46,407 research outputs found
Buffer occupancy of statistical multiplexers with periodic interchangeable traffic in ATM networks
In this paper we analyze the buffer occupancy in a statistical multiplexer in ATM networks for a special type of traffic, namely, periodic interchangeable (PI) traffic. Certain generalized Ballot theorem is applied to analyze the problem. Explicit formulas for the expected buffer occupancy are derived
Biased amino acid composition in warm-blooded animals
Among eubacteria and archeabacteria, amino acid composition is correlated with habitat temperatures. In particular, species living at high temperatures have proteins enriched in the amino acids E-R-K and depleted in D-N-Q-T-S-H-A. Here, we show that this bias is a proteome-wide effect in prokaryotes, and that the same trend is observed in fully sequenced mammals and chicken compared to cold-blooded vertebrates (Reptilia, Amphibia and fish). Thus, warm-blooded vertebrates likely experienced genome-wide weak positive selection on amino acid composition to increase protein thermostability
Electronic structure induced reconstruction and magnetic ordering at the LaAlOSrTiO interface
Using local density approximation (LDA) calculations we predict
GdFeO-like rotation of TiO octahedra at the -type interface between
LaAlO and SrTiO. The narrowing of the Ti bandwidth which results
means that for very modest values of , LDA calculations predict charge
and spin ordering at the interface. Recent experimental evidence for magnetic
interface ordering may be understood in terms of the close proximity of an
antiferromagnetic insulating ground state to a ferromagnetic metallic excited
state
Supernova-driven outflows and chemical evolution of dwarf spheroidal galaxies
We present a general phenomenological model for the metallicity distribution
(MD) in terms of [Fe/H] for dwarf spheroidal galaxies (dSphs). These galaxies
appear to have stopped accreting gas from the intergalactic medium and are
fossilized systems with their stars undergoing slow internal evolution. For a
wide variety of infall histories of unprocessed baryonic matter to feed star
formation, most of the observed MDs can be well described by our model. The key
requirement is that the fraction of the gas mass lost by supernova-driven
outflows is close to unity. This model also predicts a relationship between the
total stellar mass and the mean metallicity for dSphs in accord with properties
of their dark matter halos. The model further predicts as a natural consequence
that the abundance ratios [E/Fe] for elements such as O, Mg, and Si decrease
for stellar populations at the higher end of the [Fe/H] range in a dSph. We
show that for infall rates far below the net rate of gas loss to star formation
and outflows, the MD in our model is very sharply peaked at one [Fe/H] value,
similar to what is observed in most globular clusters. This suggests that
globular clusters may be end members of the same family as dSphs.Comment: 8 pages, 3 figures, to be published in the Proceedings of the
National Academy of Science
Prediction of thickness limits of ideal polar ultrathin films
Competition between electronic and atomic reconstruction is a constantly
recurring theme in transition-metal oxides. We use density functional theory
calculations to study this competition for a model system consisting of a thin
film of the polar, infinite-layer structure ACuO2 (A=Ca, Sr, Ba) grown on a
nonpolar, perovskite SrTiO3 substrate. A transition from the bulk planar
structure to a chain-type thin film accompanied by substantial changes to the
electronic structure is predicted for a SrCuO2 film fewer than five unit cells
thick. An analytical model explains why atomic reconstruction becomes more
favorable than electronic reconstruction as the film becomes thinner, and
suggests that similar considerations should be valid for other polar films
Numerical Study of the Two-Species Vlasov-Amp\`{e}re System: Energy-Conserving Schemes and the Current-Driven Ion-Acoustic Instability
In this paper, we propose energy-conserving Eulerian solvers for the
two-species Vlasov-Amp\`{e}re (VA) system and apply the methods to simulate
current-driven ion-acoustic instability. The algorithm is generalized from our
previous work for the single-species VA system and Vlasov-Maxwell (VM) system.
The main feature of the schemes is their ability to preserve the total particle
number and total energy on the fully discrete level regardless of mesh size.
Those are desired properties of numerical schemes especially for long time
simulations with under-resolved mesh. The conservation is realized by explicit
and implicit energy-conserving temporal discretizations, and the discontinuous
Galerkin (DG) spatial discretizations. We benchmarked our algorithms on a test
example to check the one-species limit, and the current-driven ion-acoustic
instability. To simulate the current-driven ion-acoustic instability, a slight
modification for the implicit method is necessary to fully decouple the split
equations. This is achieved by a Gauss-Seidel type iteration technique.
Numerical results verified the conservation and performance of our methods
Etching-dependent reproducible memory switching in vertical SiO2 structures
Vertical structures of SiO sandwiched between a top tungsten electrode
and conducting non-metal substrate were fabricated by dry and wet etching
methods. Both structures exhibit similar voltage-controlled memory behaviors,
in which short voltage pulses (1 s) can switch the devices between high-
and low-impedance states. Through the comparison of current-voltage
characteristics in structures made by different methods, filamentary conduction
at the etched oxide edges is most consistent with the results, providing
insights into similar behaviors in metal/SiO/metal systems. High ON/OFF ratios
of over 10 were demonstrated.Comment: 6 pages, 3 figures + 2 suppl. figure
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