bluuebunny/crossref_metadata_2025 huggingface dataset:
A second‐order homogenization procedure for multi‐scale analysis based on micropolar kinematics
Authors: Larsson Ragnar , Diebels Stefan
Published: August 2006

The paper presents a higher order homogenization scheme based on non‐linear micropolar kinematics representing the macroscopic variation within a representative volume element (RVE) of the material. On the microstructural level the micro–macro kinematical coupling is introduced as a second‐order Taylor series expansion of the macro displacement field, and the microstructural displacement variation is gathered in a fluctuation term. This approach relates strongly to second gradient continuum formulations, presented by, e.g. Kouznetsova et al. (Int. J. Numer. Meth. Engng 2002; 54:1235–1260), thus establishing a link between second gradient and micropolar theories. The major difference of the present approach as compared to second gradient formulations is that an additional constraint is placed on the higher order deformation gradient in terms of the micropolar stretch. The driving vehicle for the derivation of the homogenized macroscopic stress measures is the Hill–Mandel condition, postulating the equivalence of microscopic and macroscopic (homogenized) virtual work. Thereby, the resulting homogenization procedure yields not only a stress tensor, conjugated to the micropolar stretch tensor, but also the couple stress tensor, conjugated to the micropolar curvature tensor. The paper is concluded by a couple of numerical examples demonstrating the size effects imposed by the homogenization of stresses based on the micropolar kinematics. Copyright © 2006 John Wiley & Sons, Ltd.
A structural damage identification method based on genetic algorithm and vibrational data
Authors: Borges Carlos C. H. , Barbosa Helio J. C. , Lemonge Afonso C. C.
Published: August 2006

The problem of damage identification in framed structures using vibrational data is considered. The identification problem is modelled as an optimization task and the use of measured natural frequencies as well as modeshape information in the construction of objective functions is discussed. In a first attempt, a standard genetic algorithm is shown to be ineffective in obtaining the correct damage distribution in test problems. Using domain knowledge, modifications are introduced in the coding process, in the initial population generation, in the fitness function, and in the genetic operators, leading to a promising tool to solve this class of problems. Synthetic problems, with the addition of noise in the simulated measured data associated with the damaged structure, are analysed in order to assess the capability of the proposed technique. Copyright © 2006 John Wiley & Sons, Ltd.
Finite element code for impact collapse problems of framed structures
Authors: Lynn Kyaw Myo , Isobe Daigoro
Published: August 2006

The objective of this study is to develop a dynamic finite element code that can effectively cope with strong non‐linearities and discontinuities common in impact collapse problems, and whose calculation cost is sufficiently low to enable dynamic analyses of full‐model large‐scale structures. The adaptively shifted integration (ASI) technique is modified into the ASI‐Gauss technique to further reduce calculation cost. Algorithms considering member fractures and elemental contact are also presented. Impact collapse analysis is conducted to simulate the aircraft impact with the World Trade Center South Tower (WTC2), and the analytical results showed good agreement with the observed data. Copyright © 2006 John Wiley & Sons, Ltd.
Synthesis of contact‐aided compliant mechanisms for non‐smooth path generation
Authors: Mankame N. D. , Ananthasuresh G. K.
Published: August 2006

Topology optimization is used in this paper for the systematic synthesis of contact‐aided compliant mechanisms that trace prescribed, non‐smooth paths in response to a single, monotonically increasing input force. Intermittent contact interactions that enable these mechanisms to exhibit non‐smooth responses also lead to algorithmic difficulties when the techniques from the synthesis of ordinary compliant mechanisms are used to design contact‐aided compliant mechanisms. A sequential optimization approach based on a regularized normal contact model for large displacements is used in this work to circumvent these difficulties and to enable the use of computationally efficient, gradient‐based optimization methods. We use an objective function based on Fourier shape descriptors, which allows the designer to emphasize different aspects of the design intent (such as the shape, the size and the orientation of the output path) separately. A variable‐stiffness input spring is used to allow the synthesis procedure to choose the appropriate magnitude of the input force. An arc‐length finite element solver and heuristic measures that guard against local and global instabilities add to the robustness of the synthesis procedure as demonstrated by the two design examples presented in this paper. Copyright © 2006 John Wiley & Sons, Ltd.
Estimating the critical time‐step in explicit dynamics using the Lanczos method
Authors: Koteras J. R. , Lehoucq R. B.
Published: August 2006

The goal of our paper is to demonstrate the cost‐effective use of the Lanczos method for estimating the critical time step in an explicit, transient dynamics code. The Lanczos method can provide a significantly larger estimate for the critical time‐step than an element‐based method (the typical scheme). However, the Lanczos method represents a more expensive method for calculating a critical time‐step than element‐based methods. Our paper shows how the additional cost of the Lanczos method can be amortized over a number of time steps and lead to an overall decrease in run‐time for an explicit, transient dynamics code. We present an adaptive hybrid scheme that synthesizes the Lanczos‐based and element‐based estimates and allows us to run near the critical time‐step estimate provided by the Lanczos method. Copyright © 2006 John Wiley & Sons, Ltd.
Incremental‐secant modulus iteration scheme and stress recovery for simulating cracking process in quasi‐brittle materials using XFEM
Authors: Xiao Q. Z. , Karihaloo B. L. , Liu X. Y.
Published: August 2006

In this paper, an incremental‐secant modulus iteration scheme using the extended/generalized finite element method (XFEM) is proposed for the simulation of cracking process in quasi‐brittle materials described by cohesive crack models whose softening law is composed of linear segments. The leading term of the displacement asymptotic field at the tip of a cohesive crack (which ensures a displacement discontinuity normal to the cohesive crack face) is used as the enrichment function in the XFEM. The opening component of the same field is also used as the initial guess opening profile of a newly extended cohesive segment in the simulation of cohesive crack propagation. A statically admissible stress recovery (SAR) technique is extended to cohesive cracks with special treatment of non‐homogeneous boundary tractions. The application of locally normalized co‐ordinates to eliminate possible ill‐conditioning of SAR, and the influence of different weight functions on SAR are also studied. Several mode I cracking problems in quasi‐brittle materials with linear and bilinear softening laws are analysed to demonstrate the usefulness of the proposed scheme, as well as the characteristics of global responses and local fields obtained numerically by the XFEM. Copyright © 2006 John Wiley & Sons, Ltd.
Shear correction for Mindlin type plate and shell elements
Authors: Liu Yu , Soh Chee‐Kiong
Published: August 2006

In this paper, two shear correction methods, which can guarantee good accuracy, suitable for different materials and easy to implement, are proposed for the first‐order theory based plate and shell elements. The general variational principles based on the thermodynamic potentials are first derived, to provide a uniform frame for the different material non‐linearity. Then, the two shear correction methods are derived from the obtained general variational principles using the assumed strain and assumed stress methods, respectively. The shear correction factors (SCF) for homogeneous elastic materials are evaluated using the two methods, and the same result of 0.8 is obtained. The proposed shear correction method is then applied to an elastic‐linear hardening plastic deep beam for verification, and the conformable result is obtained as compared with the plane strain result. Copyright © 2006 John Wiley & Sons, Ltd.
Reporting of adverse drug reactions: predictors of under‐reporting in Malaysia
Authors: Aziz Zoriah , Siang Tan Ching , Badarudin Nurul Suhaida
Published: August 2006

Background

Malaysia like many other countries worldwide uses spontaneous reporting systems as a mean of collecting data on suspected adverse drug reaction (ADR). However, compared to other countries, which use the system, the reporting rate in Malaysia is very low. Why some physicians do not report ADRs is not well understood.

Objective

To identify factors, which would predict physicians' failure to send ADR reports.

Design and Setting

Face‐to‐face interview using a structured questionnaire involving physicians working at the University of Malaya Medical Centre, Malaysia.

Results

About a third of the physicians in the Centre participated. Sixty‐five of the 415 approached refused to participate. A high proportion of the respondents (81.4%) indicated that they had suspected an ADR but did not report it, while about 40% of the respondents were not aware of the existence of the national reporting system in Malaysia. Logistic regression modelling identified the variable ‘ADR considered to be too trivial or too well known to report’ as the strongest predictor of not reporting, followed by physicians' category and uncertainty that the reaction had been definitely caused by a drug.

Conclusion

Important predictor variables, which limit physicians from reporting ADR in Malaysia, were related to uncertainty of types of reaction to report, lack of awareness about the existence, function and purpose of national ADR reporting. The findings could be useful for planning strategies to improve the reporting rate. Copyright © 2006 John Wiley & Sons, Ltd.
Proteome analysis of B‐cell maturation
Authors: Salonen Johanna M. , Valmu Leena , Rönnholm Gunilla , Kalkkinen Nisse , Vihinen Mauno
Published: August 2006

Proteins affected by anti‐mIgM stimulation during B‐cell maturation were identified using 2‐DE‐based proteomics. We investigated the proteome profiles of stimulated and nonstimulated Ramos B‐cells at eight time points during 5 d and compared the obtained proteomic data to the corresponding data from DNA‐microarray studies. Anti‐mIgM stimulation of the cells resulted in significant differences (≥twofold) in the protein abundance close to 100 proteins and differences in post‐translational protein modifications. Forty‐eight up‐ or down‐regulated proteins were identified by mass spectrometric methods and database searches. The identities of a further nine proteins were revealed by comparing their positions to the known proteins in other lymphocyte 2‐DE databases. Several of the proteins are directly related to the functional and morphological characteristics of B‐cells, such as cytoskeleton rearrangement and intracellular signalling triggered by the crosslinking of B‐cell receptors. In addition to proteins known to be involved in human B‐cell maturation, we identified several proteins that were not previously linked to lymphocyte differentiation. The results provide deeper insights into the process of B‐cell maturation and may lead to novel therapeutic strategies for immunodeficiencies. An interactive 2‐DE reference map is available at http://bioinf.uta.fi/BcellProteome.
An integrated approach to mapping the proteome of the human bone marrow stromal cell
Authors: Seshi Beerelli
Published: August 2006

Bone marrow stromal cells, also known as mesenchymal stem or progenitor cells, are thought to play a critical role in hematopoiesis. Because hematopoiesis is dysregulated in leukemic individuals, expression profiling in leukemic stromal cells might yield valuable insights into mechanisms of normal and dysregulated hematopoiesis. Here, proteomics was used to identify expressed proteins in normal and leukemic bone marrow stromal cells. Isobaric tags for relative and absolute quantification (iTRAQ) technology and MS/MS were used to identify and quantify proteins in bone marrow stromal cells from two normal and two leukemic individuals. Approximately 900 distinct proteins were identified with >95% confidence, 73 of which were differentially expressed in leukemic stromal cells. cDNA microarray analysis on Affymetrix oligonucleotide gene chips showed that transcripts correlated with approximately 90% of the expressed proteins. A novel integrated approach for mining and visualization of iTRAQ data is presented. The results provide an initial assessment of the proteome in human bone marrow stromal cells, laying the groundwork for comprehensive analysis of the proteome in these cells, and ultimately, for improved understanding of normal and dysregulated hematopoiesis.
A differentially expressed proteomic analysis in placental tissues in relation to pungency during the pepper fruit development
Authors: Lee Je Min , Kim Seyoon , Lee Ji Young , Yoo Eun Young , Cho Myeong Cheoul , Cho Min Rae , Kim Byung‐Dong , Bahk Young Yil
Published: August 2006

Using proteomic analysis including 2‐DE, image analysis, and protein identification with LC‐MS/MS, an investigation aimed at a better understanding of the differentially expressed proteins and/or gene products was carried out with total cell extracts from placental tissues in nonpungent (Capsicum annuumcv. Saeng‐Ryeog #213) and pungent peppers (C. annuumcv. Saeng‐Ryeog #211). Mobilization of the most abundant proteins, which were on the gels of pH ranges of 4–7, 4.5–5.5, 5.5–6.7, and 6–9, and showed very similar profiles in the two tissues, revealing approximately 2600 protein spots consisting of 1200 on pH 4–7, 600 on 4.5–5.5, 550 on 5.5–6.7, 250 on 6–9. Of these, 37 protein spots, which appeared in only pungent tissues but not in nonpungent tissues or markedly increased in their staining intensities on the gels from pungent tissue, were selected, excised, in‐gel trypsin digested, and analyzed by LC‐ESI‐MS/MS. Peptide MS/MS data were searched against publicly available protein and EST databases, and 22 proteins were identified. Based on this result, we tested and compared the differential expression during fruit development on the 2‐DE gels with total cell extracts from placental tissues of pungent and nonpungent peppers at an interval of 10 days from 10 to 40 days after flowering. In addition, this differential protein expression was further confirmed for some subsets of candidates by Northern‐blot analysis with RNA samples from placental tissues harvested from each pepper fruit at the same sampling intervals. In this study, the physiological implications, revealed from the experimental data in the levels of proteome and transcripts, are discussed in the context of a complex biosynthesis network of capsaicinoids in pepper cells responsive to pungency.
An efficient and generic strategy for producing soluble human proteins and domains in E. coli by screening construct libraries
Authors: Cornvik Tobias , Dahlroth Sue‐Li , Magnusdottir Audur , Flodin Susanne , Engvall Benita , Lieu Victoria , Ekberg Monica , Nordlund Pär
Published: August 2006

The implementation of generic and efficient technologies for the production of recombinant eukaryotic proteins remains an outstanding challenge in structural genomics programs. We have recently developed a new method for rapid identification of soluble protein expression in E. coli, the colony filtration blot (CoFi blot). In this study, the CoFi blot was used to screen libraries where the N‐terminal translation start point was randomized. To investigate the efficiency of this strategy, we have attributed a large number of proteins to this process. In a set of 32 mammalian proteins, we were able to double the success rate (from 34 to 68%) of producing soluble and readily purifiable proteins in E. coli. Most of the selected constructs had their N‐termini close to predicted domain borders and the method therefore provides a mean for experimental “domain foot printing.” Surprisingly, for most of the targets, we also observed expressing constructs that were close to full‐length. In summary this strategy constitutes a generic and efficient method for producing mammalian proteins for structural and functional studies. Proteins 2006. © 2006 Wiley‐Liss, Inc.
Measures for the assessment of fuzzy predictions of protein secondary structure
Authors: Lee Julian
Published: August 2006

Many of the recent secondary structure prediction methods incorporate the idea of fuzzy set theory, where instead of assigning a definite secondary structure to a query residue, probability for the residue being in each of the conformational states is estimated. Moreover, continuous assignment of conformational states to the experimentally observed protein structures can be performed in order to reflect inherent flexibility. Although various measures have been developed for evaluating performances of secondary structure prediction methods, they depend only on the most probable secondary structures. They do not assess the accuracy of the probabilities produced by fuzzy prediction methods, and they cannot incorporate information contained in continuous assignments of conformational states to observed structures. Three important measures for evaluating performance of a secondary structure prediction algorithm, Q score, Segment OVerlap (SOV) measure, and the k‐state correlation coefficient (Corr), are deformed into fuzzy measures F score, Fuzzy OVerlap (FOV) measure, and the fuzzy correlation coefficient (Forr), so that the new measures not only assess probabilistic outputs of fuzzy prediction methods, but also incorporate information from continuous assignments of secondary structure. As an example of application, prediction results of four fuzzy secondary structure prediction methods, PSIPRED, PROFking, SABLE, and PREDICT, are assessed using the new fuzzy measures. Proteins 2006. © 2006 Wiley‐Liss, Inc.
On the dielectric properties of the spin crossover complex [Fe(bpp)2] [BF4]2
Authors: Guillon Thomas , Bonhommeau Sébastien , Costa José Sanchez , Zwick Antoine , Létard Jean‐François , Demont Philippe , Molnár Gábor , Bousseksou Azzedine
Published: August 2006

The thermal variation of the dielectric constant in the spin crossover complex [Fe(bpp)2] [BF4]2 displays a 16 K large hysteresis loop centered around 178 K corresponding to the spin transition temperatures. Unexpectedly, the dielectric constant has a higher value in the low‐spin state. DFT calculations were carried out to determine the microscopic electronic polarizabilities, but these latter could not be correlated with the macroscopic permittivity changes pointing the importance of the effect of the counter‐anions which must be necessarily taken into account in future DFT calculations. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polarized Raman scattering studies of nonpolar a ‐plane GaN films grown on r ‐plane sapphire substrates by MOCVD
Authors: Gao Haiyong , Yan Fawang , Li Jinmin , Wang Junxi , Yan Jianchang
Published: August 2006

Nonpolar (11$ \bar 2 $0) a ‐plane GaN thin films were grown on r ‐plane (1$ \bar 1 $02) sapphire substrates by low‐pressure metal organic chemical vapor deposition (MOCVD). The stress characteristics of the a ‐plane GaN films were investigated by means of polarized Raman scattering spectra in backscattering configurations. The experimental results show that there are strong anisotropic in‐plane stresses within the epitaxial a ‐plane GaN films by calculating the corresponding stress tensors. The temperature dependence of Raman scattering spectra was studied in the range from 100 K to 550 K. The measurements reveal that the Raman phonon frequencies decrease with increasing temperature. The temperature at which nonpolar a ‐plane GaN films are strain free is discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Precipitation kinetics of LiNbO3 and LiNb3O8 crystalline phases in thermally annealed amorphous LiNbO3 thin films
Authors: Akazawa H. , Shimada M.
Published: August 2006

The pyrochlore (LiNb3O8) phase in lithium niobate crystal does not contribute to ferroelectric or electro‐optic properties. We investigated a way to suppress the precipitation of this phase that was formed by thermally annealing amorphous LiNbO3 films. The volume fraction of LiNb3O8 with respect to LiNbO3 becomes higher during longer annealing periods and at higher annealing temperatures because of the evaporation of Li2O units from the surface. Annealing in an O2 atmosphere promotes the formation of the pyrochlore phase more than in a vacuum. We propose rapid thermal annealing of oxygen‐rich LiNbO3 film in a vacuum to provide the best solution to obtaining transparent, single LiNbO3 phase film. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dielectric properties, conduction mechanism, and possibility of nanodomain state with quantum dot formation in impurity‐doped gamma‐irradiated incommensurate TlInS2
Authors: Sardarly R. M. , Mamedov N. T. , Wakita K. , Shim Y. , Nadjafov A. I. , Samedov O. A. , Zeynalova E. A.
Published: August 2006

Temperature‐dependent dielectric and conduction properties of the impurity‐doped and gamma‐irradiated samples of TlInS2 semiconductor‐ferroelectric with incommensurate phase are presented. As found, in both cases a stable relaxor state is emerging in the material with temperature provided that the central ion in InS4 tetrahedron is replaced by an impurity atom such as Mn or Cr, or radiation dose exceeds 400 Mrad. Same as NMR‐studies, the present work drives to a conclusion that In‐displacements are among the components of the order parameter of the incommensurate phase transition. The origin of the non‐activated conductivity observed in the relaxor state of TlInS2 is assumed to be resonance tunneling executed by charge carriers from electron levels in the band gap through potential barriers created by incommensurate superstructure. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical properties and electronic band structure of AgInSe2
Authors: Ozaki Shunji , Adachi Sadao
Published: August 2006

Optical properties of a chalcopyrite semiconductor AgInSe2 have been studied by optical absorption, spectroscopic ellipsometry (SE), and thermoreflectance (TR) measurements. The measurements reveal distinct structures at energies of the critical points in the Brillouin zone. By performing the band‐structure calculation, these critical points have been successfully assigned to specific points in the Brillouin zone. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Systematic studies on electronic structures of CuInSe2 and the other chalcopyrite related compounds by first principles calculations
Authors: Maeda T. , Takeichi T. , Wada T.
Published: August 2006

We have systematically studied electronic structure of chalcopyrite‐type CuInSe2 and the other chalcopyrite compounds, ABX 2 (A = Cu, Ag; B = In, Ga, Al; X = Se, S). First‐principles calculations were performed within a density functional theory with the generalized gradient approximation (GGA), using a plane‐wave pseudopotential method. Valence band maximum (VBM) of CuBX 2 is an antibonding state of Cu 3d and Se 4p (S 3p), while conduction band minimum (CBM) is also an antibonding state derived from B n s and Se 4p (S 3p). Theoretical band gap increases at the order of In, Ga, Al and the values of sulfides, CuB S2 were larger than those of the corresponding selenides, CuB Se2. In present study, we found that the lowest unoccupied n s orbital of B atom in the conduction band shift up to higher energy. Therefore, the band gaps of CuB Se2 (CuB S2) increase at the order of In, Ga, Al with shifting of n s orbital for B atom. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic and dielectric properties of the ruthenium double perovskites La2MRuO6 (M = Mg, Co, Ni, and Zn)
Authors: Yoshii Kenji , Ikeda Naoshi , Mizumaki Masaichiro
Published: August 2006

Magnetic and dielectric properties of the ruthenium double perovskites La2MRuO6 (M = Mg, Co, Ni, and Zn) were investigated. The magnetization measurements for M = Co and Ni showed the existence of magnetic order at 20–30 K. Though the oxides with M = Zn and Mg exhibit a deviation from the Curie–Weiss law, magnetic order was not clearly observed. The result of La2ZnRuO6 was different from that previously reported, in which a ferromagnetic transition was found at around 165 K. The AC dielectric measurements for M = Co and Ni showed large dielectric constants (typically larger than 1000) at around room temperature, suggesting both the formation of short‐ranged polar regions and the magnetic origin of large dielectric constant. In addition, two peaks were found for the temperature dependence of the tan δ component for La2NiRuO6. The behavior suggests the existence of two different polar regions. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Self‐assembled nanowhiskers grown by MBE on InP(001) surface
Authors: Bouravleuv Alexei , Minami Kazuyuki , Ishibashi Takayuki , Sato Katsuaki
Published: August 2006

Ge and MnP nanowhiskers were synthesized by molecular‐beam epitaxy technique on InP(001) surface concurrently. The growth of Ge nanowhiskers is found to be assisted by Mn‐based nanocluster‐mediated vapour‐liquid‐solid mechanism of growth, whereas the growth of MnP nanowhiskers seems to be caused by catalyst‐free mechanism. Magnetic property measurements revealed that samples with prevailing Ge nanowhiskers exhibit ferromagnetic behaviour up to room temperature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Real‐time investigations of selenization reactions in the system Cu–In–Al–Se
Authors: Jost Stefan , Hergert Frank , Hock Rainer , Purwins Michael , Enderle Ralph
Published: August 2006

In this article we present results of a detailed study of selenization reactions in the quaternary system Cu–In–Al–Se and of the binary subsystem aluminum–selenium. The investigation of solid‐state reactions involved in the formation of the compound semiconductor Cu(In,Al)Se2 was performed using real‐time X‐ray diffraction (XRD) with a time resolution of 22.5 s while annealing an elemental layer stack of the metals covered with selenium. A temperature‐resolved phase analysis shows that the formation of the semiconductor takes place via metal‐selenides. Ex‐situ XRD measurements of the processed thin films show a phase segregation concerning the aluminum content of the formed chalcopyrite. Subsequent Rietveld‐refinement of real‐time measurements reveals a formation reaction of the quaternary semiconductor Cu(In,Al)Se2 from the γ‐In2Se3 related crystal structure of (Al,In)2Se3 and Cu2Se as educts. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Predicted reaction paths for the formation of multinary chalcopyrite compounds
Authors: Hergert Frank , Jost Stefan , Hock Rainer , Purwins Michael , Palm Jörg
Published: August 2006

We apply the concept of epitaxy, which has been proven to be essential for the formation of CuInSe2 and CuGaSe2 out of binary selenide compounds to multinary compounds. We show that the formation of quaternary chalcopyrites is possible starting either with binary or with mixed crystal chalcogenide compounds. The complete sets of chemical solid‐state reactions equations are given. The solid‐state reactions are expected to proceed faster, if only one sublattice needs to be rearranged. It shows out, that ternary and quaternary chalcopyrite compounds can be synthesised by fast reaction mechanisms directly from chalcogenide compounds. The fastest way to obtain chalcopyrites containing more than four elements is a stepwise process. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
ZnO based ternary transparent conductors
Authors: Polity Angelika , Meyer Bruno K. , Krämer Thorsten , Wang Changzhong , Haboeck Ute , Hoffmann Axel
Published: August 2006

ZnO1–x Sx films in the whole composition range were deposited by radio‐frequency reactive sputtering on different substrates. Raman measurements verified that the LO phonon of ZnO shifts towards lower frequencies as a function of the S content in the alloyed films. The composition dependence of the band gap energy in the ternary system was determined by optical transmission and the optical bowing parameter was found to be about 3 eV. We compare this behavior to ZnOSe films which can, however, only be synthesized in a narrow composition range close to the binary constituents ZnO and ZnSe. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Host lattice materials in the system Ca3N2–AlN–Si3N4 for white light emitting diode
Authors: Uheda K. , Hirosaki N. , Yamamoto H.
Published: August 2006

New host lattice materials whose red phosphors for white LEDs have been investigated in the ternary system Ca3N2–AlN–Si3N4, just as Ca2Si5N8 and CaSiN2:Eu were found in the binary system Ca3N2–Si3N4. A new red phosphor of CaAlSiN3:Eu which is effectively excited by blue‐GaN and near UV‐GaInN LED chips has been synthesized at 1600 °C for 2 h and subsequently at 1800 °C for 2 h under nitrogen pressure of 1 MPa. The host‐compound has an orthorhombic structure with the space group Cmc21 (No. 36), which is isotypic with LiSi2N3 and NaSi2N3. The red phosphor showed the emission peak around 650 nm which was assinged to 5d → 4f of Eu2+ ion, and its color coordinates were estimated to be 0.667 and 0.327. The optimum concentration of Eu2+ ion was 1.6 mol%. The phosphor also had a high chemical stability, high quantum output, and especially a good thermal property compared to the other phosphors, Ca2Si5N8:Eu2+ and CaSiN2:Eu2+. CaAlSiN3:Eu2+ maintained 83% of the initial efficiency above 150 °C. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Blue‐shift of absorption edge in LaTiO2N by controlling the anion nonstoichiometry
Authors: Moriga Toshihiro , Aoki Daisuke , Nishida Yasuhiro , Kitaji Kazuya , Takahara Keiko , Murai Kei‐ichiro , Nakabayashi Ichiro
Published: August 2006

The perovskite‐type oxynitride LaTiO2N was prepared by heating an oxide precursor at 950 °C for 5 hours under NH3 atmosphere at a flow rate of 1 dm3/min. The precursor was prepared by the polymerized complex method. The oxynitride obtained was almost stoichiometric, LaTi(O0.68N0.32)2.9, with a reddish orange color. The oxynitride was successively annealed at 950 °C for 3 hours under a NH3 atmosphere at flow rates of 50 cm3/min, 30 cm3/min and 10 cm3/min, respectively. The color and composition varied from yellow LaTi(O0.89N0.11)2.8 through green‐yellow LaTi(O0.93N0.07)2.9 to light‐blue LaTi(O0.98N0.02)2.9 in accordance with the decreased flow rate. The absorption edges varied from 2.28 eV for the reddish orange, 2.56 eV for the yellow, 3.17 eV for the green‐yellow, to 3.44 eV for the light‐blue oxynitrides. Annealing under NH3 is therefore effective in color tuning, mainly resulting in a blue‐shift of the absorption edge. DV‐Xα calculations support the conclusion that the lower flow rate of NH3 led to a lower amount of nitrogen and higher oxygen levels in the oxynitrides. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Crystallographic growth orientation of Cu(InGa)Se2 films in relation to substrate material nature
Authors: Yamada A. , Matsubara K. , Nakamura S. , Ishizuka S. , Sakurai K. , Tampo H. , Shibata H. , Nakanishi H. , Niki S.
Published: August 2006

Mo films deposited on glass substrates by rf sputtering, and Cu(InGa)Se2 (CIGS) films deposited on the Mo films by the three‐stage method and CuGaSe2 (CGS) films deposited directly on glass substrates by co‐evaporation of elemental source materials were observed by X‐ray diffraction (XRD) pole figure measurements. The texture analysis of the Mo films revealed a wide variety of solid‐spatial orientations, being dependent on the sputtering device configuration and deposition conditions. The in‐plane orientation of the CIGS or CGS films was affected by the Mo film texture, however, the predominant crystallographic lattice plane along the substrate surface was found to be close to (115) in any case. It must be noticed that the CIGS film is apt to grow in (115) orientation because of the lattice plane nature although this orientation cannot be detected by the XRD 2θ –θ scan due to its zero structural factor. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bismuth containing III–V quaternary alloy InGaAsBi grown by MBE
Authors: Feng G. , Oe K. , Yoshimoto M.
Published: August 2006

InGaAsBi epilayers were created on InP substrates by molecular beam epitaxy for the first time. The high crystalline quality of the InGaAsBi epilayer with smooth interface was confirmed by high resolution X‐ray diffraction measurements. Up to 2.5% Bi was incorporated in the film based on Rutherford back scattering (RBS) results. The RBS channeling spectra give clear evidence that the Bi atoms were substitutionally located in the InGaAs zinc‐blende lattice sites. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Helicon‐wave‐excited plasma sputtering deposition of Ga‐doped ZnO transparent conducting films
Authors: Sugiyama Mutsumi , Murayama Akira , Imao Takashi , Saiki Keita , Nakanishi Hisayuki , Chichibu Shigefusa F.
Published: August 2006

Sputtering deposition of Ga‐doped ZnO (ZnO:Ga) thin films was carried out using the helicon‐wave‐excited plasma sputtering (HWPS) method. The films sputtered above 150 °C had a preferential {0001} orientation. According to the surface‐damage‐free nature, the films having featureless surface morphology exhibited an optical transmittance greater than 80% in the visible spectral wavelengths. However, because the deposition temperature was limited to 250 °C, the electron mobility was limited to as low as 2–3 cm2/V s due to the small grain size (∼25 nm). The results indicate that ZnO:Ga films deposited by HWPS can be used in the transparent conducting oxide layer, provided that higher electron mobility is achieved. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
X‐ray spectroscopic investigation of forbidden direct transitions in CuGaO2 and CuInO2
Authors: Makhova L. , Wett D. , Lorenz M. , Konovalov I.
Published: August 2006

We studied experimentally the local partial density of electronic states (LPDOS) in the conduction band (CB) and in the valence band (VB) of CuGaO2 and CuInO2 by means of X‐ray absorption spectroscopy (XAS) and X‐ray emission spectroscopy (XES). The edges of both the CB and VB are found to be the copper s‐ and/or d‐states. Therefore, direct transitions between the band edges in these materials should be forbidden by symmetry selection rules. The crystal phases in the samples were identified as having delafossite structure, determined by X‐ray powder diffraction (XRD). (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Recent progress towards the development of ferromagnetic nitride semiconductors for spintronic applications
Authors: Newman N. , Wu S. Y. , Liu H. X. , Medvedeva J. , Gu Lin , Singh R. K. , Yu Z. G. , Krainsky I. L. , Krishnamurthy S. , Smith D. J. , Freeman A. J. , van Schilfgaarde M.
Published: August 2006

This article describes progress towards producing prototype magnetoelectronic structures based on III–N semiconductor materials. We focus on the materials properties connected with the key physical phenomena underlying potential spintronic devices: producing, injecting, transporting, manipulating and detecting spin‐polarized electron populations. Our experiments have shown that the maximum magnetic moment is realized for a composition of Ga0.97Cr0.03N and a substrate growth temperature of ∼1050 K. Ion channeling experiments show that ∼90% of Cr sits substitutionally on the cation site. The highest measured magnetization was 1.8μB/Cr atom (∼60% of the expected moment from band theory for ideal material) with the Curie temperature over ∼900 K. This strongly suggests a link between the CrGa impurity band and ferromagnetism and suggests that a double‐exchange‐like mechanism is responsible for the ferromagnetic ordering. The transport properties of spin‐polarized charge carriers were modeled theoretically taking into account both the Elliott–Yafet and the D'yakonov–Perel' scattering mechanisms. We include the spin–orbit interaction in the unperturbed Hamiltonian and treat scattering by ionized impurities and phonons as a perturbation. Our numerical calculations predict two orders of magnitude longer electron spin relaxation times and an order of magnitude shorter hole spin relaxation times in GaN than in GaAs. First‐principles electronic structure calculations predict that efficient spin injection can be achieved using a ferromagnetic GaN:Cr electrode in conjunction with an AlN tunnel barrier. In this structure, the electrode is found to be half‐metallic up to the interface and is thus a candidate for high‐efficiency magnetoelectronic devices. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spectroscopic phase modulated ellipsometry in application to some novel single and polycrystalline ternary compounds
Authors: Mamedov N. , Shim Y. , Toyota H. , Wakita K. , Yamamoto N. , Iida S.
Published: August 2006

The results of the application of the spectroscopic phase modulated ellipsometry (SPME) to a series of novel ternary compounds from anisotropic to polycrystalline are presented to show the high effectiveness of this optical technique with regard to the dielectric function of the new materials. Besides, SPME in specular reflection mode to study the polarization degree of the light reflected at specular angle is shown to be very informative in determination of the best conditions for optical measurements on rough surfaces such as, for example, surfaces of the polycrystalline ternary thiogallate compounds studied in this work. An incoherent approach relating the measured depolarization with the surface variance and optical constants of a material or thin film is proposed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Opto‐electronic properties and light‐emitting device application of widegap layered oxychalcogenides: LaCuOCh (Ch = chalcogen) and La2CdO2Se2
Authors: Hiramatsu Hidenori , Kamioka Hayato , Ueda Kazushige , Ohta Hiromichi , Kamiya Toshio , Hirano Masahiro , Hosono Hideo
Published: August 2006

Electronic and optical properties of widegap oxychalcogenides, LaCuOCh (Ch = chalcogen) and La2CdO2Se2, are reviewed with a focus on those relevant to their layered crystal structures, including high hole mobility, degenerate p‐type conduction, room temperature exciton, and large third order optical nonlinearity. In particular, the widegap p‐type metallic conduction was realized in Mg‐doped LaCuOSe: the first demonstration among any class of widegap materials including GaN:Mg. Furthermore, we demonstrate the room temperature operation of a blue light‐emitting diode using a pn hetero‐junction composed of a LaCuOSe epilayer and an n‐type amorphous InGaZn5O8. Those results strongly suggest that a series of the layered oxychalcogenides are applicable to the light‐emitting layers in opto‐electronic devices that operate in the ultraviolet–blue region as well as to transparent p‐type conductors. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Opto‐electronic properties and light‐emitting device application of widegap layered oxychalcogenides: LaCuOCh (Ch = chalcogen) and La2CdO2Se2
Authors: Hiramatsu Hidenori , Kamioka Hayato , Ueda Kazushige , Ohta Hiromichi , Kamiya Toshio , Hirano Masahiro , Hosono Hideo
Published: August 2006

This issue's Editor's Choice [1] reviews electronic and optical properties of various widegap oxychalcogenides which are connected to their crystal structures. Two examples are shown in the cover picture: LnCuOCh (Ln = lanthanide, Ch = chalcogen, left) and La2CdO2Se2 (right). These oxychalcogenides have layered structures composed of alternate stackings of tetrahedrally coordinated oxide and chalcogenide layers. The rectangular solids depict the unit cells of the materials.

The first author Hidenori Hiramatsu is currently working as a postdoctoral researcher in the ERATO‐SORST project of JST. His research interests include electronic and optical properties of widegap and/or layered materials, syntheses of novel oxide‐ or chalcogenide‐based materials, epitaxial growth and device application of novel materials, and unique physical properties of mixed anion materials. The article has been presented at the 15th International Conference on Ternary and Multinary Compounds in Kyoto, Japan, in 2006. Further papers from ICTMC‐15 are published in phys. stat. sol. (c) 3, No. 8 (2006).

The present issue of phys. stat. sol. (a) as well as phys. stat. sol. (c) 3, No. 9 (2006) also contain papers presented at the Fourth International Conference on Magnetic and Superconducting Materials (MSM '05) held in Agadir, Morocco.
Neutron diffraction on TmNi4Al
Authors: Toliński T. , Szytuła A. , Hoser A. , Kowalczyk A. , Andrzejewski B.
Published: August 2006

Tm and its alloys are known to create non‐collinear magnetic phases, therefore this same can be expected in the case of TmNi4Al. Indeed, we have observed that this compound, contrary to the other RNi4Al members, exhibits an additional hump in the ac magnetic susceptibility at T C2 = 2.8 K apart from the main peak at T C1 = 5.8 K. It may imply a double phase transition or an impurity phase. The magnetization curves and the neutron diffraction have been measured above the higher temperature transition, between the two transitions and below the lower temperature peak of the ac susceptibility. However, magnetization curves as well as the neutron diffraction patterns do not provide any evidence of the antiferromagnetic ordering but suggest a ferromagnetic state. There is only an increase of the intensities observed between 4.2 K and 1.8 K. Therefore, the two peaks in the ac magnetic susceptibility can be ascribed to a switch between two various slightly non‐collinear orderings of the magnetic moments and/or a small distortion of the crystallographic structure. The latter possibility results from the observed small broadening of the diffraction peaks. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Diamagnetic susceptibility of a hydrogenic donor in a quantum dot
Authors: Reuben A. Merwyn Jasper D. , Jayakumar K.
Published: August 2006

We investigate within the effective mass theory, the influence of the shape of the confining potential and the geometry of the Quantum Dot on the diamagnetic susceptibility χ dia of a hydrogenic donor using variational method. We compare χ dia of a donor in a Spherical Quantum Dot for both infinite and finite barrier model. The effect of the location of the donor and Al composition x of the Alx Ga1–x As barrier of the Quantum Dot is also studied. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computational methods for studies of multiexciton complexes
Authors: Vänskä T. , Lindberg M. , Olsen J. , Sundholm D.
Published: August 2006

Powerful computational methods are presented for studies of energy levels, photon‐recombination rates, and phonon‐relaxation rates of neutral and charged multiexciton complexes at correlated levels of theory. The electron–hole system is described by a two‐band effective‐mass Hamiltonian. The one‐particle functions are expanded in a basis set consisting of anisotropic Gaussian functions. The many‐body Hamiltonian constructed in the space of the antisymmetric products of one‐particle functions is diagonalized using general coupled‐cluster and configuration‐interaction methods. The expansion coefficients of the coupled‐cluster and configuration‐interaction wave functions are obtained by solving the corresponding equations using direct iterative algorithms. We demonstrate the potential of the computational approaches by calculating total energies of multiexciton complexes at coupled‐cluster and configuration‐interaction levels. Computational methods for studies of radiative recombination and phonon‐relaxation rates have also been developed and results are reported for radiative recombination rates and recombination energies of the exciton, biexciton, and of the positive and the negative trions confined in a InGaAs/GaAs quantum‐dot sample. Phonon‐relaxation rates have been calculated for a few low‐lying Δ g states of the exciton complex of the same quantum‐dot sample. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparative semiempirical and ab initio study of the structural and chemical properties of uric acid and its anions
Authors: Altarsha Muhannad , Monard Gérald , Castro Bertrand
Published: August 2006

Semiempirical, density functional theory (DFT), and ab initio calculations have been performed to assess the relative stabilities of 15 possible tautomer forms of neutral uric acid, and of the different urate mono‐ and dianion forms. These methods have also been used to compute ionization potentials (IPs) for uric acid and its derived anions. Overall, we have found that semiempirical calculations, in particular PM3, perform well as compared with B3LYP or MP2 computations toward these different structural and chemical properties of uric acid: the triketo form of uric acid is the most stable tautomer form of neutral uric acid. Three other tautomer forms are relatively close in energy, within the range 2–6 kcal/mol above the triketo form, with a mean energy deviation of only 1.3 kcal/mol between PM3 and DFT or ab initio results; the monoanion form of uric acid obtained by abstracting one proton in position 3 (denoted UAN) is the most stable form among all four possible urate monoanions both in gas phase and in solution; the dianion form of uric acid obtained by abstracting two protons, respectively, in positions 3 and 9 of uric acid (denoted UANN) is the most stable urate dianion form both in gas phase and in solution. However, these two most stable species do not have the lowest IPs in solution: among monoanions and dianions, respectively, the species with the lowest IPs are UAN and UANN. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
Conformational behavior of antineoplastic peptides Dolastatin 10 and Dolastatin 15 from Monte Carlo and molecular dynamics simulations
Authors: Alcaro Stefano , Marino Tiziana , Ortuso Francesco , Russo Nino
Published: August 2006

In this work, we report the results of a combined Monte Carlo (MC) and molecular dynamics (MD) approach applied to the conformational study of natural potent mitosis inhibitor Dolastatin 15. A GRID and CLogP analysis has been performed with the aim to provide some hints to the interpretation of the different behavior of Dolastatin 15 and Dolastatin 10, which has been examined in a former study. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
Comparing correlations of continuous observations from two independent populations using a sequential approach
Authors: Fazil Baksh M. , Haars Gerco , Todd Susan , Van Noord Paulus A. H. , Whitehead John
Published: August 2006

A sequential study design generally makes more efficient use of available information than a fixed sample counterpart of equal power. This feature is gradually being exploited by researchers in genetic and epidemiological investigations that utilize banked biological resources and in studies where time, cost and ethics are prominent considerations. Recent work in this area has focussed on the sequential analysis of matched case–control studies with a dichotomous trait. In this paper, we extend the sequential approach to a comparison of the associations within two independent groups of paired continuous observations. Such a comparison is particularly relevant in familial studies of phenotypic correlation using twins. We develop a sequential twin method based on the intraclass correlation and show that use of sequential methodology can lead to a substantial reduction in the number of observations without compromising the study error rates. Additionally, our approach permits straightforward allowance for other explanatory factors in the analysis. We illustrate our method in a sequential heritability study of dysplasia that allows for the effect of body mass index and compares monozygotes with pairs of singleton sisters. Copyright © 2006 John Wiley & Sons, Ltd.