Search Results

You are looking at 1 - 9 of 9 items

  • Author: S. Majumdar x
Clear All Modify Search

Abstract

Fourier integrals are set up for the field of a point charge moving uniformly in an arbitrary direction in a uniaxial medium anisotropic in ε only. The integrals break up into several parts two of which yield the ordinary and extraordinary cones with uniform azimuthal potential distribution. The remaining integrals neither contribute to the energy radiated nor affect the size and the shape of the cones, but merely distort the field within the cones. The integrals are evaluated exactly in the non-dispersive case and closed expressions for the potential are obtained. In the dispersive case, the radiation field is determined by using the asymptotic form of the Hankel functions occurring in the integrand. The resulting expressions exhibit the high azimuthal asymmetry characteristic of anisotropic fields. From the expressions derived for a pure dielectric the potential in a doubly anisotropic medium is obtained, without a fresh calculation, by making appropriate substitutions for the coordinates of the field point and the components of the dielectric tensor.

The electromagnetic field of a point charge moving uniformly in a uniaxial dispersive medium is studied in the rest frame of the charge. It is shown that the Fourier integral for the scalar potential breaks up into three integrals, two of which are formally identical to the isotropic integral and yield the ordinary and extraordinary cones. Using the convolution theorem of the Fourier transform, the third integral is reduced to an integral over the isotropic field. Dispersion is explicitly introduced into the problem and the isotropic field is evaluated on the basis of a simplified dispersion formula. The effect of dispersion on the field cone is studied as a function of the cut-off frequency.

Abstract

Background: Phenobarbital is one of the oldest, cheapest and easily available cerebroprotective drugs for the hypoxic brain. However, its potential and various actions have not been fully explored.

Aim: To evaluate the effects of Phenobarbital on levels of oxidants and anti-oxidants in term and near term neonates with hypoxic ischemic encephalopathy.

Methods: Design–randomized controlled trial. Setting–tertiary care referral perinatal centre. Procedure–asphyxiated neonates (gestation ≥34 weeks) with HIE were randomized to receive Phenobarbital 20 mg/kg IV within first six hours of life or to control group. CSF levels of malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GPx) and blood levels of vitamins A and E were estimated at 10–12 hours of age.

Results: CSF levels of MDA, SOD, GPx and blood levels of vitamins A and E were significantly lower in the Phenobarbital group (p<0.001). There was a trend towards lower levels of CSF MDA, SOD, GPx and blood vitamins A and E in babies with normal outcome as compared to babies with adverse outcome (death or neurologically abnormal at discharge).

Conclusion: Phenobarbital in the dose of 20 mg/kg IV given within 6 hours of life in term and near-term neonates with HIE, was associated with a decrease in lipid peroxides, anti-oxidant enzymes and anti-oxidant vitamins.

Abstract

High-temperature oxidation behaviour of Mo-40Ti-30Si (at.%) alloy was investigated in the temperature regime of 900-1300C in air. Isothermal weight change data recorded up to 100 h of exposure revealed parabolic weight gain kinetics at all the tested temperatures. The protective oxide scale composed with SiO2 (silica) and TiO2 (titania) forming a duplex oxide microstructure consisting of TiO2 particles embedded in the continuous SiO2 matrix. The oxide scale showed parabolic growth kinetics, and the activation energies for the scale growth were found to be 72.2 kJ/mol in 900-1200C and 324.9 kJ/mol in 1200-1300C. The kinetics of the protective scale growth on the alloy surface was mainly controlled by the growth of the silica film and the inward diffusion of oxygen through the duplex oxide layer.