Study of a simple oscillatory flow in polar fluids

Summary In the present paper, we have undertaken a comparative study of the flow behaviour of two types of fluids —Eringen's mioropolar fluid andStokes' couple stress fluid — in a simple oscillatory flow. This study was undertaken with a view to see if the close resemblance of the flow behaviour of these two fluids in steady shearing flows was maintained even in time dependent flows. We find that the flow behaviour of these two fluids are widely different in oscillatory motion.     

High pressure behavior of ZrW2O8: Gruneisen parameter and thermal properties

High pressure Raman spectroscopic studies are carried out on negative thermal expansion material ZrW2O8. The system exhibits amorphization at 2.2+/-0.3 GPa via an intermediate orthorhombic phase. In the cubic phase most modes below 50 meV are found to have negative Gruneisen parameter. Using the reported phonon density of states thermal properties are calculated and compared with the reported results. In contrast to the earlier belief, the present results show that modes of energies much higher than 10 meV also contribute substantially to the negative thermal expansion.     

ChemInform Abstract: Study of Phase Transformation in BaTe2O6 by in situ High‐Pressure X‐Ray Diffraction,Raman Spectroscopy,and First‐Principles Calculations.

The title compound is synthesized by solid state reaction of a stoichiometric mixture of BaCO₃ and TeO₂ (air, 550 °C for 6 h, and 650 °C for 12 h).     

Theoretical investigations on the chemical bonding, electronic structure, and optical properties of the metal-organic framework MOF-5

The chemical bonding, electronic structure, and optical properties of metal-organic framework-5 (MOF-5) were systematically investigated using ab initio density functional calculations. The unit cell volume and atomic positions were optimized with the Perdew-Burke-Ernzerhof (PBE) functional leading to a good agreement between the experimental and the theoretical equilibrium structural parameters. The calculated bulk modulus indicates that MOF-5 is a soft material. The estimated band gap from a density of state (DOS) calculation for MOF-5 is about 3.4 eV, indicating a nonmetallic character. As MOFs are considered as potential materials for photocatalysts, active components in hybrid solar cells, and electroluminescence cells, the optical properties of this material were investigated. The detailed analysis of chemical bonding in MOF-5 reveals the nature of the Zn-O, O-C, H-C, and C-C bonds, that is, Zn-O having mainly ionic interaction whereas O-C, H-C, and C-C exhibit mainly covalent interactions. The findings in this paper may contribute to a comprehensive understanding about this kind of material and shed insight into the synthesis and application of novel and stable MOFs.     

Terahertz imaging through self-mixing in a quantum cascade laser

We demonstrate terahertz (THz) frequency imaging using a single quantum cascade laser (QCL) device for both generation and sensing of THz radiation. Detection is achieved by utilizing the effect of self-mixing in the THz QCL, and, specifically, by monitoring perturbations to the voltage across the QCL, induced by light reflected from an external object back into the laser cavity. Self-mixing imaging offers high sensitivity, a potentially fast response, and a simple, compact optical design, and we show that it can be used to obtain high-resolution reflection images of exemplar structures.     

On the enhancement of the figure of merit in bulk nanocomposites

In this paper we make a detailed comparison of the thermoelectric properties of quantum dot superlattices with those of equivalently doped bulk material and show that a major contribution to the enhancement of the figure of merit comes from the increase of the thermoelectric power over that of bulk, in addition to the lattice thermal conductivity reduction in quantum dot superlattices. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of mercury cinnamate single crystal

Single crystals of mercury cinnamate were grown by slow evaporation of methanol solution at room temperature. The effect of mercury on the electronic structure of cinnamic acid was studied. The grown mercury cinnamate single crystals were characterized by UV, FTIR and TG-DTA. TG curve of mercury cinnamate exhibits higher thermal stability compared with cinnamic acid which was also confirmed by DTA curve. The spectroscopic studies give evidences of the distribution of the electronic charge in molecule, the delocalisation of π electrons and the reactivity of metal complexes. The Second harmonic generation efficiency is more pronounced in the presence of mercury dopant in the growth medium.     

Thermal and FTIR spectral studies in various proportions of urea thiourea mixed crystal

Mixed crystals of various proportions of urea thiourea were grown by slow evaporation of aqueous solution at room temperature. The bright and transparent crystals obtained were characterized using thermogravimetry–differential thermal analysis (TG–DTA) and FTIR spectroscopic analyses. A fitting decomposition pattern for the title compound was formulated on the TG curve which shows a two-stage mass loss between 175 and 750 °C. In this temperature range, DTA curves show exothermic peaks supporting the formulated decomposition pattern. The FTIR spectra show the characteristic absorption, vibration frequencies due to urea thiourea. Detailed structural analysis of the compound is under progress.     

Efficiency comparison of various friction models of a hydraulic cylinder in the framework of multibody system dynamics

Nonlinear Dynamics - Dynamic simulation of mechanical systems can be performed using a multibody system dynamics approach. The approach allows to account systems of other physical nature, such as...     

An interactive method for multiple-objective mathematical programming problems

An interactive method is developed for solving the general nonlinear multiple objective mathematical programming problems. The method asks the decision maker to provide partial information (local tradeoff ratios) about his utility (preference) function at each iteration. Using the information, the method generates an efficient solution and presents it to the decision maker. In so doing, the best compromise solution is sought in a finite number of iterations. This method differs from the existing feasible direction methods in that (i) it allows the decision maker to consider only efficient solutions throughout, (ii) the requirement of line search is optional, and (iii) it solves the problems with linear objective functions and linear utility function in one iteration. Using various problems selected from the literature, five line search variations of the method are tested and compared to one another. The nonexisting decision maker is simulated using three different recognition levels, and their impact on the method is also investigated.