bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential output of the high‐sensitivity rod photoreceptor: AII amacrine pathway
Authors: Petrides Artemis , Trexler E. Brady
Published: February 2008

In the mammalian retina, the scotopic threshold of ganglion cells is in part dependent on how rod inputs are summed by their presynaptic cone bipolar cells. For ON cone bipolar cells, there are two anatomical routes for rod signals: 1) cone photoreceptors receive inputs via gap junctions with the surrounding, more numerous rods; and 2) ON cone bipolar cells receive highly convergent input via gap junctions with AII amacrine cells, which each receive input from hundreds of rods. Rod‐cone coupling is thought to be utilized at higher photon fluxes relative to the AII‐ON cone bipolar pathway due to the impedance mismatch of a single small rod driving a larger cone. Furthermore, it is widely held that the convergence of high‐gain chemical synapses onto AIIs confers the highest sensitivity to ON cone bipolar cells and ganglion cells. A lack of coupling between one or more types of ON cone bipolar cells and AIIs would obviate this high‐sensitivity pathway and explain the existence of ganglion cells with elevated scotopic thresholds. To investigate this possibility, we examined Neurobiotin and glycine diffusion from AIIs to bipolar cells and found that approximately one‐fifth of ON cone bipolar cells are not coupled to AIIs. Unlike AII‐AII coupling, which changes with ambient background intensity, the fraction of noncoupled ON cone bipolar cells was unaltered by dark or light adaptation. These data suggest that one of five morphologically distinct ON cone bipolar cell types is not coupled to AIIs and suggest that AII‐ON cone bipolar coupling is modulated differently from AII‐AII coupling. J. Comp. Neurol. 507:1653–1662, 2008. © 2008 Wiley‐Liss, Inc.
A model of incompressible isotropic hyperelastic material behavior using spline interpolations of tension–compression test data
Authors: Sussman Theodore , Bathe Klaus‐Jürgen
Published: February 2008

We present a model of incompressible isotropic hyperelastic material behavior based on a strain energy description separable in terms of logarithmic strains and piecewise spline interpolations of uniaxial tension–compression test data. Valuable attributes are that no fitting of model constants is carried out and the model replicates even physically complicated test data very accurately for small and large strains and for tension and compression. The model is well suited for use in finite element analysis. Copyright © 2008 John Wiley & Sons, Ltd.
An improved Cosserat point element for axisymmetric problems in nonlinear elasticity: Comparison with other element formulations
Authors: Jabareen M. , Rubin M. B.
Published: February 2008

An improved quadrilateral Cosserat point element (CPE) has been developed for modeling torsionless axisymmetric problems in nonlinear elasticity. The CPE approach differs from standard finite element methods in that the element is considered to be a structure that is modeled using a strain energy function for homogeneous and inhomogeneous responses. The strain energy function for inhomogeneous deformations is generalized to include dependence on the reference geometry of irregular‐shaped elements. The quadrilateral CPE has four nodes with eight degrees of freedom, it needs no integration over the element region or user specified hourglass parameters. A number of examples have been considered which compare the response of the improved CPE with those of all of the four noded hyperelastic elements implemented in the computer codes ABAQUS, ADINA, ANSYS and FEAP. These examples demonstrate that the improved CPE is applicable for thin plates and shells, is as accurate as elements based on enhanced strain and incompatible mode methods and is as robust as the full integration element. Consequently, the CPE is truly a user‐friendly element that can be used with confidence for challenging problems in axisymmetric nonlinear elasticity. Copyright © 2008 John Wiley & Sons, Ltd.
Application of molecular dynamics computer simulations in the design of a minimal self‐replicating molecular machine
Authors: Weroński Paweł , Jiang Yi , Rasmussen Steen
Published: February 2008

It is commonly agreed that a chemical assembly of molecules can be considered alive if it can ingest resources and convert them into building blocks; has the ability to grow and self‐reproduce; and can evolve. In the design proposed by Rasmussen and Chen (Science 2004, 303, 963) the assembly or protocell could be as simple as a small micellar surfactant aggregate acting as a container, anchoring an informational molecule to its exterior and incorporating a metabolism within the oily interior. We present several examples of modeling such a system with molecular dynamics computer simulations. © 2008 Wiley Periodicals, Inc. Complexity, 2008.
Resonant oscillations of a granular cluster
Authors: Khain Evgeniy
Published: February 2008

Driven granular media is a fascinating example of intrinsically non‐equilibrium system. I consider an ensemble of inelastically colliding hard disks in a channel driven by two opposite thermal walls with different temperatures. When the inelasticity of collisions is large enough, a dense cluster, located closer to the colder wall, is formed. The steady state profiles are computed from the equations of granular hydrodynamics, and a good agreement with the results of molecular dynamics simulations is found. When the temperature of one of the thermal walls is varied periodically, a dense cluster develops oscillations. The oscillations amplitude reaches its maximum in a resonance, when the frequency of driving is roughly equal to the hydrodynamic frequency of oscillatory acoustic modes in the system. © 2008 Wiley Periodicals, Inc. Complexity, 2008.
Investigation of optical band gap in potassium acid phthalate single crystal
Authors: Krishnan S. , Raj C. Justin , Dinakaran S. , Das S. Jerome
Published: February 2008

Optical absorption in photonic crystals of potassium acid phthalate has been measured at room temperature, from which the band gap has been determined and the optical band gap was calculated by using absorption spectrum. The analysis of absorption coefficient in the absorption region reveals a direct band gap of 3.70 eV. Further this study includes the theoretical calculations to determine the optical constant of the material and a technique for photonic band gap tuning which is minimally required to develop the optoelectronic device. It was confirmed that potassium acid phthalate crystal has maximum transparency in the entire visible region and hence it exhibits industrial application oriented properties. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of the growth processes from vapor phase of silicon carbide epitaxial layers: Thermodynamic analysis of the high temperature processes in the system Si‐C‐H‐Cl
Authors: Lilov S. K.
Published: February 2008

In the present work are presented the results of the thermodynamic analysis of the interaction processes in the system Si‐C‐H‐Cl in the temperature interval 1000‐3000 K. The equilibrium pressures of the components in the system Si‐C‐H‐Cl with taking account the formation of the condensed phases C, Si and SiC have been determined. The optimal conditions giving the maximum yield of silicon carbide by pyrolysis of mixture of volatile compounds of carbon and silicon have been defined. The thermodynamic analysis of the examined system showed that the increasing of the content of hydrogen in the initial mixture allows to decrease the optimal temperature for obtaining of silicon carbide by the method of pyrolysis and essentially to increase its maximum possible yield. (© 2008 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of additives in supersaturated binary and ternary solutions on cluster growth by gravity driven concentration gradient studies
Authors: Anandha Babu G. , Ramasamy P.
Published: February 2008

The concentration gradients formed in long column supersaturated solutions of the binary systems Potassium dihydrogen phosphate ‐ Water, Benzophenone ‐ Ethanol, Ammonium dihydrogen phosphate – Water, Potassium hydrogen phthalate – Water and ternary systems Potassium dihydrogen phosphate – Potassium chloride ‐ Water, Benzophenone – Urea ‐ Ethanol, Ammonium dihydrogen phosphate – Urea ‐ Water, Potassium hydrogen phthalate – Ethylenediaminetetraacetic acid – Water under stirred and non‐stirred conditions have been studied. The solution concentration was measured at different heights, at different degrees of supersaturation and at different times. Weight average molecular weight, Degree of Association, Number average molecular weight, Average number of molecules per cluster and weight average cluster diameter were calculated for binary and ternary supersaturated solutions under stirred and non‐stirred conditions. Under stirred conditions concentration gradient of all the above mentioned systems decrease compared to non‐stirred conditions. The cluster sizes are estimated from concentration gradient data in the presence and absence of additives and also corresponding changes in metastable zonewidths are studied. The changes in concentration gradients of supersaturated solutions appear to be a reliable indicator of the effect of additives on cluster growth and nucleation. As long column of solution is used in growing crystal by Sankaranarayanan‐Ramasamy method the effect of gravity driven concentration gradient on critical column length is investigated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Wet‐chemical synthesis and characterization of NiBi nano‐ and micro‐particles
Authors: Odeh I. M. , Mahmoud S. , Vassilev G. P.
Published: February 2008

Preparation and characterization of NiBi nano‐ and micro‐particles are presented. Firstly, predetermined compositions were obtained by simultaneous precipitation from solutions of Bi(NO3)3 and Ni(NO3)2. The precipitates were heated under oxygen flow and in air, and thereafter reduced to metals under hydrogen flow at 673 K. Correlation between the predetermined and the actual compositions of the products was found. Characterization of the precipitates was carried out employing X‐ray diffraction, scanning and transmission electron microscopy. Nickel‐bismuth intermetallic phase (NiBi) particles with nano‐ and micro‐dimensions were observed in the samples after reduction. The other possible Ni–Bi intermediate phase (NiBi3) did not form at these conditions although its presence was expected according to the phase diagram. This finding might be useful for the implementation of Bi‐based solders where the growth of the compound NiBi3 in the solder joints must be prevented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of domain structures in PZNT93/7 crystals by chemical etching
Authors: Jin Min , Xu Jiayue , Wu Aiying , Li Xinhua , Shen Hui , He Qingbo
Published: February 2008

The domain structures in 0.93Pb (Zn1/3Nb2/3)O3‐0.07PbTiO3 (PZNT93/7) crystals were investigated by chemical etching technique. Original antiparallel 180° domains of size 20–40 μm were observed on the surface of as‐grown PZNT93/7 crystal. It was found the domain states are sensitive to the stress field induced by mechanical processing or impurities. As the composition of PZNT93/7 crystal was located near the morphotropic phase boundary, various domain configurations were observed. On the <001>‐oriented wafer, the etched a ‐ and c ‐domains revealed homogenous and island‐like patterns. The c ‐domains consist of upper and lower height regions corresponding to the tail and head of the polarization, respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the capability of revealing the pseudosymmetry of the chalcopyrite‐type crystal structure
Authors: Abou‐Ras D. , Gibmeier J. , Nolze G. , Gholinia A. , Konijnenberg P.
Published: February 2008

The tetragonal crystal‐structure type of chalcopyrites (chemical formula AIBIIICVI2) is a superstructure of sphalerite type. The c /a ratio differs generally from the ideal value 2, i.e., the crystal structure is pseudocubically distorted. For CuInSe2 and CuGaSe2 thin films, simulations demonstrate that it is theoretically possible to reveal the tetragonality in electron backscatter‐diffraction (EBSD) patterns for CuGaSe2, whereas it may not be possible for CuInSe2. EBSD experiments on CuGaSe2 thin films using the ”Advanced Fit” band‐detection method show that it is possible to extract accurate misorientation‐angle distributions from the CuGaSe2 thin film. Pole figures revealing the texture of the CuGaSe2 thin film are shown, which agree well with X‐ray texture measurements from the same layer. (© 2008 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Reduction of domain wall width in VTE treated near stoichiometric LiNbO3 crystals
Authors: Kar S. , Bartwal K. S.
Published: February 2008

LiNbO3 is a ferroelectric crystal and grows with multi domains. Different domains are separated by boundaries which are known as domain boundaries. Domain walls for congruent and VTE (Vapor Transport Equilibration) treated near stoichiometric lithium niobate samples were visualised in different crystallographic directions using chemical etching technique. The sample is etched in the mixture of HF and HNO3 (in 1:2 volume ratios) for 10 minutes at boiling temperature. Measured domain wall width was found approximately 15‐20 µm for congruent (CLN) and it reduces to 1‐3 µm for VTE treated near stoichiometric (SLN). Activation energies were also measured by two‐probe method and found to be increasing in stoichiometric sample. This activation energy is related to defect density in the crystals. Activation energy is higher for less defective crystals. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Application of mean‐separation‐works method to protein crystal nucleation
Authors: Nanev Christo N.
Published: February 2008

Using mean‐separation‐works method of Stranski and Kaischew calculations of nucleus form and energy barrier for its formation are performed for globular protein crystals. This is done on the basis of a simple model suggested for crystal nucleation of such proteins. The prerequisite for the model is the fact that strict selection of definite sticky patches on protein molecule surface is obligatory for forming crystal lattices. The calculation results are in agreement with experimental data. (© 2008 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Crystallization of AgGaS2 melts enriched with Ag2S and Ga2S3
Authors: Kokh K. A. , Sinyakova E. F. , Politov A. A.
Published: February 2008

In this work we consider experiments with directed crystallization of melts with slight deviation from stoichiometric composition of AgGaS2. The evolution of melt composition was calculated for both experiments using measured chemical composition of the solid phase. Also the difference in unit cell parameters and luminescence spectra for AgGaS2 grown from the melts was found. Both monocrystal samples and samples synthesized from elementary Ag, Ga and S were used for thermal analyses. Obtained data suggests that different ways of preparing the samples are responsible for defects concentration and thus for so wide range (70°C) of melting temperatures reported in scientific literature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural and microhardness studies of pure and thiourea doped glycine phosphite single crystal
Authors: Ezhil Vizhi R. , Kalainathan S. , Baghavan Narayana G.
Published: February 2008

Ferroelectric Glycine Phosphite (GPI) crystal have been grown from aqueous solution employing the slow cooling technique. As the crystal solubility in water depends on temperature, single crystals were grown. Transparent, colourless crystals with habit morphology weighing about 8g were obtained with in a month. The same procedure was used to grow single crystals of 10 wt% of Thiourea doped GPI (TUGPI). Formation of a new crystal was confirmed by Powder X‐ray diffraction studies as well as FTIR studies. Crystalline quality were found using rocking curve for both the crystals. Due to the presence of Thiourea in TUGPI, it improves the crystalline perfection and also enhances the growth rate. The variation of hardness on (010) faces of monoclinic GPI and TUGPI crystals, with load were studied.Vickers hardness numbers, Hv were found to decrease with the increase in load. The value of Mayer's index, ‘n ’ was found to be greater than 1.6 for GPI and TUGPI showing soft‐material category. The results are discussed in detail. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental investigation of different configurations for the seeded growth of SiC crystals via a VLS mechanism
Authors: Boutarek N. , Bonda M. , Chaussende D. , Madar R.
Published: February 2008

The growth of SiC crystals or epilayers from the liquid phase has already been reported for many years. Even if the resulting material can be of very high structural quality and the possibility to close micropipes was demonstrated, handling the liquid phase still is a challenge. Moreover, it is highly difficult to stabilize the C dissolution front and then to stabilize the growth front over a long growth time. Based on the Vapour‐Liquid‐Solid (VLS) mechanism, we present a new configuration for the growth of SiC single crystal which should allow first to simplify the liquid handling at high temperature and second to precisely control the crystal growth front. The process consists in a modified top and bottom seeded solution growth method, in which the liquid is held under electromagnetic levitation and fed from the gas phase. 3C‐SiC crystals exhibiting well‐faceted morphology were successfully obtained at 1100‐1200 °C with exceptional growth rates, varying from 1 to 1.5 mm/h in Ti‐Si melt. It was shown that the nucleation density decreases simultaneously with increasing propane partial pressure. At 1200‐1400 °C, thick homoepitaxial 6H‐SiC layers were successfully obtained in Co‐Si and Ti‐Si melts, with growth rate up to 200 µm/h. Large terraces with smooth surfaces are observed suggesting a layer by layer growth mode, and the influence of the system pressure was demonstrated. It was shown that the terrace size decrease simultaneously with increasing propane partial pressure which suggests the beginning of a two dimensional to three dimensional growth mode transition. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Defect structure and optical fixing holographic storage of Mg:Mn:Fe:LiNbO3 crystals
Authors: Wei Zheng , Qiang Gui , Yuheng Xu
Published: February 2008

Mg:Mn:Fe:LiNbO3 crystals were grown by the Czochralski method. The defect structure was analyzed by UV‐vis spectra and IR spectra. The holographic storage of Mg:Mn:Fe:LiNbO3 crystals was measured by the two color fixed method. The results show that with the increase of MgO doping concentration, the writing time becomes shorter, the dynamic range decreases, photorefractive sensitivity increases and fixing diffraction efficiency decreases. When the MgO doping concentration exceeds 4.5 mol%, the fixing diffraction efficiency approaches zero. The effect of doping Mg ions on the holographic storage properties of Mn:Fe:LiNbO3 crystals is discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
In situ measurement of growth kinetics of {100} KDP crystal faces in the presence of polyphosphate impurities
Authors: Liu Bing , Fang Chang‐Shui , Wang Sheng‐Lai , Mou Xiao‐Ming
Published: February 2008

The face growth rate and critical supersaturation of {100} face were in situ measured using the laser‐polarization‐interference technique in the presence of potassium pyrophosphate, trimetric sodium phosphate and sodium hexametaphosphate impurities. The polyphosphate impurities inhibit the growth rate of prismatic faces. The face growth rate as a function of supersaturation at different impurity concentrations, as well as critical supersaturation as a function of impurity concentrations, was found in good agreement with a two‐dimensional nucleation model in the pure system and Kubota and Mullin's model in the presence of impurities. The average distance L between active sites available for impurity adsorption as well as the edge free energy was calculated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A fast‐convergent fairness scheme for resource allocation in RPR networks
Authors: Liu Chuan‐Gang , Li Jung‐Shian
Published: February 2008

In this paper, we propose a fast‐convergent fairness scheme in IEEE 802.17 resilient packet ring (RPR) networks. In the proposed scheme, each station could rapidly approach fair rate by estimating the number of unbounded flows at each link. In addition, the fast‐convergent scheme could prevent rate oscillations in theRPR aggressive modescheme under unbalanced traffic. The estimation mechanism is simple and scalable since it is stateless without per‐flow management. Through analytical and simulation evaluations our scheme was found to be stable and speedy when compared with 802.17RPRfairness scheme or the proposeddistributed virtual‐time scheduling in ringsscheme. Our scheme could allocate bandwidth fairly and smoothly among flows and achieve high utilization at the same time in theRPRnetwork. Copyright © 2008 John Wiley & Sons, Ltd.
40 Jahre Deutsches Institut für Bautechnik – 40 Jahre sicheres und innovatives Bauen. Die Gründung des DIBt
Authors: Schmidt‐Staudinger Renate
Published: February 2008

Das Deutsche Institut für Bautechnik (DIBt) feiert 2008 sein 40‐jähriges Bestehen. 40 Jahre DIBt stehen für 40 Jahre Sicherheit und Innovationen im Bauwesen und für 40 Jahre Zulassungswesen einer zentralen Institution in der Bundesrepublik Deutschland. Ein geeigneter Anlass also, um die Geschichte des Instituts in den DIBt Mitteilungen in einer kleinen Serie näher zu beleuchten. Den Auftakt unserer Betrachtung bilden die Anfänge des deutschen Zulassungswesens und der Gründungsprozess des DIBt von 1951 bis 1968.
Synthesis, Structure, and Magnetic Properties of a New Three‐Dimensional Iron Phosphite, [C4N2H12][Fe4(H2O)3(HPO3)7]·(H2O)xx= 0.6
Authors: Mandal Sukhendu , Banerjee Debamalya , Bhat S. V. , Pati Swapan K. , Natarajan Srinivasan
Published: February 2008

A new open‐framework iron phosphite, [C4N2H12][Fe4(H2O)3(HPO3)7]·(H2O)xx= 0.6 (1), has been prepared by the hydrothermal reaction between FeCl3·6H2O, H3PO3, and piperazine. The three‐dimensional structure is comprised of a network of FeO6, FeO5(H2O), and HPO3polyhedral units connected through their vertices. The structure has layers formed by the well‐known 4.6.12‐net connectivity and is stacked in an AAAA... sequence, penetrated by the one‐dimensional pillar units, forming a three‐dimensional pillared‐layer structure. This connectivity gives rise to two independent 12‐ring channel systems. Magnetic studies indicate antiferromagnetic behavior at high temperatures, with a small ferromagnetic polarization at low temperatures.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Contributions to the Structural Chemistry of 2‐Amino Alcoholate Derivatives of Titanium and Zirconium Alkoxides and Their Partial Hydrolysis Products
Authors: Fric Helmut , Puchberger Michael , Schubert Ulrich
Published: February 2008

The structures of Ti2(OiPr)6(OCHMeCH2NH2)2 and Ti2(OiPr)6(OCH2CHMeNH2)2, obtained by reaction of Ti(OiPr)4 with the corresponding amino alcohols, were investigated to elucidate the structural influence of the organic substituents at the amino alcohol. A methyl group at the OH‐substituted carbon atom results in a larger distortion of the structure than a methyl group at the NH2‐substituted carbon. The disubstituted compound Ti2(OiPr)4(OCH2CH2NH2)4 was formed, when NaTi(OiPr)5 was reacted the amino ethanol. While one OCH2CH2NH2 ligand is chelating, the oxygen atom of the second bridges the titanium atoms, and the NH2 group is dangling. The structures of the partial hydrolysis products Ti4O4(OiPr)4(OCHPhCHMeNHMe)4 and Ti8O6(OEt)12(OCH2CH2NH2)8 were also investigated. The former contains an incomplete double‐cube Ti4O4 cluster core, the latter is made of two Ti4O3(OEt)6(OCH2CH2NH2)4 sub‐units, with a nearly planar Ti4(μ2‐O)2(μ3‐O)(μ2‐OEt)2 ring system, connected by two OEt bridges. Zr(OCH2CH2NH2)4 is a mononuclear compound with four chelating amino alcoholate ligands. The structure of Zr6(OBu)18(OCH2CH2NH2)6 is assembled from two Zr2(OBu)5(OCH2CH2NH2)3 and two Zr(OBu)4 sub‐units, which are associated by alkoxo bridges. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Visible‐Light Excitation of Infrared Lanthanide Luminescence via Intra‐Ligand Charge‐Transfer State in 1,3‐Diketonates Containing Push‐Pull Chromophores
Authors: Shavaleev Nail M. , Scopelliti Rosario , Gumy Frédéric , Bünzli Jean‐Claude G.
Published: February 2008

A new 1,3‐diketonato ligand containing both an electron‐donor [4‐(dimethylamino)benzene] and an electron‐acceptor (4‐nitrobenzene) group and its lanthanide complexes have been prepared. They display an intense intra‐ligand charge‐transfer absorption transition in the visible region of the spectrum at 400–550 nm which was utilized to achieve visible‐light excitation of metal‐centred infrared luminescence of NdIII, ErIII and YbIII ions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Reduction of Ketones with Hydrocarbon‐Soluble Calcium Hydride: Stoichiometric Reactions and Catalytic Hydrosilylation
Authors: Spielmann Jan , Harder Sjoerd
Published: February 2008

Reactions of the dimeric calcium hydride complex[(DIPP‐nacnac)CaH·thf]2 {1; DIPP‐nacnac = CH[(CMe)(2,6‐iPr2C6H3N)]2} with the α‐hydrogen containing ketones acetophenone, acetone, dibenzylketone and 2‐adamantone are smooth. In most cases not only addition but also substantial enolization is observed as a side reaction and in some cases also aldol condensation was found. Despite this unselectivity, the addition products could be isolated crystalline pure. Crystal structures of [(DIPP‐nacnac)CaOCH(Me)Ph]2 (3), [(DIPP‐nacnac)CaOCH(CH2Ph)2]2 (6) and [(DIPP‐nacnac)Ca(2‐adamantoxide)]2 (7) have been determined. The calcium hydride complex 1 is an effective catalyst in the hydrosilylation of ketones. Independent from the silane/ketone ratio, a strong preference for formation of bis‐alkoxy silanes [PhSiH(OR)2] is observed. In most cases no enoxy groups have been found in the product. This indicates that the mechanism does not involve addition of the calcium hydride to the ketone functionality. A concerted addition of silane to ketone through a six‐coordinate hypervalent silicon intermediate is proposed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
A Ruthenium‐Catalyzed Approach to the Friedländer Quinoline Synthesis
Authors: Vander Mierde Hans , Van Der Voort Pascal , De Vos Dirk , Verpoort Francis
Published: February 2008

In a modification of the Friedländer reaction, 2‐aminobenzyl alcohol is oxidatively cyclized with a variety of ketones to yield substituted quinolines. Of all the ruthenium catalysts that were tested for this reaction, the second‐generation Grubbs' catalyst gives the highest quinoline yield, in combination with KOtBu as a base. The presence of a hydrogen acceptor is required to regenerate the catalyst. Also the reaction mechanism is discussed, and the results show that there are possibly two different pathways towards quinolines.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Synthesis of Annulenes via Multiple Wittig Reactions; In‐Situ Dimerization of 1,2;5,6‐Dibenzocyclooctatetraene
Authors: Bornhöft Jan , Siegwarth Jan , Näther Christian , Herges Rainer
Published: February 2008

A simple synthetic route to tetrabenzo[16]‐ and hexabenzo[24]annulene systems using one‐pot multiple Wittig reactions is presented. We report the characterization of the all‐trans‐isomer of tetrabenzo[16]annulene by NMR spectroscopy and X‐ray diffraction. Several isomers of an unexpected, tetrabenzocyclooctatetraene dimer product are also isolated and identified by NMR‐ and X‐ray diffraction studies.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Electrochemical Characterization of In Situ Functionalized Gold Cysteamine Self‐Assembled Monolayer with 4‐Formylphenylboronic Acid for Detection of Dopamine
Authors: Shervedani Reza Karimi , Bagherzadeh Mojtaba
Published: February 2008

Functionalization of gold cysteamine (AuCA) self‐assembled monolayer with 4‐formylphenylboronic acid (BA) via Schiff's base formation, through in situ method to fabricate Au‐CA‐BA electrode is presented and described. The fabricated electrode was used as a novel sensor for accumulation and determination of dopamine (DA). The accumulation of DA as a diol on the topside of Au‐CA‐BA as a Lewis acid, was performed via esterification (AuCABADA), and followed for determination of DA. Functionalization, characterization, and determination steps were probed by electrochemical methods like cyclic voltammetry and electrochemical impedance spectroscopy. The data will be presented and discussed from which a new sensor for DA is introduced.
Preparation of an Electrode That Immobilizes NAD‐Dependent Alcohol Dehydrogenase by Using a Redox Polymer Containing 1,10‐Phenanthroline‐5,6‐dione
Authors: Motoyama Yusuke , Nakamura Nobuhumi , Ohno Hiroyuki
Published: February 2008

A redox polymer (PAHA‐Ru), modified electrode exhibited excellent catalytic activity for the electrochemical oxidation of β‐nicotinamide adenine dinucleotide (NADH). PAHA‐Ru was composed of carboxyl groups and ruthenium complexes containing 1,10‐phenanthroline‐5,6‐dione (phen‐dione). The stability of the PAHA‐Ru film was increased by incorporating poly(diallyldimethylammonium chloride) (PDDA) owing to the formation of a polyelectrolyte complex between the PAHA‐Ru and PDDA. The catalytic efficiency of the oxidation of NADH using the PAHA‐Ru/PDDA‐modified electrode was also greater than that using a PAHA‐Ru‐modified electrode. NAD‐dependent alcohol dehydrogenase (ADH) was entrapped in the PAHA‐Ru/PDDA film on the surface of the glassy carbon electrode. Electrochemical oxidation of ethanol using the ADH‐entrapped electrode was also observed.
Dissolved Cu(II) Speciation in Unpolluted Soil Solutions of a Planosolic Horizon
Authors: Pelfrêne Aurélie , Gassama Nathalie , Grimaud Daniel
Published: February 2008

Dissolved Cu(II) speciation in unpolluted soil solutions from different horizons was studied using differential pulse anodic stripping voltammetry (DPASV). Three sites were selected according to topography and monitored for three years. Experiments evidence Cu(II) can be bound by DOM (Dissolved Organic Matter) through complexation and/or adsorption reactions. The complexation capacity and the corresponding conditional stability constant were determined for complexation reactions. The adsorbing sites were titrated. A potential binding coefficient was calculated to compare both types of reactions. Results show adsorption is less frequent than complexation but exhibits higher binding coefficient.
Simulation of Redox‐Cycling Phenomena at Interdigitated Array (IDA) Electrodes: Amplification and Selectivity
Authors: Odijk M. , Olthuis W. , Dam V. A. T. , van den Berg A.
Published: February 2008

We present Finite Element Method (FEM) simulations of interdigitated array (IDA) electrode geometries to study and verify redox selectivity and redox cycling amplification factor. The simulations provide an adequate explanation of an earlier found, but poorly understood, high amplification factor (65×) in a 1 μm‐spaced IDA microdevice. Moreover, using the FEM calculations we present selectivity measurements with IDA electrodes in a mixture of two redox species, as for example dopamine and ferricyanide. We show that it is possible to electrochemically detect dopamine in presence of the stronger reductor ferricyanide, which is impossible with direct amperometric detection, with the use of IDA electrodes with proper polarization potential of the collector electrode. Using our simulations, we show that a theoretical selectivity of dopamine over ferricyanide of 11 can be achieved.
Renewable Copper and Silver Amalgam Film Electrodes of Prolonged Application for the Determination of Elemental Sulfur Using Stripping Voltammetry
Authors: Piech Robert , Baś Bogusław , Niewiara Ewa , Kubiak Władysław W.
Published: February 2008

New, renewable copper (Hg(Cu)FE) and silver (Hg(Ag)FE) based amalgam film electrodes applied for the determination of elemental sulfur using differential pulse cathodic stripping voltammetry are presented. With surface areas adjustable from 1 to 12 mm2, both electrodes are characterized by very good surface reproducibility (≤2%) and long‐term stability (a few thousand measurement cycles). The mechanical refreshing of the amalgam film takes about 1–2 seconds. The effects of various factors such as instrumental parameters and the supporting electrolyte composition were optimized. Interferences from sulfides are easily removed by the addition of acid, and bubbling with argon, for Hg(Ag)FE. In the case of Hg(Cu)FE, sulfides did not interfere. The calibration graph is linear within the studied range from 16 ng L−1 to 4.8 μg L−1 for Hg(Cu)FE, and up to 6.4 μg L−1 for Hg(Ag)FE (tacc=15 s). The correlation coefficients for the two electrodes were at least 0.997. The detection limits for a low concentration of S(0) and tacc=60 s are as low as 14 ng L−1 for Hg(Cu)FE and 4 ng L−1 for Hg(Ag)FE. The proposed method was successfully applied and validated by studying the recovery of S(0) from spiked river water.
Effect of pH on the Enantiospecificity of Homocysteine Monolayer on Au(111) for the Redox Reaction of 3,4‐Dihydroxyphenylalanine
Authors: Matsunaga Mariko , Nagasaka Makoto , Nakanishi Takuya , Sawaguchi Takahiro , Osaka Tetsuya
Published: February 2008

The effect of pH on the enantiospecificity of Au (111) electrode modified with L‐homocysteine was evaluated for the electrochemical redox reaction of 3,4‐dihydroxyphenylalanine (DOPA). Cyclic voltammetric peaks clearly exhibited enantiospecificity at pH 0.6 and 2, whereas no enantiospecificity was observed at pH 3, 4, and 5.5. Scanning tunneling microscopy confirmed the highly ordered (2√3×3√3)R30° structure of L‐homocysteine at pH 0.6, at which L‐homocysteine molecules form a dimer through the hydrogen‐bond between carboxy groups (COOH), while a disordered structure was observed at pH 5.5. These results suggest that the dimer formed in the acidic solutions at pH below 3 plays an important role in providing the enantiospecificity to the Au(111) surface.
Carboxyphenyl Covalent Immobilization of Heme Proteins and its Favorable Biocompatible Electrochemical and Electrocatalytic Characteristics
Authors: Liu Meichuan , Qi Yuan , Zhao Guohua
Published: February 2008

A novel carboxyphenyl covalent immobilization technique has been successfully developed to realize the effective attachment of two typical heme proteins, hemoglobin (Hb) and cytochrome c (Cyt‐c), onto underlying glassy carbon electrode (GCE). Primarily, the GCE surface is functionalized with aromatic 4‐carboxyphenyl (4‐CP) group by the electrochemical reduction of diazonium cations, producing covalently linked carboxyl‐terminated active GCE surface to work as a ‘bridge’. Then, Hb and Cyt‐c are readily attached to GCE through the ‘bridge’ by functional covalently combination between NH2 terminal groups of proteins and COOH terminal groups of 4‐CP, obtaining Hb/4‐CP/GCE and Cyt‐c/4‐CP/GCE. On both electrodes, well‐defined peaks attributing to the FeIII/FeII couple of heme group of Hb and Cyt‐c are clearly observed with the electron transfer rate constant (ks) evaluated to be 2.48±0.05 s−1 and 2.73±0.05 s−1, respectively. It is attractive that the formal potential (E°') of the immobilized Hb and Cyt‐c are estimated to be 50 and 100 mV (vs. SCE), respectively, which are closer to the standard redox potential of native Hb and Cyt‐c in solution, owing to the good biocompatibility of 4‐CP groups. The electrodes also exhibit fast response, high sensitivity and well stability for the amperometric detection of H2O2 at a fairly mild potential of 0 V without any mediators, obtaining rather small apparent Michaelis‐Menten constant (KMapp) values of 113 μM for Hb/4‐CP/GCE and 101 μM for Cyt‐c/4‐CP/GCE. All the experimental results indicated that the covalent graft 4‐carboxyphenyl group plays an important role in constructing a “biocompatible bridge” to help the direct electron transfer of Hb and Cyt‐c with favorable biocompatibility and good bio‐ electrocatalytic affinity in virtue of the substituted aryl group only consisting of C, H and O elements, which is similar with the constitutes of organics. It makes the system of functionalized covalent immobilization of proteins onto carbon electrode a promising platform for fabricating the third‐generation biosensors. A new approach for realizing direct electrochemistry of proteins, as well as design of novel bioelectronic devices has been accordingly provided.
Direct Heterogeneous Electron Transfer Reactions of Bacillus halodurans Bacterial Blue Multicopper Oxidase
Authors: Shleev Sergey , Wang Yan , Gorbacheva Marina , Christenson Andreas , Haltrich Dietmar , Ludwig Roland , Ruzgas Tautgirdas , Gorton Lo
Published: February 2008

Direct electron transfer reactions of Bacillus halodurans bacterial multicopper oxidase on bare spectrographic graphite, as well as bare and thiol‐modified gold electrodes were studied using cyclic voltammetry, potentiometry, amperometry, and spectroelectrochemistry. The redox potential of the T1 site of the enzyme was measured using mediatorless redox titration and found to be 325 mV±10 mV vs. NHE. From measurements with a mercaptopropionic acid‐modified gold electrode under aerobic conditions a midpoint potential of 360 mV vs. NHE for the T2/T3 copper cluster is deduced. Differing from most other characterized laccases of fungal and plant origins this bacterial enzyme exhibits bioelectrocatalytic activity at neutral pH and tolerates high chloride concentrations (200 mM), conditions that usually strongly inhibit catalysis. Moreover, it has the very high affinity towards molecular oxygen both in solution and in the adsorbed state (KM≤50 μM).
Investigation of Airbrushing for Fabricating Microelectrodes in Microfluidic Devices
Authors: Walker Corey E. , Xia Zheng , Foster Zachary S. , Lutz Brent J. , Fan Z. Hugh
Published: February 2008

We report fabrication of microelectrodes by airbrushing, a technique primarily used for commercial arts. Similar to screen‐printing, airbrushing enables conductive inks to be patterned onto a thin film. The film with ink electrodes is then laminated with a plastic substrate with microchannels to form a microfluidic device. The device is designed to implement enzyme‐catalyzed electrochemical detection for sensing hydrogen. We found that airbrushed electrodes perform in a similar fashion with screen‐printed electrodes. The cyclic voltammetric peak separation for ferrocyanide is 0.34 V, suggesting a nonreversible redox behavior as observed for the screen‐printed ink electrodes. A linear calibration curve is obtained for 2 to 20 mM ferrocyanide in a flow using chronoamperometry, which is the method we previously exploited for demonstrating enzyme‐catalyzed electrochemical detection in a large flow cell. The process parameters of airbrushing, including ink concentration, have been characterized. The benefits of fabricating electrodes by airbrushing include a simpler process, lower cost, and requiring less skill. This technique is especially useful in situations where a commercial screen‐printing machine is inaccessible.
Electrocatalytic Determination of Sulfite at Immobilized Microdroplet Liquid|Liquid Interfaces: The EIC′ Mechanism
Authors: Katif Najoua , MacDonald Stuart M. , Kelly Andrew M. , Galbraith Ewan , James Tony D. , Lubben Anneke T. , Opallo Marcin , Marken Frank
Published: February 2008

Liquid|liquid interfaces provide a natural boundary and a reactive interface where an organic phase is in contact with an aqueous analyte. The selectivity of ion transfer processes at liquid|liquid interfaces can help to provide sensitivity, introduce reactive reagents, or allow analyte accumulation at the electrode surface. In this study, microdroplet deposits of the organic liquid 4‐(3‐phenylpropyl)‐pyridine (PPP) with the ferrocenylmethyl‐dodecyldimethylammonium+ (FDA+) redox system are deposited onto a basal plane pyrolytic graphite electrode and employed to transfer anions from the aqueous into the organic phase. A clear trend of more hydrophobic anions transferring more readily (at more negative potentials) is observed and an ESI‐mass spectrometry method is developed to confirm the transfer. Subsequently, the electrocatalytic oxidation of sulfite, SO32−, within the organic phase and in the presence of different electrolyte anions is investigated. Competition between sulfite transfer and inert anion transfer occurs. The electrocatalytic sulfite oxidation is suppressed in the presence of PF6− and occurs most readily in the presence of the hydrophilic nitrate anion. The resulting process can be classified as an electrocatalytic EIC′‐process (E: electron transfer; I: ion transfer; C: chemical reaction step). The effectiveness of the electrocatalytic process is limited by i) competition during anion transfer and ii) the liquid|liquid interface acting as a diffusion barrier. The analytical sensitivity of the method is limited to ca. 100 μM SO32− (or ca. 8 ppm) and potential approaches for improvement of this limit are discussed.
The zeta potential of surface‐functionalized metallic nanorod particles in aqueous solution
Authors: Dougherty George M. , Rose Klint A. , Tok Jeffrey B.‐H. , Pannu Satinderpall S. , Chuang Frank Y. S. , Sha Michael Y. , Chakarova Gabriela , Penn Sharron G.
Published: February 2008

Metallic nanoparticles suspended in aqueous solutions and functionalized with chemical and biological surface coatings are important elements in basic and applied nanoscience research. Many applications require an understanding of the electrokinetic or colloidal properties of such particles. We describe the results of experiments to measure the zeta potential of metallic nanorod particles in aqueous saline solutions, including the effects of pH, ionic strength, metallic composition, and surface functionalization state. Particle substrates tested include gold, silver, and palladium monometallic particles as well as gold/silver bimetallic particles. Surface functionalization conditions included 11‐mercaptoundecanoic acid (MUA), mercaptoethanol (ME), and mercaptoethanesulfonic acid (MESA) self‐assembled monolayers (SAMs), as well as MUA layers subsequently derivatized with proteins. For comparison, we present zeta potential data for typical charge‐stabilized polystyrene particles. We compare experimental zeta potential data with theoretically predicted values for SAM‐coated and bimetallic particles. The results of these studies are useful in predicting and controlling the aggregation, adhesion, and transport of functionalized metallic nanoparticles within microfluidic devices and other systems.
NURBS‐enhanced finite element method for Euler equations
Authors: Sevilla R. , Fernández‐Méndez S. , Huerta A.
Published: February 2008

In this work, the NURBS‐enhanced finite element method (NEFEM) is combined with a discontinuous Galerkin (DG) formulation for the numerical solution of Euler equations of gas dynamics. With NEFEM, numerical fluxes along curved boundaries are computed much more accurately due to the exact geometric representation of the computational domain. The proper implementation of the wall boundary condition and the exact geometry provide accurate results even with a linear approximation of the solution. A detailed comparison of NEFEM in front of isoparametric finite elements is presented, demonstrating the superiority of NEFEM approach for both linear and higher‐order computations. Copyright © 2008 John Wiley & Sons, Ltd.
Safety, efficacy, and pharmacokinetics of adefovir dipivoxil in children and adolescents (age 2 to <18 years) with chronic hepatitis B
Authors: Jonas Maureen M. , Kelly Deirdre , Pollack Henry , Mizerski Jacek , Sorbel Jeff , Frederick David , Mondou Elsa , Rousseau Franck , Sokal Etienne
Published: February 2008

This study investigated the efficacy, safety, and pharmacokinetics of adefovir dipivoxil (ADV) in children and adolescents with chronic hepatitis B (CHB). A total of 173 treatment-naive and treatment-experienced children with hepatitis B e antigen (HBeAg)+ CHB were randomized to ADV or placebo. Randomization was stratified by age (2 to <7 years; >7 to <12 years; >12 to <18 years) and prior treatment. Significantly more ADV-treated subjects aged 12 to <18 years achieved the primary efficacy endpoint (serum hepatitis B virus [HBV] DNA <1,000 copies/mL and normal alanine aminotransferase) compared to placebo-treated subjects (23% versus 0%;

P

= 0.007). In the younger groups, differences between ADV and placebo at the end of blinded treatment were not statistically significant. More ADV-treated subjects had HBeAg seroconversion: 18 of 113 (15.9%) versus three of 57 (5.3%) (but

P

= 0.051), and more met the combined endpoint of HBeAg seroconversion, HBV DNA <1,000 copies/mL and normal alanine aminotransferase (12/113 versus 0/57;

P

= 0.009). No subject developed an ADV-associated mutation that has been linked to HBV DNA rebound (that is, mutations rtN236T or rtA181V). ADV plasma concentrations were comparable across groups and within the target range. ADV treatment was well tolerated; no new safety issues were identified. Treatment-related adverse events were reported for 12% of ADV-treated and 10% of placebo-treated subjects. After 48 weeks of ADV treatment, antiviral efficacy in subjects ages 12 to <18 years with HBeAg+ CHB was similar to that observed in a study in adult treatment-naive subjects with HBeAg+ CHB. ADV was not different from placebo in subjects aged 2 to 11 years despite adequate plasma ADV exposure in all three age groups.

Conclusion:

ADV showed significant antiviral efficacy in subjects aged 12 to 17 years with HBeAg+ CHB, but was not different from placebo in subjects aged 2 to 11 years.
Partially segregated neural networks for spatial and contextual memory in virtual navigation
Authors: Rauchs Géraldine , Orban Pierre , Balteau Evelyne , Schmidt Christina , Degueldre Christian , Luxen André , Maquet Pierre , Peigneux Philippe
Published: February 2008

Finding our way in a previously learned, ecologically valid environment concurrently involves spatial and contextual cognitive operations. The former process accesses a cognitive map representing the spatial interactions between all paths in the environment. The latter accesses stored associations between landmark objects and their milieu. Here, we aimed at dissociating their neural basis in the context of memory‐based virtual navigation. To do so, subjects freely explored a virtual town for 1 h, then were scanned using fMRI while retrieving their way between two locations, under four navigation conditions designed to probe separately or jointly the spatial and contextual memory components. Besides prominent commonalities found in a large hippocampo‐neocortical network classically involved in topographical navigation, results yield evidence for a partial dissociation between the brain areas supporting spatial and contextual components of memory‐based navigation. Performance‐related analyses indicate that hippocampal activity mostly supports the spatial component, whereas parahippocampal activity primarily supports the contextual component. Additionally, the recruitment of contextual memory during navigation was associated with higher frontal, posterior parietal and lateral temporal activity. These results provide evidence for a partial segregation of the neural substrates of two crucial memory components in human navigation, whose combined involvement eventually leads to efficient navigation behavior within a learned environment. © 2008 Wiley‐Liss, Inc.