Lattice thermal conductivity of skutterudite compounds

A generalized expression is used on the basis of relaxation time approximation to facilitate calculation of lattice thermal conductivity of dielectric materials as well as skutterudite family consists of compounds of the form AB₃. It is assumed that phonon scattering processes are independent and is represented by frequency dependent relaxation times. The contributions of normal three phonon scattering processes are included explicitly as redistribution of phonon momentum between two oscillation branches is considered. Magnitudes of relaxation times are estimated from the experimental data. The result for CoSb₃ is in reasonably good agreement with the experimental result in the temperature range 1–1000°K. It is observed that redistribution of phonon momentum between two oscillation branches leads to a significant suppression of thermal conductivity maximum and it is observed that for unfilled skutterudite the main dominant mechanism at the thermal conductivity maximum is three phonon normal scattering process.     

Approximate fixed-ρ solution of ‘sea-quark’ evolution equation at small-x and HERA

We found an approximate simple solution of sea-quark evolution equation in terms ofρ(=√ln(x ₀/x)/ln[ln(Q ²/Λ²)/(Q ₀ ² /Λ²)]) andζ(≡ln[ln(Q ²Λ²)/ln(Q ₀ ² /Λ²)]) in the small-x region whenρ is fixed and compared with HERA data. Agreement with data is found for largeQ ² and smallρ. Comparison with double asymptotic scaling prediction is made. We found a critical value ofρ. More data are needed to confirm this point.     

Triplet state sublevel spectroscopy applied to proteins

Triplet state sublevel spectroscopy using optical detection of magnetic resonance (ODMR) in zero magnetic field can be successfully employed to study (i) the environment of tryptophan (Trp) residues in a protein by observing the position and structure of phosphorescence spectra, zero field ODMR transitions and triplet state sublevel kinetics, (ii) the energy transfer among Trp residues, and (iii) whether any cysteine (Cys) residue is within van der Waals distance of any Trp residue by studying the complex of the protein with methylmercury(II) iodide (CH₃HgI) which binds to Cys residues. These studies are particularly important where crystal structure study is not possible. Study of the S₁ state often gives ambiguous results since fluorescence is always broad and shows multi-exponential decay. Our results on bacteriophage lysozyme T4 which contains three Trp residues at positions 126, 138 and 158 are presented. Measurements were facilitated by the use of a mutated enzyme containing one or two Trp-Tyr substitutions. The results indicate that (i) Trp 126 and 158 are solvent exposed, whereas Trp 138 is buried in a hydrophobic environment, (ii)S ↔S non-radiative energy transfer takes place predominantly from Trp 126 to Trp 158, and (iii) only Trp-158 undergoes a heavy atom perturbation, which affects selectively the z-sublevel (z is an out-of-plane axis of the indole plane) as a result of CH₃HgI binding to nearby Cys 97. We suggest that the Hg atom is located on the z-axis of Trp 158 in the complex. This interpretation is based on our investigations on the effect of orientation of heavy atom perturbers in some naphthalene-crown ether metal ion complexes.     

On use of ghost-less beam splitter in reversal shear interferometer for measurement of spatial coherence of large cross-section laser beam

A configuration of reversal shear interferometer suitable for measurement of spatial coherence of high average power, large cross-section laser beam has been discussed. Ghost-less beam splitters in which unwanted multiple reflections from the surfaces have been suppressed by total internal reflection are used for beam splitting and re-combination. Advantages and drawbacks of this configuration have been discussed.     

Anisotropic spin—lattice relaxation in the triplet state of naphtralene-h8 in n-pentane

The temperature dependence of the individual spin—lattice relaxation rate constants (W_ij) between the lowest triplet sublevels of naphthalene-h₈ in a polycrystalline Shpol'skii matrix of n-pentane have been measured between 1.2 and 2.4 K in zero field. The total sublevel decay constants are evaluated and found to be independent of temperature. The W_ij are found to be highly anisotropic, but the anisotropy pattern differs from that observed previously in a durene matrix.     

Plasma-maser interaction of langmuir wave with kinetic Alfvén wave turbulence

A theoretical study is made on the generation mechanism of Langmuir mode wave in the presence of kinetic Alfvén wave turbulence in a magnetized plasma on the basis of plasma-maser interaction. It is shown that a test high frequency Langmuir mode wave is unstable in the presence of low frequency kinetic Alfvén wave turbulence. The growth of the Langmuir wave occurs due to direct and polarization coupling terms. Because of the universal existence of the kinetic Alfvén waves in large scale plasmas, the results have potential importance in space and astrophysical radiation processes.     

Premicellar and micelle formation behavior of aqueous anionic surfactants in the presence of triphenylmethane dyes: protonation of dye in ion pair micelles

The premicellar and micelle formation behaviors of four cationic triphenylmethane dyes, viz, Pararosaniline (RN), Crystal violet (CV), Ethyl violet (EV), and Malachite green (MG), in aqueous anionic surfactant solutions of sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), and sodium dodecyl sulfonate (SDSN) have been studied by spectral and surface tension measurements. The study was carried out within a pH range where the dyes are stable in their quinoid forms. The dyes have been found to form dye–surfactant ion pairs (DSIPs) with the surfactants, at the surfactant concentrations well below their critical micelle concentration, CMC*. The DSIPs behave like nonionic surfactants and form an air–water interfacial monolayer. The DSIPs have a lower critical micelle concentration (CMC_IP), greater efficiency, and lower effectiveness than the corresponding pure surfactants. As the surfactant concentration is increased below the CMC*, the DSIPs start forming micelles of their own where the dye gets protonated and exists as a protonated dye–surfactant ion pair (PDSIP) in the ion pair micelles. As the concentration of the surfactant exceeds the CMC* of the pure surfactant, the protonation reverses gradually with the dye remaining in the micelles in solubilized form and the DSIPs in the air–water interfacial monolayer are replaced by pure surfactants. The distorted helical isomeric form (isomer B) of the dyes is favored in the PDSIPs. Copyright © 2009 John Wiley & Sons, Ltd.     

Ultrasound-Triggered Release of Ibuprofen from a Chitosan-Mesoporous Silica Composite- a Novel Approach for Controlled Drug Release

Summary: In this work, an attempt was made to synthesize a novel Chitosan-Mesoporous silica (CS-MS) hybrid composite to design a drug delivery system based on ultrasound triggered stimuli-responsive smart release. The in-vitro drug release properties of both the Mesoporous Silica (MS) and Chitosan (CS) hybrids were investigated. Ibuprofen (Ibu) was used as a model drug. The results from powder X-Ray diffraction (XRD) patterns, and BET N₂ adsorption isotherms exhibited that MS can accommodate drug molecules into the lumen of the channels and pores. Drug release, stimulated by temperature and pH of the release media was also investigated. We studied the Ultrasound (US) triggered release of Ibu in a simulated body fluid (pH 7.4). The results exhibited that US can be used as a non-invasive technique for drug release from polymeric materials. The enhancing effect of ultrasound on drug release is due to the Cavitation effect, without causing any significant destruction on the polymer morphology.     

Structural characterization of pseudo-binary semiconducting alloys using molecular simulations

Monte Carlo simulations with the Keating model have been performed to predict the lattice constant and bond length variations with composition for pseudo-binary semiconducting alloys. In general, it is observed that the deviations of the lattice constants from Vegard's law predictions are larger as the lattice mismatch between the constituent binaries increases. Further, it is noted that these alloys have partial virtual crystal model characteristics and tend to be more towards the flexible (floppy) crystal limit as compared to the rigid crystal limit. The topological rigidity parameters are bond-type dependent. The angular deviations from perfect tetrahedral structure are also measured.