bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of the electron-exchange and quantum shielding on the bremsstrahlung spectrum in degenerate quantum plasmas
Authors: Jung Young-Dae
Published: October 2013

The influence of the electron-exchange and quantum shielding on the bremsstrahlung spectrum is investigated in degenerate quantum plasmas. The impact-parameter analysis with the Shukla-Eliasson potential is applied to obtain the electron-ion bremsstrahlung radiation cross section as a function of the impact parameter, photon energy, projectile energy, electron-exchange parameter, Fermi energy, and plasmon energy. The result shows that the electron-exchange effect strongly enhances the bremsstrahlung radiation spectrum in degenerate quantum plasmas. It is also shown that the influence of the electron-exchange broadens the photon emission range in the electron-ion bremsstrahlung process. It is found that the electron-exchange effect focuses the bremsstrahlung photon energy in the soft photon domain. In addition, it is found that the bremsstrahlung radiation cross section increases with an increase of the Fermi energy and, however, decreases with increasing plasmon energy.
Light propagation characteristics of high-purity polystyrene
Authors: Nakamura Hidehito , Shirakawa Yoshiyuki , Kitamura Hisashi , Sato Nobuhiro , Shinji Osamu , Saito Katashi , Takahashi Sentaro
Published: October 2013

Organic scintillation materials involve short wavelength light emitted from polymers containing aromatic ring moieties. We have characterized high-purity (>99.9%) polystyrene (PS) as a potential scintillator. It emits ultraviolet light with a 310-nm emission maximum. We demonstrate that the effective refractive index (1.67) for PS is a function of the emission spectrum. Light yield distributions generated by 137Cs and 207Bi radioactive sources were also characterized. The light attenuation length is 41.6 ± 0.5 mm, which is ten times than expected. These results demonstrate that high-purity PS has important light propagation characteristics needed for organic scintillation materials.
Generation of high charge state platinum ions on vacuum arc plasma heated by gyrotron radiation
Authors: Yushkov G. Yu. , Vodopyanov A. V. , Nikolaev A. G. , Izotov I. V. , Savkin K. P. , Golubev S. V. , Oks E. M.
Published: October 2013

The hybrid high charge metal ion source based on vacuum arc plasma heated by gyrotron radiation into simple magnetic trap has been developed. Two types of magnetic traps were used: a mirror configuration and a cusp one with inherent “minimum-B” structure. Pulsed high power (>100 kW) gyrotrons with frequency 37.5 GHz and 75 GHz were used for heating the vacuum arc plasma injected into the traps. Two different ways were used for injecting the metal plasma—axial injection by a miniature arc source located on-axis near the microwave window, and simultaneous radial injection by a number of sources mounted radially at the midplane of the traps. This article represents all data gathered for platinum ions, thus making comparison of the experimental results obtained with different traps and injections convenient and accurate.
Modeling of structural uncertainties in Reynolds-averaged Navier-Stokes closures
Authors: Emory Michael , Larsson Johan , Iaccarino Gianluca
Published: October 2013

Estimation of the uncertainty in numerical predictions by Reynolds-averaged Navier-Stokes closures is a vital step in building confidence in such predictions. An approach to model-form uncertainty quantification that does not assume the eddy-viscosity hypothesis to be exact is proposed. The methodology for estimation of uncertainty is demonstrated for plane channel flow, for a duct with secondary flows, and for the shock/boundary-layer interaction over a transonic bump.
Study of transmission line attenuation in broad band millimeter wave frequency range
Authors: Pandya Hitesh Kumar B. , Austin M. E. , Ellis R. F.
Published: October 2013

Broad band millimeter wave transmission lines are used in fusion plasma diagnostics such as electron cyclotron emission (ECE), electron cyclotron absorption, reflectometry and interferometry systems. In particular, the ECE diagnostic for ITER will require efficient transmission over an ultra wide band, 100 to 1000 GHz. A circular corrugated waveguide transmission line is a prospective candidate to transmit such wide band with low attenuation. To evaluate this system, experiments of transmission line attenuation were performed and compared with theoretical loss calculations. A millimeter wave Michelson interferometer and a liquid nitrogen black body source are used to perform all the experiments. Atmospheric water vapor lines and continuum absorption within this band are reported. Ohmic attenuation in corrugated waveguide is very low; however, there is Bragg scattering and higher order mode conversion that can cause significant attenuation in this transmission line. The attenuation due to miter bends, gaps, joints, and curvature are estimated. The measured attenuation of 15 m length with seven miter bends and eighteen joints is 1 dB at low frequency (300 GHz) and 10 dB at high frequency (900 GHz), respectively.
Extremely high electron mobility in isotopically-enriched 28Si two-dimensional electron gases grown by chemical vapor deposition
Authors: Li Jiun-Yun , Huang Chiao-Ti , Rokhinson Leonid P. , Sturm James C.
Published: October 2013

Both depletion-mode and enhancement-mode two-dimensional electron gases (2DEGs) in isotopically enriched 28Si with extremely high mobility (522 000 cm2/V s) are presented. The samples were grown by chemical vapor deposition using enriched silane. The fraction of the spin-carrying isotope 29Si was reduced to the level of 800 ppm by 28Si enrichment, with the electron spin dephasing time expected to be as long as 2 μs. Remote impurity charges from ionized dopants and the Si/Al2O3 interface were suggested to be the dominant source for electron scattering in the enriched 28Si 2DEGs.
Molecular density functional theory of water describing hydrophobicity at short and long length scales
Authors: Jeanmairet Guillaume , Levesque Maximilien , Borgis Daniel
Published: October 2013

We present an extension of our recently introduced molecular density functional theory of water [G. Jeanmairet et al., J. Phys. Chem. Lett. 4, 619 (2013)] to the solvation of hydrophobic solutes of various sizes, going from angstroms to nanometers. The theory is based on the quadratic expansion of the excess free energy in terms of two classical density fields: the particle density and the multipolar polarization density. Its implementation requires as input a molecular model of water and three measurable bulk properties, namely, the structure factor and the k-dependent longitudinal and transverse dielectric susceptibilities. The fine three-dimensional water structure around small hydrophobic molecules is found to be well reproduced. In contrast, the computed solvation free-energies appear overestimated and do not exhibit the correct qualitative behavior when the hydrophobic solute is grown in size. These shortcomings are corrected, in the spirit of the Lum-Chandler-Weeks theory, by complementing the functional with a truncated hard-sphere functional acting beyond quadratic order in density, and making the resulting functional compatible with the Van-der-Waals theory of liquid-vapor coexistence at long range. Compared to available molecular simulations, the approach yields reasonable solvation structure and free energy of hard or soft spheres of increasing size, with a correct qualitative transition from a volume-driven to a surface-driven regime at the nanometer scale.
Calculation of driving force and local order to predict the favored and optimized compositions for Mg-Cu-Ni metallic glass formation
Authors: Wang Q. , Li J. H. , Cui Y. Y. , Liu J. B. , Liu B. X.
Published: October 2013

Based on a newly constructed Mg-Cu-Ni n-body potential, atomistic simulations revealed the underlying mechanism of metallic glass formation is the crystalline lattice collapsing while solute concentration exceeding a critical value, and predicted a quadrilateral region in the composition triangle, energetically favoring the formation of ternary Mg-Cu-Ni metallic glasses. Moreover, an optimized stoichiometry area around Mg60Cu17Ni23 was further located, at which the driving force for transforming the crystalline solid solution into a disordered state, i.e., the glassy phase reaches its maximum. Furthermore, by characterizing the local environments, the frustration of crystallization favorable short-range orders was revealed to be correlated with the optimum glass forming ability (GFA) in Mg-Cu-Ni system, interpreting the structural orgin of GFA and lending further support to the prediction results.
Progress of laser ablation for accelerator mass spectroscopy at ATLAS utilizing an ECRIS
Authors: Scott R. , Palchan T. , Pardo R. , Vondrasek R. , Kondev F. , Nusair O. , Peters C. , Paul M. , Bauder W. , Collon P.
Published: October 2013

Beams of ions from the laser ablation method of solid materials into an electron cyclotron resonance ion source (ECRIS) plasma have been used for the first time in experiments at ATLAS. Initial accelerator mass spectroscopy experiments using laser ablation for actinides and samarium have been performed. Initial results of coupling the laser system to the ECR source have guided us in making a number of changes to the original design. The point of laser impact has been moved off axis from the center of the ECR injection side. Motor control of the laser positioning mirror has been replaced with a faster and more reliable piezo-electric system, and different raster scan patterns have been tested. The use of the laser system in conjunction with a multi-sample changer has been implemented. Two major problems that are being confronted at this time are beam stability and total beam intensity. The status of the development will be presented and ideas for further improvements will be discussed.
Evaluation of thermal conductivity of single carbon nanotubes in air and liquid using a fluorescence temperature sensor
Authors: Maruyama H. , Kariya R. , Arai F.
Published: October 2013

We propose a method for evaluating thermal conductivity of a single carbon nanotube (CNT) using a fluorescent temperature sensor in liquid and air. The CNT is fixed to sensors by photofabrication. The electrode for Joule-heating of the CNT is fabricated on the sensor. Thermal conductivity of the CNT is evaluated through the temperature difference between both ends of the CNT and the heat quantity input to the CNT. In this paper, we evaluated thermal conductivity of the same CNT in air and liquid. Calculated thermal conductivity of the CNT in air (667 ± 38 [W/m·K]) is higher than that of CNT in water (484 ± 72 [W/m·K]).
High-functionality star-branched macromolecules: Polymer size and virial coefficients
Authors: Randisi Ferdinando , Pelissetto Andrea
Published: October 2013

We perform high-statistics Monte Carlo simulations of a lattice model to compute the radius of gyration Rg, the center-to-end distance, the monomer distribution, and the second and third virial coefficients of star polymers for a wide range of functionalities f, 6 ⩽ f ⩽ 120. We consider systems with a large number L of monomers per arm (100 ≲ L ≲ 1000 for f ⩽ 40 and 100 ≲ L ≲ 400 for f = 80, 120), which allows us to determine accurately all quantities in the scaling regime. Results are extrapolated to determine the behavior of the different quantities in the limit f → ∞. Structural results are finally compared with the predictions of the Daoud-Cotton model. It turns out that the blob picture of a star polymer is essentially correct up to the corona radius Rc, which depends on f and which varies from 0.7Rg for f = 6 to 1.0Rg for f = 40. The outer region (r > Rc), in which the monomer distribution decays exponentially, shrinks as f increases, but it does not disappear in the scaling regime even in the limit f → ∞. We also consider the Daoud-Cotton scaling relation \documentclass[12pt]{minimal}\begin{document}$R^2_g \sim f^{1-\nu } L^{2\nu }$\end{document}Rg2∼f1−νL2ν, which is found to hold only for f ≫ 100.
Measurements of Linac4 H− ion source beam with a magnetized Einzel lens electron dump
Authors: Midttun Øystein , Lettry Jacques , Scrivens Richard
Published: October 2013

Linac4 is a part of the upgrade of CERN’s accelerator complex for increased luminosity in the Large Hadron Collider (LHC). A new system to extract the ion beam from the plasma generator has been designed and tested, in order to improve the reliability and beam optics of the pulsed H− ion source. This paper presents the successfully implemented extraction system and three different beam measurements. The simulations compare well to the measurements and show that the plasma density was too low for the extraction system design during the measurements.
Structural, electronic, and optical properties of hybrid silicene and graphene nanocomposite
Authors: Hu Wei , Li Zhenyu , Yang Jinlong
Published: October 2013

Structural, electronic, and optical properties of hybrid silicene and graphene (S/G) nanocomposite are examined with density functional theory calculations. It turns out that weak van der Waals interactions dominate between silicene and graphene with their intrinsic electronic properties preserved. Interestingly, interlayer interactions in hybrid S/G nanocomposite induce tunable p-type and n-type doping of silicene and graphene, respectively, showing their doping carrier concentrations can be modulated by their interfacial spacing.
A multi-state fragment charge difference approach for diabatic states in electron transfer: Extension and automation
Authors: Yang Chou-Hsun , Hsu Chao-Ping
Published: October 2013

The electron transfer (ET) rate prediction requires the electronic coupling values. The Generalized Mulliken-Hush (GMH) and Fragment Charge Difference (FCD) schemes have been useful approaches to calculate ET coupling from an excited state calculation. In their typical form, both methods use two eigenstates in forming the target charge-localized diabatic states. For problems involve three or four states, a direct generalization is possible, but it is necessary to pick and assign the locally excited or charge-transfer states involved. In this work, we generalize the 3-state scheme for a multi-state FCD without the need of manual pick or assignment for the states. In this scheme, the diabatic states are obtained separately in the charge-transfer or neutral excited subspaces, defined by their eigenvalues in the fragment charge-difference matrix. In each subspace, the Hamiltonians are diagonalized, and there exist off-diagonal Hamiltonian matrix elements between different subspaces, particularly the charge-transfer and neutral excited diabatic states. The ET coupling values are obtained as the corresponding off-diagonal Hamiltonian matrix elements. A similar multi-state GMH scheme can also be developed. We test the new multi-state schemes for the performance in systems that have been studied using more than two states with FCD or GMH. We found that the multi-state approach yields much better charge-localized states in these systems. We further test for the dependence on the number of state included in the calculation of ET couplings. The final coupling values are converged when the number of state included is increased. In one system where experimental value is available, the multi-state FCD coupling value agrees better with the previous experimental result. We found that the multi-state GMH and FCD are useful when the original two-state approach fails.
Theoretical study on reaction mechanism and kinetics of HNCS with CN
Authors: Sun Cuihong , Liu Ying , Xu Baoen , Zeng Yanli , Meng Lingpeng , Zhang Shaowen
Published: October 2013

We presented a theoretical study on the detailed reaction mechanism and kinetics of the CN radical with the HNCS molecule. The barrierless minimum energy path and the most favorable entrance channel have been determined by constructing a two-dimensional potential energy surface of the C atom of CN attacking the HNCS molecule. The reaction of the C atom attacking the S atom was finally identified as the dominant entrance channel based on the rate constants' results calculated with the canonical variational transition state theory. The master equation method was employed to calculate the products' branching ratios, the overall rate constant, and the pressure dependence of the title reaction. The B3LYP/6-311+G(2d,p) method was employed for all the geometrical optimizations and a multi-level extrapolation method based on the CCSD(T) and MP2(FC) energies was employed for further energy refinements.
Effects of exciton localization on internal quantum efficiency of InGaN nanowires
Authors: Murotani Hideaki , Yamada Yoichi , Tabata Takuya , Honda Yoshio , Yamaguchi Masahito , Amano Hiroshi
Published: October 2013

The optical properties of InGaN nanowires with different emission wavelengths of 485, 515, 555, and 580 nm have been studied by means of photoluminescence (PL) and time-resolved PL (TRPL) spectroscopy. The PL peak energy of the nanowires exhibited an anomalous shift to higher energy and then to lower energy with increasing temperature. Analysis of the temperature-dependent variations in the PL peak energy let us evaluate the localization energies of excitons, which increased with increasing indium composition. TRPL measurements also revealed that the PL decay time of the nanowires increased and then became constant with decreasing emission energy, which was typical of localized excitons and enabled us to evaluate the characteristic energies of localized states. The characteristic energy increased with increasing indium composition, indicating that the density of localized states broadened with increasing indium composition. In addition, a correlation was clearly observed between the internal quantum efficiency (IQE) and localization energy of the nanowire: the IQE increased with increasing localization energy. The increase in the IQE was attributed to the increase in the degree of exciton localization as the indium composition of the nanowire increased. Moreover, it was found that with increasing excitation power density, a reduction in the IQE occurred simultaneously with a PL blue shift. This indicated that the reduction in the IQE was associated with saturation of localized states.
Dynamic response of silicon nanostructures at finite frequency: An orbital-free density functional theory and non-equilibrium Green's function study
Authors: Xu Fuming , Wang Bin , Wei Yadong , Wang Jian
Published: October 2013

Orbital-free density functional theory (OFDFT) replaces the wavefunction in the kinetic energy by an explicit energy functional and thereby speeds up significantly the calculation of ground state properties of the solid state systems. So far, the application of OFDFT has been centered on closed systems and less attention is paid on the transport properties in open systems. In this paper, we use OFDFT and combine it with non-equilibrium Green's function to simulate equilibrium electronic transport properties in silicon nanostructures from first principles. In particular, we study ac transport properties of a silicon atomic junction consisting of a silicon atomic chain and two monoatomic leads. We have calculated the dynamic conductance of this atomic junction as a function of ac frequency with one to four silicon atoms in the central scattering region. Although the system is transmissive with dc conductance around 4 to 5 e2/h, capacitive-like behavior was found in the finite frequency regime. Our analysis shows that, up to 0.1 THz, this behavior can be characterized by a classic RC circuit consisting of two resistors and a capacitor. One resistor gives rise to dc resistance and the other one accounts for the charge relaxation resistance with magnitude around 0.2 h/e2 when the silicon chain contains two atoms. It was found that the capacitance is around 5 aF for the same system.
Enhancement of higher harmonics in graphene-based coupled coplanar line microwave multipliers
Authors: Dragoman Mircea , Cismaru Alina , Dinescu Adrian , Dragoman Daniela , Stavrinidis G. , Konstantinidis G.
Published: October 2013

In this manuscript, we present results regarding frequency multiplication of microwave signals by means of graphene-based coupled coplanar line multipliers. In deep contrast with all multipliers where the power of higher harmonics decrease with frequency, in this graphene-based device the output power of higher harmonics increase with frequency due to the special configuration of the circuit which assures a constant loss beyond 30 GHz, while the losses in graphene decrease with frequency.
Predictive modeling of pedestal structure in KSTAR using EPED model
Authors: Han Hyunsun , Kwon Ohjin , Kim J. Y.
Published: October 2013

A predictive calculation is given for the structure of edge pedestal in the H-mode plasma of the KSTAR (Korea Superconducting Tokamak Advanced Research) device using the EPED model. Particularly, the dependence of pedestal width and height on various plasma parameters is studied in detail. The two codes, ELITE and HELENA, are utilized for the stability analysis of the peeling-ballooning and kinetic ballooning modes, respectively. Summarizing the main results, the pedestal slope and height have a strong dependence on plasma current, rapidly increasing with it, while the pedestal width is almost independent of it. The plasma density or collisionality gives initially a mild stabilization, increasing the pedestal slope and height, but above some threshold value its effect turns to a destabilization, reducing the pedestal width and height. Among several plasma shape parameters, the triangularity gives the most dominant effect, rapidly increasing the pedestal width and height, while the effect of elongation and squareness appears to be relatively weak. Implication of these edge results, particularly in relation to the global plasma performance, is discussed.
Power-law spatial dispersion from fractional Liouville equation
Authors: Tarasov Vasily E.
Published: October 2013

A microscopic model in the framework of fractional kinetics to describe spatial dispersion of power-law type is suggested. The Liouville equation with the Caputo fractional derivatives is used to obtain the power-law dependence of the absolute permittivity on the wave vector. The fractional differential equations for electrostatic potential in the media with power-law spatial dispersion are derived. The particular solutions of these equations for the electric potential of point charge in this media are considered.
Static and low frequency noise characterization of N-type random network of carbon nanotubes thin film transistors
Authors: Joo Min-Kyu , Mouis Mireille , Jeon Dae-Young , Kim Gyu-Tae , Kim Un Jeong , Ghibaudo Gérard
Published: October 2013

Static and low frequency noise (LFN) characterizations in two-dimensional (2D) N-type random network thin film transistors (RN-TFTs) based on single-walled carbon nanotubes were presented. For the electrical parameter extraction, the Y-function method was used to suppress the series resistance (Rsd) influence. The gate-to-channel capacitance (Cgc) was directly measured by the split capacitance-to-voltage method and compared to 2D metal-plate capacitance model (C2D). In addition, to account for the percolation-dominated 2D RN-TFTs, a numerical percolation simulation was performed. LFN measurements were also carried out and the results were well interpreted by the carrier number and correlated mobility fluctuation model. Finally, one-dimensional (1D) cylindrical analytical capacitance based model (C1D) was suggested and applied to provide better consistency between all electrical parameters based on experimental and simulation results.
On secondary and tertiary instability in electromagnetic plasma microturbulence
Authors: Pueschel M. J. , Görler T. , Jenko F. , Hatch D. R. , Cianciara A. J.
Published: October 2013

Zonal flows, widely accepted to be the secondary instability process leading to the nonlinear saturation of ion temperature gradient modes, are shown to grow at higher rates relative to the linear mode amplitude as the plasma pressure β is increased—thus, confirming that zonal flows become increasingly important in the turbulent dynamics at higher β. At the next level of nonlinear excitation, radial corrugations of the distribution function (zonal flow, zonal density, and zonal temperature) are demonstrated to modify linear growth rates moderately through perturbed-field, self-consistent gradients: on smaller scales, growth rates are reduced below the linear rate. In particular, excitation of kinetic ballooning modes well below their usual threshold is not to be expected under normal conditions. These findings strengthen the theory of the non-zonal transition [M. J. Pueschel et al., Phys. Rev. Lett. 110, 155005 (2013)].
Modified Drude model for free-carrier absorption due to bound-to-continuum transition in quantum-dot semiconductor optical amplifier
Authors: Li Xiaoming , Wang Tao , Dong Chuanbo , Tang Jian , Liu Bo , He Yu
Published: October 2013

Within the framework of the second-order perturbation theory, a model is presented to calculate the cross-section of the free-carrier absorption (FCA) due to phonon-assisted bound-to-continuum transition in quantum-dot semiconductor optical amplifier (QD-SOA). It is shown that the cross-section of the FCA in QD layer is much larger than that in bulk system when the photon energy is in the vicinity of the carrier binding energy. Conversely, when the photon energy is very large, the coefficients of the FCA for QD system and bulk system are on the same level of magnitude. And these conclusions agree well with the classical theoretical model and experimental results reported previously. In order to develop a simple and exact model to predict the FCA due to bound-to-continuum transition, a modified Drude model is proposed. The modified model contains the carrier's confinement energy between the quantum dot layer and the barrier layer. The results show that the absorption cross-section calculated from first principles is given asymptotically by the modified Drude model at room temperature, especially when the binding energy is very large.
Oxygen vacancy induced photoluminescence and ferromagnetism in SrTiO3 thin films by molecular beam epitaxy
Authors: Xu Wenfei , Yang Jing , Bai Wei , Tang Kai , Zhang Yuanyuan , Tang Xiaodong
Published: October 2013

SrTiO3 thin films were epitaxially grown on (100) SrTiO3 substrates using molecular beam epitaxy. The temperature for growth of the films was optimized, which was indicated by x-ray diffraction and further confirmed by microstructural characterization. Photoluminescence spectra show that oxygen-vacancy contributes to red and blue luminescence of oxygen-deficient post-annealed films, and a red shift was observed in blue region. On the other hand, ferromagnetism in film form SrTiO3 was observed from 5 K to 400 K and could be further enhanced with decreasing oxygen plasma partial pressure in annealing processes, which might be explained by the theory involving d0 magnetism related to oxygen-vacancy. From the cooperative investigations of optical and magnetic properties, we conclude that intrinsic defects, especially oxygen-vacancy, can induce and enhance luminescence and magnetism in SrTiO3 films.
Silver nanorod arrays for photocathode applications
Authors: Vilayurganapathy Subramanian , Nandasiri Manjula I. , Joly Alan G. , El-Khoury Patrick Z. , Varga Tamas , Coffey Greg , Schwenzer Birgit , Pandey Archana , Kayani Asghar , Hess Wayne P. , Thevuthasan Suntharampillai
Published: October 2013

We explore the use of plasmonic Ag nanorod arrays featuring enhanced photoemission as high-brightness photocathode material. Silver nanorod arrays are synthesized by the direct current electrodeposition method and their dimensionality, uniformity, crystallinity, and oxide/impurity content are characterized. The yielded arrays exhibit greatly enhanced two-photon photoemission under 400 nm femtosecond pulsed laser excitation. Plasmonic field enhancement in the array produces photoemission hot spots that are mapped using photoemission electron microscopy. The relative photoemission enhancement of nanorod hot spots relative to that of a flat Ag thin film is found to range between 102 and 3 × 103.
Excitonic bandgap dependence on stacking configuration in four layer graphene
Authors: Liu Y. P. , Goolaup S. , Lew W. S. , Purnama I. , Chandra Sekhar M. , Zhou T. J. , Wong S. K.
Published: October 2013

Different crystallographic stacking configurations in graphene provide an additional degree of freedom in the electronic structure. We have conducted systematic investigations of the transport properties of ABAB- and ABCA-stacked four-layer graphene. Our results reveal that ABAB and ABCA graphene exhibit markedly different properties as functions of both temperature and magnetic field. The temperature-dependant resistance measurement reveals that the excitonic gap of ABCA stacked graphene increases as a function of temperature, while for ABAB, a shrinking excitonic gap configuration is observed.
Low temperature transport in p-doped InAs nanowires
Authors: Upadhyay S. , Jespersen T. S. , Madsen M. H. , Krogstrup P. , Nygård J.
Published: October 2013

We present low temperature electrical measurements of p-type Indium Arsenide nanowires grown via molecular beam epitaxy using Beryllium as a dopant. Growth of p-type wires without stacking faults is demonstrated. Devices in field-effect geometries exhibit ambipolar behavior, and the temperature dependence of electron and hole field effect mobilities are extracted. At low temperatures, we observe reproducible conductance fluctuations as a result of quantum interference, and magnetoconductance data show weak antilocalization.
Loss of anisotropy in strained ultrathin epitaxial L1 Mn-Ga films
Authors: Köhler Albrecht , Knez Ivan , Ebke Daniel , Felser Claudia , Parkin Stuart S. P.
Published: October 2013

We have investigated the magnetization and loss of anisotropy in ultrathin strained and unstrained Mn-Ga films at room temperature. Two Mn-Ga compositions, one of which is doped with Co, were grown on Cr buffered MgO (001) substrates. Films with a thickness below 10 nm are highly strained and the ratio c/a vs. thickness is depending on composition. The perpendicular magnetic anisotropy is shown to be drastically reduced with decreasing thickness and increasing strain. These findings should be considered when generalizing and downscaling results obtained from films > 20 nm. The strain can effectively be reduced by introducing an additional Pt buffer and thus maintaining a high perpendicular magnetic anisotropy for a thickness as low as 6 nm.
Investigation of ion beam induced nanopattern formation near the threshold energy
Authors: Metya Amaresh , Ghose Debabrata
Published: October 2013

The nanoscale ripple formation on mica surface is studied at off-normal ion incidence angles θ under Ar+ bombardment at energies E close to or below the threshold energy for physical sputtering. A phase diagram for domains of pattern formation is presented as a function of θ and E, which shows the stability/instability bifurcation angle close to 40°. The instability grows as ripple-like structures at lower angles, while at grazing angles the pattern emerges as dense array of needles. The results support the pure mass redistribution based paradigm for surface patterning as the erosion due to sputtering essentially tends to zero.
Electronic, transport, optical, and structural properties of rocksalt CdO
Authors: Ekuma Chinedu E. , Moreno Juana , Jarrell Mark
Published: October 2013

We report electronic, optical, and structural properties of rocksalt CdO as obtained from first-principle calculations with both the Tran-Blaha modified Becke-Johnson potential using linearized augmented planewave method in WIEN2k and local density approximation (LDA) potential using the LDA Bagayoko-Zhao-Williams-Ekuma-Franklin (BZW-EF) method in implementing the linear combination of Gaussian orbitals. The results are discussed in relation to existing experimental data, particularly to the Burstein–Moss effect.
Tunable density of two-dimensional electron gas in GaN-based heterostructures: The effects of buffer acceptor and channel width
Authors: Peng Enchao , Wang Xiaoliang , Xiao Hongling , Wang Cuimei , Yin Haibo , Chen Hong , Feng Chun , Jiang Lijuan , Qu Shenqi , Kang He , Hou Xun , Wang Zhanguo
Published: October 2013

This is a theoretical study of GaN-based heterostructures with unintentionally doped (UID) GaN channel layer and high-resistivity (HR) GaN buffer layer doped by deep acceptors. Self-consistent Schrödinger-Poisson (SP) numerical simulation shows that, by increasing the acceptor concentration in the HR buffer or narrowing the width of UID channel, the quantum confinement of two-dimensional electron gas (2DEG) is enhanced, while the sheet density of 2DEG is reduced. The tuning effect of 2DEG density is attributed to the depletion effect of negative space charges composed of ionized acceptors located in the region between the UID channel and the Fermi-level pinned region in the HR buffer. For the heterostructure without the UID channel, the 2DEG can be depleted as the acceptor concentration is beyond a critical value. However, by inserting a UID channel layer, the depletion effect of buffer acceptor on 2DEG density is reduced. To gain a further insight into the physics, a simple analytical model is developed, which reproduces well the results of SP simulation. By comparing our theoretical results with the experimental ones, a good agreement is reached, thus the validity of our model is verified.
Effect of residual stress on energy storage property in PbZrO3 antiferroelectric thin films with different orientations
Authors: Ge Jun , Remiens Denis , Costecalde Jean , Chen Ying , Dong Xianlin , Wang Genshui
Published: October 2013

The effect of residual stress on energy storage property was investigated for a series of PbZrO3 thin films on SrTiO3 and Si substrates. Compressive or tensile residual stress influences the critical electric field EA for the ferroelectric-to-antiferroelectric phase transition, thus for films with (110)/(101) orientation, energy density W of films on SrTiO3 is 38% larger than films on Si; in contrast, (001)-oriented PbZrO3 films on SrTiO3 show slightly smaller W compared to films on Si. We conclude that the different responses of W to stress are related to the different constrain states in films with different orientations.
Note: Resistance spot welding using a microgripper
Authors: Hwang G. , Podrzaj P. , Hashimoto H.
Published: October 2013

Interest in thin-film nanostructures as building blocks for nanoelectronics and nanoelectromechanical systems (NEMS) is increasing. Resistance spot welding (RSW) on a nano or micro scale can play a significant role; similar to that of its macro counterpart for forming connections in device assembly processes. This Note presents a novel micron scale RSW technique using a microgripper as mobile spot welding electrodes to assemble ultra-thin film nanostructures. As an example, assembly of three-dimensional helical nanobelt (HNB) based device was successfully demonstrated using the proposed system. The spot-welding process was fully monitored by the built-in capacitive micro force sensor of the microgripper. Experiments show that RSW, using the microgripper, provides a stable electrical contact with sufficient mechanical strength for the construction of devices such as HNB based devices demonstrated here.
How Regional Inequality Affects Fiscal Decentralisation: Accounting for the Autonomy of Subcentral Governments
Authors: Sacchi Agnese , Salotti Simone
Published: October 2013

The aim of this paper is to analyse the influence of regional economic disparities on the fiscal decentralisation processes in twenty-one OECD countries over the period 1981 to 2005. We use novel and robust measures of fiscal decentralisation based on different degrees of autonomy over both expenditures and taxes granted to subcentral governments. Our results show that high regional economic disparities call for lower fiscal decentralisation. This could be interpreted as the outcome of a bargaining process driven by the relative strength and different incentives of rich and poor regions. Moreover, the extent to which responsibility and decision powers are really left to subcentral governments appears to be crucial. Thus, from a positive point of view, equity considerations seem to suggest avoidance of fiscal decentralisation processes in countries with significant regional economic disparities, notwithstanding the well-known efficiency gains.
Delivering Planning Objectives through Regional-Based Land-Use Planning and Land Policy Instruments: An Assessment of Recent Experiences in the Dutch Provinces
Authors: van Straalen Fennie M , Janssen-Jansen Leonie B , van den Brink Adri
Published: October 2013

This paper evaluates the extent to which the introduction of four new regional planning and land policy instruments in the Netherlands improves the delivery of regional planning objectives. On the basis of case-study research, we identify why and to what extent the Dutch regional authorities—the provinces—have adopted these new instruments and assess whether or not the instruments offer opportunities for improving the delivery of regional planning objectives. The study shows that regional policies and plans are often implemented without consideration of their consequences for national or local planning objectives. As a result, the instruments may not address current policy delivery needs, and may even compound local policy failures. We conclude that the use of such instruments should be accompanied by a more thorough discussion of regional planning tasks and objectives, and a debate on the role of regional authorities within the multilevel governance setting.
Syntheses, Crystal Structures, and Properties of Six Coordination Complexes Based on a Newly Designed Mercapto-thiadiazole Ligand
Authors: Wei Lu-Lu , Li Lin-Ke , Fan Li-Yan , Wang Chang-Hong , Hou Hong-Wei
Published: October 2013

Six coordination complexes were solvothermally synthesised: a 3D framework [Cd(tmtt)2]n (1), 2D architectures [Zn(tmtt)2]n (2) and [Pb(tmtt)2]n (3), 1D chain structures [Ni(tmtt)2·(H2O)2]n (4) and [Co(tmtt)2·(H2O)2]n (5), and a mononuclear structure [Hg(tmtt)2] (6). The complexes, based on self-assembly of different metal ions with a newly designed mercapto-thiadiazole ligand tmttH (tmttH = 5-[(1H-1,2,4-triazol-1-yl)methyl]-1,3,4-thiadiazole-2(3H)-thione), were characterised by single crystal X-ray diffraction analyses. Crystal structure analyses reveal that complex 1 exhibits a four-fold interpenetrating 3D framework with {64.82} topology based on two kinds of right-handed single-helical chains, 2 displays a bilayer structure, 3 presents a crown-shaped network, 4 and 5 show 1D double–helical chain structures, and 6 is a mononuclear structure. Moreover, the thermal stabilities of crystalline samples 1–6 have been investigated, and the luminescent properties of complexes 1, 2, 3, 6, and the free ligand have been studied. The results of photoluminescent measurements illustrate that 2 and 3 may serve as excellent candidates for potential photoactive materials.
Depressed pacemaker activity of sinoatrial node myocytes contributes to the age-dependent decline in maximum heart rate
Authors: Larson Eric D. , St. Clair Joshua R. , Sumner Whitney A. , Bannister Roger A. , Proenza Cathy
Published: October 2013

Significance

Maximum heart rate (mHR) declines with age, contributing to the reduced aerobic capacity of the elderly. A parallel reduction in "intrinsic heart rate" (which is measured during autonomic blockade) underlies the decline in mHR, and indicates that pacemaker function of the sinoatrial node is compromised during aging. In this study we demonstrate that the slower heart rates in the elderly result from depressed spontaneous activity of individual sinoatrial node myocytes (SAMs). Patch-clamp electrophysiology revealed that aged SAMs have slowed AP firing rates, altered AP waveforms, and changed properties of Ca
2+
currents and the cardiac "funny current,"I
f
. Our findings demonstrate that age-dependent changes ion channel activity in SAMs are a major cause of the decline in mHR during aging.
Native contacts determine protein folding mechanisms in atomistic simulations
Authors: Best Robert B. , Hummer Gerhard , Eaton William A.
Published: October 2013

Significance

Understanding the mechanism by which proteins fold to their native structure is a central problem in protein science. Clearly, interactions between residues that are in contact in the folded state (native interactions) are likely to be important for folding, but, in principle, nonnative interactions may play a role. Here, we use recently published microsecond to millisecond all-atom molecular dynamics simulations of proteins folding and unfolding to show, remarkably, that nonnative contacts are irrelevant to the mechanism of folding in most cases. This statistical analysis would be very difficult to perform by experiment. Although this is a limited set of proteins, the results nonetheless strongly support coarse-grained theoretical and simulation models of folding in which only native contacts are energetically favorable.
Ca
2+
ionophore A23187 can make mouse spermatozoa capable of fertilizing in vitro without activation of cAMP-dependent phosphorylation pathways
Authors: Tateno Hiroyuki , Krapf Dario , Hino Toshiaki , Sánchez-Cárdenas Claudia , Darszon Alberto , Yanagimachi Ryuzo , Visconti Pablo E.
Published: October 2013

Significance

Sperm capacitation enables spermatozoa to undergo the acrosome reaction and to exhibit vigorous motility called hyperactivation. At the molecular level, capacitation is associated with activation of a cAMP-dependent pathway and with the increase of intracellular pH and Ca
2+
concentrations. Ca
2+
ionophore A23187 elevates intracellular Ca
2+
and induces the acrosome reaction but renders the spermatozoa motionless. However, when the ionophore was washed away, spermatozoa recovered motility, showed hyperactivation, and were able to fertilize cumulus-intact eggs. In these conditions, sperm acquired fertilizing capacity even when the cAMP pathway was inactivated. Fertilized oocytes with A23187-treated sperm developed into normal offspring. These data indicate that a short elevation of intracellular Ca
2+
overcomes other necessary signaling pathways during capacitation and renders sperm fertile.
Party dominance and electoral institutions: framing Frelimo’s dominance in the context of an electoral governance deficit
Authors: Nuvunga Adriano , Salih M.A. Mohamed
Published: October 2013

Focusing on Frelimo’s dominance over party politics and state institutions, this article analyses the issues pertaining to the role of electoral institutions in the consolidation of this dominant position. The authors argue that in order to understand party dominance in Mozambique, it is necessary that there should be an historical perspective linking the present (that is, the constitutional reforms since the 1990s) to the past. These reforms paved the way for ‘democratisation from above’, which has continued ever since. Rather than resolving differences over electoral processes through democratic governance norms and regulatory frameworks, Frelimo has intimidated existing and emerging political parties through its control of electoral governance institutions. Frelimo’s electoral success in the first democracy-founding election became an intermittent strategy of choice facilitating its manoeuvring for winning subsequent elections, thus controlling and dominating political life. One outcome of this process is that political horse-trading has generated skewed ‘incentive structures’ that have compromised the role of opposition political parties and electoral governance institutions.
University–industry linkages and knowledge creation in Eastern and Southern Africa: some prospects and challenges
Authors: Mihyo Paschal B.
Published: October 2013

The development of technical and technological capabilities through research and innovation has dominated the African development agenda since adoption of the Lagos Plan of Action, 1980 through to the current policies of the African Union, the African Development Bank, the New Partnership for Africa’s Development (Nepad), and the African regional economic communities. University-industry linkages are the best modality for achieving this goal. In Africa, however, these linkages are weak. Where they do exist, they are based on short-term, individualised projects. Industries lack a robust research and development base to absorb knowledge generated by research and innovation institutions. Governments do not provide adequate incentives for such linkages and universities lack the mandate, organisational structures, human resources management policies, modalities for promoting the protection of intellectual property rights generated by research and innovation activities, and the necessary incentive schemes to nurture, capture, and reward talent and innovation. In order to overcome these obstacles, creative and adaptive policies are required to strengthen these linkages through financial support to industries and universities, and incentives conducive to long-term co-operation between them.
Attentional Sets Influence Perceptual Load Effects, but not Dilution Effects
Authors: Benoni Hanna , Zivony Alon , Tsal Yehoshua
Published: October 2013

Perceptual load theory [Lavie, N. (1995). Perceptual load as a necessary condition for selective attention. Journal of Experimental Psychology: Human Perception and Performance, 21, 451–468.; Lavie, N., & Tsal, Y. (1994) Perceptual load as a major determinant of the locus of selection in visual attention. Perception & Psychophysics, 56, 183–197.] proposes that interference from distractors can only be avoided in situations of high perceptual load. This theory has been supported by blocked design manipulations separating low load (when the target appears alone) and high load (when the target is embedded among neutral letters). Tsal and Benoni [(2010a). Diluting the burden of load: Perceptual load effects are simply dilution effects. Journal of Experimental Psychology: Human Perception and Performance, 36, 1645–1656.; Benoni, H., & Tsal, Y. (2010). Where have we gone wrong? Perceptual load does not affect selective attention. Vision Research, 50, 1292–1298.] have recently shown that these manipulations confound perceptual load with “dilution” (the mere presence of additional heterogeneous items in high-load situations). Theeuwes, Kramer, and Belopolsky [(2004). Attentional set interacts with perceptual load in visual search. Psychonomic Bulletin & Review, 11, 697–702.] independently questioned load theory by suggesting that attentional sets might also affect distractor interference. When high load and low load were intermixed, and participants could not prepare for the presentation that followed, both the low-load and high-load trials showed distractor interference. This result may also challenge the dilution account, which proposes a stimulus-driven mechanism. In the current study, we presented subjects with both fixed and mixed blocks, including a mix of dilution trials with low-load trials and with high-load trials. We thus separated the effect of dilution from load and tested the influence of attentional sets on each component. The results revealed that whereas perceptual load effects are influenced by attentional sets, the dilution component is not. This strengthens the notion that dilution is a stimulus-driven mechanism, which enables effective selectivity.