Phase transitions,ferroelectric behavior and second-order nonlinear optics of a new mixed sodium dihydrogen phosphate–arsenate

Aiming at the development of new proton conducting solids, recent studies of the NaH₂PO₄·H₂O–NaH₂AsO₄·H₂O system have lead to the synthesis of a new compound NaH₂(PO₄)_0.48(AsO₄)_0.52·H₂O (NDAP). Calorimetric studies have confirmed the presence of four reversible phase transitions (abbreviated by PhT), at 257/270 (PhT, IV), 261/290 (PhT, III), 267/301 (PhT, II) and 317/317.5 K (PhT, I) (for cooling/heating processes, respectively). It is shown that the III and IV phase transitions are of a first order type, with a “order-disorder and displacive” character, accompanied by specific dielectric anomalies. The behavior of the dielectric constant ε′_r and of tan δ shows that, at 272 K, the (PhT, IV) could be ferroelectric–paraelectric. As for the (PhT, III) at 296 K, it leads to a superionic–protonic phase; a jump in the conductivity is associated to this transition with an unusual high value of conductivity 1.07×10^?4 Ω^?1 cm^?1 and a low activation energy 0.39 eV (Kh. Jarraya et al.). Quandratic nonlinear (NLO) properties of NDAP powder was confirmed efficiency of the grown crystal by the Kurtz and Perry second harmonic generation (SHG) technique.     

dc and ac characterizations of electrical conducting nanoporous carbon structures based on resorcinol-formaldehyde

Structural, electrical and morphological properties of electrical conducting nanoporous carbon structures, prepared at different pyrolysis temperatures by sol–gel method, were investigated. The effect of the measurement temperature on the electrical properties of the obtained sample pyrolysed at 675 °C was studied. The imaginary and real parts of the sample impedance versus frequency, in the range of 40 Hz–100 MHz, are investigated. The Nyquist diagrams were used to identify an equivalent circuit and the fundamental parameters of the circuit are determined at different temperatures with the aim to study the contributions of the grains and boundary grains to the conductivity.     

Dual-channel spectral subtraction algorithms based speech enhancement dedicated to a bilateral cochlear implant

In this paper, two speech enhancement algorithms (SEAs) based on spectral subtraction (SS) principle have been evaluated for bilateral cochlear implant (BCI) users. Specifically, dual-channel noise power spectral estimation algorithm using power spectral densities (PSD) and cross power spectral density (CPSD) of the observed signals was studied. The enhanced speech signals were obtained using either Dual Channel Non Linear Spectral Subtraction ‘DC-NLSS’ or Dual-Channel Multi-Band Spectral Subtraction ‘DC-MBSS’ algorithms. For performance evaluation, some objective speech assessment tests relying on Perceptual Evaluation of Speech Quality (PESQ) score and speech Itakura-Saito (IS) distortion measurement were performed to fix the optimal number of frequency band needed in DC-MBSS algorithm. In order to evaluate the speech intelligibility, subjective listening tests were assessed with 50 normal hearing listeners using a specific BCI simulator and with three deafened BCI patients. Experimental results, obtained using French Lafon database corrupted by an additive babble noise at different Signal-to-Noise Ratios (SNR), showed that DC-MBSS algorithm improves speech understanding better than DC-NLSS algorithm for single and multiple interfering noise sources.     

反旋双色圆偏振激光场下Ar原子非次序双电离研究

应用经典系综方法模拟了反旋双色圆偏振激光场下Ar原子非次序双电离过程.双电离概率随激光强度变化曲线呈现出"knee"结构,表明了明显的电子关联特征.通过调节倍频与基频激光场的场强比可以实现对双电离的增强或抑制以及最优化.在"knee"结构区域的不同场强下,这种调控机制具有相似性.通过分析重碰撞和激发电离的时间特征,进一步讨论了反旋双色圆偏振激光场的强度对不同电离通道的控制规律.     

J/ψ核吸收新截面难以改变吸收机制的局面

将新发表的J/ψ核吸收截面输入强子和弦级联模型JPCIAE,计算了200AGeV/c的P-A,O-U,S-U和Pb-Pb最小偏畸碰撞中J/ψ压低因子并与实验作比较.结果表明:增大的新截面难以改变核吸收机制不易解释Pb-Pb碰撞J/ψ反常压低局面.     

Electro-Optical and Thermophysical Characterization of Poly (Tripropylene Glycol Di-Acrylate)/Liquid Crystal Composite Materials Prepared by Polymerization Induced Phase Separation

Abstract

This work examines the development and characterization of tripropylene glycol di-acrylate/liquid crystal E7 (TPGDA/LC E7) PDLCs composite materials (polymer-dispersed-liquid-crystals). These systems were produced by UV irradiation photopolymerization (PIPS) of a mixture of the monomer tripropylene glycol di-acrylate (TPGDA) and the liquid crystal E7 (LC E7, a mixture of three cyano-biphenyl and one cyano-terphenyl LCs), in the presence of 2?wt% (of the acrylate/E7 mixture) of a photoinitiator. Electro-optical, thermal and optical characterization was used to understand the effect of the LC concentration on the electro-optical and thermo-physical properties of these materials. Polarizing optical microscopy (POM) and differential scanning calorimetry (DSC) studies were performed to observe the system morphology and to determine the transition temperatures of these materials, both as a function of their composition. The findings showed a slight variation of the nematic-isotropic transition temperature, T_NI, of the LC E7 and of the glass transition temperature, T_g, of the TPGDA polymeric matrix as a function of the mass percentage of the LC E7. A very good electro-optical response for the composition 30/70?wt % TPGDA/LC E7 was obtained.     

Warm tachyon inflation and swampland criteria

In this study, the scenario of a two-component warm tachyon inflation is considered, where the tachyon field plays the role of the inflaton by driving the inflation. During inflation, the tachyon scalar field interacts with the other component of the Universe, which is assumed to be photon gas, i.e., radiation. The interacting term contains a dissipation coefficient, and the study is modeled based on two different and familiar choices of the coefficient that were studied in the literature. By employing the latest observational data, the acceptable ranges for the free parameters of the model are obtained. For any choice within the estimated ranges, there is an acceptable concordance between the theoretical predictions and observations. Although the model is established based on several assumptions, it is crucial to verify their validity for the obtained values of the free parameters of the model. It is found that the model is not self-consistent for all values of the ranges, and for some cases, the assumptions are violated. Therefore, to achieve both self-consistency and agreement with the data, the parameters of the model must be constrained. Subsequently, we consider the recently proposed swampland conjecture, which imposes two conditions on the inflationary models. These criteria rule out some inflationary models; however, warm inflation is among those that successfully satisfy the swampland criteria. We conduct a precise investigation, which indicates that the proposed warm tachyon inflation cannot satisfy the swampland criteria for some cases. In fact, for the first case of the dissipation coefficient, in which, there is dependency only on the scalar field, the model agrees with observational data. However, it is in direct tension with the swampland criteria. Nevertheless, for the second case, wherein the dissipation coefficient has a dependency on both the scalar field and temperature, the model exhibits acceptable agreement with observational data, and suitably satisfies the swampland criteria.