bluuebunny/crossref_metadata_2025 huggingface dataset:
Electric-field-induced magnetization reversal in 1–3 type multiferroic nanocomposite thin films
Authors: Zhong ChongGui , Jiang Qing , Fang JingHuai
Published: July 2009

Using a general Landau free-energy thermodynamic theory for ferroelectric (FE) and ferromagnetic (FM) phases, we investigate the magnetoelectric coupling effect on epitaxial 1–3 type multiferroic nanocomposite thin films. By taking into account the electrostrictive and magnetostrictive effects and the elastic stress arising from the FE/FM and film/substrate interfaces, we renormalize the dielectric and magnetic coefficients twice and obtain the quasi-intrinsic magnetoelectric coupling in Landau free-energy function of this multiferroic system. Then, the electrical-field-induced magnetization and polarization for different thicknesses of film in 1–3 type BaTiO3–CoFe2O3 nanocomposite system are analyzed. Our results show that an applied electric field can result in the reversal of magnetization in step with the switching of the electric polarization due to the out-of-plane elastic coupling between the interfaces of FE and FM phases, while the relaxation of the in-plane compressive stress of the thin film makes magnetization M and polarization P both decrease with increasing film thickness. These results are completely consistent with experimental ones.
A rigorous foundation of the diffusion-influenced bimolecular reaction kinetics
Authors: Kim Ji-Hyun , Lee Sangyoub
Published: July 2009

We formulate a general theory of the diffusion-influenced kinetics of irreversible bimolecular reactions occurring in the low concentration limit. Starting from the classical Liouville equation for the reactants and explicit solvent molecules, a formally exact expression for the bimolecular reaction rate coefficient is derived; the structures of reactant molecules and the sink functions may be arbitrarily complicated. The present theoretical formulation shows clearly how the well-known Noyes and Wilemski–Fixman rate theories are related and can be improved in a systematic manner. The general properties of the rate coefficient such as the long-time behavior and the upper and the lower bounds are analyzed. When the reaction can occur at a range of distance, the non-Markovianity of repeated encounter events between a reactant pair becomes significant and either the Noyes theory or the Wilemski–Fixman theory fails. The present theory provides a practical method for calculating the rate expression for such reactions, which improves significantly on the Wilemski–Fixman theory.
Molecular dynamics simulations of concentrated polymer solutions in thin film geometry. II. Solvent evaporation near the glass transition
Authors: Peter S. , Meyer H. , Baschnagel J.
Published: July 2009

We perform molecular dynamics simulations of a coarse-grained model of a polymer-solvent mixture to study solvent evaporation from supported and freestanding polymer films near the bulk glass transition temperature Tg. We find that the evaporation process is characterized by three time (t) regimes: An early regime where the initially large surplus of solvent at the film-vapor interface evaporates and the film thickness h varies little with t, an intermediate regime where h decreases strongly, and a final regime where h slowly converges toward the asymptotic value of the dry film. In the intermediate regime the decrease of h goes along with an increase of the monomer density at the retracting interface. This polymer-rich “crust” is a nonequilibrium effect caused by the fast evaporation rate in our simulation. The interfacial excess of polymer gradually vanishes as the film approaches the dry state. In the intermediate and final time regimes it is possible to describe the simulation data for h(t) and the solvent density profile ϕL(y,t) by the numerical solution of a one-dimensional diffusion model depending only on the y direction perpendicular to the interface. The key parameter of this model is the mutual diffusion coefficient DL of the solvent in the film. Above Tg we find that a constant DL allows to describe the simulation data, whereas near Tg agreement between simulation and modeling can only be obtained if the diffusion coefficient depends on y through two factors: A factor describing the slowing down of the dynamics with decreasing solvent concentration ϕL(y,t) and a factor parametrizing the smooth gradient toward enhanced dynamics as the film-vapor interface is approached.
Phase transitions and crossovers in reaction-diffusion models with catalyst deactivation
Authors: Mattos T. G. , Reis Fábio D. A. Aarão
Published: July 2009

The activity of catalytic materials is reduced during operation by several mechanisms, one of them being poisoning of catalytic sites by chemisorbed impurities or products. Here we study the effects of poisoning in two reaction-diffusion models in one-dimensional lattices with randomly distributed catalytic sites. Unimolecular and bimolecular single-species reactions are considered, without reactant input during the operation. The models show transitions between a phase with continuous decay of reactant concentration and a phase with asymptotic nonzero reactant concentration and complete poisoning of the catalyst. The transition boundary depends on the initial reactant and catalyst concentrations and on the poisoning probability. The critical system behaves as in the two-species annihilation reaction, with reactant concentration decaying as t−1/4 and the catalytic sites playing the role of the second species. In the unimolecular reaction, a significant crossover to the asymptotic scaling is observed even when one of those parameters is 10% far from criticality. Consequently, an effective power-law decay of concentration may persist up to long times and lead to an apparent change in the reaction kinetics. In the bimolecular single-species reaction, the critical scaling is followed by a two-dimensional rapid decay, thus two crossovers are found.
Self-assembly of actin monomers into long filaments: Brownian dynamics simulations
Authors: Guo Kunkun , Shillcock Julian , Lipowsky Reinhard
Published: July 2009

Brownian dynamics simulations are used to study the dynamical process of self-assembly of actin monomers into long filaments containing up to 1000 actin protomers. In order to overcome the large separation of time scales between the diffusive motion of the free monomers and the relatively slow attachment and detachment processes at the two ends of the filaments, we introduce a novel rescaling procedure by which we speed all dynamical processes related to actin polymerization and depolymerization up by the same factor. In general, the actin protomers within a filament can attain three different states corresponding to a bound adenosine triphosphate (ATP), adenosine diphosphate with inorganic phosphate (ADP/P), and ADP molecule. The simplest situation that has been studied experimentally is provided by the polymerization of ADP-actin, for which all protomers are identical. This case is used to unravel certain relations between the filament’s physical properties and the model parameters such as the attachment rate constant and the size of the capture zone, the detachment rate and the probability of the detached event, as well as the growth rate and waiting times between two successive attachment/detachment events. When a single filament is allowed to grow in a bath of constant concentration of free ADP-actin monomers, its growth rate increases linearly with the free monomer concentration in quantitative agreement with in vitro experiments. The results also show that the waiting time is governed by exponential distributions and that the two ends of a filament undergo biased random walks. The filament length fluctuations are described by a length diffusion constant that is found to attain a constant value at low ADP-actin concentration and to increase linearly with this concentration. It is straightforward to apply our simulation code to more complex processes such as polymerization of ATP-actin coupled to ATP hydrolysis, force generation by filaments, formation of filament bundles, and filament-membrane interactions.
Microanalyses of the reverse-bias leakage current increase in the laser lift off GaN-based light emitting diodes
Authors: Sun Yongjian , Yu Tongjun , Zhao Huabo , Shan Xudong , Zhang Xinzheng , Chen Zhizhong , Kang Xiangning , Yu Dapeng , Zhang Guoyi
Published: July 2009

Microanalyses of the reverse-bias leakage current increase in the laser lift off (LLO) GaN-based light emitting diodes were performed. It was found that the amount of dislocations did not obviously change after LLO process in our experiments. The conductive-atomic force microscopy images and transmission electron microscope (TEM) images results revealed that almost all screw dislocations became to be related with leakage current and the current intensity increased over 100 times after the LLO process; however, only nanopipes corresponded to leakage current in the sample without the laser irradiation. Scanning TEM images indicated microstructure changes induced by LLO process. Amount of point defects around dislocations might be responsible for the increase in leakage current by providing more levels for tunneling.
Photocurrent properties of freely suspended carbon nanotubes under uniaxial strain
Authors: Kaniber S. M. , Song L. , Kotthaus J. P. , Holleitner A. W.
Published: July 2009

The photocurrent properties of freely suspended single-walled carbon nanotubes (CNTs) are investigated as a function of uniaxial strain. We observe that at low strain, the photocurrent signal of the CNTs increases for increasing strain, while for large strain, the signal decreases, respectively. We interpret the nonmonotonous behavior by a superposition of the influence of the uniaxial strain on the resistivity of the CNTs and the effects caused by Schottky contacts between the CNTs and the metal contacts.
Energy decomposition analysis of covalent bonds and intermolecular interactions
Authors: Su Peifeng , Li Hui
Published: July 2009

An energy decomposition analysis method is implemented for the analysis of both covalent bonds and intermolecular interactions on the basis of single-determinant Hartree–Fock (HF) (restricted closed shell HF, restricted open shell HF, and unrestricted open shell HF) wavefunctions and their density functional theory analogs. For HF methods, the total interaction energy from a supermolecule calculation is decomposed into electrostatic, exchange, repulsion, and polarization terms. Dispersion energy is obtained from second-order Møller–Plesset perturbation theory and coupled-cluster methods such as CCSD and CCSD(T). Similar to the HF methods, Kohn–Sham density functional interaction energy is decomposed into electrostatic, exchange, repulsion, polarization, and dispersion terms. Tests on various systems show that this algorithm is simple and robust. Insights are provided by the energy decomposition analysis into H2, methane C–H, and ethane C–C covalent bond formation, CH3CH3 internal rotation barrier, water, ammonia, ammonium, and hydrogen fluoride hydrogen bonding, van der Waals interaction, DNA base pair formation, BH3NH3 and BH3CO coordinate bond formation, Cu-ligand interactions, as well as LiF, LiCl, NaF, and NaCl ionic interactions.
High frequency dynamics in liquid Cs at high pressure
Authors: Giordano Valentina M. , Monaco Giulio
Published: July 2009

We report on an inelastic x-ray scattering investigation of the high frequency dynamics of liquid cesium at 493 K and 1 GPa, which corresponds to a density 23% higher than that at the room pressure melting point. The analysis of the spectra, performed within the framework of the memory function approach suggests the existence of two different relaxation processes, i.e., the structural relaxation and a second faster one. The dynamical properties thus obtained are compared to those reported in the literature for room pressure conditions in order to investigate their dependence on pressure. The increase in density is found to largely affect the structural relaxation process, though leaving the acoustic damping almost unperturbed.
A new proposed approach to estimate the thermodiffusion coefficients for linear chain hydrocarbon binary mixtures
Authors: Abbasi Alireza , Saghir M. Ziad , Kawaji Masahiro
Published: July 2009

Thermodiffusion behaviors in nonassociating mixtures have an important role in separation processes of the oil industry. The variations of composition and temperature may either lessen or enhance the separation in mixtures. A new model regarding the prediction of thermodiffusion coefficients for linear chain hydrocarbon binary mixtures using the thermodynamics of irreversible process is proposed. The model predicts the net amount of heat transported based on available volume for each molecule. This newly proposed model combined with the perturbed chain statistical associating fluid theory equation of state has been applied to predict thermodiffusion coefficients for binary hydrocarbon mixtures of C10–nCi (i=5,6,7,15,16,17,18), C12–nCi (i=5,6,7,8,9), and C18–nCi (i=5,6,7,8,9,12). Comparisons of the calculated theoretical results with the experimental data show good performance of the proposed model. In particular, this model which is based on the kinetic approaches has been found to be the most reliable and represents a significant improvement over the earlier models.
Replicated photonic crystals by atomic layer deposition within holographically defined polymer templates
Authors: Graugnard E. , Roche O. M. , Dunham S. N. , King J. S. , Sharp D. N. , Denning R. G. , Turberfield A. J. , Summers C. J.
Published: July 2009

We report the replication of holographically defined photonic crystals using multistage atomic layer deposition. Low- and high-temperature atomic layer depositions were combined with selective etching to deposit and remove multiple conformal thin films within three-dimensional polymer templates. Using intermediate Al2O3 inverse replicas, temperature-sensitive SU-8 photonic crystal templates were faithfully replicated with TiO2 and GaP, greatly increasing the dielectric contrasts of the photonic crystals. Optical measurements are in good agreement with the calculated band structures.
Study of the effect of current rise time on the formation of the precursor column in cylindrical wire array Z pinches at 1 MA
Authors: Bott S. C. , Haas D. M. , Eshaq Y. , Ueda U. , Beg F. N. , Hammer D. A. , Kusse B. , Greenly J. , Shelkovenko T. A. , Pikuz S. A. , Blesener I. C. , McBride R. D. , Douglass J. D. , Bell K. , Knapp P. , Chittenden J. P. , Lebedev S. V. , Bland S. N. , Hall G. N. , Suzuki Vidal F. A. , Marocchino A. , Harvey-Thomson A. , Haines M. G. , Palmer J. B. A. , Esaulov A. , Ampleford D. J.
Published: July 2009

The limited understanding of the mechanisms driving the mass ablation rate of cylindrical wires arrays is presently one of the major limitations in predicting array performance at the higher current levels required for inertial confinement fusion (ICF) ignition. Continued investigation of this phenomenon is crucial to realize the considerable potential for wire arrays to drive both ICF and inertial fusion energy, by enabling a predictive capability in computational modeling. We present the first study to directly compare the mass ablation rates of wire arrays as a function of the current rise rate. Formation of the precursor column is investigated on both the MAPGIE (1 MA, 250ns [Mitchell et al., Rev. Sci. Instrum. 67, 1533 (1996)]) and COBRA (1 MA, 100ns [Greenly et al., Rev. Sci. Instrum. 79, 073501 (2008)]) generators, and results are used to infer the change in the effective ablation velocity induced by the rise rate of the drive current. Laser shadowography, gated extreme ultraviolet (XUV) imaging, and x-ray diodes are used to compare the dynamical behavior on the two generators, and X-pinch radiography and XUV spectroscopy provide density evolution and temperature measurements respectively. Results are compared to predictions from an analytical scaling model developed previously from MAGPIE data, based on a fixed ablation velocity. For COBRA the column formation time occurs at 116±5 ns and for Al arrays and 146±5 ns for W arrays, with Al column temperature in the range of 70–165 eV. These values lie close to model predictions, inferring only a small change in the ablation velocity is induced by the factor of 2.5 change in current rise time. Estimations suggest the effective ablation velocities for MAGPIE and COBRA experiments vary by a maximum of 30%.
Plasma relaxation and the turbulent dynamo
Authors: Shebalin John V.
Published: July 2009

Ideal magnetohydrodynamic (MHD) turbulence may be represented by finite Fourier series whose independent coefficients form a canonical ensemble described by a Gaussian probability density function containing a Hermitian covariance matrix with positive eigenvalues. When the eigenvalues at lowest wave number are very small, a large-scale coherent structure appears: a turbulent dynamo, which is seen in computations. A theoretical explanation is given and contains Taylor’s theory of force-free states. Numerical effects are examined and it is shown that larger grid sizes and smaller time steps provide for better resolution of coherent structure. Ideal hydrodynamic (HD) turbulence is examined and the results are compared and contrasted with those of ideal MHD turbulence. In particular, coherent structure appears in ideal MHD turbulence at the lowest wave number, but can occur in ideal HD turbulence only at the highest wave numbers in a simulation. In the case of real, i.e., dissipative flows, coherent structure and broken ergodicity are expected to occur in MHD turbulence at the largest scale. However, real HD turbulence at all scales and real MHD turbulence at all scales but the largest are expected to be ergodic.
Peptide aggregation and solvent electrostriction in a simple zwitterionic dipeptide via molecular dynamics simulations
Authors: Tulip P. R. , Bates S. P.
Published: July 2009

We investigate the structure of the glycyl-l-alanine dipeptide in aqueous solution at a 1:20 peptide:water concentration via classical, atomistic molecular dynamics simulations using the CHARMM22 force field, and compare to recent neutron diffraction data [S. E. McLain, A. K. Soper, and A. Watts, Eur. Biophys. J. 37, 647 (2008); S. E. McLain, A. K. Soper, I. Diadone, J. C. Smith, and A. Watts, Angew. Chem. Int. Ed. 47, 9059 (2008)]. Comparison between simulations and experiments is made using the static structure factor S(Q). The effect of water model (TIP3P, TIP4P, and SPC/E) upon the solution structure is investigated. Agreement between experiment and simulation is generally good across the entire Q range, although some model-dependent variation is observed, particularly in the predicted intensities of features in S(Q). Peptide aggregation is found to be driven by “hydrophilic” (often bifurcated) hydrogen bonds formed between carboxy and amine functional groups, although simulations suggest that the degree of aggregation is less than that observed experimentally. It is found that hydrophobic association is not significant, with hydrophobic hydration being preferred to association. Detailed examination of the solute structural motifs reveals the existence of bifurcated motifs that are suggested to be an artifact of the CHARMM force field, and may imply that classical force fields provide a flawed structural and dynamical description of such molecular fluids. Investigation of the water structure reveals the presence of an electrostrictive effect which manifests itself as an increase in the number of interstitial molecules in the water second coordination shell, in contradiction to suggestions that this phenomenon arises owing to hydrogen bond bending. Detailed analysis based upon two-dimensional distribution functions suggests an intimate link between the phenomenon of electrostriction and the behavior of water under high-pressure compression. We find the magnitude of the electrostrictive effect inferred from the neutron diffraction data to be greater than that found in the simulations. Investigation of the solvation structure suggests that the CHARMM force field overhydrates the terminal carboxy group, and that this overhydration is accompanied by the presence of bifurcated hydrogen bonds.
Optimum sizing of air heating collectors
Authors: Söylemez M. S.
Published: July 2009

A thermoeconomic feasibility analysis is presented yielding a simple algebraic optimization formula for estimating the optimum length of a typical air heating collector per unit depth. A simple economic optimization method is used in the present study by combining it with an integrated overall heat balance method for calculating maximum savings from the solar air heating. An optimum collector length was detected as a result of the present work. The number of payback years and critical length of an air heating collector were also determined by using the present optimization method.
Flexible Ge-on-polyimide detectors
Authors: Ho W. S. , Dai Y.-H. , Deng Y. , Lin C.-H. , Chen Y.-Y. , Lee C.-H. , Liu C. W.
Published: July 2009

A flexible Ge-on-polyimide photodetector is demonstrated. The single crystalline thin film of Ge was transferred on the polyimide by adhesive wafer bonding and smart-cut techniques. A simple tunneling metal-oxide-semiconductor structure is fabricated for the detector applications. Due to the transparency of the polyimide, the responsivity of the detector is sensitive to the environments. At −2 V, the photodetector on the stainless steel has responsivities of 220, 200, and 140 mA/W at wavelength of 850, 1310, and 1550 nm, respectively.
Tunneling interlayer exchange coupling between oxide ferrimagnets: Analysis for Fe3O4/vac/Fe3O4 case
Authors: Wu Han-Chun , Mryasov O. N. , Radican K. , Shvets I. V.
Published: July 2009

We have investigated tunneling interlayer exchange coupling (TIEC) between ferrimagnetic Fe3O4 films via a tunneling barrier. In this investigation we employ ab initio density functional theory to study a generic tunneling junction incorporating ferrimagnets Fe3O4/vac/Fe3O4. In contrast with previously established TIEC theory, calculated thickness dependence is nonmonotonic and accompanied by TIEC sign change. Our calculations clearly demonstrate that TIEC is controlled mainly by an interfacial oxygen induced spin polarization. These results emphasize the importance of localized and strongly directional electronic interactions at the interface, thus showing limitations of free electron model treatment of the problem.
Nonlinear nanopolaritonics: Finite-difference time-domain Maxwell–Schrödinger simulation of molecule-assisted plasmon transfer
Authors: Lopata Kenneth , Neuhauser Daniel
Published: July 2009

The effect of nonlinear excitations of a nearby two-state dipolar molecule on plasmon transfer across a pair of spherical gold nanoparticles is studied numerically using a split field finite-difference time-domain Maxwell–Schrödinger approach [K. Lopata and D. Neuhauser, J. Chem. Phys. 130, 104707 (2009)]. It is observed in the linear response regime that the molecule has a drastic effect on plasmon transfer; specifically, there is a Fano-type resonance that serves to scatter localized plasmons from x-polarization to y-polarization. With increasing nonlinearity of the molecular excitation, the scattering effect saturates due to the limited capacity of the molecule to absorb and radiate energy once the excited and ground states are equally populated.
Trimethylamine biosensor based on pentacene enzymatic organic field effect transistor
Authors: Diallo A. K. , Tardy J. , Zhang Z. Q. , Bessueille F. , Jaffrezic-Renault N. , Lemiti M.
Published: July 2009

This paper reports on an enzymatic organic field effect transistor based biosensor dedicated to the detection of trimethylamine, in view of fish freshness assessment. Flexible devices were processed on Kapton substrate with pentacene as organic semiconductor and Parylene-C as top gate dielectric. Proton sensitive dielectric surface was achieved by depositing a thin hydrogenated silicon nitride layer at moderate temperature on Parylene. An enzymatic membrane made of flavin-containing mono-oxygenase 3 cross-linked with bovine serum albumin deposited on silicon nitride completed the realization of the device. High sensitivity trimethylamine biosensing was demonstrated in the 0–8 ppm range.
The effects of shell characteristics on the current-voltage behaviors of dye-sensitized solar cells based on ZnO/TiO2 core/shell arrays
Authors: Wang Meili , Huang Changgang , Cao Yongge , Yu Qingjiang , Guo Wang , Huang Qiufeng , Liu Yuan , Huang Zhi , Huang Jiquan , Wang Hai , Deng Zhonghua
Published: July 2009

The ZnO/TiO2 core/shell structure was formed through deposition of a TiO2 coating layer on the hydrothermally fabricated ZnO nanorod arrays through radio frequency magnetron sputtering. The effects of the TiO2 shell’s characteristics on the current-voltage behaviors of the core/shell-based dye-sensitized solar cells (CS-DSSC) were investigated. As the rates of injection, transfer, and recombination of electrons of such CS-DSSC were affected significantly by the crystallization, morphology, and continuity of the TiO2 shells, the photovoltaic efficiency was accordingly varied remarkably. In addition, the efficiency was further improved by enhancing the surface area in the core/shell electrode.
Strain relaxation of SiGe in a Si/SiGe/Si heterostructure under proton irradiation
Authors: Di Z. F. , Wang Y. Q. , Nastasi M. , Bisognin G. , Berti M. , Thompson P. E.
Published: July 2009

We have studied the mechanisms underlying strained layer relaxation by means of point defect interaction. During high temperature (300 °C) proton irradiation, vacancies generated in the vicinity of SiGe layer migrate and accumulate within the compressively strained SiGe layer. The accumulating vacancies are stabilized by hydrogen, which diffuses from the implanted region, thus allowing the nucleation and growth of hydrogen-vacancy (V-H) complexes. The formation of V-H complexes is accompanied by gradual strain relief in SiGe layer. Since the diffusion of both vacancies and hydrogen is limited by the irradiation temperature, strain relaxation of the SiGe layer is not realized during room temperature (20 °C) proton irradiation. The study supports the idea that the compressive stress in the SiGe layer induces the indiffusion of vacancies and H, and reveals the important role of point defects in the strain relaxation of the strained SiGe layer.
Electron inelastic mean free paths for carbon nanotubes from optical data
Authors: Kyriakou Ioanna , Emfietzoglou Dimitris , Garcia-Molina Rafael , Abril Isabel , Kostarelos Kostas
Published: July 2009

We present a simple model dielectric response function for both bulk and individual carbon nanotubes based on a parameterization of experimental optical data and analytic dispersion relations that account for dimensionality and linewidth broadening. The model is used to calculate electron inelastic mean free paths over a broad energy range of interest to various applications.
Thermoelectric evaluation of the dopant density of p-type InAs
Authors: Wagener M. C. , Wagener V. , Botha J. R.
Published: July 2009

Thermoelectric measurements were performed on p-type InAs thin films grown by metalorganic vapor phase epitaxy. The measured Seebeck coefficient displayed an anomalous temperature dependence due to the existence of a highly conductive surface inversion layer. The effect of a degenerate conduction layer has been incorporated into our analysis and revealed that the sign-reversal temperature of the Seebeck coefficient remained unaffected by the surface layer. This finding consequently facilitated the direct determination of the acceptor density of lightly doped thin film InAs.
Plasmonic optical antennas on dielectric gratings with high field enhancement for surface enhanced Raman spectroscopy
Authors: Li Jingjing , Fattal David , Li Zhiyong
Published: July 2009

We present a rational approach toward amplifying the local electromagnetic (EM) field for surface enhanced Raman spectroscopy applications by integrating dielectric gratings capable of guided mode resonance with plasmonic optical antennas. The optical antennas are placed periodically at certain positions on the surface of a two-dimensional (2D) dielectric grating. At resonance, the grating provides a spatially confined, enhanced EM field that can further enhance the strong field of the localized surface plasmon on the nanoantenna. The numerical simulations demonstrate a cascaded enhancement from the optical antenna and the dielectric grating when the two are weakly coupled.
Jeans instability in quantum magnetoplasma with resistive effects
Authors: Ren Haijun , Wu Zhengwei , Cao Jintao , Chu Paul K.
Published: July 2009

The Jeans instability in dense quantum plasmas is investigated in the presence of two dimensional magnetic fields and resistive effects. The resistive effects are shown to introduce instability whether the perturbation is stable or not in the ideal magnetohydrodynamic model. The analytical expressions of the growth rate of Jeans instability are obtained for both the finite and remarkable resistive effects cases. The results are relevant to dense astrophysical objects, e.g., neutron stars and the interior of white dwarfs, as well as low-temperature laboratory plasmas.
Tunneling field-effect transistor with epitaxial junction in thin germanium-on-insulator
Authors: Kazazis D. , Jannaty P. , Zaslavsky A. , Le Royer C. , Tabone C. , Clavelier L. , Cristoloveanu S.
Published: July 2009

We report on the fabrication and electrical characterization at room and low temperatures of a tunneling field-effect transistor (TFET). The devices are fabricated in thin germanium-on-insulator and consist of a heavily p+-doped, epitaxially grown source, a heavily n+-doped ion implanted drain, and a standard high-κ (HfO2) gate stack with an effective gate length Leff of 60 nm, obtained by trimming. The TFETs are fabricated using an ultralarge-scale integration compatible process flow. The devices exhibit an ambipolar behavior, reasonable on/off current ratio, and improved on current compared to silicon-on-insulator TFETs.
Temperature dependence of the magnetoresistance in Fe/MgO core/shell nanoparticles
Authors: Martinez-Boubeta C. , Balcells Ll. , Valencia S. , Schmitz D. , Monty C. , Martínez B.
Published: July 2009

The temperature dependence of magnetoresistance (MR) of powdered samples consisting of spherical Fe/MgO core/shell nanoparticles was analyzed. A change of the MR from normal at room temperature to inverse at low temperatures was observed. Concomitant with this, samples showed a sudden increase in the electrical resistance when approaching TV≈120 K, i.e., indicative of the Verwey transition temperature of Fe3O4. Thus, signaling the existence of magnetite at the Fe/MgO interface, further confirmed by means of x-ray magnetic circular dichroism. The change from normal to inverse MR is related to the increase in resistance of Fe3O4 on crossing the Verwey transition and reflects the negative spin polarization of Fe3O4.
A comparison of the ideal strength between L12Co3(Al,W) and Ni3Al under tension and shear from first-principles calculations
Authors: Wang Yun-Jiang , Wang Chong-Yu
Published: July 2009

The ideal strengths of L12Co3(Al,W) in comparison with Ni3Al are investigated using the first-principles method. Results for the stress-strain relationships, ideal tensile and shear strengths are presented. The calculated elastic properties agree well with the experimental observations. Co3(Al,W) is found to have larger moduli and higher strengths, but less ductile than Ni3Al. The electronic structures indicate the directional covalentlike Co–W bonding through d-d hybridization is the origin of excellent mechanical properties of Co3(Al,W).
Broadband moth-eye antireflection coatings fabricated by low-cost nanoimprinting
Authors: Chen Q. , Hubbard G. , Shields P. A. , Liu C. , Allsopp D. W. E. , Wang W. N. , Abbott S.
Published: July 2009

Subwavelength scale antireflection moth-eye structures in silicon were fabricated by a wafer-scale nanoimprint technique and demonstrated an average reflection of 1% in the spectral range from 400 to 1000 nm at normal incidence. An excellent antireflection property out to large incident angles is shown with the average reflection below 8% at 60°. Pyramid array gave an almost constant average reflection of about 10% for an incident angle up to 45° and concave-wall column array produced an approximately linear relation between the average reflection and the incident angles. The technique is promising for improving conversion efficiencies of silicon solar cells.
Independent elaboration of steroid hormone signaling pathways in metazoans
Authors: Markov Gabriel V. , Tavares Raquel , Dauphin-Villemant Chantal , Demeneix Barbara A. , Baker Michael E. , Laudet Vincent
Published: July 2009

Steroid hormones regulate many physiological processes in vertebrates, nematodes, and arthropods through binding to nuclear receptors (NR), a metazoan-specific family of ligand-activated transcription factors. The main steps controlling the diversification of this family are now well-understood. In contrast, the origin and evolution of steroid ligands remain mysterious, although this is crucial for understanding the emergence of modern endocrine systems. Using a comparative genomic approach, we analyzed complete metazoan genomes to provide a comprehensive view of the evolution of major enzymatic players implicated in steroidogenesis at the whole metazoan scale. Our analysis reveals that steroidogenesis has been independently elaborated in the 3 main bilaterian lineages, and that steroidogenic cytochrome P450 enzymes descended from those that detoxify xenobiotics.
The archaeal cofactor F
0
is a light-harvesting antenna chromophore in eukaryotes
Authors: Glas Andreas F. , Maul Melanie J. , Cryle Max , Barends Thomas R. M. , Schneider Sabine , Kaya Emine , Schlichting Ilme , Carell Thomas
Published: July 2009

Archae possess unique biochemical systems quite distinct from the pathways present in eukaryotes and eubacteria. 7,8-Dimethyl-8-hydroxy-5deazaflavin (F
0
) and F
420
are unique deazaflavin-containing coenzyme and methanogenic signature molecules, essential for a variety of biochemical transformations associated with methane biosynthesis and light-dependent DNA repair. The deazaflavin cofactor system functions during methane biosynthesis as a low-potential hydrid shuttle F
420
/F
420
H
2
. In DNA photolyase repair proteins, the deazaflavin cofactor is in the deprotonated state active as a light-collecting energy transfer pigment. As such, it converts blue sunlight into energy used by the proteins to drive an essential repair process. Analysis of a eukaryotic (6-4) DNA photolyase from
Drosophila melanogaster
revealed a binding pocket, which tightly binds F
0
. Residues in the pocket activate the cofactor by deprotonation so that light absorption and energy transfer are switched on. The crystal structure of F
0
in complex with the
D. melanogaster
protein shows the atomic details of F
0
binding and activation, allowing characterization of the residues involved in F
0
activation. The results show that the F
0
/F
420
coenzyme system, so far believed to be strictly limited to the archael kingdom of life, is far more widespread than anticipated. Analysis of a
D. melanogaster
extract and of a DNA photolyase from the primitive eukaryote
Ostreococcus tauri
provided direct proof for the presence of the F
0
cofactor also in higher eukaryotes.
Nej1 recruits the Srs2 helicase to DNA double-strand breaks and supports repair by a single-strand annealing-like mechanism
Authors: Carter Sidney D. , Vigašová Dana , Chen Jiang , Chovanec Miroslav , Åström Stefan U.
Published: July 2009

Double-strand breaks (DSBs) represent the most severe DNA lesion a cell can suffer, as they pose the risk of inducing loss of genomic integrity and promote oncogenesis in mammals. Two pathways repair DSBs, nonhomologous end joining (NHEJ) and homologous recombination (HR). With respect to mechanism and genetic requirements, characterization of these pathways has revealed a large degree of functional separation between the two. Nej1 is a cell-type specific regulator essential to NHEJ in
Saccharomyces cerevisiae
. Srs2 is a DNA helicase with multiple roles in HR. In this study, we show that Nej1 physically interacts with Srs2. Furthermore, mutational analysis of Nej1 suggests that the interaction was strengthened by Dun1-dependent phosphorylation of Nej1 serines 297/298. Srs2 was previously shown to be recruited to replication forks, where it promotes translesion DNA synthesis. We demonstrate that Srs2 was also efficiently recruited to DSBs generated by the HO endonuclease. Additionally, efficient Srs2 recruitment to this DSB was dependent on Nej1, but independent of mechanisms facilitating Srs2 recruitment to replication forks. Functionally, both Nej1 and Srs2 were required for efficient repair of DSBs with 15-bp overhangs, a repair event reminiscent of a specific type of HR called single-strand annealing (SSA). Moreover, absence of Rad51 suppressed the SSA-defect in
srs2
and
nej1
strains. We suggest a model in which Nej1 recruits Srs2 to DSBs to promote NHEJ/SSA-like repair by dismantling inappropriately formed Rad51 nucleoprotein filaments. This unexpected link between NHEJ and HR components may represent cross-talk between DSB repair pathways to ensure efficient repair.
Design of therapeutic proteins with enhanced stability
Authors: Chennamsetty Naresh , Voynov Vladimir , Kayser Veysel , Helk Bernhard , Trout Bernhardt L.
Published: July 2009

Therapeutic proteins such as antibodies constitute the most rapidly growing class of pharmaceuticals for use in diverse clinical settings including cancer, chronic inflammatory diseases, kidney transplantation, cardiovascular medicine, and infectious diseases. Unfortunately, they tend to aggregate when stored under the concentrated conditions required in their usage. Aggregation leads to a decrease in antibody activity and could elicit an immunological response. Using full antibody atomistic molecular dynamics simulations, we identify the antibody regions prone to aggregation by using a technology that we developed called spatial aggregation propensity (SAP). SAP identifies the location and size of these aggregation prone regions, and allows us to perform target mutations of those regions to engineer antibodies for stability. We apply this method to therapeutic antibodies and demonstrate the significantly enhanced stability of our mutants compared with the wild type. The technology described here could be used to incorporate developability in a rational way during the screening of antibodies in the discovery phase for several diseases.
Functional tradeoffs determine species coexistence via the storage effect
Authors: Angert Amy L. , Huxman Travis E. , Chesson Peter , Venable D. Lawrence
Published: July 2009

How biological diversity is generated and maintained is a fundamental question in ecology. Ecologists have delineated many mechanisms that can, in principle, favor species coexistence and hence maintain biodiversity. Most such coexistence mechanisms require or imply tradeoffs between different aspects of species performance. However, it remains unknown whether simple functional tradeoffs underlie coexistence mechanisms in diverse natural systems. We show that functional tradeoffs explain species differences in long-term population dynamics that are associated with recovery from low density (and hence coexistence) for a community of winter annual plants in the Sonoran Desert. We develop a new general framework for quantifying the magnitude of coexistence via the storage effect and use this framework to assess the strength of the storage effect in the winter annual community. We then combine a 25-year record of vital rates with morphological and physiological measurements to identify functional differences between species in the growth and reproductive phase of the life cycle that promote storage-effect coexistence. Separation of species along a tradeoff between growth capacity and low-resource tolerance corresponds to differences in demographic responses to environmental variation across years. Growing season precipitation is one critical environmental variable underlying the demographic decoupling of species. These results demonstrate how partially decoupled population dynamics that promote local biodiversity are associated with physiological differences in resource uptake and allocation between species. These results for a relatively simple system demonstrate how long-term community dynamics relate to functional biology, a linkage scientists have long sought for more complex systems.
Many human large intergenic noncoding RNAs associate with chromatin-modifying complexes and affect gene expression
Authors: Khalil Ahmad M. , Guttman Mitchell , Huarte Maite , Garber Manuel , Raj Arjun , Rivea Morales Dianali , Thomas Kelly , Presser Aviva , Bernstein Bradley E. , van Oudenaarden Alexander , Regev Aviv , Lander Eric S. , Rinn John L.
Published: July 2009

We recently showed that the mammalian genome encodes >1,000 large intergenic noncoding (linc)RNAs that are clearly conserved across mammals and, thus, functional. Gene expression patterns have implicated these lincRNAs in diverse biological processes, including cell-cycle regulation, immune surveillance, and embryonic stem cell pluripotency. However, the mechanism by which these lincRNAs function is unknown. Here, we expand the catalog of human lincRNAs to ≈3,300 by analyzing chromatin-state maps of various human cell types. Inspired by the observation that the well-characterized lincRNA HOTAIR binds the polycomb repressive complex (PRC)2, we tested whether many lincRNAs are physically associated with PRC2. Remarkably, we observe that ≈20% of lincRNAs expressed in various cell types are bound by PRC2, and that additional lincRNAs are bound by other chromatin-modifying complexes. Also, we show that siRNA-mediated depletion of certain lincRNAs associated with PRC2 leads to changes in gene expression, and that the up-regulated genes are enriched for those normally silenced by PRC2. We propose a model in which some lincRNAs guide chromatin-modifying complexes to specific genomic loci to regulate gene expression.
Language policy as experiences
Authors: Shohamy Elana
Published: July 2009

Personal experiences have rarely been viewed as part of the domain of language policy, since policies are generally created from the top down, often to meet ideological or political agendas. The study of linguistic practices in a small country like Luxembourg offers particular opportunities to consider how language policy needs also to be formulated from the bottom up, since it has a direct effect on the rights and opportunities of often marginalized populations. Confronting these questions in small countries, which are hedged about with all of the complexities of their larger neighbours, may offer solutions that can be applied in due course in larger countries too.
Multiphase evaluation of myocardial bridging with dual-source computed tomography
Authors: Zhang Long Jiang , Yang Gui Fen , Zhou Chang Sheng , Huang Wei , Lu Guang Ming , Shiroishi M. S.
Published: July 2009

Background: Myocardial bridging (MB), also known as a tunneled artery, is a congenital anomaly that can be readily diagnosed with multidetector-row computed tomography (MDCT). With the advent of dual-source CT (DSCT), it may be feasible to evaluate dynamic changes of MB throughout the entire cardiac cycle.

Purpose: To determine the feasibility of dynamic evaluation of MB using DSCT.

Material and Methods: Forty-eight patients with MB of the left anterior descending artery diagnosed with multiplanar reconstruction on DSCT were included in this study. Multiphase reconstructions were performed for every subject. Image quality was assessed using a four-point scale (4 = excellent; 3 = good; 2 = adequate; 1 = not assessable). Systolic and diastolic images with optimal image quality were selected. Milking effect, defined as the narrowing of the tunneled artery during systole and its dilatation during diastole, was recorded. The stenosis rate of MB was computed.

Results: The optimal systolic and diastolic phases occurred between 40% and 70% of the R–R interval (range 20–80% of R–R interval). The image quality scores of all segments in systole and diastole were higher than or equal to 3. Diameter changes of tunneled vessel under MB in systole and diastole indicated milking effect, visualized on conventional coronary angiography (CAG). Average percentage of narrowing of the MB was 36±14%.

Conclusion: High-quality systolic and diastolic images can be acquired using DSCT. Dynamic visualization of MB is possible, and milking effect can be quantified using DSCT.
A model for non-local electron heat transport
Authors: Wang A.K. , Wang H. , Jiang H.B , Wang Z.T
Published: July 2009

Microphysically, the electromagnetic electron temperature gradient (ETG) mode is studied within the framework of electron magnetohydrodynamics (EMHD). It is discovered that the dominant electromagnetic ETG instability in the core regime of low density plasma is a short-wavelength one. The instability-induced turbulent heating makes the core electron temperature (T
e) to rise. The condition for the core T
e rise in low density plasma, obtained from the ETG instability, is consistent with the experimental observation qualitatively. Furthermore, the electromagnetic ETG instability in high density plasma is also studied and compared with the experimental results. Macrophysically, a global energy balance equation is extended to tokamak plasma from a reversed pinch one. From the equation it is shown that the edge heat pulse weakens the core T
e rise or even makes the non-local effect disappear, one phenomenon observed in experiments. Accordingly, the macro-parameter condition for the core T
e rise is obtained. Finally, the analyses of electron heat transport coefficient indicate that when the core T
e rises in response to the edge cold pulse, the heat transport coefficient reduces largely due to the excited short-wavelength electromagnetic ETG turbulence in low density plasma.
Generation control of fast electron beam by low-density foam for FIREX-I
Authors: Sakagami H. , Johzaki T. , Nagatomo H. , Mima K.
Published: July 2009

Integrated simulations for fast ignition with a cone-guided target and a 10 ps heating laser have been performed to investigate core heating properties in FIREX-I experiments. It is found that the fast electron beam intensity scales well as the inverse square root of the front electron density, and the averaged core temperature reaches a higher value when the preformed plasma on an inner surface of the cone tip has a longer scale length. As the scale length of the preformed plasma is not easily controllable, a low-density foam coated target is proposed to prevent the reduction in the fast electron beam intensity during the laser irradiation. Optimum foam density and thickness are estimated by averaged core electron temperatures calculated by the integrated simulations.
Non-perturbative statistical theory of intermittency in ITG drift wave turbulence with zonal flows
Authors: Anderson Johan , Kim Eun-jin
Published: July 2009

The probability distribution functions (PDFs) of momentum flux and zonal flow formation in ion-temperature-gradient (ITG) turbulence are investigated in two different models. The first is a general five-field model (n
i, ϕ, T
i, T
e, v
i∥) where a reductive perturbation method is used to derive dynamical equations for drift waves and a zonal flow. The second is a reduced two-field model (ϕ, T
i) that has an exact non-linear solution (bipolar vortex soliton). In both models the exponential tails of the zonal flow PDFs are found with the same scaling (
), but with different coefficients c
ZF. The PDFs of momentum flux is, however, found to be qualitatively different with the scaling (PDF ∼ exp{−c

M

R

s
}), where s = 2 and s = 3/2 in the five and two-field models, respectively.