bluuebunny/crossref_metadata_2025 huggingface dataset:
Über die Verwendung und Bedeutung von Kerbformzahlen bei der Auslegung von Faser‐Kunststoff‐Verbunden
Authors: Kremer T. , Schürmann H.
Published: June 2008

Bei der Auslegung von Bauteilen ist die Verwendung von Formzahlen, zur Beurteilung von Spannungsüberhöhungen an Ausschnitten und Kerben, ein gebräuchliches Verfahren. Auch bei geschichteten Verbundwerkstoffen kommen Formfaktoren zum Einsatz, die – neben der Form – auch von den Elastizitätseigenschaften des Verbundwerkstoffs abhängen. Die Verwendung solcher Formzahlen führt jedoch in vielen Fällen zu einer Fehlinterpretation der Spannungen am Ausschnitt. Anhand von Beispielen werden die Unzulänglichkeiten dieser Formzahlen belegt und das Entstehen einer missverständlichen Interpretation verdeutlicht.

Zur Behebung dieser Mängel wird eine neue lokale, schichtenweise Formzahl eingeführt. Die Definition der neuen lokalen, schichtenweisen Formzahl behebt die vorhandenen Mängel konventioneller Formzahlen. Anhand eines Beispiels wird die Bestimmung der neuen Formzahl erläutert. Gleichzeitig werden Kriterien entwickelt, mit deren Hilfe beurteilt werden kann, in welchen Fällen globale Formzahlen zur aussagekräftigen Beschreibung eines Ausschnitts in einem geschichteten Verbundwerkstoff verwendet werden können.
A general model for stress‐life fatigue prediction
Authors: Al‐Rubaie K. S.
Published: June 2008

From several factors that influence the fatigue behaviour of a particular material, the stress ratio or mean stress and the stress concentration factor are of great importance for the structural calculation. Since most components and structural members contain notches that could be sites of fatigue crack initiation, fatigue data from specimens with different forms of notches have to be collected. The collection of such data at various stress ratios or mean stresses is not economic and time‐consuming. Based on the Walker equivalent stress model, a general fatigue life model is presented and tested with 2024‐T3 fatigue data, available in the literature. The Walker model considered only the effect of stress ratio or mean stress on the fatigue behaviour. On the other hand, in the proposed model, the combined effect of mean stress and stress concentration factor on fatigue behaviour is demonstrated. The statistical analysis indicates that the presented model is very efficient to interpolate the fatigue life successfully, thereby reducing both time and cost.
Lamellar precipitation in Cu‐4,5 at. % In alloy
Authors: Bensaada S.
Published: June 2008

The purpose of this study is to study the lamellar precipitate morphology in the Cu‐4, 5 at. % In alloy by optical, scanning electron and transmission microscopy. It was observed that the lamellar precipitates develop starting from a grain boundary by a discontinuous reaction during an ageing at 673 K, and different lamellar orientations in the same cell were observed. The discontinuous reaction can also develop in the interphase boundaries. In the same way, the reaction front form of the precipitate during ageing was analyzed in this work.
Mechanism of 2‐methoxyestradiol‐induced apoptosis and growth arrest in human breast cancer cells
Authors: Fukui Masayuki , Zhu Bao Ting
Published: June 2008

2‐Methoxyestradiol, a well‐known nonpolar endogenous metabolite of 17β‐estradiol, has been shown to selectively induce apoptosis in a number of cancer cell lines, but not in normal cells. The mechanism of 2‐methoxyestradiol‐induced apoptosis appears to vary considerably in different cell lines examined. In the present study, we systematically analyzed the mechanisms of 2‐methoxyestradiol‐induced apoptosis in the estrogen receptor‐negative MDA‐MB‐435s human breast cancer cells. We found that 2‐methoxyestradiol induced the activation of JNK, ERK, and p38 MAPKs. 2‐methoxyestradiol‐induced JNK activation was associated with the induction of apoptosis through the mitochondrial pathways as a result of increased phosphorylation (inactivation) of the anti‐apoptotic Bcl‐2 and Bcl‐xL proteins. In comparison, 2‐methoxyestradiol‐induced activation of ERK and p38 in these cells was found to have a protective effect against 2‐MeO‐E2‐induced apoptosis. Consistent with this observation, the presence of pharmacological inhibitor of ERK or p38 enhanced 2‐methoxyestradiol‐induced apoptosis. Mechanistically, inhibition of ERK and p38 activity was associated with activation of various caspases and PARP cleavage, and it also stabilized the pro‐apoptotic proteins Bax and Bim, thereby preventing them from degradation during 2‐methoxyestradiol treatment. These results suggest that ERK and p38 MAPKs may serve as viable targets for the sensitization of human breast cancer cells to 2‐methoxyestradiol‐induced apoptosis. © 2008 Wiley‐Liss, Inc.
An assessment of the domain reduction method as an advanced boundary condition and some pitfalls in the use of conventional absorbing boundaries
Authors: Kontoe Stavroula , Zdravkovic Lidija , Potts David M.
Published: June 2008

This paper assesses the performance of two commonly used absorbing boundaries in dynamic finite element analysis of geotechnical problems in conjunction with the domain reduction method (DRM). The DRM was originally developed by Bielak et al. (Bull. Seismol. Soc. Am. 2003; 93(2):817–824) to reduce the computational cost of seismological applications, whereas Yoshimura et al. (Bull. Seismol. Soc. Am. 2003; 93(2):825–840) showed that it can be effectively used as a boundary condition. In this study a practical methodology is proposed, which employs the cone boundary of Kellezi (Soil Dyn. Earthq. Eng. 2000; 19:533–547) on the outer boundary of the reduced (step II) model of the DRM. To verify the applicability of the proposed methodology, the results using both the cone boundary and the standard viscous boundary are compared with those using an extended mesh. Finally, results using the DRM as a boundary condition are compared with those using conventional boundary conditions. Some common pitfalls in the use of absorbing boundaries are highlighted and guidance for their correct use in engineering practice is given. Copyright © 2008 John Wiley & Sons, Ltd.
Advancing nonprofit organizational effectiveness research and theory: Nine theses
Authors: Herman Robert D. , Renz David O.
Published: June 2008

Drawing on the general literature on organizational effectiveness, the specialized literature on nonprofit organizational effectiveness, and recent research in the field, this article advances nine theses, or conclusions, about the effectiveness of public benefit charitable, nonprofit organizations (NPOs). NPO effectiveness is (1) always comparative, (2) multidimensional, (3) related to board effectiveness (but how is not clear), (4) related to the use of correct management practices but not in any simple “best practices” way, and (5) a social construction. Furthermore, (6) it is unlikely that there are any universally applicable best practices that can be prescribed for all NPO boards and management, (7) organizational responsiveness is a useful organizational‐level effectiveness measure, (8) distinguishing among types of NPOs is important and useful, and (9) level of analysis makes a difference in researching and understanding effectiveness. The article concludes by considering implications for organizational practice, boards and governance practices, program evaluation, including program outcomes assessment, and capacity building and capacity builders.
Evaluating philanthropic foundations according to their social values
Authors: Whitman John R.
Published: June 2008

Philanthropic foundations are seen as enterprises committed to building what they view as a better world. Their visions of a better world are described in terms of social values that represent preferred end states for society or means of achieving such states. This article describes a procedure in which a foundation's espoused social values, made explicit, may serve as a referent to evaluate the foundation's performance. The process by which social values are determined is offered as a means to promote critical and reflective discourse not only within the foundation but with the public, especially those affected by the foundation's work.
Determinants of compensation: A study of pay, performance, and gender differences for fundraising professionals
Authors: Mesch Debra J. , Rooney Patrick M.
Published: June 2008

This study examines the determinants of compensation for fundraising professionals by addressing the following research questions: (1) Is there a significant pay‐performance relationship? (2) What are the factors that affect bonus and salary? (3) Is there a gender‐pay gap for individuals who are in the role of fundraisers? Data were collected over a four‐year period from a national sample of fundraising professionals employed across all industry classifications. Amount of money raised was the primary performance variable of interest. Bivariate tests for differences between males and females, as well as two‐stage simultaneous regressions, were used to determine the effects of fundraising performance on the pay of fundraisers. Results indicated a significant and positive pay‐performance linkage across all fundraising positions, particularly for chief development officers, as well as a consistent gender‐pay gap across fundraising positions.
Employee creativity in U.S. and Lithuanian nonprofit organizations
Authors: Jaskyte Kristina
Published: June 2008

This article reports findings from a study designed to test a model of creativity in the United States and Lithuania. Five independent variables were derived from the creativity literature: perceived leadership behaviors, organizational norms for creativity, group climate, job characteristics, and motivational orientation. They were used to predict creativity in a sample of 201 employees of nonprofit organizations. The results differed for the two countries. Interestingly, while in the United States organizational norms for creativity, extrinsic motivation, and hierarchical level were related to employee creativity, in Lithuania intrinsic motivation and education constituted major predictors of creativity. Based on the study results, I suggest practical implications for nonprofit managers on how to capitalize on their employees' creativity.
Comparison of solubility of gases and vapours in wet and dry alcohols, especially octan‐1‐ol
Authors: Abraham Michael H. , Acree William E.
Published: June 2008

Equations for the solubility of gases and vapours into dry alcohols from methanol to decan‐1‐ol and into water‐saturated alcohols from butan‐1‐ol to decan‐1‐ol have been compared through the use of the Abraham solvation equation. It is shown that there are noticeable differences in solvation into the dry and wet alcohols, and that these differences become larger as the alcohols become smaller and take up more water. The two main factors that lead to the differences in solvation are the solute hydrogen‐bond basicity, B, and solute size, L. Increase in solute hydrogen‐bond basicity favours the wet alcohols and increase in solute size favours the dry alcohols. Solute hydrogen‐bond acidity plays no part, because the hydrogen‐bond basicity of water, wet alcohols and dry alcohols is almost the same. Copyright © 2008 John Wiley & Sons, Ltd.
A statistical‐mechanical analysis of group additivity. Calculation of thermochemical values from frequency distributions
Authors: Bojesen Gustav
Published: June 2008

Molecular vibrational frequencies of homologous series plotted as cumulative frequency distributions are very similar, and the fine structure of the distributions exhibit identical features. An obvious explanation is that the changes in the molecular frequency distributions (MFDs) from one homologue to the next is independent of the chain length and of the functional groups in the molecule. Since group additivity is valid for the chosen homologous series there is here an explanation for the linearity of thermochemical values expressed by group additivity. For these properties the following hypothesis is proposed: group additivity is observed when the MFD is a sum of group frequency distributions (GFDs). This leads to additivity for the zero‐point vibrational energy which is confirmed by analysis of the frequencies of 126 organic molecules from 11 homologous series. The frequency distribution for a methylene group is estimated from that of octadecane. From this GFD combined with 11 different MFD it is possible to calculate model frequencies for the homologous series which are in good agreement with frequencies fromab initiocalculations. For three thermochemical parameters (the logarithm of the vibrational partition function, the vibrational excitation energy and the vibrational heat capacity), the combination of the estimated methylene GFD with 11 different MFDs lead to group additivity values for a methylene group which are identical over a wide temperature range. The derivation of Benson additivity for thermochemical functions from frequency distributions is at step towards a better understanding of Benson additivity. Copyright © 2008 John Wiley & Sons, Ltd.
Ru(III), Os(VIII), Pd(II) and Pt(IV) catalysed oxidation of glycyl–glycine by sodium N‐chloro‐p‐toluenesulfonamide: comparative mechanistic aspects and kinetic modelling
Authors: Jagadeesh R. V. , Puttaswamya
Published: June 2008

The Ru(III)/Os(VIII)/Pd(II)/Pt(IV)‐catalysed kinetics of oxidation of glycyl–glycine (Gly‐Gly) by sodium N‐chloro‐p‐ toluenesulfonamide (chloramine‐T; CAT) in NaOH medium has been investigated at 308 K. The stoichiometry and oxidation products in each case were found to be the same but their kinetic patterns observed are different. Under comparable experimental conditions, the oxidation‐kinetics and mechanistic behaviour of Gly‐Gly with CAT in NaOH medium is different for each catalyst and obeys the underlying rate laws:

Rate = k [CAT]t [Gly‐Gly]0 [Ru(III)][OH−]x

Rate = k [CAT]t[Gly‐Gly]x [Os(VIII)]y[OH−]z

Rate = k [CAT]t[Gly‐Gly]x [Pd(II)][OH−]y

Rate = k [CAT]t[Gly‐Gly]0 [Pt(IV)]x[OH−]y

Here, ${\rm Ts} = {\rm CH}_3 {\rm C}_6 {\rm H}_4 {\rm SO}_{2^ -}$ and x, y, z < 1 in all the cases. The anion of CAT, CH3C6H4SO2NCl−, has been postulated as the common reactive oxidising species in all the cases. Under comparable experimental conditions, the relative ability of these catalysts towards oxidation of Gly‐Gly by CAT are in the order: Os(VIII) > Ru(III) > Pt(IV) > Pd(II). This trend may be attributed to the different d‐electronic configuration of the catalysts. Further, the rates of oxidation of all the four catalysed reactions have been compared with uncatalysed reactions, under identical experimental conditions. It was found that the catalysed reaction rates are 7‐ to 24‐fold faster. Based on the observed experimental results, detailed mechanistic interpretation and the related kinetic modelling have been worked out for each catalyst. Copyright © 2008 John Wiley & Sons, Ltd.
Does the five‐member hydrogen bond ring in quinoline carboxamides exist?
Authors: Majerz Irena , Dziembowska Teresa
Published: June 2008

The presence of intramolecular NHN hydrogen bond in 4‐R‐quinoline‐2‐(N‐R′‐carboxamides) was investigated by AIM methodology. Values of electron density, elipticity, and total energy density at the bond critical point of H···N in amides were compared with respective values of H···O in their N‐oxides. Copyright © 2008 John Wiley & Sons, Ltd.
Kinetics of base‐catalyzed cyclization of 2,6‐dinitrophenylsulfanyl ethanenitrile and 2,4,6‐trinitrophenylsulfanyl ethanenitrile
Authors: Černý Jiří , Hanusek Jiří , Macháček Vladimír
Published: June 2008

The kinetics of base catalyzed cyclization of 2,6‐dinitrophenylsulfanyl ethanenitrile and 2,4,6‐trinitrophenylsulfanyl ethanenitrile giving 2‐cyano‐7‐nitrobenzo[d]thiazole‐3‐oxide and 2‐cyano‐5,7‐dinitrobenzo[d]thiazole‐3‐oxide respectively was studied in methanolic methoxyacetate, acetate, trichlorophenoxide, N‐methylmorpholine, and N‐methylpiperidine buffers at 25 °C and I = 0.1 mol L−1. It was found that reaction involves both general acid and general base catalyses whose manifestation depends on the pKa of the acid‐buffer component and the ratio of both buffer components. In weakly basic buffers the rate‐limiting step is CH bond breaking in the cyclic intermediate, while in strongly basic buffers the rate‐limiting step is the general acid‐catalyzed elimination of hydroxyl group from the intermediate. Copyright © 2008 John Wiley & Sons, Ltd.
The oxidation of alcohols to aldehydes and ketones with N‐bromosuccinimide in polyethylene glycol: an experimental and theoretical study
Authors: Fan Ji‐Cai , Shang Zhi‐Cai , Liang Jun , Liu Xiu‐Hong , Liu Yang
Published: June 2008

Oxidation of aliphatic and aromatic alcohols has been studied by using N‐bromosuccinimide (NBS) as oxidant and polyethylene glycol (PEG) as reaction medium under mild reaction conditions. Temperature and solvent effect are studied. Theoretical study is also done with the Gaussian 98 suite of program and the calculation results are in good accordance with the experimental outcome. This system offers a very clean, convenient, environmentally benign method for the oxidation of alcohols. Copyright © 2008 John Wiley & Sons, Ltd.
Thermochemistry of Species Potentially Formed During NTO/MMH Hypergolic Ignition
Authors: Osmont Antoine , Catoire Laurent , Klapötke Thomas M. , Vaghjiani Ghanshyam L. , Swihart Mark T.
Published: June 2008

This paper deals with the gas‐phase thermodynamic properties of endothermic compounds potentially formed during monomethylhydrazine (MMH)/nitrogen tetroxide (NTO) hypergolic reactivity. The standard enthalpies of formation at 298.15 K are determined by means of quantum chemistry calculations along with protocols developed for these compounds. The resultant data, currently previously unavailable for almost all of these compounds, are potentially critical to the modeling of combustion chemistry of this bipropellant combination.
Experimental Study of the Oxidative Degradation of PBX 9501 and its Components
Authors: Salazar Michael R. , Kress Joel D. , Lightfoot J. Michael , Russel Bobby G. , Rodin Wayne A. , Woods Lorelei
Published: June 2008

The results of the constituent aging study (CAS) are given, where low‐temperature (T<64 °C) aging experiments were performed on over 1100 closed‐container samples of various combinations of the components of the plastic‐bonded explosive PBX 9501. Experiments were performed on the various combinations both in the absence and presence of free‐radical stabilizers. The product gases were identified and quantified as a function of aging time. The gas data show diverse chemistry between CAS samples and initial linear increases in product gas formation. Temperature analysis of the initial production rates of gas products shows straight Arrhenius plots. The extracted activation energies and frequency factors for the formation of the individual gas products yield a single linear kinetic compensation plot suggesting a common degradation pathway for PBX 9501 and combinations of constituents that contained nitroplasticizer (a eutectic mixture of bis‐2,2‐dintropropyl acetal and bis‐2,2‐dintropropyl formal).
Thermal Decomposition of Aminonitrobenzodifuroxan
Authors: Zhang Wei , Luo Yunjun , Li Jie , Li Xiaomeng
Published: June 2008

In this study, the thermal decomposition properties of aminonitrobenzodifuroxan are studied using a differential scanning calorimeter (DSC), a thermogravimeter (TG), an X‐ray diffractometer, a mass spectrometer (MS), and a Fourier transform infrared spectrometer (FTIR). The results demonstrate that aminonitrobenzodifuroxan undergoes thermal decomposition in the solid state. Under elevated temperatures, the decomposition primarily involves two steps: separation of nitro group and ring‐scission of the furoxan circles at 198.1 °C, and decomposition of the relatively stable residues (benzofuroxan circle) at 199.1 °C. Moreover, it is found that among the products, nitrogen dioxide undergoes oxidation and catalysis on the host molecule during the whole decomposition. Based on Kissinger and Ozawa functions, we deduce that the activation energies of these two reactions are 167.68 and 204.55 kJ mol−1, respectively. The released energy (ΔH) of CL‐18 is −1781.8 J g−1.
One‐step electroless synthesis and properties of copper film deposited on silicon substrate
Authors: Ye Jing , Chen Qianwang , Xiong Ying , Chai Yisheng , Chen Peiran
Published: June 2008

A one‐step electroless deposition method was developed to synthesize sponge‐like copper film with favourable mechanical adhesion on silicon substrate. X‐ray diffraction and X‐ray photoelectron spectroscopy analysis and field emission scanning electron microscopy observations indicate that the as‐prepared copper film is polycrystalline and composed of copper nanoparticles with a diameter ranging from 45 nm to 60 nm, the thickness of the film being approximately 2 μm. Hydrogen obtained through the reaction of sodium hydroxide and silicon in ethylene glycol solution was employed to reduce in situ the copper ions to form metal copper films on the silicon substrate. The electrical and mechanical properties of the as‐prepared copper film were measured. The results show that the as‐prepared copper film possesses high resistivity and low Young's modulus due to its special structure. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Synthesis and characterization of Cu3TaIn3Se7 and CuTa2InTe4
Authors: Grima‐Gallardo P. , Calderón E. , Muñoz‐Pinto M. , Durán‐Piña S. , Quintero M. , Quintero E. , Morocoima M. , Delgado G. E. , Romero H. , Briceño J. M. , Fernandez J.
Published: June 2008

Polycrystalline samples of Cu3TaIn3Se7 and CuTa2InTe4 were synthesized by the usual melt and anneal technique. X‐ray powder diffraction showed a single phase behavior for both samples with tetragonal symmetry and unit cell parameter values a = 5.794 ± 0.002 Å, c = 11.66 ± 0.01 Å, c /a = 2.01, V = 391 ± 1 Å3 and a = 6.193 ± 0.001 Å, c = 12.400 ± 0.002 Å, c /a = 2.00, V = 475 ± 1 Å3, respectively. Differential thermal analysis (DTA) measurements suggested a complicated behavior near the melting point with several thermal transitions observed in the heating and cooling runs. From the shape of the DTA peaks it was deduced that the melting is incongruent for both materials. Magnetic susceptibility measurements (zero‐field cooling and field cooling) indicated an antiferromagnetic character with transition temperatures of T = 70 K (Cu3TaIn3Se7) and 42 K (CuTa2InTe4). A spin–glass transition was observed in Cu3TaIn3Se7 with Tf ≈ 50 K. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Silicon carbide power‐device products – Status and upcoming challenges with a special attention to traditional, nonmilitary industrial applications
Authors: Friedrichs P.
Published: June 2008

The paper is intended to give an overview of the status of SiC power devices with a focus on industrial applications. Developments intended for military applications, high frequency systems or integrated circuits will not be addressed. After being implemented in power supplies, SiC‐based devices were able to enter motor‐drive applications as well. This was made possible by considerable progress in the power rating of the devices. Performance and cost issues will be discussed in order to explain why the SiC market is developing more slowly than several market analyses have predicted so far. However, it will also be shown that SiC has gained a solid position in power electronics. For a deeper penetration of SiC‐based components into applications, the key issue is to justify the higher cost of SiC devices by working out system advantages such as a higher efficiency and cost‐saving potentials as well. A special discussion will be related to the issue of a suitable device structure for transistors. Related to this question, topics like MOSFET and JFET will be mentioned. Pros and cons of switches as well as the field of high‐voltage SiC devices will be highlighted and a short guide to decide whether the use of SiC components could be useful or not in certain applications will be given. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The band structure of a layered Hg3TeCl4 crystal formed by energy states of HgCl2 and HgTe crystals
Authors: Sznajder M. , Bercha D. M. , Kharkhalis L. Yu.
Published: June 2008

The ab‐initio calculated band structure of a not as yet investigated orthorhombic Hg3TeCl4 crystal (Pbca, D152h) was analyzed by means of the elementary energy‐bands concept. It was demonstrated that this band structure originates from that of a layered HgCl2 dielectric deformed by the presence of the HgTe structural elements. Further, it was revealed that the valence band of Hg3TeCl4 is composed of the 8‐branch elementary energy bands corresponding to the actual Wyckoff position c (x, y, z) of D152h group that indicates the presence of ionic and covalent contributions to the chemical bonding in the crystal. The existence of Davydov splitting in the 8‐branch elementary energy band situated in the low‐energy range of the valence band was observed, which is typical for layered crystals with a weak interlayer interaction between translationally nonequivalent structural units. It was shown that the anisotropy of the electron and hole effective masses does not correspond to the macroscopic anisotropy of the crystal and an explanation of this behaviour was proposed. The obtained parameters of the crystal (direct energy gap Eg = 2.49 eV as well as values of the estimated electron effective masses) indicate that it could find an application in optoelectronics. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Alternative techniques to reduce interface traps in n‐type 4H‐SiC MOS capacitors
Authors: Pensl Gerhard , Beljakowa Svetlana , Frank Thomas , Gao Kunyuan , Speck Florian , Seyller Thomas , Ley Lothar , Ciobanu Florin , Afanas'ev Valery , Stesmans Andre , Kimoto Tsunenobu , Schöner Adolf
Published: June 2008

Several alternative oxidation techniques are developed and tested with the aim to reduce the high density of interface traps Dit in n‐type 4H‐SiC MOS capacitors. A lamp furnace in combination with a microwave plasma is employed to grow thin oxide layers, which are used for an insulating stack (SiO2 and Al2O3). The treatment of the oxide with nitrogen is another way to lower Dit. We introduce N atoms prior to the oxidation by ion implantation. During the oxidation process, the implanted N‐profile is redistributed; a considerable amount of the implanted N is accumulated at the SiC/SiO2‐interface, which leads to a strong reduction of Dit and a large negative flatband voltage. The negative flatband voltage can largely be compensated by coimplantation of aluminum. A model is proposed, which explains the passivation of interface traps in n‐type 4H‐SiC MOS capacitors. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of defects in silicon carbide by Raman spectroscopy
Authors: Hundhausen M. , Püsche R. , Röhrl J. , Ley L.
Published: June 2008

We demonstrate the application of Raman spectroscopy as an optical non‐contact method for the characterization of silicon carbide (SiC). The Raman spectra provide information about the polytype and thus can give direct information about microscopic inclusions of hexagonal polytypes in 3C‐SiC grown by chemical vapor deposition (CVD) after annealing at elevated temperatures. Polytype conversion sets in at a about 1700 °C and at higher temperatures eventually results in larger domains of 6H‐SiC where twin boundaries act as barriers against a complete polytype conversion. We study shallow donor states of phosphorus‐ and nitrogen‐doped SiC using low temperature electronic Raman spectroscopy. The various low frequency transitions observed in nitrogen doped SiC are assigned to the valley‐orbit transitions of electrons in the 1s‐ground states of donors that occupy inequivalent lattice sites. During vacuum annealing at elevated temperature graphitization of the SiC surface occurs. Raman spectroscopy is used to verify that under well controlled conditions a monoatomic graphene layer exists. We observe a phonon hardening of that layer compared to free standing graphene that we ascribe mainly to strain induced by different thermal expansion coefficients of graphite and SiC. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of interface trap parameters from double‐peak conductance spectra taken on N‐implanted 3C‐SiC MOS capacitors
Authors: Krieger M. , Beljakowa S. , Trapaidze L. , Frank T. , Weber H. B. , Pensl G. , Hatta N. , Abe M. , Nagasawa H. , Schöner A.
Published: June 2008

3C‐SiC/SiO2 capacitors are fabricated by over‐oxidation of an implanted Gaussian nitrogen (N) profile and investigated by conductance spectroscopy. An unexpected double peak structure is observed in the conductance spectra indicating two types of independent traps at different energy positions in the bandgap, which change their charge state with identical time constant. A theoretical model is developed assuming two independent distributions of interface traps in the bandgap of 3C‐SiC with different trap parameters. The experimental G /ω – V and C – V spectra are simulated and the trap parameters are determined on the basis of this model. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Lifetime‐killing defects in 4H‐SiC epilayers and lifetime control by low‐energy electron irradiation
Authors: Kimoto Tsunenobu , Danno Katsunori , Suda Jun
Published: June 2008

Carrier lifetimes in n‐type 4H‐SiC epilayers have been investigated by differential microwave photoconductance decay measurements. Through a correlation study between lifetime and various deep levels, the Z1/2and/or EH6/7centers have been identified as effective recombination centers. When the Z1/2(and EH6/7) concentration is higher than 1013cm–3, the inverse carrier lifetime is in proportion to the trap concentration, and the lifetime increases with increasing excitation intensity (density of irradiated photons). Alternartively, other recombination processes limit the lifetime when the Z1/2concentration is less than 1013cm–3. In this case, the carrier lifetime is decreased by increasing the excitation intensity. Surface recombination and recombination in the substrate have been suggested based on numerical analyses as the other recombination paths. By controlling the Z1/2(and EH6/7) concentration by low‐energy electron irradiation, lifetime control has been achieved. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin properties of Hg1–xCdx Te/CdTe quantum wells
Authors: Dargys A.
Published: June 2008

Free electron and hole spin properties in Hg1–x Cdx Te/CdTe quantum wells (QWs) are considered within eight‐band k · p Hamiltonian, when the QW bands are inverted, or close to the inversion. The generic spin properties of 2D subbands are described by spin surface, an analogue of the Bloch sphere. In the inverted energy band arrangement, due to mutual interaction between conduction and valence subbands, strong deviation from the Bloch sphere is observed. However, at the normal band arrangement the spin surfaces of electrons are found to be close to spherical. The spin surfaces of the QW holes are strongly deformed in all cases, mainly due to strong spin–orbit interaction in valence bands of respective bulk semiconductors and their subsequent rearrangement due to spin–splitting. The corresponding graphs of the spin surfaces are presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ballistic transport in semiconductor superlattices with non‐zero in‐plane wave vector
Authors: Klymenko M. V. , Safonov I. M. , Shulika O. V. , Sukhoivanov I. A.
Published: June 2008

In this paper, we consider the ballistic transport of electrons propagating in the semiconductor superlattice with some angle relative to normal line for interfaces. Such propagation of electrons is characterized by a wave vector which can be decomposed in two components (the in‐plane component and the normal component). If the total energy of the electron is known, the in‐plane component can be easy recalculated into the angle of incidence using the simple analytical expression derived in the paper. The dependence of the transmissivity of electrons on the in‐plane wave vector has been computed. As a result, the angular distribution of the transmissivity is represented. Obtained results reveal that the transmissivity of electrons is strongly dependent on their angle of incidence. This relationship is characterized by slow oscillations or by sharp peaks depending on the energy of electrons. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Morphology control of GaN nanowires by vapor‐liquid‐solid growth
Authors: Inoue Y. , Tajima A. , Ishida A. , Mimura H.
Published: June 2008

We synthesized GaN nanowires on sapphire substrate by metal organic chemical vapour deposition. The GaN nanowires were grown via vapor‐liquid‐solid (VLS) growth catalyzed with Ni thin film. Shape of nanowires depended on the substrate temperature and the growth pressure. The wire‐like structure with high aspect ratio changed into the tapered structure with increasing substrate temperature, and with increasing the growth pressure. This dependency was attributed to the change of the surface diffusion length of source atoms. The VLS growth of GaN nanowire was revealed that the source species, absorbed at the eutectic droplet, came along the side wall of the nanowire as well as other semiconductor nanowires. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fabrication of AlN films at low temperature by CS‐MBE technique
Authors: Honda Tohru , Watanabe Kenji , Sugimoto Koichi , Arai Masatoshi , Takeda Kazuhisa
Published: June 2008

The low‐temperature deposition of AlN films by compound‐source molecular‐beam epitaxy (CS‐MBE) technique was studied. AlN powder was used as the source and no additional nitrogen source was introduced during the deposition. X‐ray photoelectron spectroscopy (XPS) results show that Al‐N bonds were formed in the deposited films. It was clarified that the nitrogen atoms were supplied to the substrate from the AlN source and that the oxygen concentration in the deposited AlN films depended on the residual oxygen concentration in the AlN powder used as the source. The breakdown electric field of the AlN film was over 4.2 MV/cm, which indicates that the films deposited at a low temperature of less than 300 °C can be applied as the insulator in GaN‐based electroluminescent devices. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Miniaturized InSb mid‐IR photovoltaic sensor for room temperature operation
Authors: Ueno Koichiro , Gomes Camargo Edson , Morishita Tomohiro , Sato Masayuki , Yokoyama Aya , Endo Hidetoshi , Yanagita Yoshinori , Goto Hiromasa , Kuze Naohiro
Published: June 2008

We have developed a miniaturized InSb middle‐infrared photovoltaic sensor (InSb PVS) that operates at room temperature. A single InSb photodiode of the InSb PVS consists of an InSb p+‐p–‐n+ photodiode structure grown on a semi‐insulating GaAs (100) substrate, with a p+‐Al0.17In 0.83 Sb barrier layer between p+ and p– layers to reduce diffusion of photo‐excited electrons. The n‐ and p‐type dopants used are Sn and Zn, respectively. To avoid 1/f noise, we operated our InSb photodiode in photovoltaic mode to output an open‐circuit voltage. Moreover, to improve the signal‐to‐noise ratio, 700 photodiodes arranged on a 600 × 600 μm chip were serially connected to each other. We found that the output signal voltage of the sensor depends on the Zn doping concentration in the p– layer. The peak output voltage was obtained at about 6 × 1016 cm–3, which corresponded to the minimum value of the carrier concentration in the p– layer. After packaging, the final external size of the sensor was 2.2 × 2.7 × 0.7 mm. To our knowledge, our sensor is the smallest uncooled sensor in the mid‐IR range reported up to now. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Acoustic charge and spin transport in GaAs quantum wires
Authors: Alsina F. , Stotz J. A. H. , Hey R. , Jahn U. , Santos P. V.
Published: June 2008

Optical investigation of the transport of electrons and holes in GaAs quantum wires by surface acoustic waves shows that carriers can be efficiently transported over several tens of mm. Despite the efficient charge transport, the transport distances for photoexcited spins were found to be very short.

These short spin transport lengths indicate that spin dephasing is not limited by spin motion (the DP mechanism) but rather by spin relaxation during momentum scattering. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
1.5‐µm emission of naturally‐oxidized InN crystals grown by MOVPE
Authors: Nakao M. , Shimada T. , Wakaba M. , Motegi N. , Gomyo A. , Mizuno S. , Matsuoka T.
Published: June 2008

Photoluminescence (PL) spectrum of a naturally‐oxidized InN sample has been investigated. The PL‐peak wavelength locates at around 1.53 µm, which is by 250‐300 nm shorter than that of an intrinsic InN. In addition to this PL peak shift of the InN crystals (corresponding bandgap variation) their quality seems to be improved from the analysis of PL spectra. The naturally‐oxidized layer is found to have the original lattice structure of InN from X‐ray diffraction measurements. The 8‐20% of oxygen atoms has been evaluated to be incorporated in the InN layer by the energy dispersive X‐ray spectroscopy. The PL spectra have been affected by temperature. While a PL‐peak intensity increases with temperature decrease, a PL‐peak shifts toward the longer wavelength. Such red‐shift tendency is opposite to the case of other III‐V compounds. This anomalous temperature effect has been proved from variation of PL spectra with time after excitation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
All MOVPE grown nitride‐based LED having sub mm underlying GaN
Authors: Tanaka Y. , Ando J. , Iida D. , Iwaya M. , Kamiyama S. , Amano H. , Akasaki I.
Published: June 2008

High‐quality GaN layers with thickness exceeding 100 μm were successfully grown by metalorganic vapor phase epitaxy (MOVPE) by controlling the V/III ratio during growth. The surface morphology of the thick GaN layer was found to be affected by the reactor pressure. The formation of voids during the growth of GaN on a patterned GaN/sapphire template is very effective in promoting fast etching of GaN from underneath, thereby achieving free‐standing GaN. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Luminescence observed from a junction field‐effect transistor with Nb/n‐InGaAs/Nb junction
Authors: Hayashi Yujiro , Tanaka Kazunori , Akazaki Tatsushi , Jo Masafumi , Kumano Hidekazu , Suemune Ikuo
Published: June 2008

To investigate the contribution of Cooper pairs to radiative recombination in a semiconductor, a junction fieldeffect transistor (FET) with a Nb/n‐InGaAs/Nb junction was fabricated. Electroluminescence was observed from a 110nm‐wide gap between the source and drain Nb electrodes in addition to the confirmation of the FET operation. Micro‐photoluminescence observed from the gap in the Nb electrodes was drastically enhanced at the temperature lower than the superconducting critical value of ∼ 8K. This new finding is discussed based on the proximity effect at the super‐normal junction. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of transition‐metal‐doped ZnO films by plasma‐enhanced CVD combined with RF sputtering
Authors: Yamaoka K. , Terai Y. , Yamaguchi T. , Fujiwara Y.
Published: June 2008

Transition‐metal (TM) doped zinc oxide (ZnO) films were grown by a developed plasma‐enhanced chemical vapor deposition (PECVD) technique combined with RF sputtering. In the developed system, TMs such as Fe, Cr and Ni were doped into the ZnO films by RF sputtering with a stainless‐steel electrode connected to a RF generator. X‐ray diffraction (XRD) measurements revealed that the TM‐doped ZnO films were successfully grown with c‐axis orientation at 400 °C with RF power of 25 W. The doped TMs were segregated to the surface when the films were annealed at 700 °C in O2 ambient. After higher‐temperature annealing at 800 °C, ZnO nanostructures with wire and tube shapes were formed by a catalytic influence of the segregated TMs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
TiO2 nanotubes: photocatalyst for cancer cell killing
Authors: Kalbacova M. , Macak J. M. , Schmidt‐Stein F. , Mierke C. T. , Schmuki P.
Published: June 2008

The present work reports on the use of self‐organized TiO2 nanotube layers for the photocatalytic killing of cancer cells. TiO2 nanotube layers with different dimensions (diameter 50 nm and 100 nm, thickness 800 nm and 1.3 μm, respectively) were grown by anodization of Ti. Upon low dose of UV irradiation, the vitality of cancer cells cultured on these nanotube layers was significantly affected – the cells reduced their shape and size and a significant amount of the dead cells was found. These results demonstrate that self‐organized TiO2 nanotube layers can be used for photo‐induced cancer cell killing. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Assessment of the impact of key terrestrial observing systems using DMI‐HIRLAM
Authors: Amstrup Bjarne
Published: June 2008

Following a EUCOS decision to make an assessment of the impact on NWP forecasts of different components of the current observing systems in various combinations, a number of OSEs (Observing System Experiments) have been made by a number of NWP centres, with some running global models and some limited‐area models. The Danish Meteorological Institute (DMI) carried out OSEs with the limited‐area model HIRLAM. The following runs were made by DMI (two periods, one month each): (1) A baseline system (BL); (2) BL + all aircraft wind and temperature data; (3) BL + non‐GUAN radiosonde winds; (4) BL + non‐GUAN radiosonde temperature and wind; (5) BL + wind profiler; (6) as (4) + aircraft wind and temperature; (7) as (4) + non‐GUAN radiosonde humidity; (8) as BL + all in situ data (full combined system); and (9) BL + E‐AMDAR only (no ACARS and no traditional AIREPs). The lateral boundaries for these OSEs were provided by runs made by ECMWF, which was one of the centres to make OSEs with a global model.

The main conclusions are that the radiosonde data are the most important data, closely followed by the aircraft data, and that aircraft data and radiosonde data are complementary and not redundant data. Furthermore the results show that it is important to have both wind and temperature profile data; wind data alone produce much poorer impact. Copyright © 2008 Royal Meteorological Society
QSAR Models for the Dermal Penetration of Polycyclic Aromatic Hydrocarbons Based on Gene Expression Programming
Authors: Wang Tao , Si Hongzong , Chen Pingping , Zhang Kejun , Yao Xiaojun
Published: June 2008

Gene Expression Programming (GEP) is a novel machine learning technique. The GEP is used to build nonlinear quantitative structure activity relationship model for the prediction of the Percent of Applied Dose Dermally Absorbed (PADA) over 24 h for polycyclic aromatic hydrocarbons. This model is based on descriptors which are calculated from the molecular structure. Three descriptors are selected from the descriptors pool by Heuristic Method (HM) to build a multivariable linear model. The GEP method produced a nonlinear quantitative model with a correlation coefficient and a mean error of 0.92 and 4.70 for the training set, 0.91 and 7.65 for the test set, respectively. It is shown that the GEP predicted results are in good agreement with experimental ones.
Comparative analysis of the gas‐phase reactions of cylindrospermopsin and the difference in the alkali metal cation mobility
Authors: Dörr Felipe Augusto , Tomaz José Carlos , Lopes Norberto Peporine , Pinto Ernani
Published: June 2008

Cylindrospermopsin (CYN) belongs to a group of toxins produced by several strains of freshwater cyanobacteria. It is a compact zwitterionic molecule composed of a uracil section and a tricyclic guanidinium portion with a primarily hepatotoxic effect. Using low multi‐stage and high‐resolution mass spectrometry, the gas‐phase reactions of this toxin have been investigated. Our data show that collision‐induced dissociation (CID) spectra of CYN are dominated by neutral losses, and three major initial fragmentation pathways are clearly distinguishable. Interestingly, comparative analysis of protonated and cationizated molecules showed a significant difference in the balance of the SO3 and terminal ring elimination. These data indicate that the differential ion mobility of H+, Li+, Na+ and K+ leads to different fragmentation pathways, giving rise to mass spectra with different profiles. Copyright © 2008 John Wiley & Sons, Ltd.
Isobaric metabolite interferences and the requirement for close examination of raw data in addition to stringent chromatographic separations in liquid chromatography/tandem mass spectrometric analysis of drugs in biological matrix
Authors: Yan Zhengyin , Maher Noureddine , Torres Rhoda , Cotto Carlos , Hastings Becki , Dasgupta Malini , Hyman Rolanda , Huebert Norman , Caldwell Gary W.
Published: June 2008

In addition to matrix effects, common interferences observed in liquid chromatography/tandem mass spectrometry (LC/MS/MS) analyses can be caused by the response of drug‐related metabolites to the multiple reaction monitoring (MRM) channel of a given drug, as a result of in‐source reactions or decomposition of either phase I or II metabolites. However, it has been largely ignored that, for some drugs, metabolism can lead to the formation of isobaric or isomeric metabolites that exhibit the same MRM transitions as parent drugs. The present study describes two examples demonstrating that interference caused by isobaric or isomeric metabolites is a practical issue in analyzing biological samples by LC/MS/MS. In the first case, two sequential metabolic reactions, demethylation followed by oxidation of a primary alcohol moiety to a carboxylic acid, produced an isobaric metabolite that exhibits a MRM transition identical to the parent drug. Because the drug compound was rapidly metabolized in rats and completely disappeared in plasma samples, the isobaric metabolite appeared as a single peak in the total ion current (TIC) trace and could easily be quantified as the drug since it was eluted at a retention time very close to that of the drug in a 12‐min LC run. In the second example, metabolism via the ring‐opening of a substituted isoxazole moiety led to the formation of an isomeric product that showed an almost identical collision‐induced dissociation (CID) MS spectrum as the original drug. Because two components were co‐eluted, the isomeric product could be mistakenly quantified and reported by data processing software as the parent drug if the TIC trace was not carefully inspected. Nowadays, all LC/MS data are processed by computer software in a highly automated fashion, and some analysts may spend much less time to visually examine raw TIC traces than they used to do. Two examples described in this article remind us that quality data require both adequate chromatographic separations and close examination of raw data in LC/MS/MS analyses of drugs in biological matrix. Copyright © 2008 John Wiley & Sons, Ltd.