Solid-State Physics
    Type: Microgravity Materials Science Conference 2000; Volume 2; 288-292; NASA/CP-2000-210827/VOL2
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