Dominance of rare events in some problems in statistical physics

We show how the theory of large deviations in the coin toss experiment can give some insight into nonequilibrium fluctuation theorems and intermittency in turbulence.      

Prediction of barrier inhomogeneities and carrier transport in Ni-silicided Schottky diode

Based on Quantum Mechanical (QM) carrier transport and the effects of interface states, a theoretical model has been developed to predict the anomalous current-voltage (I-V) characteristics of a non-ideal Ni-silicided Schottky diode at low temperatures. Physical parameters such as barrier height, ideality factor, series resistance and effective Richardson constant of a silicided Schottky diode were extracted from forward I-V characteristics and are subsequently used for the simulation of both forward and reverse I-V characteristics using a QM transport model in which the effects of interface state and bias dependent barrier reduction are incorporated. The present analysis indicates that the effects of barrier inhomogeneity caused by incomplete silicide formation at the junction and the interface states may change the conventional current transport process, leading to anomalous forward and reverse I-V characteristics for the Ni-silicided Schottky diode.     

Temperature dependence of hopping transport in polymeric semiconductors

We report the results of measurement and analysis of the electrical conductivity of two synthetic highly purified copolymers of the polyacene quinone radical (PAQR) type. The dc conductivity was examined as a function of temperature and pressure. The conductivity-pressure relation is observed to go as log σ versus $\text{P}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. The conductivities under moderate pressure (400–5000 atm) show linear relationships on log σ versus $\text{T}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>4</mtext>}}$ plots in the temperature range 70 K < T < 300 K. The possible interpretations as variable range hopping or as nearest neighbour hopping with distributions of activation energies are discussed.     

Dynamic analysis of non-uniform taper bars in post-elastic regime under body force loading

This paper presents a simulation study of the free flexural vibration behavior of non-uniform taper bars of circular and rectangular cross-section under body force loading due to gravity. The loading is controlled statically to take the bar to its post-elastic state so as to predict its dynamic behavior in the presence of plastic deformation. Hence the analysis is carried out in two parts; first the static problem under axial gravity loading is solved, then the dynamic problem is solved in this loaded condition. Appropriate variational method is employed to derive the set of governing equations for both the problems. The formulation is based on unknown displacement field which is approximated by finite linear combinations of orthogonal admissible functions. The present method is validated successfully with a well-known finite element package. Results are presented to investigate the effect of shape and size on the dynamic behavior of non-uniform taper bars. The study can be extended to study the post-elastic dynamic behavior of other related problems such as rotating beams and rotating disks.     

Anisotropic Cosmological Models with Perfect Fluid and Dark Energy Reexamined

We consider a self consistent system of Bianchi type-I (BI) gravitational field and a binary mixture of perfect fluid and dark energy. The perfect fluid is taken to be the one obeying the usual equation of state, i.e., p = ξε, with ζ∉[0, 1] whereas, the dark energy is considered to be obeying a quintessence-like equation of state. The modification of the ordinary quintessence lies in the fact that its pressure becomes positive if the (dark) energy density exceeds some critical value. Exact solutions to the corresponding Einstein equations are obtained. The model in consideration gives rise to a Universe which is spatially finite. Depending on the choice of problem parameters the Universe is either close with a space-time singularity, or an open one which is oscillatory, regular and infinite in time. PACS numbers: 04.20.Ha, 03.65.Pm, 04.20.Jb     

Zinc oxide-potassium ferricyanide composite thin film matrix for biosensing applications

Thin film of zinc oxide-potassium ferricyanide (ZnO-KFCN) composite has been deposited on indium tin oxide (ITO) coated corning glass using pulsed laser deposition (PLD). The composite thin film electrode has been exploited for amperometric biosensing in a mediator-free electrolyte. The composite matrix has the advantages of high iso-electric point of ZnO along with enhanced electron communication due to the presence of a redox species in the matrix itself. Glucose oxidase (GOx) has been chosen as the model enzyme for studying the application of the developed matrix to biosensing. The sensing response of the bio-electrode, GOx/ZnO-KFCN/ITO/glass, towards glucose was studied using cylic voltammetry (CV) and photometric assay. The bio-electrode exhibits good linearity from 2.78 mM to 11.11 mM glucose concentration. The low value of Michaelis-Menten constant (1.69 mM) indicates an enhanced affinity of the immobilized enzyme towards its substrate. A quassireversible system is obtained with the composite matrix. The results confirm promising application of the ZnO-KFCN composite matrix for amperometric biosensing applications in a mediator-less electrolyte that could lead to the realization of an integrated lab-on-chip device.     

Unimolecular micelles and reverse micelles based on hyperbranched polyethers—Comparative study of AB2 + A‐R and A2 + B3 + A‐R type strategies

Core‐shell type hyperbranched polymers that are capable of forming unimolecular micelles and reverse micelles in aqueous and hydrocarbon medium, respectively, were synthesized via two approaches, namely AB₂ + A‐R and A₂ + B₃ + A‐R type copolymerizations. In case of micelle‐forming polymers, an AB₂ monomer carrying a decamethylene spacer was used along with heptaethylene glycol monomethyl ether (HPEG) as the A‐R type comonomer. One the other hand, for the preparation of reverse micelle‐forming polymers, an AB₂ monomer containing an oligo(oxyethylene) spacer was used along with cetyl alcohol as the A‐R type comonomer. The former was readily soluble in water while the latter was soluble in hydrocarbon solvents like hexane. NMR spectral studies confirmed that both the approaches generated highly branched structures wherein about 65–70% of the terminal B groups were capped by the A‐R comonomer. Dye‐uptake measurements revealed that the polymers prepared via the AB₂ + A‐R approach exhibited a significantly larger uptake compared with those prepared via the A₂ + B₃ + A‐R approach. This suggests that the AB₂ + A‐R approach generates hyperbranched polymers with better defined core‐shell topology when compared with polymers prepared via the A₂ + B₃ + A‐R approach, which is in accordance with previous studies that suggest that A₂ + B₃ approach yields polymers with significantly lower branching levels and consequently less compact structures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 80–91, 2009