Direct estimate of transport length scales in semiconducting polymers

A method for determining the electron/hole transport length scale of model semiconducting polymer systems by scanning a narrow-light probe beam over the nonoverlapping anode/cathode region in asymmetric sandwich device structures is presented (see figure). Electron versus hole collection efficacy, and disorder and spatial anisotropy in the electrical transport parameters can be estimated.

Structural Insights into the Acyl Intermediates of the Plasmodium falciparum Fatty Acid Synthesis Pathway THE MECHANISM OF EXPANSION OF THE ACYL CARRIER PROTEIN CORE

Acyl carrier protein (ACP) plays a central role in fatty acid biosynthesis. However, the molecular machinery that mediates its function is not yet fully understood. Therefore, structural studies were carried out on the acyl-ACP intermediates of Plasmodium falciparum using NMR as a spectroscopic probe. Chemical shift perturbation studies put forth a new picture of the interaction of ACP molecule with the acyl chain, namely, the hydrophobic core can protect up to 12 carbon units, and additional carbons protrude out from the top of the hydrophobic cavity. The latter hypothesis stems from chemical shift changes observed in C-alpha and C-beta of Ser-37 in tetradecanoyl-ACP. C-13, N-15-Double-filtered nuclear Overhauser effect (NOE) spectroscopy experiments further substantiate the concept; in octanoyl (C-8)- and dodecanoyl (C-12)-ACP, a long range NOE is observed within the phosphopantetheine arm, suggesting an arch-like conformation. This NOE is nearly invisible in tetradecanoyl (C-14)-ACP, indicating a change in conformation of the prosthetic group. Furthermore, the present study provides insights into the molecular mechanism of ACP expansion, as revealed from a unique side chain-to-backbone hydrogen bond between two fairly conserved residues, Ile-55 HN and Glu-48 O. The backbone amide of Ile-55 HN reports a pK(a) value for the carboxylate, similar to 1.9 pH units higher than model compound value, suggesting strong electrostatic repulsion between helix II and helix III. Charge-charge repulsion between the helices in combination with thrust from inside due to acyl chain would energetically favor the separation of the two helices. Helix III has fewer structural restraints and, hence, undergoes major conformational change without altering the overall-fold of P. falciparum ACP.

Thermal stresses in a finite hollow cylinder due to an axisymmetric temperature field at the end surface

A three-dimensional exact solution for determining the thermal stresses in a finite hollow cylinder subject to a steady state axisymmetric temperature field over one of its end surfaces has been given. Numerical results for a hollow cylinder, having lenght to outer diameter ratio equal to one and inner to outer diameter ratio equal to 0.75, subjected to a symmetric temperature variation over the end surfaces of the cylinder have been given.

A Durable PEFC with Carbon-Supported Pt-TiO2 Cathode: A Cause and Effect Study

Durability is central to the commercialization of polymer electrolyte fuel cells (PEFCs). The incorporation of TiO2 with platinum (Pt) ameliorates both the stability and catalytic activity of cathodes in relation to pristine Pt cathodes currently being used in PEFCs. PEFC cathodes comprising carbon-supported Pt-TiO2 (Pt-TiO2/C) exhibit higher durability in relation to Pt/C cathodes as evidenced by cell polarization, impedance, and cyclic voltammetry data. The degradation in performance of the Pt-TiO2/C cathodes is 10% after 5000 test cycles as against 28% for Pt/C cathodes. These data are in conformity with the electrochemical surface area and impedance values. Pt-TiO2/C cathodes can withstand even 10,000 test cycles with nominal effect on their performance. X-ray diffraction, transmission electron microscope, and cross-sectional field-emission-scanning electron microscope studies on the catalytic electrodes reflect that incorporating TiO2 with Pt helps in mitigating the aggregation of Pt particles and protects the Nafion membrane against peroxide radicals formed during the cathodic reduction of oxygen. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3421970] All rights reserved.

High Rate Capability of Porous LiNi1/3Co1/3Mn1/3O2 Synthesized by Polymer Template Route

Layered LiNi1/3Co1/3Mn1/3O2, which is isostructural with LiCoO2, is considered as a potential cathode material for Li-ion batteries. Submicrometer sized porous particles are useful for high discharge rates. The present work involves a synthesis of submicrometer sized porous particles of LiNi1/3Co1/3Mn1/3O2 using a triblock copolymer as a soft template. The precursor obtained from the reaction is heated at different temperatures between 600 and 900 degrees C for 6 h to get the final product samples. The compound attains increased crystallinity with an increase in the temperature of preparation. However, there is a decrease in the surface area and also in the porosity of the sample. Nevertheless, the LiNi1/3Co1/3Mn1/3O2 sample prepared at 900 degrees C exhibits a high rate capability and stable capacity retention on cycling. The electrochemical performance of LiNi1/3Co1/3Mn1/3O2 prepared in the absence of the polymer template is inferior to that of the sample prepared in the presence of the polymer template. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3364944] All rights reserved.

Rapid growth of nanotubes and nanorods of wurtzite ZnO through microwave-irradiation of a metalorganic complex of zinc and a surfactant in solution

Large quantities of single-crystalline ZnO nanorods and nanotubes have been prepared by the microwave, irradiation of a metalorganic complex of zinc, in the presence of a surfactant. The method is simple, fast, and inexpensive (as it uses a domestic microwave oven), and yields pure nanostructures of the hexagonal wurtzite phase of ZnO in min, and requires no conventional templating. The ZnO nanotubes formed have a hollow core with inner diameter varying from 140-160 nm and a wall of thickness, 40-50 nm. The length of nanorods and nanotubes varies in the narrow range of 500-600 nm. These nanostructures have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The ZnO nanorods and nanotubes are found by SAED to be single-crystalline. The growth process of ZnO nanorods and nanotubes has been investigated by varying the surfactant concentration and microwave irradiation time. Based on the various results obtained, a tentative and plausible mechanism for the formation of ZnO nanostructures is proposed.

Electro-Oxidation of Borohydride on Rhodium, Iridium, and Rhodium-Iridium Bimetallic Nanoparticles with Implications to Direct Borohydride Fuel Cells

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.

A hybrid electrochemical-thermal method for the preparation of large ZnO nanoparticles

A simple and efficient two-step hybrid electrochemical-thermal route was developed for the synthesis of large quantity of ZnO nanoparticles using aqueous sodium bicarbonate electrolyte and sacrificial Zn anode and cathode in an undivided cell under galvanostatic mode at room temperature. The bath concentration and current density were varied from 30 to 120 mmol and 0.05 to 1.5 A/dm(2). The electrochemically generated precursor was calcined for an hour at different range of temperature from 140 to 600 A degrees C. The calcined samples were characterized by XRD, SEM/EDX, TEM, TG-DTA, FT-IR, and UV-Vis spectral methods. Rietveld refinement of X-ray data indicates that the calcined compound exhibits hexagonal (Wurtzite) structure with space group of P63mc (No. 186). The crystallite sizes were in the range of 22-75 nm based on Debye-Scherrer equation. The TEM results reveal that the particle sizes were in the order of 30-40 nm. The blue shift was noticed in UV-Vis absorption spectra, the band gaps were found to be 5.40-5.11 eV. Scanning electron micrographs suggest that all the samples were randomly oriented granular morphology.

Magnetic, electric, and dielectric properties of FeCo alloy nanoparticles dispersed in amorphous matrix

Nanocrystalline Fe53Co47 alloy was synthesized by a single-step transmetallation chemical method at room temperature. The Fe53Co47 alloy nanoparticles of 77 and 47 wt% were dispersed in silica matrix by the sol-gel process using tetraethyl orthosilcate. Structural studies reveal that the as-prepared alloy powders are in bcc phase and silica is in an amorphous state. The phase-transition temperature and Mossbauer spectra analysis of the Fe-Co alloy establishes the homogeneous alloy formation. A saturation magnetization of 218 emu/g was obtained for pure FeCo alloy at room temperature. Scanning electron microscopic analysis demonstrates the hollow-sphere morphology for FeCo alloy particles. Magnetic nanocomposite consisting of 47 wt% FeCo-silica shows enhanced thermal stability over the native FeCo alloy. Electrical and dielectric properties of 47 wt% FeCo-silica nanocomposites were investigated as a function of frequency and temperature. It was found that the dielectric constants and dielectric loss were stable throughout the measured temperature (310-373 K). Our results indicate that FeCo-silica nanocomposite is a promising candidate for high-frequency applications. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

dc reactive magnetron sputtering of titanium‐structural and optical characterization of TiO2 films

This paper deals with the reactive sputtering of titanium in an argon and oxygen mixture. The variation in cathode potential as a function of oxygen partial pressure has been explained in terms of cathode poisoning effects. The titania films deposited during this process have been studied for their structural and optical characteristics. The effect of substrate temperature (from 25 to 400 °C) and annealing (from 250 to 700 °C) on the packing density, refractive index, extinction coefficient, and crystallinity has been investigated. The refractive index varied from 2.24 to 2.46 and extinction coefficient from 2.6 × 10-3 to 10.4× 10-3 at 500 nm as the substrate temperature increased from 25 to 400 °C. The refractive index increased from 2.19 to 2.35 and extinction coefficient changed from 3.2× 10-3 to 11.6 × 10-3 at 500 nm as the annealing temperature was increased from 250 to 700 °C. Anatase and rutile phases have been observed in the films deposited at 400 °C substrate temperature and annealed at 300 °C. The changes in the optical constants at higher substrate temperature have been attributed to an increase in packing density, oxygen content, and crystallinity of the films.

Serotypic and genotypic characterization of human serotype 10 rotaviruses from asymptomatic neonates

Human rotaviruses were isolated from asymptomatic neonates at various hospitals and clinics in the city of Bangalore, India, and were found to be subgroup I specific and possess long RNA patterns (M. Sukumaran, K. Gowda, P. P. Maiya, T. P. Srinivas, M. S. Kumar, S. Aijaz, R. R. Reddy, L. Padilla, H. B. Greenberg, and C. D. Rao, Arch. Virol. 126:239-251, 1992). Three of these strains were adapted to tissue culture and found by serotype analysis and neutralization assays to be of serotype 10, a serotype commonly found in cattle but infrequently found in humans and not previously identified in neonates. By RNA-RNA hybridization, a high level of relatedness to a serotype 10 bovine rotavirus strain and a low-to-medium level of relatedness to a human rotavirus strain were observed. Since this human isolate shares a genogroup with bovine rotavirus, it is likely that it originated by interspecies transmission. A human rotavirus strain isolated from asymptomatic neonates and similar to bovine rotavirus might represent a good vaccine candidate.

Synthesis and characterization of single-crystalline alpha-MoO3 nanofibers for enhanced Li-ion intercalation applications

High quality, single-crystalline alpha-MoO3 nanofibers are synthesized by rapid hydrothermal method using a polymeric nitrosyl-complex of molybdenum(II) as molybdenum source without employing catalysts, surfactants, or templates. The possible reaction pathway is decomposition and oxidation of the complex to the polymolybdate and then surface condensation on the energetically favorable 001] direction in the initially formed nuclei of solid alpha-MoO3 under hydrothermal conditions. Highly crystalline alpha-MoO3 nanofibers have grown along 001] with lengths up to several micrometres and widths ranging between 280 and 320 nm. The alpha-MoO3 nanofibers exhibit desirable electrochemical properties such as high capacity reversibility as a cathode material of a Li-ion battery.

Influence of Substrate Temperature and Deposition Rate on Structural and Mechanical Properties of Shape Memory NiTi Films

NiTi thin films deposited by DC magnetron sputtering of an alloy (Ni/Ti:45/55) target at different deposition rates and substrate temperatures were analyzed for their structure and mechanical properties. The crystalline structure, phase-transformation and mechanical response were characterized by X-ray diffraction (XRD), Differential Scanning Calorimetry (DSC) and Nano-indentation techniques, respectively. The films were deposited on silicon substrates maintained at temperatures in the range 300 to 500 degrees C and post-annealed at 600 degrees C for four hours to ensure film crystallinity. Films deposited at 300 degrees C and annealed for 600 degrees C have exhibited crystalline behavior with Austenite phase as the prominent phase. Deposition onto substrates held at higher deposition temperatures (400 and 500 degrees C) resulted in the co-existence of Austenite phase along with Martensite phase. The increase in deposition rates corresponding to increase in cathode current from 250 to 350 mA has also resulted in the appearance of Martensite phase as well as improvement in crystallinity. XRD analysis revealed that the crystalline film structure is strongly influenced by process parameters such as substrate temperature and deposition rate. DSC results indicate that the film deposited at 300 degrees C had its crystallization temperature at 445 degrees C in the first thermal cycle, which is further confirmed by stress temperature response. In the second thermal cycle the Austenite and Martensite transitions were observed at 75 and 60 degrees C respectively. However, the films deposited at 500 degrees C had the Austenite and Martensite transitions at 73 and 58 degrees C, respectively. Elastic modulus and hardness values increased from 93 to 145 GPa and 7.2 to 12.6 GPa, respectively, with increase in deposition rates. These results are explained on the basis of change in film composition and crystallization. (C) 2010 Published by Elsevier Ltd

Altered ultrastructure of rinderpest virus and its nucleocapsids induced by 5-fluorouracil

he ultrastructure of purified rinderpest virus and intracellular viral nucleocapsids from infected vero cells treated with a subtoxic dose of 5-fluorouracil (5-Fu) (1 mug/ml), has been analysed by transmission electron microscopy, and compared with that of normal virus particle and nucleocapsids. The results reveal dramatic alterations in the structure of both virions and nucleocapsids. The surface glycoprotein projection of virions was not seen or present at a much reduced level. The intracellular nucleocapsids showed pronounced structural changes,with respect to size, shape and fine structure. The length of treated nucleocapsids is much smaller as compared to the control. The central hollow core is missing in case of drug-treated nucleocapsid and the herring bone structure is replaced by a 'beads on string' structure. The presence of N protein, which is a major structural component of nucleocapsids was seen in 5-Fu-treated cells, but it was associated with a predominantly diffused form of nucleocapsids as seen by immunoelectron microscopy. We report here the first definitive and visual evidence of altered structure of virions and their nucleocapsids after 5-Fu treatment

Design and development of a self-supported polymer electrolyte fuel cell system with anodic dead-end operation

Design and operational details for a self-supported polymer electrolyte fuel cell (PEFC) system with anodic dead-end fuel supply and internally humidified cathodic oxidant flow are described. During the PEFC operation, nitrogen and water back diffuse across the Nafion membrane from the cathode to the anode and accumulate in the anode flow channels affecting stack performance. The accumulated inert species are flushed from the stack by purging the fuel cell stack with a timer-activated purge valve to address the aforesaid problem. To minimize the system complexity, stack is designed in such a way that all the inert species accumulate in only one cell called the purge cell. A pulsed purge sequence comprises opening the valve for purge duration followed by purge-valve closing for the hold period and repeating the sequence in cycles. Since self-humidification is inadequate to keep the membrane wet, the anodic dead-end-operated PEFC stack with composite membrane comprising perflourosulphonic acid (Nafion) and silica is employed for keeping the membrane humidified even while operating the stack with dry hydrogen and internally humidified air.