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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Evidence for submergencew of magnetic flux in a growing active region

In NOAA Active Region 2372 (April 1980), 4 x 10 to the 20th power maxwell of magnetic flux concentrated within a 30" circular area disappeared overnight. Vector magnetograms show that all components of the magnetic field weakened together. If the field had weakened through diffusion or fluid flow, 80% of the original flux would still have been detected by the magnetograph within a suitably enlarged area. In fact there was at least a threefold decrease in detected flux. Evidently, magnetic field was removed from the photosphere. Since the disappearing flux was located in a region of low magnetic shear and low activity, it is unlikely that the field dissipated through reconnection. The most likely possibility is that flux submerged. Observations suggest that even in the growth phase of active regions, submergence is a strong process comparable in magnitude to emergence.

Rabin, D. M.↗
NASA NTRS1985

Design and chemical synthesis of iodine-containing molecules for application to solar-pumped I* lasers

This work is directed toward the design and chemical synthesis of new media for solar-pumped I* lasers. In view of the desirability of preparing a perfluoroalkyl iodide absorbing strongly at 300 nm, the relationship betwen perfluoroalkyl iodide structure and the corresponding absorption wavelength was reexamined. Analysis of existing data suggests that, in this family of compounds, the absorption maximum shifts to longer wavelength, as desired, as the C-I bond in the lasant is progressively weakened. Weakening of the C-I bond correlates, in turn, with increasing stability of the perfluoroalkyl radical formed upon photodissociation of the iodide. The extremely promising absorption characteristics of perfluoro-tert-butyl iodide can be accounted for on this basis. A new technique of diode laser probing to obtain precise yields of I* atoms in photodissociation was also developed.

Shiner, C. S.↗
NASA NTRS1984

A case for submergence of magnetic flux in a solar active region

In NOAA Active Region 2372 (April 1980), 4 x 10 to the 20th maxwells of magnetic flux concentrated in an area 30 arcsec across disappeared overnight. Vector magnetograms show that all components of the magnetic field weakened together. If the field had weakened through diffusion or fluid flow, 90 percent of the original flux would still have been detected by the magnetograph within a suitably enlarged area. In fact there was a threefold decrease in detected flux. Evidently, magnetic field was removed from the photosphere. Since the disappearing flux was located in a region of low magnetic shear and low activity in H-alpha and Ly-alpha, it is unlikely that the field dissipated through reconnection. It is argued that the most likely possibility is that flux submerged. The observations suggest that even during the growth phase of active regions, submergence is a strong process comparable in magnitude to emergence.

Rabin, D.↗
NASA NTRS1989

The Marr and Albus Theories of the Cerebellum: Two Eary Models of Associative Memory

The Marr and Albus theories of the cerebellum are compared and contrasted. They are shown to be similar in their analysis of the function of the mossy fibers, granule cells, Golgi cells, and Purkinje cells. They both predict motor learning in the parallel fiber synapses on the Purkinje dendrites mediated by concurrent climbing fiber input. This prediction has been confirmed by experimental evidence. In contrast, Marr predicts these synapses would be facilitated by learning, while Albus predicts they would be weakened. Experimental evidence confirms synaptic weakening.

Albus, James S.↗
NASA NTRS1993

Dynamic processes in Be star atmospheres. I - 'Dimple' formation in the He I lambda 6678 line of lambda Eridani

Several examples of weakenings of the C IV and N V resonance lines are found to coincide with the appearance of lambda 6678 dimples. The absence of variations in other UV lines and in the UV continuum at the same time or nearly the same time argues against dimples being caused by thermal variations from the underlying star. It is instead suggested that the resonance line weakenings are caused by non-LTE effects associated with the condensation of high density structures at some elevation over the star. A simple model of an opaque, essentially stationary slab which backscatters lambda 6678 line radiation into a surrounding 'penumbral' region is presented. Lambda 6678 photons are scattered a second time in this region back into the observer's line of sight and in the process acquire the local projected Doppler shift from rotation. Slabs would probably produce too little emission to be easily detected in the H alpha profile. Their detection in strong He I lines seems the best strategy among early Be stars.

Smith, Myron A.↗
NASA NTRS1992

Vacuum melting and mechanical testing of simulated lunar glasses

Lunar silicate glasses may possess superior mechanical properties compared to terrestrial glasses because the anhydrous lunar environment should prevent hydrolytic weakening of the strong Si-O bonds. This hypothesis was tested by melting, solidifying, and determining the fracture toughness of simulated mare and highlands composition glasses in a high vacuum chamber. The fracture toughness, K(IC), of the resulting glasses was obtained via microindentation techniques. K(IC) increased as the testing environment was changed from air to a vacuum of 10 exp -7 torr. However, this increase in toughness may not result solely from a reduction in the hydrolytic weakening effect; the vacuum-melting process produced both the formation of spinel crystallites on the surfaces of the glass samples and significant changes in the compositions which may have contributed to the improved K(IC).

Carsley, J. E.↗
NASA NTRS1996

A Composite Diagnosis of Synoptic-Scale Extratropical Cyclone Development over the United States

This paper presents a composite diagnosis of synoptic-scale forcing mechanisms associated with extratropical cyclone evolution. Drawn from 12 cyclone cases that occurred over the continental United States during the cool season months, the diagnosis provides a 'climatology' of development mechanisms for difference categories of cyclone evolution ranging from cyclone weakening through three stages of cyclone intensification. Computational results were obtained using an 'extended' form of the Zwack-Okossi equation applied to routine upper-air and surface data analyzed on a 230 km x 230 km grid. Results show that cyclonic vorticity advection, which maximizes in the upper troposphere, was the primary contributor to cyclone development regardless of the stage of development. A second consistent contributor to development was latent heat release. Horizontal temperature advection, often acknowledged as a development mechanism, was found to contribute to development only during more intense stages. During weakening and weaker development stages, temperature advection opposed development, as the warm-air advection invariably found at upper levels was dominated by cold air advection in the lower half of the troposphere. In the more intense stages, development was moderated by dry-adiabatic cooling associated with the ascending vertical motions.

Rolfson, Donald M.↗
NASA NTRS1999

Observations of Middle Atmosphere CO from the UARS ISAMS during the Early Northern Winter 1991/92

Structure and kinematics of carbon monoxide in the upper stratosphere and lower mesosphere (10-0.03 hPa) are studied for the early northern winter 1991/92 using the Upper Atmosphere Research Satellite Improved Stratospheric and Mesospheric Sounder (ISAMS) measurements. The study is aided by data from a 6-week parameterized-chemistry run of the Goddard Space Flight Center 3D Chemistry and Transport Model (CTM), initialized on 8 December 1991. Generally, CO mixing ratios increase with height due to the increasing source contribution from CO, photolysis. In the tropical upper stratosphere. however, a local maximum in CO mixing ratio occurs. A simple photochemical model is used to show that this feature results largely from methane oxidation. In the extratropics the photochemical lifetime of CO is long, and therefore its evolution is dictated by large-scale motion of air. evidenced by strong correlation with Ertel potential vorticity. This makes CO one of the few useful observable tracers at the stratopause level and above. Thus CO maps are used to study the synoptic evolution of the polar vortex in early January 1992. Modified Lagrangian mean mixing diagnostics are applied to ISAMS and CTM data to examine the strength of the mixing barrier at the polar vortex edge. It is demonstrated that planetary wave activity weakens the barrier. promoting vortex erosion. The vortex erosion first appears in the lower mesosphere and subsequently descends through the upper stratosphere. and is attributed to effects of planetary wave dissipation. Agreement between ISAMS and CTM is good in the horizontal distribution of CO throughout the examined period, but vertical CO gradients in the CTM weaken with time relative to the ISAMS observations.

Allen, D. R.↗
NASA NTRS2001

Impact Cratering Calculations

This research is computational /theoretical and complements the Caltech experimental program. We have developed an understanding of the basic physical processes and produced computational models and implemented these into Eulerian and Lagrangian finite element codes. The key issues we have addressed include the conditions required for: faulting (strain localization), elastic moduli weakening, dynamic weakening (layering elastic instabilities and fluidization), bulking (creation of porosity at zero pressure) and compaction of pores, frictional melting (creation of pseudotachylytes), partial and selective devolatilization of materials (e.g. CaCO3, water/ice mixtures), and debris flows.

Ahrens, Thomas J.↗
NASA NTRS2001

Impacts of ENSO on the South American Summer Monsoon During 1997-1999

Using the National Center for Environmental Prediction (NCEP) Reanalysis, and CPC Merged Analysis Product (CMAP) rainfall, we have compared and contrasted the anomalies of the South American Summer Monsoon (SASM) during two extreme years of 1997/98 (EI Nino) and 1998/99 (La Nina). The results are assessed against a "canonical" ENSO response (CER) pattern for the SASM obtained from empirical mode decomposition based on a previous period (1980-1995). Overall, the SASM anomalies compare well with CER, but with some important differences. Anomalies occurring in the warm phase of the 1997-98 El Nino are very significant and robust, while those occurring in 1998/99 La Nina, appear to be reversed from 1997/98, but are relatively weak and less well-defined. The most pronounced signal in DJF 1997/98 is the development of drought conditions in northern Brazil, excessive rainfall over northern Peru and Ecuador, and over Uruguay and southern Brazil. The tropical rainfall anomalies are associated with the eastward shift of the Walker circulation, which is represented by pronounced low-level anomalous westerlies over the equatorial eastern Pacific and easterlies over northern Brazil. The easterlies are deflected sharply southeastward by the steep topography of the Andes, enhancing the low-level jet (LLJ) along the eastern foothills of the Andes near 15-20 S. The LLJ penetrates deep into the extratropics, yielding rainfall anomalies further poleward compared to CER. During DJF 1997/98, the eastward expansion of the warm tropospheric temperature over the Nino-3 region causes anomalous geopotential height to develop in the upper troposphere above the Altiplano, leading to a strengthened Bolivian High. An upper-tropospheric jet anomaly maximum is found over the subtropical continent near 30 S, due to increasing meridional gradient of tropospheric temperature, as well as teleconnection patterns linking the South Pacific and the South Atlantic. Consistent with the CER, the South Pacific High is weakened, and the South Atlantic High is strengthened in DJF 1997/98. However, rather than appearing as a coherent large scale signal over the entire Atlantic as in CER, the South Atlantic High anomalies in DJF 1997/98 split into two separate high pressure centers; one located south of the Amazon basin, and another over the southeastern South Atlantic. The former is induced as a Rossby-wave response by ENSO-Induced sinking motion over nor-them and eastern Brazil, and the latter may be associated with extratropical teleconnection signals. Anomalous convection observed over equatorial western Africa may also have contributed to the different circulation response over the Atlantic in DFJ 1997/99 compared to the CER. Comparison of the evolution of the SASM anomalies in 1997-99 with their corresponding annual cycles, suggest that the anomalies are phase-locked to and represent either enhancement or reduction of the annual variations. Results suggest that, from a system perspective the SASM was strengthened during the 1997/98 El Nino and weakened, albeit to a lesser extent, during the 1998/99 La Nina.

Lau, K.-M.↗
NASA NTRS2001

Quasi-Equilibrium States in the Tropics Simulated by a Cloud-Resolving Model: Specific Features and Budget Analysis - Part 1

A series of long-term integrations using the two-dimensional Goddard Cumulus Ensemble (GCE) model were performed by altering imposed environmental components to produce various quasi-equilibrium thermodynamic states. Model results show that the genesis of a warm/wet quasi-equilibrium state is mainly due to either strong vertical wind shear (from nudging) or large surface fluxes (from strong surface winds), while a cold/dry quasi-equilibrium state is attributed to a remarkably weakened mixed-wind shear (from vertical mixing due to deep convection) along with weak surface winds. In general, latent heat flux and net large-scale temperature forcing, the two dominant physical processes, dominate in the beginning stage of the simulated convective systems, then considerably weaken in the final stage, which leads to quasi-equilibrium states. A higher thermodynamic regime is found to produce a larger rainfall amount, as convective clouds are the leading source of rainfall over stratiform clouds even though the former occupy much less area. Moreover, convective clouds are more likely to occur in the presence of strong surface winds (latent heat flux), while stratiform clouds (especially the well-organized type) are favored in conditions with strong wind shear (large-scale forcing). The convective systems, which consist of distinct cloud types due to the variation in horizontal winds, are also found to propagate differently. Accordingly, convective systems with mixed-wind shear generally propagate in the direction of shear, while the system with strong (multidirectional) wind shear propagates in a more complex way. Based on the results from the temperature (Q1) and moisture (Q2) budgets, cloud-scale eddies are found to act as a hydrodynamic 'vehicle' that cascades the heat and moisture vertically. Several other specific features such as atmospheric stability, CAPE, and mass fluxes are also investigated and found to be significantly different between diverse quasi-equilibrium states. Detailed comparisons between the various states are presented.

Shie, C.-L.↗
NASA NTRS2002

Impact Cratering Calculations

Many Martian craters are surrounded by ejecta blankets which appear to have been fluidized forming lobate and layered deposits terminated by one or more continuous distal scarps, or ramparts. One of the first hypotheses for the formation of so-called rampart ejecta features was shock-melting of subsurface ice, entrainment of liquid water into the ejecta blanket, and subsequent fluidized flow. Our work quantifies this concept. Rampart ejecta found on all but the youngest volcanic and polar regions, and the different rampart ejecta morphologies are correlated with crater size and terrain. In addition, the minimum diameter of craters with rampart features decreases with increasing latitude indicating that ice laden crust resides closer to the surface as one goes poleward on Mars. Our second goal in was to determine what strength model(s) reproduce the faults and complex features found in large scale gravity driven craters. Collapse features found in large scale craters require that the rock strength weaken as a result of the shock processing of rock and the later cratering shear flows. In addition to the presence of molten silicate in the intensely shocked region, the presence of water, either ambient, or the result of shock melting of ice weakens rock. There are several other mechanisms for the reduction of strength in geologic materials including dynamic tensile and shear induced fracturing. Fracturing is a mechanism for large reductions in strength. We found that by incorporating damage into the models that we could in a single integrated impact calculation, starting in the atmosphere produce final crater profiles having the major features found in the field measurements (central uplifts, inner ring, terracing and faulting). This was accomplished with undamaged surface strengths (0.1 GPa) and in depth strengths (1.0 GPa).

Ahrens, Thomas J.↗
NASA NTRS2002

The Structure of A Pacific Narrow Cold Frontal Rainband

A NOAA P-3 instrumented aircraft observed an intense, fast-moving narrow cold frontal Farmhand as it approached the Pacific Northwest coast on 19 February 2001 during the Pacific Coastal Jets Experiment. Pseudo-dual-Doppler analyses performed on the airborne Doppler radar data while the frontal system was well offshore indicated that a narrow ribbon of very high radar reflectively convective cores characterized the Farmhand at low levels with echo tops to approximately 4-5 km. The NCFR exhibited gaps in its narrow ribbon of high reflectively, probably as a result of hydrodynamic instability all no its advancing cold pool leading edge. In contrast to some earlier studies of cold frontal rainbands, density current theory described well the motion of the overall front. The character of the updraft structure associated with the heavy rainfall at its leading edge varied across the gap region. The vertical shear of the cross-frontal low-level ambient flow exerted a strong influence on the updraft character, consistent with theoretical arguments developed for squall lines describing the balance of vorticity at the leading edge. In short regions south of the gaps the vertical wind shear was strongest with the updrafts and rain shafts more intense, narrower, and more erect or even downshear tilted. North of the gaps the wind shear weakened with less intense Dihedrals which tilted upshear with a broader band of rainfall. Simulations using a nonhydrostatic mesoscale nested grid model are used to investigate the gap regions, particularly the balance of cold pool induced to pre-frontal ambient shears at the leading edge. Observations confirm the model results that the updraft character depends on the balance of vorticity at the leading edge. Downshear-tilted updrafts imply that convection south of the gap regions would weaken with time relative to the frontal segments north of the gaps since inflow air would be affected by passage through the heavy rain region before ascent, suggesting a mechanism for gap filling.

Jorgensen, David P.↗
NASA NTRS2002

Maintaining the Body's Immune System: Incidence of Latent Virus Shedding During Space Flight

Your body protects you from illness with its own security system - the immune system. This system keeps illness at bay not only by mounting a defense against foreign organisms, but also by controlling the population of bacteria and viruses that normally live in your body. But there's no need to panic: certain microbes can actually exist in your body without causing illness. Some bacteria are even beneficial - like the E. coli in the large intestine that are an important source of vitamin K. While viruses are not exactly considered beneficial, they can also inhabit the human body without causing immediate harm or infection. A good example is the herpes simplex virus type 1 (HSV1), more commonly known as cold sores or fever blisters. This virus infects 70 to 80 percent of all adults but remains latent much of the time. While latent, the virus within cells remains dormant. Activation of the dormant virus causes it to make copies of itself (known as replication) constantly detectable in body fluids such as urine or saliva in a process called shedding. When a person becomes sick or stressed, however, this weakened condition allows the virus to reactivate and multiply. These elevated levels may be enough to produce symptoms, but shedding can also occur without symptoms. This ability to shed without showing signs of infection, or asymptomatic shedding, is of great interest, as it increases the chances of infecting others. The stresses associated with space flight - adapting to microgravity, isolation from family and friends, living and working in a confined space, sleep deprivation, and busy schedules, to name but a few - may weaken astronauts' immune systems, leaving them at greater risk of viral reactivation. Members of the STS-107 crew will participate in this experiment, Incidence of Latent Viral Shedding in Space Flight, to help scientists understand how reactivation works in space, and at what level replication reaches before symptoms begin to show. This study also promises more insight into the behavior of the larger virus family, herpesvirus, which will help us understand how to prevent infection in populations on Earth and reactivation in those already infected.

Pierson, Duane↗
NASA NTRS2003

Effects of Convective Asymmetries on Hurricane Intensity: A Numerical Study

The influence of the uniform large-scale flow, beta effect, and vertical shear of the environmental flow on hurricane intensity is investigated in the context of the induced convective or potential vorticity asymmetries with a hydrostatic primitive equation hurricane model. In agreement with the previous studies, imposing of one of these environmental effects can substantially weaken the simulated tropical cyclones. In response t o the environmental influence, significant asymmetries develop with a structure similar to the spiral bands in real hurricanes, which are dominated by wavenumber-one components. The tendencies of the mean radial, azimuthal winds and temperature associated with the environment-induced convective asymmetries are evaluated respectively. The resulting asymmetries can effectively reduce hurricane intensity by directly producing the negative tendency of the mean tangential wind in the vicinity of the radius of maximum wind, and by weakening the mean radial circulation. The reduction effects are closely associated with the spiral structure of the induced asymmetries. The time lag observed between the imposition of the environmental influence and the resulting rise in the minimum central pressure is the time required for developing the spiral structure. This study also confirms the axisymmetrization process associated with the induced wavenumber-one components of potential vorticity asymmetries, but it exists only within the radius of maximum wind.

Wu, Liguang↗
NASA NTRS2003

Tropical Warm Pool Surface Heat Budgets and Temperature: Contrasts Between 1997-98 El Nino and 1998-99 La Nina

Seasonal and interannual variations of the net surface heating F(sub NET) and sea surface temperature tendency (T(sub s)/dt) in the tropical eastern Indian and western Pacific Oceans are studied. The surface heat fluxes are derived from the Special Sensor Microwave/Imager and Japanese Geostationary Meteorological Satellite radiance measurements for the period October 1997-September 2000. It is found that the magnitude of solar heating is lager than that of evaporative cooling, but the spatial variation of the latter is significantly large than the former. As a result, the spatial variations of seasonal and interannual variability of F(sub NET), follow closely that of evaporative cooling. Seasonal variations of F(sub NET) and T(sub s)/dt are significantly correlated, except for the equatorial western Pacific. The high correlation is primarily attributable to high correlation between seasonal cycles of solar heating and T(sub s)/dt. The change of F(sub NET) between 1997-98 El Nino and 1998-99 La Nina is significantly larger in the tropical eastern Indian Ocean than tropical western Pacific. For the former region, the reduced evaporative cooling arising from weakened winds during the El Nino is generally associated with enhanced solar heating due to decreased cloudiness, and thus increases the interannual variability of F(sub NET). For the latter region, the reduced evaporative cooling due to weakened winds is generally associated with but exceeds the reduced solar heating arising from increased cloudiness, and vise versa. Thus the interannual variability of F(sub NET) is reduced due to this offsetting effect. Interannual variations of F(sub NET) and T(sub s)/dt have very low correlation. This is most likely related to interannual variability of ocean dynamics, which includes the variations of solar radiation penetrating through oceanic mixed layer, upwelling of cold thermocline water, Indonesian throughflow for transporting heat from the Pacific to Indian Ocean, and interhemispheric transport in the Indian Ocean.

Chou, Shu-Hsien↗
NASA NTRS2003

Investigation Leads to Improved Understanding of Space Shuttle RSRM Internal Insulation Joints

The Space Shuttle Reusable Solid Rocket Motor (RSRM) uses an internal insulation J-joint design for the mated insulation interface between two assembled RSRM segments. In this assembled (mated) segment configuration, this J-joint design serves as a thermal barrier to prevent hot gases from affecting the case field joint metal surfaces and O-rings. A pressure sensitive adhesive (PSA) provides some adhesion between the two mated insulation surfaces. In 1995, after extensive testing, a new ODC-free PSA (free of ozone depleting chemicals) was selected for flight on RSRM-55 (STS-78). Post-flight inspection revealed that the J-joint, equipped with the new ODC-free PSA, did not perform well. Hot gas seeped inside the J-joint interface. Although not a flight safety threat, the J-joint hot gas intrusion on RSRM-55 was a mystery to the investigators since the PSA had previously worked well on a full-scale static test. A team was assembled to study the J-joint and PSA further. All J-joint design parameters, measured data, and historical performance data were re-reviewed and evaluated by subscale testing and analysis. Although both the ODC-free and old PSA were weakened by humidity, the ODC-free PSA strength was lower to start with. Another RSRM full-scale static test was conducted in 1998 and intentionally duplicated the gas intrusion. This test, along with many concurring tests, showed that if a J-joint was 1) mated with the new ODC-free PSA, 2) exposed to a history of high humidity (Kennedy Space Center levels), and 3) also a joint which experienced significant but normal joint motion (J-joint deformation resulting from motor pressurization dynamics) then that J-joint would open (allow gas intrusion) during motor operation. When all of the data from the analyses, subscale tests, and full-scale tests were considered together, a theory emerged. Most of the joint motion on the RSRM occurs early in motor operation at which point the J-joints are pulled into tension. If the new PSA has been weakened due to humidity, then the J-joint will partially pull apart (inboard side), and the J-joint surfaces will be charred by exposure to hot gases. After early operation, a J-joint that has been pulled apart will come back together as the J-joint deformation decreases. This J-joint heating event is relatively short and occurs only during the first part of motor operation. Internal instrumentation was developed for another full-scale static test in February 2000. The static test instrumentation did indeed prove this theory to be correct. Post-test inspection revealed very similar charring characteristics as observed on RSRM-55. This experience of the development of a new PSA, its testing, the RSRM-55 flight, followed by the J-joint investigation led to good 'lessons learned' and to an additional fundamental understanding of the RSRM J-joint function.

McWhorter, Bruce B.↗
NASA NTRS1988

Effect of salicylhydroxamic acid on endosperm strength and embryo growth of Lactuca sativa L. cv Waldmann's Green seeds

Salicylhydroxamic acid (SHAM) stimulated germination of photosensitive lettuce (Lactuca sativa L. cv Waldmann's Green) seeds in darkness. To determine whether SHAM acts on the embryo or the endosperm, we investigated separately effects of SHAM on growth potential of isolated embryos as well as on endosperm strength. Embryo growth potential was quantified by incubating decoated embryos in various concentrations of osmoticum and measuring subsequent radicle elongation. Growth potential of embryos isolated from seeds pretreated with 4 millimolar SHAM was equal to that of untreated controls. Rupture strength of endosperm tissue excised from seeds pretreated with SHAM was 33% less than that of controls in the micropylar region. To determine if the embryo must be in contact with the endosperm of SHAM to weaken the endosperm, some endosperms were incubated with SHAM only after dissection from seeds. Rupture strength of SHAM-treated, isolated endosperms in the micropylar region was 25% less than that of untreated controls. There was no difference in rupture strength in the cotyledonary region of endosperm isolated from seeds treated with SHAM in buffer or buffer alone. SHAM therefore stimulates germination not by enhancing embryo growth potential, but by weakening the micropylar region of the endosperm enclosing the embryo.

NASA Discipline Plant Biology↗