bluuebunny/crossref_metadata_2025 huggingface dataset:
Two vortex-blob regularization models for vortex sheet motion
Authors: Sohn Sung-Ik
Published: April 2014

Evolving vortex sheets generally form singularities in finite time. The vortex blob model is an approach to regularize the vortex sheet motion and evolve past singularity formation. In this paper, we thoroughly compare two such regularizations: the Krasny-type model and the Beale-Majda model. It is found from a linear stability analysis that both models have exponentially decaying growth rates for high wavenumbers, but the Beale-Majda model has a faster decaying rate than the Krasny model. The Beale-Majda model thus gives a stronger regularization to the solution. We apply the blob models to the two example problems: a periodic vortex sheet and an elliptically loaded wing. The numerical results show that the solutions of the two models are similar in large and small scales, but are fairly different in intermediate scales. The sheet of the Beale-Majda model has more spiral turns than the Krasny-type model for the same value of the regularization parameter δ. We give numerical evidences that the solutions of the two models agree for an increasing amount of spiral turns and tend to converge to the same limit as δ is decreased. The inner spiral turns of the blob models behave differently with the outer turns and satisfy a self-similar form. We also examine irregular motions of the sheet at late times and find that the irregular motions shrink as δ is decreased. This fact suggests a convergence of the blob solution to the weak solution of infinite regular spiral turns.
Vibrational solvatochromism. II. A first-principle theory of solvation-induced vibrational frequency shift based on effective fragment potential method
Authors: Błasiak Bartosz , Cho Minhaeng
Published: April 2014

Vibrational solvatochromism is a solvation-induced effect on fundamental vibrational frequencies of molecules in solutions. Here we present a detailed first-principle coarse-grained theory of vibrational solvatochromism, which is an extension of our previous work [B. Błasiak, H. Lee, and M. Cho, J. Chem. Phys. 139(4), 044111 (2013)] by taking into account electrostatic, exchange-repulsion, polarization, and charge-transfer interactions. By applying our theory to the model N-methylacetamide-water clusters, solute-solvent interaction-induced effects on amide I vibrational frequency are fully elucidated at Hartree-Fock level. Although the electrostatic interaction between distributed multipole moments of solute and solvent molecules plays the dominant role, the contributions from exchange repulsion and induced dipole-electric field interactions are found to be of comparable importance in short distance range, whereas the charge-transfer effect is negligible. The overall frequency shifts calculated by taking into account the contributions of electrostatics, exchange-repulsion, and polarization terms are in quantitative agreement with ab initio results obtained at the Hartree-Fock level of theory.
Effects of interface electric field on the magnetoresistance in spin devices
Authors: Tanamoto T. , Ishikawa M. , Inokuchi T. , Sugiyama H. , Saito Y.
Published: April 2014

An extension of the standard spin diffusion theory is presented by using a quantum diffusion theory via a density-gradient (DG) term that is suitable for describing interface quantum tunneling phenomena. The magnetoresistance (MR) ratio is greatly modified by the DG term through an interface electric field. We have also carried out spin injection and detection measurements using four-terminal Si devices. The local measurement shows that the MR ratio changes depending on the current direction. We show that the change of the MR ratio depending on the current direction comes from the DG term regarding the asymmetry of the two interface electronic structures.
The effect of diamagnetic flows on turbulent driven ion toroidal rotation
Authors: Lee J. P. , Barnes M. , Parra F. I. , Belli E. A. , Candy J.
Published: April 2014

Turbulent momentum redistribution determines the radial profile of rotation in a tokamak. The momentum transport driven by diamagnetic flow effects is an important piece of the radial momentum transport for sub-sonic rotation, which is often observed in experiments. In a non-rotating state, the diamagnetic flow and the E × B flow must cancel. The diamagnetic flow and the E × B flow have different effects on the turbulent momentum flux, and this difference in behavior induces intrinsic rotation. The momentum flux is evaluated using gyrokinetic equations that are corrected to higher order in the ratio of the poloidal Larmor radius to the minor radius, which requires evaluation of the diamagnetic corrections to Maxwellian equilibria. To study the momentum transport due to diamagnetic flow effects, three experimental observations of ion rotation are examined. First, a strong pressure gradient at the plasma edge is shown to result in a significant inward momentum transport due to the diamagnetic effect, which may explain the observed peaking of rotation in a high confinement mode. Second, the direction of momentum transport is shown to change as collisionality increases, which is qualitatively consistent with the observed reversal of intrinsic rotation by varying plasma density and current. Last, the dependence of the intrinsic momentum flux on the magnetic shear is found, and it may explain the observed rotation changes in the presence of lower hybrid current drive.
Position of the transverse domain wall controlled by magnetic impurities in rectangular magnetic nanowires
Authors: Toscano D. , Ferreira V. A. , Leonel S. A. , Coura P. Z. , Sato F. , Dias R. A. , Costa B. V.
Published: April 2014

We have performed numerical simulations to demonstrate that the domain wall movement can be controlled introducing a distribution of magnetic impurities in a nanowire. In particular, we have considered two identical impurities equidistant from the nanowire width axis. Pinning and scattering sites for the domain wall can be defined by magnetic impurities, consisting of a local variation of the exchange constant. The domain wall motion was induced by application of a magnetic field pulse and our results indicate that it is possible to control the domain wall position.
Raman spectroscopy study of silicon nanoribbons on Ag(110)
Authors: Speiser E. , Buick B. , Esser N. , Richter W. , Colonna S. , Cricenti A. , Ronci F.
Published: April 2014

The grating of self-assembled Si nanoribbons at the Ag(110) surface has been studied by Raman spectroscopy. The study, conducted in situ with uncapped samples, resulted in phonon frequencies in disagreement with the results of theoretical calculations reported in literature for freestanding silicene sheets and nanoribbons. These results suggest that the structure of these silicon nanoribbons is very different from the planar and lightly buckled structural models and that the influence of the substrate might be underestimated in the discussed structural models.
In-situ scanning electron microscopy and atomic force microscopy Young's modulus determination of indium oxide microrods for micromechanical resonator applications
Authors: Bartolomé Javier , Hidalgo Pedro , Maestre David , Cremades Ana , Piqueras Javier
Published: April 2014

Electric field induced mechanical resonances of In2O3 microrods are studied by in-situ measurements in the chamber of a scanning electron microscope. Young's moduli of rods with different cross-sectional shapes are calculated from the resonance frequency, and a range of values between 131 and 152 GPa are obtained. A quality factor of 1180–3780 is measured from the amplitude-frequency curves, revealing the suitability of In2O3 microrods as micromechanical resonators. The Young's modulus, E, of one of the rods is also measured from the elastic response in the force-displacement curve recorded in an atomic force microscope. E values obtained by in-situ scanning electron microscopy and by atomic force microscopy are found to differ in about 8%. The results provide data on Young's modulus of In2O3 and confirm the suitability of in-situ scanning electron microscopy mechanical resonance measurements to investigate the elastic behavior of semiconductor microrods.
Silicon-based Coulomb blockade thermometer with Schottky barriers
Authors: Tuboltsev V. , Savin A. , Rogozin V. D. , Räisänen J.
Published: April 2014

A hybrid Coulomb blockade thermometer (CBT) in form of an array of intermittent aluminum and silicon islands connected in series via tunnel junctions was fabricated on a thin silicon-on-insulator (SOI) film. Tunnel barriers in the micrometer size junctions were formed by metal-semiconductor Schottky contacts between aluminium electrodes and heavily doped silicon. Differential conductance through the array vs. bias voltage was found to exhibit characteristic features of competing thermal and charging effects enabling absolute temperature measurements over the range of ∼65 to ∼500 mK. The CBT performance implying the primary nature of the thermometer demonstrated for rather trivial architecture attempted in this work paves a route for introduction of Coulomb blockade thermometry into well-developed contemporary SOI technology.
Communication: Electron transfer mediated decay enabled by spin-orbit interaction in small krypton/xenon clusters
Authors: Zobel J. Patrick , Kryzhevoi Nikolai V. , Pernpointner Markus
Published: April 2014

In this work we study the influence of relativistic effects, in particular spin-orbit coupling, on electronic decay processes in KrXe2 clusters of various geometries. For the first time it is shown that inclusion of spin-orbit coupling has decisive influence on the accessibility of a specific decay pathway in these clusters. The radiationless relaxation process is initiated by a Kr 4s ionization followed by an electron transfer from xenon to krypton and a final second ionization of the system. We demonstrate the existence of competing electronic decay pathways depending in a subtle way on the geometry and level of theory. For our calculations a fully relativistic framework was employed where omission of spin-orbit coupling leads to closing of two decay pathways. These findings stress the relevance of an adequate relativistic description for clusters with heavy elements and their fragmentation dynamics.
Growth optimization and optical properties of AlGaNAs alloys
Authors: Kolhatkar Gitanjali , Boucherif Abderraouf , Valdivia Christopher E. , Wallace Steven G. , Fafard Simon , Aimez Vincent , Arès Richard
Published: April 2014

The effect of Al on the surface morphology of chemical beam epitaxy grown AlGaNAs alloys is studied. Pits attributed to N clustering appearing on the dilute nitride surface become smaller, denser, and more uniformly distributed in the presence of Al. This reveals that the introduction of Al results in more homogenous N atoms spatial distribution. A growth temperature study reveals the formation of 3D structures at high temperature due to phase separation. The density of these structures decreases, while their diameter and height increase when the temperature is raised from 380 °C to 565 °C. At growth temperatures in the 380–420 °C range, the phase separation is suppressed and the growth mode is 2D. At 420 °C, the N incorporation is also maximized, making it the optimum temperature. The absorption coefficient and the bandgap of AlGaNAs alloys are extracted from transmittance measurement. A good agreement is obtained between the experimentally measured bandgap and the theoretical values calculated using the band anticrossing model. A bandgap as low as 1.22 eV was reached using Al and N concentrations of ∼15% and ∼3.4%, respectively.
Communication: Spin-boson model with diagonal and off-diagonal coupling to two independent baths: Ground-state phase transition in the deep sub-Ohmic regime
Authors: Zhao Yang , Yao Yao , Chernyak Vladimir , Zhao Yang
Published: April 2014

We investigate a spin-boson model with two boson baths that are coupled to two perpendicular components of the spin by employing the density matrix renormalization group method with an optimized boson basis. It is revealed that in the deep sub-Ohmic regime there exists a novel second-order phase transition between two types of doubly degenerate states, which is reduced to one of the usual types for nonzero tunneling. In addition, it is found that expectation values of the spin components display jumps at the phase boundary in the absence of bias and tunneling.
Strain-induced energy gap variation in ZnTe/ZnMgTe core/shell nanowires
Authors: Wojnar P. , Zielinski M. , Janik E. , Zaleszczyk W. , Wojciechowski T. , Wojnar R. , Szymura M. , Kłopotowski Ł. , Baczewski L. T. , Pietruchik A. , Wiater M. , Kret S. , Karczewski G. , Wojtowicz T. , Kossut J.
Published: April 2014

Strain-induced changes of ZnTe energy gap in ZnTe/ZnMgTe core/shell nanowires arising from lattice mismatch between the core and the shell semiconductor are studied by means of optical methods. It is shown that the increase of the Mg content in the shell, as well as the increase of the shell thickness result in an effective redshift of the near band edge photoluminescence from ZnTe nanowire cores, which reflects directly the decrease of energy gap under tensile strain conditions. The conclusions are supported by theoretical calculations in terms of the valence force field model. The observed change of ZnTe energy gap can be as large as 120 meV with respect to the unstrained conditions and can be tuned in a continuous manner by adjusting shell parameters, which open a path towards an effective band gap engineering in these structures.
Experimental investigation of a relativistic magnetron with diffraction output on a repetitive short pulse generator
Authors: Li Wei , Zhang Jun , Zhang Zi-cheng , Sun Xiao-liang , Liu Yong-gui
Published: April 2014

An experimental investigation of a relativistic Magnetron with Diffraction Output (MDO) on a short voltage pulse generator, which has maximum repetition rate of 100 Hz and plateau of 2.5 ns, is detailed in this paper. Compared to the conversional solid cathode, a direct Density Modulation Cathode is capable for desired microwave radiation. When applied voltage is 200 kV and axial magnetic field is ∼0.12 T, the MDO radiates 120 MW of microwave with 2.3 GHz of central frequency. Power conversion efficiency reaches 22%. Pulse duration is 3 ns. At repetition rates of 50 Hz and 100 Hz, output microwave powers range from 90 MW to 120 MW. Life time is up to 104 shots.
Sensitivity of the interpretation of the experimental ion thermal diffusivity to the determination of the ion conductive heat flux
Authors: Stacey W. M.
Published: April 2014

A moments equation formalism for the interpretation of the experimental ion thermal diffusivity from experimental data is used to determine the radial ion thermal conduction flux that must be used to interpret the measured data. It is shown that the total ion energy flux must be corrected for thermal and rotational energy convection, for the work done by the flowing plasma against the pressure and viscosity, and for ion orbit loss of particles and energy, and expressions are presented for these corrections. Each of these factors is shown to have a significant effect on the interpreted ion thermal diffusivity in a representative DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)] discharge.
Voltage induced local hysteretic phase switching in silicon
Authors: Sekhon Jagmeet S. , Aggarwal Leena , Sheet Goutam
Published: April 2014

We report the observation of dc-bias induced 180° phase switching in silicon wafers by local-probe microscopy and spectroscopy. The switching is hysteretic and shows remarkable similarities with polarization switching in ferroelectrics as seen in piezoresponse force microscopy (PFM). This is always accompanied by a hysteretic amplitude vs. voltage curve which resembles the “butterfly loops” for piezoelectric materials. From a detailed analysis of the data obtained under different environmental and experimental conditions, we show that the hysteresis effects in phase and amplitude do not originate from ferro-electricity or piezoelectricity. This further indicates that mere observation of hysteresis effects in PFM does not confirm the existence of ferroelectric and/or piezoelectric ordering in materials. We also show that when samples are mounted on silicon for PFM measurements, the switching properties of silicon may appear on the sample even if the sample thickness is large.
Strain effects on in-plane conductance of the topological insulator Bi2Te3
Authors: Heui Hwang Jin , Kwon Sangku , Park Joonbum , Hun Kim Jong , Lee Jhinhwan , Sung Kim Jun , Lyeo Ho-Ki , Young Park Jeong
Published: April 2014

We investigated the correlation between electrical transport and mechanical stress in a topological insulator, Bi2Te3, using conductive probe atomic force microscopy in an ultrahigh vacuum environment. After directly measuring charge transport on the cleaved Bi2Te3 surface, we found that the current density varied with applied load. Current mapping revealed a variation of the current on different terraces. The current density increased in the low-pressure regime and then decreased in the high-pressure regime. This variation of current density was explained in light of the combined effect of changes in the in-plane conductance due to spin–orbit coupling and hexagonal warping.
Detection of terahertz radiation by tightly concatenated InGaAs field-effect transistors integrated on a single chip
Authors: Popov V. V. , Yermolaev D. M. , Maremyanin K. V. , Zemlyakov V. E. , Maleev N. A. , Gavrilenko V. I. , Bespalov V. A. , Yegorkin V. I. , Ustinov V. M. , Shapoval S. Yu.
Published: April 2014

A tightly concatenated chain of InGaAs field-effect transistors with an asymmetric T-gate in each transistor demonstrates strong terahertz photovoltaic response without using supplementary antenna elements. We obtain the responsivity above 1000 V/W and up to 2000 V/W for unbiased and drain-biased transistors in the chain, respectively, with the noise equivalent power below 10−11 W/Hz0.5 in the unbiased mode of the detector operation.
In situ examination of oxygen non-stoichiometry in La0.80Sr0.20CoO3−δ thin films at intermediate and low temperatures by x-ray diffraction
Authors: Biegalski M. D. , Crumlin E. , Belianinov A. , Mutoro E. , Shao-Horn Y. , Kalinin S. V.
Published: April 2014

Structural evolution of epitaxial La0.80Sr0.20CoO3−δ thin films under chemical and voltage stimuli was examined in situ using X-ray diffraction. The changes in lattice parameter (chemical expansivity) were used to quantify oxygen reduction reaction processes and vacancy concentration changes in lanthanum strontium cobaltite. At 550 °C, the observed lattice parameter reduction at an applied bias of −0.6 V was equivalent to that from the reducing condition of a 2% carbon monoxide atmosphere with an oxygen non-stoichiometry δ of 0.24. At lower temperatures (200 °C), the application of bias reduced the sample much more effectively than a carbon monoxide atmosphere and induced an oxygen non-stoichiometry δ of 0.47. Despite these large changes in oxygen concentration, the epitaxial thin film was completely re-oxidized and no signs of crystallinity loss or film amorphization were observed. This work demonstrates that the effects of oxygen evolution and reduction can be examined with applied bias at low temperatures, extending the ability to probe these processes with in-situ analytical techniques.
Measurement of the Curie temperature distribution in FePt granular magnetic media
Authors: Pisana S. , Jain S. , Reiner J. W. , Parker G. J. , Poon C. C. , Hellwig O. , Stipe B. C.
Published: April 2014

Heat assisted magnetic recording (HAMR) has been recognized as a leading technology to increase the data storage density of hard disk drives. Dispersions in the properties of the grains comprising the magnetic medium can lead to grain-to-grain Curie temperature variations, which drastically affect the jitter in the recorded magnetic transitions and limit the data storage density capabilities in HAMR. Here we present a method to measure the switching probability of an ensemble of exchange-decoupled grains with perpendicular anisotropy subject to nanosecond heating pulses. The short heat exposure time ensures that the grains switch by reaching the Curie temperature rather than through thermal activation. The switching probability can be directly interpreted as representing the Curie temperature distribution. The method is applied to two sets of samples to reveal the sensitivity of the Curie temperature distribution to FePt HAMR media fabrication parameters. This technique is of importance to engineer suitable HAMR media capable of high density magnetic recording and for fundamental studies on sources of magnetic disorder in granular magnetic media.
Domain wall motion driven by spin Hall effect—Tuning with in-plane magnetic anisotropy
Authors: Rushforth A. W.
Published: April 2014

This letter investigates the effects of in-plane magnetic anisotropy on the current induced motion of magnetic domain walls in systems with dominant perpendicular magnetic anisotropy, where accumulated spins from the spin Hall effect in an adjacent heavy metal layer are responsible for driving the domain wall motion. It is found that that the sign and magnitude of the domain wall velocity in the uniform flow regime can be tuned significantly by the in-plane magnetic anisotropy. These effects are sensitive to the ratio of the adiabatic and non-adiabatic spin transfer torque parameters and are robust in the presence of pinning and thermal fluctuations.
Improving charge injection in high-mobility rubrene crystals: From contact-limited to channel-dominated transistors
Authors: Zimmerling Tino , Batlogg Bertram
Published: April 2014

With progressively improving charge carrier mobility in organic semiconductors and miniaturization of organic field-effect transistors (OFETs), low contact resistances become ever more important. To study the capabilities of metal electrodes in OFETs and to explore the transition from contact-limited to channel-dominated transistor operation, we used flip-crystal FETs with gold electrodes having different contact resistances Rc to high-quality rubrene crystals. 4-terminal transfer and output measurements reveal that Rc decreases from 105–106 Ω cm for 15 min air exposure to 3 × 103 Ωcm for at least 5 h air exposure of the gold electrodes before the flip-crystal FET is assembled. We conclude the reduction of Rc to be caused by a growing contamination layer on the gold electrodes that weakens the electrostatic coupling between rubrene crystal and gold electrode, and lowers the Schottky contact diode parameter V0. In channel-dominated (low Rc) FETs, the mobility is in the range of 10–17 cm2/(Vs); in contrast, in contact-limited (high Rc) FETs, the apparent mobility decreases significantly with increasing contact resistance. The apparent μ – Rc dependence is not intrinsic, but rather the result of incorrect assumptions of the potential and the charge carrier density in the channel region. Thus, the development of high-mobility organic semiconductors requires further efforts to improve contacts beyond traditional metal electrodes.
Investigation of defects in In–Ga–Zn oxide thin film using electron spin resonance signals
Authors: Nonaka Yusuke , Kurosawa Yoichi , Komatsu Yoshihiro , Ishihara Noritaka , Oota Masashi , Nakashima Motoki , Hirohashi Takuya , Takahashi Masahiro , Yamazaki Shunpei , Obonai Toshimitsu , Hosaka Yasuharu , Koezuka Junichi , Yamauchi Jun
Published: April 2014

In–Ga–Zn oxide (IGZO) is a next-generation semiconductor material seen as an alternative to silicon. Despite the importance of the controllability of characteristics and the reliability of devices, defects in IGZO have not been fully understood. We investigated defects in IGZO thin films using electron spin resonance (ESR) spectroscopy. In as-sputtered IGZO thin films, we observed an ESR signal which had a g-value of g = 2.010, and the signal was found to disappear under thermal treatment. Annealing in a reductive atmosphere, such as N2 atmosphere, generated an ESR signal with g = 1.932 in IGZO thin films. The temperature dependence of the latter signal suggests that the signal is induced by delocalized unpaired electrons (i.e., conduction electrons). In fact, a comparison between the conductivity and ESR signal intensity revealed that the signal's intensity is related to the number of conduction electrons in the IGZO thin film. The signal's intensity did not increase with oxygen vacancy alone but also with increases in both oxygen vacancy and hydrogen concentration. In addition, first-principle calculation suggests that the conduction electrons in IGZO may be generated by defects that occur when hydrogen atoms are inserted into oxygen vacancies.
Label-free, real-time detection of the dynamic processes of protein degradation using oblique-incidence reflectivity difference method
Authors: Liu S. , Zhu J. H. , He L. P. , Dai J. , Lu H. B. , Wu L. , Jin K. J. , Yang G. Z. , Zhu H.
Published: April 2014

Based on the requirements for studying the dynamic process of proteinase action substrates in life science, we selected six random proteins including 1L-10, SCGB2A2, CENPQ, GST, HK1, KLHL7, as well as five different concentrations of 1L-10 proteins of 1 mg/ml, 0.5 mg/ml, 0.25 mg/ml, 0.125 mg/ml, and 0.0625 mg/ml, and fabricated two types of substrate protein microarrays, respectively. We detected the dynamic processes of proteins degraded by proteinase K using oblique-incidence reflectivity difference (OIRD) method in a label-free and real-time manner. We obtained the relevant degradation velocities and the degradation time. The experimental results demonstrate that OIRD has the ability to study proteinase action substrates which is out of reach of label methods and is expected to offer opportunities to determine protease-substrate relationships on the systems biology level.
Acoustically determined linear piezoelectric response of lithium niobate up to 1100 V
Authors: Patel N. , Branch D. W. , Schamiloglu E. , Cular S.
Published: April 2014

We present a method to measure high voltages using the piezoelectric crystal lithium niobate without using voltage dividers. A 36° Y-X cut lithium niobate crystal was coupled to two acoustic transducers, where direct current voltages were applied from 128–1100 V. The time-of-flight through the crystal was determined to be linearly dependent on the applied voltage. A model was developed to predict the time-delay in response to the applied voltage. The results show a sensitivity of 17 fs/V with a measurement error of 1 fs/V was achievable using this method. The sensitivity of this method can be increased by measuring the acoustic wave after multiple passes through the crystal. This method has many advantages over traditional techniques such as: favorable scalability for larger voltages, ease of use, cost effectiveness, and compactness.
Gyrokinetic simulations of collisionless reconnection in turbulent non-uniform plasmas
Authors: Kobayashi Sumire , Rogers Barrett N. , Numata Ryusuke
Published: April 2014

We present nonlinear gyrokinetic simulations of collisionless magnetic reconnection with non-uniformities in the plasma density, the electron temperature, and the ion temperature. The density gradient can stabilize reconnection due to diamagnetic effects but destabilize driftwave modes that produce turbulence. The electron temperature gradient triggers microtearing modes that drive rapid small-scale reconnection and strong electron heat transport. The ion temperature gradient destabilizes ion temperature gradient modes that, like the driftwaves, may enhance reconnection in some cases.
Passive magnetic shielding in static gradient fields
Authors: Bidinosti C. P. , Martin J. W.
Published: April 2014

The effect of passive magnetic shielding on dc magnetic field gradients imposed by both external and internal sources is studied for two idealized shield models: concentric spherical and infinitely-long cylindrical shells of linear material. It is found that higher-order multipoles of an externally applied magnetic field are always shielded progressively better for either geometry by a factor related to the order of the multipole. In regard to the design of internal coil systems, we determine reaction factors for the general multipole field and provide examples of how one can take advantage of the coupling of the coils to the innermost shell to optimize the uniformity of the field. Furthermore, we provide formulae relevant to active magnetic compensation systems which attempt to stabilize the interior fields by sensing and cancelling the exterior fields close to the outermost shell. Overall this work provides a comprehensive framework that is useful for the analysis and optimization of dc magnetic shields, serving as a theoretical and conceptual design guide as well as a starting point and benchmark for finite-element analysis.
Electromagnetic tuning of resonant transmission in magnetoelastic metamaterials
Authors: Matsui Tatsunosuke , Liu Mingkai , Powell David A. , Shadrivov Ilya V. , Kivshar Yuri S.
Published: April 2014

We demonstrate an analogue of electromagnetically-induced transparency (EIT) in a magnetoelastic metamaterial system and experimentally realize nonlinear electromagnetic tuning of this EIT-like transmission. We study a single meta-molecule, consisting of two split-ring resonators (SRRs) and one closed-ring resonator, with one SRR free to rotate about the common axis of the structure in response to torques induced by the microwave pump. We observe EIT-like narrow-band resonant transmission in the carefully optimized device, which we characterize in a microwave waveguide, and verify that the resonance is due to the hybridized mode of all three resonators. We demonstrate nonlinear spectral narrowing and an increase of the group delay upon increasing the pump power and show the significant role of the intrinsic rotation of the freely rotatable SRR in this process.
Investigation on the compensation effect of residual carbon impurities in low temperature grown Mg doped GaN films
Authors: Yang J. , Zhao D. G. , Jiang D. S. , Chen P. , Liu Z. S. , Le L. C. , Li X. J. , He X. G. , Liu J. P. , Zhang S. M. , Wang H. , Zhu J. J. , Yang H.
Published: April 2014

The influence of unintentionally doped carbon impurities on electrical resistivity and yellow luminescence (YL) of low-temperature (LT) grown Mg doped GaN films is investigated. It is found that the resistivity of Mg doped GaN films are closely related to the residual carbon impurity concentration, which may be attributed to the compensation effect of carbon impurities. The carbon impurity may preferentially form deep donor complex CN-ON resulting from its relatively low formation energy. This complex is an effective compensate center for MgGa acceptors as well as inducing YL in photoluminescence spectra. Thus, the low resistivity LT grown p-type GaN films can be obtained only when the residual carbon impurity concentration is sufficiently low, which can explain why LT P-GaN films with lower resistivity were obtained more easily when relatively higher pressure, temperature, or NH3/TMGa flow rate ratio were used in the LT grown Mg doped GaN films reported in earlier reports.
Simulation and characterization of millimeter-wave InAlN/GaN high electron mobility transistors using Lombardi mobility model
Authors: Du Jiangfeng , Yan Hui , Yin Chenggong , Feng Zhihong , Dun Shaobo , Yu Qi
Published: April 2014

A gate length of 0.2 μm InAlN/GaN high electron mobility transistor on SiC substrate is obtained with a maximum current gain cutoff frequency (fT) of 65.8 GHz and a maximum power gain cutoff frequency (fmax) of 143.6 GHz. Lombardi model, which takes interface roughness scattering into consideration, has been introduced to model the transconductance (gm) degradation. The simulated gm and fT with Lombardi model are 69% and 58% lower than the ones without considering interface roughness scattering, respectively. Further analysis show experimental gm, gate capacitance (Cg), and fT are consistent with results based on Lombardi model.
Improved efficiency of flexible polymer solar cells with a non-annealing active layer
Authors: Wang Mengying , Yang Liying , Xu Xuejian , Qin Wenjing , Yin Shougen
Published: April 2014

Improved power conversion efficiency (PCE) of flexible polymer bulk heterojunction solar cells based on regioregular poly(3-hexylthiophene) (P3HT) and methanofullerene [6,6]-phenyl C61-butyric acid methyl ester blends with a non-thermal annealing active layer have been obtained by using 1,2,4-trichlorobenzene as the solvent and 1,3,5-trichlorobenzene (135-TCB) as the additive. The influence of the solvent and additives on the performance and stability was investigated by atomic force microscopy (AFM), X-ray diffraction (XRD), UV-vis and thermogravimetric analysis. The easily processed device using 135-TCB as additive on the ITO coated polyester substrate exhibits a PCE of ∼3.03% with Voc of 0.60 V, Jsc of 9.07 mA/cm2 and fill factor of 55.7%, which is comparable to the device on the ITO glass substrate. AFM result revealed the enhanced performance is ascribed to the rough morphology of the active layer. So, larger interfacial area is formed. XRD measurement disclosed that the 135-TCB additive increases the crystallinity of P3HT. The accelerated heat aging decay curve showed the stability is also improved. The strategy of using the processing additive to control the morphology of flexible polymer solar cell without any thermal annealing is very attractive due to its simplicity and well suitable for future large scale production.
Germinating the seeds of three species of Pimelea sect. Epallage (Thymelaeaceae)
Authors: Silcock Richard G. , Mann Michael B.
Published: April 2014

Pimelea trichostachya Lindl., P. simplex F.Muell. and P. elongata Threlfall frequently cause pimelea poisoning of cattle. Fresh seeds of these species, belonging to sect. Epallage (Endl.) Benth. of Pimelea Gaertn. (Thymelaeaceae) are strongly dormant for years when in laboratory storage. Common methods of stimulating germination, such as scarification, dry heat and cold stratification, did not remove much of the dormancy. ‘Smoke water’ stimulated some germination but its effect was unpredictable and many seedlings then grew aberrantly. Exposure of imbibed seeds to gibberellic acid greatly and reliably improved the germination of all three species. However, the manner of application and the concentration of gibberellic acid used had to be appropriate or many young seedlings grew abnormally or died suddenly, limiting successful plant establishment rates. The dormancy type involved is non-deep Type 2 physiological. Ten days of good moisture, in addition to gibberellic acid exposure, is required before appreciable laboratory germination occurs at optimal temperatures. Thus, the mechanism by which gibberellic acid stimulates good germination does not appear to be the same as that which primes seeds for the rapid and prolific germination often seen under natural conditions in arid Australia. Seeds of P. simplex subsp. continua (J.M.Black) Threlfall proved most difficult to germinate and those of P. elongata the easiest.
The development of electrochemical methods for determining nanoparticles in the environment. Part II. Chronoamperometric study of FeS in sodium chloride solutions
Authors: Bura-Nakić Elvira , Marguš Marija , Milanović Ivana , Jurašin Darija , Ciglenečki Irena
Published: April 2014

Environmental contextIn anoxic environments FeS is both an important mediator in the Fe and S biogeochemical cycles and plays a vital role in controlling the scavenging and availability of many trace metals. Electrochemical detection of colloidal and particulate FeS in natural waters can be done by voltammetric measurements. The recorded anodic waves, however, are rather qualitative and lack information on the FeS concentration and size distribution.

AbstractThe interactions of FeS nanoparticles (NPs) with a hanging mercury drop electrode in NaCl solutions were monitored by chronoamperometric measurements. Collisions of FeS NPs with the mercury surface were studied over a wide range of electrode potentials (between 0 and –1.9V v. Ag/AgCl). Faradaic impact transients were recorded only at the negative potentials (between –1.5 and –1.9V). It was shown that the mercury electrode surface modified with a FeS adlayer catalyses sodium reduction by shifting the potentials of this process to more positive values. This catalytic process together with possible hydrogen evolution is assumed to be the physicochemical basis for the determination of FeS NPs. Chronoamperometric measurements at the electrode potential of –1.9V showed that the reduction processes of sodium and hydrogen on FeS NPs upon collision are the main cause of sharp reduction current transients. At sufficiently positive electrode potentials (~–1.5V) the colliding FeS NPs would not be immediately repelled; instead they remained adhered to the mercury surface, causing ‘staircase-like’ chronoamperometric signals. It appears that recorded reduction current transients are carrying FeS NPs’ size information, which is consistent with parallel dynamic light scattering (DLS) measurements.
Redox active motifs in selenoproteins
Authors: Li Fei , Lutz Patricia B. , Pepelyayeva Yuliya , Arnér Elias S. J. , Bayse Craig A. , Rozovsky Sharon
Published: April 2014

Significance

In redox biology, the chemistry performed by proteins that contain the rare amino acid selenocysteine is frequently critical to the detoxification of reactive species that are harmful to cellular function. Selenocysteine and cysteine partner to form a motif featuring a sulfur–selenium covalent bond in many selenoproteins. This work demonstrates that selenium NMR, when paired with calculations, can provide critical insight concerning the local environment of these enigmatic redox motifs. It details how redox potentials, conformational preferences, and mobilities of such redox motifs change when the local environment of the selenocysteine is varied. Surprisingly, reverting selenocysteine to cysteine exerts only minor effects on redox potential. These new approaches deepen our understanding of the chemical reactivity and thermodynamic properties of selenoenzymes.
Vocatives galore in audiovisual dialogue
Authors: Formentelli Maicol
Published: April 2014

The paper explores the use of vocatives in a corpus of 24 American and British films (thePavia Corpus of Film Dialogue) by comparing film dialogue with spontaneous speech. A systematic quantitative and qualitative analysis of empirical data is provided to assess how address forms used by English speakers in natural verbal exchanges are reproduced on screen, and to identify patterns of address that can be regarded as distinctive of film dialogue. The findings show a higher frequency of vocatives in film dialogue, which serve diegetic and extradiegetic functions. From a qualitative point of view, filmic speech effectively reproduces interpersonal functions and sociolinguistic variation associated with vocatives in spontaneous interactions; on the other hand, it is characterized by a sophisticated use of address strategies accounted for in terms of authorial expressivity.
Interaction in two journalistic genres
Authors: Fu Xiaoli , Hyland Ken
Published: April 2014

The study of interactive features of language has been a very productive source of insights into written discourse in recent years, revealing the ways that writers engage with readers to successfully persuade them of a particular viewpoint in a range of different genres and contexts. While a variety of approaches have illuminated our understanding of these features, the concept of interactional metadiscourse has been particularly valuable in revealing how writers project themselves into their discourse to signal their understandings of their material and their audience. In this paper we draw on Hyland’s (2005a) model of metadiscourse to explore some of the ways that interaction contributes to the success of two journalistic genres: popular science and opinion articles. Examining 200 popular science and 200 opinion texts, we show that despite the broadly similar audience and sources of these genres, authors structure their interactions very differently, contributing to the rhetorical distinctiveness of these genres. The paper not only offers a detailed account of interactional metadiscourse in these genres, but illustrates how interpersonal connections are accomplished for particular persuasive purposes in everyday public texts.
The cytoplasmic cage domain of the mechanosensitive channel MscS is a sensor of macromolecular crowding
Authors: Rowe Ian , Anishkin Andriy , Kamaraju Kishore , Yoshimura Kenjiro , Sukharev Sergei
Published: April 2014

Cells actively regulate the macromolecular excluded volume of the cytoplasm to maintain the reciprocal fraction of free aqueous solution that is optimal for intracellular processes. However, the mechanisms whereby cells sense this critical parameter remain unclear. The mechanosensitive channel of small conductance (MscS channel), which is the major regulator of turgor in bacteria, mediates efflux of small osmolytes in response to increased membrane tension. At moderate sustained tensions produced by a decrease in external osmolarity, MscS undergoes slow adaptive inactivation; however, it inactivates abruptly in the presence of cytoplasmic crowding agents. To understand the mechanism underlying this rapid inactivation, we combined extrapolated and equilibrium molecular dynamics simulations with electrophysiological analyses of MscS mutants to explore possible transitions of MscS and generated models of the resting and inactivated states. Our models suggest that the coupling of the gate formed by TM3 helices to the peripheral TM1–TM2 pairs depends on the axial position of the core TM3 barrel relative to the TM1–TM2 shaft and the state of the associated hollow cytoplasmic domain (“cage”). They also indicate that the tension-driven inactivation transition separates the gate from the peripheral helices and promotes kinks in TM3s at G113 and that this conformation is stabilized by association of the TM3b segment with the β domain of the cage. We found that mutations destabilizing the TM3b–β interactions preclude inactivation and make the channel insensitive to crowding agents and voltage; mutations that strengthen this association result in a stable closed state and silent inactivation. Steered simulations showed that pressure exerted on the cage bottom in the inactivated state reduces the volume of the cage in the cytoplasm and at the same time increases the footprint of the transmembrane domain in the membrane, implying coupled sensitivity to both membrane tension and crowding pressure. The cage, therefore, provides feedback on the increasing crowding that disengages the gate and prevents excessive draining and condensation of the cytoplasm. We discuss the structural mechanics of cells surrounded by an elastic cell wall where this MscS-specific feedback mechanism may be necessary.
The Royal African Society,
African Affairs
and Apartheid: the Mustoe Controversy OF 1970
Authors: Youé Chris
Published: April 2014

Divisions between the Royal African Society and its flagship journal African Affairs emerged in 1970 when the Vice-President of the Society, Nelson Mustoe Q.C., defended South African apartheid as ‘moral, feasible and reasonable.’ This statement, part of a letter to The Times , was offered in support of the upcoming Springbok cricket tour of Britain. The letter elicited a backlash from various groups, including the scholars behind African Affairs , and the political pressure led to the cancellation of the tour. This paper argues that the Mustoe controversy was an emblematic moment, symbolizing the transition of British Empire and commonwealth, the beginning of the political activism phase of the anti-apartheid movement in Britain, and South Africa's isolation on the world stage.
ThunderSTORM: a comprehensive ImageJ plug-in for PALM and STORM data analysis and super-resolution imaging
Authors: Ovesný Martin , Křížek Pavel , Borkovec Josef , Švindrych Zdeněk , Hagen Guy M.
Published: April 2014

Summary: ThunderSTORM is an open-source, interactive and modular plug-in for ImageJ designed for automated processing, analysis and visualization of data acquired by single-molecule localization microscopy methods such as photo-activated localization microscopy and stochastic optical reconstruction microscopy. ThunderSTORM offers an extensive collection of processing and post-processing methods so that users can easily adapt the process of analysis to their data. ThunderSTORM also offers a set of tools for creation of simulated data and quantitative performance evaluation of localization algorithms using Monte Carlo simulations.

Availability and implementation: ThunderSTORM and the online documentation are both freely accessible at https://code.google.com/p/thunder-storm/

Contact:  guy.hagen@lf1.cuni.cz

Supplementary information:  Supplementary Data are available at Bioinformatics online.
Redundancy-weighting for better inference of protein structural features
Authors: Yanover Chen , Vanetik Natalia , Levitt Michael , Kolodny Rachel , Keasar Chen
Published: April 2014

Motivation: Structural knowledge, extracted from the Protein Data Bank (PDB), underlies numerous potential functions and prediction methods. The PDB, however, is highly biased: many proteins have more than one entry, while entire protein families are represented by a single structure, or even not at all. The standard solution to this problem is to limit the studies to non-redundant subsets of the PDB. While alleviating biases, this solution hides the many-to-many relations between sequences and structures. That is, non-redundant datasets conceal the diversity of sequences that share the same fold and the existence of multiple conformations for the same protein. A particularly disturbing aspect of non-redundant subsets is that they hardly benefit from the rapid pace of protein structure determination, as most newly solved structures fall within existing families.

Results: In this study we explore the concept of redundancy-weighted datasets, originally suggested by Miyazawa and Jernigan. Redundancy-weighted datasets include all available structures and associate them (or features thereof) with weights that are inversely proportional to the number of their homologs. Here, we provide the first systematic comparison of redundancy-weighted datasets with non-redundant ones. We test three weighting schemes and show that the distributions of structural features that they produce are smoother (having higher entropy) compared with the distributions inferred from non-redundant datasets. We further show that these smoothed distributions are both more robust and more correct than their non-redundant counterparts.

We suggest that the better distributions, inferred using redundancy-weighting, may improve the accuracy of knowledge-based potentials and increase the power of protein structure prediction methods. Consequently, they may enhance model-driven molecular biology.

Contact:  cheny@il.ibm.com or chen.keasar@gmail.com