3,868 research outputs found
Geometry of random interactions
It is argued that spectral features of quantal systems with random
interactions can be given a geometric interpretation. This conjecture is
investigated in the context of two simple models: a system of randomly
interacting d bosons and one of randomly interacting fermions in a j=7/2 shell.
In both examples the probability for a given state to become the ground state
is shown to be related to a geometric property of a polygon or polyhedron which
is entirely determined by particle number, shell size, and symmetry character
of the states. Extensions to more general situations are discussed
Evidence for a lava lake on Mt. Michael volcano, Saunders Island (South Sandwich Islands) from Landsat, Sentinel-2 and ASTER satellite imagery
Mt. Michael is an active stratovolcano on Saunders Island in the South Sandwich Islands; a remote, oceanic island arc in the southern Atlantic Ocean, bordering the Southern Ocean. The arc contains the only active volcanoes in the South Georgia and South Sandwich Islands British Overseas Territory, yet little is known of their activity. Despite lava lakes being extremely rare with only a few global examples, previous analyses of satellite AVHRR imagery of Mt. Michael in the 1990s showed persistent thermal anomalies not associated with magma overflowing the crater. This suggested the existence of a lava lake inside Mt. Michael's crater. However, their study relied on 1 km resolution imagery, and there have been no long-term investigations to determine if this is a persistent feature
Enhanced prediction and prevention of drug-induced torsades de pointes
nrpages: 252status: publishe
Vapour cloud explosions in a long congested region involving methane/hydrogen mixtures
A series of large scale vapour cloud explosions in a long congested region were conducted using methane/hydrogen mixtures. The congested region measured 3 m Ă— 3 m Ă— 18 m long and was preceded by a confined region which allowed an explosion flame with some initial flame speed and turbulence to be generated which then entered the congested region. During the experiments the flame speed and explosion overpressure were measured through the congested region. The hydrogen content in the methane/hydrogen mixture was varied from 0 to 50% by volume. A key objective was to determine factors that could lead to continued flame acceleration through the congested region, such as the hydrogen concentration, the initial flame speed entering the congestion and the level of congestion. The results are reported together with some detailed observations of the complex nature of pressure traces produced by explosion events of this type
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Latent interface traps and 1/f noise in irradiated MOS devices
A delayed increase in 1/f noise is observed for pMOS transistors showing latent radiation-induced interface-trap buildup. The latent interface traps and increased noise appear to result from the same thermally activated process, likely involving hydrogen
Continuum-particle hybrid coupling for mass, momentum and energy transfers in unsteady fluid flow
The aim of hybrid methods in simulations is to communicate regions with
disparate time and length scales. Here, a fluid described at the atomistic
level within an inner region P is coupled to an outer region C described by
continuum fluid dynamics. The matching of both descriptions of matter is made
across an overlapping region and, in general, consists of a two-way coupling
scheme (C->P and P->C) which conveys mass, momentum and energy fluxes. The
contribution of the hybrid scheme hereby presented is two-fold: first it treats
unsteady flows and, more importantly, it handles energy exchange between both C
and P regions. The implementation of the C->P coupling is tested here using
steady and unsteady flows with different rates of mass, momentum and energy
exchange. In particular, relaxing flows described by linear hydrodynamics
(transversal and longitudinal waves) are most enlightening as they comprise the
whole set of hydrodynamic modes. Applying the hybrid coupling scheme after the
onset of an initial perturbation, the cell-averaged Fourier components of the
flow variables in the P region (velocity, density, internal energy, temperature
and pressure) evolve in excellent agreement with the hydrodynamic trends. It is
also shown that the scheme preserves the correct rate of entropy production. We
discuss some general requirements on the coarse-grained length and time scales
arising from both the characteristic microscopic and hydrodynamic scales.Comment: LaTex, 12 pages, 9 figure
PCV94 ANTICOAGULANT USE, THE PREVALENCE OF BRIDGING AND RELATION TO LENGTH OF STAY AMONG HOSPITALIZED PATIENTS WITH NON-VALVULAR ATRIAL FIBRILLATION
Reevaluation of the role of nuclear uncertainties in experiments on atomic parity violation with isotopic chains
In light of new data on neutron distributions from experiments with
antiprotonic atoms [ Trzcinska {\it et al.}, Phys. Rev. Lett. 87, 082501
(2001)], we reexamine the role of nuclear-structure uncertainties in the
interpretation of measurements of parity violation in atoms using chains of
isotopes of the same element. With these new nuclear data, we find an
improvement in the sensitivity of isotopic chain measurements to ``new
physics'' beyond the standard model. We compare possible constraints on ``new
physics'' with the most accurate to date single-isotope probe of parity
violation in the Cs atom. We conclude that presently isotopic chain experiments
employing atoms with nuclear charges Z < 50 may result in more accurate tests
of the weak interaction.Comment: 6 pages, 1 fig., submitted to Phys. Rev.
Variable Hard-X-Ray Emission from the Candidate Accreting Black Hole in Dwarf Galaxy Henize 2-10
We present an analysis of the X-ray spectrum and long-term variability of the nearby dwarf starburst galaxy Henize 2–10. Recent observations suggest that this galaxy hosts an actively accreting black hole (BH) with mass ~106 . The presence of an active galactic nucleus (AGN) in a low-mass starburst galaxy marks a new environment for AGNs, with implications for the processes by which "seed" BHs may form in the early universe. In this paper, we analyze four epochs of X-ray observations of Henize 2–10, to characterize the long-term behavior of its hard nuclear emission. We analyze observations with Chandra from 2001 and XMM-Newton from 2004 and 2011, as well as an earlier, less sensitive observation with ASCA from 1997. Based on a detailed analysis of the source and background, we find that the hard (2–10 keV) flux of the putative AGN has decreased by approximately an order of magnitude between the 2001 Chandra observation and exposures with XMM-Newton in 2004 and 2011. The observed variability confirms that the emission is due to a single source. It is unlikely that the variable flux is due to a supernova or ultraluminous X-ray source, based on the observed long-term behavior of the X-ray and radio emission, while the observed X-ray variability is consistent with the behavior of well-studied AGNs
Simulations of metastable decay in two- and three-dimensional models with microscopic dynamics
We present a brief analysis of the crossover phase diagram for the decay of a
metastable phase in a simple dynamic lattice-gas model of a two-phase system.
We illustrate the nucleation-theoretical analysis with dynamic Monte Carlo
simulations of a kinetic Ising lattice gas on square and cubic lattices. We
predict several regimes in which the metastable lifetime has different
functional forms, and provide estimates for the crossovers between the
different regimes. In the multidroplet regime, the
Kolmogorov-Johnson-Mehl-Avrami theory for the time dependence of the
order-parameter decay and the two-point density correlation function allows
extraction of both the order parameter in the metastable phase and the
interfacial velocity from the simulation data.Comment: 14 pages, 4 figures, submitted to J. Non-Crystalline Solids,
conference proceeding for IXth International Conference on the Physics of
Non-Crystalline Solids, October, 199
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