bluuebunny/crossref_metadata_2025 huggingface dataset:
Carrier dynamics between delocalized and localized states in type-II GaAsSb/GaAs quantum wells
Authors: Baranowski M. , Syperek M. , Kudrawiec R. , Misiewicz J. , Gupta J. A. , Wu X. , Wang R.
Published: February 2011

The carrier dynamics in type-II GaAsSb/GaAs quantum well (QW) is investigated by time-resolved photoluminescence at low temperature. A detailed analysis of the experimental data reveal a complex carrier relaxation scenario involving both delocalized and localized states. We show that the QW emission is controlled by the dynamics of the band bending effect, related to temporal changes in the spatial charge separation near the GaAsSb/GaAs heterointerface, whereas localized states play a significant role in the carrier relaxation/redistribution between QW states.
Diffusiophoresis of a nonuniformly charged sphere in an electrolyte solution
Authors: Luu Xuan-Cuong , Hsu Jyh-Ping , Tseng Shiojenn
Published: February 2011

The diffusiophoresis of a rigid, nonuniformly charged spherical particle in an electrolyte solution is analyzed theoretically focusing on the influences of the thickness of double layer, the surface charge distribution, the effect of electrophoresis, and the effect of double-layer polarization. We show that the nonuniform charge distribution on the particle surface yields complicated effect of double-layer polarization, leading to interesting diffusiophoretic behaviors. For example, if the sign of the middle part of the particle is different from that of its left- and right-hand parts, then depending upon the charge density and the fraction of the middle part, the particle can move either to the high-concentration side or to the low-concentration side. Both the diffusiophoretic velocity and its direction can be manipulated by the distribution of the surface charge density. In particular, if the electrophoresis effect is significant, then those properties are governed by the averaged surface charge density of the particle. A dipolelike particle, where its left- (right-) hand half is negatively (positively) charged, always migrates toward the low-concentration (left-hand) side, that is, it has a negative diffusiophoretic velocity. In addition, that diffusiophoretic velocity has a negative local minimum as the thickness of double layer varies.
The effect of confinement-induced shear on drop deformation and breakup in microfluidic extensional flows
Authors: Mulligan Molly K. , Rothstein Jonathan P.
Published: February 2011

Droplets of de-ionized water and four aqueous surfactant solutions were generated in oil using a microfluidic flow-focusing device. The morphological developments of the drops in extensional flow and confinement-induced shear flow at various extension rates were studied using a hyperbolic contraction. This novel approach to droplet deformation within a microfluidic device allowed the probing of droplets within a nearly uniform extensional flow. The focus of this work was to study the effect of confinement-induced shear on droplet deformation and breakup in extensional flows. Droplet deformation was found to increase with both increasing capillary number and increasing confinement, for a fixed viscosity ratio of λ=0.1, with the effect of the shear induced by confinement being quite dramatic. The addition of surfactant to the droplets resulted in the production of tails, which streamed from the rear of the droplets and produced daughter droplets much smaller than the parent droplet. In the partially confined limit, where the flow was purely extensional, a single tail was formed at the center of the droplets trailing edge. With enhanced confinement, shear effects from the wall became important, the droplets were observed to take on a bullet-like shape, and two tails formed at the trailing edge of the droplet. The critical value of the capillary number and confinement needed for the formation of tails varied with the surfactant used.
Fast polarization switching panel with high brightness and contrast ratio for three-dimensional display
Authors: Shin Hun Ki , Lee Joong Ha , Kim Jung-Wook , Yoon Tae-Hoon , Kim Jae Chang
Published: February 2011

We propose a polarization switching device using optically compensated pi cell for polarization-glass-type three-dimensional display. This device shows good optical properties such as high transmittance and low cross-talk ratio because of its fast dynamic response characteristics. To improve the brightness and contrast ratio on the right- and left-hand sides, we attach optical retardation films on each side of the polarization glasses instead of attaching the films on the polarization switching panel. From the calculation and experiment, we obtain high contrast ratios, over 200:1, on both sides and a high brightness using only one film on each side.
Thermal model for performance prediction of integrated collector storage systems
Authors: Garnier C. , Muneer T. , Currie J.
Published: February 2011

The result of many years of global research on solar water heating systems has outlined the promising approach of integrated collector storage solar water heaters (ICS-SWHs) in cold climates. This research paper aims to model the field performance of a newly developed ICS-SWH for Scottish weather conditions. Field experiments were performed to investigate the performance of the newly developed ICS-SWH and the parameters affecting it. This was followed by developing a thermal macromodel able to compare the internal temperature variation under differing external weather conditions in order to evaluate the transient performance of the ICS-SWH for field conditions. Through this work, important parameters for modeling field performance of ICS-SWH were established. The innovative modeling tool developed was found to accurately predict the bulk water temperature of the ICS-SWH for any orientation and location in the world with good accuracy.
Novel metallic states at low temperatures
Authors: Rowley S. E. , Smith R. P. , Marcano N. , Dean M. P. M. , Kusmartseva A. , Spalek L. J. , O’Farrell E. C. T. , Tompsett D. A. , Sutherland M. L. , Alireza P. L. , Ko C. , Liu C. , Pugh E. , Saxena S. S. , Lonzarich G. G.
Published: February 2011

We present an overview of unconventional metallic states arising close to magnetic quantum critical points with a focus on d-electron systems. The applicability and potential breakdowns of traditional self-consistent field theories of such materials are discussed as well as related phenomena in other systems.
David Shoenberg and the beauty of quantum oscillations
Authors: Pudalov V. M.
Published: February 2011

The quantum oscillation effect was discovered in Leiden in 1930, by W. J. de Haas and P. M. van Alphen when measuring magnetization, and by L. W. Shubnikov and de Haas when measuring magnetoresistance. Studying single crystals of bismuth, they observed oscillatory variations in the magnetization and magnetoresistance with magnetic field. Shoenberg, whose first research in Cambridge had been on bismuth, found that much stronger oscillations are observed when a bismuth sample is cooled to liquid helium temperature rather than liquid hydrogen, which had been used by de Haas. In 1938 Shoenberg went from Cambridge to Moscow to study these oscillations at Kapitza’s Institute where liquid helium was available at that time. In 1947, J. Marcus observed similar oscillations in zinc and that persuaded Schoenberg to return to this research. After that, the dHvA effect became one of his main research topics. In particular, he developed techniques for quantitative measurement of this effect in many metals. A theoretical explanation of quantum oscillations was given by L. Onsager in 1952, and an analytical quantitative theory by I. M. Lifshitz and A. M. Kosevich in 1955. These theoretical advances seemed to provide a comprehensive description of the effect. Since then, quantum oscillations have been widely used as a tool for measuring Fermi surface extremal cross-sections and all-angle electron scattering times. In his pioneering experiments of the 1960’s, Shoenberg revealed the richness and deep essence of the quantum oscillation effect and showed how the beauty of the effect is disclosed under nonlinear conditions imposed by interactions in the system under study. It was quite surprising that “magnetic interaction” conditions could cause the apparently weak quantum oscillation effect to have such strong consequences as breaking the sample into magnetic (now called “Shoenberg”) domains and forming an inhomogeneous magnetic state. With his contributions to the field of quantum oscillations and superconductivity, Shoenberg is undoubtedly one of the 20th century’s foremost scientists. We describe experiments to determine the quantitative parameters of electron–electron interactions in line with Shoenberg’s idea that quasiparticle interaction parameters can be found by analyzing quantum oscillations as modified by interactions.
Diamagnetic domains and nonlinear electromagnetic waves in normal metals (review)
Authors: Egorov V. S. , Peschansky V. G. , Stepanenko D. I.
Published: February 2011

This is a review of experimental and theoretical research on diamagnetic domains in normal metals. Considerable attention is devoted to a new, effective method for studying domain structures: muon spectroscopy based on measuring the induction using the precession frequency of muons in a magnetic field. A number of phenomena which arise in states with magnetic domains, including unusual magnetostriction and hysteresis in the de Haas-van Alphen effect, are discussed. The mechanism of nonlinearity in the propagation of low-frequency electromagnetic waves in metals with strong magnetism of their conduction electrons is examined.
Strong correlations in actinide redox reactions
Authors: Horowitz S. E. , Marston J. B.
Published: February 2011

Reduction–oxidation (redox) reactions of the redox couples An(VI)/An(V), An(V)/An(IV), and An(IV)/An(III), where An is an element in the family of early actinides (U, Np, and Pu), as well as Am(VI)/Am(V) and Am(V)/Am(III), are modeled by combining density functional theory with a generalized Anderson impurity model that accounts for the strong correlations between the 5f electrons. Diagonalization of the Anderson impurity model yields improved estimates for the redox potentials and the propensity of the actinide complexes to disproportionate.
Monte Carlo simulation of nanowires of different metals and two-metal alloys
Authors: Giménez M. C. , Schmicker Wolfgang
Published: February 2011

Nanowires of different metals and two-metal alloys have been studied by means of canonical Monte Carlo simulations and the embedded atom method for the interatomic potentials. For nanowires of gold, a relatively stable three-atom-wide chain was observed. The presence of one-atom-wide linear atomic chains is not stable in any case. For two-metal alloy nanowires, the metal with a higher surface energy tends to locate in the inner region of the nanowire.
Diamagnetism of layered organic conductors
Authors: Kirichenko O. V. , Peschansky V. G.
Published: February 2011

The temperature dependence of the magnetic susceptibility of layered organic conductors with an arbitrary dispersion law in high magnetic fields is analyzed. It is shown that the quasi-two-dimensional character of the electron energy spectrum of these conductors results in a strong dependence of the diamagnetic contribution to the magnetization on the direction of the applied magnetic field. Experimental investigation of the anisotropy of the magnetic susceptibility makes it possible to study separately the diamagnetic and paramagnetic contributions to the magnetization of layered conductors.
Quantum interference effects in a system of two tunnel point-contacts in the presence of a single scatterer: simulation of a double-tip STM experiment
Authors: Khotkevych N. V. , Kolesnichenko Yu. A. , van Ruitenbeek J. M.
Published: February 2011

The conductance of systems containing two tunnel point-contacts and a single subsurface scatterer is investigated theoretically. The problem is solved in the approximation of s-wave scattering giving analytical expressions for the wave functions and for the conductance of the system. Conductance oscillations resulting from the interference of electron waves passing through different contacts and their interference with the waves scattered by the defect are analyzed. The possibility of determining the depth of an impurity below the metal surface by using the dependence of the conductance on the distance between the contacts is discussed. It is shown that the application of an external magnetic field results in Aharonov-Bohm oscillations in the conductance, the period of which can be used to determine the depth of the defect in a double-tip STM experiment.
Localized superconducting pairs
Authors: Gantmakher V. F.
Published: February 2011

Various phenomena which aid in understanding the concept of localized superconducting pairs (the behavior of granular superconductors, the parity effect, the Berezinski–Kosterlitz–Thouless transition) are discussed. Experimental evidence of the existence of localized pairs is presented and the conditions favoring their appearance are analyzed.
Two-dimensional replica exchange approach for peptide–peptide interactions
Authors: Gee Jason , Shell M. Scott
Published: February 2011

The replica exchange molecular dynamics (REMD) method has emerged as a standard approach for simulating proteins and peptides with rugged underlying free energy landscapes. We describe an extension to the original methodology—here termed umbrella-sampling REMD (UREMD)—that offers specific advantages in simulating peptide–peptide interactions. This method is based on the use of two dimensions in the replica cascade, one in temperature as in conventional REMD, and one in an umbrella sampling coordinate between the center of mass of the two peptides that aids explicit exploration of the complete association–dissociation reaction coordinate. To mitigate the increased number of replicas required, we pursue an approach in which the temperature and umbrella dimensions are linked at only fully associated and dissociated states. Coupled with the reweighting equations, the UREMD method aids accurate calculations of normalized free energy profiles and structural or energetic measures as a function of interpeptide separation distance. We test the approach on two families of peptides: a series of designed tetrapeptides that serve as minimal models for amyloid fibril formation, and a fragment of a classic leucine zipper peptide and its mutant. The results for these systems are compared to those from conventional REMD simulations, and demonstrate good convergence properties, low statistical errors, and, for the leucine zippers, an ability to sample near-native structures.
Paired hydrogen bonds in the hydrogen halide homodimer (HI)2
Authors: Wang Z. , McElmurry B. A. , Lucchese R. R. , Bevan J. W. , Coudert L. H.
Published: February 2011

The HI homodimer was found to have structural and vibrational properties unlike any other previously studied (HX)2 system, with X = F, Cl, and Br. The infrared spectrum of (HI)2 is also observed to be distinctly different from the other members of the series. In addition, the interaction energy of the (HI)2 dimer has been calculated using the coupled-cluster with singles, doubles, and perturbative triples [CCSD(T)] level of theory. A four-dimensional morphed intermolecular potential has been generated and then morphed using available near infrared and submillimeter spectroscopic data recorded in supersonic jet expansions. The morphed potential is found to have a single global minimum with a symmetric structure having C2h symmetry. The equilibrium dissociation energy is found to be 359 cm−1 with the geometry in Jacobi coordinates of Re = 4.35 Å, θ1 = 43°, θ2 = 137°, and ϕ = 180°. The infrared spectrum is characterized by pairs of excited vibrational states resulting from the coupling of the two HI stretching modes. A qualitative model using a quadratic approximation has been fitted to obtain an estimate of this coupling. Furthermore, a morphed intermolecular potential for the vibrationally excited system was also obtained that gives a quantitative estimate of the shift in the potential due to the excitation. The submillimeter analysis is consistent with a ground state having its highest probability as a paired hydrogen bond configuration with R0 = 4.56372(1) Å and an average angle $\bar \theta = \cos ^{ - 1} ( {\langle {\cos ^2 {\kern 1pt} \theta } \rangle ^{{1/2}} } )$θ¯=cos−1(⟨cos2θ⟩1/2) = 46.40(1)° (between the diatom center of mass/center of mass axis and direction of each component hydrogen iodide molecule). On monodeuteration, however, the ground state is predicted to undergo an anomalous structural isotope change to an L-shaped HI–DI structure with highest probability at R0 = 4.51 Å, $\bar \theta _1$θ¯1 = 83°, $\bar \theta _2$θ¯2 = 177°, and ϕ = 180°. These results provide a test for large scale ab initio calculations and have implications for the interpretation of photoinduced chemistry and other properties of the dimer.
Anomalous resistivity and superconductivity in the two-band Hubbard model with one narrow band (Review)
Authors: Kagan M. Yu. , Valkov V. V.
Published: February 2011

We search for marginal Fermi-liquid behavior in the two-band Hubbard model with one narrow band. We consider the limit of low electron densities in the bands and strong intraband and interband Hubbard interactions. We analyze the influence of electron-polaron effects and other mechanisms for mass-enhancement (related to the momentum dependence of the self-energies) on the effective mass and scattering times of light and heavy components in the clean case (electron-electron scattering and no impurities). We find a tendency towards phase separation (towards negative partial compressibility of heavy particles) in the 3D case with a large mismatch between the densities of heavy and light bands in the strong coupling limit. We also find that for low temperatures and equal densities, the resistivity in a homogeneous state R(T)∝T2 behaves as a Fermi-liquid in both 3D and 2D. For temperatures greater than the effective bandwidth for heavy electrons T>Wh*, the coherence of the heavy component breaks down completely. The heavy particles move diffusively in the surrounding light particles. At the same time, light particles scatter on heavy particles as if on immobile (static) impurities. Under these conditions, the heavy component is marginal, while the light component is not. The resistivity approaches saturation for T>Wh* in the 3D case. In 2D the resistivity has a maximum and a localization tail owing to weak-localization corrections of the Altshuler-Aronov type. This behavior of resistivity in 3D could be relevant for some uranium-based heavy-fermion compounds such as UNi2Al3 and in 2D, for some other mixed-valence compounds, possibly including layered manganites. We also consider briefly the superconductive (SC) instability in this model. The leading instability tends to p-wave pairing and is governed by an enhanced Kohn–Luttinger mechanism for SC at low electron densities. The critical temperature corresponds to the pairing of heavy electrons via polarization of the light electrons in 2D.
Magnetic and superconducting properties of FeSe1−xTex (x∼0, 0.5, and 1.0)
Authors: Fedorchenko A. V. , Grechnev G. E. , Desnenko V. A. , Panfilov A. S. , Gnatchenko S. L. , Tsurkan V. V. , Deisenhofer J. , Krug von Nidda H.-A. , Loidl A. , Chareev D. A. , Volkova O. S. , Vasiliev A. N.
Published: February 2011

The magnetization of FeSe1−xTex (x∼0, 0.5, and 1.0) compounds has been studied in magnetic fields up to 50kOe and at temperatures of 2–300K. The superconducting transition was observed at Tc∼8K and 13.6–14.2K in FeSe0.963 and FeSe0.5Te0.5, respectively. For most of the samples, nonlinearity of the magnetization curves in the normal state gives evidence of a common, substantial presence of ferromagnetic impurities in these compounds. By taking these impurity effects into account, the intrinsic magnetic susceptibility χ of FeSe0.963, FeSe0.5Te0.5, and FeTe was estimated to increase gradually with Te content. For FeTe a drastic drop in χ(T) with decreasing temperature was found at TN∼70K, which is presumably related to antiferromagnetic ordering. To shed light on the observed magnetic properties, ab initio calculations of the exchange enhanced magnetic susceptibility are performed for FeSe and FeTe in the local spin density approximation.
Microwave-induced magnetooscillations and absolute negative conductivity in a multisubband two-dimensional electron system on liquid helium
Authors: Monarkha Yu. P.
Published: February 2011

It is shown that nonequilibrium filling of an upper surface subband induced by a microwave resonance can be the origin of absolute negative conductivity and zero-resistance states for a two-dimensional electron system on liquid helium in a perpendicular magnetic field. Contrary to a similar effect reported for semiconductor systems, an oscillating sign-changing correction to the dc-magnetoconductivity shows up as a result of quasi-elastic inter-subband scattering that does not involve photons. This analysis explains the remarkable magnetooscillations and zero-resistance states recently observed in electron systems on liquid helium.
A terahertz pulse emitter monolithically integrated with a quantum cascade laser
Authors: Burghoff David , Kao Tsung-Yu , Ban Dayan , Lee Alan Wei Min , Hu Qing , Reno John
Published: February 2011

A terahertz pulse emitter monolithically integrated with a quantum cascade laser (QCL) is demonstrated. The emitter facet is excited by near-infrared pulses from a mode-locked Ti:sapphire laser, and the resulting current transients generate terahertz pulses that are coupled into an electrically isolated QCL in proximity. These pulses are used to measure the gain of the laser transition at ∼2.2 THz, which clamps above threshold at ∼18 cm−1 and has a full width at half-maximum linewidth of ∼0.67 THz. The measurement also shows the existence of absorption features at different biases that correspond to misalignment of the band structure and to absorption within the two injector states. The simplicity of this scheme allows it to be implemented alongside standard QCL ridge processing and to be used as a versatile tool for characterizing QCL gain media.
Experimental demonstration of In0.53Ga0.47As field effect transistors with scalable nonalloyed source/drain contacts
Authors: Hu Jenny , Saraswat Krishna C. , Wong H.-S. Philip
Published: February 2011

We demonstrate the integration of a nonalloyed contact structure developed for III-V semiconductors to the source/drain of an In0.53Ga0.47As metal-oxide-semiconductor field effect transistor (MOSFET) with atomic layer deposition (ALD) Al2O3 high-κ dielectric. This nonalloyed contact utilizes single metals in combination with dielectric dipoles to tune the metal/semiconductor Femi level pinning toward the semiconductor’s band edge for minimal contact resistance and barrier height. The metal/III-V semiconductor effective barrier heights have been reduced by as much as 0.40 eV using SiN and 0.55 eV using Al2O3 dielectrics. With this InGaAs nMOSFET as a starting point, this contact can be applied to other III-V n-type MOSFETs, p-type MOSFETs, and Schottky Barrier field effect transistors.
Existence of an exceptional reaction pathway for H3+ formation observed in collision-induced dissociation of methane ions at 1000 eV
Authors: Shoji Fumiya , Nagai Tatsuzo , Morimoto Fumio
Published: February 2011

Dissociation of CH4+ ions at 1000 eV induced by collision with Ar atoms was investigated by measuring the kinetic energies of the ionized fragments. At small scattering angles, including zero, H+, H2+, H3+, CH3+, CH2+, CH+, and C+ fragments were observed. The attractive part of the potential in the CH4+–Ar collision system played an important role in the formation of the ionized fragments. Rainbow scattering, leading to a large scattering cross section, was shown to be responsible for the increased formation of H3+. It is proposed that on collision-induced dissociation of CH4+, its three hydrogen atoms, which form a triangle, simultaneously react and move together to form H3+.
Communication: Accurate determination of side-chain torsion angle χ1 in proteins: Phenylalanine residues
Authors: Suardíaz R. , Crespo-Otero R. , Pérez C. , Fabián J. San , de la Vega J. M. García
Published: February 2011

Quantitative side-chain torsion angle χ1 determinations of phenylalanine residues in Desulfovibrio vulgaris flavodoxin are carried out using exclusively the correlation between the experimental vicinal coupling constants and theoretically determined Karplus equations. Karplus coefficients for nine vicinal coupling related with the torsion angle χ1 were calculated using the B3LYP functional and basis sets of different size. Optimized χ1 angles are in outstanding agreement with those previously reported by employing x ray and NMR measurements.
Drop fragmentation due to hole formation during Leidenfrost impact
Authors: Biance Anne-Laure , Pirat Christophe , Ybert Christophe
Published: February 2011

Drop impacts on a smooth plate heated above the Leidenfrost temperature are investigated in the range of large Weber number. Liquid fragmentation due to the rupture of the expanding lamella during the impact—by hole nucleation and subsequent growth—is studied. Control of this rupturing process is achieved experimentally through the use of single model-defects attached to the substrate which act as an initiating spots for the hole formation, whereas the liquid does not contact the substrate. Overall, the lamella rupture is shown to take place above a critical impact velocity, the value of which decreases with increasing defect size. Comparing this rupture mechanism to classical splash, it is shown to be the relevant fragmentation phenomenon below a critical ratio between drop (R0) and defect (d) sizes of R0/d≤40.
Accurate and efficient algorithm for Bader charge integration
Authors: Yu Min , Trinkle Dallas R.
Published: February 2011

We propose an efficient, accurate method to integrate the basins of attraction of a smooth function defined on a general discrete grid and apply it to the Bader charge partitioning for the electron charge density. Starting with the evolution of trajectories in space following the gradient of charge density, we derive an expression for the fraction of space neighboring each grid point that flows to its neighbors. This serves as the basis to compute the fraction of each grid volume that belongs to a basin (Bader volume) and as a weight for the discrete integration of functions over the Bader volume. Compared with other grid-based algorithms, our approach is robust, more computationally efficient with linear computational effort, accurate, and has quadratic convergence. Moreover, it is straightforward to extend to nonuniform grids, such as from a mesh-refinement approach, and can be used to both identify basins of attraction of fixed points and integrate functions over the basins.
Achieving high efficiency laminated polymer solar cell with interfacial modified metallic electrode and pressure induced crystallization
Authors: Yuan Yongbo , Bi Yu , Huang Jinsong
Published: February 2011

We report efficient laminated organic photovoltaic device with efficiency approach the optimized device by regular method based on Poly(3-hexylthiophene-2,5-diyl) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The high efficiency is mainly attributed to the formation of a concrete polymer/metal interface mechanically and electrically by the use of electronic-glue, and using the highly conductive and flexible silver film as anode to reduce photovoltage loss and modifying its work function for efficiency hole extraction by ultraviolet/ozone treatment, and the pressure induced crystallization of PCBM.
Photoinduced magnetoresistance in organic field-effect transistors
Authors: Reichert Thomas , Saragi Tobat P. I.
Published: February 2011

We report on negative magnetoresistance (MR) of −0.46% in low external magnetic fields in pentacene field-effect transistors. This effect can only be observed if the device is irradiated. MR strongly depends on gate voltage but is independent of drain voltage. Furthermore, the MR increases as the intensity of irradiation increases and the relationship of both parameters is not linear. The dependency of MR on magnetic field is not linear either, but it follows non-Lorentzian line shape. The triplet exciton-charge reaction model is a possible explanation for negative MR in irradiated pentacene field-effect transistors.
Material anisotropy unveiled by random scattering of surface acoustic waves
Authors: Laude Vincent , Kokkonen Kimmo , Benchabane Sarah , Kaivola Matti
Published: February 2011

We consider launching a monochromatic surface acoustic wave packet on a large set of random scatterers. The interference of the multiple scattered waves creates a random pattern of ripples on the crystal surface that is recorded by optical interferometry. The Fourier transform of the amplitude and phase data of the measured wave field unveils the complete slowness curve, i.e., the wave-vector as a function of the propagation angle. A simple acoustic speckle model is proposed to explain this observation.
Experimental demonstration of Smith–Purcell radiation enhancement by frequency multiplication in open cavity
Authors: Bratman V. L. , Fedotov A. E. , Makhalov P. B.
Published: February 2011

The excitation of a low-frequency surface wave can provide coherent high-frequency Smith–Purcell radiation due to the frequency multiplication effect. The use of an open cavity allows an additional power increase due to the induced nature of the radiation. A radiation source based on these effects is experimentally demonstrated at a frequency of about 190 GHz.
Nondiffracting kagome lattice
Authors: Boguslawski Martin , Rose Patrick , Denz Cornelia
Published: February 2011

We introduce a generalized approach to generate an elementary nondiffracting beam, whose transverse intensity is distributed corresponding to a two-dimensional kagome structure. Furthermore, we present an effective experimental implementation via a computer controlled phase controlling spatial light modulator in combination with a specific Fourier filter system. Intensity and phase analysis of the kagome lattice beam accounts for an experimental wave field implementation. Altogether, the examined wave field may be a fundament for the fabrication of large two-dimensional photonic crystals or photonic lattices in kagome symmetry using miscellaneous holographic matter structuring techniques.
Ambient field effects on the current-voltage characteristics of nanowire field effect transistors
Authors: Karmalkar Shreepad , Maheswaran K. R. K. , Gurugubelli Vijayakumar
Published: February 2011

We investigate the effects of ambient field from the gate and drain contacts on the current-voltage characteristics of a vertical nanowire field effect transistor having a lightly doped ungated length near the drain. Such a device is suitable for high voltage (tens of volts) applications. It is shown that the ambient field enhances the carrier concentration and divides the ungated region into gate-controlled and drain-controlled sections, controllable by the drain contact size and bias-voltages. These phenomena have a significant impact on the drain breakdown voltage, saturation voltage, saturation current and output resistance. The effects are established with the help of measured data and numerically calculated current-voltage curves and field lines.
Germanium-tin p-i-n photodetectors integrated on silicon grown by molecular beam epitaxy
Authors: Werner J. , Oehme M. , Schmid M. , Kaschel M. , Schirmer A. , Kasper E. , Schulze J.
Published: February 2011

GeSn heterojunction p-i-n diodes with a Sn content of 0.5% are grown with a special low temperature molecular beam epitaxy. The Sn incorporation in Ge is facilitated by a very low temperature growth step in order to suppress Sn surface segregation. Diodes with sharp doping transitions are realized as double mesa structures with a diameter from 1.5 up to 80 μm. An optical responsivity of these GeSn diodes of 0.1 A/W at a wavelength of λ=1.55 μm is measured. In comparison with a pure Ge detector the optical responsivity is increased by factor of 3 as a result of Sn caused band gap reduction.
Two-color terahertz response in bilayer graphene nanoribbons with spin-orbit coupling
Authors: Liu Junfeng , Wang Bo , Ma Zhongshui , Zhang C.
Published: February 2011

We demonstrate that spin-orbit coupling can give rise to a strong terahertz response in metallic armchair bilayer graphene nanoribbons. The combination of the interlayer coupling and the spin-orbit coupling leads to double resonant optical response in the low frequency regime. The frequency separation of the two excitations is tunable with a gate voltage.
Observations of electric discharge streamer propagation and capillary oscillations on the surface of air bubbles in water
Authors: Sommers B S , Foster J E , Babaeva N Yu , Kushner Mark J
Published: February 2011

The propagation of electric discharge streamers inside bubbles in liquids is of interest for the remediation of toxins in water and plasma-based surgical instruments. The manner of streamer propagation has an important influence on the production of reactive species that are critical to these applications. Streamer propagation along the surface of electrode-attached bubbles of air in water, previously predicted by numerical simulations, has been experimentally imaged using a fast frame-rate camera. The successive pulsing of the streamer discharge inside the bubbles produced oscillations along the air–water interface. Subsequent streamers were observed to closely follow surface distortions induced by such oscillations. The oscillations likely arise from the non-uniform perturbation of the bubble driven by the electric field of the streamer and were found to be consistent with Kelvin's equation for capillary oscillations. For a narrow range of applied voltage pulse frequencies, the oscillation amplitude increased over several pulse periods indicating, potentially, resonant behaviour. We also observed coupling between bubbles wherein oscillations in a second bubble without an internal discharge were induced by the presence of a streamer in a fixed bubble.
Intense ultrashort terahertz pulses: generation and applications
Authors: Hoffmann Matthias C , Fülöp József András
Published: February 2011

Ultrashort terahertz pulses derived from femtosecond table-top sources have become a valuable tool for time-resolved spectroscopy during the last two decades. Until recently, the pulse energies and field strengths of these pulses have been generally too low to allow for the use as pump pulses or the study of nonlinear effects in the terahertz range. In this review article we will describe methods of generation of intense single cycle terahertz pulses with emphasis on optical rectification using the tilted-pulse-front pumping technique. We will also discuss some applications of these intense pulses in the emerging field of nonlinear terahertz spectroscopy.
Tuning martensitic transformation and magnetoresistance effect by low temperature annealing in Ni45Co5Mn36.6In13.4 alloys
Authors: Chen L , Hu F X , Wang J , Zhao J L , Sun J R , Shen B G , Yin J H , Pan L Q
Published: February 2011

We studied the influence of post-annealing on magnetic and transport properties in Ni45Co5Mn36.6In13.4 alloys. Our results demonstrate that post-annealing at low temperatures, ⩽300 °C, can lead to a significant change in magnetic properties, martensitic temperature (T
M) and magnetoresistance effect through structure relaxations and possible change in atomic order. It was found that T
M shifts from 314 to 283 K but the strong metamagnetic behaviour is still retained when the sample is annealed at 300 °C for 3 h. Thereupon, a large magnetoresistance effect over an extended temperature range can be achieved through controlling the heat treatment conditions. Meanwhile, the thermal stability of the novel composition is also disclosed through the investigations on low temperature annealing effect.
Efficient light harvesting and carrier transport in PbS quantum dots/silicon nanotips heterojunctions
Authors: Huang Chun-Ying , Wang Di-Yan , Wang Chun-Hsiung , Wang Yaw-Tyng , Jiang You-Ting , Yang Ying-Jay , Chen Chia-Chun , Chen Yang-Fang
Published: February 2011

Light harvesting from nanocomposites consisting of silicon (Si) nanotips and PbS quantum dots (QDs) has been investigated. We show that Si nanotips provide direct carrier transport paths, additional interfacial area and light trapping. We observe that there is a dramatic enhancement in short-circuit current (from 9.34 to 14.17 mA cm−2) with nanotips structure than that of the bulk Si wafer. In addition, with an additional electron blocking layer, the photovoltaic performance can be further increased. The nanocomposites consisting of QDs and Si nanotips therefore open a promising route for efficient light harvesting from visible to infrared with improved power conversion efficiency.
Raman scattering in InAsxSbyP1−x−y alloys grown by gas source MBE
Authors: Cheetham K J , Krier A , Patel I I , Martin F L , Tzeng J-S , Wu C-J , Lin H-H
Published: February 2011

The Raman spectra of quaternary InAs
x
Sb
y
P1−x−y
epitaxial layers nominally lattice-matched to (1 0 0) n-type InAs substrates are reported. The phonon peaks are identified for alloys covering a wide composition range extending into the miscibility gap. Three-mode behaviour was obtained across part of the composition range. InP-like longitudinal optical (LO) and transverse optical (TO) phonons were observed over the entire compositional range, but InAs-like LO phonons were only observed at high arsenic concentrations and no InSb-like TO phonons were observed. Disorder-related phonon peaks were obtained for alloy compositions within the miscibility gap.
Light-ion-irradiation-induced thermal spikes in nanoporous silica
Authors: Kucheyev S O , Wang Y M , Hamza A V , Worsley M A
Published: February 2011

Improving mechanical properties of low-density nanoporous solids has been a long standing challenge. Here, we study how alpha particle bombardment and thermal annealing can be used to improve mechanical properties of nanoporous silica aerogels analysed by depth-sensing nanoindentation. Data suggest that light-ion irradiation creates non-melting thermal spikes in unconstrained nanoligaments of the aerogel, resulting in improved ligament connectivity.
Modelling nanoparticle transport in dielectrophoretic microdevices using a Fourier–Bessel series and applications for data analysis
Authors: Bakewell D J
Published: February 2011

A Fourier–Bessel (FB) series solution is derived that describes the dielectrophoretic-driven transport of nanoparticles in a microdevice. The solution assumes that the nanoparticles do not interact and is based on a linear Fokker–Planck equation that includes the effects of thermal diffusion. The solution is applicable for a dielectrophoretic force that varies exponentially in the microdevice, such as in the far field of planar interdigitated arrays. Important applications of the FB solution are demonstrated that include simulation and system classification of nanoparticle movement under the action of weak and strong dielectrophoretic forces. Methods are demonstrated for the inverse process of estimating model parameters, such as the dielectrophoretic force, based on nanoparticle concentration data obtained experimentally. Data decomposition into separate spatial and temporal modes is demonstrated and Fourier transformation of the series solution yields a representation in the frequency domain. The frequency response predicted by transforming the time-dependent FB solution indicates the presence of a dielectrophoresis modulation bandwidth that concurs with observations of preliminary experiments.
Brownian motion with variable drift can be space filling
Authors: Antunović Tonći , Peres Yuval , Vermesi Brigitta
Published: February 2011

For

d
≥
2

d \geq 2

let

B
B

be standard

d
d

-dimensional Brownian motion. For any

α
>
1

/

d

\alpha > 1/d

we construct an

α
\alpha

-Hölder continuous function

f
:
[
0
,
1
]
→

R

d

f \colon [0,1] \to \mathbb {R}^d

so that the range of

B
−
f

B-f

covers an open set. This strengthens a result of Graversen (1982) and answers a question of Le Gall (1988).
Commuting isometries of the complex hyperbolic space
Authors: Cao Wensheng , Gongopadhyay Krishnendu
Published: February 2011

LetHCnH_{\mathbb {C}}^ndenote the complex hyperbolic space of dimensionnn. The groupU(n,1)U(n,1)acts as the group of isometries ofHCnH_{\mathbb {C}}^n. In this paper we investigate when two isometries of the complex hyperbolic space commute. Along the way we determine the centralizers.
Heat Shock Protein 72 Overexpression Prevents Early Postoperative Memory Decline after Orthopedic Surgery under General Anesthesia in Mice
Authors: Vizcaychipi Marcela P. , Xu Lijun , Barreto George E. , Ma Daqing , Maze Mervyn , Giffard Rona G.
Published: February 2011

Background

Problems with learning and memory are common after surgery in the elderly and are associated with high morbidity. Heat shock protein 72 (Hsp72) confers neuroprotection against acute neurologic injury. We hypothesized that overexpression of Hsp72 would prevent the development of postoperative memory loss.

Methods

C57BL/6 wild-type and Hsp72 overexpressing transgenic mice were randomly allocated to the following: control, isoflurane anesthesia alone, or tibial fracture during isoflurane anesthesia. Animals were trained 24 h before surgery using a fear conditioning protocol and assessed in their training environment and in a novel context on posttreatment days 1, 3, and 7. Microglial activation was assessed by immunostaining.

Results

Adult male C57BL/6 wild-type mice exhibited reduced memory evidenced by a decreased percentage freezing time on days 1 and 3 after anesthesia alone (58.8 ± 5, 46.5 ± 5 mean ± SEM) and after surgery (53.4 ± 6, 44.1 ± 7), compared with controls (78.8 ± 5, 63.4 ± 6; P < 0.05 and P < 0.001, respectively). Hsp72 mice showed no difference by treatment on any day. Similarly, nonhippocampal-dependent memory was significantly impaired on days 1 and 3 after surgery and day 3 after anesthesia. The genotype effect was significant on days 1 and 7. CD68-immunopositive activated microglia in the hippocampus varied modestly with subregion and time; on day 7, there was a significant treatment effect with no genotype effect, with more activated microglia after surgery in all regions.

Conclusion

Hsp72 overexpression is associated with prevention of postoperative hippocampal-dependent and -independent memory deficit induced by anesthesia and/or surgery. Memory deficit is not correlated with numbers of activated hippocampal microglia.
Clinician-delivered Intervention to Facilitate Tobacco Quitline Use by Surgical Patients
Authors: Warner David O. , Klesges Robert C. , Dale Lowell C. , Offord Kenneth P. , Schroeder Darrell R. , Shi Yu , Vickers Kristin S. , Danielson David R.
Published: February 2011

Background

Telephone quitlines that provide counseling support are efficacious in helping cigarette smokers quit and have been widely disseminated; currently, they are underused. Surgery represents a teachable moment for smoking cessation, which can benefit surgical outcomes; however, few surgical patients receive smoking cessation interventions. This study developed and tested a clinician-delivered intervention to facilitate quitline use by adult patients scheduled for elective surgery.

Methods

After formative work involving patients and clinicians, a brief intervention was designed to facilitate telephone quitline use. It was then evaluated in a randomized trial of 300 adults scheduled for elective surgery. A control standard brief stop-smoking intervention served as a comparator, with both interventions delivered by clinicians. The primary outcome was the use rate of a quitline accessed through a dedicated toll-free telephone number, with use defined as completing at least one full counseling session. Secondary outcomes included self-reported abstinence from cigarettes at 30 and 90 days postoperatively.

Results

Subject characteristics were similar between the two groups. Records from the designated quitline documented that 29 of 149 subjects (19.5%) in the quitline intervention group and 0 of 151 subjects in the control group completed the first full counseling session (P < 0.0001). There were no significant differences in the self-reported point-prevalent and continuous abstinence rates between groups at either 30 or 90 days postoperatively, although rates tended to be higher in the quitline intervention group.

Conclusions

Clinicians can effectively facilitate quitline use by surgical patients. Further work is necessary to evaluate the efficacy of this approach in terms of long-term abstinence from cigarette smoking.
A comparative genome analysis of the RpoS sigmulon shows a high diversity of responses and origins
Authors: Santos-Zavaleta Alberto , Gama-Castro Socorro , Pérez-Rueda Ernesto
Published: February 2011

The stationary-phase response mediated by the RpoS sigma factor (σS, σ38) has been widely studied as a general mechanism of activation of highly diverse genes that maintain cell viability. In bacteria, genes for diverse functions have been associated with this response, showing that bacteria use a large number of functions to contend with adverse conditions in their environment. However, little is known about how the genes have been functionally recruited in diverse organisms. In this work, we address the analysis of genes regulated by σS, based on a comparative genomic-scale analysis considering four versatile bacterial species that represent different lifestyles and taxonomic groups,Escherichia coliK-12,Geobacter sulfurreducens, Borrelia burgdorferiandBacillus subtilis, as well as the extent of conservation in bacterial genomes, as a means of assessing the evolution of this sigmulon across all organisms completely sequenced. The analysis presented here shows that genes associated with the σSresponse have been recruited from diverse regulons to achieve a global response. In addition, and based on the distribution of orthologues, we show a group of genes that is highly conserved among all organisms, mainly associated with glycerol metabolism, as well as diverse functional genes recruited in a lineage-specific manner.
KlHsl1 is a component of glycerol response pathways in the milk yeast Kluyveromyces lactis
Authors: Cialfi Samantha , Uccelletti Daniela , Carducci Augusto , Wésolowski-Louvel Micheline , Mancini Patrizia , Heipieper Hermann J. , Saliola Michele
Published: February 2011

InSaccharomyces cerevisiae,HSL1(NIK1) encodes a serine-threonine protein kinase involved in cell cycle control and morphogenesis. Deletion of its putative orthologue inKluyveromyces lactis,KlHSL1, gives rise to sensitivity to the respiratory inhibitor antimycin A (AA). Resistance to AA on glucose (Rag+phenotype) is associated with genes (RAG) required for glucose metabolism/glycolysis. To understand the relationship betweenRAGandKlHSL1,ragandKlhsl1Δ mutant strains were investigated. The analysis showed that all the mutants contained a phosphorylated form of Hog1 and displayed an inability to synthesize/accumulate glycerol as a compatible solute. In addition,ragmutants also showed alterations in both cell wall and membrane fatty acids. The pleiotropic defects of these strains indicate that a common pathway regulates glucose utilization and stress response mechanisms, suggesting impaired adaptation of the plasma membrane/cell wall during the respiratory–fermentative transition. KlHsl1 could be the link between these adaptive pathways and the morphogenetic checkpoint.