Study of the peak effect phenomenon in single crystals of 2H-NbSe2

The weakly pinned single crystals of the hexagonal 2H-NbSe₂ compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of the peak effect phenomenon in three crystals of 2H-NbSe₂, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability effects and pinning.     

Integral equation formulation for buoyancy-driven convection problems

An integral equation formulation for buoyancy-driven convection problems is developed and illustrated. Buoyancy-driven convection in a bounded cylindrical geometry with a free surface is studied for a range of aspect ratios and Nusselt numbers. The critical Rayleigh number, the nature of the cellular motion, and the heat transfer enhancement are computed using linear theory. Green's functions are used to convert the linear problem into linear Fredholm integral equations. Theorems are proved which establish the properties of the eigenvalues and eigenfunctions of the linear integral operator which appears in these equations.     

Obtaining functional form for chaotic time series evolution using genetic algorithm

A genetic algorithm (GA) based strategy is presented for deducing an exact or near-exact functional form from a time series. The GA formalism proposed here utilizes (i) the "postfix" representation with a view to reduce the procedural complexities and (ii) the "elitist mating" scheme to produce fitter offspring strings. The GA procedure is exemplified by considering chaotic time series of the well-known logistic, Henon and universal maps. The GA correctly recovers the underlying functional forms for the respective time series. Measurements from a number of finite-dimensional physical, biological, and other systems often give rise to complex time series and the presented methodology should prove useful in obtaining functional forms describing accurately the evolution of the time series. (c) 1999 American Institute of Physics.     

High-Performance Thin-Layer Chromatographic Determination of Itopride Hydrochloride in its Pharmaceutical Preparation and in the Bulk Drug

JPC – Journal of Planar Chromatography – Modern TLC - A normal-phase high-performance thin-layer chromatographic (HPTLC) method has been established for quantitative estimation of...     

Reactive blends derived from modified soybean oil and silicone

Reactive blends prepared from methoxysilane terminated silicone polymers and silylated soybean oil are described and characterized. Although simple mixing of soy and silicones results in gross phase separation, homogeneous polymeric products are obtained by introducing reactive sites. These products can be used as protective coatings, additives to adhesives and new sealants. Exposure of the mixtures to moisture leads to hydrolysis of the methoxysilanes and subsequent condensation of the resulting silanols that yields stable siloxane linkages between the two immiscible phases. FTIR, TGA, and swell‐gel analyses indicate effective formation of these siloxane crosslinks. Reactive blends containing less than 20% silylated oil appeared completely transparent but increasing the soy content decreased the optical transparency. SEM micrographs reveal the silicone polymer as the continuous phase with individual spherical silylated soy oil particles distributed in it. The properties of these reactive blends vary from high elongation elastomers to high modulus resins depending on the composition. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3086–3093     

The influence of a transverse magnetic field on a subnormal glow discharge in air

In subnormal glow discharge under d.c. excitation at different pressure in a varying transverse magnetic field (0 to 30 G) some measurements have been carried out for various initial average tube currents. The voltage across the discharge increases and average tube current and residual current decreases in the magnetic field. With the help of Beckman’s expression [4] for the axial field and the electron density distribution in a transverse magnetic field the observed variation of current and voltage can be satisfactorily explained. The variation of axial electric field with transverse magnetic field can be represented to a fair degree of accuracy by the derived equation. The behaviour of residual current with magnetic field has been observed in these oscillations.     

Analysis of viscoelastic behavior and dynamic mechanical relaxation of copolyester based layered silicate nanocomposites using Havriliak–Negami model

The solid‐state viscoelastic properties are examined for intercalated nanocomposites based on a copolyester and (2‐ethyl‐hexyl)dimethyl hydrogenated‐tallow ammonium montmorillonite. The nanocomposites are prepared via the direct melt intercalation technique using a conventional twin‐screw extruder. Dynamic mechanical thermal analysis of the nanocomposites is conducted using two different test setups. The dynamic mechanical relaxation spectra show an increase in the storage modulus of the nanocomposite over the entire temperature range under study as compared to the pristine polymer (except in the transition region from 70 to 80 °C). These results are analyzed using the empirical Havriliak–Negami (HN) equation. The four temperature independent HN parameters (α, β, E₀, and E_∞) and one temperature dependent parameter (τ, the relaxation time) are determined by solving the HN equation for each temperature over the range of temperatures. The calculated moduli results fit well with the experimental values of the relaxation spectra for the nanocomposites. This study shows that the HN model can be applied to polymer layered silicate nanocomposites, and it can be used to predict their dynamic mechanical properties over a wide range of temperatures and frequencies a priori. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2657–2666, 2004     

Simple and Sensitive Extractive Spectrophotometeric Method for the Assay of Mebeverine Hydrochloride in Pure and Pharmaceutical Formulations

Simple, sensitive, rapid and cost effective extraction spectrophotometric methods are described for the assay of mebeverine hydrochloride (MBH) in bulk samples and pharmaceutical formulations. These two methods (Bromophenol blue and Erichrome Black‐T) are based on the formation of chloroform soluble ion‐pair complexes of MBH with Bromophenol blue (BPB) and with Erichrome Black‐T (EBT), to form yellow and pink colored chromogen in a Glycine‐HCl buffer of pH 2.4 (BPB) and in a KCl‐HCl buffer of pH 1.4 (EBT) with absorbance maximum at 416 nm and at 524 nm for BPB and EBT respectively. The calibration graph is found to linear over 0.2–20 μg/mL (BPB) and 0.2–20 μg/mL (EBT), with molar absorptivity values of 1.8295 × 10⁴ 1 moL^?1 cm^?1 and 1.5896 × 10⁴ 1 moL^?1 cm^?1, respectively. The LOD (Limit of Detection) were found to be 0.090 μg/mL and 0.084 μg/mL and LOQ (Limit of Quantification) were 0.2997 μg/mL and 0.2730 μg/mL for the BPB and EBT method, respectively. The results of analysis for the two methods have been validated statistically and by recovery studies. The results are compared with those obtained with reported method. The proposed methods are simple, sensitive, accurate and suitable for quality control applications.     

Determination of isoniazid and hydrazine by capillary electrophoresis with amperometric detection at a Pt-particle modified carbon fiber microelectrode

Capillary electrpphoresis (CE)/electrochemical detection (EC) for the simultane-ous determination of hydrazine and isoniazid has been developed.The electrochemical method uses a novel modified electrode dispersed with ultrafine platinum particles on the surface of a 30μm carbon fiber microelectrode.The unique characteristic of the Pt-particles modified carbon fiber microelectrode is its excellent stability.The current measurement for hydrazine is more sensitive than that of isoniazid.Selective determination of trace amount of free hydrazine in isoniazid and its formulation can be achieved at applied potential of 0.5V.     

Thermodynamic approach to enhance the dispersion of graphene in epoxy matrix and its effect on mechanical and thermal properties of epoxy nanocomposites

Graphene-reinforced polymer nanocomposites are under intense investigation in recent years. In this work, graphene nanosheets have been prepared using chemical reduction method of graphene oxide. Graphene-reinforced epoxy nanocomposites show an enhancement in mechanical and thermal properties at 0.05 wt.% of graphene in epoxy matrix. Modification of graphene with polyvinylpyrrolidone (PVP) shows the significant enhancement in mechanical and thermal properties of epoxy nanocomposites. PVP-modified graphene nanosheets reduces the gap of enthalpic and entropic penalties and facilitates improved dispersion of graphene in epoxy matrix. In addition, enhanced dispersion of PVP-modified graphene in epoxy matrix results in better load transfer across graphene–epoxy interface. Glass transition temperature (T_g) of PVP-modified graphene epoxy nanocomposites increases as compared to pure epoxy because there exist an interaction between epoxy and PVP. Fractography study reveals the localized ductile fracture.