bluuebunny/crossref_metadata_2025 huggingface dataset:
Vertical turbulent diffusion in stably stratified flows
Authors: Lindborg Erik , Fedina Ekaterina
Published: January 2009

Based on a Lagrangian description of fluid particle dispersion we suggest that there is a single expression for the vertical eddy diffusivity for all scalars following fluid particles in stably stratified flows. This expression is the same as the Osborn‐Cox diffusivity for buoyancy. To test this hypothesis we carry out turbulence simulations with stable background stratification by solving the Boussinesq equations with random forcing together with the equation for a passive scalar with an initial vertical Gauss profile. The development of the mean scalar concentration is studied for three different values of the width of the profile, σ. It is found that the passive scalar diffuses in very good agreement with the classical diffusion equation if the ratio between σ and a turbulent length scale is large enough. The associated eddy diffusivity agrees exactly with the Osborn‐Cox diffusivity for buoyancy.
A mechanism for African monsoon breaks: Mediterranean cold air surges
Authors: Vizy Edward K. , Cook Kerry H.
Published: January 2009

Surges of cold air from the Mediterranean into northern Africa during the boreal summer are documented, and their influence on monsoon breaks is analyzed using Tropical Rainfall Measuring Mission rainfall estimates and reanalysis products. Between 1998 and 2006, 6–10 cold air surges occurred each summer, with low‐level temperature anomalies ranging from less than −1 K to over −6 K. Composite analysis indicates that cold air surges over northern Africa persist for 2–10 days and travel equatorward at approximately 5.5 m s–1, which is 0.5–1.5 m s–1 faster than the observed climatological low‐level meridional flow. Northern African cold surges have characteristics similar to surges observed elsewhere in the world, including a hydrostatically induced ridge of surface pressure and an amplified upper tropospheric ridge/trough pattern. The African cold surge is preceded by the passage of a shortwave trough and an intensification of the upper tropospheric subtropical westerly jet streak over the Mediterranean Sea. These events are associated with increased confluence in the jet entrance region over the central Mediterranean, an enhanced direct secondary circulation, subsidence, and low‐level ageostrophic northerly flow over northeastern Africa. Composite analysis shows that the passage of a cold surge is associated with an enhancement in convective activity over southern Algeria, western Niger, northern Mali, and Mauritania 2 to 5 days before the surge reaches the eastern Sahel (∼17.5°N), when northeasterly flow channeled between the Atlas and Ahaggar Mountains strengthens and transports relatively moist air from the western Mediterranean and eastern North Atlantic over the region and increases moisture convergence over western Africa north of 20°N. Over the eastern Sahel of Sudan and eastern Chad, the composite results reveal a break in convective activity and decrease in low‐level convergence when the surge arrives that persists for about 6 days. These results offer great promise for improving the short‐range prediction of rainfall over northern Africa.
Ribosome hijacking: a role for small protein B during trans‐translation
Authors: Nonin‐Lecomte Sylvie , Germain‐Amiot Noella , Gillet Reynald , Hallier Marc , Ponchon Luc , Dardel Frédéric , Felden Brice
Published: January 2009

Tight recognition of codon–anticodon pairings by the ribosome ensures the accuracy and fidelity of protein synthesis. In eubacteria, translational surveillance and ribosome rescue are performed by the ‘tmRNA–SmpB’ system (transfer messenger RNA–small protein B). Remarkably, entry and accommodation of aminoacylated‐tmRNA into stalled ribosomes occur without a codon–anticodon interaction but in the presence of SmpB. Here, we show that within a stalled ribosome, SmpB interacts with the three universally conserved bases G530, A1492 and A1493 that form the 30S subunit decoding centre, in which canonical codon–anticodon pairing occurs. The footprints at positions A1492 and A1493 of a small decoding centre, as well as on a set of conserved SmpB amino acids, were identified by nuclear magnetic resonance. Mutants at these residues display the same growth defects as for ΔsmpB strains. The SmpB protein has functional and structural similarities with initiation factor 1, and is proposed to be a functional mimic of the pairing between a codon and an anticodon.
Infraparticle scattering states in nonrelativistic quantum electrodynamics. II. Mass shell properties
Authors: Chen Thomas , Fröhlich Jürg , Pizzo Alessandro
Published: January 2009

We study the infrared problem in the usual model of quantum electrodynamics with nonrelativistic matter. We prove spectral and regularity properties characterizing the mass shell of an electron and one-electron infraparticle states of this model. Our results are crucial for the construction of infraparticle scattering states, which are treated in a separate paper.
On the rational monodromy-free potentials with sextic growth
Authors: Gibbons J. , Veselov A. P.
Published: January 2009

We study the rational potentials V(x), with sextic growth at infinity, such that the corresponding one-dimensional Schrödinger equation has no monodromy in the complex domain for all values of the spectral parameter. We investigate in detail the subclass of such potentials which can be constructed by the Darboux transformations from the well-known class of quasiexactly solvable potentials V=x6−νx2+l(l+1)/x2. We show that, in contrast with the case of quadratic growth, there are monodromy-free potentials which have quasirational eigenfunctions, but which cannot be given by this construction. We discuss the relations between the corresponding algebraic varieties and present some elementary solutions of the Calogero–Moser problem in the external field with sextic potential.
From carbon nanobells to nickel nanotubes
Authors: Ma S. , Srikanth V. V. S. S. , Maik D. , Zhang G. Y. , Staedler T. , Jiang X.
Published: January 2009

A generic strategy is proposed to prepare one dimensional (1D) metallic nanotubes by using 1D carbon nanostructures as the initial templates. Following the strategy, nickel (Ni) nanotubes are prepared by using carbon nanobells (CNBs) as the initial templates. CNBs are first prepared by microwave plasma enhanced chemical vapor deposition technique. Carbon/nickel core/shell structures are then prepared by electroplating the CNBs in a nickel-Watts electrolytic cell. In the final step, the carbon core is selectively removed by employing hydrogen plasma etching to obtain Ni nanotubes. The mechanism leading to Ni nanotubes is briefly discussed.
Strong influence of a magnetic layer on the critical current of Nb bridge in finite magnetic fields due to surface barrier effect
Authors: Vodolazov D. Y. , Gribkov B. A. , Klimov A. Yu. , Rogov V. V. , Vdovichev S. N.
Published: January 2009

We measured the critical current of the bilayer Nb/Co in the applied magnetic field. When the magnetic field was tilted to the axis which was perpendicular to the plane of the bilayer we observed a large difference in critical currents flowing in opposite directions. We found that the largest critical current of the bilayer exceeded the critical current of the superconductor without Co layer in a wide range of the tilted magnetic fields. The theory which takes into account the surface barrier effect for vortex entry and magnetic field of the magnetic layer gave a quantitative explanation of our experimental results.
Effect of ion beam irradiation and rubbing on the directional behavior and alignment mechanism of liquid crystals on polyimide surfaces
Authors: Lee Kang-Min , Oh Byeong-Yun , Kim Young-Hwan , Seo Dae-Shik
Published: January 2009

We investigated the effects of ion beam (IB) irradiation and rubbing on the directional behavior and alignment mechanism of liquid crystals (LCs) on polyimide (PI) surfaces. We found that the LC direction follows the IB irradiation alignment direction on the PI surface regardless of whether the irradiation occurs before or after rubbing. We assumed that the LC direction depends strongly on the C–O bonds created from C=O bonds on the PI surface broken by IB irradiation and conducted an investigation of the chemical bonding state of the PI surface by x-ray photoelectron spectroscopy.
Surface roughness evolution of nanocomposite thin films
Authors: Turkin A. A. , Pei Y. T. , Shaha K. P. , Chen C. Q. , Vainshtein D. I. , De Hosson J. Th. M.
Published: January 2009

An analysis of dynamic roughening and smoothening mechanisms of thin films grown with pulsed-dc magnetron sputtering is presented. The roughness evolution has been described by a linear stochastic equation, which contains the second- and fourth-order gradient terms. Dynamic smoothening of the growing interface is explained by ballistic effects resulting from impingements of ions to the growing thin film. These ballistic effects are sensitive to the flux and energy of impinging ions. The predictions of the model are compared with experimental data, and it is concluded that the thin film roughness can be further controlled by adjusting waveform, frequency, and width of dc pulses.
Distribution of magnetization in the finite Ising chain
Authors: García-Pelayo Ricardo
Published: January 2009

An isomorphism is shown to hold between the persistent random walk and the Ising chain, as well as between the biased, persistent random walk and the closed Ising chain in the presence of an external magnetic field. The analytical expressions for the distributions of spontaneous and induced magnetization for the Ising chain are derived using this isomorphism (we show that this derivation is significantly more laborious using the partition function).
The self-referential method for linear rigid bodies: Application to hard and Lennard-Jones dumbbells
Authors: Sweatman Martin B. , Atamas Alexander , Leyssale Jean-Marc
Published: January 2009

The self-referential (SR) method incorporating thermodynamic integration (TI) [Sweatman et al., J. Chem. Phys. 128, 064102 (2008)] is extended to treat systems of rigid linear bodies. The method is then applied to obtain the canonical ensemble Helmholtz free energy of the α-N2 and plastic face centered cubic phases of systems of hard and Lennard-Jones dumbbells using Monte Carlo simulations. Generally good agreement with reference literature data is obtained, which indicates that the SR-TI method is potentially very general and robust.
On the physical origin of the nozzle characteristic and its connection with the double-arcing phenomenon in a cutting torch
Authors: Prevosto L. , Kelly H. , Mancinelli B.
Published: January 2009

The nozzle current-voltage characteristic for a cutting arc is presented in this work. The measurements are reported using a high energy density cutting arc torch with a nozzle bore radius of 0.5 mm. The arc current was fixed at 30 A while the plenum pressure and the oxygen gas mass flow rate were varied in the range of 0.55–0.65 MPa and 0.32–0.54 g s−1, respectively. The results show a very low electron density and the lack of electron attachment at the plasma boundary layer. No ion saturation current was found. For the smallest mass flow rate value gas breakdown was found for a biasing nozzle potential close to that of the cathode, but no evidence of such breakdown was found for the larger mass flow rate values. Using an expression for the ion speed at the entry of the collisional sheath formed between the nonequilibrium plasma and the negatively biased nozzle wall together with a generalized Saha equation coupled to the ion branch of the characteristic, the radial profile of the electron temperature, the spatial distribution of the plasma density at the plasma boundary, and the sheath thickness were obtained. In particular, the obtained thickness value at the breakdown condition was in good agreement with that obtained from the oxygen Paschen’s curve. An electron temperature of about 4700–5700 K and a corresponding plasma density of the order of 1019–1020 m−3 were found close to the nozzle wall. A physical interpretation on the origin of the double-arcing phenomenon is presented, that explains why the double-arcing (that it is established when the sheath breaks down) appears at low values of the gas mass flow.
Understanding rubber friction in the presence of water using sum-frequency generation spectroscopy
Authors: Nanjundiah Kumar , Hsu Ping Yuan , Dhinojwala Ali
Published: January 2009

Infrared-visible sum-frequency-generation spectroscopy (SFG) was used to study the molecular structure of water between a poly(dimethylsiloxane) (PDMS) and a sapphire substrate. The observation of SFG peaks associated with the dangling surface hydroxyl groups (3690 cm−1) and water bands (3000–3400 cm−1) indicates that the contact spot between the PDMS lens and the sapphire substrate is heterogeneous. Within the contact spot there are regions where the methyl groups of the PDMS chains are in direct contact with the surface hydroxyl groups on the sapphire substrate. In the other regions, a thin water layer is trapped between the two surfaces with spectral features that are different from that of the unconfined water next to the sapphire or the PDMS surface. The higher adhesion and friction values observed in these experiments, compared to those expected for a uniform thin layer of water trapped between the PDMS and the sapphire substrate, are consistent with the hypothesis that the contact spot is heterogeneous. These results have important implications in understanding the sliding behavior of wet, deformable hydrophobic materials on hydrophilic substrates.
Stimulated Brillouin scattering of laser radiation in a piezoelectric semiconductor: Quantum effect
Authors: Uzma Ch. , Zeba I. , Shah H. A. , Salimullah M.
Published: January 2009

Using quantum-hydrodynamic model, the phenomenon of the stimulated Brillouin scattering of a laser radiation in an unmagnetized piezoelectric semiconductor has been examined in detail. It is noticed that the Bohm potential in the electron dynamics of the semiconductor plasma enhances drastically the growth rate of the stimulated Brillouin scattering at higher values of the electron number density of the semiconductor plasma and the wave number of the electron-acoustic wave in the semiconductor.
Long-wave instability of a multicomponent fluid layer with the Soret effect
Authors: Ryzhkov Ilya I. , Shevtsova Valentina M.
Published: January 2009

The long-wave instability of a vertical multicomponent fluid layer is investigated. The basic state is a plane parallel flow with linear profiles of temperature and composition in the cross section. The compositional stratification is induced by the Soret effect. The problem is reduced to that without cross-diffusion effect by a linear change of composition and separation ratios that characterize the Soret separation. This is the first report where such transformation is derived for the equations of multicomponent convection with thermal diffusion. It simplifies the system reducing the number of control parameters and can be applied to a variety of multidiffusive convection problems (e.g., Rayleigh–Bénard configuration). It is shown that the long-wave instability is caused by the interplay between the basic flow and concentration waves with long scale in the vertical direction. In the general case of n-component mixture, several stable regions in the parameter space are identified. A complete parametric study for ternary fluid revealed complex instability scenarios in the long-wave limit: monotonic instability in a certain range of Grashof numbers, the transition from monotonic to oscillatory instability with increasing Grashof, etc. The physical mechanisms underlying this complex behavior are discussed and explained. In addition to the long-wave stability analysis, we performed numerical calculations for finite wave numbers. These calculations showed that the monotonic long-wave perturbations represent the most unstable modes.
Integrated dye-sensitized solar cell module with conversion efficiency of 8.2%
Authors: Han Liyuan , Fukui Atsushi , Chiba Yasuo , Islam Ashraful , Komiya Ryoichi , Fuke Nobuhiro , Koide Naoki , Yamanaka Ryohsuke , Shimizu Masafumi
Published: January 2009

We investigated an integrated dye-sensitized solar cell (DSC) module composed of a number of rectangular cells connected in series. Because neighboring cells are processed in reverse, the module is known as the W-contact module. It achieves a high active area of 85% by eliminating the interconnection between neighboring cells. By adjusting the transmittance of the Pt-coated counterelectrode, the TiO2 thickness, and the composition of the electrolyte, we achieved an overall energy conversion efficiency of 8.2% (aperture area of 25.45 cm2) as measured by a public test center under AM 1.5 irradiation. This sets a record for the confirmed efficiency of a DSC submodule.
A first principles investigation of water dipole moment in a defective continuous hydrogen bond network
Authors: Scipioni Roberto , Schmidt Diedrich A. , Boero Mauro
Published: January 2009

First principles molecular dynamics simulations of an aqueous solution salt system at finite concentration containing both Na+ and Cl− ions show that a change in the distribution of the molecular dipole moment of H2O monomers appears when ions are present in solution. Simulations suggest a lowering of the dipole moments of the water molecules in the solvation shells of Na+ and Cl− as compared to the pure water case, while the dipoles of the rest of the molecules are hardly affected. However, finer analysis in terms of the Wannier centers distribution suggests a change in the electronic structure of the water molecules even in the bulk. Also a change of the H-bond network arrangement was found and correlation between dipole and MOH parameter evidences such subtle effects, suggesting a lowering of tetrahedral order in salty solutions. All these changes can be related to observable quantities such as the infrared spectra thus allowing for a rationalization of the experimental outcome on neutral aqueous solutions.
Vertical hydrodynamic focusing in glass microchannels
Authors: Lin Tony A. , Hosoi A. E. , Ehrlich Daniel J.
Published: January 2009

Vertical hydrodynamic focusing in microfluidic devices is investigated through simulation and through direct experimental verification using a confocal microscope and a novel form of stroboscopic imaging. Optimization for microfluidic cytometry of biological cells is examined. By combining multiple crossing junctions, it is possible to confine cells to a single analytic layer of interest. Subtractive flows are investigated as a means to move the analysis layer vertically in the channel and to correct the flatness of this layer. The simulation software (ADINA and Coventor) is shown to accurately capture the complex dependencies of the layer interfaces, which vary strongly with channel geometry and relative flow rates.
Investigation of compounds for magnetocaloric applications: YFe2H4.2, YFe2D4.2, and Y0.5Tb0.5Fe2D4.2
Authors: Paul-Boncour V. , Mazet T.
Published: January 2009

The magnetocaloric properties of powder samples of the monoclinic YFe2H4.2, YFe2D4.2, and Y0.5Tb0.5Fe2D4.2 compounds have been studied at their itinerant electron metamagnetic transition (TM0=131, 84, and 127 K, respectively). Large reversible entropy changes are observed, up to −ΔSM=10.83 J K−1 kg−1 for a field variation of 5 T in YFe2D4.2, making these alloys candidates for magnetic refrigeration applications. The results are compared with previously published data on other potential magnetic refrigerants with itinerant electron metamagnetic transitions.
Site-selective investigation of site symmetry and site occupation of iron in Fe-doped lithium niobate crystals
Authors: Vitova Tonya , Hormes Josef , Falk Matthias , Buse Karsten
Published: January 2009

Lithium niobate (LN) crystals, in particular after strong oxidation, are of great relevance for applications in photorefraction and nonlinear optics. Crystals doped with 2 or 4 wt % of iron are studied by extended x-ray absorption fine structure spectroscopy. The Fe atoms are observed to be sixfold coordinated by oxygen atoms and incorporated into the Li site. No evidence for formation of iron oxide clusters is found. In situ x-ray absorption spectroscopy measurements of the thermoelectric oxidation of a LN:Fe 2 wt % crystal and the analyses of the partially site-selective x-ray absorption near edge structure spectra of a LN:Fe 4 wt % crystal provide site-selective structural information. We found that the Fe2+ and Fe3+ sites have the same site symmetries and positions in the LN matrix, i.e., the Fe2+ and Fe3+ atoms are both octahedrally coordinated by six oxygen atoms and both occupy the Li site.
Impact of air exposure on the chemical and electronic structure of ZnO:Zn3N2 thin films
Authors: Bär M. , Ahn K.-S. , Shet S. , Yan Y. , Weinhardt L. , Fuchs O. , Blum M. , Pookpanratana S. , George K. , Yang W. , Denlinger J. D. , Al-Jassim M. , Heske C.
Published: January 2009

The chemical and electronic surface structure of ZnO:Zn3N2 (ZnO:N) thin films with different N contents was investigated by soft x-ray emission spectroscopy. Upon exposure to ambient air (in contrast to storage in vacuum), the chemical and electronic surface structure of the ZnO:N films changes substantially. In particular, we find that the Zn3N2∕(Zn3N2+ZnO) ratio decreases with exposure time and that this change depends on the initial N content. We suggest a degradation mechanism based on the reaction of the Zn3N2 content with atmospheric humidity.
Functionalized heterofullerenes for hydrogen storage
Authors: Sun Qiang , Wang Qian , Jena Puru
Published: January 2009

Using density functional theory, we show that Li decorated B doped heterofullerene (Li12C48B12) has the following desired properties of a hydrogen storage material. (1) The Li atoms remain isolated. (2) Through charge transfer to electron deficient C48B12 heterofullerene, the Li atoms become positively charged. (3) Each Li atom is able to bind up to three H2 molecules, which remain in molecular form, and the binding energies of successive H2 molecules are in the range of 0.135–0.172 eV/H2, suitable for ambient temperature storage. (4) The gravimetric density reaches the 9 wt % limit necessary for applications in the mobile industry.
Enhanced magnetoresistance in self-assembled monolayer of oleic acid molecules on Fe3O4 nanoparticles
Authors: Wang S. , Yue F. J. , Wu D. , Zhang F. M. , Zhong W. , Du Y. W.
Published: January 2009

Spin transport through molecules is investigated using self-assembled monolayers of oleic acid molecules on half metallic Fe3O4 nanoparticles. Fourier transform infrared spectroscopy measurements indicate that 1 ML (monolayer) molecules chemically bond to the Fe3O4 nanoparticles and the physically absorbed molecules do not exist in the samples. The magnetoresistance (MR) of cold-pressed, molecule fully covered nanoparticles is up to 7.3% at room temperature and 17.5% at 115 K under a field of 5.8 kOe. The MR ratio is more than two times larger than that of pure Fe3O4 nanoparticles. This enhanced MR is likely arising from weak spin scattering while carriers hop through the oleic acid molecules. These results show that small molecules are promising for development of future spin-based molecular electronics.
An automatic liquid-nitrogen filling system for multiple Ge detectors
Authors: Koizumi Mitsuo , Oshima Masumi , Toh Yosuke , Kimura Atsushi , Kin Tadahiro , Furutaka Kazuyoshi , Murakami Yukihiro , Osa Akihiko , Ando Shingo
Published: January 2009

In order to reduce the time and effort of the daily task of refilling Dewar vessels of Ge detectors with liquid nitrogen (LN2), we have developed an automatic LN2 filling system equipped with a LN2 plant. With this system, we were freed from the work of LN2 filling. Such an LN2 filling system is useful for moderate-scale Ge detector arrays consisting of fewer than 20 Ge detectors.
Photodetectors formed by an indium tin oxide/zinc oxide/p-type gallium nitride heterojunction with high ultraviolet-to-visible rejection ratio
Authors: Lee M. L. , Chi Ping-Feng , Sheu J. K.
Published: January 2009

In this study, indium tin oxide (ITO) or ITO/ZnO films, which were prepared by magnetron sputtering, were deposited onto p-GaN epitaxial films to form ultraviolet photodetectors (PDs). The ITO/ZnO/p-GaN heterojunction PDs behave like the p-i-n photodiodes, which characteristically exhibit low dark current, as opposed to the ITO/p-GaN PDs, which exhibit a marked bias-dependent dark current. The zero-bias rejection ratio can be improved up to 4×105 due to a further reduction in the dark current compared to the ITO/p-GaN PDs. When the incident wavelength is 360 nm, the ITO/ZnO/p-GaN heterojunction PD exhibits a zero-bias photocurrent/dark current ratio and a responsivity of approximately 8×104 and 0.015 A/W, respectively.
Electrical characteristics of lateral heterostructure organic field-effect bipolar transistors
Authors: Singh Samarendra P. , Sonar Prashant , Sellinger Alan , Dodabalapur Ananth
Published: January 2009

We describe and discuss the unique electrical characteristics of an organic field-effect transistor in which the active layer consists of a type II lateral heterojunction located approximately midway between the source and drain. The two active semiconductors on either side of the junction transport only one carrier type each, with the other becoming trapped, which leads to devices that operate in only the steady state when there is balanced electron and hole injections from the drain and source. We describe the unique transfer characteristics of such devices in two material systems.
Pt/Co/oxide and oxide/Co/Pt electrodes for perpendicular magnetic tunnel junctions
Authors: Nistor L. E. , Rodmacq B. , Auffret S. , Dieny B.
Published: January 2009

This letter presents a study of perpendicular magnetic anisotropy in oxide/Co/Pt structures, which could constitute the upper magnetic electrode of magnetic tunnel junctions. The growth of cobalt layers on SiO2 substrates shows that all 0.6 nm thick Co films are superparamagnetic, whereas perpendicular magnetic anisotropy is obtained for 1.5 nm films after annealing. Co layers grown on various Al and Mg oxides prepared by sputtering also exhibit perpendicular magnetic anisotropy after annealing. Combined with inverse Pt/Co(CoFeB)/oxide stackings, these structures allow preparing tunnel junctions with thicker magnetic electrodes and much better thermal stability than those based on standard Pt/Co multilayers.
Model-free iterative control of repetitive dynamics for high-speed scanning in atomic force microscopy
Authors: Li Yang , Bechhoefer John
Published: January 2009

We introduce an algorithm for calculating, offline or in real time and with no explicit system characterization, the feedforward input required for repetitive motions of a system. The algorithm is based on the secant method of numerical analysis and gives accurate motion at frequencies limited only by the signal-to-noise ratio and the actuator power and range. We illustrate the secant-solver algorithm on a stage used for atomic force microscopy.
Mg-doped GaN nanostructures: Energetics, magnetism, and H2 adsorption
Authors: Wang Qian , Sun Qiang , Jena Puru , Kawazoe Yoshiyuki
Published: January 2009

Using density functional theory and generalized gradient approximation for exchange and correlation potential we show that Mg-doped GaN nanocages and nanotubes can be magnetic with Mg-contributed spins distributed over the neighboring N sites. Mg atoms show no tendency for clustering due to the positive charge residing on them; they can trap hydrogen in molecular form via the charge polarization mechanism. The binding energies of hydrogen lie in the range of 0.1–0.2 eV/H2, which are ideal for storage applications under ambient thermodynamic conditions.
Spin-lattice coupling in multiferroic Pb(Fe1/2Nb1/2)O3 thin films
Authors: Peng Wei , Lemée Nathalie , Karkut Michael , Dkhil Brahim , Shvartsman Vladimir V. , Borisov Pavel , Kleemann Wolfgang , Holc Janez , Kosec Marija , Blinc Robert
Published: January 2009

We made magnetization and x-ray diffraction measurements on an epitaxial Pb(Fe1/2Nb1/2)O3 200 nm film. From the temperature dependence of the out-of-plane lattice parameter, we can assign a Burns’ temperature at Td∼640 K, a temperature at T∗∼510 K (related to the appearance of static polar nanoregions), and an anomaly occurring at 200 K. The latter is precisely the Néel temperature TN determined from magnetization and points to spin-lattice coupling at TN∼200 K. We also observe “weak ferromagnetism” up to 300 K and propose superantiferromagnetic clusters as a plausible scenario to explain this hysteresis above TN.
The dielectric response of the H2Ti3O7 nanotube investigated by valence electron energy loss spectroscopy
Authors: Wang Juan , Li Quan , Peng L.-M. , Malac Marek
Published: January 2009

The dielectric response of an anisotropic nanostructure, individual H2Ti3O7 nanotube with ∼8–10 nm diameter, has been investigated using both momentum transfer dependent and spatially resolved valence electron energy loss spectroscopies. The dielectric response of an individual nanotube is found to be dominated by several surface related excitations and defect states, although its basic electronic structure (such as the band gap and single electron interband transitions) is similar to that of TiO2. The possible origins of the surface excitations in such a tubular structure are also discussed.
Unambiguous evidence for magnetoelectric coupling of multiferroic origin in 0.73BiFeO3–0.27PbTiO3
Authors: Bhattacharjee Shuvrajyoti , Pandey V. , Kotnala R. K. , Pandey Dhananjai
Published: January 2009

Magnetization, frequency dependent dielectric, and structural studies on 0.73BiFeO3–0.27PbTiO3 in the temperature range from 300 to 600 K reveal anomalies in the unit cell parameters and the intrinsic value of the dielectric constant, free from space charge contributions, at the antiferromagnetic transition temperature (TN). Our results provide unambiguous confirmation of magnetoelectric coupling of multiferroic origin at TN and evidence for monoclinic distortion of the ferroelectric phase.
Bandwidth extension by trade-off of electrical and optical gain in a transistor laser: Three-terminal control
Authors: Then H. W. , Feng M. , Holonyak N.
Published: January 2009

We present data and describe analytically the “trade-off” between collector current gain and the differential optical gain of a heterojunction bipolar transistor laser (TL). The electrical-optical gain relationship shows that a reduction in the transistor current gain is accompanied by an increase in the differential optical gain of the TL and, as a consequence, results in a larger optical modulation bandwidth. Third-terminal electrical control can be used to enhance the optical bandwidth of a TL beyond the “gain-clamped” cutoff limitation of the carrier-photon (population) resonance characteristic of a diode laser.
Efficient generation of surface plasmon by single-nanoslit illumination under highly oblique incidence
Authors: Wang B. , Aigouy L. , Bourhis E. , Gierak J. , Hugonin J. P. , Lalanne P.
Published: January 2009

Using scanning near-field optical microscopy, we investigate the ability of nanoslits in metallic films to launch surface plasmon polaritons (SPPs) under highly oblique incidence at λ=975 nm. The SPP generation efficiency is inferred by fitting the recorded near-field data with a simple analytical model. We find a remarkably large efficiency of 20% for the front side of the slit, which is in agreement with recent theoretical predictions relying on a fully vectoral electromagnetic formalism. An even larger efficiency is predicted experimentally (44%) and theoretically (33%) for the rear side. The present near-field analysis provides a direct approach to measure SPP generation efficiencies and may find applications for characterizing SPP devices.
Experimental verification of broadband cloaking using a volumetric cloak composed of periodically stacked cylindrical transmission-line networks
Authors: Alitalo Pekka , Bongard Frédéric , Zürcher Jean-Francois , Mosig Juan , Tretyakov Sergei
Published: January 2009

Cloaking using a volumetric structure composed of stacked two-dimensional transmission-line networks is verified with numerical simulations and measurements. The measurements are done in a waveguide, in which an array of metal cylinders is inserted causing a short circuit in the waveguide. The metal cylinders are cloaked using the transmission-line structure, which “hides” the cylinders and thus enables wave propagation inside the waveguide.
A high performance In0.53Ga0.47As metal-oxide-semiconductor field effect transistor with silicon interface passivation layer
Authors: Zhu Feng , Zhao Han , Ok I. , Kim H. S. , Yum J. , Lee Jack C. , Goel Niti , Tsai W. , Gaspe C. K. , Santos M. B.
Published: January 2009

In this letter, we demonstrate a high performance In0.53Ga0.47As channel n-type metal-oxide-semiconductor field effect transistor with silicon interface passivation layer (IPL) and HfO2 gate oxide. Owing to the effectiveness of Si IPL on improving the interface quality, good device characteristics have been obtained, including the peak transconductance of 7.7 mS/mm (Lg=5 μm and Vd=50 mV), drive current of 158 mA/mm (Lg=5 μm, Vgs=Vth+2 V, and Vd=2.5 V), and the peak effective channel mobility of 1034 cm2/V s. As an important factor on device design, the impact of silicon IPL thickness on the transistor characteristics has been investigated.
Spatial distribution of oxygen vacancies in Cr-doped SrTiO3 during an electric-field-driven insulator-to-metal transition
Authors: Andreasson B. P. , Janousch M. , Staub U. , Meijer G. I.
Published: January 2009

Spatially resolved x-ray fluorescence maps are presented that show the introduction and the evolution of oxygen vacancies in chromium-doped strontium titanate during an electric-field-driven insulator-to-metal transition. The vacancies are introduced at the anode and diffuse through the crystal toward the cathode. The spatial distribution of vacancies is explained by a model describing the electrical breakdown as a percolation process. Strong differences in the vacancy distribution were found when the transition took place in air and in a hydrogen-enriched atmosphere. In air, the vacancies disappeared from the surface, whereas in the reducing hydrogen atmosphere, they remained at the surface.
HIV-1 Tat RNA silencing suppressor activity is conserved across kingdoms and counteracts translational repression of HIV-1
Authors: Qian Shuiming , Zhong Xuehua , Yu Lianbo , Ding Biao , de Haan Peter , Boris-Lawrie Kathleen
Published: January 2009

The RNA silencing pathway is an intracellular innate response to virus infections and retro-transposons. Many plant viruses counter this host restriction by RNA silencing suppressor (RSS) activity of a double-stranded RNA-binding protein, e.g., tomato bushy stunt virus P19. Here, we demonstrate P19 and HIV-1 Tat function across the plant and animal kingdoms and suppress a common step in RNA silencing that is downstream of small RNA maturation. Our experiments reveal that RNA silencing in HIV-1 infected human cells severely attenuates the translational output of the unspliced HIV-1 gag mRNA, and possibly all HIV-1 transcripts. The attenuation in gag mRNA translation is exacerbated by K51A substitution in the Tat double-stranded RNA-binding domain. Tat, plant virus RSS, or Dicer downregulation rescues robust gag translation and bolsters HIV-1 virion production. The reversal of HIV-1 translation repression by plant RSS supports the recent finding in
Arabidopsis
that plant miRNAs operate by translational inhibition. Our results identify common features between RNA silencing suppression of plant and animal viruses. We suggest that RNA silencing-mediated translation repression plays a strategic role in determining the viral set-point in a newly HIV-1-infected patient.
Active site dynamics in the zinc-dependent medium chain alcohol dehydrogenase superfamily
Authors: Baker Patrick J. , Britton K. Linda , Fisher Martin , Esclapez Julia , Pire Carmen , Bonete Maria Jose , Ferrer Juan , Rice David W.
Published: January 2009

Despite being the subject of intensive investigations, many aspects of the mechanism of the zinc-dependent medium chain alcohol dehydrogenase (MDR) superfamily remain contentious. We have determined the high-resolution structures of a series of binary and ternary complexes of glucose dehydrogenase, an MDR enzyme from
Haloferax mediterranei
. In stark contrast to the textbook MDR mechanism in which the zinc ion is proposed to remain stationary and attached to a common set of protein ligands, analysis of these structures reveals that in each complex, there are dramatic differences in the nature of the zinc ligation. These changes arise as a direct consequence of linked movements of the zinc ion, a zinc-bound bound water molecule, and the substrate during progression through the reaction. These results provide evidence for the molecular basis of proton traffic during catalysis, a structural explanation for pentacoordinate zinc ion intermediates, a unifying view for the observed patterns of metal ligation in the MDR family, and highlight the importance of dynamic fluctuations at the metal center in changing the electrostatic potential in the active site, thereby influencing the proton traffic and hydride transfer events.
Structure of the Ebola VP35 interferon inhibitory domain
Authors: Leung Daisy W. , Ginder Nathaniel D. , Fulton D. Bruce , Nix Jay , Basler Christopher F. , Honzatko Richard B. , Amarasinghe Gaya K.
Published: January 2009

Ebola viruses (EBOVs) cause rare but highly fatal outbreaks of viral hemorrhagic fever in humans, and approved treatments for these infections are currently lacking. The Ebola VP35 protein is multifunctional, acting as a component of the viral RNA polymerase complex, a viral assembly factor, and an inhibitor of host interferon (IFN) production. Mutation of select basic residues within the C-terminal half of VP35 abrogates its dsRNA-binding activity, impairs VP35-mediated IFN antagonism, and attenuates EBOV growth in vitro and in vivo. Because VP35 contributes to viral escape from host innate immunity and is required for EBOV virulence, understanding the structural basis for VP35 dsRNA binding, which correlates with suppression of IFN activity, is of high importance. Here, we report the structure of the C-terminal VP35 IFN inhibitory domain (IID) solved to a resolution of 1.4 Å and show that VP35 IID forms a unique fold. In the structure, we identify 2 basic residue clusters, one of which is important for dsRNA binding. The dsRNA binding cluster is centered on Arg-312, a highly conserved residue required for IFN inhibition. Mutation of residues within this cluster significantly changes the surface electrostatic potential and diminishes dsRNA binding activity. The high-resolution structure and the identification of the conserved dsRNA binding residue cluster provide opportunities for antiviral therapeutic design. Our results suggest a structure-based model for dsRNA-mediated innate immune antagonism by Ebola VP35 and other similarly constructed viral antagonists.
Local conformational dynamics in α-helices measured by fast triplet transfer
Authors: Fierz Beat , Reiner Andreas , Kiefhaber Thomas
Published: January 2009

Coupling fast triplet–triplet energy transfer (TTET) between xanthone and naphthylalanine to the helix–coil equilibrium in alanine-based peptides allowed the observation of local equilibrium fluctuations in α-helices on the nanoseconds to microseconds time scale. The experiments revealed faster helix unfolding in the terminal regions compared with the central parts of the helix with time constants varying from 250 ns to 1.4 μs at 5 °C. Local helix formation occurs with a time constant of ≈400 ns, independent of the position in the helix. Comparing the experimental data with simulations using a kinetic Ising model showed that the experimentally observed dynamics can be explained by a 1-dimensional boundary diffusion with position-independent elementary time constants of ≈50 ns for the addition and of ≈65 ns for the removal of an α-helical segment. The elementary time constant for helix growth agrees well with previously measured time constants for formation of short loops in unfolded polypeptide chains, suggesting that helix elongation is mainly limited by a conformational search.
Crystal structure of the conserved N-terminal domain of the peroxisomal matrix protein import receptor, Pex14p
Authors: Su Jian-Rong , Takeda Kazuki , Tamura Shigehiko , Fujiki Yukio , Miki Kunio
Published: January 2009

Pex14p is a central component of the peroxisomal protein import machinery, in which the conserved N-terminal domain mediates dynamic interactions with other peroxins including Pex5p, Pex13p, and Pex19p. Here, we report the crystal structure of the conserved N-terminal domain of Pex14p with a three-helix bundle. A hydrophobic surface is composed of the conserved residues, of which two phenylalanine residues (Phe-35 and Phe-52) protrude to the solvent. Consequently, two putative binding pockets suitable for recognizing the helical WXXXF/Y motif of Pex5p are formed on the surface by the two phenylalanine residues accompanying with positively charged residues. The structural feature agrees well with our earlier findings where F35A/L36A and F52A/L53A mutants were impaired in the interactions with other peroxins such as Pex5p and Pex13p. Pex14p variants each with Phe-to-Ala mutation at positions 35, 52, and 35/52, respectively, were defective in restoring the impaired peroxisomal protein import in
pex14
Chinese hamster ovary mutant ZP161 cells. Moreover, in GST pull-down assays His
6
-Pex5pL bound only to GST-Pex14p(25–70), not to any of GST-Pex14p(25–70)F35A, GST-Pex14p(25–70)F52A, and GST-Pex14p(25–70)F35A/F52A. Endogenous Pex5p was recruited to FLAG-Pex14p on peroxisomes in vivo but barely to FLAG-Pex14pF35A, FLAG-Pex14pF52A, and FLAG-Pex14pF35A/F52A. Collectively, Phe-35 and Phe-52 are essential for the Pex14p functions, including the interaction between Pex14p and Pex5p.
HER2
YVMA
drives rapid development of adenosquamous lung tumors in mice that are sensitive to BIBW2992 and rapamycin combination therapy
Authors: Perera Samanthi A. , Li Danan , Shimamura Takeshi , Raso Maria G. , Ji Hongbin , Chen Liang , Borgman Christa L. , Zaghlul Sara , Brandstetter Kathleyn A. , Kubo Shigeto , Takahashi Masaya , Chirieac Lucian R. , Padera Robert F. , Bronson Roderick T. , Shapiro Geoffrey I. , Greulich Heidi , Meyerson Matthew , Guertler Ulrich , Chesa Pilar Garin , Solca Flavio , Wistuba Ignacio I. , Wong Kwok-Kin
Published: January 2009

Mutations in the HER2 kinase domain have been identified in human clinical lung cancer specimens. Here we demonstrate that inducible expression of the most common HER2 mutant (HER2
YVMA
) in mouse lung epithelium causes invasive adenosquamous carcinomas restricted to proximal and distal bronchioles. Continuous expression of HER2
YVMA
is essential for tumor maintenance, suggesting a key role for HER2 in lung adenosquamous tumorigenesis. Preclinical studies assessing the in vivo effect of erlotinib, trastuzumab, BIBW2992, and/or rapamycin on HER2
YVMA
transgenic mice or H1781 xenografts with documented tumor burden revealed that the combination of BIBW2992 and rapamycin is the most effective treatment paradigm causing significant tumor shrinkage. Immunohistochemical analysis of lung tumors treated with BIBW2992 and rapamycin combination revealed decreased phosphorylation levels for proteins in both upstream and downstream arms of MAPK and Akt/mTOR signaling axes, indicating inhibition of these pathways. Based on these findings, clinical testing of the BIBW2992/rapamycin combination in non-small cell lung cancer patients with tumors expressing HER2 mutations is warranted.
Increasing Cu bioavailability inhibits Aβ oligomers and tau phosphorylation
Authors: Crouch Peter J. , Hung Lin Wai , Adlard Paul A. , Cortes Mikhalina , Lal Varsha , Filiz Gulay , Perez Keyla A. , Nurjono Milawaty , Caragounis Aphrodite , Du Tai , Laughton Katrina , Volitakis Irene , Bush Ashley I. , Li Qiao-Xin , Masters Colin L. , Cappai Roberto , Cherny Robert A. , Donnelly Paul S. , White Anthony R. , Barnham Kevin J.
Published: January 2009

Cognitive decline in Alzheimer's disease (AD) involves pathological accumulation of synaptotoxic amyloid-β (Aβ) oligomers and hyperphosphorylated tau. Because recent evidence indicates that glycogen synthase kinase 3β (GSK3β) activity regulates these neurotoxic pathways, we developed an AD therapeutic strategy to target GSK3β. The strategy involves the use of copper-
bis
(thiosemicarbazonoto) complexes to increase intracellular copper bioavailability and inhibit GSK3β through activation of an Akt signaling pathway. Our lead compound Cu
II
(gtsm) significantly inhibited GSK3β in the brains of APP/PS1 transgenic AD model mice. Cu
II
(gtsm) also decreased the abundance of Aβ trimers and phosphorylated tau, and restored performance of AD mice in the Y-maze test to levels expected for cognitively normal animals. Improvement in the Y-maze correlated directly with decreased Aβ trimer levels. This study demonstrates that increasing intracellular copper bioavailability can restore cognitive function by inhibiting the accumulation of neurotoxic Aβ trimers and phosphorylated tau.
HLA class I molecules consistently present internal influenza epitopes
Authors: Wahl Angela , Schafer Fredda , Bardet Wilfried , Buchli Rico , Air Gillian M. , Hildebrand William H.
Published: January 2009

Cytotoxic T lymphocytes (CTL) limit influenza virus replication and prevent morbidity and mortality upon recognition of HLA class I presented epitopes on the surface of virus infected cells, yet the number and origin of the viral epitopes that decorate the infected cell are unknown. To understand the presentation of influenza virus ligands by human MHC class I molecules, HLA-B*0702-presented viral peptides were directly identified following influenza infection. After transfection with soluble class I molecules, peptide ligands unique to infected cells were eluted from isolated MHC molecules and identified by comparative mass spectrometry (MS). Then CTL were gathered following infection with influenza and viral peptides were tested for immune recognition. We found that the class I molecule B*0702 presents 3–6 viral ligands following infection with different strains of influenza. Peptide ligands derived from the internal viral nucleoprotein (NP418–426and NP473–481) and from the internal viral polymerase subunit PB1 (PB1329–337) were presented by B*0702 following infection with each of 3 different influenza strains; ligands NP418–426, NP473–481, and PB1329–337derived from internal viral proteins were consistently revealed by class I HLA. In contrast, ligands derived from hemagglutinin (HA) and matrix protein (M1) were presented intermittently on a strain-by-strain basis. When tested for immune recognition, HLA-B*0702 transgenic mice responded to NP418–426and PB1329–337consistently and NP473–481intermittently while ligands from HA and M1 were not recognized. These data demonstrate an emerging pattern whereby class I HLA reveal a handful of internal viral ligands and whereby CTL recognize consistently presented influenza ligands.