bluuebunny/crossref_metadata_2025_split huggingface dataset:
Alternative Method for Determining the Shear Deformation Potential of the Valence Band in III‐V Semiconductor Quantum Wells
Authors: Rau G. , Klipstein P. C. , Nicopoulos V. Nikos , Johnson N. F. , Tribe W. R. 
Published: July 2007

AbstractWe present an alternative method for determining the shear deformation potential b of the valence band in III‐V semiconductors. Instead of bulk semiconductors we use quantum well structures and apply uniaxial stress perpendicular to the growth direction. Using analytical solutions we show that the first confined hole state has a pronounced and characteristic nonlinear energy shift with respect to stress. This allows the hydrostatic and shear deformation potentials a and b to be determined independently from the stress dependence of the bandgap only, which can be measured by a wider range of experimental techniques than those necessary for obtaining deformation potentials from bulk material. Measurements on a (GaAs)10/(AIAs)10 superlattice yielded a value for b which is in good agreement with recent results from bulk measurements and hence support the validity of our proposed method.
Determination of Gain and Loss Mechanisms in Semiconductor Lasers Using Pressure Techniques
Authors: O'Reilly E. P. , Jones G. , Silver M. , Adams A. R. 
Published: July 2007

AbstractBoth the gain and loss mechanisms in semiconductor lasers are determined in large part by the band structure of the laser active region and the surrounding material layers. Uniaxial stress measurements confirm the predicted variation of gain and threshold characteristics due to the incorporation of axial strain, with large tensile or compressive strain reducing the carrier and current density required to reach threshold. The combination of hydrostatic pressure measurements and band structure calculations enables identification of the dominant loss mechanisms in semiconductor lasers, identifying leakage from the active to the cladding region as the dominant loss mechanism in GaInP/AIGaInP visible lasers, and Auger recombination as the dominant loss mechanism and cause of the temperature sensitivity of long wavelength (1.3 to 1.55 μm) lasers.
Raman Scattering and Photoluminescence of Mn‐Doped Nanocrystals of ZnS Formed by the Pressure Cycle Method
Authors: Kobayashi M. , Iwata H. , Hanzawa H. , Yoshiue T. , Endo S. 
Published: July 2007

AbstractZn1−xMnxS (x = 0.043) undergoes a pressure‐induced phase transition at 14.1 GPa from the zincblende to the NaCl structure. We have measured Raman scattering for a pressure released sample after compressing up to 16 GPa in a diamond anvil cell. The LO peak has shifted to lower energy compared with a virgin sample, which indicates the quantum confinement of LO phonons in nanocrystals formed by the pressure cycle. The diameter of nanocrystals is estimated to be 8 nm according to the spatial correlation model, in agreement with the value estimated from X‐ray diffraction data. The observed decrease of photoluminescence intensity and the shortening of the decay time for the 4T1 → 6A1 transition within the Mn2+ ion are ascribed to the formation of nonradiative centers in the nanocrystals.
High‐pressure Raman Scattering and Optical Absorption Study of β‐GeS2
Authors: Popović Z. V. , Holtz M. , Reimann K. , Syassen K. 
Published: July 2007

AbstractWe have measured Raman scattering and optical absorption spectra of layered β‐GeS2 at pressures up to 15GPa. Frequency shifts of selected internal bond bending and stretching modes are discussed, and three external (rigid‐layer) modes are identified. Changes in the Raman spectra near 9 GPa clearly indicate a structural phase transition. The pressureinduced red shift of the optical absorption edge shows a change in slope at about the same pressure. Samples turn opaque near 15 GPa, indicating a second transition to a disordered phase. The pressureinduced phase changes are reversible.
Kinetic Features of Crystallization of Cubic Boron Nitride Single Crystals in the BNLiH(N,Se) System
Authors: Gameza L. M. , Shipilo V. B. , Savchuk V. A. 
Published: July 2007

AbstractWe have investigated the effect of selenium additions on the kinetics of the degree and rate of hexagonal to cubic BN conversion (hBN → cBN) as well as on the linear rate of the cBN crystal growth in the BN‐LiH(N,Se) system. Experiments were performed in the temperature range 1940 to 2080 K at a pressure of 4.3 GPa. For 0.5, 1.0, and 3.0 mass% selenium addition, the activation energy of the process of cBN formation is found to be 45.0, 39.0, and 34.0 kJ/mol, respectively. The resulting crystals showed n‐type conduction with a resistivity of 105 to 108 Ω cm and a dislocation density of 105 to 103 cm−2.
Emission of a Half‐Rectangular Dislocation Loop from a Mode I Crack Tip
Authors: Zhang Tong‐Yi 
Published: July 2007

AbstractEnergies for emission of a half‐rectangular dislocation loop from a mode I crack tip are investigated in the present work. Optimum aspect ratio of length to width of the half‐rectangular loop, critical dislocation size, and activation energy for dislocation emission are calculated by determining the saddle point of the total energy profile as a function of the length and the width. The activation energy obtained for the half‐rectangular loop is less than a quarter of that obtained for a semicircu‐ lar loop. The effects of the self‐energy correction parameter and the radius of the dislocation core on the activation energy are also reported here.
Modeling of Threading Dislocation Density Reduction in Heteroepitaxial Layers I. Geometry and Crystallography
Authors: Romanov A. E. , Pompe W. , Beltz G. , Speck J. S. 
Published: July 2007

AbstractThe geometry of threading dislocations (TDs), non‐equilibrium defects that are generated as a result of stress relaxation in thin films, is considered in order to provide a basis for their reduction behavior during heteroepitaxial growth. This paper, the first of a two‐part series, discusses the geometric possibility for reactions between TDs as a result of film growth. It is demonstrated that effective TD motion and reaction are responsible for their overall reduction. The reactions become possible if pairs of TDs come within a critical distance: γA for annihilation reactions, γF for fusion reactions, and γS for scattering reactions. The model is used to explain the experimentally observed l/h (h is the film thickness) dependence on TD density. The crystallographic consideration of TDs in the case of (001) growth of f.c.c. semiconductor films is presented and possible reactions between TDs in this case are analyzed.
First Principle Calculations of the Basic Thermodynamic Properties of Titanium and Vanadium Nitrides
Authors: Milevskii A. G. , Lisenko A. A. , Morozov M. M. , Zhurakovskii E. A. 
Published: July 2007

AbstractIn this paper we present the results of volume and thermal dependent energy calculations for a binary system using density functional theory based on APW electronic structure calculations as well as the Debye model for accounting for lattice vibrations. Our APW calculations of ground state equilibrium properties of TiN and VN are close to those obtained by the LMTO method but are in better agreement with experiment. By minimization of the resulting free energy with respect to volume we obtained temperature dependent lattice parameters and coefficients of thermal expansion.
Mobility of a Two‐Dimensional Hole Gas in a SiSiGeSi Quantum Well Based on a New Wave Function
Authors: Kundu S. , Raychaudhuri S. , Ghosh S. 
Published: July 2007

AbstractThe distribution of two‐dimensional holes in a SiGe quantum well (QW) depends significantly on the well width, as it is nearly sinusoidal for very narrow wells and becomes of double heterojunction type for wider wells. In this paper a new wave function has been proposed to account for the distribution at all well widths. The temperature variation of mobility has been studied along with the well width dependence of the mobility. The relative contributions of different scattering mechanisms have been studied. The effect of screening has also been included. The results when compared with mobilities computed for other standard wave functions agree well with the sinusoidal wave function for very thin wells and with the Fang‐Howard wave function for much wider wells. For intermediate well widths, the mobilities based on the new wave function show better agreement with experimental data than for the other two wave functions that are, respectively, valid only at the two extremes.
Electronic Structure of Metal Azides
Authors: Gordienko A. B. , Zhuravlev Yu. N. , Poplavnoi A. S. 
Published: July 2007

AbstractCalculations of energy band structure, density of states, electronic density, and chemical bond parameters for a series of MeN3, where Me  Na, K, Rb, Cs, Ag, Tl have been given. The density functional theory and pseudopotential technique in mixed basis have been used. The valence band has been shown to be essentially formed from azideion states for alkali metal azides. The conduction band contains two subbands separated by a band gap. The first band is responsible for the anion states, while the second one is responsible for the cation ones. Silver d‐states and thallium s‐states have been seen to change greatly the structure of both the valence and conduction bands for AgN3 and TlN3, viz. the upper valence bands are of a mixed anion‐cation nature, the conduction band bottom consists of cation states, but the anion contributions increase when the energy grows.
Calculated Crystal Field Parameters in RCo5 and RNi5 Systems
Authors: Novák P. 
Published: July 2007

AbstractWe report an ab‐initio calculation of the crystal field parameters Blm of rare earth (R) ions in intermetallic RM5 compounds (M  Ni, Co). The parameter with given l and m is calculated by integrating the product of the spherical (l,m) component of the crystal potential and the radial density of 4f electrons of the rare earth ion. The potential results from the self‐consistent calculation of the electronic structure of RM5 using the full potential LAPW method, while the density of the 4f electrons is taken from an LSDA‐SIC atomic calculation, in which the electron occupation numbers are fxed to their values in the corresponding RM5 system. The sensitivity of results to the parameters which enter the calculation is tested.
Inelastic Electron Interactions in the Energy Range 50 eV to 10 keV in Insulators: Alkali Halides and Metal Oxides
Authors: Akkerman A. , Boutboul T. , Breskin A. , Chechik R. , Gibrekhterman A. , Lifshitz Y. 
Published: July 2007

AbstractCalculations of electron inelastic mean free paths and stopping powers for several alkali halides (KF, KCl, KBr, and KI) and metal oxides (BeO, MgO, SiO2, and Al2O3) have been performed in the 50 eV to 10 keV energy range. The complex dielectric formalism, improved to include the energy gap, was used for estimating the valence part of the transport characteristics, whereas the part related to electron‐core interactions was evaluated according to Gryzinski's theory. An extended comparison of these calculations with the available experimental data as well as with other theoretical predictions is presented. Trends of the energy dependence of the inelastic mean free path and stopping power in alkali halides are studied. The role of the plasmon deexcitation process as a source for low‐energy electrons in secondary electron emission spectra is discussed. The presented data can be used in Monte‐Carlo simulations of electron transport in the considered materials.
Study of Balance Equations for Hot‐Electron Transport in an Arbitrary Energy Band (II))
Authors: Wu Hang‐Sheng , Wu M. W. , Huang Xian‐Xiang 
Published: July 2007

AbstractIn the present paper it is pointed out that the frictional forces and the energy transfer rate appearing in the balance equations for the hot‐electron transport problem all depend explicitly on the electric field. Their expressions are rederived with the electric field dependent corrections to O(E1) included. These expressions are identical with those of Lei‐Ting except that in the latter the electron energy appearing in the delta function and the distribution function are replaced by coresponding new‐defined field dependent ones. The significance of such substitutions for obtaining the correct result is discussed in detail.
Dielectric Investigation of α‐LiIO3
Authors: Jacobsohn L. G. , Lunkenheimer P. , Laeri F. , Vietze U. , Loidl A. 
Published: July 2007

AbstractThe dielectric properties of hexagonal lithium iodate (α‐LiIO3) single crystals have been studied at frequencies 10−2 Hz⩽v⩽109 Hz and temperatures 100K ⩽ T ⩽ 500 K. Pure and iron doped crystals were investigated. Below approximately 10 kHz, the electric response of the LiIO3 crystals is almost entirely dominated by the accumulation of space charges at the electrodes. At least two types of ionic charge carriers seem to contribute to the observed conductivity. In addition, dc measurements revealed that electronic conductivity cannot be neglected in α‐LiIO3. At frequencies above some 100 kHz the real part of the conductivity σ follows a power law σ′ ∼ vs with relatively small exponents s for both, the doped and the undoped compounds. The temperature dependence of σ in this region behaves thermally activated with two energy barriers. The high‐frequency limit of the dielectric constant ε∞ has been determined. In addition, the data have been evaluated using the modulus formalism.
Screening of active ingredients of herbal medicine for interaction with CYP450 3A4
Authors: Lee S. S. , Zhang B. , He M. L. , Chang V. S. C. , Kung H. F. 
Published: July 2007

AbstractA two‐step algorithm is adopted in the screening of herbal species which possess significant inhibitory effects on cytochrome P450 3A4 (CYP450 3A4). The algorithm comprises an initial stage of high throughput screening with Herbochip®for the identification of herbal fractions that exhibit interactions with CYP450 3A4. Fifty commonly used TCM species were screened with seven showing a positive signal reflecting interaction. In the inhibition assays that followed, six of the seven species gave a signal.Sophora flavescensstood out as it gave the highest number of wells with a response, the highest maximum index was 0.96, and the median index was 0.55. The selection of TCM species with inhibitory effects on CYP450 carries the potential role of its use to boost the effects of known therapeutic agents, a mechanism that has been exploited in the design of regimens for the treatment of HIV infection. Copyright © 2007 John Wiley & Sons, Ltd.
Protective effect of Lycium barbarum on doxorubicin‐induced cardiotoxicity
Authors: Xin Yan‐Fei , Zhou Guo‐Liang , Deng Zu‐Yue , Chen Yun‐Xiang , Wu Yue‐Guo , Xu Pan‐Sheng , Xuan Yao‐Xian 
Published: July 2007

AbstractThe objective of this work was to explore the hypothesis that Lycium barbarum (LB) may be protective against doxorubicin (DOX)‐induced cardiotoxicity through antioxidant‐mediated mechanisms. Male SD rats were treated with distilled water or a water extract of LB (25 mg/kg, p.o.) daily and saline or DOX (5 mg/kg, i.v.) weekly for 3 weeks. Mortality, general condition and body weight were observed during the experiment. DOX‐induced cardiotoxicity was assessed by electrocardiograph, heart antioxidant activity, serum levels of creatine kinase (CK) and aspartate aminotransferase (AST) and histopathological change. The DOX group showed higher mortality (38%) and worse physical characterization. Moreover, DOX caused myocardial injury manifested by arrhythmias and conduction abnormalities in ECG (increased QT and ST intervals and ST elevation), a decrease of heart antioxidant activity, an increase of serum CK and AST, as well as myocardial lesions. Pretreatment with LB significantly prevented the loss of myofibrils and improved the heart function of the DOX‐treated rats as evidenced from lower mortality (13%), normalization of antioxidative activity and serum AST and CK, as well as improving arrhythmias and conduction abnormalities. These results suggested that LB elicited a typical cardioprotective effect on DOX‐related oxidative stress. Furthermore, in vitro cytotoxic study showed the antitumor activity of DOX was not compromised by LB. It is possible that LB could be used as a useful adjunct in combination with DOX chemotherapy. Copyright © 2007 John Wiley & Sons, Ltd.
A class of optimal solutions of the matrix Nehari‐extension problem
Authors: Halikias G. D. 
Published: July 2007

AbstractThe degrees of freedom that are available in the solution set of the multivariable Nehari‐extension problem are used to minimize an 𝒢2‐type cost and an ‘entropy‐like’ cost associated with the smaller singular values of the (optimal) error system. The optimal extensions are constructed via a diagonalization procedure based on a (normalized) Schmidt pair of the Hankel operator induced by the function which is approximated.
Allowable parameter variations and robustness recovery in LQG regulators
Authors: Kim Sang Woo , Kwon Wook Hyun , Lee Joon Hwa 
Published: July 2007

AbstractIn this paper, the bounds of allowable parameter variations in the LQG regulator for fixed weighting matrices are obtained and the asymptotic properties of these bounds with respect to weighting matrices are analysed. It is shown that the guaranteed bounds of allowable parameter variations, which are independent of weighting matrices, are often small but not necessarily small under some conditions. It is also shown that under some conditions, the allowable bounds of the LQG regulator can become as large as those of the LQ regulator. In addition, a loop transfer recovery method for perturbed systems is derived under which the LQG regulator may possess the same robustness as the LQ regulator. Examples are given to validate these results.
H∞ estimation for discrete‐time linear uncertain systems
Authors: Xie Lihua , de Souza Carlos E. , Fu Minyue 
Published: July 2007

AbstractThis paper is concerned with the problem of H∞ estimation for linear discrete‐time systems with time‐varying norm‐bounded parameter uncertainty in both the state and output matrices. We design an estimator such that the estimation error dynamics is quadratically stable and the induced operator norm of the mapping from noise to estimation error is kept within a prescribed bound for all admissible uncertainties. A Riccati equation approach is proposed to solve the estimation problem and it is shown that the solution is related to two algebraic Riccati equations.
A factorization principle for stabilization of linear control systems
Authors: Ball Joseph A. , Helton J. William , Verma Madanpal 
Published: July 2007

AbstractBy introducing a fictitious signal y0 if necessary we define a transform magnified image which generalizes the passage from the scattering to the chain formalism in circuit theory. Given a factorization 𝒫˜ = ⊖R of 𝒫˜ where R is a block matrix function with a certain key block equal to a minimal phase (or outer) matrix function, we show that a given compensator u = Ky is internally stabilizing for the system 𝒫 if and only if a related compensator K′ is stabilizing for ⊖. Factorizations 𝒫˜ = ⊖R with ⊖ having a certain block upper triangular form lead to an alternative derivation of the Youla parametrization of stabilizing compensators. Factorizations with ⊖ equal to a J‐inner matrix function (in a precise weak sense) lead to a parametrization of all solutions K of the H∞ problem associated with 𝒫. This gives a new solution of the H∞ problem completely in the transfer function domain. Computation of the needed factorization 𝒫˜ = ⊖R in terms of a state‐space realization of 𝒫 leads to the state‐space formulas for the solution of the H∞ problem recently obtained in the literature.
Design of minimax controllers for linear systems with non‐zero initial states under specified information structures
Authors: Didinsky Garry , Başar Tamer 
Published: July 2007

AbstractIn this paper, we obtain the solution to the discrete‐time, linear‐quadratic, finite‐horizon disturbance rejection problem, withhard boundson the disturbance and with a known or an unknown non‐zero initial state. It is shown that there exist two regions in the space of initial conditions: one where a pure‐strategy saddle point exists, and the other where no pure‐strategy saddle point exists. In the latter region, the structure of the minimax controller is fixed throughout, and a saddle point exists in the class of mixed policies. The paper also develops a general algorithm for the construction of such saddle points under different information structures, and illustrates this algorithm on a numerical example.
Stability margins of singular perturbation systems via state‐feedback control
Authors: Cheng Chiu‐Pin , Li Tzuu‐Hseng S. , Sun York‐Yih 
Published: July 2007

AbstractThe gain and phase margins of singular perturbation systems are analysed under unmodelled high‐frequency dynamics control, composite control, and the original full‐order linear quadratic (LQ) control. The analysis is on the basis that there is a good relation between the minimum singular value of return difference transfer matrix and the stability margins. We begin with the examination of stability margins of subsystems and then show that state‐feedback control design of subsystems could preserve gain and phase margins for the original full‐order singularly perturbed system if the singular perturbation parameter epsiv; is sufficiently small.The effectiveness of ε on stability margins is formulated and determined. It is found that the effectiveness can be evaluated by a simple method. Two examples are exploited to illustrate the analytic results.
Robust system‐parameter identification: The influence functional approach
Authors: Asato Michael S. , Poor H. Vincent 
Published: July 2007

AbstractThe influence functional, developed by Martin and Yohai, is an asymptotic robustness measure of a parameter estimate's sensitivity to the infinitesimal occurrence of correlated outlier contamination of a measurement sequence. Here, the usefulness of the influence functional as a tool for characterizing estimator robustness in system parameter identification is explored. In particular, this utility is illustrated by examining the influence functional as a measure of robustness for the choice of the error‐shaping function in the correlation or instrumental variables approach to system parameter identification.
Optimal H2 and H∞ fixed‐order dynamic compensation using canonical forms
Authors: Byrns Edward V. , Sweriduk Gregory D. , Calise Anthony J. 
Published: July 2007

AbstractThis paper presents a technique for designing fixed order dynamic compensators in controller canonical form which are robust to both structured and unstructured uncertainty. The formulation uses an approach which combines an H2 and H∞ optimization process. Specifically, a quadratic performance index is minimized subject to a constraint on the H∞ norm of the closed loop transfer function from disturbances to controlled outputs. This provides robustness to unstructured uncertainty. To provide robustness to structured uncertainty, an upper bound is computed for the worst case parameter variations, and it is then included in the derivation of the optimality conditions. A robust controller for a jetfoil boat is used to demonstrate this design technique.For the specific case of no structured uncertainty, the results of this approach using the canonical form compensator are analytically related to the previously published results for a fixed‐order dynamic compensator. It is demonstrated that the use of the canonical form greatly simplifies the system of necessary conditions.