Raman spectral studies of Zr4+‐rich BaZrxTi1−xO3(0.5⩽x⩽1.00) phase diagram

This paper reports a systematic study of the composition and the temperature‐dependent‐Raman spectra of Zr⁴⁺‐rich BaZr_xTi_1−xO₃ (BZT) ceramic compositions (0.50⩽x⩽1.00). On the basis of the dielectric behavior of Zr rich BZT ceramics, the observed relaxor behavior has been hypothesized as a result of increasing long‐range interactions of nanosized, Ti⁴⁺‐rich polar regions in a Zr⁴⁺‐rich nonpolar matrix. Beyond an optimum concentration of BaTiO₃ (BT) in the nonpolar matrix of BaZrO₃ (x⩽0.75), a critical size and density of the polar regions is reached when the polar clusters start showing the relaxor like behavior, which finally show classical relaxor behavior for compositions with x = 0.5 and 0.6. This hypothesis is strongly supported from the Raman data on Zr‐rich BZT presented in this paper. Well‐defined BT Raman spectra for 5% BT in BZT composition were recorded, which followed completely up to the 50% Ti addition in the BZT samples. The temperature‐dependent Raman spectra collected on the BZT ceramics far beyond the dielectric transition temperatures supported the existence of the nano‐polar BT regions, like in typical relaxor samples. The full width at half‐maximum (FWHM), integrated intensity of the peaks in the Raman spectra has been analyzed to further support the conclusions. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of launching condition in response time analysis for few selected tapered porous clad optical fiber gas sensors

In this paper, the effect of launching condition of light and the geometry of the sensing region in the case of detection of gases using attenuated total internal reflection (ATR) technique in multimode step index tapered fiber has been described. Using ray approach the response time of the sensor in case of parabolic, linear and exponential-linear tapered optical fiber have been carried out. It has been shown that launching condition and geometry of the sensing region effect the sensitivity of the sensor. Out of three designs the sensor having exponential-linear tapered with selected ray launching has maximum sensitivity and low response time of the sensor.     

Effect of nanofillers on thermal and transport properties of potassium iodide–polyethylene oxide solid polymer electrolyte

In order to enhance the ionic conductivity of polyethylene oxide (PEO)–KI(80:20) based alkaline polymer electrolytes, nanosized inorganic filler ZnS has been incorporated into PEO–KI matrix and the corresponding nanocomposite polymer electrolytes are synthesized by the usual solution casting procedure. Atomic force microscope image of composite polymer electrolyte exhibits that the introduction of ZnS nanoparticles changes the surface morphology and aggregates them to form an arborization pattern. The prepared nanocomposite polymer electrolyte reveals an ionic conductivity of about 10^?4 S cm^?1 for 5 wt% ZnS at room temperature.     

Evidence of partial gap opening and Ce-site dilution effects in a heavy fermion compound CeNiGe2

We report the results of magnetisation, non-linear dc susceptibility, electrical transport, and heat capacity measurements on Y-substituted heavy fermion CeNiGe₂. Investigations are carried out on the compounds CeNiGe₂, Ce_0.9Y_0.1NiGe₂, Ce_0.8Y_0.2NiGe₂ and Ce_0.6Y_0.4NiGe₂. It is observed that with the increase in Y-concentration, the magnetic ordering temperature decreases. For CeNiGe₂, below ordering temperature Arrott plots suggest the presence of spin density wave (SDW). Third- and fifth-order dc susceptibility indicates magnetic instability which possibly leads to partial gap opening resulting in the observation of SDW. These observations are further investigated through resistivity and heat capacity measurements which also point toward partial gap opening in CeNiGe₂. Interestingly, with the increase in Y-substitution, it is noted that the gap opening is suppressed and also shifted towards lower temperature. Moreover, our investigations reveal absence of non-Fermi liquid behaviour or zero field quantum critical point even after 40% dilution of Ce-site.     

A closed-form solution of the Black–Litterman model with conditional value at risk

We consider a portfolio optimization problem of the Black–Litterman type, in which we use the conditional value-at-risk (CVaR) as the risk measure and we use the multi-variate elliptical distributions, instead of the multi-variate normal distribution, to model the financial asset returns. We propose an approximation algorithm and establish the convergence results. Based on the approximation algorithm, we derive a closed-form solution of the portfolio optimization problems of the Black–Litterman type with CVaR.     

Theoretical Model of Electrode Polarization and AC Electroosmotic Fluid Flow in Planar Electrode Arrays

Strong frequency-dependent fluid flow has been observed near the surface of microelectrode arrays. Modeling this phenomenon has proven to be difficult, with existing theories unable to account for the qualitative trend observed in the frequency spectra of this flow. Using recent electrode polarization results, a more comprehensive model of the double layer on the electrode surface is used to obtain good theoretical agreement with experimental data. Copyright 2001 Academic Press.     

Some remarks on conjugate closed groups

Let G be a group. In this note we define conjugate closed groups, which are briefly called CC — Groups. These groups form a proper subclass of T — Groups. We prove that if G = Z(G) × H, then G is conjugate closed if and only if H is conjugate closed. We also show that a finite group G is semisimple, conjugate closed and perfect if and only if it is a direct product of non-abelian and simple groups.     

Non-Markovian Green function for plasma turbulence

We consider the Green function appropriate for weak plasma turbulence and show that, after a sufficiently long time, it approaches the Green function for a Markovian system.     

Credit risk estimation using payment history data: a comparative study of Turkish retail stores

Our paper presents a comparative study applying logistic regression and multiple criteria decision analysis tools to the operations of wholesalers to assess the credit risk of their retailers using payment history data and to cluster the risky customers by ranking their risk levels. Our sample comprises approximately 6,000 retailer customers and 600.000 transactions of one of the major wholesalers of Turkey. Our findings emphasize the importance of using payment history and some non-financial factors data for predicting the creditworthiness of a firm.