A basic inequality for submanifolds in a cosymplectic space form

For submanifolds tangent to the structure vector field in cosymplectic space forms, we establish a basic inequality between the main intrinsic invariants of the submanifold, namely its sectional curvature and scalar curvature on one side; and its main extrinsic invariant, namely squared mean curvature on the other side. Some applications including inequalities between the intrinsic invariant $\delta_{M}$ and the squared mean curvature are given. The equality cases are also discussedComment: Latex 9 page

Index of quasi-conformally symmetric semi-Riemannian manifolds

We find the index of $\widetilde{\nabla}$-quasi-conformally symmetric and $\widetilde{\nabla}$-concircularly symmetric semi-Riemannian manifolds, where $\widetilde{\nabla}$ is metric connection

Topological Quantum Phase Transition in 5dd Transition Metal Oxide Na2_2IrO3_3

We predict a quantum phase transition from normal to topological insulators in the 5$d$ transition metal oxide Na$_2$IrO$_3$, where the transition can be driven by the change of the long-range hopping and trigonal crystal field terms. From the first-principles-derived tight-binding Hamiltonian we determine the phase boundary through the parity analysis. In addition, our first-principles calculations for Na$_2$IrO$_3$ model structures show that the interlayer distance can be an important parameter for the existence of a three-dimensional strong topological insulator phase. Na$_2$IrO$_3$ is suggested to be a candidate material which can have both a nontrivial topology of bands and strong electron correlations

A Micromechanical Model for Viscoelastic-Viscoplastic Analysis of Particle Reinforced Composite

This study introduces a time-dependent micromechanical model for a viscoelastic-viscoplastic analysis of particle-reinforced composite and hybrid composite. The studied particle-reinforced composite consists of solid spherical particle and polymer matrix as constituents. Polymer constituent exhibits time-dependent or inelastic responses, while particle constituent is linear elastic. Schapery's viscoelastic integral model is additively combined with a viscoplastic constitutive model. Two viscoplastic models are considered: Perzyna's model and Valanis's endochronic model. A unit-cell model with four particle and polymer sub-cells is generated to obtain homogenized responses of the particle-reinforced composites. A time-integration algorithm is formulated for solving the time-dependent and inelastic constitutive model for the isotropic polymers and nested to the unit-cell model of the particle composites. Available micromechanical models and experimental data in the literature are used to verify the proposed micromechanical model in predicting effective viscoelasticviscoplastic responses of particle-reinforced composites. Filler particles are added to enhance properties of the matrix in the fiber reinforced polymer (FRP) composites. The combined fiber and particle reinforced matrix forms a hybrid composite. The proposed micromechanical model of particle-reinforced composites is used to provide homogenized properties of the matrix systems, having filler particles, in the hybrid composites. Three-dimensional (3D) finite element (FE) models of composite's microstructures are generated for two hybrid systems having unidirectional long fiber and short fiber embedded in cubic matrix. The micromechanical model is implemented at the material (Gaussian) points of the matrix elements in the 3D FE models. The integrated micromechanical-FE framework is used to examine time-dependent and inelastic behaviors of the hybrid composites

Linear-TT resistivity at high temperature

The linear-$T$ resistivity is one of the characteristic and universal properties of strange metals. There have been many progress in understanding it from holographic perspective (gauge/gravity duality). In most holographic models, the linear-$T$ resistivity is explained by the property of the infrared geometry and valid at low temperature limit. On the other hand, experimentally, the linear-$T$ resistivity is observed in a large range of temperatures, up to room temperature. By using holographic models related to the Gubser-Rocha model, we investigate how much the linear-$T$ resistivity is robust at higher temperature above the superconducting phase transition temperature. We find that strong momentum relaxation plays an important role to have a robust linear-$T$ resistivity up to high temperature.Comment: 21 pages, 6 figures, v2: references adde

Near-Infrared Spectroscopy of Infrared-Excess Stellar Objects in the Young Supernova Remnant G54.1+0.3

We present the results of broadband near-infrared spectroscopic observations of the recently discovered mysterious stellar objects in the young supernova remnant G54.1+0.3. These objects, which show significant mid-infrared-excess emission, are embedded in a diffuse loop structure of ~1' in radius. Their near-infrared spectra reveal characteristics of late O- or early B-type stars with numerous H and He I absorption lines, and we classify their spectral types to be between O9 and B2 based on an empirical relation derived here between the equivalent widths of the H lines and stellar photospheric temperatures. The spectral types, combined with the results of spectral energy distribution fits, constrain the distance to the objects to be 6.0 ± 0.4 kpc. The photometric spectral types of the objects are consistent with those from the spectroscopic analyses, and the extinction distributions indicate a local enhancement of matter in the western part of the loop. If these objects originate via triggered formation by the progenitor star of G54.1+0.3, then their formations likely began during the later evolutionary stages of the progenitor, although a rather earlier formation may still be possible. If the objects and the progenitor belong to the same cluster of stars, then our results constrain the progenitor mass of G54.1+0.3 to be between 18 and ~35 M_☉ and suggest that G54.1+0.3 was either a Type IIP supernova or, with a relatively lower possibility, Type Ib/c from a binary system

Enhanced terahertz conductivity in ultra-thin gold film deposited onto (3-mercaptopropyl) trimethoxysilane (MPTMS)-coated Si substrates

Various material properties change considerably when material is thinned down to nanometer thicknesses. Accordingly, researchers have been trying to obtain homogeneous thin films with nanometer thickness but depositing homogeneous few nanometers thick gold film is challenging as it tends to form islands rather than homogenous film. Recently, studies have revealed that treating the substrate with an organic buffer, (3-mercaptopropyl) trimethoxysilane (MPTMS) enables deposition of ultra-thin gold film having thickness as low as 5 nm. Different aspects of MPTMS treatment for ultrathin gold films like its effect on the structure and optical properties at visible wavelengths have been investigated. However, the effect of the MPTMS treatment on electrical conductivity of ultra-thin gold film at terahertz frequency remains unexplored. Here, we measure the complex conductivity of nanometer-thick gold films deposited onto an MPTMS-coated silicon substrate using terahertz time-domain spectroscopy. Following the MPTMS treatment of the substrate, the conductivity of the films was found to increase compared to those deposited onto uncoated substrate for gold films having the thickness less than 11 nm. We observed 5-fold enhancement in the conductivity for a 7 nm-thick gold film. We also demonstrate the fabrication of nanoslot-antenna arrays in 8.2-nm-thick gold films. The nanoslot-antenna with MPTMS coating has resonance at around 0.5 THz with an electric field enhancement of 44, whereas the nanoslot-antenna without MPTMS coating does not show resonant properties. Our results demonstrate that gold films deposited onto MPTMS-coated silicon substrates are promising advanced materials for fabricating ultra-thin terahertz plasmonic devices