bluuebunny/crossref_metadata_2025 huggingface dataset:
miRNAs in development and pathogenesis of the nervous system
Authors: Nowak Jakub S. , Michlewski Gracjan
Published: July 2013

The human nervous system expresses approximately 70% of all miRNAs (microRNAs). Changing levels of certain ubiquitous and brain-specific miRNAs shape the development and function of the nervous system. It is becoming clear that misexpression of some miRNAs can contribute towards neurodevelopmental disorders. In the present article, we review the current knowledge of the role of miRNAs in development and pathogenesis of the nervous system.
Target of rapamycin (TOR) kinase in Trypanosoma brucei: an extended family
Authors: Saldivia Manuel , Barquilla Antonio , Bart Jean-Mathieu , Diaz-González Rosario , Hall Michael N. , Navarro Miguel
Published: July 2013

The complex life cycle of Trypanosoma brucei provides an excellent model system to understand signalling pathways that regulate development. We described previously the classical functions of TOR (target of rapamycin) 1 and TOR2 in T. brucei. In a more recent study, we described a novel TOR kinase, named TOR4, which regulates differentiation from the proliferative infective form to the quiescent form. In contrast with TOR1 loss-of-function, down-regulation of TOR4 triggers an irreversible differentiation process through the development of the insect pre-adapted quiescent form. TOR4 governs a signalling pathway distinct from those controlled by the conventional TOR complexes TORC1 and TORC2. Depletion of TOR4 induces all well-known characteristics of the quiescent developmental stage in trypanosomes, including expression of the PAD (proteins associated with differentiation) surface proteins and transcriptional down-regulation of the VSG (variant surface glycoprotein) gene. TOR4 kinase forms a structurally and functionally distinct complex named TORC4. TOR4 associates with LST8 (lethal with sec-13 protein 8) and other factors including an armadillo-domain-containing protein and the major vault protein, which probably serves as a scaffold for this kinase. Research in T. brucei, a protozoan parasite that diverged from the eukaryotic tree early in evolution, may help to uncover new functions of TOR kinases.
Terminal loop-mediated regulation of miRNA biogenesis: selectivity and mechanisms
Authors: Castilla-Llorente Virginia , Nicastro Giuseppe , Ramos Andres
Published: July 2013

Regulating the expression of individual miRNAs (microRNAs) is important for cell development and function. The up- or down-regulation of the processing of specific miRNA precursors to the mature active form represents one tool to control miRNA concentration and is mediated by proteins that recognize the terminal loop of the RNA precursors. Terminal loop recognition is achieved by the combined action of several RNA-binding domains. The proteins can then regulate the processing by recruiting RNA enzymes, changing the RNA structure and preventing or enhancing the accessibility and processing activity of the core processing complexes. The present review focuses on how terminal loop-binding proteins recognize their RNA targets and mediate their regulatory function(s), and highlights how terminal loop-mediated regulation relates to the broader regulation of mRNA metabolism.
Phosphorylation of substrates destined for secretion by the Fam20 kinases
Authors: Tagliabracci Vincent S. , Xiao Junyu , Dixon Jack E.
Published: July 2013

Since the discovery of protein kinases, protein phosphorylation has emerged as a key regulatory mechanism. The majority of phosphoproteins reside within the nucleus and cytoplasm; however, many secreted proteins are phosphorylated by unknown kinases located within the secretory pathway and/or in the extracellular space. The Fam20 kinases are emerging as the enzymes responsible for phosphorylating secreted proteins and proteoglycans. Evolutionary analysis reveals that these kinases are exclusively present in metazoans and contain conserved features that are common among all eukaryotic protein kinases. Mutations in the Fam20 family members cause disorders of biomineralization in humans that highlight the physiological significance of secreted protein phosphorylation.
Structural constraints and functional divergences in CASK evolution
Authors: LaConte Leslie , Mukherjee Konark
Published: July 2013

CASK (Ca2+/calmodulin-activated serine kinase) is a synaptic protein that interacts with the cytosolic tail of adhesion molecules such as neurexins, syncam and syndecans. It belongs to the MAGUK (membrane-associated guanylate kinase) family of scaffolding proteins which are known to decorate cell–cell junctions. CASK is an essential gene in mammals, critical for neurodevelopment. Mutations in the CASK gene in humans result in phenotypes that range from intellectual disability to lethality. Despite its importance, CASK has a single genetic isoform located in the short arm of the X chromosome near an evolutionary breakpoint. Surprisingly, CASK is a non-essential gene in invertebrates and displays functional divergence. In the present article, we describe the phylogenetic differences in existing CASK orthologues. The CASK gene has undergone a huge expansion in size (~55-fold). Almost all of this expansion is a direct result of an increase in the size of the introns. The coding region of CASK orthologues, and hence the protein, exhibit a high degree of evolutionary conservation. Within the protein, domain arrangement is completely conserved and substitution rates are higher in the connecting loop regions [L27 (Lin2, Lin7)] than within the domain. Our analyses of single residue substitutions and genotype–phenotype relationships suggest that, other than intronic expansion, the dramatic functional changes of CASK are driven by subtle (non-radical) primary structure changes within the CASK protein and concomitant changes in its protein interactors.
Nutrients and growth factors in mTORC1 activation
Authors: Efeyan Alejo , Sabatini David M.
Published: July 2013

Growth factors and nutrients regulate the mTORC1 [mammalian (or mechanistic) target of rapamycin complex 1] by different mechanisms. The players that link growth factors and mTORC1 activation have been known for several years and mouse models have validated its relevance for human physiology and disease. In contrast with the picture for growth factor signalling, the means by which nutrient availability leads to mTORC1 activation have remained elusive until recently, with the discovery of the Rag GTPases upstream of mTORC1. The Rag GTPases recruit mTORC1 to the outer lysosomal surface, where growth factor signalling and nutrient signalling converge on mTORC1 activation. A mouse model of constitutive RagA activity has revealed qualitative differences between growth-factor- and nutrient-dependent regulation of mTORC1. Regulation of mTORC1 activity by the Rag GTPases in vivo is key for enduring early neonatal starvation, showing its importance for mammalian physiology.
Techniques to examine nucleotide binding by pseudokinases
Authors: Lucet Isabelle S. , Babon Jeffrey J. , Murphy James M.
Published: July 2013

Approximately 10% of the human kinome has been classified as pseudokinases due to the absence of one or more of three motifs known to play key roles in the catalytic activities of protein kinases. Structural and functional studies are now emerging, reclassifying this ‘dead’ kinase family as essential signalling molecules that act as crucial modulators of signal transduction. This raises the prospect that pseudokinases may well represent an as-yet-unexplored class of drug targets. However, the extent to which nucleotide binding and catalytic activity contribute to the biological functions of pseudokinases remains an area of great controversy. In the present review, we discuss the advantages and disadvantages of the different methods employed to characterize the nucleotide-binding properties and activity of pseudokinases.
Regulation of Janus kinases by SOCS proteins
Authors: Kershaw Nadia J. , Murphy James M. , Lucet Isabelle S. , Nicola Nicos A. , Babon Jeffrey J.
Published: July 2013

JAKs (Janus kinases) are essential mediators of almost all biological signalling events initiated by haemopoietic and immune cytokines. However, aberrant and/or prolonged JAK-induced signalling is detrimental and can give rise to a number of inflammatory and proliferative pathologies. For this reason, the tyrosine kinase activity of the JAKs is carefully regulated at a number of different levels. Primarily, this is achieved by: (i) ensuring that the catalytic domain is ‘switched off’ under basal conditions, and (ii) inhibiting the activity of JAK after it has been switched on. Whereas the first mode of inhibition is mediated by JAK's own pseudokinase domain as well as the action of phosphatases, the second is achieved by the action of the SOCS (suppressor of cytokine signalling) proteins, negative-feedback inhibitors of JAK-mediated signalling. The present review focuses on the mode of action of SOCS1 and SOCS3, the two most potent JAK inhibitors.
Adaptation to chronic mTOR inhibition in cancer and in aging
Authors: Gilley Rebecca , Balmanno Kathryn , Cope Claire L. , Cook Simon J.
Published: July 2013

The mTOR [mammalian (or mechanistic) target of rapamycin] protein kinase co-ordinates catabolic and anabolic processes in response to growth factors and nutrients and is a validated anticancer drug target. Rapamycin and related allosteric inhibitors of mTORC1 (mTOR complex 1) have had some success in specific tumour types, but have not exhibited broad anticancer activity, prompting the development of new ATP-competitive mTOR kinase inhibitors that inhibit both mTORC1 and mTORC2. In common with other targeted kinase inhibitors, tumours are likely to adapt and acquire resistance to mTOR inhibitors. In the present article, we review studies that describe how tumour cells adapt to become resistant to mTOR inhibitors. mTOR is a central signalling hub which responds to an array of signalling inputs and activates a range of downstream effector pathways. Understanding how this signalling network is remodelled and which pathways are invoked to sustain survival and proliferation in the presence of mTOR inhibitors can provide new insights into the importance of the various mTOR effector pathways and may suggest targets for intervention to combine with mTOR inhibitors. Finally, since chronic mTOR inhibition by rapamycin can increase lifespan and healthspan in nematodes, fruitflies and mice, we contrast these studies with tumour cell responses to mTOR inhibition.
Activating Janus kinase pseudokinase domain mutations in myeloproliferative and other blood cancers
Authors: Constantinescu Stefan N. , Leroy Emilie , Gryshkova Vitalina , Pecquet Christian , Dusa Alexandra
Published: July 2013

The discovery of the highly prevalent activating JAK (Janus kinase) 2 V617F mutation in myeloproliferative neoplasms, and of other pseudokinase domain-activating mutations in JAK2, JAK1 and JAK3 in blood cancers, prompted great interest in understanding how pseudokinase domains regulate kinase domains in JAKs. Recent functional and mutagenesis studies identified residues required for the V617F mutation to induce activation. Several X-ray crystal structures of either kinase or pseudokinase domains including the V617F mutant of JAK2 pseudokinase domains are now available, and a picture has emerged whereby the V617F mutation induces a defined conformational change around helix C of JH (JAK homology) 2. Effects of mutations on JAK2 can be extrapolated to JAK1 and TYK2 (tyrosine kinase 2), whereas JAK3 appears to be different. More structural information of the full-length JAK coupled to cytokine receptors might be required in order to define the structural basis of JH1 activation by JH2 mutants and eventually obtain mutant-specific inhibitors.
Design‐based computational procedure for performance prediction and analysis of single‐phase self‐excited induction generator
Authors: Murthy S. S. , Singh Bhim , Sandeep Vuddanti
Published: July 2013

The study presents a design‐based computational procedure for determining the performance of a single‐phase two‐winding self‐excited induction generator (SEIG) taking the machine design details as the input data. The magnetisation characteristic that forms the basis of analysis is obtained using the B–H curve of the core material and by employing an appropriate curve‐fitting/regression technique that leads to obtain Vg–Im variation from which Vg–Xm variation can be derived. The predicted parameters and performance characteristics of a single‐phase SEIG are compared with the corresponding experimental results. This procedure can be a powerful tool for improved design of such machines. Effects of variation of typical design parameters on performance are presented to demonstrate its utility.
Calorimetric concept for measurement of power losses up to 2 kW in electric drives
Authors: Kosonen Antti , Aarniovuori Lassi , Pyrhönen Juha , Niemelä Markku , Backman Jari
Published: July 2013

Accurate measurement of power losses in high‐efficiency devices is difficult. Measurement standards for industrial converters and complete electric drives, including both motors and converters, will come into effect soon, and measurement methods for these devices should be included. In the calorimetric method, the power losses are measured directly. However, the calorimeters presented previously are mainly tailored systems, and therefore, they typically have very complicated constructions. Hence, their applicability to the evaluation of general electric drives is limited. A functional calorimetric measurement concept is suggested in this study for power losses up to 2 kW. Such a power loss can be applied with present‐day power electronic converters up to 110 kW. The construction of the concept is simple and lightweight. It does not require a complex structure or a large area in the measurement site. The concept is scalable and duplicable for different sizes. Different devices with different cablings can be measured without any problems. The combined standard heat loss measurement uncertainty for the calorimeter is ±0.4%.
Improved method for the scalar control of induction motor drives
Authors: Smith Andrew , Gadoue Shady , Armstrong Matthew , Finch John
Published: July 2013

Many control schemes have been proposed for induction motors, which are in themselves highly complex non‐linear and sometimes internally unstable systems. One of the most accurate control schemes is encodered rotor flux orientated vector control. The advantages and disadvantages of this control are well known and several variations, or reduced vector schemes, have been proposed. This study introduces an improved encoderless scalar, or approximated vector, control method for induction machines which can be applied to general purpose applications that do not require the most precise control. The proposed method overcomes practical difficulties and is suitable for industrial applications. The slip compensated stator flux linkage oriented scheme proposed in this study does not require flux estimation or a speed sensor, only requiring nameplate data, stator current and stator resistance measurement, which can easily be determined at start‐up. Simulation and experimental investigations including field weakening operation and the effect of stator resistance variation demonstrate the improved performance of the new scheme compared to previous open loop V/Hz and stator resistive compensated schemes especially at low rotor speeds.
Improved decoupled model of mutually coupled dual‐channel SRM with consideration of magnetic saturation in dual‐channel operation
Authors: Ding Wen , Lou Jianyong , Liu Ling
Published: July 2013

This study proposes an improved decoupled model of mutually coupled dual‐channel switched reluctance machine (DCSRM) based on the equivalent inductance and flux linkage characteristics that consider magnetic saturation in dual‐channel operation (DCO) mode. A three‐dimensional finite‐element analysis (FEA) is used to calculate the static phase equivalent inductance of DCSRM for the simultaneous two‐phase excitation with consideration of saturation. And an indirect experimental test is performed to measure the equivalent flux linkage under the simultaneous two‐phase excitation and compared with the FEA results. In this improved decoupled model, the phase equivalent inductances and flux linkages in each channel are independent to each other and separately expressed as a function of rotor position and their own phase current. The static magnetic characteristics, details of modelling procedure and performances prediction for the DCSRM under DCO mode without and with consideration of saturation are compared. Finally, an experimental set‐up for a 12/8 DCSRM drive system based on dSPACE is built and the simulation and experimental results are compared, which verifies high accuracy of this improved modelling method.
New design solution for static eccentricity in single stator–single rotor axial flux induction motors
Authors: Nasiri‐Gheidari Zahra , Lesani Hamid
Published: July 2013

This study proposes a new design solution for static eccentricity in axial flux induction motors (AFIMs). There are two definitions for static eccentricity in AFIMs. In the first approach, that is, commonly used for double‐side machines, the rotor axis does not coincide with the stator bore but rotor rotates around its own shaft. So, the air‐gap of motor is not uniform. Usually, in single stator–single rotor arrangement the rotor integrates with rotating parts of mechanical load. So, when static eccentricity occurs, air‐gap length remains uniform. Rotor axis remains parallel with stator axis whereas it does not coincide with the stator bore. Based on the authors’ knowledge, the latter approach has not been considered before. Therefore in this study a new definition for static eccentricity factor in direct drive is presented. Also, an optimisation is done to decrease the effect of static eccentricity on motor performance. The mathematical model of studied motor in transient and steady state is used based on d–q axis theory. In particular, the proposed model considers the effect of core saturation, and both approaches for modelling static eccentricity. Finally, studied motor is constructed and tested. All parameters of studied motor are calculated based on experimental measurements.
Förderung des Obst- und Gemüseverzehrs bei Schulkindern – Mission (im-)possible?
Authors: Behrendt I. , Krawinkel M.
Published: July 2013

Eine Ernährung, reich an Obst und Gemüse, ist wichtig für die physische und kognitive Entwicklung des Kindes sowie zur Prävention ernährungsabhängiger Erkrankungen. In Deutschland wurden im Mai 2009 insgesamt 816 Schulkinder (Jungen und Mädchen im Alter von 10-13 Jahren) von 14 allgemeinbildenden Schulen in Mittelhessen zum Obst- und Gemüseverzehr befragt. Anschließend wurden von November 2009–April 2010 in 7 Schulen schulische Aktivitäten zur Förderung des Obst- und Gemüseverzehrs durchgeführt. Die Interventionsgruppe erhielt Arbeitsblätter zum Thema Obst und Gemüse und führte weitere ernährungsbildende Aktivitäten durch. Die anderen sieben Schulen dienten als Kontrollgruppe. Nach der Interventionsphase wurden alle Schulen im Rahmen eines follow-up survey erneut befragt. Beide Surveys basierten auf demselben standardisierten Fragebogen zur Erfassung des Obst- und Gemüseverzehrs. Der Vergleich des baseline survey und follow-up zeigte innerhalb der Interventionsgruppe keine Veränderung der Verzehrmenge. In der Kon­trollgruppe ging der Obstverzehr allerdings signifikant zurück (p=0,034). Die Intervention beeinflusst die Diversität der verzehrten Obst- und Gemüsesorten positiv. Die PRO GREENS-Strategien bieten eine Grundlage zur Förderung des Obst- und Gemüseverzehrs bei Schulkindern. Sie sind allerdings hinsichtlich Einbezugs der Eltern, Erlebnisorientierung, Verhältnisprävention und Aufbau von langfristigen Kooperationen weiter zu verbessern, um eine vielseitige Lebensmittelauswahl und Nährstoffaufnahme zu gewährleisten.
Note: Recombination of H+ and OH− ions along water wires
Authors: Lee Song Hi , Rasaiah Jayendran C.
Published: July 2013

Transport and recombination of hydrogen and hydroxide ions along a hydrogen-bonded water wire are studied by molecular dynamics simulation using a dissociating model for water. The results are compared with a recent CP-MD study of neutralization in bulk water [A. Hassanali, M. K. Prakrash, H. Eshet, and M. Parrinello, Proc. Natl. Acad. Sci. U.S.A. 108, 20410 (2011)]10.1073/pnas.1112486108. The translocation of H+ and OH− along the wire is faster than in the bulk water, followed by compression of the water wire when two water molecules separate the transported ions. Neutralization occurs with the concerted transfer of three protons as in the bulk water, followed by energy dissipation along the water chain.
A modified kinetic theory for frictional granular flows in dense and dilute regimes
Authors: Chialvo Sebastian , Sundaresan Sankaran
Published: July 2013

Continuum modelingof granular and gas-solid flows generally involves the use of a kinetic-theory (KT) model for the particulate phase, and the most widely used KT models have been derived for dilute flows of smooth, frictionless spheres. In reality, however, granular particles are frictional and can achieve dense packing, and these features must be taken into account to improve rheological predictions in these flow scenarios. Existing approaches in the literature for producing closed-form KT-based models employ empirical modifications to adapt the original models for use in dense and frictional systems. In this article, we investigate the capacity for such modifications to improve the rheological predictions of the Garzó–Dufty (GD) KT model[V. Garzó and J. W. Dufty, “Dense fluid transport for inelastic hard spheres,” Phys. Rev. E59, 5895–5911 (1999)]10.1103/PhysRevE.59.5895. On the basis of molecular dynamics simulations of homogeneous, simple shear flows of soft, frictional spheres, we propose a new expression for the radial distribution function at contact as well as modifications to the GD expressions for shear stress and energy dissipation rate. These changes account for dense-regime scalings observed in inertial-number models as well as the effects of interparticle friction while preserving the dynamic nature of the KT model.
Instabilities and nonlinear dynamics of concentrated active suspensions
Authors: Ezhilan Barath , Shelley Michael J. , Saintillan David
Published: July 2013

Suspensions of active particles, such as motile microorganisms and artificial microswimmers, are known to undergo a transition to complex large-scale dynamics at high enough concentrations. While a number of models have demonstrated that hydrodynamicinteractions can in some cases explain these dynamics, collective motion in experiments is typically observed at such high volume fractions that steric interactions between nearby swimmers are significant and cannot be neglected. This raises the question of the respective roles of steric vs hydrodynamic interactions in these dense systems, which we address in this paper using a continuum theory and numerical simulations. The model we propose is based on our previous kinetic theoryfor dilute suspensions, in which a conservation equation for the distribution function of particle configurations is coupled to the Stokes equations for the fluid motion [D. Saintillan and M. J. Shelley,“Instabilities, pattern formation, and mixing in active suspensions,” Phys. Fluids20, 123304 (2008)]10.1063/1.3041776. At high volume fractions,steric interactions are captured by extending classic models for concentrated suspensions of rodlike polymers, in which contacts between nearby particles cause them to align locally. In the absence of hydrodynamic interactions, this local alignment results in a transition from an isotropic base state to a nematic base state when volume fraction is increased. Using a linear stability analysis, we first investigate the hydrodynamic stability of both states. Our analysis shows that suspensions of pushers, or rear-actuated swimmers, typically become unstable in the isotropic state before the transition occurs; suspensions of pullers, or head-actuated swimmers, can also become unstable, though the emergence of unsteady flows in this case occurs at a higher concentration, above the nematic transition. These results are also confirmed using fully nonlinear numerical simulations in a periodic cubic domain, where pusher and puller suspensions are indeed both found to exhibit instabilities at sufficiently high volume fractions; these instabilities lead to unsteady chaotic states characterized by large-scale correlated motions and strong density fluctuations. While the dynamics in suspensions of pushers are similar to those previously reported in the dilute regime, the instability of pullers is novel and typically characterized by slower dynamics and weaker hydrodynamic velocities and active input power than in pusher suspensions at the same volume fraction.
Grating monochromator for electron cyclotron resonance ion source operation
Authors: Muto Hideshi , Ohshiro Yukimitsu , Yamaka Shouichi , Watanabe Shin-ichi , Oyaizu Michihiro , Kubono Shigeru , Yamaguchi Hidetoshi , Kase Masayuki , Hattori Toshiyuki , Shimoura Susumu
Published: July 2013

Recently, we started to observe optical line spectra from an ECR plasma using a grating monochromator with a photomultiplier. The light intensity of line spectrum from the ECR plasma had a strong correlation with ion beam intensity measured by a magnetic mass analyzer. This correlation is a significant information for beam tuning because it allows the extraction of the desired ion species from the ECR plasma. Separation of ion species of the same charge to mass ratio with an electromagnetic mass analyzer is known to be an exceptionally complex process, but this research gives new insights into its simplification. In this paper, the grating monochromator method for beam tuning of a Hyper-ECR ion source as an injector for RIKEN azimuthal varying field (AVF) cyclotron is described.
Relation of exact Gaussian basis methods to the dephasing representation: Theory and application to time-resolved electronic spectra
Authors: Šulc Miroslav , Hernández Henar , Martínez Todd J. , Vaníček Jiří
Published: July 2013

We recently showed that the dephasing representation (DR) provides an efficient tool for computing ultrafast electronic spectra and that further acceleration is possible with cellularization [M. Šulc and J. Vaníček, Mol. Phys. 110, 945 (2012)]10.1080/00268976.2012.668971. Here, we focus on increasing the accuracy of this approximation by first implementing an exact Gaussian basis method, which benefits from the accuracy of quantum dynamics and efficiency of classical dynamics. Starting from this exact method, the DR is derived together with ten other methods for computing time-resolved spectra with intermediate accuracy and efficiency. These methods include the Gaussian DR, an exact generalization of the DR, in which trajectories are replaced by communicating frozen Gaussian basis functions evolving classically with an average Hamiltonian. The newly obtained methods are tested numerically on time correlation functions and time-resolved stimulated emission spectra in the harmonic potential, pyrazine S0/S1 model, and quartic oscillator. Numerical results confirm that both the Gaussian basis method and the Gaussian DR increase the accuracy of the DR. Surprisingly, in chaotic systems the Gaussian DR can outperform the presumably more accurate Gaussian basis method, in which the two bases are evolved separately.
A versatile apparatus for on-line emission channeling experiments
Authors: Silva M. R. , Wahl U. , Correia J. G. , Amorim L. M. , Pereira L. M. C.
Published: July 2013

The concept and functionality of an apparatus dedicated to emission channeling experiments using short-lived isotopes on-line at ISOLDE/CERN is described. The setup is assembled in two functional blocks – (a) base stand including beam collimation, implantation and measurement chamber, cryogenic extension, and vacuum control system and (b) Panmure goniometer extension including maneuvering cradle and sample heating furnace. This setup allows for in situ implantation and sample analysis in the as-implanted state and upon cooling down to 50 K and during annealing up to 1200 K. The functionality of the setup will be illustrated with the example of establishing the lattice location of 56Mn probes implanted into GaAs.
Effect of Fe substitution for Co on structure, electrical resistivity, and magnetic properties of Heusler type Co2−xFe1+xSi alloys
Authors: Srinivas K. , Prasanna Kumari T. , Manivel Raja M. , Kamat S. V.
Published: July 2013

The effect of substitution of Fe for Co on structure, electrical resistivity, and magnetic properties of full Heusler type Co2−xFe1+xSi (0 ≤ x ≤ 1) alloys was investigated. The order-disorder transitions were studied by X-ray diffraction measurements followed by Rietveld refinement analysis as well as by 57Fe Mössbauer spectroscopy. The results revealed that these alloys consist of mostly L21 ordered phase and some B2 disordered phase up to x < 0.25. However, for x ≥ 0.25, the alloys consisted of L21 ordered phase and DO3 disordered phase. The electrical resistivity behaviour with temperature showed two distinct regions. In region I, the resistivity exhibited two-magnon scattering mechanism (T9/2 dependence) showing a signature of half-metallic ferromagnetism. However, in region II, the resistivity behaviour was governed by Tn power law and n value was found to vary from 2.98 to 1.38 with increasing Fe content. The room temperature magnetization studies confirmed the enhancement of the magnetic moment with increasing Fe substitution up to x = 0.5 in Co2−xFe1+xSi alloys. However, upon further increasing Fe content, the magnetic moment was found to decrease and this was explained in terms of localization effects originating mainly in the Co anti-site disorder.
Photoelectron velocity-map imaging spectroscopic and theoretical study on the reactivity of the gold atom toward CH3SH, CH3OH, and H2O
Authors: Qin Zhengbo , Cong Ran , Wu Xia , Liu Zhiling , Xie Hua , Tang Zichao , Jiang Ling , Fan Hongjun
Published: July 2013

Photoelectron velocity-map imaging spectroscopy has been used to study the reaction of the anionic gold atom with the HR (R = SCH3, OCH3, OH) molecules. The solvated [Au⋯HR]− and inserted [HAuR]− products have been experimentally observed for R = SCH3, whereas only solvated [Au⋯HR]− products were found for R = OCH3 and OH. This significant difference in the photoelectron spectra suggests the different reactivity of the Au− toward the CH3SH, CH3OH, and H2O molecules. Second order Møller–Plesset perturbation theory and coupled-cluster single double triple excitation calculations have been performed to aid the structural assignment of the spectra and to explore the reaction mechanism. Activation energies for the isomerizations of the solvated structures to the inserted ones in the Au−/Au + HR reactions (R = OCH3 and OH) are predicted to be much higher than those for the Au−/Au + CH3SH reactions, supporting the experimental observation. Theoretical calculations provide the evidence that the intriguing [HAuSCH3]− product may be formed by the attachment of the electron onto the neutral HAuSCH3 species or the isomerization from the anionic [Au⋯HSCH3]− one. These findings should be helpful for understanding the feature that the thiols are able to form the staple motifs, whereas CH3OH and H2O are not.
Low temperature diffusion of Li atoms into Si nanoparticles and surfaces
Authors: Nienhaus Hermann , Karacuban Hatice , Krix David , Becker Felix , Hagemann Ulrich , Steeger Doris , Bywalez Robert , Schulz Christof , Wiggers Hartmut
Published: July 2013

The diffusion of Li atoms deposited on hydrogen-passivated Si(001) surfaces, chemically oxidized Si(001) surfaces, Si nanoparticle films, and thick SiO2 layers is investigated with electron-beam induced Auger electron spectroscopy. The nanoparticles exhibit an average diameter of 24 nm. The Li metal film is evaporated at a sample temperature below 120 K. The reappearance of the Si substrate Auger signal as a function of time and temperature can be measured to study the Li diffusion into the bulk material. Values for the diffusion barrier of 0.5 eV for H:Si(001) and 0.3 eV for the ox-Si(001) and Si nanoparticle films are obtained. The diffusion of the Li atoms results in the disruption of the crystalline Si surfaces observed with atomic force microscopy. Contrasting to that, the Si nanoparticle films show less disruption by Li diffusion due to filling of the porous films detected with cross section electron microscopy. Silicon dioxide acts as a diffusion barrier for temperatures up to 300 K. However, the electron beam induces a reaction between Li and SiO2, leading to LiOx and elemental Si floating on the surface.
Transformation from insulating p-type to semiconducting n-type conduction in CaCu3Ti4O12-related Na(Cu5/2Ti1/2)Ti4O12 ceramics
Authors: Li Ming , Sinclair Derek C.
Published: July 2013

A double doping mechanism of Na+ + ½ Ti4+ → Ca2+ + ½ Cu2+ on the general formula Ca1−xNax(Cu3−x/2Tix/2)Ti4O12 has been used to prepare a series of isostructural CaCu3Ti4O12 (CCTO)-type perovskites. A complete solid solution exists for 0 ≤ x ≤ 1 and all compositions exhibit incipient ferroelectric behaviour with higher than expected intrinsic relative permittivity. Although CCTO ceramics typically exhibit n-type semiconductivity (room temperature, RT, resistivity of ∼10–100 Ω cm), Na(Cu5/2Ti1/2)Ti4O12 (NCTO) ceramics sintered at 950 °C consist of two insulating bulk phases (RT resistivity > 1 GΩ cm), one p-type and the other n-type. With increasing sintering temperature/period, the p-type phase transforms into the n-type phase. During the transformation, the resistivity and activation energy for electrical conduction (Ea ∼ 1.0 eV) of the p-type phase remain unchanged, whereas the n-type phase becomes increasingly conductive with Ea decreasing from ∼ 0.71 to 0.11 eV with increasing sintering temperature. These changes are attributed to small variations in stoichiometry that occur during high temperature ceramic processing with oxygen-loss playing a crucial role.
Rainwater- and air-driven 40 mm bladeless electromagnetic energy harvester
Authors: Zhao Dan , Khoo Joe
Published: July 2013

A 40 mm electromagnetic energy harvester driven by both rainwater and air is designed and experimentally tested. Its performance is first assessed by measuring the system response for 4 different levels of air flow excitations. It shows that about 0.5 W power is generated. Parametric analysis is then conducted in terms of the disc number, exhaust flow rates, and the inter-disc distance. Finally, it is used to harness energy from rainwater. It is found the harvester works much better than the air-driven one. And its energy conversion efficiency is reduced with increased disc diameter. The maximum electric current is 4.5 mA.
Spin-dependent Fano resonance in an impurity-doped graphene coupled to ferromagnetic leads
Authors: Yang Fubin , Cheng Yan , Liu Futi , Chen Xiangrong
Published: July 2013

We investigate the spin-dependent Fano resonance in an impurity-doped graphene sheet coupled to ferromagnetic (FM) leads at low temperatures. By the nonequilibrium Green's function theory, we calculate the linear conductance of the system, which possesses a different Fano structure both in the parallel and anti-parallel configuration of the FM leads. The results come from the quantum interference between resonant and nonresonant processes in the system. Our studies indicate that the system is an ideal platform to investigate the Fano physics, even in some relevant experiments.
Passivation of In0.53Ga0.47As/ZrO2 interfaces by AlN atomic layer deposition process
Authors: Weiland C. , Rumaiz A. K. , Price J. , Lysaght P. , Woick J. C.
Published: July 2013

Reducing defects at III-V/high-k interfaces is essential for optimizing devices built on these materials. Here, the role of an interfacial AlN process at In0.53Ga0.47As/ZrO2 interfaces is investigated by hard x-ray photoelectron spectroscopy (HAXPES) and capacitance/voltage (C-V) measurements. C-V measurements show a significant reduction in the density of interface traps with the interfacial AlN process and a capping TiN layer. To elucidate the specific role of the AlN process, blanket films with various deposition processes are compared. The AlN process alone (without subsequent dielectric deposition) reduces InGaAs oxide levels below the HAXPES detection limit, even though the AlN is ultimately found to be oxidized into AlOx with only trace N incorporation, yet AlN passivation provides a lower Dit (density of interface traps) when compared with an H2O-based Al2O3 deposition. The AlN process does not passivate against re-oxidation of the InGaAs during an O3 based ZrO2 deposition process, but it does provide passivation against As-As development during subsequent TiN deposition. The role of chemical defects in the C-V characteristics is also discussed.
Dislocation nucleation on a near surface void leading to surface protrusion growth under an external electric field
Authors: Pohjonen A. S. , Parviainen S. , Muranaka T. , Djurabekova F.
Published: July 2013

The stress exerted on a conducting material surface by an external electric field can cause plastic deformation if the stress is concentrated somewhere in the material. Such concentration can occur due to the presence of a near surface void. The plastic deformation can lead to growth of a protrusion on the surface. To investigate the conditions where such a mechanism can operate, we employ concurrent electrodynamics-molecular dynamics simulations, analyze the distribution of stress near the void by using both the molecular dynamics and finite element method, and compare the result to the analytical expression for a void located deep in the bulk. By applying an electric field of exaggerated strength we are able to simulate the plastic deformation process within the timespan allowed by molecular dynamics simulations. In reality, longer timespans would allow for the initiation of the proposed mechanism at electric field strengths much lower than the values assumed for the simulations in the present work.
Critical state model for magneto-elastic problem of thin superconducting disks
Authors: Huang Chen-Guang , Yong Hua-Dong , Zhou You-He
Published: July 2013

The magneto-elastic problem of a thin superconducting disk in a perpendicular magnetic field is analyzed with field-dependent critical current. We calculate numerically the body force distribution and discuss the field dependence of Jc on the magneto-elastic behavior during field ascent and descent for three critical state models: Bean, Kim, and exponential models. The results show that when considering a field dependence of Jc, the flux and remagnetization fronts have a larger moving speed towards the center of a disk relative to the Bean model. Simultaneously, the most dangerous stage of possible cracking for the disk will arrive early in the field decreasing stage. The magnetostriction loops are also presented during a full cycle of the applied field. It is interesting that the calculated magnetostriction loops for the Kim and exponential models are quite similar to the corresponding magnetostriction curves at low and high temperatures measured in the experiment.
Multiferroic properties of CoFe2O4/Bi3.4La0.6Ti3O12 bilayer structure at room temperature
Authors: Charris-Hernández A. , Melgarejo R. , Barrionuevo D. , Kumar A. , Tomar M. S.
Published: July 2013

Bi3.4La0.6Ti3O12/CoFe2O4 bilayer films were synthesized by chemical solution method and deposited by spin coating on Pt (Pt/TiO2/SiO2/Si) substrate. X-ray diffraction of the bilayer system revealed the composite-like structure. The leakage current is less than 10−7 A at electric field below100 kV/cm, and it shows the ohmic behavior. Dielectric constant decreases with increasing frequency and reaches to 140 at 10−6 Hz. Bi3.4La0.6Ti3O12/CoFe2O4 system shows the co-existence of ferroelectric polarization (Pr) = 51 μC/cm2 and magnetization (Mr) = 206 emu/cm3 at room temperature. Observed ferromagnetic and ferroelectric responses in bilayer system may be useful for bi-functional devices.
Picosecond inverse magnetostriction in galfenol thin films
Authors: Jäger J. V. , Scherbakov A. V. , Linnik T. L. , Yakovlev D. R. , Wang M. , Wadley P. , Holy V. , Cavill S. A. , Akimov A. V. , Rushforth A. W. , Bayer M.
Published: July 2013

Coherent high-amplitude precession of the magnetization and spin waves with frequencies up to 40 GHz are generated by injecting picosecond compressive and shear acoustic pulses into nanometer-sized galfenol (Fe81Ga19) films. The magnetization modulation is due to the picosecond inverse magnetostrictive effect. The oscillations of the magnetization measured by magneto-optical Kerr rotation last for several nanoseconds, and the maximum modulation of the in-plane effective magnetic field is as high as 40 mT. These results in combination with a comprehensive theoretical analysis show that galfenol films possess excellent properties for ultrafast magnetization control based on the picosecond inverse magnetostrictive effect.
Correlation between field dependent electrical conduction and dielectric breakdown in a SiCOH based low-k (k = 2.0) dielectric
Authors: Wu C. , Li Y. , Barbarin Y. , Ciofi I. , Croes K. , Bömmels J. , De Wolf I. , Tőkei Zs.
Published: July 2013

The electrical conduction of a SiCOH based ultralow-k (k = 2.0) dielectric is investigated over an electric field range from 1.0 MV/cm to breakdown. Below 4.0 MV/cm, space-charge-limited current dominates the leakage. Above 5.0 MV/cm, a transition is found from trap-assisted Fowler-Nordheim (F-N) tunneling to F-N tunneling. It is hypothesized that under F-N tunneling stress, intrinsic material degradation causes positively charged defects generated in the dielectric. Moreover, this change of the dominant conduction path has a significant impact on the time dependent dielectric breakdown lifetime behavior.
Huge increase in gas phase nanoparticle generation by pulsed direct current sputtering in a reactive gas admixture
Authors: Polonskyi Oleksandr , Peter Tilo , Mohammad Ahadi Amir , Hinz Alexander , Strunskus Thomas , Zaporojtchenko Vladimir , Biederman Hynek , Faupel Franz
Published: July 2013

Using reactive DC sputtering in a gas aggregation cluster source, we show that pulsed discharge gives rise to a huge increase in deposition rate of nanoparticles by more than one order of magnitude compared to continuous operation. We suggest that this effect is caused by an equilibrium between slight target oxidation (during “time-off”) and subsequent sputtering of Ti oxides (sub-oxides) at “time-on” with high power impulse.
Electron energy and angle distribution of GaAs photocathodes
Authors: Chen Zhanghui , Jiang Xiangwei , Li Jingbo , Li Shushen , Wang Linwang
Published: July 2013

A precise Monte Carlo model is developed to investigate the electron energy and angle distribution of the transmission-mode GaAs (100) photocathode at room temperature. Both distributions are important for high-quality electron sources. The results show that the energy loss (0.1309 eV) and the angle-dependent energy distribution curves fit well with experimental data. It is found that 65.24% of the emission electrons come from Γ valley, 33.62% from L valley, and 1.15% from X valley. The peak of the energy distribution curve is contributed by both Γ and L-valley electrons, while the high-energy part is contributed by Γ-valley electrons rather than L electrons, which is different from previous inference and can be attributed to the narrow energy range of L-valley electrons. However, L-valley electrons have a larger angular spread than Γ-valley electrons and lead to the spread of the emission cone. The further simulation indicates that increasing the hole concentration or the thickness of the first activation layer can improve the angle distribution, but the energy distribution will turn to be slightly more dispersive. Temperature effect on the two distributions is also analyzed. The energy distribution curve moves towards the higher energy while the angle distribution curve moves towards the lower value when the temperature declines.
Unipolar resistive switching behavior in Pt/HfO2/TiN device with inserting ZrO2 layer and its 1 diode-1 resistor characteristics
Authors: Lee Dai-Ying , Tsai Tsung-Ling , Tseng Tseung-Yuen
Published: July 2013

Transition of resistive switching (RS) behavior from bipolar to unipolar is observed in Pt/ZrO2/HfO2/TiN device. Due to the lower oxygen vacancy concentration of the HfO2 layer, formation/rupture of the conducting filament is confined in the HfO2 layer. To fulfill one diode and one resistor (1D1R) structure, the electrical relation between the RS device and diode is investigated. A Pt/InZnO/CoO/Pt/TiN oxide diode is fabricated to provide enough forward current and large forward/reverse current ratio to achieve unipolar RS behavior. The 1D-1R structure with Pt/ZrO2/HfO2/TiN resistive random access memory shows robust retention and nondestructive readout property at 85 °C.
Investigation of tow-step electrical degradation behavior in a-InGaZnO thin-film transistors with Sm2O3 gate dielectrics
Authors: Chen Fa-Hsyang , Her Jim-Long , Hung Meng-Ning , Pan Tung-Ming
Published: July 2013

We investigate the electrical stress-induced instability in amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) with Sm2O3 gate dielectrics. Tow-step electrical degradation behavior in Sm2O3 a-IGZO TFT devices was found under high gate and drain voltage stress during 1000 s. A typical small positive shift followed by an unusual negative shift of threshold voltage is characterized in our TFT devices. We believe that the positive shift of the threshold voltage is due to charge trapping in the gate dielectric and/or at the channel/dielectric interfaces, while the negative shift of threshold voltage can be attributed to the generation of extra electrons from oxygen vacancies in the a-IGZO channel. We suggested that the amount of oxygen vacancies and the quality of the high-κ gate dielectric probably affect the degradation behavior of a-IGZO TFT devices.
A dielectric-barrier discharge enhanced plasma brush array at atmospheric pressure
Authors: Li Xuemei , Tang Jie , Zhan Xuefang , Yuan Xin , Zhao Zhongjun , Yan Yanyue , Duan Yixiang
Published: July 2013

This study developed a large volume cold atmospheric plasma brush array, which was enhanced by a dielectric barrier discharge by integrating a pair of DC glow discharge in parallel. A platinum sheet electrode was placed in the middle of the discharge chamber, which effectively reduced the breakdown voltage and working voltage. Emission spectroscopy diagnosis indicated that many excited argon atoms were distributed almost symmetrically in the lateral direction of the plasma. The concentration variations of reactive species relative to the gas flow rate and discharge current were also examined.
On the visibility of very thin specimens in annular bright field scanning transmission electron microscopy
Authors: Phillips P. J. , Klie R. F.
Published: July 2013

Annular bright field (ABF) scanning transmission electron microscopy (STEM) is emerging as an important observation mode for its ability to simultaneously image both heavy and light elements. However, recent results have demonstrated that in the limit of a very thin specimen (a few atomic layers), the ABF and high angle annular dark field (HAADF) signals cease to be intuitively related: a phenomenon which is generally irrelevant when imaging “normal” specimens. ABF/HAADF STEM observations and multislice image simulations of two catalyst samples of differing atomic weights are presented; it is shown that the nature of the ABF signal is specimen dependent.