Investigation of Complex Impedance and Modulus Properties of Nd Doped 0.5BiFeO3-0.5PbTiO3 Multiferroic Composites

0.5BiNdxFe1-xO3-0.5PbTiO3 (x=0.05, 0.10, 0.15, 0.20) composites were successfully synthesized by a solid state reaction technique. At room temperature X-ray diffraction shows tetragonal structure for all concentrations of Nd doped 0.5BiFeO3-0.5PbTiO3 composites. The nature of Nyquist plot confirms the presence of bulk effects only for all compositions of Nd-doped 0.5BiFeO3-0.5PbTiO3 composites. The bulk resistance is found to decreases with the increasing in temperature as well as Nd concentration and exhibits a typical negative temperature coefficient of resistance (NTCR) behavior. Both the complex impedance and modulus studies have suggested the presence of non-Debye type of relaxation in the materials. Conductivity spectra reveal the presence of hopping mechanism in the electrical transport process of the materials. The activation energy of the composite increases with increasing Nd concentration and were found to be 0.28, 0.27, 0.31 and 0.32eV for x=0.05, 0.10, 0.15, 0.20 respectively at 200-275 oC for conduction process.Comment: 22 pages, 12 figures, 2 tables, 34 Referenc

Effect of electron corelation on superconducting pairing symmetry

The role of electron correlation on different pairing symmetries are discussed in details where the electron correlation has been treated within the slave boson formalism. It is shown that for a pure $s$ or pure $d$ wave pairing symmetry, the electronic correlation suppresses the $s$ wave gap magnitude (as well as the $T_c$) at a faster rate than that for the $d$ wave gap. On the otherhand, a complex order parameter of the form ($s+id$) shows anomalous temperature dependence. For example, if the temperature ($T_{c}^d$) at which the $d$ wave component of the complex order parameter vanishes happens to be larger than that for the $s$ wave component ($T_{c}^s$) then the growth of the $d$ wave component is arrested with the onset of the $s$ wave component of the order parameter. In this mixed phase however, we find that the suppression in different components of the gap as well as the corresponding $T_c$ due to coulomb correlation are very sensitive to the relative pairing strengths of $s$ and $d$ channels as well as the underlying lattice. Interestingly enough, in such a scenario (for a case of $T_{c}^s > T_{c}^d$) the gap magnitude of the $d$ wave component increases with electron correlation but not $T_{c}^d$ for certain values of electron correlation. However, this never happens in case of the $s$ wave component. We also calculate the temperature dependence of the superconducting gap along both the high symmetry directions ($\Gamma$ - M and $\Gamma$ - X) in a mixed $s+id$ symmetry pairing state and the thermal variation of the gap anisotropy ($\frac{\Delta_{\Gamma - M}}{\Delta_{\Gamma - X}}$) with electron correlation. The results are discussed with reference to experimental observations.Comment: 22 pages, latex, 12 figures (attached in ps /eps) Journal : Accepted for publication in Euro. J. Phys

Anti-isospectral Transformations, Orthogonal Polynomials and Quasi-Exactly Solvable Problems

We consider the double sinh-Gordon potential which is a quasi-exactly solvable problem and show that in this case one has two sets of Bender-Dunne orthogonal polynomials . We study in some detail the various properties of these polynomials and the corresponding quotient polynomials. In particular, we show that the weight functions for these polynomials are not always positive. We also study the orthogonal polynomials of the double sine-Gordon potential which is related to the double sinh-Gordon case by an anti-isospectral transformation. Finally we discover a new quasi-exactly solvable problem by making use of the anti-isospectral transformation.Comment: Revtex, 19 pages, No figur

Study on Mechanical Behavior of Polymer based Composites with and without Wood Dust Filler

Particulate fillers are of considerable interest, not only from an economic viewpoint, but as modifiers especially the physical properties of the polymer. A notable advance in the polymer industry has been the use of fiber and particulate fillers as reinforcements in polymer matrix. Over the last few decades, the considerable attention has been devoted towards wood dust filled polymer composites due to its many advantages. These include mainly the improved nvironmental performance, due to the use of biodegradable materials and the reduction in the use of non-renewable (oil based) resources throughout the whole life cycle of the composite; the low cost of wood flour; the lower specific weight of these fillers, in comparison to the traditional mineral-inorganic ones; the improvement in safety for the production employees and the special aesthetic properties of the composites. Although there are several reports in the literature which discuss the mechanical behavior of wood/polymer composites, however, very limited work has been done on effect of wood dust fillers on mechanical behavior glass fiber based polymer composites. Against this background, the present research work has been undertaken, with an objective to explore the potential utilization of wood dust filler as a reinforcing material in polymer composites and to investigate its effect on the mechanical behaviour of the resulting composites. Finally, the SEM analysis has been made on fractured surfaces of composites after different tests

Relaxation of Collective Excitations in LJ-13 Cluster

We have performed classical molecular dynamics simulation of $Ar_{13}$ cluster to study the behavior of collective excitations. In the solid ``phase'' of the cluster, the collective oscillation of the monopole mode can be well fitted to a damped harmonic oscillator. The parameters of the equivalent damped harmonic oscillator-- the damping coefficient, spring constant, time period of oscillation and the mass of the oscillator -- all show a sharp change in behavior at a kinetic temperature of about $7.0^oK$. This marks yet another characteristic temperature of the system, a temperature $T_s$ below which collective excitations are very stable, and at higher temperatures the single particle excitations cause the damping of the collective oscillations. We argue that so long as the cluster remains confined within the global potential energy minimum the collective excitations do not decay; and once the cluster comes out of this well, the local potential energy minima pockets act as single particle excitation channels in destroying the collective motion. The effect is manifest in almost all the physical observables of the cluster.Comment: Revised and enlarged. 6 pages RevTeX style. 7 eps figures available on request. To appear in J Chem Phy

Study and Implementation of 3G Mobile Security

In the last decade there has been an exponential rise in use of mobile devices. 3G is the latest mobile technology that is currently in widespread use. The Universal Mobile Telecommunications System (UMTS) is the most popular third generation mobile communication systems, which reposes on the popularity of the ‘second generation’ GSM system by introducing high quality services while retaining its essential and robust security features. Wireless communication is less secure, and mobility entails higher security risks than stationary devices. Security is the foremost concern in today’s mobile communication systems. Latest security mechanisms are needed to protect the singular features introduced in 3G technology. The security framework for 3G mobile networks is considered, and the various protocols for protection of the network access interface are studied and analyzed