Anisotropic fluid spheres in general relativity

A procedure is developed to find static solutions for anisotropic fluid spheres from known static solutions for perfect fluid spheres. The method is used to obtain four exact analytical solutions of Einstein’s equations for spherically symmetric self-gravitating distribution of anisotropic matter. The solutions are matched to the Schwarzschild exterior metric. The physical features of one of the solutions are briefly discussed. Many previously known perfect fluid solutions are derived as particular cases.     

Synthesis,anti‐bacterial,anti‐asthmatic and anti‐diabetic activities of novel N‐substituted‐2‐(benzo[d]isoxazol‐3‐ylmethyl)‐1H‐benzimidazoles

Synthesis of a series of novel class of N‐substituted‐2‐(benzo[d]isoxazol‐3‐ylmethyl)‐1H‐benzimidazoles ( 4 ) by the condensation of o‐phenylenediamine ( 1 ) with benzo[d]isoxazol‐3‐yl‐acetic acid ( 2 ) and subsequent reactions with different types of electrophiles have been reported. Some compounds exhibited promising anti‐bacterial activity against Salmonella typhimurium, however poor activity against Staphylococcus aureus. The compound 4t was found to have high activity even at 1 μg/ml compared to Cephalexin against S. aureus. The biological activity against PDE‐IV for potential anti‐asthmatic effect and against DP‐IV and PTP‐1B for potential anti‐diabetic effects was disappointing.     

Radiating Kerr particle in Einstein universe

A generalized Kerr-NUT type metric is considered in connection with Einstein field equations corresponding to perfect fluid plus a pure radiation field. A general scheme for obtaining the exact solutions of these field equations is developed. Two physically meaningful particular cases are investigated in detail. One gives the field of a radiating Kerr particle embedded in the Einstein universe. The other solution may probably represent a deSitter-like universe pervaded by a pure radiation field.     

The transition width and critical current density measurements on slow-cooled YBa2Cu3O7−x superconductor

It is shown that by adopting a very gradual programmed cooling procedure in oxygen environment one can obtain a sharp transition (ΔT _c⋍1 K) in YBa₂Cu₃O_7−x while retaining the high-T _c value (⋍105 K) of samples prepared by a semi-wet route. This is attributed to a maximum occupancy of oxygen at 0 1/2 0 sites and a near-perfect ordering of vacancies at 1/2 0 0 sites in the orthorhombic unit cell which maximizes the availability of conduction paths in the form of continuous CuO₄ chains. Critical current densities (J _c) of 204 A cm⁻² are obtained for bulk samples at 77 K. It is suggested that the intergrain coupling is weak and thus limits the transportJ _c-values.     

Temperature hysteretic effect and its influence on colossal magnetoresistance of La0.33Nd0.33Ca0.33MnO3

Electrical resistance (R) measurements of a bulk La_0.33Nd_0.33Ca_0.33MnO₃ perovskite in magnetic fields up to 40 kOe have revealed anomalous temperature hysteretic effects both in 0 Oe and 20 kOe magnetic fields. The sharp peak observed in the R vs. T plot indicates the occurrence of metal-to-insulator (M-I) transition at a temperature of T _MI=110 K and 140 K, for cooling and warming paths, respectively. An applied magnetic field of 20 kOe reduces the resistance and shifts T _MI to 160 K and 185 K for cooling and warming, respectively. We have observed a much higher resistance in the cooling path than in the warming path leading to the hysteretic resistance ratio (R _cool/R _warm) of 200 at 110 K and 1.8 at 160 K for 0 Oe and 20 kOe, respectively. Record values of colossal magnetoresistance (CMR) have been achieved. The CMR value reaches nearly 99% in the temperature ranges of 90 K to 140 K and 90 K to 170 K for 20 kOe and 40 kOe magnetic fields in the cooling mode, respectively. The observed unusual behavior is attributed to the co-existence of La-rich and Nd-rich domains assumed to be distributed randomly in the compound.     

Investigating the vortex melting phenomenon in BSCCO crystals using magneto-optical imaging technique

Using a novel differential magneto-optical imaging technique we investigate the phenomenon of vortex lattice melting in crystals of Bi₂Sr₂CaCu₂O₈ (BSCCO). The images of melting reveal complex patterns in the formation and evolution of the vortex solid-liquid interface with varying field (H)/temperature (T). We believe that the complex melting patterns are due to a random distribution of material disorder/inhomogeneities across the sample, which create fluctuations in the local melting temperature or field value. To study the fluctuations in the local melting temperature/field, we have constructed maps of the melting landscape T _m(H, r), viz., the melting temperature (T _m) at a given location (r) in the sample at a given field (H). A study of these melting landscapes reveals an unexpected feature: the melting landscape is not fixed, but changes rather dramatically with varying field and temperature along the melting line. It is concluded that the changes in both the scale and shape of the landscape result from the competing contributions of different types of quenched disorder which have opposite effects on the local melting transition.     

An experimental limit on the coupling of a light neutral pseudoscalar particle to hadrons

Detailed results of an experiment, looking for a short-lived neutral particle decaying by ane ⁺ e ⁻ pair in the decay of the 3.68 MeV (3/2) state in¹³C, whose decay is predominantly M1, are presented. An upper limit of 7 × 10⁻⁵ has been placed on the branching ratio for decay through such a particle with a mass in the range 1.7 to 1.9 MeV/c². This leads to an upper limit of 10⁻⁶ for the coupling of such a particle to nucleons. Such a limit rules out the explanation of thee ⁺ ande ⁻ peaks recently observed in heavy ion collisions, as due to the decay of a neutral particle.     

HPTLC Method for Determination of Colchicine in a Pharmaceutical Formulation

JPC – Journal of Planar Chromatography – Modern TLC - An HPTLC method, using an internal standard, for analysis of colchicine in a pharmaceutical formulation, has been established and...     

Altered Membrane Mechanics Provides a Receptor-Independent Pathway for Serotonin Action

Serotonin, an important signaling molecule in humans, has an unexpectedly high lipid membrane affinity. The significance of this finding has evoked considerable speculation. Here we show that membrane binding by serotonin can directly modulate membrane properties and cellular function, providing an activity pathway completely independent of serotonin receptors. Atomic force microscopy shows that serotonin makes artificial lipid bilayers softer, and induces nucleation of liquid disordered domains inside the raft-like liquid-ordered domains. Solid-state NMR spectroscopy corroborates this data at the atomic level, revealing a homogeneous decrease in the order parameter of the lipid chains in the presence of serotonin. In the RN46A immortalized serotonergic neuronal cell line, extracellular serotonin enhances transferrin receptor endocytosis, even in the presence of broad-spectrum serotonin receptor and transporter inhibitors. Similarly, it increases the membrane binding and internalization of oligomeric peptides. Our results uncover a mode of serotonin–membrane interaction that can potentiate key cellular processes in a receptor-independent fashion.