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

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

The Carriers of the Interstellar Unidentified Infrared Emission Features: Constraints from the Interstellar C-H Stretching Features at 3.2-3.5 Micrometers

The unidentified infrared emission (UIE) features at 3.3, 6.2, 7.7, 8.6, and 11.3 micrometer, commonly attributed to polycyclic aromatic hydrocarbon (PAH) molecules, have been recently ascribed to mixed aromatic/aliphatic organic nanoparticles. More recently, an upper limit of <9% on the aliphatic fraction (i.e., the fraction of carbon atoms in aliphatic form) of the UIE carriers based on the observed intensities of the 3.4 and 3.3 micrometer emission features by attributing them to aliphatic and aromatic C-H stretching modes, respectively, and assuming A_34./A_3.3~0.68 derived from a small set of aliphatic and aromatic compounds, where A_3.4 and A_3.3 are respectively the band strengths of the 3.4 micrometer aliphatic and 3.3 micrometer aromatic C-H bonds. To improve the estimate of the aliphatic fraction of the UIE carriers, here we analyze 35 UIE sources which exhibit both the 3.3 and 3.4 micrometer C-H features and determine I_3.4/I_3.3, the ratio of the power emitted from the 3.4 micrometer feature to that from the 3.3 micrometer feature. We derive the median ratio to be ~ 0.12. We employ density functional theory and second-order perturbation theory to compute A_3.4/A_3.3 for a range of methyl-substituted PAHs. The resulting A_3.4/A_3.3 ratio well exceeds 1.4, with an average ratio of ~1.76. By attributing the 3.4 micrometer feature exclusively to aliphatic C-H stretch (i.e., neglecting anharmonicity and superhydrogenation), we derive the fraction of C atoms in aliphatic form to be ~2%. We therefore conclude that the UIE emitters are predominantly aromatic.Comment: 14 pages, 5 figures, 1 table; accepted for publication in The Astrophysical Journa

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$_{2}$ 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 $\mu$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$^{4}$ were demonstrated.Comment: 6 pages, 3 figures + 2 suppl. figure

A Tale of Two Mysteries in Interstellar Astrophysics: The 2175 Angstrom Extinction Bump and Diffuse Interstellar Bands

The diffuse interstellar bands (DIBs) are ubiquitous absorption spectral features arising from the tenuous material in the space between stars -- the interstellar medium (ISM). Since their first detection nearly nine decades ago, over 400 DIBs have been observed in the visible and near-infrared wavelength range in both the Milky Way and external galaxies, both nearby and distant. However, the identity of the species responsible for these bands remains as one of the most enigmatic mysteries in astrophysics. An equally mysterious interstellar spectral signature is the 2175 Angstrom extinction bump, the strongest absorption feature observed in the ISM. Its carrier also remains unclear since its first detection 46 years ago. Polycyclic aromatic hydrocarbon (PAH) molecules have long been proposed as a candidate for DIBs as their electronic transitions occur in the wavelength range where DIBs are often found. In recent years, the 2175 Angstrom extinction bump is also often attributed to the \pi--\pi* transition in PAHs. If PAHs are indeed responsible for both the 2175 Angstrom extinction feature and DIBs, their strengths may correlate. We perform an extensive literature search for lines of sight for which both the 2175 Angstrom extinction feature and DIBs have been measured. Unfortunately, we found no correlation between the strength of the 2175 Angstrom feature and the equivalent widths of the strongest DIBs. A possible explanation might be that DIBs are produced by small free gas-phase PAH molecules and ions, while the 2175 Angstrom bump is mainly from large PAHs or PAH clusters in condensed phase so that there is no tight correlation between DIBs and the 2175 Angstrom bump.Comment: 45 pages, 3 figures, 4 tables, published in Ap

Aperiodic Quantum Random Walks

We generalize the quantum random walk protocol for a particle in a one-dimensional chain, by using several types of biased quantum coins, arranged in aperiodic sequences, in a manner that leads to a rich variety of possible wave function evolutions. Quasiperiodic sequences, following the Fibonacci prescription, are of particular interest, leading to a sub-ballistic wavefunction spreading. In contrast, random sequences leads to diffusive spreading, similar to the classical random walk behaviour. We also describe how to experimentally implement these aperiodic sequences.Comment: 4 pages and 4 figure