Physical implication of two problems in transition prediction of boundary layers based on linear stability theory

Up to now,the most widely used method for transition prediction is the one based on linear stability theory.When it is applied to three-dimensional boundary layers,one has to choose the direction,or path,along which the growth rate of the disturbance is to be integrated.The direction given by using saddle point method in the theory of complex variable function is seen as mathematically most reasonable.However,unlike the saddle point method applied to water waves,here its physical meaning is not so obvious,as the frequency and wave number may be complex.And on some occasions,in advancing the integration of the growth rate of the disturbance,up to a certain location,one may not be able to continue the integration,because the condition for specifying the direction set by the saddle point method can no longer be satisfied on the basis of continuously varying wave number.In this paper,these two problems are discussed,and suggestions for how to do transition prediction under the latter condition are provided.     

A new nonlinear optical silicate carbonate K2Ca[Si2O5](CO3) with a hybrid structure of kalsilite and soda-like layered fragments

Single crystals of a new silicate carbonate, K₂Ca[Si₂O₅](CO₃), have been synthesized in a multi-components hydrothermal solution with a pH value close to neutral and a high concentration of a carbonate mineralizer. The new compound has an axial structure (s.g. P6₃22) with unit cell parameters a = 5.04789 (15), c = 17.8668 (6) Å. Pseudosymmetry of the structure corresponds to s.g. P6₃/mmc which is broken only by one oxygen position. The structure consists of two layered fragments: one of the type of the mineral kalsilite (KAlSiO₄) and the other of the high-temperature soda-like α-Na₂CO₃, Ca substituting for Na. The electro-neutral layer K₂[Si₂O₅] (denoted K) as well as the layer Ca(CO₃) (denoted S) may separately correspond to individual structures. In K₂Ca[Si₂O₅](CO₃) the S-K layers are connected together via Ca-O interactions between Ca atoms from the carbonate layer and apical O atoms from the silicate one, and also via K-O interlayer interactions. A hypothetical acentric structure, sp.gr. P-62c, is predicted on the basis of the order-disorder theory. It presents another symmetrical option for the arrangement of K-layers relative to S-layers. The K,Ca-silicate-carbonate powder produces a moderate SHG signal that is two times larger that of the α-quartz powder standard and close to other silicates with acentric structures and low electronic polarizability.     

Synthesis and ferroelectric behavior of Gd doped BNT ceramics

In the present work, polycrystalline (Bi_1−xGd_x)_0.5Na_0.5TiO₃ (BGNT) ceramics with low amount of rare earth ion Gd³⁺ (x = 0, 0.02, 0.03, 0.04) have been synthesized by a semi–wet technique. XRD patterns show single phase formation for all the samples with a rhombohedral structure at room temperature. FE-SEM images show decrease in grain size with Gd concentration. The temperature dependence of dielectric constant has revealed that the depolarization temperature ‘T_d’ decreases with increasing x and the temperature ‘T_m’ of maximum dielectric constant increases initially for x = 0.02 thereafter decreases. All the samples have shown saturated hysteresis (P–E) loop at room temperature. The BGNT ceramic system for composition, x = 0.02 exhibits improved piezoelectric properties and strong ferroelectricity. With increasing temperature, polarization has been found to be reduced and deformed P–E loops are observed around ‘T_d’.     

Study of electron-vibrational interaction and concentration quenching effect of Cu+ ions in lithium based sulphate phosphors

The objective of this work is to study electron-vibrational interaction (EVI) and concentration quenching and their manifestation in experimental photoluminescence spectra of Cu⁺ ion in various lithium based phosphors namely, Li₂SO₄, LiNaSO₄ and LiKSO₄. The main parameters of EVI, such as the Stokes shift, Huang-Rhys factor and zero-phonon line positions, were estimated. The studied systems shows strong electron lattice coupling. The validity of results was established by modeling the shape of the emission spectra, which was found to be in good agreement with experimental photoluminescence spectra. The concentration quenching study is also carried out for these compounds. The studied systems correspond to the nearest neighbor energy transfer mechanism.     

Measurements of the optical absorption coefficient of Ar8+ ion implanted silicon layers using the photothermal radiometry and the modulated free carrier absorption methods

This paper presents a method of the measurement of the optical absorption coefficient of the Ar⁸⁺ ions implanted layers in the p-type silicon substrate. The absorption coefficient is calculated using a value of the attenuation of amplitudes of a photothermal radiometry (PTR) and/or a modulation free carrier absorption (MFCA) signals and the implanted layer thickness calculated by means of the TRIM program. The proposed method can be used to indicate the amorphization of the ions implanted layers.     

Pd‐initiated polymerization of diazo compounds bearing dialkoxyphosphinyl group and hydrolysis of the resulting polymers and oligomers to afford phosphonic acid‐containing products

Pd‐initiated polymerization and oligomerization of diazo compounds containing a dialkoxyphosphinyl group are described. Polymerization of 2‐dialkoxyphosphinylethyl diazoacetates with π‐allylPdCl‐based initiating systems afforded C? C main chain polymers bearing phosphonate on each main chain carbon atom. The quantitative transformation of the side chain phosphonate to phosphonic acid resulted in the formation of water soluble polymers having the acid groups accumulated around their main chains, although the carbonyl ester linkage in the side chain was cleaved via intramolecular acid‐assisted hydrolysis in water at 80 °C. Pd‐initiated oligomerization of diethyl diazomethylphosphonate yielded an oligomeric product bearing diethoxyphosphiny groups directly attached to its main chain carbons, with unexpected incorporation of azo group in the main chain framework. Hydrolysis of the phosphonate of the oligomer afforded a water‐soluble product, which was revealed to show higher proton conductivity than poly(vinylphosphonic acid) under certain conditions. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1742–1751     

Temperature memory effect and its stability revealed via differential scanning calorimetry in ethylene‐vinyl acetate within glass transition range

In this article, we reveal the temperature memory effect (TME) in a commercial thermoplastic polymer, namely ethylene‐vinyl acetate (EVA), within its glass transition range via a series of differential scanning calorimeter (DSC) tests. In addition, we investigate the influence of heating holding time and also compare the observed TME in current study with that of shape memory alloys (SMAs). It is concluded that the TME via DSC (without any macroscopic shape change) is achievable within the glass transition range of a polymer. Conversely, although the observed TME shares the many similar features as those in SMAs, due to the nature of micro‐Brownian motion in the glass transition of polymers, the resulted TME is strongly affected by the heating holding time. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1731–1737     

Nonreciprocal devices in integrated optics

This article reviews the solutions that have been studied for the implementation of nonreciprocal devices in integrated optics. These components, either isolators or circulators, use the nonreciprocal interaction between light and a magnetic medium. The only two isolators that have been experimented on to date are described in detail with their advantages and drawbacks, and some solutions are proposed to overcome the difficulties encountered.     

A contact process with a semi-infected state on the complete graph

In this paper, we are concerned with a contact process with a semi-infected state on the complete graph C_n with n vertices. Our model is a special case of a general model introduced by Schinazi in 2003. In our model, each vertex is in one of three states, namely, “healthy,” “semi-infected,” or “fully-infected.” Only fully-infected vertices can infect others. A healthy vertex becomes semi-infected when being infected while a semi-infected vertex becomes fully-infected when being further infected. Each (semi- and fully-) infected vertex becomes healthy at constant rate. Our main result shows a phase transition for the waiting time until extinction of the fully-infected vertices. Conditioned on all the vertices are fully-infected when t = 0, we show that fully-infected vertices survive for exp?{O(n)} units of time when the infection rate λ > 4 while they die out in O(log?n) units of time when λ < 4.