bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of lumbar‐epidural administration of tramadol on lower urinary tract function
Authors: Singh S.K. , Agarwal M.M. , Batra Y.K. , Kishore A.V.K. , Mandal A.K.
Published: July 2007

Aims

Intrathecal and epidural administration of µ‐agonist opioids is associated with urinary retention, a potentially serious adverse‐event. In animal studies tramadol has been found not to affect voiding function. We evaluated urodynamic effects of epidural tramadol in humans.

Methods

Fifteen adults planned for cystoscopy under local‐anesthesia underwent urodynamics (UDS) at baseline and 30 min after administration of 100 mg tramadol in lumbar‐epidural space. UDS consisted of filling cystometry, pressure‐flow study and pelvic floor electromyography (EMG). Subsequently, all underwent cystoscopy and were observed for 6 hr.

Results

After injection of tramadol, a significant rise was observed in bladder capacity (391.8 ± 179.6 ml vs. 432.7 ± 208.8 ml; P = 0.019) and compliance (60.1 ± 51.5 ml/cm H2O vs. 83.0 ± 63.0 ml/cm H2O; P = 0.011) without a significant change in filling pressure (22.5 ± 13.2 cm H2O vs. 24.1 ± 15.1 cm H2O; P = 0.576). Filling sensations were delayed significantly (P ≤ 0.05). EMG during filling phase showed a significant fall (P = 0.027). Peak flow‐rate (Qmax), average flow‐rate, postvoid residue and detrusor pressure‐at‐Qmax did not show significant change from baseline (P > 0.05). Three patients had bladder outlet obstruction which did not worsen after the injection. Guarding reflex was inhibited in seven out of 12 patients who had it at baseline (P = 0.016).

Conclusions

Epidural tramadol increases the bladder capacity and compliance and delays filling‐sensations, without ill effect on voiding. This seems true even for patients with obstructed outflow; however, due to small number of patients a definite conclusion cannot be derived. These results will guide clinician to avoid catheterization in cases where epidural tramadol is used for postoperative pain. The inhibitory effects of tramadol on EMG activity are intriguing and need further studies. Neurourol. Urodynam. © 2007 Wiley‐Liss, Inc.
Numerical study of natural convection in a cavity of high aspect ratio by using the lattice Boltzmann method
Authors: Jami Mohammed , Amraqui Samir , Mezrhab Ahmed , Abid Cherifa
Published: July 2007

A comprehensive numerical study has been conducted to investigate two‐dimensional, steady heat transfer of natural convection in a divided enclosure of high aspect ratio. The vertical walls of the enclosure are maintained at different temperatures, while the horizontal walls are adiabatics. A numerical hybrid scheme with lattice Boltzmann for fluid velocity and finite difference for the temperature is adopted. Parametric studies of the effects of aspect ratio, number and length of partitions attached to the cold wall of the enclosure on heat transfer and fluid flow have been
performed. Copyright © 2007 John Wiley & Sons, Ltd.
Alternating copolymers of electron‐rich arylamine and electron‐deficient 2,1,3‐benzothiadiazole: Synthesis, characterization and photovoltaic properties
Authors: Huo Lijun , He Chang , Han Minfang , Zhou Erjun , Li Yongfang
Published: July 2007

A series of alternating copolymers of electron‐rich arylamine and electron‐deficient 2,1,3‐benzothiadiazole (BT), PV‐BT, DP‐BT, and TP‐BT, were synthesized by Heck coupling reaction. UV–vis absorption and fluorescence spectra show that the copolymerization of electron‐rich diphenylamine (DP), triphenylamine (TP), MEH‐PV (PV), and electron‐deficient BT results in low‐bandgap conjugated polymers. Within the three copolymers of PV‐BT, DP‐BT, and TP‐BT, TP‐BT possesses the highest hole mobility of 4.68 × 10− 5 cm2/V, as determined from the space charge limited current (SCLC) model. The bulk heterojunction‐typed polymer solar cells (PSCs) were fabricated with the blend of the copolymers and PCBM as the photosensitive layer. The power conversion efficiencies (PCE) of the PSCs based on PV‐BT, DP‐BT, and TP‐BT reached 0.26%, 0.39%, and 0.52%, respectively, under the illumination of AM 1.5, 100 mW/cm2. The results indicate that TP‐BT is a promising photovoltaic polymer for PSCs. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3861–3871, 2007
2,4,6‐trichlorophenyl acrylate emulsion‐templated porous polymers (PolyHIPEs). Morphology and reactivity studies
Authors: Leber Nermina , Fay Jonathan D. B. , Cameron Neil R. , Krajnc Peter
Published: July 2007

A series of monolithic crosslinked polymers with 2,4,6‐trichlorophenyl acrylate as a reactive component was prepared by free radical polymerization of the internal phases of high internal phase emulsions (HIPEs). The volume ratio of water to oil phase (void volume; 60–90%), crosslinker type (divinylbenzene or ethylenglycol dimethacrylate) and quantity (30–50 mol %) and type of porogenic solvent (chlorobenzene, toluene, chloroform, dichloroethane) were altered to study these effects on the structure and reactivity of the monolithic polymers. The polymer supports were characterized by scanning electron microscopy (SEM), FTIR spectroscopy, elemental analysis and mercury intrusion porosimetry. SEM images revealed an open cellular structure with voids between 1 and 12 μm and window sizes between 0.3 and 3 μm. The porogen had an influence on the surface area, being larger with added porogen and the influence being highest with toluene. Adding toluene also influenced the void size, increasing the average diameter from ∼2 μm (no porogen) to ∼12 μm (added toluene). Monolithic supports were functionalized by reaction of the ester moieties with tris(2‐aminoethyl)amine derivative and by hydrolysis of the ester groups to carboxylic acids. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4043–4053, 2007
Systematic study of the fluorescence decays of amino‐coumarin dyes in polymer matrices
Authors: Felorzabihi Neda , Haley Jeffrey C. , Bardajee Ghasem R. , Winnik Mitchell A.
Published: July 2007

We measured the fluorescence decays of seven different amino‐coumarin dyes in polymer films of poly(methyl methacrylate) (PMMA), poly(styrene) (PS), and ethylene‐butene rubber (EBR); as well as in the small molecule analogs ethyl acetate and toluene. Many of the dye‐solvent and dye‐polymer combinations exhibited single exponential decays with lifetimes ranging from 2.3 to 3.9 ns. Small deviations from single exponential behavior occurred for most of the dyes in EBR. Significant deviations from single exponential behavior occurred for 7‐(diethylamino)‐2‐oxo‐2H‐1‐benzopyran‐3‐carboxylic acid (coumarin‐3) in ethyl acetate and in all polymer matrices and 2,3,6,7‐tetrahydro‐11‐oxo‐1H,5H,11H‐[1]benzopyrano[6,7,8‐ij]quinolizin‐10‐carboxylic acid (coumarin‐343) in all of the polymer matrices. Time‐resolved fluorescence spectra indicated the presence of two different excited states for coumarin‐3 and coumarin‐343 in PMMA; these spectra were qualitatively different from the time‐resolved spectra of coumarin‐3 in ethyl acetate. We rationalize these results in terms of the chemical functionalities of the various dyes. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2333–2343, 2007
Effect of Grinding Media Shapes on Breakage Parameters
Authors: Ipek Halil
Published: July 2007

In the present study, the effect of grinding media shape on breakage parameters was investigated. Balls and cylpebs were used as the grinding media. It was observed that the grinding of quartz obeyed first‐order breakage kinetics in the case of balls and cylpebs. Higher breakage rates were noted with cylpebs than with balls. Furthermore, it was found that the primary breakage distribution function is dependent on the feed size (i.e., non‐normalizable), but independent of the grinding media shape. The effect of grinding time on the product size distribution has also been investigated. Following four and ten minute grindings, cylpebs produced a relatively finer product compared to balls.
S100A8, S100A9, and the S100A8/A9 complex in circulating blood are not associated with prostate cancer risk—A re‐evaluation study
Authors: Ludwig Stefan , Stephan Carsten , Lein Michael , Loening Stefan A. , Jung Klaus
Published: July 2007

BACKGROUND

To evaluate the diagnostic performance of plasma S100A8, S100A9, and the S100A8/A9 complex as novel markers to discriminate between benign and malignant prostatic diseases as recently suggested for S100A9.

METHODS

The study included 90 prostate cancer (PCa) patients (pN0M0, n = 50; pN1M0, n = 27; M1, n = 13), 50 controls without PCa, and six patients within 72 hr after radical prostatectomy for repeated measurements. The S100 proteins were analyzed with specific ELISAs. Comparisons were made to the prostate‐specific antigen (tPSA) and the ratio of free to tPSA (%fPSA).

RESULTS

The plasma concentrations of the S100 proteins in controls had either significantly higher values (S100A8; P = 0.020) or the tendency to higher values compared with the results in PCa patients. Differences between the three PCa groups were almost negligible. No correlation could be found between S100 protein levels and PSA concentration (rs = −0.110 to 0.433, P = 0.317–0.433) or prostate volume (rs = −0.038 to 0.018, P = 0.676–0.844). Tumor stage and tumor grade had no observed effect on S100 protein concentrations. After prostatectomy, there were discordant elimination kinetics for PSA and the S100 proteins, as the S100 proteins partially increased while PSA continuously decreased. Analyses of receiver‐operating curves showed that, compared with PSA, S100A8, S100A9, and S100A8/A9 did not improve the differentiation between patients with and without PCa, while the discrimination ability was significantly lower than that of %fPSA.

CONCLUSIONS

Our re‐evaluation study showed that S100A8, S100A9, and the complex S100A8/A9 were less indicative than %fPSA and that they are not suitable to replace PSA. Prostate 67: 1301–1307, 2007. © 2007 Wiley‐Liss, Inc.
The Right Medicine –a new manifesto from the drug industry
Authors: Chaplin Steve
Published: July 2007

Steve Chaplin analyses the ABPI's recent manifesto that argues the case for patients having earlier access to new products. Copyright © 2007 Wiley Interface Ltd
Photostructural transformations in amorphous chalcogenide semiconductors
Authors: Shpotyuk O. I.
Published: July 2007

The mechanism of photoinduced structural transformations in amorphous As2S3 is studied with the differential IR Fourier spectroscopy technique in the 400 to 100 cm−1 region. It is established that the irreversible photostructural effect observed in freshly evaporated thin films is accompanied by switching of homopolar chemical bonds into heteropolar ones. The stage of reversible photodarkening is realized in a‐As2S3 samples after a first cycle of photoexposure and thermoannealing. The corresponding destruction‐polymerization reaction is opposite to that obtained for irreversible changes. The whole scheme of photo‐ and thermoinduced structural transformations in a‐As2S3 is presented as a multicyclic process of coordination defect formation and annihilation.
Application of a model of interacting atomic chains for the description of edge dislocations
Authors: Landu A. I.
Published: July 2007

An extension of a previous work is presented in which a theoretical model of interacting atomic chains (IACs) was proposed which represents a multi‐dimensional (two‐ or three‐dimensional) generalization of the classical Frenkel‐Kontorova (discrete sine‐Gordon) model. The previous paper considered the application of the IACs model to the description of the crowdion in anisotropic crystals. Now we prove that this model can be used for computer simulations of edge dislocations. The computer calculated data agree well with analytical results of elasticity theory. The IACs model is compared to other theoretical models proposed in the literature to describe dislocations in the crystal.
Intersubband coulomb scattering effecton high‐field hot‐electron transport in a quantum wire
Authors: Wu M. W. , Yu Z. G. , Lei X. L.
Published: July 2007

Hot‐electron transport properties of AlxGa1−xAs/GaAs quantum wires under high electric fields are studied by means of the balance‐equation approach using a model with multiple species of carriers. Each transverse subband is assumed to have its own electron temperature, Fermi level, and mean drift velocity differing from other nondegenerate subbands. The intersubband Coulomb interactions are taken into account perturbatively for the first time together with acoustic and polar optic phonon scatterings in the numerical calculation. Our calculation shows that although the electron temperatures, Fermi levels, and drift velocities of different subbands differ markedly from each other, the overall average drift velocity and the resultant nonlinear mobility are very close to those predicted by the conventional model assuming single species of carriers in the multisubband quantum wire system.
Computer Simulation of Point Defects at Finite Temperatures
Authors: Monti A. M.
Published: July 2007

A self‐consistent calculation method based on conjugate gradients is applied to obtain the atomic structure and thermodynamic properties of microstructural defects in solids at finite temperatures. The lattice free energy, described in the local harmonic approximation, consists of two contributions: static and vibrational. The former depends on the atomic coordinates, which change with thermal expansion. The latter explicitly depends on temperature and frequencies of the normal modes. Frequencies, obtained in an Einstein‐type approximation, are implicit functions of atomic coordinates, therefore they may also change with thermal expansion. The formation free energy for self‐interstitials and vacancy‐type defects is calculated for Cu over the broad temperature range 0 to 1200 K. A remarkable decrease of the formation free energy with temperature increase is observed. Such decrease is near 20% for vacancy‐type defects and 35% for self‐interstitials, over the whole temperature range.
Electronic and Crystal Structure of the ZrCu Intermetallic Compound Close to the Point of Structural Transformation
Authors: Zhalko‐Titarenko A. V. , Yevlashina M. L. , Antonov V. N. , Yavorskii B. Yu. , Koval Yu. N. , Firstov G. S.
Published: July 2007

It is found that cooling of the B2 high‐temperature phase of ZrCu above the martensitic transition (MT) point is not accompanied by essential changes of its electronic structure. MT in ZrCu is realized generally by the formation of two monoclinic martensites with positive volume effect. The electronic structure of the B2 phase of ZrCu demonstrates a sharp peak of the electron density of states just above the Fermi level, which plays a stabilization role related to the shear deformation above MT. This stabilization effect rapidly weakens on cooling and can be the possible origin of the lattice instability of the high‐temperature B2 phase of the ZrCu intermetallic compound.
The Energy States of Excitons in a Harmonic Quantum Dot
Authors: El‐Said M.
Published: July 2007

The eigenenergies of low‐lying states of excitons in a quantum dot with a harmonic confining potential are obtained by solving the effective‐mass Hamiltonian using the shifted 1/N expansion method. The ground state binding energy is in excellent agreement with previous results.
Dominant Traps in Liquid Phase Epitaxial GaAs Studied by Controlled Doping with Indium and Antimony
Authors: Mallik K. , Dhar S.
Published: July 2007

Photocapacitance measurements in the photon energy range of 0.64 to 1.27 eV are done on GaAs layers grown by liquid phase epitaxy (LPE) and doped with varying amounts of indium (In) and antimony (Sb). Two hole traps with optical ionization energies of 0.65 and 0.79 eV are revealed in the material which are assumed to be two levels associated with the hole trap B reported in the literature. In addition, the hole trap A, usually found in LPE GaAs is also detected here by optical deep level transient spectroscopy (ODLTS) technique. The results of trap density measurements, as functions of isoelectronic doping concentration, indicate that VGa is an active constituent of the hole traps in LPE GaAs. The concentration of the 0.79 eV trap is found to be reduced in the material with high concentration of Sb. The analysis of photocapitance data using the existing theoretical models indicates the presence of an electron trap with activation energy of 0.75 eV in the heavily Sb‐doped material. This trap may be identified with the second charge state of the SbGa electron trap, obtained previously in bulk and metalorganic vapor phase epitaxial GaAs doped with Sb. The sharp reduction of the 0.79 eV hole trap density in Sb‐doped materials is explained by assuming the complex GaAsV, as its source.
Phonons in F.C.C. Thorium
Authors: Verma M. L. , Rathore R. P. S.
Published: July 2007

The generalized form of the exponential potential is suitably extended to account for a) a realistic realization of interactions at small separations, b) embodying three‐body and electronic effects into the interaction through the parameters n and m, respectively, in an alternative and simpler form, c) a model free from the usual fitting procedure. The efficacy of the potential known as extended generalized exponential potential (EGEP) so developed is employed to compute the phonon dispersion in thorium. The predictions show good agreement with experimental findings.
Electromagnetic Properties of a Type‐II Superconducting Rotating Cylinder
Authors: Saif A. G. , Refai T. F. , El‐Sabagh M. A.
Published: July 2007

The electromagnetic field distributions and solutions for an infinitely long superconducting cylinder rotating about its axis and placed parallel to an infinitely long normal conducting wire carrying an alternating current are obtained. The propagation behavior of the fields within the cylinder are investigated in terms of the propagation constant as a function of the London penetration depth. The power loss and the torque on the cylindrical surface are calculated. Satisfactory agreement with previous results is achieved.
Amorphization of a Disordered Ferrimagnetic Alloy
Authors: Kaneyoshi T.
Published: July 2007

The effects of amorphization on the resultant magnetization in a disordered ferrimagnetic alloy consisting of spin‐1/2 and spin‐3/2 atoms are discussed by the use of mean‐field theory. A number of interesting phenomena, such as the magnetization curves not predicted by the Néel theory, are obtained from the amorphization process.
Angle‐Dependent Scattering at Interfaces in Magnetic Multilayers
Authors: Gu R. Y. , Sheng L. , Xing D. Y. , Liu M.
Published: July 2007

An extended quasiclassical model with angle‐dependent transmission coeficients at interfaces is used to give a more realistic picture of transport processes which take place in Fe/Cr multilayers. Each Fe/Cr interface is considered as a thin region where Fe and Cr are mixed, its effective transmission coefficients are derived. Calculations of resistivities and magnetoresistance (MR) show that the new treatment of interfaces can enhance the contribution of interfaces to the MR and, in order to fit the experimental results for the MR, requires mean free paths which are closer to their real values estimated from resistivity measurements.
Theory of Twofold Coordinated Silicon and Germanium Atoms in Solid Silicon Dioxide
Authors: Sokolov V. O. , Sulimov V. B.
Published: July 2007

Computer simulation of twofold coordinated silicon and germanium atoms in solid silicon dioxide is performed in a cluster approach with various boundary conditions with the help of the quantumchemical MO method MNDO. Optical absorption and luminescence in the twofold coordinated atoms are found to disagree with those of oxygen‐deficient centres in solid silicon dioxide. It is concluded that the twofold coordinated atoms are no good models of oxygen‐deficient centres.
Interactive Kinetics in Thermoluminescence (TL) and Its Effect on Glow Curves and Their Growth as a Function of Dose
Authors: Sunta C. M. , Kulkarni R. N. , Yoshimura E. M. , Mol A. W. , Piters T. M. , Okuno E.
Published: July 2007

Glow curve calculations are presented for a system of interactive traps in which the deep trap population is an order of magnitude greater than that of the active TL traps. It is shown that the glow peak exhibits a first‐order type of kinetic behaviour even when recombination does not predominate over retrapping. Under most of the dose ranges it is the recapture by the deep traps which is responsible for this kinetic behaviour. The likely reason for the apparent dominance of first‐order kinetics appears to be the interaction between the active TL traps and the deep traps. Another important consequence of interactive kinetics is that the growth of TL intensity with dose becomes supralinear. The interactive nature of the traps thus provides an interpretation not only for the kinetic behaviour of the glow peaks but explains also their supralinearity.
Electron Transport in Vapor‐Deposited Layers of 2‐Methyl‐2‐Pentyl‐1,3‐Bis(Dicyanomethylene)Indane
Authors: Borsenberger P. M. , Magin E. H. , van der Auweraer M. , de Schryver F. C.
Published: July 2007

Electron mobjlities are measured in vapor‐deposited amorphous layers of 2‐methyl‐2‐pentyl‐1, 3‐ bis(dicyanomethylene)indane, a highly polar acceptor compound with a dipole moment of 3.9 D. The results are described within the framework of a formalism based on disorder, due to Bässler and coworkers. The parameters of the formalism are σ, the variance of the hopping site energies, μ0 a prefactor mobility, and Σ, the degree of positional disorder. Experimental values of σ, μ0, and Σ are 0.112 eV, 1.6 × 10−3cm2/Vs, and 1.6. The variance of site energies can be described by a model based on dipolar disorder. A comparison of the prefactor mobility with literature values for vapor‐deposited acceptor glasses suggests that the prefactor is dependent on dipole moment, decreasing with increasing moment. The degree of positional disorder is similar to that observed in a wide range of vapor‐deposited molecular glasses and attributed to packing constraints.
Matching of a Bent Step‐Index Single‐Mode Fiber by a Modal Equivalent Slab Waveguide Structure
Authors: Haubenreisser W. , Ecke W. , Schröter S. , Schwotzer G. , Willsch R.
Published: July 2007

A novel procedure of matching the modal properties of a bent step‐index single‐mode fiber (BSSF) by the ones of an equivalent slab waveguide (ESW) structure is presented. On applying this procedure the actual BSSF structure is modelled in the first step by an equivalent straight anisotropic single‐mode fiber (SASF) and in the second step this SASF structure is modally matched by an ESW structure. It is shown that for given BSSF (or SASF) input parameters only the derived ESW parameters can describe the modal features (birefringence, cut‐off thickness and wavelength, single‐mode operation range as well as the numerical aperture) of an actual BSSF structure rigorously and consistently within the framework of a slab model analysis.
Segregation Driving Forces on the (111) and (110) Faces of a CuAg Alloy
Authors: Jouaiti A. , Mosser A. , Raiser D. , Romeo M.
Published: July 2007

Using a tight‐binding Isingmodel (TBIM), the segregation energy on the (111) face of a Cu‐Ag 0.45 at% alloy and on the (110) face of a Cu‐Ag 0.30 at% alloy as a function of surface coverage, is derived from equilibrium segregation experiments. It is shown that a surface size effect term which depends on the square of the surface concentration has to be introduced in the segregation energy of the (111) face in order to take into account the surface strain energy which occurs in the first layer when the silver atoms segregate at the surface. On the contrary, on the (110) face the segregation energy expression reveals that the surface size effect does not depend on the silver surface concentration. Also, the effective surface pair interaction βs can be determined and related to the effective bulk pair interaction βb through the relation βs = 1.37βb, for the (111) face and βs = 1.61βb for the (110) face, which is in good agreement with theoretical predictions.
Some Comments on q‐Calculus of a Harmonic Oscillator
Authors: Chatterjee R.
Published: July 2007

The eigenvalues of a q‐deformed quantum harmonic oscillator are shown to be a Fibonacci number sequence for a particular choice of q‐values. The necessary details of its derivation and the justification are provided.
The Properties of Isolated Magnetic Vortices
Authors: Bocdanov A. , Hubert A.
Published: July 2007

Isolated magnetic vortices are stabilized by an antisymmetric exchange interaction, the so‐called Dzyaloshinsky interaction, which can be represented as an energy contribution linear in the first spatial derivatives of the magnetization vector. In contrast, vortex lines are demonstrated to be unstable in the bulk of regular uniaxial ferromagnets. They collapse spontaneously under the influence of anisotropy or an applied magnetic field. In reduced units the differential equation for isolated vortices contains two parameters: the reduced magnetic field h along the crystal axis and the material parameter \documentclass{article}\pagestyle{empty}\begin{document}$ \overline \chi $\end{document} which describes the relative contribution of the Dzyaloshinsky interaction term. Isolated vortices turn out to be always metastable for large fields, independent of \documentclass{article}\pagestyle{empty}\begin{document}$ \overline \chi $\end{document} as long as this parameter is positive. At low or negative fields they become unstable by two different mechanisms depending on the \documentclass{article}\pagestyle{empty}\begin{document}$ \overline \chi $\end{document}‐value, but altogether these micromagnetic structures turn out to be stable in a remarkably wide range of parameters. At the end possible applications are considered.
Interband Transition Strength and Magneto‐Absorption Spectrum in Type‐I Superlattices in In‐Plane Magnetic Fields
Authors: Gondar J. López , da Costa B. A. S. , Dickstein F.
Published: July 2007

Using a simplified parabolic band model approach within the framework of the envelope function approximation, the influence of in‐plane magnetic fields on the electronic and optical properties of type‐I superlattices is studied. The results are in qualitative agreement with experimental facts previously reported, as well as with previous theoretical results obtained using more elaborated and toilsome methods. Furthermore, this approach allows to advance, in a great extent, in the analytical treatment of interband transitions, leading straightforwardly to some general conclusions. The not well understood case of high magnetic field effects (magnetic length comparable with the superlattice period) is studied in detail. There strong variations of the interband transition strengths as function of the cyclotron orbit center position are found, a fact which is directly connected with the broadening and final saturation of the magneto‐absorption spectrum with increasing fields. A consistent explanation of such strong variations is given in terms of magnetic subband mixing.
Theory of Third‐Order Nonlinear Photoconductivity and Third‐Order Photogalvanic Effect in Glass
Authors: Sokolov V. O. , Sulimov V. B.
Published: July 2007

The general theory of a third‐order generalized photoconductivity in glass is developed using a density matrix approach in the generalized master equation approximation. The theory is applied to third‐order photogalvanic effect in glass in connection with photoinduced second‐harmonic generation in silica.
The 130 K Transition in Bi Oxides Heavily Doped by Iron Phthalocyanine Superconductivity versus Magnetism
Authors: Grigoryan L. , Yakushi K. , Chakravarty N.
Published: July 2007

The observation and detailed investigation of the highly reproducible transition with onset at 130 K are reported in samples of Bi oxides (both 2212 and 2223 systems) doped with iron phthalocyanine, involving effects of temperature, magnetic field, and chemical composition on dc magnetization and microwave absorption spectra of the samples. The experimental magnetic data are suggestive of a superconducting nature of the transition; however, no reliable electrical resistivity drop is observed at 130 K to confirm the occurrence of superconductivity.
Interband Optical Absorption and Plasma Effects in Half‐Metallic XMnY Ferromagnets
Authors: Kirillova M. M. , Makhnev A. A. , Shreder E. I. , Dyakina V. P. , Gorina N. B.
Published: July 2007

The frequency dependence of the real and imaginary parts of the complex dielectric constant ϵ(ω) in compounds XMnY (X = Ni, Pd, Pt, Cu; Y = Sb, Sn) having Clb structure are investigated in the spectral range ħω = 0.05 to 8 eV. The values of conduction electron plasma and relaxation frequencies ωp and γ, respectively, are determined. The evolution of interband conduction and electron energy‐loss function ‐Im (ε−1) for varying compositions is studied. In all the compounds, apart from the main absorption band located in the spectral range 1 to 7 eV, a low‐energy (ħω = 0.3 to 0.7 eV) interband absorption is revealed. An estimation is made of the energy gap at point Γ of the Brillouin zone in the minority‐spin subbands (↓) for NiMnSb using optical data.
Substrate Misorientation, Multi‐Quantum‐Barrier, and Thermal Annealing Effects in MgZnSSe and ZnCdSe Compounds and Blue‐Green II‐VI Light Emitting Devices
Authors: Kishino K. , Ichimura Y. , Yoshida A. , Kuramoto M. , Satake M.
Published: July 2007

Multi‐quantum‐barrier (MQB), substrate misorientation, and thermal annealing effects are investigated in MgZnSSe and ZnCdSe compounds and blue‐green II‐VI light emitting devices. The heterobarrier enhancement of MgZnSSe/ZnSe MQBs is analyzed to be 100 meV, using the experimental band offset of ΔEc ≈ 0.65ΔEg. By use of MQB effect, low threshold current density operation below 1 kA/cm2 can be expected in 480 nm blue emission ZnCdSe/MgZnSSe lasers. For N‐doped MgZnSSe grown on intentionally misoriented GaAs substrates, the decreased net acceptor concentration with misorientation angle is discussed, concluding that the enhanced sulfur incorporation by substrate misorientation plays some role in degradation. It is clarified that ZnSe and ZnSSe are not degraded up to 400°C annealing, while MgZnSSe is even at 350 to 400°C annealing. The light output of ZnCdSe/ZnSe MQW LEDs is enhanced by thermal annealing (325°C, 7 min), by a factor of three.
Effect of Tilted Substrates on p‐Type Doping in ZnSe and ZnCdSe/ZnSe Quantum Wells
Authors: Matsuoka T. , Ohno T. , Ohki A. , Kawaguchi Y.
Published: July 2007

Tilted GaAs substrates are used to increase the acceptor concentration in p‐type ZnSe by nitrogen doping and to improve the properties of ZnCdSe/ZnSe quantum wells. An acceptor concentration twice as large as that on a (100) substrate is obtained reproducibly, except for (111) substrates, on which ZnSe films show high resistivity. The PL characteristics of ZnCdSe/ZnSe single quantum wells (SQWs) on an (n11) substrate are also examined. The PL spectrum shows a blue shift and the PL intensity is higher with an (n11) substrate than with a (100) substrate. A ZnCdSe/ZnSe MQW separate confinement structure (SCH) laser diode (LD) is fabricated on a (711)A substrate. The built‐in voltage of the LD is by 5 V lower than for an LD on a (100) substrate.
Computation of Elastic and Dynamic Properties of the Liquid Phase of Noble Metals Illustrating Typically for Molten Ag and Cu
Authors: Rao R. V. Gopala , Venkatesh R.
Published: July 2007

The potential function as formulated by Bretonnet and Deroache is applied to liquid Cu and Ag to derive longitudinal and transverse phonon frequencies, the power spectrum, and the velocity autocorrelation function. From these phonon frequencies the elastic constants are evaluated. They are also calculated with the help of Schofield's equations which are computed through the first and second derivatives of the potential energy. The values are found to be in satisfactory agreement with each other. The ratio of the areas in negative regions of the velocity correlation function for these f.c.c. packed liquids are found to be equal to the ratio of their atomic weights. The characteristic frequencies calculated by several methods are in satisfactory agreement with each other. The nearest‐neighbour distance obtained by different methods is also given. It is observed that the ωL (k) maximum occurs around kF, the Fermi wave vector. From the velocity of sound calculated from the experimental compressibility and kF the ωL (k) maximum is computed and is found to be in reasonable agreement with other values.
The Electronic Energy Bands of RbNO3 at the Γ‐Point at 461 K
Authors: El‐Dib A. M. , Hassan H. F. , Mohammed M. A. , Gabber A. A.
Published: July 2007

A semiempirical self‐consistent charge LCAO method is used to calculate the electronic energy bands of the cubic phase of RbNO3 at 461 K at the Γ‐point. The energy levels of the hypothetical „RbNO3”︁ molecule and the NO3− ion are also calculated. The population densities, overlap charges, and effective charges on atoms are studied. The effect of the first‐ and second‐nearest neighbours is considered in these calculations.
The Thermopower of a Structurally Disordered Hubbard Model
Authors: Liu K. L.
Published: July 2007

The thermopower S of a structurally disordered Hubbard model with a quasi‐exponential transfer integral is studied. Two cases are considered: (i) the infinite‐U case near half‐filling and (ii) the finite‐U case with various electronic concentrations. Approximations for the required correlation functions are constructed based on their short‐time expansions which are carried out to higher orders in the electronic hopping. For both cases, S is found to be in accord with the generalized Heikes formula at high temperatures. In the temperature range where the thermal energy is comparable to the characteristic hopping energy, the thermopower of case (ii) varies rapidly with decreasing temperature.
Correlations in the coherent transient electron‐hole system
Authors: Keldysh L. V.
Published: July 2007

In the frequency domain close to the intrinsic absorption threshold the dynamic polarization, accompanying propagation of a strong electromagnetic pulse, is a dense cloud of electron‐hole pairs, free or bound to excitons or both. In order to investigate the structure and properties of this system in a wide range of pumping field strengths and frequencies, including both the exciton resonance and continuum edge, two simplified models are introduced and discussed, both substituting an effective short‐range interaction instead of the usual Coulomb potential. To go beyond the mean‐field approximation (MFA) the correlation effects are accounted for phenomenologically in this interaction. Results for both ‐ (quasi‐) stationary regime and transient response ‐ are presented. Possible inelastic relaxation mechanisms and kinetics are discussed. For not too fast (in the “excitonic” time scale) varying pumping field strengths the Boltzmann equation for renormalized Galitskii‐Elesin quasi‐particles is derived.
Persistent spectral hole‐burning phenomenon of semiconductor quantum dots
Authors: Masumoto Y. , Okamoto S. , Yamamoto T. , Kawazoe T.
Published: July 2007

The persistent spectral hole‐burning (PSHB) phenomenon is observed generally in nanocrystalline semiconductors, CdSe, CuBI, and CuBr, embedded in glass and crystal. In the inhomogeneously broadened exciton absorption spectra of these quantum dots, the spectral hole and its associated structure are produced by the narrow‐band laser excitation and are conserved for more than several hours at 2K. The hole depth grows in proportion to the logarithm of the burning fluence. Thermal‐annealing and light‐induced hole‐filling phenomena are observed. The hole burning takes place by tunneling through potential barriers with broadly distributed barrier heights and thicknesses. Photoionization of dots and carrier tunneling into traps in the host are the most probable origins of the PSHB phenomenon. A possible application of the PSHB phenomenon is discussed.
Collective optical response of molecular aggregates
Authors: Fidder H. , Wiersma D. A.
Published: July 2007

Relative fluorescence quantum yield, fluorescence lifetime, optical dephasing, and absorption line shift data are presented for both excitonic transitions of the pseudoisocyanine (PIC) J‐aggregate. The data indicate activation of the optical dephasing by exciton‐acoustic phonon scattering at low temperatures. Above approximately 80 K the optical dephasing, line shift as well as the fluorescence lifetime lengthening call for activation by high frequency phonons. Moreover, resonance Raman data indicate the delocalization of low frequency vibrational modes in the aggregate.
Optically induced excitation density flops in semiconductors
Authors: Cundiff S. T. , Knorr A. , Feldmann J. , Koch S. W. , Gobel E. O. , Nickel H.
Published: July 2007

The optically induced excitation density in a semiconductor multiple quantum well is experimentally observed to go through a maximum at sufficiently high excitation intensity. This is achieved by using the interaction of two copropagating ultrafast optical pulses to extract the temporal dependence of the optically induced polarization, which is proportional to the temporal derivative of the excitation density. Solutions to the Maxwell semiconductor Bloch equations show that the observations are a manifestation of Rabi flopping in semiconductors. The results confirm the presence of many‐body modifications to the Rabi flopping for the excitation conditions used in the experiment.
Coherent exciton–photon interaction and pulse propagation effects of bound exciton states in CdS
Authors: Jütte M. , Stolz H. , von der Osten W.
Published: July 2007

Measuring the transform‐limited time‐resolved spectrum of a coherent laser pulse allows one to determine the amplitude and phase of the pulse electric field. From the reshaping of pulses transmitted through a thin semiconductor platelet in resonance with an exciton transition in case of the donor bound exciton in CdS the effects of coherent exciton–photon interaction for different laser intensities can be studied. While at low intensities the expected polariton beating connected with the formation of a 0π‐pulse is observed, at sufficiently high intensities changes in the pulse shape occur that are ascribed to self‐induced transparency of the bound exciton states.
Ultrafast relaxation of photoexcited electrons in undoped GaAs measured by absorption saturation of spin‐orbit‐split transitions
Authors: Alexandrou A. , Berger V. , Hulin D. , Thierry‐Mieg V.
Published: July 2007

An ultrafast redistribution time of less than 40 fs for nonequilibrium photoexcited electron densities as low as 9 × 1016 cm−3 is reported. The electron populations thermalize within 100 to 200 fs after the end of the pump pulse and the cooling of the thermalized electrons to the lattice is observed. These results are obtained from femtosecond pumppprobe measurements yielding differential absorption signals directly proportional to the electron distribution function and independent of the hole distribution. This is achieved by using transitions from the unoccupied split‐off valence band to test the electron populations in the conduction band.
Coherent transport in superlattices and tunneling structures
Authors: Jauho Antti‐Pekka
Published: July 2007

Some recent theoretical studies of carrier transport in semiconductor heterostructures are reviewed, where the coherence of the charge carriers leads to significant effects in the time domain. In particular we examine (i) a resonant tunneling system where the current, as a response to a time‐dependent drive voltage, displays oscillations, and (ii) the time‐dependent motion of carriers in a superlattice under external bias, which displays a significant structure in addition to conventional Bloch oscillations.
Four‐wave‐mixing theory beyond the semiconductor Bloch equations
Authors: Axt V. M. , Stahl A. , Mayer E. J. , Bolivar P. Haring , Nüsse S. , Ploog K. , Köhler K.
Published: July 2007

Four‐wave‐mixing (FWM) experiments using a dynamical density matrix model of the semiconductor band edge are discussed. Higher‐order correlation functions are retained which are neglected in the commonly used RPA treatment leading to the semiconductor Bloch equations. In order to terminate the hierarchy of the equations of motion for the higher‐order density matrices systematically a truncation scheme controlled by orders in the driving field is applied. For any prescribed order n in the exciting field a closed set of equations is obtained from which the dielectric response up to order n can be calculated exactly. In addition it turns out that in a coherently driven system part of the remaining density matrices become redundant and can be eliminated. Four‐wave‐mixing experiments are dominated by third‐order contributions. Applying the above‐described results one ends up with only two functions in this case. These are the excitonic and the biexcitonic transition densities. As an application of our method the example of a GaAs single quantum well is studied. Two pulses with finite lengths are assumed such that both heavy‐and light‐hole excitons are excited. The influence of the biexciton contribution on the polarization properties of the FWM signal is analyzed and compared with experimental results.
Influence of propagation effects on the coherent optical response of semiconductors
Authors: Knorr A. , Stroucken T. , Schulze A. , Girndt A. , Koch S. W.
Published: July 2007

Femtosecond pulse propagation phenomena in semiconductors and semiconductor heterostructures are theoretically investigated. It is shown that the linear pulse propagation through a spatially inhomogeneous structure (multiple quantum wells) is substantially modified in comparison to the homogeneous case. For spatially homogeneous structures (bulk material), the nonlinear interplay between propagation and many‐body effects is investigated in four‐wave‐mixing geometry. For an inverted semiconductor collinear pump‐probe propagation is analyzed to study the ultrafast gain dynamics in amplifiers.
Energy band structure of K2SeO4 single crystals
Authors: Kityk I. V. , Andrievskii B. V.
Published: July 2007

The energy band structure and electronic properties of K2SeO4 single crystals (space group D) are presented. The ab initio LCAO method is used. The corresponding calculational technique is described briefly. Anaytical expressions for the overlapping matrix elements are obtained. Results are reported for the valence and conduction band energies and densities of states. In terms of these, a consistent explanation of the experimental measurements on K2SeO4 single crystals is obtained.
Bound hole states in direct‐gap semiconductors with screw dislocations
Authors: Razumova M. A. , Khotyaintsev V. N.
Published: July 2007

The dispersion law of holes bound at a screw dislocation in cubic semiconductors is calculated on the basis of deformation potential theory taking into account the threefold degeneracy of the valence band maximum in a perfect crystal. The lowest dislocation band (the corresponding azimuthal quantum number is m = 0) is slightly affected by the anisotropy of the effective mass. Only the change of the effective mass is observed. The states with azimuthal number m ≠ 0 are considerably more affected by the anisotropy of the effective mass. A mixing of longitudinal and transverse motions (with respect to the dislocation line direction) takes place and terms linear in k‖ appear in the dispersion law. The optical transitions associated with these states are intense for a polarization of light transverse with respect to the dislocation line and may cause circular dichroism in the absorption. The long‐wave edge of the dislocation absorption on the whole is formed by transitions from the deepest band m = 0 and is polarized along the Burgers vector b.
The low‐temperature dependence of coercivity in NdFeB magnets
Authors: Hu Jifan , Kou X. C. , Kronmüller H.
Published: July 2007

The influence of the spin reorientation phenomenon on the nucleation field of NdFeB magnets is analyzed based on the theory of micromagnetism. Results indicate that the temperature dependence of coercivity in the whole temperature range can be well described by the equation Hc = (2K1/Ms) × αKαψ – NeffMs when taking into account the effect of the spin reorientation in the low‐temperature range.
Anisotropy of the ZnO single crystal reflectivity in the region of residual rays
Authors: Venger E. F. , Melnichuk A. V. , Melnichuk L. Yu. , Pasechnik Yu. A.
Published: July 2007

The consistent parameters of hexagonal zinc oxide single crystals are obtained in the frame of the one‐oscillator model by analyzing the dispersion spectra of IR light reflection. The anisotropy coefficients of the electron effective masses and the plasmon damping Coefficients are measured. The calculated values of electron mobility and conductivity for zinc oxide are in good agreement with the reference data available.
The Influence of Permanent Magnetic and Alternative Electric Fields on the Dislocation Dynamics in Ionic Crystals
Authors: Golovin Yu. I. , Morgunov R. B. , Tyutyunnik A. V.
Published: July 2007

The dislocation dynamics are investigated in NaCl single crystals treated by permanent magnetic (B = 1 T) or alternating electric (E = 200 kV/m, f = 50 Hz) fields. It is shown that the field treatment before mechanical loading causes long‐lived (≈1 h at T = 300 K) excited states of both local obstacles and edge dislocations. It leads to an increase of dislocation displacements up to two times and the number of mobile dislocations up to 1.5 times.
Pressure Dependence of Electron and Positron Band Structures in Elemental Semiconductors
Authors: Alkhafaji S. T. , Amrane N. , Bouarissa N. , Badi N. , Soudini B. , Sehil M. , Aourag H.
Published: July 2007

On the basis of the local pseudopotential method and the independent particle approximation, the electron and positron band structures of Si, Ge, C, and α‐Sn with respect to the variation of pressure are discussed. The positron band structure in a periodic lattice is similar to its electron counterpart. Some physical properties of these semiconductors such as the homopolar gap and the bulk modulus are calculated from the positron band structure.
An Analytical Model for Screened Coulomb Interaction in a C60 Cluster
Authors: Cappellini G. , Bechstedt F. , Bosin A. , Casula F.
Published: July 2007

An analytical model for the static screened Coulomb interaction of a semiconductor sphere that accurately reproduces the screening properties of an icosahedral C60 cluster is presented. Compared with the static screened Coulomb interaction determined after polarizability calculations it yields the same value for nearest‐neighbor interaction energy and the same antiscreening effect for distant sites for points located on the nuclear grid of a free molecule. Also the static dipole molecular polarizability turns out to be in good agreement with that calculated after different theoretical methods. When extended to finite frequencies, without introducing other parameters, the present model reproduces the main resonance around 20 eV of the optical absorption spectrum for the gas phase C60 and the giant plasmon resonance around 28 eV observed in C60 fullerites via electron energy loss spectroscopy. These results turn out to be largely insensitive to the details of the model.
Interaction of Curved Vortex Lines with the Surface of a High‐Temperature Superconducting Sphere
Authors: Saif A. G.
Published: July 2007

The uniaxial anisotropic London equation is used to study the effects of the surface of a high‐temperature superconducting sphere on a curved vortex lattice. Using the generalized spherical functions (GSF), the field distributions inside and outside the sample are determined. Moreover, the current density, the forces on the vortex segments, and the Gibbs free energy of the system are calculated in the frame of the GSF. Agreement with previous results is achieved in the isotropic limiting case.