bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron spin resonance studies of Bi0.6Ca(0.4−x)SrxMnO3
Authors: Kurian Joji , Singh R.
Published: April 2010

The temperature dependent electron spin resonance (ESR) studies were carried out on Bi0.6Ca(0.4−x)SrxMnO3 (0≤x≤0.4). The variation of charge ordering temperature, TCO, and Néel temperature, TN, are obtained from plots of double integrated (DI) intensity and linewidth (ΔH) of the ESR signal as a function of temperature. In the temperature range T>TCO, the sample is in the paramagnetic phase and the magnetic interactions are dominated by ferromagnetic (FM) spin correlations. In the range TN<T<TCO, the FM and antiferromagnetic (AFM) correlations coexist. The sample with x=0 has TCO=313 K and TN=150 K. With the increase in Sr content from the FM correlations increase resulting in the weakening of the CO and AFM transitions. The CO and the AFM transitions are barely noticed in the sample with x=0.1 indicating the melting of charge-ordered state. The CO transition reappears for x=0.16 at a temperature of ∼390 K. The growth of high TCO phases is a nonlinear evolution process with increase in Sr content.
Impact of ultrathin transition metal buffer layers on Fe3O4 thin films
Authors: Jayathilaka P. B. , Bauer C. A. , Williams D. V. , Monti M. C. , Markert J. T. , Miller Casey W.
Published: April 2010

3000 Å Fe3O4 (magnetite) thin films were simultaneously grown on (001) MgO single crystal substrates with and without 30 Å buffer layers of Fe, Cr, Mo, and Nb. For all samples, the Verwey transition temperature (TV) occurs between 119 and 125 K, indicating good oxygen stoichiometry. We observe highly oriented (001) Fe3O4 with Mo and no buffer layer, reduced (001) texture with Nb and Fe, and polycrystalline growth with Cr. Mo, Cr, and unbuffered magnetite show typical magnetic behavior, whereas Nb and Fe buffers lead to anomalous magnetic properties that may be due to interfacial reactivity.
An extremely long range exchange coupling in CrTe/ZnTe/MnTe trilayer
Authors: Lu H. , Bi J. F. , Teo K. L. , Liew T. , Chong T. C.
Published: April 2010

We present the results on the exchange coupling in the zinc-blende CrTe/spacer/MnTe structure with ZnTe acting as a spacer layer (SL). The magnetic hysteresis (M-H) loops show significant shifts in both horizontal and vertical directions. A nonmonotonic variation of the exchange bias field (HE) and coercivity (HC) with the SL thickness is observed. The Curie temperature decreases as the SL thickness increases. The maximum of HE and HC values occur at a SL thickness of 12 ML (monolayer). Strikingly, the exchange coupling remains noticeable even the thickness of SL reaches 24 ML. The exchange bias field and vertical shift are discussed on the basis of frozen ferromagnetic moment model.
Magnetic nanostructures for the manipulation of individual nanoscale particles in liquid environments (invited)
Authors: Vavassori P. , Gobbi M. , Donolato M. , Cantoni M. , Bertacco R. , Metlushko V. , Ilic B.
Published: April 2010

The manipulation of geometrically constrained magnetic domain walls (DWs) in nanoscale magnetic strips attracted much interest recently, with proposals for prospective memory and logic devices. Here we demonstrate that the high controllability of the motion of geometrically constrained DWs allows for the manipulation of individual nanoparticles in solution on a chip with the active control of position at the nanometer scale. Our approach exploits the fact that magnetic nanoparticles in suspension can be captured by a DW, whose position can be manipulated with nanometer scale accuracy in specifically designed magnetic nanowire structures. We hereby show that the precise control over DW nucleation, displacement, and annihilation processes in such nanostructures allows for the capture, transport, and release of magnetic nanoparticles. As magnetic nanoparticles with functionalized surfaces are widely used as molecule carriers or labels for single molecule studies, cell manipulation, and biomagnetic sensing, the accurate control over the handling of the single magnetic nanoparticle in suspension is a crucial building block for several applications in biotechnology, nanochemistry, and nanomedicine.
All-optical 90-degree switching of magnetization in a ferromagnetic Ga0.98Mn0.02As microbar
Authors: Aoyama J. , Kobayashi S. , Munekata H.
Published: April 2010

All-optical, 90° switching of magnetization has been carried out successfully in a laterally magnetized (Ga,Mn)As microbar with a scanning laser magneto-optical microscope. No external magnetic field was applied during switching. Light was used primarily as local excitation source to elevate the lattice temperature (>TC/2) at which cubic and uniaxial anisotropies become near equal. Lithography-induced magnetic anisotropy plays a key role in that it breaks the degeneracy of fourfold cubic anisotropy of (Ga,Mn)As to a considerable extent.
Postannealing effect on properties of hydrogenated amorphous Si(Mn) magnetic semiconductors
Authors: Yao Jia-Hsien , Chen Ming-Yuan , Tsai Jai-Lin , Lan Ming-Der , Chin Tsung-Shune
Published: April 2010

Postannealing effect was studied on films of hydrogenated amorphous silicon with Mn addition grown by magnetron cosputtering. Structural, magnetic, and electrical properties were investigated. We did not detect any second phases or clusters after annealing. Annealing enhances saturation magnetization, electrical conductivity, and carrier concentration by about 250%, 350%, and two orders of magnitude, respectively. Anomalous Hall effect was observed at 100 K, indicating ferromagnetism mediated by charge carriers. Moreover, the hydrogen concentration was determined by elastic recoil detection methods. The results revealed that there is no hydrogen effusion during annealing. The reason of property enhancement by annealing arises from the thermal energy to promote hydrogen diffusion; hence, a more homogeneous distribution and lessens defect density.
Asymmetry in the reorientation process of magnetization for crossing the [11¯] and the [110] directions in Ga1−xMnxAs epilayers
Authors: Kim Yungjun , Chung Sunjae , Lee Sanghoon , Liu X. , Furdyna J. K.
Published: April 2010

The magnetization reversal processes of ferromagnetic Ga1−xMnxAs films with different Mn concentrations have been investigated using the planar Hall effect. The field scan of the planar Hall resistance (PHR) showed an asymmetric behavior for the reorientation of magnetization crossing the [11¯0] and the [110] directions. The magnetic anisotropy fields and the domain pinning field distributions of the films are obtained from the angle dependence of the PHR measurements. The magnetic anisotropy and pinning field distribution in the samples provided explanation for the observed asymmetric behavior in the magnetization reorientation process of Ga1−xMnxAs film.
Formation of coherent vortex streets and transport reduction in electron temperature gradient driven turbulence
Authors: Nakata M. , Watanabe T.-H. , Sugama H. , Horton W.
Published: April 2010

Vortex structures in slab electron temperature gradient (ETG) driven turbulence are investigated by means of a gyrokinetic simulation with high phase-space resolution. Depending on parameters that determine the eigenfrequency of the linear ETG modes, two different flow structures, i.e., statistically steady turbulence with a weak zonal flow and coherent vortex streets along a strong zonal flow, are observed. The former involves many isolated vortices and their mergers with complicated motion and leads to steady electron heat transport. When the latter is formed, phase difference and high wavenumber components of potential and temperature fluctuations are reduced, and the electron heat transport decreases significantly. It is also found that the phase matching with the potential fluctuation is correlated with the reduction in the imaginary part of the perturbed distribution function, and it occurs not only for the temperature fluctuation but also for any nth velocity moments. A traveling wave solution of a Hasegawa–Mima type equation derived from the gyrokinetic equation with the ETG agrees well with the coherent vortex streets found in the slab ETG turbulence.
Derivation of reduced two-dimensional fluid models via Dirac’s theory of constrained Hamiltonian systems
Authors: Chandre C. , Tassi E. , Morrison P. J.
Published: April 2010

We present a Hamiltonian derivation of a class of reduced plasma two-dimensional fluid models, an example being the Charney–Hasegawa–Mima equation. These models are obtained from the same parent Hamiltonian model, which consists of the ion momentum equation coupled to the continuity equation, by imposing dynamical constraints. It is shown that the Poisson bracket associated with these reduced models is the Dirac bracket obtained from the Poisson bracket of the parent model.
Time reversible molecular dynamics algorithms with holonomic bond constraints in the NPH and NPT ensembles using molecular scaling
Authors: Ingebrigtsen Trond , Heilmann Ole J. , Toxvaerd Søren , Dyre Jeppe C.
Published: April 2010

A modification of the constrained equations of motion of Kalibaeva et al. [Mol. Phys. 101, 765 (2003)] in the NPH and NPT ensembles is presented. The modified equations of motion are discretized using central-difference techniques, and the derived integrators are time reversible and conserve the invariant phase space measure. The constraint algorithm builds on the work of Toxvaerd et al. [J. Chem. Phys. 131, 064102 (2009)] in the NVE and NVT ensembles: it thus conserves the holonomic bond constraints at the finite machine precision level in the NPH and NPT ensembles. The algorithms were tested on a system of n=320 ortho-terphenyl molecules, arriving at the target temperature and pressure in a low and high pressure state. Isobaric heat capacities in the NPH and NPT ensembles were calculated for comparison using the fluctuation formulas as well as the thermodynamic definition. The heat capacities agree within the estimated uncertainties.
Chaotic mixing via streamline jumping in quasi-two-dimensional tumbled granular flows
Authors: Christov Ivan C. , Ottino Julio M. , Lueptow Richard M.
Published: April 2010

We study, numerically and analytically, the singular limit of a vanishing flowing layer in tumbled granular flows in quasi-two-dimensional rotating containers. The limiting behavior is found to be identical under the two versions of the kinematic continuum model of such flows, and the transition to the limiting dynamics is analyzed in detail. In particular, we formulate the no-shear-layer dynamical system as a piecewise isometry. It is shown how such a discontinuous map, through the concordant mechanism of streamline jumping, leads to the physical mixing of granular matter. The dependence of the dynamics of Lagrangian particle trajectories on the tumbler fill fraction is also established through Poincaré sections, and, in the special case of a half-full tumbler, chaotic behavior is shown to disappear completely in the singular limit. At other fill levels, stretching in the sense of shear strain is replaced by spreading due to streamline jumping. Finally, we use finite-time Lyapunov exponents to establish the manifold structure and understand “how chaotic” the limiting piecewise isometry is.
Main phase transition in lipid bilayers: Phase coexistence and line tension in a soft, solvent-free, coarse-grained model
Authors: Hömberg Martin , Müller Marcus
Published: April 2010

We devise a soft, solvent-free, coarse-grained model for lipid bilayer membranes. The nonbonded interactions take the form of a weighted-density functional, which allows us to describe the thermodynamics of self-assembly and packing effects of the coarse-grained beads in terms of a density expansion of the equation of state and weighting functions that regularize the microscopic bead densities, respectively. Identifying the length and energy scales via the bilayer thickness and the thermal energy scale, kBT, the model qualitatively reproduces key characteristics (e.g., bending rigidity, area per molecule, and compressibility) of lipid membranes. We employ this model to study the main phase transition between the fluid and the gel phase of the bilayer membrane. We accurately locate the phase coexistence using free energy calculations and also obtain estimates for the bare and the thermodynamic line tension.
A small radius hydrogen discharge: An effective source of volume produced negative ions
Authors: Paunska Ts. , Shivarova A. , Tarnev Kh.
Published: April 2010

Free-fall regime maintenance of hydrogen discharges is analyzed based on numerical solutions of a set of equations involving the balance equations of the charged particles [electrons, the three types of the positive ions (H+, H2+, and H3+), and negative H− ions] and of the neutral species (hydrogen atoms H and vibrationally excited molecules), the momentum equations of the positive ions, the electron energy balance equation, and the Poisson equation, all together 25 differential equations. The obtained results for varying discharge radius show strong accumulation of the negative ions in the on-axis region of the discharge when the discharge radius is small, which leads to a concept for a design of a volume-production based source as a matrix of small radius discharges. The variation in the negative ion density with changing gas pressure and electron density at the discharge axis is also analyzed.
Electric-field modulation of magnetic properties of Fe films directly grown on BiScO3–PbTiO3 ceramics
Authors: Wang Jing , Hu Jiamian , Wang Han , Jiang He , Wu Zhangben , Ma Jing , Wang Xiaohui , Lin Yuanhua , Nan C. W.
Published: April 2010

An electric-field modulation of the magnetic properties through converse magnetoelectric effect was reported in Fe films directly grown on BiScO3–PbTiO3 (BSPT) ceramics based on the magneto-optical Kerr effect. When an electric field was applied on the piezoelectric BSPT ceramics, the coercive field (Hc) of the ferromagnetic Fe films changed dramatically and an upto 60% change in Hc was observed. The Hc electric field curve essentially tracked the dependence of the piezostrain of the BSPT ceramics on the electric field, which definitely demonstrated the magnetic-mechanical-electric coupling in such film-on-substrate composite structures.
Eddy damped quasinormal Markovian theory for chemically reactive scalars in isotropic turbulence
Authors: Xia Yanjun , Liu Yang , Vaithianathan T. , Collins Lance R.
Published: April 2010

The eddy damped quasinormal Markovian theory has been applied to the mixing of three scalars undergoing an isothermal, bimolecular chemical reaction of the form: A+B→C, with a reaction rate constant that is independent of the scalar concentrations. The model is an extension of the work by Vaithianathan, Ulitsky, and Collins [Proc. Combust. Inst. 29, 2139 (2002)] to allow for unequal initial molar concentrations of the reactant species and differences in the molecular diffusivities of the three scalars, thereby enabling the effect of differential diffusion to be studied. Comparisons of the model with results from direct numerical simulations are in good agreement for the low-order statistics considered here. The model also was used to explore the effect of the parameters (Reynolds number, Schmidt number, and Damköhler number) on the scalar statistics. The results show that differential diffusion effects decrease with increasing Reynolds number, as has been observed for nonreacting scalars. However, statistics involving the product species (e.g., cross correlation coefficients ρAC and ρBC) have the opposite trend with Damköhler number, which raises the question of the role of differential diffusion for the intermediate species in a turbulent flame, where the unity Lewis number assumption is often invoked on the basis of the high Reynolds number even though the Damköhler number too is quite large.
The structure of the velocity field in a confined flow driven by an array of opposed jets
Authors: Krawczynski J. F. , Renou B. , Danaila L.
Published: April 2010

We investigate the confined flow in a new turbulence box configuration. Fluid is injected through two sets of 16 vertically opposed jets and outflows through two top/bottom porous planes. The resulting flow is generated by pairs of opposed round jets with backflow and their subsequent interactions. The research issue being addressed here is that of the dependence of the velocity field structure on two parameters: the injection Reynolds number based on jet diameter Reinj, which is varied between 6000 and 28000, and the flow geometry. The latter issue is addressed by investigating two kinds of flow geometries: (i) recirculating opposed jets (ROJ), for which the distance among two consecutive jet nozzles is 2.4 diameters and the nozzle-to-nozzle distance among each two opposed jets is 6 diameters, and (ii) simple opposed jets (SOJ), for which the distance among two consecutive jet nozzles is 4 diameters and the nozzle-to-nozzle distance among each two opposed jets is 10 diameters. The instantaneous aspect of the flow field is dominated by vortical structures and it is strongly dependent on the flow geometry. For both flow geometries, no coherence between each two consecutive pairs of jets is observed. All the statistics (dimensionless profiles of mean velocities and kinetic energy, derived quantities, and inner scales) do not depend on the Reynolds number and they are only the result of the flow geometry. The ROJ geometry leads to a flow which is characterized by strong interactions between opposed and neighboring jets which lead to both top-bottom and left-right instabilities in the central region. This leads to a strong energy and enstrophy injection, which imposes its signature on the two-dimensional kinetic energy spectra regime, characterized by a kxy−3 scaling, associated to the vortical structures present in the flow. The classical kxy−5/3 regime is very poorly represented, most likely because it is supposed to be present at scales smaller than the particle image velocimetry cut-off. Only a small volume of the chamber is characterized by local homogeneity and isotropy. The SOJ geometry is associated to flow which exhibits large regions that are locally homogeneous and isotropic. However, the top-bottom instabilities remain present. The mean pressure increase in the center of the chamber is of maximum 20% of the dynamic pressure at the inlet and decreases with increasing Reynolds number. The two-dimensional kinetic energy spectra clearly exhibit the classical kxy−5/3 scaling range; this is the signature of pure turbulence that finds enough space to develop. A fine-scale analysis is performed for both flow geometries in a particular point where the return flow is locally homogeneous, isotropic, and Gaussian. After an estimation of the mean energy dissipation rate according to various methods, we find that the Reynolds number based on the Taylor microscale scales as Reinj1/2, as in classical flows, and attains a maximum value of 350.
Shielding of a test charge: Role of plasma production and loss balance
Authors: Khrapak Sergey A. , Ivlev Alexey V. , Morfill Gregor E.
Published: April 2010

Shielding of a test charge in a highly collisional plasma is studied taking into account plasma production and loss processes. It is shown that the electric potential distribution is in general different from the conventional Debye–Hückel (exponentially screened Coulomb) form. The obtained results can be of great importance for a variety of phenomena including basic interactions, transport, phase transitions, and self-organization in conventional electron-ion and complex (dusty) plasmas.
Structural and dynamical properties of ionic liquids: Competing influences of molecular properties
Authors: Spohr Heidrun V. , Patey G. N.
Published: April 2010

Room temperature ionic liquids differ from molten salts in many ways, our work concentrates on two distinguishing features. These are large cation-anion size disparities and at least one ionic species where the center of mass and the center of charge do not coincide. In earlier work, we examined the influences of these features in isolation on simple spherical models. This paper extends this work to ionic liquid models where both features are present, and where the characteristic distance σ+−′ determining the strength of the Coulombic attractions is unconstrained. We consider the interplay among these molecular features and elucidate their relative importance to the behavior of ionic liquids. Particular attention is focused on the transport properties. We find that size disparity, charge location, and σ+−′ can all have large (often competing) effects. In our models, size disparity and small charge displacements lead to weakly bound, directional ion pairs, and the resulting asymmetric ion-counterion distribution gives rise to increased diffusion coefficients, consequently lower viscosity, and increased conductivity. These observations are analogous to effects reported in the literature, and we see similarities between the directional ion pairs in our models and directional cation-anion pairing through weak hydrogen bonding in room temperature ionic liquids. In our models, large charge displacements lead to strongly bound, long-lived, directional ion pairs, and in this regime the trends noted above are reversed, increased viscosities, and decreased conductivities are observed. Recently, creating more strongly hydrogen bonded, directional ion pairs has been put forward as possible means of achieving larger viscosity reductions. The trend reversal that we observe suggests that this might not work in practice.
Glass transition and fragility in the simple molecular glassformer CS2 from CS2–S2Cl2 solution studies
Authors: Zhao Zuofeng , Huang Wei , Richert Ranko , Angell C. Austen
Published: April 2010

With an interest in finding the fragility for a simple, single component, molecular glassformer, we have determined the dielectric relaxation and glass transition behavior for a series of glasses in the CS2–S2Cl2 and CS2-toluene systems. Crystallization of CS2 can be completely avoided down to the composition 20 mol% second component, and the fragility proves almost independent of CS2 content in each system. Since the glass temperature Tg obtained from both thermal studies and from dielectric relaxation (using Tg,diel=Tτ=100 s) is quite linear over the whole composition range in each system, and since relaxation time data for pure CS2 fall on the same master plot when scaled by the linearly extrapolated Tg value, we deduce that pure CS2 has the same high fragility as the binary solutions. The value is m=86, as for ortho-terphenyl (OTP). Based on observations of independent studies for the vibrational density of states (VDoS) (of inherent structures for OTP and instantaneous, at-temperature structures for CS2), we attribute the high fragility to an excess vibrational heat capacity (defined by Cp (vib, excess)=dS(vib, excess)/d ln T) originating in the behavior of the low frequency modes of the VDoS (the boson peak modes). Both low frequency DoS and anharmonicity increase with increasing temperature, augmenting the configurational entropy drive to the top of the system energy landscape. The surprising implication is that fragility is determined in the vibrational, not configurational, manifold of microstates.
Experimental production and identification of electron temperature gradient modes
Authors: Wei X. , Sokolov V. , Sen A. K.
Published: April 2010

The electron temperature gradient (ETG) mode, which is believed to be one of the strongest candidates for the anomalous electron energy transport in plasmas, is difficult to detect in experiments because of its high frequency (∼MHz) and short wavelength (k⊥ρe≤1). Using a dc bias heating scheme of the core plasma, we are able to produce a sufficiently strong ETG for exciting ETG modes in the Columbia linear machine [R. Scarmozzino, A. K. Sen, and G. A. Navratil, Phys. Fluids 31, 1773 (1988)]. A high frequency mode at ∼2 MHz, with azimuthal wave numbers m∼14–16 and parallel wave number k∥∼0.01 cm−1, has been observed. The frequency range is consistent with the result of a kinetic dispersion relation of slab ETG modes with appropriate E⃑×B⃑ Doppler shift. The scaling of its fluctuation level with the temperature gradient scale length and the radial structure are found to be roughly consistent with theoretical expectations. Therefore, this is one of the first direct definitive identifications of ETG modes.
Excitation of ion cyclotron waves by a spiraling ion beam in a magnetized dusty plasma cylinder
Authors: Sharma Suresh C. , Sharma Jyotsna
Published: April 2010

A spiraling ion beam propagating through a magnetized dusty plasma cylinder drives electrostatic ion cyclotron waves to instability via cyclotron interaction. Numerical calculations of the growth rate and unstable mode frequencies have been carried out for the typical parameters of dusty plasma experiments in the two limits, namely, long parallel wavelength and short parallel wavelength. It is found that as the density ratio of negatively charged dust grains to electrons increases, the unstable mode frequency and the growth rate of the instability of the ion cyclotron waves increase in both the limits. The growth rate of the instability increases by a factor of ∼2.5 when the density ratio of negatively charged dust grains changes from 1.0 to 4.0 in the limit of short parallel wavelengths. Moreover, the growth rate increases with the density ratio of negatively charged dust at higher values in the present case in the limit of long parallel wavelengths. The growth rate of the unstable mode has the largest value for the modes whose eigenfunctions peak at the location of the beam. The growth rate of the instability scales as the one-third power of the beam current in both limits.
Origin of cononsolvency, based on the structure of tetrahydrofuran-water mixture
Authors: Hao Jinkun , Cheng He , Butler Paul , Zhang Li , Han Charles C.
Published: April 2010

The origin of poly(N-isopropylacrylamide) (PNIPAM) cononsolvency in tetrahydrofuran-water (THF-water) mixture was studied from the point of view of mixed solvent structure. The dynamic equilibrium of THF-water composition fluctuation in the mixed solvent system was found to be the main variable for this cononsolvency effect. Temperature and THF content dependences of composition fluctuation were studied by a combination of small angle neutron scattering (SANS), dynamic laser light scattering, and viscometry. A lower critical solution temperature (LCST) type phase diagram for THF-water mixture was established by SANS. The composition fluctuation in THF-water system reaches the maximum at about 20 mol % THF content at constant temperature and increases with temperature as getting closer to the phase boundary. This kind of composition fluctuation induces PNIPAM cononsolvency. When the THF content is lower than 4.5 mol %, the composition fluctuation influence of the THF-water structure is quite weak and most of water structure is not disturbed. Then, at low THF content, poly(N-isopropylacrylamide-co-ethylene glycol) (PNIPAM-co-PEG) microgel can still form hydrogen bonds with water and exist in the swollen state. The basic phase transition behavior of the microgel in THF-water is relatively similar to that in pure water, except for the shift of LCST to lower temperature. With THF content increasing to 20 mol %, the influence of composition fluctuation in the THF-water mixture becomes dominant. Solvent-solvent interaction is stronger than mixed solvent-polymer interaction. So PNIPAM does not dissolve in the mixed solvent, and the microgel is in the collapsed state. Further increase in THF content abates the contribution of composition fluctuation, and the structures of mixed solvents tend to be that in pure THF. PNIPAM becomes soluble again via Van der Waals interaction between THF and polymer.
Continuous operation of high bit rate quantum key distribution
Authors: Dixon A. R. , Yuan Z. L. , Dynes J. F. , Sharpe A. W. , Shields A. J.
Published: April 2010

We demonstrate a quantum key distribution with a secure bit rate exceeding 1 Mbit/s over 50 km fiber averaged over a continuous 36 h period. Continuous operation of high bit rates is achieved using feedback systems to control path length difference and polarization in the interferometer and the timing of the detection windows. High bit rates and continuous operation allows finite key size effects to be strongly reduced, achieving a key extraction efficiency of 96% compared to keys of infinite lengths.
Electroluminescence behavior of ZnO/Si heterojunctions: Energy band alignment and interfacial microstructure
Authors: You J. B. , Zhang X. W. , Zhang S. G. , Tan H. R. , Ying J. , Yin Z. G. , Zhu Q. S. , Chu Paul K.
Published: April 2010

n-ZnO/p-Si heterojunction light-emitting diodes (LEDs) show weak defect-related electroluminescence (EL). In order to analyze the origin of the weak EL, the energy band alignment and interfacial microstructure of ZnO/Si heterojunction are investigated by x-ray photoelectron spectroscopy. The valence band offset (VBO) is determined to be 3.15±0.15 eV and conduction band offset is −0.90±0.15 eV, showing a type-II band alignment. The higher VBO means a high potential barrier for holes injected from Si into ZnO, and hence, charge carrier recombination takes place mainly on the Si side rather than the ZnO layer. It is also found that a 2.1 nm thick SiOx interfacial layer is formed at the ZnO/Si interface. The unavoidable SiOx interfacial layer provides to a large number of nonradiative centers at the ZnO/Si interface and gives rise to poor crystallinity in the ZnO films. The weak EL from the n-ZnO/p-Si LEDs can be ascribed to the high ZnO/Si VBO and existence of the SiOx interfacial layer.
Power law scaling during physical vapor deposition under extreme shadowing conditions
Authors: Mukherjee S. , Gall D.
Published: April 2010

A qualitative model that relates the period of the surface roughness to the vertical and spherical growth rates of glancing angle deposited (GLAD) nanorods suggests that rod self-shadowing is responsible for the previously reported temperature dependence in the rod width. Atomic shadowing interactions between neighboring rods as well as surface islands on the rod growth fronts control the morphological evolution which is quantified by the growth exponent p that relates the rod width w (=Ahp) to their height h. An analytical formalism predicts linear dependences of p and A on the average island separation and provides an explanation for reported anomalous p values. Experimental validation using new and previously published GLAD data for Al, Cr, Nb, and Ta shows quantitative agreement for all metallic systems under consideration and confirms the predicted dependences. In addition, a discontinuity in the p versus homologous deposition temperature θ suggests a critical value θc=0.24±0.02 for a transition from two-dimensional to three-dimensional island growth, which is independently confirmed by a discontinuity in the measured island width.
Shear-mode piezoelectric properties of ternary Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals
Authors: Wang Wei , Liu Da'an , Zhang Qinhui , Ren Bo , Zhang Yaoyao , Jiao Jie , Lin Di , Zhao Xiangyong , Luo Haosu
Published: April 2010

A systematic study of the optimized orientation and temperature dependence of shear-mode piezoelectric properties for ternary Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT or PIMNT) piezocrystals was carried out. It was found that [111]-poled samples presented the best shear piezoelectric properties when driving along [11¯0] (the thickness direction). The electromechanical coupling coefficient k15 and piezoelectric coefficient d15 and g15 were found to be 96.4%, 5966 pC/N, and 0.047 Vm/N, respectively, for optimum-cut samples with platinum (Pt) electrode. Besides, the maximum service temperature for shear mode is around 105 °C, which is much higher than PMNT single crystals.
State-selected imaging studies of formic acid photodissociation dynamics
Authors: Huang Cunshun , Zhang Cuimei , Yang Xueming
Published: April 2010

The photodissociation dynamics of formic acid have been studied using the velocity map ion imaging at the UV region. The measurements were made with resonance enhancement multiphoton ionization (REMPI) spectroscopy and dc slicing ion imaging. The OH REMPI spectrum from the photodissociation of formic acid at 244 nm has been recorded. The spectrum shows low rotational excitation (N≤4). By fixing the probe laser at the specific rotational transitions, the resulting OH images from various dissociation wavelengths have been accumulated. The translational energy distributions derived from the OH images imply that about half of the available energies go to the photofragments internal excitation. The dissociation dynamics of formic acid were also discussed in view of the recent theoretical calculations.
Role of c-screw dislocations on indium segregation in InGaN and InAlN alloys
Authors: Lei Huaping , Chen Jun , Ruterana Pierre
Published: April 2010

Indium segregation induced by c-screw dislocations in wurtzite InGaN and InAlN alloys is investigated with molecular dynamics based on Stillinger–Weber potentials [Stillinger and Weber, Phys. Rev. B 31, 5262 (1985)]. Beginning with the analysis of atomic structures and energetic stability of c-screw dislocations in AlN, GaN, and InN compounds, their interaction with In atoms in GaN and AlN is explored. The results show that In atoms reduce the core energy of c-screw dislocation when they are located at the center of the core region. The distance dependence of the interaction energy indicates that In atoms will tend to gather around the dislocation line and form an In-rich region. These results agree with experimental observations in InGaN and should predict a similar behavior in InAlN.
The transport and quantum capacitance properties of epitaxial graphene
Authors: Xia J. L. , Chen Fang , Tedesco J. L. , Gaskill D. K. , Myers-Ward R. L. , Eddy C. R. , Ferry D. K. , Tao N. J.
Published: April 2010

Epitaxial graphene field effect transistors were fabricated, characterized, and studied. Both the capacitance and transport measurements were performed on the same devices using an electrochemical gate. The quantum capacitance of the epitaxial graphene was extracted, which was similar to that of exfoliated graphene near the Dirac point, but it exhibits a large sublinear behavior at high carrier densities. The recently developed self-consistent theory for charged impurities in graphene is found to provide a reasonable description of the transport data, but a more complete theory is needed to explain both the transport and quantum capacitance data for the epitaxial graphene devices.
A broadband and high-gain metamaterial microstrip antenna
Authors: Li Le-Wei , Li Ya-Nan , Yeo Tat Soon , Mosig Juan R. , Martin Olivier J. F.
Published: April 2010

A broad bandwidth and high gain rectangular patch antenna was specifically designed in this paper using planar-patterned metamaterial concepts. Based on an ordinary patch antenna, the antenna has isolated triangle gaps and crossed strip-line gaps etched on the metal patch and ground plane, respectively. Demonstrated to have left-handed characteristics, the patterned metal patch and finite ground plane form a coupled capacitive-inductive circuit of negative index metamaterial. It is shown to have great impact on the antenna performance enhancement in terms of the bandwidth significantly broadened from a few hundred megahertz to a few gigahertz, and also in terms of high efficiency, low loss, and low voltage standing wave ratio. Experimental data show a reasonably good agreement between the simulation and measured results. This antenna has strong radiation in the horizontal direction for some specific applications within the entire band.
Theoretical investigation of a high efficiency and broadband subterahertz gyrotron
Authors: Chen Nai-Ching , Chang Tsun-Hsu , Yuan Ching-Pin , Idehara Toshitaka , Ogawa Isamu
Published: April 2010

This study investigates the electron dynamics of gyrotron interaction in a tapered waveguide and proposes an interaction structure for a 0.2 THz TE02 reflective gyrotron backward-wave oscillator (gyro-BWO). The design shows the advantages of high power, continuous, and broadband frequency tuning, mode converter free, and inherently possesses mode-selective ability to suppress the potentially competing TE22 mode. Calculated results indicate that the reflective TE02 gyro-BWO is capable of generating a peak power of 3.3 kW corresponding to 26.3% interacting efficiency with a broad 3dB tuning bandwidth of 6.9 GHz at beam current Ib=0.5 A and beam voltage Vb=25 kV.
Electronic and magnetic properties of zigzag graphene nanoribbon with one edge saturated
Authors: Xu B. , Yin J. , Xia Y. D. , Wan X. G. , Jiang K. , Liu Z. G.
Published: April 2010

We investigated the energetic stability, electronic, and magnetic properties of the zigzag graphene nanoribbons with one edge saturated by two hydrogen atoms, the other edge saturated by one hydrogen atom by using density-functional theory (DFT). The energy of the ferromagnetic semiconductor state is the lowest state for these nanoribbons. The energy difference between the antiferromagnetic states and the ferromagnetic states varies inversely with the nanoribbon width. Both the band gaps and the magnetic moments in the zigzag graphene nanoribbons with one edge saturated are larger than those of zigzag graphene nanoribbons.
Czech Physical Planning at the Crossroads: Towards the Regulation of Large-Scale Retail Developments?
Authors: Spilková Jana , Perlín Radim
Published: April 2010

The second half of the 1990s saw a dynamic development of Czech retailing and its spatial structure. Recent massive development of large-area commercial outlets in particular has revealed some problematic aspects and has also raised the question of whether their construction needs to be regulated. The role of local government in the decision processes concerning such developments is extremely weak and these processes are also complicated by a notably high level of bureaucracy. Although legislative documents proclaim the concept of sustainability as a key principle of future spatial development, its practical application will always depend on the will of the individual participants in the negotiation process. The authors argue that if a regulative approach to planning is chosen in the Czech Republic, planning offices must be respected bodies with enforceable rights and bound to act as strong authorities and effective agents of spatial plnning.
The Contradictions in ‘Alternative’ Service Delivery: Governance, Business Models, and Sustainability in Municipal Water Supply
Authors: Furlong Kathryn , Bakker Karen
Published: April 2010

Restructuring municipal water supply using ‘alternative service delivery’ models is a growing trend. The author examines potential contradictions between ‘alternative service delivery’ business models, on the one hand, and goals of good governance and sustainability on the other. A case study of water conservation and efficiency programs implemented by municipal water utilities in Canada is used to show that specific alternative service delivery (ASD) models which seek greater distance between management and government can create incentives which deter utilities from pursuing important social and environmental goals. The neoliberal governance reform that commonly accompanies and encourages ASD tends to exacerbate its deficiencies vis-à-vis conservation in the water sector. Still, the prevalent government-led service delivery model can impose trade-offs of its own. Strategic (rather than ideological) improvements in governance can enable municipalities to reap the benefits of a variety of business models (including ASD) without compromising sustainability objectives.
Diversity of Practical Quota Systems for Farmland Preservation: A Multicountry Comparison and Analysis
Authors: Tan Rong , Beckmann Volker
Published: April 2010

Diverse quota systems are designed and implemented in different countries to preserve farmland. Choosing a quota system for farmland preservation is thus an important issue for policy makers and researchers. In order to explain this diversity and reveal shared principles for the choice of a quota system in practice, we compare typical quota arrangements in four countries through a model of transaction cost economics (TCE). We examine agricultural zoning in the Netherlands, the transferable development right in the US, command-and-control quotas and their supplemented trading mode in China, and the debated tradable planning permits for land-use control in Germany. Our comparison not only shows that extending TCE into tradable quota theory is feasible, but also compares experience with the tools of farmland preservation across the four countries. Furthermore, the shared principles we discover could also be reference points for the rest of the world.
Sectoral Volatility and Regional Growth in the European Union
Authors: Ezcurra Roberto
Published: April 2010

I investigate the relationship between short-term instability and output growth in the European regions, using disaggregated data for six manufacturing activities over the period 1980–2006. The results show a positive link between sectoral volatility and growth. This finding is robust to the inclusion of additional explanatory variables in the analysis and is not driven by any specific sector or country. The observed relationship suggests that traditional stabilization policies that attempt to reduce the fluctuations of the business cycle may be harmful for regional growth in the long run.
Networking for Development in the North: Power, Trust, and Local Democracy
Authors: Bjørnå Hilde , Aarsæther Nils
Published: April 2010

This paper addresses modes and effects of local government involvement in development projects. In particular, it examines public–private interactions with regard to networking and power relations. The study is based on four development projects involving local authorities, located in two neighbouring municipalities in northern Norway. In these we find that most relationships are balanced and that a networking mode underpins the capacity of ‘getting things done’ or ‘power to’. ‘Power over’ relations, however, are observed over time, related to critical events in the implementation of the projects, and demanding explanations that exceed network analysis approaches. Rather than being classified as a distinct type of governance, networking and networks should be regarded as elements of varying importance in processes that also involve hierarchical and market-based inputs. In the processes studied, we found municipal leaders capable of resuming control by staging metagoverning activities.
Laurie Glimcher: Merging cell biology and immune function
Authors: Sedwick Caitlin
Published: April 2010

Glimcher pursues a cross-disciplinary understanding of how cell biology affects the immune system.
Convergence of Notch and β-catenin signaling induces arterial fate in vascular progenitors
Authors: Yamamizu Kohei , Matsunaga Taichi , Uosaki Hideki , Fukushima Hiroyuki , Katayama Shiori , Hiraoka-Kanie Mina , Mitani Kohnosuke , Yamashita Jun K.
Published: April 2010

Molecular mechanisms controlling arterial–venous specification have not been fully elucidated. Previously, we established an embryonic stem cell differentiation system and demonstrated that activation of cAMP signaling together with VEGF induces arterial endothelial cells (ECs) from Flk1+ vascular progenitor cells. Here, we show novel arterial specification machinery regulated by Notch and β-catenin signaling. Notch and GSK3β-mediated β-catenin signaling were activated downstream of cAMP through phosphatidylinositol-3 kinase. Forced activation of Notch and β-catenin with VEGF completely reconstituted cAMP-elicited arterial EC induction, and synergistically enhanced target gene promoter activity in vitro and arterial gene expression during in vivo angiogenesis. A protein complex with RBP-J, the intracellular domain of Notch, and β-catenin was formed on RBP-J binding sites of arterial genes in arterial, but not venous ECs. This molecular machinery for arterial specification leads to an integrated and more comprehensive understanding of vascular signaling.
Activation of cyclin B1–Cdk1 synchronizes events in the nucleus and the cytoplasm at mitosis
Authors: Gavet Olivier , Pines Jonathon
Published: April 2010

The cyclin B–Cdk1 kinase triggers mitosis in most eukaryotes. In animal cells, cyclin B shuttles between the nucleus and cytoplasm in interphase before rapidly accumulating in the nucleus at prophase, which promotes disassembly of the nuclear lamina and nuclear envelope breakdown (NEBD). What triggers the nuclear accumulation of cyclin B1 is presently unclear, although the prevailing view is that the Plk1 kinase inhibits its nuclear export. In this study, we use a biosensor specific for cyclin B1–Cdk1 activity to show that activating cyclin B1–Cdk1 immediately triggers its rapid accumulation in the nucleus through a 40-fold increase in nuclear import that remains dependent on Cdk1 activity until NEBD. Nevertheless, a substantial proportion of cyclin B1–Cdk1 remains in the cytoplasm. The increase in nuclear import is driven by changes in the nuclear import machinery that require neither Plk1 nor inhibition of nuclear export. Thus, the intrinsic link between cyclin B1–Cdk1 activation and its rapid nuclear import inherently coordinates the reorganization of the nucleus and the cytoplasm at mitotic entry.
Hsp90–Sgt1 and Skp1 target human Mis12 complexes to ensure efficient formation of kinetochore–microtubule binding sites
Authors: Davies Alexander E. , Kaplan Kenneth B.
Published: April 2010

The formation of functional kinetochores requires the accurate assembly of a large number of protein complexes. The Hsp90–Sgt1 chaperone complex is important for this process; however, its targets are not conserved and its exact contribution to kinetochore assembly is unclear. Here, we show that human Hsp90–Sgt1 interacts with the Mis12 complex, a so-called keystone complex required to assemble a large fraction of the kinetochore. Inhibition of Hsp90 or Sgt1 destabilizes the Mis12 complex and delays proper chromosome alignment due to inefficient formation of microtubule-binding sites. Interestingly, coinhibition of Sgt1 and the SCF subunit, Skp1, increases Mis12 complexes at kinetochores and restores timely chromosome alignment but forms less-robust microtubule-binding sites. We propose that a balance of Mis12 complex assembly and turnover is required for the efficient and accurate assembly of kinetochore–microtubule binding sites. These findings support a novel role for Hsp90–Sgt1 chaperones in ensuring the fidelity of multiprotein complex assembly.
αE-catenin regulates actin dynamics independently of cadherin-mediated cell–cell adhesion
Authors: Benjamin Jacqueline M. , Kwiatkowski Adam V. , Yang Changsong , Korobova Farida , Pokutta Sabine , Svitkina Tatyana , Weis William I. , Nelson W. James
Published: April 2010

αE-catenin binds the cell–cell adhesion complex of E-cadherin and β-catenin (β-cat) and regulates filamentous actin (F-actin) dynamics. In vitro, binding of αE-catenin to the E-cadherin–β-cat complex lowers αE-catenin affinity for F-actin, and αE-catenin alone can bind F-actin and inhibit Arp2/3 complex–mediated actin polymerization. In cells, to test whether αE-catenin regulates actin dynamics independently of the cadherin complex, the cytosolic αE-catenin pool was sequestered to mitochondria without affecting overall levels of αE-catenin or the cadherin–catenin complex. Sequestering cytosolic αE-catenin to mitochondria alters lamellipodia architecture and increases membrane dynamics and cell migration without affecting cell–cell adhesion. In contrast, sequestration of cytosolic αE-catenin to the plasma membrane reduces membrane dynamics. These results demonstrate that the cytosolic pool of αE-catenin regulates actin dynamics independently of cell–cell adhesion.