Dual phononic and photonic band gaps in a periodic array of pillars deposited on a thin plate

We study theoretically the simultaneous existence of phononic and photonic band gaps in a periodic array of silicon pillars deposited on a homogeneous thin silica plate. Several lattices, namely, square, triangular, and honeycomb are investigated for a wide range of geometrical parameters. We discuss the most suitable cases for dual phononic-photonic band gaps, especially in comparison to the more conventional structures constituted by a periodic array of holes in a membrane

Avalanche spatial structure and multivariable scaling functions: Sizes, heights, widths, and views through windows

We introduce a systematic method for extracting multivariable universal scaling functions and critical exponents from data. We exemplify our insights by analyzing simulations of avalanches in an interface using simulations from a driven quenched Kardar-Parisi-Zhang (qKPZ) equation. We fully characterize the spatial structure of these avalanches-we report universal scaling functions for size, height, and width distributions, and also local front heights. Furthermore, we resolve a problem that arises in many imaging experiments of crackling noise and avalanche dynamics, where the observed distributions are strongly distorted by a limited field of view. Through artificially windowed data, we show these distributions and their multivariable scaling functions may be written in terms of two control parameters: the window size and the characteristic length scale of the dynamics. For the entire system and the windowed distributions we develop accurate parametrizations for the universal scaling functions, including corrections to scaling and systematic error bars, facilitated by a novel software environment SloppyScaling

The effect of the spin-orbit interaction on the band gap of half-metals

The spin-orbit interaction can cause a nonvanishing density of states (DOS) within the minority-spin band gap of half-metals around the Fermi level. We examine the magnitude of the effect in Heusler alloys, zinc-blende half metals and diluted magnetic semiconductors, using first-principles calculations. We find that the ratio of spin-down to spin-up DOS at the Fermi level can range from below 1% (e.g. 0.5% for NiMnSb) over several percents (4.2% for (Ga,Mn)As) to 13% for MnBi.Comment: 5 pages, 3 figure

Surface Half-Metallicity of CrAs in the Zinc-Blende Structure

The development of new techniques such as the molecular beam epitaxy have enabled the growth of thin films of materials presenting novel properties. Recently it was made possible to grow a CrAs thin-film in the zinc-blende structure. In this contribution, the full-potential screened KKR method is used to study the electronic and magnetic properties of bulk CrAs in this novel phase as well as the Cr and As terminated (001) surfaces. Bulk CrAs is found to be half-ferromagnetic for all three GaAs, AlAs and InAs experimental lattice constants with a total spin magnetic moment of 3 $\mu_B$. The Cr-terminated surface retains the half-ferromagnetic character of the bulk, while in the case of the As-termination the surface states destroy the gap in the minority-spin band.Comment: 4 pages, 2 figures, new text, new titl

Appearance of Half-Metallicity in the Quaternary Heusler Alloys

I report systematic first-principle calculations of the quaternary Heusler alloys like Co$_2$[Cr$_{1-x}$Mn$_x$]Al, Co$_2$Mn[Al$_{1-x}$Sn$_x$] and [Fe$_{1-x}$Co$_x$]$_2$MnAl. I show that when the two limiting cases (x=0 or 1) correspond to a half-metallic compound, so do the intermediate cases. Moreover the total spin moment $M_t$ in $\mu_B$ scales linearly with the total number of valence electrons $Z_t$ (and thus with the concentration $x$) following the relation $M_t=Z_t-24$, independently of the origin of the extra valence electrons, confirming the Slater-Pauling behavior of the normal Heusler alloys. Finally I discuss in all cases the trends in the atomic projected DOSs and in the atomic spin moments.Comment: 4 pages, 3 figures, 2 Table

Smoothed particle hydrodynamics (SPH) model for coupled analysis of a damaged ship with internal sloshing in beam seas

The flooding of a damaged ship in waves is a complex process, often coupled with the internal and external liquid motion together with the ship hull motion. Paramount to the operation safety, in order to improve the prediction accuracy of ship motion during the flooding process, the strip theory is applied to study the dynamic response of the damaged ship in beam seas; a smoothed particle hydrodynamics (SPH) model is developed to consider the coupling effects of various factors including internal sloshing of intact cabins and damaged cabins and external waves. The numerical wave tank with a perfectly matched layer absorbing boundary condition is established and validated by the experimental results. The detailed sensitivity study is carried out focusing on the effects of damaged opening sizes, the relative position of opening, and the incident wave and the liquid loading conditions on the dynamic response of the damaged ship in regular beam waves. It is observed that the flooding process was slowed down and interrupted by the water exchanges at the damaged opening due to the dynamic motion. Compared with the opening facing the incident wave, the back one endangered the ship pronouncedly with large amplitude and frequency roll motion. It is also revealed that the liquid tank in the damaged ship imposes a significant influence on its rolling response. It is further demonstrated that the present SPH model is capable of handling the nonlinear phenomenon in a flooding process of a damaged ship

Introduction to half-metallic Heusler alloys: Electronic Structure and Magnetic Properties

Intermetallic Heusler alloys are amongst the most attractive half-metallic systems due to the high Curie temperatures and the structural similarity to the binary semiconductors. In this review we present an overview of the basic electronic and magnetic properties of both Heusler families: the so-called half-Heusler alloys like NiMnSb and the the full-Heusler alloys like Co$_2$MnGe. \textit{Ab-initio} results suggest that both the electronic and magnetic properties in these compounds are intrinsically related to the appearance of the minority-spin gap. The total spin magnetic moment $M_t$ scales linearly with the number of the valence electrons $Z_t$, such that $M_t=Z_t-24$ for the full-Heusler and $M_t=Z_t-18$ for the half-Heusler alloys, thus opening the way to engineer new half-metallic alloys with the desired magnetic properties.Comment: 28 pages, submitted for a special issue of 'Journal of Physics D: Applied Physics' on Heusler alloy

Towards New Half-Metallic Systems: Zinc-Blende Compounds of Transition Elements with N, P, As, Sb, S, Se, and Te

We report systematic first-principles calculations for ordered zinc-blende compounds of the transition metal elements V, Cr, Mn with the sp elements N, P, As, Sb, S, Se, Te, motivated by recent fabrication of zinc-blende CrAs, CrSb, and MnAs. They show ferromagnetic half-metallic behavior for a wide range of lattice constants. We discuss the origin and trends of half-metallicity, present the calculated equilibrium lattice constants, and examine the half-metallic behavior of their transition element terminated (001) surfaces.Comment: 2nd Version: lattice constants calculations added, text revise

Bridge-specific fragility analysis: when is it really necessary?

In seismic assessment of bridges the research focus has recently shifted on the derivation of bridge-specific fragility curves that account for the effect of different geometry, structural system, component and soil properties, on the seismic behaviour. In this context, a new, component-based methodology for the derivation of bridge-specific fragility curves has been recently proposed by the authors, with a view to overcoming the inherent difficulties in assessing all bridges of a road network and the drawbacks of existing methodologies, which use the same group of fragility curves for bridges within the same typological class. The main objective of this paper is to critically assess the necessity of bridge-specific fragility analysis, starting from the effect of structure-specific parameters on component capacity (limit state thresholds), seismic demand, and fragility curves. The aforementioned methodology is used to derive fragility curves for all bridges within an actual road network, with a view to investigating the consistency of adopting generic fragility curves for bridges that fall within the same class and quantifying the degree of over- or under-estimation of the probability of damage when generic bridge classes are considered. Moreover, fragility curves for all representative bridges of the analysed concrete bridge classes are presented to illustrate the differentiation in bridge fragility for varying structural systems, bridge geometry, total bridge length and maximum pier height. Based on the above, the relevance of bridge-specific fragility analysis is assessed, and pertinent conclusions are drawn

Slater-Pauling Behavior of the Half-Ferromagnetic Full-Heusler Alloys

Using the full-potential screened Korringa-Kohn-Rostoker method we study the full-Heusler alloys based on Co, Fe, Rh and Ru. We show that many of these compounds show a half-metallic behavior, however in contrast to the half-Heusler alloys the energy gap in the minority band is extremely small. These full-Heusler compounds show a Slater-Pauling behavior and the total spin-magnetic moment per unit cell (M_t) scales with the total number of valence electrons (Z_t) following the rule: M_t=Z_t-24. We explain why the spin-down band contains exactly 12 electrons using arguments based on the group theory and show that this rule holds also for compounds with less than 24 valence electrons. Finally we discuss the deviations from this rule and the differences compared to the half-Heusler alloys.Comment: 10 pages, 8 figures, revised figure 3, new text adde