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NASA NTRS1999

Experimentally Determined Crack Location and Mixed Mode Stress Intensity Factors

This presentation first examines five strain field equations: the two modes of the Westergaard equations, and a mixed mode; the generalized coordinate system, and the significance testing of coefficients. It also discusses the weighted multiple linear least squares method, which shows why it is difficult to find the crack tip. The presentation then discusses the experiments to examine stress intensity. Lastly, comparison of finite element method results and experimental results is reviewed.

Zachary, Loren W.↗
NASA NTRS1998

Locations of Bromide Ions in Tetragonal Lysozyme Crystals

Anions have been shown to play a dominant role in the crystallization of chicken egg-white lysozyme from salt solutions. Previous studies employing X-ray crystallography have found one chloride ion binding site in the tetragonal crystal form of the protein and four nitrate ion binding sites in the monoclinic form. In this study the anion positions in the tetragonal form were determined from the difference Fourier map obtained from lysozyme crystals grown in bromide and chloride solutions. Five possible anion-binding sites were found in this manner. Some of these sites were in pockets containing basic residues while others were near neutral, but polar, residues. The sole chloride ion binding site found in previous studies was confirmed, while four further sites were found which corresponded to the four binding sites found for nitrate ions in monoclinic crystals. The study suggests that most of the anion-binding sites in lysozyme remain unchanged even when different anions and different crystal forms of lysozyme are employed.

Lim, Kap↗
NASA NTRS1998

Chorus Source Locations from VLF Poynting Flux Measurements with the Polar Spacecraft

Previous studies have used indirect evidence to argue that whistler-mode chorus emissions are generated near the magnetic equator. In this paper a spatial survey of wave normals and Poynting vectors computed from three-component electric and magnetic field measurements is used to show that chorus is generated very close to the magnetic equator. One surprising result is that there are almost no chorus emissions propagating toward the magnetic equator, such as might be expected from high-latitude magnetospheric reflections. The absence of a reflected component indicates that the chorus is reabsorbed, probably by Landau damping, before returning to the magnetic equatorial plane.

LeDocq, M. J.↗
NASA NTRS1998

Location of Bromide Ions in Tetragonal Lysozyme Crystals

Anions have been shown to play a dominant role in the crystallization of chicken egg white lysozyme from salt solutions. Previous studies employing X-ray crystallography had found one chloride ion binding site in the tetragonal crystal form of the protein and four nitrate ion binding sites in the monoclinic form. In this study the anion positions in the tetragonal form were determined from the difference Fourier map obtained from lysozyme crystal grown in bromide and chloride solutions. Five possible anion binding sites were found in this manner. Some of these sites were in pockets containing basic residues while others were near neutral, but polar, residues. The sole chloride ion binding site found in previous studies was confirmed, while four of these sites corresponded to four binding sites found for nitrate ions in monoclinic crystals. The study suggests that most of the anion binding sites in lysozyme remain unchanged, even when different anions and different crystal forms of lysozyme are employed.

Lim, Kap↗
NASA NTRS1998

Locating and Determining the Nature of a Persistent Hard X-Ray Source GROJ1814-12

The nature of the persistent hard X-ray source GROJ1814-12 discovered by BATSE a year ago is puzzling. Several potential X-ray sources are in the approximately 25 ft radius error box. Our XTE scanning observation attempted to determine the exact position of the hard X-ray source with respect with other sources. No obvious candidate is emerging from the analysis. A report is being prepared by the observing group. The persistent hard X-ray source GROJ1814-12 might be an example of a low-mass X-ray binary producing a strong flux of hard X-rays, and therefore be of the greatest importance for the theory of neutron star emission.

Tavani, Marco↗
NASA NTRS1999

Approximate Co-Location of Precipitation and Low-Level Westerlies in Tropical Monthly Means

In summer monsoon regions the monthly mean precipitation regions coincide approximately well with regions of westerlies at low-levels. An included chart shows a 15-year (1979-1993) mean August 850 hPa zonal wind from NCEP/NCAR reanalysis dataset and Xie-Arkin precipitation. It shows a region of westerlies covering most of Northern Indian Ocean and extending to northwestern Pacific. This region coincides well with the region with precipitation greater than 6 mm/day. Obviously the coincidence is not exact; the region of larges; zonal wind in the Arabian Sea is in a region of relatively low precipitation and is far from the region of maximum precipitation in Bay of Bengal. Also, in a zonally averaged sense between 40E and 140E, the latitude of maximum precipitation is slightly higher than that of the maximum zonal wind. Low-level westerlies are also found in regions west of Central America and in western Africa north of the equator. These regions are also closely associated with precipitation centers. Across equator from these westerlies regions there are regions of strong easterlies. Also, on their poleward side the westerly regions are flanked by weaker easterly regions. In February, similar observation can be found in the Australian monsoon area and in South America monsoon region; again the regions of westerlies coincide well with regions of maximum precipitation. As in the northern hemisphere, the maximum precipitation is found to the cast of the maximum zonal wind. The two maxima lie almost at the same latitude with that of the westerlies slightly closer to the equator. In the non-monsoon seasons the low- level westerlies can also be found in the tropical precipitation regions, the longitudinal range of the westerlies is undiminished and the speed of the westerlies is not much weaker than that found in February. The interpretation of these observational facts is the goal of this investigation. The approach taken is numerical simulation with the Goddard Earth Observation Systems atmospheric general circulation model, and its aqua-planet version, combined with theoretical arguments.

Choa, Winston C.↗
NASA NTRS1999

Unusual Bow Shock and Magnetopause Locations During May 11-12, 1999

On May 11 and 12, 1999, when the solar wind proton density dropped to only about 3% of its nominal value, WIND and IMP 8 (and possibly Lunar Prospector) encountered the Earth's bow shock at unusually large distances. These observations, at 57-63 Re, correspond to the most distant crossings of the bow shock ever recorded. This paper will present observations from Interball-1 and Geotail, showing the bow shock near its nominal position, and from IMP 8 and WIND (and perhaps Lunar Prospector) crossing the bow shock at increasing radial distances. The bow shock is extremely weak by the time of its observation by WIND. However, a clear jump in both the magnetic field strength and solar wind bulk velocity is quite apparent, although with no significant changes in solar wind proton density. The nature of this dissipating shock will be discussed. Also, interball-1 has observed the magnetopause at an unusually large standoff distance. The observed motion of the magnetopause and bow shock will be compared with model predictions. This set of observations provide an excellent test case for the behavior of gas dynamic and MHD models under extreme conditions.

Szabo, Adam↗
NASA NTRS1999

STS-93: Crew Arrival and PR Location

The primary objective of the STS-93 mission was to deploy the Advanced X-ray Astrophysical Facility, which had been renamed the Chandra X-ray Observatory in honor of the late Indian-American Nobel Laureate Subrahmanyan Chandrasekhar. The mission was launched at 12:31 on July 23, 1999 onboard the space shuttle Columbia. The mission was led by Commander Eileen Collins. The crew was Pilot Jeff Ashby and Mission Specialists Cady Coleman, Steve Hawley and Michel Tognini from the Centre National d'Etudes Spatiales (CNES). This videotape shows the astronauts arriving at Kennedy and an inspection in the clean room.

Source record↗
NASA NTRS1999

Feasibility Assessment of Thermal Barriers for RSRM Nozzle Joint Locations

Solid rockets, including the Space Shuttle solid rocket motor, are generally manufactured in large segments which are then shipped to their final destination where they are assembled. These large segments are sealed with a system of primary and secondary 0-rings to contain combustion gases inside the rocket which are at pressures of up to 900 psi and temperatures of up to 5500 F. The seals are protected from hot combustion gases by thick layers of phenolic insulation and by joint-filling compounds between these layers. Recently, though, routine inspections of nozzle-to-case joints in the Shuttle solid rocket motors during disassembly revealed erosion of the primary O-rings. Jets of hot gas leaked through gaps in the joint-filling compound between the layers of insulation and impinged on the O-rings. This is not supposed to take place, so NASA and Thiokol, the manufacturer of the rockets, initiated an investigation and found that design improvements could be made in this joint. One such improvement would involve using NASA Lewis braided thermal barriers as another level of protection for the O-ring seals against the hot combustion gases.

Steinetz, Bruce M.↗
NASA NTRS1998

Performance of Duplex Communication Between a LEO Satellite and Terrestrial Location Using a GEO Constellation

A network comprised of a terrestrial site, a constellation of three GEO satellites and a LEO satellite is modeled and simulated. Continuous communication between the terrestrial site and the LEO satellite is facilitated by the GEO satellites. The LEO satellite has the orbital characteristics of the International Space Station. Communication in the network is based on TCP/IP over ATM, with the ABR service category providing the QoS, at OC-3 data rate. The OSPF protocol is used for routing. We simulate FTP file transfers, with the terrestrial site serving as the client and the LEO satellite being the server. The performance characteristics are presented.

Robinson, Daryl C.↗
NASA NTRS2000

Locating the Periodic Transient GRO J1849-03; Gamma-Ray Luminous Supernovae Remnants

We obtained one 50 ks observation of the Monoceros supernova remnant under this proposal. This supernova remnant was selected because it overlaps the error box of a gamma-ray source. Much to our surprise, we discovered a hard x-ray point source instead of the diffuse hard x-ray emission we expected from the supernova remnant. A paper on the discovery of the hard x-ray source and on follow-up optical observations identifying a likely Bestar companion was published in the Astrophysical Journal. Subsequently, a reanalysis of the same data yielded the detection of pulsations from the x-ray source. These results were also published in the Astrophysical Journal. Subsequent x-ray observations, which we performed under later proposals, have shown that the x-ray pulsar has a characteristic spin-down age of less than 1400 years in a binary system. The system is likely the first discovered very young, highly-energetic, rotation-powered pulsar in a binary system and offers an exciting opportunity to study the infancy and early evolution of neutron-star binaries.

Kaaret, P.↗
NASA NTRS2001

Effects of Selected Task Performance Criteria at Initiating Adaptive Task Real locations

In the current report various performance assessment methods used to initiate mode transfers between manual control and automation for adaptive task reallocation were tested. Participants monitored two secondary tasks for critical events while actively controlling a process in a fictional system. One of the secondary monitoring tasks could be automated whenever operators' performance was below acceptable levels. Automation of the secondary task and transfer of the secondary task back to manual control were either human- or machine-initiated. Human-initiated transfers were based on the operator's assessment of the current task demands while machine-initiated transfers were based on the operators' performance. Different performance assessment methods were tested in two separate experiments.

Montgomery, Demaris A.↗
NASA NTRS2001

Locating Anomalies in Complex Data Sets Using Visualization and Simulation

The research goals are to create a simulation framework that can accept any combination of models written at the gate or behavioral level. The framework provides the ability to fault simulate and create scenarios of experiments using concurrent simulation. In order to meet these goals we have had to fulfill the following requirements. The ability to accept models written in VHDL, Verilog or the C languages. The ability to propagate faults through any model type. The ability to create experiment scenarios efficiently without generating every possible combination of variables. The ability to accept adversity of fault models beyond the single stuck-at model. Major development has been done to develop a parser that can accept models written in various languages. This work has generated considerable attention from other universities and industry for its flexibility and usefulness. The parser uses LEXX and YACC to parse Verilog and C. We have also utilized our industrial partnership with Alternative System's Inc. to import vhdl into our simulator. For multilevel simulation, we needed to modify the simulator architecture to accept models that contained multiple outputs. This enabled us to accept behavioral components. The next major accomplishment was the addition of "functional fault models". Functional fault models change the behavior of a gate or model. For example, a bridging fault can make an OR gate behave like an AND gate. This has applications beyond fault simulation. This modeling flexibility will make the simulator more useful for doing verification and model comparison. For instance, two or more versions of an ALU can be comparatively simulated in a single execution. The results will show where and how the models differed so that the performance and correctness of the models may be evaluated. A considerable amount of time has been dedicated to validating the simulator performance on larger models provided by industry and other universities.

Panetta, Karen↗
NASA NTRS2001

A Comparison of Co-located Ozonesonde and Lidar Measurements

As part of the NDSC, the GSFC mobile Ozone Lidar instrument has participated in numerous validation campaigns around the world. During all of these campaigns, ozonesondes were flown as part of the intercomparisons. This poster summarizes the results of these campaigns, and indicates that there are some biases between the sonde and lidar measurements.

McGee, Thomas J.↗
NASA NTRS2002

Aerothermal Instrumentation Loads To Implement Aeroassist Technology in Future Robotic and Human Missions to MARS and Other Locations Within the Solar System

The strategy of NASA to explore space objects in the vicinity of Earth and other planets of the solar system includes robotic and human missions. This strategy requires a road map for technology development that will support the robotic exploration and provide safety for the humans traveling to other celestial bodies. Aeroassist is one of the key elements of technology planning for the success of future robot and human exploration missions to other celestial bodies. Measurement of aerothermodynamic parameters such as temperature, pressure, and acceleration is of prime importance for aeroassist technology implementation and for the safety and affordability of the mission. Instrumentation and methods to measure such parameters have been reviewed in this report in view of past practices, current commercial availability of instrumentation technology, and the prospects of improvement and upgrade according to the requirements. Analysis of the usability of each identified instruments in terms of cost for efficient weight-volume ratio, power requirement, accuracy, sample rates, and other appropriate metrics such as harsh environment survivability has been reported.

Parmar, Devendra S.↗
NASA NTRS1997

Does the Mueller-Lyer Illusion Include the Misperception of Egocentric Location?

The reported absence of egocentric localization errors when pointing open-loop at the vertices of the Mueller-Lyer (M-L) illusion figure was confirmed in several studies which were designed to ensure the normal strength of the illusion during the pointing responses. However, when one of the two 'fins' was removed, the resulting M-L figure was substantially mislocalized. A theory of the expanding and contracting spatial effects of fins is proposed to explain these results.

Welch, Robert B.↗
NASA NTRS2002

Determining the Location and Radiative Impact of Thin Cirrus Clouds using Terra data

Thin cirrus clouds (with optical depth tau much less than 1) play a potentially important role in the Earth atmosphere. The Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra satellite has a channel at 1.375 microns that is specifically designed to detect these clouds. During two three-day periods from December 2000 and June 2001, I show that thin cirrus clouds are ubiquitous throughout the tropics. These thin cirrus generally have optical depths below 0.05 and appear with greater frequency and optical depth near deep convection. Regressing top-of-atmosphere outgoing longwave flux data from the Clouds and the Earth's Radiant Energy System (CERES) against optical depth, we calculate that these thin clouds decrease outgoing longwave flux by approx. 1 W/sq m/(0.01 tau). This translates into longwave forcing of several W/sq m near convection and zero away from convection. Averaging over the whole tropics, these thin cirrus decrease average longwave forcing is approx. 1.4 W/sq m.

Dessler, A. E.↗
NASA NTRS2003

Sensor Web in Antarctica: Developing an Intelligent, Autonomous Platform for Locating Biological Flourishes in Cryogenic Environments

The most rigorous tests of the ability to detect extant life will occur where biotic activity is limited by severe environmental conditions. Cryogenic environments are among the most severe-the energy and nutrients needed for biological activity are in short supply while the climate itself is actively destructive to biological mechanisms. In such settings biological activity is often limited to brief flourishes, occurring only when and where conditions are at their most favorable. The closer that typical regional conditions approach conditions that are actively hostile , the more widely distributed biological blooms will be in both time and space. On a spatial dimension of a few meters or a time dimension of a few days, biological activity becomes much more difficult to detect. One way to overcome this difficulty is to establish a Sensor Web that can monitor microclimates over appropriate scales of time and distance, allowing a continuous virtual presence for instant recognition of favorable conditions. A more sophisticated Sensor Web, incorporating metabolic sensors, can effectively meet the challenge to be in "the right place in the right time". This is particularly of value in planetary surface missions, where limited mobility and mission timelines require extremely efficient sample and data acquisition. Sensor Webs can be an effective way to fill the gap between broad scale orbital data collection and fine-scale surface lander science. We are in the process of developing an intelligent, distributed and autonomous Sensor Web that will allow us to monitor microclimate under severe cryogenic conditions, approaching those extant on the surface of Mars. Ultimately this Sensor Web will include the ability to detect and/or establish limits on extant microbiological activity through incorporation of novel metabolic gas sensors. Here we report the results of our first deployment of a Sensor Web prototype in a previously unexplored high altitude East Antarctic Plateau "micro-oasis" at the MacAlpine Hills, Law Glacier, Antarctica.

Delin, K. A.↗