bluuebunny/crossref_metadata_2025 huggingface dataset:
An embedding method for simulation of immobilized enzyme kinetics and transport in sessile hydrogel drops
Authors: Wong Chao‐Jen , Nadim Ali
Published: March 2008

A newly‐developed embedding method for simulating enzyme kinetics and transport occurring within axisymmetric 3D domains is presented. The physical problem is pertinent to gel‐pad microarrays for assessment of enzymatic activity. An enzyme is immobilized uniformly within a hydrogel which is spotted onto a solid surface in the form of a sessile drop, taking on a spherical cap shape. An aqueous solution containing substrate flows slowly past the porous drop. The substrate diffuses into the drop and is converted to product with the help of the enzyme. The product accumulates in and diffuses out of the drop and is taken away by the flow. Spatiotemporal distribution of the product, monitored via fluorescence, can be used to quantify the enzyme kinetics. This process is described by a system of nonlinear reaction‐diffusion partial differential equations, modeling the diffusive transport and enzymatic reaction. The computational domain contains both the hydrogel drop and the bulk fluid phases. The embedding method is a computational technique that enables the use of finite differences on a regular Cartesian grid for simulation of multiphase problems with complex interfaces/boundaries. It uses a volume‐fraction‐based approach, similar to the volume‐of‐fluid (VOF) method, to implement the boundary conditions that must be applied at the interface between the phases. The main advantage of the embedding method is its simplicity, which results in code generation that can be highly optimized. In the present work, we apply the embedding method to the aforementioned two‐phase reaction‐diffusion problem and validate the results by comparing to a number of exact solutions available in simpler geometries and to results obtained using a finite‐volume method on an unstructured body‐fitted mesh. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The multiple intermediate configuration approach and its influence on DIRK/MLNA finite element procedures
Authors: Quint Karsten J. , Hartmann Stefan
Published: March 2008

This article treats the solution of evolutionary equations based on two plastic intermediate configurations which arise in large plastic deformations within the finite element context. For this purpose high order time integration methods, diagonallyimplicit Runge‐Kutta methods (DIRK), in combination with the Multilevel‐Newton algorithm (MLNA) are used. To preserve plastic incompressibility a projection method is applied and its influence is studied. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Physical aspect of mathematical description of the Doppler effect
Authors: Gawinecki Jerzy August , Rafa Józef
Published: March 2008

We present the Doppler effect as a solution to a wave equation concerning waves generated by a moving in space source of the wave that periodically changes it's signal in time. The solution has been reached by basing on the Cagniard‐de Hoop's method. The reached conclusion of the analysis proves that the Doppler effect presents the change in the frequency of the received signal as well as the change of it's phase. In conclusion these changes are inhomogeitic and anisotropic. This research has been successfully applied in telecommunication and in locating sources of radiation of electromagnetic waves. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Some numerical methods for approximating modified Bessel functions
Authors: Rappoport Juri
Published: March 2008

In this paper the numerical Tau methods for the approximation of the kernels of Kontorovitch–Lebedev integral transforms are described. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The use of an hourglass stabilized solid‐shell finite element in forming simulations — theoretical aspects and first industrial applications
Authors: Schwarze Marco , Reese Stefanie
Published: March 2008

The method of reduced integration with hourglass stabilization is one of the most powerful techniques in the field of finite element technology. Caused by the use of a reduced number of integration points it leads to very efficient finite element formulations. To avoid the appearance of non‐physical zero‐energy modes an hourglass stabilization is necessary. This paper presents an adaptive hourglass stabilization strategy motivated by the hyperelastic formulation of finite inelasticity. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Differential geometry and the red blood cell
Authors: Vayo Westcott
Published: March 2008

The usual mathematical expressions for the shape of the red blood cell, whether in rectangular or polar coordinates, are very complicated and difficult to use analytically. We have found that by using parametric equations and Jacobean elliptic functions to describe the cell things are much easier. The usual differential geometric concepts can be adapted to find interesting new formulas for ideas like Fick's Law, etc. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Advances in math search
Authors: Youssef Abdou
Published: March 2008

As digital libraries of mathematical and scientific contents become available, it is essential to have math‐aware search systems. The search systems must understand math symbols and structures, and allow users to enter queries that involve not only text keywords but also mathematical expressions and fragments of expressions. In addition, the search results must be presented in a way that enables the user to find the desired information rapidly. This short paper gives a quick overview of the state of the art of math search, and focuses on the math search system that the author has developed for the Digital Library of Mathematical Functions (DLMF) project of the National Institute of Standards and Technology. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the discrete compactness of hp edge finite elements
Authors: Boffi Daniele
Published: March 2008

We investigate the relationship between Discrete Compactness Property and the conditions introduced in [1] for the convergence of eigenvalue problems in mixed form; we shall show that both aspects can be put in the same unified framework. As a corollary of our theory, we can show that the hp version of rectangular Raviart–Thomas elements can be successfully applied to the approximation of Laplace eigenmodes in mixed form. This follows from the analogous result for edge elements presented in [2]. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fructose‐induced N‐terminal glycation of enkephalins and related peptides
Authors: Jakas Andreja , Vinković Marijana , Smrečki Vilko , Šporec Maja , Horvat Štefica
Published: March 2008

The formation of glycation products in model systems consisting of fructose and the endogenous opioid peptides not containing lysine residue, such as Leu‐enkephalin (Tyr‐Gly‐Gly‐Phe‐Leu) and Met‐enkephalin (Tyr‐Gly‐Gly‐Phe‐Met), or of their fragments, Tyr‐Gly‐Gly‐Phe and Tyr‐Gly‐Gly, was examined. N‐(2‐Deoxy‐aldos‐2‐yl)‐peptides (Heyns compounds) as well as diastereoisomeric imidazolidinone compounds were identified as reaction products of N‐terminal amino group glycation for each of the peptides studied. The structure of the glycation products and relative configuration of C‐2 substituents on the imidazolidinone ring in diastereoisomers were determined by NMR experiments. The chemical and enzymatic stability of the fructose‐derived glycated products of Leu‐ and Met‐enkephalin was studied in phosphate‐buffered saline (pH 7.4) and in human serum at 37 °C. The obtained results revealed that glycation increases the stability of the parent peptide to enzymatic degradation. As a result of different configuration at the newly formed stereogenic center, large stability differences in the 2S* and 2R* isomers of the imidazolidinone compounds were observed. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd.
n and k testing of magnetic heads with imaging spectroscopic ellipsometry
Authors: Vaupel M. , Yunfeng Song , Zhimin Yuan
Published: March 2008

The method of imaging spectroscopic ellipsometry is applied on magnetic read/write heads of hard disks. By means of spectroscopic ellipsometry, an optical model of the TiC/Al2O3 substrate including surface roughness and concentration gradient of TiC in the alumina substrate is generated. Surface roughness is measured with both ellipsometry and atomic force microscopy (AFM). The granular structure of TiC/Al2O3 is investigated in micrographs of n and k. It is discussed how Delta mapping of the magnetic pole area of the head can be used to measure DLC coating thickness and the variation of chemical constitution of the metal substrate. Repeatability of measurements of Delta is optimized in a one µm2 region of interest (ROI) on a metal stripe of the magnetic pole. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polarization optics of interfaces and thin films
Authors: Azzam R. M. A.
Published: March 2008

The differential reflection of p‐ and s‐polarized light by interfaces and thin films is central to the theory and applications of ellipsometry. It is also the basis of a wide variety of optical devices for the control and analysis of polarized light such as polarizers, polarizing and polarization‐preserving beam splitters, and quarter‐wave and half‐wave retarders. New insight into the correlation between optical properties of film and substrate materials and reflection properties is emphasized. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spectroscopic ellipsometry study of thin diffusion barriers of TaN and Ta for Cu interconnects in integrated circuits
Authors: Rudra S. , Wächtler T. , Friedrich M. , Louis S. J. , Himcinschi C. , Zimmermann S. , Schulz S. E. , Silaghi S. , Cobet C. , Esser N. , Gessner T. , Zahn D. R. T.
Published: March 2008

The objective of this work is to study the optical and electrical properties of tantalum nitride and tantalum barrier thin films used against copper diffusion in Si in integrated circuits using spectroscopic ellipsometry in the VUV and UV–visible range. Single layers of tantalum nitride and bilayer films of Ta/TaN were produced by reactive magnetron sputtering on Si(100) substrates covered with a native oxide layer. Ellipsometric measurements were performed in the energy range from 0.73–8.7 eV and the dielectric functions were simulated using Drude–Lorentz model and effective medium approximation (EMA) in order to obtain information regarding film thickness, film composition, free carrier plasma energy, mean relaxation time and electrical resistivity. The film thickness clearly affects the electrical resistivity and the electron mean free path. It was observed that for films of Ta on TaN even after maintaining the deposition condition suitable for the β‐phase of Ta, it turned out to be a mixture of α‐ and β‐phases with higher contribution of the α‐phase. It is shown that even a very small intermixture of two different phases of Ta can be determined accurately using ellipsometry. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of Si1–xGex:H thin films with graded composition and structure by real time spectroscopic ellipsometry
Authors: Podraza N. J. , Li Jing , Wronski C. R. , Dickey E. C. , Horn M. W. , Collins R. W.
Published: March 2008

Silicon‐germanium (Si1−x Gex:H) thin films have been prepared by plasma enhanced chemical vapor deposition of SiH4 and GeH4 and measured during growth using real time spectroscopic ellipsometry. A two‐layer virtual interface analysis has been applied to study the structural evolution of Si1−x Gex:H films that initially nucleate in the amorphous (a) phase, but evolve to the microcrystalline (μc) phase with accumulated thickness. The compositional evolution of alloy‐graded a‐Si1−x Gex:H has been studied as well using similar methods. Both types of films are of interest for Si‐based photovoltaic devices. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A FEM‐based application for numerical calculations of ellipsometric data
Authors: Wiklund H. , Arwin H. , Järrendahl K.
Published: March 2008

For modeling of advanced optical structures there is a need for stronger and more flexible modeling tools. Our aim is to develop and verify an application tool for calculations based on the Finite Element Method (FEM) of optical structures. To be able to understand which effects in the results that arises from limitations in the model, we begin by verifying the application tool for the most basic surface structures and gradually increase the complexity of the structures. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Enhancement in ellipsometric thin film sensitivity near surface plasmon resonance conditions
Authors: Arwin H. , Poksinski M. , Johansen K.
Published: March 2008

Ellipsometry used in internal reflection mode exhibits enhanced thin film sensitivity if operated close to surface plasmon resonance conditions. Compared to conventional ellipsometry, the changes in the ellipsometric parameter Δ are several orders of magnitude larger. Here, the origin of this large sensitivity is discussed by analysing thin film approximations of the complex reflectance ratio. It is found that the thickness sensitivity in Δ is proportional to the inverse of the difference between the intrinsic and the radiation‐induced damping of the surface plasmons. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The optical Hall effect
Authors: Hofmann T. , Herzinger C. M. , Krahmer C. , Streubel K. , Schubert M.
Published: March 2008

Classic electrical Hall effect measurements are standard for electrical characterization of free charge carriers in semiconductor layer structures. We demonstrate that magnetooptic generalized ellipsometry at long wavelengths when applied to conducting or semiconducting multilayer or nanoscopically in‐homogeneous structures can yield equivalent and even much increased information. We term this new method optical Hall effect, because it finds simple explanation within the model described by E. H. Hall for the occurrence of the transverse and longitudinal voltages augmented by non‐locality of the charge response in time. Transverse and longitudinal birefringence cause magnificent anisotropic polarization responses unraveling rich information on free charge properties of complex‐structured samples due to external magnetic fields and collective movement of bound and unbound charge carriers. We demonstrate that with our technique density, type, mobility, effective mass including anisotropy can be measured without any electrical contact in buried structures, and which may have been inaccessible to any true electrical evaluation thus far. We predict a realm of applications for the optical Hall effect in future materials research and engineering. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
PIII nitriding of fcc‐alloys containing Ni and Cr
Authors: Lutz Johanna , Gerlach Jürgen W. , Mändl Stephan
Published: March 2008

Face‐centred cubic (fcc) alloys such as austenitic stainless steel, Ni base alloys and Co base alloys are important materials with a high corrosion resistance. Nitrogen insertion by PIII into all these alloys at moderate temperatures leads to the formation of an expanded austenite structure. A similar activation energy for the thermally assisted diffusion of about 0.75 eV was found for steel and CoCr alloys with CrN precipitates beyond 400 °C in both systems. However, a double layer structure was observed for CoCr, similar to Ni alloys, in contrast to a single layer for austenitic steel. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Production of nitrogen‐containing carbon plasma using shunting arc discharge for carbon nitride films preparation
Authors: Takaki K. , Imanishi K. , Murakami T. , Mukaigawa S. , Fujiwara T. , Suda Y. , Yukimura K.
Published: March 2008

A magnetically driven carbon‐shunting arc discharge was generated in nitrogen gas circumstance and amorphous carbon nitride (a‐CNx) films were prepared. A silicon substrate was immersed into the plasma, and a series of pulse voltage was applied to the substrate synchronizing with ignition of the shunting arc with a peak current of 1.7 kA. The ambient nitrogen gas pressure was varied in wide range. The shunting arc plasma was successfully produced and was accelerated along carbon rails. Heating energy to generate the shunting arc had minimum value for variation of the ambient gas pressure. A spectroscopic measurement from the plasma light emission showed that the produced plasma contained nitrogen particles in ambient nitrogen gas circumstance. X‐ray photoelectron spectroscopy (XPS) analysis showed that the prepared carbon films contained nitrogen and was obtained to be N/C ratio of 0.35 at 2 Pa nitrogen gas pressure. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bose‐Einstein condensation of dipolar excitons in double and single quantum wells
Authors: Timofeev V. B. , Gorbunov A. V.
Published: March 2008

Experiments connected with dipolar exciton Bose‐Einstein condensation in ring lateral traps in GaAs/AlGaAs Schottky‐ diode heterostructures with double and single quantum wells are presented. The observed behaviour of luminescence spectra and patterned luminescence structure in circular ring traps, as well as linear polarization of luminescence and long‐range spatial coherence of Bose condensate are discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Plasma assisted molecular beam epitaxy of AlGaN/GaN high electron mobility transistors
Authors: Aidam R. , Kirste L. , Kunzer M. , Müller S. , Waltereit P.
Published: March 2008

We report on the plasma‐assisted molecular beam epitaxy (PAMBE) of AlGaN/GaN high electron mobility transistors (HEMTS). Growth was performed on MOCVD grown GaN Templates and 4H‐SiC(0001) wafers with 3” diameter. In a detailed study of GaN growth conditions the growth rate was varied between 0.28 and 0.5 µm/h. Under optimized conditions, the surface root mean square roughness was less than 0.6 nm. Low temperature PL measurements in the range 1.9 to 3.8 eV showed only the exciton‐emission with a FWHM of 12 meV. AlGaN‐HEMT structures on GaN‐templates exhibited room temperature Hall mobilities of 1600 cm2/Vs and sheet electron concentration of 8 × 1012/cm2. On SiC mobilities of 1220 cm2/Vs were achieved. Current‐voltage output characteristics of PAMBE grown AlGaN/GaN HEMTs on SiC showed a drain current density about 0.8 A/mm for a gate bias of +1V and only small dispersion. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Is Auger recombination responsible for the efficiency rollover in III‐nitride light‐emitting diodes?
Authors: Bulashevich K. A. , Karpov S. Yu.
Published: March 2008

Practically all III‐nitride light emitting diodes (LEDs) suffer from the efficiency rollover that occurs at high electric currents in the devices and limits their performance. At the moment, the mechanisms responsible for the rollover are not yet confidently identified despite the crucial importance of this problem for the LED production. On the basis of simulation, we suggest that the Auger recombination is a likely mechanism, producing the efficiency reduction at high currents. Using an empirically estimated Auger recombination coefficient, we argue for significance of this mechanism under practical operation conditions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Reliable nitride‐based near‐ultraviolet light‐emitting diodes with meshed p‐GaN
Authors: Kuo C. W. , Chen C. M. , Feng H. C. , Kuo C. H.
Published: March 2008

This investigation presents nitride‐based near ultraviolet (n‐UV) light emitting diodes (LEDs) with a meshed p‐GaN layer. With 20 mA injection current, it was found that forward voltages were 3.29, 3.31 and 3.39 V while output powers were 7.5, 9.0 and 10.6 mW for the planar indium‐tinoxide (ITO) LED, mesh ITO LED and meshed p‐GaN LED, respectively. The larger LED output power is attributed to increased light extraction efficiency. It was also found that we could use such a meshed p‐GaN layer to achieve reliable nitride‐based n‐UV LEDs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Improvement of hydrogen generation efficiency using GaN photoelectrochemical reaction in electrolytes with alcohol
Authors: Fujii Katsushi , Nakayama Hitoshi , Sato Keiichi , Kato Takashi , Cho Meoung‐Whan , Yao Takafumi
Published: March 2008

Photoelectrochemical water reduction using n‐type GaN in electrolytes with/without alcohol was investigated. For both cases, hydrogen evolution from counterelectrode was observed without bias. Hydrogen gas amount using 1.0 mol/L NaOH electrolyte with alcohol was approximately double compared to that without alcohol where the total current flow charges are similar at 300 min. The amount of hydrogen evolution was almost coincidence with the amount calculated from the total charge flow. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation on conductivity at the GaN/AlN/SiC substrate interface for vertical nitride power FETs
Authors: Wakamiya Y. , Hasegawa F. , Kawanishi H.
Published: March 2008

Power FETs are the next promising application of AlGaN/GaN hetero‐structures. In order to reduce the device size and thermal conductivity, power nitride FETs should be a vertical structure on a conductive SiC or Si substrate. An AlN or/and AlN/GaN multi‐buffer layer is inevitable to grow GaN on a SiC or Si substrate by MOVPE, therefore, current flow at the GaN/AlN/SiC interface is one of the important issues to be investigated. 17 to 350 nm AlN layers were grown on 8o off n–‐epitaxial 4H‐SiC substrates and on a GaN/AlGaN/AlN/SiC structure by alternate‐source‐feeding MOVPE. Ni/AlN/n‐‐epi‐4H‐SiC sample showed Schottky characteristics except 350nm thick AlN sample, indicating that the AlN was not working as an insulator. On the other hand, Ni/AlN/GaN/n–‐epi‐4H‐SiC sample turned out MIS characteristics for the same AlN thickness. This difference can be explained by the heterovalent atomic structure at the interface between AlN(III‐V) and SiC(IV‐IV). (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Deep centers in semi‐insulating Fe‐doped native GaN substrates grown by hydride vapour phase epitaxy
Authors: Fang Z.‐Q. , Claflin B. , Look D. C. , Elhamri S. , Smith H. E. , Mitchel W. C. , Hanser D. , Preble E. A. , Evans K. R.
Published: March 2008

Electrical properties, Fe concentration, and deep centers in semi‐insulating Fe‐doped GaN substrates grown by hydride vapor phase epitaxy (HVPE) were characterized by temperature‐dependent Hall‐effect measurements, secondary ion mass spectroscopy, and thermally stimulated current (TSC) spectroscopy. Five adjacent samples from a low‐[Fe] wafer displayed very high resistivity, dominated by a center at 0.94 eV. At least six traps were observed in the samples by TSC, with trap B (0.56‐0.60 eV) being dominant. A metastable trap A1 at ∼0.82 eV appeared after white‐light illumination at 300 K. A sample from a high‐[Fe] wafer displayed a lower resistivity, dominated by a center at 0.58 eV. The largest TSC peak in this sample was trap A1, although trap B also appeared. These TSC traps are compared with deep‐level‐transient‐spectroscopy traps reported in conductive epitaxial and bulk HVPE‐GaN. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of thin protective AlN layers on sapphire substrates at 1065 °C for hydride vapor phase epitaxy of AlN above 1300 °C
Authors: Tajima J. , Kubota Y. , Togashi R. , Murakami H. , Kumagai Y. , Koukitu A.
Published: March 2008

A thin protective AlN layer was grown on a (0001) sapphire substrate at 1065 °C for main AlN layer growth at high temperature (> 1300 °C) by hydride vapor phase epitaxy (HVPE). The formation of surface pits on the surface of the epitaxial AlN layer, grown directly on the sapphire substrate at 1320 °C, could be prevented by growing the protective layer. The full‐width at half‐maximum (FWHM) of X‐ray diffraction (XRD) rocking curves of asymmetric (10 $\bar 1$ 0) and symmetric (0002) AlN decreased to 19.8 and 9.6 min, respectively. The concentration of oxygen impurities in the layer grown at 1320 °C was also reduced from 3 × 1019 to 4 × 1018 cm−3 by protecting sapphire substrate at 1065 °C. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermal analysis of GaN powder formation via reaction of gallium ethylenediamine tetraacetic acid complexes with ammonia
Authors: Liu Yu‐Huai , Koide Shinya , Miyake Hideto , Hiramatsu Kazumasa , Nakamura Atsushi , Nambu Nobuyoshi
Published: March 2008

The reaction mechanism of gallium ethylenediamine tetraacetic acid (Ga[(OOCCH2)2–N–CH2–CH2–N–(CH2COO)2]NH4) (Ga‐EDTA)with ammonia was investigated. The Ga‐EDTA·NH4 complex powders were analyzed by thermogravimetric and differential thermal analysis (TG/DTA) under flow of ammonia gas and nitrogen gas. From the TG/DTA results, it is shown that the precursors undergo a sharp mass loss at about 296 °C (step I) due to the release of organic groups, followed by further releasing of organic groups (297∼ 552 °C, step II), elimination of carbon and formation of GaN (552 ∼ 650 °C, step III), GaN crystallization and further elimination of carbon (650 ∼ 850 °C, step IV), the improvement of GaN crystal quality (600 ∼ 1100 °C, step‐IV) and the initial decomposition of GaN powders. The X‐ray diffraction analysis of the powders indicates that proper sintering temperature for GaN powders should be approximate to 1100 °C. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
GaInN light emitting diodes with AlInN/GaN distributed Bragg reflector on Si
Authors: Ishikawa H. , Jimbo T. , Egawa T.
Published: March 2008

We report the effect of inserting a lattice‐matched AlInN/GaN distributed Bragg reflector (DBR) on the performance of GaInN light emitting diodes (LEDs) on Si substrates. The lattice‐matched AlInN/GaN DBR is superior to the previously used AlGaN/AlN DBR with respect to the suppression of cracking and the interface smooth ness. The light output power (PEL) of the LED increases with increasing number of pairs in the DBR and agrees well with the calculated one. The PEL of the 14.5‐pair AlInN/GaN DBR LED is about 3.6‐fold higher than that of the non‐DBR LED. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High quantum efficiency of semipolar GaInN/GaN quantum wells
Authors: Feneberg Martin , Lipski Frank , Schirra Martin , Sauer Rolf , Thonke Klaus , Wunderer Thomas , Brückner Peter , Scholz Ferdinand
Published: March 2008

The development of efficient GaInN/GaN based light emitting devices is hampered by built‐in electric fields. These fields, arising from piezoelectric and spontaneous polarization, separate electron and hole wavefunctions and reduce their spatial overlap. Therefore, the internal quantum efficiency is drastically reduced in the presence of built‐in fields.

To decrease the detrimental influence of the polarization fields on quantum efficiency, growth on non‐ or semipolar crystal facets is conducted. We investigate samples containing quantum wells grown on the {1$\bar 1$01} facet (tilt angle from (0001) is θ = 62°) of selectively grown GaN stripes and compare them to samples grown on the commonly used c plane. We experimentally determine direction and strength of built‐in polarization fields. These fields are used to compute overlap integrals and to estimate the internal quantum efficiency of semipolar quantum wells in comparison to polar and nonpolar ones. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Normally‐off AlGaN/GaN MOSHFETs with HfO2 gate oxide
Authors: Sugiura S. , Kishimoto S. , Mizutani T. , Kuroda M. , Ueda T. , Tanaka T.
Published: March 2008

Normally‐off AlGaN/GaN MOSHFETs with a thick HfO2 as a gate oxide have been fabricated. The HfO2 with a thickness of 100 nm was deposited by pulsed‐laser deposition. The threshold voltage was 3 V and the maximum drain current was 730 mA/mm at a gate voltage of 10 V. The maximum transconductance was 185 mS/mm, which was about 8 times larger than that of the GaN MOSFETs. The field effect mobility was 900–1500 cm2/Vs, which is also higher than that of the GaN MOSFETs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Silanization of inner surfaces of nanoelectrospray ionization emitters for reduced analyte adsorption
Authors: Choi Yong Seok , Wood Troy D.
Published: March 2008

During the course of nanoelectrospray ionization (nanoESI) of substance P, an unusual type of signal reduction was observed with flow rates <10 nL/min. This reduction in signal appears to be induced by the adsorption of positively charged analytes onto negatively charged free silanol groups on the inner surface of emitters; analytes with higher pI values (such as substance P) exhibit greater tendency for adsorption. Support for this hypothesis is demonstrated by the decrease in signal reduction in the presence of concentrated salts or for emitters whose internal silanols have been covalently silanized. Emitters treated with hexamethyldisilazane or 3‐aminopropyltriethoxysilane showed higher analyte signals for substance P than untreated emitters, suggesting a reduction of analyte adsorption onto the inner walls of silanized emitters. The efficacy of reduced peptide adsorption was demonstrated for emitters silanized with 3‐aminopropyltriethoxysilane using a simple peptide mixture as well as a more complex peptide mixture (a tryptic digest of horse hemoglobin). Copyright © 2008 John Wiley & Sons, Ltd.
Sorting of seeds by hydrochory
Authors: Chambert S. , James C. S.
Published: March 2008

The species composition of riparian vegetation is determined by a variety of processes, including the dispersal of seeds. The seed types that end up at certain locations are determined by their particular characteristics as well as the prevailing hydrology and the physical characteristics of the river channel. A conceptual model is proposed to identify the hydraulic processes involved in the hydrochory pathway that may lead to differential response of different seed types and hence their sorting. The results of a series of laboratory experiments are presented to demonstrate the sorting between seed types by these processes. The behaviour of non‐buoyant seeds during settling and entrainment is shown to be consistent with that of mineral sediments, and their sorting can therefore be described by existing sediment transport theory. Significant sorting of buoyant seed types takes place during transport under the influence of wind and during ingress into marginal emergent vegetation, trapping by vegetation and stranding during receding flows on sloping channel banks. Copyright © 2008 John Wiley & Sons, Ltd.
Behaviour of Ti6Al4V implant alloy in vitro after plastic deformation by bending
Authors: Kierzkowska Agnieszka , Krasicka‐Cydzik Elzbieta
Published: March 2008

Electrochemical and biological tests were used to evaluate in vitro the behaviour of anodised Ti6Al4V ELI samples after plastic deformation by bending. The implant rods of 6 mm diameter, anodised in H3PO4 acid solution, were used. Bending of implant rods was performed according to typical intra‐surgical procedure applied during pre‐shaping stage of implantation. The electrochemical properties were evaluated on the corrosion potential Ecorr and the results of the electrochemical impedance spectroscopy tests (EIS) of deformed samples immersed in simulated body fluid (SBF). Biological behaviour was estimated in contact with human osteoblasts. Electrochemical and biological changes demonstrated that mechanically disturbed anodic layer strived to achieve ‘the state of balance’ during immersion in electrolyte. After ∼6 days in SBF the former bi‐layer structure of the anodic surface layer was recovered. Moreover, all samples irrespective of bending angle achieved similar values of Ecorr corresponding to the corrosion potential of the sample deformed at the 20° angle. Biological tests in vitro confirmed that deformation of anodic surface layer on implant titanium alloy also stimulated its bioactivity. The observed higher number of osteoblasts and enzyme level are conducive for the formation of hydroxyapatite crystals (ALP), which stimulate in‐growth of bone tissue and accelerate healing process. Copyright © 2008 John Wiley & Sons, Ltd.
Combined XPS, SIMS, and AFM analyses of silicon nanocrystals embedded in silicon oxide layers
Authors: Vanzetti L. , Barozzi M. , Iacob E. , Bersani M. , Pucker G. , Bellutti P.
Published: March 2008

Silicon nanocrystals (Si‐ncs) embedded in a dielectric matrix (e.g. Si3N4, SiO2) attract significant interest for their use in silicon‐based devices such as memories, light amplifiers, and light emitting diodes. Si‐ncs in an SiO2 matrix are generally obtained through thermal annealing of silicon‐rich oxide (SRO) at elevated temperatures (900–1200 °C). In this study, we have investigated the composition of annealed SRO layers close to the interfaces with Si3N4, or c‐Si with XPS, SIMS, and atomic force microscopy (AFM). The analyses indicate an approximately 2‐nm thick Si‐depleted region close to both the Si3N4 and c‐Si interface formed after annealing at 1050 °C. The formation of this Si‐depleted layer is of importance for both electrical transport and charge storage in annealed SRO. Copyright © 2008 John Wiley & Sons, Ltd.
Zero inflation in ordinal data: Incorporating susceptibility to response through the use of a mixture model
Authors: Kelley Mary E. , Anderson Stewart J.
Published: March 2008

The aim of this paper is to produce a methodology that will allow users of ordinal scale data to more accurately model the distribution of ordinal outcomes in which some subjects are susceptible to exhibiting the response and some are not (i.e. the dependent variable exhibits zero inflation). This situation occurs with ordinal scales in which there is an anchor that represents the absence of the symptom or activity, such as ‘none’, ‘never’ or ‘normal,’ and is particularly common when measuring abnormal behavior, symptoms, and side effects. Due to the unusually large number of zeros, traditional statistical tests of association can be non‐informative. We propose a mixture model for ordinal data with a built‐in probability of non‐response, which allows modeling of the range (e.g. severity) of the scale, while simultaneously modeling the presence/absence of the symptom. Simulations show that the model is well behaved and a likelihood ratio test can be used to choose between the zero‐inflated and the traditional proportional odds model. The model, however, does have minor restrictions on the nature of the covariates that must be satisfied in order for the model to be identifiable. The method is particularly relevant for public health research such as large epidemiological surveys where more careful documentation of the reasons for response may be difficult. Copyright © 2008 John Wiley & Sons, Ltd.
Organizational antecedents of second‐order competences
Authors: Danneels Erwin
Published: March 2008

According to dynamic capability theory, some firms are better able than others at altering their resource base by adding, reconfiguring, and deleting resources or competences. This study focuses on the first form of dynamic capability: the competence to build new competences. Two such second‐order competences are studied: the ability to explore new markets and the ability to explore new technologies—referred to as marketing and R&D second‐order competences, respectively. Using two wave panel data on a sample of U.S. public manufacturing firms, five organizational antecedents of these second‐order competences are examined: willingness to cannibalize, constructive conflict, tolerance for failure, environmental scanning, and resource slack. Willingness to cannibalize, constructive conflict, scanning, and slack have contemporaneous effects, while scanning also has a lagged effect and slack has a U‐shaped lagged effect on marketing and R&D second‐order competences. Copyright © 2008 John Wiley & Sons, Ltd.
Strategies for preparing integrated faculty: The center for the integration of research, teaching, and learning
Authors: Austin Ann E. , Connolly Mark R. , Colbeck Carol L.
Published: March 2008

This chapter describes a comprehensive program to prepare science, technology, engineering, and mathematics (STEM) doctoral students for faculty careers that integrate research and education.
Career preparation for doctoral students: The University of Kansas history department
Authors: Levin Eve
Published: March 2008

A historian chronicles her department's efforts to reorient its graduate program to prepare students pragmatically for their careers.
Microanalysis of Gothic mural paintings (15th century) in Slovenia: Investigation of the technique used by the Masters
Authors: Kriznar A. , Ruiz‐Conde A. , Sánchez‐Soto P. J.
Published: March 2008

The present article focuses on an interdisciplinary research on cultural heritage concerning the microanalysis of Gothic mural paintings made during the 15th century in Slovenia. The samples were chosen from the churches of Crngrob (1453), Mirna (1463–1465), Mevkuž (1465) and Mače (1467), attributed to two of the most important Gothic painters of that period of time: Master Bolfgang and Master of Mače. The chemical and phase composition of all the mortars, number of their layers and selection of the pigments were of interest. For this purpose, fragments of mural paintings were studied with several instrumental techniques: optical microscopy (OM), SEM‐EDX, x‐ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). In early artworks, the mortar was made using a mixture of lime and more or less clean sand. Later, crushed lime‐rock or marble instead of sand was added to lime. The pigments identified by EDX microanalysis of cross sections previously studied by OM, are of earth or mineral origin. Therefore, they are durable in fresco and lime techniques: lime white, yellow and red natural or burned ochres, green earth and azurite. The results confirmed the high technical quality of both painters and the relationships between the teacher and the disciple. Master Bolfgang and Master of Mače combine three basic techniques of mural painting: fresco, secco and lime techniques. This kind of investigation and methodology allow us to know better the Central European Art and the Slovenian Art in the Adriatic zone, as well as the general map of European Art in the 14–15th centuries. Copyright © 2008 John Wiley & Sons, Ltd.
Syntheses, Structures and Spectroscopic Characterization of Extended Waugh‐Type Polyoxometalates with Metal Ions as Linkers
Authors: Cheng Haiyan , Ren Yuanhang , Liu Shuxia , Xie Linhua
Published: March 2008

Two extended Waugh‐type polyoxometalates compounds, (NH4)4Na2[MnMo9O32]·6H2O (1) and (NH4)2Na2[{Cu(H2O)4}(MnMo9O32)]·5H2O (2) have been synthesized and characterized. Both of the left‐handed and right‐handed [MnMo9O32]6− polyanions enantiomers can be observed in compounds 1 and 2. In compound 1, the homochiral [MnMo9O32]6− polyanions enantiomers are linked by sodium ions to form two kinds of alternately arranged 2D polymeric sheets, which are further stacked into a 3D framework. In compound 2, the homochiral [MnMo9O32]6− polyanions enantiomers are linked by [(H2O)2Cu(μ2‐H2O)2Na(H2O)2]3+ bimetal aggregates to form two kinds of alternately arranged zigzag chains, which are further weaved into a 2D polymeric sheet by sodium ions. In addition, the influence of the synthesis conditions has also been studied.
Coordination Mode of the Nickel(II) Cation with N‐Diisopropoxyphosphinyl‐p‐bromothiobenzamide
Authors: Safin Damir A. , Sokolov Felix D. , Baranov Sergey V. , Szyrwiel Łukasz , Babashkina Maria G. , Shakirova Elmira R. , Hahn F. Ekkehardt , Kozlowski Henryk
Published: March 2008

Reaction of the potassium salt of N‐diisopropoxyphosphinyl‐p‐bromothiobenzamide p‐BrC6H4C(S)NHP(O)(OiPr)2 (HL) with Ni(NO3)2 in aqueous EtOH leads to complex of formula [Ni(HL‐O)2(L‐O,S)2] (1). The structure of 1 was investigated by single crystal X‐ray diffraction analysis, IR, 1H and 31P{1H} NMR spectroscopy, MALDI and microanalysis. The nickel(II) ion in 1 has a tetragonal‐bipyramidal environment, (Oax)2(Oeq)2(Seq)2, with two neutral ligand molecules coordinated in axial positions through the oxygen atoms of the P=O groups. The equatorial plane of bipyramide is formed by two anionic ligands involving 1,5‐O,S‐coordination mode. The chelating ligands are bound in trans configuration.
Synthesis and Spectroscopic Characterization of the Benzaldehyde Schiff Base of S‐Allyldithiocarbazate and its Copper(II) Complex and the X‐ray Crystal Structure of Bis[S‐allyl‐β‐N‐benzylidene)dithiocarbazato]Copper(II)
Authors: Yazdanbakhsh M. , Heravi M. M. , Takjoo R. , Frank W.
Published: March 2008

S‐allyl‐β‐N‐(benzylidene)dithiocarbazate (sabdtc, 1), prepared from hydrazine hydrate, carbon disulfide, allyl bromide and benzaldehyde, reacts with copper(II) nitrate in ethanol solution to form the complex Cu(sabdtc)2 (2). 1 function as a single negatively charged bidentate chelating ligand and coordinates via the azomethine nitrogen atom and thioenolate sulfur atom to the metal ion. 1 and 2 were characterized by elemental analyses, 1H NMR, 13C NMR, UV/Vis, IR, and mass spectra. Spectroscopic evidences suggest a four‐coordinate distorted square planar structure for 2. The molecular and crystal structure of 2 was determined by single crystal X‐ray analysis. Crystallographic data for 2 at 291(2) K: space group C2/c, a = 20.340(3), b = 15.503(3), c = 7.659(1) Å, β = 95.96(2)°, Z = 4, R1 = 0.044 and wR2 = 0.0689.
Synthesis and Structure of the Novel Pentaselenidohexaarsenate(I,II) Cluster Anion [As6Se5]2−
Authors: Kromm Anna , Sheldrick William S.
Published: March 2008

Methanolothermal reaction of [MnCl3(9‐ane‐N3)] with As2Se3 at 150 °C in the presence of Cs2CO3 affords violet‐coloured [Mn(9‐ane‐N3)2]As6Se5 (1). Its novel tricyclic selenidoarsenate(I,II) anion [As6Se5]2− contains two five‐membered [As3As(Se)Se] rings that are symmetry‐related by a crystallographic C2 axis passing through the common AsI‐AsI bond between their respective first two ring members. The adjacent AsI atoms in the individual rings are bridged by the Se atom of the third [As4Se] ring.
Catalytic Induced Thermal Conversion of Amorphous Carbon into Single Walled Carbon Nanotubes
Authors: Joshi Ravi , Schierholz Roland , Schneider Jörg J. , Haridoss Prathap
Published: March 2008

Single walled carbon nanotubes (SWNTs) have caught extensive attention in the field of material science and electronics. Their formation typically uses plasma arc or CVD techniques [1–3]. So far, formation of SWCNTs just by thermal conversion of amorphous, non graphitic carbon which is a nearly ubiquitous carbon source is challenging but has not been reported so far. We herein demonstrate the catalytic growth of SWNTs from an amorphous carbon source (activated charcoal powder, ‘Aktivkohle’) mediated by three different catalytically active metals; metallic nickel, nickel derived from bis(η5‐cyclopentadienyl)nickel (nickelocene) and yttrium formed in situ from yttrium oxide.
Cerium Complex with Four Types of Ligands: (NH4)6[Ce(H2W12O40)(C4H2O4)(NO3)(H2O)3]
Authors: Shi Dongmei , Chen Yaguang , Pang Haijun
Published: March 2008

A novel polymer (NH4)6[Ce(H2W12O40)(C4H2O4)(NO3)(H2O)3] (1) has been constructed at room temperature and characterized by single crystal X‐ray structural analyses, elemental analyses, cyclic voltammetry, IR spectrum, and thermogravimetry. X‐ray structural analysis reveals that through the W–Ot′–Ce–Ob–W linkages a one‐dimension infinitely linear chain with alternating cations and anions is formed. 1 represents the first characterized compound that the Ce3+ ions are coordinated by four different types of ligands, and maleinate as ligands in constructing LnPOM architecture.
1,5‐Diamino‐4‐methyltetrazolium 5‐Nitrotetrazolate – Synthesis, Testing and Scale‐up
Authors: Klapötke Thomas M. , Miró Sabaté Carles , Welch Jan M.
Published: March 2008

1,5‐Diamino‐4‐methyltetrazolium 5‐nitrotetrazolate (2b) was synthesized in high yield from 1,5‐diamino‐4‐methyltetrazolium iodide (2a) and highly sensitive silver 5‐nitrotetrazolate (AgNT). A safer synthesis, suitable for scale‐up, is introduced involving reaction of the previously unreported 1‐amino‐5‐imino‐4‐methyltetrazole free base (2) with ammonium 5‐nitrotetrazolate. Both new compounds (2 and 2b) were fully characterized using vibrational (IR and Raman) and multinuclear NMR spectroscopy (1H, 13C, 14N, 15N), elemental analysis and single crystal X‐ray diffraction. The hydrogen‐bonding networks of both materials are described in terms of their graph‐sets. Compound 2b is hydrolytically stable with a high melting point and concomitant decomposition at 160 °C. The sensitivity of the energetic salt 2b towards impact (>30 J) and friction (>360 N) was tested. The constant volume energy of combustion (ΔcU) of 2b was measured experimentally using bomb calorimetry. In addition, the detonation parameters (detonation pressure and velocity) of the nitrotetrazolate salt were calculated from the energy of formation, the crystal density and the molecular formula using the EXPLO5 computer code (P = 15.5·GPa, D = 6749 m s−1) and are similar to that of TNT and nitroguanidine making 2b of prospective interest in propellant charge formulations or, in combination with a suitable oxidizer, as a solid propellant.
A Highly Hexane Soluble Lithium Salt and other Starting Materials of the Fluorinated Weakly Coordinating Anion [Al{OC(CF3)2(CH2SiMe3)}4]−
Authors: Müller Lutz O. , Krossing Ingo
Published: March 2008

The lithium salt of the weakly coordinating alkoxyaluminate anion Li[Al(OC(CF3)2(CH2SiMe3))4] (2) is soluble in polar and even in non‐polar solvents. Especially the solubility in n‐hexane confirms 2 to be an excellent candidate for Li ion catalysis. Its polymeric structure consists of a seven coordinated Li+ cation, coordinating a [Al(OC(CF3)2(CH2SiMe3)]− anion that serves as hexadentate O2F4 ligand and a further bridging F atom of a second anion. Compound 2 reacts with ClCPh3 giving the [CPh3]+ salt which is at least stable in CD2Cl2 over days at 298 K, but decomposes after storage at 333 K for several days.
Obesity, insulin resistance and diabetes — a worldwide epidemic
Authors: Seidell Jacob C.
Published: March 2008

Obesity is now commonly defined in adults as a BMI > 30 kg/m2. The prevalence of obesity in established market economies (Europe, USA, Canada, Australia, etc.) varies greatly, but a weighed estimate suggests an average prevalence in the order of 15–20 %. The prevalence in these countries generally shows increasing trends over time. Obesity is also relatively common in Latin America, but much less so in sub-Saharan Africa and Asia where the majority of the world population lives. Nevertheless obesity rates are increasing there as well and, more importantly, rates of diabetes are increasing even more quickly, particularly in Asian countries. The risks of type 2 diabetes mellitus in these countries tend to increase sharply at levels of BMI generally classified as acceptable in European and North American white people. There have been suggestions to adopt specific classifications of obesity in Asians (e.g. BMI 23 for overweight and 25 or 27 kg/m2 for obesity) and this will greatly affect the prevalence estimates of obesity worldwide (currently at about 250 million people). Particularly for health promotion purposes BMI may be replaced by a classification based on waist circumference, but also specific classifications for different ethnic groups may be necessary. The number of diabetics has been projected to increase from 135 million in 1995 to 300 million in 2025. Much of this increase will be seen in Asia. In summary, both obesity and type 2 diabetes are common consequences of changing lifestyles (increased sedentary lifestyles and increased energy density of diets). Both are potentially preventable through lifestyle modification on a population level, but this requires a coherent and multifaceted strategy. Such strategies are not developed or implemented. These developments point toward the great urgency to develop global and national plans for adequate prevention and management of obesity and type 2 diabetes mellitus.