bluuebunny/crossref_metadata_2025_split huggingface dataset:
On a Hypothesis on the Molecule Vacancies in PbTe
Authors: Moldovanova M. , Assenov R. 
Published: January 2007

AbstractThe temperature dependence of the current carriers mobility in SnTe(I) and PbTe (I) synthesized in presence of SnI2 or PbI2 respectively was studied. An experimental formula was established, showing that current carriers scattering in SnTe(I) is due to vacancies at constant Hall coefficient.For PbTe (I) crystallized from tellurium solution by traveling heater method the mobility is high (between 2.104 and 4.104 cm2/Vs) and the Hall coefficient is constant within the interval 77 K–450 K. Only within 77 K–160 K interval the current carriers scattering is due to vacancies.A hypothesis is proposed based on the presence of molecular vacancies (VpbTe). These vacancies do not change electron gas concentration but do change the carriers mobility. Specimens with a negligibly low lead atoms vacancies Concentration were investigated. An empirical expression is established which shows that their mobility depends on molecular vacancies concentration and explains observed weak temperature influence upon carriers mobility. These results are obtained only from Hall coefficient and electric conductivity measurements within the 77 K–160 K temperature interval.
Validity of the Lattice‐Parameter Vegard‐Rule in Cd1‐xZnxTe Solid Solutions
Authors: Schenk M. , Hähnert I. , Duong L. T. H. , Niebsch H.‐H. 
Published: January 2007

AbstractCd1‐xZnxTc crystals of different composition (0 ⩽ x ⩽ 1) were grown by the vertical Bridgman method and by synthesis in Te excess. After careful surface preparation of crystal slices, their Zn:Cd ratios were ascertained by wavelength‐dispersive X‐ray spectroscopy (WDXS), and the lattice parameters of the same slice regions were measured by X‐ray diffractometry. The Vegard rule concerning the linear lattice‐parameter dependence on composition is – in contrast with earlier literature data – exactly valid within the limits of error (Δx ⩽ ±0.01 and Δa/a ⩽ 3.7. 10−4) and follows the equation a(x) = (0.64822 ‐ 0.03792x) nm. After annealing some slices at different temperatures and controlled partial pressure conditions in ordcr to find possible phase separations or cation ordering effects, neither the lattice parameters were changed nor additonal interferences were found. A published occurrence of a rhomhohedral phase could not be confirmed by means of powder diffraction analysis. The results are discussed in relation to own electron diffraction investigations and to EXAFS literature data.
Relation of the Hydrostatic Electrostrictive Coefficient of Cubic Dielectrics with other Material Constants
Authors: Kloos G. 
Published: January 2007

AbstractA simple relation is derived that links the hydrostatic coefficient of quadratic electrostriction with the volume compressibility and an expression involving the dielectric constant. The first part of the derivation is mainly macroscopic and applicable to dielectrics with cubic symmetry. Making use of the Born‐Mayer potential, an expression of the derivative of the ionic polarizability with respect to volume is given in the second part. A negative sign of the hydrostatic coefficient is predicted for typical alkali halides. This result is in agreement with recent experimental findings reported in the literature, if the observed values are corrected for the influence of electrostatic stresses in an alternative way.
A Simple Model for Evaluation of Electronic Polarizabilities of Chalcopyrity Semiconductors
Authors: Reddy R. R. , Ahammed Y. Nazeer , Reddy C. V. K. , Buddhudu S. 
Published: January 2007

AbstractSimple correlations between the energy gap, optical electronegativity and the refractive index are given for some ternary chalcopyrite semiconductors. Refractive indices and electronic polarizabilities are evaluated. Results are in good agreement (±5.3%) with the experimental values, better than those of the valus (±19.5−28%) using bond charge model and plasma frequency formalism.
Theoretical Study of Ge Implanted Silicon Subjected to Pulsed Excimer (XeCl) Laser Radiation
Authors: Klinger D. , Auleytner J. , Z̊ymierska D. 
Published: January 2007

AbstractA theoretical study of time‐dependent temperature profiles in Ge implanted silicon crystal subjected to excimer pulsed laser irradiation is presented. The minimum depth of the annealing process is calculated with assumed laser beam parameters.
Study on the Morphological Change of Growing Ag Crystallites by in‐situ SEM Observation
Authors: Horii Akira , Kawanowa Hitoshi , Kamei Masayuki , Yumoto Hisami , Gotoh Yoshihiko , Gonda Takehiko 
Published: January 2007

AbstractThe morphology of the initial growth stage of Ag thin films on Mo(110) substrate was investigated in‐situ by the scanning electron microscope (SEM). A great majority of the Ag crystallites showed a truncated Wulff's equilibrium shape of the face‐centered‐cubic (fcc) structure with epitaxial orientation [10]Ag//[11]Mo, (111)Ag//(110)Mo with the substrate temperature of 400 °C. In‐situ SEM observation during the growth revealed two kinds of particular morphological change of Ag crystallites, namely (1) rotation of an Ag crystallite and (2) reformation of the crystal faces of the Ag crystallite. However, a small number of Ag crystal particles showed Wulff‐polyhedron truncated by the (100) plane parallel to the substrate surface (oriented to the 〈100〉 axis normal to the substrate surface).
The as‐Grown SiC (0001) Surface as Observed by Reflection Electron Microscopy
Authors: Marek T. , Heindl J. , Strunk H. P. , Eckstein R. , Müller St. G. , Hofmann D. 
Published: January 2007

AbstractReflection electron microscopy (REM), capable of imaging surfaces in high resolution, reveals that the risers and treads in the terrace growth surfaces of vapor grown SiC(0001) bulk crystals are characterized on a microscopic scale by growth steps. At the risers microscopic growth occurs by the ‘step flow mode’. At the treads, growth occurs by island formation and by operation of growth spirals.
Simulation of the Fluidized‐bed Crystallizers (II) Productivity Related Aspects
Authors: Belcu M. , Turtoi D. 
Published: January 2007

AbstractThe very intensive system self‐regulation renders the evacuated‐crystal size reduction a less efficient method for the productivity increase. The most promising possibilities seem to be:

Recirculation of some already‐grown crystals and their insertion as seeds on the crystallizer bottom;
The use of a supplementary crystallizer, with considerably reduced dimensions, in order to produce a seeds flux numerically equal to the flux of crystals evacuated as product
.
Electrical Conductivity in Polycrystalline Copper Oxide Thin Films
Authors: Roy B. N. , Wright T. 
Published: January 2007

AbstractThis study presents a preliminary investigation on the electrical properties and the electronic structure of the copper‐oxygen system. Thin films, prepared by high vacuum sputtering on glass and MgO substrates, were oxidised both at constant temperatures and by heating continuously from a low to a high temperature, and the variations in the resistance with oxidation were measured. The final oxide was found to be CuO. The room temperature resistance after oxidation is very much higher than that before oxidation, indicating a transition from metal to insulator. At oxidation temperatures below 600 K, the conductivity decreased gradually; a steeper decrease occurred at higher temperatures when an apparent semiconducting behaviour was observed in some cases. At temperatures above 600 K, the behaviour of the conductivity followed the form σ(T) = σ(0) + αTβ, which suggested weak localization or electron‐electron interaction.
XRD Line Broadening Studies on Mullite
Authors: Serrano F. J. , Bastida J. , Amigó J. M. , Sanz A. 
Published: January 2007

AbstractAn X‐ray diffraction microstructural study on 110, 220, 001 and 111 peaks has been performed on mullite in the temperature range of primary mullite formation in order to monitor nucleation and growth process. Considering the crystallinity of the starting kaolinites, a greater disorder of the kaolinite has been found to enhance the mullite formation. Isothermal growth is related to a decrease in the Al2O3 content of mullite.
Modification of Fluid Flow and Heat Transport in Vertical Bridgman Configurations by Rotating Magnetic Fields
Authors: Dold P. , Benz K. W. 
Published: January 2007

AbstractApplying a rotating magnetic field to an electrically conducting liquid, a Lorentz force is induced which generates a melt rotation of a certain angular velocity. A cylindrical gallium melt (aspect ratio 2.5) has been used as a model liquid. The melt has been heated from the bottom (Ra = 106) or from the top (Ra = −106) and the resulting temperature fluctuations in the melt have been measured in dependence on the rotating field strength (Bmax = 30 mT). In the case of the unstable gradient 0.8 mT are sufficient to dominate the buoyancy driven convection and to reduce the amplitude of the buoyancy caused temperature oscillations for more than one order of magnitude. At the same time, the fluctuation frequency increases with the field strength. In the case of the stabilizing temperature gradient, low amplitude/high frequency temperature fluctuations are generated by the rotating magnetic field, indicating the transition to a time‐dependent flow. In both cases we see an increase of the convective heat transport for magnetic inductions higher than approximately 5 m T.Applying the rotating magnetic field to the Bridgman growth of gallium doped germanium, the same behavior can be seen: Growing with a top‐seeded arrangement, the intensity of the dopant striations is decreased and their frequency is increased. Growing with a bottom‐seeded arrangement, the interface curvature changes from concave to convex and the flow becomes time‐dependent.
Axial temperature distribution in Silicon‐Germanium grown by the RF‐heated float zone technique
Authors: Schulz D. , Wollweber J. , Darowski N. , Schröder W. 
Published: January 2007

AbstractIm Konzentrationsbereich von 0 bis 25 at% Germanium wurde das Segregationsverhalten von Sili‐zium‐Germanium‐Einkristallen gezüchtet mit Hilfe des HF‐beheizten tiegelfreien Zonenschmelzver‐fahrens untersucht. Vollstündig versetzungsfreie Kristalle mit bis zu 8 at% Germanium wurden gezüchtet. Störungen des einkristalline Wachstum waren im wesentlichen auf konstitutionelle Unterkühlung zurückzuführen. Mittels pyrometrischer Temperaturmessung wurde der Anstieg der axialen Temperaturverteilung ΔT/ΔZ in der Nähe der Wachstumsphasengrenze bestimmt und daraus die kritische Ziehgeschwindigkeit abgeleitet. Die Messungen zeigten, daß mit zunehmenden Germaniumgehalt der Temperaturgradient im Kristall größer wird.
Twinning due to Transformation from a more Favourable Energetic Transition Structure to a Higher Symmetrical Arrangement: Five‐radiated Intergrowth Crystals of Metals (III)
Authors: Krafczyk Susanne , Jacobi Hans , Follner Heinz 
Published: January 2007

AbstractParts I and II investigated twins that form when a more favourable energetic transition structure initially occurs which then, at a certain growth stage (presumably in the nm‐range), transform into a more symmetric structural arrangement. These transition structures, which could explain the transformation between the twin individuals, were found using lattice energy calculations on organic substances such as pentaerythrite, 1,2,4,5‐tetrabromobenzene, 3,5‐dimethylbenzoic acid, and maleic acid. The formation of a more favourable energetic but symmetrically lower transition structure is more likely. when lattice pseudosymmetries are present. Experimentally proving these transition structures is extremely difficult because of their low volume. It has nevertheless been possible to detect such a transition structure — around which crystal growth begins — in many metallic vapour‐deposit layers. Crystal growth begins around a core and then continues as a three‐dimensional periodically ordered cubic face‐centered structure, at which point twins form. In Part III, the attempt is made to confirm these processes with energy calculations.
On the Formation of Dislocation Hollow Cores on Cleaved {100} Faces of L‐Arginine Phosphate Monohydrate Single Crystals
Authors: Sangwal K. , Sanz F. 
Published: January 2007

AbstractThermodynamic conditions and energy considerations for the formation of hollow cores at the emergence points of monolayer cleavage steps associated with screw dislocations on the cleaved {100} faces of LAP single crystals are discussed. Analysis of the formation of hollow cores and the change of the curvature of steps in the vicinity of their origins reveals that dislocations responsible for the origin of hollow cores have stress fields due to trapped mother liquor of different supersaturations. The results also show that (1) the radius of a hollow core is inversely proportional to the one‐third power of the interface supersaturation while the volume of hollow corés increases exponentially with their radius, and that (2) the strain energy associated with a dislocation is responsible for the formation of an equilibrium hollow core of a particular depth at the origins of cleavage steps associated with dislocations.
The Structure and Unusual Optical Textures of Smectic C2 Phases of New Tail‐to‐Tail Twins
Authors: Weissflog W. , Richter S. , Dietzmann E. , Rise J. , Diele S. , Schiller P. , Pelzl G. 
Published: January 2007

AbstractNew tail‐to‐tail twins with alkyl or perfluorinated spacers were synthesized. The mesomorphic properties were studied by polarizing microscopy and X‐ray diffraction measurements. It was found that the smectic C phase is a Sc2 phase with alternating tilt and an intercalated structure. The alternating tilt gives rise to an unusual schlieren texture which exhibits not only singularities with the strength s = ±1 but also those with s = ±1/2 and s = ±3/2.
Crystal and Molecular Structure of 1‐Ethyl‐3‐[tris(trimethylsiloxanyl)silyl]pyrrolinium Hydrochloride
Authors: Rudert R. , Schmaucks G. 
Published: January 2007

AbstractThe crystal and molecular structure of 1‐Ethyl‐3[tris(trimethylsiloxyl)silyl]pyrrolinium hydro‐chloride (C15H38N+O3Si4 · C1−) has been determined by direct methods. The title compound crystallizes in the monoclinic space group C2/c with a = 20.640(3), b = 19.494(2), c = 27.34(3) Å, β = 90.60(4)°, V = 11000(13) Å3, Z = 16, Dx = 1.034 Mg m−3. There are two molecules with different conformations in the crystal. The pyrroline rings are non‐planar.‐The SiOSi angles range from 149(1)° to 163(1)°. Two of the SiMe3 groups are disordered. All molecules are connected by C1− – N+ contacts and C1− ‐ HN+ hydrogen bonds to form double chains.
The Crystal and Molecular Structure of 1‐Allyl‐5‐benzoyl‐4‐phenylpyrimidine‐2‐one hemihydrate
Authors: Öztürk S. , Akkurt M. , Hökelek T. , Yildirim İ. 
Published: January 2007

AbstractThe crystal structure of C20H16N2O2. 0.5 H2O has been determined from three dimensional X‐ray diffraction data. The crystals are monoclinic, space group C 2/c, with a = 24.491(3) Å, b =10.241(2) Å, c = 16.643(2) Å, β =126.63(1)°, V = 3350.0(9) Å3, Dcalc = 1.290 g. cm−3, Z = 8. The structure was solved by direct methods and refined by least‐squares methods to a final R = 0.0625 for 1358 observed unique reflections (F2 ⩾ 2σ(F2)].
The Electrical Degradation and Coloration in Iron Doped KTa1‐xNbxO3 Single Crystals
Authors: Guan Q. , Yin X. , Wang J. , Wei J. , Liu Y. 
Published: January 2007

AbstractThe electrical degradation and coloration experiments were investigated in Fe‐doped KTa1‐xNbxO3 crystals. The leakage currents of the crystals increase when dc voltages were applied, and a dark region moved from the anode to the cathode. Reversing the electrodes can lead to the dark region move back. The oxygen vacancies and color center defects are considered to play roles in the process.
Peculiarities of the B8‐Solid Solution Formation in Ni(Sb,Sn) and Co(Sb,Sn) Systems Studied by Mossbauer Effect Method
Authors: Vasilev E. A. , Tkachenko T. M. 
Published: January 2007

AbstractQuadrupole splitting and effective characteristic temperatures of 119Sn in Ni(Sb,Sn) and Co(Sb,Sn) solid solutions with B8‐type structure have been studied by Mossbauer Effect method. The electric field gradient at metalloid atoms was estimated in point charge model for different variants of local environment.On the basis of the comparison between experimental Quadruple Splitting values and estimated Electric Field Gradient ones it was concluded that MeII‐Sn pairs occur more often than MeII‐Sb when the amount of transition metal in ditrigonal‐dibipyramidal positions is less than 0.10.
Fibrillation potentials following spinal cord injury: Improvement with neurotrophins and exercise
Authors: Burns Anthony S. , Boyce Vanessa S. , Tessler Alan , Lemay Michel A. 
Published: January 2007

AbstractFibrillation potentials and positive sharp waves (spontaneous potentials) are the electrophysiological hallmark of denervated skeletal muscle, and their detection by intramuscular electromyography (EMG) is the clinical gold standard for diagnosing denervated skeletal muscle. Surprisingly, spontaneous potentials have been described following human and experimental spinal cord injury (SCI) in muscles innervated by spinal cord segments distal to the level of direct spinal injury. To determine whether electrophysiological abnormalities are improved by two therapeutic interventions for experimental SCI, neurotrophic factors and exercise training, we studied four representative hindlimb muscles in adult domestic short‐hair cats following complete transection of the spinal cord at T11–T12. In untreated cats, electrophysiological abnormalities persisted unchanged for 12 weeks postinjury, the longest duration studied. In contrast, fibrillations and positive sharp waves largely resolved in animals that underwent weight‐supported treadmill training or received grafts containing fibroblasts genetically modified to express brain‐derived neurotrophic factor and neurotrophin‐3. These findings suggest that neurotrophins and activity play an important role in the poorly understood phenomenon of fibrillations distal to SCI. Muscle Nerve, 2007
On the optimality of the observability inequalities for parabolic and hyperbolic systems with potentials
Authors: Duyckaerts Thomas , Zhang Xu , Zuazua Enrique 
Published: January 2007

In this paper we prove the optimality of the observability inequality for parabolic systems with potentials in even space dimensionsn⩾2. This inequality (derived by E. Fernández-Cara and the third author in the context of the scalar heat equation with potentials in any space dimension) asserts, roughly, that for small time, the total energy of solutions can be estimated from above in terms of the energy localized in a subdomain with an observability constant of the order of\mathrm{\exp }(C\|a\|_{\infty }^{2/ 3}),abeing the potential involved in the system. The problem of the optimality of the observability inequality remains open for scalar equations.The optimality is a consequence of a construction due to V.Z. Meshkov of a complex-valued bounded potentialq = q(x)in\mathbb{R}^{2}and a nontrivial solutionuof\mathrm{\Delta }u = q(x)uwith the decay property|u(x)|⩽\mathrm{\exp }(−|x|^{4/ 3}). Meshkov's construction may be generalized to any even dimension. We give an extension to odd dimensions, which gives a sharp decay rate up to some logarithmic factor and yields a weaker optimality result in odd space-dimensions.We address the same problem for the wave equation. In this case it is well known that, in space-dimensionn = 1, observability holds with a sharp constant of the order of\mathrm{\exp }(C\|a\|_{\infty }^{1/ 2}). For systems in even space dimensionsn⩾2we prove that the best constant one can expect is of the order of\mathrm{\exp }(C\|a\|_{\infty }^{2/ 3})for anyT > 0and any observation domain. Based on Carleman inequalities, we show that the positive counterpart is also true whenTis large enough and the observation is made in a neighborhood of the boundary. As in the context of the heat equation, the optimality of this estimate is open for scalar equations.We address similar questions, for both equations, with potentials involving the first order term. We also discuss issues related with the impact of the growth rates of the nonlinearities on the controllability of semilinear equations. Some other open problems are raised.
Neural Network Analyses of Infrared Spectra for Classifying Cell Wall Architectures
Authors: McCann Maureen C. , Defernez Marianne , Urbanowicz Breeanna R. , Tewari Jagdish C. , Langewisch Tiffany , Olek Anna , Wells Brian , Wilson Reginald H. , Carpita Nicholas C. 
Published: January 2007

Abstract
About 10% of plant genomes are devoted to cell wall biogenesis. Our goal is to establish methodologies that identify and classify cell wall phenotypes of mutants on a genome-wide scale. Toward this goal, we have used a model system, the elongating maize (Zea mays) coleoptile system, in which cell wall changes are well characterized, to develop a paradigm for classification of a comprehensive range of cell wall architectures altered during development, by environmental perturbation, or by mutation. Dynamic changes in cell walls of etiolated maize coleoptiles, sampled at one-half-d intervals of growth, were analyzed by chemical and enzymatic assays and Fourier transform infrared spectroscopy. The primary walls of grasses are composed of cellulose microfibrils, glucuronoarabinoxylans, and mixed-linkage (1 → 3),(1 → 4)-β-d-glucans, together with smaller amounts of glucomannans, xyloglucans, pectins, and a network of polyphenolic substances. During coleoptile development, changes in cell wall composition included a transient appearance of the (1 → 3),(1 → 4)-β-d-glucans, a gradual loss of arabinose from glucuronoarabinoxylans, and an increase in the relative proportion of cellulose. Infrared spectra reflected these dynamic changes in composition. Although infrared spectra of walls from embryonic, elongating, and senescent coleoptiles were broadly discriminated from each other by exploratory principal components analysis, neural network algorithms (both genetic and Kohonen) could correctly classify infrared spectra from cell walls harvested from individuals differing at one-half-d interval of growth. We tested the predictive capabilities of the model with a maize inbred line, Wisconsin 22, and found it to be accurate in classifying cell walls representing developmental stage. The ability of artificial neural networks to classify infrared spectra from cell walls provides a means to identify many possible classes of cell wall phenotypes. This classification can be broadened to phenotypes resulting from mutations in genes encoding proteins for which a function is yet to be described.