bluuebunny/crossref_metadata_2025 huggingface dataset:
Aspects of the Population Dynamics of Corophium curvispinum G. O. Sars in Reed Belts along a Trophic Gradient in Lake Balaton (Hungary)
Authors: Muskó Ilona B. , Lakatos Gyula , Bíró Péter , Zólyomi Zsolt
Published: February 2007

The population structure, abundance (ind m−2), biomass and reproduction of Corophium curvispinum, an important element of the littoral fauna, have been studied at four sampling stations on the northern shoreline of Lake Balaton (Keszthely Bay, Szigliget Bay, Bozsai Bay and Paloznak Bay) three times a year (spring, summer and autumn) in Phragmites growing period from May 1991 to October 1993 and in summer 1994. The sampling stations represent the trophic gradient of the lake.

The environmental parameters (Chlorophyll‐a content of the plankton and of the reed periphyton, and suspended solid content of the water) were significantly higher (ANOVA) in the western basin (Keszthely and Szigliget bays) than in the eastern basin (Bozsai and Paloznak bays). However, the population parameters (length of the animals, percentage of juveniles, length of ovigerous females, percentage of ovigerous females and fecundity) did not differ significantly between the two basins. Both the abundance and biomass were higher in the middle than in the westernmost and easternmost bays but the difference is not significant.

The ovigerous females were significantly bigger in spring than in summer and autumn. The egg number per female was also significantly greater in spring than in summer and autumn. The length of ovigerous females and the fecundity in summer did not differ significantly from those of autumn data.

There is a significant positive correlation (Spearman rank correlation) between both abundance and biomass and the above environmental parameters. The length of ovigerous females and the fecundity were inversely correlated with the plankton Chlorophyll‐a concentrations.

The abundance of C. curvispinum in the reed belt of Lake Balaton is greater than in several parts of the Dnieper and Volga. However, it is much lower than in the Don, Oka, Danube and Rhine rivers.
Evolution of gastrulation in the ray‐finned (actinopterygian) fishes
Authors: Cooper Mark S. , Virta Valerie C.
Published: February 2007

Sometime before or during the early Mesozoic era, new lineages of actinopterygian (ray‐finned) fishes radically transformed their mode of gastrulation. During this evolutionary transformation, yolky endoderm was a hotspot for ontogenetic change. As holoblastic cleavage patterns were modified into meroblastic cleavage patterns, major changes in cell identity specification occurred within the mesendodermal marginal zone, as well as in the superficial epithelium of the embryo. These cellular identity changes resulted in the appearance of two novel extra‐embryonic tissues within the embryos of teleostean fishes: the enveloping layer (EVL) and the yolk syncytial layer (YSL). The generation of these extra‐embryonic tissues prompted major morphogenetic changes within the Organizer Region. As these evolutionary changes occurred, the outermost cell layer of the Organizer (the Organizer Epithelium) was apparently retained as a signaling center necessary for the establishment of left–right embryonic asymmetry in the embryo. Conserved and derived features of Organizer morphogenesis and gastrulation within ancient lineages of ray‐finned fishes provide important insights into how the genetically encoded cell behaviors of early morphogenesis can be altered during the course of evolution. In particular, a highly divergent form of actinopterygian gastrulation, which is found in the annual fishes of South America, demonstrates that no aspect of vertebrate gastrulation is inherently immutable to evolutionary change. J. Exp. Zool. (Mol. Dev. Evol.) 308B:591–608, 2007. © 2007 Wiley‐Liss, Inc.
Ultrastructural studies of midgut epithelium formation in Lepisma saccharina L. (Insecta, Zygentoma)
Authors: Rost‐Roszkowska M. M. , Piłka M. , Szymska R. , Klag J.
Published: February 2007

At the end of embryogenesis of Lepisma saccharina L. (Insecta, Zygentoma), when the stomodaeum and proctodaeum are completely formed, the midgut epithelium is replaced by the primary midgut, a yolk mass is surrounded by a cell membrane. Midgut epithelium formation begins in the 1st larval stage. Energids migrate toward the yolk periphery and aggregate just beneath the cell membrane. They are gradually enclosed by cell membrane folds of the primary midgut. Single cells are formed. Succeeding energids join just formed cells. Thus, groups of cells, regenerative cell groups, are formed. Their number gradually increases. The external cells of the regenerative cell groups transform into epithelial cells and their basal regions spread toward the next regenerative cell groups. Epithelial cells of neighboring regenerative cell groups join each other to form the epithelium. At the end of the 2nd larval stage, just before molting, degeneration of newly the formed epithelium begins. Remains of organelles and basal membrane occur between the regenerative cell groups. The new epithelium is formed from the regenerative cell groups, which are now termed stem cells of the midgut epithelium. J. Morphol., 2007. © 2007 Wiley‐Liss, Inc.
Is There any Relation Between the Solubility of a Polymeric Additive and its Performance as a Pour Point Reducer?
Authors: Mansur Claudia R. E. , Lima Aline F. , Spinelli Luciana S. , González Gaspar , Lucas Elizabete F.
Published: February 2007

In this work, polymeric additives based on poly(ethylene‐co‐vinyl acetate) were chemically modified by inserting different contents of hydrocarbon chains (C14). The performance of the modified copolymers as organic deposition inhibitors (ODI) was evaluated using a model system composed of different types of paraffins by measuring the pour point and viscosity of these systems. The phase behavior of the modified copolymers was evaluated in systems with different solubility parameters in order to correlate the additive's performance as ODI and the esteem solubility parameter of these modified copolymers. The results show that the EVA modified copolymers performed better ODI than those obtained for non‐modified copolymer. However, the molecule must retain a hydrophobic‐lypophobic balance in order to keep its capacity to modify the paraffin crystal. Moreover, copolymers with similar solubility parameters did not present the same pour‐point values, which suggests that the solubility of the additive is important, but is not the only factor that influences the additive performance.
Development of a Method to Evaluate the Performance of Aqueous Polymer Solutions as Drag Reduction Agents in Bench Scale
Authors: Figueiredo Marcos S. , Almeida Lucilla C. , Costa Francileide G. , Clarisse Márcia D. , Lopes Léa , Leal Rafael , Martins André L. , Lucas Elizabete F.
Published: February 2007

This work describes a method to evaluate, in reduced scale, the performance of polymer samples as drag reduction agents in aqueous solutions. To measure the pressure drop in a turbulent regime, a specially adapted capillary viscosimeter was used, with reduced dimensions adapted to produce the desired regime and adequate pressure measurement points. To verify the technique's reliability, samples of polyacrylamide were synthesized with different molar masses, by varying the quantity of the polymerization initiator. The molar masses obtained were determined by size exclusion chromatography (SEC). The efficiency of the polymer as a drag reducer, as expected, increased as the molar mass increased, which validates the use of this method to study the drag reduction properties of polymer materials in aqueous solutions.
Structured Thermoplastic/Thermoset Blends Using Block Copolymers
Authors: Fine Thomas , Pascault Jean‐Pierre
Published: February 2007

Thermoplastic/thermoset blends have been compatibilized by block copolymers. The thermoplastic is poly(phenylene ether) and the thermoset precursors are a liquid epoxy, diglycidyl ether of bisphenol A (DGEBA) and an aromatic diamine (4,4′ methylene bis [3 chloro 2,6 diethylaniline], MCDEA). The triblock poly(styrene‐ b‐butadiene‐b‐methyl methacrylate), SBM has been chosen because (i) PS blocks interact very favourably with PPE (ii) PMMA blocks remain miscible with the thermoset during the whole curing process, and (iii) PB mid blocks are expected to cover the interface. Morphologies of blends were observed by Transmission Electron Microscopy and phase composition evaluated by Dynamic Mechanical Thermal Analysis. It was observed that the strong repulsion between PPE and PMMA blocks governs the organization of the blend before and during the curing process. During polymerization a purification of the matrix is induced. As expected, a large proportion of block copolymer is at the interface between the matrix and nodules. It was demonstrated that the number of SBM micelles and their degree of dispersion is the main parameter controlling the mechanical properties.
Styrene Suspension Polymerization Using a Stirred Vertical Tubular Reactor
Authors: Nogueira André L. , Machado Ricardo A. F. , Quadri Marintho B.
Published: February 2007

Suspension polymerization reactions are commonly carried out in tank reactors designed with low values for the H/D ratio (Height/Diameter). As polymerization reactions are frequently high exothermic, the superficial area of these equipments are not enough high to adequately release the heat generated by the reaction. In this case, additional systems are necessary to provide cooling fluids with sufficiently low temperatures in order to maintain constant the polymerization temperature in the tank reactor. On the other hand, tubular reactors can be considered economically attractive because their high superficial area for heat exchange (high H/D) can improve temperature control and reduce operational costs. The present work uses a vertical tubular reactor to carry out the batch styrene suspension polymerization and evaluate the effects of the reactor and stirring system configuration on the polystyrene PSD (Particle Size Distribution). According to the results, besides a very good temperature control due to the reactor geometry, polystyrene particles with relatively narrow particle size distributions can be successfully produced in a stirred vertical tubular reactor.
Measurement of the Emitted Light Polarization State in Oriented and Non‐Oriented PPV Films
Authors: Alliprandini‐Filho Paulo , Silva R. A. , da Silva George B. , Neto N. M. Barbosa , Cury L. A. , Moreira R. L. , Marlleta Alexandre
Published: February 2007

In this work we report the influence of the molecular orientation on the light emission polarization of poly (p‐phenylene vinylene) (PPV) films. The oriented film was processed via the Langmuir‐Blodgett (LB) technique while the non‐ordered one was processed by casting technique. By means of an ellipsometry experiment, the information about the polarization state of the emitted light was obtained via Stokes parameters and the dissymmetry factor (g). The experiments were carried out at room and low temperature (10 K) and in the phonon‐replicas range at 543 and 633 nm. We have observed a high dependence in the g factor and in the ellipticity of the emission spectra for LB films as function of the spectrum region, i. e., the phonon‐replicas. This effect is attributed to the memory of the circular polarization that is lost by thermal disorder when the emission occurs distant from the zero‐ phonon peak.
Characteristics of Liposomes Prepared by the Modified Reverse‐Phase Evaporation Method: 31P‐NMR and TEM Study
Authors: Pentak Danuta , Sułkowski Wiesław W. , Maślanka Sławomir , Wolińska Agnieszka , Duber Stanisław , Sułkowska Anna
Published: February 2007

The NMR spectroscopy was used to determine a structure and physicochemical properties of liposomes prepared from L‐α‐phosphatidylcholine dipalmitoyl (DPPC) by the modified reverse‐phase evaporation method (mREV). 31P‐NMR study of the liposome in the temperature range from 340K to 350K allowed us to suggest that the single‐bilayered liposome has been obtained. Transmission electron micrographs (TEM) showed that the liposome vesicles, obtained with the use of the modified (mREV) method, were spherical in shape and in majority they were less than 100 nm in diameter.
Biomimetic Particles
Authors: Lincopan Nilton , Rosa Heloísa , Carmona‐Ribeiro Ana M.
Published: February 2007

Electrostatically driven bilayer coverage from bilayer fragments onto oppositely charged latex produces a highly homodisperse particulate for biomolecules adsorption. Polystyrene sulfate (PSS) particles were covered with single cationic dioctadecyldimethylammonium bromide (DODAB) bilayers. Biomolecules adsorbed were DNA, bovine serum albumin (BSA), cholera toxin (CT) and a mixture of purified 18 kDa/14 kDa Taenia crassiceps proteins (18/14‐Tcra). Firstly, the DODAB/PSS assembly was characterized at 1 mM NaCl and 5 × 109 PSS particles/mL over a range of DODAB concentrations (0.001 ‐1 mM) by means of dynamic light scattering for particle sizing and zeta‐potential analysis. 0.01 mM DODAB was enough to produce perfectly homodisperse and cationic bilayer‐covered particles. Secondly, under these experimental conditions, BSA, CT, and 18/14‐Tcra adsorbed onto biomimetic bilayer‐covered particles yielding langmuirian isotherms with 1.23 × 1017, 0.82 × 1017, 3.37 × 1017 molecules per m2 at limiting adsorption and affinity constants (K) of 3.17 × 1010, 3.39 × 1010, and 1.75 × 1010 M−1, respectively. For DNA adsorption, isotherms did not attain an adsorption maximum up to 20 micrograms/mL DNA. PSS/DODAB/biomolecule assemblies were also characterized by means of dynamic light scattering and zeta‐potential analysis yielding highly monodisperse particles at and above maximal adsorption. In summary cationic bilayer‐covered particles are a novel, highly organized and, possibly, general support for biomolecules immobilization.
Polyurethanes Elastomers Based on Poly(ε‐caprolactone) Diol: Biodegradation Evaluation
Authors: Kloss Juliana , de Souza Fernanda S. M. , da Silva Edilsa R. , Dionísio Jair Alves , Akcelrud Leni , Zawadzki Sônia Faria
Published: February 2007

Sumary: Plastics materials are widely used in the manufacturing of many products like bags, packings, electronic components among other applications. Most polymers are extremely durable and this durability cause serious environmental problems because of the large amount of waste discarded mainly in the urban centers. Thus, biodegradable polymers are a potencial way to minimize these problems. Polyurethanes based on poly(ε‐caprolactone) (PCL) as soft segment were prepared taking into account the biodegradable charater of this last compound. The hard segment was built up by reaction between tolylene diisocyanate (TDI) and a chain extender (1,4‐butanediol) or two crosslinking agents (sucrose or glucose). The biodegradation behavior of the polyurethanes was verified using solid and submerged fermentation and using natural conditions under the soil. The analysis indicated that the biodegradation was affected by the PCL segment, hard segment content, intermolecular interations manly H bonds and crosslinking.
Thermal Degradation of Natural Rubber Male Condoms
Authors: Bó Maria Cristina , Lopes Léa , Visconte Leila Lea Yuan , Nunes Regina Célia Reis
Published: February 2007

Condoms play an important role in the prevention of human immunodeficiency virus transmission. The prediction of condom shelf life became a high priority for the international and national committees responsible for the standardization of the quality of the product. In this work, two sets of batches of natural rubber condoms from three manufactures were compared to investigate the effect of the total sulphur, in their formulations, on the thermal degradation of the products. One set was manufactured in 1999–2000, and the other was manufactured in 2004–2005. The techniques used were differential scanning calorimetry (DSC) and thermogravimetry (TGA) in different atmospheres, as well as elemental analysis in the determination of the total sulphur present in the condoms. The results show that the profile of the thermal behavior is very similar to all condoms. No clear correlation between the amount of sulphur in the formulations and the thermal behavior of the products was found. This study intended to contribute to the development of a method for predicting shelf life of natural rubber male condoms.
Elastic solutions of displacements for a transversely isotropic full space with inclined planes of symmetry subjected to a point load
Authors: Hu Ting‐Bin , Wang Cheng‐Der , Liao Jyh‐Jong
Published: February 2007

This work presents analytical solutions for displacements caused by three‐dimensional point loads in a transversely isotropic full space, in which transversely isotropic planes are inclined with respect to the horizontal loading surface. In the derivation, the triple Fourier transforms are employed toyield integral expressions of Green's displacement; then, the triple inverse Fourier transforms and residue calculus are performed to integrate the contours. The solutions herein indicate that the displacements are governed by (1) the rotation of the transversely isotropic planes (ϕ), (2) the type and degree of material anisotropy (E/E′, ν/ν′, G/G′), (3) the geometric position (r, φ, ξ) and (4) the types of loading (Px, Py, Pz). The solutions are identical to those of Liao and Wang (Int. J. Numer. Anal. Methods Geomechanics 1998; 22(6):425–447) if the full space is homogeneous and linearly elastic and the transversely isotropic planes are parallel to the horizontal surface. Additionally, a series of parametric study is conducted to demonstrate the presented solutions, and to elucidate the effect of the aforementioned factors on the displacements. The results demonstrate that the displacements in the infinite isotropic/transversely isotropic rocks, subjected to three‐dimensional point loads could be easily determined using the proposed solutions. Also, these solutions could realistically imitate the actual stratum of loading situations in numerous areas of engineering. Copyright © 2007 John Wiley & Sons, Ltd.
Physical properties of Bi‐doped CdTe thin films deposited by cosputtering
Authors: Becerril M. , Vigil‐Galán O. , Contreras‐Puente G. , Sánchez‐Meza E. , Zelaya‐Angel O.
Published: February 2007

The structural, morphological, electrical, and optical properties of CdTe–Bi cosputtered thin films related with composition are presented. The films were grown on Corning glass substrates at room temperature from a CdTe–Bi target. The composition measurements show that the Bi content in the films ranges from x = 0.0 to x = 6.37 at%, depending on the area fraction covered by the Bi piece attached to the CdTe target. The structure of the annealed films was determined from X‐ray diffraction measurements. Two kinds of structures were observed, depending on the Bi content: (1) CdTe polycrystalline films containing a small amount of Bi that is probably incorporated in the Cd and Te sites of the CdTe lattice. (2) Amorphization of the polycrystalline films, with higher Bi content. From the experimental results, we concluded that using this deposition method n/p‐type Bi‐doped CdTe polycrystalline films can be produced with electrical resistivity between 102–103 Ω cm and electron mobility between 101 and 102 cm2 V–1 s–1. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Laser‐doping of silicon carbide for p–n junction and LED fabrication
Authors: Bet Sachin , Quick Nathaniel , Kar Aravinda
Published: February 2007

The high melting point and the limited diffusion of impurities in silicon carbide have greatly restricted the use of conventional ion implantation and furnace to incorporate and activate dopants. A laser doping technique overcomes these obstacles for doping silicon carbide and other wide band gap semiconductors. This paper presents the work on fabrication of p–n junction diodes and blue light emitting diodes using laser doping technique. A p–n junction was created by laser doping a silicon carbide wafer with aluminum (p‐type) and nitrogen (n‐type). Optical interferometer profilometer scan showed that there was no damage on the surface post laser doping. Secondary ion mass spectrometry (SIMS) was carried to estimate the dopant concentration and depth. The effects of laser doping on the current–voltage characteristics were studied. The junctions were characterized by capacitance–voltage and electroluminescence measurements. A broad electroluminescence peak was observed around 498.8 nm wavelength, characterizing the p–n junction as a blue light‐emitting diode. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Study on the local structure and the spin‐Hamiltonian parameters for Cu3+ ions in Al2O3 crystal
Authors: Wei Qun , Yang Zi‐Yuan , Xu Qi‐Ming
Published: February 2007

The relations between the spin‐Hamiltonian (SH) parameters and crystal structure of Al2O3:Cu3+ crystal have been established using the SH theory. On the basis of this, the SH parameters of Al2O3:Cu3+ crystal have been calculated, and the problem of too many adjustable parameters in previous work has been solved. The calculated results are in good agreement with experiment data. This shows that the model we adopted is reasonable. The results show that, when a Cu3+ ion is doped into Al2O3 crystal, it does not occupy Al3+ site accurately, but moves 0.0214 nm along the C3‐axis. The contributions to SH parameters from spin triplet and spin singlet are also discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phonon spectrum of compact ceramics: two‐dimensional ordered model
Authors: Salamatov E. I.
Published: February 2007

The low‐frequency range of the phonon spectrum of an ordered two‐dimensional composite, modeling compact nanoceramics is theoretically investigated by the finite‐difference time‐domain method. The necessary conditions for the complete gap to arise have been determined. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Peculiar band gap structure of graphene nanoribbons
Authors: Ezawa Motohiko
Published: February 2007

Graphene nanoribbons are quasi‐one‐dimensional meterials with finite width. Characterizing a wide class of nanoribbons by edge shape and width, we make a systematic analysis of their electronic properties. The band gap structure of nanoribbons is shown to exhibit a valley structure with stream‐like sequences of metallic or almost metallic nanoribbons. Among them, all zigzag nanoribbons are metallic, and armchair nanoribbons are metallic by period of 3. We find that these stream‐like sequences correspond to equi‐width curves, and that the band gap of chiral and armchair nanoribbons oscillate as a function of the width. Furthermore a possible application of nanoribbons to nanoelectronics is discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
GaN ballistic negative‐differential‐conductivity diode for potential THz applications
Authors: Dyson A. , Ridley B. K. , Aslan B. , Cha H. Y. , Chen X. , Schaff W. J. , Spencer M. G. , Eastman L. F.
Published: February 2007

We present details of the development of a GaN ballistic diode designed with THz applications in mind. Parallel theoretical and experimental analysis has shown that negative‐differential‐resistance (NDR) can only be achieved when hot electrons are injected into the drift region, contact and spreading resistances must be minimized in order to maximize the field in the drift layer. NDR remains achievable even in the presence of collision dominated transport or when transport is space‐charge limited. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin‐dependent tunneling in modulated structures of (Ga,Mn)As
Authors: Sankowski P. , Kacman P. , Majewski J. A. , Dietl T.
Published: February 2007

The spin‐dependent tunneling in layered structures based on (Ga,Mn)As, in particular the dependence of the tunneling current on magnetization direction, is studied theoretically. To capture the complexity of the tunneling effects in these semiconductor devices we combine a multi‐orbital tight‐binding approach with Landauer‐Büttiker formalism. This theory allows us to reproduce the tunneling anisotropic magnetoresistance effects observed in (Ga,Mn)As/GaAs Esaki‐Zener diodes. The model is also used to describe the in‐plane and out‐of‐plane anisotropy of tunneling magnetoresistance in (Ga,Mn)As‐based trilayers. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin currents in AC‐driven double quantum dots
Authors: Sánchez Rafael , Platero Gloria , Aguado Ramón , Cota Ernesto
Published: February 2007

We analyze spin transport through an AC driven double quantum dot device which acts as a spin pump and spin filter. The AC field brings into resonance electronic states in both quantum dots, producing electron pumping. The AC potential affects not only the inter‐dot tunneling but also the tunneling through the contacts by photon‐assisted tunneling proccesses involving photon absorption and emission through the barrier contacts. These processes produce additional resonances in the current characteristics which flows in opposite direction for each spin polarization contribution to the electronic current. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
N‐N pair effects on GaInNAs semiconductor optical amplifiers
Authors: Alexandropoulos D. , Vogiatzis N. , Qiu Y. N. , Pozo J. , Syvridis D. , Rorison J. M.
Published: February 2007

We explore the effects of N‐N pairs on the amplifying properties of GaInNAs based Semiconductor Optical Amplifiers. The bandstructure of GaInNAs is calculated with the 3 band anti‐crossing model to account for the N‐N pairs for the conduction band and k·p theory for the valence bands. For the calculation of the GaInNAs amplifier properties we adopt a multi‐sectioning approach to the rate equation that accounts for amplified spontaneous emission. Based on these we discuss the merits of N‐N pairs for GaInNAs semiconductor optical amplifiers. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Raman and TEM studies of Ge nanocrystal formation in SiOx:Ge/SiOx multilayers
Authors: Dana A. , Ağan S. , Tokay S. , Aydınlı A. , Finstad T. G.
Published: February 2007

Alternating germanosilicate‐siliconoxide layers of 10‐30 nm thickness were grown on Si substrates by plasma enhanced chemically vapor deposition (PECVD). The compositions of the grown films were determined by X‐ray photoelectron spectroscopy measurements. The films were annealed at temperatures varying from 670 to 1000 °C for 5 to 45 minutes under nitrogen atmosphere. High resolution cross section TEM images, electron diffraction and electron energy‐loss spectroscopy as well as energy‐dispersive X‐ray analysis (EDAX) data confirm presence of Ge nanocrystals in each layer. The effect of annealing on the Ge nanocrystal formation in multilayers was investigated by Raman spectroscopy and Transmission Electron Microscopy (TEM). As the annealing temperature is raised to 850 °C, single layer of Ge nanocrystals observed at lower annealing temperatures is transformed into a double layer with the smaller sized nanocrystals closer to the substrate SiO2 interface. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin dynamics through homogeneous magnetic superlattices
Authors: Cardoso J. L. , Pereyra P.
Published: February 2007

We study the spin dynamics of a 2DEG moving across a magnetic superlattice. We describe the spin transitions induced by sectionally homogeneous tilted magnetic fields and the spatial evolution of spin‐1/2 wave functions: amplitude and phase, in terms of the tilting angle, the Fermi energy and the magnetic field strengths. Clear signatures of coherent spin mixing and coherent spin flipping processes are shown. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural and optical properties of InP quantum dots grown on GaAs (001)
Authors: de Godoy M. P. F. , Nakaema M. K. K. , Lopes J. M. J. , Morschbacher M. J. , Iikawa F. , Brasil M. J. S. P. , Magalhães‐Paniago R. , Bortoleto J. R. R. , Cotta M. A.
Published: February 2007

We present structural and optical properties of type‐II self‐assembled InP/GaAs quantum dots using different techniques. The results reveal that the uncapped InP dots present an efficient optical emission and are partially relaxed: strain relaxation increases with the amount of InP deposited. The photoluminescence spectra show two optical emission bands associated to the quantum dots, in agreement with the bi‐modal dot‐height distribution observed by atomic force microscopy. We observed distinct photoluminescence results for uncapped and capped samples, which are mainly attributed to surface state and strain relaxation effects. A remarkable result is the large blue shift of the optical emission band from uncapped sample as compared to capped one for increasing excitation intensities. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coherent control of an asymmetric semiconductor quantum well structure
Authors: Dynes James F. , Paspalakis Emmanuel
Published: February 2007

We study coherent control of an asymmetric semiconductor quantum well by simultaneous application of a laser field and its second harmonic. The relative phase of the applied laser fields is externally altered. The electron population and the small signal absorption and dispersion spectra of a weak probe field propagating through such a quantum well structure are computed and are found to be strongly phase dependent. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Surface acoustic wave mediated effects in a coupled multi quantum well
Authors: Ebbecke J. , Pierz K.
Published: February 2007

A coupled multi‐quantum well GaAs/AlGaAs heterostructure has been doped in such a way that the widest quantum well is composed of a conductive layer of a two‐dimensional electron gas whereas the narrower quantum wells are free of mobile charge carriers at low temperatures. Photoluminescence measurements exhibit a broad signal of the coupled quantum wells and a surface acoustic wave has been used to excite the electronic system. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of growth conditions on morphologies of the ZnO nanostructures
Authors: Erol A. , Arikan M. C.
Published: February 2007

Nano‐scaled zinc oxide combs/ribbons, nanorods, nanorods with sharp needle‐like tips and hexagonal‐shaped nanoparticles have been synthesized by using vapor liquid solid (VLS) growth technique under different growth conditions. Morphologies of the obtained nanostructures were examined by using X‐Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive Spectroscopy (EDS) techniques. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence of nanocrystals embedded in oxide matrices
Authors: Estrada C. , Gonzalez J. A. , Kunold A. , Reyes‐Esqueda J. A. , Pereyra P.
Published: February 2007

We used the theory of finite periodic systems to explain the photoluminescence spectra dependence on the average diameter of nanocrystals embedded in oxide matrices. Because of the broad matrix band gap, the photoluminescence response is basically determined by isolated nanocrystals and sequences of a few of them. With this model we were able to reproduce the shape and displacement of the experimentally observed photoluminescence spectra. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Creation and detection of spin‐polarized current using quantum point contact with spin‐orbit interaction
Authors: Yokouchi Hiroto , Eto Mikio
Published: February 2007

We have proposed that quantum point contacts (QPCs) can be a useful tool for producing spin‐polarized currents in the presence of Rashba spin‐orbit (SO) interaction [J. Phys. Soc. Jpn. 74, 1934 (2005)]. No magnetic field is required. When the conductance through a QPC is quantized in units of 2e2/h, the current is spin‐polarized in the transverse direction. This spin polarization, which can be larger than 50% in InGaAs heterostructures, is elucidated using the S‐matrix formalism. We also examine transport properties of a QPC connected to a ferromagnetic lead and show how to detect the spin‐polarized current from the QPC. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polarization dependence of intraband transitions in QDIPs
Authors: Gebhard T. , Souza P. L. , Schrey F. F. , Strasser G. , Unterrainer K. , Pires M. P. , Landi S. M. , Villas‐Boas J. M. , Studart N.
Published: February 2007

Photocurrent measurements were carried out on doped and undoped InAs/InGaAs/InP quantum dot structures. A photocurrent peak is observed at 5 μm for the undoped sample, which is identified as a bound to bound transition. Additional peaks are detected for the doped structure, which, with the help of a simple 1D model, are tentatively identified as transitions from a dot bound state to a quantum well state. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electron scattering through a quantum dot
Authors: Castelano L. K. , Hai G.‐Q. , Lee M.‐T.
Published: February 2007

We study the electron scattering through a quantum dot using quantum scattering theory. The elastic, inelastic, and spin‐flip scattering cross‐sections are obtained by solving the Lippmann‐Schwinger equations within the multichannel scattering model. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Broadband staircase quantum well infrared photodetector: working in long wavelength infrared range (LWIR)
Authors: Hostut M. , Kartal D. , Ergun Y. , Sokmen İ.
Published: February 2007

We present a theoretical investigation of a staircase‐like quantum well infrared photodetector (QWIP). It detects wavelength between 7.6 μm and 13.5 μm range at an applied electric field of F = 1.9x104 V/cm at 77 K. The dark current density was found to be around 2x10–7 A/cm2 at operating bias, which is lower than the conventional QWIPs in the literature. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin‐polarized current in a magnetic barrier structure under microwave radiation
Authors: Seo K. C. , Ihm G. , Lee S. J.
Published: February 2007

We have proposed a magnetic barrier structure with dc and ac electric fields between the barriers. We have found a significant amount of spin polarization and resonant structure in the transmission as a function of energy. Sets of Fano resonance peaks are clearly observed only for spin‐down electrons while the inelastic tunneling processes associated with absorption/emission of photons are observed for both spin electrons. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Persistent photoconductivity effect on weak localization in AlxGa1–xAsySb1–y/InAs quantum wells
Authors: Ishida S. , Fujimoto A. , Takeda K. , Shibasaki I.
Published: February 2007

Weak‐field magnetoconductance (MC) caused by the weak localization (WL) in AlxGa1–xAsySb1–y/InAs quantum wells (QWs) has been studied by means of tuning the carrier density n via the positive and negative persistent photoconductivity effects in order to explore the origin of spin‐orbit interaction (SOI). We have found the weak antilocalization (WAL) in extremely weak magnetic fields developing with increasing n. The MC has been fitted by taking account of the spin‐Zeeman effect on the SOI arising from the spin splitting in asymmetric systems. The SO field (Bso) inferred has been found to be almost independent of n, thereby confirming the dominant role of the Rashba field as the cause of SOI in our InAs QWs. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A study on the formation of MnFe2O4 nano‐powder by coprecipitation method
Authors: Azadmanjiri J. , Salehani H. K.
Published: February 2007

The microstructure and magnetic properties of manganese ferrite nano powder obtained from MnCl2·4H2O, (NH4)2Fe(SO4)2·6H2O, FeCl3·6H2O and NaOH by coprecipitation and aging in isothermal static conditions at temperature lower than 370 K, has been investigated by X‐ray diffraction (XRD), Transmission electron micrograph (TEM) and vibrating sample magnetometer (VSM). The results reveal the influence of the temperature on the particle size distribution as well as on the structure and composition of the ferrite phase. The magnetic properties of the ferrite are also presented. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The polarizability and the photoionization cross‐section under the external fields for donor impurities in quantum well‐wire
Authors: Koksal M. , Kasapoglu E. , Sari H. , Sokmen I.
Published: February 2007

In this study, we have calculated the donor impurity binding energy, donor impurity related photoionization cross‐section and polarizability in symmetric GaAs/Ga1–x Alx As quantum well‐wire as a function of the impurity positions, dimensions of the structures and external electric and magnetic field, the calculations were performed within the effective mass approximation, using a variational method. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical properties of copper and silver nanowires grown in a nanoporous alumina template
Authors: Green S. , Cortes A. , Riveros G. , Gómez H. , Dalchiele E. A. , Marotti R. E.
Published: February 2007

The optical properties of metallic nanowires (NW) grown in a dielectric template are investigated. The metallic NW of copper or of silver were grown into the nanoporous structure of commercially available alumina membranes. The optical reflectance of the metallodielectric samples prepared at different conditions are compared to each other and to unfilled alumina membranes. A simple model based on the Bruggeman approximation can be used to understand the results and to compare them to the bulk material. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Surface strain and hexagonal/cubic polymorphism in InGaN epitaxy: first‐principles study
Authors: Nakayama T. , Takei Y.
Published: February 2007

The energetics and the growth dynamics of InGaN layers on strained InN substrates are studied using the first‐principles calculations. It is shown that the diffusion of adsorbed atoms on the surface is suppressed when the grown layers receive the tensile stress from the substrate.and the bonding between adsorbed and surface atoms is weakened. The present results indicate that the surface strain is one of relevant factors to promote InGaN hexagonal/cubic polymorphism in epitaxy. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microscopic theory for intersubband spontaneous emission
Authors: Pereira M. F. , Wacker A.
Published: February 2007

The amplified spontaneous emission spectra of quantum‐cascade laser structures is computed with a Keldysh Green's functions theory. We show that the emission spectra are sharpened in comparison to gain spectra due to wave guide propagation. In addition the different dependence on level occupation causes moderate differences between gain and emission peak positions. Our fit‐parameter‐free theory is valid in ranges of strong nonequilibrium, where fit‐parameters do not even exist. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Detection of terahertz radiation in a slit‐grating gated field‐effect transistor
Authors: Aizin G. , Popov V. , Polischuk O.
Published: February 2007

We calculate the spectra of the resonant terahertz photoresponse associated with higher‐order plasmon resonances in a grating‐gated field‐effect transistor with two‐dimensional electron channel. The dependence of the photoresponse on both the dc bias current and the grating slit width is studied. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Enhancement of electron drift velocity in a quantum well by confinement of polar optical phonons
Authors: Požela Juras , Požela Karolis , Jucienė Vida
Published: February 2007

New approaches to decrease the electron–polar optical (PO) phonon scattering rate in double heterostructures by using phonon barriers (reflective to PO phonons and transparent for electrons) are proposed. Twofold decrease of the electron–PO phonon scattering rate in the AlGaAs/GaAs/AlGaAs quantum well by inserting the InAs phonon barriers is achieved. The enhancement of high electric field drift velocity in the AlGaAs/GaAs/AlGaAs heterostructure with the inserted one monolayer InAs phonon barriers compared with that heterostructure without barriers is observed experimentally. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic and electronic properties of transition metal nitride strained layers
Authors: Ribeiro M. , Scolfaro L. M. R. , Teles L. K. , Marques M. , Ferreira L. G.
Published: February 2007

We present a theoretical study with ab initio techniques on magnetic and electronic properties of 3d transition metal mononitrides. We perform the calculations in the wurtzite (w) and the zincblende (zb) structures, and find the tendency of all zb mononitrides to become half‐metallic (HM) under hydrostatic strain. MnN, CrN, and VN become HM with integer magnetic moments of 4, 3 and 2μB, respectively. CrN shows ferromagnetism (FM) throughout the range of our lattice constant calculations, while VN is FM beyond the lattice constant of 4.65 Å. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Control of polarization of polariton lasers
Authors: Glazov M. M. , Shelykh I. A. , Malpuech G. , Laussy F. , Kavokin K. V. , Kavokin A. V.
Published: February 2007

The polarization of semiconductor microcavities with embedded quantum wells (QWs) in the regime of polariton lasing is studied theoretically. We expect the emitted light to be linearly polarized, with the degree of polarization as well as its direction determined by the asymmetry of QW interfaces or localization of excitons on the anisotropic islands of QW width fluctuations. The ways to control the direction of polarization using external electric field are analyzed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of built‐in electric fields in AlGaN/GaN heterostructures grown on misoriented 4H‐SiC substrate by contactless electroreflectance
Authors: Syperek M. , Motyka M. , Kudrawiec R. , Misiewicz J. , Rudzinski M. , Hageman P. R. , Larsen P. K.
Published: February 2007

Room temperature contactless electroreflectance technique was used to investigate the built‐in electric field in AlGaN/GaN heterostructure grown by metaloorganic chemical vapour deposition on [0001] 4H‐SiC substrate. Two heterostructures have been studied: one grown with a misorientation angle (8 degrees toward [11‐20] crystallographic direction of the substrate) and second without misorientation angle. For both heterostructures strong AlGaN‐related resonance with Franz‐Keldysh oscillation (FKO) has been observed. The built‐in electric field in the AlGaN layer was extracted from the FKO period [0.26 MV/cm and 0.47 MV/cm for samples without and with misorientation, respectively]. It has been concluded that the substrate orientation angle has a great impact on the built‐in electric field and charge distribution across the AlGaN/GaN structure. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence temperature dependence of doped parabolic quantum wells
Authors: Tabata A. , Martins M. R. , Oliveira J. B. B. , Lamas T. E. , Duarte C. A. , Quivy A. A. , Gusev G. M.
Published: February 2007

Parabolic quantum wells (PQWs) have been studied by temperature dependent photoluminescence (PL). Two kind of samples have been studied. Concerning the undoped sample, the dominant luminescences were the bulk GaAs and the fundamental transition of the PQW. The evolution on temperature of the energy position of both PL emissions follows the well known Varshing formula. For the doped samples strong radiative recombination of the electron gas with photogenerated holes was observed. At low temperature strong Fermi level enhancement occurs in the luminescence as a result of the multi‐electron‐hole scattering, which is smear out increasing the temperature. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Theoretical investigations on the energy relaxation in twodimensional GaN systems
Authors: Tas M. , Tanatar B.
Published: February 2007

We theoretically study the energy relaxation of hot electrons via LO‐phonon emission in two‐dimensional GaN systems. We employ a model in which electrons and the lattice are in equilibrium separately, and the effective electron temperature is much larger than the lattice temperature. We include the dynamical screening of electrons, electron‐phonon interactions reduced phonon self‐energy correction, the hot‐phonon, and the.nite‐size effects. The power loss to acoustic phonons is also considered. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ballistic effect and optical properties of Si nanocrystallite structures
Authors: Torchynska T. V.
Published: February 2007

The purpose of this work is to clarify the type of corresponding radiative transitions and the PL mechanism in the big silicon nano‐crystallites with the size from the range of 10‐150 nm, which is higher than an exciton Bohr radius (≤5 nm) in corresponding bulk crystal. Photoluminescence in this type of Si nanocrystals is analyzed from the point of view of new concept based on the hot carrier ballistic transport role in the excitation of oxide‐related defects at the Si/SiOx interface. The role of hot carrier ballistic transport in the modification of photocurrent spectra of Si NC device structures is discussed as well. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Exciton thermal escape in symmetric InAs quantum dots in InGaAs/GaAs well structures
Authors: Casas Espinola J. L. , Torchynska T. V. , Polupan G. , Peña Sierra R.
Published: February 2007

The photoluminescence and its temperature dependence have been investigated for the ensembles of InAs quantum dots embedded in symmetric In0.15Ga0.85As/GaAs quantum wells with different PL intensities. The solution of the set of rate equations for exciton dynamics was used to analyze the nature of thermal activation energies of the QD photoluminescence quenching. It is revealed two different stages of thermally activated quenching of the QD PL intensity caused by thermal escape of excitons from the In0.15Ga0.85As/GaAs QW into the GaAs barrier and from the QDs into the QWs with their subsequent nonradiative recombination. The variety of activation energies of PL thermal quenching is discussed as well. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microwave induced negative resistance states in 2D electron gas with periodic modulation
Authors: Torres Manuel , Kunold Alejandro
Published: February 2007

We study the microwave‐induced photoconductivity of a two‐dimensional electron system (2DES) in the presence of a magnetic field and a two‐dimensional modulation. The microwave and Landau contributions are exactly taken into account, while the periodic potential is treated perturbatively. The longitudinal resistivity exhibits oscillations, periodic in ω /ωc . Negative resistance states (NRS) develop for sufficiently high electron mobility and microwave power. This phenomenon appears in a narrow window region of values of the lattice parameter (a), around a ∼ lB, where lB is the magnetic length. It is proposed that these phenomena may be observed in artificially fabricated arrays of periodic scatterers at the interface of ultraclean heterostructures. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence energy trend for ground and excited states in InAs quantum dots in a well InGaAs/GaAs structures
Authors: Velazquez Lozada E. , Torchynska T. V. , Dybiec M. , Ostapenko S. , Eliseev P. G. , Stintz A. , Malloy K. J.
Published: February 2007

This paper presents the photoluminescence study at 80K and scanning photoluminescence spectroscopy investigation of the ground and multi excited states at 80 and 300K in InAs quantum dots (QDs) inserted in symmetric In0.15Ga0.85As/GaAs QW structures created at different QD growth temperatures. It is shown that some of the structures investigated exhibit a spatial long range variation of the average QD size in the QD ensemble across the sample. This long range QD size inhomogeneity was used for an investigation of the multi excited state energy trend versus ground state energy (or QD sizes). Experimental results were compared with the electron‐hole level energy trend versus QD size predicted theoretically on the base of the 8‐band k·p approach. Some anti correlation between experimental and theoretical results has been revealed and discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)