bluuebunny/crossref_metadata_2025 huggingface dataset:
Polarization retention on short, intermediate, and long time scales in ferroelectric thin films
Authors: Lou X. J.
Published: May 2009

We developed a model with no adjustable parameter for retention loss at short and long time scales in ferroelectric thin-film capacitors. We found that the predictions of this model are in good agreement with the experimental observations in the literature. In particular, it explains why a power-law function shows better fitting than a linear-log relation on a short time scale (10−7 s to 1 s) and why a stretched exponential relation gives more precise description than a linear-log plot on a long time scale (>100 s), as reported by many researchers in the past. More severe retention losses at higher temperatures and in thinner films have also been correctly predicted by the present theory.
Distribution of dislocations in GaSb and InSb epilayers grown on GaAs (001) vicinal substrates
Authors: Li Meicheng , Qiu Yongxin , Liu Guojun , Wang Yutian , Zhang Baoshun , Zhao Liancheng
Published: May 2009

GaSb and InSb epilayers grown on GaAs (001) vicinal substrates misoriented toward (111) plane were studied using high resolution x-ray diffraction. The results show that GaSb and InSb epilayers take on positive crystallographic tilt, and the asymmetric distribution of 60° misfit dislocations in {111} glide planes have an effect on the tilt. In addition, the vicinal substrate influences the distribution of the threading dislocations in {111} glide planes, and the density of dislocation in the (111) plane is higher than in the (1¯1¯1) plane. A model was proposed to interpret the distribution of full width at half maximum, which can help us understand the formation and glide process of the dislocations.
Spectral theory of interacting ferrite magnetoelectric particles
Authors: Kamenetskii E. O.
Published: May 2009

The linear magnetoelectric effect provides a special route for local linking magnetic and electric properties. In recently published paper [E. O. Kamenetskii, M. Sigalov, and R. Shavit, J. Appl. Phys. 105, 013537 (2009)], it was shown that no local junctions of the electric and magnetic properties appear from the induced parameters of small electromagnetic scatterers and that point magnetoelectric particles can be realized in quasi-two-dimensional ferrite disks due to the dynamical symmetry breaking effects of the magnetic-dipolar-mode microwave oscillations. These results raise questions about structures of the near fields surrounding magnetoelectric particles and focus our attention on fundamental aspects of interaction between such particles. The fact that for magnetic-dipolar modes in a ferrite disk one has evident quantumlike attributes puts special demands on the methods used for study of interacting magnetoelectric particles. A proper model for coupled particles should be based on the spectral characteristics of the magnetic-dipolar-mode oscillations and an analysis of the overlap integrals for interacting eigenoscillating magnetoelectric elements. In this paper, we present theoretical studies of spectral properties of laterally coupled magnetoelectric ferrite-disk particles. We show that there exists the “exchange” mechanism of interaction between the particles, which is distinctive from the magnetostatic interaction between classical magnetic dipoles and the electromagnetic interaction between small electromagnetic scatterers. The spectral method of interacting magnetoelectric particles proposed in this paper underlies the theory of “magnetoelectric molecules” and furthers realization of dense microwave magnetoelectric composites.
Enhanced magnetic properties of FePt nanoparticles codeposited on Ag nanoislands
Authors: Castaldi L. , Giannakopoulos K. , Travlos A. , Boukos N. , Niarchos D. , Boukari S. , Beaurepaire E.
Published: May 2009

Ag nanoislands have been used as nucleation sites for FePt nanoparticles when deposited on SiO2 surfaces by electron beam evaporation. We demonstrate that it is possible to nucleate FePt nanoparticles on predeposited Ag clusters and that this results in a significant improvement of the hard magnetic Ag/FePt nanoparticles’ properties. We find that, besides the usual annealing treatments, a simple predeposition of Ag nanoclusters promotes the formation of the FePt L10 phase at larger FePt nominal thicknesses (fFePt). All the nanoparticles studied are ferromagnetic, except for those FePt samples deposited with lower nominal thicknesses (fFePt∼1.8 nm), which are superparamagnetic. The presence of Ag seeds promotes the A1/L10 transition, which results in a remarkable enhancement of the coercivity (Hc) for both the as-deposited and the annealed samples. Maximum Hc of 8.9 and 9.4 kOe are obtained for the Ag/FePt nanoparticles with fFePt∼1.8 and 3.5 nm, respectively. Our results are a strong indication that the nucleation of the FePt nanoparticles on Ag nanoclusters can promote significant magnetic hardening of the FePt nanoparticles by easing the transition from the disordered to the ordered phase.
Refining the weighted stochastic simulation algorithm
Authors: Gillespie Dan T. , Roh Min , Petzold Linda R.
Published: May 2009

The weighted stochastic simulation algorithm (wSSA) recently introduced by Kuwahara and Mura [J. Chem. Phys. 129, 165101 (2008)] is an innovative variation on the stochastic simulation algorithm (SSA). It enables one to estimate, with much less computational effort than was previously thought possible using a Monte Carlo simulation procedure, the probability that a specified event will occur in a chemically reacting system within a specified time when that probability is very small. This paper presents some procedural extensions to the wSSA that enhance its effectiveness in practical applications. The paper also attempts to clarify some theoretical issues connected with the wSSA, including its connection to first passage time theory and its relation to the SSA.
Electric current induced liquid metal flow: Application to coating of micropatterned structures
Authors: Dutta I. , Kumar P.
Published: May 2009

Although electric fields have been widely used to induce flow of electrolytes, electrically induced long-range flow of metallic liquids has never been reported. Here we show that liquid pure metals can be made to flow in a continuous stream by applying an electric current to an underlying conductive film. This flow occurs in the direction of applied current and is thought to be driven by liquid electromigration. The phenomenon is expected to engender many applications where controlled delivery of a continuous liquid metal stream is desired, such as microfluidics, nanolithography, and patterned conformal coatings. The last application is demonstrated here.
General treatment of paramagnetic relaxation enhancement associated with translational diffusion
Authors: Kruk D. , Kowalewski J.
Published: May 2009

A theory of nuclear spin relaxation in isotropic liquids for nuclear spins interacting with electron spins, residing in other molecules (the outer-sphere relaxation), is presented. The approach, valid outside of the Redfield limit for electron spin relaxation, is an extension of the Swedish slow motion theory [Benetis et al., Mol. Phys. 48, 329 (1983); Nilsson and Kowalewski, J. Magn. Reson. 146, 345 (2000)] for inner-sphere relaxation. It is demonstrated that the outer-sphere relaxation rate can be expressed as an integral of a product of a translational diffusion correlation function and a function analogous to the inner-sphere spectral density. A numerical implementation of the theory is described and applied to a large number of realistic parameter sets for S=7/2 and S=1, which may correspond to Gd(III) and Ni(II) systems. It is shown that the outer-sphere contribution is relevant and should be included into the analysis of nuclear magnetic relaxation dispersion relaxation profiles, especially for slow relative translational diffusion and fast molecular tumbling.
Determination of the ionization and dissociation energies of the hydrogen molecule
Authors: Liu Jinjun , Salumbides Edcel J. , Hollenstein Urs , Koelemeij Jeroen C. J. , Eikema Kjeld S. E. , Ubachs Wim , Merkt Frédéric
Published: May 2009

The transition wave number from the EF Σ1g+(v=0,N=1) energy level of ortho-H2 to the 54p11(0) Rydberg state below the X+ Σ2g+(v+=0,N+=1) ground state of ortho-H2+ has been measured to be 25 209.997 56±(0.000 22)statistical±(0.000 07)systematic cm−1. Combining this result with previous experimental and theoretical results for other energy level intervals, the ionization and dissociation energies of the hydrogen molecule have been determined to be 124 417.491 13(37) and 36 118.069 62(37) cm−1, respectively, which represents a precision improvement over previous experimental and theoretical results by more than one order of magnitude. The new value of the ionization energy can be regarded as the most precise and accurate experimental result of this quantity, whereas the dissociation energy is a hybrid experimental-theoretical determination.
Evaporation of a thin droplet on a thin substrate with a high thermal resistance
Authors: Dunn G. J. , Wilson S. K. , Duffy B. R. , Sefiane K.
Published: May 2009

A mathematical model for the quasisteady evaporation of a thin liquid droplet on a thin substrate that incorporates the dependence of the saturation concentration of vapor at the free surface of the droplet on temperature is used to examine an atypical situation in which the substrate has a high thermal resistance relative to the droplet (i.e., it is highly insulating and/or is thick relative to the droplet). In this situation diffusion of heat through the substrate is the rate-limiting evaporative process and at leading order the local mass flux is spatially uniform, the total evaporation rate is proportional to the surface area of the droplet, and the droplet is uniformly cooled. In particular, the qualitative differences between the predictions of the present model in this situation and those of the widely used “basic” model in which the saturation concentration is independent of temperature are highlighted.
Influence of thermal effects on buoyancy-driven convection around autocatalytic chemical fronts propagating horizontally
Authors: Rongy L. , Schuszter G. , Sinkó Z. , Tóth T. , Horváth D. , Tóth A. , De Wit A.
Published: May 2009

The spatiotemporal dynamics of vertical autocatalytic fronts traveling horizontally in thin solution layers closed to the air can be influenced by buoyancy-driven convection induced by density gradients across the front. We perform here a combined experimental and theoretical study of the competition between solutal and thermal effects on such convection. Experimentally, we focus on the antagonistic chlorite-tetrathionate reaction for which solutal and thermal contributions to the density jump across the front have opposite signs. We show that in isothermal conditions the heavier products sink below the lighter reactants, providing an asymptotic constant finger shape deformation of the front by convection. When thermal effects are present, the hotter products, on the contrary, climb above the reactants for strongly exothermic conditions. These various observations as well as the influence of the relative weight of the solutal and thermal effects and of the thickness of the solution layer on the dynamics are discussed in terms of a two-dimensional reaction-diffusion-convection model parametrized by a solutal RC and a thermal RT Rayleigh number.
Lensless Fourier transform digital holographic interferometer for diffusivity measurement of miscible transparent liquids
Authors: Sheoran Gyanendra , Anand Arun , Shakher Chandra
Published: May 2009

Lensless Fourier transform digital holographic technique is applied for measurement of diffusion in miscible transparent liquid solutions. The phase information at two time instances and a synthetic plane wavefront is used to determine the diffusion coefficient. The experiment was conducted to measure the diffusion coefficient of aqueous solution of NaCl in water. The measured values of diffusion coefficient deviates approximately 1.06% from the values given in literature.
Preparation of metal mixed plastic superconductors: Electrical properties of tin-antimony thin films on plastic substrates
Authors: Stephenson Andrew P. , Divakar Ujjual , Micolich Adam P. , Meredith Paul , Powell Ben J.
Published: May 2009

Metal mixed polymers are a cheap and effective way to produce flexible metals and superconductors. As part of an on-going effort to learn how to tune the properties of these systems with ion implantation, we present a study of the electrical properties of these systems prior to metal mixing. We show that the electrical properties of tin-antimony thin films are remarkably robust to variations in the substrate morphology. We demonstrate that the optical absorbance of the films at a fixed wavelength provides a reliable and reproducible characterization of the relative film thickness. We find that as the film thickness is reduced, the superconducting transition in the unimplanted thin films is broadened, but the onset of the transition remains at ∼3.7 K, the transition temperature of bulk Sn. This is in marked contrast to the behavior of metal mixed films, which suggests that the metal mixing process has a significant effect on the physics of the superconducting state beyond that achieved by reducing the film thickness alone.
Giant electrocaloric effect in lead-free thin film of strontium bismuth tantalite
Authors: Chen Hao , Ren Tian-Ling , Wu Xiao-Ming , Yang Yi , Liu Li-Tian
Published: May 2009

Giant electrocaloric effect was observed in lead-free material for the first time. A demonstration of large electrocaloric effect in 200 nm sol-gel thin film SrBi2Ta2O9 is described here. The ferroelectric hysteresis loops and the film permittivity were measured. The extracted data characterized the electrocaloric temperature change, up to 4.93K in 12V (i.e., 0.41 K V−1) near the Curie point. It is concluded that the giant electrocaloric effect exists in lead-free materials, and a large family of layered perovskite oxides may exhibit analogical property. The absence of lead allows eco-friendly application and enhances compatibility with integrated circuit process in future applications.
Influence of the branches width on the nonlinear output characteristics of InAlAs/InGaAs-based three-terminal junctions
Authors: Iñiguez-de-la-Torre I. , González T. , Pardo D. , Gardès C. , Roelens Y. , Bollaert S. , Mateos J.
Published: May 2009

In this work, the influence of the geometry of the different branches on the output characteristics of InAlAs/InGaAs three-branch junctions is analyzed. At room temperature experimental measurements show that when increasing the width of the horizontal branches, the nonlinear behavior persists, even if less pronounced. This implies a reduction in the (typically high) impedance of these nanodevices, which is quite interesting in order to minimize the influence of parasitic capacitances on their cutoff frequency and to decrease the reflected power due to the mismatch with the 50 Ω standard equipment. The width of the vertical branch is also a relevant parameter, nonlinear effects being more important for narrow branches. In both cases surface charges at the etched boundaries of the branches play a key role. Monte Carlo simulations (performed with a self-consistent surface charge model recently proposed by the authors) are used to explain the physical origin of the observed behavior and to improve the device performance. We focus on the enhancement of their efficiency as a way to develop their promising functionalities in various analog and digital circuits.
Nanostructures and defects in thermoelectric AgPb18SbTe20 single crystal
Authors: Wu Lijun , Zheng Jin-Cheng , Zhou Juan , Li Qiang , Yang Jihui , Zhu Yimei
Published: May 2009

Nanoparticles play key roles in reducing thermal conductivity, and hence increasing figure of merit for many thermoelectric materials. We have studied the structure of AgPb18SbTe20 (LAST-18) using high resolution imaging, nanoelectron diffraction, energy dispersive spectrum, and electron energy loss spectrum, and observed a range of nanoparticles with different sizes (from less than 1nm to more than 10nm) and shape (sphere, ellipse, square, etc.). The lattice parameters of the nanoparticles have a wide range from 0.601to0.655nm, while those of the matrix have a range from 0.633to0.646nm. The nanoparticles are formed due to the ordering of Pb and Ag–Sb. There are four ordered structures with primitive cubic, primitive tetragonal (T1, a≈a0∕√2, c≈a0, here, a0 is the lattice parameter of the rocksalt-type matrix), primitive tetragonal (T2, a≈a0∕√2, c≈2a0), and body-centered tetragonal (T3, a≈a0∕√2, c≈3a0) lattices, respectively. Antiphase domains, twins, and phase separations were often observed in the nanoparticles. The strain field in the surrounding matrix due to the presence of nanoparticles was retrieved from the high resolution images. The characteristic that the strain field is anisotropic and extends to large area is considered to enhance the scattering of the phonons. The results provide quantitative structure information about nanoparticles, that is essential for the understanding of the origin of the high thermoelectric performance in this class of materials.
Annealing of nanoindentation-induced high pressure crystalline phases created in crystalline and amorphous silicon
Authors: Ruffell S. , Haberl B. , Koenig S. , Bradby J. E. , Williams J. S.
Published: May 2009

Thermally induced phase transformation of Si-III/Si-XII zones formed by nanoindentation has been studied during low temperature (200<T<300 °C) thermal annealing by Raman microspectroscopy and transmission electron microscopy. Two sizes of spherical indenter tips have been used to create substantially different volumes of phase transformed zones in both crystalline (c-Si) and amorphous silicon (a-Si) to study the zone size and starting matrix effects. The overall transformation is from Si-III/XII to poly- or nanocrystalline Si-I through intermediate phases of Si-XIII and Si-IV. Attempts have been made to determine the exact transformation pathways. Two scenarios are possible: either Si-XII first transforms to Si-III before transforming to Si-I through the intermediate phases or that Si-XII goes through the intermediate phases while Si-III transforms directly to Si-I. Finally, the phase transformations are slower in the larger indents and the starting matrix (crystalline or amorphous) has a substantial effect on the transformation kinetics of the small indents compared to the larger ones. We attribute this increased stability to both matrix effects (nucleation) and a difference in overall residual stress in indents made in a-Si compared to c-Si.
Synthesis and characterization of highly spin-polarized single-phase Co1−xFexS2 films
Authors: Manno M. , Frakie R. , Leighton C.
Published: May 2009

Tunable spin polarizations up to 85% have been reported in bulk Co1−xFexS2. In this paper, we report on the synthesis of polycrystalline Co1−xFexS2 thin films on Al2O3(0001) and SrTiO3(001) by ex situ sulfidation of epitaxial Co1−xFex. As a function of sulfidation temperature (TS), the films evolve from unreacted Co1−xFex, through a mixed phase dominated by Co1−xFexS, to single-phase Co1−xFexS2 at TS≥350 °C. At optimized deposition conditions, the films are sulfur stoichiometric, have an average in-plane grain size of 35 nm, surface roughness of 3.7 nm (at a thickness of 56 nm), and are delamination-free up to 300 nm. The Curie temperature, saturation magnetization, resistivity, and magnetoresistance are similar to those of bulk. Significantly, we find 1.0μB/Co at x=0.15 and a vanishing spin-flip electron-magnon scattering signature in magnetotransport, consistent with the very highly polarized state observed in bulk crystals. Ex situ sulfidation is therefore a simple route to the formation of Co1−xFexS2 films, opening up the possibility of exploiting this unique material in fundamental studies of heterostructured spintronic devices.
A “gentle” nodal suspension for measurements of the acoustic attenuation in materials
Authors: Cesarini E. , Lorenzini M. , Campagna E. , Martelli F. , Piergiovanni F. , Vetrano F. , Losurdo G. , Cagnoli G.
Published: May 2009

Loss angle measurements in ultralow mechanical loss materials is normally affected by a large systematic error due to the excess losses introduced by the suspension system used to hold the samples. Crystals such as sapphire and silicon or amorphous materials such as fused silica can have loss angles in the range of 10−10–10−7; such materials are of extreme interest in the detection of small displacements as it is required in quantum measurements, frequency stabilization, Micro Electro-Mechanical Systems (MEMS), and gravitational wave research. In the system proposed here the sample is suspended in equilibrium on top of a sphere, touching on one of the nodal points of vibration. The advantage of this system, as compared to others used so far, is twofold: (i) one surface only of the sample is touched and the contact surface is minimized because of the absence of applied forces; (ii) some relevant parameters of the suspension can be measured and eventually varied, giving the experimentalist the possibility to identify whether the measured loss is limited by the suspension system in use or it is an intrinsic property of the sample under investigation. The measurements of a 75 mm diameter and 3 mm thickness disk of Suprasil®311 gave a loss angle ϕ of 5×10−8.
Chaos synchronization basing on symbolic dynamics with nongenerating partition
Authors: Wang Xingyuan , Wang Mogei , Liu Zhenzhen
Published: May 2009

Using symbolic dynamics and information theory, we study the information transmission needed for synchronizing unidirectionally coupled oscillators. It is found that when sustaining chaos synchronization with nongenerating partition, the synchronization error will be larger than a critical value, although the required coupled channel capacity can be smaller than the case of using a generating partition. Then we show that no matter whether a generating or nongenerating partition is in use, a high-quality detector can guarantee the lead of the response oscillator, while the lag responding can make up the low precision of the detector. A practicable synchronization scheme basing on a nongenerating partition is also proposed in this paper.
Interfacial electronic states of tetracene deposited on Si(111)
Authors: Guan Dandan , Mao Hongying , Chen Meiliang , Dou Weidong , Song Fei , Zhang Hanjie , Li Haiyang , He Pimo , Chen Hongzheng , Bao Shining
Published: May 2009

The interfacial electronic states of tetracene on Si(111) 7×7 substrate were studied by using ultraviolet photoelectron spectroscopy (UPS). After deposition of tetracene on the Si(111) 7×7 surface, the features originating from the tetracene molecule appear at 1.55, 3.36, 6.78, 9.24, and 10.76 eV below the Fermi level; they shift in binding energy with increasing organic film coverage. From the UPS measurements, the work function of the sample surface was found to decrease with increasing molecular coverage in the submonolayer range suggesting that an interfacial dipole is formed. A density functional theory calculation had also been carried out to determine the favorable adsorption structure. The molecule near the top of a center adatom with the longer molecular axis along the [11¯0] azimuth is the most favorable.
Abrupt contraction flow of magnetorheological fluids
Authors: Kuzhir P. , López-López M. T. , Bossis G.
Published: May 2009

Contraction and expansion flows of magnetorheological fluids occur in a variety of smart devices. It is important therefore to learn how these flows can be controlled by means of applied magnetic fields. This paper presents a first investigation into the axisymmetric flow of a magnetorheological fluid through an orifice (so-called abrupt contraction flow). The effect of an external magnetic field, longitudinal or transverse to the flow, is examined. In experiments, the pressure-flow rate curves were measured, and the excess pressure drop (associated with entrance and exit losses) was derived from experimental data through the Bagley correction procedure. The effect of the longitudinal magnetic field is manifested through a significant increase in the slope of the pressure-flow rate curves, while no discernible yield stress occurs. This behavior, observed at shear Mason numbers 10<Mnshear<100, is interpreted in terms of an enhanced extensional response of magnetorheological fluids accompanied by shrinkage of the entrance flow into a conical funnel. At the same range of Mason numbers, the transverse magnetic field appears not to influence the pressure drop. This can be explained by a total destruction of magnetic particle aggregates by large hydrodynamic forces acting on them when they are perpendicular to the flow. To support these findings, we have developed a theoretical model connecting the microstructure of the magnetorheological fluid to its extensional rheological properties and predicting the pressure-flow rate relations through the solution of the flow equations. In the case of the longitudinal magnetic field, our model describes the experimental results reasonably well.
Probability density optical tomography of confined quasiparticles in a semiconductor microcavity
Authors: Nardin Gaël , Paraïso Taofiq K. , Cerna Roland , Pietka Barbara , Léger Yoan , El Daif Ounsi , Morier-Genoud François , Deveaud-Plédran Benoît
Published: May 2009

We present the optical tomography of the probability density of quasiparticles, the microcavity polaritons, confined in three dimensions by cylindrical traps. Collecting the photoluminescence emitted by the quasimodes under continuous nonresonant laser excitation, we reconstruct a three-dimensional mapping of the photoluminescence, from which we can extract the spatial distribution of the confined states at any energy. We discuss the impact of the confinement geometry on the wave function patterns and give an intuitive understanding in terms of a light-matter quasiparticle confined in a box.
Absence of CO dissociation on Mo(112)
Authors: Yakovkin I. N. , Petrova N. V.
Published: May 2009

We revisit the problem of CO adsorption and thermal dissociation on the Mo(112) surface by means of density-functional calculations of binding energies, local densities of states, and CO vibrational frequencies for various configurations of equilibrated adlayers. The bridge-on-row adsorption sites on the Mo(112) surface are found to be the most favorable and CO molecules will occupy less stable in-furrow sites only after the completing of the first monolayer. At low coverages, CO molecules are tilted by ∼40° with respect to the normal to the surface (the β state), but with increasing coverage, due to lateral interactions, attain an upright orientation with the carbon end down (the α state). The tilting of CO results in a significant elongation of the C–O bond (to 1.20 Å) and, consequently, the C–O stretching vibration frequency decreases to 1159 cm−1. Nonetheless, the β state cannot be attributed to the precursor to CO dissociation, because the estimated potential barrier for the dissociation (∼2.8 eV) substantially exceeds the chemisorption energy (2.1 eV), which makes the thermally induced CO dissociation on Mo improbable. With estimated chemisorption energies, Monte Carlo simulations have shown that the two-peak shape of TPD spectra can be explained without involving the CO dissociation. We predict also that the lack of dissociation can be detected in photoemission studies for CO on Mo(112) by the presence of the −23 and −7 eV peaks, characteristic of chemisorbed CO, and absence of the −18 and −5 eV peaks characteristic of adsorbed O atoms.
The effect of N2 flow rate on discharge characteristics of microwave electron cyclotron resonance plasma
Authors: Ding Wan-Yu , Xu Jun , Lu Wen-Qi , Deng Xin-Lu , Dong Chuang
Published: May 2009

The properties of plasma in Ar/N2 microwave electron cyclotron resonance discharge with a percentage of N2 flow rate ranging from 5% to 50% have been studied in order to understand the effect of N2 flow rate on the mechanical properties of silicon nitride films. N2+ radicals as well as N2, N+ are found by optical emission spectroscopy analysis. The evolution of plasma density, electron kinetic energy, N2+, N2, and N+ emission lines from mixed Ar/N2 plasma on changing mixture ratio has been studied. The mechanisms of their variations have been discussed. Moreover, an Ar/N2 flow ratio of 2/20 is considered to be the best condition for synthesizing a-Si3N4, which has been confirmed in the as-deposited silicon nitride films with quite good mechanical properties by nanoindentation analyses.
Bimolecular reaction rates from ring polymer molecular dynamics
Authors: Collepardo-Guevara Rosana , Suleimanov Yury V. , Manolopoulos David E.
Published: May 2009

We describe an efficient procedure for calculating the rates of bimolecular chemical reactions in the gas phase within the ring polymer molecular dynamics approximation. A key feature of the procedure is that it does not require that one calculate the absolute quantum mechanical partition function of the reactants or the transition state: The rate coefficient only depends on the ratio of these two partition functions which can be obtained from a thermodynamic integration along a suitable reaction coordinate. The procedure is illustrated with applications to the three-dimensional H+H2, Cl+HCl, and F+H2 reactions, for which well-converged quantum reactive scattering results are computed for comparison. The ring polymer rate coefficients agree with these exact results at high temperatures and are within a factor of 3 of the exact results at temperatures in the deep quantum tunneling regime, where the classical rate coefficients are too small by several orders of magnitude. This is probably already good enough to encourage future applications of the ring polymer theory to more complex chemical reactions, which it is capable of treating in their full dimensionality. However, there is clearly some scope for improving on the ring polymer approximation at low temperatures, and we end by suggesting a way in which this might be accomplished.
Low temperature thermal transport in partially perforated silicon nitride membranes
Authors: Yefremenko V. , Wang G. , Novosad V. , Datesman A. , Pearson J. , Divan R. , Chang C. L. , Downes T. P. , McMahon J. J. , Bleem L. E. , Crites A. T. , Meyer S. S. , Carlstrom J. E.
Published: May 2009

The thermal transport in partially trenched silicon nitride membranes has been studied in the temperature range from 0.3 to 0.6 K, with the transition edge sensor (TES), the sole source of membrane heating. The test configuration consisted of Mo/Au TESs lithographically defined on silicon nitride membranes 1 μm thick and 6 mm2 in size. Trenches with variable depth were incorporated between the TES and the silicon frame in order to manage the thermal transport. It was shown that sharp features in the membrane surface, such as trenches, significantly impede the modes of phonon transport. A nonlinear dependence of thermal resistance on trench depth was observed. Partial perforation of silicon nitride membranes to control thermal transport could be useful in fabricating mechanically robust detector devices.
Parameter identification and projective synchronization between different chaotic systems
Authors: Sun Fei , Peng Haipeng , Luo Qun , Li Lixiang , Yang Yixian
Published: May 2009

In this paper, adaptive generalized projective synchronization and parameter identification in different chaotic systems are carefully revisited. We use a concrete counterexample to demonstrate that the result in a previous work [R. Li, W. Xu, and S. Li, Phys. Lett. A 367, 199 (2007)] is imperfect, where a scheme of generalized projective synchronization is proposed for parameter identification with some drawbacks on ignoring the conditions which ensure the parameter convergence. We further discuss the two conditions of parameter convergence, which are linear independence and persistent excitation. A special relationship between them is addressed to estimate unknown model parameters effectively.
Acceleration of soliton by nonlinear Landau damping of dust-helical waves
Authors: Ehsan Zahida , Tsintsadze Nodar L. , Vranjes J. , Poedts S.
Published: May 2009

The problem of nonlinear Landau damping of helicon waves in dusty plasma in particular emphasis to the acceleration of soliton is presented here. This in the framework of a collisionless, anisotropic homogeneous dusty plasma in one dimension, can be well described by two coupled dynamical equations of the generalized Zakharov type, with one extra nonlocal term coming from Landau damping. Nonlinear-nonlocal term gives rise to essential contributions relative to the local term. Then under different conditions, kinetic nonlinear Schrödinger equation is constructed and nonlinear decrement is obtained for two cases. It is noticed that the time dependant term in the ponderomotive force plays a significant role for this kind of damping. Additionally, it is shown that nonlinear Landau damping leads to the amplitude modulation of dust helicon waves, further modulational instability, and maximal growth rate is obtained when the group velocity of the helicon wave reaches the dust-acoustic speed. It is demonstrated that how the nonlinear Landau damping leads to the acceleration of soliton, which is eventually slowed down after transferring some of its energy to the wave. Emission of dust-acoustic wave by accelerated soliton is discussed briefly.
Transverse dielectric properties of boron nitride nanotubes by ab initio electric field calculations
Authors: Lan Hai-Ping , Ye Lin-Hui , Zhang Shuang , Peng Lian-Mao
Published: May 2009

Extensive ab initio finite electric-field calculations are performed to study the static transverse dielectric properties of boron nitride nanotubes via the sawtooth potential approach. It is shown that the transverse polarizability is proportional to the tube radius rather than to the square of it, and that the screening factor is not a constant but decreases monotonically with increasing tube radius. A classical cylindrical dielectric shell model, with a dielectric constant of 5.90 and an effective shell thickness of 2.50 Å, is shown to reproduce very well the ab initio results for both single- and multiwalled boron nitride nanotubes.
Effect of illumination intensity and temperature on open circuit voltage in organic solar cells
Authors: Kumar Pankaj , Jain S. C. , Kumar Hemant , Chand Suresh , Kumar Vikram
Published: May 2009

The effect of illumination intensity and temperature on open circuit voltage (Voc) in organic photovoltaic devices has been investigated. Voc is observed to saturate at high illumination intensities. The illuminated J-V characteristics at different intensities intersect the dark characteristic at a single point. This intersection point is shown to be equal to the built-in voltage (Vbi) in the sample. A reduction in temperature shows increment in saturated Voc. This increment in saturated Voc is attributed to the variation of Vbi with temperature. A model has been presented that explains the observed behavior of Vbi at different temperatures.
Special optical geometry for measuring twist elastic module K22 and rotational viscosity γ1 of nematic liquid crystals
Authors: Dubtsov A. V. , Pasechnik S. V. , Shmeliova D. V. , Tsvetkov V. A. , Chigrinov V. G.
Published: May 2009

A special nontraditional optical geometry with a pure twist deformation induced by a homogeneous “in-plane” electric field in the layer of nematic liquid crystal (LC) is presented. A quantitative agreement of the theoretical and experimental results of the measured LC birefringence is obtained. A method for measuring the twist elastic module K22 and the rotational viscosity coefficient γ1 of nematic LC is proposed.
Capacitance enhancement in the accumulation region of C-V characteristics in metal-insulator-semiconductor capacitors consisting of pentacene and poly(4-vinylphenol)
Authors: Jeong Seung Hyeon , Song Chung Kun , Yi Mihye
Published: May 2009

We report a peculiar enhancement in the accumulation capacitance Cacc in the capacitance-voltage (C-V) characteristics of metal-insulator-semiconductor capacitors consisting of poly(4-vinylphenol) (PVP) and pentacene. Cacc at low frequency C-V was five times larger than the PVP dielectric capacitance CPVP. Cacc decreased as the frequency was increased and returned to the level of CPVP at 1 MHz. The origin of the capacitance enhancement appears to be associated with water molecules adsorbed into the PVP dielectric film when considering the correlation with the concentration of PVP polymer in which OH phenol is known to absorb water molecules.
The effect of localized surface plasmon on the photocurrent of silicon nanocrystal photodetectors
Authors: Kim Sang-Kyun , Cho Chang-Hee , Kim Baek-Hyun , Choi Yong-Seok , Park Seong-Ju , Lee Kimoon , Im Seongil
Published: May 2009

We report on the photocurrent of silicon nanocrystal (Si NC) photodetectors (PDs) that contain silver (Ag) islands. Here, a larger increase in the photocurrent of Si NC PDs was observed with increasing Ag island size. The maximum increase occurred at the wavelength of the Ag surface plasmon resonance and redshifted as the size of the Ag islands increased. As a result, a 97% increase in photocurrent generation was observed and this was attributed mostly to the coupling of Si NC with the localized surface plasmon of the Ag islands in Si NC PDs.
A tunable acoustic filter made by periodical structured materials
Authors: Wang Jingshi , Xu Xiaodong , Liu Xiaojun , Xu Gangcan
Published: May 2009

Three kinds of the periodical structures are designed as low-pass, high-pass, and band-pass filters for elastic wave. The theoretical simulations have proved that the periodical surface slots can act as a low-pass filter for elastic wave. With increasing depth of the surface periodical structure in the sample, the cutoff frequency of the low-pass filter is decreased. Unlike the surface periodical structure, the periodical subsurface structure can work as a high-pass filter for elastic wave. The cutoff frequency of the high-pass filter is suppressed by the increase of the subsurface structure thickness. When the two periodical structures are combined together, the band-pass filter is obtained, in which the pass band is determined by the cutoff frequencies of the low-pass and high-pass filters.
On the controversial nature of the 1 B1u and 2 B1u states of trans-stilbene: The n-electron valence state perturbation theory approach
Authors: Angeli Celestino , Improta Roberto , Santoro Fabrizio
Published: May 2009

The nature of two lowest-energy states of Bu symmetry of trans-stilbene and the accurate calculation of their vertical excitation energy have been the subject of a controversy because time dependent density functional theory (TD-DFT) calculations, in agreement with experimental observations, have questioned the results obtained with multireference perturbation theory (MRPT) in the CASPT2 implementation. This paper aims to solve this controversy. By using a different version of MRPT, the n-electron valence state perturbation theory method, the description provided by TD-DFT is confirmed: the lowest Bu singlet state has a HOMO→LUMO nature and a large oscillator strength (HOMO refers to highest occupied molecular orbital and LUMO refers to lowest unoccupied molecular orbital), while the second Bu singlet state has a mixed HOMO−1→LUMO and HOMO→LUMO+1 nature, has an oscillator strength almost vanishing, and is located at 0.6–0.7 eV higher than the first excited state. The computed vertical excitation energy to the first state (3.8–4.0 eV) is in good agreement with the experimental value.
Evolution of the electrically exploding wire observed with a Mach–Zehnder interferometer
Authors: Mao Zhiguo , Zou Xiaobing , Wang Xinxin , Jiang Weihua
Published: May 2009

The evolution of an exploding titanium wire embedded in 10 kPa air was studied with Mach–Zehnder interferometry. The exploding wire is characterized by a central dense core as well as the surrounding plasma and a rapidly expanding gas shell. Based on the fringe shifts, the electron density of the plasma and the increased density in the gas shell were calculated to be about 1.94×1018/cm3 and 4.78×10−4 g/cm3, respectively. The expanding speed of the gas shell is about 2.28 km/s. A thermal expansion lag of the dense vapor core and two-phase vaporization of the wire were observed. Due to the wire exploding in “under heat” mode, the first phase of the vaporization is by the Joule heating and the second one by the plasma heating.
The work-Hamiltonian connection and the usefulness of the Jarzynski equality for free energy calculations
Authors: Zimanyi Eric N. , Silbey Robert J.
Published: May 2009

The connection between work and changes in the Hamiltonian for a system with a time-dependent Hamiltonian has recently been called into question, casting doubt on the usefulness of the Jarzynski equality for calculating free energy changes. In this paper, we discuss the relationship between two possible definitions of free energy and show how some recent disagreements regarding the applicability of the Jarzynski equality are the result of different authors' using different definitions of free energy. Finally, in light of the recently raised doubts, we explicitly demonstrate that it is indeed possible to obtain physically relevant free energy profiles from molecular pulling experiments by using the Jarzynski equality and the results of Hummer and Szabo.
Changes in quinic acid metabolism during fruit development in three kiwifruit species
Authors: Marsh Ken B. , Boldingh Helen L. , Shilton Rebecca S. , Laing William A.
Published: May 2009

Kiwifruit are novel in that they contain high levels of quinic acid (1–2% w/w), which contributes to the flavour, sugar/acid balance and health-giving properties of the fruit. In a study of quinic acid storage and metabolism in three kiwifruit species (Actinidia chinensis Planch. var. chinensis, Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson var. deliciosa and Actinidia arguta (Sieb. et Zucc.) Planch. ex Miq. var. arguta) quinic acid accumulation occurred principally in the early stages (<60 days after anthesis; (DAA)) of fruit development. The present study established that there are separate quinate dehydrogenase (QDH) and shikimate dehydrogenase (SDH) activities in kiwifruit, probably representing different proteins. Quinate dehydrogenase activity was at a maximum around the time of greatest quinic acid accumulation and declined markedly in late fruit development, and was also higher in the species that accumulated the largest amounts of quinic acid (A. chinensis and A. deliciosa). In contrast, SDH activity was highest in the early stages of fruit development and only declined to 30–50% at later stages of fruit development in all three species. Dehydroquinate synthase gene expression levels measured by quantitative real-time PCR showed a high level in the early season, which was sustained through the mid-season. The quantitative real-time PCR results for a kiwifruit EST that had homology to chloroplastic isoforms of SDH showed an induction in the middle to late season; therefore, the high level of SDH activity in the early season (<30 DAA) may have resulted from the expression of a cytosolic isoform of the enzyme. The results are also consistent with the relative levels of the bifunctional dehydroquinate dehydratase/SDH enzyme and QDH enzyme controlling the accumulation and utilisation of quinic acid in kiwifruit.
Molecular cloning, expression and mapping of the translational initiation factor eIF1 gene in Oryza sativa
Authors: Rangan Latha , Rout Anusuya , Sudarshan Medhavi , Gregorio Glenn
Published: May 2009

Protein translation is very sensitive to salt stress and the proteins involved in this process may be an important determinant of salt tolerance. We isolated a rice cDNA clone (OseIF1) from a salt-tolerant indica cultivar (Pokkali) subjected to 150 mm NaCl, the deduced amino acid sequence of which had homology with the Sui1 suppressor locus in Saccharomyces cerevisiaei Hansen. The sequence contains 753 bp with an open-reading frame of 345 bp and shares similarity with the sequences of Sui1 and eIF1 in plants and mammals. Southern analysis indicates that the gene is present in more than a single copy per haploid genome and mapped to chromosome 1 of rice. Expression of the gene was increased by salt stress and also upregulated after exogenous ABA and mannitol treatments, suggesting that its induction is related to the water-deficit effect of high salt.
Differential photosynthetic performance and photoprotection mechanisms of three Mediterranean evergreen oaks under severe drought stress
Authors: Peguero-Pina José Javier , Sancho-Knapik Domingo , Morales Fermín , Flexas Jaume , Gil-Pelegrín Eustaquio
Published: May 2009

The ability of three Mediterranean oaks (Quercus coccifera L., Quercus ilex ssp. ballota (Desf.) Samp and Quercus suber L.) to cope with intense drought was investigated. Water stress reduced stomatal conductance and photosynthesis in these species. Drought-mediated changes in photosynthetic-related parameters allowed the characterisation of the specific photo-protective mechanisms. Specifically, Q. suber downregulated photosynthetic electron transport rates (ETR) closing PSII reaction centres (i.e. decreasing photochemical quenching) and through an antheraxanthin (A) + zeaxanthin (Z)-mediated diminished intrinsic PSII efficiency (Φexc.). These changes were lower in Q. coccifera and Q. ilex ssp. ballota, which decreased further ETR photo-inactivating PSII centres (evidenced by their low predawn Fv/Fm ratios at high water stress). The predawn Fv/Fm ratio decreased in Q. coccifera largely due to Fm decreases, whereas in Q. ilex ssp. ballota Fv/Fm decreases were due to F0 increases, below –4 MPa. These Fv/Fm decreases were well correlated with increases in the A + Z photo-protective pigments. An analysis of dark respiration and photorespiration as alternative electron sinks under intense drought stress also revealed interspecific differences. The largest imbalance between electrons generated and consumed increased potentially oxidative damage in Q. suber. Subsequently, only Q. suber showed loss of chlorophyll, which is one of the main targets of oxidative damage. Data suggest that Q. coccifera and Q. ilex ssp. ballota seem more able than Q. suber to withstand highly xeric conditions. Therefore, our results question the consideration of Mediterranean evergreen oaks as a homogeneous physiological group.
Functional transition in the floral receptacle of the sacred lotus (Nelumbo nucifera): from thermogenesis to photosynthesis
Authors: Miller Rebecca E. , Watling Jennifer R. , Robinson Sharon A.
Published: May 2009

The receptacle of the sacred lotus is the main source of heat during the thermogenic stage of floral development. Following anthesis, it enlarges, greens and becomes a fully functional photosynthetic organ. We investigated development of photosynthetic traits during this unusual functional transition. There were two distinct phases of pigment accumulation in receptacles. Lutein and photoprotective xanthophyll cycle pigments accumulated first with 64 and 95% of the maximum, respectively, present before anthesis. Lutein epoxide comprised 32% of total carotenoids in yellow receptacles, but declined with development. By contrast, more than 85% of maximum total chlorophyll, β-carotene and Rubisco were produced after anthesis, and were associated with significant increases in maximum electron transport rates (ETR) and photochemical efficiency (Fv/Fm). Leaves and mature receptacles had similar Rubisco content and ETRs (>200 μmol m−2 s−1), although total chlorophyll and total carotenoid contents of leaves were significantly higher than those of green receptacles. Receptacle δ13C before anthesis was similar to that of leaves; consistent with leaf photosynthesis being the source of C for these tissues. In contrast, mature receptacles had significantly lower δ13C than leaves, suggesting that 14–24% of C in mature receptacles is the result of refixation of respired CO2.