bluuebunny/crossref_metadata_2025 huggingface dataset:
Atypical protein kinases of the RIO family in archaea
Authors: Esser Dominik , Siebers Bettina
Published: January 2013

Atypical protein kinases of the RIO (right open reading frame) kinase family are found in all three domains of life, emphasizing their essential function. In all archaeal genomes sequenced to date, typically two, but at least one, members of the RIO kinase family have been identified. Although the function of RIO kinases in Archaea remains to be resolved, bioinformatics analysis (e.g. comparison of the phylogenetic distribution and gene neighbourhood analysis, as well as interaction analysis) in combination with the available phosphoproteome study of Sulfolobus solfataricus provided some first hints to the possible function as well as revealed some putative target proteins for RIO kinases in Archaea. This study suggests a possible function of archaeal RIO kinases in RNA and/or DNA binding/processing translation initiation or ribosomal biogenesis resembling the assumed physiological role in yeast.
Platelet mitochondrial function: from regulation of thrombosis to biomarker of disease
Authors: Zharikov Sergey , Shiva Sruti
Published: January 2013

Circulating blood platelets contain small numbers of fully functional mitochondria. Accumulating evidence demonstrates that these mitochondria regulate the pro-thrombotic function of platelets through not only energy generation, but also redox signalling and the initiation of apoptosis. Beyond its regulation of haemostasis, platelet mitochondrial function has also traditionally been used to identify and study mitochondrial dysfunction in human disease, owing to the easy accessibility of platelets compared with other metabolically active tissues. In the present article, we provide a brief overview of what is currently known about the function of mitochondria in platelets and review how platelet mitochondria have been used to study mitochondrial function in human disease.
Type IV secretion machinery: molecular architecture and function
Authors: Chandran Vidya
Published: January 2013

Bacteria have evolved several secretion machineries to bring about transport of various virulence factors, nutrients, nucleic acids and cell-surface appendages that are essential for their pathogenesis. T4S (Type IV secretion) systems are versatile secretion systems found in various Gram-negative and Gram-positive bacteria and in few archaea. They are large multisubunit translocons secreting a diverse array of substrates varying in size and nature from monomeric proteins to nucleoprotein complexes. T4S systems have evolved from conjugation machineries and are implicated in antibiotic resistance gene transfer and transport of virulence factors in Legionella pneumophila causing Legionnaires’ disease, Brucella suis causing brucellosis and Helicobacter pylori causing gastroduodenal diseases. The best-studied are the Agrobacterium tumefaciens VirB/D4 and the Escherichia coli plasmid pKM101 T4S systems. Recent structural advances revealing the cryo-EM (electron microscopy) structure of the core translocation assembly and high-resolution structure of the outer-membrane pore of T4S systems have made paradigm shifts in the understanding of T4S systems. The present paper reviews the advances made in biochemical and structural studies and summarizes our current understanding of the molecular architecture of this mega-assembly.
Palmitoylation, pathogens and their host
Authors: Blanc Mathieu , Blaskovic Sanja , van der Goot F. Gisou
Published: January 2013

S-Palmitoylation, the only reversible post-translational lipid modification, confers unique biochemical and functional properties to proteins. Although it has long been known that viral proteins are palmitoylated, recent studies reveal that this modification plays a critical role for pathogens of all kinds and at multiple steps of their life cycle. The present review examines the involvement of S-palmitoylation in infection by viruses, bacteria and parasites and illustrates how pathogens have evolved to manipulate the host palmitoylation machinery.
Using Grounded Theory Method in Information Systems: The Researcher as Blank Slate and Other Myths
Authors: Urquhart Cathy , Fernández Walter
Published: January 2013

The use of grounded theory method (GTM) as a research method in information systems (IS) has gradually increased over the years as qualitative research in general has become more prevalent. The method offers a systematic way to generate theory from data, but is rarely used to its full potential in IS as a number of myths and misunderstandings about GTM prevent researchers from getting the full potential out of the method. To address this problem, we advance the general level of knowledge of GTM. We clarify aspects of the method that are often misunderstood by novice users or casual observers and provide guidance to address common problems. Exemplars from the IS literature are used to illustrate the concepts and to promote the informed use of the methodology. By doing so, this paper will contribute to improving the use of the method and to the quality and dissemination of grounded theory research outcomes.
Understanding the Dominance and Advocacy of the Design-Oriented Research Approach in the Business Informatics Community: A History-Based Examination
Authors: Heinrich Lutz J , Riedl René
Published: January 2013

The objective of this article is to explain the dominance and advocacy of the design- oriented research approach in Wirtschaftsinformatik (Business Informatics or BI), one of the major Information Systems (IS) communities. To this end, we employed a research approach based on autobiographical material. Sixteen well-known BI scholars served as informants, and provided career autobiographies in which they document their perceptions and observations regarding the genesis and development of BI. The average age of this sample of contemporary witnesses is 70 years, signifying a rich body of experience. Based on an interpretive analysis of the data, we find that the design of IS is deeply rooted in BI's history, and our results also show that there have always been close relationships with practice. As a consequence, we conclude that the success of BI as an academic community is inseparably associated with systems design, implementation, and engineering. Against this background, we argue that it is unlikely that BI will weaken its design orientation in the future, although external forces signify a shift to a more behaviouristic research approach. In order to balance the internal strength of the community and the external forces, we suggest a ‘theory-driven design approach’ as a viable strategy for the future orientation of the community.
Configuration interaction in delta-doped heterostructures
Authors: Rozhansky I. V. , Averkiev N. S. , Lähderanta E.
Published: January 2013

We analyze the tunnel coupling between an impurity state located in a δ-layer and the 2D delocalized states in the quantum well (QW) located at a few nanometers from the δ-layer. The problem is formulated in terms of Anderson–Fano model as configuration interaction between the carrier bound state at the impurity and the continuum of delocalized states in the QW. An effect of this interaction on the interband optical transitions in the QW is analyzed. The results are discussed regarding the series of experiments on the GaAs structures with a δ-Mn layer.
An absence of the Anderson transition in high-resistance alloys with a high electron density
Authors: Gantmakher V. F.
Published: January 2013

In three-dimensional electron systems with a high electron density it is not possible to reach the Anderson transition neither by increasing disorder nor by a combination of static disorder with a dynamic one (by high temperature), or by selecting a material with a large deformation potential and a large constant of electron-phonon interaction.
Electronic structure of lead telluride-based alloys, doped with vanadium
Authors: Skipetrov E. P. , Golovanov A. N. , Slynko E. I. , Slynko V. E.
Published: January 2013

The crystal structure, composition, galvanomagnetic properties in low magnetic fields (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T), and the Shubnikov–de Haas effect (T = 4.2 K, B ≤ 7 T) are studied in Pb1−x−ySnxVyTe (x = 0, 0.05–0.18) alloys synthesized by the Bridgman technique with variable vanadium impurity concentrations. It is shown that increasing the vanadium content leads to the formation of regions enriched in vanadium and of microscopic inclusions of compounds with compositions close to V3Te4. In Pb1−yVyTe stabilization of the Fermi level by a deep vanadium level, an insulator–metal transition, and a rise in the free electron concentration are observed as the vanadium content is increased. The variation in the free charge carrier concentration with increasing vanadium concentration in Pb1−yVyTe and Pb1−x−ySnxVyTe (x = 0.05–0.18) alloys is compared. Possible models for rearrangement of the electronic structure in Pb1−x−ySnxVyTe alloys with vanadium doping are discussed.
Pseudogap state and strong scattering of current carriers by local spin moments as mechanisms for the semiconducting properties of near-stoichiometric iron-vanadium-aluminum alloys
Authors: Lonchakov A. T. , Marchenkov V. V. , Okulov V. I. , Okulova K. A.
Published: January 2013

New experimental evidence is obtained on the physical nature of the semiconducting properties of Fe2−xV1+xAl alloys with near-stoichiometric (x = 0) compositions. We examine the low-temperature thermal emf of two alloys: one is enriched in vanadium and exhibits a pseudogap in the electron density of states at the Fermi energy, while in the other, which is depleted in vanadium, the scattering of electrons by localized spins has a stronger influence. The experimental temperature dependences of the thermal emf at low temperatures display some characteristic anomalies that are observed here for the first time and are manifestations of these two effects. Existing theory is used to interpret the anomalous contributions of both effects (types), determine their characteristic parameters, and establish the conditions under which they appear in V-depleted and V-enriched alloys. Data on the thermal emf in magnetic fields show that that the thermal emf decreases substantially as the magnetic field is increased, confirming the key role of the mechanism of current carrier scattering by localized moments.
Charge transfer transitions in the photoluminescence spectra of Zn1−xMexO (Me = Mn, Ni, Co) oxide compounds
Authors: Sokolov V. I. , Gruzdev N. B. , Pustovarov V. A. , Churmanov V. N.
Published: January 2013

Crystals of Zn1−xCoxO and Zn1−xNixO are studied by photoluminescence at temperatures of 8 and 90 K. By resolving the spectra into sums of gaussian distributions and using the known positions of donor and acceptor levels of 3d-impurities relative to the edges of the allowed bands, the observed peaks in the photoluminescence spectra are interpreted in terms of radiative recombination through donor and acceptor levels of nickel and cobalt ions. These results are compared with previously observed features of the photoluminescence spectra of Zn1−xMnxO crystals.
Large room temperature magnetoresistance of transparent Fe and Ni doped ZnO thin films
Authors: Chikoidze E. , Boshta M. , Sayed M. H. , Dumont Y.
Published: January 2013

The electrical, optical, and magnetic properties of pure, 1%Fe, and 1%Ni doped ZnO thin films grown by spray pyrolysis technique were studied. All samples are transparent (T ≈ 85%) in VIS and near infrared region of wavelength. Ni and Fe doped ZnO layers are paramagnetic. Resistivity versus temperature has semiconducting behavior. Large value of magnetoresistance at 300 K at 1.3 T: MR = 56%/T for 1%Fe doped ZnO and MR = 28%/T for 1%Ni doped samples have been observed. These exceptional values of MR at room temperature originate probably from hopping conductivity in polycrystalline diluted magnetic semiconductor in paramagnetic high dilution limit.
Evolution of collective motion in a model glass-forming liquid during physical aging
Authors: Shavit Amit , Douglas Jack F. , Riggleman Robert A.
Published: January 2013

At temperatures moderately below their glass transition temperature, the properties of many glass-forming materials can evolve slowly with time in a process known as physical aging whereby the thermodynamic, mechanical, and dynamic properties all drift towards their equilibrium values. In this work, we study the evolution of the thermodynamic and dynamic properties during physical aging for a model polymer glass. Specifically, we test the relationship between an estimate of the size of the cooperative rearrangements taking the form of strings and the effective structural relaxation time predicted by the Adam-Gibbs relationship for both an equilibrium supercooled liquid and the same fluid undergoing physical aging towards equilibrium after a series of temperature jumps. We find that there is apparently a close correlation between a structural feature of the fluid, the size of the string-like rearrangements, and the structural relaxation time, although the relationship for the aging fluid appears to be distinct from that of the fluid at equilibrium.
The first jamming crossover: Geometric and mechanical features
Authors: Ciamarra Massimo Pica , Sollich Peter
Published: January 2013

The jamming transition characterizes athermal systems of particles interacting via finite range repulsive potentials, and occurs on increasing the density when particles cannot avoid making contacts with those of their first coordination shell. We have recently shown [M. Pica Ciamarra and P. Sollich, e-print arXiv:1209.3334] that the same systems are also characterized by a series of jamming crossovers. These occur at higher volume fractions as particles are forced to make contact with those of subsequent coordination shells. At finite temperature, the crossovers give rise to dynamic and thermodynamic density anomalies, including a diffusivity anomaly and a negative thermal expansion coefficient. Density anomalies may therefore be related to structural changes occurring at the jamming crossovers. Here we elucidate these structural changes, investigating the evolution of the structure and of the mechanical properties of a jammed system as its volume fraction varies from the jamming transition to and beyond the first jamming crossover. We show that the first jamming crossover occurs at a well defined volume fraction, and that it induces a rearrangement of the force network causing a softening of the system. It also causes qualitative changes in the normal mode density of states and the spatial properties of the normal mode vectors.
Electronic structure and optical properties of InAs/GaSb/AlSb/GaSb superlattice
Authors: Lang Xiao-Li , Xia Jian-Bai
Published: January 2013

The electronic structure and optical properties of InAs/GaSb/AlSb/GaSb superlattice (M-structure) are investigated in the framework of eight-band effective-mass theory, with the interface potential considered. The calculated energy gaps agree excellently with the experimental results. Via calculations, we find that the electronic structure of M-structure strongly depends on the geometrical structure of superlattice. The electron effective mass increases notably with the thickness of GaSb and AlSb layers, and AlSb layer is more favorable to obtain large electron effective mass than GaSb layer. Increased thickness of AlSb layer also leads to larger variation range of valence band maximum (VBM) and so M-structure has more tunable VBM than InAs/GaSb superlattice. Also the VBM of M-structure rises considerably with the increment of GaSb layer thickness and is almost independent of InAs layer thickness. We further find that M-structure has no remarkable superior optical absorption coefficient over InAs/GaSb superlattice. However, with larger electron effective mass and more tunable valence band maximum compared with InAs/GaSb superlattice, M-structure can be used as barrier in InAs/GaSb superlattice infrared detector to reduce the dark current. And the quantum efficiency of infrared photodiodes will not depend on the bias voltage when the M-structure is appropriately doped and carefully designed based on the dependence of its electronic structure on the superlattice geometry.
CO2-helium and CO2-neon mixtures at high pressures
Authors: Mallick B. , Ninet S. , Le Marchand G. , Munsch P. , Datchi F.
Published: January 2013

The properties of mixtures of carbon dioxide with helium or neon have been investigated as a function of CO2 concentration and pressure up to 30 GPa at room temperature. The binary phase diagrams of these mixtures are determined over the full range of CO2 concentrations using visual observations and Raman scattering measurements. Both diagrams are of eutectic type, with a fluid-fluid miscibility gap for CO2 concentrations in the range [5, 75] mol. % for He and [8, 55] mol. % for Ne, and a complete separation between the two components in the solid phase. The absence of alloys or stoichiometric compounds for these two binary systems is consistent with the Hume-Rothery rules of hard sphere mixtures. The Raman spectra and x-ray diffraction patterns of solid CO2 embedded in He or Ne for various initial concentrations have been measured up to 30 GPa and 12 GPa, respectively. The frequencies of the Raman modes and the volume of solid phase I are identical, within error bars, to those reported for 100% CO2 samples, thus confirming the total immiscibility of CO2 with He and Ne in the solid phase. These results demonstrate the possibility to perform high-pressure experiments on solid CO2 under (quasi-)hydrostatic conditions using He or Ne as pressure transmitting medium.
Shape-dependent charge and spin transport through an electron waveguide
Authors: Ban Yue , Sherman E. Ya.
Published: January 2013

We study electron transport in nanosized semiconductor waveguides of different shapes. The spin-dependent transport through these nonuniform nanostructures is investigated in the presence of spin-orbit coupling of the Rashba and Dresselhaus types. The resulting spin rotation strongly depends on the shape of the waveguide. The crossover from the classical motion to the tunneling regime can be controlled in the waveguide with narrowing by modulating the strength of the Rashba spin-orbit coupling.
Atomistic simulation based prediction of the solvent effect on the molecular mobility and glass transition of poly (methyl methacrylate)
Authors: Mishra Shawn , Keten Sinan
Published: January 2013

We present an investigation of the retained solvent effect on the glass transition temperature (Tg) of poly(methyl methacrylate) (PMMA) through all-atom molecular dynamics simulations. Addition of a weakly interactive solvent, tetrahydrofuran (THF), causes a depression of the PMMA Tg that can be identified through an analysis of the mean squared displacement of the polymer chains from atomistic trajectories. Our results are in very good agreement with an atomistically informed theoretical model based on free volume theory and demonstrate the applicability of molecular simulation to discern solvent effects on polymer thermomechanical behavior in silico.
Structural, magnetic and x-ray absorption studies of NdCo1−xNixO3 (0 ≤ x ≤ 0.5)
Authors: Kumar Vinod , Kumar Yogesh , Kumar Rajesh , Shukla D. K. , Arora S. K. , Shvets I. V. , Kumar Ravi
Published: January 2013

We have systematically investigated the effect of Ni substitution on the structural and magnetic properties of NdCoO3. Single phase nature and orthorhombic Pbnm structure is confirmed by the Reitveld refinement of X-ray diffraction data in all samples. X-ray absorption near edge spectroscopy of Co and Ni K-edges reveals the presence of trivalent state of Ni and Co ions in all samples. Composition dependent crossover from canted antiferromagnetic (AFM) (for x < 0.3) to spin glass behavior (for x ≥ 0.3) is observed in magnetic measurements. Low temperature ferromagnetic (FM) component in doped samples is attributed to the stabilization of Co+3 ions in intermediate-spin (IS) state t52ge1g with S = 1 The FM and AFM are observed to coexist as confirmed by M-H hysteresis. Nd sublattice seems to inhibit the magnetic contribution from Co ions, and we ruled out the possibility of charge disproportion induced by Ni substitution leading to FM interactions in these systems as proposed in different reports.
Generation-dependent charge carrier transport in Cu(In,Ga)Se2/CdS/ZnO thin-film solar-cells
Authors: Nichterwitz Melanie , Caballero Raquel , Kaufmann Christian A. , Schock Hans-Werner , Unold Thomas
Published: January 2013

Cross section electron-beam induced current (EBIC) and illumination-dependent current voltage (IV) measurements show that charge carrier transport in Cu(In,Ga)Se2 (CIGSe)/CdS/ZnO solar-cells is generation-dependent. We perform a detailed analysis of CIGSe solar cells with different CdS layer thicknesses and varying Ga-content in the absorber layer. In conjunction with numerical simulations, EBIC and IV data are used to develop a consistent model for charge and defect distributions with a focus on the heterojunction region. The best model to explain our experimental data is based on a p+ layer at the CIGSe/CdS interface leading to generation-dependent transport in EBIC at room temperature. Acceptor-type defect states at the CdS/ZnO interface cause a significant reduction of the photocurrent in the red-light illuminated IV characteristics at low temperatures (red kink effect). Shallow donor-type defect states at the p+ layer/CdS interface of some grains of the absorber layer are responsible for grain specific, i.e., spatially inhomogeneous, charge carrier transport observed in EBIC.
Ultrafast heating and magnetic switching with weak external magnetic field
Authors: Li J. M. , Xu B. X. , Zhang J. , Ye K. D.
Published: January 2013

The TbFeCo magneto-optical media with the coercivity of bigger than 1.0 kOe are used for the investigation of ultrafast heating and magnetic switching with the weak external magnetic field. It has been found that the laser-induced active region becomes larger with an external magnetic field because the boundary of the active region is magnetized with the assistance of the external field during the ultrafast heating. According to this physical phenomenon, the so called “mark expansion method” has been proposed for visual observation of ultrafast switching marks. Using this method, the ultrafast magnetic switching in TbFeCo media has been studied using 40 fs laser pulse with linear polarization. The result shows that the ultrafast magnetic switching can be implemented by the laser pulse with assistance of the weak external field of about 0.7 kOe. Further studies show that the area percentage of the magnetic mark expansion relative to its thermal mark decreases with the increasing of the laser pulse energy. There exists the threshold pulse energy that the active region is fully magnetized. The theoretical analysis of electron, spin, and lattice temperatures has been conducted to the active region of the media where the maximum spin temperature is close to the Curie temperature of the media. The result indicates that the media become active at 4.137 ps and the ultrafast heating plays a key role for the ultrafast magnetic switching. The weak external magnetic field provides sufficient driving force to control the magnetization direction in the media.
The reduced dynamics of an exciton coupled to a phonon bath: A new approach combining the Lang-Firsov transformation and the perturbation theory
Authors: Pouthier Vincent
Published: January 2013

To go beyond the Born approximation, a new method is introduced for describing the reduced dynamics of an exciton coupled to a phonon bath. Two unitary transformations are applied for accounting for the exciton-phonon entanglement through a dual dressing mechanism affecting both the exciton and the phonons. In doing so, one obtains an analytical expression of the exciton reduced density matrix without integrating numerically any generalized master equation. Therefore, by using a quite simple model that can be solved exactly, it has been shown that the proposed method is particularly suitable for describing the exciton dynamics over a rather broad region in the parameter space. However, although the method shows many strengths, it also exhibits weaknesses and it accidentally breaks down owing to the occurrence of specific resonances.
An apparatus for concurrent measurement of thermoelectric material parameters
Authors: Kallaher R. L. , Latham C. A. , Sharifi F.
Published: January 2013

We describe an apparatus which concurrently and independently measures the parameters determining thermoelectric material conversion efficiency: the Seebeck coefficient, thermal conductivity, and electrical resistivity. The apparatus is designed to characterize thermoelectric materials which are technologically relevant for waste heat energy conversion, and may operate from room temperature to 400 °C. It is configured so the heat flux is axially confined along two boron nitride rods of known thermal conductance. The Seebeck coefficient and thermal conductivity are obtained in steady-state using a differential technique, while the electrical resistivity is obtained using a four-point lock-in amplification method. Measurements on the newly developed NIST Seebeck standard reference material are presented in the temperature range from 50 °C to 250 °C.
Ni6Cr5MoO18: A compensated half metal predicted from first-principles
Authors: Wang Jing , Zu Ningning , Solovyev Igor V. , Wu Zhijian
Published: January 2013

NiCrO3 is semiconducting. It contains six molecular units in the conventional cell. By substituting one of the six Cr atoms with Mo in the conventional cell, Ni6Cr5MoO18 is predicted to be a potential candidate of compensated half metal by first-principles calculations. Cr dz2 band, which is empty in NiCrO3, is partially filled in Ni6Cr5MoO18 and it is the band that makes the spin up channel to be metallic. The Mo 4d states are non-magnetic and have no contribution to the density of states in the vicinity of the Fermi level. The compensated half metallic properties are robust against the electron correlation.
Electric-field and temperature dependence of the activation energy associated with gate induced drain leakage
Authors: Alnuaimi Aaesha , Nayfeh Ammar , Koldyaev Victor
Published: January 2013

We examined the effect of temperature and electric field on the activation energy (Ea) of gate-induced drain leakage (GIDL) of a MOSFET. The measured GIDL current shows a temperature dependence consistent with a non-tunneling mechanism. In the low-electric-field regime and for temperatures above 55 °C, Ea is about 0.4 eV and drops from 0.4 eV to 0.1 eV as the applied gate voltage goes below VFB in the accumulation direction (decreased for the n-channel MOSFET). This suggests that electron-hole-pair generation at Si/SiO2 interface traps (Dit), enhanced by the electric field (the Poole-Frenkel effect), dominates GIDL in that regime. For temperatures below 55 °C, Ea is less than 0.15 eV for both weak and strong electric fields and displays minimal temperature dependence, indicating inelastic trap-assisted tunneling or phonon-assisted tunneling from a trap. In the very strong-electric-field regime (>1 MV/cm), band-to-band tunneling is the dominant mechanism.
Effects of germanium and nitrogen incorporation on crystallization of N-doped Ge2+xSb2Te5 (x = 0,1) thin films for phase-change memory
Authors: Cheng Limin , Wu Liangcai , Song Zhitang , Rao Feng , Peng Cheng , Yao Dongning , Liu Bo , Xu Ling
Published: January 2013

The phase-change behavior and microstructure changes of N-doped Ge3Sb2Te5 [N-GST(3/2/5)] and Ge2Sb2Te5 [GST(2/2/5)] films during the phase transition from an amorphous to a crystalline phase were studied using in situ temperature-dependent sheet resistance measurements, X-ray diffraction, and transmission electron microscopy. The optical band gaps of N-GST(3/2/5) films are higher than that of GST(2/2/5) film in both the amorphous and face-centered-cubic (fcc) phases. Ge nitride formation by X-ray photoelectron spectroscopy analysis increased the optical band gap and suppressed crystalline grain growth, resulting in an increase in the crystallization temperature and resistance in the fcc phase. As a result, the Ge- and N-doped GST(2/2/5) composite films can be considered as a promising material for phase-change memory application because of improved thermal stability and reduced power consumption.
Reduction of the fast electron angular dispersion by means of varying-resistivity structured targets
Authors: Debayle A. , Gremillet L. , Honrubia J. J. , d'Humières E.
Published: January 2013

We present novel structured targets capable of collimating laser-generated fast electrons through dense plasmas. The proposed targets are made of narrow high- and low-Z filaments leading to a transversely modulated electrical resistivity profile. When featuring a spatially decreasing density, these targets permit both to guide the fast electrons and reduce their angular dispersion. The principle of our target design is explained by a theoretical model. Two-dimensional particle-in-cell simulations are performed to demonstrate its efficiency.
Eliminating defects from graphene monolayers during chemical exfoliation
Authors: Kumar Srivastava Pawan , Ghosh Subhasis
Published: January 2013

Graphene layers with and without defects have been grown by chemically exfoliating graphite in organic solvents and characterized by different spectroscopic techniques. It has been shown that defects can be controlled in graphene layers while intercalating different organic molecules in graphite. The transfer characteristics of transistors fabricated on graphene monolayers exfoliated using organic solvent with low dielectric constant and low boiling point show almost no shift of minimum conductivity point, i.e., Dirac point, indicating defect free pristine graphene.
Nonlinear canonical gyrokinetic Vlasov equation and computation of the gyrocenter motion in tokamaks
Authors: Xu Yingfeng , Wang Shaojie
Published: January 2013

The nonlinear canonical gyrokinetic Vlasov equation is obtained from the nonlinear noncanonical gyrokinetic theory using the property of the coordinate transform. In the linear approximation, it exactly recovers the previous linear canonical gyrokinetic equations derived by the Lie-transform perturbation method. The computation of the test particle gyrocenter motion in tokamaks with a large magnetic perturbation is presented and discussed. The numerical results indicate that the second-order gyrocenter Hamiltonian is important for the gyrocenter motion of the trapped electron in tokamaks with a large magnetic perturbation.
Gyroviscous stress in weakly magnetized plasmas
Authors: Barnes D. C.
Published: January 2013

The gyroviscous stress is computed for a weakly magnetized plasma, i.e., one in which the thermal ion gyroradius may exceed the equilibrium gradient scale length. A simple and useful formula is derived and shown to reduce to the previous strongly magnetized result. Applicability is illustrated with a typical field-reversed configuration equilibrium solution. This form is the most useful to date for the study of kinetic ion phenomena in weakly magnetized plasmas within a fluid model.
Instability, mixing, and transition to turbulence in a laser-driven counterflowing shear experiment
Authors: Doss F. W. , Loomis E. N. , Welser-Sherrill L. , Fincke J. R. , Flippo K. A. , Keiter P. A.
Published: January 2013

In a turbulence experiment conducted at the Omega Laser Facility [Boehly et al., Opt. Commun. 133, 495 (1997)]], regions of 60 mg/cc foam are separated by an aluminum plate running the length of a 1.6 mm shock tube. Two counter-propagating laser-driven shocks are used to create a high speed, ΔV=140 km/s shear flow environment, sustained for ∼10 ns, while canceling the transverse pressure gradient across the interface. The spreading of the aluminum by shear-instability-induced mixing is measured by x-ray radiography. The width of the mix region is compared to simulations. Reynolds numbers ≳4×105 are achieved within the layer. Following the onset of shear, we observe striations corresponding to the dominant mode growth and their transition through non-linear structures to developed turbulence.
Analytic expression for poloidal flow velocity in the banana regime
Authors: Taguchi M.
Published: January 2013

The poloidal flow velocity in the banana regime is calculated by improving the l = 1 approximation for the Fokker-Planck collision operator [M. Taguchi, Plasma Phys. Controlled Fusion 30, 1897 (1988)]. The obtained analytic expression for this flow, which can be used for general axisymmetric toroidal plasmas, agrees quite well with the recently calculated numerical results by Parker and Catto [Plasma Phys. Controlled Fusion 54, 085011 (2012)] in the full range of aspect ratio.
Bismide-nitride alloys: Promising for efficient light emitting devices in the near- and mid-infrared
Authors: Sweeney S. J. , Jin S. R.
Published: January 2013

GaAsBiN is a potentially interesting alloy which may be exploited in near- and mid-infrared photonic devices. Here we present the predicted band parameters such as band gap (Eg), the spin-orbit splitting energy (ΔSO), band offsets and strain of GaAsBiN on GaAs versus N and Bi compositions based on recent experimental data. We also show how bismuth may be used to form alloys whereby ΔSO > Eg thereby providing a means of suppressing non-radiative CHSH (hot-hole producing) Auger recombination and inter-valence band absorption. We determine the optimum conditions where ΔSO > Eg, which is expected to improve the high-temperature performance and thermal stability of light emitting devices. It is also shown that preferential band offsets are achievable with GaAsBiN, which makes this material system promising for photonic devices operating in the near- and mid-infrared.
Design and modeling of InP-based InGaAs/GaAsSb type-II “W” type quantum wells for mid-Infrared laser applications
Authors: Pan C. H. , Lee C. P.
Published: January 2013

We have theoretically studied the InP based InGaAs/GaAsSb /InAlAs type-II “W” quantum wells (QWs) using the eight band k.p theory. The trade-off between the emission wavelength and the magnitude of the transition matrix element was investigated with various structural parameters of the “W” QWs. For the same emission wavelength, the devices with thinner InGaAs/GaAsSb layers and a higher Sb content in GaAsSb could provide higher transition strength. The gain spectra and their peak values at various carrier densities were calculated. We have also found that a more balanced electron and hole masses in the type-II “W” QWs can benefit the material gain. In our designed cases, we have seen that the reduced hole effective mass due to a higher Sb content can partially compensate the gain loss caused by the reduced transition matrix element. Based on the optimized design, a material gain above 103 cm−1 is readily achievable for a single properly designed “W” quantum well.
Investigation of laser-driven proton acceleration using ultra-short, ultra-intense laser pulses
Authors: Fourmaux S. , Buffechoux S. , Albertazzi B. , Capelli D. , Lévy A. , Gnedyuk S. , Lecherbourg L. , Lassonde P. , Payeur S. , Antici P. , Pépin H. , Marjoribanks R. S. , Fuchs J. , Kieffer J. C.
Published: January 2013

We report optimization of laser-driven proton acceleration, for a range of experimental parameters available from a single ultrafast Ti:sapphire laser system. We have characterized laser-generated protons produced at the rear and front target surfaces of thin solid targets (15 nm to 90 μm thicknesses) irradiated with an ultra-intense laser pulse (up to 1020 W⋅cm−2, pulse duration 30 to 500 fs, and pulse energy 0.1 to 1.8 J). We find an almost symmetric behaviour for protons accelerated from rear and front sides, and a linear scaling of proton energy cut-off with increasing pulse energy. At constant laser intensity, we observe that the proton cut-off energy increases with increasing laser pulse duration, then roughly constant for pulses longer than 300 fs. Finally, we demonstrate that there is an optimum target thickness and pulse duration.
Optical properties of SrTiO3 on silicon(100)
Authors: Tian Yao , Adamo Carolina , Schlom Darrell G. , Burch Kenneth S.
Published: January 2013

Epitaxial buffer layers enable the many functionalities found in perovskites to be integrated with silicon. However, epitaxial growth of SrTiO3 on silicon is tricky and has so far only been achieved by molecular beam epitaxy. Nonetheless, previous investigations of these films were limited by the amorphous layer occurring at the interface. Through a combination of improved interface quality and an improved model, we report the optical properties of SrTiO3 films on Si(100) investigated by spectroscopic ellipsometry. We find that the data are best described by a model with two different SrTiO3 layers, potentially resulting from variations in the oxygen content.
Significant ferrimagnetisms observed in superlattice composed of antiferromagnetic LaFeO3 and YMnO3
Authors: Chen Y. B. , Zhou Jian , Zhang Shan-Tao , Wu Fei-Xiang , Yao Shu-Hua , Gu Zheng-Bin , Wu Di , Chen Yan-Feng
Published: January 2013

A series of LaFeO3/YMnO3 superlattices with various thicknesses are synthesized epitaxially on (001) and (111) SrTiO3 substrates. X-ray diffraction, high-resolution cross-sectional transmission electron microscopy, and sub-nanometer-scale resolved electron energy loss spectroscopy characterizations prove that grown superlattices have designed layer-by-layer structures, and there is atomically sharp interface between two successive constituent layers. Temperature-dependent magnetization and magnetic hysteresis loop measurements substantiate that there is significant ferrimagnetism generated at LaFeO3/YMnO3 interfaces. The generated ferrimagnetism is discussed by considering the magnetic structures in each constituent layer.
Micro-fabricated lead zirconate titanate bent cantilever energy harvester with multi-dimensional operation
Authors: Park J. C. , Khym S. , Park J. Y.
Published: January 2013

At present, a cantilever with an inertial mass at its free end is the most widely used form for a vibration-based energy harvester, due to its simple structure and fabrication. However, the one-dimensional operation limits device installation. We first report a multi-dimensional piezoelectric cantilever-type energy harvester that oscillates not only in the vertical direction but also in the radial direction. While the conventional cantilever-type energy harvester maintains almost its maximum output power when it is installed within 20° of the operating direction, the proposed device presents the significantly improved result that the output power is independent of the installation angle.
Elastic and anelastic properties close to the Curie temperature of Fe-based bulk metallic glass
Authors: Torrens-Serra J. , Stoica M. , Bednarcik J. , Eckert J. , Kustov S.
Published: January 2013

Linear and non-linear ultrasonic damping, Young's modulus, and non-linear modulus defect have been studied in a Fe-based bulk metallic glass close to its Curie temperature, TC. We found that the acoustic technique used offers four different parameters which can be used to evaluate the TC. We show that ultrasonic measurements at a frequency of around 105 Hz detect both critical phenomena close to TC and intrinsic magnetomechanical damping in the ferromagnetic state. However, the values of absorption and Young's modulus anomaly observed over the critical range are quite low and do not permit reliable analysis of the critical exponents.
In-depth analysis of injection-seeded long external cavity InGaN/GaN surface-emitting laser
Authors: Zeng X. , Boïko D. L. , Cosendey G. , Glauser M. , Carlin J.-F. , Grandjean N.
Published: January 2013

Optically pumped InGaN/GaN quantum well (QW) vertical-external-cavity surface-emitting laser operating at 420 nm wavelength with external cavity length of up to 50 mm has been realized. Use of injection seeding enables us to reach lasing operation even for pump pulse duration just slightly exceeding the external cavity roundtrip time. The carrier lifetime in the QWs was measured to be 2.5 ns, and lasing emission was obtained under pump pulses shorter (400 ps) or longer (10 ns) than the carrier lifetime in QWs. We studied experimentally the dependence of the lasing threshold on the length of external cavity and provided a model to explain this dependence. Further detailed measurements of the near field and far field patterns, optical spectrum, spontaneous emission factor, and delay time to emission of the lasing pulse confirm lasing at the external cavity mode.
Demonstration and modeling of multi-bit resistance random access memory
Authors: Yang Xiang , Chen Albert B. K. , Joon Choi Byung , Chen I-Wei
Published: January 2013

Although intermediates resistance states are common in resistance random access memory (RRAM), two-way switching among them has not been demonstrated. Using a nanometallic bipolar RRAM, we have illustrated a general scheme for writing/rewriting multi-bit memory using voltage pulses. Stability conditions for accessing intermediate states have also been determined in terms of a state distribution function and the weight of serial load resistance. A multi-bit memory is shown to realize considerable space saving at a modest decrease of switching speed.
TaPht1;4, a high-affinity phosphate transporter gene in wheat (Triticum aestivum), plays an important role in plant phosphate acquisition under phosphorus deprivation
Authors: Liu Xiaoman , Zhao Xiaolei , Zhang Lijun , Lu Wenjing , Li Xiaojuan , Xiao Kai
Published: January 2013

An expressed sequence tag (EST) highly similar to BdPT1–4, a phosphate transporter (PT) gene in Brachypodium distachyon, was obtained in a wheat root cDNA subtractive suppression library containing genes that respond to low-phosphate (Pi) stress. The DNA sequence covering this EST (designated as TaPht1;4) was determined based on screening a wheat DNA library. TaPht1;4 consists of two exons and one intron and encodes a 555 amino acid (aa) polypeptide with a molecular weight of 60.85 kDa and an isoelectric point of 7.60. TaPht1;4 contains 12 conserved membrane-spanning domains similar to previously reported PTs in diverse plant species. Yeast complement analysis in low-Pi medium confirmed that TaPht1;4 confers the capacity to uptake Pi to MB192, a yeast strain with a defective high-affinity PT; with an apparent Km of 35.3 μM. The TaPht1;4 transcripts were specifically detected in the root and were highly induced under Pi deficiency. TaPht1;4 was also expressed following a diurnal pattern, i.e. high levels during daytime and low levels during night-time. TaPht1;4 overexpression and downregulation dramatically altered the plant phenotypic features under low-Pi conditions. Samples that overexpressed TaPht1;4 had significantly improved growth traits and accumulated more Pi than the wild-type plant and those with downregulated TaPht1;4 expression. Therefore, TaPht1;4 is a high-affinity PT gene that plays a critical role in wheat Pi acquisition under Pi deprivation.
Retinal degeneration depends on Bmi1 function and reactivation of cell cycle proteins
Authors: Zencak Dusan , Schouwey Karine , Chen Danian , Ekström Per , Tanger Ellen , Bremner Rod , van Lohuizen Maarten , Arsenijevic Yvan
Published: January 2013

The epigenetic regulator Bmi1 controls proliferation in many organs. Reexpression of cell cycle proteins such as cyclin-dependent kinases (CDKs) is a hallmark of neuronal apoptosis in neurodegenerative diseases. Here we address the potential role of Bmi1 as a key regulator of cell cycle proteins during neuronal apoptosis. We show that several cell cycle proteins are expressed in different models of retinal degeneration and required in the
Rd1
photoreceptor death process. Deleting E2f1, a downstream target of CDKs, provided temporary protection in
Rd1
mice. Most importantly, genetic ablation of
Bmi1
provided extensive photoreceptor survival and improvement of retinal function in
Rd1
mice, mediated by a decrease in cell cycle markers and regulators independent of p16
Ink4a
and p19
Arf
. These data reveal that Bmi1 controls the cell cycle-related death process, highlighting this pathway as a promising therapeutic target for neuroprotection in retinal dystrophies.
The steady-state mosaic of disturbance and succession across an old-growth Central Amazon forest landscape
Authors: Chambers Jeffrey Q. , Negron-Juarez Robinson I. , Marra Daniel Magnabosco , Di Vittorio Alan , Tews Joerg , Roberts Dar , Ribeiro Gabriel H. P. M. , Trumbore Susan E. , Higuchi Niro
Published: January 2013

Old-growth forest ecosystems comprise a mosaic of patches in different successional stages, with the fraction of the landscape in any particular state relatively constant over large temporal and spatial scales. The size distribution and return frequency of disturbance events, and subsequent recovery processes, determine to a large extent the spatial scale over which this old-growth steady state develops. Here, we characterize this mosaic for a Central Amazon forest by integrating field plot data, remote sensing disturbance probability distribution functions, and individual-based simulation modeling. Results demonstrate that a steady state of patches of varying successional age occurs over a relatively large spatial scale, with important implications for detecting temporal trends on plots that sample a small fraction of the landscape. Long highly significant stochastic runs averaging 1.0 Mg biomass⋅ha
−1
⋅y
−1
were often punctuated by episodic disturbance events, resulting in a sawtooth time series of hectare-scale tree biomass. To maximize the detection of temporal trends for this Central Amazon site (e.g., driven by CO
2
fertilization), plots larger than 10 ha would provide the greatest sensitivity. A model-based analysis of fractional mortality across all gap sizes demonstrated that 9.1–16.9% of tree mortality was missing from plot-based approaches, underscoring the need to combine plot and remote-sensing methods for estimating net landscape carbon balance. Old-growth tropical forests can exhibit complex large-scale structure driven by disturbance and recovery cycles, with ecosystem and community attributes of hectare-scale plots exhibiting continuous dynamic departures from a steady-state condition.
Tryptophan at the transmembrane–cytosolic junction modulates thrombopoietin receptor dimerization and activation
Authors: Defour Jean-Philippe , Itaya Miki , Gryshkova Vitalina , Brett Ian C. , Pecquet Christian , Sato Takeshi , Smith Steven O. , Constantinescu Stefan N.
Published: January 2013

Dimerization of single-pass membrane receptors is essential for activation. In the human thrombopoietin receptor (TpoR), a unique amphipathic RWQFP motif separates the transmembrane (TM) and intracellular domains. Using a combination of mutagenesis, spectroscopy, and biochemical assays, we show that W515 of this motif impairs dimerization of the upstream TpoR TM helix. TpoR is unusual in that a specific residue is required for this inhibitory function, which prevents receptor self-activation. Mutations as diverse as W515K and W515L cause oncogenic activation of TpoR and lead to human myeloproliferative neoplasms. Two lines of evidence support a general mechanism in which W515 at the intracellular juxtamembrane boundary inhibits dimerization of the TpoR TM helix by increasing the helix tilt angle relative to the membrane bilayer normal, which prevents the formation of stabilizing TM dimer contacts. First, measurements using polarized infrared spectroscopy show that the isolated TM domain of the active W515K mutant has a helix tilt angle closer to the bilayer normal than that of the wild-type receptor. Second, we identify second-site R514W and Q516W mutations that reverse dimerization and tilt angle changes induced by the W515K and W515L mutations. The second-site mutations prevent constitutive activation of TpoR W515K/L, while preserving ligand-induced signaling. The ability of tryptophan to influence the angle and dimerization of the TM helix in wild-type TpoR and in the second-site revertants is likely associated with its strong preference to be buried in the headgroup region of membrane bilayers.