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The electrocatalysis of charge/discharge reactions of alkaline-iron electrodes with and without the Bi 2 S 3 additive have been studied using cyclic voltammetry at different sweep rates and temperatures. The activation energy barriers for the iron-dissolution reaction on the iron electrodes with and without the sulfide additive are found to be 11.5 and 35.5 kJ mol -1 , respectively, suggesting that the presence of sulfide additive in iron-active material lowers the activation barrier for the iron dissolution reaction appreciably.

A decision aid used to calculate signal coverage areas and signal interference regions in beyond line of sight (BLOS) high frequency (HF) communications systems is described. The interference and coverage capabilities of HF-BLOS communications systems are influenced by the ionospheric environment through which radio signals must propagate. A technique based on the tactical use of signal propagation which exploits knowledge of the ionosphere coupled with ray-tracing techniques may be used to minimise signal interference and maximise signal coverage. Such improvements are achieved without resorting to sophisticated systems techniques such as antenna nulling or coding. This paper investigates the tactical propagation technique via the development of a BLOS-HF frequency management decision aid. The decision aid employs an ionospheric environmental model and a communications model to predict both the interference and coverage of a HF communications link. Using these models the decision aid recommends system configurations (e.g. best frequency) which avoid known locations whilst maximising communications coverage. (5 pages)

Densification behavior of alpha silicon carbide (SiC) during vacuum hot pressing was studied up to 1900C with sintering additives based on AlN and Y2O3 in different proportions. Near theoretical density was obtained with a total sintering additive content of 4 vol.. The microstructure of SiC sintered with AlNY2O3 revealed fine equiaxed grains against the additional elongated grains exhibited by SiC sintered with AlN alone. The SiC having high density exhibited very good strength, elastic modulus, high thermal conductivity, low coefficient of thermal expansion and excellent polishability for telescope mirror applications. � 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

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Mesoporous carbon (MC)-Poly (3,4-ethylenedioxythiophene) (PEDOT) composites are synthesized using structure-directing agents and explored as catalyst supports for polymer electrolyte fuel cell (PEFC) electrodes. To this end, platinum nanoparticles are deposited onto the composite supports as also on Vulcan XC-72 carbon black from platinum salts by formaldehyde reduction. The morphologies and crystallinity of Pt/Vulcan XC-72 and various Pt/PEDOT-MC are characterized using powder X-ray diffraction and transmission electron microscopy, which suggest Pt nanoparticles to be uniformly dispersed onto the supports. The durability of MC-PEDOT-supported catalysts in PEFCs is attributed to enhanced corrosion-resistance of MC. Indeed, the non-destructive functionalization of MC with conducting polymer makes them promising catalyst-supports for PEFCs.

Electrochemical oxidation of borohydride is studied on nanosized rhodium, iridium, and bimetallic rhodium-iridium catalysts supported onto Vulcan XC72R carbon. The catalysts are characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy in conjunction with cyclic voltammetry and polarization studies. The studies reveal that a 20 wt % bimetallic Rh-Ir catalyst supported onto carbon (Rh-Ir/C) is quite effective for the oxidation of borohydride. Direct borohydride fuel cell with Rh-Ir/C as the anode catalyst and Pt/C as the cathode catalyst exhibits a peak power density of 270 mW/cm(2) at a load current density of 290 mA/cm(2) as against 200 mW/cm(2) at 225 mA/cm(2) for Rh/C and 140 mW/cm(2) at 165 mA/cm(2) for Ir/C while operating at 80 degrees C. The synergistic catalytic activity for the bimetallic Rh-Ir nanoparticles toward borohydride oxidation is corroborated by density-functional theory calculations using electron-localization function. (C) 2010 The Electrochemical Society. [DOI:10.1149/1.3442372] All rights reserved.

Nonlinear changes of the refractive index are observed by electromagnetic interaction of laser light with germanium nanoparticles. Self-phase modulated optical fringes are used to reveal the nonlinear optical response of germanium nanoparticles at the wavelength of 514.5 nm. The intensity dependence (photo-induced) and size dependence of the refractive index are studied using self-phase modulation of the laser beam. The optical fringe patterns, which are observed due to photo-induced refractive indices, are found to depend on the size of the nanoparticle. The Drude model is also utilized to explore the origin of the photo-induced refractive index of the germanium nanoparticles. It is found that photo-excited electrons contribute appreciably to the nonlinear changes of the refractive index.

Nafion-silica composite membranes are fabricated by embedding silica particles as inorganic fillers in perfluorosulfonic acid ionomer by a novel water hydrolysis process. The process precludes the use of an added acid but exploits the acidic characteristic of Nafion facilitating an in situ polymerization reaction through a sol-gel route. The use of Nafion as acid helps in forming silica/siloxane polymer within the membrane. The inorganic filler materials have high affinity to water and assist proton transport across the electrolyte membrane of the polymer electrolyte fuel cell (PEFC) even under low relative humidity (RH) conditions. In the present study, composite membranes have been tested in hydrogen/oxygen PEFCs at varying RH between 100 and 18% at elevated temperatures. Attenuated total reflectance-Fourier transform infrared spectroscopy and scanning electron microscopy studies suggest an evenly distributed siloxane polymer with Si-OH and Si-O-Si network structures in the composite membrane. At the operational cell voltage of 0.4 V, the PEFC with an optimized silica-Nafion composite membrane delivers a peak power density value five times higher than that achievable with a PEFC with conventional Nafion-1135 membrane electrolyte while operating at a RH of 18% at atmospheric pressures.

Acidic polyvinyl alcohol/polyacrylic acid blend hydrogel electrolytes (BHEs) were prepared by cross-linking with glutaraldehyde and perchloric acid. These acidic BHEs were treated suitably to realize alkaline and neutral BHEs. Amorphicity of BHEs was followed by differential scanning calorimetry. Ionic conduction in acidic BHEs was found to take place by a Grotthus-type mechanism whereas in alkaline and neutral BHEs it was due to a segmental motion mechanism. Ionic conductivity of BHEs was found to range between 10(-3) and 10(-2) S cm(-1). Electrochemical capacitors assembled with acidic polyvinyl alcoholhydrogel electrolyte yielded a maximum capacitance of similar to 60 and 1000 F g(-1) with BP carbon and RuO(x)center dot xH(2)O/C electrodes, respectively.

Layered $LiMn_{1-x}M_{x}O_{2}$ (M=Ni, Al, Mg) has been synthesized over a wide range of composition by ion-exchange from their sodium precursors and characterized. Both the lattice parameters (a and c) of the hexagonal unit cell increase with x for Ni and Mg substitutions but decrease for Al substitution. As reflected by the broad powder X-ray diffraction peaks, scanning electron micrographs show agglomeration of submicrometer-size particles. The discharge capacity of these cathode materials varies with the nature and concentration of the substituents. $LiMn_{0.95}Ni_{0.05}O_{2}$ exhibits a specific capacity of about 220 mAh $g^{-1}$ during the initial cycling, which decays gradually to about 150 mAh $g^{-1}$ after 30 charge-discharge cycles. $LiMn_{0.95}Al_{0.05}O_{2}$ and $LiMn_{0.95}Mg_{0.05}O_{2}$ yield capacity values of 180 and 150 mAh $g^{-1}$, respectively. Cyclic voltammetry, galvanostatic intermittent titration, and ac impedance data corroborate the observed discharge capacity behavior of these cathode materials.

A novel layered-material, $LiMn_{0.9}Ni_{0.05}Fe_{0.05}O_2$ with $O3-LiCoO_2$ structure and high electrochemical stability, has been synthesized by an ion exchange method. Specific capacity values of 250 mAh $g^-1$ at C/10 rate and 210 mAh $g^-1$ at C/2 rate have been obtained with little loss in capacity during 30 charge-discharge cycles conducted in the study. The X-ray diffraction and infrared spectroscopy data on the cycled samples suggest that the layered structure in $LiMn_{0.9}Ni_{0.05}Fe_{0.05}O_2$ is preserved after repeated charge-discharge cycles supporting stable specific capacity values. Owing to the high capacity and good stability, $LiMn_{0.9}Ni_{0.05}Fe_{0.05}O_2$ is attractive as a cathode material in Li-ion cells.

Lightweight plastic grids for lead/acid battery plates have been prepared from acrylonitrile butadiene styrene copolymer. The grids have been coated with a conductive and corrosion-resistant tin oxide layer by a novel rapid thermally activated chemical reaction process. X-ray powder diffraction and X-ray photoelectron spectroscopy show the coated tin oxide film to be $SnO_2$-like. The grids are about 75% lighter than conventional lead/acid battery grids. A 6 V/1 Ah lead/acid battery has been assembled and characterized employing positive and negative plates made from these grids. The energy density of such a lead/acid battery is believed to be more than 50 Wh/kg.

A one-dimensional, biphasic, multicomponent steady-state model based on phenomenological transport equations for the catalyst layer, diffusion layer, and polymeric electrolyte membrane has been developed for a liquid-feed solid polymer electrolyte direct methanol fuel cell (SPE- DMFC). The model employs three important requisites: (i) implementation of analytical treatment of nonlinear terms to obtain a faster numerical solution as also to render the iterative scheme easier to converge, (ii) an appropriate description of two-phase transport phenomena in the diffusive region of the cell to account for flooding and water condensation/evaporation effects, and (iii) treatment of polarization effects due to methanol crossover. An improved numerical solution has been achieved by coupling analytical integration of kinetics and transport equations in the reaction layer, which explicitly include the effect of concentration and pressure gradient on cell polarization within the bulk catalyst layer. In particular, the integrated kinetic treatment explicitly accounts for the nonhomogeneous porous structure of the catalyst layer and the diffusion of reactants within and between the pores in the cathode. At the anode, the analytical integration of electrode kinetics has been obtained within the assumption of macrohomogeneous electrode porous structure, because methanol transport in a liquid-feed SPE- DMFC is essentially a single-phase process because of the high miscibility of methanol with water and its higher concentration in relation to gaseous reactants. A simple empirical model accounts for the effect of capillary forces on liquid-phase saturation in the diffusion layer. Consequently, diffusive and convective flow equations, comprising Nernst-Plank relation for solutes, Darcy law for liquid water, and Stefan-Maxwell equation for gaseous species, have been modified to include the capillary flow contribution to transport. To understand fully the role of model parameters in simulating the performance of the DMCF, we have carried out its parametric study. An experimental validation of model has also been carried out. (C) 2003 The Electrochemical Society.

Electrochemical capacitors have been devised using hybrid electrolytes containing either lithium or magnesium salt and high-density graphite (HDG) electrodes. The cells exhibit single-electrode discharge capacitance of 355 $\mu$ $F/cm^2$ at $1\hspace{2mm} mA/cm^2$ discharge rate for magnesium-containing ormolytes at 80°C. Typical response times have been calculated to be of the order of 0.28 s for magnesium ion and 0.73 s for lithium ion containing ormolytes. A typical coin-type cell exhibits excellent cyclability of more than $10^3$ cycles at a discharge current density of $1\hspace{2mm}mA/cm^2$.

We present a microscopic many-body multichannel theory of interference effects between Raman scattering from phonon (discrete) and gap (continuum) pair electronic excitations in a superconductor with d y 2 −y 2 pairing symmetry. The theoretical results so obtained give a quantitative description of our low temperature Raman scattering experiments on laser ablated nearly twin-free superconducting thin films of YBa 2 Cu 3 O 7 .

A method is described which enables monthly predictions to be made for the attenuation statistics of radio links in the frequency range 10-50 GHz, using data available in global meteorological databases. The method is applicable to satellite-Earth, aircraft-Earth and aircraft-aircraft links, and can cover a wide range of availabilities (90% to 99.99%,). Examples of monthly predictions are given for a range of climates in the European region. The method includes models for the effects of clouds and gaseous absorption, which are particularly important for the 30 to 50 GHz range at for low availabilities. Although experimental data at 30-50 GHz with acceptably long record length are relatively few, predicted monthly statistics can be integrated to give annual statistics and comparisons with such data illustrate the success of the approach.

The relative abundances of S+· and CS+· resulting from the collision-induced dissociation of CS2+· have been measured, as functions of initial relative kinetic energy and scattering angle, in a crossed-beam apparatus in which a beam of CS2+· ions intersects, at fight angles, a beam of a monatomic target gas. At zero scattering angle the CS+·/S+· peak-height ratio increases as the relative kinetic energy increases because a higher proportion of CS2+· ions are excited above the dissociation threshold for CS+·. For the heavier target gases (Ar, Kr, Xe), the CS+·/S+· peak-height ratio, for a constant laboratory kinetic energy, decreases as the scattering angle increases. The increase in the relative abundance of S+· is attributed to an increasing proportion of CS2+· ions being excited beyond the second dissociation threshold for the formation of S+· as the internal excitation increases with scattering angle.

A combined molecular beam—mass spectrometer apparatus has been used to measure the average kinetic energy Et released during the unimolecular decomposition of CO2 ion clusters in the field-free region of the mass spectrometer. For the reaction (CO2), n→ (CO2n−1+CO2, the measured value for Et is found to increase as n increases from 3 to 13.

Electrochemical data are reported for oxygen reduction on platinized coconut-shell charcoal electrodes in 2.5M $H_2SO_4$, and 7M $H_3P0_4$. In both these media the electrodes exhibit good activity and can sustain currents up to $600 mA cm^{-2}$ at a polarization of about 400 mV from their rest potentials. The overall performance is comparable with the best type of carbonsupported platinum electrodes reported in the literature.

Open-circuit, potential-time transients during the discharge of alkaline porous iron electrodes at various states-of-charge have been studied. It has been possible to arrive at a correlation between the parameters of the selfdischarge kinetics and the observed potential-recovery time constants. The study also provides a method of estimating state-of-charge of the rechargeable alkaline iron electrode.

The performance of electrodes made from coconut-shell charcoal in alkaline fuel cells and metal/air batteries is reported. The electrode can be loaded with practically acceptable current densities of 500 - 2000 $A/m^2$ without deterioration for periods up to about 200 h. To achieve this performance, optimization of electrode structure was found to be necessary.Several chemical and physical techniques were employed to this end. Results show that coconut-shell charcoal is an excellent, low-cost substrate for porous carbon based air electrodes and further work may enhance its potentialities.

Dispersions of $Al_2O_3$ as well as $CeO_2$ a in $CaF_2$ are found to enhance the conductivity of $CaF_2$ . Both these systems are biphasic and the electrical conduction in them is purely ionic in nature. At 650 K the increase in the ionic conductivity of the dispersed solid electrolyte system $CaF_2-Al_20_3$ a is by about two orders of magnitude in relation to the conductivity of the host electrolyte $CaF_2$, whereas for the $CaF_2-CeO_2$ system it is about three orders of magnitude. Some aspects of the increase in the ionic conductivities of $CaF_2-Al_20_ 3$ and $CaF_2-CeO_2$ electrolytes can be explained by a recent theoretical model. It is proposed that a substantial enhancement in the vacancy concentration of $CaF_2$, brought about by the attraction of $F^-$ ions to the surface of $Al_20_3$ (or $CeO_2$) , is responsible for the low temperature increase in the ionic conductivity of $CaF_2$.

Results are presented of a series of calculations in which an attempt has been made to reproduce experimental peak profiles that result from the collision-induced dissociation of polyatomic ions. The calculations show that the peak profiles are insensitive to the details of the collisional energy transfer distribution, but that the shape of the peaks is influenced by changes in the kinetic energy release distribution. For two collision-induced fission reactions, those of the ethanol and propanol ions, good agreement between the experimental and calculated peak profiles is obtained using a quasi-equilibrium theory (QET) kinetic energy release distribution. In the case of the acetone ion decomposition, however, alternative forms of the kinetic energy release distribution have to be considered, in order for the calculated result to reproduce the experimental peak profile.

The electrochemical activity for oxygen reduction in acid and alkali electrolytes of carbon electrodes with platinum-group bimetal catalysts, viz., Pt---Ru and Pt---Pd, has been measured as a function of electrode composition. Electrodes containing 4 wt.% Pt + 6 wt.% Pd have been found to exhibit the maximum catalytic activity, and this is also higher than that of the individual metal catalysts.

A generalized formulation is described of the evaluation of configurational energies of isolated defects and defect pairs which includes an improved treatment of the relaxation of ions nearest to the defects. The energies of association between vacancy pairs and divalent cation impurity-vacancy pairs in the first three associated states of KCl are calculated employing this method and these values are compared with earlier theoretical estimates.

In this study, we have considered two states of India one from North (Uttar Pradesh) and other from south (Kerala). The objective of this present paper is to measure the inequality in terms of standard of living index for both states and Uttar Pradesh and Kerala by using popular statistical techniques for measurement of inequality.

The energies of ion migration in KCl through isolated vacancies, vacancy pairs, trivacancies, and interstitials have been investigated. A path-variation study in the case of vacancy and vacancy-pair mechanisms show that the usually assumed path in the (100) plane is the most probable one. Trivacancies do not seem to contribute to high-temperature conduction. On the other hand, the formation of a Frenkel defect pair and interstitialcy migration through a collinear path may be responsible for the nonrandom deviations in ionic conductivity data at high temperatures.

The following mechanisms for ion movement in AgCl and AgBr have been studied: direct vacancy migration, direct interstitial migration and collinear as well as noncollinear jumps of interstitial ions. For the last two processes, we have carried out a path-variation study. The activation energies are high (⩾1.0 eV) for all the migration mechanisms considered here except for the collinear jump which has an activation energy around 0.6 eV. For both the collinear and noncollinear jumps, the paths of migration have been worked out.

The ion-pair reaction between trilaurylammonium fluoride (TLAH)F and (TLAH) 2 [OsCl 5 I] in nonpolar solvents gives trans -[OsCl 4 FI] 2− . This is the first species where F and I are present in the same octahedron. The pure complex is separated by cellulose ion exchange chromatography and characterized by different reactions, analysis, vibrational, and UV-vis spectra. The results show that F and I are trans to each other.

The electron impact ionization of hydrogen-bonded clusters of water and ammonia results in the formation of stable doubly charged ions only when the cluster size exceeds a critical value. The observed minimum cluster size for water is (H 2 O) 35 H 2 2+ and for ammonia is (NH 3 ) 51 H 2 + . From a knowledge of the relative hydrogen-bond strenghts, it has been possible to account for the size difference between these ions and to qualitatively discuss the locations of the positive charges within each cluster.

Road transportation, as an important requirement of modern society, is presently hindered by restrictions in emission legislations as well as the availability of petroleum fuels, and as a consequence, the fuel cost. For nearly 270 years, we burned our fossil cache and have come to within a generation of exhausting the liquid part of it. Besides, to reduce the greenhouse gases, and to obey the environmental laws of most countries, it would be necessary to replace a significant number of the petroleum-fueled internal-combustion-engine vehicles (ICEVs) with electric cars in the near future. In this article, we briefly describe the merits and demerits of various proposed electrochemical systems for electric cars, namely the storage batteries, fuel cells and electrochemical supercapacitors, and determine the power and energy requirements of a modern car. We conclude that a viable electric car could be operated with a 50 kW polymer-electrolyte fuel cell stack to provide power for cruising and climbing, coupled in parallel with a 30 kW supercapacitor and/or battery bank to deliver additional short-term burst-power during acceleration.

The energies of association between a divalent anion impurity and an anion vacancy in KCI have been evaluated fro three associated states. Distribution of these I′ CI -V′ CI pairs has been worked out over the temperature range 300-1000°K.

Experimental diffusion measurements show that migration enthalpies of Cl − , Br − and I − in NaCl are comparable, while that of F − is considerably lower. Earlier studies had shown that migration enthalpies of Na + , K + , Rb + and Cs + in NaCl were similar. The polarised point ion model predicts migration energies of ions (by vacancy mechanism) to monotonically increase with ion size, contrary to experiment. Inversely, the shell model calculations rightly predict the variation of migration energies with ionic size. Thus, migration energies by vacancy mechanism do not vary significantly for ions larger than the host ions. However, in the case of the small ions, Li + and F − , the migration energies by vacancy mechanism are much lower and in good agreement with experiment for F − .

Heats of mixing of solid solutions of CsCl with CsBr, KCl and RbCl have been obtained by precise measurements of heats of solution in water. The results show evidence for the stabilization of the NaCl (Fm3m) structure in the Cs1–xKxCl and Cs1–xRbxCl systems at a specific value of x. The experimental results are compared with results from ionic lattice calculations.

Interaction energies of cation-anion vacancy pairs and divalent cation impurity-vacancy pairs in caesium halides have been evaluated by means of ionic lattice calculations with a rigorous treatment of the relaxations of ions in the vicinity of the defects. The binding energy of the first associated vacancy pair is lower than the Coulombic value, while that of the second associated pair is close to the Coulombic value. The binding energies of the divalent cation impurity-vacancy pairs vary in the order, third > fourth > second > first associated state, the energy of the second bound pair being close to the Coulombic value.

Chapitre 13; Since their discovery, G protein-coupled receptors (GPCRs) constitute one of the most studied proteins leading to important discoveries and perspectives in terms of their biology and implication in physiology and pathophysiology. This is mostly linked to the remarkable advances in the development and application of the biophysical resonance energy transfer (RET)-based approaches, including bioluminescence and fluorescence resonance energy transfer (BRET and FRET, respectively). Indeed, BRET and FRET have been extensively applied to study different aspects of GPCR functioning such as their activation and regulation either statically or dynamically, in real-time and intact cells. Consequently, our view on GPCRs has considerably changed opening new challenges for the study of GPCRs in their native tissues in the aim to get more knowledge on how these receptors control the biological responses. Moreover, the technological aspect of this field of research promises further developments for robust and reliable new RET-based assays that may be compatible with high-throughput screening as well as drug discovery programs.