bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polarization Reversal for Electromagnetic Waves in Semiconductors
Authors: Holter Ø. , Leer E. 
Published: July 2007

AbstractExtrinsic semiconductors have three charged species, and hence satisfy the requirement for polarization reversal of the two electromagnetic wave modes. This effect is investigated by using cold plasma wave theory in the limit of small collision frequencies. It is shown that polarization reversal is possible for frequencies less than the hole cyclotron frequency in n‐type materials, and for frequencies above the electron cyclotron frequency in p‐type materials, when the angle between the magnetic field and the wave vector exceeds a certain critical value. For this angle the modes are critically coupled. As a particular example for application an n‐InSb sample is considered.
Plastic Deformation and Creep of Sodium Chloride Crystals at Liquid Helium Temperatures
Authors: Tesh J. R. , Whitworth R. W. 
Published: July 2007

AbstractThe plastic deformation of single crystals of NaCl in uniaxial compression was studied between 1.5 and 4.2 °K and also at 77 °K. The flow stress increased rapidly with decreasing temperature, being about 2.3 kp mm−2 at 2 °K. Flow occurred by the widening of dislocation bands, and considerable amounts of transient creep were observed. Analysis of the creep constant, stress dependence of strain rate, and temperature dependence of flow stress lead to the conclusion that the deformation can be explained in terms of the thermally activated motion of dislocations.
Plastic Deformation of Corundum Single Crystals
Authors: Klassen‐Neklyudova M. V. , Govorkov V. G. , Urusovskaya A. A. , Voinova N. N. , Kozlovskaya E. P. 
Published: July 2007

AbstractThe stress‐strain curves and the defect structure of corundum single crystals (sapphire and ruby) were studied. The influence of impurity (Cr) presence, crystallographic orientation, temperature, and deformation rate was investigated. Chromium makes corundum harder and causes a yield point phenomenon. The yield point was also increased by the transition from 60° to 90° orientation of the specimens, by lowering the temperature, and by an increase in the deformation rate. In 60°‐specimens the deformation occurs by means of gliding on basal planes in 〈1120〉 and 〈1010〉 directions. In 90°‐samples beside this one gliding in (1010), (1011), (2021) and (2243) is found.
The Electronic Structure of 3d Transition Metals
Authors: Galperin F. M. , Gavrilov N. A. 
Published: July 2007

AbstractIn the present paper each point of the lattice is assumed to be surrounded by a neutral sphere of the radius R < rs for pure ferromagnetic metals and R > rs for non‐ferromagnetic 3d‐metals while in the Stern method the neutral sphere is the Wigner‐Seitz sphere of radius rs. The atom in the sphere is taken as characterized by the starting electronic configuration depending on the type of the crystal structure: 3dC−24s2 for f.c.c. (Ni and Sc), 3dC−14s1 for h.c.p. (Co and Ti), 3dC for b.c.c. (Fe, Cr, V. α‐Mn), C being the number of electrons out of the argon shell of the neutral atom in the ground state. Only one of all the lattice points is surrounded by the so‐called central sphere; the atom in it interacts with its nearest neighbours when R < rs as also with next‐nearest neighbours, when R > rs. Owing to this interaction the starting electronic configuration mentioned is transformed into an electronic configuration actually realized in metals. The electronic structure calculated on this basis is in agreement with that calculated by some other methods.
Spatial Distribution of Magnetic Moments
Authors: Galperin F. M. , Alpaev Yu. A. , Kizhaev F. G. 
Published: July 2007

AbstractAn attempt is made to calculate the various contributions to the atomic magnetic moment and to express them in terms of the electronic structure parameters. In a previous paper the authors consider the metal as consisting of neutral atoms of one and the same kind while in the present one two kinds of neutral atoms in a crystal are considered and a calculation is made of the configurational interaction between them, the spin polarization of hybridized unpaired conduction electrons, and the effect of this polarization on the electronic structure.
Parametric Instability and Resonance Effects in Semiconductors
Authors: Karageorgy‐Alkalaev P. M. , Leiderman A. Yu. 
Published: July 2007

AbstractThe possibility of distortion of stable distributions of non‐equilibrium carriers in semiconductors (dielectrics) due to the dependence of dielectric permittivity and mobility on the electric field strength or filling rate of impurity centres is considered. It is shown that a semiconductor possesses resonance properties in the self‐oscillation regime.
Optical Absorption in the Visible Range of Cu0.8−xZn0.2Pdx Alloys with 0 ≦ x ≦ 0.2 at Room Temperature1)
Authors: Mamola K. , Schröder K. 
Published: July 2007

AbstractThe optical absorptivity A of Cu0.8−xZn0.2Pdx alloys (0 ± x ± 0.2) was measured as a function of the wavelength between 250 nm < λ < 800 nm at room temperature in a vacuum system with < 10−6 Torr. A has a peak (or shoulder) close to 380 nm for x = 0.1. The alloy with x = 0.2 has a minimum at this wavelength. It is proposed that palladium impurities are responsible for virtual energy states which lead to an increase in A below 300 nm and above 500 nm. Additionally palladium in higher concentrations absorbs part of the extra electrons of zinc in the copper‐zinc matrix. This leads to the minimum of A in the alloy with 20 at% palladium.
The Effect of Pressure on Superconducting State Parameters and Transition Temperature of Simple Metal Superconductors
Authors: Rajput J. S. , Gupta A. K. 
Published: July 2007

AbstractA method is presented for the theoretical calculation of the logarithmic volume derivatives of the three superconducting state parameters, the phonon interaction parameter, the coulomb pseudopotential, and the energy renormalization parameter. The two representative cases of lead and aluminium have been studied. The initial linear drop of Tc when plotted against change in volume, which is experimentally observed fact, is theoretically confirmed.
On the Diffusion of H and D in Pd between 50 and 300 °K
Authors: Arons R. R. , Tamminga Y. , de Vries G. 
Published: July 2007

AbstractFrom 50 to 300 °K the jump rates of H and D in the β‐phase of Pd are described by the sum of two thermally activated processes. At higher temperatures the activation energy is found to be 2500 °K, whereas at low temperatures values of 1750 and 1450 °K for H and D, respectively, are obtained. The results are explained by tunneling from activated states.
General Threshold Theory of Electronic Emission from the Surface of a Metal
Authors: Brodskii A. M. , Gurevich Yu. Ya. , Levich V. G. 
Published: July 2007

AbstractA unified theory of field‐, thermo‐, and photoemission from metal surface is considered, and the general quantum‐mechanical methods for the investigation of the threshold phenomena are applied. As result the corresponding final expressions are obtained in such a form that it is possible to apply immediately the well known methods of scattering theory for their investigation. Thus, a rigorous foundation for existing formula of emission phenomena is given leading to a more exact form and to restrictions of the frames of their applicability without using any concrete model. Some explanations of the emission phenomena which by traditional theory could not be explained, are suggested. Beside this the new approach to emission phenomena permits further generalization.
The Effect of Charged Impurities on the Yield Point of Silicon
Authors: Siethoff H. 
Published: July 2007

AbstractDislocation‐free silicon single crystals heavily doped with phosphorus and boron are dynamically deformed in compression at high temperatures. Doping in the extrinsic region affects the yield point of silicon in two different ways: At high strain rates the activation energy of dislocation velocity as measured by the lower yield stress is decreased by phosphorus but is not changed by boron. At low strain rates marked deviations from this behaviour are observed. The lower yield stress becomes independent of strain rate, but still depends exponentially on deformation temperature and linearly on doping concentration. These results are interpreted on the basis of a strong short‐range electrostatic interaction between charged dislocations and oppositely charged solute atoms leading to impurity clouds around the dislocations.
Nonlocal Model Potential Calculation of Phonon Spectra of the Hexagonal Close‐Packed Metals
Authors: Eschrig H. , Wonn H. 
Published: July 2007

AbstractThe influence of nonlocality of the Heine‐Abarenkov model potential on phonon spectra is investigated. A simple approximation for the nonlocality is used to evaluate this influence. Calculations are carried out for the h.c.p.‐metals. It is shown that the usual local approximation of the potential is not valid for calculations of the phonon spectra.
ENDOR, the F‐Center Ground State, and Conduction Bands in Alkali Halide Crystals
Authors: Fowler W. B. , Kunz A. B. 
Published: July 2007

AbstractAlthough both experiment and theory indicate that the lowest conduction‐band minimum in most alkali halides is at k = 0, recent theoretical analysis by Grachev, Deigen, and Pekar of ENDOR data on the F‐center ground state suggests that in KCl and NaF the lowest minima may be away from k = 0, along the (100) direction. In this paper we discuss the problem of precise calculation of the F‐center ground state and interpretation of ENDOR data. We present the result of a calculation, based on a new local‐orbital approximation to the Hartree‐Fock equations, of the F‐center ground state in KCl. This calculation does not agree in all respects with experimental results. We present a critical analysis of the technique of Grachev et al., and show that if one uses different ENDOR data and a slightly different approach, the case for (100) minima in KCl is considerably weakened.
Surface States on Clean and on Cesium‐Covered Cleaved Silicon Surfaces
Authors: Mönch W. 
Published: July 2007

AbstractThe surface conductivity of p‐type Si crystals cleaved in UHV and covered with Cs up to a monolayer was measured. With increasing Cs coverage θ the surface conductivity, Δσ, initially decreases from the value of the clean surface and reaches the minimum at θ = 0.005. After a subsequent increase Δσ remains constant from θ = 0.015 to 0.25 and exhibits a steep increase for further coverage up to θ = 1. From these surface conductivities the positions of the Fermi level EF at the surface are calculated. At the clean surface the intrinsic level Ei lies 0.27 eV above EF and shifts with increasing θ to 0.27 eV below EF at θ = 1. From the dependence of (EF – Ei)s on Cs coverage the distribution of surface states can be calculated since the adsorbed Cs atoms are ionized, giving one electron to a Si surface state. At the clean surface there are two surface state bands, one with donor states 0.31 eV below Ei and a density of 8.5 × 1013 cm−2eV−1, and another one with acceptor states 0.13 eV below Ei, 0.05 eV wide and with a density of 5.7 × 1013 cm−2 eV−1. For each adsorbed Cs atom a new surface acceptor state is created in a band 0.1 eV above Ei and 0.03 eV wide.
On the Phonon Avalanche Generated by Spin‐Lattice Relaxation in a Bottlenecked Crystal
Authors: Böttger H. 
Published: July 2007

AbstractThe phonon avalanche phenomenon is investigated using Zubarev's density‐matrix formalism. A system of differential equations is derived which determines the time dependence of the spin and phonon temperatures. This system essentially differs from that gained from simple rate equations. The relevance of the phase‐memory time T2 for the decay of the inverted spin system is revealed.
On the Nature of X‐Centres in NaCl Crystals with Anionic Impurities
Authors: Tsal N. A. , Didyk R. I. 
Published: July 2007

AbstractThe effects of heat treatment and light on the conversion of F‐ into X‐centres have been investigated in specially treated NaCl crystals with hydroxyl impurities. The mechanism of the stimulating action of the impurity in the F → X conversion is analysed. The results of the work are treated from a viewpoint of a new model of X‐centres, according to which these centres are “quasicolloidal” formations, occurring at the initial stage of F‐centre coagulation. Suggestions are presented about the mechanism of a direct formation of quasicolloidal centres (X‐centres) in crystals under high‐dose γ‐irradiation.
Intraband Magnetic Breakdown in Tellurium
Authors: Anzin V. B. , Bresler M. S. , Farbshtein I. I. , Kosichkin Yu. V. , Veselago V. G. 
Published: July 2007

AbstractThe investigation of the Shubnikov‐de Haas effect in tellurium revealed some unusual phenomena which can be explained by an intraband magnetic breakdown of hole trajectories in k‐space close to the saddle‐point of the hole energy spectrum. These features of the magnetoresistance behaviour including, for example, the occurrence of the zeroth oscillation maximum in a magnetic field perpendicular to the trigonal axis in the case of an energy band with completely lifted spin degeneracy, are in satisfactory quantitative agreement with the existing theory of intraband magnetic breakdown.
On the Theory of the Low‐Temperature Galvanomagnetic Effects in Semiconductors in Strong Electric Fields
Authors: Kachlishvili Z. S. 
Published: July 2007

AbstractGalvanomagnetic effects have been studied by using the Boltzmann kinetic equation, when the energy of hot carriers is scattered on acoustic phonons and the momentum on statical defects. Calculations are carried out for any angle between the directions of the electric and magnetic field in the approximation of a parabolic law of dispersion and a scalar effective mass. General expressions of the galvanomagnetic characteristics were obtained both under specified current conditions and under specified electric field conditions.
Etude de la transition „Low Spin”︁‐„High Spin”︁ dans les complexes octaédriques d'ion de transition
Authors: Wajnflasz J. 
Published: July 2007

AbstractCertains complexes hexacoordonnés d'ion de transition 3d présentent une variation anormale du nombre effectif de magnétons de Bohr avec la température. Ces complexes possèdent deux états d'équilibre stable caractérisés simultanément par des rayons ioniques distincts et par des niveaux fondamentaux distants de quelques centaines de degrés Kelvin, qui appartiennent à des représentations différents. Les champs cristallins, associés à ces deux états d'équilibre, sont de part et d'Autre de Δπ, pour lequel les énergies correspondantes aux deux représentations sont égales. Un modèle d'Ising, faisant intervenir une interaction entre ions de transition voisins, permet et de rendre compte des différents comportements magnétiques de ces complexes, et de délimiter un domaine d'existence d'une transition du premier ordre entre les états „low spin”︁ et „high spin”︁.
Two‐Photon Spectroscopy in CsI and CsBr
Authors: Fröhlich D. , Staginnus B. , Onodera Y. 
Published: July 2007

AbstractTwo‐photon measurements with polarized light on CsI and CsBr are reported. A three‐band model is derived, which describes the observed polarization dependence of the two‐photon absorption for CsI.
Concentration Dependence of Internal Friction in AlMg Alloy
Authors: Belson J. , Lemercier D. , Moser P. , Vigier P. 
Published: July 2007

AbstractAn internal friction peak in a series of Al‐Mg alloys containing up to 12.1 wt% Mg has been studied at torsional frequencies in the range 0.4 to 98 Hz. The temperature at which the maximum occurred was found to vary according to the Arrhenius equation with an activation energy of 1.4 eV. The peak height was found to be proportional to C C where CAl and CMg are the atomic concentrations of Al and Mg, respectively. The peak as measured after slow furnace cooling, at 0.4 Hz, was displaced to lower temperatures as a result of quenching. The magnitude of this displacement appeared to increase with increasing Mg concentration. – The results, coupled with those of complementary electron microscopy and X‐ray lattice parameter studies, substantiate previous interpretation of the peak in 5 to 7% Mg alloys at ≈ 1 Hz as being due to Zener reordering.
Some features of the transverse thermomagnetic effect in bismuth
Authors: Gitsu D. V. , Muntyanu F. M. , Fedorko A. S. 
Published: July 2007

AbstractThe transverse Nernst‐Ettingshausen (N‐E) effect in Bi samples with different crystallographic orientation is discussed. It is found that in samples in which the temperature gradient is directed along one of the basic crystallographic directions (bisector, C2 or C3) and a non‐zero component of the magnetic field along the C2‐axis (which is assumed to be the X‐axis) is present, the value comprises mixed even terms. It is shown that the conditions for even terms in transverse N‐E effect are identical with those for odd terms in longitudinal N‐E effect [2].
Evaluation of model compounds–polypropylene film interactions by Fourier transformed infrared spectroscopy (FTIR) method
Authors: Safa Laurent , Zaki Oussama , Leprince Yamin , Feigenbaum Alexandre 
Published: July 2007

AbstractThe interactions of methyl esters, methyl ketones and aldehyde compounds with polypropylene (PP) film were investigated. PP film, placed on a glass vial, was immersed in aqueous solution containing a model flavour compound. After a determined time at 45°C, the PP film was analysed by Fourier transform infrared spectroscopy (FTIR), allowing us to follow the speed of sorption and to quantify its relative rate.  For PP films, we observed that the sorption strongly depended on the structure of sorbed molecules. For each functional group of flavour compounds, the sorption increased as the carbon chain number increased. A linear chain of 12–14 carbons favours the sorption more than a linear chain of eight carbons.  Concerning functions, the rate of sorption usually decreases from esters to ketones and to aldehydes.  High sorption was observed for flavour compounds with a low difference of solubility parameter (SP) value between the film and flavour [(δpolymer − δflavour)2 value]. Furthermore, by using the proposed thermodynamic affinity concept, represented as the contribution of three interactive molecular forces [dispersion (dd), polar (dp) and hydrogen bonding (dh)] between two SP values of film and flavour, packaging materials with high flavour preservation against sorption can be designed.  We have a good correlation between the kinetic sorption by FTIR and the SP concept. Copyright © 2007 John Wiley & Sons, Ltd.
Virtual surgery simulation for medical training using multi‐resolution organ models
Authors: Kim Jung , Choi Changmok , De Suvranu , Srinivasan Mandayam A. 
Published: July 2007

AbstractBackgroundReal‐time simulation of organ deformation is one of the biggest challenges in virtual surgery, due to the conflicting requirements of real‐time interactivity and simulation realism. In this paper we propose a method to overcome this challenge by introducing a multi‐resolution modelling technique.MethodsIn our approach a reasonably coarse global model is locally enhanced, using a mesh subdivision and smoothing algorithm. The global model is based on a discretization of the boundary integral representation of three‐dimensional deformable objects. Local refinements are provided at the tool‐tissue interaction region by a local subdivision technique.ResultsAs an example, we have developed a deformable human kidney model generated from the Visible Human Dataset, with tissue properties determined fromin vivoanimal experiments. A mixed reality laparoscopic surgical training system has been developed, using an abdominal mannequin and force feedback devices.ConclusionsThe use of precomputation and structural re‐analysis techniques results in a very rapid computation procedure. Validation of the simulator is in progress. Copyright © 2007 John Wiley & Sons, Ltd.
An online active set strategy to overcome the limitations of explicit MPC
Authors: Ferreau H. J. , Bock H. G. , Diehl M. 
Published: July 2007

AbstractNearly all algorithms for linear model predictive control (MPC) either rely on the solution of convex quadratic programs (QPs) in real time, or on an explicit precalculation of this solution for all possible problem instances. In this paper, we present an online active set strategy for the fast solution of parametric QPs arising in MPC. This strategy exploits solution information of the previous QP under the assumption that the active set does not change much from one QP to the next. Furthermore, we present a modification where the CPU time is limited in order to make it suitable for strict real‐time applications. Its performance is demonstrated with a challenging test example comprising 240 variables and 1191 inequalities, which depends on 57 parameters and is prohibitive for explicit MPC approaches. In this example, our strategy allows CPU times of well below 100 ms per QP and was about one order of magnitude faster than a standard active set QP solver. Copyright © 2007 John Wiley & Sons, Ltd.
Evaluation of environmental attitudes: Analysis and results of a scale applied to university students
Authors: Fernández‐Manzanal Rosario , Rodríguez‐Barreiro Luis , Carrasquer Jose 
Published: July 2007

AbstractOver the last few decades, environmental work has increased significantly. An important part of this has to do with attitudes. This research presents the design and validation of an environmental attitudes scale aimed at university students. Detailed information on development and validation of the scale is provided. Similarly, it presents the data derived from its application to a specimen group of students. The number of students involved in the whole research is 952. The results of the work show that a certain level of worry exists among the students regarding environmental problems, which is apparent in the need to increase environmental education and research. Some differences in environmental attitudes were also found between first year students and final year students and male and female students. These results lead us to insist on the importance of bringing about changes in the curriculum to increase environmentalism in the university. © 2007 Wiley Periodicals, Inc. Sci. Ed 91:988–1009, 2007
Item readability and science achievement in TIMSS 2003 in South Africa
Authors: Dempster Edith R. , Reddy Vijay 
Published: July 2007

AbstractThis study investigated the relationship between readability of 73 text‐only multiple‐choice questions from Trends in International Mathematics and Science Study (TIMSS) 2003 and performance of two groups of South African learners: those with limited English‐language proficiency (learners attending African schools) and those with better English‐language proficiency (learners attending non‐African schools). Both groups were exposed to the same intended curriculum, but differed with respect to the quality of teaching they received, the availability of resources, and the level of functionality of their schools. Learners from non‐African schools performed significantly better than learners from African schools. Three readability factors (sentence complexity, unfamiliar words, and long words) were analyzed. High sentence complexity resulted in random guessing in non‐African schools, and favoring an incorrect answer in African schools. Some TIMSS items have complex wording, with numerous prepositional phrases and clauses, and unclear questions. Recommendations for maximum readability and comprehensibility were not met, and these items are therefore invalid for learners with limited English‐language proficiency. Learners employ a range of strategies in attempting to answer questions that they do not understand. Overall, though, poor readability of TIMSS items does not fully account for South African learners' poor performance in TIMSS. © 2007 Wiley Periodicals, Inc. Sci. Ed 91:906–925. 2007