bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of the degree of order of InGaP on its hardness determined using nanoindentation
Authors: Zakaria A. , Fetzer C. M. , Goorsky M. S.
Published: October 2010

Spontaneous atomic ordering takes place during metal-organic vapor phase epitaxy when certain semiconductors alloys start forming long-range arrangements different from their standard lattice unit cells. In the case of InGaP, a zincblende semiconductor, the ordered CuPt(B) structure consists of alternating Ga and In rich (1¯11) and (11¯1) planes. In this investigation, InGaP was deposited on (001) Ge wafers with a 6° miscut toward the [111] direction in two consecutive experiments. A surfactant was used in experiment A while depositing InGaP to induce a lower degree of order. high resolution x-ray diffraction was used to calculate composition and strain of the InGaP epilayers. The symmetric (004) as well as the asymmetric (224) glancing exit reflections were used. The results enabled the extraction of a theoretical band gap energy Eg corrected for strain effects. Photoluminescence was used to measure the actual Eg. By comparing the two, the degree of order η was determined to be 0.12–0.15 for wafers from experiment A and 0.43–0.44 for wafers from experiment B. Atomic force microscopy AFM demonstrated that all experimental wafers had a surface rms roughness of 6.1–7.4 Å. Extensive nanoindentation measurements were performed on samples from both experiments. It was determined that the degree of order has no effect on the nanoindentation hardness of InGaP. Using 1/2 (115) superlattice reflection scans, the InGaP ordered domains size was estimated to be 28.5 nm for sample B1. No superlattice peak was detected in sample A1. The large ordered domain size in B1 explains why no order-hardening behavior was observed in InGaP.
Overview of the beam emission spectroscopy diagnostic system on the National Spherical Torus Experiment
Authors: Smith D. R. , Feder H. , Feder R. , Fonck R. J. , Labik G. , McKee G. R. , Schoenbeck N. , Stratton B. C. , Uzun-Kaymak I. , Winz G.
Published: October 2010

A beam emission spectroscopy (BES) system has been installed on the National Spherical Torus Experiment (NSTX) to study ion gyroscale fluctuations. The BES system measures Dα emission from a deuterium neutral heating beam. The system includes two optical views centered at r/a≈0.45 and 0.85 and aligned to magnetic field pitch angles at the neutral beam. f/1.5 collection optics produce 2–3 cm spot sizes at the neutral beam. The initial channel layout includes radial arrays, poloidal arrays, and two-dimensional grids. Radial arrays provide coverage from r/a≈0.1 to beyond the last-closed flux surface. Photodetectors and digital filters provide high-sensitivity, low-noise measurements at frequencies of up to 1 MHz. The BES system will be a valuable tool for investigating ion gyroscale turbulence and Alfvén/energetic particle modes on NSTX.
Nonlinear optical studies on nanocolloidal Ga–Sb–Ge–Se chalcogenide glass
Authors: Tintu R. , Nampoori V. P. N. , Radhakrishnan P. , Thomas Sheenu
Published: October 2010

In this paper we report the preparation and the optical studies on nanocolloidal solutions of Ga5Sb10Ge25Se60 for the first time. The optical band gap of the material is found to be tunable depending on the cluster size. The cluster formation and the dependence of the cluster size with concentration were confirmed by the scanning electron microscope analysis. Nonlinear optical characterization of these solutions were studied by the Z-scan technique using an Nd:YAG laser (532 nm, 7 ns, 10 Hz).The studies show that the material is highly nonlinear. The solutions show reverse saturable absorption, which makes it useful for optical limiting applications.
Mixing of granular material in rotating cylinders with noncircular cross-sections
Authors: Prasad D. V. N. , Khakhar D. V.
Published: October 2010

We study, experimentally and theoretically, the mixing of monodisperse colored beads in rotating cylinders with different cross-sectional shapes (square, star, and a circle with two and four triangular wedges), operating in the continuous flow regime, to understand the role of cross-sectional shape on the mixing process. The evolution of the mixed state is quantified using two measures: the intensity of segregation and the centroid distance. The mixing rate index, defined as the specific rate of change of the intensity of segregation with time, is initially lower in all the noncircular cross-sections compared to a circle. It increases monotonically in noncircular cross-sections, whereas it is nearly constant in a circle. This corresponds to a faster than exponential decay of the intensity of segregation for noncircular cross-sections as compared to an exponential decay for a circular cross-section. The decay of centroid distance is oscillatory in a circle, whereas it is monotonic in noncircular cross-sections. A significant improvement in the mixing rate is obtained for noncircular cross-sections relative to circular cross-sections. The mixing rate is highest for the circle with four wedges; the mixing rates for square and star cross-sections are slightly lower. The circle with two wedges has the lowest mixing rate among the noncircular cross-sections. Experiments with smaller glass beads, in which the particle diffusivity is significantly smaller, yield a mixing rate very close to that for the larger particles. Mixing patterns obtained experimentally at short times are well predicted by a convective diffusion model that includes a time-periodic velocity field for the noncircular cross-sections. A quantitative comparison of model predictions with experiments in terms of the intensity of segregation and the centroid distance shows a reasonably good agreement for the different shapes and for the two particle sizes. A scaling analysis is presented to explain the insensitivity of the mixing rate to particle size despite a significant variation in diffusivity. Mixing patterns for a tracer blob and the mixing rates obtained for the different mixers are found to be related to the regions of the chaotic advection in computed Poincaré maps. For the systems studied, the mixing rate increases with an increase in the number of corners in the geometry, but is relatively unaffected by the ratio of the maximum to minimum diameter of the cross-section.
Distilling entanglement from arbitrary resources
Authors: Buscemi Francesco , Datta Nilanjana
Published: October 2010

We obtain the general formula for the optimal rate at which singlets can be distilled from any given noisy and arbitrarily correlated entanglement resource by means of local operations and classical communication (LOCC). Our formula, obtained by employing the quantum information spectrum method, reduces to that derived by Devetak and Winter [Proc. R. Soc. London, Ser. A 461, 207 (2005)], in the special case of an independent and identically distributed resource. The proofs rely on a one-shot version of the so-called “hashing bound,” which, in turn, provides bounds on the one-shot distillable entanglement under general LOCC.
Influence of the potential difference between the two gate electrodes on the single electron transport
Authors: Song Li , Gao Jie , Chen Shuwei , Zhang Chuanyu
Published: October 2010

We investigate the effect of the potential difference ΔVg between the two gate electrodes on the quantized acoustoelectric current induced by surface acoustic wave. A significant improvement on the precision of the quantized acoustoelectric current is achieved as a result of the potential difference ΔVg. Our calculated results demonstrate that the static potential barrier height is dramatically changed by ΔVg, and these changes can affect the shape of the quantum well, hence, the probability of events that contribute to the error in the quantized current is affected. Furthermore, the effect of the potential difference on the acoustoelectric current in the presence of the impurity potential is investigated.
The mechanism of low-k SiOCH film modification by oxygen atoms
Authors: Braginsky O. V. , Kovalev A. S. , Lopaev D. V. , Malykhin E. M. , Mankelevich Yu. A. , Rakhimova T. V. , Rakhimov A. T. , Vasilieva A. N. , Zyryanov S. M. , Baklanov M. R.
Published: October 2010

The interaction of oxygen atoms with three types of plasma enhanced chemical vapor deposition low-k SiOCH films is studied. The samples were treated by O atoms in the far plasma afterglow conditions in a special experimental system designed for this study. The experimental system allowed avoiding the effect of ions and vacuum ultraviolet (VUV) photons on surface reactions and controlling the oxygen atom concentration over the samples. Fourier-transform infrared spectroscopy, x-ray fluorescence, and atomic force microscopy techniques were used to analyze the changes occurring in low-k films. Monte Carlo model for O atom interaction with low-k material that includes penetration, recombination, and reactions with methyl groups was developed. It is shown that the surface recombination on the pore wall surface determines the profile and penetration depth of O atoms into the films. The reaction of O atoms with methyl groups has lower probability and therefore proceeds in the background mode.
Fractional protein dynamics seen by nuclear magnetic resonance spectroscopy: Relating molecular dynamics simulation and experiment
Authors: Calandrini Vania , Abergel Daniel , Kneller Gerald R.
Published: October 2010

We propose a fractional Brownian dynamics model for time correlation functions characterizing the internal dynamics of proteins probed by NMR relaxation spectroscopy. The time correlation functions are represented by a broad distribution of exponential functions which are characterized by two parameters. We show that the model describes well the restricted rotational motion of N–H vectors in the amide groups of lysozyme obtained from molecular dynamics simulation and that reliable predictions of experimental relaxation rates can be obtained on that basis.
Impedance spectroscopy of BaTiO3 cubes suspended in lossy liquids as a physical model of two-phase system
Authors: Jasinski Piotr , Petrovsky Vladimir , Dogan Fatih
Published: October 2010

Impedance spectroscopy techniques were used for analysis of the physical model in a two-phase system toward determining of dielectric constant of dielectric particles suspended in liquids at various solids loading (volume fraction) levels. Model experimental studies were conducted using BaTiO3 as a dielectric material that was prepared as small cubes of uniform size (2×2×1 mm). Barium titanate (BT) cubes having a dielectric constant of 3850 were immersed in liquids of low dielectric constant and moderate electrical conductivity. Measured impedance spectra consisted of two semicircles, which were fitted for (R∥C)(R∥C) equivalent circuit. The parameters obtained from fitting were compared with the data acquired from simulations of brick layer models and Maxwell–Wagner effective media model. In the investigated range of volume fractions the Maxwell–Wagner model correlates well with the data extracted from measurements.
Angular effects of nanostructure-covered femtosecond laser induced periodic surface structures on metals
Authors: Hwang Taek Yong , Guo Chunlei
Published: October 2010

In this paper, we study nanostructure-covered laser induced periodic surface structures (NC-LIPSSs) on metals produced by femtosecond laser pulses incident at various angles. For the first time, we show that the dependence of NC-LIPSS period on the incident beam angle deviates significantly from that of regular LIPSSs studied previously using longer laser pulses. Our study shows that this deviation is due to the nanostructures on LIPSSs that can be explained by the Maxwell–Garnett theory of effective media.
Volume of supercooled water under pressure and the liquid-liquid critical point
Authors: Mishima Osamu
Published: October 2010

The volume of water (H2O) was obtained at about 200–275 K and 40–400 MPa by using emulsified water. The plot of volume against temperature showed slightly concave-downward curvature at pressures higher than ≈200 MPa. This is compatible with the liquid-liquid critical-point hypothesis, but hardly with the singularity-free scenario. When the critical point is assumed to exist at ≈50 MPa and ≈223 K, the experimental volume and the derived compressibility are qualitatively described by the modified Fuentevilla–Anisimov scaling equation.
Spectral properties and 1.55 μm laser operation of Ce3+:Yb3+:Er3+:NaLa(WO4)2 crystal
Authors: Gong Xinghong , Chen Yujin , Lin Yanfu , Huang Jianhua , Luo Zundu , Huang Yidong
Published: October 2010

A series of x at. %Ce3+:10 at. %Yb3+:1 at. %Er3+:NaLa(WO4)2 (x=0,10,…,50) crystal powders were prepared by high temperature solid phase reaction. The effect of Ce3+ concentration on the I411/2→I413/2 transition of Er3+ ions was analyzed. A single crystal of 48 at. %Ce3+:10.4 at. %Yb3+:1.6 at. %Er3+:NaLa(WO4)2 was grown by the Czochralski method. 1.2 W quasicontinuous-wave laser around 1.55 μm was realized when a 2.61 mm thick c-cut slice of the crystal was pumped by a diode laser at 970 nm. The achieved highest slope efficiency was 12.3% and the threshold was 3.8 W.
Investigation on the orderly growth of thick zinc phthalocyanine films on Ag(100) surface
Authors: Dou Weidong , Tang Yongbing , Lee C. S. , Bao S. N. , Lee S. T.
Published: October 2010

The growth of zinc phthalocyanine (ZnPc) on Ag(100) surface from monolayer to multilayer was investigated by low-energy electron diffraction, x-ray diffraction, and high-resolution electron energy loss spectroscopy (HREELS). At monolayer coverage, ZnPc molecules form an ordered film with molecular planes parallel to the substrate. The same structure is maintained as the film thickness increases. HREELS analysis shows that intermolecular π-π interaction dominates during the film growth from monolayer to multilayer. The π-d interaction between the adsorbates and the substrate is only applicable in the first adlayer. Stronger intermolecular-layer interaction is observed at higher coverages.
Investigation of antirelaxation coatings for alkali-metal vapor cells using surface science techniques
Authors: Seltzer S. J. , Michalak D. J. , Donaldson M. H. , Balabas M. V. , Barber S. K. , Bernasek S. L. , Bouchiat M.-A. , Hexemer A. , Hibberd A. M. , Kimball D. F. Jackson , Jaye C. , Karaulanov T. , Narducci F. A. , Rangwala S. A. , Robinson H. G. , Shmakov A. K. , Voronov D. L. , Yashchuk V. V. , Pines A. , Budker D.
Published: October 2010

Many technologies based on cells containing alkali-metal atomic vapor benefit from the use of antirelaxation surface coatings in order to preserve atomic spin polarization. In particular, paraffin has been used for this purpose for several decades and has been demonstrated to allow an atom to experience up to 10 000 collisions with the walls of its container without depolarizing, but the details of its operation remain poorly understood. We apply modern surface and bulk techniques to the study of paraffin coatings in order to characterize the properties that enable the effective preservation of alkali spin polarization. These methods include Fourier transform infrared spectroscopy, differential scanning calorimetry, atomic force microscopy, near-edge x-ray absorption fine structure spectroscopy, and x-ray photoelectron spectroscopy. We also compare the light-induced atomic desorption yields of several different paraffin materials. Experimental results include the determination that crystallinity of the coating material is unnecessary, and the detection of CC double bonds present within a particular class of effective paraffin coatings. Further study should lead to the development of more robust paraffin antirelaxation coatings, as well as the design and synthesis of new classes of coating materials.
Rotational and spin viscosities of water: Application to nanofluidics
Authors: Hansen J. S. , Bruus Henrik , Todd B. D. , Daivis Peter J.
Published: October 2010

In this paper we evaluate the rotational viscosity and the two spin viscosities for liquid water using equilibrium molecular dynamics. Water is modeled via the flexible SPC/Fw model where the Coulomb interactions are calculated via the Wolf method which enables the long simulation times required. We find that the rotational viscosity is independent of the temperature in the range from 284 to 319 K. The two spin viscosities, on the other hand, decrease with increasing temperature and are found to be two orders of magnitude larger than that estimated by Bonthuis et al. [Phys. Rev. Lett. 103, 144503 (2009)] We apply the results from molecular dynamics simulations to the extended Navier–Stokes equations that include the coupling between intrinsic angular momentum and linear momentum. For a flow driven by an external field the coupling will reduce the flow rate significantly for nanoscale geometries. The coupling also enables conversion of rotational electrical energy into fluid linear momentum and we find that in order to obtain measurable flow rates the electrical field strength must be in the order of 0.1 MV m−1 and rotate with a frequency of more than 100 MHz.
Quantum dynamics of dissociative chemisorption of CH4 on Ni(111): Influence of the bending vibration
Authors: Krishnamohan G. P. , Olsen R. A. , Kroes G.-J. , Gatti F. , Woittequand S.
Published: October 2010

Two-dimensional, three-dimensional, and four-dimensional quantum dynamic calculations are performed on the dissociative chemisorption of CH4 on Ni(111) using the multiconfiguration time-dependent Hartree (MCTDH) method. The potential energy surface used for these calculations is 15-dimensional (15D) and was obtained with density functional theory for points which are concentrated in the region that is dynamically relevant to reaction. Many reduced dimensionality calculations were already performed on this system, but the molecule was generally treated as pseudodiatomic. The main improvement of our model is that we try to describe CH4 as a polyatomic molecule by including a degree of freedom describing a bending vibration in our three-dimensional and four-dimensional models. Using a polyspherical coordinate system, a general expression for the 15D kinetic energy operator is derived, which discards all the singularities in the operator and includes rotational and Coriolis coupling. We use seven rigid constraints to fix the CH3 umbrella of the molecule to its gas phase equilibrium geometry and to derive two-dimensional, three-dimensional, and four-dimensional Hamiltonians, which were used in the MCTDH method. Only four degrees of freedom evolve strongly along the 15D minimum energy path: the distance of the center of mass of the molecule to the surface, the dissociative CH bond distance, the polar orientation of the molecule, and the bending angle between the dissociative CH bond and the umbrella. A selection of these coordinates is included in each of our models. The polar rotation is found to be important in determining the mode selective behavior of the reaction. Furthermore, our calculations are in good agreement with the finding of Xiang et al. [J. Chem. Phys. 117, 7698 (2002)] in their reduced dimensional calculation that the helicopter motion of the umbrella symmetry axis is less efficient than its cartwheel motion for promoting the reaction. The effect of pre-exciting the bend modes is qualitatively incorrect at higher energies, suggesting the necessity of including additional rotational and vibrational degrees of freedom in the model.
Graphene as a transparent conductive support for studying biological molecules by transmission electron microscopy
Authors: Nair R. R. , Blake P. , Blake J. R. , Zan R. , Anissimova S. , Bangert U. , Golovanov A. P. , Morozov S. V. , Geim A. K. , Novoselov K. S. , Latychevskaia T.
Published: October 2010

We demonstrate the application of graphene as a support for imaging individual biological molecules in transmission electron microscope (TEM). A simple procedure to produce free-standing graphene membranes has been designed. Such membranes are extremely robust and can support practically any submicrometer object. Tobacco mosaic virus has been deposited on graphene samples and observed in a TEM. High contrast has been achieved even though no staining has been applied.
Critical transport of polymeric electrolytes in wavy-rough microtube
Authors: Chu Z. Kwang-Hua
Published: October 2010

We obtain the steady velocities and volume flow rates (up to the second order) of polymeric electrolytes along the cross-section of an (approximated) wavy-rough microtube by using the verified Eyring’s transition rate model and boundary perturbation method. Our numerical results show that the wavy-roughness could tune the electric-field-driven transport especially for larger forcing due to the larger surface-to-volume ratio and slip-velocity effect. We also found a rather low electrical resistance for certain critical temperature after careful selection of geometric and material parameters.
Defect-free Ge-on-insulator with (100), (110), and (111) orientations by growth-direction-selected rapid-melting growth
Authors: Toko Kaoru , Tanaka Takanori , Ohta Yasuharu , Sadoh Taizoh , Miyao Masanobu
Published: October 2010

Defect-free Ge-on-insulator (GOI) with various crystal orientations is essential to realize high-speed and multifunctional devices. Seeded rapid-melting growth of GOI is investigated as a function of seed-orientations and growth-directions. From (100)-oriented Si seeds, Ge growth with a (100) orientation propagates for all growth-directions, however, rotational-growth is observed for some directions when Si seeds with (110) and (111) orientations are used. Such rotational-growth can be completely suppressed by selecting the growth-directions deviating from ⟨111⟩ by more than 35°. Transmission-electron-microscopy observation shows no-stacking fault and no-dislocations. Consequently, defect-free GOI with (100), (110), and (111) orientation is achieved, which demonstrates high-hole mobility (∼1100 cm2/V s).
Direct laser writing of amorphous silicon on Si-substrate induced by high repetition femtosecond pulses
Authors: Kiani Amirkianoosh , Venkatakrishnan Krishnan , Tan Bo
Published: October 2010

This research aimed to study the effects of laser parameters on direct silicon amorphorization. It was found that higher repetition rate of laser pulses gives smooth morphology with better repeatability. Increasing pulse duration and number of pulses were seen to increase the line width. However, increasing the number of pulses does not result in ablation of the target area. An analytical model is developed for the calculation of the average surface temperature after n-pulses; it was found that for a constant power and a constant repetition rate, an increase in the pulse number does not correspond to a significant increase in the surface temperature. Moreover, at the controlled laser power level, the surface temperature will not exceed the melting point of silicon. Therefore, thermal induced damage is not observed during the amorphization.
Silver Schottky contacts to a-plane bulk ZnO
Authors: Kim Hogyoung , Kim Haeri , Kim Dong-Wook
Published: October 2010

The temperature dependent electrical properties of Ag Schottky contacts to a-plane bulk ZnO single crystal were investigated in the temperature range of 100–300 K. The variation in the barrier heights was described by a double Gaussian distribution with two different regions in the temperature range of 200–300 and 100–180 K. The modified Richardson plot in the temperature range of 200–300 K produced the Richardson constant of 29 A cm−2 K−2 which is similar to the theoretical value of 32 A cm−2 K−2 for n-type ZnO, indicating that the inhomogeneous barrier height with the thermionic emission model can explain the current transport well in this region. Below 200 K, the bulk carriers start to freeze out and the induced oxygen vacancies in the interface region, probably due to the formation of silver oxide at the Ag–ZnO interface, will influence significantly the current transport by creating very thin interfacial layer that is susceptible to electron tunneling.
Effect of periodicity on optical forces between a one-dimensional periodic photonic crystal waveguide and an underlying substrate
Authors: Ma Jing , Povinelli Michelle L.
Published: October 2010

We numerically investigate the attractive optical force between a suspended one-dimensional periodic photonic crystal waveguide and underlying substrate in a silicon-on-insulator platform. We show that the optical force is enhanced by designing the waveguide cross section to make the mode approach the band edge or substrate light line. We show that for periodic waveguides, the optical force is nonmonotonic with waveguide-substrate separation. This effect may enable the design of compact, integrated optical power limiters.
Phase stability and decomposition products of Ti–Al–Ta–N thin films
Authors: Rachbauer R. , Holec D. , Mayrhofer P. H.
Published: October 2010

Ab initio calculations of quaternary alloys were used to predict the phase stability of (Ti1−xAlx)1−yTayN. Experimental observation of a dual phase structure containing wurtzite AlN and cubic Ti1−yTayN after thermal decomposition of sputter deposited thin films by vacuum annealing to 1400 °C is in excellent agreement with the calculated phase stabilities of the investigated compositions. We found positive mixing enthalpies for Ti1−xAlxN and Al1−yTayN, with maximum values of 0.25 eV/atom and 0.30 eV/atom, respectively, but negative values for Ti1−yTayN over the whole composition range. The difference in lattice parameters obtained from experiments and ab initio calculations is within ∼1%.
Gas flow dependence of ground state atomic oxygen in plasma needle discharge at atmospheric pressure
Authors: Sakiyama Yukinori , Knake Nikolas , Schröder Daniel , Winter Jörg , Schulz-von der Gathen Volker , Graves David B.
Published: October 2010

We present clear evidence that ground state atomic oxygen shows two patterns near a surface in the helium plasma needle discharge. Two-photon absorption laser-induced fluorescence spectroscopy, combined with gas flow simulation, was employed to obtain spatially-resolved ground state atomic oxygen densities. When the feed gas flow rate is low, the radial density peaks along the axis of the needle. At high flow rate, a ring-shaped density distribution appears. The peak density is on the order of 1021 m−3 in both cases. The results are consistent with a previous report of the flow-dependent bacterial killing pattern observed under similar conditions.
Radon–Nikodým type theorem for α-completely positive maps
Authors: Heo Jaeseong , Ji Un Cig
Published: October 2010

We introduce a new notion of α-completely positive map on a C∗-algebra as a generalization of the notion of completely positive map. Then we study a theorem of the Radon–Nikodým type that there is a one-to-one correspondence between α-completely positive maps and positive operators and, as an application of the Radon–Nikodým type theorem, we give a characterization of pure α-completely positive maps. Finally, we study a covariant version of the Stinespring’s theorem for a covariant α-completely positive map (see Theorem 4.3).
On the low energy behavior of Regge poles
Authors: Hiscox A. , Brown B. M. , Marletta M.
Published: October 2010

We investigate the behavior of Regge poles in the low energy limit. With the use of small argument asymptotics of the spherical Hankel functions, we show that for a finite square well potential, the associated Regge poles tend to the spectral points of the limiting self-adjoint problem. This is generalized to a compactly supported potential by applying a resolvent argument to the difference of the nonzero and zero energy wavefunctions. Furthermore, by an integral equation method we prove analogous results for a potential such that |(1+r)U(r)| is integrable. This confirms the experimental results which show that Regge poles formed during low energy electron elastic scattering become stable bound states.
Solutions of certain fractional kinetic equations and a fractional diffusion equation
Authors: Saxena R. K. , Mathai A. M. , Haubold H. J.
Published: October 2010

In view of the usefulness and importance of kinetic equations in certain physical problems, the authors derive an explicit solution of a fractional kinetic equation of general character that unifies and extends earlier results. Further, an alternative shorter method based on a result developed by the authors is given to derive the solution of a fractional diffusion equation. Solutions are represented in terms of H-functions and generalized Mittag–Leffler functions.
Stochastic flocking dynamics of the Cucker–Smale model with multiplicative white noises
Authors: Ahn Shin Mi , Ha Seung-Yeal
Published: October 2010

We present a strong asymptotic stochastic flocking estimate for the stochastically perturbed Cucker–Smale model. We characterize a form of multiplicative white noises and present sufficient conditions on the control parameters to guarantee the almost sure exponential convergence toward constant equilibrium states. When the strength of multiplicative noises is sufficiently large, we show that the strong stochastic flocking occurs even for negative communication weights.
Generalized MICZ-Kepler system, duality, polynomial, and deformed oscillator algebras
Authors: Marquette Ian
Published: October 2010

We present the quadratic algebra of the generalized MICZ-Kepler system in three-dimensional Euclidean space E3 and its dual, the four-dimensional singular oscillator, in four-dimensional Euclidean space E4. We present their realization in terms of a deformed oscillator algebra using the Daskaloyannis construction. The structure constants are, in these cases, functions not only of the Hamiltonian but also of other integrals commuting with all generators of the quadratic algebra. We also present a new algebraic derivation of the energy spectrum of the MICZ-Kepler system on the three sphere S3 using a quadratic algebra. These results point out also that results and explicit formula for structure functions obtained for quadratic, cubic, and higher order polynomial algebras in the context of two-dimensional superintegrable systems may be applied to superintegrable systems in higher dimensions with and without monopoles.
An analytical formulation for the modified Paschen’s curve
Authors: Tirumala Rakshit , Go David B.
Published: October 2010

The modified Paschen’s curve describes the gaseous breakdown potential (voltage) in microscale gaps, when deviations from the traditional Paschen’s curve occur [F. Paschen, Ann. Phys. 273, 69 (1889)]. The deviation is due to ion-enhanced field emission that occurs in the high electric field of microgaps and acts as an additional cathode electron source. The present work derives an analytical formulation for the effect of ion-enhanced field emission and the modified Paschen’s curve that uses a consistent, single breakdown criterion. The proposed model does not require the fitting factor required in prior models and constitutes a single analytical equation for microscale breakdown and the modified Paschen’s curve.
X-ray refraction-contrast computed tomography images using dark-field imaging optics
Authors: Sunaguchi Naoki , Yuasa Tetsuya , Huo Qingkai , Ichihara Shu , Ando Masami
Published: October 2010

If an x-ray beam containing internal information derived from sample soft tissue is incident upon a Laue-case analyzer, the beam will subsequently split into a forwardly diffracted beam and a separate diffracted beam. Using these beams acquired simultaneously, a refraction-contrast computed tomography (CT) imaging system for biomedical use with lower radiation dose can be easily realized, and has a high depicting capability on the soft tissues compared with conventional x-ray CT based on absorption contrast principles. In this paper, we propose an imaging system using dark-field imaging for CT measurement based on a tandem system of Bragg- and Laue-case crystals with two two-dimensional detectors, along with a data-processing method to extract information on refraction from the measured entangled intensities by use of rocking curve fitting with polynomial functions. Reconstructed images of soft tissues are presented and described.
High oxidation state at the epitaxial interface of γ-Al2O3 thin films grown on Si(111) and Si(001)
Authors: El Kazzi M. , Merckling C. , Saint-Girons G. , Grenet G. , Silly M. , Sirotti F. , Hollinger G.
Published: October 2010

High resolution synchrotron radiation x-ray photoelectron spectroscopy allowed us to identify the chemical bonding at the interface between epitaxial γ-Al2O3 and Si substrate. The experiments were performed on 1 nm thick epitaxial γ-Al2O3 layers grown on both Si(111) and Si(001) substrates. In both cases, the Si 2p core level decomposition recorded at photon energy of 160 eV provided evidence for the absence of Si2+ and Si3+ species and the presence of two different Si4+ species. A microscopic model is proposed for the interface obtained with two incomplete SiO2 planes based on the Si 2p3/2 line shape.
Transport through a mixed-valence molecular transistor in the sequential-tunneling regime: Theoretical insight from the two-site Peierls–Hubbard model
Authors: Hsu Liang-Yan , Tsai Te-Wei , Jin Bih-Yaw
Published: October 2010

Transport through a mixed-valence system in the sequential-tunneling region is investigated using the master equation method and a simple two-site Peierls–Hubbard model that includes electron-phonon (e-p) coupling, electron hopping, and electron-electron (e-e) repulsion. The characteristics of Coulomb diamonds in the conductance spectra under three regimes are discussed. In the regime of zero e-p coupling, we found that the widths of Coulomb diamonds are dominated by the competition of electron-hopping and Coulomb repulsion. In the regime of weak and intermediate e-p coupling, by virtue of the normal-mode transformation we found that coupling to the symmetric-mode decreases the widths of Coulomb diamonds. In the regime of strong e-p coupling, an analytical expression for the widths of Coulomb diamonds can be derived using the small polaron transformation. The derived formula provides a new way to estimate e-e interactions and e-p couplings experimentally.
Light-configured mesogenic azopolymer stabilized liquid crystals
Authors: Thibault-Maheu Olivier , Galstian Tigran , Bessette André , Zhao Yue
Published: October 2010

Triple-functionality guest is introduced into nematic liquid crystal host. Resonant interaction of light with the azobenzene segment of the guest and the mesogeneity of the latter are used to generate reorientation of host molecules. The reactive character of the guest is then used to permanently fix the obtained molecular orientation of the whole guest-host system. Electro-optic study of obtained material is provided to quantify the parameters of the obtained orientational configuration.
Anomalous phase behavior in a model fluid with only one type of local structure
Authors: Prestipino Santi , Saija Franz , Malescio Gianpietro
Published: October 2010

We present evidence that the concurrent existence of two populations of particles with different effective diameters is not a prerequisite for the occurrence of anomalous phase behaviors in systems of particles interacting through spherically symmetric unbounded potentials. Our results show that an extremely weak softening of the interparticle repulsion, which yields a single nearest-neighbor separation, is able to originate a wide spectrum of unconventional features including reentrant melting, solid polymorphism, as well as thermodynamic, dynamic, and structural anomalies. These findings extend the possibility of anomalous phase behavior to a class of systems much broader than currently assumed.
A shear thickening phenomenon in magnetic field controlled-dipolar suspensions
Authors: Tian Yu , Jiang Jile , Meng Yonggang , Wen Shizhu
Published: October 2010

A shear thickening phenomenon in dipolar suspensions of magnetorheological (MR) fluid is reported. The stress of the MR fluid abruptly decreases when the applied magnetic field increases to above a critical value under a small constant shear rate. It abruptly increases when the shear rate is higher than a critical value under a constant magnetic field, accompanied by a change in normal stress during shear thickening or unshear thickening processes. A shear-thickened structure is important for an MR fluid to obtain a high yield stress, which is beyond the prediction of a traditional dipole or multipole interaction model.
Overlapping-gate architecture for silicon Hall bar field-effect transistors in the low electron density regime
Authors: Willems van Beveren L. H. , Tan K. Y. , Lai N. S. , Dzurak A. S. , Hamilton A. R.
Published: October 2010

We report the fabrication and study of Hall bar field-effect transistors in which an overlapping-gate architecture allows four-terminal measurements of low-density two-dimensional electron systems while maintaining a high density at the Ohmic contacts. Comparison with devices made using a standard single gate show that measurements can be performed at much lower densities and higher channel resistances, despite a reduced peak mobility. We also observe a voltage threshold shift which we attribute to negative oxide charge, injected during electron-beam lithography processing.
A theoretical investigation of electric properties of L-arginine phosphate monohydrate including environment polarization effects
Authors: Fonseca T. L. , Sabino J. R. , Castro M. A. , Georg H. C.
Published: October 2010

The dipole moment (μ), linear polarizability (α¯), and first hyperpolarizability (βtot) of the asymmetric unit of L-arginine phosphate (LAP) monohydrate crystal are investigated using the supermolecule approach in combination with an iterative electrostatic polarization scheme. Environment polarization effects are attained by assuring the convergence of the dipole moment of LAP embedded in the polarization field of the surrounding molecules whose atomic sites are treated as point charges. The results obtained show that in the presence of the embedding charges, the value of μ is increased by 9% but the static values of α¯ and βtot are decreased, respectively, by 3% and 13%, as compared with the isolated situation. The MP2/6-311+G(d) model predicts for the in-crystal dipole moment the converged value of 33 D, in good concordance with the available experimental result of 32 D. Our estimates for the converged results of α¯ and βtot are, respectively, 22.51×10−24 and 5.01×10−30 esu. Dispersion effects are found to have a small impact on the nonlinear optical responses of LAP in the visible region. In addition, MP2/6-311G results obtained for βtot by using isolated and embedded LAP dimers show that crystal packing effects have a significant contribution of the electrostatic interactions. Our results suggest that the role of the crystal environment is to minimize the effects of the intermolecular interactions in the electric properties. That is, μ and βtot gain a more additive character in the presence of the field of the embedding charges. This is specially marked for βtot.
Polymer-mediated spatial organization of nanoparticles in dense melts: Transferability and an effective one-component approach
Authors: Chakrabarti Rajarshi , Schweizer Kenneth S.
Published: October 2010

We study two problems in the framework of the integral equation theory of polymer-mediated spatial organization of nanoparticles in dense melts motivated by multiscale simulation and many body physics issues. How nonspherical nanoparticle shape modifies polymer-induced interactions under dilute nanoparticle conditions is investigated over a range of primary particle sizes and interfacial cohesion strengths. Nonuniversal consequences of nonspherical shape are found for the pair-correlation function on local scales and some qualitative differences on larger scales due primarily to intraparticle connectivity constraints. For a large enough nanoparticle site diameter, the potentials of mean force (PMF) for all shapes studied (sphere, rod, disk, compact tetrahedral cluster) exhibit linear scaling with the size ratio of nanoparticle to polymer monomer site diameter and quite good “transferability.” The ability of a simple effective one-component approach, based on the dilute nanoparticle PMF as an effective pair-decomposable potential, to describe interparticle structure at nonzero volume fractions is also studied. Although not generally quantitatively accurate due to neglect of many body correlation effects, especially at high nanoparticle loadings and near contact separations, the simple approach captures rather well many aspects of the real space structure. The errors incurred depend systematically on whether interfacial cohesion strength results in contact aggregation, steric stabilization, or bridging. For the filler collective static structure factor, many body effects are weakest for local cage scale correlations and grow significantly at smaller wavevectors under depletion or bridging conditions.
A Nyquist analysis of glassy dynamics, aging, and discrete basins of attraction in a small system
Authors: Sharma Prerna , Ghosh Shankar , Bhattacharya S.
Published: October 2010

The process of attachment of a deformable polystyrene colloidal particle to a planar substrate shows features of slow relaxation and aging, typically observed in many-body disordered and glassy systems. This slow dynamics is attributed to the presence of polymeric tethers constituting a few internal degrees of freedom. The effects of these few degrees of freedom are revealed by a Nyquist analysis of the data that demonstrate the existence of only a few discernible basins of attraction as the system reaches the ground state and thus provides a minimal model of complexity and glassy dynamics.
Nuclear momentum distribution in solid and liquid HF from ab initio calculation
Authors: Krzystyniak M.
Published: October 2010

A calculation of nuclear momentum distribution of liquid and solid hydrogen fluoride was performed. In both systems, density functional theory generalized gradient approximation functional of Perdew, Burke, and Ernzerhof was used for the calculation: for liquid hydrogen fluoride, using an atom centered basis set for an isolated molecule with optimized geometry, and for solid hydrogen fluoride using plane-wave basis sets on optimized orthorhombic crystal cell. For liquid hydrogen fluoride, a semiclassical approach was adopted with the vibrational contribution to momentum distribution obtained from the density functional theory calculation and translational and rotational contributions calculated classically. Nuclear momentum distribution in the solid hydrogen fluoride was calculated entirely quantum mechanically using phonon dispersion and vibrational density of states calculated in the framework of plane-wave density functional theory. Theoretical results were contrasted with recently obtained results of Compton (deep inelastic) neutron scattering on liquid and solid hydrogen fluoride. In case of liquid hydrogen fluoride, almost a perfect agreement between theory and experiment was achieved within the harmonic Born–Oppenheimer approximation. For the solid system under investigation, the harmonic approximation leads to small (4%) overestimation of the square root of the second moment indicating that neutron Compton scattering technique is sensitive to proton delocalization due to hydrogen bonding in solid hydrogen fluoride.
On the measure of electron correlation and entanglement in quantum chemistry based on the cumulant of the second-order reduced density matrix
Authors: Alcoba D. R. , Bochicchio R. C. , Lain L. , Torre A.
Published: October 2010

In this paper we propose a functional of the many-body cumulant of the second-order reduced density matrix within the spin-free formalism of quantum chemistry which quantifies the idea of electron correlation and allows one to detect spin entanglement. Its properties are rigorously stated and discussed for spin-adapted pure states. Numerical determinations are performed for both equilibrium conformations and dissociation processes in molecular systems.
Extended Additivity Model of Parameter log(L16)
Authors: Havelec Pavel , Ševčík Jiří G. K.
Published: October 2010

An additivity model of the apolar solute-solvent parameter log(L16) was verified using sets of 939 nonaromatic and 1075 aromatic compounds. Unbiased distributions of errors and of the contribution significance level were statistically tested. An analysis of the CH2 group contribution in 34 homologous series indicates that the differences among the homologous series are statistically insignificant and related to interactional contributions rather than to the nature of the CH2 group.
Standard Thermodynamic Functions of Some Isolated Ions at 100–1000 K
Authors: Loewenschuss A. , Marcus Y.
Published: October 2010

The standard thermodynamic functions (Cp°, S°, H° and (G°−H0°)/T) at 100 to 1000 K of 24 polyatomic gaseous ions are reported, based on structural and spectroscopic data from the literature. These ions supplement the 130 ions previously studied and are: zirconyl, hydrotelluride, amide, selenocyanate, tellurocyanate, orthoborate, metaphosphate, arsenite, orthosilicate, tetrachloropalladate(II), tetrabromopalladate(II), tetrachloroplatinate(II), tetrabromoplatinate(II), hexafluorophosphate, hexafluoroarsenate, hexafluoroantimonate, hexabromoplatinate(IV), tetracyanonickelate, tetracyanomercurate, octacyanomolybdate(IV), sulfamate, benzoate, guanidinium, and glycine as cation, zwitterion, and anion.
Early deficits in synaptic mitochondria in an Alzheimer's disease mouse model
Authors: Du Heng , Guo Lan , Yan Shiqiang , Sosunov Alexander A. , McKhann Guy M. , ShiDu Yan Shirley
Published: October 2010

Synaptic dysfunction and the loss of synapses are early pathological features of Alzheimer's disease (AD). Synapses are sites of high energy demand and extensive calcium fluctuations; accordingly, synaptic transmission requires high levels of ATP and constant calcium fluctuation. Thus, synaptic mitochondria are vital for maintenance of synaptic function and transmission through normal mitochondrial energy metabolism, distribution and trafficking, and through synaptic calcium modulation. To date, there has been no extensive analysis of alterations in synaptic mitochondria associated with amyloid pathology in an amyloid β (Aβ)-rich milieu. Here, we identified differences in mitochondrial properties and function of synaptic vs. nonsynaptic mitochondrial populations in the transgenic mouse brain, which overexpresses the human mutant form of amyloid precursor protein and Aβ. Compared with nonsynaptic mitochondria, synaptic mitochondria showed a greater degree of age-dependent accumulation of Aβ and mitochondrial alterations. The synaptic mitochondrial pool of Aβ was detected at an age as young as 4 mo, well before the onset of nonsynaptic mitochondrial and extensive extracellular Aβ accumulation. Aβ-insulted synaptic mitochondria revealed early deficits in mitochondrial function, as shown by increased mitochondrial permeability transition, decline in both respiratory function and activity of cytochrome
c
oxidase, and increased mitochondrial oxidative stress. Furthermore, a low concentration of Aβ (200 nM) significantly interfered with mitochondrial distribution and trafficking in axons. These results demonstrate that synaptic mitochondria, especially Aβ-rich synaptic mitochondria, are more susceptible to Aβ-induced damage, highlighting the central importance of synaptic mitochondrial dysfunction relevant to the development of synaptic degeneration in AD.