AC Conductivity in Boron Doped Amorphous Conducting Carbon Films on the Insulating Side of MI Transition

Boron doped amorphous conducting carbon films show MI transition induced by doping. In this paper we discuss the ac conductivity of the films, which lie on the insulating side of MI transition. The ac conductivity data is analyzed as a function of frequency as well as temperature for both real as well as imaginary part of the conductivity data. The ac conductivity of these samples shows enhanced interaction effect at low temperature. The conduction mechanism at high frequency and at low temperature is due to the tunneling mechanism. At intermediate temperatures and at moderate frequencies, the conductivity data is in good agreement with extended pair approximation modified for interaction effect. At high temperature and at low frequencies, the mechanism of ac conductivity is similar to that of dc conduction. The conductivity data for the insulating samples near the boundary of MI transition were analyzed using an RC element model. While fitting the impedance data, a new type of constant phase element (inductive instead of capacitive) was found to be appropriate. At present the origin of this inductive CPE is not is clear but we believe its origin is in the electron-electron interaction, which makes any attempt of applied frequency a slower response. Our ac conductivity results are well explained by tunneling models rather than hopping models.Comment: in revie

Bulk Viscous Cosmological Models in Barber's Second Self Creation Theory

Barber's second self creation theory with bulk viscous fluid source for an LRS Bianchi type-I metric is considered by using deceleration parameter to be constant where the metric potentials are taken as function of $x$ and $t$. The coefficient of bulk viscosity is assumed to be a power function of the mass density. Some physical and geometrical features of the models are discussedComment: latex, 10 pages, submitted in Int. J. Mod. Phys.

On the Generalized Birth-Death Process and its Linear Versions

In this paper, we consider a generalized birth-death process (GBDP) and examined its linear versions. Using its transition probabilities, we obtain the system of differential equations that governs its state probabilities. The distribution function of its waiting-time in state $s$ given that it starts in state $s$ is obtained. For a linear version of it, namely, the generalized linear birth-death process (GLBDP), we obtain the probability generating function, mean, variance and the probability of ultimate extinction of population. Also, we obtain the maximum likelihood estimate of one of its parameter. The differential equations that govern the joint cumulant generating functions of the population size with cumulative births and cumulative deaths are derived. In the case of constant birth and death rates in GBDP, the explicit forms of the state probabilities, joint probability mass functions of population size with cumulative births and cumulative deaths, and their marginal probability mass functions are obtained. It is shown that the Laplace transform of a stochastic integral of GBDP satisfies its Kolmogorov backward equation with certain scaled parameters. Also, the first two moments of the stochastic path integral of GLBDP are obtained. Later, we consider the immigration effect in GLBDP for two different cases. An application of a linear version of GBDP and its stochastic path integral to vehicles parking management system is discussed

Comparative Analysis of Free Space Optics and Single Mode Fiber

In this paper we have done comparative analysis of free space optics and single mode fibre optical channels system. Performance study is done for variable ranges 1km, 50km and 100km for the FSO and SMF channels. Single Mode Fiber and Free Space Optical Channel is observed that maximum Q factor, minimum bit error rate and signal power. FSO requires no licensing or frequency synchronization. It also provides the transmission of data with unlimited bandwidth. Results expose the ability of improving the Q factor by using these channels and the optimum effect concluded at (1km) length of optical rang by using the FSO channel i.e. the quality factor and signal power were increased to reach (1943 ) and (22.46dBm) respectively and MIN. BER is zero

An Optimum Allocation with a Family of Estimators Using Auxiliary Information in Sample Survey

The problem of obtaining optimum allocation using auxiliary information in stratified random sampling. An optimum allocation with a family of estimators is obtained and its efficiency is compared with that of Neyman allocation based on Srivastava (1971) class of estimators and the optimum allocation suggested by Zaidi et al., (1989). It is shown that the proposed allocation is better in the sense having smaller variance compared to other optimum allocation

Modeling Repulsive Gravity with Creation

There is a growing interest in the cosmologists for theories with negative energy scalar fields and creation, in order to model a repulsive gravity. The classical steady state cosmology proposed by Bondi, Gold and Hoyle in 1948, was the first such theory which used a negative kinetic energy creation field to invoke creation of matter. We emphasize that creation plays very crucial role in cosmology and provides a natural explanation to the various explosive phenomena occurring in local (z<0.1) and extra galactic universe. We exemplify this point of view by considering the resurrected version of this theory - the quasi-steady state theory, which tries to relate creation events directly to the large scale dynamics of the universe and supplies more natural explanations of the observed phenomena. Although the theory predicts a decelerating universe at the present era, it explains successfully the recent SNe Ia observations (which require an accelerating universe in the standard cosmology), as we show in this paper by performing a Bayesian analysis of the data.Comment: The paper uses an old SNeIa dataset. With the new improved data, for example the updated gold sample (Riess et al, astro-ph/0611572), the fit improves considerably (\chi^2/DoF=197/180 and a probability of goodness-of-fit=18%

Converging Cylindrical Shock Waves in a Nonideal Gas With an Axial Magnetic Field

This paper analyses the propagation of converging cylindrical shock waves in a nonidealgas, in the presence of an axial magnetic field. Chester-Chisnell-Whitham’s method has beenemployed to determine the shock velocity and the other flow-variables just behind the shockin the cases, when (i) the gas is weakly ionised before and behind the shock front, (ii) the gasis strongly ionised before and behind the shock front, and (iii) nonionised gas undergoes intenseionisation as a result of the passage of the shock. The effects of the nonidealness of the gas,the conductivity of the gas, and the axial magnetic field have been investigated. It is found thatin the case (i), an increase in the value of parameter ( ) characterising the nonidealness of thegas accelerates the convergence of the shock. In the case (ii), the shock speed and pressurebehind the shock increase very fast as the axis is approached; and this increase occurs earlierif the strength of the initial magnetic field is increased. In the case (iii), for smaller values of theinitial magnetic field, the shock speed, and pressure behind the shock decrease very fast afterattaining a maximum; and for higher values of the initial magnetic field, the tendency of decreaseappears from the beginning. This shows that the magnetic field has damping effect on the shockpropagation. In the case (iii), it was also found that the growth of the shock in the initial phaseand decay in the last phase were faster when it was converging in a nonideal gas in comparisonwith that in a perfect gas. Further, it has been shown that the gas-ionising nature of the shockhas damping effect on its convergence

Isothermal Shock Wave in Magnetogasdynamics

The problem of propagation of a plane isothermal discontinuity (shock) wave in a homogeneous semi-infinite body of a perfect gas, in the presence of amagnetic field have been solved. It has been shown that under certain definiteconditions, the density p at the wave front may be arbitrarily high for a singlecompression pulse. A certain class of solutions of the present problem for a nonhomogeneous semi-infinite body have been derived. Such solutions are expected to be of great importance in compression problems of plasma