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At least 469 records · Page 26

Mars volatile evolution: Implications of the recent measurement of O-17 in water from the SNC meteorites

Oxygen, carbon, and hydrocarbon isotopes in water and carbon dioxide in the Martian environment can fractionate due to processes involving escape to space, exchange between atmospheric and non-atmospheric species, and exchange of atoms between different molecules. As a result, the ratios of O-18/O-17/O-16, C-13/C-12 and D/H in atmospheric and surface species are sensitive indicators of the integrated effects of outgassing and volatile evolution over geologic time. Previously, I summarized all of the available observations of isotopic abundances and compared them with models of fractionation in order to see which scenarios of volatile evolution were most plausible. Presently, I have included in the models the possible evolution of O-17 due to loss to space in order to see whether these measurements are consistent with various scenarios for atmospheric evolution.

Jakosky, Bruce M.↗

Microcraters on Mars: Evidence of past climatic variations

On Mars, we do not expect to see the full spectrum of crater sizes that we see on the Moon, because the Martian atmosphere decelerates smaller incoming meteorites. Mars climate models predict thirty-fold variations in Mars' atmospheric pressure due to large amplitude quasi-periodic variations in Mars' obliquity. More recent studies have shown that uncertainties in Mars' moment of inertia may have resulted in an underestimation of this range. In this study, we find that potential variations in the mass of the Martian atmosphere should have dramatic effects on the production rates of centimeter sized craters on the surface of Mars, and suggest that observations of the densities of Martian microcraters would provide an important validation of the astronomical theory for Martian climate change.

Vasavada, A. R.↗

The neurochemical and neuropharmacological basis of motion sickness

An apparatus suitable for producing motion sickness in laboratory animals and constructed at the university is herein described. The apparatus is a modified version of that previously described by Fox and Daunton. It consists of a 66-inch steel arm anchored at the center to a wooden platform and attached to a motor that makes the arm move in a see-saw fashion. At each end of the steel arm is mounted an aluminum disc that can be rotated by a motorized device. Detachable cages are mounted on each disc for animal holding. The animal can then be exposed to rotational motion by rotation of the aluminum disc, or to see-saw motion simultaneously (Cross-coupled). The apparatus is presently being used in our laboratory to study the neuropharmacological basis of motion sickness in the rat. The device can be adapted for use with other animal species by modifying the cage mounted on the aluminum discs.

Walker, C. A.↗

An interim overview of LDEF materials findings

The flight and retrieval of the National Aeronautics and Space Administration's Long Duration Exposure Facility (LDEF) provided an opportunity for the study of the low-Earth orbit (LEO) environment and long-duration space environmental effects (SEE) on materials that is unparalleled in the history of the U.S. Space Program. The remarkable flight attitude stability of LDEF enables specific analyses of various individual and combined effects of LEO environmental parameters on identical materials on the same space vehicle. This paper provides an overview of the interim LDEF materials findings of the Principal Investigators and the Materials Special Investigation Group. In general, the LDEF data is remarkably consistent; LDEF will provide a 'benchmark' for materials design data bases for satellites in low-Earth orbit. Some materials were identified to be encouragingly resistant to LEO SEE for 5.8 years; other 'space qualified' materials displayed significant environmental degradation. Molecular contamination was widespread; LDEF offers an unprecedented opportunity to provide a unified perspective of unmanned LEO spacecraft contamination mechanisms. New material development requirements for long-term LEO missions have been identified and current ground simulation testing methods/data for new, durable materials concepts can be validated with LDEF results. LDEF findings are already being integrated into the design of Space Station Freedom.

Stein, Brad A.↗

The use of the wavelet cluster analysis for asteroid family determination

The asteroid family determination has been analysis method dependent for a longtime. A new cluster analysis based on the wavelet transform has allowed an automatic definition of families with a degree of significance versus randomness. Actually this method is rather general and can be applied to any kind of structural analysis. We will rather concentrate on the main features of the method. The analysis has been performed on the set of 4100 asteroid proper elements computed by Milani and Knezevic (see Milani and Knezevic 1990). Twenty one families have been found and influence of the chosen metric has been tested. The results have beem compared to Zappala et al.'s ones (see Zappala et al 1990) obtained by the use of a completely different method applied to the same set of data. For the first time, a good overlapping has been found between both method results, not only for the big well known families but also for the smallest ones.

Benjoya, Phillippe↗

Applied Information Systems Research Program (AISRP). Workshop 2: Meeting Proceedings

The Earth and space science participants were able to see where the current research can be applied in their disciplines and computer science participants could see potential areas for future application of computer and information systems research. The Earth and Space Science research proposals for the High Performance Computing and Communications (HPCC) program were under evaluation. Therefore, this effort was not discussed at the AISRP Workshop. OSSA's other high priority area in computer science is scientific visualization, with the entire second day of the workshop devoted to it.

Source record↗

The peculiar velocities of rich clusters in the hot and cold dark matter scenarios

We present the results of a study of the peculiar velocities of rich clusters of galaxies. The peculiar motion of rich clusters in various cosmological scenarios is of interest for a number of reasons. Observationally, one can measure the peculiar motion of clusters to greater distances than galaxies because cluster peculiar motions can be determined to greater accuracy. One can also test the slope of distance indicator relations using clusters to see if galaxy properties vary with environment. We have used N-body simulations to measure the amplitude and rms cluster peculiar velocity as a function of bias parameter in the hot and cold dark matter scenarios. In addition to measuring the mean and rms peculiar velocity of clusters in the two models, we determined whether the peculiar velocity vector of a given cluster is well aligned with the gravity vector due to all the particles in the simulation and the gravity vector due to the particles present only in the clusters. We have investigated the peculiar velocities of rich clusters of galaxies in the cold dark matter and hot dark matter galaxy formation scenarios. We have derived peculiar velocities and associated errors for the scenarios using four values of the bias parameter ranging from b = 1 to b = 2.5. The growth of the mean peculiar velocity with scale factor has been determined and compared to that predicted by linear theory. In addition, we have compared the orientation of force and velocity in these simulations to see if a program such as that proposed by Bertschinger and Dekel (1989) for elliptical galaxy peculiar motions can be applied to clusters. The method they describe enables one to recover the density field from large scale redshift distance samples. The method makes it possible to do this when only radial velocities are known by assuming that the velocity field is curl free. Our analysis suggests that this program if applied to clusters is only realizable for models with a low value of the bias parameter, i.e., models in which the peculiar velocities of clusters are large enough that the errors do not render the analysis impracticable.

Rhee, George F.↗

Information technologies for astrophysics circa 2001

It is easy to extrapolate current trends to see where technologies relating to information systems in astrophysics and other disciplines will be by the end of the decade. These technologies include miniaturization, multiprocessing, software technology, networking, databases, graphics, pattern computation, and interdisciplinary studies. It is less easy to see what limits our current paradigms place on our thinking about technologies that will allow us to understand the laws governing very large systems about which we have large data sets. Three limiting paradigms are as follows: saving all the bits collected by instruments or generated by supercomputers; obtaining technology for information compression, storage, and retrieval off the shelf; and the linear model of innovation. We must extend these paradigms to meet our goals for information technology at the end of the decade.

Denning, Peter J.↗

Optical system analysis for the ground based EXVM

The MSFC's Experimental Vector Magnetograph (EXVM) is an instrument that observes a 4.4 x 8.8 arcmin field of the sun. The transverse and longitudinal components of the surface magnetic field and the line-of-sight velocities of the photospheric gases can be determined from polarimetric and spectral analysis of the 525.02 nm absorption line of Fe 1. The EXVM has been breadboarded and tested in the laboratory. The optics of the EXVM were tested with a point-diffraction (Smartt) interferometer. The 12 inch Cassegrain telescope was found to have 0.20 waves RMS (at 525.02 nm) of aberration. The post-telescope relay optics were nearly diffraction limited on-axis and had about one wave of primary coma as the predominant aberration at full-field. From theoretical modulation transfer function (MTF) curves of known aberrations, it was concluded that the EXVM should attain a maximum spatial resolution of about 0.5 arcseconds. A resolution test target indicated maximum angular resolutions better than 0.6 arcsec on-axis and 0.7 arcsec at full-field-of-view. A 2D inch heliostat (sun-tracking mirror) was used to direct sunlight into the lab and into the EXVM. Solar images obtained were limited by atmospheric seeing effects. During brief moments of good seeing, angular resolutions of about 1 arcsecond were realized with the EXVM.

Hillman, L. W.↗

Fire protection for launch facilities using machine vision fire detection

Fire protection of critical space assets, including launch and fueling facilities and manned flight hardware, demands automatic sensors for continuous monitoring, and in certain high-threat areas, fast-reacting automatic suppression systems. Perhaps the most essential characteristic for these fire detection and suppression systems is high reliability; in other words, fire detectors should alarm only on actual fires and not be falsely activated by extraneous sources. Existing types of fire detectors have been greatly improved in the past decade; however, fundamental limitations of their method of operation leaves open a significant possibility of false alarms and restricts their usefulness. At the Civil Engineering Laboratory at Tyndall Air Force Base in Florida, a new type of fire detector is under development which 'sees' a fire visually, like a human being, and makes a reliable decision based on known visual characteristics of flames. Hardware prototypes of the Machine Vision (MV) Fire Detection System have undergone live fire tests and demonstrated extremely high accuracy in discriminating actual fires from false alarm sources. In fact, this technology promises to virtually eliminate false activations. This detector could be used to monitor fueling facilities, launch towers, clean rooms, and other high-value and high-risk areas. Applications can extend to space station and in-flight shuttle operations as well; fiber optics and remote camera heads enable the system to see around obstructed areas and crew compartments. The capability of the technology to distinguish fires means that fire detection can be provided even during maintenance operations, such as welding.

Schwartz, Douglas B.↗

Problems for the standard black hole/accretion disk models in Cygnus X-1?

Archival EXOSAT and HEAO1-A2 data from Cyg X-1 show the 'high energy excess' above 10 keV seen in X-ray observations of AGN. Using a likelihood ratio test, we are for the first time able to distinguish conclusively in favor of Compton reflection rather than partial covering as the origin of the high energy excess. This supports the idea of an X-ray illuminated accretion disk in Cyg X-1, but the line equivalent width is smaller by a factor of 2-3 than that expected from such a disk. While the larger optical depth required for reflection as opposed to line emission admit the possibility of seeing line without reflection, the converse is not possible. To see a reflection spectrum, including the strong iron absorption edge, implies that strong iron emission must be observed as the line and edge are causally linked.

Done, C.↗

The genesis of starbursts and infrared emission in the centers of galaxies

We present 10.8-micron maps of the central regions of 21 IR-luminous galaxies. Each map, obtained using the NASA MSFC bolometer array at the IRTF, has a resolution of about 4 arcsec and spans typically 25 x 20 arcsec. Some of the galaxies have also been mapped at 12.5, 19.2, and 30/microns. The sample consists primarily of starburst galaxies but includes several Seyferts and LINERs. On average, the flux detected in each map is about 58 percent of that detected at 12 microns by IRAS. We see a variety of morphologies, including compact and elongated sources and more complex distributions exhibiting such features as kiloparsec-size rings and double lobes. The mid-IR radiation is emitted by dust particles, and for two of the galaxies we see spatial color variations attributable to the presence of very small grains and consistent with their depletion in the starbursts. The mid-IR emission traces the dust heated by the youngest stars. Comparison of the distributions of intense star formation and the dense neutral interstellar medium for eight of these galaxies demonstrates that the two are intimately linked.

Telesco, C. M.↗

On a logical basis for division of responsibilities in statistical practice

The purpose of this paper is to explain principles for division of responsibilities between the statistician and the people that he works with, and reasons why this division of responsibilities is important -- that is, how it improves the performance of both statistician and expert in subject-matter. The aim is to find and illustrate principles of practice by which statisticians may make effective use of their knowledge of theory. The specialist in statistical methods may find himself applying the same basic theory in a dozen different fields in a week, rotating through the same projects the next week. Or, he may work day after day primarily in a single substantive field. Either way, he requires rules of practice. A statement of statistical reliability should present any information that might help the reader to form his own opinion concerning the validity of conclusions likely to be drawn from the results. The aim of a statistical report is to protect the client from seeing merely what he would like to see; to protect him from losses that could come from misuse of results. A further aim is to forestall unwarranted claims of accuracy that the client's public might otherwise accept.

Deming, W. Edwards↗

Computational mechanics needs study

In order to assess the needs in computational mechanics over the next decade, we formulated a questionnaire and contacted computational mechanics researchers and users in industry, government, and academia. As expected, we found a wide variety of computational mechanics usage and research. This report outlines the activity discussed with those contacts, as well as that in our own organizations. It should be noted that most of the contacts were made before the recent decline of the defense industry. Therefore, areas which are strongly defense-oriented may decrease in relative importance. In order to facilitate updating of this study, names of a few key researchers in each area are included as starting points for future literature surveys. These lists of names are not intended to represent those persons doing the best research in that area, nor are they intended to be comprehensive. They are, as previously stated, offered as starting points for future literature searches. Overall, there is currently a broad activity in computational mechanics in this country, with the breadth and depth increasing as more sophisticated software and faster computers become more available. The needs and desires of the workers in this field are as diverse as their background and organizational products. There seems to be some degree of software development in any organization (although the level of activity is highly variable from one organization to another) which has any research component in its mission. It seems, however, that there is considerable use of commercial software in almost all organizations. In most industrial research organizations, it appears that very little actual software development is contracted out, but that most is done in-house, using a mixture of funding sources. Government agencies vary widely in the ratio of in-house to out-house ratio. There is a considerable amount of experimental verification in most, but not all, organizations. Generally, the amount of experimental verification is more than we expected. Of all the survey contacts, one or two believe that the resources they are allocated are sufficient, but most do not. Some believe they have only half the resources they need. Some see their resource deficits as short-term, while others see it as a trend which will continue or perhaps worsen. The pessimism is stronger in the defense and aerospace industry. When considering only the nonlinear development efforts, there appears to be an even mix of geometric and material nonlinearity. There is not much particular emphasis in linear analysis unless it is in extension of current analysis capabilities to larger problems. The primary exception is concern about modeling of composites, where proven methodologies have trailed element and computer hardware development. Most of the people we spoke to use finite element techniques, but there is some finite difference and boundary element work ongoing. There is also some interest in multiple methods. Coupling of finite elements and boundary elements appears to be of high interest, since the two analysis types are complementary.

Griffin, O. Hayden, Jr.↗

Thermogeologic mapping of the Moon from lunar orbit

The Infrared Scanning Radiometer (ISR) onboard the Apollo 17 Command-Service Module (CSM) mapped thermal emission of the lunar surface from orbit. Measured temperature values span the diurnal range of lunar temperatures (85 K to 400 K) and have an accuracy of approximately plus or minus 2 K. Surface spatial resolution at nadir is 2.2 km. This Apollo data is being revisited using data presentation software for the Macintosh computer, which was not available 20 years ago, even on mainframes. The new thermal images exhibit subtleties in the delineation of geophysical surface units that were unappreciated in the original survey of the data. Looking first at nighttime thermal emission from the ground tracks over Oceanus Procellarum to Mare Orientale, we have confirmed and expanded on earlier observations of regolith differences between mare and highlands and of a scheme for relative age-dating of larger impact craters of the Copernican age. We see an impact crater near Lenz, just north of Orientale, which exhibits an extraordinarily fresh ejecta blanket. Photography of this area is extremely poor, but we can see the feature in the Galileo data. We plan to derive geophysical surface properties of the overflown region using thermal models of regolith structures.

Mendell, W. W.↗

Toward astrometric tracking with the infrared spatial interferometer

Infrared interferometric demonstrations with the University of California, Berkeley's infrared spatial interferometer (ISI) on Mt. Wilson explore the potential of infrared and optical astrometry for deep space tracking, reference frame development, and DSN science. Astrometric data taken and analyzed over the last five years from the ISI have shown that instrumental and atmospheric effects limit current demonstrations. The benefits of sensitivity upgrades, which were performed in 1991 and 1992, have been demonstrated by comparing point-to-point phase fluctuations for the fall 1989 and fall 1992 observing epochs. This comparison showed that point-to-point phase fluctuations due to tropospheric and quantum noise, for optimal integration times of 0.2 sec, are approaching the 0.1-cycle level needed to reliably connect the interferometric phase. The increase in sensitivity, coupled with that arising from very recent hardware upgrades, will greatly enhance phase-connection capabilities necessary for astrometry in the presence of atmospheric refractivity fluctuations. The current data set suggests that atmospheric fluctuations on Mt. Wilson during the best seeing are dominated by a low-lying component, approximately 25 m high, which may be minimized with in situ calibration in the future. During poor seeing conditions that currently prohibit the interferometric phase connection necessary for astrometry, fluctuations seem to be generated by atmospheric inhomogeneities at much higher altitudes above Mt. Wilson. Data taken over the last year suggest that the ISI will soon be able to achieve 50- to 100-nrad astrometry in a single observing session, employing current ground-based laser distance interferometer calibrations to minimize atmospheric effects.

Treuhaft, R. N.↗

Observations of loops and prominences

We review recent observations by the Yohkoh-SXT (Soft X-ray Telescope) in collaboration with other spacecraft and ground-based observatories of coronal loops and prominences. These new results point to problems that SoHO will be able to address. With a unique combination of rapid-cadence digital imaging (greater than or equal to 32 s full-disk and greater than or equal to 2 s partial-frame images), high spatial resolution (greater than or equal to 2.5 arcsec pixels), high sensitivity (EM less than or equal to 10(exp 42) cm(exp -3)), a low-scatter mirror, and large dynamic range, SXT can observe a vast range of targets on the Sun. Over the first 21 months of Yohkoh operations SXT has taken over one million images of the corona and so is building up an invaluable long-term database on the large-scale corona and loop geometry. The most striking thing about the SXT images is the range of loop sizes and shapes. The active regions are a bright tangle of magnetic field lines, surrounded by a network of large-scale quiet-Sun loops stretching over distances in excess of 105 km. The cross-section of most loops seems to be constant. Loops displaying significant Gamma's are the exception, not the rule, implying the presence of widespread currents in the corona. All magnetic structures show changes. Time scales range from seconds to months. The question of how these structures are formed, become filled with hot plasma, and are maintained is still open. While we see the propagation of brightenings along the length of active-region loops and in X-ray jets with velocities of several hundred km/s, much higher velocities are seen in the quiet Sun. In XBP flares, for example, velocities of over 1000 km/s are common. Active-region loops seem to be in constant motion, moving slowly outward, carrying plasma with them. During flares, loops often produce localized brightenings at the base and later at the apex of the loop. Quiescent filaments and prominences have been observed regularly. Their coronal manifestation seems to be an extended arcade of loops overlying the filament. Reliable alignment of the ground-based data with the X-ray images make it possible to make a detailed intercomparison of the hot and cold plasma structures over extended periods. Hence we are able to follow the long-term evolution of these structures and see how they become destabilized and erupt.

Strong, Keith T.↗

Lessons learned applying CASE methods/tools to Ada software development projects

This paper describes the lessons learned from introducing CASE methods/tools into organizations and applying them to actual Ada software development projects. This paper will be useful to any organization planning to introduce a software engineering environment (SEE) or evolving an existing one. It contains management level lessons learned, as well as lessons learned in using specific SEE tools/methods. The experiences presented are from Alpha Test projects established under the STARS (Software Technology for Adaptable and Reliable Systems) project. They reflect the front end efforts by those projects to understand the tools/methods, initial experiences in their introduction and use, and later experiences in the use of specific tools/methods and the introduction of new ones.

Blumberg, Maurice H.↗