bluuebunny/crossref_metadata_2025 huggingface dataset:
Post‐transcriptional regulation of gene expression in yeast under ethanol stress
Authors: Izawa Shingo , Inoue Yoshiharu
Published: May 2009

The selective export of mRNA from the nucleus plays an important role in the regulation of yeast gene expression under ethanol‐stressed conditions, and it has been clarified that expression of the transcriptionally activated HSP (heat‐shock protein) genes are inhibited in the mRNA processing and export steps. In actual alcoholic fermentation, during the late brewing process for wine in which the ethanol concentration has been increased, the export of bulk poly(A)+ (polyadenylated) mRNA is blocked and protein synthesis is considerably repressed. These observations clearly suggest that variation in the mRNA level is not necessarily reflected in the variation of the protein level in yeast cells during the brewing process. The present minireview outlines the regulation of yeast gene expression at the mRNA‐processing and nuclear‐export steps under ethanol‐stressed conditions, highlighting their usefulness in the brewing industry.
Controlling transistor threshold voltages using molecular dipoles
Authors: Vasudevan Smitha , Kapur Neeti , He Tao , Neurock Matthew , Tour James M. , Ghosh Avik W.
Published: May 2009

We develop a theoretical model for how organic molecules can control the electronic and transport properties of an underlying transistor channel to whose surface they are chemically bonded. The influence arises from a combination of long-ranged dipolar electrostatics due to the molecular head groups as well as short-ranged charge transfer and interfacial dipole driven by equilibrium band alignment between the molecular backbone and the reconstructed semiconductor surface atoms.
The influence of fabrication deviations on the photonic band gap of three-dimensional inverse woodpile nanostructures
Authors: Woldering Léon A. , Mosk Allard P. , Tjerkstra R. Willem , Vos Willem L.
Published: May 2009

The effects of unintended deviations from ideal inverse woodpile photonic crystals on the photonic band gap are discussed. Such deviations occur during the nanofabrication of the crystal. By computational analyses it is shown that the band gap of this type of crystal is robust to most types of deviations that relate to the radii, position, and angular alignment of the pores. However, the photonic band gap is very sensitive to tapering of the pores, i.e., conically shaped pores instead of cylindrical pores. To obtain three-dimensional inverse woodpile photonic crystals with a large volume, our work shows that with modern fabrication performances, reduction in tapering contributes most significantly to a high photonic strength.
Temperature effects in the mechanical desorption of an infinitely long lattice chain: Re-entrant phase diagrams
Authors: Skvortsov A. M. , Klushin L. I. , Fleer G. J. , Leermakers F. A. M.
Published: May 2009

We consider the mechanical desorption of an infinitely long lattice polymer chain tethered at one end to an adsorbing surface. The external force is applied to the free end of the chain and is normal to the surface. There is a critical value of the desorption force ftr at which the chain desorbs in a first-order phase transition. We present the phase diagram for mechanical desorption with exact analytical solutions for the detachment curve: the dependence of ftr on the adsorption energy ε (at fixed temperature T) and on T (at fixed ε). For most lattice models ftr(T) displays a maximum. This implies that at some given force the chain is adsorbed in a certain temperature window and desorbed outside it: the stretched state is re-entered at low temperature. We also discuss the energy and heat capacity as a function of T; these quantities display a jump at the transition(s). We analyze short-range and long-range excluded-volume effects on the detachment curve ftr(T). For short-range effects (local stiffness), the maximum value of ftr decreases with stiffness, and the force interval where re-entrance occurs become narrower for stiffer chains. For long-range excluded-volume effects we propose a scaling ftr∼T1−ν(Tc−T)ν/ϕ around the critical temperature Tc, where ν=0.588 is the Flory exponent and ϕ≈0.5 the crossover exponent, and we estimated the amplitude. We compare our results for a model where immediate step reversals are forbidden with recent self-avoiding walk simulations. We conclude that re-entrance is the general situation for lattice models. Only for a zigzag lattice model (where both forward and back steps are forbidden) is the coexistence curve ftr(T) monotonic, so that there is no re-entrance.
Tapered optical fibers as tools for probing magneto-optical trap characteristics
Authors: Morrissey Michael J. , Deasy Kieran , Wu Yuqiang , Chakrabarti Shrabana , Nic Chormaic Síle
Published: May 2009

We present a novel technique for measuring the characteristics of a magneto-optical trap (MOT) for cold atoms by monitoring the spontaneous emission from trapped atoms coupled into the guided mode of a tapered optical nanofiber. We show that the nanofiber is highly sensitive to very small numbers of atoms close to its surface. The size and shape of the MOT, determined by translating the cold atom cloud across the tapered fiber, is in excellent agreement with measurements obtained using the conventional method of fluorescence imaging using a charge coupled device camera. The coupling of atomic fluorescence into the tapered fiber also allows us to monitor the loading and lifetime of the trap. The results are compared to those achieved by focusing the MOT fluorescence onto a photodiode and it was seen that the tapered fiber gives slightly longer loading and lifetime measurements due to the sensitivity of the fiber, even when very few atoms are present.
Roles of the bias fields in the exchange interaction between the electron and hole spins in quantum wells
Authors: Miah M. Idrish
Published: May 2009

We study the electric-field effects on the spin polarization (P) in dependence of the strength and orientation of the magnetic field in GaAs quantum wells by photoluminescence measurements. The P in a transverse magnetic field is found to oscillate. The transverse electron and heavy-hole g-factors are estimated from the dependences of the oscillation frequency on magnetic field and applied bias. Measurements with the angular variations in the magnetic field show that both the oscillation frequency and decay rate are increased with increasing the angle from the transverse direction. It is, however, shown that the application of the bias to the quantum wells weakens the exchange interaction between the electron and hole spins.
Full-dimensional ab initio potential energy surface and vibrational configuration interaction calculations for vinyl
Authors: Sharma Amit R. , Braams Bastiaan J. , Carter Stuart , Shepler Benjamin C. , Bowman Joel M.
Published: May 2009

The potential energy landscape and two permutationally invariant, full-dimensional ab initio-based potential energy surfaces (PESs) for the doublet vinyl radical, C2H3, are described. The first of the two surfaces, denoted as PES/S, describes the equivalent CH2CH global minimum and the saddle point separating them, planar and nonplanar H-atom migration saddle points, a methylcarbyne local minimum that is due to a Jahn–Teller conical intersection, and the saddle point connecting it with the global minimum. The second PES, denoted PES/D, contains all stationary points of PES/S and in addition describes dissociation to C2H2+H fragments, including the saddle point to dissociation along a least-energy path. The surfaces are least-squares fits to electronic energies obtained with use of the spin-restricted coupled cluster singles and doubles with perturbative treatment of triples method and augmented correlation consistent polarized valence triple zeta basis sets, using permutationally invariant polynomials in “Morse variables” and a many-body expansion. PES/S is a fit to roughly 34 000 and PES/D to roughly 50 000 electronic structure energies. PES/S is used in full-dimensional, vibrational configuration interaction calculations of the vinyl zero-point energy and fundamental vibrational energies, which are compared to recent experiments.
Large zero-field spin splitting in AlGaN/AlN/GaN/AlN heterostructures
Authors: Lisesivdin S. B. , Balkan N. , Makarovsky O. , Patanè A. , Yildiz A. , Caliskan M. D. , Kasap M. , Ozcelik S. , Ozbay E.
Published: May 2009

This work describes Shubnikov–de Haas (SdH) measurements in Al0.22Ga0.78N/AlN/GaN/AlN heterostructures. Our experiments coupled with the analysis of the Hall data at various temperatures confirm the formation of a two-dimensional electron gas (2DEG) at the AlN/GaN interface. A beating pattern in the SdH oscillations is also observed and attributed to a zero-field spin splitting of the 2DEG first energy subband. The values of the effective spin-orbit coupling parameter and zero-field spin-split energy are estimated and compared with those reported in the literature. We show that zero-field spin-split energy tends to increase with increasing sheet electron density and that our value (12.75 meV) is the largest one reported in the literature for GaN-based heterostructures.
Assessment of the fatigue transformation zone in bulk metallic glasses using positron annihilation spectroscopy
Authors: Liu M. , Vallery R. S. , Gidley D. W. , Launey M. E. , Kruzic J. J.
Published: May 2009

Depth-profiled Doppler broadening spectroscopy of positron annihilation on fatigue fracture surfaces of two amorphous Zr44Ti11Ni10Cu10Be25 metallic glass specimens reveals the presence of a layer of increased free volume induced by cyclic deformation, as compared to surfaces that have been etched to remove any surface damage. The damage layer, or fatigue transformation zone (FTZ), is generated by the propagating fatigue crack tip and the deduced size of that zone is similar to the predicted cyclic plastic zone size at a number of locations where the crack grew at different stress intensities. The presence of the FTZ is independent of the initial amount of bulk free volume, which was varied between the two specimens by structural relaxation via annealing, and the free volume sites generated in the zone are distinct from those typical of the bulk, as evidenced by the higher S parameter. Such observations support the concept that the mechanically induced free volume within the FTZ zone controls the fatigue crack growth rates rather than the initial free volume of the bulk material.
Evolution of size, morphology, and magnetic properties of CuO nanoparticles by thermal annealing
Authors: Narsinga Rao G. , Yao Y. D. , Chen J. W.
Published: May 2009

Cupric oxide (CuO) nanoparticles with different morphologies were synthesized by thermal annealing of the copper hydroxide at various temperatures. Significant changes in both the particle size and the morphology with the annealing temperature (TA) were observed. The average particle size (d) increases from 13 to 33 nm and the morphology varies from ellipsoidal to rodlike as TA increases from 150 to 550 °C. The formation of these morphologies is explained in terms of the variation in the interplanar H-bonds breaking rate with different temperatures. The magnetic measurements reveal the presence of weak ferromagnetic interaction and the blocking behavior in these nanoparticles. The magnetic field dependence of the superparamagnetic blocking temperature (TB) follows the Brown equation. In addition, the linear variation in zero field cooled susceptibility with particle size is consistent with the predictions of Néel model for the uncompensated spins. These surface spins are responsible for the observed anomalous magnetic properties of CuO nanoparticles.
Distributed luminescence from alkyl-capped silicon quantum dots
Authors: Rostron R. J. , Horrocks B. R. , Roberts G.
Published: May 2009

Orange luminescence attributable to a core of silicon atoms in alkyl-capped crystalline quantum dots excited at λa=355 and 405 nm is investigated as a function of applied intensity and time. The intensity of luminescence displays a linear power dependence on the intensity of the applied field, from which an exponent n=0.94±0.02 commensurate with single-photon absorption is derived. The dependence of luminescence on time is observed to be strongly nonexponential and is optimally accounted for by a probability density function which describes a continuous distribution of two decay times: the behavior is characteristic of a pair of elementary steps connected with light emission within a distribution of local environments, or a single rate process supported by two environments. Nonlinear least-squares fits to the time dependent luminescence formulated on this basis with a Gaussian, Lorentzian, or log-normal distribution of rates return most probable lifetimes T¯1=21±1 μs and T¯2=3.7±0.8 μs. The widths of the distributions vary between σ1=0.01–0.03 μs−1 and σ2=0.14–1.1 μs−1 associated with 1/T¯1 and 1/T¯2, respectively.
Spin-transfer torque driven magnetic antivortex dynamics by sudden excitation of a spin-polarized dc
Authors: Xing Xiang-Jun , Li Shu-Wei
Published: May 2009

Spin dynamics of antivortices excited by sudden action of a spin-polarized dc is reported. Two main excitation modes are found with increased current density, involving a translational (gyrotropic) mode and a core reversal mode. The former mode can be described by Thiele’s equation, which accounts for the orbital distortion in view of the modified restoring force by nontrivial structures nucleated at sample edges. The final states of the system in the translational mode are obtained, being either a domain wall state or a vortex state, depending on the current density. The frequency of gyromotion is dependent on dot sizes. Within a threshold radius, the off-centered antivortex can freely relax back to the dot center.
Photo-induced refractive index change of amorphous tin-doped As2S8 films and its application to strip waveguide fabrication
Authors: Sun B. , Chen B. X. , Sui G. R. , Wang G. D. , Zou L. E. , Iso M. , Hamanaka H.
Published: May 2009

The amorphous chalcogenide glass Sn1As20S79 is demonstrated to undergo permanent changes in refractive index on irradiation with ultraviolet light. The refractive properties of this material and the effect of annealing at temperatures below the glass transition temperature are investigated in detail. An Sn1As20S79 strip waveguide is fabricated using this photoinduced refractive index change, and the device is shown to function as expected with good propagation characteristics for the 632.8 nm guided mode.
Anisotropic ion-enhanced diffusion during ion nitriding of single crystalline austenitic stainless steel
Authors: Martinavičius A. , Abrasonis G. , Möller W. , Templier C. , Rivière J. P. , Declémy A. , Chumlyakov Y.
Published: May 2009

Nitrogen diffusion is investigated in single crystalline austenitic stainless steel AISI 316L during ion beam nitriding and subsequent annealing at three different crystalline orientations. After nitriding at 400 °C and ion energy of 1 keV, the N penetration depth depends significantly on the crystalline orientation, with the highest penetration depth for (001) orientation. The experimental observations are quantitatively reproduced by fitting using the model of diffusion under the influence of traps. During subsequent isothermal annealing, the N diffusion becomes significantly slower than during nitriding and independent of the orientation. Possible mechanisms of the anisotropic ion-enhanced N diffusion are discussed.
Effects of doping on ferroelectric properties and leakage current behavior of KNN-LT-LS thin films on SrTiO3 substrate
Authors: Abazari M. , Safari A.
Published: May 2009

We report the effects of Ba, Ti, and Mn dopants on ferroelectric polarization and leakage current of (K0.44Na0.52Li0.04)(Nb0.84Ta0.1Sb0.06)O3 (KNN-LT-LS) thin films deposited by pulsed laser deposition. It is shown that donor dopants such as Ba2+, which increased the resistivity in bulk KNN-LT-LS, had an opposite effect in the thin film. Ti4+ as an acceptor B-site dopant reduces the leakage current by an order of magnitude, while the polarization values showed a slight degradation. Mn4+, however, was found to effectively suppress the leakage current by over two orders of magnitude while enhancing the polarization, with 15 and 23 μC/cm2 remanent and saturated polarization, whose values are ∼70% and 82% of the reported values for bulk composition. This phenomenon has been associated with the dual effect of Mn4+ in KNN-LT-LS thin film, by substituting both A- and B-site cations. A detailed description on how each dopant affects the concentrations of vacancies in the lattice is presented. Mn-doped KNN-LT-LS thin films are shown to be a promising candidate for lead-free thin films and applications.
Oxygen precipitation heterogeneously nucleating on silicon phosphide precipitates in heavily phosphorus-doped Czochralski silicon
Authors: Zeng Yuheng , Ma Xiangyang , Tian Daxi , Wang Weiyan , Gong Longfei , Yang Deren , Que Duanlin
Published: May 2009

Through comparison between the oxygen precipitation (OP) behaviors in heavily and lightly phosphorus (P)-doped Czochralski silicon (CZ-Si) crystals subjected to low-high two-step anneal of 600, 650, or 750 °C/8 h+1050 °C/16 h, we have found that in heavily P-doped CZ-Si, OP is much stronger in the case with the nucleation anneal at 600 or 650 °C while it is to some extent suppressed in the case with the nucleation anneal at 750 °C in contrast to lightly doped CZ-Si where nucleation is enhanced at 750 °C. Transmission electron microscopy investigation reveals that silicon phosphide precipitates of face-centered-cubic SiP form during the nucleation anneal at temperatures 650 °C and below. The SiP precipitates act as the heterogeneous nuclei for OP during the subsequent high temperature anneal while the oxygen precipitate nuclei containing certain amounts of P atoms generate during the nucleation anneal at 750 °C. They are further coarsened to be larger oxygen precipitates during the subsequent high temperature anneal. Of significance is that the oxygen precipitate nucleation mechanism operating at certain temperatures for heavily P-doped CZ-Si is found to be completely different from that of lightly P-doped CZ-Si. We believe that the present work provides a further insight into OP in CZ-Si.
Temperature dependence of the specific resistance in Ti/Al/Ni/Au Ohmic contacts on (NH4)2Sx treated n-type GaN
Authors: Lin F. , Shen B. , Huang S. , Xu F. J. , Lu L. , Song J. , Mei F. H. , Ma N. , Qin Z. X. , Zhang G. Y.
Published: May 2009

The temperature dependence of the specific contact resistance in annealed Ti/Al/Ni/Au multilayers on (NH4)2Sx treated n-type GaN has been studied in the temperature range from 25 to 600 °C by the transmission line technique. It is found that the specific contact resistivity ρc of the sample treated with (NH4)2Sx solution for 5 min at 90 °C decreases with increasing measuring temperature, while the ρc of the sample treated with (NH4)2Sx solution for 25 min at 90 °C increases with increasing measuring temperature. Excellent agreement with the “5 min treated” sample can be obtained by the field emission model with an average Schottky barrier height (SBH) ϕB=1.05 eV. Meanwhile, a field emission model with a temperature-dependent effective SBH is suggested to be responsible for the “25 min treated” sample in which metal/semiconductor interface potential pinch-off may occur. The high-resolution transmission electron microscope results support the above model.
Chirped-microwave assisted magnetization reversal
Authors: Wang Zihui , Wu Mingzhong
Published: May 2009

This paper reports simulation results on microwave-assisted magnetization reversal in magnetic thin films with perpendicular anisotropy. In comparison with frequency-fixed microwaves, frequency-chirped microwaves have higher efficiency in pumping magnetization precession and, therefore, can lead to more significant reduction in switching fields. Through the use of chirped microwaves, switching with low fields is also possible for large damping films.
Photoluminescence of ZnO nanorod-TiO2 nanotube hybrid arrays produced by electrodeposition
Authors: Yang Yang , Wang Xiaohui , Sun Changku , Li Longtu
Published: May 2009

The fabrication and structure characterization of ZnO nanorod-TiO2 nanotube hybrid arrays are reported. ZnO nanorods were electrodeposited onto the TiO2 nanotubes to form nanorod-nanotube hybrid arrays. Scanning electron microscopy showed that the ZnO nanorods were tightly grown together with TiO2 nanotubes. And the as-prepared ZnO nanorods have single crystal structures, which were grown along the [0001] direction. Both photoluminescence (PL) signals of ZnO nanorods and TiO2 nanotubes were observed in the PL spectrum of hybrid arrays. The observed PL signals of ZnO nanorods with visible broadband emission were induced by structure-dependent defects in ZnO nanorods.
Origin of the large strain response in (K0.5Na0.5)NbO3-modified (Bi0.5Na0.5)TiO3–BaTiO3 lead-free piezoceramics
Authors: Jo Wook , Granzow Torsten , Aulbach Emil , Rödel Jürgen , Damjanovic Dragan
Published: May 2009

The mechanism of the giant unipolar strain recently observed in a lead-free piezoceramic, 0.92(Bi0.5Na0.5)TiO3−0.06BaTiO3−0.02(K0.5Na0.5)NbO3 [S.-T. Zhang, A. B. Kounga, E. Aulbach, H. Ehrenberg, and J. Rödel, Appl. Phys. Lett. 91, 112906 (2007) was investigated. The validity of the previously proposed mechanism that the high strain comes both from a significant volume change during the field-induced phase transition, from an antiferroelectric to a ferroelectric phase and the domain contribution from the induced ferroelectric phase was examined. Monitoring the volume changes from the simultaneously measured longitudinal and transverse strains on disk-shaped samples showed that the phase transition in this specific material does not involve any notable volume change, which indicates that there is little contribution from a volume change due to the phase transition to the total strain response. Temperature dependent hysteresis measurements on unpoled samples of a nearby ferroelectric composition, 0.93(Bi0.5Na0.5)TiO3−0.06BaTiO3−0.01(K0.5Na0.5)NbO3 demonstrated that the origin of the large strain is due to the presence of a nonpolar phase that brings the system back to its unpoled state once the applied electric field is removed, which leads to a large unipolar strain.
Light-induced boron-oxygen defect generation in compensated p-type Czochralski silicon
Authors: Macdonald D. , Rougieux F. , Cuevas A. , Lim B. , Schmidt J. , Di Sabatino M. , Geerligs L. J.
Published: May 2009

The concentration of boron-oxygen defects generated in compensated p-type Czochralski silicon has been measured via carrier lifetime measurements taken before and after activating the defect with illumination. The rate of formation of these defects was also measured. Both the concentration and the rate were found to depend on the net doping rather than the total boron concentration. These results imply that the additional compensated boron exists in a form that is not able to bond with the oxygen dimers, thus prohibiting the formation of the defect. This could be explained by the presence of boron-phosphorus complexes, as proposed in previous work. Evidence for reduced carrier mobilities in compensated silicon is also presented, which has implications for photoconductance-based carrier lifetime measurements and solar cell performance.
Influence of interface transmissivity and inelastic scattering on the electronic entropy and specific heat of diffusive superconductor-normal metal-superconductor Josephson junctions
Authors: Rabani Hassan , Taddei Fabio , Giazotto Francesco , Fazio Rosario
Published: May 2009

We study theoretically the electronic entropy and specific heat in diffusive superconductor-normal metal-superconductor Josephson junctions. In particular, we consider the influence of nonidealities occurring in an actual experiment, such as the presence of barriers at the normal (N) metal-superconductor interfaces, the spin-flip, and inelastic scattering in the N-metal region and quasiparticle subgap states in the superconductors. We find that spin-flip and inelastic scattering do not have, for typical parameters values, a large effect. On the contrary, the presence of barriers suppresses the superconducting correlations in the N region, with the consequence that the entropy and the specific heat get reduced eventually to those in the absence of superconductivity for opaque interfaces. Finally we suggest an experiment and check that it is possible, under realistic conditions, to measure the dependence of electronic specific heat on the phase difference between the superconductors.
Sloshing of a layered fluid with a free surface as a Hamiltonian system
Authors: Sciortino G. , Adduce C. , La Rocca M.
Published: May 2009

The aim of this paper is the investigation of a layered sloshing fluid system using both a new Hamiltonian mathematical model and new laboratory experiments. The mathematical model is defined for a cylindrical tank with an arbitrary shape and subjected to an arbitrary rigid motion. The model consists of a pure evolution system of partial differential first order equations in the canonical four unknowns: water elevation at the upper free surface and at the separation surface and the gap in momentum potential density computed at each fluid surface. The system of equations is obtained by avoiding the construction of the Hamiltonian and its variational derivatives. An important advantage of this formulation, with respect to the Lagrangian formulation, is that the nonevolution constraint, which imposes for each fluid the same velocity component along the normal direction of the separation surface, is fulfilled by the model itself. The model implementation needs to define the so-called Neumann–Dirichlet operators, which are computed by an efficient algorithm, for any instantaneous configuration of the two fluid domains. A numerical integration of the model is performed by a suitable Galerkin projection of the evolution equations. New laboratory experiments, simulating the sloshing of a layered fluid system, inside a tank with a squared cross section, were performed. The experiments, with a two-dimensional sloshing, were carried out by varying the forcing frequency, the oscillation amplitude and the ratio of the two fluids’ depths. In some experiments, a traveling wave, with a shape similar to a moving hydraulic jump, was observed at the separation surface. Measurements of the space-time evolution of both the free and the separation surfaces were performed and compared with the model’s predictions. A good agreement between the model predictions and laboratory measurements is found, even for strong nonlinear cases such as the traveling wave.
Discrete rotating waves in a ring of coupled mechanical oscillators with strong damping
Authors: Qin Wen-Xin , Zhang Pei-Lin
Published: May 2009

By establishing the monotonicity in a ring of coupled oscillators with strong damping, we show the global stability of the discrete rotating wave, whose existence is demonstrated by applying the Schauder fixed point theorem.
Steady state solutions for nonlinear Schrödinger equation arising in optics
Authors: Yang Yisong , Zhang Ruifeng
Published: May 2009

In this paper, we use the method of calculus of variations to develop an existence theory for the steady state solutions of a nonlinear Schrödinger equation modeling light waves propagating in a photorefractive crystal. We show via direct minimization and mountain-pass argument that there exist steady state solutions realizing a continuous spectrum of energy points or wavenumbers.
Efficient terahertz generation by carbon nanotubes within the limited space-charge accumulation regime
Authors: Pennington G. , Wickenden A. E.
Published: May 2009

This paper investigates the generation of power at terahertz frequencies by a single-walled semiconducting carbon nanotube (s-SWCNT). The prediction of negative differential resistance (NDR) in s-SWCNTs allows for their consideration as a Gunn-type oscillator. Here we consider the regime of limited-space-charge accumulation within nanotubes biased with a potential along the tube axis. This regime minimizes the growth of high-field domain regions, which may be destructive to the nanotube, and allows for efficient high-power operation. Results show that a high-power, efficient, miniaturized, room temperature source of terahertz radiation is possible by appropriate biasing of the s-SWCNT element in the NDR region of operation. Nanotubes of diameter (d) 0.8–4.5 nm are considered. The generated ac power (Pac) is found to range in the μW/μm range, reaching values as high as 13 μW/μm at high bias and small diameter. Very large generation efficiencies (η) were found with a maximum value of 20% at high bias and small d. For a fixed dc bias field to NDR threshold field ratio, performance parameters are found to decrease with increasing s-SWCNT tube diameter as Pac∼d−2 and η∼d−1/3. Frequencies of operation where found to span the terahertz regime, indicating that a s-SWCNT may serve as the active element in terahertz oscillator diodes.
Maximizing the probability of detection for pure states
Authors: Łuczak Andrzej
Published: May 2009

We show that for an infinite number of linearly independent pure states there exists a uniquely determined simple measurement maximizing the probability of detection, generalizing thus the result known for a finite number of states. We also comment on the problem of the existence of an optimal measurement for a sequence of arbitrary normal states in the general Bayes approach.
In situ positioning of a few hundred micrometer-sized cleaved surfaces for soft-x-ray angle-resolved photoemission spectroscopy by use of an optical microscope
Authors: Muro Takayuki , Kato Yukako , Matsushita Tomohiro , Kinoshita Toyohiko , Watanabe Yoshio , Sekiyama Akira , Sugiyama Hiroshi , Kimura Masato , Komori Satoshi , Suga Shigemasa , Okazaki Hiroyuki , Yokoya Takayoshi
Published: May 2009

A method to position samples with small cleaved regions has been developed to be applied to the angle-resolved photoemission spectroscopy (ARPES) which uses soft-x-ray synchrotron radiation focused down to 160×180 μm2. A long-working-distance optical microscope is used for the sample observation. A selected region on a sample can be optimally set at the position of measurements, which is realized by the spatial resolution of the photoelectron analyzer. Using this method, electronic band dispersions of bulk silicon have been measured by ARPES for a partially cleaved region with a size of ∼200×500 μm2.
Fractional statistics description applied to adsorption of alkane binary mixtures in zeolites
Authors: Dávila M. , Riccardo J. L. , Ramirez-Pastor A. J.
Published: May 2009

In the present paper, the multicomponent adsorption of polyatomic species is described as a fractional statistics problem, based on Haldane’s statistics. Site exclusion is characterized by a “mutual exclusion matrix” g, which relates to the sizes of the different species and lattice geometry. The adsorption process has been monitored through total and partial isotherms, energy of adsorption and configurational entropy of the adsorbed phase. The thermodynamic functions calculated for a monomer-dimer mixture were applied to describe the adsorption of methane-ethane mixtures in zeolites. In the case of zero lateral interactions, the present approach was compared to the well-known ideal adsorbed solution theory. The results show that the treatment of this complex problem can be significantly simplified if looked up from the new theoretical perspective.
Linking microscopic guest properties to macroscopic observables in clathrate hydrates: Guest-host hydrogen bonding
Authors: Alavi Saman , Susilo Robin , Ripmeester John A.
Published: May 2009

Molecular dynamics simulations are used to compare microscopic structures and guest dynamics to macroscopic properties in structure II clathrate hydrates with cyclopentane, tetrahydrofuran (THF), 1,3-dioxolane, tetrahydropyran (THP), and p-dioxane as guests. Significant differences are observed between structural parameters and rotational dynamics for the different guests. The simulations show the formation of guest-host hydrogen bonds between the ether oxygen atoms of THF and THP and the cage water hydrogen atoms of the clathrate but the absence of similar hydrogen bonds in the clathrate hydrates of the other guests on the time scale of the calculations. This guest-host hydrogen bonding leads to the formation of Bjerrum L-defects in the clathrate water lattice where two adjacent water molecules have no covalently bonded hydrogen atom between them. Unlike Bjerrum defects of ice lattices, these guest-induced L-defects are not accompanied by the formation of a D-defect at an adjacent site in the water lattice. At the simulation temperature of 200 K, the guest-water hydrogen bonds in the THF clathrate are short lived (lifetime less than 1 ps) but in the THP they are longer lived (a minimum of 100 ps). A van’t Hoff plot for the probability of defect formation in THF as a function of temperature gives an activation barrier of ∼8.3 kJ/mol for guest-host defect formation in the THF clathrate. The consequences of the defect formation on the thermal expansivity, isothermal compressibility, dipole-dipole correlation function, and mechanical stability of the clathrate are discussed.
Parasitic capacitance influence of potential-sensing electrodes on four-electrode liquid impedance measurements
Authors: Mazzeo Brian A.
Published: May 2009

Four-electrode techniques are used to minimize the effects of electrode polarization on measurements of the frequency-dependent impedance of conductive solutions. Basic circuit analysis confirms that an ideal Schwan-type four-electrode measurement can theoretically determine the polarization-free impedance of a sample. However, circuit analysis including parasitic effects indicates that the input impedance of the potential-sensing electrodes will be a significant influence on the measurement. This is verified in experiments on conductive solutions employing measurements of the gain and phase between potential-sensing electrodes in a four-electrode arrangement. The electrode impedance is varied by adding capacitors in parallel with the probes. The combined theory and experimental data indicate that parasitic capacitance of the potential-sensing electrodes is non-negligible and will alter the measured capacitance at all frequencies and even distort conductivity measurements at high-frequencies. This result has significant implications for the feasibility of broadband measurements of liquids based on four-electrode impedance methods.
Observation of microwave plasmons in one-dimensional conjugated polymer chain
Authors: Mondal B. , Majumdar D. , Ghosh A. , Saha S. K.
Published: May 2009

Observation of extremely low frequency plasmons in highly ordered quasi-one-dimensional (quasi-1D) interrupted metallic polymer chain segments is reported. Rice and Bernascony [Phys. Rev. Lett. 29, 113 (1972)] predicted giant permittivity in interrupted 1D metal strands because of quantum confinement. We have used this quasi-1D electron system with giant permittivity to realize 1D plasmons in microwave frequency. Polypyrrole nanorods with ordered and aligned chains have been synthesized. These ordered and perfectly conjugated systems interrupted by defects are ideal systems to achieve giant permittivity and as a result, 1D microwave plasmons, which have potential applications in microwave devices, are observed.
Acousto-optic modulator based frequency stabilized diode laser system for atom trapping
Authors: McDowall Peter D. , Andersen Mikkel F.
Published: May 2009

We report on an inexpensive commercial laser diode stabilized to the D2-line in rubidium using a simple scheme. The linewidth was reduced to 1.3 MHz without an external cavity, making it suitable for laser cooling and trapping. The system is very robust and the laser frequency can be changed rapidly (within 51 μs) while the laser remains in lock. The frequency of the locked laser drifts less than 850 kHz peak-to-peak over 25 h. We demonstrate laser cooling and trapping using our system.
Accurate microfour-point probe sheet resistance measurements on small samples
Authors: Thorsteinsson Sune , Wang Fei , Petersen Dirch H. , Hansen Torben Mikael , Kjær Daniel , Lin Rong , Kim Jang-Yong , Nielsen Peter F. , Hansen Ole
Published: May 2009

We show that accurate sheet resistance measurements on small samples may be performed using microfour-point probes without applying correction factors. Using dual configuration measurements, the sheet resistance may be extracted with high accuracy when the microfour-point probes are in proximity of a mirror plane on small samples with dimensions of a few times the probe pitch. We calculate theoretically the size of the “sweet spot,” where sufficiently accurate sheet resistances result and show that even for very small samples it is feasible to do correction free extraction of the sheet resistance with sufficient accuracy. As an example, the sheet resistance of a 40 μm (50 μm) square sample may be characterized with an accuracy of 0.3% (0.1%) using a 10 μm pitch microfour-point probe and assuming a probe alignment accuracy of ±2.5 μm.
Fabrication and performance of a monolithic dye-sensitized TiO2/Cu(In,Ga)Se2 thin film tandem solar cell
Authors: Wenger Sophie , Seyrling Sieghard , Tiwari Ayodhya N. , Grätzel Michael
Published: May 2009

Tandem solar cells using different bandgap absorbers allow efficient photovoltaic conversion in a wide range of the solar spectrum. The optical gaps of the dye-sensitized solar cell and the Cu(In,Ga)Se2 solar cell are ideal for application in double-junction devices and a mechanically stacked device has been reported recently. We report on the monolithic integration of these subcells to cut optical losses at needless interfaces and material costs, achieving 12.2% conversion efficiency at full sunlight. The high open-circuit voltage confirms the series connection, but corrosion of the Cu(In,Ga)Se2 cell by the redox mediator (I−/I3− couple) of the dye-sensitized cell and an associated voltage loss (≈140 mV) limits performance.
High-power, null-type, inverted pendulum thrust stand
Authors: Xu Kunning G. , Walker Mitchell L. R.
Published: May 2009

This article presents the theory and operation of a null-type, inverted pendulum thrust stand. The thrust stand design supports thrusters having a total mass up to 250 kg and measures thrust over a range of 1 mN to 5 N. The design uses a conventional inverted pendulum to increase sensitivity, coupled with a null-type feature to eliminate thrust alignment error due to deflection of thrust. The thrust stand position serves as the input to the null-circuit feedback control system and the output is the current to an electromagnetic actuator. Mechanical oscillations are actively damped with an electromagnetic damper. A closed-loop inclination system levels the stand while an active cooling system minimizes thermal effects. The thrust stand incorporates an in situ calibration rig. The thrust of a 3.4 kW Hall thruster is measured for thrust levels up to 230 mN. The uncertainty of the thrust measurements in this experiment is ±0.6%, determined by examination of the hysteresis, drift of the zero offset and calibration slope variation.
A robust method for measurement of fluctuation parallel wavenumber in laboratory plasmas
Authors: Poli F. M. , Podestà M. , Fasoli A.
Published: May 2009

Measuring the parallel wavenumber is fundamental for the experimental characterization of electrostatic instabilities. It becomes particularly important in toroidal geometry, where spatial inhomogeneities and curvature can excite both drift instabilities, whose wavenumber parallel to the magnetic field is finite, and interchange instabilities, which typically have vanishing parallel wavenumber. We demonstrate that multipoint measurements can provide a robust method for the discrimination between the two cases.
Cluster synchronization in community networks with nonidentical nodes
Authors: Wang Kaihua , Fu Xinchu , Li Kezan
Published: May 2009

In this paper dynamical networks with community structure and nonidentical nodes and with identical local dynamics for all individual nodes in each community are considered. The cluster synchronization of these networks with or without time delay is studied by using some feedback control schemes. Several sufficient conditions for achieving cluster synchronization are obtained analytically and are further verified numerically by some examples with chaotic or nonchaotic nodes. In addition, an essential relation between synchronization dynamics and local dynamics is found by detailed analysis of dynamical networks without delay through the stage detection of cluster synchronization.
Inverse synchronizations in coupled time-delay systems with inhibitory coupling
Authors: Senthilkumar D. V. , Kurths J. , Lakshmanan M.
Published: May 2009

Transitions between inverse anticipatory, inverse complete, and inverse lag synchronizations are shown to occur as a function of the coupling delay in unidirectionally coupled time-delay systems with inhibitory coupling. We have also shown that the same general asymptotic stability condition obtained using the Krasovskii–Lyapunov functional theory can be valid for the cases where (i) both the coefficients of the Δ(t) (error variable) and Δτ=Δ(t−τ) (error variable with delay) terms in the error equation corresponding to the synchronization manifold are time independent and (ii) the coefficient of the Δ term is time independent, while that of the Δτ term is time dependent. The existence of different kinds of synchronization is corroborated using similarity function, probability of synchronization, and also from changes in the spectrum of Lyapunov exponents of the coupled time-delay systems.
Applications of the wave kinetic approach: From laser wakefields to drift wave turbulence
Authors: Trines R. M. G. M. , Bingham R. , Silva L. O. , Mendonça J. T. , Shukla P. K. , Murphy C. D. , Dunlop M. W. , Davies J. A. , Bamford R. , Vaivads A. , Norreys P. A.
Published: May 2009

Nonlinear wave-driven processes in plasmas are normally described by either a monochromatic pump wave that couples to other monochromatic waves or as a random phase wave coupling to other random phase waves. An alternative approach involves a random or broadband pump coupling to monochromatic and/or coherent structures in the plasma. This approach can be implemented through the wave kinetic model. In this model, the incoming pump wave is described by either a bunch (for coherent waves) or a sea (for random phase waves) of quasiparticles. This approach has been applied to both photon acceleration in laser wakefields and drift wave turbulence in magnetized plasma edge configurations. Numerical simulations have been compared to experiments, varying from photon acceleration to drift mode-zonal flow turbulence, and good qualitative correspondences have been found in all cases.
Microscopic structure and thermodynamics of a core-softened model fluid: Insights from grand canonical Monte Carlo simulations and integral equations theory
Authors: Pizio Orest , Dominguez Hector , Duda Yurko , Sokołowski Stefan
Published: May 2009

We have studied the microscopic structure and thermodynamic properties of isotropic three-dimensional core-softened model fluid by using extensive grand canonical Monte Carlo computer simulations and Ornstein–Zernike integral equations with hypernetted chain and Rogers–Young closures. Applied simulation tools permit to obtain insights into the properties of the model in addition to available molecular dynamics data of other authors. We discuss equation of state in the density–chemical potential projection and explore the temperature dependence of the chemical potential along different isochores. The limits of the region of anomalous behavior of the structural and thermodynamic properties are established by investigating derivatives resulting from the equation of state, pair contribution to excess entropy, and translational order parameter. Besides, we evaluate the dependence of the heat capacity on temperature and density. The microscopic structure is discussed in terms of the pair distribution functions and corresponding structure factors. We have established that the hypernetted chain approximation is not successful to capture the region of anomalies in contrast to Rogers–Young approximation, but is very accurate for high fluid densities. Thus we have studied the onset for crystallization transition within this theoretical framework. Moreover, using the replicated Ornstein–Zernike integral equations with hypernetted chain closure, we explore the possibility of glass transition and described it in terms of transition density and chemical potential.
Doppler widths in electron quasielastic scattering from molecular gases
Authors: Moreh R. , Nemirovsky D.
Published: May 2009

Recent quasielastic electron scattering experiments on some molecular gases at Ee≥1.8 keV have shown that the scattering is from single isotopes of the atomic components of the gas. The scattered electron lines at definite angles are Doppler broadened by the instantaneous kinetic energy (KE) of the scattering atoms. We calculated the KE of the scattering atoms by accounting for translation, rotation, and all normal modes of vibrations of the molecule. The results reveal some large and fundamental differences from literature estimates.
Resistive switching characteristics in Pr0.7Ca0.3MnO3 thin films on LaNiO3-electrodized Si substrate
Authors: Chang Wen-Yuan , Liao Jeng-Hwa , Lo Yun-Shan , Wu Tai-Bor
Published: May 2009

The resistive switching characteristics of Pr0.7Ca0.3MnO3 (PCMO) thin films deposited on LaNiO3 (LNO)-electrodized Si substrate were investigated. Highly (100)-textured PCMO films were grown on the (100)-oriented LNO electrode. They exhibited reversible and steady bistable resistance switching behavior. The resistive switching behavior of PCMO capacitors on LNO is related to the trap-controlled space charge limited current mechanism and LNO/PCMO/LNO capacitor exhibits the strongest resistive switching effect with a resistance ratio for about two orders of magnitude.
Accurate interaction energies at density functional theory level by means of an efficient dispersion correction
Authors: Krishtal Alisa , Vanommeslaeghe Kenno , Olasz András , Veszprémi Tamás , Van Alsenoy Christian , Geerlings Paul
Published: May 2009

This paper presents an approach for obtaining accurate interaction energies at the density functional theory level for systems where dispersion interactions are important. This approach combines Becke and Johnson’s [J. Chem. Phys. 127, 154108 (2007)] method for the evaluation of dispersion energy corrections and a Hirshfeld method for partitioning of molecular polarizability tensors into atomic contributions. Due to the availability of atomic polarizability tensors, the method is extended to incorporate anisotropic contributions, which prove to be important for complexes of lower symmetry. The method is validated for a set of 18 complexes, for which interaction energies were obtained with the B3LYP, PBE, and TPSS functionals combined with the aug-cc-pVTZ basis set and compared with the values obtained at the CCSD(T) level extrapolated to a complete basis set limit. It is shown that very good quality interaction energies can be obtained by the proposed method for each of the examined functionals, the overall performance of the TPSS functional being the best, which with a slope of 1.00 in the linear regression equation and a constant term of only 0.1 kcal/mol allows to obtain accurate interaction energies without any need of a damping function for complexes close to their exact equilibrium geometry.