Polarisation-dependent dielectric processes in ferroelectric liquid crystals

The behaviour of dielectric relaxation process has been investigated in four ferroelectric liquid crystal (FLC) materials having different spontaneous polarisation (Ps) values. Ps effect on the permittivity in four different FLCs has been carried out in highly anchored sample cells around ~8 μm thick. It has been found that the main contribution to the dielectric permittivity in chiral Smectic C (SmC*) phase is due to Goldstone mode (GM) and partially unwound helical mode (p-UHM). In higher PS value FLC materials, the p-UHM process is found to dominate the dielectric properties. It has also been observed that p-UHM process is highly dependent on the probing ac voltage and temperature, whereas GM is found to be weakly dependent of probing voltage and temperature in SmC* phase of all the studied FLC materials. The influential contribution of p-UHM has exhibited the dielectric properties in its intrinsic frequency range making the materials suitable for futuristic display and photonics devices.     

Transition to chaos in a driven pendulum with nonlinear dissipation

The Melnikov-Holmes method is used to study the onset of chaos in a driven pendulum with nonlinear dissipation. Detailed numerical studies reveal many interesting features like a chaotic attractor at low frequencies, band formation near escape from the potential well and a sequence of subharmonic bifurcations inside the band that accumulates at the homoclinic bifurcation point.     

Synthesis of amphiphilic poly(N‐vinylcaprolactam) using ATRP protocol and antibacterial study of its silver nanocomposite

Atom transfer radical polymerization (ATRP) of N‐vinylcaprolactam (NVCL) was studied by uisng ethyl‐2‐bromoisobutyrate (EIB) as initiator in 1,4‐dioxane. It led to controlled radical polymerization of NVCL, with the molecular weight increased along with the conversion of monomer and a relatively narrow molecular weight distribution could be obtained, as determined by gel permeation chromatography. ¹H NMR showed that the major population of poly(N‐vinylcaprolactam) (PVCL) retained the chain‐end functional group. The living nature of the ATRP for NVCL was confirmed by the experiments of PVCL chain extension. PVCL was further investigated for its ability to form micelles in aqueous media. Self‐assembling of the amphiphilic PVCL leads to the formation of their micellar aggregates in aqueous media which was confirmed by transmission electron microscope. The critical micelle concentration value was calculated from the photophysical changes of Pyrene‐1‐Carboxaldehyde by UV absorption studies and was found to be 0.0320 mg/mL. The polymer nanocomposite was synthesized and examined in view of antibacterial effect against Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Proteus mirabilis, and Klebsiella pneumonae. It was found that polymer nanocomposite possess strong antibacterial activity against Enterococcus faecalis with minimum inhibitory concentration value of 32 μg/mL. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Aspects of stochastic resonance in Josephson junction,bimodal maps and coupled map lattice

We present the results of extensive numerical studies on stochastic resonance and its characteristic features in three model systems, namely, a model for Josephson tunnel junctions, the bistable cubic map and a coupled map lattice formed by coupling the cubic maps. Some interesting features regarding the mechanism including multisignal amplification and spatial stochastic resonance are shown.     

Efficient use of correlation entropy for analysing time series data

The correlation dimension D ₂ and correlation entropy K ₂ are both important quantifiers in nonlinear time series analysis. However, use of D ₂ has been more common compared to K ₂ as a discriminating measure. One reason for this is that D ₂ is a static measure and can be easily evaluated from a time series. However, in many cases, especially those involving coloured noise, K ₂ is regarded as a more useful measure. Here we present an efficient algorithmic scheme to compute K ₂ directly from a time series data and show that K ₂ can be used as a more effective measure compared to D ₂ for analysing practical time series involving coloured noise.      

Broadly tunable parametric line emission from β-barium borate on pumping with picosecond pulses

Tunable line emission (LE) over a large wavelength region (340–980 nm) is obtained by pumping thick crystals of β-barium borate (BBO) with picosecond pulses at 532 nm. Phenomena of group velocity dispersion, diffraction and phase matching take place simultaneously such that the radiation shows specific features that are characteristic of (i) strongly coupled fundamental and harmonic fields, (ii) amplified phase matched superfluorescence, (iii) conical emission and (iv) four wave mixing.     

f-α Spectrum of circle map

We present an analytic perturbative method for calculatingf(α) and the generalized dimensionD _q of the critical invariant circle of the polynomial circle map. The scaling behaviour is found to depend onz, the exponent defining the map. The asymptotic bounds of the scaling constantsα(z) andδ(z) are verified analytically.     

Linear scaling relations near onset of chaos for the Josephson junction model

The transition region from order to chaos is analysed numerically in a model system, viz. the Josephson junction. This reveals linear scaling relations for Lyapunov exponents and the Lyapunov dimensions with indices close to one.     

Resonance phenomena in discrete systems with bichromatic input signal

We undertake a detailed numerical study of the twin phenomenon of stochastic and vibrational resonance in a discrete model system in the presence of bichromatic input signal. A two parameter cubic map is used as the model that combines the features of both bistable and threshold systems. In addition to the results already shown for continuous systems, our analysis brings out several interesting features both for vibrational and stochastic resonance, including the existence of a cross over behavior between the two. In the regime of vibrational resonance, it is shown that the additional high frequency forcing can change the effective value of the system parameter resulting in the shift of the bistable window. In the case of stochastic resonance, the study reveals a fundamental difference between the bistable and threshold mechanisms in the response, with respect to multisignal input.     

Design of a Sensitive Electrochemical Sensor Based on Ferrocene-reduced Graphene Oxide/Mn-spinel for Hydrazine Detection

Herein, we report construction of a ferrocene-reduced graphene oxide-Mn spinel modified glassy carbon electrode (Fc−G/Mn₃O₄/GCE) as a sensitive electrochemical probe for hydrazine detection via its oxidation. The synergistic effect of ferrocene, graphene oxide and Mn₃O₄ provides it a great electrocatalytic effect. The electrochemical investigations of Fc−G/Mn₃O₄/GCE were studied using cyclic voltammetry, while differential pulse voltammetry was utilized for recording the electrocatalytic sensing of hydrazine. The prepared Fc−G/Mn₃O₄ offers a platform for sensitive and selective detection of low-level hydrazine in two linear ranges from 0.045 to 108 μM and 108 to 653 μM with limit of detection 8.5 nM. Real sample analysis was also performed in local industrial water samples with satisfactory recovery results.