bluuebunny/crossref_metadata_2025 huggingface dataset:
Ormak nears collisionless regime
Authors: Rothenberg Marian S.
Published: December 2011

The Ormak experiment at Oak Ridge National Laboratory has advanced appreciably toward the so-called collisionless regime in studies that increase the expectation for reaching the “reactor regime” without damaging loss from instabilities. Plasma ions have travelled about five to ten times around the torus before scattering 90 deg, and no new anomalous effects were observed. The result gives increased confidence that no additional empirical components are needed to explain the scaling of ion temperature in this regime, that the same combination of the classical laws of atomic and plasma physics plus empiricism (pseudoclassical scaling) hold true here as in previous experiments. Ormak was able to reach a higher degree of collisionlessness, although the ion temperatures reached did not necessarily exceed temperatures reached in some other experiments, because of its fatdoughnut geometry. These results were described at the March meeting on toroidal plasma confinement in Garching, Germany.
High-energy physics horizons
Authors: Panofsky Wolfgang K. H.
Published: December 2011

A horizon is a boundary beyond which we cannot see. But one can speculate on what lies beyond it, and I shall try to do so for three aspects of high-energy physics: its technology, its need for support and planning, and—what makes the other two parts worth caring about—the prospects for significant new discoveries.
Interaction of a liquid flow around a micropillar with a gas jet
Authors: Elcock D. , Jung J. , Kuo C.-J. , Amitay M. , Peles Y.
Published: December 2011

An experimental study was conducted to investigate two-phase flow characteristics resulting from gas jet injection into a 225 μm high by 1500 μm wide microchannel. The jet was injected from a 25 μm wide slit on the downstream side of a 150 μm diameter pillar. The liquid Reynolds number (Re = ρUD/μ) based on pillar diameter ranged from 100 to 700, and the average gas momentum coefficient (ρjetUjetAjet/ρmainUmainAref), defined as the ratio of gas momentum to liquid momentum, ranged from 1.6 × 10−5 to 3.368 × 10−1. Flow visualization, micro particle image velocimetry (μPIV), and micro particle tracing velocimetry (μPTV) were used to elucidate the two-phase flow patterns, liquid velocity field, and bubble dynamics. Two modes of gas jets were observed in which bubbles either formed and detached at the pillar or formed an attached ligament that sheared bubbles from its trailing edge. The modes were determined to be primarily Reynolds number dependent. Both modes were observed to positively affect turbulent kinetic energy in the microchannel. The momentum coefficient of the gas jet had the most significant effect at low Reynolds numbers, when bubble formation took place at the pillar.
Nonlinear stability of the ideal magnetohydrodynamic interchange mode at marginal conditions in a transverse magnetic field
Authors: Bagaipo Jupiter , Guzdar P. N. , Hassam A. B.
Published: December 2011

The stability of the ideal magnetohydrodynamic (MHD) interchange mode at marginal conditions is studied. A sufficiently strong constant magnetic field component transverse to the direction of mode symmetry provides the marginality conditions. A systematic perturbation analysis in the smallness parameter, |b2/Bc|1/2, is carried out, where Bc is the critical transverse magnetic field for the zero-frequency ideal mode and b2 is the deviation from Bc. The calculation is carried out to third order including nonlinear terms. It is shown that the system is nonlinearly unstable in the short wavelength limit, i.e., a large enough perturbation results in instability even if b2/Bc > 0 (linearly stable). The normalized amplitude for instability is shown to scale as |b2/Bc|1/2. A nonlinear, compressible, MHD simulation is done to check the analytic result. Good agreement is found, including the critical amplitude scaling.
Doping profile of InP nanowires directly imaged by photoemission electron microscopy
Authors: Hjort M. , Wallentin J. , Timm R. , Zakharov A. A. , Andersen J. N. , Samuelson L. , Borgström M. T. , Mikkelsen A.
Published: December 2011

InP nanowires (NWs) with differently doped segments were studied with nanoscale resolution using synchrotron based photoemission electron microscopy. We clearly resolved axially stacked n-type and undoped segments of the NWs without the need of additional processing or contacting. The lengths and relative doping levels of different NW segments as well as space charge regions were determined indicating memory effects of sulfur during growth. The surface chemistry of the nanowires was monitored simultaneously, showing that in the present case, the doping contrast was independent of the presence or absence of a native oxide.
Impact of film thickness of organic semiconductor on off-state current of organic thin film transistors
Authors: Nurul Islam M.
Published: December 2011

Impact of film thickness on off-state current of bottom contact organic thin film transistor has been investigated using two dimensional numerical simulations and analytical model. Off-state current of the device reduces by six orders of magnitude as film thickness is scaled from 45 nm to 10 nm, with rate of reduction in off-state current being slow first and then significantly higher. An analytical model for off-state current has been developed to offer an insight into above results of off-state current, and the model predictions are found in good agreement with reported experimental results. The developed model is especially important for the device with smaller film thickness as at such film thicknesses, space charge limited current model is inadequate to explain off-state current of such devices. A horizon for scaling device channel length through a reduction in film thickness only has been explored using an analytical model and simulation results. Off-state current of a shorter channel length (L) device can be comparable to a relatively longer channel length (i.e., L + δL) device if the fractional reduction in film thickness becomes equal to square of the fractional reduction in channel length. Following such reduction in film thickness successively for a number of steps, an expression for film thickness corresponding to the device with a desired value of channel length has been developed and verified with simulation results. Although the device with larger film thickness has a problem of poor subthreshold performance, it, in general, has advantage of better mobility. To alleviate this problem of the device with larger film thickness, a stack contact device has been proposed. An investigation of its subthreshold performance shows that its off-state current can be significantly lower as compared to conventional contact device.
Coherent control of molecular torsion
Authors: Parker Shane M. , Ratner Mark A. , Seideman Tamar
Published: December 2011

We propose a coherent, strong-field approach to control the torsional modes of biphenyl derivatives, and develop a numerical scheme to simulate the torsional dynamics. By choice of the field parameters, the method can be applied either to drive the torsion angle to an arbitrary configuration or to induce free internal rotation. Transient absorption spectroscopy is suggested as a probe of torsional control and the usefulness of this approach is numerically explored. Several consequences of our ability to manipulate molecular torsional motions are considered. These include a method for the inversion of molecular chirality and an ultrafast chiral switch.
On the true optical properties of zinc nitride
Authors: García Núñez C. , Pau J. L. , Hernández M. J. , Cervera M. , Piqueras J.
Published: December 2011

Refractive index (n) and extinction coefficient (k) of Zn3N2 layers deposited by radio-frequency magnetron sputtering at temperatures (Ts) between 298 and 523 K were determined by spectroscopic ellipsometry. Results showed strong variations of the apparent optical constants with Ts and time attributed to surface effects. Resonant Rutherford backscattering and spectroscopic ellipsometry confirmed the formation of a ZnO surface layer provoked by the ambient exposure. Samples grown at low Ts presented the lowest surface roughness and exhibited 2.0 < n < 2.8 and 0.6 < k < 1.0 in the 1.5–4.5 eV energy range. The extracted n and k values accurately reproduced the reflectance properties.
Infrared absorption of gaseous benzoylperoxy radical C6H5C(O)OO recorded with a step-scan Fourier-transform spectrometer
Authors: Golec Barbara , Chen Jin-Dah , Lee Yuan-Pern
Published: December 2011

A step-scan Fourier-transform infrared spectrometer coupled with a multipass absorption cell was utilized to monitor the transient species produced in gaseous reactions of benzoyl radical, C6H5CO, with O2. C6H5CO was produced either from photolysis of acetophenone, C6H5C(O)CH3, at 248 nm, or from photolysis of a mixture of benzaldehyde, C6H5CHO, and Cl2 at 355 nm. Two intense bands near 1830 and 1226 cm−1 are assigned to the C=O stretching (ν6) and the C−C stretching mixed with C−H deformation (ν13) modes, and two weaker bands near 1187 and 1108 cm−1 are assigned to the ν14 (C−H deformation) and ν16 (O−O stretching /C−H deformation) modes of C6H5C(O)OO, the benzoylperoxy radical. These observed vibrational wave numbers and relative infrared intensities agree with those reported for syn-C6H5C(O)OO isolated in solid Ar and values predicted for syn-C6H5C(O)OO with the B3LYP/cc-pVTZ method. The simulated rotational contours of the two intense bands based on rotational parameters predicted with the B3LYP/cc-pVTZ method fit satisfactorily with experimental results.
Simulation of transient infrared spectra of a photoswitchable peptide
Authors: Kobus Maja , Lieder Martin , Nguyen Phuong H. , Stock Gerhard
Published: December 2011

In transient infrared (IR) experiments, a molecular system may be photoexcited in a nonstationary conformational state, whose time evolution is monitored via IR spectroscopy with high temporal and structural resolution. As a theoretical formulation of these experiments, this work derives explicit expressions for transient one- and two-dimensional IR spectra and discusses various levels of approximation and sampling strategies. Adopting a photoswitchable octapeptide in water as a representative example, nonequilibrium molecular dynamics simulations are performed and the photoinduced conformational dynamics and associated IR spectra are discussed in detail. Interestingly, it is found that the time scales of dynamics and spectra may differ from residue to residue by up to an order of magnitude. Considering merely the cumulative spectrum of all residues, the contributions of the individual residues largely compensate each other, which may explain the surprisingly small frequency shifts and short photoproduct rise times found in experiment. Even when a localized amide I mode is probed (e.g., via isotope labeling), the vibrational frequency shift is shown to depend in a complicated way on the conformation of the entire peptide as well as on the interaction with the solvent. In this context, various issues concerning the interpretation of transient IR spectra and conformational dynamics in terms of a few exponential time scales are discussed.
Effects of radiofrequency on dust particle dynamics in a plasma reactor
Authors: Horn C. , Davoudabadi M. , Shotorban B.
Published: December 2011

A numerical solution is obtained for the electron and ion number densities, and electric field of an rf argon plasma in a low pressure reactor utilizing a one-dimensional model. These variables are used to solve the equations describing the dynamical behavior of a dust particle under the influence of the electrical, gravity, and ion and neutral drag forces. The effects of the rf oscillations of the plasma on the dust particle are investigated through comparisons made between two sets of results. The first set is generated by a model in which the rf-period-averaged plasma variables are used in the dust particle equations while the second set is generated using the instantaneous plasma variables, without rf-period averaging. These two sets of results including the positions and charges of, and the various forces acting on the dust particles with different sizes and densities, are compared and significant differences are found.
Dopant concentration imaging in crystalline silicon wafers by band-to-band photoluminescence
Authors: Lim S. Y. , Phang S. P. , Trupke T. , Cuevas A. , Macdonald D.
Published: December 2011

In this work, we present two techniques for spatially resolved determination of the dopant density in silicon wafers. The first technique is based on measuring the formation rate of iron-acceptor pairs, which is monitored by band-to-band photoluminescence in low injection. This method provides absolute boron concentration images on p-type wafers, even if compensating dopants such as phosphorus are present, without reference to other techniques. The second technique is based on photoluminescence images of unpassivated wafers, where the excess carrier concentration is pinned by a high surface recombination rate. This rapid technique is applicable to either p- or n-type wafers, when the bulk carrier lifetime is much longer than the transit time to the surface. The relative sensitivities and advantages of the two techniques are discussed.
The order-disorder transition in GeTe: Views from different length-scales
Authors: Matsunaga T. , Fons P. , Kolobov A. V. , Tominaga J. , Yamada N.
Published: December 2011

GeTe is a narrow band gap semiconductor that undergoes a ferroelectric-to-paraelectric phase transition at ∼705 K. While earlier studies of average structure using Bragg diffraction concluded that the transition was displacive, structural probing of short and intermediate order shows evidence for an order-disorder transition. Here, we report and contrast the structure on different length scales with temperature using a radial distribution function analysis obtained from x-ray based total scattering and show that the order-disorder model is consistent with experiment.
Simple method of determining plasma impedance of streamer discharge in atmospheric air
Authors: Okano Daisuke
Published: December 2011

For atmospheric streamer discharges using a lightning impulse generator, we demonstrate a method of determining the plasma impedance in a streamer region by analyzing the periodic attenuated discharge waveforms having high-frequency components. When the streamer region in the plasma can be treated as an equivalent series circuit model including resistance and inductance elements, the regression waveforms obtained by reducing and smoothing the discharge waveforms are analyzed in the equivalent circuit. We found that the streamer resistance increased exponentially with time after the discharge, whereas the streamer inductance and series impedance were constant at 4.0 Ω for longer than the first period of the discharge waveforms. Moreover, the slope of the regression curve increases more rapidly for the positive streamer resistance than for the negative resistance. Finally, the absolute values of the streamer impedance versus time were 3.3–19 Ω and 3.5–9.0 Ω for positive and negative discharges, respectively.
Electron mobility, Hall scattering factor, and sheet conductivity in AlGaN/AlN/GaN heterostructures
Authors: Asgari A. , Babanejad S. , Faraone L.
Published: December 2011

In this paper, we present a study of the effect of temperature on the two-dimensional electron mobility, Hall scattering factor, and sheet conductivity, using a fully numerical calculation in unintentionally doped AlxGa1−xN/AlN/GaN heterostructures. The analysis of our results clearly indicates that the effect of partial sub-band occupancy is considerable, especially at higher operating temperatures when more than one sub-band is occupied. The comparison of our calculated results with published experimental data is shown to be in good agreement.
Heterodyne picosecond thermoreflectance applied to nanoscale thermal metrology
Authors: Dilhaire S. , Pernot G. , Calbris G. , Rampnoux J. M. , Grauby S.
Published: December 2011

Picosecond thermoreflectance is an unprecedented powerful technique for nanoscale heat transfer analysis and metrology, but different sources of artifacts were reported in the literature making this technique difficult to use for long delay (several ns) thermal analysis. We present in this paper a new heterodyne picosecond thermoreflectance (HPTR) technique. As it uses two slightly frequency shifted lasers instead of a mechanical translation stage, it is possible to avoid all artifacts leading to erroneous thermal parameter identifications. The principle and set-up are described as well as the model. The signal delivered by the HPTR experiment is calculated for each excitation configurations, modulating or not the pump beam. We demonstrate the accuracy of the technique in the identification of the thermal conductivity of a 50 nm thick SiO2 layer. Then, we discuss the role of the modulation frequency for nanoscale heat transfer analysis.
Faraday rotation enhancement of gold coated Fe2O3 nanoparticles: Comparison of experiment and theory
Authors: Dani Raj Kumar , Wang Hongwang , Bossmann Stefan H. , Wysin Gary , Chikan Viktor
Published: December 2011

Understanding plasmonic enhancement of nanoscale magnetic materials is important to evaluate their potential for application. In this study, the Faraday rotation (FR) enhancement of gold coated Fe2O3 nanoparticles (NP) is investigated experimentally and theoretically. The experiment shows that the Faraday rotation of a Fe2O3 NP solution changes from approximately 3 rad/Tm to 10 rad/Tm as 5 nm gold shell is coated on a 9.7 nm Fe2O3 core at 632 nm. The results also show how the volume fraction normalized Faraday rotation varies with the gold shell thickness. From the comparison of experiment and calculated Faraday rotation based on the Maxwell-Garnett theory, it is concluded that the enhancement and shell dependence of Faraday rotation of Fe2O3 NPs is a result of the shifting plasmon resonance of the composite NP. In addition, the clustering of the NPs induces a different phase lag on the Faraday signal, which suggests that the collective response of the magnetic NP aggregates needs to be considered even in solution. From the Faraday phase lag, the estimated time of the full alignment of the magnetic spins of bare (cluster size 160 nm) and gold coated NPs (cluster size 90 nm) are found to be 0.65 and 0.17 μs. The calculation includes a simple theoretical approach based on the Bruggeman theory to account for the aggregation and its effect on the Faraday rotation. The Bruggeman model provides a qualitatively better agreement with the experimentally observed Faraday rotation and points out the importance of making a connection between component properties and the average “effective” optical behavior of the Faraday medium containing magnetic nanoparticles.
Optimal pinning synchronization on directed complex network
Authors: Nian Fuzhong , Wang Xingyuan
Published: December 2011

In this paper, pinning synchronization on directed network was considered. By analyzing, some general synchronization criteria on directed network were established. And then, we verified it on directed globally coupled network, directed scale-free network, and directed small-world network, respectively. The pinning nodes were selected, respectively, according to order of in-degrees and out-degrees. Through comparing and analyzing simulations, the optimal pinning scheme was found, and a practical principle was induced finally.
Behavior of peptides combining 1 alanine residue and 8 glycine residues on papain associated with structural fluctuations
Authors: Nishiyama Katsuhiko
Published: December 2011

I investigated the behavior of the peptides combining 1 ALA residue and 8 GLY residues on papain associated with structural fluctuations via molecular dynamics and docking simulations. Although the chance of binding to sites near the active center of papain was reduced by replacing the GLY residue in 9GLY with ALA residue, binding stability was improved by the replacement. Furthermore, both the chance and binding stability were greatly affected by positioning of ALA residue in the peptides. Residue in peptides should be replaced in view of the balance between chance of binding to sites near active center and binding stability.
Holomorphic supercurves and supersymmetric sigma models
Authors: Groeger Josua
Published: December 2011

We introduce a natural generalisation of holomorphic curves to morphisms of supermanifolds, referred to as holomorphic supercurves. More precisely, supercurves are morphisms from a Riemann surface, endowed with the structure of a supermanifold which is induced by a holomorphic line bundle, to an ordinary almost complex manifold. They are called holomorphic if a generalised Cauchy-Riemann condition is satisfied. We show, by means of an action identity, that holomorphic supercurves are special extrema of a supersymmetric action functional.
Post-growth annealing induced change of conductivity in As-doped ZnO grown by radio frequency magnetron sputtering
Authors: To C. K. , Yang B. , Su S. C. , Ling C. C. , Beling C. D. , Fung S.
Published: December 2011

Arsenic-doped ZnO films were fabricated by radio frequency magnetron sputtering method at a relatively low substrate temperature of 200 °C. Post-growth annealing in air was carried out up to a temperature of 1000 °C. The samples were characterized by Hall measurement, positron annihilation spectroscopy (PAS), secondary ion mass spectroscopy (SIMS), and cathodoluminescence (CL). The as-grown sample was of n-type and it converted to p-type material after the 400 °C annealing. The resulting hole concentration was found to increase with annealing temperature and reached a maximum of 6 × 1017 cm−3 at the annealing temperature of 600 °C. The origin of the p-type conductivity was consistent with the AsZn(VZn)2 shallow acceptor model. Further increasing the annealing temperature would decrease the hole concentration of the samples finally converted the sample back to n-type. With evidence, it was suggested that the removal of the p-type conductivity was due to the dissociation of the AsZn(VZn)2 acceptor and the creation of the deep level defect giving rise to the green luminescence.
Size effects on gamma radiation response of magnetic properties of barium hexaferrite powders
Authors: McCloy John , Kukkadapu Ravi , Crum Jarrod , Johnson Brad , Droubay Tim
Published: December 2011

Little is currently known about the effects of gamma-ray irradiation on oxide magnet materials. In particular, the effect of particle size on radiation susceptibility was investigated. Two commercial powders of BaFe12O19 were thoroughly characterized, then exposed to 1 MGy of gamma radiation from a 60Co source. AC susceptibility and DC magnetometry and Mössbauer spectroscopy were performed after irradiation and compared to pre-irradiated measurements. DC magnetization and AC susceptibility decreased for both samples with the relative change of DC magnetization being larger for the micrometer-sized particles and the relative change of the AC susceptibility being larger for the nanometer-sized particles. Mössbauer spectroscopy indicated a decrease in both the hyperfine fields and in their distribution for each Fe site, particularly in the larger particle sample. Decreases in susceptibility are believed to be due to radiation-induced amorphization at the particle surfaces as well as amorphization and nucleation of new crystallites at internal crystallite boundaries, resulting in overall reduction in the particle magnetic moment. This radiation damage mechanism is different than that seen in previous studies of neutron and heavy ion irradiation of BaFe12O19.
Compact coupling of light from conventional photonic wire to slow light waveguides
Authors: Üstün Kadir , Kurt Hamza
Published: December 2011

In this study, efficient input and output power coupling schemes for transition regions at the interface of conventional and slow light waveguides are investigated. By optimizing the tapered nano-tip of the input and output slab waveguides that support a group index of 3.58, we achieved 97% coupling efficiency to a square-lattice based slow light photonic crystal waveguide with a group index of 1200. The complementary slow waveguide structure based on triangular-lattice is also designed to support same order of magnitude slow light mode and targeted to alleviate the severity of the coupling loss. An acceptable efficiency value is recorded for the second type of slow waveguide mode. For the sake of targeting only input and output coupling losses, we made an assumption that other loss mechanisms are absent in the structure. The successful demonstration of effective and compact slow light couplers will assist the deployment of slow light devices in important applications, such as nonlinear optics, optical buffers, and optical delay lines.
High-precision soft x-ray polarimeter at Diamond Light Source
Authors: Wang H. , Dhesi S. S. , Maccherozzi F. , Cavill S. , Shepherd E. , Yuan F. , Deshmukh R. , Scott S. , van der Laan G. , Sawhney K. J. S.
Published: December 2011

The development and performance of a high-precision polarimeter for the polarization analysis in the soft x-ray region is presented. This versatile, high-vacuum compatible instrument is supported on a hexapod to simplify the alignment with a resolution less than 5 μrad, and can be moved with its own independent control system easily between different beamlines and synchrotron facilities. The polarimeter can also be used for the characterization of reflection and transmission properties of optical elements. A W/B4C multilayer phase retarder was used to characterize the polarization state up to 1200 eV. A fast and accurate alignment procedure was developed, and complete polarization analysis of the APPLE II undulator at 712 eV has been performed.
Anomalously high thermoelectric power factor in epitaxial ScN thin films
Authors: Kerdsongpanya Sit , Van Nong Ngo , Pryds Nini , Žukauskaitė Agnė , Jensen Jens , Birch Jens , Lu Jun , Hultman Lars , Wingqvist Gunilla , Eklund Per
Published: December 2011

Thermoelectric properties of ScN thin films grown by reactive magnetron sputtering on Al2O3(0001) wafers are reported. X-ray diffraction and elastic recoil detection analyses show that the composition of the films is close to stoichiometry with trace amounts (∼1 at. % in total) of C, O, and F. We found that the ScN thin-film exhibits a rather low electrical resistivity of ∼2.94 μΩm, while its Seebeck coefficient is approximately ∼−86 μV/K at 800 K, yielding a power factor of ∼2.5 × 10−3 W/mK2. This value is anomalously high for common transition-metal nitrides.
Defects control for improved electrical properties in (Ba0.8Sr0.2)(Zr0.2Ti0.8)O3 films by Co acceptor doping
Authors: Miao Jun , Hooi Chew Khian , Jiang Yong
Published: December 2011

(Ba0.8Sr0.2)(Zr0.2Ti0.8)O3 (BSZT) films were grown on La0.5Sr0.5CoO3 buffered (001) SrTiO3 substrates by pulsed laser deposition. Effects of Co doping on electrical properties of the films were investigated to establish material design through defects control. The doping led to a significant improvement in the electrical properties with reduction in leakage current and dielectric loss. In addition, the dielectric tunability and figure of merit were enhanced, implying that Co-doped BSZT films are promising materials for tunable microware applications. Our detail studies suggest that the improved electrical properties of Co-doped BSZT films are closely related to defect concentrations in the films.
Transport and noise spectroscopy of MWCNT/HDPE composites with different nanotube concentrations
Authors: Barone C. , Pagano S. , Neitzert H. C.
Published: December 2011

Electrical current transport and low-frequency noise spectra of multiwall carbon nanotubes in high-density polyethylene matrix have been measured in a temperature range between 10 and 300K. The dc electrical investigations suggest that these composites can be regarded as a random resistor network, where the resistors are formed by tunnel junctions between carbon nanotubes. A crossover of the conduction from a low-field to a high-field regime is found in current-voltage characteristics. In particular, the high-field regime has a strong dependence on carbon nanotube concentration. Noise measurements reveal a standard 1/f behavior due to resistance fluctuations. However, in samples with different concentration of nanotubes, an unusual temperature dependence of the noise is observed. The samples with higher percentage of nanotubes seem to be the most promising ones for devices application, since their noise level is lower in the whole investigated temperature range.
Modulating resistive switching by diluted additive of poly(vinylpyrrolidone) in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)
Authors: Yang J. , Zeng F. , Wang Z. S. , Chen C. , Wang G. Y. , Lin Y. S. , Pan F.
Published: December 2011

Here we report a convenient and economic method to modulate resistive switching of a bipolar resistive memory based on Al/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/Al. We found that diluted additive of poly(vinylpyrrolidone) (PVP) in PEDOT:PSS could enlarge the ON/OFF ratio from 103 to 105 and keep a long retention time over 105 s. Besides, the effects of PVP on switching process were studied by detailed analyses of I-V curves, atomic force microscopy images, X-ray photoelectron spectroscopy, and Raman spectra. The enhancement of the resistive window is due to the loss of PEDOT, charge traps, and conformation change induced by PVP.
Saturation effects in femtosecond laser ablation of silicon-on-insulator
Authors: Zhang Hao , van Oosten D. , Krol D. M. , Dijkhuis J. I.
Published: December 2011

We report a surface morphology study on single-shot submicron features fabricated on silicon on insulator by tightly focused femtosecond laser pulses. In the regime just below single-shot ablation threshold nano-tips are formed, whereas in the regime just above single-shot ablation threshold, a saturation in the ablation depth is found. We attribute this saturation by secondary laser absorption in the laser-induced plasma. In this regime, we find excellent agreement between the measured depths and a simple numerical model. When the laser fluence is further increased, a sharp increase in ablation depth is observed accompanied by a roughening of the ablated hole.
Planar jumping-drop thermal diodes
Authors: Boreyko Jonathan B. , Zhao Yuejun , Chen Chuan-Hua
Published: December 2011

Phase-change thermal diodes rectify heat transport much more effectively than solid-state ones, but are limited by either the gravitational orientation or one-dimensional configuration. Here, we report a planar phase-change diode scalable to large areas with an orientation-independent diodicity of over 100, in which water/vapor is enclosed by parallel superhydrophobic and superhydrophilic plates. The thermal rectification is enabled by spontaneously jumping dropwise condensate which only occurs when the superhydrophobic surface is colder than the superhydrophilic surface.
A dual-mode quantum dot laser operating in the excited state
Authors: Grillot F. , Naderi N. A. , Wright J. B. , Raghunathan R. , Crowley M. T. , Lester L. F.
Published: December 2011

A dual-mode laser operating in the excited states (ESs) of a quantum dot is realized by combining asymmetric pumping and external optical feedback stabilization. In generating two single-mode emission peaks, a mode separation ranging from 1.3-THz to 3.6-THz is demonstrated over temperature. This effect is attributed to the unique carrier dynamics of the quantum-dot gain medium via the excited state inhomogeneous linewidth coupled with a proper external control. These results are particularly important towards the development of future THz optoelectronic sources with compact size, low fabrication cost, and high performance.
Laminar flow of a gas in a tube with large temperature differences
Authors: Higuera F. J.
Published: December 2011

The laminar low Mach number flow of a gas in a tube is analyzed for very small and very large values of the inlet-to-wall temperature ratio. When this ratio tends to zero, pressure forces confine the cold gas to a thin core around the axis of the tube. This core is neatly bounded by an ablation front that consumes it at a finite distance from the tube inlet. When the temperature ratio tends to infinity, the temperature of the gas increases smoothly from the wall to the axis of the tube and the shear stress and heat flux are positive at the wall despite the fact that the viscosity and thermal conductivity of the gas scaled with their inlet values tend to zero at the wall.
High-performance vertical polymer nanorod transistors based on air-stable conjugated polymer
Authors: Chao Yu-Chiang , Chung Chin-Ho , Zan Hsiao-Wen , Meng Hsin-Fei , Ku Ming-Che
Published: December 2011

A vertical polymer nanorod transistor was realized based on an air-stable poly[5,5′-bis(3-dodecyl-2-thienyl)-2,2′-bithiophene] with a high highest occupied molecular orbital energy level. The influence of the work function of the emitter on the performances of the space-charge-limited transistor was investigated. When MoO3/Al was used as the top emitter and indium tin oxide was used as the bottom collector, the operating voltage of 0.6 V, the on/off current ratio of 4 × 104, and the switching swing of 105 mV/decade were achieved. A low-power-consumption inverter was also demonstrated.
Strong substrate effects of Joule heating in graphene electronics
Authors: Li X. , Kong B. D. , Zavada J. M. , Kim K. W.
Published: December 2011

The effect of Joule heating on graphene electronic properties is investigated by self-consistent use of full-band Monte Carlo electron dynamics and three-dimensional heat transfer simulations. Several technologically important substrate materials are examined: SiO2, SiC, hexagonal BN, and diamond. Results illustrate that the choice of substrate has a major impact via heat conduction and surface polar phonon scattering. Particularly, the poor thermal conductivity of SiO2 leads to significant Joule heating and saturation velocity degradation in graphene characterized by the 1/n decay. Considering the overall characteristics, BN appears to compare favorably against the other substrate choices for graphene electronic applications.
Role of Pb(Zr0.52Ti0.48)O3 substitution in multiferroic properties of polycrystalline BiFeO3 thin films
Authors: Yan F. , Zhu T. J. , Lai M. O. , Lu L.
Published: December 2011

Multiferroic materials are of considerable interest due to the intriguing science and application potential. Effects of Pb(Zr0.52Ti0.48)O3 (PZT) modification on the structural, electrical, ferroelectric domain structure and ferromagnetic properties of BiFeO3 (BFO) polycrystalline films were investigated in detail. A morphotropic phase boundaries between rhombohedral perovskite (R3c) and tetragonal (P4 mm) were found in the PZT modified BFO thin films. 2% and 5% PZT modified BFO films exhibit uniform surface, larger domain size, fewer domain walls density, and lower electrical conductivity comparing with the pure BFO film. The 2% and 5% PZT modified BFO thin films show well saturated P-E hysteresis loops with improved remnant polarization close to 76.8 and 96.7 μC/cm2. The improved ferroelectric and dielectric properties of the PZT modified BFO films are attributed to the modified phase structure and bond lengths of Bi-O, decreased concentration of defects and defect dipole complexes, and different domain structures. The saturated magnetizations under a magnetic field of 5 000 Oe at room temperature are 8.5, 11.4, and 14.3 emu/cm3 for the pure, 2% and 5% PZT modified BFO films, respectively. The elevated magnetic properties of PZT modified BFO may be due to the distorted spin cycloid, varied canting angle of Fe-O-Fe bond via the Zr/Ti substitution, and suppressed spiral spin structure via Pb ions substitution of Bi ions.
Vacancies, twins, and the thermal stability of ultrafine-grained copper
Authors: Saldana C. , King A. H. , Stach E. A. , Compton W. D. , Chandrasekar S.
Published: December 2011

Ultrafine-grained metals have impressive strength but lack the thermal stability necessary for most applications. Nano-scale, deformation twinned copper microstructures exhibit a rare combination of strength and stability. While storing less energy in their interfaces than other nanostructured metals, they also exhibit lower vacancy supersaturations, reducing the driving force and mobility for microstructure evolution. From a thermal stability perspective, the nano-twinned microstructure may thus be preferred over the more commonly produced nano-scale equiaxed microstructures.
Enhanced-heating effect during photoacoustic imaging-guided high-intensity focused ultrasound
Authors: Cui Huizhong , Yang Xinmai
Published: December 2011

Photoacoustic imaging (PAI) technique has been used to monitor thermal lesion formation during high-intensity focused ultrasound (HIFU) treatment. While previous studies focused on photoacoustic detection of changes in temperature during HIFU treatment, we report an enhanced-heating effect when PAI is used to monitor HIFU treatment. We found that the temperature induced by HIFU could be significantly enhanced when the diagnostic laser system for photoacoustic detection was operating during HIFU treatment. This finding demonstrates an advantage of using PAI to guide HIFU therapy.
Broadband energy-harvesting hybrid solar cells employing nanocomposites of polythiophene:ternary PbSSe nanocrystals
Authors: Nam Minwoo , Kim Sungwoo , Kim Taehoon , Kim Sang-Wook , Lee Kee-Keun
Published: December 2011

Hybrid solar cells (HSCs) incorporating narrow band gap PbSSe nanocrystals (NCs) in a conjugated polymer were developed for the extensive use of solar radiation up to the near infrared (NIR) range. The developed cell, composed of poly(3-hexylthiophene) (P3HT):PbSSe NC composites with 1:1 weight ratio, exhibited a large light-harvesting efficiency over a broad range, in which the external quantum efficiency reached 0.3% at 1100 nm. These promising results were attributed to the well-assembled percolation networks with large interfacial junctions and the efficient use of broad solar spectrum due to the use of narrow band gap ternary NCs.
Smart catheter flow sensor for real-time continuous regional cerebral blood flow monitoring
Authors: Li Chunyan , Wu Pei-Ming , Hartings Jed A. , Wu Zhizhen , Ahn Chong H. , LeDoux David , Shutter Lori A. , Narayan Raj K.
Published: December 2011

We present a smart catheter flow sensor for real-time, continuous, and quantitative measurement of regional cerebral blood flow using in situ temperature and thermal conductivity compensation. The flow sensor operates in a constant-temperature mode and employs a periodic heating and cooling technique. This approach ensures zero drift and provides highly reliable data with microelectromechanical system-based thin film sensors. The developed flow sensor has a sensitivity of 0.973 mV/ml/100 g/min in the range from 0 to 160 ml/100 g/min with a linear correlation coefficient of R2 = 0.9953. It achieves a resolution of 0.25 ml/100 g/min and an accuracy better than 5 ml/100 g/min.
Living with predators: a focus on the issues of human - crocodile conflict within the lower Zambezi valley
Authors: Wallace Kevin M. , Leslie Alison J. , Coulson Tim
Published: December 2011

Context
Human–wildlife conflict is a global problem and increasing worldwide as people and wildlife compete for limited resources. Conflict between people and crocodiles, especially in Africa, is recognised as a serious problem. The people of the Chiawa Game Management Area are heavily dependent on the Zambezi River for several resources from potable water and irrigating fields to a source of food (subsistence and small-scale commercial fishing).

Aims
To assess the spatial and temporal scale of human–crocodile conflict (HCC) and identify associated factors, with a view to recommending mitigation measures.

Methods
A questionnaire survey and Zambia Wildlife Authority data were utilised to estimate the scale of HCC.

Key results
Between 2000 and 2009, there were 98 crocodile attacks on people, 62.2% were fatal. Most of the attacks occurred while canoe fishing (57.1%) and collecting water (29.6%). Crocodiles were disliked and seen as a ‘problem’ by the majority of the populace. Even though crocodiles are a charismatic mega-fauna species, being employed within the tourism industry had only a minor positive effect on people’s attitudes. The area is an important location for crocodile egg and adult harvesting, although the local population gains no financial benefit. An increase in the number of boreholes in the villages was suggested by the local people as the primary mitigation measure, as well as the removal of crocodiles by various means.

Conclusions
Although people displayed an understanding of the risks of crocodile attack, very few actually employed mitigation techniques or utilised protective barriers when at the river. Increased water-access points (and their maintenance) in the villages would reduce people’s dependency on the river. The negative attitude towards crocodiles is an issue that has to be addressed to allow successful implementation of long-term conservation strategies.

Implications
Understanding local people’s attitudes towards wildlife is an important aspect within any conservation management plan.Competition for limited resources by people and wildlife is guaranteed to cause confrontations. The existing mitigation for human crocodile conflict in Zambia is ineffective. The negative attitude towards wildlife needs to be addressed and a suitable response formulated. The most favoured type of mitigation suggested by local people was more boreholes and the removal of crocodiles. Photograph by Kevin Wallace.
3D structure of the
Yersinia entomophaga
toxin complex and implications for insecticidal activity
Authors: Landsberg Michael J. , Jones Sandra A. , Rothnagel Rosalba , Busby Jason N. , Marshall Sean D. G. , Simpson Robert M. , Lott J. Shaun , Hankamer Ben , Hurst Mark R. H.
Published: December 2011

Toxin complex (Tc) proteins are a class of bacterial protein toxins that form large, multisubunit complexes. Comprising TcA, B, and C components, they are of great interest because many exhibit potent insecticidal activity. Here we report the structure of a novel Tc, Yen-Tc, isolated from the bacterium
Yersinia entomophaga
MH96, which differs from the majority of bacterially derived Tcs in that it exhibits oral activity toward a broad range of insect pests, including the diamondback moth (
Plutella xylostella
). We have determined the structure of the Yen-Tc using single particle electron microscopy and studied its mechanism of toxicity by comparative analyses of two variants of the complex exhibiting different toxicity profiles. We show that the A subunits form the basis of a fivefold symmetric assembly that differs substantially in structure and subunit arrangement from its most well characterized homologue, the
Xenorhabdus nematophila
toxin XptA1. Histopathological and quantitative dose response analyses identify the B and C subunits, which map to a single, surface-accessible region of the structure, as the sole determinants of toxicity. Finally, we show that the assembled Yen-Tc has endochitinase activity and attribute this to putative chitinase subunits that decorate the surface of the TcA scaffold, an observation that may explain the oral toxicity associated with the complex.
Discovery of a phenotypic switch regulating sexual mating in the opportunistic fungal pathogen
Candida tropicalis
Authors: Porman Allison M. , Alby Kevin , Hirakawa Matthew P. , Bennett Richard J.
Published: December 2011

Sexual reproduction can promote genetic diversity in eukaryotes, and yet many pathogenic fungi have been labeled as obligate asexual species. It is becoming increasingly clear, however, that cryptic sexual programs may exist in some species, and that efficient mating requires the necessary developmental switch to be triggered. In this study we investigate
Candida tropicalis
, an important human fungal pathogen that has been reported to be asexual. Significantly, we demonstrate that
C. tropicalis
uses a phenotypic switch to regulate a cryptic program of sexual mating. Thus, diploid a and α cells must undergo a developmental transition to the mating-competent form, and only then does efficient cell-cell conjugation take place resulting in the formation of stable a/α tetraploids. We show that both the phenotypic switch and sexual mating depend on the conserved transcriptional regulator Wor1, which is regulated by temperature in other fungal species. In contrast,
C. tropicalis
mating occurs efficiently at both 25 °C and 37 °C, suggesting that it could occur in the mammalian host and have direct consequences for the outcome of an infection. Transcriptional profiling further reveals that ≈400 genes are differentially expressed between the two phenotypic states, including the regulatory factor Wor1. Taken together, our results demonstrate that
C. tropicalis
has a unique sexual program, and that entry to this program is controlled via a Wor1-mediated, metastable switch. These observations have direct implications for the regulation and evolution of cryptic sexual programs in related fungal pathogens.
Covalent modification of reduced flavin mononucleotide in type-2 isopentenyl diphosphate isomerase by active-site-directed inhibitors
Authors: Nagai Takuya , Unno Hideaki , Janczak Matthew Walter , Yoshimura Tohru , Poulter C. Dale , Hemmi Hisashi
Published: December 2011

Evidence for an unusual catalysis of protonation/deprotonation by a reduced flavin mononucleotide cofactor is presented for type-2 isopentenyl diphosphate isomerase (IDI-2), which catalyzes isomerization of the two fundamental building blocks of isoprenoid biosynthesis, isopentenyl diphosphate and dimethylallyl diphosphate. The covalent adducts formed between irreversible mechanism-based inhibitors, 3-methylene-4-penten-1-yl diphosphate or 3-oxiranyl-3-buten-1-yl diphosphate, and the flavin cofactor were investigated by X-ray crystallography and UV-visible spectroscopy. Both the crystal structures of IDI-2 binding the flavin-inhibitor adduct and the UV-visible spectra of the adducts indicate that the covalent bond is formed at C4a of flavin rather than at N5, which had been proposed previously. In addition, the high-resolution crystal structures of IDI-2-substrate complexes and the kinetic studies of new mutants confirmed that only the flavin cofactor can catalyze protonation of the substrates and suggest that N5 of flavin is most likely to be involved in proton transfer. These data provide support for a mechanism where the reduced flavin cofactor acts as a general acid/base catalyst and helps stabilize the carbocationic intermediate formed by protonation.
‘I'm just there to ease the burden’: the parent support adviser role in English schools and the question of emotional labour
Authors: Cullen Stephen M. , Cullen Mairi‐Ann , Lindsay Geoff
Published: December 2011

In 2005, the Department for Education and Skills announced a £40 million investment in a new school support worker role, the parent support adviser (PSA), for 20 English local authorities. A pilot project ran from 2006–2008 and resulted in the establishment of 717 PSAs in 1167 schools. The national evaluation of the project forms the evidential basis of this paper, with interviews conducted with 69 PSAs, 85 PSA line managers and 105 parents and a database recording casework with nearly 21,000 parents. This paper focuses on the nature of the PSA role as the first centrally funded parent support role in English schools. The theoretical framework provided by the concept of ‘emotional labour’ and the development of the concept represented by the 4Ps typology provides the conceptual structure. This paper argues that although the characteristics of the PSA role appear to place it within the category of work requiring emotional labour, PSAs and parents regard that aspect of the role in a positive light. For the PSAs there was little evidence that emotional labour necessary for the role of PSA led to dissonance between role and worker or alienation from the product of PSA labour.