bluuebunny/crossref_metadata_2025 huggingface dataset:
A method for computing the solubility limit of solids: Application to sodium chloride in water and alcohols
Authors: Paluch Andrew S. , Jayaraman Saivenkataraman , Shah Jindal K. , Maginn Edward J.
Published: September 2010

We present an adaptable method to compute the solubility limit of solids by molecular simulation, which avoids the difficulty of reference state calculations. In this way, the method is highly adaptable to molecules of complex topology. Results are shown for solubility calculations of sodium chloride in water and light alcohols at atmospheric conditions. The pseudosupercritical path integration method is used to calculate the free energy of the solid and gives results that are in good agreement with previous studies that reference the Einstein crystal. For the solution phase calculations, the self-adaptive Wang–Landau transition-matrix Monte Carlo method is used within the context of an expanded isothermal-isobaric ensemble. The method shows rapid convergence properties and the uncertainty in the calculated chemical potential was 1% or less for all cases. The present study underpredicts the solubility limit of sodium chloride in water, suggesting a shortcoming of the molecular models. Importantly, the proper trend for the chemical potential in various solvents was captured, suggesting that relative solubilities can be computed by the method.
Light output enhancement of GaN-based flip-chip light-emitting diodes fabricated with SiO2/TiO2 distributed Bragg reflector coated on mesa sidewall
Authors: Baik K. H. , Min B. K. , Kim J. Y. , Kim H. K. , Sone C. , Park Y. , Kim H.
Published: September 2010

We report on the enhanced light output of GaN-based flip-chip light-emitting diodes (LEDs) fabricated with SiO2/TiO2 distributed Bragg reflector (DBR) on mesa sidewall. At the wavelength of 400 nm, five pairs of SiO2/TiO2 DBR coats on the GaN layer showed a normal-incidence reflectivity as high as 99.1%, along with an excellent angle-dependent reflectivity. As compared to the reference LED, the LED fabricated with the DBR-coated mesa sidewall showed an increased output power by a factor of 1.32 and 1.12 before and after lamp packaging, respectively. This could be attributed to an efficient reflection of the laterally guided mode at the highly reflective mesa sidewall, enhancing the subsequent extraction of light through the sapphire substrate.
The self limiting effect of hydrogen cluster in gas jet under liquid nitrogen temperature
Authors: Han Jifeng , Yang Chaowen , Miao Jingwei , Fu Pengtao , Luo Xiaobing , Shi Miangong
Published: September 2010

The generation of hydrogen clusters in gas jet is tested using the Rayleigh scattering method under liquid nitrogen temperature of 79 K. The self limiting effect of hydrogen cluster is studied and it is found that the cluster formation is greatly affected by the number of expanded molecules. The well designed liquid nitrogen cold trap ensured that the hydrogen cluster would keep maximum size for maximum 15 ms during one gas jet. The scattered light intensity exhibits a power scaling on the backing pressure ranging from 5 to 48 bar with the power value of 4.1.
Plasmonic inverse rib waveguiding for tight confinement and smooth interface definition
Authors: Benisty H. , Besbes M.
Published: September 2010

A plasmonic inverse rib optical waveguide geometry is proposed and investigated, inspired by the recent CdS-nanorod-on-silver plasmonic laser. The proposed technology is suitable for large scale fabrication. It only uses a single wet resist development and several coatings onto a flat metal surface to define the waveguide geometry. It thus relieves the need to etch or lift-off a noble metal. High-index sol-gel inverse ribs are privileged candidates for the tightest confinement. We investigate and explain the guidance mostly for the case of Au and the wavelengths around λ=633 nm. We get spot sizes down to ∼25×60 nm2. We notably describe how easily the tight confinement is granted and the reasons why only a single critical step defines the modal geometry. We finally detail how the classical building-blocks of integrated optics such as distributed reflectors and couplers can be made within the very same approach and integrated into devices for which losses are described.
Annealing neutron damaged silicon bipolar transistors: Relating gain degradation to specific lattice defects
Authors: Fleming R. M. , Seager C. H. , Lang D. V. , Campbell J. M.
Published: September 2010

Isochronal anneal sequences have been carried out on pnp and npn transistors irradiated with fast neutrons at a variety of fluences. The evolution of base and collector currents was utilized to characterize the annealing behavior of defects in both the emitter-base depletion region and the neutral base. Various annealing biases, theoretical modeling, as well as previous deep level transient spectroscopy (DLTS) data, were used to assign the relative magnitude of each of the important defects to the total recombination current. We find that donor-vacancy pairs in the neutral n-type base of our pnp transistors are responsible for about 1/3 of the postdamage lifetime degradation, while the remaining recombination currents can be largely attributed to a cluster-related divacancylike defect which has no shallow state DLTS emission peak. This latter defect anneals gradually from 350 to 590 K. Generation/recombination currents in the base-emitter junctions in both types of devices were found to anneal in a similar, gradual fashion, suggesting that this same cluster-related intrinsic lattice defect is also responsible for the large, damage-induced base currents.
A classical molecular dynamics investigation of the free energy and structure of short polyproline conformers
Authors: Moradi Mahmoud , Babin Volodymyr , Roland Christopher , Sagui Celeste
Published: September 2010

Folded polyproline peptides can exist as either left-(PPII) or right-handed (PPI) helices, depending on their environment. In this work, we have characterized the conformations and the free energy landscapes of Ace–(Pro)n–Nme, n=2,3,…,9, and 13 peptides both in vacuo and in an implicit solvent environment. In order to enhance the sampling provided by regular molecular dynamics simulations, we have used the recently developed adaptively biased molecular dynamics method—which provides an accurate description of the free energy landscapes in terms of a set of relevant collective variables—combined with Hamiltonian and temperature replica exchange molecular dynamics methods. The collective variables, which are chosen so as to reflect the stable structures and the “slow modes” of the polyproline system, were based primarily on properties of length and of the cis/trans isomerization associated with the prolyl bonds. Results indicate that the space of peptide structures is characterized not just by pure PPII and PPI structures, but rather by a broad distribution of stable minima with similar free energies. These results are in agreement with recent experimental work. In addition, we have used steered molecular dynamics methods in order to quantitatively estimate the free energy difference of PPI and PPII for peptides of the length n=2,…,5 in vacuo and implicit water and qualitatively investigate transition pathways and mechanisms for the PPII to PPI transitions. A zipper-like mechanism, starting from either the center of the peptide or the amidated end, appear to be the most likely mechanisms for the PPII→PPI transition for the longer peptides.
Molecular dynamics studies of ionically conducting glasses and ionic liquids: Wave number dependence of intermediate scattering function
Authors: Habasaki J. , Ngai K. L.
Published: September 2010

Dynamical heterogeneity is a key feature to characterize both acceleration and slowing down of the dynamics in interacting disordered materials. In the present work, the heterogeneous ion dynamics in both ionically conducting glass and in room temperature ionic liquids are characterized by the combination of the concepts of Lévy distribution and multifractality. Molecular dynamics simulation data of both systems are analyzed to obtain the fractional power law of the k-dependence of the dynamics, which implies the Lévy distribution of length scale. The multifractality of the motion and structures makes the system more complex. Both contributions in the dynamics become separable by using g(k,t) derived from the intermediate scattering function, Fs(k,t). When the Lévy index obtained from Fs(k,t) is combined with fractal dimension analysis of random walks and multifractal analysis, all the spatial exponent controlling both fast and slow dynamics are clarified. This analysis is generally applicable to other complex interacting systems and is deemed beneficial for understanding their dynamics.
Nonequilibrium two-fluid plasmas can generate magnetic fields and flows simultaneously
Authors: Saleem Hamid
Published: September 2010

A new analytical solution of the set of highly nonlinear two-fluid equations is presented to explain the mechanism for the generation of “seed” magnetic field and plasma flow by assuming the density n to have a profile like an exponential in xy-plane and temperature profiles of electrons (ions) to be linear in yz-plane. It is shown that the baroclinic vectors ∇Ψ×∇Tj (where Ψ=ln n¯; n¯ is normalized density and Tj denote the temperatures of electrons and ions for j=e,i) can generate not only the magnetic field but the plasma flow as well. It is also pointed out that the electron magnetohydrodynamics model has inconsistencies because it does not take into account the ion dynamics while the magnetic field is produced on slow time scale. The estimate of the magnitude of the magnetic field in a classical laser plasma using this model is in agreement with the experimental observations.
Electrostatic solitary wave and double layer in a plasma with heavy ions and nonthermally distributed electrons
Authors: Choi C.-R. , Min K.-W. , Woo M.-H. , Ryu C.-M.
Published: September 2010

The existence condition for bump and dip type, as well as double layer (DL), solutions of electrostatic solitary waves (ESWs) in a nonthermal electron plasma with heavy ions is investigated by a pseudopotential method. It is found that the nonthermality of electrons determines the existence of the DL solution and that the amplitude of ESWs is enhanced by the density of heavy ions. When the heavy ion density is beyond a certain critical value, ESWs and DLs cannot exist. It is also found that both the lower and upper critical Mach numbers are reduced by the presence of heavy ions.
Universal sum and product rules for random matrices
Authors: Rogers Tim
Published: September 2010

The spectral density of random matrices is studied through a quaternionic generalization of the Green’s function, which precisely describes the mean spectral density of a given matrix under a particular type of random perturbation. Exact and universal expressions are found in the high-dimension limit for the quaternionic Green’s functions of random matrices with independent entries when summed or multiplied with deterministic matrices. From these, the limiting spectral density can be accurately predicted.
Preferential solvation dynamics in liquids: How geodesic pathways through the potential energy landscape reveal mechanistic details about solute relaxation in liquids
Authors: Nguyen Crystal N. , Stratt Richard M.
Published: September 2010

It is not obvious that many-body phenomena as collective as solute energy relaxation in liquid solution should ever have identifiable molecular mechanisms, at least not in the sense of the well-defined sequence of molecular events one often attributes to chemical reactions. What can define such mechanisms, though, are the most efficient relaxation paths that solutions take through their potential energy landscapes. When liquid dynamics is dominated by slow diffusive processes, there are mathematically precise and computationally accessible routes to searching for such paths. We apply this observation to the dynamics of preferential solvation, the relaxation around a newly excited solute by a solvent composed of different components with different solvating abilities. The slow solvation seen experimentally in these mixtures stems from the dual needs to compress the solvent and to do solvent-solvent exchanges near the solute. By studying the geodesic (most efficient) paths for this combined process in a simple atomic liquid mixture, we show that the mechanism for preferential solvation features a reasonably sharp onset for slow diffusion, and that this diffusion involves a sequential, rather than concerted, series of solvent exchanges.
Kinetic Monte Carlo simulation of shape transition of strained quantum dots
Authors: Lam Chi-Hang
Published: September 2010

The pyramid-to-dome transition in GexSi1−x on Si(100) initiated by step formation on pyramidal quantum dots is atomistically simulated using a multistate lattice model in two-dimensions incorporating effective surface reconstructions. Under quasiequilibrium growth conditions associated with low deposition rates, the transition occurs at island size nc following nc∼x−1.69 independent of temperature and deposition rate. The shape transition is found to be an activated process. Results are explained by a theory based on simple forms of facet energies and elastic energies estimated using a shallow island approximation. An asymptotic scaling relation nc1/d∼x−2 for x→0 applicable to d=2 or 3 dimensions is derived. The shape transition energy barrier can be dominated by the interface energy between steep and shallow facets.
Imaging mesoscopic nuclear spin noise with a diamond magnetometer
Authors: Meriles Carlos A. , Jiang Liang , Goldstein Garry , Hodges Jonathan S. , Maze Jeronimo , Lukin Mikhail D. , Cappellaro Paola
Published: September 2010

Magnetic resonance imaging can characterize and discriminate among tissues using their diverse physical and biochemical properties. Unfortunately, submicrometer screening of biological specimens is presently not possible, mainly due to lack of detection sensitivity. Here we analyze the use of a nitrogen-vacancy center in diamond as a magnetic sensor for nanoscale nuclear spin imaging and spectroscopy. We examine the ability of such a sensor to probe the fluctuations of the “classical” dipolar field due to a large number of neighboring nuclear spins in a densely protonated sample. We identify detection protocols that appropriately take into account the quantum character of the sensor and find a signal-to-noise ratio compatible with realistic experimental parameters. Through various example calculations we illustrate different kinds of image contrast. In particular, we show how to exploit the comparatively long nuclear spin correlation times to reconstruct a local, high-resolution sample spectrum.
Reconstruction in quantum field theory with a fundamental length
Authors: Soloviev M. A.
Published: September 2010

In this paper, we establish an analog of Wightman’s reconstruction theorem for nonlocal quantum field theory with a fundamental length. In our setting, the Wightman generalized functions are defined on test functions analytic in a complex ℓ-neighborhood of the real space and are localizable at scales large compared to ℓ. The causality condition is formulated as continuity of the field commutator in an appropriate topology associated with the light cone. We prove that the relevant function spaces are nuclear and derive the kernel theorems for the corresponding classes of multilinear functionals, which provides the basis for the reconstruction procedure. Special attention is given to the accurate determination of the domain of the reconstructed quantum fields in the Hilbert space of states. We show that the primitive common invariant domain must be suitably extended to implement the (quasi)localizability and causality conditions.
Synthesis, growth, and characterization of Nd-doped SrGdGa3O7 crystal
Authors: Zhang Y. Y. , Zhang H. J. , Yu H. H. , Wang J. Y. , Gao W. L. , Xu M. , Sun S. Q. , Jiang M. H. , Boughton R. I.
Published: September 2010

A disordered Nd:SrGdGa3O7 (Nd:SGGM) laser crystal was grown by the Czochralski method. The space group and effective segregation coefficient of Nd3+ were determined to be P4¯21m and 1.36, respectively. Thermal properties, including the average linear thermal expansion coefficient, thermal diffusivity, specific heat, and thermal conductivity were measured. It was found that the thermal conductivity increases with increasing temperature, indicating glasslike behavior. Sellmeier’s equations were fitted by measuring the refractive indices in the range of 253–2325 nm. The polarization absorption and emission spectra were measured at room temperature, and Judd–Ofelt analysis was carried out to calculate the fluorescence branching ratios from the upper F43/2 state and the fluorescence lifetime. The stimulated emission cross section for the F43/2→I411/2 transition was calculated to be 2.00×10−20 cm2. Finally, a diode-pumped laser experiment at 1.06 μm is described. Thermal, optical, and laser properties have shown that Nd:SGGM crystals are promising for use as disordered laser materials.
The effect of annealing on the junction profile of CoFeB/MgO tunnel junctions
Authors: He Hui , Zhernenkov Kirill , Vadalá Miriana , Akdogan Numan , Gorkov Dmitry , Abrudan Radu M. , Toperverg Boris P. , Zabel Hartmut , Kubota Hitoshi , Yuasa Shinji
Published: September 2010

The tunnelling magnetoresistance of CoFeB/MgO tunnel junctions is exceptionally high, although the electrodes and the barrier are grown at room temperature in the amorphous state. For their functionality annealing steps up to high temperatures are required. We have analyzed in detail the changes in the chemical and magnetization profile upon annealing up to 360°. The multilayers used for this study are similar to those which are used in magnetic tunnel junctions, however with five repeats. In particular, we have used hard non-resonant and soft resonant magnetic x-ray scattering in order to unravel any changes upon annealing. The multilayers exhibit superior structural quality, which hardly changes with annealing. Surprisingly, only little recrystallization of the CoFeB and the MgO layers can be discerned by x-ray diffraction.
Guided-mode resonance excitation on multimode planar periodic waveguide
Authors: Sun Tianyu , Wu Dongmin
Published: September 2010

Planar periodic waveguides are applied to design numerous passive guided-mode resonance (GMR) elements. Key to achieving these devices with desired spectral properties is placement and manipulation of the resonance peaks. It has been shown that, the resonance locations closely track the dispersion curves of the leaky modes. In this paper, taking Bragg reflection due to periodicity and coupling between different modes into account, we investigate the dispersion relations of leaky modes in multimode planar periodic waveguides, both for s-polarized (TE mode) and p-polarized (TM mode) incident waves. Exploiting the characteristics of leaky mode dispersions in full range of the first Brillouin zone, we offer the ways to construct some novel optical elements, for example, polarization independent and angular tolerant GMR filters.
Investigation of Fe–Si–N films as magnetic overcoat for high density recording disk drives
Authors: Gauvin M. , Fullerton E. E. , Talke F. E.
Published: September 2010

A 50-nm-thick Fe–Si–N films were deposited via reactive magnetron cosputtering of independent Fe and Si targets, in Ar/N2 gas mixture, under different dc Fe target power conditions. Magnetic properties, mechanical hardness and tribological properties were characterized as a function of the Fe target power by magnetometry, nanoindentation, and nanoscratch testing, respectively. Deposited samples were found to be ferromagnetic with a coercivity of approximately 20 Oe and a saturation magnetization increasing from 200 to 1100 emu/cm3 as a function of Fe sputter power, i.e., values typical of soft magnetic materials. The mechanical hardness was found to be between 50% and 70% of the hardness of a pure SiNx film. Nanotribological properties of films deposited with a Fe target power ≥80 W degraded rapidly.
Influence of neodymium concentration on excitation and emission properties of Nd doped gallium oxide nanocrystalline films
Authors: Podhorodecki A. , Banski M. , Misiewicz J. , Lecerf C. , Marie P. , Cardin J. , Portier X.
Published: September 2010

Gallium oxide and more particularly β-Ga2O3 matrix is an excellent material for new generation of devices electrically or optically driven as it is known as the widest band gap transparent conductive oxide. In this paper, the optical properties of neodymium doped gallium oxide films grown by magnetron sputtering have been analyzed. The influence of the Nd ions concentration on the excitation/emission mechanisms of Nd ions and the role of gallium oxide matrix have been investigated. The grain size reduction into gallium oxide films have been observed when concentration of Nd increases. It has been found for all samples that the charge transfer is the main excitation mechanism for Nd ions where defect states play an important role as intermediate states. As a consequence Nd emission efficiency increases with temperature giving rise to most intensive emission at 1087 nm at room temperature.
Detecting excess ionizing radiation by electromagnetic breakdown of air
Authors: Granatstein Victor L. , Nusinovich Gregory S.
Published: September 2010

A scheme is proposed for detecting a concealed source of ionizing radiation by observing the occurrence of breakdown in atmospheric air by an electromagnetic wave whose electric field surpasses the breakdown field in a limited volume. The volume is chosen to be smaller than the reciprocal of the naturally occurring concentration of free electrons. The pulse duration of the electromagnetic wave must exceed the avalanche breakdown time (10–200 ns) and could profitably be as long as the statistical lag time in ambient air (typically, microseconds). Candidate pulsed electromagnetic sources over a wavelength range, 3 mm>λ>10.6 μm, are evaluated. Suitable candidate sources are found to be a 670 GHz gyrotron oscillator with 200 kW, 10 μs output pulses and a Transversely Excited Atmospheric-Pressure (TEA) CO2 laser with 30 MW, 100 ns output pulses. A system based on 670 GHz gyrotron would have superior sensitivity. A system based on the TEA CO2 laser could have a longer range >100 m.
Intrinsic noise and division cycle effects on an abstract biological oscillator
Authors: Stamatakis Michail , Mantzaris Nikos V.
Published: September 2010

Oscillatory dynamics are common in biological pathways, emerging from the coupling of positive and negative feedback loops. Due to the small numbers of molecules typically contained in cellular volumes, stochastic effects may play an important role in system behavior. Thus, for moderate noise strengths, stochasticity has been shown to enhance signal-to-noise ratios or even induce oscillations in a class of phenomena referred to as “stochastic resonance” and “coherence resonance,” respectively. Furthermore, the biological oscillators are subject to influences from the division cycle of the cell. In this paper we consider a biologically relevant oscillator and investigate the effect of intrinsic noise as well as division cycle which encompasses the processes of growth, DNA duplication, and cell division. We first construct a minimal reaction network which can oscillate in the presence of large or negligible timescale separation. We then derive corresponding deterministic and stochastic models and compare their dynamical behaviors with respect to (i) the extent of the parameter space where each model can exhibit oscillatory behavior and (ii) the oscillation characteristics, namely, the amplitude and the period. We further incorporate division cycle effects on both models and investigate the effect of growth rate on system behavior. Our results show that in the presence but not in the absence of large timescale separation, coherence resonance effects result in extending the oscillatory region and lowering the period for the stochastic model. When the division cycle is taken into account, the oscillatory region of the deterministic model is shown to extend or shrink for moderate or high growth rates, respectively. Further, under the influence of the division cycle, the stochastic model can oscillate for parameter sets for which the deterministic model does not. The division cycle is also found to be able to resonate with the oscillator, thereby enhancing oscillation robustness. The results of this study can give valuable insight into the complex interplay between oscillatory intracellular dynamics and various noise sources, stemming from gene expression, cell growth, and division.
High resolution electronic spectroscopy of 9-fluorenemethanol in the gas phase: New insights into the properties of Π-hydrogen bonds
Authors: Miller Diane M. , Young Justin W. , Morgan Philip J. , Pratt David W.
Published: September 2010

Rotationally resolved S1←S0 fluorescence excitation spectra of 9-fluorenemethanol (9FM) and deuterated 9-fluorenemethanol (9FMD) have been observed and assigned. Two conformers were detected; sym-9FM and unsym-9FM. The sym conformer has the –OH group symmetrically placed above the fluorene short axis, with its hydrogen atom pointing towards the top of an aromatic ring, whereas the unsym conformer has the –OH group tilted away from this axis, with its hydrogen atom pointing towards the side of an aromatic ring. Only the sym conformer shows a tunneling splitting associated with the torsional motion of the –OH group; the unsym conformer is “rigid.” Additionally, a third subband was observed in the spectrum of sym-9FMD, evidencing secondary minima on the potential energy surfaces of the ground and excited electronic states. Studies of these surfaces along the –OH torsional coordinate provide new insights into the properties of π-hydrogen bonds.
The barrier method: A technique for calculating very long transition times
Authors: Adams D. A. , Sander L. M. , Ziff R. M.
Published: September 2010

In many dynamical systems, there is a large separation of time scales between typical events and “rare” events which can be the cases of interest. Rare-event rates are quite difficult to compute numerically, but they are of considerable practical importance in many fields, for example, transition times in chemical physics and extinction times in epidemiology can be very long, but are quite important. We present a very fast numerical technique that can be used to find long transition times (very small rates) in low-dimensional systems, even if they lack detailed balance. We illustrate the method for a bistable nonequilibrium system introduced by Maier and Stein and a two-dimensional (in parameter space) epidemiology model.
Exact on-event expressions for discrete potential systems
Authors: Bannerman Marcus N. , Lue Leo
Published: September 2010

The properties of systems composed of atoms interacting though discrete potentials are dictated by a series of events which occur between pairs of atoms. There are only four basic event types for pairwise discrete potentials and the square-well/shoulder systems studied here exhibit them all. Closed analytical expressions are derived for the on-event kinetic energy distribution functions for an atom, which are distinct from the Maxwell–Boltzmann distribution function. Exact expressions are derived that directly relate the pressure and temperature of equilibrium discrete potential systems to the rates of each type of event. The pressure can be determined from knowledge of only the rate of core and bounce events. The temperature is given by the ratio of the number of bounce events to the number of disassociation/association events. All these expressions are validated with event-driven molecular dynamics simulations and agree with the data within the statistical precision of the simulations.
Free volume in imidazolium triflimide ([C3MIM][NTf2]) ionic liquid from positron lifetime: Amorphous, crystalline, and liquid states
Authors: Dlubek G. , Yu Yang , Krause-Rehberg R. , Beichel W. , Bulut S. , Pogodina N. , Krossing I. , Friedrich Ch.
Published: September 2010

Positron annihilation lifetime spectroscopy (PALS) is used to study the ionic liquid 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide [C3MIM][NTf2] in the temperature range between 150 and 320 K. The positron decay spectra are analyzed using the routine LifeTime-9.0 and the size distribution of local free volumes (subnanometer-size holes) is calculated. This distribution is in good agreement with Fürth’s classical hole theory of liquids when taking into account Fürth’s hole coalescence hypothesis. During cooling, the liquid sample remains in a supercooled, amorphous state and shows the glass transition in the ortho-positronium (o-Ps) lifetime at 187 K. The mean hole volume varies between 70 Å3 at 150 K and 250 Å3 at 265–300 K. From a comparison with the macroscopic volume, the hole density is estimated to be constant at 0.20×1021 g−1 corresponding to 0.30 nm−3 at 265 K. The hole free volume fraction varies from 0.023 at 185 K to 0.073 at Tm+12 K=265 K and can be estimated to be 0.17 at 430 K. It is shown that the viscosity follows perfectly the Cohen–Turnbull free volume theory when using the free volume determined here. The heating run clearly shows crystallization at 200 K by an abrupt decrease in the mean ⟨τ3⟩ and standard deviation σ3 of the o-Ps lifetime distribution and an increase in the o-Ps intensity I3. The parameters of the second lifetime component ⟨τ2⟩ and σ2 behave parallel to the o-Ps parameters, which also shows the positron’s (e+) response to structural changes. During melting at 253 K, all lifetime parameters recover to the initial values of the liquid. An abrupt decrease in I3 is attributed to the solvation of e− and e+ particles. Different possible interpretations of the o-Ps lifetime in the crystalline state are briefly discussed.
The effect of Co on room temperature positive magnetoresistance in the CoxC1−x/Si system
Authors: Zhang Xin , Zhang Xiaozhong , Wan Caihua
Published: September 2010

Co x  C 1 − x granular films and pure carbon films were deposited on n-type Si substrates using the pulsed laser deposition method. Three types of samples were obtained: pure C/Si, CoxC1−x granular film/Si with Co dispersed in the C film, and CoxC1−x/Si with Co segregated at the interface. After comparing the physical properties and structures of these three types of samples, we found that the segregation of Co at the interface not only increased the maximum value of magnetoresistance but also improved the magnetoresistance sensitivity in the CoxC1−x/Si system.
Hydrogen storage in Li and Ti decorated borazine: A first-principles study
Authors: Li Meng , Li Jinming , Sun Qiang , Jia Yu
Published: September 2010

The capacity of hydrogen storage in alkali metal (Li, Na, or K), alkaline-earth metal (Be, Mg, or Ca), or Ti decorated borazine has been investigated by using the first-principles calculations based on density functional theory. Our results indicated that alkali metals could bind strongly to the inorganic molecule borazine and, especially, Li decorated borazine exhibits the highest hydrogen storage capacity up to 10.4 wt % theoretically. The adsorption energies of hydrogen molecules are in the range of −0.10∼−0.15 eV/H2 (−0.23∼−0.28 eV/H2 for local density approximation calculation) which are acceptable for reversible H2 adsorption/desorption near ambient temperature. We also found that the hydrogen storage capacity of Ti decorated borazine is about 7.2 wt %, less than that of the Li decorated system, but the adsorption energies are in the range of −0.16∼−0.24 eV/H2 due to the Kubas interaction, which is larger than that of the Li decorated borazine and the system is also suitable for reversible H2 adsorption/desorption near ambient temperature.
Transport properties of electrons in fractal magnetic-barrier structures
Authors: Sun Lifeng , Fang Chao , Guo Yong
Published: September 2010

Quantum transport properties in fractal magnetically modulated structures are studied by the transfer-matrix method. It is found that the transmission spectra depend sensitively not only on the incident energy and the direction of the wave vector but also on the stage of the fractal structures. Resonance splitting, enhancement, and position shift of the resonance peaks under different magnetic modulation are observed at four different fractal stages, and the relationship between the conductance in the fractal structure and magnetic modulation is also revealed. The results indicate the spectra of the transmission can be considered as fingerprints for the fractal structures, which show the subtle correspondence between magnetic structures and transport behaviors.
Observation of partially incoherent ⟨110⟩ boundaries between polar nanodomains in Na1/2Bi1/2TiO3 single crystals
Authors: Yao Jianjun , Ge Wenwei , Yang Yaodong , Luo Liang , Li Jiefang , Viehland D. , Bhattacharyya Somnath , Zhang Qinhui , Luo Haosu
Published: September 2010

The ferroelectric domain structure of Na1/2Bi1/2TiO3 single crystals was investigated by transmission electron microscopy (TEM) and piezoforce microscopy (PFM). Bright-field TEM and PFM images revealed the presence of polar nanodomains, whose boundaries had a tendency to align along the ⟨110⟩. High resolution TEM images revealed planar defects along these ⟨110⟩ boundaries, which partially relaxed the coherency of the lattice.
Temperature dependence of electroabsorption dynamics in an InAs quantum-dot saturable absorber at 1.3 μm and its impact on mode-locked quantum-dot lasers
Authors: Cataluna M. A. , Malins D. B. , Gomez-Iglesias A. , Sibbett W. , Miller A. , Rafailov E. U.
Published: September 2010

We report temperature-dependent absorption recovery times in an InAs p-i-n ridge waveguide quantum-dot modulator under low reverse bias, investigated via subpicosecond pump-probe measurements. The measured decrease in absorption recovery time with increasing temperature (293–319 K) is in excellent agreement with a thermionic emission model. A similar trend in pulse duration with increasing temperature is also observed from a two-section mode-locked quantum-dot laser fabricated from a similar epitaxial structure. These measurements confirm the key role of the absorber recovery time in the reduction in the pulses generated by two-section mode-locked quantum-dot lasers, both at room and elevated temperatures.
Reduction in surface recombination and enhancement of light emission in silicon photonic crystals treated by high-pressure water-vapor annealing
Authors: Fujita Masayuki , Gelloz Bernard , Koshida Nobuyoshi , Noda Susumu
Published: September 2010

We propose and demonstrate the application of high-pressure water-vapor annealing (HWA) to silicon photonic crystals for surface passivation. We find that the photoluminescence intensity from a sample treated with HWA is enhanced by a factor of ∼6. We confirm that this enhancement originates from a reduction in the surface-recombination velocity (SRV) by a factor of ∼0.4. The estimated SRV is as low as 2.1×103 cm/s at room temperature. These results indicate that HWA is a promising approach for efficient surface passivation in silicon photonic nanostructures.
Spectral variations in background light emission of surface-enhanced resonance hyper Raman scattering coupled with plasma resonance of individual silver nanoaggregates
Authors: Itoh Tamitake , Yoshikawa Hiroyuki , Yoshida Ken-ichi , Biju Vasudevanpillai , Ishikawa Mitsuru
Published: September 2010

We demonstrate the origin of spectral variations in background light emission of surface enhanced resonance hyper Raman scattering (SERHRS) from single Ag nanoaggregates. Ag nanoaggregate-by-nanoaggregate variations in background light emission spectra are related to plasma (plasmon) resonance spectra. Temporal variations in background light emission spectra with temporal blueshifts in plasma resonance spectra are also observed under continuous laser excitation. Both types of the variations in background light emission are reproduced by multiplying background light emission spectra measured from a Ag microaggregate by Lorentz function spectra derived from plasma resonance spectra. The reproduction reveals that second electromagnetic (EM) enhancement by plasma resonance is the origin of the variations. Additionally, spectral variations in background light emission of SERHRS are similar to that of surface enhanced resonance Raman scattering (SERRS). The similarity indicates that both types of background light emission commonly obtain second EM enhancement from identical plasma resonance.
Stability, geometry, and electronic structure of an alternative I-III-VI2 material, CuScS2: A hybrid density functional theory analysis
Authors: Scanlon David O. , Watson Graeme W.
Published: September 2010

Cu based I-III-VI2 materials have received much attention due to their utility in solar cell applications. The vast majority these studies have focused on materials with group IIIA cations as the trivalent metal. In this study we utilize the screened hybrid exchange functional, HSE06, to investigate the stability of CuScS2 in the crystal structures of all the other I-III-VI2 materials, and find that it preferentially forms in its own unique structure. We analyze the electronic structure and optical properties of CuScS2 and in light of this discuss its semiconducting ability.
Continuous-time random walk as a guide to fractional Schrödinger equation
Authors: Lenzi E. K. , Ribeiro H. V. , Mukai H. , Mendes R. S.
Published: September 2010

We argue that the continuous-time random walk approach may be a useful guide to extend the Schrödinger equation in order to incorporate nonlocal effects, avoiding the inconsistencies raised by Jeng et al. [J. Math. Phys. 51, 062102 (2010)]. As an application, we work out a free particle in a half space, obtaining the time dependent solution by considering an arbitrary initial condition.
The effect of flap parameters on fluid rectification in a microfluidic diode
Authors: Singh Kunwar Pal , Kumar Manoj
Published: September 2010

We have studied the effect of flap parameters on fluid rectification in a microfluidic diode. We use Navier–Stokes equations and arbitrary Lagrangian–Eulerian formulation to obtain dynamics of fluid flow and motion of the flap. The flap opens during forward flow and seals against a stopper during reverse flow. This allows flow in the forward direction and prevents it in the reverse direction. The rectifier is fluidic analog to a semiconductor diode in function because it rectifies fluid flow. Velocity-pressure (V-P) curves analog to the current-voltage (I-V) curves of the electronic diode has been obtained. The effect of the flap parameters, such as length, thickness, and Young’s modulus has been found out. The transient response of the flap and fluid flow under oscillating pressure driven flow has also been obtained.
The symmetries of the fine gradings of sl(nk,C) associated with direct product of Pauli groups
Authors: Han Gang
Published: September 2010

A grading of a Lie algebra is called fine if it could not be further refined. For a fine grading of a simple Lie algebra, we define its Weyl group to describe the symmetry of this grading. It is already known that the Weyl group of the fine grading of sl(n,C) induced by the action of the group Πn of the generalized Pauli matrices of rank n is SL(2,Zn), where Zn is the cyclic group of order n. In this paper, we consider the fine grading of sl(nk,C) induced by the action of the group of k-fold tensor product of the generalized Pauli matrices of rank n. We prove that its Weyl group is Sp(2k,Zn) and is generated by transvections; therefore, this generalizes the previous result.
High-performance transparent thin-film transistor based on Y2O3/In2O3 with low interface traps
Authors: Zhang H. Z. , Liang L. Y. , Chen A. H. , Liu Z. M. , Yu Z. , Cao H. T. , Wan Q.
Published: September 2010

High-performance Y2O3/In2O3-based transparent thin-film transistors were processed featuring low thermal budget. The device shows a field-effect mobility of 43.5 cm2 V−1 s−1, a subthreshold swing of 0.28 V/decade, and an on/off current ratio of 108. These results are attributed to the high dielectric constant of Y2O3 and unique electronic structure of In2O3. Furthermore, the cubic phases of crystalline Y2O3 and In2O3 films have the identical crystal structure with a small lattice mismatch, which provides a well-defined dielectric/semiconductor interface for the optimal performance.
Origins of size-dependent lattice dilatation in tetragonal Sn nanowires: Surface stress and growth stress
Authors: Shin Ho Sun , Yu Jin , Song Jae Yong , Park Hyun Min , Kim Yong-Sung
Published: September 2010

Through experiments and theoretical analyses, we demonstrate that Sn nanowires can shrink or expand when the radius decreases from 120 to 1.2 nm. Single crystalline nanowires manifest [100]-longitudinal lattice dilatations that originate from the strong anisotropy of the surface stress. Compressive growth stress, which is generated in the radial direction during the growth of nanowires within templates, leads to greater elongation due to the Poisson effect. The surface stress-induced lattice strains are intrinsic, whereas the growth stress-induced lattice strains can be released. For polycrystalline nanowires, lattice contractions occur because the anisotropy of surface stresses is effectively reduced.
Triboelectric activation of ferroelectric liquid crystal memory devices
Authors: Choudhary A. , Joshi T. , Biradar A. M.
Published: September 2010

The switching of ferroelectric liquid crystal (FLC) memory device is achieved by triboelectric effect of externally connected insulator to the sample through a conductor. The positive and negative charges are induced by triboelectrification of polymers, depending on the nature of materials, and utilized to get the bright and dark states of the FLC memory device. These switching states are analyzed by electro-optical studies. This technique of polarization switching proves to be powerful for FLC devices exhibiting long-term memory. The charges, developed on the electrodes by this nonconventional technique, generate enough potential to switch the FLC molecules in memory state.
Temperature dependent switching mechanism of (Pb0.92La0.08)(Zr0.65Ti0.35)O3 investigated by small and large signal measurements
Authors: Schaab Silke , Granzow Torsten
Published: September 2010

The transition region between the field induced ferroelectric and the ergodic phase in relaxor ferroelectrics offers the possibility to study the switching behavior as a function of the increasing relaxor character of the system. Here, field dependent small and large signal measurements are presented. The results obtained at distinct temperatures below the transition temperature Tt for (Pb0.92La0.08)(Zr0.65Ti0.35)O3 concerning P(E), S(E), ϵ33(E), and d33(E) display a strong temperature dependence. Analysis of the reversible and irreversible domain processes leads to the conclusion that switching occurs through an intermediate nanodomain state even in the ferroelectric regime.
Thermoelectric properties of electrostatically tunable antidot lattices
Authors: Goswami Srijit , Siegert Christoph , Shamim Saquib , Pepper Michael , Farrer Ian , Ritchie David A. , Ghosh Arindam
Published: September 2010

We report on the fabrication and characterization of a device which allows the formation of an antidot lattice (ADL) using only electrostatic gating. The antidot potential and Fermi energy of the system can be tuned independently. Well defined commensurability features in magnetoresistance as well as magnetothermopower are observed. We show that the thermopower can be used to efficiently map out the potential landscape of the ADL.
Interferometric detection of mode splitting for whispering gallery mode biosensors
Authors: Knittel Joachim , McRae Terry G. , Lee Kwan H. , Bowen Warwick P.
Published: September 2010

Sensors based on whispering gallery mode resonators can detect single nanoparticles and even single molecules. Particles attaching to the resonator induce a doublet in the transmission spectrum which provides a self-referenced detection signal. However, in practice this spectral feature is often obscured by the width of the resonance line which hides the doublet structure. This happens particularly in liquid environments that reduce the effective Q factor of the resonator. In this paper we demonstrate an interferometric setup that allows the direct detection of the hidden doublet and thus provides a pathway for developing practical sensor applications.
Presence-Experiences—The Eventalisation of Urban Space
Authors: Pløger John
Published: September 2010

Cultural events are, as part of an urban development strategy, about (symbolic) representations, but for the human beings participating in the event it may include acts of in/visibility (anonymity versus expressivity) and different articulations of meaning or subjectivity in space. A particular kind of event that cities are not so interested in supporting an unorganised or spontaneous event, even though they give cities the image of tolerance. All such singular events have the potential of shaping what is going to happen in a real contingent situation because they are affected by circumstances. Such events are attractive to the participants because of the possible outcome of being situatively placed within virtual connectivities and assemblages, or as in focus here, the attraction of the eventalisation of space and presence-experiences. Following Michel Foucault on ‘eventalisation’ and Hans Martin Gumbrecht on ‘presence-events’, I focus on subcultural and subpolitical groups trying to capture urban commercial spaces and to reverse or reveal their symbolic meaning. Using the oppositional youth group Pirate Parties, I argue that it is exactly the eventalisation and the presence quality of space that make these events a desired experience and the qualities of the presence-experience more desired than, for instance, the political content of the event. Why it is so is theoretically and philosophically explored by discussing the expressive signification of such events. If expressive and presence qualities should be experienced as emotional, sensate, and cognitively important, the how of the eventalisation is important. Different aspects of the eventalisation of spaces—such as the subject qualities, or singular multiplicity, of circumstances—are discussed here that point to the vital and virtual qualities of presence-event spaces and the eventalisation of urban space.
Goatsucker: Toward a Spatial Theory of State Secrecy
Authors: Paglen Trevor
Published: September 2010

While the question of state secrecy has become a topic of much political debate, relatively little attention has been paid to the topic in academic literature. Most of the literature adopts one of several frameworks. In the legal literature, state secrecy has been examined as a historical and constitutional question. Social scientists have tended to follow Weber in examining secrecy as a question of regulation and bureaucracy or have focused on the cultural play of visibility and invisibility that is often characteristic of state secrecy. This paper, by way of contrast, uses the development of the F-117A ‘stealth fighter’ as a case study to give a spatial account of secrecy. I show how state secrecy gives rise to numerous spatial, political, juridical, and even ecological contradictions and propose that a spatial understanding of state secrecy foregrounding these contradictions provides a fruitful basis for a deeper understanding of state secrecy.