bluuebunny/crossref_metadata_2025 huggingface dataset:
Length-dependent mechanical properties of gold nanowires
Authors: Han Jing , Fang Liang , Sun Jiapeng , Han Ying , Sun Kun
Published: December 2012

The well-known “size effect” is not only related to the diameter but also to the length of the small volume materials. It is unfortunate that the length effect on the mechanical behavior of nanowires is rarely explored in contrast to the intensive studies of the diameter effect. The present paper pays attention to the length-dependent mechanical properties of 〈111〉-oriented single crystal gold nanowires employing the large-scale molecular dynamics simulation. It is discovered that the ultrashort Au nanowires exhibit a new deformation and failure regime-high elongation and high strength. The constrained dislocation nucleation and transient dislocation slipping are observed as the dominant mechanism for such unique combination of high strength and high elongation. A mechanical model based on image force theory is developed to provide an insight to dislocation nucleation and capture the yield strength and nucleation site of first partial dislocation indicated by simulation results. Increasing the length of the nanowires, the ductile-to-brittle transition is confirmed. And the new explanation is suggested in the predict model of this transition. Inspired by the superior properties, a new approach to strengthen and toughen nanowires-hard/soft/hard sandwich structured nanowires is suggested. A preliminary evidence from the molecular dynamics simulation corroborates the present opinion.
Phase transformation in hexagonal ErMnO3 under high pressure
Authors: Lin Chuanlong , Liu Jing , Li Xiaodong , Li Yanchun , Chu Shenqi , Xiong Lun , Li Rui
Published: December 2012

The pressure-induced phase transition of the hexagonal manganite ErMnO3 has been investigated using the synchrotron x-ray diffraction technique up to 57.6 GPa in a diamond anvil cell. The hexagonal structure exhibits anisotropic compression behavior. The bulk modulus (B0) is 168(3) GPa with B0′ = 4.0 (fixed). At room temperature, ErMnO3 undergoes a hexagonal-to-orthorhombic phase transition at ∼20.2 GPa, but coexists with the orthorhombic phase up to the highest pressure of 57.6 GPa. When laser-heated to 1500-2000 K, the hexagonal ErMnO3 transforms to a denser orthorhombic perovskite structure completely at ∼17 GPa, accompanied by ∼11% volume reduction. The distortion and tilts of the octahedra MnO6 in the orthorhombic structure decrease with increasing pressure. The bulk modulus of the orthorhombic structure is 214(4) GPa with B0′ = 4.0 (fixed), larger than that of the hexagonal structure. The orthorhombic structure ErMnO3 is stable at least up to ∼45 GPa and can be quenched.
Photoconductivity and characterization of nitrogen incorporated hydrogenated amorphous carbon thin films
Authors: Dwivedi Neeraj , Kumar Sushil , Carey J. D. , Malik Hitendra K. , Govind
Published: December 2012

The observation and origin of photoconductivity in high base pressure (∼10−3 Torr) grown nitrogen incorporated hydrogenated amorphous carbon (a-C:H:N) thin films is reported. The magnitude of conductivity at room temperature was measured to increase by nearly two orders of magnitude and exhibits a maximum ratio of photoconductivity to dark conductivity of 1.5 as the nitrogen content increased to 15.1 at. %. X-ray photoelectron spectroscopy, micro-Raman spectroscopy, and Fourier transform infrared spectroscopy reveal enhanced sp2 bonding at higher nitrogen contents. Residual film stress, Tauc band gap, hardness, and elastic modulus are all found to decrease with addition of nitrogen. The electrical characteristics suggest the creation of a-C:H:N/p-Si heterojunction diodes having rectifying behavior. The conductivity and electrical characteristics are discussed in term of band model, and the results show that high quality a-C:H:N films can be grown at high base pressures with properties comparable to those grown at low base pressures.
Improvement of characteristics of InGaN-based laser diodes with undoped InGaN upper waveguide layer
Authors: Chen P. , Feng M. X. , Jiang D. S. , Zhao D. G. , Liu Z. S. , Li L. , Wu L. L. , Le L. C. , Zhu J. J. , Wang H. , Zhang S. M. , Yang H.
Published: December 2012

In the structure of conventional InGaN-based laser diodes, considerable optical absorption loss exists in the p-doped region, especially in the p-doped upper waveguide layer. A structure of InGaN-based laser diodes with an undoped InGaN upper waveguide layer instead of p-doped GaN was designed and optimized. Instead of being located between AlGaN EBL and AlGaN cladding layer, the undoped InGaN layer was positioned between the AlGaN electron blocking layer and the active region of multi-quantum well. The optical and electrical characteristics of this type of laser diodes were simulated by the commercial software lastip, and it was found that the optical absorption loss was obviously lowered. Further theoretical analysis showed that the undoped InGaN upper waveguide layer eliminated the influence of electron leakage current, leading to a reduction of threshold current density and an increase of output light power of the InGaN-based laser diodes.
Fundamental issues in fluid modeling: Direct substitution and aliasing methods
Authors: Robson R. E. , Nicoletopoulos P. , Hildebrandt M. , White R. D.
Published: December 2012

It is shown how the accuracy of fluid models of charged particles in gases can be improved significantly by direct substitution of swarm transport coefficient data, rather than cross sections, into the average collision terms. This direct substitution method emerges in a natural way for fluid formulations in which the role of the mean energy is transparent, whatever the mass of the charged particles in equation (ions or electrons), and requires no further approximations. The procedure is illustrated by numerical examples for electrons, including the operational window of E/N for an idealized Franck-Hertz experiment. Using the same fluid formulation, we develop an aliasing method to estimate otherwise unknown mobility data for one type of particle, from known mobility data for another type of particle. The method is illustrated for muons in hydrogen, using tabulated data for protons in the same gas.
Design for ultrahigh-Q position-controlled nanocavities of single semiconductor nanowires in two-dimensional photonic crystals
Authors: Danang Birowosuto Muhammad , Yokoo Atsushi , Taniyama Hideaki , Kuramochi Eiichi , Takiguchi Masato , Notomi Masaya
Published: December 2012

Using finite-difference time-domain simulation, we show that ultrahigh-Q nanocavities can be obtained through the manipulation of a single semiconductor nanowire (NW) inside a slot in a line defect of a two-dimensional photonic crystal. By controlling the design and its lattice parameters of the photonic crystal, we have achieved a quality factor Q larger than 106 and a mode volume Vc smaller than 0.11 μm3 (1.25 of a cubic wavelength in the NW) for a cavity peak in the telecommunication band. This design is useful for realizing a position-controlled cavity in a photonic crystal. Here, we also discuss the small dependence of the Q-factor, the Vc, and the cavity peak in relation to the position of the NW inside the slot and the potential application to the cavity quantum electrodynamics using the embedded-emitter NW.
Electronic structure of epitaxial germanium—Metal germanate interfaces
Authors: Li H. , Lin L. , Robertson J.
Published: December 2012

We have calculated the electronic structure of various Ge-based high dielectric constant oxides LaGeOx and HfGeOx using hybrid functional methods. The band gaps of bulk La2Ge2O7 and La2GeO5 are found to be both close to 5.0 eV and the band gap of HfGeO4 is about 5.5 eV. We have also built fully bonded epitaxial interface models of LaGeOx, HfGeOx, and Al2O3 on Ge(100) with no dangling bonds. The calculated valence band offsets for LaGeOx, HfGeOx, and Al2O3 on Ge(100) are 3.0 eV, 3.0 eV, and 3.0 eV, respectively.
Ferroelectricity enhanced by disorder in collinear-magnetism-induced multiferroic state
Authors: Yao Xiaoyan
Published: December 2012

To understand the fantastic static-disorder-enhanced ferroelectricity observed in Ca3Co2−xMnxO6 compound, the multiferroic state originated from the up-up-down-down spin order in different conditions of disorder is simulated by using Monte Carlo algorithm on a three-dimensional elastic Ising model with dilution. The spin structure factor and the correlation of ionic displacements are calculated to show the detailed variations of microscopic magnetic and ferroelectric structures. It is indicated that in the pure system without disorder the frustration from the long-ranged interchain interaction disrupts the up-up-down-down spin order and the corresponding ferroelectric domain, and hence suppresses the ferroelectric polarization (P). When disorder is introduced by doping a few spin defects, the frustration can be relaxed around these defects. Then the disturbance upon ferroelectric domain is lessened and hereby P is recovered effectively. The result obtained gives a clear microscopic scenario of the static-disorder-enhanced ferroelectricity observed in Ca3Co2−xMnxO6 compound.
Electron attachment to fluorocarbon radicals
Authors: Shuman Nicholas S. , Miller Thomas M. , Viggiano A. A.
Published: December 2012

Thermal electron attachment rate constants for a series of small fluorocarbon radicals (CF2, C2F3, 1-C3F7, 2-C3F7, C3F5, CF3O) were measured from 300 to 600 K using the variable electron and neutral density attachment mass spectrometry method. With the exception of CF2, for which no attachment was observed, all species exclusively underwent dissociative attachment to yield F−. The magnitude and temperature dependences of the rate constants varied significantly between species; however, attachment was in all cases inefficient, never exceeding 2% of the calculated collisional value. The data are interpreted and extrapolated to conditions inaccessible to the experiment using a kinetic modeling approach to the electron attachment process.
The origin of giant dielectric relaxation and electrical responses of grains and grain boundaries of W-doped CaCu3Ti4O12 ceramics
Authors: Thongbai Prasit , Jumpatam Jutapol , Putasaeng Bundit , Yamwong Teerapon , Maensiri Santi
Published: December 2012

The origin of giant dielectric relaxation behavior and related electrical properties of grains and grain boundaries (GBs) of W6+-doped CaCu3Ti4O12 ceramics were studied using admittance and impedance spectroscopy analyses based on the brick–work layer model. Substitution of 1.0 at. % W6+ caused a slight decrease in GB capacitance, leading to a small decrease in the low-frequency dielectric constant. Surprisingly, W6+ doping ions have remarkable effects on the macroscopic dielectric relaxation and electrical properties of grains. X-ray photoelectron spectroscopy analysis suggested that the large enhancements of grain resistance and conduction activation energy of grains for the W6+-doped CaCu3Ti4O12 ceramic are caused by reductions in concentrations of Cu3+ and Ti3+ ions. Considering variation of dielectric properties together with changes in electrical properties of the W6+-doped CaCu3Ti4O12 ceramic, correlation between giant dielectric properties and electrical responses of grains and GBs can be described well by the internal barrier layer capacitor model. This model can ascribe mechanisms related to giant dielectric response and relaxation behavior in CaCu3Ti4O12 ceramics.
Electronic structure and transport properties of sulfur-passivated graphene nanoribbons
Authors: Mandal Bikash , Sarkar Sunandan , Pramanik Anup , Sarkar Pranab
Published: December 2012

Electronic structure of newly synthesized sulfur-terminated graphene nanoribbons (S-GNRs) has been presented from the calculations based on ab initio density functional theory and non-equilibrium Green's function (NEGF) method. The calculations reveal that zigzag-edged S-GNRs (Z-S-GNRs) are thermodynamically more stable than armchair edged S-GNRs (A-S-GNRs). It has been observed that the band gap of S-GNRs depends both on ribbon width and edge symmetry. The calculated band gap, in case of A-S-GNRs, is also supported by the presence of threshold bias in the I-V characteristics obtained from NEGF formalism. It is shown that all A-S-GNRs having width up to 1.50 nm are semiconducting but the Z-S-GNRs of similar widths are metallic. For A-S-GNRs, the width dependent band-gap hierarchy follows three different trends which seem to be different from that of H-passivated GNRs. The band-gaps for A-S-GNRs arise from both quantum confinement as well as crucial effect of edge, where the passivating S atoms play an important role. Band-gap may be further tuned by introducing other passivating atoms like Se and Te. The semiconducting ribbons, when attached to doped metallic ribbons, show negative differential resistance phenomena as indicated by the observed I-V characteristics.
Topological chaos, braiding and bifurcation of almost-cyclic sets
Authors: Grover Piyush , Ross Shane D. , Stremler Mark A. , Kumar Pankaj
Published: December 2012

In certain two-dimensional time-dependent flows, the braiding of periodic orbits provides a way to analyze chaos in the system through application of the Thurston-Nielsen classification theorem (TNCT). We expand upon earlier work that introduced the application of the TNCT to braiding of almost-cyclic sets, which are individual components of almost-invariant sets [Stremler et al., “Topological chaos and periodic braiding of almost-cyclic sets,” Phys. Rev. Lett. 106, 114101 (2011)]. In this context, almost-cyclic sets are periodic regions in the flow with high local residence time that act as stirrers or “ghost rods” around which the surrounding fluid appears to be stretched and folded. In the present work, we discuss the bifurcation of the almost-cyclic sets as a system parameter is varied, which results in a sequence of topologically distinct braids. We show that, for Stokes’ flow in a lid-driven cavity, these various braids give good lower bounds on the topological entropy over the respective parameter regimes in which they exist. We make the case that a topological analysis based on spatiotemporal braiding of almost-cyclic sets can be used for analyzing chaos in fluid flows. Hence, we further develop a connection between set-oriented statistical methods and topological methods, which promises to be an important analysis tool in the study of complex systems.
A scintillator-based online detector for the angularly resolved measurement of laser-accelerated proton spectra
Authors: Metzkes J. , Karsch L. , Kraft S. D. , Pawelke J. , Richter C. , Schürer M. , Sobiella M. , Stiller N. , Zeil K. , Schramm U.
Published: December 2012

In recent years, a new generation of high repetition rate (∼10 Hz), high power (∼100 TW) laser systems has stimulated intense research on laser-driven sources for fast protons. Considering experimental instrumentation, this development requires online diagnostics for protons to be added to the established offline detection tools such as solid state track detectors or radiochromic films. In this article, we present the design and characterization of a scintillator-based online detector that gives access to the angularly resolved proton distribution along one spatial dimension and resolves 10 different proton energy ranges. Conceived as an online detector for key parameters in laser-proton acceleration, such as the maximum proton energy and the angular distribution, the detector features a spatial resolution of ∼1.3 mm and a spectral resolution better than 1.5 MeV for a maximum proton energy above 12 MeV in the current design. Regarding its areas of application, we consider the detector a useful complement to radiochromic films and Thomson parabola spectrometers, capable to give immediate feedback on the experimental performance. The detector was characterized at an electrostatic Van de Graaff tandetron accelerator and tested in a laser-proton acceleration experiment, proving its suitability as a diagnostic device for laser-accelerated protons.
Shock tube investigation of quasi-steady drag in shock-particle interactions
Authors: Wagner Justin L. , Beresh Steven J. , Kearney Sean P. , Pruett Brian O. M. , Wright Elton K.
Published: December 2012

A reassessment of historical drag coefficient data for spherical particles accelerated in shock-induced flows has motivated new shock tube experiments of particle response to the passage of a normal shock wave. Particle drag coefficients were measured by tracking the trajectories of 1-mm spheres in the flow induced by incident shocks at Mach numbers 1.68, 1.93, and 2.04. The necessary data accuracy is obtained by accounting for the shock tube wall boundary layer growth and avoiding interactions between multiple particles. Similar to past experiments, the current data clearly show that as the Mach number increases, the drag coefficient increases substantially. This increase significantly exceeds the drag predicted by incompressible standard drag models, but a recently developed compressible drag correlation returns values quite close to the current measurements. Recent theoretical work and low particle accelerations indicate that unsteadiness should not be expected to contribute to the drag increase over the relatively long time scales of the experiments. These observations suggest that elevated particle drag coefficients are a quasi-steady phenomenon attributed to increased compressibility rather than true flow unsteadiness.
Refocused continuous-wave decoupling: A new approach to heteronuclear dipolar decoupling in solid-state NMR spectroscopy
Authors: Vinther Joachim M. , Nielsen Anders B. , Bjerring Morten , van Eck Ernst R. H. , Kentgens Arno P. M. , Khaneja Navin , Nielsen Niels Chr.
Published: December 2012

A novel strategy for heteronuclear dipolar decoupling in magic-angle spinning solid-state nuclear magnetic resonance (NMR) spectroscopy is presented, which eliminates residual static high-order terms in the effective Hamiltonian originating from interactions between oscillating dipolar and anisotropic shielding tensors. The method, called refocused continuous-wave (rCW) decoupling, is systematically established by interleaving continuous wave decoupling with appropriately inserted rotor-synchronized high-power π refocusing pulses of alternating phases. The effect of the refocusing pulses in eliminating residual effects from dipolar coupling in heteronuclear spin systems is rationalized by effective Hamiltonian calculations to third order. In some variants the π pulse refocusing is supplemented by insertion of rotor-synchronized π/2 purging pulses to further reduce the residual dipolar coupling effects. Five different rCW decoupling sequences are presented and their performance is compared to state-of-the-art decoupling methods. The rCW decoupling sequences benefit from extreme broadbandedness, tolerance towards rf inhomogeneity, and improved potential for decoupling at relatively low average rf field strengths. In numerical simulations, the rCW schemes clearly reveal superior characteristics relative to the best decoupling schemes presented so far, which we to some extent also are capable of demonstrating experimentally. A major advantage of the rCW decoupling methods is that they are easy to set up and optimize experimentally.
Experimental study from linear to chaotic regimes on a terahertz-frequency gyrotron oscillator
Authors: Alberti S. , Ansermet J.-Ph. , Avramides K. A. , Braunmueller F. , Cuanillon P. , Dubray J. , Fasel D. , Hogge J.-Ph. , Macor A. , de Rijk E. , da Silva M. , Tran M. Q. , Tran T. M. , Vuillemin Q.
Published: December 2012

Basic wave-particle interaction dynamics from linear to chaotic regimes is experimentally studied on a frequency tunable gyrotron generating THz radiation in continuous mode (200 W) at 263 GHz which will be used for dynamic nuclear polarization nuclear magnetic resonance spectroscopy applications. In the studied system, the nonlinear dynamics associated to the wave-particle interaction is dominated by longitudinal mode competition of a given transverse TEm,p cavity-mode. This study covers a wide range of control parameter from gyro-traveling wave tube (gyro-TWT) to gyro-backward wave oscillator (gyro-BWO) like interactions for which extensive theoretical studies have been performed in the past on a simplified system. Besides the common route to chaos characterized by period doubling, other routes have been identified among which some are characterized by line-width frequency-broadening on the side-bands. The complex nonlinear dynamics is in good agreement with the theory and the experimental results are discussed on the basis of the prediction obtained with the nonlinear time-dependent self-consistent codes TWANG and EURIDICE both based on a slow-time scale formulation of the self-consistent equations governing the wave-particle dynamics.
Levitating spherical particle in a slightly tapered tube at low Reynolds numbers: Application to the low-flow rate rotameters
Authors: Champmartin S. , Ambari A. , Chhabra R. P.
Published: December 2012

In this study, a theoretical framework is developed to predict the equilibrium conditions of a non-neutrally buoyant sphere placed in a vertical conical tube as encountered in liquid rotameters. The analysis presented herein is applicable for a sphere heavier than the surrounding fluid, situated on the axis of a slightly tapered tube. The sphere is subject to the laminar flow conditions with the Reynolds numbers ranging between the Stokes type regimes up to values corresponding to slightly inertial regimes. In this work, we assume that the aperture angle of the tube is small and that the drag force is mainly due to the dissipation located in the gap between the tube and the sphere. Under these conditions, it is possible to consider the tube as locally cylindrical and we can use the results previously obtained for the correction factor of the Stokes force on a sphere subject to a Poiseuille flow in a tube of constant cross-section. We obtain an equation relating the flow rate to the vertical position of the sphere in the tube and the validity of this analysis is demonstrated by applying it to a commercially available rotameter. The present study provides a simple but sound theoretical method to calibrate such flowmeters.
A single coil radio frequency gradient probe for nuclear magnetic resonance applications
Authors: Christofield N. , Sobieski D. N. , Erker J. C. , May S. , Augustine M. P.
Published: December 2012

A single coil nuclear magnetic resonance (NMR) probehead and associated electronics capable of asynchronously applying both homogeneous and inhomogeneous radio frequency (rf) pulses to solid, liquid, or gaseous samples is described. This equipment can be interfaced with a conventional single channel NMR spectrometer. Carefully placed PIN diodes on the NMR probehead are used to switch the coil between a homogeneous end tapped configuration and an inhomogeneous center tapped rf gradient configuration. This approach dramatically improves channel isolation in comparison to existing two coil designs. Descriptions of the new probehead, the transistor-transistor logic (TTL) controlled dc pulser for PIN diode gating, and the high power rf switch are provided. Several NMR pulse sequences are used to test the channel isolation and probe performance. Finally an application to liquid phase solvent suppression is provided.
Near-field fluorescence thermometry using highly efficient triple-tapered near-field optical fiber probe
Authors: Fujii T. , Taguchi Y. , Saiki T. , Nagasaka Y.
Published: December 2012

A novel local temperature measurement method using fluorescence near-field optics thermal nanoscopy (Fluor-NOTN) has been developed. Fluor-NOTN enables nanoscale temperature measurement in situ by detecting the temperature-dependent fluorescence lifetime of CdSe quantum dots (QDs). In this paper, we report a novel triple-tapered near-field optical fiber probe that can increase the temperature measurement sensitivity of Fluor-NOTN. The performance of the proposed probe was numerically evaluated by the finite difference time domain method. Due to improvements in both the throughput and collection efficiency of near-field light, the sensitivity of the proposed probe was 1.9 times greater than that of typical double-tapered probe. The proposed shape of the triple-tapered core was successfully fabricated utilizing a geometrical model. The detected signal intensity of dried layers of QDs was greater by more than two orders than that of auto-fluorescence from the fiber core. In addition, the near-field fluorescence lifetime of the QDs and its temperature dependence were successfully measured by the fabricated triple-tapered near-field optical fiber probe. These measurement results verified the capability of the proposed triple-tapered near-field optical fiber probe to improve the collection efficiency of near-field fluorescence.
Liquid-liquid transition in ST2 water
Authors: Liu Yang , Palmer Jeremy C. , Panagiotopoulos Athanassios Z. , Debenedetti Pablo G.
Published: December 2012

We use the weighted histogram analysis method [S. Kumar, D. Bouzida, R. H. Swendsen, P. A. Kollman, and J. M. Rosenberg, J. Comput. Chem. 13, 1011 (1992)10.1002/jcc.540130812] to calculate the free energy surface of the ST2 model of water as a function of density and bond-orientational order. We perform our calculations at deeply supercooled conditions (T = 228.6 K, P = 2.2 kbar; T = 235 K, P = 2.2 kbar) and focus our attention on the region of bond-orientational order that is relevant to disordered phases. We find a first-order transition between a low-density liquid (LDL, ρ ≈ 0.9 g/cc) and a high-density liquid (HDL, ρ ≈ 1.15 g/cc), confirming our earlier sampling of the free energy surface of this model as a function of density [Y. Liu, A. Z. Panagiotopoulos, and P. G. Debenedetti, J. Chem. Phys. 131, 104508 (2009)10.1063/1.3229892]. We demonstrate the disappearance of the LDL basin at high pressure and of the HDL basin at low pressure, in agreement with independent simulations of the system's equation of state. Consistency between directly computed and reweighted free energies, as well as between free energy surfaces computed using different thermodynamic starting conditions, confirms proper equilibrium sampling. Diffusion and structural relaxation calculations demonstrate that equilibration of the LDL phase, which exhibits slow dynamics, is attained in the course of the simulations. Repeated flipping between the LDL and HDL phases in the course of long molecular dynamics runs provides further evidence of a phase transition. We use the Ewald summation with vacuum boundary conditions to calculate long-ranged Coulombic interactions and show that conducting boundary conditions lead to unphysical behavior at low temperatures.
A subKelvin scanning probe microscope for the electronic spectroscopy of an individual nano-device
Authors: Quaglio T. , Dahlem F. , Martin S. , Gérardin A. , Winkelmann C. B. , Courtois H.
Published: December 2012

We present a combined scanning force and tunneling microscope working in a dilution refrigerator that is optimized for the study of individual electronic nano-devices. This apparatus is equipped with commercial piezo-electric positioners enabling the displacement of a sample below the probe over several hundred microns at very low temperature, without excessive heating. Atomic force microscopy based on a tuning fork resonator probe is used for cryogenic precise alignment of the tip with an individual device. We demonstrate the local tunneling spectroscopy of a hybrid Josephson junction as a function of its current bias.
Density-functional global optimization of (La2O3)n clusters
Authors: Ding Xun-Lei , Li Zi-Yu , Meng Jing-Heng , Zhao Yan-Xia , He Sheng-Gui
Published: December 2012

Structures of stoichiometric (La2O3)n (n = 1–6) clusters have been systematically studied by theoretical calculations. Global minimum structures for these clusters are determined by genetic algorithm based global optimizations at density functional level. The ground state structure for La6O9 was found to be highly symmetric with point group Oh and the centered oxygen atom has the coordination number as large as six, which is the same as the highest coordination number of oxygen atoms in bulk La2O3. Analysis of the binding energies shows that La6O9 has a high stability among the studied clusters. The energies of the highest occupied/lowest unoccupied molecular orbitals, vertical ionization energy, and vertical electron affinity of each cluster are provided. Electronic structure of La6O9 is discussed by analysis of the frontier molecular orbitals and unpaired spin density distributions of charged clusters.
Theoretical prediction of the reaction of s-triazine with nitrate radical: A new possible route to generate oxy-s-triazine
Authors: Zhang Ji-Dong , Cheng Xin-Lu
Published: December 2012

Oxy-s-triazine (OST) is one of the important Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) decomposition products, while it is yet not fully clear how it is formed up to now. The study systematically investigates the reaction of s-triazine (TAZ) with nitrate radical (NO3) using computational chemistry methods, for which three entrance channels are devised, resulting in the formation of four isomers of OST. Based on the analysis of the barrier heights and the reaction exothermicities, the pathway to form OST3 through hydrogen atom abstraction and rebound mechanism is likely to be the main channel in the reactions of TAZ with NO3 radical. Our study puts forward a new possible route to generate OST.
A bright cadmium-free, hybrid organic/quantum dot white light-emitting diode
Authors: Yang Xuyong , Divayana Yoga , Zhao Dewei , Swee Leck Kheng , Lu Fen , Tiam Tan Swee , Putu Abiyasa Agus , Zhao Yongbiao , Volkan Demir Hilmi , Wei Sun Xiao
Published: December 2012

We report a bright cadmium-free, InP-based quantum dot light-emitting diode (QD-LED) with efficient green emission. A maximum brightness close to 700 cd/m2 together with a relatively low turn-on voltage of 4.5 V has been achieved. With the design of a loosely packed QD layer resulting in the direct contact of poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (poly-TPD) and 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) in the device, a ternary complementary white QD-LED consisting of blue component (poly-TPD), green component (QDs), and red component (exciplex formed at the interface between poly-TPD and TPBi) has been demonstrated. The resulting white QD-LED shows an excellent color rendering index of 95.
Tunable self-biased magnetoelectric response in homogenous laminates
Authors: Zhou Yuan , Chul Yang Su , Apo Daniel J. , Maurya Deepam , Priya Shashank
Published: December 2012

In this study, we demonstrate self-biased magnetoelectric effect in homogenous two-phase magnetostrictive-piezoelectric laminates. Our results illustrate the method for tuning the magnitude of self-bias effect and provide understanding behind the hysteretic changes. We model this phenomenon by considering the magnetization hysteresis with shape-induced demagnetization effect. The self-biased response was found to be directly related to the nature of magnetization and can be tuned by variation in demagnetization state and the resultant differential magnetic flux distribution. These results present significant advancement toward development of AC magnetic field sensor and magnetoelectric composite based on-chip devices by eliminating the need for DC bias.
Step free energies at faceted solid-liquid interfaces from equilibrium molecular dynamics simulations
Authors: Frolov T. , Asta M.
Published: December 2012

In this work a method is proposed for computing step free energies for faceted solid-liquid interfaces based on atomistic simulations. The method is demonstrated in an application to (111) interfaces in elemental Si, modeled with the classical Stillinger-Weber potential. The approach makes use of an adiabatic trapping procedure, and involves simulations of systems with coexisting solid and liquid phases separated by faceted interfaces containing islands with different sizes, for which the corresponding equilibrium temperatures are computed. We demonstrate that the calculated coexistence temperature is strongly affected by the geometry of the interface. We find that island radius is inversely proportional to superheating, allowing us to compute the step free energy by fitting simulation data within the formalism of classical nucleation theory. The step free energy value is computed to be γst = 0.103 ± 0.005 × 10−10 J/m. The approach outlined in this work paves the way to the calculation of step free energies relevant to the solidification of faceted crystals from liquid mixtures, as encountered in nanowire growth by the vapor-liquid-solid mechanism and in alloy casting. The present work also shows that at low undercoolings the Stillinger-Weber interatomic potential for Si tends to crystallize in the wurtzite, rather than the diamond-cubic structure.
Capillary effects on floating cylindrical particles
Authors: Dixit Harish N. , Homsy G. M.
Published: December 2012

In this study, we develop a systematic perturbation procedure in the small parameter, B1/2, where B is the Bond number, to study capillary effects on small cylindrical particles at interfaces. Such a framework allows us to address many problems involving particles on flat and curved interfaces. In particular, we address four specific problems: (i) capillary attraction between cylinders on flat interface, in which we recover the classical approximate result of Nicolson [“The interaction between floating particles,” Proc. Cambridge Philos. Soc. 45, 288–295 (1949)10.1017/S0305004100024841], thus putting it on a rational basis; (ii) capillary attraction and aggregation for an infinite array of cylinders arranged on a periodic lattice, where we show that the resulting Gibbs elasticity obtained for an array can be significantly larger than the two cylinder case; (iii) capillary force on a cylinder floating on an arbitrary curved interface, where we show that in the absence of gravity, the cylinder experiences a lateral force which is proportional to the gradient of curvature; and (iv) capillary attraction between two cylinders floating on an arbitrary curved interface. The present perturbation procedure does not require any restrictions on the nature of curvature of the background interface and can be extended to other geometries.
MoO3/Ag/MoO3 anode in organic photovoltaic cells: Influence of the presence of a CuI buffer layer between the anode and the electron donor
Authors: Makha M. , Cattin L. , Lare Y. , Barkat L. , Morsli M. , Addou M. , Khelil A. , Bernède J. C.
Published: December 2012

MoO3/Ag/MoO3 (MAM) multilayer structures (layers thickness 20 nm/10 nm/35 nm) are used as anode in CuPc/C60/Alq3/Al organic photovoltaic cells. The averaged transmittance (400 nm-800 nm) of these MoO3/Ag/MoO3 multilayer structures is 70% ± 2% and their sheet resistance is 3.5 ± 1.0 Ω/sq. When these multilayer structures are used as anode, the power conversion efficiency of the MoO3/Ag/MoO3/CuPc/C60/Alq3/Al cells is around 1%, this efficiency is increased of 50% when a thin CuI film (3 nm) is introduced at the interface between the anode and the organic film. This improvement is attributed to the templating effect of CuI on the CuPc molecules.
Room-temperature method for minimizing light-induced degradation in crystalline silicon
Authors: Lindroos J. , Yli-Koski M. , Haarahiltunen A. , Savin H.
Published: December 2012

Although light-induced degradation (LID) in crystalline silicon is attributed to the formation of boron-oxygen recombination centers, copper contamination of silicon has recently been observed to result in similar degradation. As positively charged interstitial copper stays mobile at room temperature in silicon, we show that the bulk copper concentration can be reduced by depositing a large negative charge onto the wafer surface. Consequently, light-induced degradation is reduced significantly in both low- and high-resistivity boron-doped Czochralski-grown silicon.
Fluorescence resonance energy transfer-based molecular logic circuit using a DNA scaffold
Authors: Nishimura Takahiro , Ogura Yusuke , Tanida Jun
Published: December 2012

This paper presents a method of information processing using biomolecular input signals and fluorescence resonance energy transfer (FRET) signaling constructed on a DNA scaffold. Logic operations are achieved by encoding molecular inputs into an arrangement of fluorescence dyes using simple DNA reactions and by evaluating a logic expression using local photonic signaling that is much faster than DNA reactions. Experimental results verify the operation of a complete set of Boolean logic functions (AND, OR, NOT) and combinational logic operations using a FRET-signal cascade.
Determination of the deep donor-like interface state density distribution in metal/Al2O3/n-GaN structures from the photocapacitance–light intensity measurement
Authors: Matys M. , Adamowicz B. , Hashizume T.
Published: December 2012

We developed a method for determining of the deep donor-like interface state density distribution Dit(E) at the insulator/wide bandgap semiconductor interface in metal/insulator/semiconductor structures from the measurements of photocapacitance vs. ultraviolet light intensity CL(Φ). From the comparison of theoretical and experimental CL(Φ) curves we obtained the continuous donor Dit(E) in the energy range between 0.15 eV and 1 eV from the valence band top for a metal/Al2O3/n-GaN device. In addition, the acceptor-like interface state Dit(E) in the upper part of the bandgap was determined from the capacitance-voltage method.
Internal frequency mixing in a single optomechanical resonator
Authors: Huang Chenguang , Fan Jiahua , Zhang Ruoyu , Zhu Lin
Published: December 2012

In this letter, we observe that both the fundamental radial breathing mode and the flapping mode couple to a high Q optical mode and generate frequency mixing through the nonlinear optical transfer function in a single nitride optomechanical resonator. The harmonic generation of the flapping mode produces a comb-like frequency mixing spectrum. Instead of using the external pump modulation, we show that the regenerative oscillation of an internal mechanical mode can be used as a modulation source for optomechanical RF mixing.
Quantum capacitance in topological insulators under strain in a tilted magnetic field
Authors: Tahir M. , Schwingenschlögl U.
Published: December 2012

Topological insulators exhibit unique properties due to surface states of massless Dirac fermions with conserved time reversal symmetry. We consider the quantum capacitance under strain in an external tilted magnetic field and demonstrate a minimum at the charge neutrality point due to splitting of the zeroth Landau level. We also find beating in the Shubnikov de Haas oscillations due to strain, which originate from the topological helical states. Varying the tilting angle from perpendicular to parallel washes out these oscillations with a strain induced gap at the charge neutrality point. Our results explain recent quantum capacitance and transport experiments.
The progression of small-follicle reserves in the ovaries of wild African elephants (Loxodonta africana) from puberty to reproductive senescence
Authors: Stansfield F. J. , Nöthling J. O. , Allen W. R.
Published: December 2012

This study aimed to determine whether the follicle reserve in the ovary of the African elephant declines progressively after puberty and whether its depletion constrains the fertility of older females. Elephant ovaries were fixed in 4% neutral buffered formalin and small-follicle counts made using stereological protocols. Excepting a slight rise in small-follicle numbers between 16 and 25 years of age, there was a trend for follicle numbers to fall from puberty to 70 years. Reproductive status did not impact significantly on small-follicle numbers (P = 0.31). The number of early primary follicles, initially higher in number than true primary follicles, fell from post-puberty to nil at 45 years of age. Six of the seven oldest animals in the study showed signs of recent ovarian activity in the form of antral follicles, corpora lutea or large corpora nigra. The four oldest elephants (mean age 69 years) had a median small-follicle count of 11 113. In summary, it appears that the elephant ovary is capable of supplying oocytes for ovulation right up to the time of death at the age of maximum life expectancy, although the follicle reserve becomes depleted in some older elephants.
Molecular control of oocyte meiotic arrest and resumption
Authors: Liu Lei , Kong Nana , Xia Guoliang , Zhang Meijia
Published: December 2012

Mammalian oocytes within Graafian follicles are arrested at prophase I by factors from surrounding follicle cells, and resume meiosis after an LH surge from the pituitary. The maintenance of meiotic arrest requires high levels of cAMP, resulting from G-protein-coupled receptor (GPR) 3 and/or GPR12 activation of adenylyl cyclase within the oocyte. Recent studies indicate that natriuretic peptide precursor C (NPPC), acting via its cognate receptor NPR2, increases cGMP levels in granulosa cells; the cGMP then diffuses into oocytes and inhibits phosphodiesterase 3A activity and cAMP hydrolysis. Meiotic resumption is induced by LH via the generation of epidermal growth factor (EGF)-like growth factors in mural granulosa cells that activate EGF receptors in cumulus cells. However, the exact mechanisms underlying the actions of these growth factors on oocyte maturation are unclear. Herein we summarise the regulatory functions of NPPC and NPR2 in maintaining oocyte meiotic arrest and discuss the possibility that LH could stimulate meiotic resumption by decreasing NPPC content and NPR2 activity.
Genetic diversity in the
Jatropha
genus and its potential application.
Authors: Xu Wei Xu Wei , Sujatha Mulpuri Sujatha Mulpuri , Liu AiZhong Liu AiZhong
Published: December 2012

Jatropha curcas
L., a drought tolerant, monoecious perennial shrub, has gained attention in the tropics and sub-tropics during the past decade as a potential biodiesel crop. Adequate genetic diversity for key agronomic traits is of fundamental importance in crop improvement programmes particularly for crops such as
J. curcas
, which are in the early stages of domestication. In
J. curcas
, genetic diversity in local populations and worldwide collections has been estimated using both dominant and co-dominant molecular markers systems such as random amplified polymorphic DNA (RAPD), inter simple sequence repeats (ISSRs), sequence-characterized amplified region (SCAR), amplified fragment length polymorphism (AFLP), simple sequence repeats (SSRs) and single-nucleotide polymorphism (SNPs), etc. Assessment of genetic variation using molecular markers unequivocally established the existence of rich genetic diversity in the germplasm from Central and South American regions and narrow genetic base in populations from Asia and Africa. Establishment of phylogenetic relationships among
Jatropha
species using molecular markers has been limited to species naturalized and distributed in India. Research expansion over the past decade has indicated the availability of considerable genetic variation in the genus Jatropha for vegetative and floral traits linked to productivity, seed oil content, fatty acid profiles, toxicity (phorbol esters, curcin), etc. The diverse genetic sources identified in
J. curcas
germplasm and the compatible wild species need to be exploited for genetic improvement of the crop through conventional breeding and interspecific gene transfer, which could be further accelerated through marker-aided selection.
PARENTHOOD AND RETIREMENT
Authors: Hank Karsten , Korbmacher Julie M.
Published: December 2012

This study uses retrospective life-history data from the SHARELIFE project for an initial assessment of the long-term relationship between individuals' reproductive history and retirement in 13 Continental European countries, focussing in particular on possible gender, cohort, and welfare regime differences. Our analysis provides some weak evidence that having (more) children is associated with later retirement among men, reflecting a continuation of the male provider role well into the late career phase. When distinguishing between women born before and after 1940, we detect striking cohort differences in retirement behaviours of mothers and childless individuals: while mothers belonging to the older cohorts tend to exit the labour force later than their childless counterparts, those born post-1940 exhibit a greater propensity to enter retirement earlier. This finding is discussed against the background of cross-national (i.e., welfare regime) differences in younger mothers' employment opportunities as well as differential economic and institutional opportunities for women (mothers, respectively) to retire early. We conclude with suggestions for future research.
Readiness to Engage in Treatments for Personality Disorder
Authors: McMurran Mary
Published: December 2012

Treatment non-completion in personality disorder (PD) treatments is prevalent and non-completers show poorer treatment outcomes than completers. Identifying risk factors for non-completion, and particularly causal risk factors, is important to inform criteria for treatment selection, design treatments that are responsive to non-completion risk, and design interventions to minimise non-completion. Risk factors lie in a number of domains, including individual, treatment, and environmental characteristics. A model of Readiness to Engage in Treatment for Personality Disorders is presented to guide research and assessment. Pre-therapy preparation is one potentially valuable approach to improving treatment engagement and retention, and examples of interventions are described. Throughout this review, the relevance of research to forensic services is specifically highlighted.
Explicating the Construct of Psychopathy: Development and Validation of a Conceptual Model, the Comprehensive Assessment of Psychopathic Personality (CAPP)
Authors: Cooke DavidJ. , Hart StephenD. , Logan Caroline , Michie Christine
Published: December 2012

Psychopathic personality disorder (PPD) has important clinical and forensic implications. But much more effort has been devoted to assessing or diagnosing PPD than to explicating or defining it. In the first part of this paper, we describe the development of a conceptual model or “concept map” of PPD. Based on a systematic review of descriptions of PPD in the clinical and research literature, as well as consultation with subject matter experts, we identified key features of the disorder and translated them into 33 symptoms, presented as natural language (i.e., non-technical) trait descriptive adjectives or adjectival phrases. Each symptom in turn was defined by three synonymous adjectives or adjectival phrases. The 33 symptoms were grouped rationally to reflect six domains of personality functioning. In the second part of the paper, we discuss research completed and in progress intended to validate the CAPP conceptual model.