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## Generalized pencils of rays in statistical wave optics

### Pramana (1983-02-01) 20: 105-124 , February 01, 1983

The recently introduced generalized pencil of Sudarshan which gives an exact ray picture of wave optics is analysed in some situations of interest to wave optics. A relationship between ray dispersion and statistical inhomogeneity of the field is obtained. A paraxial approximation which preserves the rectilinear propagation character of the generalized pencils is presented. Under this approximation the pencils can be computed directly from the field conditions on a plane, without the necessity to compute the cross-spectral density function in the entire space as an intermediate quantity. The paraxial results are illustrated with examples. The pencils are shown to exhibit an interesting scaling behaviour in the far-zone. This scaling leads to a natural generalization of the Fraunhofer range criterion and of the classical van Cittert-Zernike theorem to planar sources of arbitrary state of coherence. The recently derived results of radiometry with partially coherent sources are shown to be simple consequences of this scaling.

## Inner-shell excitation of alkali-metal atoms

### Pramana (1990-07-01) 35: 89-94 , July 01, 1990

Inner-shell excitation of alkali-metal atoms, which leads to auto-ionization, is investigated. Comparison is made with other available data. Basic difficulties in making accurate calculations for inner-shell excitation process are discussed. Suggestions are made for further study of inner-shell process in atoms and ions.

## Weak electron acoustic double layers in a multicomponent plasma

### Pramana (1987-04-01) 28: 399-408 , April 01, 1987

Formation of electron acoustic double layers in a magneto-plasma with two ion species is investigated. The existence of double layers propagating almost perpendicular to the magnetic field in a plasma with two distinct ion species and cold electron is discussed.

## Current observational constraints on inflationary models

### Gravitation and Cosmology (2008-01-01) 14: 38-40 , January 01, 2008

We review current observational constraints on inflationary models and show that the Λ-inflation is observationally favored.

## Fractional order phase transition in lipid bilayer: dipalmitoyllecithin

### Pramana (1982-07-01) 19: 43-49 , July 01, 1982

Dipalmitoyllecithin (DPL) shows an order ← → disorder pressure transition which is neither of first order nor of second order but can be treated as a fractional order (3/2 order) transition. The Ising model formalism is adopted for the study of such a system. A suitable equilibrium constant is defined which generates a 3/2 order transition. Transition curves are obtained and compared with the experimental curves of Liu and Kay. Reverse transition curves are also obtained and the system exhibits hysteresis effect. An approximate expression connecting transition pressures at different temperatures is obtained and the calculated and the experimental values are in good agreement.

## Design and fabrication of a time-of-flight spectrometer for studies of multiple ionization of gases by charged particle impact

### Pramana (2002-04-01) 58: 623-638 , April 01, 2002

A time-of-flight spectrometer has been designed and fabricated for measuring the charge state distributions of target ions produced in collisions of keV-electrons with gaseous target atoms/molecules. The design details of the spectrometer and the description of experimental procedures for optimizing various parameters are presented and discussed. The working principle of the spectrometer, its time- and mass-focussing conditions, transmissions and detection efficiency etc. are given. A few typical test runs on multiple ionization of Ne and Ar gas atoms are illustrated. These spectra are found to yield the time resolution of about 10 ns for Ar^{4+} ion peak in 24.0 keV e^{−} — Ar collisions while the mass resolution of the spectrometer is obtained about 10% at mass *m*=20.

## Chaos in Josephson junctions

### Pramana (1997-02-01) 48: 637-654 , February 01, 1997

A detailed analysis of the control space characterization of phase locked states and chaotic attractors in Josephson junctions is presented, based on a model that includes both quadratic damping and cosine interference terms. In addition, some novel features of the nonlinear characteristics of the junction like evolution of basin boundaries, bifurcation structure analysis and scaling behaviour of Lyapunov exponent are discussed.

## Phonon drag effect in three- and two-dimensional electron systems

### Pramana (1987-05-01) 28: 489-501 , May 01, 1987

The nonequilibrium phonon flow drags the electrons, and depending upon experimental conditions manifests itself in the acoustoelectric current, acoustomagnetic field or acoustoelectric field. The results of these phenomena in Sn, Al, Ga, Ag measured with SQUID technique are discussed.

In the two-dimensional (2D) case the phonon drag is studied on the interface of bicrystals and on the cleavage (111) surface of Ge and on the inversion layer on (111) (100) planes of Si. In all these cases the phonon drag is about two orders of magnitude larger than in metals with the same charge density. This is due to the drag of surface electrons by nonequilibrium phonon of the whole specimen.

The Kohn resonance of phonons with Fermi surface and topological transitions on Fermi surface of 2D electrons produced sharp singularities of phonon drag effect in 2D cases.

## Flare-associated surge prominence on 1980 october 30

### Journal of Astrophysics and Astronomy (1987-12-01) 8: 295-303 , December 01, 1987

The Hα observations of a flare-associated surge prominence on 1980 October 30 have been described. Morphology and dynamics of the surge prominence have been presented. From our observations and analysis we have estimated the magnetic field associated with surge material to be about 35 gauss which is in good agreement with the earlier result of Tandberg-Hanssen & Malville (1974). It has been determined that coronal pressure is not acting as a resistive force on the outward expansion of the surge into the corona. The kinetic energy of the surge was about 10^{28} erg, which is 2 orders less than required for the mass to escape the chromosphere. It appears that the flare-associated surge prominence was perhaps a result of kink instability in the flaring region.

## Some new radiating Kerr-Newman solutions

### Pramana (1991-07-01) 37: 1-11 , July 01, 1991

Three exact non-static solutions of Einstein-Maxwell equations corresponding to a field of flowing null radiation plus an electromagnetic field are presented. These solutions are non-static generalizations of the well known Kerr-Newman solution. The current vector is null in all the three solutions. These solutions are the electromagnetic generalizations of the three generalized radiating Kerr solutions discussed by Vaidya and Patel. The solutions discussed by us describe the exterior gravitational fields of rotating radiating charged bodies. Many known solutions are derived as particular cases.