7,167 research outputs found
Evaluation of performance impairment by spacecraft contaminants
The environmental contaminants (isolated as off-gases in Skylab and Apollo missions) were evaluated. Specifically, six contaminants were evaluated for their effects on the behavior of juvenile baboons. The concentrations of contaminants were determined through preliminary range-finding studies with laboratory rats. The contaminants evaluated were acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), trichloroethylene (TCE), heptane and Freon 21. When the studies of the individual gases were completed, the baboons were also exposed to a mixture of MEK and TCE. The data obtained revealed alterations in the behavior of baboons exposed to relatively low levels of the contaminants. These findings were presented at the First International Symposium on Voluntary Inhalation of Industrial Solvents in Mexico City, June 21-24, 1976. A preprint of the proceedings is included
Magnetic confinement of the superconducting condensate in superconductor/ferromagnet hybrid composites
The influence of an inhomogeneous magnetic field on the magnetoresistance of
thin Al films, used in different superconductor/ferromagnet hybrids, has been
investigated. Two contrasting magnetic textures with out-of-plane magnetization
are explored, namely (i) a plain film in a multidomain state and (ii) an array
of micro-sized dots. The stray fields of the ferromagnetic structures confine
the superconducting condensate and, accordingly, modify the condition for the
nucleation of superconductivity. By switching between different magnetic states
of the ferromagnet, this confinement can be tuned at will, hereby reversibly
changing the dependence of the critical temperature Tc on an external magnetic
field H. In particular, the continuous evolution from a conventional linear
Tc(H) dependence with a single maximum to a reentrant superconducting phase
boundary with multiple Tc peaks has been demonstrated
Peanut-shaped bulges in face-on disk galaxies
We present high resolution absorption-line spectroscopy of 3 face-on
galaxies, NGC 98, NGC 600, and NGC 1703 with the aim of searching for
box/peanut (B/P)-shaped bulges. These observations test and confirm the
prediction of Debattista et al. (2005) that face-on B/P-shaped bulges can be
recognized by a double minimum in the profile of the fourth-order Gauss-Hermite
moment h_4. In NGC 1703, which is an unbarred control galaxy, we found no
evidence of a B/P bulge. In NGC 98, a clear double minimum in h_4 is present
along the major axis of the bar and before the end of the bar, as predicted. In
contrast, in NGC 600, which is also a barred galaxy but lacks a substantial
bulge, we do not find a significant B/P shape.Comment: 4 pages, 1 figure. To appear in "Tumbling, twisting, and winding
galaxies: Pattern speeds along the Hubble sequence", E. M. Corsini and V. P.
Debattista (eds.), Memorie della Societa` Astronomica Italian
Shot Noise Enhancement in Resonant Tunneling Structures in a Magnetic Field
We have observed that the shot noise of tunnel current, I, in
GaSb-AlSb-InAs-AlSb-GaSb double-barrier structure under a magnetic field can
exceed 2qI. The measurements were done at T=4K in fields up to 5T parallel to
the current. The noise enhancement occurred at each of the several
negative-differential conductance regions induced by the tunneling of holes
through Landau levels in the InAs quantum well. The amount of the enhancement
increased with the strength of the negative conductance and reached values up
to 8qI. These results are explained qualitatively by fluctuations of the
density of states in the well, but point out the need for a detailed theory of
shot noise enhancement in resonant tunneling devices.Comment: 4 pages, RevTex, 3 figure
Evaluation of the CNS and cardiovascular effects of prolonged exposure to bromotrifluromethane (CBrF3)
The proposed use of bromotrifluoromethane (CBrF3) as a fire extinguishant in aircraft, spacecraft and submarines has stimulated increasing interest and research in the toxicological properties of this compound. In a spacecraft, because of its unique recirculating life support system, the introduction of CBrF3 by leakage or intentional discharge, will result in continuous exposure of crewman to low concentrations of this compound for periods of up to 7 days, or possibly even longer. The effects of low concentrations of CBrF3, under continuous exposure conditions, on the CNS and cardiovascular systems of animals to enable an assessment of these risks were investigated
Shot noise of large charge quanta in superconductor/semiconductor/superconductor junctions
We have found experimentally that the noise of ballistic electron transport
in a superconductor/semiconductor/superconductor junction is enhanced relative
to the value given by the general relation, S_V=2eIR^2coth(eV/2kT), for two
voltage regions in which this expression reduces to its thermal and shot noise
limits. The noise enhancement is explained by the presence of large charge
quanta, with effective charge q*=(1+2Delta/eV)e, that generate a noise spectrum
S_V=2q*IR^2, as predicted in Phys. Rev. Lett. 76, 3814 (1996). These charge
quanta result from multiple Andreev reflections at each junction interface,
which are also responsible for the subharmonic gap structure observed in the
voltage dependence of the junction's conductance.Comment: 5 pages, 5 figures, submitted to Physical Review B as a Rapid
Communication. v2 author name in reference corrected. v3 added references. v4
clarifications in the text and reference added thanks to C. Urbin
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