5,462 research outputs found
NMR Knight shifts and linewidths in the NiâPdâP and NiâPtâP metallic glasses: Composition and temperature dependences
NMR Knight shift and linewidth measurements are reported for the ^(31)P nuclei in the metallic glasses (Ni_(0.50)Pd_(0.50))100â_xP_x (where x=16 to 26.5) and (Ni_yPd_(1ây))_(80)P_(20) (where y=0.20 to 0.80), and both the ^(31)P and 195Pt nuclei in the metallic glass (Ni_yPt_(1ây))_(75)P_(25) (where y=0.20 to 0.68). The results are discussed in terms of the amorphous structure, electronic structure, and stability of transition metal + metalloid metallic glasses
Do topological models provide good information about vulnerability in electric power networks?
In order to identify the extent to which results from topological graph
models are useful for modeling vulnerability in electricity infrastructure, we
measure the susceptibility of power networks to random failures and directed
attacks using three measures of vulnerability: characteristic path lengths,
connectivity loss and blackout sizes. The first two are purely topological
metrics. The blackout size calculation results from a model of cascading
failure in power networks. Testing the response of 40 areas within the Eastern
US power grid and a standard IEEE test case to a variety of attack/failure
vectors indicates that directed attacks result in larger failures using all
three vulnerability measures, but the attack vectors that appear to cause the
most damage depend on the measure chosen. While our topological and power grid
model results show some trends that are similar, there is only a mild
correlation between the vulnerability measures for individual simulations. We
conclude that evaluating vulnerability in power networks using purely
topological metrics can be misleading
An inflight refill unit for replenishing research animal drinking water
This paper presents the design process and development approach for a method of maintaining sufficient quantities of water for research animals during a Shuttle mission of long duration. An inflight refill unit (IRU) consisting of two major subsystems, a fluid pumping unit (FPU) and a collapsible water reservoir (CWR), were developed. The FPU provides the system measurement and controls, pump, water lines, and plumbing necessary to collect water coming into the unit from the potable water system and pump it out into the RAHF drinking water tanks. The CWR is a Kevlar (TM) reinforced storage bladder connected to the FPU, which has a capacity of 6 liters in its expanded volume and functions to store the water collected from the potable water system, allowing for transport of the water back to the Spacelab where it is pumped into each of two research animal holding facilities. Additional components of the IRU system include the inlet and outlet fluid hoses, a power cable for providing 29V direct current spacecraft electrical power to the pump within the FPU, a tether system for the unit when in use in Spacelab, and an adapter for mating the unit to the orbiter waste collection system in order to dump excess water after use in Spacelab
A comparison of optical and radar measurements of mesospheric winds and tides
Optical measurements of mesospheric winds by FabryâPerot spectrometers, FPSs, at Mawson, 67.6°S 62.9°E, and Davis, 68.6°S 78.0°E, Antarctica are compared with similar measurements obtained using a spacedâantenna MF radar at Davis. The FPSs observed the OH emission. Different analysis procedures, used to determine the mean wind, and amplitude and phase of the semidiurnal tide, have been compared. At these latitudes the diurnal tide is weak and the semiâdiurnal tide, although highly variable in amplitude, is usually the dominant periodicity. When comparing the amplitude and phase of the semidiurnal tide good agreement is obtained between measurements by the two instruments
Bi-partite mode entanglement of bosonic condensates on tunneling graph
We study a set of spatial bosonic modes localized on a graph
The particles are allowed to tunnel from vertex to vertex by hopping along the
edges of We analyze how, in the exact many-body eigenstates of the
system i.e., Bose-Einstein condensates over single-particle eigenfunctions, the
bi-partite quantum entanglement of a lattice vertex with respect to the rest of
the graph depends on the topology of Comment: 3 Pages LaTeX, 2 Figures include
XMM-NEWTON Observations of Red AGN
XMM-Newton spectra of five red, 2MASS AGN, selected from a sample observed by
Chandra to be relatively X-ray bright and to cover a range of hardness ratios,
confirm the presence of substantial absorbing material in three sources with
optical classifications ranging from Type 1 to Type 2. A flat (hard), power law
continuum is observed in the other two. The combination of X-ray absorption and
broad optical emission lines suggests either a small (nuclear) absorber or a
favored viewing angle so as to cover the X-ray source but not the broad
emission line region (BELR). A soft excess is detected in all three Type 1
sources. We speculate that this may arise in an extended region of ionised gas,
perhaps linked with the polarised (scattered) optical light present in these
sources. The spectral complexity revealed by XMM-Newton emphasizes the
limitations of the low S/N \chandra data. The new results strengthen our
earlier conclusions that the observed X-ray continua of red AGN are unusually
hard at energies >2 keV. Their observed spectra are consistent with
contributing significantly to the missing hard/absorbed population of the
Cosmic X-ray Background (CXRB) although their intrinsic power law slopes are
typical of broad-line (Type 1) AGN (Gamma ~1.7-1.9). This suggests that the
missing X-ray-absorbed CXRB population may include Type 1 AGN/QSOs in addition
to the Type 2 AGN generally assumed.Comment: 29 page
Spitzer/MIPS Observations of Stars in the Beta Pictoris Moving Group
We present Multiband Imaging Photometer for Spitzer (MIPS) observations at 24
and 70 microns for 30 stars, and at 160 microns for a subset of 12 stars, in
the nearby (~30 pc), young (~12 Myr) Beta Pictoris Moving Group (BPMG). In
several cases, the new MIPS measurements resolve source confusion and
background contamination issues in the IRAS data for this sample. We find that
7 members have 24 micron excesses, implying a debris disk fraction of 23%, and
that at least 11 have 70 micron excesses (disk fraction of >=37%). Five disks
are detected at 160 microns (out of a biased sample of 12 stars observed), with
a range of 160/70 flux ratios. The disk fraction at 24 and 70 microns, and the
size of the excesses measured at each wavelength, are both consistent with an
"inside-out" infrared excess decrease with time, wherein the shorter-wavelength
excesses disappear before longer-wavelength excesses, and consistent with the
overall decrease of infrared excess frequency with stellar age, as seen in
Spitzer studies of other young stellar groups. Assuming that the infrared
excesses are entirely due to circumstellar disks, we characterize the disk
properties using simple models and fractional infrared luminosities. Optically
thick disks, seen in the younger TW Hya and eta Cha associations, are entirely
absent in the BPMG.
Additional flux density measurements at 24 and 70 microns are reported for
nine Tucanae-Horologium Association member stars. Since this is <20% of the
association membership, limited analysis on the complete disk fraction of this
association is possible.Comment: Accepted for Ap
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