Two new refined shear displacement models for functionally graded sandwich plates

Two refined displacement models, RSDT1 and RSDT2, are developed for a bending analysis of functionally graded sandwich plates. Unlike any other theory, the number of unknown functions involved is only four, as against five in case of other shear deformation theories. The developed models are variationally consistent, have strong similarity with classical plate theory in many aspects, do not require shear correction factor, and give rise to transverse shear stress variation such that the transverse shear stresses vary parabolically across the thickness satisfying shear stress-free surface conditions. The accuracy of the analysis presented is demonstrated by comparing the results with solutions derived from other higher-order models. The functionally graded layers are assumed to have isotropic, two-constituent material distribution through the thickness, and the modulus of elasticity, Poisson’s ratio of the faces, and thermal expansion coefficients are assumed to vary according to a power-law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic ceramic material. Numerical results for deflections and stresses of functionally graded metal–ceramic plates are investigated. It can be concluded that the proposed models are accurate and simple in solving the bending behavior of functionally graded plates.     

Lead-Free Semiconductors with High Absorption: Insight into the Optical Properties of K2GeSnBr6 and K2GeSnI6 Halide Double Perovskites

JETP Letters - Structural, electronic and optical properties for halide double perovskites compounds K2GeSnBr6 and K2GeSnI6 are studied in this work. Based on the (FP-LAPW) method, the previous...     

DFT study of magneto-volume effects in iron and cobalt nitrides

Largely investigated, both theoretically and experimentally, the iron-nitrogen system (Fe-N) shows large magneto-volume effects, where N element plays an important role. On the other side, the cobalt-nitrogen (Co-N) system magnetic properties are less known. We present here a first principles comparative study, within density functional theory framework of these two systems in order to get further insights into the role of nitrogen within these insertion alloys. The properties of the cobalt nitride are firstly discussed with respect to Fe-N ones, and then the two systems are treated within Slater-Pauling-Friedel model whose limitations are shown.     

Development and validation of a sensitive solid phase extraction/hydrophilic interaction liquid chromatography/mass spectrometry method for the accurate determination of glucosamine in dog plasma

A sensitive and accurate LC/MS method was developed for the monitoring of glucosamine (GLcN) dog plasmatic concentration. In this scope, relatively low plasmatic concentrations of GLcN were expected, ranging from 50 to 1000 ng/mL. Liquid chromatography coupled to simple quadrupole mass spectrometry detection (LC/MS) was selected bringing the selectivity and the sensitivity needed for this application. Additionally, a solid phase extraction (SPE) step was performed to reduce matrix and ion suppression effects. Due to the ionisable character of the compound of interest, a mixed-mode strong cation exchange (Plexa PCX) disposable extraction cartridge (DEC) was selected. The separation was carried out on a Zorbax SB-CN column (5 μm, 4.6 mm i.d. × 250 mm), considering hydrophilic interaction liquid chromatography (HILIC). Indeed, the mobile phase was made of methanol and 5 mM ammonium hydrogen carbonate buffer at pH 7.5 (95/5, v/v). The detection was led at m/z ratios of 180.0 and 417.0, for GLcN and IS, respectively. Reliability of the results was demonstrated through the validation of the method using an approach based on the accuracy profile allowing managing the risk associated to the use of these methods in routine analysis: it is thus guaranteed that each future result will fall in the ±30% acceptance limits with a probability of at least 90%. Successful application of the method to a preliminary pharmacokinetic study illustrated the usefulness of the method for pre-clinical studies.     

The Bresse system in thermoelasticity

In this paper, we consider the Bresse system coupled with the Fourier law of heat conduction. We prove that the decay rate of the solution is very slow. In fact, we show that the L²‐norm of the solution decays with the rate of (1 + t)^?1/12 similar to the one obtained for the Timoshenko system. In addition, we found that the wave speed of the first two equations still control the decay rate of the solution with respect to the regularity of the initial data. This seems to be the first result dealing with the behavior of the Cauchy problem in the Bresse–Fourier model. Copyright © 2014 John Wiley & Sons, Ltd.     

A new five-unknown refined theory based on neutral surface position for bending analysis of exponential graded plates

In the present paper, a new sinusoidal higher-order plate theory is developed for bending of exponential graded plates. The effects due to transverse shear and normal deformations are both included. The number of unknown functions involved in the present theory is only five as against six or more in case of other shear and normal deformation theories. The theory accounts for sinusoidal distribution of the transverse shear strains, and satisfies the zero traction boundary conditions on the surfaces of the plate without using shear correction factor. Based on the sinusoidal shear and normal deformation theory, the position of neutral surface is determined and the governing equilibrium equations based on neutral surface are derived. There is no stretching–bending coupling effect in the neutral surface-based formulation, and consequently, the governing equations of functionally graded plates based on neutral surface have the simple forms as those of isotropic plates. Numerical results of present theory are compared with three-dimensional elasticity solutions and other higher-order theories reported in the literature. It can be concluded that the proposed theory is accurate and efficient in predicting the bending response of exponential graded plates.     

Global non‐existence of solutions of a class of wave equations with non‐linear damping and source terms

In this paper we consider the non‐linear wave equation a,b>0, associated with initial and Dirichlet boundary conditions. We prove, under suitable conditions on α,β,m,p and for negative initial energy, a global non‐existence theorem. This improves a result by Yang (Math. Meth. Appl. Sci. 2002; 25 :825–833), who requires that the initial energy be sufficiently negative and relates the global non‐existence of solutions to the size of Ω. Copyright © 2004 John Wiley & Sons, Ltd.     

Nahm's equations and root systems

A method of deriving solutions to Nahm's equations based on root structure of simple Lie algebras is given. As an illustration of this method the recently found solutions to Nahm's equations with tetrahedral and octahedral symmetries are shown to correspond to A ₂ and A ₃ root systems.     

Pyrrolizidine alkaloids from Solenanthus lanatus DC. with acetylcholinesterase inhibitory activity

The whole plant ethanolic extract of Solenanthus lanatus was used for the isolation of acetylcholinesterase inhibitors. A new pyrrolizidine alkaloid, 7-O-angeloylechinatine N-oxide, 1, was isolated together with three known compounds of the same class (3′-O-acetylheliosupine N-oxide, 2, heliosupine N-oxide, 3, and heliosupine, 4), by bioassay-guided approach. Their structures were elucidated by spectroscopic methods. All the isolated compounds showed inhibition activity against the AChE, with IC₅₀ 0.53–0.60 mM.     

Experimental study of an earth-to-air heat exchanger coupled to the solar chimney for heating and cooling applications in arid regions

Journal of Thermal Analysis and Calorimetry - Arid regions around the world are characterized by hard summer and winter seasons, which leads to thermal discomfort. The southwest of Algeria is...