4f-electric quadrupolar anomalies in PrCu2Si2 and its pseudoternary solid solutions

Experimental observations for possible presence of 4f quadrupolar Kondo effect in PrCu₂Si₂ are critically discussed. A comparison of the low temperature properties of the alloys, Pr _x Y_1–x Cu₂Si₂ (x=0.05, 0.2 and 0.4), seems to signal the existence of 4f electric quadrupolar glass phenomenon around 4K forx=0.2.     

Density matrix renormalization group study of incompressible fractional quantum Hall states

We develop the density-matrix renormalization group (DMRG) technique for numerically studying incompressible fractional quantum Hall (FQH) states on the sphere. We calculate accurate estimates for ground-state energies and excitation gaps at FQH filling fractions nu=1/3 and nu=5/2 for systems that are considerably larger than the largest ever studied by exact diagonalization. We establish, by carefully comparing with existing numerical results on smaller systems, that DMRG is a highly effective numerical tool for studying incompressible FQH states.     

Simultaneous Determination of Acetylsalicylic Acid and Caffeine in Pharmaceutical Formulation by First Derivative Synchronous Fluorimetric Method

A sensitive, rapid, and specific assay has been developed for the simultaneous determination of acetylsalicylic acid and caffeine in commercial tablets based on their natural fluorescence. The mixture of these drugs was resolved by first derivative synchronous fluorimetric technique using two scans. At Δλ=106 nm, using first derivative synchronous scanning, only acetylsalicylic acid yields a detectable signal at 316 nm (peak to zero method) which is unaffected by caffeine. At Δλ=30 nm, the signal of caffeine at 288 nm (peak to zero method) is not affected by acetylsalicylic acid. The range of application is between 0.021 and 41.62 μg ml⁻¹ (correlation coefficient, R=0.9995) for acetylsalicylic acid and between 0.4486 and 44.86 μg ml⁻¹ (correlation coefficient, R=0.99786) for caffeine. The recovery range of 98.40–102% for acetylsalicylic acid and 90–100.5% for caffeine from their synthetic mixture was reported. Overall recovery of both compounds about 97–99% for acetylsalicylic acid and 97–98% for caffeine was obtained from real sample analysis. The detection limits are 0.0013 μg ml⁻¹ and 0.0306 μg ml⁻¹ for acetylsalicylic acid and caffeine, respectively. The relative standard deviation (n=10) for 20 μg ml⁻¹ of acetylsalicylic acid is 2.75% and for 2.2 μg ml⁻¹of caffeine is 1.7%.     

Photovoltaic structures using AgSb(S x Se1−x )2 thin films as absorber

Photovoltaic structures were prepared using AgSb(S _x Se_1?x )₂ as absorber and CdS as window layer at various conditions via a hybrid technique of chemical bath deposition and thermal evaporation followed by heat treatments. Silver antimony sulfo selenide thin films [AgSb(S _x Se_1?x )₂] were prepared by heating multilayers of sequentially deposited Sb₂S₃/Ag dipped in Na₂SeSO₃ solution, glass/Sb₂S₃/Ag/Se. For this, Sb₂S₃ thin films were deposited from a chemical bath containing SbCl₃ and Na₂S₂O₃. Then, Ag thin films were thermally evaporated on glass/Sb₂S₃, followed by selenization by dipping in an acidic solution of Na₂SeSO₃. The duration of dipping was varied as 3, 4 and 5 h. Two different heat treatments, one at 350 °C for 20 min in vacuum followed by a post-heat treatment at 325 °C for 2 h in Ar, and the other at 350 °C for 1 h in Ar, were applied to the multilayers of different configurations. X-ray diffraction results showed the formation of AgSb(S _x Se_1?x )₂ thin films as the primary phase and AgSb(S,Se)₂ and Sb₂S₃ as secondary phases. Morphology and elemental detection were done by scanning electron microscopy and energy dispersive X-ray analysis. X-ray photoelectron spectroscopic studies showed the depthwise composition of the films. Optical properties were determined by UV–vis–IR transmittance and reflection spectral analysis. AgSb(S _x Se_1?x )₂ formed at different conditions was incorporated in PV structures glass/FTO/CdS/AgSb(S _x Se_1?x )₂/C/Ag. Chemically deposited post-annealed CdS thin films of various thicknesses were used as window layer. J–V characteristics of the cells were measured under dark and AM1.5 illumination. Analysis of the J–V characteristics resulted in the best solar cell parameters of V _oc = 520 mV, J _sc = 9.70 mA cm^?2, FF = 0.50 and η = 2.7 %.     

Nucleation efficiency of R134a as a sensitive liquid for superheated drop emulsion detector

Superheated emulsion detector is known to detect neutrons, γ-rays and other charged particles. The present work includes the study of nucleation efficiency of superheated drops of one of the CFC-free liquids, R134a (C₂H₂F₄), to fast neutrons, its response to γ-rays from ²⁴¹Am and ¹³⁷Cs and compare its nucleation efficiency with that of R12. The observation indicates that because of the presence of hydrogen, the nucleation efficiency is less in R134a than in R12 in the present neutron energy range of consideration. R134a is one of the most environment-friendly, commercially available liquid that is suitable for superheated drop detector, specially in neutron dosimetry and one needs to investigate it in detail.     

Improved pulse schemes for separated local field spectroscopy for static and spinning samples

An improved pulse sequence for SLF experiments based on the magic sandwich (MS) scheme for homo-nuclear dipolar decoupling is proposed. The sequence incorporates a double MS, both on I and S spins and has been named as EXE-MS2. The proposed scheme which has a scaling factor of 1 is observed to be free from low intensity artifacts and provides better line-widths particularly for S spins labeled at multiple sites. The pulse sequence which has been applied on static oriented samples incorporates the EXE scheme where direct polarization of the S spin in the B(0) field is utilized in the place of polarization inversion and is observed to perform well without any loss of sensitivity while ensuring considerable reduction in rf power input into the sample. The EXE scheme has also been tested for solid samples under MAS.     

Monte Carlo Methods for Estimating Interfacial Free Energies and Line Tensions

Excess contributions to the free energy due to interfaces occur for many problems encountered in the statistical physics of condensed matter when coexistence between different phases is possible (e.g. wetting phenomena, nucleation, crystal growth, etc.). This article reviews two methods to estimate both interfacial free energies and line tensions by Monte Carlo simulations of simple models, (e.g. the Ising model, a symmetrical binary Lennard-Jones fluid exhibiting a miscibility gap, and a simple Lennard-Jones fluid). One method is based on thermodynamic integration. This method is useful to study flat and inclined interfaces for Ising lattices, allowing also the estimation of line tensions of three-phase contact lines, when the interfaces meet walls (where “surface fields” may act). A generalization to off-lattice systems is described as well. The second method is based on the sampling of the order parameter distribution of the system throughout the two-phase coexistence region of the model. Both the interface free energies of flat interfaces and of (spherical or cylindrical) droplets (or bubbles) can be estimated, including also systems with walls, where sphere-cap shaped wall-attached droplets occur. The curvature-dependence of the interfacial free energy is discussed, and estimates for the line tensions are compared to results from the thermodynamic integration method. Basic limitations of all these methods are critically discussed, and an outlook on other approaches is given.     

Calculation of geometrical coupling coefficients for the hyperspherical harmonics approach

An elegant and fast method for the calculation of geometrical structure coefficients needed for an expansion of a few-body wavefunction and interaction in hyperspherical harmonics has been proposed. A sum rule for the GSC has also been derived, which is useful for an independent check of the coefficients. The proposed method of computation is many orders of magnitude faster than conventional methods.