Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “source range”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

COBE Final Report: Dirbe Celestial Calibration

We report the results of a comparative study of the COsmic Background Explorer/Diffuse InfraRed Background Experiment (COBE/DIRBE) photometric calibration over about 100 selected stellar and non-stellar calibration objects across a wide range of the DIRBE instrument dynamic range, wavelength coverage, and source temperature. A statistical comparison of the DIRBE-reported flux to the accepted values from the literature (as summarized in the CIO) provides an independent verification of the DIRBE point source calibration.

Burdick, Shawn V.↗
NASA NTRS1995

Spectral and Temporal Characteristics of X-Ray-Bright Stars in the Pleiades

We follow up our deep ROSAT imaging survey of the Pleiades (Stauffer et al. 1994) with an analysis of the spectral and temporal characteristics of the X-ray-bright stars in the Pleiades. Raymond & Smith (1977) one and two-temperature models have been used to fit the position-sensitive proportional counter (PSPC) pulse-height spectra of the dozen or so brightest sources associated with late-type Pleiades members. The best-fit temperatures suggest hot coronal temperatures for K, M, and rapidly rotating G stars, and cooler temperatures for F and slowly rotating G stars. In order to probe the many less X-ray-luminous stars, we have generated composite spectra by combining net counts from all Pleiades members according to spectral type and rotational velocity. Model fits to the composite spectra confirm the trend seen in the individual spectral fits. Particularly interesting is the apparent dependence of coronal temperature on L(sub x)/L(sub bol). A hardness-ratio analysis also confirms some of these trends. The PSPC data have also revealed a dozen or so strong X-ray flares with peak X-ray luminosities in excess of approx. 10(exp 30) ergs/sec. We have modeled the brightest of these flares with a simple quasi-static cooling loop model. The peak temperature and emission measure and the inferred electron density and plasma volume suggest a very large scale flaring event. The PSPC data were collected over a period of approx. 18 months, allowing us to search for source variability on timescales ranging from less than a day (in the case of flares) to more than a year between individual exposures. On approximately year-long timescales, roughly 25% of the late-type stars are variable. Since the Pleiades was also intensively monitored by the imaging instruments on the Einstein Observatory, we have examined X-ray luminosity variations on the 10 yr timescale between Einstein and ROSAT and find that up to 40% of the late-type stars are X-ray variable. Since there is only marginal evidence for increased variability on decade-long timescales, the variability observed on long and short timescales may have a common physical origin.

Gagne, Marc↗
NASA NTRS1997

The High Throughput X-ray Spectroscopy (HTXS) Mission

The HTXS mission concept combines large effective area (approximately 15,000 sq cm at 1 keV), high spectral resolution (E/Delta(E) approximately 300-3000), and broad energy bandpass (0.25-40 keV and possibly up to 100 keV) by using replicated optics together with a complement of spectroscopic instrumentation including reflection gratings readout by charge-coupled device detectors (CCDs), quantum micro-calorimeters, and cadmium zinc telluride (CZT) or comparable high energy detectors. An essential feature of this concept involves minimization of cost (approximately $350M for development and approximately $500-600M including launches) and risk by building six identical modest satellites to achieve the large area. Current mission and technology studies are targeted towards a new start in the 2002 timeframe, with first launch around 2005-2006. The HTXS mission represents a major advance, providing as much as a factor of 100 increase in sensitivity over currently planned high resolution X ray spectroscopy missions. HTXS will mark the start of a new era when high quality X ray spectra will be obtained for all classes of X ray sources, over a wide range of luminosity and distance. With its increased capabilities, HTXS will address many fundamental astrophysics questions such as the origin and distribution of the elements from carbon to zinc, the formation and evolution of clusters of galaxies, the validity of general relativity in the strong gravity limit, the evolution of supermassive black holes in active galactic nuclei, the details of supernova explosions and their aftermath, and the mechanisms involved in the heating of stellar coronae and driving of stellar winds.

White, N. E.↗
NASA NTRS1997

Evidence from Quasi-Periodic Oscillations for a Millisecond Pulsar in the Low Mass X-Ray Binary 4U 0614+091

We have detected quasi-periodic oscillations (QPOs) near 1 kHz from the low mass X-ray binary 4U 0614+091 in observations with RXTE. The observations span several months and sample the source over a large range of X-ray luminosity. In every interval QPOs are present above 400 Hz with fractional RMS amplitudes from 3 to 12% over the full PCA band. At high count rates, two high frequency QPOs are detected simultaneously. The difference of their frequency centroids is consistent with a constant value of 323 Hz in all observations. During one interval a third signal is detected at 328 +/- 2 Hz. This suggests the system has a stable 'clock' which is most likely the neutron star with spin period 3.1 msec. Thus, our observations of 4U 0614+091 and those of 4U 1728-34 provide the first evidence for millisecond pulsars within low-mass X-ray binary systems and reveal the 'missing-link' between millisecond radiopulsars and the late stages of binary evolution in low mass X-ray binaries. The constant difference of the high frequency QPOs sug,,ests a beat-frequency interpretation. In this model, the high frequency QPO is associated with the Keplerian frequency of the inner accretion disk and the lower frequency QPO is a 'beat' between the differential rotation frequency of the inner disk and the spinning neutron star. Assuming the high frequency QPO is a Keplerian orbital frequency for the accretion disk, we find a maximum mass of 1.9 solar mass and a maximum radius of 17 km for the neutron star.

Ford, E.↗
NASA NTRS2003

TerraHertz Free Electron Laser Applications for Satellite Remote Sensing

The development of a Free Electron Laser (EL) operating in the terahertz frequency regime by the group at the University of Hawaii (Elias et al.) represents a significant new opportunity in the area of atmospheric remote sensing. The FEL has 2 salient features that create a unique opportunity. First of all it represents the only source in this frequency range with sufficient power to enable lidar instrumentation. Secondly its very high electrical efficiency (several times more efficient than any currently employed spaceborne laser) renders it a strong candidate for use in satellite remote sensing. On the negative side the atmosphere is rather strongly absorbing throughout this frequency range due primarily to the water vapor continuum absorption. This means that the instruments using this laser will not be able to access the lower troposphere because of its very high water concentration.. However the instrument will be very capable of measurements in the upper troposphere and stratosphere. A passive instrument, the Microwave Limb Sounder on the UARS satellite operated by Jet Propulsion Laboratory, has already demonstrated that this wavelength region can be used for chemical species with strong emission lines. A lidar would complement the capabilities of this instrument by providing the capability to measure absorbing species in the upper atmosphere. I will discuss the design of such an instrument in greater detail and estimate its performance in measuring a number of chemical species of interest to the Earth Science community.

Heaps, William S.↗
NASA NTRS2003

The Constellation-X Observatory

The Constellation X-ray mission will revolutionize X-ray spectroscopy and will provide a key component of NASA's '!Beyond Einstein" program. Over the past 35 years, X-ray astronomy has grown from infancy to near-maturity and is now an indispensable astrophysical tool. Constellation-X will transform this field from the exploratory spectroscopic era of Chandra and XMM to an era of fully comprehensive spectroscopic studies. The mission will consist of four 1.6-meter X-ray telescopes orbiting the Earth/Sun system. By providing a factor of 100 increase in throughput over previous missions, as well as high spectral resolution and a broad energy bandpass, Constellation-X will obtain high quality spectra for all classes of X-ray sources over a wide range of luminosity and redshift. It will study the warping of space and time near black holes, determine the distribution of ordinary matter, dark matter and dark energy, and probe detailed physical processes that occur at temperatures, densities and pressures far beyond those achievable in Earth-bound laboratories.

Weaver, Kimberly↗
NASA NTRS2004

The Chandra Large Area Synoptic X-ray Survey (CLASXS) of the Lockman Hole-Northwest: The X-ray Catalog

We present the X-ray catalog and basic results from our Chandra Large Area Synoptic X-ray Survey (CLASXS) of the Lockman Hole-Northwest field. Our 9 ACIS-I fields cover a contiguous solid angle of approx. 0.4 sq deg and reach fluxes of 5 x 10(exp -16) ergs/sq cm/s (0.4-2 keV) and 3 x 10(exp -15) ergs/sq cm/s (2-8 keV). Our survey bridges the gap between ultradeep pencil-beam surveys, such as the Chandra Deep Fields (CDFs), and shallower, large area surveys, allowing a better probe of the X-ray sources that contribute most of the 2-10 keV cosmic X-ray background (CXB). We find a total of 525 X-ray point sources and 4 extended sources. At approx. 10(exp -14)ergs/sq cm/s (2-8 keV), our number counts are significantly higher than those of several non-contiguous, large area surveys. Such a large difference is an indication of clustering in the X-ray sources. On the other hand, the integrated flux from the CLASXS field, combined with ASCA and Chandra ultradeep surveys, is consistent with results from other large area surveys, within the variance of the CXB. We see spectral evolution in the hardening of the sources at fluxes below 10(exp -14) ergs/sq cm/s, which agrees with previous observations from Chandra and XMM-Newton. About 1/3 of the sources in the CLASXS field have multiple observations, allowing variability tests. Above 4 x 10(exp -14) ergs/sq cm/s (0.4-8 keV), approx. 61% of the sources are variable. We also investigated the spectral variability of the variable sources. While most show spectral softening with increasing flux, or no significant spectral change, there are a few sources that show a different trend. Four extended sources in CLASXS is consistent with the previously measured LogN-LogS of galaxy clusters. Using X-ray spectra and optical colors, we argue that 3 of the 4 extended sources are galaxy clusters or galaxy groups. We report the discovery of a gravitational lensing arc associated with one of these sources. Using red sequence and brightest cluster galaxy methods, we find that the redshifts of the extended sources are in the range z approx. 0.5 - 1. The inferred masses within the Einstein radii are consistent with the mass profiles of local groups scaled to the same virial radii.

Yang, Y.↗
NASA NTRS2004

On the Inversion for Mass (Re)Distribution from Global (Time-Variable) Gravity Field

The well-known non-uniqueness of the gravitational inverse problem states the following: The external gravity field, even if completely and exactly known, cannot Uniquely determine the density distribution of the body that produces the gravity field. This is an intrinsic property of a field that obeys the Laplace equation, as already treated in mathematical as well as geophysical literature. In this paper we provide conceptual insight by examining the problem in terms of spherical harmonic expansion of the global gravity field. By comparing the multipoles and the moments of the density function, we show that in 3-S the degree of knowledge deficiency in trying to inversely recover the density distribution from external gravity field is (n+l)(n+2)/2 - (2n+l) = n(n-1)/2 for each harmonic degree n. On the other hand, on a 2-D spherical shell we show via a simple relationship that the inverse solution of the surface density distribution is unique. The latter applies quite readily in the inversion of time-variable gravity signals (such as those observed by the GRACE space mission) where the sources over a wide range of the scales largely come from the Earth's Surface.

Chao, Benjamin F.↗
NASA NTRS2006

Assessment of Bulk Absorber Properties for Multi-Layer Perforates in Porous Honeycomb Liners

CONTINUING progress in materials technology provides potential for improved acoustic liners for attenuating broadband fan noise emissions from aircraft engine nacelles. Conventional liners (local-reacting perforate-over-honeycomb structures) provide significant narrow-band attenuation, but limited attenuation over wide bandwidths. Two approaches for increasing attenuation bandwidth are to (1) replace the honeycomb structure with bulk material, or (2) cascade multiple layers of perforate/honeycomb structures. Usage of the first approach is limited because of mechanical and maintenance reasons, while multi-layer liners are limited to about three layers because of their additional mechanical complexity, depth and weight. The current research concerns a novel approach reported by the University of Cincinnati, in which a single-layer conventional liner is converted into an extended-reaction, broadband absorber by making the honeycomb core structure porous. This modified single-layer liner requires no increase in depth and weight, and minimal increase in mechanical complexity. Langley has initiated research to identify potential benefits of liner structures with porous cell walls. This research has two complementary goals: (1) develop and validate experimental techniques for treating multi-layer perforates (representative of the internal cells of a liner with porous cell walls) as 1-D bulk materials, and (2) develop analytical approaches to validate this bulk material assumption. If successful, the resultant model can then be used to design optimized porous honeycomb liners. The feasibility of treating an N-layer perforate system (N porous plates separated by uniform air gaps) as a one-dimensional bulk absorber is assessed using the Two-Thickness Method (TTM), which is commonly used to educe bulk material intrinsic acoustic parameters. Tests are conducted with discrete tone and random noise sources, over an SPL range sufficient to determine the nonlinearity of the test specimens, for test specimens consisting of 5, 10 and 15% porous plates. Measured impedances for two liner thicknesses (e.g., 12 and 24 layers) are used as input to the TTM to determine the characteristic impedance and propagation constant that characterize these liners as bulk absorbers. These parameters are then used to calculate the predicted impedance of liners with different thicknesses (e.g., 36 layers), and a comparison of predicted and measured impedances for these other thicknesses is used to determine the efficacy of this approach. Finally, an independent method is used to educe the propagation constant for a single representative sample, and excellent comparison between the results for this method and those for the TTM provides increased confidence in the results achieved with the TTM. In general, the results demonstrate these multi-layer perforates can be acceptably treated as bulk absorbers.

Jones, Michael G.↗
NASA NTRS1998

Isophot - Photometric Calibration of Point Sources

We discuss the photometric calibration of ISOPHOT for point sources in the wavelength range from 3.2 to 240 ??or the aperture photometer and the FIR camera section.

Infrared instrumentation ISO ISOPHOT calibration i↗
NASA NTRS2006

Series Connected Buck-Boost Regulator

A Series Connected Buck-Boost Regulator (SCBBR) that switches only a fraction of the input power, resulting in relatively high efficiencies. The SCBBR has multiple operating modes including a buck, a boost, and a current limiting mode, so that an output voltage of the SCBBR ranges from below the source voltage to above the source voltage.

Birchenough, Arthur G.↗
NASA NTRS2006

Series Connected Buck-Boost Regulator

A Series Connected Buck-Boost Regulator (SCBBR) that switches only a fraction of the input power, resulting in relatively high efficiencies. The SCBBR has multiple operating modes including a buck, a boost, and a current limiting mode, so that an output voltage of the SCBBR ranges from below the source voltage to above the source voltage.

Birchenough, Arthur G.↗
NASA NTRS2006

The Cosmological Evolution of Radio Sources with CENSORS

The CENSORS survey, selected from the NVSS, has been followed up using EIS, K-band imaging and spectroscopic observations to produce a radio sample capable of probing the source density in the regime: z greater than 2.5. With a current spectroscopic completeness of 62%, CENSORS has been used in direct modeling of RLF evolution and in V/V(sub max) tests. There is evidence for a shallow decline in number density of source in the luminosity range 10(sup 26) - 10(sup 27)WHz(sup -1) at 1.4GHz.

astronomy↗
NASA NTRS1997

Long-wavelength PTSI infrared detectors and method of fabrication thereof

Extended cutoff wavelengths of PtSi Schottky infrared detectors in the long wavelength infrared (LWIR) regime have been demonstrated for the first time. This result was achieved by incorporating a 1-nm-thick p+ doping spike at the PtSi/Si interface. The extended cutoff wavelengths resulted from the combined effects of an increased electric field near the silicide/Si interface due to the p+ doping spike and the Schottky image force. The p+ doping spikes were grown by molecular beam epitaxy at 450 degrees Celsius using elemental boron as the dopant source, with doping concentrations ranging from 1.times.10.sup.19 to 1.times.10.sup.21 cm.sup.-3. The cutoff wavelengths were shown to increase with increasing doping concentrations of the p+ spikes.

Lin, True-Lon↗
NASA NTRS2007

Scientific Uses and Directions of SPDF Data Services

From a science user's perspective, the multi-mission data and orbit services of NASA's Space Physics Data Facility (SPDF) project perform as a working and highly functional heliophysics virtual observatory. CDAWeb enables plots, listings and file downloads for current data across the boundaries of missions and instrument types (and now including data from THEMIS and STEREO), VSPO access to a wide range of distributed data sources. SSCWeb, Helioweb and our 3D Animated Orbit Viewer (TIPSOD) provide position data and query logic for most missions currently-important to heliophysics science. OMNIWeb with its new extension to 1- and 5- minute resolution provides interplanetary parameters at the Earth's bow shock as a unique value-added data product. To enable easier integrated use of our capabilities by developers and by the emerging heliophysics VxOs, our data and services are available through webservices-based APls as well as through our direct user interfaces. SPDF has also now developed draft descriptions of its holdings in SPASE-compliant XML In addition to showcasing recent enhancements to SPDF capabilities, we will use these systems and our experience in developing them: to demonstrate a few typical science use cases; to discuss key scope and design issues among users, service providers and end data providers; and to identify key areas where existing capabilities and effective interface design are still inadequate to meet community needs.

Fung, Shing↗
NASA NTRS2007

Detector Noise Characterization and Performance of MODIS Thermal Emissive Bands

MODIS has 16 thermal emissive bands, a total of 160 individual detectors (10 for each spectral bands), located on the two cold focal plane assemblies (CFPA). MODIS TEB detectors were fully characterized pre-launch in a thermal vacuum (TV) environment using a NIST traceable blackbody calibration source (BCS) with temperatures ranging from 170 to 340K. On-orbit the TEB detectors are calibrated using an on-board blackbody (BB) on a scan-by-scan basis. For nominal on-orbit operation, the on-board BB temperature is typically controlled at 285K for Aqua MODIS and 290K for Terra MODIS. For the MODIS TEB calibration, each detector's noise equivalent temperature difference (NEdT) is often used to assess its performance and this parameter is a major contributor to the calibration uncertainty. Because of its impact on sensor calibration and data product quality, each MODIS TEB detector's NEdT is monitored on a daily basis at a fixed BB temperature and completely characterized on a regular basis at a number of BB temperatures. In this paper, we describe MODIS on-orbit TEB NEdT characterization activities, approaches, and results. We compare both pre-launch and on-orbit performance with sensor design specification and examine detector noise characterization impact on the calibration uncertainty. To date, 135 TEB detectors (out of a total of 160 detectors) in Terra MODIS (launched in December 1999) and 158 in Aqua MODIS (launched in May 2002) continue to perform with their NEdT below (or better than) their design specifications. A complete summary of all TEB noisy detectors, identified both pre-launch and on-orbit, is provided.

Xiong, X.↗
NASA NTRS2009

Testbed for LISA Photodetectors

The Laser Interferometer Space Antenna (LISA) is a gravitational wave observatory consisting of three spacecraft separated by 5 million km in an equilateral triangle whose center follows the Earth in orbit around the Sun but offset in orbital phase by 20 degrees. LISA is designed to observe sources in the frequency range of 0.1 mHz-100 mHz by measuring fluctuations of the inter-spacecraft separation with laser interferometry. Quadrant photodetectors are used to measure both separation and angular orientation. Noise level, phase and amplitude inhomogeneities of the semiconductor response, and channel cross-talk between quadrant cells need to be assessed in order to ensure the 10 pm/Square root(Hz) sensitivity required for the interferometric length measurement in LISA. To this end, we are currently developing a testbed that allows us to evaluate photodetectors to the sensitivity levels required for LISA. A detailed description of the testbed and preliminary results will be presented.

Guzman, Felipe↗
NASA NTRS2012

Induction of Cell Death through Alteration of Oxidants and Antioxidants in Epithelial Cells Exposed to High Energy Protons

Radiation affects several cellular and molecular processes including double strand breakage, modifications of sugar moieties and bases. In outer space, protons are the primary radiation source which poses a range of potential health risks to astronauts. On the other hand, the use of proton radiation for tumor radiation therapy is increasing as it largely spares healthy tissues while killing tumor tissues. Although radiation related research has been conducted extensively, the molecular toxicology and cellular mechanisms affected by proton radiation remain poorly understood. Therefore, in the present study, we irradiated rat epithelial cells (LE) with different doses of protons and investigated their effects on cell proliferation and cell death. Our data showed an inhibition of cell proliferation in proton irradiated cells with a significant dose dependent activation and repression of reactive oxygen species (ROS) and antioxidants, glutathione and superoxide dismutase respectively as compared to control cells. In addition, apoptotic related genes such as caspase-3 and -8 activities were induced in a dose dependent manner with corresponding increased levels of DNA fragmentation in proton irradiated cells than control cells. Together, our results show that proton radiation alters oxidant and antioxidant levels in the cells to activate apoptotic pathway for cell death.

Ramesh, Govindarajan↗