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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

The fracture behavior of graphite/epoxy laminates

The results of uniaxial tensile tests conducted on a variety of graphite/epoxy laminates containing narrow rectangular slits and square or circular holes with various aspect ratios are discussed. The techniques used to study stable-crack or damage-zone growth - namely, birefringence coatings, COD gages, and microscopic observations are discussed. Initial and final-fracture modes are discussed as well as the effect of notch size and shape and laminate type on the fracture process. Characteristic lengths are calculated using the point, average and inherent flaw theories and comparisons with observations are discussed. Further, the effect of flaw geometry on stress states and deformations is assessed.

Yeow, Y. T.↗
NASA NTRS1983

Leaf water stress detection utilizing thematic mapper bands 3, 4 and 5 in soybean plants

The total and diffuse radiance responses of Thematic Mapper bands 3 (0.63-0.69 microns), 4 (0.76-0.90 microns), and 5 (1.55-1.75 microns) to water stress in a soybean canopy are compared. Polarization measurements were used to separate the total from the diffuse reflectance; the reflectances were compared statistically at a variety of look angles at 15 min intervals from about 09.00 until 14.00 hrs EST. The results suggest that remotely sensed data collected in the photographic infrared region (TM4) are sensitive to leaf water stress in a 100 percent canopy cover of soybeans, and that TM3 is less sensitive than TM4 for detection of reversible foliar water stress. The mean values of TM5 reflectance data show similar trends to TM4. The primary implication of this study is that remote sensing of water stress in green plant canopies is possible in TM4 from ground-based observations primarily through the indirect link of leaf geometry.

Holben, B. N.↗
NASA NTRS1985

A high energy Space Station (HESS) array for studying extremely energetic cosmic rays

The scientific aims and design concept of a High-Energy Space Station (HESS) cosmic-ray detector array are discussed. The current state of knowledge on cosmic-ray acceleration and high-energy interactions is briefly reviewed, and the need for observations yielding elemental composition and spectra in the 10-10,000-TeV/nucleon range is demonstrated. It is predicted that 2 yr of observations with a space-borne detector of geometry factor 30 sq m sr would provide adequate data to determine the acceleration mechanism (by comparing the energy level at which the spectra of He nuclei and protons break). A modular HESS array comprising W/scintillator/PM-tube calorimeter modules and Cerenkov charge-sensitive detector modules and weighing about 30 tonnes is described. The array could be assembled on orbit after transport in the Space Shuttle cargo bay, and data could be taken as soon as one or two layers of modules had been attached to the mounting-frame/support-electronics unit.

Ormes, J. F.↗
NASA NTRS1988

Duct flow nonuniformities: Effect of struts in SSME HGM II(+)

A numerical study, using the INS3D flow solver, of laminar and turbulent flow around a two dimensional strut, and three dimensional flow around a strut in an annulus is presented. A multi-block procedure was used to calculate two dimensional laminar flow around two struts in parallel, with each strut represented by one computational block. Single block calculations were performed for turbulent flow around a two dimensional strut, using a Baldwin-Lomax turbulence model to parameterize the turbulent shear stresses. A modified Baldwin-Lomax model was applied to the case of a three dimensional strut in an annulus. The results displayed the essential features of wing-body flows, including the presence of a horseshoe vortex system at the junction of the strut and the lower annulus surface. A similar system was observed at the upper annulus surface. The test geometries discussed were useful in developing the capability to perform multiblock calculations, and to simulate turbulent flow around obstructions located between curved walls. Both of these skills will be necessary to model the three dimensional flow in the strut assembly of the SSME. Work is now in progress on performing a three dimensional two block turbulent calculation of the flow in the turnaround duct (TAD) and strut/fuel bowl juncture region.

Burke, Roger↗
NASA NTRS1989

Experiments in swept-wing transition

Stability and transition experiments are conducted on a 45 degree sweep airfoil in the ASU Unsteady Wind Tunnel. Combined flow-visualization techniques and hot-wire measurements are used in conjuction with stability-code calculations to map out transition behavior for this flow geometry. Both steady and unsteady crossflow vortices are observed and at this time there is no contradiction with the theoretical predictions.

Saric, William S.↗
NASA NTRS1990

New radio detections of early-type pre-main-sequence stars

Results of VLA radio continuum observations of 13 early-type pre-main-sequence stars selected from the 1984 catalog of Finkenzeller and Mundt are presented. The stars HD 259431 and MWC 1080 were detected at 3.6 cm, while HD 200775 and TY CrA were detected at both 3.6 and 6 cm. The flux density of HD 200775 has a frequency dependence consistent with the behavior expected for free-free emission originating in a fully ionized wind. However, an observation in A configuration suggests that the source geometry may not be spherically symmetric. In contrast, the spectral index of TY CrA is negative with a flux behavior implying nonthermal emission. The physical mechanism responsible for the nonthermal emission has not yet been identified, although gyrosynchrotron and synchrotron processes cannot be ruled out.

Skinner, Stephen L.↗
NASA NTRS1993

Friction and oxidative wear of 440C ball bearing steels under high load and extreme bulk temperatures

Unlubricated sliding friction and wear of 440C steels in an oxygen environment have been studied under a variety of load, speed, and temperature ranging from approximately -185 to 675 deg C. A specially designed test apparatus with a ball-on-flat geometry has been used for this purpose. The observed dependencies of the initial coefficient of friction, the average dynamic coefficient of friction, and the wear rate on load, speed, and test temperatures have been examined from the standpoint of existing theories of friction and wear. High contact temperatures are generated during the sliding friction, causing rapid oxidation and localized surface melting. A combination of fatigue, delamination, and loss of hardness due to tempering of the martensitic structure is responsible for the high wear rate observed and the coefficient of friction.

Chaudhuri, Dilip K.↗
NASA NTRS1993

Submission of Earth-based ring occultation observations to the NASA planetary data system rings discipline node

This is a technical report summarizing our progress in our program of contributing high quality Earth-based occultation observations to NASA's Planetary Data System (PDS) Rings Node. During our first year of funding, we selected five data sets for eventual inclusion in the PDS Rings Node. These were Uranus occultation observations obtained by the PI and co-workers from the IRTF of event stars U34 (26 April 1986), U1052 (5 May 1988), U65 (21 June 1990), U7872 (25 June 1991), and U7808 (28 June 1991). In our original proposal, we described four tasks: data sets to a common format; documentation of the occultation observations and associated calibrations; calculation of the occultation geometry for each event; establish prototype PDS templates. As discussed in our renewal proposal, submitted 8 June 1993, we have completed the first three tasks, and are working on the fourth. As an indication of our progress to date, we provide information about each of the data sets, their formats, the documentation, and the method used for reconstructing the occultation geometry.

French, Richard G.↗
NASA NTRS1994

NO2 column changes induced by volcanic eruptions

Nitrogen dioxide slant column amounts measured by ground-based remote sensing from Lauder, New Zealand (45 deg S) and Campbell Island (53 deg S) during the second half of 1991 and early 1992 show anomalously low values that are attributed to the effects of volcanic eruptions. It is believed that the eruptions of Mount Pinatubo in the Philippines in June 1991 and possibly Mount Hudson in Chile in August 1991 are responsible for the stratospheric changes, which first became apparent in July 1991. The effects in the spring of 1991 are manifested as a reduction in the retrieved NO2 column amounts from normal levels by 35 to 45 percent, and an accompanying increase in the overnight decay of NO2. The existence of an accurate long-term record of column NO2 from the Lauder site enables us to quantify departures from the normal seasonal behavior with some confidence. Simultaneous retrievals of column ozone agree well with Dobson measurements, confirming that only part of the NO2 changes can be attributed to a modification of the scattering geometry by volcanic aerosols. Other reasons for the observed behavior are explored, including the effects of stratospheric temperature increases resulting from the aerosol loading and the possible involvement of heterogeneous chemical processes.

Johnston, Paul V.↗
NASA NTRS1994

Non-radial magnetic field structures in the solar corona

We report on the structure and geometry of coronal magnetic fields inferred from the observations of meter-decimeter type 3 and moving type 4 radio bursts, associated with an H(alpha) flare. This is the first report of type 3 radio bursts from the Nancay radioheliograph after it acquired the two dimensional multifrequency capability. Dispersion of the radio source positions with frequency suggests that open and closed field lines are considerably inclined to the radial direction which is consistent with the connectivity observed in the magnetogram. We suggest that multiple arch systems are involved in the type 4 emission. From the polarization and dispersion characteristics of the type 4 source, we infer that the emission is due to fundamental plasma emission.

Gopalswamy, N.↗
NASA NTRS2003

Translocation of a Polymer Chain across a Nanopore: A Brownian Dynamics Simulation Study

We carried out Brownian dynamics simulation studies of the translocation of single polymer chains across a nanosized pore under the driving of an applied field (chemical potential gradient). The translocation process can be either dominated by the entropic barrier resulted from restricted motion of flexible polymer chains or by applied forces (or chemical gradient across the wall), we focused on the latter case in our studies. Calculation of radius of gyrations at the two opposite sides of the wall shows that the polymer chains are not in equilibrium during the translocation process. Despite this fact, our results show that the one-dimensional diffusion and the nucleation model provide an excellent description of the dependence of average translocation time on the chemical potential gradients, the polymer chain length and the solvent viscosity. In good agreement with experimental results and theoretical predictions, the translocation time distribution of our simple model shows strong non-Gaussian characteristics. It is observed that even for this simple tubelike pore geometry, more than one peak of translocation time distribution can be generated for proper pore diameter and applied field strengths. Both repulsive Weeks-Chandler-Anderson and attractive Lennard-Jones polymer-nanopore interaction were studied, attraction facilitates the translocation process by shortening the total translocation time and dramatically improve the capturing of polymer chain. The width of the translocation time distribution was found to decrease with increasing temperature, increasing field strength, and decreasing pore diameter.

Tian, Pu↗
NASA NTRS2011

Gas Modelling in the Disc of HD 163296

We present detailed model fits to observations of the disc around the Herbig Ae star HD 163296. This well-studied object has an age of approx. 4Myr, with evidence of a circumstellar disc extending out to approx. 540AU. We use the radiation thermo-chemical disc code ProDiMo to model the gas and dust in the circumstellar disc of HD 163296, and attempt to determine the disc properties by fitting to observational line and continuum data. These include new Herschel/PACS observations obtained as part of the open-time key program GASPS (Gas in Protoplanetary Systems), consisting of a detection of the [Oi] 63 m line and upper limits for several other far infrared lines. We complement this with continuum data and ground-based observations of the CO-12 3-2, 2-1 and CO-13 J=1-0 line transitions, as well as the H2 S(1) transition. We explore the effects of stellar ultraviolet variability and dust settling on the line emission, and on the derived disc properties. Our fitting efforts lead to derived gas/dust ratios in the range 9-100, depending on the assumptions made. We note that the line fluxes are sensitive in general to the degree of dust settling in the disc, with an increase in line flux for settled models. This is most pronounced in lines which are formed in the warm gas in the inner disc, but the low excitation molecular lines are also affected. This has serious implications for attempts to derive the disc gas mass from line observations. We derive fractional PAH abundances between 0.007 and 0.04 relative to ISM levels. Using a stellar and UV excess input spectrum based on a detailed analysis of observations, we find that the all observations are consistent with the previously assumed disc geometry

Tilling, I.↗
NASA NTRS2012

Survival of Flux Transfer Event (FTE) Flux Ropes Far Along the Tail Magnetopause

During intervals of southward IMF, magnetic reconnection can result in the formation of flux transfer events (FTEs) on the dayside magnetopause which travel along the magnetopause in the anti-sunward direction. Of particular interest is their fate and the role they play transporting solar wind plasma into the magnetosphere. We present the discovery of FTEs far along the distant tail magnetopause (x = 67 Earth radii) using data from ARTEMIS on the dusk flank magnetopause under southward/duskward IMF conditions. The identification of several events is further supported by excellent fits to a force-free flux rope model. The axis of each structure is principally north-south, i.e., perpendicular to the Sun-Earth line. Simultaneous observations by THEMIS on the dayside magnetopause indicate that FTEs are being produced there, although perhaps 2-4 times smaller in size. The convection time from the dayside magnetopause to ARTEMIS is 30 min, and the FTEs have a flux content comparable to those typically observed on the dayside magnetopause, indicating that these features are in quasi-equilibrium as they are convected downtail. By considering the relative orientations of the FTEs observed by THEMIS and ARTEMIS, the magnetic field geometry is consistent with the FTEs being produced on the dayside magnetopause along an extended X-line in the presence of IMF By and bending as they are convected to the flanks.

ARTEMIS↗
NASA NTRS2013

Multitemporal Cross-Calibration of the Terra MODIS and Landsat 7 ETM+ Reflective Solar Bands

In recent years, there has been a significant increase in the use of remotely sensed data to address global issues. With the open data policy, the data from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Enhanced Thematic Mapper Plus (ETM+) sensors have become a critical component of numerous applications. These two sensors have been operational for more than a decade, providing a rich archive of multispectral imagery for analysis of mutitemporal remote sensing data. This paper focuses on evaluating the radiometric calibration agreement between MODIS and ETM+ using the near-simultaneous and cloud-free image pairs over an African pseudo-invariant calibration site, Libya 4. To account for the combined uncertainties in the top-of-atmosphere (TOA) reflectance due to surface and atmospheric bidirectional reflectance distribution function (BRDF), a semiempirical BRDF model was adopted to normalize the TOA reflectance to the same illumination and viewing geometry. In addition, the spectra from the Earth Observing-1 (EO-1) Hyperion were used to compute spectral corrections between the corresponding MODIS and ETM+ spectral bands. As EO-1 Hyperion scenes were not available for all MODIS and ETM+ data pairs, MODerate resolution atmospheric TRANsmission (MODTRAN) 5.0 simulations were also used to adjust for differences due to the presence or lack of absorption features in some of the bands. A MODIS split-window algorithm provides the atmospheric water vapor column abundance during the overpasses for the MODTRAN simulations. Additionally, the column atmospheric water vapor content during the overpass was retrieved using the MODIS precipitable water vapor product. After performing these adjustments, the radiometric cross-calibration of the two sensors was consistent to within 7%. Some drifts in the response of the bands are evident, with MODIS band 3 being the largest of about 6% over 10 years, a change that will be corrected in Collection 6 MODIS processing.

MODIS↗
NASA NTRS2018

Methane on Mars: New Insights into the Sensitivity of CH4 with the NOMAD/ExoMars Spectrometer Through Its First In-Flight Calibration

The Nadir and Occultation for MArs Discovery instrument (NOMAD), onboard the ExoMars Trace Gas Orbiter (TGO) spacecraft was conceived to observe Mars in solar occultation, nadir, and limb geometries, and will be able to produce an outstanding amount of diverse data, mostly focused on properties of the atmosphere. The infrared channels of the instrument operate by combining an echelle grating spectrometer with an Acousto- Optical Tunable Filter (AOTF). Using in-flight data, we characterized the instrument performance and parameterized its calibration. In particular: an accurate frequency calibration was achieved, together with its variability due to thermal effects on the grating. The AOTF properties and transfer function were also quantified, and we developed and tested a realistic method to compute the spectral continuum transmitted through the coupled grating and AOTF system. The calibration results enabled unprecedented insights into the important problem of the sensitivity of NOMAD to methane abundances in the atmosphere. We also deeply characterized its performance under realistic conditions of varying aerosol abundances, diverse albedos and changing illumination conditions as foreseen over the nominal mission. The results show that, in low aerosol conditions, NOMAD single spectrum, 1σ sensitivity to CH4 is around 0.33 ppbv at 20 km of altitude when performing solar occultation's, and better than 1 ppbv below 30 km. In dusty conditions, we show that the sensitivity drops to 0 below 10 km. In Nadir geometry, results demonstrate that NOMAD will be able to produce seasonal maps of CH4 with a sensitivity around 5 ppbv over most of planet's surface with spatial integration over 5×5° bins. Results show also that such numbers can be improved by a factor of ~10 to ~30 by data binning. Overall, our results quantify NOMAD's capability to address the variable aspects of Martian climate.

Liuzzi, Giuliano↗
NASA NTRS1980

Earth radiation budget measurements from satellites and their interpretation for climate modeling and studies

The annual and seasonal averaged Earth atmosphere radiation budgets derived from the most complete set of satellite observations available are presented. The budgets were derived from a composite of 48 monthly mean radiation budget maps. Annually and seasonally averaged radiation budgets are presented as global averages and zonal averages. The geographic distribution of the various radiation budget quantities is described. The annual cycle of the radiation budget was analyzed and the annual variability of net flux was shown to be largely dominated by the regular semi and annual cycles forced by external Earth-Sun geometry variations. Radiative transfer calculations were compared to the observed budget quantities and surface budgets were additionally computed with particular emphasis on discrepancies that exist between the present computations and previous surface budget estimates.

Vonderhaar, T. H.↗
NASA NTRS1998

A Viewing Angle-Kinetic Luminosity Scheme for BL Lacertae Objects

We propose a unified classification for BL Lacertae objects (BLs), focusing on the synchrotron peak frequency of the spectral energy distribution. The unification scheme is based on the angle theta that describes the orientation of the relativistic jet and on the electron kinetic luminosity Lamba(sub kin) of the jet. We assume that Lamba(sub kin) scales with the size of the jet (r) in a self-similar fashion (Lamba(sub kin) is proportional to r(exp 2)), as supported by observational data. The jets are self-similar in geometry and have the same pressure and median magnetic field at the inlet, independent of size. The self-similarity is broken for the highest energy electrons, which radiate mainly at high frequencies, since for large sources they suffer more severe radiative energy losses over a given fraction of the jet length. We calculate the optically thin synchrotron spectrum using an accelerating inner jet model based on simple relativistic gas dynamics and show that it can fit the observed infrared-to-X-ray spectrum of PKS 2155-304. We couple the accelerating jet model to the unification scheme and compare the results to complete samples of BLs. The negative apparent evolution of X-ray-selected BLs is explained as a result of positive evolution of the jet electron kinetic luminosity Lamba(sub kin). We review observational arguments in favor of the existence of scaled-down accretion disks and broad emission-line regions in BLs. The proposed unification scheme can explain the lack of observed broad emission lines in X-ray-selected BLs as well as the existence of those lines preferentially in luminous radio-selected BLs. Finally, we review observational arguments that suggest the extension of this unification scheme to all blazars.

Georganopoulos, Markos↗
NASA NTRS2008

Suzaku Observation of the Dwarf Nova V893 Scorpii: The Discovery of a Partial X-Ray Eclipse

V893 Sco is an eclipsing dwarf nova that had attracted little attention from X-ray astronomers until it was proposed as the identification of an RXTE all-sky slew survey (XSS) source. Here we report on the po inted X-ray observations of this object using Suzaku. We confirm V893 Sco to be X-ray bright, whose spectrum is highly absorbed for a dwar f nova. We have also discovered a partial X-ray eclipse in V893 Sco. This is the first time that a partial eclipse is seen in Xray light c urves of a dwarf nova. We have successfully modeled the gross features of the optical and X-ray eclipse light curves using a boundary layer geometry of the X-ray emission region. Future observations may lead to confirmation of this basic picture, and allow us to place tight co nstraints on the size of the X-ray emission region. The partial X-ray eclipse therefore should make V893 Sco a key object in understanding the physics of accretion in quiescent dwarf nova.

Mukai, Koji↗