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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Studies Of Single-Event-Upset Models

Report presents latest in series of investigations of "soft" bit errors known as single-event upsets (SEU). In this investigation, SEU response of low-power, Schottky-diode-clamped, transistor/transistor-logic (TTL) static random-access memory (RAM) observed during irradiation by Br and O ions in ranges of 100 to 240 and 20 to 100 MeV, respectively. Experimental data complete verification of computer model used to simulate SEU in this circuit.

Zoutendyk, J. A.↗
NASA NTRS1988

Infrared Attenuation Of Thallium Bromoiodide Fibers

Report presents measurements of attenuation of infrared signals in unclad 381-micrometer-diameter optical fibers of thallium bromoiodide. Measurements of attentuation in TI(Br,I) fibers in wavelength ranges of 1.2 to 3.4 micrometer and 3 to 11 micrometer compare with those of two other groups of researchers.

Goebel, John↗
NASA NTRS1987

Ureilites - Trace element clues to their origin

The question of the origin of ureilites was reexamined using new data obtained by radiochemical NAA for Ag, Au, Bi, Br, Cd, Cs, Ge, In, Ir, Ni, Pd, Os, Rb, Re, Sb, Se, Te, Tl, U, and Zn in two vein separates from Haveroe and Kenna and a bulk sample of Kenna. Vein material was found to be enriched in all elements analyzed, except Zn, and to account for most of the carbon, noble gases, and, presumably, siderophiles in the meteorite. The results support the earlier interpretation of Higuchi et al. (1976) on the composition of ureilite parent body (similar to C3V or H3, but not C3O chondrites).

Janssens, Marie-Josee↗
NASA NTRS1988

H2 and H I emission line imaging of the ring nebula (NGC 6720)

Infrared emission-line images of the v = 1-0 S(1) transition of molecular hydrogen and Br-gamma recombination line of atomic hydrogen which cover the entire extent of NGC 6720, the Ring nebula. The maps presented here are the highest angular resolution images of these transitions yet produced for this object and have very low relative positional uncertainty. As a result, the spatial stratification of the ionized and shocked molecular zones within the nebula is clearly resolved. These data, and data from the Infrared Astronomical Satellite, are used to determine the H2, H I, and dust mass within the nebula. Energy sources for the dust heating, formation and destruction of the H2, and overall evolution of the nebula are also discussed.

Greenhouse, Matthew A.↗
NASA NTRS1988

Hydrogen line and continuum emission in young stellar objects. I - Excitation model

Two mechanisms that populate the n = 2 level of hydrogen after the Lyman continuum is depleted are identified. They are ionization of N I from its excited states, followed by charge-exchange between N II and H I, and Ly-beta line wing absorption. Both processes involve absorption of the sub-Lyman continuum between 11 and 13.6 eV. With population in level n = 2 thus maintained, the strong Brackett line fluxes observed are then produced as a result of Balmer photoionization. The magnitude of the sub-Lyman continuum dictates the fraction of Balmer continuum that will be absorbed. Numerical calculations for four young stellar objects with luminosity ranging from 10 to 10,000 solar are performed, and it is concluded that this two-step process of sub-Lyman continuum absorption followed by Balmer photoionization can account for the great majority of observed Brackett line fluxes. The location and mass of the emitting as as determined from the Brackett line fluxes are reported. The Br-alpha luminosity is calculated as a function of the mass loss rate.

Kwan, John↗
NASA NTRS1987

Water on Mars

It is reported that the SNC meteorites are a factor of 2 richer in moderately volatile elements (Na, K, P, etc.) and some volatile elements (Cl, Br, I, S) compared to the Earth and Mars. It is proposed that Mars accreted homogeneously, with the result that all the water except trace amounts (on reaction with metallic Fe) was converted to H(sub 2) and escaped. This model predicts a total Mars H(sub 2)O inventory of 18 ppm (equivalent to an ocean 80 m deep on the planet), and a value for Earth of 300 ppm, close to the actual abundance.

Waenke, H.↗
NASA NTRS1988

Nonaqueous chemical etch for YBa2Cu3O(7-x)

A nonaqueous chemical etch, with Br as the active ingredient, is described which removes the insulating hydroxides and carbonates that form on high-temperature superconductor surfaces as a result of atmospheric exposure. X-ray photoemission spectra have been recorded before and after etching YBa2Cu3O(7-x) films. It is found that, after the etch, the high binding energy O 1s and Ba 3d peaks associated with surface contaminants are greatly reduced, the Y:Ba:Cu ratio is close to the expected 1:2:3, and the oxidation state of the Cu(2+) is not affected. The resistance of an etched film reaches zero at 78 K, compared to 81 K for a similar unetched film. The suitability of other nonaqueous halogen-based etches is discussed, as is the applicability of this etch to other high-Tc superconductors.

Vasquez, R. P.↗
NASA NTRS1988

Comparison of the degradation effects of heavy ion, electron, and cobalt-60 irradiation in an advanced bipolar process

Experimental measurements are reported of the degradation effects of high-energy particles (heavy Br ions and electrons) and Co-60 gamma-rays on the current gain of minimum-geometry bipolar transistors made from an advanced process. The data clearly illustrate the total-ionizing-dose vs particle-fluence behavior of this bipolar transistor produced by an advanced process. In particular, bulk damage from Co-60 gamma rays in bipolar transistors (base transport factor degradation) and surface damage in bipolar transistors from ionizing radiation (emitter-efficiency degradation) have been observed. The true equivalence between various types of radiation for this process technology has been determined on the basis of damage from the log K1 intercepts.

Zoutendyk, John A.↗
NASA NTRS1989

Hydrogen line and continuum emission in young stellar objects. II - Theoretical results and observational constraints

Theoretical results for H I emission from YSOs are compared with available observations. IR line and radio continuum properties have been gathered for 29 objects that include a number of T Tau stars, several emission-line stars with IR excesses, and many heavily obscured luminous YSOs. The present excitation model can account for the observed Brackett line and radio continuum fluxes of YSOs with luminosities of 20-100,000 solar luminosities. It is argued that the observed Br-alpha line and 6-cm free-free continuum emissions are best explained in terms of a core-halo structure. The small core (ranging from r less than about 30 AU for a 10,000-solar luminosity YSO to r less than about 0.2 AU for a 10-solar luminosity YSO) is responsible for generating the strong IR line fluxes, while the surrounding diffuse halo dominates the 6-cm emission.

Alonso-Costa, Jose L.↗
NASA NTRS1989

Nonaqueous chemical depth profiling of YBa2Cu3O(7-x)

A nonaqueous solution of Br in absolute ethanol (EtOH) has recently been reported to be effective at removing nonsuperconducting surface species from YBa2Cu3O(7-x) films, leaving the surface close to the ideal stoichiometry. This same etchant is shown here to be an effective bulk etchant in chemical depth profiling through 1-micron-thick films. The Cu remains in the 2 + oxidation state and the stoichiometry, as determined by X-ray photoelectron spectroscopy, is close to ideal and nearly constant throughout the profile, indicating the absence of any large preferential etching effects. The reaction of YBa2Cu3O(7-x) films with HF/EtOH, HCl/EtOH, and I/EtOH solutions is also reported.

Vasquez, R. P.↗
NASA NTRS1989

An infrared study of starbursts in the interacting galaxy pair Arp 299 (NGC 3690+IC 694)

Extensive infrared observations have been obtained of the three active regions in Arp 299. Multiaperture JHK photometry reveals that the colors of the three regions are totally different from each other, and that there are very red nuclei smaller than 4 arcsec in two of them. Multiaperture spectroscopy of the Br-gamma and the shock-excited H2 lines shows that both the atomic and molecular lines are spatially extended, indicating that Arp 299 is undergoing an active episode of star formation not only in its nuclei but also well outside of them. Although there is some evidence that suggests the presence of a compact, active galactic nucleus, a simple starburst model can explain the bolometric luminosities, production rates of ionizing photons, and H24 line luminosities of each active region in Arp 299. However, each starburst cannot last longer than 10 to the 8th yr.

Nakagawa, Takao↗
NASA NTRS1989

Spectroscopic images of NGC 7027 in the near-infrared dust emission features

Isophote maps derived from spatially resolved moderate spectral resolution images of the planetary nebula NGC 7027 in the 3.28-micron and 3.4-micron 'unidentified' emission features, and in the Br-alpha hydrogen recombination line are presented. Comparison of these images clearly shows that the 3.28-micron emission is spatially more extended than the ionized gas. Analysis and modeling of the spatial distribution of the 3.28-micron feature strength suggest that roughly equal amounts of feature emission appear to come from within the H II region and from a shell outside the H II region. The spatial distribution of the 3.4-micron feature emission is found to be similar to that of the 3.28-micron feature emission.

Woodward, C. E.↗
NASA NTRS1989

Synthesis of organic salts with large second-order optical nonlinearities

The variation of the anion counterion in the presently formulated organic salts, whose cation possesses large molecular hyperpolarizability, will in many cases yield materials with large powder second-harmonic generation efficiencies. The highest such efficiency is three orders of magnitude greater than that of the urea used as a reference compound. It is demonstrated that such nonconventional donors as Br(-) and the pyrenyl moiety can be incorporated into molecules which, in the requisite crystallographic environment, will exhibit substantial bulk susceptibilities.

Marder, Seth R.↗
NASA NTRS1989

Trace element abundance determinations by Synchrotron X Ray Fluorescence (SXRF) on returned comet nucleus mineral grains

Trace element analyses were performed on bulk cosmic dust particles by Proton Induced X Ray Emission (PIXE) and Synchrotron X Ray Fluorescence (SXRF). When present at or near chondritic abundances the trace elements K, Ti, Cr, Mn, Cu, Zn, Ga, Ge, Se, and Br are presently detectable by SXRF in particles of 20 micron diameter. Improvements to the SXRF analysis facility at the National Synchrotron Light Source presently underway should increase the range of detectable elements and permit the analysis of smaller samples. In addition the Advanced Photon Source will be commissioned at Argonne National Laboratory in 1995. This 7 to 8 GeV positron storage ring, specifically designed for high-energy undulator and wiggler insertion devices, will be an ideal source for an x ray microprobe with one micron spatial resolution and better than 100 ppb elemental sensitivity for most elements. Thus trace element analysis of individual micron-sized grains should be possible by the time of the comet nucleus sample return mission.

Flynn, G. J.↗
NASA NTRS1989

The measurement of trace elements in interplanetary dust and cometary particles by ultra-high sensitivity INAA

Today the major elemental composition of interplanetary dust particles (IDPs) is routinely determined in many laboratories. These and mineralogical studies have revealed the presence of at least two major types of IDPs, chondritic and refractory. Preliminary results of a successful attempt to determine abundances of a large suite of trace elements from both chondritic and refractory IDPs are reported. The analytical procedure can be used in the grain-by-grain analysis of returned cometary samples. Chondritic and refractory IDPs are characterized by standard scanning electron microscopy and energy dispersive x ray spectroscopy (SEM-EDX) techniques. With this system, detection limits for many elements are well below picogram levels, and some approach femtogram levels. This technique is non-destructive, although some sample handling is required, so particles can be analyzed by other techniques after instrument neutron activation analysis (INAA) is completed. Data is presently being reduced from the analyses of 7 IDPs. These are U2015E10, U2015F1, W7029-A2, W7029-A3, W7013A8, LACl (all chondritic) and 705 (refractory). So far, 17 different major and trace elements were detected and measured in these particles, including rare earths and some very volatile elements (Br and Zn).

Zolensky, M. E.↗
NASA NTRS1989

Mapping and spectroscopy of the 3.3 microns feature in Orion

The results of spectroscopy of the 3.3 microns feature, H2 emission, and Br alpha, obtained in a spatial cut across the Orion ionization front are presented. The spatial distribution of the 3.3 microns feature peaks between the ionization front and the H2 peak are observed. The shape of the 3.3 microns feature observed at high spectral resolution shows no changes in regions of varying ultraviolet flux and density. The results are discussed in terms of current models for the 3.3 microns emission feature.

Sellgren, K.↗
NASA NTRS1990

The 3.3 micron feature, H2, and ionized gas in the Orion bar

The results of spectroscopy of the 3.3 micron feature, H2 emission, P-alpha, and Br-alpha, obtained along a line perpendicular to the Orion ionization front, are presented. The intensity of the 3.3 micron feature reaches a maximum between the ionization front and the H2 peak. The 3.33 micron spatial distribution appears to be due to destruction of the emitting material within the H II region and extinction of the exciting radiation between the edge of the H II region and the H2 peak, resulting in a maximum between the ionization front and the H2 peak. The H2 peak is consistent with either being due to a shock front or being due to UV-pumped fluorescence from dense clumps of H2. The width of the 3.3 micron feature observed at high spectral resolution is constant in regions of varying UV flux. It is suggested that the strength of the UV field is not the cause of the variations in the 3.3 micron feature width observed in other sources, but rather that these variations are caused by a compositional change related to the age of the emitting material.

Sellgren, K.↗
NASA NTRS1990

A near-infrared spectroscopic study of the starburst core of M82

Near-IR spectroscopy of the M82 starburst core is presented, including complete J, H, and K band spectra with a resolution of 0.0035-micron for the inner 60 pc of the galaxy. Also, spatial profiles along the starburst ridge are presented for Br-gamma, molecular hydrogen, and forbidden Fe II line fluxes. Emission from shocked molecular hydrogen is detected from the core of M82. The distribution of features across the starburst disk are mapped to study the relationships between spectral diagnostics. The observations are used to test the appropriateness of single-beam, aggregate models for studying the physical conditions in starbursts.

Lester, D. F.↗