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At least 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Electric and kinematic structure of the Oklahoma mesoscale convective system of 7 June 1989

Balloon soundings of electric field in Oklahoma mesoscale convective systems (MCS) were obtained by the National Severe Storms Laboratory in the spring of 1989. This study focuses on a sounding made in the rearward edge of an MCS stratiform rain area on 7 June 1989. Data from Doppler radars, a lightning ground-strike location system, satellite, and other sources is used to relate the mesoscale attributes of the MCS to the observed electric-field profile.

Hunter, Steven M.↗
NASA NTRS1993

Atmospheric methyl bromide - Trends and global mass balance

A decadal time series of global CH3Br concentrations in the earth's atmosphere is presented. It is shown that average concentrations are about 10 pptv and during the last 4 yr may be increasing at 0.3 +/- 0.1 pptv/yr. It is estimated that the atmospheric lifetime of CH3Br that is due to reaction with OH is about 2 yr, which results in a calculated global emission rate of about 100 Gg/yr. Ocean supersaturations of 140-180 percent are observed, and atmospheric concentrations over the open oceans are higher than at comparably located coastal sites. The ocean source is estimated to be about 35 Gg/yr. The remaining emissions must come from other natural sources and anthropogenic activities.

Khalil, M. A. K.↗
NASA NTRS1991

The use of satellite data to determine the distribution of ozone in the troposphere

Measurements from two independent satellite data sets have been used to derive the climatology of the integrated amount of ozone in the troposphere. These data have led to the finding that large amounts of ozone pollution are generated by anthropogenic activity originating from both the industrialized regions of the Northern Hemisphere and from the southern tropical regions of Africa. To verify the existence of this ozone anomaly at low latitudes, an ozonesonde capability has been established at Ascension Island (8 deg S, 15 deg W) since July 1990. According to the satellite analyses, Ascension Island is located downwind of the primary source region of this ozone pollution, which likely results from the photochemical oxidation of emissions emanating from the widespread burning of savannas and other biomass. These in situ measurements confirm the existence of large amounts of ozone in the lower atmosphere. A summary of these ozonesonde data to date will be presented. In addition, we will present some ozone profile measurements from SAGE II which can be used to provide upper tropospheric ozone measurements directly in the tropical troposphere. A preliminary comparison between the satellite observations and the ozonesonde profiles in the upper troposphere and lower stratosphere will also be presented.

Fishman, Jack↗
NASA NTRS1995

A search for pre-main-sequence stars in high-latitude molecular clouds. 3: A survey of the Einstein database

In order to discern whether the high-latitude molecular clouds are regions of ongoing star formation, we have used X-ray emission as a tracer of youthful stars. The entire Einstein database yields 18 images which overlap 10 of the clouds mapped partially or completely in the CO (1-0) transition, providing a total of approximately 6 deg squared of overlap. Five previously unidentified X-ray sources were detected: one has an optical counterpart which is a pre-main-sequence (PMS) star, and two have normal main-sequence stellar counterparts, while the other two are probably extragalactic sources. The PMS star is located in a high Galactic latitude Lynds dark cloud, so this result is not too suprising. The translucent clouds, though, have yet to reveal any evidence of star formation.

Caillault, Jean-Pierre↗
NASA NTRS1996

Relativity effects for space-based coherent lidar experiments

An effort was initiated last year in the Astrionics Laboratory at Marshall Space Flight Center to examine and incorporate, if necessary, the effects of relativity in the design of space-based lidar systems. A space-based lidar system, named AEOLUS, is under development at Marshall Space Flight Center and it will be used to accurately measure atmospheric wind profiles. Effects of relativity were also observed in the performance of space-based systems, for example in case of global positioning systems, and corrections were incorporated into the design of instruments. During the last summer, the effects of special relativity on the design of space-based lidar systems were studied in detail, by analyzing the problem of laser scattering off a fixed target when the source and a co-located receiver are moving on a spacecraft. Since the proposed lidar system uses a coherent detection system, errors even in the order of a few microradians must be corrected to achieve a good signal-to-noise ratio. Previous analysis assumed that the ground is flat and the spacecraft is moving parallel to the ground, and developed analytical expressions for the location, direction and Doppler shift of the returning radiation. Because of the assumptions used in that analysis, only special relativity effects were involved. In this report, that analysis is extended to include general relativity and calculate its effects on the design.

Gudimetla, V. S. Rao↗
NASA NTRS1998

Ultrasonic Leak Detection System

A system for detecting ultrasonic vibrations. such as those generated by a small leak in a pressurized container. vessel. pipe. or the like. comprises an ultrasonic transducer assembly and a processing circuit for converting transducer signals into an audio frequency range signal. The audio frequency range signal can be used to drive a pair of headphones worn by an operator. A diode rectifier based mixing circuit provides a simple, inexpensive way to mix the transducer signal with a square wave signal generated by an oscillator, and thereby generate the audio frequency signal. The sensitivity of the system is greatly increased through proper selection and matching of the system components. and the use of noise rejection filters and elements. In addition, a parabolic collecting horn is preferably employed which is mounted on the transducer assembly housing. The collecting horn increases sensitivity of the system by amplifying the received signals. and provides directionality which facilitates easier location of an ultrasonic vibration source.

Youngquist, Robert C.↗
NASA NTRS2004

VLA Imaging of Protoplanetary Environments

We summarize the major accomplishments of our program to use high angular resolution observations at millimeter wavelengths to probe the structure of protoplanetary disks in nearby regions of star formation. The primary facilities used in this work were the Very Large Array (VLA) of the National Radio Astronomy Observatories (NRAO) located in New Mexico, and the recently upgraded Australia Telescope Compact Array (ATCA), located in Australia (to access sources in the far southern sky). We used these facilities to image thermal emission from dust particles in disks at long millimeter wavelengths, where the emission is optically thin and probes the full disk volume, including the inner regions of planet formation that remain opaque at shorter wavelengths. The best resolution obtained with the VLA is comparable to the size scales of the orbits of giant planets in our Solar System (< 10 AU).

Wilner, David J.↗
NASA NTRS2004

The Herbig Ae Star HD 163296 in X-Rays

Chandra X-ray imaging spectroscopy of the nearby Herbig Ae star HD 163296 at 100 AU angular resolution is reported. A point-like, soft (kT approximately 0.5 approximately kev), emission-line source is detected at the location of the star with an X-ray luminosity of 4.0e29 erg/s. In addition, faint emission along the direction of a previously-detected Ly-alpha-emitting jet and Herbig-Haro outflow may be present. The relatively low luminosity, lack of a hard spectral component, and absence of strong X-ray variability in HD 163296 can be explained as originating from optically-thin shock-heated gas accreting onto the stellar surface along magnetic field lines. This would require a (dipole) magnetic field strength at the surface of HD 163296 of at least approximately 100 approximately G and perhaps as high as several kG.

Swartz, Douglas A.↗
NASA NTRS2005

X-Ray and Infrared Observations of Embedded Young Stars in NGC 2264

Images of the NGC 2264 star-forming region, which we have acquired with the XMM-Newton spacecraft, reveal strong X-ray emission from three deeply embedded (Av > 10 mag) young stellar objects in the vicinity of Allen's infrared source (AFGL 989 = IRS 1) and Castelaz & Grasdalen s infrared source (RNO-EW = IRS 2). Thermal plasma models for the brightest source in X-rays, located 11 southwest of Allen's star, yield a quasi-steady luminosity of Lx = 10 ergs s-1 and an extraordinarily high X-ray temperature of 100 MK. The high temperature is consistent with the presence of emission lines of Fe xxv and Fe xxvi at photon energies of 6.7 and 6.9 keV, respectively. An even higher temperature of nearly 140 MK was observed during the rise phase of a powerful impulsive X-ray flare of another young star in the IRS 2 region. Moderate-resolution near-infrared (1-4 um) spectra of the embedded objects, obtained at the NASA Infrared Telescope Facility, exhibit deep water ice absorption bands, as well as a variety of emission and absorption features of H I, CO, and both neutral and ionized metals.

Simon, Theordore↗
NASA NTRS2002

Information architecture for a planetary 'exploration web'

'Web services' is a common way of deploying distributed applications whose software components and data sources may be in different locations, formats, languages, etc. Although such collaboration is not utilized significantly in planetary exploration, we believe there is significant benefit in developing an architecture in which missions could leverage each others capabilities. We believe that an incremental deployment of such an architecture could significantly contribute to the evolution of increasingly capable, efficient, and even autonomous remote exploration.

middleware messaging IT infrastructure web service↗
NASA NTRS1986

Fused silica diaphragm module for high temperature pressure transducers

A high temperature pressure transducer and sensing apparatus to determine the deflection of the transducer diaphragm is disclosed. The pressure transducer utilizes a fused silica diaphragm (12) which is illuminated at selected locations by a coherent laser source (52) via optical fibers (38, 46). The light reflected by the diaphragm (12) forms interference fringe patterns which are focused by gradient index rod lenses (36) on the ends of optical fibers (40, 48) for transmission to a fringe counting circuit (54). By digital techniques, the fringe count is converted into a determination of diaphragm deflection.

Berthold, III, John W.↗
NASA NTRS2009

The Orbiting Astrophysical Spectrometer In Space (OASIS)

The Orbiting Astrophysical Spectrometer In Space (OASIS) is an Advanced Concept currently understudy at NASA as a mission for the next decade. The goal of the OASIS mission is to identify a local site or sites where galactic cosmic rays (GCR) originate and are accelerated. The mission will allow GCR data to be used to investigate how elements are made and distributed in the galaxy and to improve our understanding of supernovae and the nucleosynthesis of the heavy elements needed for life. OASIS consists of two instruments that provide complementary data on the location and nature of the source(s) through investigating the composition of ultraheavy nuclei and the energy spectrum of electrons. OASIS will measure the relative abundances in the actinide group to determine the age of the r-process material in GCRs. The presence of young r-process material would indicate that GCRs are a sample of the interstellar medium in OB associations. OASIS will follow the electron spectrum to its high-energy end. The energy where this spectrum ends will tell us the distance to the nearest GCR source(s). OASIS will look for spectral features and anisotropy in the high energy electron spectrum that are expected to appear when only a few of the nearest sources can contribute the electron flux. Possibly these measurements will lead to the identification of the nearest cosmic ray electron source.

Christl, Mark J.↗
NASA NTRS2012

DC and Structured Electric Fields Observed on the C/NOFS Satellite and Their Association with Longitude, Plasma Density, and Solar Activity

Observations of DC electric fields and associated E x B plasma drifts gathered by the Vector Electric Field Investigation (VEFI) on the Air Force Communication/Navigation Outage Forecasting System (C/NOFS) satellite are presented. We show statistical averages of the vector fields and resulting E x B plasma flows for the first three years of operations as a function of season, longitude, local time, and Fl 0.7 conditions. Magnetic field data from the VEFI science magnetometer are used to compute the plasma flows. Although typically displaying eastward and outward-directed fields during the day and westward and downward-directed fields at night, the data from DC electric field detector often reveal variations from this pattern that depend on longitude, solar activity, and plasma density. Clear "wave-4" tidal effects in both electric field components have been detected and will be presented. Zonal plasma drifts show a marked variation with solar activity and may be used as a proxy for neutral winds at night. Evidence for pre-reversal enhancements in the meridional drifts that depend on solar activity is present for some longitudes, and are corroborated by clear evidence in the plasma density data that the spacecraft journeyed below the F-peak during evenings when the rise in the ionosphere is most pronounced. In addition to DC electric fields, the data reveal considerable electric field structures at large scales (approx 100's of km) that are usually confined to the nightside. Although such electric field structures are typically associated with plasma density depletions and structures, what is surprising is the number of cases in which large amplitude, structured DC electric fields are observed without a significant plasma density counterpart structure, including their appearance at times when the ambient plasma density appears relatively quiescent. We investigate the mapping of structured electric fields along magnetic field lines from distant locations and consider tropospheric thunderstorm sources to explain some of the observations. The dependence of the structuring on season and solar activity will be reported and discussed.

Pfaff, Robert↗
NASA NTRS2006

Investigation of Post-Flight Solid Rocket Booster Thermal Protection System

After every Shuttle mission, the Solid Rocket Boosters (SRBs) are recovered and observed for missing material. Most of the SRB is covered with a cork-based thermal protection material (MCC-l). After the most recent shuttle mission, STS-114, the forward section of the booster appeared to have been impacted during flight. The darkened fracture surfaces indicated that this might have occurred early in flight. The scope of the analysis included microscopic observations to assess the degree of heat effects and locate evidence of the impact source as well as chemical analysis of the fracture surfaces and recovered foreign material using Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy/Energy Dispersive Spectroscopy. The amount of heat effects and presence of soot products on the fracture surface indicated that the material was impacted prior to SRB re-entry into the atmosphere. Fragments of graphite fibers found on these fracture surfaces were traced to slag inside the Solid Rocket Motor (SRM) that forms during flight as the propellant is spent and is ejected throughout the descent of the SRB after separation. The direction of the impact mark matches with the likely trajectory of SRBs tumbling prior to re-entry.

Nelson, Linda A.↗
NASA NTRS2014

Uncovering the Putative B-Star Binary Companion of the SN 1993J Progenitor

The Type IIb supernova (SN) 1993J is one of only a few stripped-envelope SNe with a progenitor star identified in pre-explosion images. SN IIb models typically invoke H envelope stripping by mass transfer in a binary system. For the case of SN 1993J, the models suggest that the companion grew to 22 solar mass and became a source of ultraviolet (UV) excess. Located in M81, at a distance of only 3.6 Mpc, SN 1993J offers one of the best opportunities to detect the putative companion and test the progenitor model. Previously published near-UV spectra in 2004 showed evidence for absorption lines consistent with a hot (B2 Ia) star, but the field was crowded and dominated by flux from the SN. Here we present Hubble Space Telescope Cosmic Origins Spectrograph and Wide-Field Camera 3 observations of SN 1993J from 2012, at which point the flux from the SN had faded sufficiently to potentially measure the UV continuum properties from the putative companion. The resulting UV spectrum is consistent with contributions from both a hot B star and the SN, although we cannot rule out line-of-sight coincidences.

Hubble Space Telescope Cosmic Origins Spectrograph↗
NASA NTRS2014

The Rise of SN 2014J in the Nearby Galaxy M 82

We report on the discovery of SN 2014J in the nearby galaxy M 82. Given its proximity, it offers the best opportunity to date to study a thermonuclear supernova over a wide range of the electromagnetic spectrum. Optical, near-IR and mid-IR observations on the rising lightcurve, orchestrated by the intermediate Palomar Transient Factory (iPTF), show that SN 2014J is a spectroscopically normal Type Ia supernova, albeit exhibiting high-velocity features in its spectrum and heavily reddened by dust in the host galaxy. Our earliest detections start just hours after the fitted time of explosion. We use high-resolution optical spectroscopy to analyze the dense intervening material and do not detect any evolution in the resolved absorption features during the lightcurve rise. Similarly to other highly reddened Type Ia supernovae, a low value of total-to-selective extinction, R (sub V) less than or approximately equal to 2, provides the best match to our observations. We also study pre-explosion optical and near-IR images from HST with special emphasis on the sources nearest to the SN location.

galaxy↗
NASA NTRS2013

The Scaling of Broadband Shock-Associated Noise with Increasing Temperature

A physical explanation for the saturation of broadband shock-associated noise (BBSAN) intensity with increasing jet stagnation temperature has eluded investigators. An explanation is proposed for this phenomenon with the use of an acoustic analogy. To isolate the relevant physics, the scaling of BBSAN peak intensity level at the sideline observer location is examined. The equivalent source within the framework of an acoustic analogy for BBSAN is based on local field quantities at shock wave shear layer interactions. The equivalent source combined with accurate calculations of the propagation of sound through the jet shear layer, using an adjoint vector Green's function solver of the linearized Euler equations, allows for predictions that retain the scaling with respect to stagnation pressure and allows for saturation of BBSAN with increasing stagnation temperature. The sources and vector Green's function have arguments involving the steady Reynolds- Averaged Navier-Stokes solution of the jet. It is proposed that saturation of BBSAN with increasing jet temperature occurs due to a balance between the amplication of the sound propagation through the shear layer and the source term scaling.

Miller, Steven A. E.↗
NASA NTRS2014

Probabilistic 21st and 22nd Century Sea-Level Projections at a Global Network of Tide-Gauge Sites

Sea-level rise due to both climate change and non-climatic factors threatens coastal settlements, infrastructure, and ecosystems. Projections of mean global sea-level (GSL) rise provide insufficient information to plan adaptive responses; local decisions require local projections that accommodate different risk tolerances and time frames and that can be linked to storm surge projections. Here we present a global set of local sea-level (LSL) projections to inform decisions on timescales ranging from the coming decades through the 22nd century. We provide complete probability distributions, informed by a combination of expert community assessment, expert elicitation, and process modeling. Between the years 2000 and 2100, we project a very likely (90% probability) GSL rise of 0.5–1.2 m under representative concentration pathway (RCP) 8.5, 0.4–0.9 m under RCP 4.5, and 0.3–0.8 m under RCP 2.6. Site-to-site differences in LSL projections are due to varying non-climatic background uplift or subsidence, oceanographic effects, and spatially variable responses of the geoid and the lithosphere to shrinking land ice. The Antarctic ice sheet (AIS) constitutes a growing share of variance in GSL and LSL projections. In the global average and at many locations, it is the dominant source of variance in late 21st century projections, though at some sites oceanographic processes contribute the largest share throughout the century. LSL rise dramatically reshapes flood risk, greatly increasing the expected number of “1-in-10” and “1-in-100” year events.

sea level↗