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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 649 records · Page 36
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NASA NTRS2003

Light Scattering by Gaussian Particles: A Solution with Finite-Difference Time Domain Technique

The understanding of single-scattering properties of complex ice crystals has significance in atmospheric radiative transfer and remote-sensing applications. In this work, light scattering by irregularly shaped Gaussian ice crystals is studied with the finite-difference time-domain (FDTD) technique. For given sample particle shapes and size parameters in the resonance region, the scattering phase matrices and asymmetry factors are calculated. It is found that the deformation of the particle surface can significantly smooth the scattering phase functions and slightly reduce the asymmetry factors. The polarization properties of irregular ice crystals are also significantly different from those of spherical cloud particles. These FDTD results could provide a reference for approximate light-scattering models developed for irregular particle shapes and can have potential applications in developing a much simpler practical light scattering model for ice clouds angular-distribution models and for remote sensing of ice clouds and aerosols using polarized light. (copyright) 2003 Elsevier Science Ltd. All rights reserved.

Sun, W.↗
NASA NTRS2005

Style Differences

The International Space Station Expedition 11 crew, set for liftoff Apr. 15 from the Baikonur Cosmodrome, is to perform two extravehicular activities-one in Russian and the other in U.S. spacesuits, a unique combination that points up different national space-operating styles. The outgoing Expedition 10 commander, astronaut Leroy Chiao, addressed the differences in an e-mail exchange from the ISS. Chiao is well qualified to discuss these topics, having logged four shuttle-based EVAs in the American suit and two in the Russian Orlan, the most recent one Mar. 28. Chiao and Expedition 10 cosmonaut Salizhan Sharipov are to return to Earth in their own Soyuz Apr. 25.

Covault, Craig↗
NASA NTRS2005

Regional Studies of Highland-Lowland Age Differences Across the Mars Crustal Dichotomy Boundary

Regional differences in crater retention ages (CRAs) across the Mars dichotomy boundary are compared to the global highland-lowland age difference previously determined from visible and buried impact basins based on MOLA-derived Quasi-Circular Depressions (QCDs). Here Western Arabia (WA) is compared with Ismenius Lacus (IL). We find the buried lowlands in the two regions have total CRAs essentially identical to the global average. Even more intriguing, the WA cratered terrain appears to have a CRA like that of the adjacent buried lowlands,

Frey, H. V.↗
NASA NTRS2005

Two Successive Martian Years on the Orbit: Similarities and Differences of CO2 Seasonal Cycle from HEND/ODYSSEY Data

The three years of Mars Odyssey successful work on the martian orbit provide a lot of new information about peculiarities of long term variations of CO2 seasonal cycle. To start such analysis we have used observations of neutron albedo of Mars obtained by High Energy Neutron detector (HEND) mounted onboard Mars Odyssey spacecraft. The high latitude northern and southern regions of Mars are affected by global redistribution of atmospheric CO2 which resulted in 25% of atmospheric mass condensed on martian surface of these regions during winter period of time. The seasonal deposit is formed starting from 60N/60S latitudes and achieve its maximal thickness about 1 m at latitudes close to martian poles. Changes of CO2 deposit thickness is the reason for significant variations of neutron flux above martian poles from summer to winter seasons because CO2 frost effectively hides upper water rich surface layers from the orbit observations in neutrons and gamma-rays. This effect was used to estimate column density of CO2 deposit at different latitudes on North and South of Mars and reconstruct multidimensional model of CO2 deposit showing how snow depth varies as function of latitude, longitude and time. In this presentation we tried to make a next step in our study of martian seasonal CO2 cycle and look for similarities and differences between two successive martian years.

Litvak, M. L.↗
NASA NTRS2004

Comparison of different cooling regimes within a shortened liquid cooling/warming garment on physiological and psychological comfort during exercise

The aim of this study was to compare the effectiveness of different cooling regime intensities to maintain physiological and subjective comfort during physical exertion levels comparable to that engaged in during extravehicular activities (EVA) in space. We studied eight subjects (six males, two females) donned in our newly developed physiologically based shortened liquid cooling/warming garment (SLCWG). Rigorous (condition 1) and mild (condition 2) water temperature cooling regimes were compared at physical exertion levels comparable to that performed during EVA to ascertain the effectiveness of a lesser intensity of cooling in maintaining thermal comfort, thus reducing energy consumption in the portable life support system. Exercise intensity was varied across stages of the session. Finger temperature, rectal temperature, and subjective perception of overall body and hand comfort were assessed. Finger temperature was significantly higher in the rigorous cooling condition and showed a consistent increase across exercise stages, likely due to the restriction of heat extraction because of the intensive cold. In the mild cooling condition, finger temperature exhibited an overall decline with cooling, indicating greater heat extraction from the body. Rectal temperature was not significantly different between conditions, and showed a steady increase over exercise stages in both rigorous and mild cooling conditions. Ratings of overall comfort were 30% higher (more positive) and more stable in mild cooling (p<0.001). The mild cooling regime was more effective than rigorous cooling in allowing the process of heat exchange to occur, thus maintaining thermal homeostasis and subjective comfort during physical exertion.

NASA Discipline Life Sciences Technologies↗
NASA NTRS2002

Comparison Made of Operating Characteristics of Spiral Bevel Gears Manufactured Using Different Methods

Spiral bevel gears are important components on all current rotorcraft drive systems. These components are required to operate at high speeds, high loads, and for an extremely large number of load cycles. In this application, spiral bevel gears are used to redirect the shaft from the horizontal gas turbine engine to the vertical rotor. Because of the high expense of manufacturing these gears, methods that can achieve the same level of performance at reduced cost are highly desirable to aerospace gear manufacturers. Gears manufactured for aerospace applications use high-quality materials and are manufactured to tight tolerances. Special manufacturing machine tools and computer numerically controlled coordinate measurement systems have enabled rotorcraft drive system manufacturers to produce extremely high-quality gears during their normal production. Because of low production rates for rotorcraft, these gears are manufactured in small batches, and thus are unable to benefit from the economics of high production numbers as in other industries. In this investigation, two different manufacturing methods, face-milled and face-hobbed, were used to fabricate spiral bevel gears. For face-milled spiral bevel gears, grinding of the contacting surfaces is the final manufacturing step. At least two different specialty machines are needed to generate the teeth for face-milled spiral bevel gears. For face-hobbed gears, hard cutting is the final manufacturing process. The same machine is used to rough cut and finish cut the gears. This study compared the operational behavior of face-milled spiral bevel gears with that of face-hobbed spiral bevel gears. Test hardware was manufactured to fit within NASA Glenn Research Center's Spiral Bevel Test Facility and to aerospace quality standards. Tests were conducted for stress, vibration, and noise. A comparison of the results attained indicated that the face-hobbed gears had a lower alternating stress level with a more even distribution of loading across the teeth, and slightly reduced levels of vibration and noise. Results of this study show that the face-hobbed method is a viable and lower-cost alternative for producing aerospace-quality spiral-bevel gears.

Handschuh, Robert F.↗
NASA NTRS2006

A Simple Test to Determine the Effectiveness of Different Braze Compositions for Joining Ti-Tubes to C/C Composite Plates

A simple tube-plate joint tensile test was implemented to compare the effectiveness of commercial brazes, namely, TiCuNi, TiCuSil, and Cu-ABA, used for bonding Ti-tubes joined to C-C composite plates. The different braze systems yielded different; yet, repeatable results. The Cu-ABA system proved to have about twice the load-carrying ability of the other two systems due to the fact that the bonded area between the braze material and the C-C plate was largest for this system. The orientation of the surface fiber tows also had a significant effect on load-carrying ability with tows oriented perpendicular to the tube axis displaying the highest failure loads. Increasing the process load and modifying the surface of the C-C plate by grooving out channels for the Ti-Tube to nest in resulted in increased load-carrying ability for the TiCuSil and Cu-ABA systems due to increased bonded area and better penetration of the braze material into the C-C composite.

Morscher, Gregory N.↗
NASA NTRS2005

The Different Wavelengths of Radio Science

Radio Science covers many different avenues. This summer I attempted to work in each of the different avenues to learn the full range of subjects covered by Radio Science. I began my summer by traveling to Greece for the 3rd International Planetary Probe Workshop (IPPW-3). I went as a co-author of the Doppler Wind Experiment (DWE) team paper. My first job when I returned from Greece was to update the Radio Science activities webpage. I then used Fast Fourier Transforms (FFT) to find radio signals in recorded Radio Science experimental data and determine frequencies and powers. I read about and ran Fortran code being used to determine wind measurements on Huygens. I formatted and revised the abstracts and data lengths for the DVD data sets. By performing these tasks, I also learned the Unix operating system as well as a small amount of shell programming.

Malecha, Jessica L.↗
NASA NTRS2005

Different Pathogenesis of CCR5-Using Primary HIV-1 Isolates from Non-Switch and Switch Virus Patients in Human Lymphoid Tissue Ex Vivo

CCR5-utilizing HIV-1 variants (R5) typically transmit infection and dominate its early stages, whereas emergence of CXCR4-using (X4 or R5X4) HIV-1 is often associated with disease progression. However, such a switch in co-receptor usage can only be detected in approximately onehalf of HIV-infected patients (switch virus patients), and progression to immunodeficiency may also occur in patients without detectable switch in co-receptor usage (non-switch virus patients). Here, we used a system of ex vivo-infected tonsillar tissue to compare the pathogenesis of sequential primary R5 HIV-1 isolates from the switch and non-switch patients. Inoculation of ex vivo tissue with these R5 isolates resulted in viral replication and CCR5(+)CD4(+) T cell depletion. The levels of such depletion by HIV-1 isolated from non-switch virus patients were significantly higher than those by R5 HIV-1 isolates from switch virus patients. T cell depletion seemed to be controlled by viral factors and did not significantly vary between tissues from different donors. In contrast, viral replication did not correlate with the switch status of the patients; in tissues fiom different donors it varied 30-fold and seemed to be controlled by a combination of viral and tissue factors. Nevertheless, replication-level hierarchy among sequential isolates remained constant in tissues from various donors. Viral load in vivo was higher in switch virus patients compared to non-switch virus patients. The high cytopathogenicity of CCR5(+)CD4(+) T cells by R5 HIV-1 isolates from non-switch virus patients may explain the steady decline of CD4(+) T cells in the absence of CXCR4 using virus; elimination of target cells by these isolates may limit their own replication in vivo.

Iarlsson, Ingrid↗
NASA NTRS2008

Residual Strength Characterization of Unitized Structures Fabricated Using Different Manufacturing Technologies

This viewgraph presentation describes residual strength analysis of integral structures fabricated using different manufacturing procedures. The topics include: 1) Built-up and Integral Structures; 2) Development of Prediction Methodology for Integral Structures Fabricated using different Manufacturing Procedures; 3) Testing Facility; 4) Fracture Parameters Definition; 5) Crack Branching in Integral Structures; 6) Results and Discussion; and 7) Concluding Remarks.

Seshadri, B. R.↗
NASA NTRS2008

Analysis of EUV, UV, and H-alpha Emission from Two Very Different Prominences

We analyze the properties of a pair of prominences observed the UV and EUV in April 2004. One was a generally quiet prominence which exhibited a period of activation. Another was a large "coronal cloud" type prominence. Both were observed by SOHO/SUMER, TRACE, and in H$\alpha$ by BBSO and MLSO. The quiet prominence was also observed by the SOHO/CDS instrument. TRACE and H$\alpha$ data provide 2D images on with time cadences on the order of 1 minute. The SUMER data was taken from a single slit location with a 90 second cadence and included a number of lines spanning the temperature range 80,000 to 1.6 million K. This observing program was designed to allow us to study prominence dynamics . CDS raster data was taken with a slower cadence, in lines formed at temperatures from 20,000 - 1 million K. We combine these different data sets to analyze the thermal properties, including differential emission measures (DEMs), of these very different prominences, and compare the results to those of prominences previously analyzed by ourselves and others.

Kucera, T.↗
NASA NTRS2009

Re-evaluation of an Optimized Second Order Backward Difference (BDF2OPT) Scheme for Unsteady Flow Applications

Recent experience in the application of an optimized, second-order, backward-difference (BDF2OPT) temporal scheme is reported. The primary focus of the work is on obtaining accurate solutions of the unsteady Reynolds-averaged Navier-Stokes equations over long periods of time for aerodynamic problems of interest. The baseline flow solver under consideration uses a particular BDF2OPT temporal scheme with a dual-time-stepping algorithm for advancing the flow solutions in time. Numerical difficulties are encountered with this scheme when the flow code is run for a large number of time steps, a behavior not seen with the standard second-order, backward-difference, temporal scheme. Based on a stability analysis, slight modifications to the BDF2OPT scheme are suggested. The performance and accuracy of this modified scheme is assessed by comparing the computational results with other numerical schemes and experimental data.

Vatsa, Veer N.↗
NASA NTRS2010

Computational Fluid Dynamics (CFD) Simulations of Jet Mixing in Tanks of Different Scales

For long-duration in-space storage of cryogenic propellants, an axial jet mixer is one concept for controlling tank pressure and reducing thermal stratification. Extensive ground-test data from the 1960s to the present exist for tank diameters of 10 ft or less. The design of axial jet mixers for tanks on the order of 30 ft diameter, such as those planned for the Ares V Earth Departure Stage (EDS) LH2 tank, will require scaling of available experimental data from much smaller tanks, as well designing for microgravity effects. This study will assess the ability for Computational Fluid Dynamics (CFD) to handle a change of scale of this magnitude by performing simulations of existing ground-based axial jet mixing experiments at two tank sizes differing by a factor of ten. Simulations of several axial jet configurations for an Ares V scale EDS LH2 tank during low Earth orbit (LEO) coast are evaluated and selected results are also presented. Data from jet mixing experiments performed in the 1960s by General Dynamics with water at two tank sizes (1 and 10 ft diameter) are used to evaluate CFD accuracy. Jet nozzle diameters ranged from 0.032 to 0.25 in. for the 1 ft diameter tank experiments and from 0.625 to 0.875 in. for the 10 ft diameter tank experiments. Thermally stratified layers were created in both tanks prior to turning on the jet mixer. Jet mixer efficiency was determined by monitoring the temperatures on thermocouple rakes in the tanks to time when the stratified layer was mixed out. Dye was frequently injected into the stratified tank and its penetration recorded. There were no velocities or turbulence quantities available in the experimental data. A commercially available, time accurate, multi-dimensional CFD code with free surface tracking (FLOW-3D from Flow Science, Inc.) is used for the simulations presented. Comparisons are made between computed temperatures at various axial locations in the tank at different times and those observed experimentally. The affect of various modeling parameters on the agreement obtained are assessed.

Breisacher, Kevin↗
NASA NTRS2010

Gender Differences in Isokinetic Strength after 60 and 90 d Bed Rest

Recent reports suggest that changes in muscle strength following disuse may differ between males and females. PURPOSE: To examine potential gender differences in strength changes following 60 and 90 d of experimental bed rest. METHODS: Isokinetic extensor and flexor strength of the knee (60deg and 180deg/s, concentric only), ankle (30deg/s, concentric and eccentric), and trunk (60deg/s, concentric only) were measured following 60 d (males: n=4, 34.5+/-9.6 y; females: n=4, 35.5+/-8.2 y) and 90 d (males: n=10, 31.4+/-4.8 y; females: n=5, 37.6+/-9.9 y) of 6-degree head-down-tilt bed rest (BR; N=23). Subjects were fed a controlled diet (55%/15%/ 30%, CHO/PRO/FAT) that maintained body weight within 3% of the weight recorded on Day 3 of bed rest. After a familiarization session, testing was conducted 6 d before BR and 2 d after BR completion. Peak torque and total work were calculated for the tests performed. To allow us to combine data from both 60- and 90-d subjects, we used a mixed-model statistical analysis in which time and gender were fixed effects and bed rest duration was a random effect. Log-transformations of strength measures were utilized when necessary in order to meet statistical assumptions. RESULTS: Main effects were seen for both time and gender (p<0.05), showing decreased strength in response to bed rest for both males and females, and males stronger than females for most strength measures. Only one interaction effect was observed: females exhibited a greater loss of trunk extensor peak torque at 60 d versus pre-BR, relative to males (p=0.004). CONCLUSION: Sixty and 90 d of BR induced significant losses in isokinetic muscle strength of the locomotor and postural muscles of the knee, ankle, and trunk. Although males were stronger than females for most of the strength measures that we examined, only changes in trunk extensor peak torque were greater for females than males at day 60 of bed rest

English, K. L.↗
NASA NTRS2010

Observed Differences in Spectral Microphysical Retrievals from MODIS

The microphysical structure of clouds is of fundamental importance for understanding a variety of cloud radiation and physical processes. With the advent of MODIS (Moderate Resolution Imaging Spectroradiometer) on the NASA EOS Terra and Aqua platforms, simultaneous global/daily 1km retrievals of cloud effective particle size are available using the heritage 3.7 an band from AVHRR as well as the 1.6 and 2.1 m shortwave IR bands. The MODIS cloud product (MOD06/MYD06 for MODIS Terra and Aqua, respectively) provides separate effective radii results using each of these spectral bands. It has been found that significant differences can occur between the three size retrievals, mainly for liquid water marine boundary layer clouds and especially in broken (low cloud fraction) regimes. In particular, for such regimes, effective radii derived from the MODIS 2.1 lim band can be substantially larger than retrievals from the Heritage 3.7 lam band. In this paper, we present global and regional results of the differences, including correlations, view angle dependencies, and algorithm sensitivities for the existing MODIS Collection 5 product.

Platnick, Steven E.↗
NASA NTRS2011

Improved Flaw Detection and Characterization with Difference Thermography

Flaw detection and characterization with thermographic techniques in graphite polymer composites is often limited by localized variations in the thermographic response. Variations in properties such as acceptable porosity, variations in fiber volume content and surface polymer thickness result in variations in the thermal response that in general cause significant variations in the initial thermal response. These variations result in a noise floor that increases the difficulty of detecting and characterizing deeper flaws. The paper investigates comparing thermographic responses taken before and after a change in state in a composite to improve the detection of subsurface flaws. A method is presented for registration of the responses before finding the difference. A significant improvement in the detectability is achieved by comparing the differences in response. Examples of changes in state due to application of a load and impact are presented.

Winfree, William P.↗
NASA NTRS2010

Differences Between VLBI2010 and S/X Hardware

While the overall architecture is similar for the station hardware in current S/X systems and in the VLBI2010 systems under development, various functions are implemented differently. Some of these differences, and the reasons behind them, are described here.

Corey, Brian↗