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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Evolution of Gravity Receptors in the Ear

The general status of a grant to investigate the origins and evolution of two hair cell types in the ears of a teleost fish, Astronotus ocellatus (the oscar), is presented. First, it was demonstrated that the cells in the rostral end of the saccule of the , Carassius auratus, are type 1-like, while those at the caudal end are type 2 cells. It was demonstrated that the dichotomy of hair cell types found in the utricle of the oscar is also found in the goldfish. Second, the lateral line system of the oscar was examined using gentamicin sulphate, an ototocix drug that destroys type 1- like hair cells but does not appear to damage type 2 hair cells. It was demonstrated that the hair cells found in neuromasts of lateral line canal organs were totally destroyed within 1 day of treatment, while the hair cells in free neuromasts were undamaged after 12 days of treatment. Third, it was demonstrated that the calyx, the specialized nerve ending, is not unique to amniotes and that it is present at least in the cristae of semicirular canals in goldfish. These results have demonstrated that: (1) there are multiple hair cell types in the vestibular endorgans of the ear of fishes, (2) these hair cell types are very similar to those found in the mammalian vestibular endorgans, (3) the nerve calyx is also present in fishes, and (4) multiple hair cell types and the calyx have evolved far earlier in the course of vertebrate evolution than heretofore thought. Understanding the structure of the vestibular endorgans has important implications for being able to understand how these organs respond to gravistatic, acceleration and acoustic input. The vestibular endorgans of fishes may provide an ideal system in which to analyze functional differences in hair cells. Not only are the two hair cell types similar to those found in mammals, they are located in very discrete regions in each endorgan. Thus, it is relatively easy to gain access to cells of one or the other type. The presence of two cell types in the lateral line have equally significant implications for studies of the vestibular system.

Popper, Arthur N.↗
NASA NTRS2007

Critical Issues for Cu(InGa)Se2 Solar Cells on Flexible Polymer Web

Elemental in-line evaporation on glass substrates has been a viable process for the large-area manufacture of CuInSe2-based photovoltaics, with module efficiencies as high as 12.7% [1]. However, lightweight, flexible CuInSe2-based modules are attractive in a number of applications, such as space power sources. In addition, flexible substrates have an inherent advantage in manufacturability in that they can be deposited in a roll-to-roll configuration allowing continuous, high yield, and ultimately lower cost production. As a result, high-temperature polymers have been used as substrates in depositing CuInSe2 films [2]. Recently, efficiency of 14.1% has been reported for a Cu(InGa)Se2-based solar cell on a polyimide substrate [3]. Both metal foil and polymer webs have been used as substrates for Cu(InGa)Se2-based photovoltaics in a roll-to-roll configuration with reasonable success [4,5]. Both of these substrates do not allow, readily, the incorporation of Na into the Cu(InGa)Se2 film which is necessary for high efficiency devices [3]. In addition, polymer substrates, can not be used at temperatures that are optimum for Cu(InGa)Se2 deposition. However, unlike metal foils, they are electrically insulating, simplifying monolithically-integrated module fabrication and are not a source of impurities diffusing into the growing film. The Institute of Energy Conversion (IEC) has modified its in-line evaporation system [6] from deposition onto glass substrates to roll-to-roll deposition onto polyimide (PI) film in order to investigate key issues in the deposition of large-area Cu(InGa)Se2 films on flexible polymer substrates. This transition presented unexpected challenges that had to be resolved. In this paper, two major problems, spitting from the Cu source and the cracking of Mo back contact film, will be discussed and the solution to each will be presented.

Eser, Erten↗
NASA NTRS1976

Gas absorption cell photometer for rocket observations of local interstellar helium

A photometer sensitive in the 584-A line of He I, incorporating a helium-gas absorption cell, has been developed. The helium is confined at a pressure of 0.2 torr between thin-metal-foil broad-band ultraviolet filters. The cell contains sufficient helium to absorb 584-A radiation scattered from atmospheric helium. The ratio of fluxes seen with the cell full and empty provides a valuable datum for fitting models of the local interstellar medium, which is independent of solar 584-A flux, interstellar helium density, and photometer sensitivity.-

Freeman, J.↗
NASA NTRS1977

Extreme ultraviolet photometer for observations of helium in interplanetary space

A four-channel photometer sensitive to two solar EUV lines which are resonantly scattered by helium gas was developed for flight on the Apollo-Soyuz Test Project. Two channels observed the 58.4-nm line of He I and used helium gas resonant absorption cells to determine the intensities of the center and wings of that line. The other two channels observed the 30.4-nm line of He II. The instrument surveyed much of the celestial sphere during a series of slow rolling maneuvers by the Apollo spacecraft. The experiment operated properly, and usable data were obtained. Study of the distributions of flux seen, and of the ratio 58.4-nm fluxes seen with gas cells full and empty, will refine current understanding of several poorly known properties of the local interstellar medium. Study of the 30.4-nm flux distribution will refine present knowledge of the structure of the earth's plasmasphere.

Bowyer, S.↗
NASA NTRS1984

Laser-assisted solar cell metallization processing

Laser-assisted processing techniques utilized to produce the fine line, thin metal grid structures that are required to fabricate high efficiency solar cells are examined. Two basic techniques for metal deposition are investigated; (1) photochemical decomposition of liquid or gas phase organometallic compounds utilizing either a focused, CW ultraviolet laser (System 1) or a mask and ultraviolet flood illumination, such as that provided by a repetitively pulsed, defocused excimer laser (System 2), for pattern definition, and (2) thermal deposition of metals from organometallic solutions or vapors utilizing a focused, CW laser beam as a local heat source to draw the metallization pattern.

Dutta, S.↗
NASA NTRS1980

Observations of interstellar helium with a gas absorption cell - Implications for the structure of the local interstellar medium

A photometer sensitive at the 584 A line of He 1, incorporating a helium gas resonance absorption cell, was flown on the Apollo-Soyuz Test Project in July 1975. The instrument observed much of the night-time sky, and returned 42 min of usable data. The data were analyzed by fitting to a model of resonant scattering of solar 584 A flux from nearby interstellar helium. Good model fits were obtained for an interstellar gas bulk velocity vector pointing toward alpha = 72 deg, delta = +15 deg, with speed 20 km/s, with interstellar medium temperatures from 5000 to 20,000 K and with neutral interstellar helium density (8.9 plus or minus 10 to the -3rd/cu cm). In the context of theoretical studies of the interstellar medium by McKee and Ostriker (1977), the results may indicate that the sun lies in the warm, partially ionized periphery of a cold interstellar cloud, surrounded by a high-temperature gas heated by old supernova remnants.

Freeman, J.↗
NASA NTRS1982

Skylab observations of H I Lyman-alpha

The H I Lyman-alpha profiles obtained with the Skylab SO82-B spectrograph at spectral and spatial resolutions of 60 mA and 2 arcsec x 60 arcsec are presented. Profile variations are illustrated from center to limb, at different heights above the limb, and over a cell and network boundary. The Lyman-alpha core exhibits weak or no limb darkening, whereas the line wings show weak limb darkening. Above the limb, the Lyman-alpha core integrated intensity and line width remain in essence constant up to plus 12 arcsec and may result from resonance scattering of chromospheric radiation by coronal neutral hydrogen or from spicules. On the disk, intensities in the line core are seen as correlating well with the H-alpha network; however, the Lyman-alpha wing intensities are found to correlate better with the transition region lines. The average of profiles acquired over the cell and network region is found to be similar to profiles obtained in the cell.

Roussel-Dupre, D.↗
NASA NTRS2003

Glucose-dependent insulinotropic peptide stimulates thymidine incorporation in endothelial cells: role of endothelin-1

We have previously characterized the receptor for glucose-dependent insulinotropic polypeptide (GIPR) in vascular endothelial cells (EC). Different EC types were found to contain distinct GIPR splice variants. To determine whether activation of the GIPR splice variants resulted in different cellular responses, we examined GIP effects on human umbilical vein endothelial cells (HUVEC), which contain two GIPR splice variants, and compared them with a spontaneously transformed human umbilical vein EC line, ECV 304, which contains four GIPR splice variants. GIP dose-dependently stimulated HUVEC and ECV 304 proliferation as measured by [3H]thymidine incorporation. GIP increased endothelin-1 (ET-1) secretion from HUVEC but not from ECV 304. Use of the endothelin B receptor blocker BQ-788 resulted in an inhibition of [3H]thymidine incorporation in HUVEC but not in ECV 304. These findings suggest that, although GIP increases [3H]thymidine incorporation in both HUVEC and ECV 304, this proliferative response is mediated by ET-1 only in HUVEC. These differences in cellular response to GIP may be related to differences in activation of GIPR splice variants.

NASA Discipline Clinical Medicine↗
NASA NTRS1997

Mechanical signals in plant development: a new method for single cell studies

Cell division, which is critical to plant development and morphology, requires the orchestration of hundreds of intracellular processes. In the end, however, cells must make critical decisions, based on a discrete set of mechanical signals such as stress, strain, and shear, to divide in such a way that they will survive the mechanical loads generated by turgor pressure and cell enlargement within the growing tissues. Here we report on a method whereby tobacco protoplasts swirled into a 1.5% agarose entrapment medium will survive and divide. The application of a controlled mechanical load to agarose blocks containing protoplasts orients the primary division plane of the embedded cells. Photoelastic analysis of the agarose entrapment medium can identify the lines of principal stress within the agarose, confirming the hypothesis that cells divide either parallel or perpendicular to the principal stress tensors. The coincidence between the orientation of the new division wall and the orientation of the principal stress tensors suggests that the perception of mechanical stress is a characteristic of individual plant cells. The ability of a cell to determine a shear-free orientation for a new partition wall may be related to the applied load through the deformation of the matrix material. In an isotropic matrix a uniaxial load will produce a rotationally symmetric strain field, which will define a shear-free plane. Where high stress intensities combine with the loading geometry to produce multiaxial loads there will be no axis of rotational symmetry and hence no shear free plane. This suggests that two mechanisms may be orienting the division plane, one a mechanism that works in rotationally symmetrical fields, yielding divisions perpendicular to the compressive tensor, parallel to the long axis of the cell, and one in asymmetric fields, yielding divisions parallel to the short axis of the cell and the compressive tensor.

NASA Discipline Number 40-50↗
NASA NTRS1995

Damage and Recovery of Hair Cells in Fish Canal (But Not Superficial) Neuromasts after Gentamicin Exposure

Recent evidence demonstrating the presence of two types of sensory hair cells in the ear of a telcost fish (Astronotus ocellatus, the oscar) indicates that hair cell heterogeneity may exist not only in amniotic vertebrates but also in anamniotes. Here we report that a similar heterogeneity between hair cell types may also occur in the other mechanosensory organ of the oscar, the lateral line. We exposed oscars to the aminoglycoside (ototoxic) antibiotic gentamicin sulfate and found damaged sensory hair cells in one class of the lateral line receptors, the canal neuromasts, but not in the other class, the superficial neuromasts. This effect was not due to the canal environment. Moreover, new ciliary bundles on hair cells of the canal neuromasts were found after, and during, gentamicin exposure. The pattern of hair cell destruction and recovery in canal neuromasts is similar to that of type 1-like hair cells found in the striolar region of the utricle and lagena of the oscar after gentamicin treatment. These results suggest that the hair cells in the canal and superficial neuromasts may be similar to type 1-like and type 2 hair cells, respectively, in the fish ear.

Song, Jiakun↗
NASA NTRS2011

Kinetic Simulations of Current-Sheet Formation and Reconnection at a Magnetic X Line

The integration of kinetic effects into macroscopic numerical models is currently of great interest to the plasma physics community, particularly in the context of magnetic reconnection. We are examining the formation and reconnection of current sheets in a simple, two-dimensional X-line configuration using high resolution particle-in-cell (PIC) simulations. The initial potential magnetic field is perturbed by thermal pressure introduced into the particle distribution far from the X line. The relaxation of this added stress leads to the development of a current sheet, which reconnects for imposed stress of sufficient strength. We compare the evolution and final state of our PIC simulations with magnetohydrodynamic simulations assuming both uniform and localized resistivities, and with force-free magnetic-field equilibria in which the amount of reconnect ion across the X line can be constrained to be zero (ideal evolution) or optimal (minimum final magnetic energy). We will discuss implications of our results for reconnection onset and cessation at kinetic scales in dynamically formed current sheets, such as those occurring in the terrestrial magnetotail and solar corona.

Black, C.↗
NASA NTRS1986

Braille Reading Systems

Two proposed electromechanical systems for making braille characters produced relatively inexpensively. Similar in operating principle to dotmatrix printers, two methods use electronically actuated pins to reproduce characters from information stored on magnetic tape. First, one or more pins scanned over blank page and energized at intervals to emboss text on paper, one or more dots at time. Second, handheld device containing one or more character-generator cells used by reader to scan lines of text manually.

Garner, H. D.↗
NASA NTRS1994

The evolution of convective storms from their footprints on the sea as viewed by synthetic aperture radar from space

SEASAT synthetic aperture radar (SAR) echoes from the sea have previously been shown to be the result of rain and winds produced by convective stroms; rain damps the surface waves and causes ech-free holes, while the diverging winds associated with downdraft generate waves and associated echoes surrounding the holes. Gust fronts are also evident. Such a snapshot from 8 July 1978 has been examined in conjunction with ground-based radar. This leads to the conclusion that the SAR storm footprints resulted from storm processes that occurred up to an hour or more prior to the snapshot. A sequence of events is discerned from the SAR imagery in which new cell growth is triggered in between the converging outflows of two preexisting cells. In turn, the new cell generates a mini-squall line along its expanding gust front. While such phenomena are well known over land, the spaceborne SAR now allows important inferences to be made about the nature and frequency of convective storms over the oceans. The storm effects on the sea have significant implications for spaceborne wind scatterometry and rainfall measurements. Some of the findings herein remain speculative because of the great distance to the Miami weather radar-the only source of corroborative data.

Atlas, David↗
NASA NTRS2000

Sunspots and Giant-Cell Convection

From analysis of Doppler velocity images from SOHO/MDI, Hathaway et al (2000, Solar Phys., in press) have found clear evidence for giant convection cells that fill the solar surface, have diameters 3 - 10 times that typical of supergranules, and have lifetimes approx. greater than 10 days. Analogous to the superposition of the granular convection on the supergranular convection, the approx. 30,000 km diameter supergranules are superposed on these still larger giant cells. Because the giant cells make up the large-scale end of a continuous power spectrum that peaks at the size scale of supergranules, it appears that the giant cells are made by the same mode of convection as the supergranules. This suggests that the giant cells are similar to supergranules, just longer-lived, larger in diameter, and deeper. Here we point out that the range of lengths of large bipolar sunspot groups is similar to the size range of giant cells. This, along with the long lives (weeks) of large sunspots, suggests that large sunspots sit in long-lived, deep downflows at the corners of giant cells, and that the distance from leader to follower sunspots in large bipolar groups is the distance from one giant-cell corner to the next. By this line of reasoning, an unusually large and strong downdraft might pull in both legs of a rising spot-group magnetic flux loop, resulting in the formation of a delta sunspot. This leads us to suggest that a large, strong giant-cell corner downdraft should be present at the birthplaces of large delta sunspots for some time (days to weeks) before the birth. Thus, early detection of such downdrafts by local helioscismology might provide an early warning for the formation of those active regions (large delta sunspot groups) that produce the Sun's most violent flares and coronal mass ejections. This work is supported by NASA's Office of Space Science through the Solar Physics Branch of its Sun-Earth Connection Program.

Moore, Ron L.↗
NASA NTRS1995

Optimization of Time-Dependent Particle Tracing Using Tetrahedral Decomposition

An efficient algorithm is presented for computing particle paths, streak lines and time lines in time-dependent flows with moving curvilinear grids. The integration, velocity interpolation and step-size control are all performed in physical space which avoids the need to transform the velocity field into computational space. This leads to higher accuracy because there are no Jacobian matrix approximations or expensive matrix inversions. Integration accuracy is maintained using an adaptive step-size control scheme which is regulated by the path line curvature. The problem of cell-searching, point location and interpolation in physical space is simplified by decomposing hexahedral cells into tetrahedral cells. This enables the point location to be done analytically and substantially faster than with a Newton-Raphson iterative method. Results presented show this algorithm is up to six times faster than particle tracers which operate on hexahedral cells yet produces almost identical particle trajectories.

Kenwright, David↗
NASA NTRS2006

Power System Concepts for the Lunar Outpost: A Review of the Power Generation, Energy Storage, Power Management and Distribution (PMAD) System Requirements and Potential Technologies for Development of the Lunar Outpost

This paper will review potential power system concepts for the development of the lunar outpost including power generation, energy storage, and power management and distribution (PMAD). In particular, the requirements of the initial robotic missions will be discussed and the technologies considered will include cryogenics and regenerative fuel cells (RFC), AC and DC transmission line technology, high voltage and low voltage power transmission, conductor materials of construction and power beaming concepts for transmitting power to difficult to access locations such as at the bottom of craters. Operating conditions, component characteristics, reliability, maintainability, constructability, system safety, technology gaps/risk and adaptability for future lunar missions will be discussed for the technologies considered.

Khan, Z.↗
NASA NTRS2010

Development and Application of Agglomerated Multigrid Methods for Complex Geometries

We report progress in the development of agglomerated multigrid techniques for fully un- structured grids in three dimensions, building upon two previous studies focused on efficiently solving a model diffusion equation. We demonstrate a robust fully-coarsened agglomerated multigrid technique for 3D complex geometries, incorporating the following key developments: consistent and stable coarse-grid discretizations, a hierarchical agglomeration scheme, and line-agglomeration/relaxation using prismatic-cell discretizations in the highly-stretched grid regions. A signi cant speed-up in computer time is demonstrated for a model diffusion problem, the Euler equations, and the Reynolds-averaged Navier-Stokes equations for 3D realistic complex geometries.

Nishikawa, Hiroaki↗
NASA NTRS1994

Interhemispheric asymmetry of the high-latitude ionospheric convection pattern

The assimilative mapping of ionospheric electrodynamics technique has been used to derive the large-scale high-latitude ionospheric convection patterns simultaneously in both northern and southern hemispheres during the period of January 27 to 29, 1992. When the interplanetary magnetic field (IMF) B(sub z) component is negative, the convection patterns in the southern hemisphere are basically the mirror images of those in the northern hemisphere. The total cross-polar cap potential drops in the two hemispheres are similar. When B(sub z) is positive and absolute value of B(sub y) greater than B(sub z), the convection configurations are mainly determined by B(sub y) and they may appear as normal 'two-cell' patterns in both hemispheres much as one would expect under southward IMF conditions. However, there is a significant difference in the cross-polar-cap potential drop between the two hemispheres, with the potential drop in the southern (summer) hemisphere over 50% larger than that in the northern (winter) hemisphere. As the ratio of absolute value of B(sub y)/B(sub z) decreases (less than one), the convection configuration in the two hemispheres may be significantly different, with reverse convection in the southern hemisphere and weak but disturbed convection in the northern hemisphere. By comparing the convection patterns with the corresponding spectrograms of precipitating particles, we interpret the convection patterns in terms of the concept of merging cells, lobe cells, and viscous cells. Estimates of the ' merging cell' potential drops, that is, the potential ascribed to the opening of the dayside field lines, are usually comparable between the two hemispheres, as they should be. The 'lobe cell' provides a potential between 8.5 and 26 kV and can differ greatly between hemispheres, as predicted. Lobe cells can be significant even for southward IMF, if absolute value of B(sub y) greater than the absolute value of B(sub z). To estimate the potential drop of the 'viscous cells,' we assume that the low-latitude boundary layer is on closed field lines. We find that this potential drop varies from case to case, with a typical value of 10 kV. If the source of these cells is truly a viscous interaction at the flank of the magnetopause, the process is likely spatially and temporally varying rather than steady state.

Lu, G.↗