bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic properties of Co50−xNixMn25Al25 alloys with B2 structure
Authors: Okubo A. , Xu X. , Umetsu R. Y. , Kanomata T. , Ishida K. , Kainuma R.
Published: April 2011

Magnetic properties of the B2 phase in Co50−xNixMn25Al25 alloys were investigated. Spontaneous magnetization Ms measured at 4.2 K increases linearly with increasing x in the region of x ≤ 30 in accordance with following the generalized Slater-Pauling (GSP) line. However, Ms abruptly decreases with increasing x and deviates from the GSP line in the Ni-rich region of x > 30, suggesting a drastic change in the density of states at the Fermi energy. The Curie temperature TC decreases monotonically with increasing x and significantly decreases in the region of x > 30. Antiferromagnetic evidence is clearly observed at x > 45, and the Néel temperature TN increases with increasing x, in reaching the value of the B2 phase in Ni2MnAl.
Dynamical magnetotransport in Ln0.6Sr0.4MnO3 (Ln = La, Sm)
Authors: Naik V. B. , Rebello A. , Mahendiran R.
Published: April 2011

We compare radio frequency electrical transport in Ln0.6Sr0.4MnO3 (Ln = La and Sm). AC resistance (R) and reactance (X) were simultaneously measured as a function of temperature (T), magnetic field (H), and frequency (f). The R(T, H = 0 G) in La0.6Sr0.4MnO3 (LSMO) shows a broad insulator-metal transition around 247 K below the Curie temperature (TC) for f ≤ 2 MHz but a steplike increase at TC for f ≥ 3 MHz. Conversely, R(T, H = 0 G) in Sm0.6Sr0.4MnO3 exhibits a single peak at TC = 116±2 K for f = 0.1 MHz which splits into two peaks accompanied by a dip at TC for higher frequencies. While the low temperature peak shifts upward rapidly with the increasing H (μ0H > 1 T) for f = 5 MHz, the high temperature peak is insensitive to the magnetic field. A large ac magnetoresistance (ΔR/R= −32%) and magnetoreactance (ΔX/X = −21%) at a low magnetic field (H = 70 mT) is observed in LSMO around TC in contrast to a positive ΔR/R (=170%) and a negative ΔX/X (= −94%) at μ0H = 7 T. We discuss the possible origins of the observed effects.
Resistive switching behaviors in Bi2Sr2CaCu2O8+d (Bi-2212) stacks
Authors: Kim Sang-Jae
Published: April 2011

A coupled stacked Josephson junctions (SJJs) with completely perforated holes of 0.2 μm × 0.4 μm in high-Tc superconducting Bi2Sr2CaCu2O8+d (Bi-2212) were fabricated using a 3D focused ion beam etching method. We investigated external field angle θi dependence of junction resistance Rj at various magnetic fields and temperatures. When a constant external magnetic fields He value of 1 T and a bias current Ib value of 1 μA were applied to the sample with changing external field angle θi, unspecified equidistant and periodic peak structures in the SJJs were induced. The periodic peaks of Rj shows the resistive switching transition from zero resistance state to resistance state.
Are there superspin glasses?
Authors: Skomski R.
Published: April 2011

The effect of magnetostatic and exchange interactions on the spin structure of interacting nanoparticles and granular nanomagnets is investigated by model calculations. Effective exchange stiffnesses for inhomogeneous media are defined and determined for some geometries and interactions, and it is argued that typical ensembles of interacting small nanoparticles are micromagnetic systems rather than superspin glasses or superferromagnets. The spin structures of granular magnets often have the character of interaction domains, with far-reaching implications for magnetic phenomena such as hysteresis-loop overskewing.
Magnetoresistance, critical current density, and magnetic flux pinning mechanism in nickel doped BaFe2As2 single crystals
Authors: Shahbazi M. , Wang X. L. , Lin Z. W. , Zhu J. G. , Dou S. X. , Choi K. Y.
Published: April 2011

The critical current density, Jc, flux pinning behavior and magneto- resistance results of BaFe2-xNixAs2 single crystal have been investigated in fields up to 13 T over a temperature range of 2 to 20 K. The magnetoresistance below the superconducting transition temperature (Tc) shows Arrhenius thermally activated behavior: ρ = ρoexp(-Uo(T,H)/kBT), where Uo is the thermally activated energy. BaFe2-xNixAs2 exhibits high thermally activated flux flow energy with a very weak field dependence. Jc is as high as 2 × 105 A/cm2 for zero magnetic field at 2 K. Jc was found to decrease for B < 1 T, but showed a very weak field dependence and remained nearly constant with increasing magnetic field for B > 1 T at T = 2, 5, and 10 K. Flux jumping was also observed in magnetization loops at very low temperature for large sample, which is related to the high Jc in the single crystal. A peak effect was observed at 10 K.
Electrical and optical characterization of DNA molecules as a function of concentration in aqueous solution
Authors: Polcari A. , Romano P. , Sabatino L. , Vecchio E. del , Consales M. , Cusano A. , Cutolo A. , Colantuoni V.
Published: April 2011

We present experimental data on the electrical and optical behavior of circular and linear plasmid DNA molecules embedded in an aqueous matrix. From the electrical point of view, the results indicate that the presence of water is essential when the DNA concentration is not sufficient to ensure conduction patterns, consistent with the conduction mechanisms proposed for DNA molecules. In fact, as droplets are layered on the substrate, a nonlinear behavior of the current-voltage curves is observed; when water evaporates, the conductivity decreases to a very low value that resembles the high resistivity of the substrate. As more droplets are added, the current increases giving higher conductivity, as expected, since more molecules participate into the conduction process. The conduction behavior of DNA could be due to a tunneling transport of charges inside the molecule, the tunneling barrier being the adenine-thymine bridge between consecutive guanine-cytosine base pairs. A hopping channel, activated by the water surrounding the molecules, could act as an additional mechanism between different molecules. Optical reflectance measurements, performed in the wavelength range 230–450 nm on dried samples, obtained by complete evaporation of the aqueous matrix containing plasmid DNA under UV-VIS light, reveal absorption in the wavelength range 230–300 nm, typical of DNA-based materials. Moreover, in correspondence of the absorption region, the higher the DNA concentration, the higher the reflectance reduction. This suggests that the DNA concentration strongly influences the spectral behavior of biological layers. Finally, we present preliminary results exploiting the possibility to control the morphological and optical features of DNA layers by means of proper lighting procedures. Both electrical and optical measurements indicate that the DNA concentration is a crucial parameter for technical applications. The results reported here provide a contribution for the possible use of DNA molecules in the field of electro-optical biosensors.
Study of the magnetoresistance of magnetic film modified by using ion beams
Authors: Suk J. , Jeon I. , Kim T. , Song J. , Lee J.
Published: April 2011

We have studied the magnetoresistance (MR) of locally modified Cu(20 nm)/AlOx(1 nm)/NiFe(20 nm)/AlOx(1 nm)/Cu(3 nm) on a Si substrate. The local modification was performed by irradiating Cu ion beams on a photoresist wire-covered film. After irradiation, the hysteresis loop shows step-like behavior at a specific ion dose, which is caused by the difference in the switching fields of the irradiated and unirradiated region of the film. Because of this, plateau-like behavior is observed in the transverse MR measurement of the film with 1 × 1016 ions/cm2. A cross-sectional transmission electron microscopy image shows the irradiation induced intermixing of the magnetic layer with nonmagnetic layers.
A cryogenic surface-electrode elliptical ion trap for quantum simulation
Authors: Clark Robert J. , Lin Ziliang , Diab Kenan S. , Chuang Isaac L.
Published: April 2011

Two-dimensional crystals of trapped ions are a promising system with which to implement quantum simulations of challenging problems such as spin frustration. Here, we present a design for a surface-electrode elliptical ion trap which produces a 2-D ion crystal and is amenable to microfabrication, which would enable higher simulated coupling rates, as well as interactions based on magnetic forces generated by currents which may be incorporated into the trap structure. Working in an 11 K cryogenic environment, we experimentally verify to within 10% a numerical model of the structure of ion crystals in the trap, given the measured trap anisotropy. We also explore the possibility of implementing quantum simulation using magnetic forces, and calculate J-coupling rates on the order of 103 s-1 for a trap scale of 10 μm, using a current of 1 A.
Effect of post-annealing on martensitic transformation and magnetocaloric effect in Ni45Co5Mn36.7In13.3 alloys
Authors: Chen L. , Hu F. X. , Wang J. , Shen J. , Sun J. R. , Shen B. G. , Yin J. H. , Pan L. Q. , Huang Q. Z.
Published: April 2011

The metamagnetic alloy Ni45Co5Mn36.7In13.3 was fabricated by conventional arc-melting technique. Subsequent annealing may relax the stress and modify the atom ordering, thus influencing the magnetic properties and martensitic transformation behaviors. Our studies demonstrate that post-annealing at temperatures ≤ 300 °C can lead to a significant change in the magnetic properties and martensitic temperature (TM). Annealing the sample at 300 °C for 3 h can cause a decrease of as much as 30 K in TM (from 319 to 289 K) while retaining strong metamagnetic behaviors. The field-induced metamagnetic transition is accompanied with a large magnetocaloric effect. With an increase in the annealing temperature, the magnitude of the effective magnetic entropy change decreases somewhat, while the refrigeration capacity shows a slight increase.
Synthesis and characterization of core/shell Fe3O4/ZnSe fluorescent magnetic nanoparticles
Authors: Vargas José M. , McBride Amber A. , Plumley John B. , Fichou Yann , Memon Tosifa A. , Shah Vichiksha , Cook Nathaniel C. , Akins Brian A. , Rivera Antonio C. , Smolyakov Gennady A. , O’Brien James R. , Adolphi Natalie L. , Smyth Hugh D. C. , Osiński Marek
Published: April 2011

We report on the successful preparation and characterization of fluorescent magnetic core/shell Fe3O4/ZnSe nanoparticles (NPs) with a spherical shape by organometallic synthesis. The 7 nm core/3 nm shell NPs show good magnetic and photoluminescence (PL) responses. The observed PL emission/excitation spectra are shifted to shorter wavelengths, compared to a reference ZnSe NP sample. A dramatic reduction of PL quantum yield is also observed. The temperature dependence of the magnetization for the core/shell NPs shows the characteristic features of two coexisting and interacting magnetic (Fe3O4) and nonmagnetic (ZnSe) phases. Compared to a reference Fe3O4 NP sample, the room-temperature Néel relaxation time in core/shell NPs is three times longer.
Preparation of anisotropic Nd(Fe,Mo)12N1.0 magnetic materials by strip casting technique and direct nitrogenation for the strips
Authors: Han Jingzhi , Liu Shunquan , Xing Meiying , Lin Zhong , Kong Xiangpeng , Yang Jinbo , Wang Changsheng , Du Honglin , Yang Yingchang
Published: April 2011

The Nd(Fe,Mo)12-type alloys are prepared by strip casting technique, and direct nitrogenation of the strips without precrushing is executed in this paper. It is found that 6 h annealing treatment at 1050  °C for the strips is enough to obtain the single-phase Nd(Fe,Mo)12 compounds. The strips can be directly nitrogenated at 620   °C to obtain interstitial Nd(Fe,Mo)12N1.0 materials, and a spontaneous pulverization phenomenon in the strips induced by nitrogenation is found. The results indicate that the nitrogenation process of the strips can be used to prepare Nd(Fe,Mo)12N1.0 interstitial nitrides and pulverize the casted strips into fine particles simultaneously. Base on this, we propose a new technical route of preparing Nd(Fe,Mo)12NX magnetic powders without precrushing and obtain anisotropic NdFe10.5Mo1.5N1.0 powders with a remanence of Br = 1.08 T, a coercivity of iHc = 400 kA/m, and a maximum energy product of (BH)max = 144 kJ/m3.
Full dispersion versus Debye model evaluation of lattice thermal conductivity with a Landauer approach
Authors: Jeong Changwook , Datta Supriyo , Lundstrom Mark
Published: April 2011

Using a full dispersion description of phonons, the thermal conductivities of bulk Si and Bi2Te3 are evaluated using a Landauer approach and related to the conventional approach based on the Boltzmann transport equation. A procedure to extract a well-defined average phonon mean-free-path from the measured thermal conductivity and given phonon-dispersion is presented. The extracted mean-free-path has strong physical significance and differs greatly from simple estimates. The use of simplified dispersion models for phonons is discussed, and it is shown that two different Debye temperatures must be used to treat the specific heat and thermal conductivity (analogous to the two different effective masses needed to describe the electron density and conductivity). A simple technique to extract these two Debye temperatures is presented and the limitations of the method are discussed.
GaSb molecular beam epitaxial growth on p-InP(001) and passivation with in situ deposited Al2O3 gate oxide
Authors: Merckling C. , Sun X. , Alian A. , Brammertz G. , Afanas’ev V. V. , Hoffmann T. Y. , Heyns M. , Caymax M. , Dekoster J.
Published: April 2011

The integration of high carrier mobility materials into future CMOS generations is presently being studied in order to increase drive current capability and to decrease power consumption in future generation CMOS devices. If III–V materials are the candidates of choice for n-type channel devices, antimonide-based semiconductors present high hole mobility and could be used for p-type channel devices. In this work we first demonstrate the heteroepitaxy of fully relaxed GaSb epilayers on InP(001) substrates. In a second part, the properties of the Al2O3/GaSb interface have been studied by in situ deposition of an Al2O3 high-κ gate dielectric. The interface is abrupt without any substantial interfacial layer, and is characterized by high conduction and valence band offsets. Finally, MOS capacitors show well-behaved C–V with relatively low Dit along the bandgap, these results point out an efficient electrical passivation of the Al2O3/GaSb interface.
Some exact solutions for debris and avalanche flows
Authors: Pudasaini Shiva P.
Published: April 2011

Exact analytical solutions to simplified cases of nonlinear debris avalanche model equations are necessary to calibrate numerical simulations of flow depth and velocity profiles on inclined surfaces. These problem-specific solutions provide important insight into the full behavior of the system. In this paper, we present some new analytical solutions for debris and avalanche flows and then compare these solutions with experimental data to measure their performance and determine their relevance. First, by combining the mass and momentum balance equations with a Bagnold rheology, a new and special kinematic wave equation is constructed in which the flux and the wave celerity are complex nonlinear functions of the pressure gradient and the flow depth itself. The new model can explain the mechanisms of wave advection and distortion, and the quasiasymptotic front bore observed in many natural and laboratory debris and granular flows. Exact time-dependent solutions for debris flow fronts and associated velocity profiles are then constructed. We also present a novel semiexact two-dimensional plane velocity field through the flow depth. Second, starting with the force balance between gravity, the pressure gradient, and Bagnold’s grain-inertia or macroviscous forces, we construct a simple and very special nonlinear ordinary differential equation to model the steady state debris front profile. An empirical pressure gradient enhancement factor is introduced to adequately stretch the flow front and properly model nonhydrostatic pressure in granular and debris avalanches. An exact solution in explicit form is constructed, and is expressed in terms of the Lambert–Euler omega function. Third, we consider rapid flows of frictional granular materials down a channel. The steady state mass and the momentum balance equations are combined together with the Coulomb friction law. The Chebyshev radicals are employed and the exact solutions are developed for the velocity profile and the debris depth. Similarly, Bagnold’s fluids are also used to construct alternative exact solutions. Many interesting and important aspects of all these exact solutions, their applications to real-flow situations, and the influence of model parameters are discussed in detail. These analytical solutions, although simple, compare very well with experimental data of debris flows, granular avalanches, and the wave tips of dam break flows. A new scaling law for Bagnold’s fluids is established to relate the settlement time of debris deposition. It is found analytically that the macroviscous fluid settles (comes to a standstill) considerably faster than the grain-inertia fluid, as manifested by dispersive pressure.
Bandgap opening in boron nitride confined armchair graphene nanoribbon
Authors: Seol Gyungseon , Guo Jing
Published: April 2011

Graphene nanoribbons (GNRs) have seized strong interest. Recent studies show that domains of graphene in monolayer hexagonal boron nitride (h-BN) can be synthesized. Using the first principle calculations we have studied the electronic properties of armchair GNRs (AGNRs) confined by BN nanoribbons (BNNRs). While, H-terminated AGNRs have a close to zero bandgap with the width index of 3p+2, AGNRs confined by BNNRs exhibit a considerable bandgap. The bandgap opening is primarily due to perturbation to the on-site potentials of atoms at AGNR edges. A tight binding model is parameterized to confirm this mechanism and enable future device studies.
A comb-sampling method for enhanced mass analysis in linear electrostatic ion traps
Authors: Greenwood J. B. , Kelly O. , Calvert C. R. , Duffy M. J. , King R. B. , Belshaw L. , Graham L. , Alexander J. D. , Williams I. D. , Bryan W. A. , Turcu I. C. E. , Cacho C. M. , Springate E.
Published: April 2011

In this paper an algorithm for extracting spectral information from signals containing a series of narrow periodic impulses is presented. Such signals can typically be acquired by pickup detectors from the image-charge of ion bunches oscillating in a linear electrostatic ion trap, where frequency analysis provides a scheme for high-resolution mass spectrometry. To provide an improved technique for such frequency analysis, we introduce the CHIMERA algorithm (Comb-sampling for High-resolution IMpulse-train frequency ExtRAaction). This algorithm utilizes a comb function to generate frequency coefficients, rather than using sinusoids via a Fourier transform, since the comb provides a superior match to the data. This new technique is developed theoretically, applied to synthetic data, and then used to perform high resolution mass spectrometry on real data from an ion trap. If the ions are generated at a localized point in time and space, and the data is simultaneously acquired with multiple pickup rings, the method is shown to be a significant improvement on Fourier analysis. The mass spectra generated typically have an order of magnitude higher resolution compared with that obtained from fundamental Fourier frequencies, and are absent of large contributions from harmonic frequency components.
Blackbody-like emission of terahertz radiation from AlGaN/GaN heterostructure under electron heating in lateral electric field
Authors: Shalygin V. A. , Vorobjev L. E. , Firsov D. A. , Sofronov A. N. , Melentyev G. A. , Lundin W. V. , Nikolaev A. E. , Sakharov A. V. , Tsatsulnikov A. F.
Published: April 2011

The authors report on the observation and study of terahertz radiation emission from modulation-doped AlGaN/GaN heterostructure under conditions of heating of a two-dimensional electron gas in the lateral electric field. The experimental results are compared with the theoretical model of blackbody-like emission from hot two-dimensional electrons. Complementary transport measurements and a theoretical simulation were carried out to determine the dependence of effective electron temperature on electric field. The role of nonequilibrium optical phonon accumulation is discussed.
Vortex core scattering and pinning by impurities in nanomagnets
Authors: Toscano D. , Leonel S. A. , Dias R. A. , Coura P. Z. , Costa B. V.
Published: April 2011

The dynamical behavior of a magnetic nanoparticle contaminated by pointlike impurities is studied by using a spin dynamics numerical simulation. It was observed that the impurities can behave both as pinning (attractive) and as scattering (repulsive) sites. A Gaussian profile was observed for the interaction potential energy ranging up to two lattice parameters. Using the known values of the parameters for Permalloy-79 we have calculated the interaction energy of the vortex core with a single defect. We estimated the interaction range as approximately 10nm. Both results agree quite well with experimental measurements.
Lubricant distribution and its effect on slider air bearing performance over bit patterned media disk of disk drives
Authors: Wu Lin
Published: April 2011

The distribution dynamics of a thin lubricant film on a bit-patterned media disk and its effect on the performance of the ultralow flying air bearing slider of disk drives are studied by direct numerical simulations. Our analysis shows that the physics governing lubricant distribution dynamics changes when deep enough sub-100-nm nanostructures are patterned on the disk surface. Air shearing under the slider that dominates lubricant flow on a flat disk may become negligible on a bit-patterned media disk. Surface tension and disjoining pressure become dominant factors instead. Our results show that disks with nanoscale patterns/roughness may no longer be treated as flat, and the air bearing load may strongly depend not only on the geometric detail of disk patterns but also on how lubricants are distributed on the patterns when slider-disk clearance is reduced to sub-10-nm. Air bearing load and consequently the slider’s flying attitude are affected by disk pattern geometry, average lubricant thickness, and material properties of lubricant such as the surface tension coefficient and Hamaker constant. The significantly expanded parameter space, upon which ultralow flying slider’s dynamics depends, has to be seriously considered in evaluating the head/disk interface tribology performance of next generation patterned media magnetic recording systems.
Design of lossless anchors for microacoustic-wave resonators utilizing phononic crystal strips
Authors: Hsu Feng-Chia , Hsu Jin-Chen , Huang Tsun-Che , Wang Chin-Hung , Chang Pin
Published: April 2011

In micromechanical acoustic-wave resonators, energy dissipation through the anchors into the substrates may result in a low quality (Q) factor. To eliminate the ill effect of anchor losses, a design of lossless anchor based on phononic crystal (PC) strips for the microacoustic-wave resonators is presented. PC strips with acoustic forbidden bands are introduced to suppress the anchor loss and to serve as the suspensions for bar-type resonators. Numerical analysis shows that the acoustic energy leak can be effectively suppressed and the stored energy inside the resonators can be enhanced. A high-Q resonator with minimized anchor loss is expected.
Relativistic effects on nonlinear lower hybrid oscillations in cold plasma
Authors: Maity Chandan , Chakrabarti Nikhil , Sengupta Sudip
Published: April 2011

Nonlinear lower hybrid mode in a quasineutral magnetized plasma is analyzed in one space dimension using Lagrangian coordinates. In a cold fluid, we treat electron fluid relativistically, whereas ion fluid nonrelativistically. The homotopy perturbation method is employed to obtain the nonlinear solution which also finds the frequency-amplitude relationship for the lower hybrid mode. The solution indicates that the amplitude of oscillation increases due to the weak relativistic effects. The appearance of density spikes is not ruled out in a magnetized plasma.
Maximal dimension of invariant subspaces admitted by nonlinear vector differential operators
Authors: Zhu Chunrong , Qu Changzheng
Published: April 2011

In this paper, the dimension of invariant subspaces admitted by m-component nonlinear vector differential operators is estimated. It is shown that if the m-component nonlinear vector differential operators of order k preserves the invariant subspace \documentclass[12pt]{minimal}\begin{document}$W^1_{n_1}\times \cdots \times W^m_{n_m}$\end{document}Wn11×⋯×Wnmm, where \documentclass[12pt]{minimal}\begin{document}$W_{n_q}^q$\end{document}Wnqq is the space generated by solutions of linear ordinary differential equations of order nq (q = 1, …, m), then max {n1, …, nm} ⩽ 2mk + 1. To illustrate the approach, examples of nonlinear vector differential operators admitting invariant subspace \documentclass[12pt]{minimal}\begin{document}$W^1_{n_1}\times W^2_{n_2}$\end{document}Wn11×Wn22 with max {n1, n2} = 9 and three-component nonlinear vector differential operators admitting invariant subspace \documentclass[12pt]{minimal}\begin{document}$W^1_{n_1}\break\times W^2_{n_2}\times W^3_{n_3}$\end{document}Wn11×Wn22×Wn33 with max {n1, n2, n3} = 13 are presented.
A vacuum-ultraviolet laser pulsed field ionization-photoelectron study of sulfur monoxide (SO) and its cation (SO+)
Authors: Lam Chow-Shing , Wang Hailing , Xu Yuntao , Lau Kai-Chung , Ng C. Y.
Published: April 2011

Vacuum ultraviolet (VUV) laser pulsed field ionization-photoelectron (PFI-PE) spectroscopy has been applied to the study of the sulfur monoxide radical (SO) prepared by using a supersonically cooled radical beam source based on the 193 nm excimer laser photodissociation of SO2. The vibronic VUV-PFI-PE bands for the photoionization transitions SO+(X2Π1/2; v+ = 0) ← SO(X3Σ−; v = 0); and SO+(2Π3/2; v+ = 0) ← SO(X3Σ−; v = 0) have been recorded. On the basis of the semiempirical simulation of rotational branch contours observed in these PFI-PE bands, we have obtained highly precise ionization energies (IEs) of 83 034.2 ± 1.7 cm−1 (10.2949 ± 0.0002 eV) and 83 400.4 ± 1.7 cm−1 (10.3403 ± 0.0002 eV) for the formation of SO+(X2Π1/2; v+ = 0) and SO+(2Π3/2; v+ = 0), respectively. The present VUV-PFI-PE measurement has enabled the direct determination of the spin-orbit coupling constant (A0) for SO+(X2Π1/2,3/2) to be 365.36 ± 0.12 cm−1. We have also performed high-level ab initio quantum chemical calculations at the coupled-cluster level up to full quadruple excitations and complete basis set (CBS) extrapolation. The zero-point vibrational energy correction, the core-valence electronic correction, the spin-orbit coupling, and the high-level correction are included in the calculation. The IE[SO+(X2Π1/2,3/2)] and A0 predictions thus obtained are found to be in remarkable agreement with the experimental determinations.
Identifying severity of electroporation through quantitative image analysis
Authors: Morshed Bashir I. , Shams Maitham , Mussivand Tofy
Published: April 2011

Electroporation is the formation of reversible hydrophilic pores in the cell membrane under electric fields. Severity of electroporation is challenging to measure and quantify. An image analysis method is developed, and the initial results with a fabricated microfluidic device are reported. The microfluidic device contains integrated microchannels and coplanar interdigitated electrodes allowing low-voltage operation and low-power consumption. Noninvasive human buccal cell samples were specifically stained, and electroporation was induced. Captured image sequences were analyzed for pixel color ranges to quantify the severity of electroporation. The method can detect even a minor occurrence of electroporation and can perform comparative studies.
Simultaneous-trajectory surface hopping: A parameter-free algorithm for implementing decoherence in nonadiabatic dynamics
Authors: Shenvi Neil , Subotnik Joseph E. , Yang Weitao
Published: April 2011

In this paper, we introduce a trajectory-based nonadiabatic dynamics algorithm which aims to correct the well-known overcoherence problem in Tully's popular fewest-switches surface hopping algorithm. Our simultaneous-trajectory surface hopping algorithm propagates a separate classical trajectory on each energetically accessible adiabatic surface. The divergence of these trajectories generates decoherence, which collapses the particle wavefunction onto a single adiabatic state. Decoherence is implemented without the need for any parameters, either empirical or adjustable. We apply our algorithm to several model problems and find a significant improvement over the traditional algorithm.
Exact solutions of fractional Schrödinger-like equation with a nonlocal term
Authors: Jiang Xiaoyun , Qi Haitao , Xu Mingyu
Published: April 2011

We study the time-space fractional Schrödinger equation with a nonlocal potential. By the method of Fourier transform and Laplace transform, the Green function, and hence the wave function, is expressed in terms of H-functions. Graphical analysis demonstrates that the influence of both the space-fractal parameter α and the nonlocal parameter ν on the fractional quantum system is strong. Indeed, the nonlocal potential may act similar to a fractional spatial derivative as well as fractional time derivative.
Optimization of the current pulse for spin-torque switches
Authors: Dunn Tom , Kamenev Alex
Published: April 2011

We address optimization of the spin current intensity profile needed to achieve spin torque switching of a nanomagnet. For systems with Ohmic dissipation we prove that the optimal current drives the magnetization along the trajectory, which is exact time-reversed replica of the relaxation trajectory toward the equilibrium. In practice it means that the optimal current is very nearly twice the minimal critical current needed to switch the magnet. Pulse duration of such an optimal current is a slow logarithmic function of temperature and the required probability of switching.
Current-induced effective field in perpendicularly magnetized Ta/CoFeB/MgO wire
Authors: Suzuki T. , Fukami S. , Ishiwata N. , Yamanouchi M. , Ikeda S. , Kasai N. , Ohno H.
Published: April 2011

The current-induced effective field in perpendicularly magnetized Ta/CoFeB/MgO wire was investigated. A threshold field decrease of 6.4 kOe/mA was observed by measuring the threshold field of Hall resistance versus the magnetic field curve with various bias currents. The decrease was probably caused by the in-plane effective field, mainly due to the Rashba effect. The effective field of the Ta/CoFeB/MgO wire was smaller and opposite in direction compared to that of Pt/Co/AlOx previously reported.
Controlling fluorescence from N2 inside femtosecond laser filaments in air by two-color laser pulses
Authors: Xu H. L. , Azarm A. , Chin S. L.
Published: April 2011

We experimentally demonstrate the feasibility of controlling the fluorescence emission of nitrogen molecules in air induced by femtosecond laser filamentation by using a pump-probe method. An obvious enhancement or reduction in the filament-induced fluorescence signals of nitrogen molecules can be realized when a blue (400 nm) or an infrared (1338 nm) laser pulse is used as the probe. The completely opposite effect is ascribed to the excitation enhancement of ionization and population trapping of some highly excited states including Rydberg states of nitrogen molecules.
Large-scale characterization of peptide-MHC binding landscapes with structural simulations
Authors: Yanover Chen , Bradley Philip
Published: April 2011

Class I major histocompatibility complex proteins play a critical role in the adaptive immune system by binding to peptides derived from cytosolic proteins and presenting them on the cell surface for surveillance by T cells. The varied peptide binding specificity of these highly polymorphic molecules has important consequences for vaccine design, transplantation, autoimmunity, and cancer development. Here, we describe a molecular modeling study of MHC-peptide interactions that integrates sampling techniques from protein–protein docking, loop modeling, de novo structure prediction, and protein design in order to construct atomically detailed peptide binding landscapes for a diverse set of MHC proteins. Specificity profiles derived from these landscapes recover key features of experimental binding profiles and can be used to predict peptide binding with reasonable accuracy. Family wide comparison of the predicted binding landscapes recapitulates previously reported patterns of specificity divergence and peptide-repertoire diversity while providing a structural basis for observed specificity patterns. The size and sequence diversity of these structure-based binding landscapes enable us to identify subtle patterns of covariation between peptide sequence positions; analysis of the associated structural models suggests physical interactions that may mediate these sequence correlations.
Semiconductor to metallic transition and polaron conduction in nanostructured cobalt ferrite
Authors: Rahman Atta ur , Rafiq M A , Karim S , Maaz K , Siddique M , Hasan M M
Published: April 2011

In this paper we report semiconductor to metal transition and polaron conduction in nanostructured cobalt ferrite. The material was prepared by the coprecipitation technique. Average particle size was determined to be ∼10 nm by x-ray diffraction and transmission electron microscope analysis. A detailed electrical characterization was performed in the frequency range 20 Hz–2 MHz and temperature range between 300 and 400 K. Nanostructured cobalt ferrite exhibits semiconductor behaviour from 300 to 330 K. From 330 to 400 K it has metallic behaviour. The change at ∼330 K is attributed to a change in cation distribution as obtained from Mössbauer spectroscopy. The ac conductivity of cobalt ferrite followed σac ∝ ω
s
dependence. The observed variation of the exponent ‘s’ with temperature suggests that overlapping large polaron tunnelling is the dominant conduction mechanism from 300 to 400 K and in the frequency range 20 Hz–2 MHz.
Main chamber sources and edge transport of tungsten in H-mode plasmas at ASDEX Upgrade
Authors: Dux R. , Janzer A. , Pütterich T.
Published: April 2011

In the fully tungsten clad ASDEX Upgrade, the sputtering rates of tungsten have been determined at all relevant plasma facing components using fast spectroscopic measurements with temporal resolution down to 0.5 ms. The sputtering strongly increases during an edge-localized mode (ELM) and the ELMs are often the dominant cause of tungsten sputtering. A modelling approach was employed to calculate the tungsten source at the limiters and the resulting tungsten density at the pedestal top inside the H-mode edge transport barrier (ETB). In the ETB, it is assumed that tungsten transport is collisional, i.e. behaves like other impurities. The collisional transport leads to strong inward drifts and steep density gradients in the ETB, which are flattened during an ELM causing an efflux of tungsten. The collisional transport in the ETB is also calculated for typical ITER conditions and the resulting tungsten density profiles as well as the transport of the helium ash through the ETB are evaluated.
Numerical simulation of fast ion loss detector measurements for fishbones on JET
Authors: von Thun C. Perez , Perona A. , Johnson T. , Reich M. , Sharapov S.E. , Kiptily V.G. , Cecconello M. , Salmi A. , Goloborod'ko V.Ya. , Pinches S.D. , García-Muñoz M. , Darrow D. , Brix M. , Voitsekhovitch I.
Published: April 2011

A synthetic diagnostic model for the simulation of energy and pitch angle resolved measurements of fast ion losses obtained by 2D scintillation-type detectors is presented and subsequently tested on a JET discharge with fishbones (previously documented in Perez von Thun et al
2010 Nucl. Fusion
50 084009). The simulated energy and pitch angle distributions at the detector are found to be in excellent agreement with the measurements. The simulations further suggest that nearly all the fast ion losses take place in the early growth phase of the fishbone cycle, and reach their maximum well ahead of the magnetic perturbation peak.
Contactless electromagnetic phase-shift flowmeter for liquid metals
Authors: Priede Jānis , Buchenau Dominique , Gerbeth Gunter
Published: April 2011

We present a concept and test results of an eddy-current flowmeter for liquid metals. The flow rate is determined by applying a weak ac magnetic field to a liquid metal flow and measuring the flow-induced phase disturbance in the external electromagnetic field. The phase disturbance is found to be more robust than that of the amplitude used in conventional eddy-current flowmeters. The basic characteristics of this type of flowmeter are analysed using simple theoretical models, where the flow is approximated by a solid body motion. Design of such a flowmeter is presented and its test results are reported.
Invertible linear maps on simple Lie algebras preserving commutativity
Authors: Wang Dengyin , Chen Zhengxin
Published: April 2011

Let

g

\mathfrak {g}

be a finite-dimensional simple Lie algebra of rank

l
l

over an algebraically closed field of characteristic zero. An invertible linear map

φ
\varphi

on

g

\mathfrak {g}

is called preserving commutativity in both directions if, for any

x
,
y
∈

g

x, y\in \mathfrak {g}

,

[
x
,
y
]
=
0

[x,y]=0

⇔
\Leftrightarrow

[
φ
(
x
)
,
φ
(
y
)
]
=
0

[\varphi (x),\varphi (y)]=0

. The group of all such maps on

g

\mathfrak {g}

is denoted by

P
z
p
(

g

)

Pzp (\mathfrak {g})

. It is shown in this paper that, if

l
=
1

l=1

, then

P
z
p
(

g

)
=
G
L
(

g

)

Pzp(\mathfrak {g})=GL(\mathfrak {g})

; otherwise,

P
z
p
(

g

)
=
A
u
t
(

g

)
×

F
∗

I

g

Pzp(\mathfrak {g})=Aut (\mathfrak {g})\times F^*I_{\mathfrak {g}}

, where

F
∗

I

g

F^*I_{\mathfrak {g}}

denotes the group of all non-zero scalar multiplication maps on

g

\mathfrak {g}

.
Reasoning with bio-ontologies: using relational closure rules to enable practical querying
Authors: Blondé Ward , Mironov Vladimir , Venkatesan Aravind , Antezana Erick , De Baets Bernard , Kuiper Martin
Published: April 2011

Motivation: Ontologies have become indispensable in the Life Sciences for managing large amounts of knowledge. The use of logics in ontologies ranges from sound modelling to practical querying of that knowledge, thus adding a considerable value. We conceive reasoning on bio-ontologies as a semi-automated process in three steps: (i) defining a logic-based representation language; (ii) building a consistent ontology using that language; and (iii) exploiting the ontology through querying.

Results: Here, we report on how we have implemented this approach to reasoning on the OBO Foundry ontologies within BioGateway, a biological Resource Description Framework knowledge base. By separating the three steps in a manual curation effort on Metarel, a vocabulary that specifies relation semantics, we were able to apply reasoning on a large scale. Starting from an initial 401 million triples, we inferred about 158 million knowledge statements that allow for a myriad of prospective queries, potentially leading to new hypotheses about for instance gene products, processes, interactions or diseases.

Availability: SPARUL code, a query end point and curated relation types in OBO Format, RDF and OWL 2 DL are freely available at http://www.semantic-systems-biology.org/metarel.

Contact:  ward.blonde@ugent.be

Supplementary Information:  Supplementary data are available at Bioinformatics online.
Lipo-chitooligosaccharide Signaling in Endosymbiotic Plant-Microbe Interactions
Authors: Gough Clare , Cullimore Julie
Published: April 2011

The arbuscular mycorrhizal (AM) and the rhizobia-legume (RL) root endosymbioses are established as a result of signal exchange in which there is mutual recognition of diffusible signals produced by plant and microbial partners. It was discovered 20 years ago that the key symbiotic signals produced by rhizobial bacteria are lipo-chitooligosaccharides (LCO), called Nod factors. These LCO are perceived via lysin-motif (LysM) receptors and activate a signaling pathway called the common symbiotic pathway (CSP), which controls both the RL and the AM symbioses. Recent work has established that an AM fungus, Glomus intraradices, also produces LCO that activate the CSP, leading to induction of gene expression and root branching in Medicago truncatula. These Myc-LCO also stimulate mycorrhization in diverse plants. In addition, work on the nonlegume Parasponia andersonii has shown that a LysM receptor is required for both successful mycorrhization and nodulation. Together these studies show that structurally related signals and the LysM receptor family are key components of both nodulation and mycorrhization. LysM receptors are also involved in the perception of chitooligosaccharides (CO), which are derived from fungal cell walls and elicit defense responses and resistance to pathogens in diverse plants. The discovery of Myc-LCO and a LysM receptor required for the AM symbiosis, therefore, not only raises questions of how legume plants discriminate fungal and bacterial endosymbionts but also, more generally, of how plants discriminate endosymbionts from pathogenic microorganisms using structurally related LCO and CO signals and of how these perception mechanisms have evolved.
Effect of Foliarly Applied Spirotetramat on Reproduction of Heterodera avenae on Wheat Roots
Authors: Smiley R. W. , Marshall J. M. , Yan G. P.
Published: April 2011

The cereal cyst nematode, Heterodera avenae, has the potential to reduce yields of cereal crops in the Pacific Northwest. Spirotetramat (Movento) is a foliar-applied insecticide with ambimobile translocation that reduces fecundity of sucking insects which feed on roots as well as foliage. Spirotetramat (88 g/ha) was applied to foliage during 2010 in two wheat fields infested by H. avenae near St. Anthony, ID and Palouse, WA. In Idaho, two applications at 2-week intervals during late spring to plants already exhibiting swollen white females reduced the postharvest density of H. avenae eggs plus juveniles by 35% (P = 0.03) compared to the nontreated control. In Washington, a single application before white females became apparent reduced the nematode density by 78% (P = 0.01). Grain yields and test weights were not significantly affected by application of spirotetramat at either location. In addition, symptomatic plants from the Idaho field were transplanted into greenhouse pots and treated with spirotetramat. One application (110 g/ha) reduced numbers of eggs plus juveniles/plant by 78% (P = 0.02). Spirotetramat effectively reduced H. avenae populations and warrants further evaluation as a substitute for crop rotations or long fallow periods that reduce nematode population densities in infested fields.
Comparison of Water Displacement and WinRHIZO Software for Plant Root Parameter Assessment
Authors: Pang W. , Crow W. T. , Luc J. E. , McSorley R. , Giblin-Davis R. M. , Kenworthy K. E. , Kruse J. K.
Published: April 2011

Water-displacement and WinRHIZO root-scanning methods were compared for efficacy of root damage assessment. Results from both methods were similar and a highly significant relationship was found between the two methods in trial one (r2 = 0.9968, P < 0.0001) and trial two (r2 = 0.9988, P < 0.0001). Both protocols provide consistent root volume measurements; however, water displacement is preferred as an economical method if a quick evaluation of a large amount of roots is essential. For a more detailed root morphological and architectural analysis, WinRHIZO root scanning provides additional information about several root parameters that cannot be measured by simple water displacement.
Stem-Pitting Citrus tristeza virus Predominantly Transmitted by the Brown Citrus Aphid from Mixed Infections Containing Non-Stem-Pitting and Stem-Pitting Isolates
Authors: Brlansky R. H. , Roy Avijit , Damsteegt V. D.
Published: April 2011

Citrus tristeza virus (CTV) is a phloem-limited Closterovirus that produces a variety of symptoms in various Citrus spp. One of these symptoms is stem pitting (SP). SP does not occur in all Citrus spp. but when it does it may cause low tree vigor, decline, and an economic reduction in fruit size and yield. Historically, the first appearance of CTV-SP in a citrus area often occurs after the introduction of the most efficient CTV vector, the brown citrus aphid (BCA), Toxoptera citricida. Hypotheses for this association range from the introduction of these strains in new planting materials to the increased ability of BCA to transmit SP strains from existing CTV sources. It is known that CTV often exists as a complex of isolates or subisolates. Single and multiple BCA transmissions have been used to separate different genotypes or strains of CTV from mixed CTV infected plants. This study was initiated to determine what the BCA transmits when an exotic severe SP CTV isolate B12 from Brazil or B408 from Dominican Republic are mixed with a non-SP (NSP) isolate, FS627 from Florida. Biological and molecular data was generated from grafted mixtures of these isolates and their aphid-transmitted subisolates. Single-strand conformation polymorphism patterns of the 5′ terminal region of open reading frame (ORF) 1a, the overlapping region of ORF1b and ORF2, and the major coat protein gene region of NSP and SP CTV-grafted plants remained unchanged but the patterns of doubly inoculated plants varied. The haplotype diversity within SP isolates B12, B408, and mixtures of NSP and SP isolates (FS627/B12 and FS627/B408) and aphid-transmitted subisolates from doubly inoculated plants was determined by analysis of the haplotype nucleotide sequences. Aphid transmission experiments, symptoms, and molecular analyses showed that SP-CTV was more frequently transmitted with or without NSP-CTV from mixed infections.
A collisional perspective on quadrupedal gait dynamics
Authors: Lee David V. , Bertram John E. A. , Anttonen Jennifer T. , Ros Ivo G. , Harris Sarah L. , Biewener Andrew A.
Published: April 2011

The analysis of terrestrial locomotion over the past half century has focused largely on strategies of mechanical energy recovery used during walking and running. In contrast, we describe the underlying mechanics of legged locomotion as a collision-like interaction that redirects the centre of mass (CoM). We introduce the collision angle, determined by the angle between the CoM force and velocity vectors, and show by computing the collision fraction, a ratio of actual to potential collision, that the quadrupedal walk and gallop employ collision-reduction strategies while the trot permits greater collisions. We provide the first experimental evidence that a collision-based approach can differentiate quadrupedal gaits and quantify interspecific differences. Furthermore, we show that this approach explains the physical basis of a commonly used locomotion metric, the mechanical cost of transport. Collision angle and collision fraction provide a unifying analysis of legged locomotion which can be applied broadly across animal size, leg number and gait.