Study of electrical and dielectric properties of styrene-acrylonitrile/graphite sheets composites

This paper reports the structural, electrical, dielectric and mechanical properties of the Styrene-acrylonitrile (SAN)/graphite sheets (GS) composites. The composites were prepared by in situ polymerization. The variation of electrical conductivity, dielectric constant and ac conductivity as a function of volume fraction of GS was found to follow the power law model. The dielectric constant and dissipation factor of SAN/GS composites increased significantly near the percolation. The frequency dependence of dielectric constant, dissipation factor and ac conductivity was also analyzed. Nearly ohmic behavior of current density with electric field was observed above the percolation threshold. The composite was found to possess the hardness of pure polymer at the threshold value of GS.     

Neural network-based nonlinear tracking control of kinematically redundant robot manipulators

In this paper, neural network-based nonlinear dynamical control of kinematically redundant robot manipulators is considered. The neural network-based controller achieves end-effector trajectory tracking as well as subtask tracking effectively. A feedforward neural network is employed to learn the parametric uncertainties, existing in the dynamical model of the robot manipulator. The whole system is shown to be stable in the sense of Lyapunov. Numerical simulation studies are carried out for a 3R planar robot manipulator to show the effectiveness of the control scheme.     

PSPICE circuit simulation of microbolometer infrared detectors with noise sources

In this paper, we present a method of incorporating various types of noise in circuit simulation of a microbolometer infrared detector to analyze the effect of noise on its performance. This ability of simulating electro-thermal performance of microbolometers in circuit simulation platform along with their noise performance allows designing of its suitable readout integrated circuit (ROIC). Being an electro-thermal device, a microbolometer has both the electrical and thermal components interacting with each other. Therefore, the noise sources existing in standard circuit simulators cannot predict the noise of a microbolometer correctly. Disturbances coming from the background radiation, device temperature fluctuations, flicker noise and the Johnson noise etc. contribute in the total noise of a microbolometer element. All these components of noise can be incorporated using the proposed simulation technique. The technique also allows modifying the frequency response of the noise in simulations as per the user defined noise spectrum, making it suitable for any type of microbolometer.     

Synthesis and electrochemical characterization of graphene nanoflakes and LiFe<Subscript>0.97</Subscript>Ni<Subscript>0.03</Subscript>PO<Subscript>4</Subscript>/C for lithium-ion battery

The graphene nanoflakes and olivine-type LiFe_0.97Ni_0.03PO₄/C (LFNP3/C) samples have been synthesized as anode and cathode materials, respectively. Physicochemical characterization of the graphene nanoflakes and LFNP3/C material were studied using X-ray diffraction (XRD) and scanning electron microscope (SEM). The XRD patterns reveal the formation of the pure phase of both the synthesized samples. SEM micrographs disclose the formation of spherically shaped nanosized particles for LFNP3/C while graphene shows flake-type morphology. CR2032 half and full coin cells were assembled for electrochemical testing of the synthesized samples. Cyclic voltammetry (CV) results indicate that the graphene-based half-cells, i.e., GN1H and GN2H, possess reduction peak/plateau around 0.17 V while LFNP3/C cathode shows discharging voltage plateau at 3.4 V vs. Li/Li⁺. The discharge capacities were found to be 700, 900, and 153 mAhg^?1 for GN1H, GN2H, and LFNP3/C half-cells vs. Li/Li⁺, respectively. Among full cells, LFPGN1F with γ = 0.75 (mass/capacity balancing factor) shows better charging/discharging profile at each C-rate as compared to LFPGN2F with γ = 0.55. LFPGN1F delivered an initial discharge capacity of around 154 mAhg^?1 at 0.1C and even at a high discharge rate of 1C, it retained ~97% of the discharge capacity as compared to the initial cycle at the same rate.     

Poly(vinyl chloride)-based macrocyclic membrane sensors for magnesium

Poly(vinyl chloride)-based membranes of macrocycles 4,11-dimethyl-2,4,9,11-tetraethyl-1,5,8,12-tetraaza cyclotetradeca-1,8-diene (I) and 4,11-dioxa-2,9-dimethyl-1,5,8,12-tetraaza cyclotetradeca-1,8-diene (II) with sodium tetraphenyl borate (STB) as an anion excluder and dibutyl phthalate (DBP), dioctyl phthalate (DOP), dibutylbutyl phosphonate (DBBP) and 1-chloronaphthalene (CN) as plasticizing solvent mediators were prepared and investigated as magnesium selective electrodes. The best performance was observed having the composition (II)-PVC-STB-DBP in the ratio 2:10:1:7, which works well over a wide concentration range (1.9x10(-6) to 1.0x10(-1) M) with a Nernstian slope of 29 mV per decade of activity between pH 2.5 and 6.5. These electrodes have been found to be chemically inert showing a fast response time of 15 s and were used over a period of 3 months with good reproducibility (S=+/-0.2 mV). The selectivity coefficient values for mono-, di- and trivalent cations indicate excellent selectivity for Mg(2+) over a large number of cations. The electrodes have also been used successfully in partially non-aqueous medium and as an indicator electrode in the potentiometric titration of Mg(2+) with EDTA. Anions such as Cl(-) and SO(4)(2-) do not interfere in the working of the electrode. The practical utility of the membrane sensor has also been observed in solutions contaminated with detergents (cetyltrimethyl ammonium bromide and sodium dodecyl sulphate). Above all, the membrane sensor has been very successfully used to analyse some babyfood products and soft drinks for the determination of Mg(2+).     

Oxidation of organic compounds by vanadium(v) : Part I. Monohydric alcohols

The oxidation of various monohydric alcohols with pentavalent vanadium in sulphuric acid medium is described. Optimum conditions for quantitative oxidation and the reaction mechanisms are discussed.     

Study of Sb substitution for Pr in the Pr0.67Ba0.33MnO3 system

We study the effect of Sb substitution for Pr in the hole-doped system Pr_0.67Ba_0.33MnO₃ (PBMO) for different doping levels of Sb. The two electrical resistivity transitions observed in the pristine sample PBMO shift to low temperatures on Sb doping with an overall increase in the electrical resistivity. The significant local lattice distortion and the grain boundary effects caused by the large cation size mismatch between Pr³⁺ and Sb³⁺ suppresses the double-exchange (DE) interaction and enhances the super-exchange (SE) interaction. The compounds show a significant and increasing value of magnetoresistance at temperatures below the Curie temperature, not expected from the DE model. The Curie temperature decreases with increase in Sb content but the saturation magnetization is little affected by the substitution. The spins, however, stay well aligned in the low-temperature regime. Our X-ray near-edge absorption spectra (XANES) and core level photoemission (XPS) data clearly show the Sb cation to be in +3 state and rule out any possibility of e-doping in our compounds.     

Synthesis,characterization and microbiocidal studies of novel ionic liquid tagged Schiff bases

The synthesis of novel imidazolium ionic liquid, tagged Schiff, has been described. The synthesis was achieved in three steps from 2,4-dihydroxybenzaldehyde by selective alkylation with 1,3-dibromopropane, followed by reaction with 1-methylimidazole and Schiff base formation with aromatic amines. The compounds were evaluated for antibacterial and antifungal activities. The ionic liquid tagged Schiff base 4a showed the inhibition of both Gram positive and Gram negative bacteria. It also showed broad spectrum antifungal activity against all four tested fungi; however, 4f showed highest antifungal activity against A. niger.     

Impedance spectroscopy and conductivity studies in SrBi2(Ta1−xWx)2O9 ferroelectric ceramics

Complex impedance spectroscopy (CIS) technique has been utilized to investigate the intra- and intergranular contributions to the impedance in pristine and wolframium (tungsten, W) -substituted strontium bismuth tantalate [SrBi₂(Ta_1−xW_x)₂O₉ (SBTW); x=0.0, 0.025, 0.05, 0.075, 0.1 and 0.2] ceramics as a function of temperature and frequency. CIS studies reveal that the electrical relaxation process was temperature dependent and non-Debye type. The temperature dependence of the relaxation time was found to obey the Arrhenius law. DC conductivity of the studied samples obtained from the CIS data decreased for W content upto x=0.05, followed by a subsequent increase with x>0.05. Electrical conductivity data including the typical values of the activation energies at high temperature indicated that the conductivity in the studied ceramics was essentially due to the contribution of doubly ionized oxygen vacancies to the conduction process.