bluuebunny/crossref_metadata_2025 huggingface dataset:
Gene Profiles and Electrophysiology of Doublecortin-Expressing Cells in the Subventricular Zone after Ischemic Stroke
Authors: Liu Xian Shuang , Chopp Michael , Zhang Xue Guo , Zhang Rui Lan , Buller Ben , Hozeska-Solgot Ann , Gregg Sara R , Zhang Zheng Gang
Published: October 2008

Stroke increases neuroblasts in the subventricular zone (SVZ) of the lateral ventricle and these neuroblasts migrate toward the ischemic boundary to replace damaged neurons. Using brain slices from the nonischemic adult rat and transgenic mice that expressed enhanced green fluorescent protein (EGFP) concomitantly with doublecortin (DCX), a marker for migrating neuroblasts, we recorded electrophysiological characteristics while simultaneously analyzing the gene expression in single SVZ cells. We found that SVZ cells expressing the DCX gene from the nonischemic rat had a mean resting membrane potential (RMP) of −30 mV. DCX—EGFP-positive cells in the nonischemic SVZ of the transgenic mouse had a mean RMP of −25 ± 7 mV and did not exhibit Na+ currents, characteristic of immature neurons. However, DCX—EGFP-positive cells in the ischemic SVZ exhibited a hyperpolarized mean RMP of −54 ± 18 mV and displayed Na+ currents, indicative of more mature neurons. Single-cell multiplex RT-PCR analysis revealed that DCX—EGFP-positive cells in the nonischemic SVZ of the transgenic mouse expressed high neural progenitor marker genes, Sox2 and nestin, but not mature neuronal marker genes. In contrast, DCX—EGFP-positive cells in the ischemic SVZ expressed tyrosine hydroxylase, a mature neuronal marker gene. Together, these data indicate that stroke changes gene profiles and the electrophysiology of migrating neuroblasts.
Glibenclamide Reduces Inflammation, Vasogenic Edema, and Caspase-3 Activation after Subarachnoid Hemorrhage
Authors: Simard J Marc , Geng Zhihua , Woo S Kyoon , Ivanova Svetlana , Tosun Cigdem , Melnichenko Ludmila , Gerzanich Volodymyr
Published: October 2008

Subarachnoid hemorrhage (SAH) causes secondary brain injury due to vasospasm and inflammation. Here, we studied a rat model of mild-to-moderate SAH intended to minimize ischemia/hypoxia to examine the role of sulfonylurea receptor 1 (SUR1) in the inflammatory response induced by SAH. mRNA for Abcc8, which encodes SUR1, and SUR1 protein were abundantly upregulated in cortex adjacent to SAH, where tumor-necrosis factor-α (TNFα) and nuclear factor (NF)κB signaling were prominent. In vitro experiments confirmed that Abcc8 transcription is stimulated by TNFα. To investigate the functional consequences of SUR1 expression after SAH, we studied the effect of the potent, selective SUR1 inhibitor, glibenclamide. We examined barrier permeability (immunoglobulin G, IgG extravasation), and its correlate, the localization of the tight junction protein, zona occludens 1 (ZO-1). SAH caused a large increase in barrier permeability and disrupted the normal junctional localization of ZO-1, with glibenclamide significantly reducing both effects. In addition, SAH caused large increases in markers of inflammation, including TNFα and NFκB, and markers of cell injury or cell death, including IgG endocytosis and caspase-3 activation, with glibenclamide significantly reducing these effects. We conclude that block of SUR1 by glibenclamide may ameliorate several pathologic effects associated with inflammation that lead to cortical dysfunction after SAH.
Excess-silver-induced bridge formation in a silver sulfide atomic switch
Authors: Wang Zhongchang , Gu Tingkun , Tada Tomofumi , Watanabe Satoshi
Published: October 2008

Structural properties and electron transport of a Ag2S atomic switch composed of Ag–Ag2S–Ag heterostructure are investigated by nonequilibrium Green’s function calculations considering the effect of excess Ag in the Ag2S layer. In addition to confirming experimentally the formation of the Ag bridge inside Ag2S, the bridge is found to consist of units having a structure similar to that of the Ag (111) face in the bulk Ag. The analyses of Mulliken population, transmission spectra, and current-voltage characteristics reveal that the bridge has a conductive and metallic nature.
Some aspects of exciton thermal exchange in InAs quantum dots coupled with InGaAs/GaAs quantum wells
Authors: Torchynska T. V.
Published: October 2008

Photoluminescence (PL), its temperature and excitation power dependences, and PL excitation spectra have been investigated in InAs quantum dots (QDs) embedded in In0.15Ga0.85As/GaAs quantum wells (QWs) as a function of QD density. The QD density varied from 1.1×1011 down to 1.3×1010 cm−2 with the increase in QD growth temperature at the molecular beam epitaxy processing. A set of rate equations for exciton dynamics (relaxation into QWs and QDs, and thermal escape) has been solved to analyze the mechanism of PL thermal quenching in studied structures. Three stages have been revealed in thermal decay of the PL intensity of InAs QDs. Presented mathematical analysis provides the explanations of the mechanism of PL thermal decay as well as the peculiarities of PL excitation power dependences and PL excitation spectra. A variety of activation energies of PL thermal decay and the localization of nonradiative defects in InGaAs/GaAs QW structures with different InAs QD density are discussed as well.
The influence of Coulomb centers located in HfO2/SiO2 gate stacks on the effective electron mobility
Authors: Barraud Sylvain , Bonno Olivier , Cassé Mikaël
Published: October 2008

In this paper, we present an experimental and theoretical study on the reduction in electron mobility in metal-oxide-semiconductor field-effect transistors (MOSFETs) with a TiN/HfO2/SiO2 gate stack. Through low temperature mobility measurements down to 100 K, it is shown that the scattering mechanism responsible for the mobility degradation in MOSFETs with gate stack integrating HfO2 material is weakly dependent on temperature. Furthermore, the effect of vicinity of HfO2 is demonstrated through two SiO2 interfacial layers (ILs) of thicknesses 1 and 2 nm showing that the electron mobility is further reduced by decreasing the IL thickness. Both of these observations lead us to identify the remote-Coulomb scattering (RCS) as being the main factor limiting low-field mobility. In order to investigate more deeply the effect of Coulomb centers located in the gate stack, we have developed and used a RCS-limited mobility model. This model includes image charge, inversion layer quantization with upper subbands, a finite IL thickness, and dielectric screening. The induced Coulomb scattering potential is calculated for various high-κ permittivities and charge locations inside the gate stack. The impact of the amount and location of fixed charges, inside the gate dielectric as well as the increase in the IL dielectric constant for thin SiO2 layer on the RCS-limited mobility are investigated and discussed. Good agreement is obtained between theory and experiment over a large range of temperatures (100–300 K) and IL thicknesses (1–2 nm). As a result, by combining both experimental and theoretical data we confirm that the mobility degradation is mainly explained by a charge density located at the HfO2/SiO2 interface. At room temperature the charge density was evaluated to be 1.5×1013 cm−2.
Comparison of mean flow similarity laws in zero pressure gradient turbulent boundary layers
Authors: Monkewitz Peter A. , Chauhan Kapil A. , Nagib Hassan M.
Published: October 2008

The paper presents an in depth assessment of different similarity laws for the mean velocity profile in zero pressure gradient (ZPG) turbulent boundary layers (TBL's) in comparison with mostly experimental and few computational data. The emphasis is on the descriptions which are complete in the sense that a full representation of the mean velocity profile, its streamwise evolution and all integral parameters, including the friction factor and the shape factor, are provided as a function of Reynolds number. The first such complete description is the classical two-layer theory with its characteristic logarithmic mean velocity profile in the region where the two layers overlap, henceforth referred to as the “log law.” The main alternative scalings which have been proposed over the last decade have led to power law descriptions of the turbulent mean velocity profile. Since the different descriptions were calibrated with different data sets, the controversy over the relative merits of the different approaches has lingered on. The purpose of the present paper is to measure the principal competing theories against the same vast data set of more than 300 mean velocity profiles from more than twenty different sources. The results confirm the conclusions of numerous authors that the log law provides a fully self-consistent and accurate description of all the mean quantities and demonstrates conclusively that the same cannot be achieved by the competing power law theories. Along the way, it is also argued that the traditional description of the outer velocity profile in terms of a wall-normal coordinate normalized to unity at a hypothetical boundary layer “edge” δ and a “wake parameter” Π is not robust with respect to the fit of the outer velicity profile and should therefore not be used in theoretical arguments.
Investigation of the effect of in situ annealing of FePt nanodots under high vacuum on the chemical states of Fe and Pt by x-ray photoelectron spectroscopy
Authors: Murugesan M. , Bea J. C. , Yin C.-K. , Nohira H. , Ikenaga E. , Hattori T. , Nishijima M. , Fukushima T. , Tanaka T. , Miyao M. , Koyanagi M.
Published: October 2008

The chemical states of Fe and Pt in in situ annealed L10 structured FePt nanodots formed by self-assembled nanodot deposition method have been systematically investigated by angle resolved x-ray photoelectron spectroscopy. From the Fe3p and the Pt4f core level x-ray photoelectron (XP) spectra, it is evident that both the Fe and Pt of the nanodots were oxidized in the as-grown state. After the in situ annealing under high vacuum, a peak corresponding to metallic Fe begins to appear, and subsequently the metallic peak fraction increased with the increase in the annealing temperature. In line with this, the peak fraction of the respective oxides is drastically decreased. Irrespective of the annealing temperatures, it is inferred from the intensity of the XP spectrum that the Fe atom of the FePt nanodots is highly prone to oxidation than the Pt atom. Nevertheless, the valence band spectra of the as-grown FePt nanodot film clearly depict the presence of metallic Fe–Pt alloy. We would like to explain the results of the core level and valence band XP spectra as follows: only the peripheral Fe and Pt atoms of the as-formed FePt nanodots are bonded to the oxygen of the cosputtered SiO2 matrix, whereas the metallic core of the as-formed FePt nanodots is always preserved. The very good vacuum ambient during postannealing highly promotes the dissociation of oxygen from the metal oxides via reduction reaction. This results into an increase in the fraction of metallic Fe and Pt at the periphery of FePt nanodots and the formation of high quality SiO2 matrix after annealing. Similar results were also observed for the monatomic W as well as Pt nanodots embedded in SiO2 matrix. Hence, this simple, rather effective method of in situ annealing of metal dots dispersed in an insulating matrix can be readily employed in the fabrication of high-density nanodot memory devices.
Interpreting the Coulomb-field approximation for generalized-Born electrostatics using boundary-integral equation theory
Authors: Bardhan Jaydeep P.
Published: October 2008

The importance of molecular electrostatic interactions in aqueous solution has motivated extensive research into physical models and numerical methods for their estimation. The computational costs associated with simulations that include many explicit water molecules have driven the development of implicit-solvent models, with generalized-Born (GB) models among the most popular of these. In this paper, we analyze a boundary-integral equation interpretation for the Coulomb-field approximation (CFA), which plays a central role in most GB models. This interpretation offers new insights into the nature of the CFA, which traditionally has been assessed using only a single point charge in the solute. The boundary-integral interpretation of the CFA allows the use of multiple point charges, or even continuous charge distributions, leading naturally to methods that eliminate the interpolation inaccuracies associated with the Still equation. This approach, which we call boundary-integral-based electrostatic estimation by the CFA (BIBEE/CFA), is most accurate when the molecular charge distribution generates a smooth normal displacement field at the solute-solvent boundary, and CFA-based GB methods perform similarly. Conversely, both methods are least accurate for charge distributions that give rise to rapidly varying or highly localized normal displacement fields. Supporting this analysis are comparisons of the reaction-potential matrices calculated using GB methods and boundary-element-method (BEM) simulations. An approximation similar to BIBEE/CFA exhibits complementary behavior, with superior accuracy for charge distributions that generate rapidly varying normal fields and poorer accuracy for distributions that produce smooth fields. This approximation, BIBEE by preconditioning (BIBEE/P), essentially generates initial guesses for preconditioned Krylov-subspace iterative BEMs. Thus, iterative refinement of the BIBEE/P results recovers the BEM solution; excellent agreement is obtained in only a few iterations. The boundary-integral-equation framework may also provide a means to derive rigorous results explaining how the empirical correction terms in many modern GB models significantly improve accuracy despite their simple analytical forms.
A thermal spike model of grain growth under irradiation
Authors: Kaoumi D. , Motta A. T. , Birtcher R. C.
Published: October 2008

The experimental study of grain growth in nanocrystalline metallic foils under ion irradiation showed the existence of a low-temperature regime (below about 0.15–0.22Tm), where grain growth is independent of the irradiation temperature, and a thermally assisted regime where grain growth is enhanced with increasing irradiation temperature. A model is proposed to describe grain growth under irradiation in the temperature-independent regime, based on the direct impact of the thermal spikes on grain boundaries. In the model, grain-boundary migration occurs by atomic jumps, within the thermal spikes, biased by the local grain-boundary curvature driving. The jumps in the spike are calculated based on Vineyard’s analysis of thermal spikes and activated processes using a spherical geometry for the spike. The model incorporates cascade structure features such as subcascade formation, and the probability of subcascades occurring at grain boundaries. This results in a power law expression relating the average grain size with the ion dose with an exponent equal to 3, in agreement with the experimental observations. The model is applied to grain growth observed in situ in a transmission electron microscope in a wide range of doses, temperature, and irradiation conditions for four different pure metals, and shown to predict well the results in all applicable cases. Some discussions are also presented on the expansion of the model to the thermally assisted regime. The paper is organized in six sections. Section I gives background and literature review, while Secs. II and III review experimental methods and results for in situ grain growth under irradiation. Section IV derives the model proposed to find the grain-growth equation in the nonthermal regime, and in Sec. V the model is applied to the results. In Sec. VI grain growth in the thermally assisted regime is discussed and Sec. VII presents the conclusions.
The equivalent thermal properties of a single fracture
Authors: Sangaré D. , Thovert J.-F. , Adler P. M.
Published: October 2008

The normal resistance and the tangential conductivity of a single fracture with Gaussian or self-affine surfaces are systematically studied as functions of the nature of the materials in contact and of the geometrical parameters. Analytical formulas are provided in the lubrication limit for fractures with sinusoidal apertures; these formulas are used to substantiate empirical formulas for resistance and conductivity. Other approximations based on the combination of series and parallel formulas are tested.
Nonextensive kinetics of fluorescence resonance energy transfer
Authors: Rolinski Olaf J. , Birch David J. S.
Published: October 2008

Some fluorescence dyes in complex media, such as those found in biology, demonstrate nonextensive kinetics, which implies representing their fluorescence decays in terms of lifetime distributions rather than simple exponentials. Complex kinetics usually discourage application to lifetime sensors, as it is believed, that additional molecular mechanisms employed for detection of an analyte will make the resulting kinetics ambiguous and the sensor response inconclusive. In this paper we investigate theoretically the applicability of complex dye kinetics as a fluorescence resonance energy transfer based lifetime sensor and demonstrate that the nonextensive nature of its kinetics does not decrease the sensing performance, and indeed even provides richer structural information than a simple exponential behavior.
Correlation between conductivity or diffusivity and activation energy in amorphous solids
Authors: Sharma Manju , Yashonath S.
Published: October 2008

There exist many investigations of ionic transport in a variety of glasses. These studies exhibit strong correlation between ionic conductivity and activation energy: Typically, it is found that higher conductivity is associated with lower activation energies and vice versa. Although there are explanations for this at a phenomenological level, there is no consistent physical picture to explain the correlation between conductivity and activation energy. We have carried out molecular dynamics simulation as a function of the size of the impurity atom or diffusant (both neutral and charged) in a host amorphous matrix. We find that there is a maximum in self-diffusivity as a function of the size of the impurity atom suggesting that there is an appropriate size for which the diffusivity is maximum. The activation energy is found to be the lowest for this size of the impurity. A similar maximum has been previously found in other condensed phases, such as confined fluids and dense liquids, and has its origin in the levitation effect. The implications of this result for understanding ionic conductivity in glasses are discussed. Our results suggest that there is a relation between microscopic structure of the amorphous solid, diffusivity or conductivity, and activation energy. The nature of this relationship is discussed in terms of the levitation parameter showing that diffusivity is maximum when the size of the neck or doorway radius is comparable with the size of the diffusant. Our computational results here are in excellent agreement with independent experimental results of Nascimento et al. [Braz. J. Phys. 35, 626 (2005)] that structural features of the glass are important in determining the ionic conductivity.
Chemical state and atomic structure of Ge2Sb2Te5 system for nonvolatile phase-change random access memory
Authors: Jung Min-Cherl , Kim Ki-Hong , Lee Young-Mi , Eom Jae-Hyeon , Im Jino , Yoon Young-Gui , Ihm Jisoon , Song Se Ahn , Jeong Hong-Sik , Shin Hyun-Joon
Published: October 2008

We present chemical state information on contamination-free Ge2Sb2Te5 thin film using high-resolution x-ray photoelectron spectroscopy (HRXPS) and the corresponding theoretical understanding of the chemical states, on both amorphous and metastable phases, illuminating the phase-change mechanism of the system. HRXPS data revealed that the Sb 4d shallow core level was split into two components having different binding energies and that the spin-orbit splitting feature of the Ge 3d level was enhanced as the system became metastable. Negligible change was observed in the Te 4d shallow core level, and in contrary to the previous report’s prediction less change in valance band spectra was observed. The results imply that Sb movement is also involved in the phase-change mechanism and that acquisition of shallow core-level spectra can be a useful measure for understanding phase-change mechanism. Hydrogenated SbTe6 octahedral-like cluster model was introduced to schematically interpret the generation of the two components in the Sb 4d level in metastable state, having an isotropic six-bonds configuration, and an anistropic six-bonds (three-short and three-elongated bonds) configuration. The amorphous state was modeled to have three-short bonds configuration. Finally, Stibnite-like building block model was used to show that the existence of the above two configurations for Sb atoms is feasible in the Ge2Sb2Te5 system.
Winnerless competition principle and prediction of the transient dynamics in a Lotka–Volterra model
Authors: Afraimovich Valentin , Tristan Irma , Huerta Ramon , Rabinovich Mikhail I.
Published: October 2008

Predicting the evolution of multispecies ecological systems is an intriguing problem. A sufficiently complex model with the necessary predicting power requires solutions that are structurally stable. Small variations of the system parameters should not qualitatively perturb its solutions. When one is interested in just asymptotic results of evolution (as time goes to infinity), then the problem has a straightforward mathematical image involving simple attractors (fixed points or limit cycles) of a dynamical system. However, for an accurate prediction of evolution, the analysis of transient solutions is critical. In this paper, in the framework of the traditional Lotka–Volterra model (generalized in some sense), we show that the transient solution representing multispecies sequential competition can be reproducible and predictable with high probability.
Nanoliter liquid characterization by open whispering-gallery mode dielectric resonators at millimeter wave frequencies
Authors: Shaforost E. N. , Klein N. , Vitusevich S. A. , Offenhäusser A. , Barannik A. A.
Published: October 2008

We present an approach for identification and concentration determination of liquids of pico to nanoliter volumes at a frequency of 35 GHz based on a whispering-gallery mode (WGM) dielectric resonator technique. A quasioptical coupling scheme based on dielectric image waveguides was employed to excite high-Q running wave WGMs with uniform azimuthal field distribution in cylindrical sapphire disks with quality factors up to 4×105 at room temperature. Measurement of the liquid induced changes in the resonator quality factor and resonance frequency has been performed for droplets down to 90 pl volume spotted at different positions on the surface of the sapphire disk. We have employed our method for concentration determination of ethanol, glucose, and albumin dissolved in water. Solutions with concentration values well below 10% could be clearly separated from pure water. Our method is promising for the characterization of biological liquids.
Effects of submonolayer Mg on CoFe–MgO–CoFe magnetic tunnel junctions
Authors: Huang J. C. A. , Hsu C. Y. , Chen W. H. , Lee Y. H. , Chen S. F. , Liu C. P. , Tzeng Yonhua
Published: October 2008

CoFe–MgO–CoFe magnetic tunnel junctions (MTJs) were fabricated by means of ion beam sputtering of MgO as well as subsequent thin films on CoFe. We demonstrated that when a submonolayer of Mg was deposited on the CoFe layer prior to the deposition of MgO, profound improvement in the performance of the CoFe–Mg–MgO–CoFe MTJ was achieved compared to that without the Mg layer. ac impedance measurement indicated that the interfacial Mg layer resulted in fivefold increase in the magnetoresistance ratio from 0.76% for MTJs without it to 4% for that with it. Complex-capacitance (CC) spectra of MTJs showed that the contribution in the relaxation frequency by textured MgO increased. This indicated that the submonolayer Mg improved the texture of the subsequently deposited MgO. Bias-dependent complex-impedance (CI) spectra reveal that interfacial defects were also suppressed due to the submonolayer of Mg. Results obtained from x-ray reflectivity and transmission electronic microscopy were also consistent with those of CI and CC.
Accurate and efficient calculation of van der Waals interactions within density functional theory by local atomic potential approach
Authors: Sun Y. Y. , Kim Yong-Hyun , Lee Kyuho , Zhang S. B.
Published: October 2008

Density functional theory (DFT) in the commonly used local density or generalized gradient approximation fails to describe van der Waals (vdW) interactions that are vital to organic, biological, and other molecular systems. Here, we propose a simple, efficient, yet accurate local atomic potential (LAP) approach, named DFT+LAP, for including vdW interactions in the framework of DFT. The LAPs for H, C, N, and O are generated by fitting the DFT+LAP potential energy curves of small molecule dimers to those obtained from coupled cluster calculations with single, double, and perturbatively treated triple excitations, CCSD(T). Excellent transferability of the LAPs is demonstrated by remarkable agreement with the JSCH–2005 benchmark database [P. Jurečka et al. Phys. Chem. Chem. Phys. 8, 1985 (2006)], which provides the interaction energies of CCSD(T) quality for 165 vdW and hydrogen-bonded complexes. For over 100 vdW dominant complexes in this database, our DFT+LAP calculations give a mean absolute deviation from the benchmark results less than 0.5kcal∕mol. The DFT+LAP approach involves no extra computational cost other than standard DFT calculations and no modification of existing DFT codes, which enables straightforward quantum simulations, such as ab initio molecular dynamics, on biomolecular systems, as well as on other organic systems.
Concentration fluctuations in fluid mixtures
Authors: Mazo Robert M.
Published: October 2008

The B matrix of the Kirkwood–Buff theory of solutions describes number fluctuations of the component species. We show how, when the eigenvalues of the B matrix are widely different in magnitude, the description of the fluctuations can be simplified by restriction to a lower dimensional subspace of composition space. This simplification entails a loss of accuracy, which is argued to be often acceptable. The development is illustrated by application to water-urea and water −2,2,2 trifluoroethanol solutions. It is concluded that in these cases, the fluctuations of the components are coupled primarily by keeping the amount of void space in the solution almost constant.
Nonequilibrium fluctuation-dissipation theorem of Brownian dynamics
Authors: Chen L. Y.
Published: October 2008

Studying the Brownian motion of a system driven by an external control from one macroscopic state to another macroscopic state, this paper presents the derivation of a nonlinear fluctuation-dissipation theorem (FDT). The new FDT relates the nonequilibrium work to the equilibrium free-energy difference in a very simple manner. It is valid wherever the Brownian dynamics is applicable. It recovers the well-known Crooks fluctuation theorem (CFT) within the quasiequilibrium regime where the dissipative work is nearly zero. It will also be shown that the CFT’s fundamental assumption of microscopic reversibility is not obeyed in experiments such as mechanically unfolding biological molecules, in which the external driving forces depend on the system’s coordinates.
Multidimensional, autoresonant three-wave interactions
Authors: Yaakobi O. , Friedland L.
Published: October 2008

The theory of autoresonant three-wave interactions is generalized to more than one space and/or time variation of the background medium. In the most general case, the three waves propagate in a four-dimensional (4D) slowly space-time varying background, with an embedded 3D linear resonance hypersurface, where the linear frequency and wave-vector matching conditions of the three waves are satisfied exactly. The autoresonance in the system is the result of weak nonlinear frequency shifts and nonuniformity in the problem and is manifested by satisfaction of the nonlinear resonance conditions in an extended region of space-time adjacent to the resonance surface despite the variation of the background. The threshold condition for autoresonance is found and further discussed in application to stimulated Raman scattering in a 1D, time-dependent plasma case. Asymptotic description of the autoresonant waves far away from the resonance surface is obtained. The theory is illustrated and tested in 2D numerical simulations.
Properties of microwave plasma torch operating at a low pressure
Authors: Cho Soon C. , Uhm Han S. , Hong Yong C. , Kim Jae H.
Published: October 2008

A microwave plasma torch system is attached to a low-pressure chamber in this study. The electric field induced in a quartz discharge tube by microwave radiation breaks down the gas at a sufficiently low pressure, igniting the plasma, which is continuously sustained by the microwave radiation. The plasma profile at a very low pressure is shown to be asymmetric with higher density on the incoming side of the microwaves. The gas temperature at the bright spot of the torch plasma measured via the optical emission from hydroxide radicals is shown to increase drastically upon high-pressure operation as the microwave power increases. The electron density at the torch flame is measured by recording the Stark broadening of the hydrogen Balmer beta line. The plasma density increases as the microwave power increases. The typical argon plasma density of a plasma torch powered at 500W under a pressure of 150Torr is on the order of 1014∕cm3. The electron temperature in the argon torch plasma was estimated to be 1.5 eV, thereby effectively exciting the molecules in the torch gas. Disintegration of nitrogen fluoride (NF3) indicates that a microwave plasma torch operating at a low pressure can efficiently generate an abundant amount of chemical radicals.
Symmetry, full symmetry groups, and some exact solutions to a generalized Davey–Stewartson system
Authors: Li Biao , Ye Wang-Chuan , Chen Yong
Published: October 2008

The Lie symmetry algebra of a generalized Davey–Stewartson (GDS) system is obtained. The general element of this algebra depends on eight arbitrary functions of time, which has a Kac–Moody–Virasoro loop algebra structure and is isomorphic to that of the standard integrable Davey–Stewartson equations under certain conditions imposed on parameters and arbitrary functions. Then based on the symmetry group direct method proposed by Lou and Ma [J. Phys. A 38, L129 (2005)] the full symmetry groups of the GDS system are obtained. From the full symmetry groups, both the Lie symmetry group and a group of discrete transformations can be obtained. Finally, some exact solutions involving sech-sech2-sech2 and tanh-tanh2-tanh2 type solitary wave solutions are presented by a generalized subequation expansion method.
Development of high resolution Michelson interferometer for stable phase-locked ultrashort pulse pair generation
Authors: Okada Takumi , Komori Kazuhiro , Goshima Keishiro , Yamauchi Shohgo , Morohashi Isao , Sugaya Takeyoshi , Ogura Mutsuo , Tsurumachi Noriaki
Published: October 2008

We developed a high resolution Michelson interferometer with a two-frequency He–Ne laser positioning system in order to stabilize the relative phase of a pulse pair. The control resolution corresponded to a 12 as time resolution or a phase of 1.5° at 900 nm. This high resolution Michelson interferometer can generate a phase-locked pulse pair either with a specific relative phase such as 0 or π radians or with an arbitrary phase. Coherent control of an InAs self-assembled quantum dot was demonstrated using the high resolution Michelson interferometer with a microspectroscopy system.
Atomic-scale structure and composition of tungsten carbide reinforced diamondlike carbon films
Authors: Scharf T. W. , Romanes M. C. , Mahdak K. C. , Hwang J. Y. , Banerjee R. , Evans R. D. , Doll G. L.
Published: October 2008

This study presents the true atomic-scale structure and composition of hard/lubricious nanocomposite diamondlike carbon (DLC) films. Nanocrystalline tungsten carbide (∼2–4 nm precipitates) in mixed sp3/sp2 amorphous C–H matrices was characterized using the combination of three-dimensional atom probe (3DAP) tomography and transmission electron microscopy. Excellent correspondence in structural and chemical layering was observed (alternating ∼25 nm thick carbon-rich and tungsten-rich layers) with 3DAP also revealing C32+ and C2H4+ species in the carbon-rich layers and W2+, WC2+, C+, and C2+ species in the tungsten-rich layers. 3D morphology and chemical partitioning of the WC nanoprecipitates in the tungsten-rich layers are also discussed.
Energetic electron acceleration during multi-island coalescence
Authors: Pritchett P. L.
Published: October 2008

The mechanisms for the production of relativistic electrons associated with the coalescence/reconnection of multiple magnetic islands are investigated using two-dimensional particle-in-cell simulations for the case where the initial island half width L is comparable to the ion inertia length. Configurations without and with a uniform magnetic guide field are considered. Significant energization occurs only when the number of islands is reduced to 2 or 3 with wavelength satisfying kxL≲0.2. The energization proceeds in two distinct stages. In the first stage, a small number of electrons are accelerated to relativistic energies at the X-line by the inductive electric field, corresponding to perpendicular acceleration in the absence of the guide field and parallel/anti-parallel acceleration with a guide field. The second stage is associated with the final coalescence into one large island and produces a considerably larger number of relativistic electrons. With a guide field, this stage is dominated by the formation of elongated density cavities along one pair of separatrices and continued direct acceleration at the X-line. Without the guide field, the direct X-line acceleration becomes unimportant, and the acceleration is localized in the flux pile-up regions and results from the curvature drift interacting with the localized inductive electric field. Typically, some 15%–20% of the decrease in magnetic field energy is transferred to the electrons, with a few percent appearing in relativistic (E∕mec2>0.3) electrons.
Transfer characteristics in graphene field-effect transistors with Co contacts
Authors: Nouchi Ryo , Shiraishi Masashi , Suzuki Yoshishige
Published: October 2008

Graphene field-effect transistors with Co contacts as source and drain electrodes show anomalous distorted transfer characteristics. The anomaly appears only in short-channel devices (shorter than approximately 3 μm) and originates from a contact-induced effect. Band alteration of a graphene channel by the contacts is discussed as a possible mechanism for the anomalous characteristics observed.
Ultrafast phase-resolved pump-probe measurements on a quantum cascade laser
Authors: Kuehn W. , Parz W. , Gaal P. , Reimann K. , Woerner M. , Elsaesser T. , Müller T. , Darmo J. , Unterrainer K. , Austerer M. , Strasser G. , Wilson L. R. , Cockburn J. W. , Krysa A. B. , Roberts J. S.
Published: October 2008

The dynamics of optical gain in an InGaAs/AlInAs quantum cascade laser is studied in midinfrared pump-probe measurements. Pump and probe pulses of identical wavelength, polarization, and propagation direction through the laser waveguide are detected separately by electro-optic sampling. For injection currents below the lasing threshold, we observe an absorption decrease in the laser transition with a ≈3 ps recovery time. Above threshold, the gain strongly saturates and shows a fast recovery time decreasing with current. Such kinetics is superimposed by oscillations with a frequency of 0.8 THz originating from coherent electron tunneling through the injection barrier.
Geometrical correlations of quantum dots in InAs/GaAs superlattice structure from electron tomography
Authors: Wu Y. H. , Chang L. , Chen L. C. , Chen H. S. , Chen F. R.
Published: October 2008

In this study, the three-dimensional (3D) information about the structural properties of quantum dots (QDs) in InAs/GaAs superlattice structure has been illustrated using electron tomography in the mode of high-angle angular dark-field scanning transmission electron microscopy. Comparison of this 3D reconstruction with the two-dimensional projection at the same positions is made. The structural properties of embedded quantum dots have been evaluated from electron tomography. The correlation relationship of QDs in superlattice structure has been understood by accurate measurements of 3D geometric positions, which can be free of the overlapping effect from 2D cross section along different crystallographic orientations.
Development of UHV dynamic nanostencil for surface patterning
Authors: Guo Haiming , Martrou David , Zambelli Tomaso , Dujardin Erik , Gauthier Sébastien
Published: October 2008

A dynamic nanostencil system based on a movable atomic force microscopy (AFM) cantilever-borne mask has been developed in ultrahigh vacuum environment. This system is conceived to offer an outstanding nanopatterning capability of nanometer precision as well as in situ AFM characterization with a large scanning range. Evaporation experiments in both static and dynamic mode have been performed successfully on this system, and some crucial technical problems of stencilling technique such as resolution and clogging are investigated. As an important application of molecular electronics, a method to fabricate and connect nanoscale structures with microelectrodes by accurately combining it with static stenciling is presented.
Mg composition dependent strain analysis in nonpolar a-plane MgxZn1−xO films
Authors: Saraf G. , Lu Y. , Siegrist T.
Published: October 2008

Nonpolar a-plane (112¯0) MgxZn1−xO (a-MgxZn1−xO) films are deposited on (011¯2) r-sapphire substrates using metalorganic chemical vapor deposition with varying Mg composition (x from 0 to 0.25). Unit cell parameters with Mg composition are determined by high-resolution triple-axis x-ray diffraction. In-plane strain along the c-axis [0001] and m-axis [11¯00] in the films is anisotropic and increases with increasing Mg composition. The in-plane strain anisotropy changes with Mg composition in a-MgxZn1−xO. Calculations are carried out to determine the influence of Mg content on the residual interfacial strain.
Phase retrieval for improved three-dimensional velocimetry of dynamic x-ray blood speckle
Authors: Irvine S. C. , Paganin D. M. , Dubsky S. , Lewis R. A. , Fouras A.
Published: October 2008

High-resolution synchrotron-based x-ray phase-contrast images of in vitro blood flow have been collected. We demonstrate that the application of a single-image phase retrieval algorithm to the images leads to improved detail in particle image velocimetry correlation peaks. Out-of-plane variation in flow has been extracted from the peaks leading to the three-dimensional reconstruction of velocity across an axially symmetric cylinder.
Vortex Bose glass in ErBa2Cu3Oy films with size-controlled nanorods
Authors: Horii S. , Kai H. , Mukaida M. , Yamada K. , Teranishi R. , Ichinose A. , Matsumoto K. , Yoshida Y. , Kita R. , Shimoyama J. , Kishio K.
Published: October 2008

Anomalous changes in irreversibility lines (ILs) and critical current properties depending on growth conditions were demonstrated in ErBa2Cu3Oy films with Ba–(Nb,Er)–O nanorods. Despite the formation of nanorods in the matrix at all growth temperatures (Ts), Bose-glass-like vortex pinning was strengthened with decreasing Ts. In particular, the behavior of ILs can be understood in terms of the morphology of introduced nanorods, and Ts strongly affects the vortex states. Our present study suggests the importance of optimization of growth conditions in the production process of rare-earth-based coated conductors containing nanorods as vortex-pinning centers.
Effects of the thickness asymmetry of nanostructured exchange-coupled trilayers on their dynamic magnetization switching
Authors: Kim K. S. , Lee K. J. , Lim S. H.
Published: October 2008

The effects of thickness asymmetry (Δt) on the dynamic magnetization switching of exchange-coupled trilayers are investigated in this study. Elliptical thin films that have lateral dimensions of 200×100 nm2 are considered. A significant difference in the dynamic switching behavior is observed depending on Δt. Both the switching field and the switching time decrease as Δt increases. A Fourier analysis of the magnetization oscillation, which is followed by the initial coherent rotation, shows multiple oscillation frequencies. This tendency is more pronounced at a larger Δt. The main oscillation frequency tends to increase with an increase in Δt.
Stress-induced α″ martensitic (110) twinning in β-Ti alloys
Authors: Ping D. H. , Yamabe-Mitarai Y. , Cui C. Y. , Yin F. X. , Choudhry M. A.
Published: October 2008

A fully transformed α″ martensite with stress-induced nanoscale {110}, {021}-type compound twin or a 90° rotation twin has been experimentally explored and unambiguously characterized in traditional β-type Ti alloys, which usually undergo a partial martensitic transformation [a β grain partially transformed into α″ with internal (111) twin] by quenching. This newly observed twinning, which matches with the predication based on the deformation twinning theory of Bilby and Crocker [Proc. R. Soc. 288, 241 (1965)], can help to explain the deformation mechanism and aid future development of advanced materials.
Development of the Meat Standards Australia (MSA) prediction model for beef palatability
Authors: Watson R. , Polkinghorne R. , Thompson J. M.
Published: October 2008

In this paper, the statistical aspects of the methodology that led to the Meat Standards Australia (MSA) prediction model for beef palatability are explained and described. The model proposed here is descriptive: its intention is to describe the large amounts of data collected by MSA. The model is constrained to accord with accepted meat science principles. The combined dataset used in development of the prediction model reported is around 32 000 rows × 140 columns. Each row represents a sample tasted by 10 consumers; each column specifies a variable relating to the sample tested. The developed model represents the interface between experimental data, scientific evaluation and commercial application. The model is used commercially to predict consumer satisfaction, in the form of a score out of 100, which in turn determines a grade outcome. An important improvement of the MSA model relative to other beef grading systems is that it assigns an individual consumer-based grade result to specific muscle portions cooked by designated methods; it does not assign a single grade to a carcass.
Ubiquitylated PCNA plays a role in somatic hypermutation and class-switch recombination and is required for meiotic progression
Authors: Roa Sergio , Avdievich Elena , Peled Jonathan U. , MacCarthy Thomas , Werling Uwe , Kuang Fei Li , Kan Rui , Zhao Chunfang , Bergman Aviv , Cohen Paula E. , Edelmann Winfried , Scharff Matthew D.
Published: October 2008

Somatic hypermutation (SHM) and class-switch recombination (CSR) of Ig genes are dependent upon activation-induced cytidine deaminase (AID)-induced mutations. The scaffolding properties of proliferating cell nuclear antigen (PCNA) and ubiquitylation of its residue K164 have been suggested to play an important role organizing the error-prone repair events that contribute to the AID-induced diversification of the Ig locus. We generated knockout mice for PCNA (
Pcna
−/−
), which were embryonic lethal. Expression of PCNA with the K164R mutation rescued the lethal phenotype, but the mice (
Pcna
−/−
tg

K164R

) displayed a meiotic defect in early pachynema and were sterile. B cells proliferated normally in
Pcna
−/−
tg

K164R

mice, but a PCNA-K164R mutation resulted in impaired
ex vivo
CSR to IgG1 and IgG3, which was associated with reduced mutation frequency at the switch regions and a bias toward blunt junctions. Analysis of the heavy chain V186.2 region after NP-immunization showed in
Pcna
−/−
tg

K164R

mice a significant reduction in the mutation frequency of A:T residues in W
A
motifs preferred by polymerase-η (Polη), and a strand-biased increase in the mutation frequency of G residues, preferentially in the context of AID-targeted
G
YW motifs. The phenotype of
Pcna
−/−
tg

K164R

mice supports the idea that ubiquitylation of PCNA participates directly in the meiotic process and the diversification of the Ig locus through class-switch recombination (CSR) and somatic hypermutation (SHM).
A bilingual word superiority effect in Irish speakers
Authors: Lyddy Fiona , Roche-Dwyer Catherine
Published: October 2008

The present study employed a dual-language version of the Reicher-Wheeler task to examine the word superiority effect (WSE) in Irish-English bilinguals and L1 English speakers with some Irish language proficiency. Superior skills in written English would be expected in both groups. Forty-nine participants completed a word–letter WSE forced-choice task in both Irish and English. For both languages, and for both groups, an advantage was found for words over letters. The word–letter difference for English stimuli exceeded that for Irish stimuli, at 9% and 4% respectively; however this difference between the languages did not reach statistical significance. Performance did not differ significantly between the two groups, despite a trend suggesting a lower WSE in English for the bilingual group. The lack of difference based on proficiency may reflect the high frequency words employed or similar exposure to written Irish in the two groups, given the dominance of the English language.
Socio-cultural predictors of reading literacy in fourth graders in Lima, Peru
Authors: Silva Silvia Morales , Verhoeven Ludo , Leeuwe Jan van
Published: October 2008

This study investigates socio-cultural cognitive literacy predictors for reading literacy (RL), tested in 314 fourth graders from two different levels of social economic status in Lima, Peru. The following variables were tested as predictors: word decoding, vocabulary, motivation to read, reading strategies, intellectual maturity, gender, home literacy climate and social economic status. RL (reading literacy) was measured using an adapted version of the PIRLS Reading Literacy test. By using structural equation modelling, a total of 34 percent of the variance in RL could be explained. In addition to word decoding and vocabulary, motivation and social economic status were discovered to be directly predictive of RL. Furthermore, social economic status and home literacy climate were discovered to be important factors in determining the variation in other predictor variables. Intellectual maturity and gender did not appear to be significant factors contributing to RL level.