bluuebunny/crossref_metadata_2025 huggingface dataset:
Formulation of magnetically perturbed time-dependent density functional theory
Authors: Seth Michael , Ziegler Tom
Published: October 2007

A formulation of time-dependent density functional theory (TDDFT) in the presence of a static imaginary perturbation is derived. A perturbational approach is applied leading to corrections to various orders in the quantities of interest, namely, the excitation energies and transition densities. The perturbed TDDFT equations are relatively straightforward to derive but the resulting expressions are rather cumbersome. Simplifications of these equations are suggested. Both the simplified and full expressions are used to obtain equations for first- and second-order corrections to the excitation energy, the first-order correction to the transition density, and the corrections for both quantities to first-order in two different perturbations. This formulation, called magnetically perturbed TDDFT, details how conventional TDDFT calculations can be corrected to allow for the inclusion of a static magnetic field and/or spin-orbit coupling.
Electrodiffusion: A continuum modeling framework for biomolecular systems with realistic spatiotemporal resolution
Authors: Lu Benzhuo , Zhou Y. C. , Huber Gary A. , Bond Stephen D. , Holst Michael J. , McCammon J. Andrew
Published: October 2007

A computational framework is presented for the continuum modeling of cellular biomolecular diffusion influenced by electrostatic driving forces. This framework is developed from a combination of state-of-the-art numerical methods, geometric meshing, and computer visualization tools. In particular, a hybrid of (adaptive) finite element and boundary element methods is adopted to solve the Smoluchowski equation (SE), the Poisson equation (PE), and the Poisson-Nernst-Planck equation (PNPE) in order to describe electrodiffusion processes. The finite element method is used because of its flexibility in modeling irregular geometries and complex boundary conditions. The boundary element method is used due to the convenience of treating the singularities in the source charge distribution and its accurate solution to electrostatic problems on molecular boundaries. Nonsteady-state diffusion can be studied using this framework, with the electric field computed using the densities of charged small molecules and mobile ions in the solvent. A solution for mesh generation for biomolecular systems is supplied, which is an essential component for the finite element and boundary element computations. The uncoupled Smoluchowski equation and Poisson-Boltzmann equation are considered as special cases of the PNPE in the numerical algorithm, and therefore can be solved in this framework as well. Two types of computations are reported in the results: stationary PNPE and time-dependent SE or Nernst-Planck equations solutions. A biological application of the first type is the ionic density distribution around a fragment of DNA determined by the equilibrium PNPE. The stationary PNPE with nonzero flux is also studied for a simple model system, and leads to an observation that the interference on electrostatic field of the substrate charges strongly affects the reaction rate coefficient. The second is a time-dependent diffusion process: the consumption of the neurotransmitter acetylcholine by acetylcholinesterase, determined by the SE and a single uncoupled solution of the Poisson-Boltzmann equation. The electrostatic effects, counterion compensation, spatiotemporal distribution, and diffusion-controlled reaction kinetics are analyzed and different methods are compared.
Numerical and experimental investigation of microchannel flows with rough surfaces
Authors: Lilly T. C. , Duncan J. A. , Nothnagel S. L. , Gimelshein S. F. , Gimelshein N. E. , Ketsdever A. D. , Wysong I. J.
Published: October 2007

A conical surface roughness model applicable to particle simulations has been developed. The model has been experimentally validated for channel flows using helium and nitrogen gases at Reynolds numbers from 0.01 to 10 based on inlet conditions. To efficiently simulate gas-surface interaction, molecular collisions with the actual rough surface are simulated by collisions with a randomly positioned conical hole having a fixed opening angle. This model requires only one surface parameter, average surface roughness angle. This model has also been linked to the Cercignani-Lampis scattering kernel as a required reference for use in deterministic kinetic solvers. Experiments were conducted on transitional flows through a 150μm tall, 1cm wide, 1.5cm long microchannel where the mean free path is on the order of the roughness size. The channel walls were made of silicon with: (i) polished smooth surfaces, (ii) regular triangular roughness, and (iii) regular square roughness with characteristic roughness scales of <1μm, 11μm, and 29μm, respectively. For the triangular roughness, mass flow reductions ranged from 6% at the higher stagnation pressures tested to 25% at the lower stagnation pressures tested when compared to the smooth channel.
Time-dependent quantum Monte Carlo and the stochastic quantization
Authors: Christov Ivan P.
Published: October 2007

We examine the relation between the recently proposed time-dependent quantum Monte Carlo (TDQMC) method and the principles of stochastic quantization. In both TDQMC and stochastic quantization, particle motion obeys stochastic guidance equations to preserve quantum equilibrium. In this way the probability density of the Monte Carlo particles corresponds to the modulus square of the many-body wave function at all times. However, in TDQMC, the motion of particles and guide waves occurs in physical space unlike in stochastic quantization where it occurs in configuration space. Hence, the practical calculation of time evolution of many-body fully correlated quantum systems becomes feasible within the TDQMC methodology. We illustrate the TDQMC technique by calculating the symmetric and antisymmetric ground state of a model one-dimensional helium atom, and the time evolution of the dipole moment when the atom is irradiated by a strong ultrashort laser pulse.
Chemiluminescent detection of neutral gaseous radicals
Authors: Grankin V. P. , Styrov V. V. , Karpov E. G.
Published: October 2007

This paper presents a systematic approach to the development of novel solid-state chemical sensors on the basis of heterogeneous chemiluminescence. The method is applicable for the identification and measurements of concentration of H, O, and other gaseous chemical radicals, where utilization of standard techniques is difficult. The luminescence is invoked during Eley-Rideal recombination of the radicals in question on the surface of the sensor core. A technique is discussed to separate the contributions of Eley-Rideal and Langmuir-Hinshelwood mechanisms, and to select appropriate materials for the sensor emitter fabrication. Typical sensor characteristics include sensitivity of 105cm−3, working gas pressures of 10−8–101Torr, and measurement time ∼1s.
First principle study of Co2MnSi/GaAs(001) heterostructures
Authors: Ghaderi Nahid , Hashemifar S. Javad , Akbarzadeh Hadi , Peressi Maria
Published: October 2007

We have studied the electronic and magnetic properties of Co2MnSi/GaAs(001) heterostructure within the framework of the density functional theory by using the plane wave pseudopotential approach, with the aim of identifying possible interface morphologies where the peculiar half-metallic character of the constituent Heusler alloy is conserved. Among the different possible patterns, for the ideal abrupt SiMn/As interface we have identified two geometries characterized by high symmetry and low formation energy, corresponding to (a) both Si and Mn atoms in bridge sites between As and to (b) Si atoms on top of As and Mn atoms at hollow sites. The former one is particularly promising for spin injection, showing a spin polarization of 100% also at interface. We investigated also the corresponding Mn-rich interfaces, obtained from the ideal ones by substituting interfacial Si atoms by Mn, i.e., MnMn/As. In such a case, spin polarization is fully conserved at the other interface pattern. Band alignments for the majority and minority spin channels are also discussed.
PFabrication of gold tips by chemical etching in aqua regia
Authors: Bonaccorso F. , Calogero G. , Di Marco G. , Maragò O. M. , Gucciardi P. G. , Giorgianni U. , Channon K. , Sabatino G.
Published: October 2007

We present a method to produce sharp gold tips for applications in apertureless near-field optical microscopy and spectroscopy. Thin gold wires are tapered by chemical etching in aqua regia, covered by an isooctane protective layer. Tips with apical radii of curvature of <50 nm are obtained with a 40% yield. The tip performances have been checked by shear-force imaging of amyloid fibrils samples and compared to optical fiber probes. The analysis of the tip morphology, carried out by scanning electron microscopy, shows the existence of two different etching processes occurring in bulk and at the liquid-liquid interface. A simple analytical model is presented to describe the dynamics of the tip formation at the liquid-liquid meniscus interface that fits remarkably well the experimental results in terms of tip shape and length.
Current-voltage characteristics of LiNbO3∕La0.69Ca0.31MnO3 heterojunction and its tunability
Authors: Guo S. M. , Zhao Y. G. , Xiong C. M. , Huang W. G. , Cheng Z. H. , Xi X. X.
Published: October 2007

The authors have fabricated LiNbO3∕La0.69Ca0.31MnO3 heterojunctions by growing LiNbO3 on La0.69Ca0.31MnO3 single crystals. Rectifying behavior was found in these junctions, which can be tuned by applied magnetic field. A band diagram is proposed to account for the junction behavior. A voltage pulse-induced resistive switching was also observed, which can be understood by considering the ferroelectric polarization at the junction interface. The ability to tune transport properties of ferroelectric-ferromagnetic heterojunctions by magnetic field and electric polarization is potentially significant for their electronic applications.
Enhancement of the high-order harmonic generation from the gold plume using the time-resolved plasma spectroscopy
Authors: Ganeev Rashid A. , Elouga Bom Luc B. , Ozaki Tsuneyuki
Published: October 2007

We present systematic time-resolved investigations of plasma conditions for achieving the maximum cutoff and maximum conversion efficiency of high-order harmonic generation from gold plasma within the plateau. We analyzed harmonic generation under different laser-plasma conditions. We also performed simulations to calculate the ionization state of the gold plasma, the free electron density, and singly charged ion density at different prepulse intensities. By optimizing the plasma conditions, we observed a harmonic cutoff at the 53rd order (λ=15.09nm). We estimate the conversion efficiency of the harmonics within the plateau region to be 2×10−6.
Effect of collisions on dust particle charging via particle-in-cell Monte-Carlo collision
Authors: Rovagnati B. , Davoudabadi M. , Lapenta G. , Mashayek F.
Published: October 2007

In this paper, the effect of collisions on the charging and shielding of a single dust particle immersed in an infinite plasma is studied. A Monte-Carlo collision (MCC) algorithm is implemented in the particle-in-cell DEMOCRITUS code to account for the collisional phenomena which are typical of dusty plasmas in plasma processing, namely, electron-neutral elastic scattering, ion-neutral elastic scattering, and ion-neutral charge exchange. Both small and large dust particle radii, as compared to the characteristic Debye lengths, are considered. The trends of the steady-state dust particle potential at increasing collisionality are presented and discussed. The ions and electron energy distributions at various locations and at increasing collisionality in the case of large particle radius are shown and compared to their local Maxwellians. The ion-neutral charge-exchange collision is found to be by far the most important collisional phenomenon. For small particle radius, collisional effects are found to be important also at low level of collisionality, as more ions are collected by the dust particle due to the destruction of trapped ion orbits. For large particle radius, the major collisional effect is observed to take place in proximity of the presheath. Finally, the species energy distribution functions are found to approach their local Maxwellians at increasing collisionality.
Ion implantation of silicon at the nanometer scale
Authors: Bianconi Marco , Bergamini Fabio , Cristiani Stefano , Lulli Giorgio
Published: October 2007

Si O 2 layers (∼0.5μm thick) thermally grown on (100) Si were irradiated with 12.5MeV Ti ions at 109cm−2 fluence, and subsequently exposed to the HF vapor, in order to selectively etch the latent tracks generated by the passage of swift ions. Nearly cylindrical nanoholes having diameters as small as 25nm, with an average value of 54±5nm, were generated by this procedure. The nanopatterned SiO2 layer served as a mask for selective amorphization of the underlying Si, achieved by implantation with 180keV Ar+ ions at a fluence of 2.0×1015cm−2. Dip in aqueous HF solution was then performed to selectively etch ion amorphized Si, thus transferring the nanometric pattern of the SiO2 mask to the underlying substrate. As expected, the maximum depth of amorphizazion in Si, and consequently of etching depth, decreases when the hole radius decreases below values of the order of the lateral ion straggling. The effect has been characterized and investigated by the comparison of experiments and three dimensional Monte Carlo simulations.
Effect of cooling field on the antiferromagnetic interlayer coupling and exchange biasing in two antiferromagnetically coupled Co∕Pt multilayers
Authors: Liu Z. Y. , Xu B. , He J. L. , Yu D. L. , Tian Y. J. , Yu G. H.
Published: October 2007

In this work, we have investigated the effect of cooling field on the antiferromagnetic interlayer coupling and exchange biasing in the [Pt(5Å)∕Co(4Å)]4∕NiO(11Å)∕[Co(4Å)∕Pt(5Å)]4 multilayer with perpendicular anisotropy. When the cooling field lies between the switching fields of the top and bottom Co∕Pt multilayers at 400K, it has been found that both the out-of-plane interlayer coupling and the interfacial exchange biasing fields depend strongly on the cooling field, which is closely related to the magnetic domain configurations in the Co∕Pt multilayers and the NiO spacer at the cooling field. When the magnetic domains in the Co∕Pt multilayers and the unstable magnetic domains in the NiO spacer are removed at the high enough cooling field at 400K, both the out-of-plane interlayer coupling and the interfacial exchange biasing fields after cooling tend to be constant with little dependence on the cooling field.
Pseudosymmetry collineations
Authors: Haesen Stefan , Verstraelen Leopold
Published: October 2007

The pseudosymmetric spaces are a generalization of the spaces of constant sectional curvature in the sense that a scalar-valued curvature function, now depending on two planes, is assumed to be isotropic. From the study of the pseudosymmetry condition, a new set of tensors on the manifold receives attention and an invariance group on this set of tensors is introduced, the so-called pseudosymmetry collineations. This group is the infinitesimal counterpart of the pseudosymmetry condition. Their relationship with other types of transformations is discussed and, as an example, the pseudosymmetry collineations for the vacuum pp-waves are explicitly obtained.
Photoresponse properties of Al∕n-β-FeSi2 Schottky diodes using β-FeSi2 single crystals
Authors: Ootsuka Teruhisa , Fudamoto Yasunori , Osamura Masato , Suemasu Takashi , Makita Yunosuke , Fukuzawa Yasuhiro , Nakayama Yasuhiko
Published: October 2007

We have clearly observed photoresponse properties in an Al∕n-β-FeSi2 structure using β-FeSi2 single crystals grown by chemical vapor transport. A photocurrent is observed for photons with energies greater than 0.68eV. It increases sharply with increasing photon energy and attains a maximum at approximately 0.95eV (1.31μm). The photocurrent originated from the photoexcited electrons in the Al and the band-to-band photoexcited carriers in the β-FeSi2 located under the Al contact. The photoresponsivity increased upon high-temperature annealing, reaching 58mA∕W at 0.95eV after annealing at 800°C for 8h.
Thermopower and Co K-edge studies of potassium sodium cobalt oxyhydrates Na0.33K0.02(H2O)1.33CoO2−δ and Na0.07K0.21(H2O)0.63CoO2−δ
Authors: Liu Chia-Jyi , Liao Chia-Yuan , Wang Jung-Sheng , Nayak Pradipta K. , Lin Zhi-Ru , Sheu Hwo-Shuenn
Published: October 2007

We report measurements of the thermopower and Co K-edge x-ray absorption spectroscopy on bilayer and monolayer (Na,K)x(H2O)yCoO2−δ. According to the Co K-edge x-ray absorption spectra, the Co oxidation number for bilayer hydrate Na0.33K0.02(H2O)1.33CoO2−δ is higher than that of monolayer hydrate Na0.07K0.21(H2O)0.63CoO2−δ with a chemical shift of 3.5eV, which is in sharp contrast with Co K-edge x-ray absorption spectroscopy and cerimetric titration results for Nax(H2O)yCoO2−δ, where there is essentially no difference of the oxidation number of Co between bilayer and monolayer sodium cobalt oxyhydrates. According to thermopower analysis, band narrowing is observed when γ-Na0.7CoO2 is transformed to potassium sodium cobalt oxyhydrates.
Bias-induced orbital hybridization in diblock co-oligomer diodes
Authors: Hu G. C. , Wei J. H. , Xie S. J.
Published: October 2007

We investigate current rectification in diblock co-oligomer diode molecules on the basis of the Su-Schrieffer-Heeger model [Phys. Rev. B 22, 2099 (1980)] combined with the nonequilibrium Green’s function formalism. The current rectification observed in experiment [M. K. Ng et al., J. Am. Chem. Soc 124, 11862 (2002)] is well explained by the mechanism of bias-induced asymmetric hybridization of molecular orbitals. The positive bias tends to delocalize molecular orbitals through the hybridization, which produces a sharp increase in current at the threshold voltage; while the negative bias enhances the mismatch of energy levels and has no effect on the hybridization and the current.
Electroactivate shape-memory polymer filled with nanocarbon particles and short carbon fibers
Authors: Leng Jinsong , Lv Haibao , Liu Yanju , Du Shanyi
Published: October 2007

In addition to the fabrication of shape-memory thermoset polymer nanocomposites filled with conductive nanoparticles and fiber fillers, this paper is focused on factors which would influence the electrical property of this type of material. It is shown that the particulate additives are dispersed homogeneously within the matrix and served as interconnections between the fibers, while the fibrous additives act as long distance charge transporter by forming local conductive paths. The electrical conductivity of the nanocomposite which contains 5wt% carbon nanoparticles and 2wt% short carbon fiber is 2.32S∕cm by four-point van der Pauw method, and can be induced by 24V voltages.
Observation of delocalized transport and low-dimensionality effects in disordered carbon thin films
Authors: Bhattacharyya Somnath
Published: October 2007

Delocalized transport in a batch of amorphous carbon thin films is shown via a positive slope of the reduced activation energy below a certain temperature and a large value of conductivity minima. A crossover of dimensionality from three-dimensional (3D) to two-dimensional (2D) weak localization below the transition temperature and a signature of electron-electron interactions in 3D can be found in these films, which is significantly different from many other forms of carbon. The dimensionality crossover suggests 2D resonant tunneling between carbon clusters due to the increase of the phase coherence length and a low tunnel effective mass of electrons.
Device for characterization of thermal effusivity of liquids using photothermal beam deflection
Authors: Sandoval-Romero G. E. , García-Valenzuela A. , Sánchez-Pérez C. , Hernández-Cordero J. , Muratikov Kyrill L.
Published: October 2007

We propose and study a novel optoelectronic device for thermal characterization of materials. It is based on monitoring the photothermal deflection of a laser beam within a slab of a thermo-optic material in thermal contact with the sample under study. An optical angle sensor is used to measure the laser deflection providing a simple and experimental arrangement. We demonstrate its principle and a simple procedure to measure thermal effusivity of liquids. The proposed device could be implemented into a compact sensor head for remote measurements using electrical and fiber optic links.
Passive all-optical diode using asymmetric nonlinear absorption
Authors: Philip Reji , Anija M. , Yelleswarapu Chandra S. , Rao D. V. G. L. N.
Published: October 2007

Saturable and reverse saturable absorptions are well-known phenomena, originating from the imaginary component of the third order nonlinear optical susceptibility. We note that structures with an axially asymmetric nonlinear absorption can be easily realized from saturable and reverse saturable absorption materials arranged in tandem. In this paper, the basic transmission behavior of such a structure is worked out. Detailed numerical simulations demonstrate passive all-optical diode behavior, and the results are verified experimentally. The principle will work for all light polarizations, has no phase-matching restrictions, and can be extended to a large number of available nonlinear media for possible applications.
An intercepted feedback mode for light sensitive spectroscopic measurements in atomic force microscopy
Authors: Smoliner J. , Brezna W.
Published: October 2007

In most atomic force microscopes (AFMs), the motion of the tip is detected by the deflection of a laser beam shining onto the cantilever. AFM applications such as scanning capacitance spectroscopy or photocurrent spectroscopy, however, are severely disturbed by the intense stray light of the AFM laser. For this reason, an intercepted feedback method was developed, which allows to switch off the laser temporarily while the feedback loop keeps running. The versatility of this feedback method is demonstrated by measuring tip-force dependent Schottky barrier heights on GaAs samples.
Delayed-switch-on effect in metal-insulator-metal organic memories
Authors: Wang M. L. , Zhou J. , Gao X. D. , Ding B. F. , Shi Z. , Sun X. Y. , Ding X. M. , Hou X. Y.
Published: October 2007

We report a delayed-switch-on effect in organic memories; i.e., the organic memory devices can automatically switch from off state to on state after a certain period of time when biased at voltages below the threshold voltage. Meanwhile, the lower the voltage is, the longer the switching time will be. The time scales from milliseconds to about 104s with decreasing voltage. Moreover, by applying a certain voltage between threshold voltage and Vmax, intermediate states are also obtained. The existence of filamentary microconducting channels in the organic layer is proposed to be responsible for the observed switching phenomenon.
On the correlation between phase evolution of lipoplexes/anionic lipid mixtures and DNA release
Authors: Caracciolo Giulio , Pozzi Daniela , Caminiti Ruggero , Marchini Cristina , Montani Maura , Amici Augusto , Amenitsch Heinz
Published: October 2007

We investigated the structural evolution of three lipoplex formulations when interacting with anionic lipids by synchrotron small angle x-ray diffraction, while the extent of DNA release from lipoplexes by anionic lipids was evaluated by gel electrophoresis. Lipoplexes formed lamellar phases when mixed with anionic dioleoylphosphatidylglycerol (DOPG), while promoting the formation of nonbilayer structures when mixed with anionic dioleoylphosphatidic acid (DOPA). However, lipoplexes exhibited a virtually identical extent of DNA release when mixed with DOPG or DOPA. Thus, the recently proposed correlation between the formation of nonlamellar phases in lipoplex/anionic lipid mixtures and the increase of DNA release does not seem to exist.
Higher ionic conductive ceria-based electrolytes for solid oxide fuel cells
Authors: Omar Shobit , Wachsman Eric D. , Nino Juan C.
Published: October 2007

Codoping is used to enhance the ionic conductivity of ceria-based electrolytes. Sm3+ and Nd3+ were selected as codopants to promote low migration energy paths for oxygen vacancy diffusion, thereby increasing the ionic conductivity. Moreover, the use of codopants also increases the pre-exponential factor in the Arrhenius relationship, thus further improving the ionic conductivity. The ionic conductivity of SmxNdxCe1−2xO2−δ solid solutions is measured using electrochemical impedance spectroscopy. It was observed that for Sm0.075Nd0.075Ce0.85O2−δ, the grain ionic conductivity was 14.0×10−3Scm−1 at 550°C, which makes it one of the most promising ceria-based electrolytes for intermediate temperature solid oxide fuel cells.
A waveguide slit array antenna fabricated with subwavelength periodic grooves
Authors: Huang Cheng , Du Chunlei , Luo Xiangang
Published: October 2007

This paper presents a waveguide slit array antenna with high gain and narrow beamwidth. This antenna is formed by subwavelength slits surrounded with periodic grooves. The far field radiation characteristics of the improved antenna are investigated. Simulation results show that the gain of the antenna with a designed working frequency is improved by 11dB and a strong beam can be obtained. The physical mechanism for the performance improvement is governed by the resonance excitation of surface electromagnetic waves and can be well described by the coherent superposition of power radiated from the grooves and central slits.
Self-tuning mechanisms of nonlinear split-ring resonators
Authors: Powell David A. , Shadrivov Ilya V. , Kivshar Yuri S. , Gorkunov Maxim V.
Published: October 2007

We study both theoretically and experimentally the dynamic tunability of the magnetic resonance of a single nonlinear split-ring resonator with varactor diode at microwave frequencies. We demonstrate different tuning regimes with and without an inductive coil in parallel with the varactor. We show that the coil changes the sign of the nonlinearity and eliminates the memory effect caused by charge accumulation across the varactor. In addition, at higher powers the nonlinear response of the split-ring resonator becomes multivalued, paving a way for creating bistable tunable metamaterials.
Barrier performance of ultrathin Ni–Ti film for integrating ferroelectric capacitors on Si
Authors: Liu B. T. , Yan X. B. , Zhang X. , Cheng C. S. , Li F. , Bian F. , Zhao Q. X. , Guo Q. L. , Wang Y. L. , Li X. H. , Zhang X. Y. , Li C. R. , Wang Y. S.
Published: October 2007

Ultrathin amorphous Ni–Ti film is investigated as conductive diffusion barrier layer to integrate La0.5Sr0.5CoO3∕PbZr0.4Ti0.6O3∕La0.5Sr0.5CoO3 (LSCO/PZT/LSCO) capacitors on silicon. X-ray photoelectron spectroscopy results demonstrate that Ni in LSCO∕Ni–Ti∕Si heterostructure is not oxidized after 550°C annealing in oxygen. The structural properties of LSCO∕PZT∕LSCO∕Ni–Ti∕Si are characterized by x-ray diffraction and transmission electron microscopy. It is found that Ni–Ti film is still amorphous and that there are no discernible reactions at the interfaces of the sample. LSCO/PZT/LSCO capacitor, measured at 5V, possesses very good ferroelectric properties, such as low coercive field (∼1.28V), high remnant polarization (∼27.9μC∕cm2), and good fatigue-free characteristic, implying that ultrathin amorphous Ni–Ti film can be used as barrier layer for fabricating high-density ferroelectric random access memories.
Evidence for low density of nonradiative defects in ZnO nanowires grown by metal organic vapor-phase epitaxy
Authors: Robin I. C. , Gauron B. , Ferret P. , Tavares C. , Feuillet G. , Dang Le Si , Gayral B. , Gérard J. M.
Published: October 2007

Low temperature cathodoluminescence and temperature dependent time resolved photoluminescence are used to investigate the emission properties of ZnO nanowires grown by metal organic vapor phase epitaxy. Low temperature cathodoluminescence images show that the emission process is more efficient in ZnO nanowires than in the underlying two dimensional layer. Temperature dependent photoluminescence spectra and decay time measurements give a detailed insight on the role of the donor bound exciton, the free exciton, and the nonradiative channels in the emission process. In particular, it is shown that up to room temperature, the escape toward nonradiative channels is limited because of the very low defect density in the ZnO nanowires.
Spin polarized tunneling in a ferromagnetic Zener diode
Authors: Comesaña E. , Gehring G. A.
Published: October 2007

Calculations of the tunneling current as a function of voltage for a Zener diode where both sides are ferromagnetic have been performed. The current is evaluated as a function of the voltage and of the magnetization on each side of the diode. The tunneling magnetoresistance is analyzed. Two cases are considered, one that corresponds to Mn doped GaAs in which the ferromagnetism is stronger on the p side of the diode and the other that corresponds to ZnO where there are likely to be many more carriers on the n side of the diode.
Metal heterowaveguide superlattices for a plasmonic analog to electronic Bloch oscillations
Authors: Lin Weihua , Wang Guo Ping
Published: October 2007

A metal heterowaveguide superlattice constructed by alternately stacking two metal gap waveguides with gradually changed geometric thicknesses for observing time-resolved plasmon Bloch oscillations (PBOs) is presented. Analytical result from the transfer matrix method reveals the appearance of tilted plasmonic minibands and minigaps, and plasmonic Wannier-Stark ladder in frequency domain, indicating the existence of time-resolved PBO effects in such superlattices. Finite-difference time-domain simulations on the dynamic evolution of plasmon propagation in the superlattices demonstrate the analytical prediction.
Tunable optical negative-index metamaterials employing anisotropic liquid crystals
Authors: Wang Xiande , Kwon Do-Hoon , Werner Douglas H. , Khoo Iam-Choon , Kildishev Alexander V. , Shalaev Vladimir M.
Published: October 2007

A full-wave analysis technique based on the finite element-boundary integral method is developed and used to rigorously treat the scattering from periodically structured metamaterials incorporating anisotropic liquid crystals (LCs) and dispersive materials. Reconfiguration of the negative-index metamaterials is achieved by controlling the magnetic resonance via tuning permittivity of the embedded anisotropic LCs. Numerical results show that the refractive index of the metamaterials can be reconfigured by tuning the director orientation of anisotropic LCs or by using temperature-dependent LCs. The design configurations and their characteristics in the near- and the mid-infrared ranges are presented.
The effects of nickel germanosilicide contacts on the biaxial compressive stress in thin epitaxial silicon-germanium alloys on silicon
Authors: Chopra Saurabh , Ozturk Mehmet C. , Misra Veena , Ren Zhongqiao , McNeil L. E.
Published: October 2007

When a thin Si1−xGex epitaxial layer is grown on Si, it is under biaxial compression. In this letter, it is shown that a nickel germanosilicide (NiSi1−xGex) layer formed on Si1−xGex can significantly reduce the in-plane compressive strain in Si1−xGex. It is proposed that the observed reduction is due to the biaxial tensile stress applied by the NiSi1−xGex layer. Because the Si1−xGex bandgap is a strong function of the strain, this is expected to have a strong impact on the metal-semiconductor barrier height and the contact resistivity of the interface if the metal Fermi level is pinned near the Si1−xGex midgap.
Roughness corrections to the Casimir force: The importance of local surface slope
Authors: van Zwol P. J. , Palasantzas G. , De Hosson J. Th. M.
Published: October 2007

This paper concentrates on a study where finite conductivity corrections are included in the theoretical description of the effects of roughness on the Casimir force. The roughness data were taken from gold films evaporated onto silicon and polysterene spheres. We conclude that for a detailed comparison with experimental data, i.e., at the level of at least 5% at short separations below 200nm, the lateral dimensions of roughness for real films should be included in the theoretical considerations. Moreover, if the rms roughness is considerable, high local surface slopes are shown to have a significant effect on the Casimir force.
Analysis of a wafer bonded Ge∕Si heterojunction by transmission electron microscopy
Authors: Kanbe Hiroshi , Miyaji Masayuki , Hirose Mami , Nitta Noriko , Taniwaki Masafumi
Published: October 2007

A wafer-bonded Ge∕Si heterojunction was observed using transmission electron microscopy to analyze its crystallographic properties and to reveal atomic profiles at the interface by energy dispersive x-ray spectroscopy. There was a 2nm thick transition layer at the heterojunction, where an aligned lattice image from Si to Ge together with a disordered lattice image could be observed. In the Si layer close to the interface, islandlike modified regions were observed to exist, where a large amount of Ge was detected. Oxygen was also detected accumulated at the interface.
Bridges to sustainable tropical health
Authors: Singer Burton H. , de Castro Marcia Caldas
Published: October 2007

Ensuring sustainable health in the tropics will require bridge building between communities that currently have a limited track record of interaction. It will also require new organizational innovation if much of the negative health consequences of large-scale economic development projects are to be equitably mitigated, if not prevented. We focus attention on three specific contexts: (i) forging linkages between the engineering and health communities to implement clean water and sanitation on a broad scale to prevent reworming, after the current deworming-only programs, of people by diverse intestinal parasites; (ii) building integrated human and animal disease surveillance infrastructure and technical capacity in tropical countries on the reporting and scientific evidence requirements of the sanitary and phytosanitary agreement under the World Trade Organization; and (iii) developing an independent and equitable organizational structure for health impact assessments as well as monitoring and mitigation of health consequences of economic development projects. Effective global disease surveillance and timely early warning of new outbreaks will require a far closer integration of veterinary and human medicine than heretofore. Many of the necessary surveillance components exist within separate animal- and human-oriented organizations. The challenge is to build the necessary bridges between them.
TRPM7 channels in hippocampal neurons detect levels of extracellular divalent cations
Authors: Wei Wen-Li , Sun Hong-Shuo , Olah Michelle E. , Sun Xiujun , Czerwinska Elzbieta , Czerwinski Waldemar , Mori Yasuo , Orser Beverley A. , Xiong Zhi-Gang , Jackson Michael F. , Tymianski Michael , MacDonald John F.
Published: October 2007

Exposure to low Ca
2+
and/or Mg
2+
is tolerated by cardiac myocytes, astrocytes, and neurons, but restoration to normal divalent cation levels paradoxically causes Ca
2+
overload and cell death. This phenomenon has been called the “Ca
2+
paradox” of ischemia–reperfusion. The mechanism by which a decrease in extracellular Ca
2+
and Mg
2+
is “detected” and triggers subsequent cell death is unknown. Transient periods of brain ischemia are characterized by substantial decreases in extracellular Ca
2+
and Mg
2+
that mimic the initial condition of the Ca
2+
paradox. In CA1 hippocampal neurons, lowering extracellular divalents stimulates a nonselective cation current. We show that this current resembles TRPM7 currents in several ways. Both (
i
) respond to transient decreases in extracellular divalents with inward currents and cell excitation, (
ii
) demonstrate outward rectification that depends on the presence of extracellular divalents, (
iii
) are inhibited by physiological concentrations of intracellular Mg
2+
, (
iv
) are enhanced by intracellular phosphatidylinositol 4,5-bisphosphate (PIP
2
), and (
v
) can be inhibited by Gαq-linked G protein-coupled receptors linked to phospholipase C β1-induced hydrolysis of PIP
2
. Furthermore, suppression of TRPM7 expression in hippocampal neurons strongly depressed the inward currents evoked by lowering extracellular divalents. Finally, we show that activation of TRPM7 channels by lowering divalents significantly contributes to cell death. Together, the results demonstrate that TRPM7 contributes to the mechanism by which hippocampal neurons “detect” reductions in extracellular divalents and provide a means by which TRPM7 contributes to neuronal death during transient brain ischemia.
Mortality traps and the dynamics of health transitions
Authors: Bloom David E. , Canning David
Published: October 2007

An examination of life expectancy in 1963 reveals twin peaks in the empirical distribution across countries: one group of countries clustered around a life expectancy of 40 years and a second group clustered around a life expectancy of 65 years. By 2003, the mode of each cluster had moved up by ≈10 years. Although the two groups are similar in that within each of them, there is progress toward higher life expectancy, a number of countries appear to have made the jump from the high-mortality cluster to the low-mortality cluster. We reject the hypothesis that these changes reflect a simple convergence process. The data instead suggest continuous advances among many countries within clusters, with advances in life expectancy in some nations resulting in a jump from one cluster to the other.
Dentate gyrus-specific manipulation of β-Ca
2+
/calmodulin-dependent kinase II disrupts memory consolidation
Authors: Cho Min H. , Cao Xiaohua , Wang Deheng , Tsien Joe Z.
Published: October 2007

Although the functions of α-Ca
2+
/calmodulin-dependent kinase II (CaMKII) have been studied extensively, the role of βCaMKII, a coconstituent of the CaMKII holoenzyme in synaptic plasticity, learning, and memory has not been examined
in vivo
. Here we produce a transgenic mouse line in which the inducible and reversible manipulation of βCaMKII activity is restricted to the hippocampal dentate gyrus, the region where long-term potentiation was originally discovered. We demonstrate that βCaMKII activity in the dentate gyrus selectively impaired long-term potentiation in the dentate perforant path, but not in the CA1 Schaffer collateral pathway. Although the transgenic mice showed normal 1-day memories, they were severely impaired in 10-day contextual fear memory. Systematic manipulations of dentate βCaMKII activity during various distinct memory stages further reveal the initial day within the postlearning consolidation period as a critical time window that is highly sensitive to changes in βCaMKII activity. This study provides evidence not only for the functional role of βCaMKII in the dentate gyrus plasticity and hippocampal memory, but also for the notion that the mismatch between the actual learning pattern and reactivation patterns in the dentate gyrus circuit can underlie long-term memory consolidation.
The transcription elongation factor TFIIS is a component of RNA polymerase II preinitiation complexes
Authors: Kim Bong , Nesvizhskii Alexey I. , Rani P. Geetha , Hahn Steven , Aebersold Ruedi , Ranish Jeffrey A.
Published: October 2007

In this article, we provide direct evidence that the evolutionarily conserved transcription elongation factor TFIIS functions during preinitiation complex assembly. First, we identified TFIIS in a mass spectrometric screen of RNA polymerase II (Pol II) preinitiation complexes (PICs). Second, we show that the association of TFIIS with a promoter depends on functional PIC components including Mediator and the SAGA complex. Third, we demonstrate that TFIIS is required for efficient formation of active PICs. Using truncation mutants of TFIIS, we find that the Pol II-binding domain is the minimal domain necessary to stimulate PIC assembly. However, efficient formation of active PICs requires both the Pol II-binding domain and the poorly understood N-terminal domain. Importantly, Domain III, which is required for the elongation function of TFIIS, is dispensable during PIC assembly. The results demonstrate that TFIIS is a PIC component that is required for efficient formation and/or stability of the complex.
Tracing the effects of the Little Ice Age in the tropical lowlands of eastern Mesoamerica
Authors: Lozano-García Ma. del Socorro , Caballero Margarita , Ortega Beatriz , Rodríguez Alejandro , Sosa Susana
Published: October 2007

The causes of late-Holocene centennial to millennial scale climatic variability and the impact that such variability had on tropical ecosystems are still poorly understood. Here, we present a high-resolution, multiproxy record from lowland eastern Mesoamerica, studied to reconstruct climate and vegetation history during the last 2,000 years, in particular to evaluate the response of tropical vegetation to the cooling event of the Little Ice Age (LIA). Our data provide evidence that the densest tropical forest cover and the deepest lake of the last two millennia were coeval with the LIA, with two deep lake phases that follow the Spörer and Maunder minima in solar activity. The high tropical pollen accumulation rates limit LIA's winter cooling to a maximum of 2°C. Tropical vegetation expansion during the LIA is best explained by a reduction in the extent of the dry season as a consequence of increased meridional flow leading to higher winter precipitation. These results highlight the importance of seasonal responses to climatic variability, a factor that could be of relevance when evaluating the impact of recent climate change.
Defining Genocide
Authors: De Waal Alex
Published: October 2007

IF WE ACCEPT COLIN POWELL’S ASSURANCE THAT GENOCIDE HAS BEEN COMMITTED IN SUDAN’S DARFUR REGION, THEN DON’T WE HAVE A LEGAL OBLIGATION TO DO SOMETHING ABOUT IT — OR IS THIS ABOUT SOMETHING ELSE ALTOGETHER?
Sexy Snaps
Authors: Bourke Joanna
Published: October 2007

TECHNOLOGY HAS GIVEN US EVERYTHING FROM LASER-GUIDED MUNITIONS, TOMAHAWK CRUISE MISSILES AND SPY SATELLITES TO THE DIGITAL CAMERA THAT ENABLES US TO FRAME OUR DESTRUCTIVENESS SIMPLY AND CHEAPLY
With a Little Help From Our Friends
Authors: Gearty Conor
Published: October 2007

TORTURE IS WRONG AND INEFFECTIVE. SO HOW IS IT MAKING A COMEBACK?
Looking-Glass Laws
Authors: Rodley Nigel
Published: October 2007

‘WHEN I USE A WORD IT MEANS EXACTLY WHAT I WANT IT TO MEAN,’ SAYS HUMPTY DUMPTY TO ALICE IN THROUGH THE LOOKING-GLASS. WHICH IS MORE OR LESS WHERE WE ARE WITH THE US AND ITS INTERPRETATION OF INTERNATIONAL LAW
How To Make a Torturer
Authors: Crelinsten Ronald
Published: October 2007

TORTURERS ARE MADE BY THE REGIMES THEY SERVE, FABRICATED IN THE INTERESTS OF GOVERNMENTS AND BUREAUCRACIES THAT WOULD PERSUADE US TO BELIEVE IN TORTURE
Behind the Sunglasses
Authors: Dorfman Ariel
Published: October 2007

CHILE HAS DONE ITS BEST TO FORGET ITS PAST; BUT WHEN YOU DRAG ONE THING FROM UNDER A STONE, OTHERS EMERGE…
From Plov To Paella
Authors: Whitfield Susan
Published: October 2007

OIL AND TERRORISM HAVE AGAIN FOCUSED ATTENTION ON A REGION THAT ONCE OCCUPIED THE CENTRE OF WORLD HISTORY
Elegy for the Union
Authors: Fitzherbert George , Toktoev Zamir
Published: October 2007

DIFFERENCES OF OPINION BETWEEN THE GENERATIONS IN POST-SOVIET KYRGYZSTAN
Strategic Bedfellows
Authors: Dzhanguzhin Rustam , Tait Arch
Published: October 2007

THE POST-SOVIET REPUBLICS OF CENTRAL ASIA ARE ENJOYING A NEW POLITICAL STATUS, WITH RUSSIA AND THE WEST COMPETING FOR THEIR FAVOURS
What Chance the Media?
Authors: Panfilov Oleg , Tait Arch
Published: October 2007

THE FUTURE OF THE PRESS IN CENTRAL ASIA IS DEPENDENT ON HOW FAR A NEW GENERATION OF JOURNALISTS RECOGNISES THE NEED TO ENSURE IT IS OF HIGH QUALITY AND COMMERCIALLY VIABLE
Ferghana Canal
Authors: Eistenstein Sergei
Published: October 2007

A shooting-script by Sergei Eisenstein, from a treatment by Piotr Pavlenko and Eisenstein, 1, 2 and 3 August 1939. Of the published 657 shot indications, only the first 145 are reproduced below, forming a fourteenth-century prologue to the modern drama of Soviet Uzbekistan’s reclamation of its desert wastes. In the film’s Tamerlane will be found more resemblance to Adolf Hitler than to the heroic figure of Marlowe’s tragedy.
In the Misery of Darfur
Authors: Simon Catherine
Published: October 2007

THE REFUGEE CAMPS AROUND EL GENEINA ARE POPULATED ALMOST ENTIRELY BY WOMEN AND CHILDREN. UNDER THEIR MAKESHIFT SHELTERS THE WOMEN TELL OF THE DAYS OF PEACE WHEN THEY DID NOT LIVE IN FEAR — AND THEN OF THE WAR
Rab11 Is Required for Membrane Trafficking and Actomyosin Ring Constriction in Meiotic Cytokinesis ofDrosophilaMales
Authors: Giansanti Maria Grazia , Belloni Giorgio , Gatti Maurizio
Published: October 2007

Rab11 is a small GTPase that regulates several aspects of vesicular trafficking. Here, we show that Rab11 accumulates at the cleavage furrow of Drosophila spermatocytes and that it is essential for cytokinesis. Mutant spermatocytes form regular actomyosin rings, but these rings fail to constrict to completion, leading to cytokinesis failures. rab11 spermatocytes also exhibit an abnormal accumulation of Golgi-derived vesicles at the telophase equator, suggesting a defect in membrane–vesicle fusion. These cytokinesis phenotypes are identical to those elicited by mutations in giotto (gio) and four wheel drive (fwd) that encode a phosphatidylinositol transfer protein and a phosphatidylinositol 4-kinase, respectively. Double mutant analysis and immunostaining for Gio and Rab11 indicated that gio, fwd, and rab11 function in the same cytokinetic pathway, with Gio and Fwd acting upstream of Rab11. We propose that Gio and Fwd mediate Rab11 recruitment at the cleavage furrow and that Rab11 facilitates targeted membrane delivery to the advancing furrow.
Escape mortality of cod, saithe, and haddock in a Barents Sea trawl fishery
Authors: Ingólfsson Ólafur Arnar , Soldal Aud Vold , Huse Irene , Breen Mike
Published: October 2007

Ingólfsson, Ó. A., Soldal, A. V., Huse, I., and Breen, M. 2007. Escape mortality of cod, saithe, and haddock in a Barents Sea trawl fishery. – ICES Journal of Marine Science, 64: 000–000. We investigated the survival of gadoid fish in the Barents Sea escaping from a demersal trawl during commercial fishing conditions, with and without a sorting grid, at high and low levels of fishing intensity. The mortality of cod and saithe was negligible and unrelated to experimental conditions. Haddock mortality was generally greater than observed in earlier experiments and inversely related to fish length. Any possible effects of experimental conditions were hidden by large variability in the observed rates of mortality. We conclude that the observed mortality of haddock is confounded by methodological problems, particularly the instability of the observation cages, and does not reflect the true escape mortality. Cod and saithe are capable of surviving the stress of passage through, and escape from, the trawl, whereas haddock are more vulnerable, despite being a closely related species.