bluuebunny/crossref_metadata_2025 huggingface dataset:
The function of phosphatidylinositol 5-phosphate 4-kinase γ (PI5P4Kγ) explored using a specific inhibitor that targets the PI5P-binding site
Authors: Clarke Jonathan H. , Giudici Maria-Luisa , Burke John E. , Williams Roger L. , Maloney David J. , Marugan Juan , Irvine Robin F.
Published: December 2014

NIH-12848 (NCGC00012848-02), a putative phosphatidylinositol 5-phosphate 4-kinase γ (PI5P4Kγ) inhibitor, was explored as a tool for investigating this enigmatic, low activity, lipid kinase. PI5P4K assays in vitro showed that NIH-12848 inhibited PI5P4Kγ with an IC50 of approximately 1 μM but did not inhibit the α and β PI5P4K isoforms at concentrations up to 100 μM. A lack of inhibition of PI5P4Kγ ATPase activity suggested that NIH-12848 does not interact with the enzyme's ATP-binding site and direct exploration of binding using hydrogen–deuterium exchange (HDX)-MS (HDX-MS) revealed the putative PI5P-binding site of PI5P4Kγ to be the likely region of interaction. This was confirmed by a series of mutation experiments which led to the identification of a single PI5P4Kγ amino acid residue that can be mutated to its PI5P4Ks α and β homologue to render PI5P4Kγ resistant NIH-12848 inhibition. NIH-12848 (10 μM) was applied to cultured mouse principal kidney cortical collecting duct (mpkCCD) cells which, we show, express PI5P4Kγ that increases when the cells grow to confluence and polarize. NIH-12848 inhibited the translocation of Na+/K+-ATPase to the plasma membrane that occurs when mpkCCD cells grow to confluence and also prevented reversibly their forming of ‘domes’ on the culture dish. Both these NIH-12848-induced effects were mimicked by specific RNAi knockdown of PI5P4Kγ, but not that of PI5P4Ks α or β. Overall, the data reveal a probable contribution of PI5P4Kγ to the development and maintenance of epithelial cell functional polarity and show that NIH-12848 is a potentially powerful tool for exploring the cell physiology of PI5P4Ks.
Ubiquitin C-terminal hydrolases cleave isopeptide- and peptide-linked ubiquitin from structured proteins but do not edit ubiquitin homopolymers
Authors: Bett John S. , Ritorto Maria Stella , Ewan Richard , Jaffray Ellis G. , Virdee Satpal , Chin Jason W. , Knebel Axel , Kurz Thimo , Trost Matthias , Tatham Michael H. , Hay Ronald T.
Published: December 2014

Modification of proteins with ubiquitin (Ub) occurs through a variety of topologically distinct Ub linkages, including Ube2W-mediated monoubiquitylation of N-terminal alpha amines to generate peptide-linked linear mono-Ub fusions. Protein ubiquitylation can be reversed by the action of deubiquitylating enzymes (DUBs), many of which show striking preference for particular Ub linkage types. Here, we have screened for DUBs that preferentially cleave N-terminal Ub from protein substrates but do not act on Ub homopolymers. We show that members of the Ub C-terminal hydrolase (UCH) family of DUBs demonstrate this preference for N-terminal deubiquitylating activity as they are capable of cleaving N-terminal Ub from SUMO2 and Ube2W, while displaying no activity against any of the eight Ub linkage types. Surprisingly, this ability to cleave Ub from SUMO2 was 100 times more efficient for UCH-L3 when we deleted the unstructured N-terminus of SUMO2, demonstrating that UCH enzymes can cleave Ub from structured proteins. However, UCH-L3 could also cleave chemically synthesized isopeptide-linked Ub from lysine 11 (K11) of SUMO2 with similar efficiency, demonstrating that UCH DUB activity is not limited to peptide-linked Ub. These findings advance our understanding of the specificity of the UCH family of DUBs, which are strongly implicated in cancer and neurodegeneration but whose substrate preference has remained unclear. In addition, our findings suggest that the reversal of Ube2W-mediated N-terminal ubiquitylation may be one physiological role of UCH DUBs in vivo.
Directional modulation‐enhanced retrodirective array
Authors: Ding Yuan , Fusco Vincent
Published: December 2014

Unlike the mathematical techniques adopted in classical cryptographic technology at higher protocol layers, it is shown that characteristics intrinsic to the physical layer can be exploited to secure useful information. It is shown that a retrodirective array can be made to operate more securely by incorporating directional modulation (DM) concepts. The presented new approach allows DM to operate in a multipath environment. Previously, DM systems could only operate in free space.
AC analysis of temperature effects on conversion efficiency of CuInGaSe2 solar cells
Authors: Kim Hong Tak , Kim Chang Duk , Kim Maeng Jun , Sohn Young‐Soo
Published: December 2014

The temperature effect on a CuInGaSe2 (CIGS) solar cell was investigated in the temperature range −10 to 80°C using direct current (DC) and alternating current (AC) characteristic analysis of CIGS solar cells. The change rates of short‐circuit current density (Jsc), open‐circuit voltage (Voc), fill factor (FF) and efficiency (η) with respect to temperature were investigated. In addition, the variation of impedance, total capacitance and dynamic resistance due to the temperature change implied that the width of the depletion region in a p–n junction shrank, and the effective minority carrier lifetime (τeff) decreased. Consequently, Jsc changed slightly due to the balance between the variation of the energy bandgap (Eg) and τeff. However, Voc linearly decreased due to the relationship of Eg when the temperature increased. From these results, it has been concluded that Voc plays an important role in the characteristics of the CIGS solar cell with change of temperature.
Design of mechanical stiffness switch for hydraulic quadruped robot legs inspired by equine distal forelimb
Authors: Cho Jungsan , Park Sangdeok , Kim Kabil
Published: December 2014

A new method, inspired by the gait of horses, for regulating the ground reaction force of a quadruped walking robot, is proposed. The method uses the mechanical stiffness switch with a dual‐spring structure inspired by an equine distal forelimb. This includes the use of a low‐stiffness spring activated at the moment of touchdown and a high‐stiffness spring for the support phase. This method has been applied to Jinpoong, a hydraulic quadruped walking robot, and has contributed to the robot's stable gait on uneven terrain.
Nano‐ampere PTAT current source with temperature inaccuracy <±1°C
Authors: Chouhan S.S. , Halonen K.
Published: December 2014

The architecture for generating a nano‐ampere proportional to absolute temperature (PTAT) current source is proposed. The circuit has been designed and fabricated in a standard 180 nm CMOS technology. Measurements were performed on 10 prototypes in the temperature range of −40 to +85°C. The operating supply voltage of the proposed circuit is 850 mV ± 10%. The measured averaged temperature inaccuracy and the linearity of the proposed architecture is between +0.86/− 0.93°C and +0.69/−0.75%, respectively.
6.2 GHz 0.5 mW two‐dimensional oscillator array‐based injection‐locked frequency divider in 0.18 μm CMOS
Authors: Yu Xiaopeng , Song Xiong , Lim Wei Meng , Yeo Kiat‐Seng
Published: December 2014

A new two‐dimensional oscillator array‐based injection‐locked frequency divider is proposed. Instead of using the conventional analogue tuning technique or the one‐dimensional delay chain, a two‐dimensional array is implemented to digitally and precisely control the total delay in the oscillator core. This makes it possible to achieve a programmable delay, hence attaining potential programmable division ratios for the injection‐locked divider. Fabricated in a standard 0.18 μm CMOS technology, a prototype chip, namely a divide‐by‐4/5 prescaler using this technique, is able to work up to 6.2 GHz with 0.5 mW power consumption from a 1.8 V supply voltage.
Compact lowpass filter with wide stopband using stepped impedance hairpin units
Authors: Liu Shuai , Xu Jun , Xu Zhitao
Published: December 2014

A novel microstrip lowpass filter (LPF) with a wide stopband is presented. The basic resonator is composed of two stepped impedance hairpin units with one embedded in another, which can obtain two more transmission zeros and extend a wide stopband. Based on the proposed resonator, a demonstration LPF of compact size, sharp transition and wide stopband has been designed, fabricated and measured. The proposed filter exhibits a small size of 0.081λg × 0.113λg, where λg is the waveguide length at the cutoff frequency of 1.6 GHz. Results show good agreement with simulations and the 20 dB rejection stopband can be extended to more than 15 GHz.
Calibration of multiple fish‐eye cameras using a wand
Authors: Fu Qiang , Quan Quan , Cai Kai‐Yuan
Published: December 2014

Fish‐eye cameras are becoming increasingly popular in computer vision, but their use for three‐dimensional measurement is limited partly because of the lack of an accurate, efficient and user‐friendly calibration procedure. For such a purpose, the authors propose a method to calibrate the intrinsic and extrinsic parameters (including radial distortion parameters) of two/multiple fish‐eye cameras simultaneously by using a wand under general motions. Thanks to the generic camera model used, the proposed calibration method is also suitable for two/multiple conventional cameras and mixed cameras (e.g. two conventional cameras and a fish‐eye camera). Simulation and real experiments demonstrate the effectiveness of the proposed method. Moreover, the authors develop the camera calibration toolbox, which is available online.
Self characterization of a coded aperture array for neutron source imaging
Authors: Volegov P. L. , Danly C. R. , Fittinghoff D. N. , Guler N. , Merrill F. E. , Wilde C. H.
Published: December 2014

The neutron imaging system at the National Ignition Facility (NIF) is an important diagnostic tool for measuring the two-dimensional size and shape of the neutrons produced in the burning deuterium-tritium plasma during the stagnation stage of inertial confinement fusion implosions. Since the neutron source is small (∼100 μm) and neutrons are deeply penetrating (>3 cm) in all materials, the apertures used to achieve the desired 10-μm resolution are 20-cm long, triangular tapers machined in gold foils. These gold foils are stacked to form an array of 20 apertures for pinhole imaging and three apertures for penumbral imaging. These apertures must be precisely aligned to accurately place the field of view of each aperture at the design location, or the location of the field of view for each aperture must be measured. In this paper we present a new technique that has been developed for the measurement and characterization of the precise location of each aperture in the array. We present the detailed algorithms used for this characterization and the results of reconstructed sources from inertial confinement fusion implosion experiments at NIF.
Coupled slow and fast surface dynamics in an electrocatalytic oscillator: Model and simulations
Authors: Nascimento Melke A. , Nagao Raphael , Eiswirth Markus , Varela Hamilton
Published: December 2014

The co-existence of disparate time scales is pervasive in many systems. In particular for surface reactions, it has been shown that the long-term evolution of the core oscillator is decisively influenced by slow surface changes, such as progressing deactivation. Here we present an in-depth numerical investigation of the coupled slow and fast surface dynamics in an electrocatalytic oscillator. The model consists of four nonlinear coupled ordinary differential equations, investigated over a wide parameter range. Besides the conventional bifurcation analysis, the system was studied by means of high-resolution period and Lyapunov diagrams. It was observed that the bifurcation diagram changes considerably as the irreversible surface poisoning evolves, and the oscillatory region shrinks. The qualitative dynamics changes accordingly and the chaotic oscillations are dramatically suppressed. Nevertheless, periodic cascades are preserved in a confined region of the resistance vs. voltage diagram. Numerical results are compared to experiments published earlier and the latter reinterpreted. Finally, the comprehensive description of the time-evolution in the period and Lyapunov diagrams suggests further experimental studies correlating the evolution of the system's dynamics with changes of the catalyst structure.
Non-adiabatic dynamics of isolated green fluorescent protein chromophore anion
Authors: Zhao Li , Zhou Pan-Wang , Li Bin , Gao Ai-Hua , Han Ke-Li
Published: December 2014

On-the-fly ab initio molecular dynamics calculations have been performed to investigate the relaxation mechanism of green fluorescent protein chromophore anion under vacuum. The CASSCF surface hopping simulation method based on Zhu-Nakamura theory is applied to present the real-time conformational changes of the target molecule. The static calculations and dynamics simulation results suggest that not only the twisting motion around bridging bonds between imidazolinone and phenoxy groups but the strength mode of C=O and pyramidalization character of bridging atom are major factors on the ultrafast fluorescence quenching process of the isolated chromophore anion. The abovementioned factors bring the molecule to the vicinity of conical intersections on its potential energy surface and to finish the internal conversion process. A Hula-like twisting pattern is displayed during the relaxation process and the entire decay process disfavors a photoswitching pattern which corresponds to cis-trans photoisomerization.
Symmetric model of compressible granular mixtures with permeable interfaces
Authors: Saurel Richard , Le Martelot Sébastien , Tosello Robert , Lapébie Emmanuel
Published: December 2014

Compressible granular materials are involved in many applications, some of them being related to energetic porous media. Gas permeation effects are important during their compaction stage, as well as their eventual chemical decomposition. Also, many situations involve porous media separated from pure fluids through two-phase interfaces. It is thus important to develop theoretical and numerical formulations to deal with granular materials in the presence of both two-phase interfaces and gas permeation effects. Similar topic was addressed for fluid mixtures and interfaces with the Discrete Equations Method (DEM) [R. Abgrall and R. Saurel, “Discrete equations for physical and numerical compressible multiphase mixtures,” J. Comput. Phys. 186(2), 361-396 (2003)] but it seemed impossible to extend this approach to granular media as intergranular stress [K. K. Kuo, V. Yang, and B. B. Moore, “Intragranular stress, particle-wall friction and speed of sound in granular propellant beds,” J. Ballist. 4(1), 697-730 (1980)] and associated configuration energy [J. B. Bdzil, R. Menikoff, S. F. Son, A. K. Kapila, and D. S. Stewart, “Two-phase modeling of deflagration-to-detonation transition in granular materials: A critical examination of modeling issues,” Phys. Fluids 11, 378 (1999)] were present with significant effects. An approach to deal with fluid-porous media interfaces was derived in Saurel et al. [“Modelling dynamic and irreversible powder compaction,” J. Fluid Mech. 664, 348-396 (2010)] but its validity was restricted to weak velocity disequilibrium only. Thanks to a deeper analysis, the DEM is successfully extended to granular media modelling in the present paper. It results in an enhanced version of the Baer and Nunziato [“A two-phase mixture theory for the deflagration-to-detonation transition (DDT) in reactive granular materials,” Int. J. Multiphase Flow 12(6), 861-889 (1986)] model as symmetry of the formulation is now preserved. Several computational examples are shown to validate and illustrate method’s capabilities.
On the NP-completeness of the Hartree-Fock method for translationally invariant systems
Authors: Whitfield James Daniel , Zimborás Zoltán
Published: December 2014

The self-consistent field method utilized for solving the Hartree-Fock (HF) problem and the closely related Kohn-Sham problem is typically thought of as one of the cheapest methods available to quantum chemists. This intuition has been developed from the numerous applications of the self-consistent field method to a large variety of molecular systems. However, as characterized by its worst-case behavior, the HF problem is NP-complete. In this work, we map out boundaries of the NP-completeness by investigating restricted instances of HF. We have constructed two new NP-complete variants of the problem. The first is a set of Hamiltonians whose translationally invariant Hartree-Fock solutions are trivial, but whose broken symmetry solutions are NP-complete. Second, we demonstrate how to embed instances of spin glasses into translationally invariant Hartree-Fock instances and provide a numerical example. These findings are the first steps towards understanding in which cases the self-consistent field method is computationally feasible and when it is not.
Massively parallel molecular-dynamics simulation of ice crystallisation and melting: The roles of system size, ensemble, and electrostatics
Authors: English Niall J.
Published: December 2014

Ice crystallisation and melting was studied via massively parallel molecular dynamics under periodic boundary conditions, using approximately spherical ice nano-particles (both “isolated” and as a series of heterogeneous “seeds”) of varying size, surrounded by liquid water and at a variety of temperatures. These studies were performed for a series of systems ranging in size from ∼1 × 106 to 8.6 × 106 molecules, in order to establish system-size effects upon the nano-clusters” crystallisation and dissociation kinetics. Both “traditional” four-site and “single-site” and water models were used, with and without formal point charges, dipoles, and electrostatics, respectively. Simulations were carried out in the microcanonical and isothermal-isobaric ensembles, to assess the influence of “artificial” thermo- and baro-statting, and important disparities were observed, which declined upon using larger systems. It was found that there was a dependence upon system size for both ice growth and dissociation, in that larger systems favoured slower growth and more rapid melting, given the lower extent of “communication” of ice nano-crystallites with their periodic replicae in neighbouring boxes. Although the single-site model exhibited less variation with system size vis-à-vis the multiple-site representation with explicit electrostatics, its crystallisation-dissociation kinetics was artificially fast.
The adsorption of α-cyanoacrylic acid on anatase TiO2 (101) and (001) surfaces: A density functional theory study
Authors: Ma Jin-Gang , Zhang Cai-Rong , Gong Ji-Jun , Yang Bing , Zhang Hai-Min , Wang Wei , Wu You-Zhi , Chen Yu-Hong , Chen Hong-Shan
Published: December 2014

The adsorption of α-cyanoacrylic acid (CAA) on anatase TiO2 (101) and (001) surfaces, including adsorption energies, structures, and electronic properties, have been studied by means of density functional theory calculations in connection with ultrasoft pseudopotential and generalized gradient approximation based upon slab models. The most stable structure of CAA on anatase TiO2 (101) surface is the dissociated bidentate configuration where the cyano N and carbonyl O bond with two adjacent surface Ti atoms along [010] direction and the dissociated H binds to the surface bridging O which connects the surface Ti bonded with carbonyl O. While for the adsorption of CAA on (001) surface, the most stable structure is the bidentate configuration through the dissociation of hydroxyl in carboxyl moiety. The O atoms of carboxyl bond with two neighbor surface Ti along [100] direction, and the H from dissociated hydroxyl interacts with surface bridging O, generating OH species. The adsorption energies are estimated to be 1.02 and 3.25 eV for (101) and (001) surfaces, respectively. The analysis of density of states not only suggests the bonds between CAA and TiO2 surfaces are formed but also indicates that CAA adsorptions on TiO2 (101) and (001) surfaces provide feasible mode for photo-induced electron injection through the interface between TiO2 and CAA. This is resulted from that, compared with the contribution of CAA orbitals in valence bands, the conduction bands which are mainly composed of Ti 3d orbitals have remarkable reduction of the component of CAA orbitals.
Finite-size scaling study of shear viscosity anomaly at liquid-liquid criticality
Authors: Roy Sutapa , Das Subir K.
Published: December 2014

We study the equilibrium dynamics of a symmetrical binary Lennard-Jones fluid mixture near its consolute criticality. Molecular dynamics simulation results for the shear viscosity, η, from a microcanonical ensemble are compared with those from a canonical ensemble with various thermostats. It is observed that the Nosé-Hoover thermostat is a good candidate for this purpose, and is therefore adopted for the quantification of the critical singularity of η, to avoid the temperature fluctuations (or even drifts) that are often encountered in microcanonical simulations. Via a finite-size scaling analysis of our simulation data we have been able to confirm that the shear viscosity exhibits a weak critical singularity in agreement with the theoretical predictions.
Multichannel photodiode detector for ultrafast optical spectroscopy
Authors: Mertelj T. , Vujičić N. , Borzda T. , Vaskivskyi I. , Pogrebna A. , Mihailovic D.
Published: December 2014

Construction and characterization of a multichannel photodiode detector based on commercially available components with high signal to noise of ∼106 and a rapid frame rate, suitable for time resolved femtosecond spectroscopy with high repetition femtosecond sources, is presented.
Collisionless electron heating in periodic arrays of inductively coupled plasmas
Authors: Czarnetzki U. , Tarnev Kh.
Published: December 2014

A novel mechanism of collisionless heating in large planar arrays of small inductive coils operated at radio frequencies is presented. In contrast to the well-known case of non-local heating related to the transversal conductivity, when the electrons move perpendicular to the planar coil, we investigate the problem of electrons moving in a plane parallel to the coils. Two types of periodic structures are studied. Resonance velocities where heating is efficient are calculated analytically by solving the Vlasov equation. Certain scaling parameters are identified. The concept is further investigated by a single particle simulation based on the ergodic principle and combined with a Monte Carlo code allowing for collisions with Argon atoms. Resonances, energy exchange, and distribution functions are obtained. The analytical results are confirmed by the numerical simulation. Pressure and electric field dependences are studied. Stochastic heating is found to be most efficient when the electron mean free path exceeds the size of a single coil cell. Then the mean energy increases approximately exponentially with the electric field amplitude.
Formation of a new archetypal Metal-Organic Framework from a simple monatomic liquid
Authors: Metere Alfredo , Oleynikov Peter , Dzugutov Mikhail , O’Keeffe Michael
Published: December 2014

We report a molecular-dynamics simulation of a single-component system of particles interacting via a spherically symmetric potential that is found to form, upon cooling from a liquid state, a low-density porous crystalline phase. Its structure analysis demonstrates that the crystal can be described by a net with a topology that belongs to the class of topologies characteristic of the Metal-Organic Frameworks (MOFs). The observed net is new, and it is now included in the Reticular Chemistry Structure Resource database. The observation that a net topology characteristic of MOF crystals, which are known to be formed by a coordination-driven self-assembly process, can be reproduced by a thermodynamically stable configuration of a simple single-component system of particles opens a possibility of using these models in studies of MOF nets. It also indicates that structures with MOF topology, as well as other low-density porous crystalline structures can possibly be produced in colloidal systems of spherical particles, with an appropriate tuning of interparticle interaction.
Raman spectra and electron-phonon coupling in disordered graphene with gate-tunable doping
Authors: Childres Isaac , Jauregui Luis A. , Chen Yong P.
Published: December 2014

We report a Raman spectroscopy study of graphene field-effect transistors with a controlled amount of defects introduced in graphene by exposure to electron-beam irradiation. Raman spectra are taken at T = 8 K over a range of back gate voltages (Vg) for various irradiation dosages (Re). We study effects in the Raman spectra due to Vg-induced doping and artificially created disorder at various Re. With moderate disorder (irradiation), the Raman G peak with respect to the graphene carrier density (nFE) exhibits a minimum in peak frequency and a maximum in peak width near the charge-neutral point (CNP). These trends are similar to those seen in previous works on pristine graphene and have been attributed to a reduction of electron-phonon coupling strength (D) and removal of the Kohn anomaly as the Fermi level moves away from the CNP. We also observe a maximum in I2D/IG and weak maximum in ID/IG near the CNP. All the observed dependences of Raman parameters on nFE weaken at stronger disorder (higher Re), implying that disorder causes a reduction of D as well. Our findings are valuable for understanding Raman spectra and electron-phonon physics in doped and disordered graphene.
Effect of tunnel injection through the Schottky gate on the static and noise behavior of GaInAs/AlInAs high electron mobility transistor
Authors: Moro-Melgar Diego , Mateos Javier , González Tomás , Vasallo Beatriz G.
Published: December 2014

By using a Monte Carlo simulator, the influence of the tunnel injection through the Schottky contact at the gate electrode of a GaInAs/AlInAs High Electron Mobility Transistor (HEMT) has been studied in terms of the static and noise performance. The method used to characterize the quantum tunnel current has been the Wentzel-Kramers-Brillouin (WKB) approach. The possibility of taking into account the influence of the image charge effect in the potential barrier height has been included as well. Regarding the static behavior, tunnel injection leads to a decrease in the drain current ID due to an enhancement of the potential barrier controlling the carrier transport through the channel. However, the pinch-off is degraded due to the tunneling current. Regarding the noise behavior, since the fluctuations in the potential barrier height caused by the tunnel-injected electrons are strongly coupled with the drain current fluctuations, a significant increase in the drain-current noise takes place, even when the tunnel effect is hardly noticeable in the static I-V characteristics, fact that must be taken into account when designing scaled HEMT for low-noise applications. In addition, tunnel injection leads to the appearance of full shot noise in the gate current.
Reliable wet-chemical cleaning of natively oxidized high-efficiency Cu(In,Ga)Se2 thin-film solar cell absorbers
Authors: Lehmann Jascha , Lehmann Sebastian , Lauermann Iver , Rissom Thorsten , Kaufmann Christian A. , Lux-Steiner Martha Ch. , Bär Marcus , Sadewasser Sascha
Published: December 2014

Currently, Cu-containing chalcopyrite-based solar cells provide the highest conversion efficiencies among all thin-film photovoltaic (PV) technologies. They have reached efficiency values above 20%, the same performance level as multi-crystalline silicon-wafer technology that dominates the commercial PV market. Chalcopyrite thin-film heterostructures consist of a layer stack with a variety of interfaces between different materials. It is the chalcopyrite/buffer region (forming the p-n junction), which is of crucial importance and therefore frequently investigated using surface and interface science tools, such as photoelectron spectroscopy and scanning probe microscopy. To ensure comparability and validity of the results, a general preparation guide for “realistic” surfaces of polycrystalline chalcopyrite thin films is highly desirable. We present results on wet-chemical cleaning procedures of polycrystalline Cu(In1-xGax)Se2 thin films with an average x = [Ga]/([In] + [Ga]) = 0.29, which were exposed to ambient conditions for different times. The hence natively oxidized sample surfaces were etched in KCN- or NH3-based aqueous solutions. By x-ray photoelectron spectroscopy, we find that the KCN treatment results in a chemical surface structure which is – apart from a slight change in surface composition – identical to a pristine as-received sample surface. Additionally, we discover a different oxidation behavior of In and Ga, in agreement with thermodynamic reference data, and we find indications for the segregation and removal of copper selenide surface phases from the polycrystalline material.
Note: High-speed Z tip scanner with screw cantilever holding mechanism for atomic-resolution atomic force microscopy in liquid
Authors: Reza Akrami Seyed Mohammad , Miyata Kazuki , Asakawa Hitoshi , Fukuma Takeshi
Published: December 2014

High-speed atomic force microscopy has attracted much attention due to its unique capability of visualizing nanoscale dynamic processes at a solid/liquid interface. However, its usability and resolution have yet to be improved. As one of the solutions for this issue, here we present a design of a high-speed Z-tip scanner with screw holding mechanism. We perform detailed comparison between designs with different actuator size and screw arrangement by finite element analysis. Based on the design giving the best performance, we have developed a Z tip scanner and measured its performance. The measured frequency response of the scanner shows a flat response up to ∼10 kHz. This high frequency response allows us to achieve wideband tip-sample distance regulation. We demonstrate the applicability of the scanner to high-speed atomic-resolution imaging by visualizing atomic-scale calcite crystal dissolution process in water at 2 s/frame.
Studies and optimization of Pohang Light Source-II superconducting radio frequency system at stable top-up operation with beam current of 400 mA
Authors: Joo Youngdo , Yu Inha , Park Insoo , Chun Myunghwan , Lee Byung-Joon , Hwang Ilmoon , Ha Taekyun , Shin Seunghwan , Sohn Younguk
Published: December 2014

After three years of upgrading work, the Pohang Light Source-II (PLS-II) is now successfully operating. The final quantitative goal of PLS-II is a top-up user-service operation with beam current of 400 mA to be completed by the end of 2014. During the beam store test up to 400 mA in the storage ring (SR), it was observed that the vacuum pressure around the radio frequency (RF) window of the superconducting cavity rapidly increases over the interlock level limiting the availability of the maximum beam current storing. Although available beam current is enhanced by setting a higher RF accelerating voltage, it is better to keep the RF accelerating voltage as low as possible in the long time top-up operation. We investigated the cause of the window vacuum pressure increment by studying the changes in the electric field distribution at the superconducting cavity and waveguide according to the beam current. In our simulation, an equivalent physical modeling was developed using a finite-difference time-domain code. The simulation revealed that the electric field amplitude at the RF window is exponentially increased as the beam current increases, thus this high electric field amplitude causes a RF breakdown at the RF window, which comes with the rapid increase of window vacuum pressure. The RF accelerating voltage of PLS-II RF system was set to 4.95 MV, which was estimated using the maximum available beam current that works as a function of RF voltage, and the top-up operation test with the beam current of 400 mA was successfully carried out.
Statistical analysis and modeling of intermittent transport events in the tokamak scrape-off layer
Authors: Anderson Johan , Halpern Federico D. , Xanthopoulos Pavlos , Ricci Paolo , Furno Ivo
Published: December 2014

The turbulence observed in the scrape-off-layer of a tokamak is often characterized by intermittent events of bursty nature, a feature which raises concerns about the prediction of heat loads on the physical boundaries of the device. It appears thus necessary to delve into the statistical properties of turbulent physical fields such as density, electrostatic potential, and temperature, focusing on the mathematical expression of tails of the probability distribution functions. The method followed here is to generate statistical information from time-traces of the plasma density stemming from Braginskii-type fluid simulations and check this against a first-principles theoretical model. The analysis of the numerical simulations indicates that the probability distribution function of the intermittent process contains strong exponential tails, as predicted by the analytical theory.
Electron heating during magnetic reconnection: A simulation scaling study
Authors: Shay M. A. , Haggerty C. C. , Phan T. D. , Drake J. F. , Cassak P. A. , Wu P. , Oieroset M. , Swisdak M. , Malakit K.
Published: December 2014

Electron bulk heating during magnetic reconnection with symmetric inflow conditions is examined using kinetic particle-in-cell simulations. Inflowing plasma parameters are varied over a wide range of conditions, and the increase in electron temperature is measured in the exhaust well downstream of the x-line. The degree of electron heating is well correlated with the inflowing Alfvén speed cAr based on the reconnecting magnetic field through the relation ΔTe=0.033 mi cAr2, where ΔTe is the increase in electron temperature. For the range of simulations performed, the heating shows almost no correlation with inflow total temperature Ttot=Ti+Te or plasma β. An out-of-plane (guide) magnetic field of similar magnitude to the reconnecting field does not affect the total heating, but it does quench perpendicular heating, with almost all heating being in the parallel direction. These results are qualitatively consistent with a recent statistical survey of electron heating in the dayside magnetopause (Phan et al., Geophys. Res. Lett. 40, 4475, 2013), which also found that ΔTe was proportional to the inflowing Alfvén speed. The net electron heating varies very little with distance downstream of the x-line. The simulations show at most a very weak dependence of electron heating on the ion to electron mass ratio. In the antiparallel reconnection case, the largely parallel heating is eventually isotropized downstream due a scattering mechanism, such as stochastic particle motion or instabilities. The simulation size is large enough to be directly relevant to reconnection in the Earth's magnetosphere, and the present findings may prove to be universal in nature with applications to the solar wind, the solar corona, and other astrophysical plasmas. The study highlights key properties that must be satisfied by an electron heating mechanism: (1) preferential heating in the parallel direction; (2) heating proportional to mi cAr2; (3) at most a weak dependence on electron mass; and (4) an exhaust electron temperature that varies little with distance from the x-line.
Defect properties of Sb- and Bi-doped CuInSe2: The effect of the deep lone-pair s states
Authors: Park Ji-Sang , Yang Ji-Hui , Ramanathan Kannan , Wei Su-Huai
Published: December 2014

Bi or Sb doping has been used to make better material properties of polycrystalline Cu2(In,Ga)Se2 as solar cell absorbers, including the experimentally observed improved electrical properties. However, the mechanism is still not clear. Using first-principles method, we investigate the stability and electronic structure of Bi- and Sb-related defects in CuInSe2 and study their effects on the doping efficiency. Contrary to previous thinking that Bi or Sb substituted on the anion site, we find that under anion-rich conditions, the impurities can substitute on cation sites and are isovalent to In because of the formation of the impurity lone pair s states. When the impurities substitute for Cu, the defects act as shallow double donors and help remove the deep InCu level, thus resulting in the improved carrier life time. On the other hand, under anion-poor conditions, impurities at the Se site create amphoteric deep levels that are detrimental to the device performance.
Resonant cavity mode enabled wireless power transfer
Authors: Chabalko Matthew J. , Sample Alanson P.
Published: December 2014

This letter proposes using the electromagnetic resonant modes of a hollow metallic structure to provide wireless power to small receivers contained anywhere inside. The coupling between a large chamber (used as a cavity resonator) and a small wire loop (used as a receiver) is studied. An analytic expression for the coupling coefficient between the fields in the cavity and a loop receiver is derived. This model is validated against simulation and experimental results. Finally, wireless power transfer is demonstrated at an efficiency of over 60% for large volumes in the structure, even though the receiver is a small 7.6 cm square shaped loop and the distance to the source probe is greater than 1 m. This technique for wireless power transfer has thus far been unexplored, and the results here serve as a starting point for resonant cavity mode wireless power systems with many receivers having arbitrary locations and orientations.
Study on Zeeman-split spoof surface plasmon polaritons by use of spin-sensitive enhanced electromagnetic transmission
Authors: Wu Li-Ting , Guo Rui-Peng , Guo Tian-Jing , Yang Mu , Cui Hai-Xu , Cao Xue-Wei , Chen Jing
Published: December 2014

Structured metal surfaces could support spoof surface plasmon polaritons (SPPs), the dispersion of which is determined by the cutoff condition of guided modes in the nanostructures. We show that we can achieve split spoof SPPs by breaking the degeneracy of guided helical modes in concentric nanostructures via the classic analogue of the Zeeman effect. This split effect is shown to be observable from the spectra of enhanced electromagnetic transmission. Spin-sensitive enhanced electromagnetic transmission and the associated characteristics of field are investigated. Transmission branches versus parallel wavevector can be satisfactorily fitted by using the dispersion of spoof SPPs.
Low power ovonic threshold switching characteristics of thin GeTe6 films using conductive atomic force microscopy
Authors: Manivannan Anbarasu , Myana Santosh Kumar , Miriyala Kumaraswamy , Sahu Smriti , Ramadurai Ranjith
Published: December 2014

Minimizing the dimensions of the electrode could directly impact the energy-efficient threshold switching and programming characteristics of phase change memory devices. A ∼12–15 nm AFM probe-tip was employed as one of the electrodes for a systematic study of threshold switching of as-deposited amorphous GeTe6 thin films. This configuration enables low power threshold switching with an extremely low steady state current in the on state of 6–8 nA. Analysis of over 48 different probe locations on the sample reveals a stable Ovonic threshold switching behavior at threshold voltage, VTH of 2.4 ± 0.5 V and the off state was retained below a holding voltage, VH of 0.6 ± 0.1 V. All these probe locations exhibit repeatable on-off transitions for more than 175 pulses at each location. Furthermore, by utilizing longer biasing voltages while scanning, a plausible nano-scale control over the phase change behavior from as-deposited amorphous to crystalline phase was studied.
Efficient excitation of guided acoustic waves in semiconductor nanorods through external metallic acoustic transducer
Authors: Yang Szu-Chi , Wu Yueh-Chun , Mante Pierre-Adrien , Chen Chien-Cheng , Chen Hung-Pin , Chou Hsiang-Yu , Shih Min-Hsiung , Sun Chi-Kuang
Published: December 2014

We demonstrate that guided acoustic waves inside a nanorod can be excited through an external metallic acoustic transducer. By attaching gold nanodisks on top of GaAs nanorods, the femtosecond optical excitation on the external acoustic transducer enables the generation of guided acoustic waves in the rods. The propagation behavior and mode shape of the observed guided acoustic waves are analyzed. These observations would not only lead to the development of superior external transducers for acoustic imaging, but also provide an experimental system for the study of the acoustic phonon transport behavior in nanorods and nanowires.
Effects of light illumination on electron velocity of AlGaN/GaN heterostructures under high electric field
Authors: Guo Lei , Yang Xuelin , Feng Zhihong , Lv Yuanjie , Cheng Jianpeng , Sang Ling , Xu Fujun , Tang Ning , Wang Xinqiang , Ge Weikun , Shen B.
Published: December 2014

We have investigated the variation of electron velocity in AlGaN/GaN heterostructures depending on illuminating light intensity and wavelength. It is shown that the electron velocity at high electric field increases under above-band light illumination. This electron velocity enhancement is found to be related to the photo-generated cold holes which interact with hot electrons and thus accelerate the energy relaxation at high electric field. The results suggest an alternative way to improve the electron energy relaxation rate and hence the electron velocity in GaN based heterostructures.
Structural observation of piezoelectric inhomogeneity in a mixed-orientation Na0.5Bi0.5TiO3 perovskite thin film
Authors: Carbone D. , Pateras A. I. , Bussone G. , Evans P. G. , Cornelius T. W. , Bousquet M. , Boulle A. , Gautier B. , Duclère J. R.
Published: December 2014

Thin films of the lead-free ferroelectric Na0.5Bi0.5TiO3 grown on thin-film Pt electrodes supported by SrTiO3 substrates have a complex microstructure consisting of crystalline grains with three distinct major crystallographic orientations. The piezoelectric response measured in spatially separated sub-micron grains using time-resolved synchrotron x-ray microdiffraction is highly inhomogeneous even among grains sharing the same major orientation. The piezoelectric coefficient d33 varies by nearly a factor of two in a series of areas sharing the 〈001〉 orientation. The piezoelectric inhomogeneity is linked to the peculiar microstructure of the film, arising from local variations in the stress imposed by surrounding grains with different crystallographic orientations and differing directions of the ferroelectric remnant polarization. A systematic nonlinearity of the piezoelectric strain is observed in applied electric fields with small magnitudes in all regions, consistent with the coexistence of domains of differing polarization direction at zero applied electric field.
Terbium gallium garnet ceramic-based Faraday isolator with compensation of thermally induced depolarization for high-energy pulsed lasers with kilowatt average power
Authors: Yasuhara Ryo , Snetkov Ilya , Starobor Alexey , Palashov Oleg
Published: December 2014

A scalable aperture Faraday isolator for high-energy pulsed lasers with kW-level average power was demonstrated using terbium gallium garnet ceramics with water cooling and compensation of thermally induced depolarization in a magnetic field. An isolation ratio of 35 dB (depolarization ratio γ of 3.4 × 10−4) was experimentally observed at a maximum laser power of 740 W. By using this result, we estimated that this isolator maintains an isolation ratio of 30 dB for laser powers of up to 2.7 kW. Our results provide the solution for achieving optical isolation in high-energy (100 J to kJ) laser systems with a repetition rate greater than 10 Hz.
Heat-driven spin transport in a ferromagnetic metal
Authors: Xu Yadong , Yang Bowen , Tang Chi , Jiang Zilong , Schneider Michael , Whig Renu , Shi Jing
Published: December 2014

As a non-magnetic heavy metal is attached to a ferromagnet, a vertically flowing heat-driven spin current is converted to a transverse electric voltage, which is known as the longitudinal spin Seebeck effect (SSE). If the ferromagnet is a metal, this voltage is also accompanied by voltages from two other sources, i.e., the anomalous Nernst effect in both the ferromagnet and the proximity-induced ferromagnetic boundary layer. By properly identifying and carefully separating those different effects, we find that in this pure spin current circuit the additional spin current drawn by the heavy metal generates another significant voltage by the ferromagnetic metal itself which should be present in all relevant experiments.
Encapsulated high frequency (235 kHz), high-Q (100 k) disk resonator gyroscope with electrostatic parametric pump
Authors: Ahn C. H. , Nitzan S. , Ng E. J. , Hong V. A. , Yang Y. , Kimbrell T. , Horsley D. A. , Kenny T. W.
Published: December 2014

In this paper, we explore the effects of electrostatic parametric amplification on a high quality factor (Q > 100 000) encapsulated disk resonator gyroscope (DRG), fabricated in 〈100〉 silicon. The DRG was operated in the n = 2 degenerate wineglass mode at 235 kHz, and electrostatically tuned so that the frequency split between the two degenerate modes was less than 100 mHz. A parametric pump at twice the resonant frequency is applied to the sense axis of the DRG, resulting in a maximum scale factor of 156.6 μV/(°/s), an 8.8× improvement over the non-amplified performance. When operated with a parametric gain of 5.4, a minimum angle random walk of 0.034°/√h and bias instability of 1.15°/h are achieved, representing an improvement by a factor of 4.3× and 1.5×, respectively.
Energy harvesting with stacked dielectric elastomer transducers: Nonlinear theory, optimization, and linearized scaling law
Authors: Tutcuoglu A. , Majidi C.
Published: December 2014

Using principles of damped harmonic oscillation with continuous media, we examine electrostatic energy harvesting with a “soft-matter” array of dielectric elastomer (DE) transducers. The array is composed of infinitely thin and deformable electrodes separated by layers of insulating elastomer. During vibration, it deforms longitudinally, resulting in a change in the capacitance and electrical enthalpy of the charged electrodes. Depending on the phase of electrostatic loading, the DE array can function as either an actuator that amplifies small vibrations or a generator that converts these external excitations into electrical power. Both cases are addressed with a comprehensive theory that accounts for the influence of viscoelasticity, dielectric breakdown, and electromechanical coupling induced by Maxwell stress. In the case of a linearized Kelvin-Voigt model of the dielectric, we obtain a closed-form estimate for the electrical power output and a scaling law for DE generator design. For the complete nonlinear model, we obtain the optimal electrostatic voltage input for maximum electrical power output.
Impact of rumen emptying on rumen fermentation and animal welfare in cannulated sheep
Authors: Silberberg M. , Boissy A. , Rira M. , Delval E. , Chandèze H. , Doreau M.
Published: December 2014

Emptying the rumen of animals fitted with rumen cannulas is a regularly used experimental technique. This study in sheep aimed to evaluate whether total rumen emptying (TRE) results in disturbances in digestive parameters such as rumen pH, fermentation and microbial ecosystem, and whether it affects animal welfare. Eight adult wethers from two breeds offered hay and water ad libitum were rumen-emptied manually. Ruminal parameters were assessed 2 days before and 7 days after TRE. Welfare was assessed by measuring behavioural and cardiac responses to TRE involving human handling. Behavioural and cardiac measurements were performed (i) 2 h before, (ii) during and (iii) 2 h after the rumen emptying–filling session on wethers exposed to the same TRE operator. Results showed that TRE did not affect most of the digestive parameters analysed (ruminal pH, bacteria, methanogens) but did modify Dasytricha population and volatile fatty acid concentrations. Likewise, rumen emptying did not alter most behavioural and cardiac parameters, and we found no TRE-related change in fear reactions to the operator.