bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonexponential magnetization thermal decay of a single-domain particle: Numerical computations using the dynamic Fokker–Planck equation
Authors: Zhang Kezhao
Published: February 2009

Nonexponential thermal decay of magnetization in a single-domain particle has been studied by numerically solving the Fokker–Planck equation as an initial value problem as well as an eigenvalue problem. The probability of not switching and switching time distribution is calculated for a wide range of applied fields and KuV/kBT values. In the low and intermediate energy barrier region, the switching time distribution is nonexponential. The switching time distribution is nonmonotonic and has one peak. For time less than the peak time, the distribution can be well fitted with inverse Gauss distribution; for time longer than the peak time, the distribution is exponential. The time constant of the exponential decay is equal to the inverse of the smallest eigenvalue of the Fokker–Planck equation. Furthermore, the switching time at the peak location of the distribution is a logarithmic function of the smallest eigenvalue.
Bounds on the dynamic magnetic properties of multiresonant nanostructure composites in exchange resonance model
Authors: Zhou P. H. , Deng L. J.
Published: February 2009

Existing bounds expression established on the sum of the gyromagnetic losses is limited by static magnetic interactions. In this paper, we deduce a bounds relation from the Bloch–Bloembergen theorem to depict both the uniform resonance and exchange resonance. It is shown to agree with experiments, of particular relevance to the competition between static magnetic force and exchange interaction. An analytic explanation on favorable multiresonance phenomenon in nanocrystalline iron flakes is achieved.
High-quality antiferromagnetic EuTiO3 epitaxial thin films on SrTiO3 prepared by pulsed laser deposition and postannealing
Authors: Fujita Koji , Wakasugi Naoki , Murai Shunsuke , Zong Yanhua , Tanaka Katsuhisa
Published: February 2009

We report on epitaxial growth and magnetic properties of EuTiO3 thin films with a perovskite structure. Single crystalline EuTiO3 films with atomically flat surface are grown on (001) surface of SrTiO3 by pulsed laser deposition (PLD) and subsequent annealing in reducing atmosphere. The as-deposited films possess the crystal structure with an elongated c-axis and tend to stabilize ferromagnetically ordered Eu2+ spins at low temperatures. Postannealing at 1000 °C relaxes the out-of-plane lattice strain, and brings about a drastic change in magnetic structure; the annealed film becomes an antiferromagnet below Néel temperature of 5.1 K. The change in magnetic properties accompanied by the modification in lattice constant is discussed.
The simulated photoelectron spectrum of 1-propynide
Authors: Papas Brian N. , Schuurman Michael S. , Yarkony David R.
Published: February 2009

The negative ion photoelectron spectrum of 1-propynide is computed by employing the multimode vibronic coupling approach. A three-state quasidiabatic Hamiltonian, Hd, is reported, which accurately represents the ab initio determined equilibrium geometries and harmonic frequencies of the ground X̃ A21 state as well as the low-lying Jahn–Teller distorted components of the Ã E2 excited state. It also reproduces both the minimum energy crossing point (MECP) on the symmetry-required E2x-E2y conical intersection seam and the MECP on the same symmetry A21-E2x conical intersection seam. Hd includes all terms through second order in internal coordinates for both the diagonal and off-diagonal blocks. It is centered at the E2x-E2y MECP and is determined using ab initio gradients and derivative couplings near both the E2x-E2y MECP and the X̃ A21 equilibrium geometry. This construction is enabled by a recently reported normal equation based algorithm. The C3v symmetry of the system is used to significantly reduce the computational cost of the ab initio treatment. This Hd is then expressed in a vibronic basis that is chosen for its ability to reduce the dimension of the vibronic expansion. The vibronic Hamiltonian matrix is diagonalized to obtain a negative ion photoelectron spectrum for 1-propynide-h3. The determined spectrum compares favorably with previous spectroscopic results. In particular, the lines attributable to the E2 state are found to be much weaker than those corresponding to the A21 state of 1-propynyl. This diminution of the E2 state is attributable principally to the E2x-A21 conical intersection rather than an intrinsically small electronic transition moment for the production of the E2 state.
Magnetic field threshold for runaway generation in tokamak disruptions
Authors: Fülöp T. , Smith H. M. , Pokol G.
Published: February 2009

Experimental observations show that there is a magnetic field threshold for runaway electron generation in tokamak disruptions. In this work, two possible reasons for this threshold are studied. The first possible explanation for these observations is that the runaway beam excites whistler waves that scatter the electrons in velocity space prevents the beam from growing. The growth rates of the most unstable whistler waves are inversely proportional to the magnetic field strength. Taking into account the collisional and convective damping of the waves it is possible to derive a magnetic field threshold below which no runaways are expected. The second possible explanation is the magnetic field dependence of the criterion for substantial runaway production obtained by calculating how many runaway electrons can be produced before the induced toroidal electric field diffuses out of the plasma. It is shown, that even in rapidly cooling plasmas, where hot-tail generation is expected to give rise to substantial runaway population, the whistler waves can stop the runaway formation below a certain magnetic field unless the postdisruption temperature is very low.
Inertial effects in the orientational relaxation of rodlike molecules in a uniaxial potential
Authors: Kalmykov Yuri P. , Titov Serguey V. , Coffey William T.
Published: February 2009

The inertial rotational Brownian motion and dielectric relaxation of an assembly of noninteracting rodlike polar molecules in a uniaxial potential are studied. The infinite hierarchy of differential-recurrence relations for the equilibrium correlation functions is generated by averaging the governing inertial Langevin equation over its realizations in phase space. The solution of this hierarchy for the one-sided Fourier transforms of the relevant correlation functions is obtained using matrix continued fractions yielding the longitudinal dipole correlation function, the correlation time, and the complex polarizability, which are calculated for typical values of the model parameters. Pronounced inertial effects appear in these characteristics in the high-frequency region for low damping. The exact longitudinal correlation time is compared with the predictions of the Kramers theory of the escape rate of a Brownian particle from a potential well as extended by Mel’nikov and Meshkov [J. Chem. Phys. 85, 1018 (1986)]. In the low temperature limit, the universal Mel’nikov and Meshkov formula for the inverse of the escape rate provides a good estimate of the longitudinal correlation time for all values of the dissipation including the very low damping, very high damping, and Kramers turnover regimes. Moreover, the low-frequency part of the spectra of the longitudinal correlation function may be approximated by a single Lorentzian with a halfwidth determined by this universal escape rate formula.
Response to “Comment on ‘Electronic structure and zone-center phonon modes in multiferroic bulk BiFeO3’ ” [J. Appl. Phys. 105, 036108 (2009)]
Authors: Tütüncü H. M. , Srivastava G. P.
Published: February 2009

We agree with the comment made by Hermet et al. on our recent paper [J. Appl. Phys. 103, 083712 (2008)] regarding the zone-center phonon modes in multiferroic bulk BiFeO3. In this reply we show that our correctly assigned modes are in agreement with their results.
Bias effect in photocurrent response of Si nanocrystals
Authors: Zhang R. , Chen X. Y. , Shen W. Z.
Published: February 2009

We report on the photocurrent response of hydrogenated nanocrystalline silicon (nc-Si:H) thin films under external bias voltages. The band gap transition and internal photoemission photocurrent of the nc-Si:H thin films can be enhanced and controlled by adjusting the depletion and inversion layers in the metal-semiconductor junction through the external bias voltage. The photocurrent response from the internal photoemission is found to be able to extend the photodetection wavelength of the Si material to the optical telecommunication range of 1.3–1.6 μm.
Structural, elastic, electronic, and phonon properties of zinc-blende and wurtzite BeO
Authors: Duman S. , Sütlü A. , Bağcı S. , Tütüncü H. M. , Srivastava G. P.
Published: February 2009

The results of ab initio calculations of the structural, elastic, electronic, and phonon properties of BeO in both zinc-blende and wurtzite structures are presented. Our calculations are based on the application of plane-wave basis, pseudopotentials, and the generalized gradient approximation of the density functional scheme. Our total energy calculations indicate that the wurtzite phase has lower energy (around 5.8 meV) than zinc-blende phase. It is found that for the two crystal phases the values of the equilibrium atomic volume and of the bulk modulus and its pressure derivative are almost identical. The zinc-blende and wurtzite phases are predicted to be characterized with indirect (and smaller) and direct band gaps, respectively. The maximum longitudinal optical and transverse optical phonon frequencies in the zinc-blende phase compare well to the average of the corresponding E1 and A1 modes in the wurtzite phase.
Design and fabrication of SU8 encapsulated digital magnetic carriers for high throughput biological assays
Authors: Hong B. , Hayward T. J. , Jeong J.-R. , Cooper J. F. K. , Palfreyman J. J. , Mitrelias T. , Ionescu A. , Bland J. A. C. , Barnes C. H. W.
Published: February 2009

A design of a biological molecule carrier is presented for the application of high throughput multiplexing biological assays. This carrier contains a bit addressable “magnetic barcode” made of either Permalloy or cobalt thin films, sandwiched between two planar SU8 protective layers. We describe how the design of the magnetic carriers is optimized by engineering the coercivity of each barcode element, allowing the number of available signatures to be increased. Fully encapsulated digital magnetic carriers which carry a 5 bit addressable barcode were also fabricated and are presented. Writing and reading of digital carriers were both performed after releasing in dried solution.
Modeling of the effects of different substrate materials on the residual thermal stresses in the aluminum nitride crystal grown by sublimation
Authors: Lee R. G. , Idesman A. , Nyakiti L. , Chaudhuri J.
Published: February 2009

A three-dimensional numerical finite element modeling method is applied to compare interfacial residual thermal stress distribution in AlN single crystals grown by using different substrates such as silicon carbide, boron nitride, tungsten, tantalum carbide, and niobium carbide. A dimensionless coordinate system is used which reduces the numbers of computations and hence simplifies the stress analysis. All components of the stress distribution, both in the film and in the substrate, including the normal stress along the growth direction as well as in-plane normal stresses and shear stresses are fully investigated. This information about the stress distribution provides insight into understanding and controlling the AlN single crystal growth by the sublimation technique. The normal stress in the film at the interface along the growth direction and the shear stresses are zero except at the edges, whereas in-plane stresses are nonzero. The in-plane stresses are compressive when TaC and NbC substrates are used. A small compressive stress might be beneficial in prohibiting crack growth in the film. The compressive stress in the AlN is lower for the TaC substrate than that for the NbC. Tensile in-plane stresses are formed in the AlN for 6H-SiC, BN, and W substrates. This tensile stress in the film is detrimental as it will assist in the crack growth. The stress concentration at the edges of the AlN film at the interface is compressive in nature when TaC and NbC are used as a substrate. This causes the film to bend downward (i.e., convex shape) and assist it to adhere to the substrate. The AlN film curves upward or in a concave shape when SiC, BN, and W substrates are used since the stress concentration at the edges of the AlN film is tensile at the interface and this may cause detachment of the film from the substrate.
Influence of metallic nanoparticles on upconversion processes
Authors: Esteban R. , Laroche M. , Greffet J.-J.
Published: February 2009

It is well known that Raman scattering and fluorescence can be enhanced by the presence of metallic nanoparticles. Here, we derive simple equations to analyze the influence of metallic nanoparticles on upconversion processes such as nonradiative energy transfer or excited state absorption. We compare the resulting expressions with the more familiar Raman and fluorescence cases and find significant differences. We use numerical simulations to calculate the upconverted signal enhancement achievable by means of metallic spheres of different radii and find particles of 100–400 nm radius at infrared frequencies to be favorable. We also discuss the considerable challenges involved in using metallic particles to enhance upconversion for solar energy.
Structural characterization by x-ray methods of novel antimicrobial gallium-doped phosphate-based glasses
Authors: Pickup D. M. , Moss R. M. , Qiu D. , Newport R. J. , Valappil S. P. , Knowles J. C. , Smith M. E.
Published: February 2009

Antimicrobial gallium-doped phosphate-based glasses of general composition (P2O5)0.45(CaO)0.16(Na2O)0.39−x(Ga2O3)x (where x=0, 0.01, 0.03, and 0.05) have been studied using the advanced synchrotron-based techniques of Ga K-edge x-ray absorption spectroscopy and high-energy x-ray diffraction to provide a structural insight into their unique properties. The results show that the Ga3+ ions are octahedrally coordinated. Furthermore, substitution of Na2O by Ga2O3 strengthens the phosphate network structure because the presence of GaO6 octahedra inhibits the migration of the remaining Na+ ions. The results are discussed in terms of the use of Na2O–CaO–P2O5 glasses as controlled-delivery devices for antimicrobial Ga3+ ions in biomedical applications. We are thereby able to relate the atomic-scale environment of the Ga3+ ions beneficially to the glass dissolution, and thus to their ability to disrupt bacterial cell activity by usurping the role of iron.
Topological chaos and mixing in a three-dimensional channel flow
Authors: Chen Jie , Stremler Mark A.
Published: February 2009

Passive mixing is investigated in a mathematical model of steady, three-dimensional, laminar flow through a rectangular channel. Efficient stirring is achieved by imposing spatially periodic transverse boundary velocities that generate asymmetric, counter-rotating rolls aligned with the channel axis. The flow is designed and analyzed using the concept of topological chaos, in which complexity is embedded in the flow through the motion of periodic orbits. A lid-driven flow producing topological chaos is found to stir better than a related flow with solid inserts considered previously [M. D. Finn, S. M. Cox, and H. M. Byrne, Phys. Fluids 15, L77 (2003)]. The results demonstrate that topological chaos and the Thurston–Nielsen classification theorem can provide insight into mixing enhancement in steady, three-dimensional flows.
The stability of a bubble in a weakly viscous liquid subject to an acoustic traveling wave
Authors: Shaw S. J.
Published: February 2009

The volume oscillations, translation, and axisymmetric deformation of a bubble in an acoustic traveling wave are considered. Assuming the bubble translation and deformation is small, but placing no restriction on the volume oscillations, a combination of the Rayleigh dissipation function and perturbation analysis is employed to account for the effects of viscosity in the absence of vorticity to third order in the small interaction terms. Contributions from the acoustic field are also determined to this order, while the free oscillation terms are drawn from a previously derived model correct to the same order of analysis. To permit the study of large amplitude acoustic forcing, appropriate compressibility terms are phenomenologically added to the volume pulsation equation. Stability maps of driving pressure versus driving frequency and driving pressure versus the equilibrium bubble radius are presented. A predominant number of results are for micron-sized bubbles driven in the ultrasonic regime, but the behavior of larger bubbles driven at frequencies in the kilohertz range is also considered. In all cases, bubbles driven above the natural frequency of their respective volume oscillations are markedly more stable with regard to the acoustic driving amplitude, consistent with previous observations. Below these respective natural frequency values, the stability/instability fronts display a much more complex structure. Accounting for shape mode viscous damping causes a general increase in bubble stability, together with a reduction in the stability/instability front complexity. In the case of micron-sized bubbles this stabilization is markedly more significant for bubbles driven above the natural frequency of the respective volume mode oscillations; for larger bubbles driven in the kilohertz range, the influence of shape mode damping is less significant.
Nonlinear self-interaction of geodesic acoustic modes in toroidal plasmas
Authors: Sasaki M. , Itoh K. , Nagashima Y. , Ejiri A. , Takase Y.
Published: February 2009

A self-nonlinear process involving the geodesic acoustic mode (GAM) was analyzed. GAMs nonlinearly excite higher harmonics as quasimodes. In the fluid picture, the Reynolds stress is modeled by the drift wave action. Other nonlinear terms such as the coupling between parallel velocity and vorticity, and between density and vorticity, were also considered, and evaluated using linear eigenmodes. We considered nonlinearities up to the third order. Analytic expressions for the amplitude of the second harmonic GAM and the saturation level of the fundamental GAM were derived. The validity of the theory is discussed based on a comparison of experimental results with theoretical predictions.
A highly parallelizable integral equation theory for three dimensional solvent distribution function: Application to biomolecules
Authors: Yokogawa Daisuke , Sato Hirofumi , Imai Takashi , Sakaki Shigeyoshi
Published: February 2009

Three dimensional (3D) hydration structure is informative to clarify the functions of hydrated waters around a protein. We develop a new approach to calculate 3D solvation structure with reasonable computational cost. In the present method, the total solvation structure is obtained using conventional one dimensional reference interaction site model (RISM) followed by integrating the 3D fragment data, which are evaluated around each atom (site) of solute. Thanks to this strategy, time-consuming 3D fast Fourier transformation, which is required in 3D-RISM theory, can be avoided and high-parallel performance is achieved. The method is applied to small molecular systems for comparison with 3D-RISM. The obtained results by the present method and by 3D-RISM show good agreement. The hydration structures for a large protein computed by the present method are also consistent with those obtained by x-ray crystallography.
Homotopy perturbation method to obtain exact special solutions with solitary patterns for Boussinesq-like B(m,n) equations with fully nonlinear dispersion
Authors: Yıldırım Ahmet
Published: February 2009

In this paper, we studied the Boussinesq-like equations with fully nonlinear dispersion B(m,n) equations which exhibit solutions with solitary patterns. New exact solitary solutions of the equations are found. The two special cases, B(2,2) and B(3,3), are chosen to illustrate the concrete scheme of the homotopy perturbation method in B(m,n) equations. The nonlinear equations B(m,n) are addressed for two different cases, namely when m=n being odd and even integers. General formulas for the solutions of B(m,n) equations are established.

This article is being retracted effective 20 September 2012.
Structure of presheath-sheath in magnetized electronegative plasma
Authors: Yasserian Kiomars , Aslaninejad Morteza , Ghoranneviss Mahmood
Published: February 2009

The structure of an electronegative discharge is investigated in the presence of an oblique, uniform, and constant magnetic field. For different magnetic field strengths, the densities of the positive ion, electron, as well as negative ion have been calculated. Furthermore, the profiles of positive ion’s velocity and electric potential are obtained. Under high values of electronegativity and for sufficiently cold negative ions, different magnetic field values constitute three types of discharge structure. For a very small magnetic field strength, a uniform structure is formed; for an intermediate magnetic field, a stratified multiple layer structure emerges, which is followed by electric potential oscillations; while for an intense magnetic field, these oscillations disappear. The flux of the positive ion reaching the cathode as a function of the magnetic field strength is also obtained and the result is compared with the electropositive discharge.
Development of a Couette–Taylor flow device with active minimization of secondary circulation
Authors: Schartman E. , Ji H. , Burin M. J.
Published: February 2009

A novel Taylor–Couette experiment has been developed to produce rotating shear flows for the study of hydrodynamic and magnetohydrodynamic instabilities which are believed to drive angular momentum transport in astrophysical accretion disks. High speed, concentric, corotating cylinders generate the flow where the height of the cylinders is twice the radial gap width. Ekman pumping is controlled and minimized by splitting the vertical boundaries into pairs of nested, differentially rotating rings. The end rings and cylinders comprise four independently driven rotating components which provide flexibility in developing flow profiles. The working fluids of the experiment are water, a water-glycerol mix, or a liquid gallium alloy. The mechanical complexity of the apparatus and large dynamic pressures generated by high speed operation with the gallium alloy presented unique challenges. The mechanical implementation of the experiment and some representative results obtained with laser Doppler velocimetry in water are discussed.
Extraordinary transmission in planar waveguide loaded with anisotropic metamaterials
Authors: Feng Yijun , Teng Xiaohua , Wang Zhengbin , Zhao Junming , Jiang Tian
Published: February 2009

Ordinary planar waveguide cannot support electromagnetic (EM) wave propagating at frequency below the cut-off frequency of the waveguide, due to the evanescent wave nature of the EM wave in such waveguide. We have found by theoretical analysis that extraordinary EM wave transmission could occur for transverse-electric modes at frequency below the cut-off frequency of the hollow waveguide by inserting different kinds of anisotropic metamaterials (AMMs) in the hollow waveguide. Such transmission of EM energy has no lower cut-off frequency and is due to the conversion of the evanescent wave into propagating mode inside the AMMs, which is quite different from that in the case of waveguide loaded with an isotropic left-handed material slab. We have verified the extraordinary phenomenon by performing circuit analog of the planar waveguide loaded with different kinds of AMMs through realization with transmission line metamaterials.
A versatile electron-ion coincidence spectrometer for photoelectron momentum imaging and threshold spectroscopy on mass selected ions using synchrotron radiation
Authors: Garcia Gustavo A. , Soldi-Lose Héloïse , Nahon Laurent
Published: February 2009

We present a photoelectron-photoion coincidence (PEPICO) spectrometer named DELICIOUS II which combines a velocity map imaging apparatus with a Wiley–McLaren time of flight analyzer for the study of gas phase samples in interaction with the synchrotron radiation (SR). This versatile system is capable of providing photoelectron images on mass-selected compounds with kinetic energy resolutions of ΔE/E=5% and a 17 eV bandwidth, as well as threshold photoelectron spectra with a measured resolution of 0.8 meV, as demonstrated on the 3p−1 ionization of argon. This instrument is also employed for threshold PEPICO experiments, allowing the selection of the parent ion’s internal state with sub-meV resolution for light masses (<40 amu) and with typically 2 meV resolution for a mass of 100 amu and with a mass resolving power above 200. The continuous operation of the extraction fields and the independence from the electron’s time of flight are well adapted to the quasicontinuous multibunch mode of the SR. This, together with the high transmission of both the electron and ion detection, allows a high coincidence counting rate and facilitates the subtraction of false coincidences. We illustrate the spectrometer’s coincidence principle of operation with examples from the valence photoionization of an Ar+Xe mixture and of CF4.
Rapid thermal oxidation of silicon nanowires
Authors: Krylyuk Sergiy , Davydov Albert V. , Levin Igor , Motayed Abhishek , Vaudin Mark D.
Published: February 2009

Oxidation kinetics of silicon nanowires (SiNWs) subjected to rapid thermal oxidation (RTO) at 900 °C and 1000 °C in dry oxygen for exposure times ranging from 1 to 7.5 min is reported. For 1 min, SiNWs exhibit an enhanced oxidation rate compared to planar silicon, but for longer exposures the oxidation rates of SiNWs and planar Si are similar. Compared to furnace oxidation of SiNWs, RTO provides faster average oxidation rates and a weaker dependence of oxide shell thickness on the NW diameter. Our results demonstrate that RTO is an efficient approach for controlled oxidation of SiNWs.
Tunneling in two-dimensional systems using a higher-order Herman–Kluk approximation
Authors: Hochman Gili , Kay Kenneth G.
Published: February 2009

A principal weakness of the Herman–Kluk (HK) semiclassical approximation is its failure to provide a reliably accurate description of tunneling between different classically allowed regions. It was previously shown that semiclassical corrections significantly improve the HK treatment of tunneling for the particular case of the one-dimensional Eckart system. Calculations presented here demonstrate that the lowest-order correction also substantially improves the HK description of tunneling across barriers in two-dimensional systems. Numerical convergence issues either do not arise or are easily overcome, so that the calculations require only a moderate number of ordinary, real, classical trajectories.
Hot electron energy distributions from ultraintense laser solid interactions
Authors: Chen Hui , Wilks S. C. , Kruer W. L. , Patel P. K. , Shepherd R.
Published: February 2009

Measurements of electron energy distributions from ultraintense (>1019 W/cm2) laser solid interactions using an electron spectrometer are presented. The effective hot electron temperatures (Thot) have been measured for laser intensities (Iλ2) from 1018 to 1021 W/cm2 μm2 for the first time, and Thot is found to increase as (Iλ2)0.34±0.04. This scaling agrees well with the empirical scaling published by Beg et al. [Phys. Plasmas 4, 447 (1997)], and was modeled by particle-in-cell simulations.
The influence of interface modifier on the performance of nanostructured ZnO/polymer hybrid solar cells
Authors: Lin Yun-Yue , Lee Yi-Ying , Chang Liuwen , Wu Jih-Jen , Chen Chun-Wei
Published: February 2009

We have demonstrated an improvement of photovoltaic performance based on the nanostructured ZnO/poly(3-hexylthiophene) (P3HT) hybrid through interface molecular modification on ZnO nanorod surface. By probing the carrier dynamics at ZnO/P3HT interfaces, we have found that the interfacial molecules can play the role of assisting charge separation and suppression of back recombination at interfaces, which accounts for the observed enhanced short circuit current (Jsc) and open circuit voltage (Voc) in photovoltaic performance.
Lower-temperature crystallization of CoFeB in MgO magnetic tunnel junctions by using Ti capping layer
Authors: Ibusuki Takahiro , Miyajima Toyoo , Umehara Shinjiro , Eguchi Shin , Sato Masashige
Published: February 2009

Effects of capping materials on magnetoresistance (MR) properties of MgO magnetic tunnel junctions (MTJs) with a CoFeB free layer were investigated. MR ratios of samples with various capping materials showed a difference in annealing temperature dependence. MTJ with a Ti capping layer annealed at 270°C showed a MR ratio 1.4 times greater than that with a conventional Ta or Ru capping layer. Secondary ion mass spectroscopy and high-resolution transmission electron microscopy images revealed that crystallization of CoFeB was remarkably affected by adjacent materials and the Ti capping layer adjoining CoFeB acted as a boron-absorption layer. These results suggest that the crystallization process can be controlled by choosing proper capping materials. Ti is one of the effective materials that accelerate the crystallization of CoFeB layers at lower annealing temperature.
Absolute photodetachment cross section measurements of the O− and OH− anion
Authors: Hlavenka P. , Otto R. , Trippel S. , Mikosch J. , Weidemüller M. , Wester R.
Published: February 2009

Absolute total photodetachment cross sections of O− and OH− anions stored in a multipole radio frequency trap have been measured using a novel laser depletion tomography method. For OH− the total cross sections of 8.5(1)stat(3)syst and 8.1(1)stat(7)syst×10−18 cm2, measured at 662 and 632 nm, respectively, were found constant in the temperature range of 8–300 K. The O− cross sections 5.9(1)stat(2)syst and 6.3(1)stat(2)syst×10−18 cm2 measured at 170 K at 662 and 532 nm, respectively, agree within error estimations with preceding experiments and increase the accuracy of the widely used calibration standard for relative photodetachment measurements of diverse atomic and molecular species.
Enhancement of transverse thermoelectric power factor in tilted Bi/Cu multilayer
Authors: Kanno Tsutomu , Yotsuhashi Satoshi , Sakai Akihiro , Takahashi Kouhei , Adachi Hideaki
Published: February 2009

We investigated transverse thermoelectric response in tilted Bi/Cu multilayer. Estimation through an equivalent circuit model showed that transverse thermoelectric power factor (PF) reaching 155 μW/cm K2 is possible with optimum device parameters. Finite element analysis confirmed the validity of the estimation using tensorial representation, which implicitly assumes homogeneous anisotropy. The Bi/Cu multilayer was fabricated by pressure injection of molten Bi into a periodically slitted Cu block. The measurement of the fabricated sample verified an enhancement in transverse PF up to 50.1 μW/cm K2, which is approximately 1.5 times greater than the conventional PF of constituent Bi, 34 μW/cm K2.
Harvesting triplet excitons for application in polymer solar cells
Authors: Arif M. , Yang K. , Li L. , Yu P. , Guha S. , Gangopadhyay S. , Förster M. , Scherf U.
Published: February 2009

Triplet enhanced ladder-type poly (para-phenylene) polymer (PhLPPP) with covalently bound trace amounts of palladium blended with a fullerene derivative [[6,6]-phenyl C61-butyric acid methyl ester (PCBM)] shows power conversion efficiencies (PCE) almost ten times greater than with pristine ladder-type polymer (with no palladium atom) blended with PCBM. The steady state optical properties of the triplet and nontriplet-enhanced polymers are comparable; the enhanced PCE and external quantum efficiency in PhLPPP photovoltaics are attributed to the presence of long-lived mobile triplet excitons. Furthermore, the luminescence from PhLPPP blends measured in a delayed setup correlates very well with the efficiency of the solar cells.
Photoinduced effects in thin films of Te20As30Se50 glass with nonlinear characterization
Authors: Fedus K. , Boudebs G. , de Araújo Cid B. , Cathelinaud M. , Charpentier F. , Nazabal V.
Published: February 2009

We discuss the influence of photoinduced effects (PIEs) on the measurements of nonlinear refractive indices and nonlinear absorption coefficients. A chalcogenide glass film Te20As30Se50 was studied using picosecond laser pulses at 1064 nm. The nonlinear imaging technique with phase object (NIT-PO) and the Z-scan technique were applied and their results are compared. The NIT-PO technique reveals clearly the influence of PIE on the samples’ response, while by using the Z-scan technique we measured the deepness of ablated regions (holes) produced during the measurements.
Strain-controlled electronic properties and magnetorelaxor behaviors in electron-doped CaMnO3 thin films
Authors: Xiang P.-H. , Yamada H. , Sawa A. , Akoh H.
Published: February 2009

We have fabricated epitaxial thin films of electron-doped manganite Ca1−xCexMnO3 (CCMO) with 0≤x≤0.08. The transport properties of CCMO films are very sensitive to substrate-controlled epitaxial strain. For the CCMO(x=0.05) film, the metallic transport characteristic is observed only on a nearly lattice-matched NdAlO3 (NAO) substrate, while tensilely and compressively stressed films are insulating. The CCMO(x=0.06) film on the NAO substrate shows a large magnetoresistance characteristic of a magnetorelaxor. This behavior can be explained in terms of the phase separation and the irreversible growth of the metallic domain in antiferromagnetic insulating matrix.
Room-temperature operation of a 2.25 μm electrically pumped laser fabricated on a silicon substrate
Authors: Rodriguez J. B. , Cerutti L. , Grech P. , Tournié E.
Published: February 2009

We report on a GaSb-based type-I laser structure grown by molecular beam epitaxy on a (001) silicon substrate. A thin AlSb nucleation layer followed by a 1 μm thick GaSb buffer layer was used to accommodate the very large lattice mismatch existing with the silicon substrate. Processed devices with mesa geometry exhibited laser operation in pulsed mode with a duty cycle up to 10% at room temperature.
Observation of persistent photoconductance in single ZnO nanotube
Authors: Liu Peng , She Guangwei , Liao Zhaoliang , Wang Yao , Wang Zhenzhong , Shi Wensheng , Zhang Xiaohong , Lee Shuit-Tong , Chen Dongmin
Published: February 2009

Vertically aligned ZnO nanotube fabricated on an indium tin oxide substrate is found to exhibit strong persistent photoconductivity (PPC). Excitation wavelength-dependent conductance measurement on individual ZnO nanotube reveals the presence of defect states at 240 meV above the valence band edge, which are directly associated with the PPC effect. Our observations are consistent with the hypothesis that double ionization of defect-localized states is responsible for the PPC effect.
Reduction in critical current for spin transfer switching in perpendicular anisotropy spin valves using an in-plane spin polarizer
Authors: Law Randall , Tan Ei-Leen , Sbiaa Rachid , Liew Thomas , Chong Tow Chong
Published: February 2009

We describe a strategy to reduce spin transfer switching (STS) currents in CoFe/Pd-based perpendicular anisotropy single spin valves (SSVs) by the insertion of an in-plane spin polarizer, thus creating a modified-dual spin valve (m-DSV). For SSV devices, concurrent STS of both magnetic layers was observed for positive currents, making the parallel-to-antiparallel (P→AP) transition impossible. In m-DSV devices, we observed a 60% reduction in the energy barrier for AP→P transitions and a 40% reduction in JcAP→P with 10 ns STS current pulses compared to SSV devices. Furthermore, the m-DSV structure enabled the soft layer to switch independently from the hard layer via STS.
Considerations of the Obstacles and Opportunities to Formalizing Cross-National Policy Transfer to the United States: A Case Study of the Transfer of Urban Environmental and Planning Policies from Germany
Authors: Dolowitz David P , Medearis Dale
Published: February 2009

Not enough has been written about the import, adaptation, and application of urban environmental and planning policies from abroad into the United States. Even less has been written about the voluntary cross-national transfer and application of environmental policies by American subnational actors and institutions. It is our intent to begin redressing this by discussing the transfer of urban environmental and planning policies from Germany to the United States during the early part of the 21st century. This discussion is informed by data drawn from governmental reports and planning statements and over thirty-five interviews with US urban environmental and planning practitioners operating in Germany and the United States. What we discover is that, unlike more rational models of policy transfer, the voluntary importation of environmental and planning policies into the US is seldom a problem-focused, goal-oriented process. Rather, what we find is that a better depiction of the transfer and adoption process is of a relatively anarchic situation. This appears to occur due to a range of institutional and cultural filters that predispose American policy makers against gathering (and using) information and experiences from abroad. We find that this filtering process tends to encourage policy makers to discount (or reject outright) the usefulness of overseas models and that, when they do engage in this process, any information gathered appears to be based less upon well-researched and analyzed data than embedded ‘tacit’ knowledge.
Exploring the likelihood and mechanism of a climate-change-induced dieback of the Amazon rainforest
Authors: Malhi Yadvinder , Aragão Luiz E. O. C. , Galbraith David , Huntingford Chris , Fisher Rosie , Zelazowski Przemyslaw , Sitch Stephen , McSweeney Carol , Meir Patrick
Published: February 2009

We examine the evidence for the possibility that 21st-century climate change may cause a large-scale “dieback” or degradation of Amazonian rainforest. We employ a new framework for evaluating the rainfall regime of tropical forests and from this deduce precipitation-based boundaries for current forest viability. We then examine climate simulations by 19 global climate models (GCMs) in this context and find that most tend to underestimate current rainfall. GCMs also vary greatly in their projections of future climate change in Amazonia. We attempt to take into account the differences between GCM-simulated and observed rainfall regimes in the 20th century. Our analysis suggests that dry-season water stress is likely to increase in E. Amazonia over the 21st century, but the region tends toward a climate more appropriate to seasonal forest than to savanna. These seasonal forests may be resilient to seasonal drought but are likely to face intensified water stress caused by higher temperatures and to be vulnerable to fires, which are at present naturally rare in much of Amazonia. The spread of fire ignition associated with advancing deforestation, logging, and fragmentation may act as nucleation points that trigger the transition of these seasonal forests into fire-dominated, low biomass forests. Conversely, deliberate limitation of deforestation and fire may be an effective intervention to maintain Amazonian forest resilience in the face of imposed 21st-century climate change. Such intervention may be enough to navigate E. Amazonia away from a possible “tipping point,” beyond which extensive rainforest would become unsustainable.
The minimum information principle and its application to neural code analysis
Authors: Globerson Amir , Stark Eran , Vaadia Eilon , Tishby Naftali
Published: February 2009

The study of complex information processing systems requires appropriate theoretical tools to help unravel their underlying design principles. Information theory is one such tool, and has been utilized extensively in the study of the neural code. Although much progress has been made in information theoretic methodology, there is still no satisfying answer to the question: “What is the information that a given property of the neural population activity (e.g., the responses of single cells within the population) carries about a set of stimuli?” Here, we answer such questions via the minimum mutual information (MinMI) principle. We quantify the information in any statistical property of the neural response by considering all hypothetical neuronal populations that have the given property and finding the one that contains the minimum information about the stimuli. All systems with higher information values necessarily contain additional information processing mechanisms and, thus, the minimum captures the information related to the given property alone. MinMI may be used to measure information in properties of the neural response, such as that conveyed by responses of small subsets of cells (e.g., singles or pairs) in a large population and cooperative effects between subunits in networks. We show how the framework can be used to study neural coding in large populations and to reveal properties that are not discovered by other information theoretic methods.
A Z-DNA sequence reduces slipped-strand structure formation in the myotonic dystrophy type 2 (CCTG)·(CAGG) repeat
Authors: Edwards Sharon F. , Sirito Mario , Krahe Ralf , Sinden Richard R.
Published: February 2009

All DNA repeats known to undergo expansion leading to human neurodegenerative disease can form one, or several, alternative conformations, including hairpin, slipped strand, triplex, quadruplex, or unwound DNA structures. These alternative structures may interfere with the normal cellular processes of transcription, DNA repair, replication initiation, or polymerase elongation and thereby contribute to the genetic instability of these repeat tracts. We show that (CCTG)·(CAGG) repeats, in the first intron of the
ZNF9
gene associated with myotonic dystrophy type 2, form slipped-strand DNA structures in a length-dependent fashion upon reduplexing. The threshold for structure formation on reduplexing is between 36 and 42 repeats in length. Alternative DNA structures also form in (CCTG)
58
·(CAGG)
58
and larger repeat tracts in plasmids at physiological superhelical densities. This represents an example of a sequence that forms slipped-strand DNA from the energy of DNA supercoiling. Moreover, Z-DNA forms in a (TG)·(CA) tract within the complex repeat sequence 5′ of the (CCTG)

n

·(CAGG)

n

repeat in the
ZNF9
gene. Upon reduplexing, the presence of the flanking sequence containing the Z-DNA-forming tract reduced the extent of slipped-strand DNA formation by 62% for (CCTG)
57
·(CAGG)
57
compared with 58 pure repeats without the flanking sequence. This finding suggests that the Z-DNA-forming sequence in the DM2 gene locus may have a protective effect of reducing the potential for slipped-strand DNA formation in (CCTG)

n

·(CAGG)

n

repeats.
A rosette-type, self-renewing human ES cell-derived neural stem cell with potential for in vitro instruction and synaptic integration
Authors: Koch Philipp , Opitz Thoralf , Steinbeck Julius A. , Ladewig Julia , Brüstle Oliver
Published: February 2009

An intriguing question in human embryonic stem cell (hESC) biology is whether these pluripotent cells can give rise to stably expandable somatic stem cells, which are still amenable to extrinsic fate instruction. Here, we present a pure population of long-term self-renewing rosette-type hESC-derived neural stem cells (lt-hESNSCs), which exhibit extensive self-renewal, clonogenicity, and stable neurogenesis. Although lt-hESNSCs show a restricted expression of regional transcription factors, they retain responsiveness to instructive cues promoting the induction of distinct subpopulations, such as ventral midbrain and spinal cord fates. Using lt-hESNSCs as a donor source for neural transplantation, we provide direct evidence that hESC-derived neurons can establish synaptic connectivity with the mammalian nervous system. Combining long-term stability, maintenance of rosette-properties and phenotypic plasticity, lt-hESNSCs may serve as useful tool to study mechanisms of human NSC self-renewal, lineage segregation, and functional in vivo integration.
LapD is a bis-(3′,5′)-cyclic dimeric GMP-binding protein that regulates surface attachment by
Pseudomonas fluorescens
Pf0–1
Authors: Newell Peter D. , Monds Russell D. , O'Toole George A.
Published: February 2009

The second messenger cyclic dimeric GMP (c-di-GMP) regulates surface attachment and biofilm formation by many bacteria. For
Pseudomonas fluorescens
Pf0–1, c-di-GMP impacts the secretion and localization of the adhesin LapA, which is absolutely required for stable surface attachment and biofilm formation by this bacterium. In this study we characterize LapD, a unique c-di-GMP effector protein that controls biofilm formation by communicating intracellular c-di-GMP levels to the membrane-localized attachment machinery via its periplasmic domain. LapD contains degenerate and enzymatically inactive diguanylate cyclase and c-di-GMP phosphodiesterase (EAL) domains and binds to c-di-GMP through a degenerate EAL domain. We present evidence that LapD utilizes an inside-out signaling mechanism: binding c-di-GMP in the cytoplasm and communicating this signal to the periplasm via its periplasmic domain. Furthermore, we show that LapD serves as the c-di-GMP receptor connecting environmental modulation of intracellular c-di-GMP levels by inorganic phosphate to regulation of LapA localization and thus surface commitment by
P. fluorescens
.
Evidence that family 35 carbohydrate binding modules display conserved specificity but divergent function
Authors: Montanier Cedric , van Bueren Alicia Lammerts , Dumon Claire , Flint James E. , Correia Marcia A. , Prates Jose A. , Firbank Susan J. , Lewis Richard J. , Grondin Gilles G. , Ghinet Mariana G. , Gloster Tracey M. , Herve Cecile , Knox J. Paul , Talbot Brian G. , Turkenburg Johan P. , Kerovuo Janne , Brzezinski Ryszard , Fontes Carlos M. G. A. , Davies Gideon J. , Boraston Alisdair B. , Gilbert Harry J.
Published: February 2009

Enzymes that hydrolyze complex carbohydrates play important roles in numerous biological processes that result in the maintenance of marine and terrestrial life. These enzymes often contain noncatalytic carbohydrate binding modules (CBMs) that have important substrate-targeting functions. In general, there is a tight correlation between the ligands recognized by bacterial CBMs and the substrate specificity of the appended catalytic modules. Through high-resolution structural studies, we demonstrate that the architecture of the ligand binding sites of 4 distinct family 35 CBMs (CBM35s), appended to 3 plant cell wall hydrolases and the
exo
-β-
d
-glucosaminidase CsxA, which contributes to the detoxification and metabolism of an antibacterial fungal polysaccharide, is highly conserved and imparts specificity for glucuronic acid and/or Δ4,5-anhydrogalaturonic acid (Δ4,5-GalA). Δ4,5-GalA is released from pectin by the action of pectate lyases and as such acts as a signature molecule for plant cell wall degradation. Thus, the CBM35s appended to the 3 plant cell wall hydrolases, rather than targeting the substrates of the cognate catalytic modules, direct their appended enzymes to regions of the plant that are being actively degraded. Significantly, the CBM35 component of CsxA anchors the enzyme to the bacterial cell wall via its capacity to bind uronic acid sugars. This latter observation reveals an unusual mechanism for bacterial cell wall enzyme attachment. This report shows that the biological role of CBM35s is not dictated solely by their carbohydrate specificities but also by the context of their target ligands.