Synthesis of high molecular weight polymer nanoparticles by [Cp2ZrCl2] catalyzed emulsion polymerization

An early transition metal metallocene compound, Cp₂ZrCl₂, with an anionic surfactant, sodium n‐dodecyl sulfate (SDS) as emulsifier and NaBPh₄ as cocatalyst has been found to be an effective catalytic system for polymerization and copolymerization of monomers like styrene and methyl methacrylate in aqueous medium. The diameters of the latex particles were found to be in between 20 and 40 nm. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Period adding bifurcation in a logistic map with memory

We introduce a single step memory dependence in the fully chaotic logistic map. This makes it a two dimensional system in general. However, we show that by using composite functions to define two one dimensional maps, it is possible to obtain some analytic results for the bifurcation structure. Numerical results support the calculated bifurcation scheme and, in addition, yield a further insight which allows the calculation of the convergence ratio for a new period adding scenario.     

Early Detection of Breast Cancer: Synthesis and Characterization of Novel Target Specific NIR-Fluorescent Estrogen Conjugate for Molecular Optical Imaging

Estrogen induced proliferation of existing mutant cells is widely understood to be the major risk determining factor in the development of breast cancer. Hence determination of the Estrogen Receptor[ER] status is of paramount importance. We have carried out the synthesis and characterization of a novel NIR fluorescent dye conjugate aimed at measuring ER+ve status in-vivo. The conjugate was synthesized by ester formation between 17-β estradiol and a cyanine dye namely: bis-1, 1-(4-sulfobutyl) indotricarbocyanine-5-carboxylic acid, sodium salt. The replacement of the sodium ion in the ester by a larger glucosammonium ion was found to enhance the hydrophilicity and reduce the toxic effect on cell lines. The excitation and emission peaks for the dye were recorded as 750 and 788 nm respectively; ideal for non-invasive optical imaging owing to minimal tissue attenuation and auto-fluorescence at these wavelengths. The dye (NIRDC1) has a significant drop in plasma-protein binding therefore leading to marked improvement in pharmacokinetic profile such as dye evacuation in comparison to ICG. In addition the dye showed enhanced fluorescence quantum yield, molar extinction coefficient and linearity in fluorescence relative to ICG. This dye can be potentially used as a target specific exogenous contrast agent in molecular optical imaging for early detection of breast cancer.     

Structural and optoelectronic properties of vacuum evaporated SnS thin films annealed in argon ambient

In this work, 650 nm polycrystalline SnS thin films were grown by thermal evaporation of high purity tin sulfide powder at 250 °C substrate temperature, followed by post deposition annealing at 200 °C and 300 °C for 2, 4 and 6 h, and at 400 °C for 2 and 4 h in argon ambient. The XRD pattern of the as-deposited and annealed SnS films led to the conclusion that the as-deposited films were polycrystalline in nature with preferentially oriented along (1 1 1) direction. The direct bandgap of all the films was found to be observed between 1.33 and 1.53 eV. Except for annealing at 400 °C all the films were nearly stoichiometric in nature, suggesting lower rate of desulfurization at that ambient. However, higher annealing temperature has resulted in the segregation of tin phase. All the films showed good absorption in the visible range. The as-deposited and annealed films showed p-type conductivity. Hall measurement revealed the carrier concentration and mobility ranging from 10¹⁵ to 10¹⁶ cm⁻³ and 0.8 to 31.6 cm² V⁻¹ s⁻¹ respectively. The photoconductivity measurements of all the SnS films were carried out by recording the lowering of resistance of the respective films with time under illumination.     

Absence of morphotropic phase boundary effects in BiFeO<Subscript>3</Subscript>–PbTiO<Subscript>3</Subscript> thin films grown via a chemical multilayer deposition method

We report an unusual behavior observed in (BiFeO₃)_1−x –(PbTiO₃) _x (BF–xPT) thin films prepared using a multilayer chemical solution deposition method. Films of different compositions were grown by depositing several bilayers of BF and PT precursors of varying BF and PT layer thicknesses followed by heat treatment in air. X-ray diffraction showed that samples of all compositions show mixing of two compounds resulting in a single-phase mixture, also confirmed by transmission electron microscopy. In contrast to bulk compositions, samples show a monoclinic (M_A-type) structure suggesting disappearance of the morphotropic phase boundary (MPB) at x=0.30 as observed in the bulk. This is accompanied by the lack of any enhancement of the remanent polarization at the MPB, as shown by the ferroelectric measurements. Magnetic measurements showed an increase in the magnetization of the samples with increasing BF content. Significant magnetization in the samples indicates melting of spin spirals in the BF–xPT films, arising from a random distribution of iron atoms. Absence of Fe²⁺ ions was corroborated by X-ray photoelectron spectroscopy measurements. The results illustrate that thin film processing methodology significantly changes the structural evolution, in contrast to predictions from the equilibrium phase diagram, besides modifying the functional characteristics of the BP-xPT system dramatically.     

Performance of two-hop infrastructure based multi-antenna regenerative relaying in Rayleigh fading channel

Cooperative relaying is considered as an effective technique to enlarge the coverage area and enhance the system capacity for the future wireless systems. In this paper, an infrastructure based multi-antenna cooperative relay network has been investigated. Closed form expressions of outage probability and average error rate have been derived, when the relay and the destination perform selection combining of the signals. The relay is assumed to operate in the adaptive decode and forward mode. The effect of number of antennas installed on the relay and their placement has also been studied.     

Uncompensated magnetization in the layered molecular antiferromagnet {N(n-C5H11)4[MnFe(ox)3]}∞

Studies on the magnetic properties of the molecular antiferromagnetic material {N(n-C₅H₁₁)₄[Mn^IIFe^III(ox)₃]}_∞, carried out by various physical techniques (AC/DC magnetic susceptibility, magnetization, heat capacity measurements and Mössbauer spectroscopy) at low temperatures, have been presented. Different experimental observations complement each other and provide a clue for the observation of an uncompensated magnetization below the Néel temperature and short-range correlations persisting high above T_N. It is understood that the honeycomb layered structure of the compound contains non-equivalent magnetic sub-lattices, (Mn^II–ox–Fe^III_A–...) and (Mn^II–ox–Fe^III_B–...), where different responses of the Fe^III_A and Fe^III_B spin sites towards an external magnetic field might be responsible for the observation of the uncompensated magnetization in this compound at T < T_N. The present magnetic system is an S = 5/2 2-D Heisenberg antiferromagnet system with the intralayer exchange parameter J/k_B = −3.29 K. A very weak interlayer exchange interaction was anticipated from the spin wave modeling of the magnetic heat capacity for T < 0.5T_N. The positive sign of the coupling between the layers has been concluded from the Mössbauer spectrum in the applied magnetic field. Frustration in the magnetic interactions gives rise to the uncompensated magnetic moment in this compound at low temperatures.     

Effect of Temperature and Ionic Concentration on Self-Assembled Films of Chicago Sky Blue

We employ a layer-by-layer adsorption technique for deposition on solid substrates of polyionic films of Chicago Sky Blue. Film growth was significant with the increasing number of layers. Photochemical properties of these films are investigated for different ionic concentrations. A significant blue shift is observed with the increasing ionic strength of the solution, suggesting the formation of aggregation. Temperature effect studies show some preferable reorientation of molecules in the film during cooling process. Most remarkable observation is that the absorption intensity is the highest for a particular degree of inclination. Deposition time is fixed at 15rain because adsorption kinetics results show saturation after 15 min.     

Correlating flame geometry in opposed-flow flame spread over thin fuels

Numerical analysis and scale analysis are combined in a novel manner in this work to develop closed-form expressions for flame geometry in opposed-flow flame spread over condensed fuels. A scale analysis is used to relate different geometric attributes to appropriate non-dimensional parameters. A comprehensive numerical model is then used to generate a large set of numerical data for flame height, flame length, and pyrolysis length as functions of different fuel and oxidizer parameters for flame spread in the thermal, kinetic, and radiative regimes. The numerical data is then correlated to scaled expressions and the unknown coefficients are numerically determined. It is shown that flame length, flame height, and pyrolysis length can be expressed in terms of the preheat length in different regimes of flame spread. An experimental approach is outlined to measure the preheat length necessary for accurately predicting the flame structure. Experimental images obtained from interferometry in two different regimes – downward spreading configuration and quiescent microgravity environment – are consistent with the proposed flame height correlation.