bluuebunny/crossref_metadata_2025 huggingface dataset:
Presence of immunoreactive gonadotropin releasing hormone (GnRH) and its receptor (GnRHR) in rat ovary during pregnancy
Authors: Sengupta Anamika , Chakrabarti Nilkanta , Sridaran Rajagopala
Published: October 2007

The present study aims at quantification of gonadotropin releasing hormone (GnRH) by radioimmunoassay, relative expression of its mRNA by real‐time PCR accompanied by its cellular localization in the rat ovary by immunonohistochemistry (IHC) during different time points of pregnancy. To determine the involvement of endogenous ovarian GnRH in receptor mediated local autocrine/paracrine functions within the ovary, the cell specific localization of the classical receptor for GnRH (GnRHR) in the ovary by IHC and expression pattern of its mRNA were studied during pregnancy. Receptor expression during each time point within the ovary was reconfirmed by Western blot analysis accompanied by densitometric analysis of the signal intensity. Results reveal that the content of ovarian GnRH reaches its maximum on Day 20. The densitometric analysis of GnRHR receptor expression from Western blot study exhibits a decreasing trend by Day 20. Presence of GnRH and GnRHR mRNA in the ovary indicates the local synthesis of both ligand and receptor in the rat ovary. Differential expression of GnRH/GnRHR in the corpus luteum throughout pregnancy strengthens the hypothesis of the involvement of ovarian GnRH in local ovarian functions by receptor‐mediated mechanisms. The expression of GnRH and GnRHR in the atretic antral follicles is indicative of the possible involvement of this decapeptide in processes like follicular atresia. The expression of GnRH/GnRHR in the nonatretic antral follicles and their oocytes requires further in‐depth investigation. Collectively, this study for the first time reveals the presence of endogenous ovarian GnRH/GnRHR supporting their possible involvement in local autocrine/paracrine functions during pregnancy. Mol. Reprod. Dev. 75: 1031–1044, 2007. © 2007 Wiley‐Liss, Inc.
Strain and stress computations in stochastic finite element methods
Authors: Ghosh Debraj , Farhat Charbel
Published: October 2007

This paper focuses on the computation of statistical moments of strains and stresses in a random system model where uncertainty is modeled by a stochastic finite element method based on the polynomial chaos expansion. It identifies the cases where this objective can be achieved by analytical means using the orthogonality property of the chaos polynomials and those where it requires a numerical integration technique. To this effect, the applicability and efficiency of several numerical integration schemes are considered. These include the Gauss–Hermite quadrature with the direct tensor product—also known as the Kronecker product—Smolyak's approximation of such a tensor product, Monte Carlo sampling, and the Latin Hypercube sampling method. An algorithm for reducing the dimensionality of integration under a direct tensor product is also explored for optimizing the computational cost and complexity. The convergence rate and algorithmic complexity of all of these methods are discussed and illustrated with the non‐deterministic linear stress analysis of a plate. Copyright © 2007 John Wiley & Sons, Ltd.
An explicit discontinuous Galerkin method for non‐linear solid dynamics: Formulation, parallel implementation and scalability properties
Authors: Noels L. , Radovitzky R.
Published: October 2007

An explicit‐dynamics spatially discontinuous Galerkin (DG) formulation for non‐linear solid dynamics is proposed and implemented for parallel computation. DG methods have particular appeal in problems involving complex material response, e.g. non‐local behavior and failure, as, even in the presence of discontinuities, they provide a rigorous means of ensuring both consistency and stability. In the proposed method, these are guaranteed: the former by the use of average numerical fluxes and the latter by
the introduction of appropriate quadratic terms in the weak formulation. The semi‐discrete system of ordinary differential equations is integrated in time using a conventional second‐order central‐difference explicit scheme. A stability criterion for the time integration algorithm, accounting for the influence of the DG discretization stability, is derived for the equivalent linearized system. This approach naturally lends itself to efficient parallel implementation. The resulting DG computational framework is implemented in three dimensions via specialized interface elements. The versatility, robustness and scalability of the overall computational approach are all demonstrated in problems involving stress‐wave propagation and large plastic deformations. Copyright © 2007 John Wiley & Sons, Ltd.
Polymeric photoacid generators for direct photochemical modification of surface
Authors: Jung Sung‐Ouk , Jung Myung‐Sup , Choi Tae‐Lim , Huh Nam , Ko Christopher , Jung Hee‐Tae
Published: October 2007

To achieve easy spin coating and enhanced efficiency in the photolithographic process for the direct photochemical modification of surface, we incorporated photoacid generator (PAG) into polymer backbone. Bis‐(4‐hydroxy‐phenyl)‐(4‐methoxy‐3,5‐dimethyl‐phenyl)‐sulfonium chloride was synthesized as a monomer, and was polymerized with sebacoyl chloride and terephthaloyl chloride. The resulting polymeric PAG in chloride salt form was converted to the p‐toluenesulfonate and 1‐naphthol‐5‐sulfonate forms with ion‐exchange reactions. By the photolithographic process with the polymeric PAG, the protecting groups of the linker molecules self‐assembled onto a glass plate were micropatterned to produce an amine pattern for the microarray of oligonucleotides. The acids generated from the polymeric PAG effectively deprotect the acid‐labile protecting groups of the linker molecules through a chemical amplification process in the exposed region. After the treatment of the patterned amino groups with a fluorescent dye, the pattern profiles were observed with a fluorescence scanner. The fluorescence image reveals a well‐defined pattern at a micro level, which clearly indicates that the polymeric PAGs have a great potential in photochemical surface modification for the microarray of oligonucleotides. Copyright © 2007 John Wiley & Sons, Ltd.
Effect of polymerization methods on the residual monomer level of acrylic resin denture base polymers
Authors: Çelebi Nilüfer , Yüzügüllü Bulem , Canay Şenay , Yücel Ülkü
Published: October 2007

Wearing dental acrylic prosthesis causes adverse reactions to oral tissues due to bioactive leachables from resins such as residual methyl methacrylate (MMA). The aim of this study is to apply the high performance liquid chromatography (HPLC) method to quantify and compare the amount of MMA monomers released from denture base resin polymers processed by the conventional compression molding method (Paladent), microwave polymerization (Acron MC), and injection molding technique (PalaXpress). Six specimens of 10 ± 0.2 mm in diameter and 2.0 ± 0.2 mm in thickness of each material were prepared according to manufacturer's instructions. Specimens were stored in nanopure water at room temperature (23 ± 2°C) for 4 hr, 48 hr, 8 days, and 15 days separately. Residual MMA released into water was determined with HPLC for all time intervals. Data for all time intervals were analyzed among each group using the Friedman test and differences were found to be statistically significant for all time intervals for Acron MC, Paladent, and PalaXpress (p > 0.05). Kruskal–Wallis test was used to compare changes of residual MMA within time intervals among denture base resin groups and statistically significant differences were found between all time intervals (p > 0.05). Acron MC exhibited significantly lower residual MMA leach compared both to Paladent and PalaXpress, and Paladent showed more residual MMA leach compared to PalaXpress. Residual MMA leach for Acron MC, PalaXpress, and Paladent showed statistically significant leach in the first 48 hr of immersion in water followed by gradual longer‐lasting moderate increase until the 15 day interval which was not statistically significant (p < 0.05). Copyright © 2007 John Wiley & Sons, Ltd.
Enhanced swelling and adsorption properties of AAm‐AMPSNa/clay hydrogel nanocomposites for heavy metal ion removal
Authors: Kaşgöz Hasine , Durmuş Ali , Kaşgöz Ahmet
Published: October 2007

Novel type hydrogel‐clay nanocomposites based on the acrylamide (AAm)‐ 2‐acrylamido‐ 2‐methylpropane sulfonic acid (AMPS) sodium salt and clay were synthesized via in situ copolymerization in aqueous solution. Samples were characterized by determining total basic group (TGB) content and swelling degree, XRD analysis, and FTIR spectroscopy. Effects of monomer ratio and clay amount on the swelling properties of the samples were investigated. It was found that the hydrogel/clay nanocomposites exhibited improved swelling capacity compared with the hydrogels. Samples were used to remove heavy metal ions (Cu (II), Cd (II), and Pb (II)) from aqueous solution in competitive and non‐competitive conditions for the first time. The effects of time and pH of the initial metal ion solution on the adsorption capacity were investigated and selectivity properties of the samples were evaluated. It was found that incorporation of a low amount of clay (10% (wt)) into the polymer structure increased the heavy metal ion adsorption capacity of the sample. It was concluded that the AAm‐AMPS/clay nanocomposites could be used as novel type, fast‐responsive, and high capacity sorbent materials in heavy metal removing processes. Copyright © 2007 John Wiley & Sons, Ltd.
Immune‐compromised state in the rat pancreas after chronic alcohol exposure: the role of peroxisome proliferator‐activated receptor γ
Authors: Fortunato F , Berger I , Gross M‐L , Rieger P , Buechler MW , Werner J
Published: October 2007

Alcohol exposure is known to sensitize acinar cells to various insults but the pathophysiological mechanisms of alcoholic pancreatitis remain unknown. Alcohol abuse has been shown to mediate an anti‐inflammatory response and periods of immune suppression seem to be associated with organ injury and mortality. The purpose of this study was to determine the mechanisms by which alcohol exerts transcriptional activities in the rat pancreas and how alcohol alters the inflammatory response. Using the Lieber–DeCarli alcohol/control diet, rats that were fed with alcohol over 14 weeks demonstrated a decrease of inflammatory cells in pancreatic tissue compared to controls. The anti‐inflammatory effects of alcohol were confirmed by decreased expression of pro‐inflammatory cytokines including TNFα, IL‐1β, IL‐18, TGFβ, and MCP‐1. In addition, alcohol significantly increased the activity of PPARγ, which is a known anti‐inflammatory transcription factor, while pro‐inflammatory factors including AP‐2 and EGR‐1 were significantly suppressed. NFκB binding showed a tendency towards a reduction. Electron microscopy studies revealed enlarged and injured mitochondria and lysosomes, accompanied by peri‐cellular fibrosis. Furthermore, alcohol exposure increased the activities of trypsin and cathepsin B, both known to be critical in initiating acinar cell injury and pancreatitis. Despite the known alcohol‐mediated acinar cell and mitochondrial injury, the mitochondrial‐mediated apoptotic pathway was attenuated. These data demonstrate that the pancreas exposed to alcohol maintains an anti‐inflammatory state by activating PPARγ. Intracellular mitochondrial and lysosomal damage after chronic alcohol exposure induces premature activation of digestive enzymes and establishment of peri‐cellular fibrosis in the absence of inflammation. Copyright © 2007 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Detection of high‐mobility group proteins A1 and A2 represents a valid diagnostic marker in post‐pubertal testicular germ cell tumours
Authors: Franco R , Esposito F , Fedele M , Liguori G , Pierantoni GM , Botti G , Tramontano D , Fusco A , Chieffi P
Published: October 2007

The high‐mobility group A (HMGA) non‐histone chromosomal proteins HMGA1 and HMGA2 are architectural factors. They are abundantly expressed during embryogenesis and in most malignant neoplasias, whereas their expression is low or absent in normal adult tissues. Their over‐expression is known to have a causal role in cellular neoplastic transformation. Previous studies from our group have shown that their expression is restricted to specific germinal cells. In this study we have evaluated, by immunohistochemistry, the expression of HMGA1 and HMGA2 in a series of post‐pubertal testicular tumours of different histological types, including 30 seminomas, 15 teratomas, 15 embryonal carcinomas and 10 mixed germinal tumours with a prominent yolk sac tumour component. HMGA1 protein expression was detected in all seminomas and embryonal carcinomas analysed, but not in teratomas or yolk sac carcinomas. Conversely, HMGA2 was present only in embryonal carcinomas and yolk sac carcinomas, but not in seminomas or teratomas. The immunohistochemical data were further confirmed by Western blot and, at the mRNA level, by RT–PCR analyses. These findings indicate that HMGA1 and HMGA2 are differently expressed with respect to the state of differentiation of testicular germ cell tumours (TGCTs), with over‐expression of both proteins in pluripotential embryonal carcinoma cells and loss of expression of HMGA1 in yolk sac tumours and of both proteins in the mature adult tissue of teratoma areas. Therefore, the different profiles of HMGA1 and HMGA2 protein expression could represent a valuable diagnostic tool in some cases in which the histological differential diagnosis is problematic. Copyright © 2007 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Nonmedical prescribing: managing patients with respiratory disease
Authors: Pearson Keith
Published: October 2007

Our series Nonmedical prescribing gives an overview of the work that can be done by nonmedical prescribers and what can be achieved. Here Keith Pearson, a supplementary prescriber for Salford PCT, describes his roles within local GP practices. Copyright © 2007 Wiley Interface Ltd
National Audit Office calls for more cost‐effective prescribing
Authors: Chaplin Steve
Published: October 2007

Steve Chaplin describes the cost‐cutting measures recommended by the National Audit Office in their recent report on prescribing costs in primary care. Copyright © 2007 Wiley Interface Ltd
Management of menopausal symptoms: the risks and benefits
Authors: Currie Heather , Guttinger Anja
Published: October 2007

Despite recent controversy, hormone replacement therapy remains the mainstay of treatment of menopausal symptoms. Our Drug review considers the risks and benefits of the current treatment options, followed by sources of further information, an analysis of prescription data and the Datafile. Copyright © 2007 Wiley Interface Ltd
Clenil Modulite, a CFC‐free MDI with no adjustment on switching
Authors: Chaplin Steve , Head Steve
Published: October 2007

Clenil Modulite is the first CFC‐free metered‐dose inhaler directly interchangeable with existing CFC‐containing inhalers. In our New products review, Steve Chaplin presents the clinical data relating to its bioequivalence and Dr Steve Head comments on its place in treatment. Copyright © 2007 Wiley Interface Ltd
Elastic‐constant systematics in f.c.c. metals, including lanthanides–actinides
Authors: Ledbetter Hassel , Migliori Albert
Published: October 2007

For f.c.c. metals, using Blackman's diagram of dimensionless elastic‐constant ratios, we consider the systematics of physical properties and interatomic bonding. We focus especially on the lanthanides–actinides La, Ce, Yb, Th, U, Pu, those for which we know some monocrystal elastic constants. Their behavior differs from the other f.c.c. metals, and all except La show a negative Cauchy pressure, contrary to most f.c.c. metals, which show a positive Cauchy pressure. Among the lanthanides–actinides, δ‐Pu stands apart, consistent with its many odd physical properties. Based on elastic‐constant correlations, we suggest that δ‐Pu possesses a strong s‐electron interatomic‐bonding component together with a covalent component. Elastically, δ‐Pu shows properties similar to Yb. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Combined resonance and resonant detection of modulated terahertz radiation in a micromachined high‐electron mobility transistor
Authors: Hu Yabo , Ryzhii Maxim , Hagiwara Ichiro , Shur Michael S. , Ryzhii Victor
Published: October 2007

We analyze the operation of a resonant detector of modulated terahertz (THz) radiation based on a micromachined high‐electron mobility transistor (HEMT) with a microcantilever (MC) as mechanically floating gate. Using the device model, which describes both MC mechanical motion and plasma effects in the HEMT twodimensional electron channel, we calculate the output gate and source‐drain ac currents and the detector responsivity as functions of the modulation and carrier frequencies in linear and saturation regimes of the HEMT operation. It is shown that the THz detector responsivity exhibit sharp and high maxima under the conditions of both mechanical and plasma resonances. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coulomb‐mediated electron bunching in tunneling through coupled quantum dots
Authors: Kiesslich G. , Schöll E. , Hohls F. , Haug R. J.
Published: October 2007

The recent observation of super‐Poissonian shot noise in the tunneling current through two layers of selfassembled quantum dots is analyzed and discussed in terms of a sequential tunneling model for a single weakly coupled quantum dot stack.We demonstrate that the phenomenon of bunching in the electron transfer can be explained by the sole effect of Coulomb interaction between electrons inside the stack. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin‐Hall effect and spin coherent waves in semiconductors with Rashba spin‐orbit interaction
Authors: Kleinert P. , Bryksin V. V.
Published: October 2007

Based on rigorous quantum‐kinetic equations for the spin‐density matrix, spin‐charge coupled drift‐diffusion equations are derived for a strongly confined twodimensional hole gas. An electric field leads to a coupling between the spin and charge degrees of freedom. For weak spin‐orbit interaction, this coupling gives rise to the intrinsic spin‐Hall effect that occurs in the diffusive regime. There exists a threshold value of the spin‐orbit coupling constant that separates spin diffusion from ballistic spin transport. In the latter regime, undamped spin‐coherent oscillations are observed. Their relationship to the zitterbewegung is discussed. The analytic results are compared with an exact microscopic approach valid in the ballistic regime. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quantum Fermi's golden rule for semiconductor nanodevices
Authors: Rossi Fausto
Published: October 2007

We shall revisit the conventional adiabatic or Markov approximation, stressing its intrinsic failure in describing the proper quantum‐mechanical evolution of a generic subsystem interacting with its environment. In particular, we shall show that – contrary to the semiclassical case – the Markov limit does not preserve the positivedefinite character of the corresponding density matrix, thus leading to highly non‐physical results. To overcome this problem, we shall propose an alternative adiabatic procedure which (i) in the semiclassical limit reduces to the standard Fermi's golden rule, and (ii) describes a genuine Limblad evolution, thus providing a reliable/robust treatment of energy‐dissipation and dephasing processes in electronic quantum devices. Compared to standard master‐equation formulations, the proposed approach does not involve/require any reduction or average procedure, exactly as for the derivation of the well known Fermi's golden rule. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Theoretical study of optical excitation in quantum dots by circularly polarized light
Authors: Ishikawa T. , Eto M.
Published: October 2007

We study theoretically electron states in quantum dots and their excitations by circularly polarized light. First, we calculate the hole states in a quantum dot modeled by three‐dimensional harmonic confinement potential. In the bulk direct‐gap semiconductors, the k · p perturbation method around Γ point adequately yields heavy‐hole, light‐hole and split‐off bands. We adopt the effective‐mass approximation based on the k · p perturbation method and obtain quantized energy levels for holes in the quantum dot. The ground levels are two‐fold degenerate and mainly consist of |j, m 〉 = |3/2, ±3/2〉 components. It should be mentioned that a small amount of |3/2, ±1/2〉 components are coherently mixed in the states. Second, we examine an electron‐hole excitation by the irradiation of circularly polarized light σ–. The main component of the exciton is |3/2, ‐3/2〉 hole|1/2, ‐1/2〉electron. The electron state|1/2, 1/2〉electron is also excited owing to the mixture between |3/2, ±3/2〉 and |3/2, ±1/2〉 components in the hole states, which should lead to an inaccuracy in the manipulation of electron spins. The Overhauser field created by nuclear spins plays a role when it is larger than an external magnetic field. It randomizes the direction of electron spins excited by the circularly polarized light σ‐ in an ensemble of self‐assembled quantum dots. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of decoherence in 1D systems, a comparison between distinguishable‐ and indistinguishable‐particle collisions
Authors: Buscemi Fabrizio , Bordone Paolo , Bertoni Andrea
Published: October 2007

We give a quantitative evaluation of the entanglement dynamics in scattering events between two electrons interacting via Coulomb potential in 1D systems, We apply a method, specifically designed for indistinguishable particles, based on the calculation of the von Neumann entropy of the system density matrix. From the timedependent numerical solution of the two‐particle wavefunction we evaluate the entanglement evolution for different spin configurations. The procedure allows to understand the mechanisms that govern entanglement creation and its connection with the characteristic physical parameters and initial conditions of the system. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cutoff frequency characteristics of gate‐controlled hot‐electron transistors by Monte Carlo simulation
Authors: Igarashi Mitsuhiko , Furuya Kazuhito , Miyamoto Yasuyuki
Published: October 2007

The high‐speed characteristics and off characteristics of a novel transistor with a hot‐electron launcher and a transit layer of an intrinsic semiconductor whose current is controlled by an insulated gate are evaluated by Monte Carlo simulation. The dependences of the cutoff frequencyfTon the gate insulator thickness, collector bias voltage, gate length and transit layer length are clarified. For the optimum structure consisting of InP/InGaAs/W as the emitter/transit layer/collector, Au as the gate and bisbenzocyclobutene (BCB) as the gate insulator and the surrounding material,fTis 1.4 THz at the collector current density of 1.6 MA/cm2. The collector current can be controlled over four orders of magnitude by a gate voltage swing of 0.6 V. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Monte Carlo analysis of memory effects in nano‐scale rectifying diodes
Authors: Iñiguez‐de‐la‐Torre I. , González T. , Pardo D. , Mateos J.
Published: October 2007

We analyze hysteresis effects taking place for certain bias conditions in nano‐scale rectifying diodes as a consequence of the variation of the surface states occupation at the sidewalls of the trenches etched to define the channel. Such effects can be used for memory purposes. A model for the storage/release of surface charges is proposed and, implemented in a Monte Carlo (MC) simulator, is able to provide a microscopic interpretation of this effect. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Monte Carlo simulation of plasma oscillations in ultra‐thin layers
Authors: Millithaler J.‐F. , Varani L. , Palermo C. , Pousset J. , Knap W. , Mateos J. , González T. , Perez S. , Pardo D. , Reggiani L.
Published: October 2007

We investigate the dispersion of the plasma frequency associated with the free carriers in a InGaAs layer of length L in the range 0.1‐1 μm as a function of the thickness W and carrier concentration at thermal equilibrium T = 300 K. To this purpose we use a Monte Carlo simulator coupled with a two dimensional Poisson solver. To take into account the fringing effects of the electric field, the layer is embedded in a dielectric medium (vacuum) along the transverse direction. The fluctuations of the voltage at the center of the sample are extracted and their spectral density calculated by Fourier transform of their autocorrelation function.

For W = 100 nm and carrier concentrations of 1016 ÷ 1018 cm–3 the spectral density shows peaks which are in good agreement with the 3D expression of the plasma frequency. For W ≤ 10 nm the spectral density of voltage fluctuations exhibits a peak that depends on L, thus implying that the oscillation mode exhibits a dispersion. The corresponding frequency values are in good agreement with the 2D expression of the plasma frequency obtained for a ballistic regime within the in‐plane approximation for the electric field. Simulations evidence a region of cross‐over between the 2D and 3D plasma frequencies for width W around 20 nm. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coherent control of carrier capture and wave front dynamics in homogeneously excited quantum wire‐dot systems
Authors: Kuhn Tilmann , Reiter Doris , Axt Vollrath Martin
Published: October 2007

We study the coherent control of capture and transport processes in a quantum wire‐quantum dot‐system which is homogeneously excited by ultrafast laser pulses. Due to the carrier capture into the quantum dot a spatial profile of the carrier density in the wire region builds up exhibiting wave fronts moving away from the dot. In the presence of a dot with two or more bound levels wave fronts resulting from the capture into different states can clearly be distinguished. By using a pair of phase locked pulses the capture rates into different levels but also the spatio‐temporal dynamics in the wire region can be coherently controlled. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Monte Carlo investigation of carrier transport in fabricated back‐to‐back Schottky diodes: Influence of direct quantum tunnelling and temperature
Authors: Pascual E. , Rengel R. , Reckinger N. , Tang X. , Bayot V. , Dubois E. , Martín M. J.
Published: October 2007

In this paper we present a Monte Carlo investigation of charge transport‐including quantum tunnelling effects in fabricated back‐to‐back n‐type Schottky barriers in the reverse bias regime. The effect of the variation of the temperature over the current density and over different internal magnitudes like carrier density, electric field, etc. together with velocity distribution functions and the density of scattering mechanisms has been analyzed. The study of transport in the space charge region evidences important quasi‐ballistic characteristics, thus becoming an important issue to be tackled in the modelling of Schottky‐based devices with reverse biased junctions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Extended time delayed feedback control of stochastic dynamics in a resonant tunneling diode
Authors: Schöll E. , Majer N. , Stegemann G.
Published: October 2007

We investigate the influence of extended time delayed feedback upon the spatio‐temporal current density patterns in a double barrier resonant tunnelling diode. The parameters of the device are chosen to reflect a situation where the only stable state of the system is a spatially inhomogeneous ”filamentary” steady state. The addition of weak Gaussian white noise to the system gives rise to spatially inhomogeneous self‐sustained temporal oscillations that can be quite coherent. Applying a single time delayed feedback can either increase or decrease the regularity of the noise‐induced spatio‐temporal dynamics. In this work we show that using multiple time delayed feedback provides means to increase the temporal regularity even further and to enlarge the parameter regime in which no delay‐induced bifurcations occur. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Control of noise‐induced spatiotemporal patterns in superlattices
Authors: Hizanidis Johanne , Schöll Eckehard
Published: October 2007

We investigate a semiconductor superlattice exhibiting complex dynamics of electron accumulation and depletion fronts (travelling field domains) in the presence of noise and control. In the uncontrolled system noise is able to induce electron charge front motion through the device when the system is prepared near a global bifurcation which yields it highly sensitive to fluctuations. The associated current density oscillations exhibit a maximum of coherence at an optimal noise intensity, a phenomenon known as coherence resonance. We show how control in the form of a time‐delayed feedback signal affects the noise‐induced dynamics. We observe that control induces a limit cycle in a wide range of the control parameter space and therefore destroys the effect of coherence resonance. For low noise intensity, time‐delayed feedback control enhances the regularity (coherence) of the noisy oscillations considerably. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Monte Carlo study of 2D electron gas transport including Pauli exclusion principle in highly doped silicon
Authors: Carosella F. , Saint‐Martin J. , Bournel A. , Galdin‐Retailleau S. , Dollfus P.
Published: October 2007

A Multi Sub‐band Monte Carlo Simulator improved to efficiently include the Pauli Exclusion Principle is presented. It is used to study the transport in highly doped and ultra‐thin silicon film. Both steady state and transient regime of transport for silicon films under uniform driving field are investigated. Such approach aims to be carried out in a full device simulator to improve the modeling of the access region of nano‐Double Gate MOSFETs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamics of microwave‐induced processes in photoexcited GaAs/AlGaAs heterostructures
Authors: Baskin I. , Ashkinadze B. M. , Cohen E. , Pfeiffer L. N.
Published: October 2007

Photoluminescence (PL) of high‐quality GaAs/AlGaAs–based heterostructures (HS) shows a remarkable time‐dependent response to microwave irradiation pulses at temperature 2 K. The mw‐frequency was 36 GHz and the modulation pulse widths varied in a wide range. Sharp PL intensity flashes (reaching 100 fold enhancement) at the leading or/and trailing mw‐pulse edges are observed. The transient PL response exhibits a complex interplay of various mw‐induced physical processes: electron heating, electron and exciton density changes as well as an interaction of electrons, holes and excitons with non‐equilibrium acoustic phonons that are emitted by the mw‐heated 2DEG. It is noted that in commonly studied cw, mw‐induced PL (or resistivity) modulation, the observed (cw) effects are determined by a combination of these processes. We developed a model that considers the instantaneous mw‐induced electron heating and following relaxation of the photoexcited electrons, excitons and acoustic phonon flux. Using this model we simulate various types of mw‐induced PL transients observed in undoped HS's as well as in HS's that contain a 2DEG. These simulations prove that non‐equilibrium acoustic phonons play an important role in the mw‐induced PL dynamics. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quantum non‐locality in systems with open boundaries: From the Wigner‐function formalism to non‐homogeneous Markovian master equations
Authors: Taj David , Rossi Fausto
Published: October 2007

We shall discuss the role of electrical contacts within the conventional treatment of quantum devices based on the Wigner‐Function formalism. Our analysis will show that the artificial spatial separation between device active region and external reservoirs, being intrinsically incompatible with the non‐local character of quantum mechanics, may produce highly non‐physical results like boundary‐driven negative probability distributions.

To overcome this serious limitation, we shall propose a new strategy to properly separate device and reservoir degrees of freedom, based on the well known projection techniques used in the formal theory of open systems. Our main result is a non‐Markovian master equation, where dissipation and dephasing phenomena are also induced by the presence of spatially external particle reservoirs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ultrafast optical Kerr effect of excitons weakly confined in GaAs thin films
Authors: Kanno Atsushi , Katouf Redouane , Kojima Osamu , Ishi‐Hayase Junko , Tsuchiya Masahiro , Isu Toshiro
Published: October 2007

We investigate ultrafast response of optical Kerr effect (OKE) induced by excitons weakly confined in GaAs thin films. The observed decay time of optical response agrees approximately with incident pulse duration. At 100‐fs pulse irradiation the response time is estimated to be 170 fs, though the exciton lifetime is about 10 ns. It is considered that the ultrafast response of OKE is caused by not population relaxation but orientation relaxation of excitons. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Direct observation of Landau damping in a solid state plasma
Authors: Hasselbeck M. P. , Seletskiy D. , Dawson L. R. , Sheik‐Bahae M.
Published: October 2007

We use ultrafast THz spectroscopy to study Landau damping in a coherent plasma system. A series of InSb‐based bulk heterostructures provide increasing spatial confinement that restricts the scattering wave vector in the electron‐electron interaction. This results in a dramatic reduction of the plasma contribution to the radiation signal. The experimental results are explained by model calculations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Generation of TeraHertz radiation assisted by optical phonons in nitride‐based quantum wells and heterolayers
Authors: Shiktorov P. , Starikov E. , Gružinskis V. , Varani L. , Palermo C. , Torres J. , Chusseau L.
Published: October 2007

To analyze the main features of THz radiation generation caused by optical‐phonon transit‐time resonance in the case of bidimensional transport, a simplified analytical model is developed in terms of generalized parameters of bulk materials and 2D structures. In the framework of such a model and direct Monte Carlo simulations, it is shown that for a given material: (i) the generation conditions are the same in quantum wells and heterolayers, and they can be characterized by the same parameter related to the effective width of the 2D‐channel and with the optical phonon momentum, (ii) a considerable increase up to 5 times of the high‐frequency cut‐off for THz radiation generation is predicted in going from 3D to 2D transport. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Few‐particle electron dynamics in coupled quantum dots with phonon interaction
Authors: Bertoni Andrea , Climente Juan I. , Rontani Massimo , Goldoni Guido , Hohenester Ulrich
Published: October 2007

The time evolution of a correlated multi‐electron state in a semiconductor coupled quantum dot, interacting with the acoustic phonon bath, is calculated within the master equation formalism, including electron‐electron interaction exactly through the configuration‐interaction approach. The system is evolved after an initialization phase, with the system under strong bias, leading to the charge density mainly localized in one of the dots. When the system is evolved (in unbiased condition), damped multi‐frequency charge oscillations are found, which strongly depend on the 3D system geometry and initialization. We describe the approach used to obtain the multi‐electron states and to include the phonon‐induced transitions between them in the time evolution. Furthermore, the effect of a magnetic field applied in the axial direction of the vertical double‐dot cylindrical structure is discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
3D Monte Carlo simulation including full Coulomb interaction under high electron concentration regimes
Authors: Uechi Tadayoshi , Fukui Takayuki , Sano Nobuyuki
Published: October 2007

We construct 3D Monte Carlo (MC) simulations including the full Coulomb interaction as accurately as possible. In order to achieve this goal, the usual strategy for the MC approach is employed; the Coulomb potential is split into the long‐range and the short‐range parts. The long‐range part of the Coulomb potential is taken into account by solving the Poisson equation, in which the simulation parameters such as mesh size, charged‐particle size, time step etc are carefully optimized by performing the particle simulations with turning off artificially all short‐ranged scatterings. The short‐range part of the Coulomb potential is incorporated into the MC simulations as scattering processes by developing a new scattering model, in which the impurities are localized in real space. It is shown that the present 3D MC simulations successfully explain the entire regime of the electron mobility as a function of impurity concentrations. In addition, it is found for the first time that the plasma frequency is modulated due to localization of the background impurities. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimization strategy based on genetic algorithms and neural networks applied to a polymerization process
Authors: Curteanu Silvia , Leon Florin
Published: October 2007

The article presents a simple and general methodology, especially destined to the optimization of complex, strongly nonlinear systems, for which no extensive knowledge or precise models are available. The optimization problem is solved by means of a simple genetic algorithm, and the results are interpreted both from the mathematical point of view (the minimization of the objective function) and technological (the estimation of the achievement of individual objectives in multiobjective optimization). The use of a scalar objective function is supported by the fact that the genetic algorithm also computes the weights attached to the individual objectives along with the optimal values of the decision variables. The optimization strategy is accomplished in three stages: (1) the design and training of the neural model by a new method based on a genetic algorithm where information about the network is coded into the chromosomes; (2) the actual optimization based on genetic algorithms, which implies testing different values for parameters and different variants of the algorithm, computing the weights of the individual objectives and determining the optimal values for the decision variables; (3) the user's decision, who chooses a solution based on technological criteria. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
Partitioning of atomization energy
Authors: Vyboishchikov Sergei F.
Published: October 2007

The present work provides a technique for partitioning the atomization energy of a molecule into diatomic contributions. The method is largely based on the redistribution of the kinetic energy term in Mayer's energy partitioning and uses free‐atom energies as a reference. The comparison of Mayer's original method, the alternative Ichikawa–Yoshida approach, and the new atomization energy partitioning (AEP) shows that the new approach has advantages in describing trends in diatomic energies in molecules with triple bonds, as well as for hydrogen bonds. The proposed AEP is a viable alternative to Mayer's energy partitioning method. © 2007 Wiley Periodicals, Inc. Int. J. Quantum Chem, 2008
The non‐destructive identification of solid over‐the‐counter medications using single particle aerosol mass spectrometry
Authors: Martin Audrey N. , Farquar George R. , Jones A. Daniel , Frank Matthias
Published: October 2007

Single over‐the‐counter medication tablets were analyzed in real time using Single Particle Aerosol Mass Spectrometry (SPAMS). Dual‐polarity time‐of‐flight mass spectra were obtained for micrometer‐sized single particles dislodged from a single tablet without destroying the shape or markings of each tablet. The solid tablet was placed in a modified‐top glass vial and shaken to dislodge and introduce micrometer‐sized particles into the SPAMS system. Unique spectra from these particles were obtained in less than 1 s for single tablets of aspirin, ibuprofen, pseudoephedrine, phenylephrine, loratadine, or diphenhydramine. The signals obtained allowed the non‐destructive identification of an individual tablet in seconds. SPAMS presents an ideal system for high‐throughput analysis of solid drugs. Copyright © 2007 John Wiley & Sons, Ltd.
Oligodeoxyribonucleotide Association with Single‐Walled Carbon Nanotubes Studied by SPM
Authors: Lahiji Roya R. , Dolash Bridget D. , Bergstrom Donald E. , Reifenberger Ronald
Published: October 2007

Studies have been performed on both as‐received and chemically oxidized single‐walled carbon nanotubes (SWCNTs) grown by two different growth methods to better understand the preferential association of the oligodeoxyribonucleotide T30 (ODN) with SWCNTs. Samples of T30 ODN:SWCNT were examined under ambient conditions using non‐contact scanning probe microscope (SPM) techniques. The resulting images show different morphologies ranging from tangled networks of SWCNTs to individual, well‐dispersed isolated SWCNTs as the sonication time is increased. SPM images of well‐dispersed, as‐received SWCNTs reveal isolated features that are 1.4 to 2.8 nm higher than the bare SWCNT itself. X‐ray photoemission spectroscopy (XPS) confirmed these features to be T30 ODN in nature. Chemically oxidizing the SWCNTs before sonication is found to be an effective way to increase the number of T30 ODN features.
Preparation of a Panoscopic Mimic Diatom from a Silicon Compound
Authors: Fei Bin , Hu Zhigang , Lu Haifeng , Xin John H.
Published: October 2007

Inspired by biological design principles, a panoscopic mimic diatom was created by hierarchical self‐assembly of reactive amphiphiles in a multiphase medium comprising hexadecane, ethanol, water, and hydrochloric acid. Through simple stirring at room temperature, mesolamellar macroporous capsules covering oil droplets were obtained in large quantity, which was confirmed by NMR spectroscopy, X‐ray diffraction, scanning electron microscopy, and thermogravimetry. At the mesoscale, amphiphilic C16Si(OH)3 assembled into bilayer lamellae through polycondensation, hydrophobic interaction, and H bonding. At the micrometer scale, the bilayer lamellae nucleated at the interface and grew into a polar phase, thus leading to delicate microcages or mimic diatoms. Moreover, the microcages tended to interconnect and fuse into a continuous coating at the centimeter scale, which provided hydrophobicity through the micropatterned surface. This paradigm for creating hierarchical materials with multiphases could lead to new “synthetic” material technologies and novel fascinating materials with anisotropic properties.
Enhancement of Polymer Luminescence by Excitation‐Energy Transfer from Multi‐Walled Carbon Nanotubes
Authors: Henley Simon J. , Hatton Ross A. , Chen Guan Y. , Gao Chao , Zeng Hailin , Kroto Harold W. , Silva S. Ravi P.
Published: October 2007

Carbon nanotubes have been shown to efficiently quench luminescence from conjugated polymers when incorporated in a composite. However, shown here is an up to 100‐fold increase in the visible photoluminescence signal from fluorescent chromophores in nylon 10,10 by incorporating multi‐walled carbon nanotubes (MWCNTs). Using 325‐ and 488‐nm excitation the optical absorption by MWCNTs embedded within the polymer matrix is demonstrated, followed by efficient excitation‐energy transfer to emissive chromophores intrinsic to the polymer but only when the MWCNTs are acid functionalised. Furthermore, the MWCNTs are shown to significantly retard photobleaching of fluorescent centers in the nylon composites. These remarkable properties greatly advance the prospects of utilizing MWCNTs in organic solar cells and electroluminecent devices to improve performance.
Using the Ring‐Shaped Protein TRAP to Capture and Confine Gold Nanodots on a Surface.
Authors: Heddle Jonathan G. , Fujiwara Isamu , Yamadaki Hirokazu , Yoshii Shigeo , Nishio Kazuaki , Addy Christine , Yamashita Ichiro , Tame Jeremy R. H.
Published: October 2007

The cavity of the toroidal protein TRAP (trp RNA‐binding attenuation protein) is modified to capture gold nanodots in solution. By engineering a titanium‐binding peptide onto one surface of the ring it is also possible to bind it specifically and tightly to a TiO2 surface. TRAP bound in this way is then used to capture gold nanodots and attach them to prepared surfaces. Gold‐protein complexes are observed using atomic force microscopy and transmission electron microscopy. The modified TRAP is used to build gold nanodots into the SiO2 layer of a metal oxide semiconductor. This is the first use of a ring protein, rather than the more commonly used spherical protein cages, to constrain nanodots to a surface. This method is an important addition to the current range of bionanotechnology tools and may be the basis for future, multicomponent electronic devices.
Relationship between lung area at ultrasound examination and lung volume assessment with magnetic resonance imaging in isolated congenital diaphragmatic hernia
Authors: Jani J. , Cannie M. , Done E. , Van Mieghem T. , Van Schoubroeck D. , Gucciardo L. , Dymarkowski S. , Deprest J. A.
Published: October 2007

Objectives

To prospectively examine the relationship between contralateral lung area measured by two‐dimensional (2D) ultrasound examination and contralateral and total fetal lung volume (FLV) estimated by magnetic resonance imaging (MRI) in the assessment of fetuses with congenital diaphragmatic hernia (CDH).

Methods

Sixty‐six fetuses with isolated CDH were entered in this prospective study. Contralateral fetal lung area was measured by 2D ultrasonography using the longest axis method. Ipsilateral, contralateral and total FLV were measured using multiplanar axial T2‐weighted MRI. Regression analysis was used to determine the significance of associations between contralateral lung area and contralateral and total FLV, and the predicted total FLV was subsequently calculated using the regression equation. Univariate regression analysis was used to investigate the effect on the proportionate difference between the predicted and the observed total FLV of gestational age, proportionate volume of ipsilateral vs. total FLV, side of CDH, intrathoracic herniation of the liver and intratracheal presence of a balloon.

Results

The 66 fetuses underwent a total of 191 paired 2D ultrasound and MRI examinations at a median gestational age of 30 (range, 18–38) weeks. It was possible to visualize and measure the contralateral lung area by 2D ultrasound, as well as both the ipsilateral and contralateral lung volumes by MRI, in all instances. There was a significant association between contralateral lung area and contralateral lung volume (r = 0.86; P < 0.001) and with total FLV (r = 0.84; P < 0.001). Univariate regression analysis showed that the proportionate difference between the predicted and the observed total FLV was significantly associated with the proportionate volume of ipsilateral vs. total FLV but not with gestational age, side of CDH, intrathoracic herniation of the liver or intratracheal presence of the balloon.

Conclusions

In CDH, contralateral lung area measurement by 2D ultrasound correlates well with the total FLV estimated by MRI, irrespective of gestational age, liver herniation or side of herniation. Inconsistencies between the two measurements are attributable to the contribution of the ipsilateral lung to the total lung volume. Copyright © 2007 ISUOG. Published by John Wiley & Sons, Ltd.