bluuebunny/crossref_metadata_2025_split huggingface dataset:
First‐principles study on elastic properties and phase stability of III–V compounds
Authors: Wang S. Q. , Ye H. Q. 
Published: October 2003

AbstractThe results of first‐principles plane‐wave pseudopotential calculations of the elastic constants for a total of 25 III–V binary phases of both zincblende and wurtzite poly‐types are presented. In addition, the study shows that the relaxation of internal parameters is extremely important to the accuracy of the results. A larger anisotropy factor favors the wurtzite structure while the zincblende structure is preferred for lower anisotropy factors. The boron phases have quite different behavior in both their elastic and structural properties from the other III–V compounds. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computation of optical properties of Si‐based photonic crystals with varying pore diameters
Authors: Hillebrand R. , Jamois C. , Schilling J. , Wehrspohn R. B. , Hergert W. 
Published: October 2003

AbstractTwo‐dimensional Si‐based photonic crystals of triangular lattice type are routinely fabricated by electrochemical pore etching of prestructured Si‐wafers. The radius of the pores can be modulated during the growth process. Based on Maxwell's equations, we theoretically study the optical properties (band structures, electromagnetic fields) of such photonic crystals by applying models with modulated pore diameters. The models are systematically varied with respect to the pore diameters and the pore profiles in the growth direction. Thus, the dielectric contrast between the central narrow core and the outer wide cladding parts can be controlled in analogy to slab structures. We identify conditions for the confinement of the electromagnetic fields inside the core region. The confinement is quantified by correlating the fields with the pore geometry. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Study on additive effective interaction between vertical Bloch lines
Authors: Tang G. D. , Liu Y. , Hu H. N. , Liu Y. P. , Sun H. Y. , Nie X. F. 
Published: October 2003

AbstractThe properties of hard magnetic domains in garnet bubble films were studied. The formula for the domain wall energy of circular hard magnetic domains was improved by adding an assumptive effective interaction energy term between vertical Bloch lines. This satisfactorily interpreted the behavior of hard domains subjected to a static bias magnetic field, which had remained unclear for many years, and also successfully interpreted the temperature character of the hard domains. Therefore, this assumptive effective interaction energy can act as a clue to derive exactly the interaction between vertical Bloch lines. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of group II–VI semiconductor quantum dots with strong quantum confinement and low size dispersion
Authors: Pandey Praveen K. , Sharma Kriti , Nagpal Swati , Bhatnagar P. K. , Mathur P. C. 
Published: October 2003

AbstractCdTe quantum dots embedded in glass matrix are grown using two‐step annealing method. The results for the optical transmission characterization are analysed and compared with the results obtained from CdTe quantum dots grown using conventional single‐step annealing method. A theoretical model for the absorption spectra is used to quantitatively estimate the size dispersion in the two cases. In the present work, it is established that the quantum dots grown using two‐step annealing method have stronger quantum confinement, reduced size dispersion and higher volume ratio as compared to the single‐step annealed samples. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Far‐infrared absorption due to shallow acceptors in semi‐insulating GaAs in dependence on EL2 bleaching
Authors: Gomeniuk Y. V. , Alt H. Ch. , Kretzer U. 
Published: October 2003

AbstractFar‐infrared absorption in semi‐insulating GaAs due to electronic transitions of shallow acceptors was measured in dependence on conditions of bleaching the GaAs intrinsic defect EL2. The far‐infrared spectra were compared with the results of near‐infrared spectroscopy of EL2 fundamental state. It was found that under conditions of low intensity illumination the neutral acceptors can coexist with the neutral EL2 defect. The model is proposed which explains the effects that were not observed previously, such as depopulation of neutral shallow acceptors at low temperature, and the charge redistribution between different shallow acceptor levels at increasing temperature for the samples co‐doped with zinc and carbon. It is shown that far‐infrared spectroscopy is suitable for quantitative evaluation of the shallow acceptor concentration in GaAs material. The corresponding calibration factors are given. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Minority carrier diffusion lengths and optical self‐absorption coefficient in undoped GaN
Authors: Matoussi A. , Boufaden T. , Guermazi S. , Eljani B. , Mlik Y. , Toureille A. 
Published: October 2003

AbstractIn this paper we report electron beam induced current (EBIC) measurements on Schottky diodes on undoped GaN samples grown by the metal organic vapor phase epitaxy method on porous silicon substrates. A 2D simulation model was applied to perform the theoretical EBIC profiles and to compare with the experimental one. A minority carrier diffusion length (L) for holes of 0.72 μm was measured in the space charge region, indicating constant diffusivity of 6.48 cm2/s and a lifetime coefficient of 0.8 ns. An increase of L is observed as the probe source is moved from the Schottky junction to the bulk material. This increase was related to the polarization effects that are preponderant in group III–nitride devices. Far from the depletion layer (greater than 0.91 μm) the measured current is produced by the reabsorbed recombination radiation process. This corresponds to an optical self‐absorption coefficient of ap = 0.112 μm−1. The results show that the transport parameters depend on the growth technology. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamic and thermodynamic properties of solid helium in the reduced all‐neighbours approximation of the self‐consistent phonon theory
Authors: Malinowska‐Adamska C. , Słoma P. , Tomaszewski J. 
Published: October 2003

AbstractThe results of studies of physical properties of solid helium obtained with the help of the reduced all‐neighbours approximation of the self‐consistent phonon theory are presented. The results of calculation of the temperature and pressure variations of the quantities describing the dynamics and thermodynamics of solid He‐3 and He‐4 obtained in terms of the (exp m) Buckingham the (n m) Lennard‐Jones and the (exp exp) Morse renormalized potentials are given and compared with experimental and other theoretical data. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Temperature dependence of the indirect band gap and related optical parameters of (NH4)2ZnCl4:xSr2+ single crystals
Authors: Gaffar M. A. , Abu El‐Fadl A. , Bin Anooz S. 
Published: October 2003

AbstractOptical transmittance measurements were carried out near the absorption edge of (NH4)2ZnCl4:xSr2+ single crystals, where x = 0.00, 0.020, 0.039, 0.087 or 0.144 wt%. The dependence of the absorption coefficient (α) on photon energy in the range 3.4–6.4 eV and on temperature in the range 276–350 K was examined. With increasing temperature the absorption edge was shifted to the lower energy side; this shift was attributed to the temperature dependence of electron–lattice interactions. Due to the presence of Sr2+ in (NH4)2ZnCl4:xSr2+ a change in the absorption band centred at 5.30 eV was observed. In the case of higher strontium doping, the optical absorption coefficient showed a ‘pre‐transition’ stage just before the onset of the band‐to‐band transition. Exponential dependence of α on hν according to the Urbach rule was observed and the Urbach parameters were determined. The steepness parameter was strongly affected by doping; its behaviour at 319 K evidently showed the antiferroelectric to commensurate phase transition. The temperature dependence of Eg was also estimated using data for the steepness parameter, and hence Eg at different temperatures and Sr2+ concentrations was evaluated. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A new concept for the calculation of the mobile dislocation density in constitutive models of strain hardening
Authors: Roters F. 
Published: October 2003

AbstractA new concept for the calculation of the mobile dislocation density in constitutive models is presented. In contrast to earlier approaches this concept does not use rate equations to calculate the evolution of the mobile dislocation density but is based on the minimization of the flow stress in each increment. In comparison to a concept using a constant value for the mobile dislocation density the new concept results in a more realistic stress strain relation, especially when applied to strain rate change experiments. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Relaxation phenomena in the Blume–Emery–Griffiths model near the critical and multicritical points
Authors: Erdem R. , Ekiz C. , Keskin M. 
Published: October 2003

AbstractThe relaxation behaviour of the Blume–Emery–Griffiths (BEG) model Hamiltonian with bilinear and biquadratic nearest‐neighbour ferromagnetic exchange interaction and crystal field interactions is studied by using the molecular field approximation (MFA) and Onsager's theory of irreversible thermodynamics. First the equilibrium behaviour and the phase diagrams of the model in MFA are given briefly in order to understand the relaxation behaviour. Then, Onsager theory is applied to the model and the set of linear differential equations, which is also called the kinetic or rate equations, is obtained. By solving these equations a set of relaxation times is calculated and examined for temperatures near the critical and multicritical points. It is found that one of the relaxation times (τ1) is sharply cusped at the triple and critical points, whereas it approaches infinity near the critical‐end point. On the other hand, the other relaxation time (τ2) displays a jump‐discontinuity behaviour at the triple and critical points but it has a cusp at the critical‐end point. A maximum of τ2 has also been observed above the critical‐end point. Moreover, similar calculations are performed for non‐zero magnetic field (H) to investigate the effect of H on relaxation times. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of interface between two ferroelectrics in a film on polarization distribution
Authors: Lü Tianquan , Zheng Zhiren , Sun Punan 
Published: October 2003

AbstractUsing Ginzburg and Devonshire theory the polarization distribution is studied for a ferroelectric film consisting of two different materials with an interface parallel to the spontaneous polarization. The numerical results show that a much thinner transition layer between two materials can influence the polarization in a larger range. The temperature and the Curie‐temperature difference between two bulk materials are two sensitive influencing factors and the change of the thickness of the transition layer has little influence. The rise of temperature or Curie‐temperature difference between two bulk materials will widen the distribution range of inhomogeneous polarization. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ordering and strain‐induced D–D interaction in Lu–D
Authors: Blanter M. S. , Granovskiy E. B. , Magalas L. B. 
Published: October 2003

AbstractSpecific values of D–D strain‐induced (elastic) interaction energy are used to analyze the unusual structure of the ordered solid solution Lu–D. Formation of the chains of interstitial atoms is due to both electronic and elastic interaction of the interstitials. At the same time, the main reason for the chain‐pair formation is the strain‐induced long‐range elastic interaction. Pairs of chains in antiphase are more advantageous than pairs of chains in phase from energy considerations. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Heisenberg model on a stacked‐triangular lattice: spin Green function approach
Authors: Du A. , Li J. , Wei G. Z. 
Published: October 2003

AbstractUsing a spin Green function approach, we have studied the magnetic properties of a stacked‐triangular Heisenberg model, in which the triangular lattice is in the xy plane and the triangular nets are stacked in parallel along the z axis. We consider both the quasi‐two‐ and the quasi‐one‐dimensional cases and suppose the interaction between the nearest‐neighbor spins to be antiferromagnetic or ferromagnetic. By computing the magnetization and the transition temperature of the system, we find that the geometrical frustration introduced by the antiferromagnetic exchange in a triangular lattice brings about an additional spin fluctuation, which results in a decrease of the staggered magnetization and a lowering of the transition temperature compared to the system without geometrical frustration. In the quasi‐two‐dimensional case, the exchange strength |J| in the xy plane is much larger than |J′| along the z direction (|J| ≫ |J′|), and in the quasi‐one‐dimensional case (|J| ≪ |J′|) the transition temperatures can be expressed in approximation forms as TN = S(S + 1)|J|/[aln (|J/J′|) + b and TN = cS(S + 1)(|JJ′|)1/2, respectively. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Atomic‐scale simulations of the interaction between dislocations and tilt grain boundaries in α‐iron
Authors: Saraev D. , Schmauder S. 
Published: October 2003

AbstractThe interaction of lattice dislocations with symmetric and asymmetric tilt grain boundaries has been simulated for different grain boundary misorientation angles by means of the molecular dynamics method using embedded atom method (EAM) potentials. An edge dislocation is equidistantly placed between a grain boundary and a free surface. The movement of the dislocation occurs during relaxation in the absence of external stress and is a result of competitive attractions from the grain boundary and the free surface. The evolution of the position of the dislocation is analysed. An attraction force from the grain boundary has been found in all cases. The strongest attraction has been observed for the cases when the glide plane of the dislocation is perpendicular to the grain boundary. A similar effect has been found for low and room temperatures. An analysis of microscopic stresses has also been performed. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Gallium‐rich reconstructions on GaAs(001)
Authors: Pristovsek M. , Tsukamoto S. , Ohtake A. , Koguchi N. , Orr B. G. , Schmidt W. G. , Bernholc J. 
Published: October 2003

AbstractGa‐rich reconstructions on GaAs(001) surfaces were prepared by annealing and Ga dosing of Molecular Beam Epitaxy grown samples and analyzed in‐situ by Reflectance Anisotropy Spectroscopy and Reflection High‐Energy Electron Diffraction. Annealing or dosing gallium above about 800 K invariably results in a (4 × 2)/c(8 × 2) reconstruction. Lowering the temperature or annealing below 800 K results in a (2 × 6)/(3 × 6) reconstruction. By dosing the (2 × 6)/(3 × 6) reconstruction with more than 0.2 monolayer of gallium, it transforms into a (4 × 6) reconstruction. The observed translational symmetries and measured RAS spectra are compared with results of first‐principles calculations. None of the (2 × 6) structures proposed in the literature is energetically stable. The RAS spectrum calculated for the ζ(4 × 2) model resembles reasonably the data measured for the (4 × 2) surface. The RAS spectra calculated for (2 × 6) symmetries indicate that mixed Ga‐As dimers likely are a structural element of the corresponding surface reconstructions. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Homogeneous linewidth of quantum well excitons from resonance fluorescence spectra
Authors: Schwedt D. , Nacke Ch. , Stolz H. , Eshlaghi S. , Reuter D. , Wieck A. 
Published: October 2003

AbstractWe report high resolution measurements of resonance fluorescence spectra of high quality GaAs quantum wells after small bandwidth cw excitation. The resulting spectra can be well described with means of light scattering from a statistically distributed ensemble of three‐level‐systems. Using this model we are able to separate the homogeneous linewidth from the inhomogeneous ensemble response. Thus, we present a simple linear tool for sample characterization. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Composition dependent energy band gaps for the ternary alloy Si1−x−yGexCy
Authors: Shim Kyurhee , Bae Jung‐Wook , Lim Jong‐Soo , Lee Kyong‐Won , Kim Yunsoo , Rabitz Herschel 
Published: October 2003

AbstractThe universal tight binding method based on sp3s* basis functions is used to calculate the electronic structure of the ternary alloy Si1−x−yGexCy. The dependences of the fundamental band gaps (E(Γ), E(Δ), E(L), and E(X)) are obtained and investigated for small concentrations of carbon (0 ≤ y ≤ 0.05). It is found that the presence of carbon in the alloy Si1−x−yGexCy results in a very significant change (i.e., reduction) of the alloy bond length with a small change of the energy band gaps. The energy band gap increases upon adding carbon to the strained alloy. However, the energy band gap decreases upon adding carbon while keeping the alloy lattice matched to the substrate Si. The calculated band gaps are in good agreement with the limited available experimental data and ab initio results. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Zero‐phonon lines in the d → f luminescence of LiYF4 : Er3+
Authors: Chen Yonghu , Kirm Marco , Negodin Evgueni , True Marcus , Vielhauer Sebastian , Zimmerer Georg 
Published: October 2003

AbstractHigh‐resolution analysis of spin‐allowed and spin‐forbidden VUV d → f luminescence of a heavy rare earth ion in a wide band gap host crystal clearly yields zero‐phonon lines, indicating intermediate coupling. Although the chosen system (LiYF4 : Er3+) has a complicated ground‐state structure, zero‐phonon lines for nearly all of the eight Stark levels of the ground state are observed. Striking similarities between d → f and f → f emission support the assignments. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
SMILIB: Rapid Assembly of Combinatorial Libraries in SMILES Notation
Authors: Schüller Andreas , Schneider Gisbert , Byvatov Evgeny 
Published: October 2003

AbstractA software tool was developed for fast combinatorial library enumeration (SMILIB). Its particular features are its simplicity to use, high flexibility in constructing combinatorial libraries and high speed of library construction. SMILIB offers the possibility to construct very large combinatorial libraries using the flexible and portable SMILES format. Libraries are generated at rates of approximately 30,000 molecules per minute. Combinatorial building blocks are attached to scaffolds by means of linkers rather than to concatenate them directly. This allows for creation of easily customized libraries using linkers of different size and chemical nature. A web interface for a limited web‐based version of the software is available at URL: www.modlab.de. An unlimited binary version of SMILIB for command line execution on Linux systems is available from this URL.
Development of a Genetic Algorithm to Design and Identify Peptides that can Cross the Blood‐Brain Barrier
Authors: Teixidó Meritxell , Belda Ignasi , Roselló Xavier , González Sonia , Fabre Myriam , Llorá Xavier , Bacardit Jaume , Garrell Josep M. , Vilaró Senen , Albericio Fernando , Giralt Ernest 
Published: October 2003

AbstractThe design of peptide drugs to treat central nervous system (CNS) diseases is hampered by our ignorance of the factors that determine whether a given peptide can cross the blood‐brain‐barrier (BBB). We are developing an approach to this problem that combines computer‐aided ligand design, parallel synthesis of peptide libraries, and biological evaluation using in vitro BBB models. We present a genetic algorithm (GA) to search for peptides that can cross the BBB. In the design and optimization of this GA we used a genetic meta‐algorithm to optimize the GA parameters. The GA is validated in silico by virtual screening of a peptide library of more than 1015 molecules. We used a virtual fitness function dervied from statistical analysis of the few experimental data on peptide‐BBB permeability available.
Automated Sorting of Beads from a “One‐Bead‐Two‐Compounds” Combinatorial Library of Metalloproteinase Inhibitors
Authors: Christensen Caspar , Groth Thomas , Bruun Schiødt Christine , Tækker Foged Niels , Meldal Morten 
Published: October 2003

AbstractThe development and use of an instrument that automatically separates non‐fluorescent beads from fluorescent beads are described. The scope of the instrument was tested by on‐bead screening of a solid phase combinatorial library synthesized on the aqueous compatible PEGA library resin [1]. The one‐bead‐two‐compounds library [12] consisted of approx. 160.000 putative phosphinic peptide inhibitors, encoded by ladder synthesis [22] for facile analysis by MALDI‐TOF mass spectrometry, and each bead also contained a common fluorescence‐quenched substrate. The library was screened for activity against MMP‐9; several beads with inhibitory activity were selected from the library by the novel fully automated sorting method and analyzed by MALDI‐TOF MS for structural elucidation.
Collection of Bioactive Reference Compounds for Focused Library Design
Authors: Schneider Petra , Schneider Gisbert 
Published: October 2003

AbstractA collection of reference molecules for ligand‐based library design was compiled from the recent scientific literature. Selected properties of this set of 4,236 drugs and drug candidates were analyzed and compared to previous studies. Lipophilicity and molecular weight distributions revealed a trend toward larger, more lipophilic molecules of newer drug candidates. Using the compound collection as a source of reference data, a method for visualization of molecule distributions in a pharmacophore space by self‐organizing maps (SOM) was developed which can be used for virtual library design. Potential applications of this “pharmacophore road map” approach are discussed.
Epothilones: Quantitative Structure Activity Relations Studied by Support Vector Machines and Artificial Neural Networks
Authors: Bleckmann Annalen , Meiler Jens 
Published: October 2003

AbstractIn this paper the relation between the structure of epothilones (a new class of anti‐tumour agents) and their potential to influence the tubulin‐microtubule equilibrium is investigated. Insights into the character of the tubulin‐epothilone interactions are derived as the accuracy and reliability of support vector machines and artificial neural networks to model such relations quantitatively is compared. Both methods are well qualified to model relationships between the structure of epothilone derivatives and their anti‐tumour activities. Artificial neural networks achieve lower residual standard deviations (22%) compared to support vector machines (25%) and better classification results (89% compared to 75%). However, the reproducibility of the results is greater for support vector machines, which suggests a stronger convergence. The mapping of the influence of individual structural descriptors on the three‐dimensional epothilone structure suggests one side of the rather flat molecule to be more important for its activity. The “LIBSVM” software which is used for simulating the support vector machines is freely available from www.csie.ntu.edu.tw/~cjlin/libsvm. The Program “Smart” which is used for simulating artificial neural networks is free for academic use and can be obtained together with the database of epothilones and their activities from www.jens‐meiler.de.