bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure of a class III engineered cephalosporin acylase: comparisons with class I acylase and implications for differences in substrate specificity and catalytic activity
Authors: Golden Emily , Paterson Rachel , Tie Wan Jun , Anandan Anandhi , Flematti Gavin , Molla Gianluca , Rosini Elena , Pollegioni Loredano , Vrielink Alice
Published: February 2013

The crystal structure of the wild-type form of glutaryl-7-ACA (7-aminocephalosporanic acid) acylase from Pseudomonas N176 and a double mutant of the protein (H57βS/H70βS) that displays enhanced catalytic efficiency on cephalosporin C over glutaryl-7-aminocephalosporanic acid has been determined. The structures show a heterodimer made up of an α-chain (229 residues) and a β-chain (543 residues) with a deep cavity, which constitutes the active site. Comparison of the wild-type and mutant structures provides insights into the molecular reasons for the observed enhanced specificity on cephalosporin C over glutaryl-7-aminocephalosporanic acid and offers the basis to evolve a further improved enzyme variant. The nucleophilic catalytic serine residue, Ser1β, is situated at the base of the active site cavity. The electron density reveals a ligand covalently bound to the catalytic serine residue, such that a tetrahedral adduct is formed. This is proposed to mimic the transition state of the enzyme for both the maturation step and the catalysis of the substrates. A view of the transition state configuration of the enzyme provides important insights into the mechanism of substrate binding and catalysis.
Outsiders: An Exploratory History of IS in Corporations
Authors: Gannon Brian
Published: February 2013

This paper is an exploratory study that provides a brief history of information systems (IS) in corporations that are not part of the Information Technology sector, such as retailers, banks, government agencies and so on. It looks at the development of the IS function and the changing roles of IS practitioners in such organisations over the past 60 years, and assesses how they perceived themselves and were perceived by their peers, by business colleagues and by others. It uses the testimony of successful IS practitioners to provide a grounded perspective on the history of the IS worker over this time. The research identifies a trajectory of a gradual diminishment in the role and status of the IS worker in the corporation over the lifetime of the discipline. It observes that the IS worker has experienced changed fortunes: from a position of influence at the outset, leading to a peak of status and reward in the years up to the millennium; and to the present day where the occupation has a much lower profile. It ascribes this to the increasing commoditisation of IS, manifested by phenomena such as end-user computing, outsourcing and cloud computing. The paper is of relevance to academics who are interested in IS in the corporate organisation; to business professionals, who are sometimes bewildered by their IS colleagues; and to those who work in IS. The research is presented as an interpretative study and is intended to help future researchers frame questions and design research projects. It also aims to inform and witness, and provide a perspective on a currently neglected part of the business world.
Differential scanning calorimetric determination of the thermal properties of amorphous Co60Fe20B20 and Co40Fe40B20 thin films
Authors: Chen Yuan-Tsung , Lin S. H. , Hsieh W. H.
Published: February 2013

The thermal stability of Co60Fe20B20 and Co40Fe40B20 thin films are investigated by non-isothermal and isothermal thermal analysis. The differential scanning calorimetry results of amorphous Co60Fe20B20 and Co40Fe40B20 thin films showed the crucial glass forming ability index, γ and γm. The Kissinger formula was applied to calculate the activation energy (Q) of crystallization to measure its resistance of crystallization; 3000 Å was a critical thickness. Based on the non-isothermal and isothermal thermal analysis, it reveals that the thermal stability and incubation time of Co60Fe20B20 films are better than Co40Fe40B20 films.
Scattering due to large cluster embedded in quantum wells
Authors: Liu Changbo , Zhao Guijuan , Liu Guipeng , Song Yafeng , Zhang Heng , Jin Dongdong , Li Zhiwei , Liu Xianglin , Yang Shaoyan , Zhu Qinsheng , Wang Zhanguo
Published: February 2013

Two dimensional electron gas mobility limited by the scattering of large cluster is studied. From this study, we find that the scattering caused by conduction band offset between host well and multiple mini-quantum well (mini-QW) series aligned along the QW channel, i.e., quantum pits, can be treated as a variable in our calculation. The results show that the mobility increases with increasing barrier height, which is opposite to the well-known interface roughness scattering mobility. To make the calculation simple, the InxGa1−xN/InyGa1−yN QW double-heterostructure is selected to along (112¯0) non-polarized direction, along which the barrier and well are both flat.
Determination of the charge neutrality level of poly(3-hexylthiophene)
Authors: Wang Wenfeng , Alsmeier Jan H. , Wolak Matthäus , Schlaf Rudy
Published: February 2013

The Al/poly(3-hexylthiophene) (P3HT) and Ag/P3HT interfaces were investigated using photoemission spectroscopy in combination with in situ thin-film deposition. The P3HT thin films were deposited directly into high vacuum from solution on the two metal substrates using an electrospray system and characterized via photoemission spectroscopy. The electronic structure and charge injection barriers at these interfaces were determined from the evaluation of the resulting spectra sequences. A linear correlation between barrier heights and substrate work functions was observed from the collected data in combination with previously published results, suggesting that the “Induced Density of Interfaces States” model for small molecular materials is also valid for conjugated polymer interfaces. The corresponding P3HT “screening factor” as well as its charge neutrality level was determined to be 0.48 and 3.44 eV, respectively.
Carrier dynamics and photoluminescence quenching mechanism of strained InGaSb/AlGaSb quantum wells
Authors: Jahan Nahid A. , Hermannstädter Claus , Sasakura Hirotaka , Rotter Thomas J. , Ahirwar Pankaj , Balakrishnan Ganesh , Kumano Hidekazu , Suemune Ikuo
Published: February 2013

GaSb based quantum wells (QWs) show promising optical properties in near-infrared spectral range. In this paper, we present photoluminescence (PL) spectroscopies of InxGa1−xSb/AlyGa1−ySb QWs and discuss the possible thermal quenching and non-radiative carrier recombination mechanisms of the QW structures. The In and Al concentrations as well as the QW thicknesses were precisely determined with the X-ray diffraction measurements. Temperature dependent time-integrated and time-resolved PL spectroscopies resulted in the thermal activation energies of ∼45 meV, and the overall self-consistent calculation of the band parameters based on the measured physical values confirmed that the activation energies are due to the hole escape from the QW to the barriers. The relation of the present single carrier escape mechanism with the other escape mechanisms reported with other material systems was discussed based on the estimated band offset. The relation of the present thermal hole escape to the Auger recombination was also discussed.
General formulation for magnetohydrodynamic wave propagation, fire-hose, and mirror instabilities in Harris-type current sheets
Authors: Hau L.-N. , Lai Y.-T.
Published: February 2013

Harris-type current sheets with the magnetic field model of B⇀=Bx(z)x̂+By(z)ŷ have many important applications to space, astrophysical, and laboratory plasmas for which the temperature or pressure usually exhibits the gyrotropic form of p↔=p∥b̂b̂+p⊥(I↔−b̂b̂). Here, p∥ and p⊥ are, respectively, to be the pressure component along and perpendicular to the local magnetic field, b̂=B→/B. This study presents the general formulation for magnetohydrodynamic (MHD) wave propagation, fire-hose, and mirror instabilities in general Harris-type current sheets. The wave equations are expressed in terms of the four MHD characteristic speeds of fast, intermediate, slow, and cusp waves, and in the local (k∥,k⊥,z) coordinates. Here, k∥ and k⊥ are, respectively, to be the wave vector along and perpendicular to the local magnetic field. The parameter regimes for the existence of discrete and resonant modes are identified, which may become unstable at the local fire-hose and mirror instability thresholds. Numerical solutions for discrete eigenmodes are shown for stable and unstable cases. The results have important implications for the anomalous heating and stability of thin current sheets.
The orbital-specific virtual local triples correction: OSV-L(T)
Authors: Schütz Martin , Yang Jun , Chan Garnet Kin-Lic , Manby Frederick R. , Werner Hans-Joachim
Published: February 2013

A local method based on orbital specific virtuals (OSVs) for calculating the perturbative triples correction in local coupled cluster calculations is presented. In contrast to the previous approach based on projected atomic orbitals (PAOs), described by Schütz [J. Chem. Phys. 113, 9986 (2000)]10.1063/1.1323265, the new scheme works without any ad hoc truncations of the virtual space to domains. A single threshold defines the pair and triple specific virtual spaces completely and automatically. It is demonstrated that the computational cost of the method scales linearly with molecular size. Employing the recommended threshold a similar fraction of the correlation energy is recovered as with the original PAO method at a somewhat lower cost. A benchmark for 52 reactions demonstrates that for reaction energies the intrinsic accuracy of the coupled cluster with singles and doubles excitations and a perturbative treatment of triples excitations method can be reached by OSV-local coupled cluster theory with singles and doubles and perturbative triples, provided a MP2 correction is applied that accounts for basis set incompleteness errors as well as for remaining domain errors. As an application example the interaction energies of the guanine-cytosine dimers in the Watson-Crick and stacked arrangements are investigated at the level of local coupled cluster theory with singles and doubles and perturbative triples. Based on these calculations we propose new complete-basis-set-limit estimates for these interaction energies at this level of theory.
Bimetallic cages
Authors: Fournier René , Afzal-Hussain Sabeen
Published: February 2013

We report the results of density functional theory for 39 clusters AxBy (x + y = 10 or 12) where A and B are metals from group 1, 2, 11, 12, 13, or 14 of the periodic table. The chemical compositions were chosen to satisfy an electronic shell closing criterion. We performed an unbiased search for the global minimum (GM) by taboo search in descriptor space in each case. Eight of the 39 putative GM are cages even though none of the clusters contains gold, a metal with a well known propensity to form cages. These cages are large enough to accommodate a dopant atom with an atomic radius varying between 0.7 Å and 1.2 Å. The chemical compositions most likely to produce cages have an element of group 11 alloyed with an element of group 2, 12, or 13.
Synchrotron radiation-based far-infrared spectroscopic ellipsometer with full Mueller-matrix capability
Authors: Stanislavchuk T. N. , Kang T. D. , Rogers P. D. , Standard E. C. , Basistyy R. , Kotelyanskii A. M. , Nita G. , Zhou T. , Carr G. L. , Kotelyanskii M. , Sirenko A. A.
Published: February 2013

We developed far-IR spectroscopic ellipsometer at the U4IR beamline of the National Synchrotron Light Source in Brookhaven National Laboratory. This ellipsometer is able to measure both, rotating analyzer and full-Mueller matrix spectra using rotating retarders, and wire-grid linear polarizers. We utilize exceptional brightness of synchrotron radiation in the broad spectral range between about 20 and 4000 cm−1. Fourier-transform infrared (FT-IR) spectrometer is used for multi-wavelength data acquisition. The sample stage has temperature variation between 4.2 and 450 K, wide range of θ–2θ angular rotation, χ tilt angle adjustment, and X-Y-Z translation. A LabVIEW-based software controls the motors, sample temperature, and FT-IR spectrometer and also allows to run fully automated experiments with pre-programmed measurement schedules. Data analysis is based on Berreman's 4 × 4 propagation matrix formalism to calculate the Mueller matrix parameters of anisotropic samples with magnetic permeability μ ≠ 1. A nonlinear regression of the rotating analyzer ellipsometry and/or Mueller matrix (MM) spectra, which are usually acquired at variable angles of incidence and sample crystallographic orientations, allows extraction of dielectric constant and magnetic permeability tensors for bulk and thin-film samples. Applications of this ellipsometer setup for multiferroic and ferrimagnetic materials with μ ≠ 1 are illustrated with experimental results and simulations for TbMnO3 and Dy3Fe5O12 single crystals. We demonstrate how magnetic and electric dipoles, such as magnons and phonons, can be distinguished from a single MM measurement without adducing any modeling arguments. The parameters of magnetoelectric components of electromagnon excitations are determined using MM spectra of TbMnO3.
A micro gas chromatography column with a micro thermal conductivity detector for volatile organic compound analysis
Authors: Sun J. H. , Cui D. F. , Chen X. , Zhang L. L. , Cai H. Y. , Li H.
Published: February 2013

In this paper, a micro gas chromatography (μGC) system contained a μGC column and a micro thermal conductivity detector (μTCD) was proposed. In order to reduce the volume of the system, some micro heaters were integrated on the surface and backside of the GC column, which could provide a robust temperature programming capability and rapidly increase the temperature of the μGC column. In addition, a silicon-glass μTCD with four-thermistor thermal conductivity cells that can offer significant advantages over previously reported designs including low dead volume, good thermal isolation, and elimination of the thermal noise was proposed in this paper. Experimental results have indicated that the μGC system with a detection limit of several ppm concentration levels separated and detected the benzene, toluene, and styrene in less than 3 min, and the μGC system also exhibited a good linear response in the test range.
Symmetry classification of variable coefficient cubic-quintic nonlinear Schrödinger equations
Authors: Özemir C. , Güngör F.
Published: February 2013

A Lie-algebraic classification of the variable coefficient cubic-quintic nonlinear Schrödinger equations involving 5 arbitrary functions of space and time is performed under the action of equivalence transformations. It is shown that the symmetry group can be at most four-dimensional in the case of genuine cubic-quintic nonlinearity. It may be five-dimensional (isomorphic to the Galilei similitude algebra \documentclass[12pt]{minimal}\begin{document}$\operatorname{\mathfrak {gs}}(1)$\end{document}gs(1)) when the equation is of cubic type, and six-dimensional (isomorphic to the Schrödinger algebra \documentclass[12pt]{minimal}\begin{document}$\mathfrak {sch}(1)$\end{document}sch(1)) when it is of quintic type.
Combined effects of gas pressure and exciting frequency on electron energy distribution functions in hydrogen capacitively coupled plasmas
Authors: Abdel-Fattah E. , Sugai H.
Published: February 2013

The combined effects of the variation of hydrogen pressure (40–400 mTorr) and exciting frequency (13.56–50 MHz) on the electron energy probability function (EEPF) and other plasma parameters in capacitively coupled hydrogen H2 discharge at fixed discharge voltage were investigated using rf-compensated Langmuir probe. At a fixed exciting frequency of 13.56 MHz, the EEPF evolved from Maxwellian-like distribution to a bi-Maxwellian distribution when the H2 pressure increased, possibly due to efficient vibrational excitation. The electron density largely increased to a peak value and then decreased with the increase of H2 pressure. Meanwhile, the electron temperature and plasma potential significantly decrease and reaching a minimum at 120 mTorr beyond, which saturated or slightly increases. On the other hand, the dissipated power and electron density markedly increased with increasing the exciting frequency at fixed H2 pressure and voltage. The electron temperatures negligibly dependent on the driving frequency. The EEPFs at low pressure 60 mTorr resemble Maxwellian-like distribution and evolve into a bi-Maxwellian type as frequency increased, due to a collisonless (stochastic) sheath-heating in the very high frequency regime, while the EEPF at hydrogen pressure ≥120 mTorr retained a bi-Maxwellian-type distribution irrespective of the driving frequency. Such evolution of the EEPFs shape with the driving frequency and hydrogen pressure has been discussed on the basis of electron diffusion processes and low threshold-energy inelastic collision processes taking place in the discharge. The ratio of stochastic power to bulk power heating ratio is dependent on the hydrogen pressure while it is independent on the driving frequency.
Design and performance evaluation of polyvinyl alcohol/polyimide coated optical fibre grating-based humidity sensors
Authors: Alwis L. , Sun T. , Grattan K. T. V.
Published: February 2013

Optical fibre grating based sensors make a significant contribution to relative humidity measurement for various applications and a number of different designs and sensor configurations have been produced and discussed in the literature. Recent developments have included using sensitive polymers and indeed other materials that experience a variation of their physical and optical properties as a result of the absorption of moisture and which thus creates a modification of the characteristic spectral features of the gratings used. The strain and the effective refractive index of the gratings are affected by the change induced by the polymer and these effects were calibrated against the relative humidity variations that initially induce variations in the polymer layer. In this work, an evaluation is made of the performance characteristics of two different moisture sensitive polymers, i.e., polyimide and polyvinyl alcohol, as the basis of such sensors, while at the same time using different types of fibre gratings i.e., fibre Bragg gratings and long period gratings. Their performance is discussed in light of the operation of similar types of polymer-coated and other grating based sensors reported in the literature.
Full-field transmission x-ray imaging with confocal polycapillary x-ray optics
Authors: Sun Tianxi , MacDonald C. A.
Published: February 2013

A transmission x-ray imaging setup based on a confocal combination of a polycapillary focusing x-ray optic followed by a polycapillary collimating x-ray optic was designed and demonstrated to have good resolution, better than the unmagnified pixel size and unlimited by the x-ray tube spot size. This imaging setup has potential application in x-ray imaging for small samples, for example, for histology specimens.
Nonlinear susceptibility and dynamic hysteresis loops of magnetic nanoparticles with biaxial anisotropy
Authors: Ouari Bachir , Titov Serguey V. , El Mrabti Halim , Kalmykov Yuri P.
Published: February 2013

The nonlinear ac susceptibility and dynamic magnetic hysteresis (DMH) of a single domain ferromagnetic particle with biaxial anisotropy subjected to both external ac and dc fields of arbitrary strength and orientation are treated via Brown's continuous diffusions model [W. F. Brown, Jr., Phys. Rev. 130, 1677 (1963)] of magnetization orientations. The DMH loops and nonlinear ac susceptibility strongly depend on the dc and ac field strengths, the polar angle between the easy axis of the particle, the external field vectors, temperature, and damping. In contrast to uniaxial particles, the nonlinear ac stationary response and DMH strongly depend on the azimuthal direction of the ac field and the biaxiality parameter Δ.
Comparison for non-local hydrodynamic thermal conduction models
Authors: Marocchino A. , Tzoufras M. , Atzeni S. , Schiavi A. , Nicolaï Ph. D. , Mallet J. , Tikhonchuk V. , Feugeas J.-L.
Published: February 2013

Inertial confinement fusion and specifically shock ignition involve temperatures and temperature gradients for which the classical Spitzer-Härm thermal conduction breaks down and a non-local operator is required. In this article, two non-local electron thermal conduction models are tested against kinetic Vlasov-Fokker-Planck simulations. Both models are shown to reproduce the main features of thermal heat front propagation at kinetic timescales. The reduction of the thermal conductivity as a function of the scalelength of the temperature gradient is also recovered. Comparisons at nanosecond timescales show that the models agree on the propagation velocity of the heat front, but major differences appear in the thermal precursor.
Binding energy levels of a slowly moving ion in dusty plasmas
Authors: Hu Hongwei , Li Fuli
Published: February 2013

The near field electric potential of a slowly moving ion in complex plasmas is studied. We find that the potential consists of the Debye-Hückel potential, the wake potential, and the potential associated with charge fluctuations. The binding energy levels of the ion are calculated by use of the Ritz variation method. The results show that the binding energy levels are related to the magnetic quantum number m. The binding energy levels are affected by speed of the ion and dust grain number density. In contract to isolated ion or static ion in plasmas, the binding energy levels of the ion are pushed up and even become unbounded.
Enhancement of the performance of InAs quantum dots solar cell by surface modification using Poly-L-Lysine homopolymers
Authors: Makableh Y. F. , Vasan R. , Lee S. , Manasreh O. M.
Published: February 2013

The enhancement of InAs quantum dots solar cell was reported for surface modification by implementing Poly-L-Lysine (PLL) homopolymers as an anti-reflection coating. Dip coating method was used to coat the solar cell surface with PLL. The current-voltage, spectral response, and external quantum efficiency measurements were performed to characterize the solar cell. Furthermore, the transmission spectra of GaAs were obtained before and after PLL coating. At least 25% increase in the performance of the InAs quantum dots solar cell was achieved as depicted in the current voltage, external quantum efficiency, and spectral response measurements.
Longitudinal instability of a liquid rim
Authors: Agbaglah Gilou , Josserand Christophe , Zaleski Stéphane
Published: February 2013

We study the transverse instability of a retracting liquid rim using a long wavelength approximation model and full numerical simulations. We observe that the instability of the rim is driven both by the Rayleigh-Taylor mechanism because of the initial rim acceleration, and by the Rayleigh-Plateau one. The coupling between the rim and the sheet stabilizes the rim at long wavelength. Full numerical simulations are in good agreement with the model and the subsequent break-up of droplets is observed in the numerical simulations when the instability is strong enough.
Reconfigurable ground states in connected double-dot system
Authors: Jain S. , Fradin F. Y. , Pearson J. E. , Novosad V. , Bader S. D.
Published: February 2013

Controlling the polarity of a vortex core in patterned magnetic arrays of double-dot systems was recently shown via a nonlinear spin dynamics manipulation procedure. In the present work, we utilize the microwave absorption amplitude to monitor this polarity switching transition as the excitation field is increased from the linear to nonlinear regime and back. A representative phase diagram is constructed for the two coupled-modes of the double dot system as a function of excitation frequency and amplitude.
Influence of nanoscale geometry on the dynamics of wicking into a rough surface
Authors: Quan Lai Chang , Thi Mai Trong , Zheng H. , Lee P. S. , Leong K. C. , Lee Chengkuo , Choi W. K.
Published: February 2013

The dynamics of imbibition into the roughness of a surface was investigated with hexagonal arrays of anisotropic nanofins fabricated with interference lithography and metal assisted chemical etching. It was found that viscous drag caused by the nanofins is similar to that caused by open nano-channels of equal length and height containing the same volume of liquid. In addition, the energy dissipated by form drag for a given driving pressure was determined to be directly proportional to the volume of fluid between nanofin planes that are flat and normal to the imbibition direction.
Direct and quantitative broadband absorptance spectroscopy on small objects using Fourier transform infrared spectrometer and bilayer cantilever probes
Authors: Hsu Wei-Chun , Tong Jonathan K. , Liao Bolin , Burg Brian R. , Chen Gang
Published: February 2013

A measurement platform is introduced that combines a bilayer cantilever probe with a Fourier transform infrared spectrometer to measure absolute spectral absorptance between wavelengths of 3 μm and 18 μm directly and quantitatively. The enhanced sensitivity provided by the cantilever probe enables the quantitative characterization of micro- and nanometer-sized samples. Validation of the technique is carried out by measuring the absorptance spectrum of a doped silicon thin film with a backside aluminum layer and found to agree well with the theoretical predictions. The presented technique is especially attractive for samples such as individual nanowires or nanoparticles, isolated molecules, powders, and photonic structures.
Elucidation of ambient gas effects in organic nano-floating-gate nonvolatile memory
Authors: She Xiao-Jian , Liu Chang-Hai , Zhang Jing-Yu , Gao Xu , Wang Sui-Dong
Published: February 2013

Pentacene-based organic field-effect transistor nonvolatile memories employing nano-floating-gate show high performance in vacuum, typically with field-effect mobility of 0.6 cm2/Vs, memory window of 45 V, reading ON/OFF ratio over 106, and excellent retention ability and programming/erasing endurance. The memory performance is unstable in air, which is demonstrated to result mainly from the device operation instability in O2. The O2-induced acceptor-like trap states reduce the electron supply in pentacene during programming, limiting the electron trapping into the nano-floating-gate and thus suppressing the positive threshold voltage shift. The corresponding hole trapping during erasing is not effectively influenced by the ambient gas effects.
Measurement of 10 zJ energy dissipation of adiabatic quantum-flux-parametron logic using a superconducting resonator
Authors: Takeuchi N. , Yamanashi Y. , Yoshikawa N.
Published: February 2013

Adiabatic quantum-flux-parametron (AQFP) logic has the potential to operate with an ultimately small bit energy of several zeptojoules; however, this is too small to measure by conventional techniques. We measure such a small energy dissipation by coupling a superconducting resonator with an AQFP gate, where the insertion loss is sensitively varied with the small dissipation due to the very high Q factor of the resonator. We designed and implemented a 5 GHz superconducting resonator coupled with an AQFP gate. Measurement results show that the bit energy of the gate is ∼10 zJ at 5 GHz operation.
The growth of microcrystalline silicon oxide thin films studied by in situ plasma diagnostics
Authors: Kirner S. , Gabriel O. , Stannowski B. , Rech B. , Schlatmann R.
Published: February 2013

The crystallinity and refractive index of microcrystalline silicon oxide (μc-SiOx:H) n-layers and their dependence on the pressure and radio frequency power during the deposition process is correlated with plasma properties derived from in situ diagnostics. From process gas depletion measurements, the oxygen content of the layers was calculated. High crystallinities were observed for increased pressures and decreased powers, indicating clear differences to trends previously shown for microcrystalline silicon (μc-Si:H) material, which are explained by the varying oxygen incorporation. Amorphous/microcrystalline silicon (a-Si:H/μc-Si:H) tandem solar cells with μc-SiOx:H intermediate reflector layers deposited at optimized pressures showed greatly improved series resistances.
Femtosecond diffraction dynamics of laser-induced periodic surface structures on fused silica
Authors: Höhm S. , Rosenfeld A. , Krüger J. , Bonse J.
Published: February 2013

The formation of laser-induced periodic surface structures (LIPSS) on fused silica upon irradiation with linearly polarized fs-laser pulses (50 fs pulse duration, 800 nm center wavelength) is studied experimentally using a transillumination femtosecond time-resolved (0.1 ps-1 ns) pump-probe diffraction approach. This allows to reveal the generation dynamics of near-wavelength-sized LIPSS showing a transient diffraction at specific spatial frequencies even before a corresponding permanent surface relief was observed. The results confirm that the ultrafast energy deposition to the materials surface plays a key role and triggers subsequent physical mechanisms such as carrier scattering into self-trapped excitons.
Ultrafast modulation of near-field heat transfer with tunable metamaterials
Authors: Cui Longji , Huang Yong , Wang Ju , Zhu Ke-Yong
Published: February 2013

We propose a mechanism of active near-field heat transfer modulation relying on externally tunable metamaterials. A large modulation effect is observed and can be explained by the coupling of surface modes, which is dramatically varied in the presence of controllable magnetoelectric coupling in metamaterials. We finally discuss how a practical picosecond-scale thermal modulator can be made. This modulator allows manipulating nanoscale heat flux in an ultrafast and noncontact (by optical means) manner.
The source of the threading dislocation in GaSb/GaAs hetero-structures and their propagation mechanism
Authors: Wang Yi , Ruterana P. , Kret S. , El Kazzi S. , Desplanque L. , Wallart X.
Published: February 2013

The misfit and threading dislocations during GaSb epitaxy on GaAs substrate were investigated by weak beam dark field and high angle dark field scanning transmission electron microscopy. The geometric phase analysis and dislocation density tensor analysis were next used to analyze the strain around the threading dislocations and quantify the corresponding Burgers vectors. It is shown that there are three types of threading dislocations (mixed, edge, and pair of mixed types) close to the interface, which originate from the 60°, Lomer, and 60° pair misfit dislocations, respectively. During the growth of the epitaxial layer, the edge type as well as the pair of mixed threading dislocations split into two mixed type dislocations for the glide in {111} planes. Eventually, only mixed type dislocations have been observed at the surface of thick GaSb layers.
Fabrication and electrical transport properties of binary Co-Si nanostructures prepared by focused electron beam-induced deposition
Authors: Porrati F. , Kämpken B. , Terfort A. , Huth M.
Published: February 2013

CoSi-C binary alloys have been fabricated by focused electron beam-induced deposition by the simultaneous use of dicobaltoctacarbonyl, Co2(CO)8, and neopentasilane, Si5H12, as precursor gases. By varying the relative flux of the precursors, alloys with variable chemical composition are obtained, as shown by energy dispersive x-ray analysis. Room temperature electrical resistivity measurements strongly indicate the formation of cobalt silicide and cobalt disilicide nanoclusters embedded in a carbonaceous matrix. Temperature-dependent electrical conductivity measurements show that the transport properties are governed by electron tunneling between neighboring CoSi or CoSi2 nanoclusters. In particular, by varying the metal content of the alloy, the electrical conductivity can be finely tuned from the insulating regime into the quasi-metallic tunneling coupling regime.
Correlation between Ti source/drain contact and performance of InGaZnO-based thin film transistors
Authors: Choi Kwang-Hyuk , Kim Han-Ki
Published: February 2013

Ti contact properties and their electrical contribution to an amorphous InGaZnO (a-IGZO) semiconductor-based thin film transistor (TFT) were investigated in terms of chemical, structural, and electrical considerations. TFT device parameters were quantitatively studied by a transmission line method. By comparing various a-IGZO TFT parameters with those of different Ag and Ti source/drain electrodes, Ti S/D contact with an a-IGZO channel was found to lead to a negative shift in VT (−Δ 0.52 V). This resulted in higher saturation mobility (8.48 cm2/Vs) of a-IGZO TFTs due to effective interfacial reaction between Ti and an a-IGZO semiconducting layer. Based on transmission electron microcopy, x-ray photoelectron depth profile analyses, and numerical calculation of TFT parameters, we suggest a possible Ti contact mechanism on semiconducting a-IGZO channel layers for TFTs.
Microstructural defects in GaN thin films grown on chemically vapor-deposited graphene layers
Authors: Yoo Hyobin , Chung Kunook , In Park Suk , Kim Miyoung , Yi Gyu-Chul
Published: February 2013

Microstructural defects in GaN thin films grown on graphene produced via chemical vapor deposition have been investigated using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). EBSD analysis reveals the preferred orientations of the GaN films. We further examined the microstructural defects such as grain boundaries and threading dislocations present in the films using TEM. Plan-view TEM analysis showed presence of both high- and low-angle grain boundaries and the threading dislocations mostly bound to those grain boundaries. Moreover, the characteristics and behavior of the threading dislocations were also investigated using cross-section TEM analysis.
Communication: Transfer of more than half the population to a selected rovibrational state of H2 by Stark-induced adiabatic Raman passage
Authors: Mukherjee Nandini , Dong Wenrui , Harrison John A. , Zare Richard N.
Published: February 2013

By using Stark-induced adiabatic Raman passage (SARP) with partially overlapping nanosecond pump (532 nm) and Stokes (683 nm) laser pulses, 73% ± 6% of the initial ground vibrational state population of H2 (v = 0, J = 0) is transferred to the single vibrationally excited eigenstate (v = 1, J = 0). In contrast to other Stark chirped Raman adiabatic passage techniques, SARP transfers population from the initial ground state to a vibrationally excited target state of the ground electronic surface without using an intermediate vibronic resonance within an upper electronic state. Parallel linearly polarized, co-propagating pump and Stokes laser pulses of respective durations 6 ns and 4.5 ns, are combined with a relative delay of ∼4 ns before orthogonally intersecting the molecular beam of H2. The pump and Stokes laser pulses have fluences of ∼10 J/mm2 and ∼1 J/mm2, respectively. The intense pump pulse generates the necessary sweeping of the Raman resonance frequency by ac (second-order) Stark shifting the rovibrational levels. As the frequency of the v = 0 → v = 1 Raman transition is swept through resonance in the presence of the strong pump and the weaker delayed Stokes pulses, the population of (v = 0, J = 0) is coherently transferred via an adiabatic passage to (v = 1, J = 0). A quantitative measure of the population transferred to the target state is obtained from the depletion of the ground-state population using 2 + 1 resonance enhanced multiphoton ionization (REMPI) in a time-of-flight mass spectrometer. The depletion is measured by comparing the REMPI signal of (v = 0, J = 0) at Raman resonance with that obtained when the Stokes pulse is detuned from the Stark-shifted Raman resonance. No depletion is observed with either the pump or the Stokes pulses alone, confirming that the measured depletion is indeed caused by the SARP-induced population transfer from the ground to the target state and not by the loss of molecules from photoionization or photodissociation. The two-photon resonant UV pulse used for REMPI detection is delayed by 20 ns with respect to the pump pulse to avoid the ac Stark shift originating from the pump and Stokes laser pulses. This experiment demonstrates the feasibility of preparing a large ensemble of isolated molecules in a preselected single quantum state without requiring an intermediate vibronic resonance.
Radiative transfer and diffusion limits for wave field correlations in locally shifted random media
Authors: Ammari Habib , Bossy Emmanuel , Garnier Josselin , Jing Wenjia , Seppecher Laurent
Published: February 2013

The aim of this paper is to develop a mathematical framework for opto-elastography. In opto-elastography, a mechanical perturbation of the medium produces a decorrelation of optical speckle patterns due to the displacements of optical scatterers. To model this, we consider two optically random media, with the second medium obtained by shifting the first medium in some local region. We derive the radiative transfer equation for the cross-correlation of the wave fields in the media. Then we derive its diffusion approximation. In both the radiative transfer and the diffusion regimes, we relate the correlation of speckle patterns to the solutions of the radiative transfer and the diffusion equations. We present numerical simulations based on our model which are in agreement with recent experimental measurements.
Flexible, compressible, hydrophobic, floatable, and conductive carbon nanotube-polymer sponge
Authors: Han Jin-Woo , Kim Beomseok , Li Jing , Meyyappan M.
Published: February 2013

A flexible, compressible, hydrophobic, ice-repelling, floatable, and conductive carbon nanotube (CNT)-polydimethylsiloxane (PDMS) sponge is presented. The microporous sponge-like PDMS scaffold fabricated with a sugar cube template is capable of CNT uptake. The CNT-PDMS sponge (CPS) is deformable and compressible up to 90%. The Young's modulus varies from 22 KPa to 200 KPa depending on the applied strain. The conductive pathways via the CNT network increase with compressive strain similar to a variable resistor or pressure sensor. The softness of the CPS can be utilized for artificial skin to grip sensitive objects. In addition, the contact angle of water droplets on CPS shows 141°, and thus the hydrophobic nature of the CPS can be exploited as a floating electrode. Furthermore, the hydrophobicity is maintained below freezing temperature, allowing an ice-repelling electrode.
The equivalence of the Chern-Simons-Schrödinger equations and its self-dual system
Authors: Huh Hyungjin , Seok Jinmyoung
Published: February 2013

In this paper, we discuss the equivalence of the second order Chern-Simons-Schrödinger equations and its first order self-dual system.
Selective A- or B-site single termination on surfaces of layered oxide SrLaAlO4
Authors: Biswas A. , Rossen P. B. , Ravichandran J. , Chu Y.-H. , Lee Y.-W. , Yang C.-H. , Ramesh R. , Jeong Y. H.
Published: February 2013

We demonstrate that thermal annealing in cation controlled environments is an effective means to obtain atomically flat and chemically single terminated surfaces of a layer structured substrate. The effectiveness of the cation controlled annealing method is proved with SrLaAlO4, which is a representative layer structured substrate of A2BO4 type. Potassium ion scattering, in particular, shows that the method allows not only single termination but also selective termination of either A- or B-site on the substrate. We further demonstrate that the chemical nature of underlying SrLaAlO4 substrates is of critical importance in the growth of SrRuO3 thin films resulting in different morphologies and transport properties.
Orientation-dependent binding energy of graphene on palladium
Authors: Kappes Branden B. , Ebnonnasir Abbas , Kodambaka Suneel , Ciobanu Cristian V.
Published: February 2013

Using density functional theory calculations, we show that the binding strength of a graphene monolayer on Pd(111) can vary between physisorption and chemisorption depending on its orientation. By studying the interfacial charge transfer, we have identified a specific four-atom carbon cluster that is responsible for the local bonding of graphene to Pd(111). The areal density of such clusters varies with the in-plane orientation of graphene, causing the binding energy to change accordingly. Similar investigations can also apply to other metal substrates and suggests that physical, chemical, and mechanical properties of graphene may be controlled by changing its orientation.
Electrodynamic control of the nanofiber alignment during electrospinning
Authors: Grasl Christian , Arras Matthias M. L. , Stoiber Martin , Bergmeister Helga , Schima Heinrich
Published: February 2013

A technique is presented to electrospin straight and aligned fibers on a stationary featureless target. Two parallel rotatable plate-like auxiliary electrodes were applied with a time-varying square wave potential. Thereby, the electrospinning jet was periodically deflected between the electrodes, which led to an aligned fiber-deposition. Straight fibers were deposited at a potential difference of 11 kV and a switching frequency of 40 Hz between the auxiliary electrodes. With this setup, freely adjustable orientations can be achieved regardless of the targets design or its movement.
Photocurrent induced by two-photon excitation in ZnTeO intermediate band solar cells
Authors: Tanaka Tooru , Miyabara Masaki , Nagao Yasuhiro , Saito Katsuhiko , Guo Qixin , Nishio Mitsuhiro , Yu Kin M. , Walukiewicz Wladek
Published: February 2013

Intermediate band (IB) solar cell structures based on ZnTeO highly mismatched alloy were examined to demonstrate a photocurrent induced by a two-photon excitation (TPE) process. Two types of the devices, with and without a blocking layer for the IB, are prepared. The device with a blocked IB exhibits small external quantum efficiency (EQE) in photon energy range in which electron transitions from valence band (VB) to IB take place, implying the electron accumulation in IB. The enhancement of EQE is observed in TPE experiments as a result of electron transition from VB to conduction band via IB.
Negative spin-exchange splitting in the exciton fine structure of AlN
Authors: Feneberg Martin , Fátima Romero María , Neuschl Benjamin , Thonke Klaus , Röppischer Marcus , Cobet Christoph , Esser Norbert , Bickermann Matthias , Goldhahn Rüdiger
Published: February 2013

The exact energy position of the free exciton transition and thus the lowest band gap in bulk wurtzite AlN are still under discussion. By combined high resolution optical emission and absorption experiments on a sample with (11¯00) surface, we resolve the fine structure of the lowest energy free exciton and determine an electron-hole spin-exchange interaction constant of j=−4 meV. This results in a low energy Γ1 exciton at 6.032 eV and a high energy Γ5 component at 6.040 eV. Only the latter one is observable for (0001) oriented AlN films due to selection rules.
In situ observation of nickel as an oxidizable electrode material for the solid-electrolyte-based resistive random access memory
Authors: Sun Jun , Liu Qi , Xie Hongwei , Wu Xing , Xu Feng , Xu Tao , Long Shibing , Lv Hangbing , Li Yingtao , Sun Litao , Liu Ming
Published: February 2013

In this letter, we dynamically investigate the resistive switching characteristics and physical mechanism of the Ni/ZrO2/Pt device. The device shows stable bipolar resistive switching behaviors after forming process, which is similar to the Ag/ZrO2/Pt and Cu/ZrO2/Pt devices. Using in situ transmission electron microscopy, we observe in real time that several conductive filaments are formed across the ZrO2 layer between Ni and Pt electrodes after forming. Energy-dispersive X-ray spectroscopy results confirm that Ni is the main composition of the conductive filaments. The ON-state resistance increases with increasing temperature, exhibiting the feature of metallic conduction. In addition, the calculated resistance temperature coefficient is equal to that of the 10–30 nm diameter Ni nanowire, further indicating that the nanoscale Ni conductive bridge is the physical origin of the observed conductive filaments. The resistive switching characteristics and the conductive filament's component of Ni/ZrO2/Pt device are consistent with the characteristics of the typical solid-electrolyte-based resistive random access memory. Therefore, aside from Cu and Ag, Ni can also be used as an oxidizable electrode material for resistive random access memory applications.
Riverine flow and spawning requirements of Macquaria ambigua oriens: implications for conservation and management
Authors: Cockayne B. J. , McDougall A. J. , Espinoza T. , Burndred K. R. , Thrupp C. L. , Broadfoot C. D. , Finn M. A.
Published: February 2013

Understanding the life-history attributes of aquatic species is integral to the development of environmental-flow strategies in regulated river systems. This is particularly important when species are under continual and increasing pressure from water-resource development. In this study, the water temperature and flow requirements for spawning of the Fitzroy River golden perch (Macquaria ambigua oriens) were investigated over 4 years at 22 sites in the Fitzroy River catchment. Eggs, larvae and young-of-year (YOY) M. ambigua oriens were sampled on a variety of flow events to determine the environmental requirements for spawning. Eggs and larvae of M. ambigua oriens were detected during natural flow events generally with a minimum of 1.5 m river rise and duration of 7 days. Spawning was associated with the peak and/or recession of the first or second post-winter flow event where water temperatures exceeded 24°C. Our data suggests that it is important to protect a range of flows, not just flood flows, as previously documented for this species. The interaction of spawning flows with existing and future water-resource development should be considered to ensure maintenance of the population viability of M. ambigua oriens.
Crystal structure of aldoxime dehydratase and its catalytic mechanism involved in carbon-nitrogen triple-bond synthesis
Authors: Nomura Junpei , Hashimoto Hiroshi , Ohta Takehiro , Hashimoto Yoshiteru , Wada Koichi , Naruta Yoshinori , Oinuma Ken-Ichi , Kobayashi Michihiko
Published: February 2013

Aldoxime dehydratase (OxdA), which is a unique heme protein, catalyzes the dehydration of an aldoxime to a nitrile even in the presence of water in the reaction mixture. Unlike the utilization of H
2
O
2
or O
2
as a mediator of catalysis by other heme-containing enzymes (e.g., P450), OxdA is notable for the direct binding of a substrate to the heme iron. Here, we determined the crystal structure of OxdA. We then constructed OxdA mutants in which each of the polar amino acids lying within ∼6 Å of the iron atom of the heme was converted to alanine. Among the purified mutant OxdAs, S219A had completely lost and R178A exhibited a reduction in the activity. Together with this finding, the crystal structural analysis of OxdA and spectroscopic and electrostatic potential analyses of the wild-type and mutant OxdAs suggest that S219 plays a key role in the catalysis, forming a hydrogen bond with the substrate. Based on the spatial arrangement of the OxdA active site and the results of a series of mutagenesis experiments, we propose the detailed catalytic mechanism of general aldoxime dehydratases: (
i
) S219 stabilizes the hydroxy group of the substrate to increase its basicity; (
ii
) H320 acts as an acid-base catalyst; and (
iii
) R178 stabilizes the heme, and would donate a proton to and accept one from H320.