bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved two level model of mid-infrared quantum cascade lasers for analysis of direct intensity modulation response
Authors: Webb J. F. , Haldar M. K.
Published: February 2012

The direct intensity modulation response of quantum cascade lasers can be accurately calculated from a three-level model. However, the calculations are algebraically complex. An alternative two-level model gives simpler expressions and more readily provides insight into the role of parameters influencing the modulation response. The object of this paper is to improve the two-level model and analyze the direct intensity modulation response. The modified model will simplify theoretical investigation of modulation related phenomena.
Epitaxial Ag(001) grown on MgO(001) and TiN(001): Twinning, surface morphology, and electron surface scattering
Authors: Chawla J. S. , Gall D.
Published: February 2012

Epitaxial Ag(001) layers were deposited on MgO(001) in order to study electron surface scattering. X-ray reflection indicates 3D layer nucleation with a high rms surface roughness of 1.0 nm for a layer thickness d = 3.5 nm. X-ray diffraction shows that {111} twins form at d < 11 nm, followed by 2nd generation twinning for 11 nm < d < 120 nm. Increasing the growth temperature from 25 to 150 °C suppresses 2nd generation twinning and reduces the twin density by 2 orders of magnitude. In situ deposition of epitaxial 2.5-nm-thick TiN(001) underlayers prior to Ag deposition results in twin-free single-crystal Ag(001) with 10 × smoother surfaces for d = 3.5 nm. This is attributed to a better wetting on the higher energy TiN(001) than MgO(001) surface, resulting in the absence of 3D nuclei with exposed {111} facets, which facilitate twin nucleation. The twinned Ag/MgO layers have a higher resistivity ρ than the single crystal Ag/TiN layers at both 298 and 77 K, due to electron scattering at grain and twin boundaries. The ρ for single-crystal Ag layers increases with decreasing d, which is well explained with known surface scattering models and provides specularity parameters for the Ag-vacuum and the Ag-air interfaces of p = 0.8 ± 0.1 and 0.4 ± 0.1, respectively. A comparison with corresponding epitaxial Cu(001) layers shows that ρAg < ρCu for d > 50 nm, consistent with known bulk values. However, ρAg > ρCu for d < 40 nm. This is attributed to the larger electron mean free path for electron-phonon scattering and a correspondingly higher resistivity contribution from surface scattering in Ag than Cu. In contrast, air exposure causes ρAg < ρCu for all d, due to diffuse scattering at the oxidized Cu surface and the correspondingly higher Cu resistivity.
Bifurcation phenomena in an impulsive model of non-basal testosterone regulation
Authors: Zhusubaliyev Zhanybai T. , Churilov Alexander N. , Medvedev Alexander
Published: February 2012

Complex nonlinear dynamics in a recent mathematical model of non-basal testosterone regulation are investigated. In agreement with biological evidence, the pulsatile (non-basal) secretion of testosterone is modeled by frequency and amplitude modulated feedback. It is shown that, in addition to already known periodic motions with one and two pulses in the least period of a closed-loop system solution, cycles of higher periodicity and chaos are present in the model in hand. The broad range of exhibited dynamic behaviors makes the model highly promising in model-based signal processing of hormone data.
Microdroplet oscillations during optical pulling
Authors: Ellingsen Simen Å.
Published: February 2012

It was recently shown theoretically that it is possible to pull a spherical dielectric body towards the source of a laser beam [J. Chen, J. Ng, Z. Lin, and C. T. Chan, “Optical pulling force,” Nat. Photonics 5, 531 (2011)], a result with immediate consequences to optical manipulation of small droplets. Optical pulling can be realized, e.g., using a diffraction-free Bessel beam, and is expected to be of great importance in manipulation of microscopic droplets in micro- and nanofluidics. Compared to conventional optical pushing, however, the ratio of optical net force to stress acting on a droplet is much smaller, increasing the importance of oscillations. We describe the time-dependent surface deformations of a water microdroplet under optical pulling to linear order in the deformation. Shape oscillations have a lifetime in the order of microseconds for droplet radii of a few micrometers. The force density acting on the initially spherical droplet is strongly peaked near the poles on the beam axis, causing the deformations to take the form of jet-like protrusions.
Many-body interactions between particles in a polydisperse polymer fluid
Authors: Woodward Clifford E. , Forsman Jan
Published: February 2012

We use a continuum chain model and develop an analytical theory for the interaction between many spheres immersed in a fluid of ideal polydisperse polymers. Assuming local spherical symmetry of the polymer field about each particle, combined with a local approximation, compact expressions are derived for the many-body interaction between the spheres. We use a mean-field approximation to investigate the fluid-fluid phase diagram for the mixture.
Overtone-induced dissociation and isomerization dynamics of the hydroxymethyl radical (CH2OH and CD2OH). I. A theoretical study
Authors: Kamarchik E. , Rodrigo C. , Bowman J. M. , Reisler H. , Krylov A. I.
Published: February 2012

The dissociation of the hydroxymethyl radical, CH2OH, and its isotopolog, CD2OH, following the excitation of high OH stretch overtones is studied by quasi-classical molecular dynamics calculations using a global potential energy surface (PES) fitted to ab initio calculations. The PES includes CH2OH and CH3O minima, dissociation products, and all relevant barriers. Its analysis shows that the transition states for OH bond fission and isomerization are both very close in energy to the excited vibrational levels reached in recent experiments and involve significant geometry changes relative to the CH2OH equilibrium structure. The energies of key stationary points are refined using high-level electronic structure calculations. Vibrational energies and wavefunctions are computed by coupled anharmonic vibrational calculations. They show that high OH-stretch overtones are mixed with other modes. Consequently, trajectory calculations carried out at energies about ∼3000 cm−1 above the barriers reveal that despite initial excitation of the OH stretch, the direct OH bond fission is relatively slow (10 ps) and a considerable fraction of the radicals undergoes isomerization to the methoxy radical. The computed dissociation energies are: D0(CH2OH → CH2O + H) = 10 188 cm−1, D0(CD2OH → CD2O + H) = 10 167 cm−1, D0(CD2OH → CHDO + D) = 10 787 cm−1. All are in excellent agreement with the experimental results. For CH2OH, the barriers for the direct OH bond fission and isomerization are: 14 205 and 13 839 cm−1, respectively.
Overtone-induced dissociation and isomerization dynamics of the hydroxymethyl radical (CH2OH and CD2OH). II. Velocity map imaging studies
Authors: Ryazanov M. , Rodrigo C. , Reisler H.
Published: February 2012

The dissociation of the hydroxymethyl radical, CH2OH, and its isotopolog, CD2OH, following excitation in the 4ν1 region (OH stretch overtone, near 13 600 cm−1) was studied using sliced velocity map imaging. A new vibrational band near 13 660 cm−1 arising from interaction with the antisymmetric CH stretch was discovered for CH2OH. In CD2OH dissociation, D atom products (correlated with CHDO) were detected, providing the first experimental evidence of isomerization in the CH2OH ↔ CH3O (CD2OH ↔ CHD2O) system. Analysis of the H (D) fragment kinetic energy distributions shows that the rovibrational state distributions in the formaldehyde cofragments are different for the OH bond fission and isomerization pathways. Isomerization is responsible for 10%–30% of dissociation events in all studied cases, and its contribution depends on the excited vibrational level of the radical. Accurate dissociation energies were determined: D0(CH2OH → CH2O + H) = 10 160 ± 70 cm−1, D0(CD2OH → CD2O + H) = 10 135 ± 70 cm−1, D0(CD2OH → CHDO + D) = 10 760 ± 60 cm−1.
Ring-shaped velocity distribution functions in energy-dispersed structures formed at the boundaries of a proton stream injected into a transverse magnetic field: Test-kinetic results
Authors: Voitcu Gabriel , Echim Marius M.
Published: February 2012

In this paper, we discuss the formation of ring-shaped and gyro-phase restricted velocity distribution functions (VDFs) at the edges of a cloud of protons injected into non-uniform distributions of the electromagnetic field. The velocity distribution function is reconstructed using the forward test-kinetic method. We consider two profiles of the electric field: (1) a non-uniform E-field obtained by solving the Laplace equation consistent with the conservation of the electric drift and (2) a constant and uniform E-field. In both cases, the magnetic field is similar to the solutions obtained for tangential discontinuities. The initial velocity distribution function is Liouville mapped along numerically integrated trajectories. The numerical results show the formation of an energy-dispersed structure due to the energy-dependent displacement of protons towards the edges of the cloud by the gradient-B drift. Another direct effect of the gradient-B drift is the formation of ring-shaped velocity distribution functions within the velocity-dispersed structure. Higher energy particles populate the edges of the proton beam, while smaller energies are located in the core. Non-gyrotropic velocity distribution functions form on the front-side and trailing edge of the cloud; this effect is due to remote sensing of energetic particles with guiding centers inside the beam. The kinetic features revealed by the test-kinetic solutions have features similar to in-situ velocity distribution functions observed by Cluster satellites in the magnetotail, close to the neutral sheet.
Controllable chemical vapor deposition of large area uniform nanocrystalline graphene directly on silicon dioxide
Authors: Sun Jie , Lindvall Niclas , Cole Matthew T. , Wang Teng , Booth Tim J. , Bøggild Peter , Teo Kenneth B. K. , Liu Johan , Yurgens August
Published: February 2012

Metal-catalyst-free chemical vapor deposition (CVD) of large area uniform nanocrystalline graphene on oxidized silicon substrates is demonstrated. The material grows slowly, allowing for thickness control down to monolayer graphene. The as-grown thin films are continuous with no observable pinholes, and are smooth and uniform across whole wafers, as inspected by optical-, scanning electron-, and atomic force microscopy. The sp2 hybridized carbon structure is confirmed by Raman spectroscopy. Room temperature electrical measurements show ohmic behavior (sheet resistance similar to exfoliated graphene) and up to 13% of electric-field effect. The Hall mobility is ∼40 cm2/Vs, which is an order of magnitude higher than previously reported values for nanocrystalline graphene. Transmission electron microscopy, Raman spectroscopy, and transport measurements indicate a graphene crystalline domain size ∼10 nm. The absence of transfer to another substrate allows avoidance of wrinkles, holes, and etching residues which are usually detrimental to device performance. This work provides a broader perspective of graphene CVD and shows a viable route toward applications involving transparent electrodes.
Phase locking of high power relativistic backward wave oscillator using priming effect
Authors: Teng Yan , Song Wei , Sun Jun , Xiao Renzhen , Song Zhimin , Zhang Ligang , Zhang Zhiqiang , Zhang Lijun , Zhang Yuchuan , Li Jiawei , Fang Jinyong
Published: February 2012

The phase-locking approach using the priming effect is developed for high power relativistic backward wave oscillators (RBWO). A plasma switch is conceived to avoid the feedback effect. In experiment, multicavity RBWO of 200 MW with the 73 MHz half power bandwidth is phase-locked under the injection power ratio 0.044 for the frequency separation of 20 MHz. We found that it takes more time to reach stable phase-locking than to achieve saturation of RBWO generation. The external signal of higher power results in the longer time duration of phase locking. Besides phase-locking, the priming effect leads to longer microwave pulse duration.
Size dependent melting behaviors of nanocrystalline in particles embedded in amorphous matrix
Authors: Mu J. , Zhu Z. W. , Zhang H. F. , Fu H. M. , Wang A. M. , Li H. , Hu Z. Q.
Published: February 2012

The composites of In nanoparticles embedded in Al-based amorphous matrix were synthesized. As the content of In increases, the average size of In nanoparticles increases. The melting behaviors of embedded In nanoparticles were investigated, indicating that the melting temperature is suppressed, and the smaller the size is, the lower the melting temperature is. It is confirmed by comparing the differential scanning calorimetry curves with those of the size distribution. The size dependent melting behaviors of nanoparticles were discussed with the thermodynamic model.
Charge transport in amorphous low bandgap conjugated polymer/fullerene films
Authors: Kim Jung Yong , Cho Hyunduck , Noh Seunguk , Lee Yoonkyoo , Nam Young Min , Lee Changhee , Jo Won Ho
Published: February 2012

The structural and charge transport properties of a low bandgap copolymer poly(3-hexylthiophene-alt-6,7-dimethyl-4,9-bis-(4-hexylthien-2yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline) (P(3HT-MeTDQ)) and its blend with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are investigated. Thermal analysis, X-ray scattering diffraction (XRD), atomic force microscopy and transmission electron microscopy (TEM) of P(3HT-MeTDQ) reveal that the polymer is amorphous in solid state. As the hole mobility of P(3HT-MeTDQ) was measured by the time-of-flight photoconductivity method, the mobility was 3.35 × 10−4 cm2/V s, which is very comparable to that of semicrystalline poly(3-hexyl thiophene). When the mobility of amorphous P(3HT-MeTDQ) was analyzed according to the Gaussian disorder model, the polymer has the energetic and positional disorders with the values of σ = 62 meV and Σ = 1.7, respectively, indicating that the polymer has a relatively narrow Gaussian distribution of transport states. Interestingly, when P(3HT-MeTDQ) is blended with PCBM, the amorphous P(3HT-MeTDQ) becomes partially ordered, as evidenced by observation of two discernible XRD peaks at 2θ = 5° (d = 17.7 Å) and 25.5° (d = 3.5 Å) corresponding to the interchain distance and π-stacking distance, respectively. The bicontinuous network morphology was identified at the blend with 60 wt. % PCBM by TEM, at which the charge carrier transport changes from hole-only to ambipolar.
Phase transition hysteresis of ferroelectric Sr5EuTi3Nb7O30 ceramics with tetragonal tungsten bronze structure
Authors: Li Zhu Xiao , Ming Chen Xiang
Published: February 2012

The first-order ferroelectric transition of Sr5EuTi3Nb7O30 tungsten bronze ceramics was investigated together with the thermal history dependence of dielectric properties and differential scanning calorimetry (DSC) analysis. Moreover, the diffuse dielectric maximum appeared at a temperature above the ferroelectric transition, and this phenomenon had been reported in ferroelectrics with perovskite structure, but had never been observed in tungsten bronzes. Large hysteresis in the ferroelectric transition and severe depression of T0 were observed in both the permittivity-temperature and DSC curves, and were attributed to the complex nature of the tetragonal tungsten bronze structure. The DSC measurements were also used to get better insight into the gradual stability of the ferroelectric phase after cooling from the high temperature paraelectric phase. The abnormal splitting of the endothermic peaks was observed during the DSC measurements with lower start temperature or longer aging time. Two possible mechanisms were suggested. One was the separation of ferroelectric phase due to the compositional inhomogeneity. In another possible mechanism, the polar nanoregions coexisting with the ferroelectric domains were suggested and would possibly transit into the paraelectric phase at temperature below the ferroelectric transition.
Bidirectional operation of vertical organic triodes
Authors: Fischer Axel , Siebeneicher Philipp , Kleemann Hans , Leo Karl , Lüssem Björn
Published: February 2012

Due to their effective short channel length of only a few hundred nanometers, vertical organic triodes (VOTs) have a high potential to overcome problems of low current densities and switching speed in current organic field effect transistors (OFETs). Furthermore, VOTs are easy to build because no sub-structuring of the base contact is necessary. Nevertheless, these devices are poorly investigated. In literature, two different working mechanisms are suggested: hot carrier transport through the metallic base or transport of charge carriers through a permeable base electrode. As a strong asymmetry is expected for function principle based on hot carriers, we are able to distinguish between both mechanisms by examining the bidirectional transmission properties of the VOT consisting of electron transporting materials. We show that high transmission values (>95%) are possible for both directions, suggesting a base contact with openings forming a grid electrode.
Tip geometry effects in dopant profiling by scanning microwave microscopy
Authors: Humer I. , Eckhardt C. , Huber H. P. , Kienberger F. , Smoliner J.
Published: February 2012

In this paper, the impact of the tip radius on dopant profiling by scanning microwave microscopy is investigated. The cantilevers are very likely to erode in such measurements, and thus, a two-dimensional Poisson solver was used to calculate the lateral spatial resolution as a function of tip radius and doping. Moreover, a strong correlation between the slope of the calibration curves and the tip diameter was found. The slope of the calibration curves increases toward −0.5 and saturates as the radius approaches values of 150 nm, which is in agreement with experimental data obtained from scanning microwave microscopy.
Note: Studies on x-ray production in electron cyclotron resonance x-ray source based on ridged cylindrical cavity
Authors: Selvakumaran T. S. , Baskaran R.
Published: February 2012

A ridged cylindrical cavity has been designed using MICROWAVE STUDIO programme and it is used in the electron cyclotron resonance (ECR) x-ray source. The experimental parameters of the source are optimized for maximizing the x-ray output, and an x-ray dose rate of ∼1000 μSv/h was observed at 20 cm from the port, for 500 W of microwave power without using any target. With the molybdenum target located at optimum position of the ridged cavity, the dose rate is found to be increased only by 10%. In order to understand the experimental observation, the electric field pattern of the cavity with the target placed at various radial distances is studied. In this note, the experimental and theoretical studies on ECR x-ray source using the ridged cylindrical cavity are presented.
Mean-field quantum dynamics with magnetic fields
Authors: Lührmann Jonas
Published: February 2012

We consider a system of N bosons in three dimensions interacting through a mean-field Coulomb potential in an external magnetic field. For initially factorized states we show that the one-particle density matrix associated with the solution of the N-body Schrödinger equation converges to the projection onto the solution of the magnetic Hartree equation in trace norm and in energy as N → ∞. Estimates on the rate of convergence are provided.
Thermal conductivity of 1.3 μm InAs/GaAs quantum dot laser active material from chirp and 3ω measurements
Authors: Ge Zhongyang , Moat Patricia , Xie Jing , Hu Junjie , Huang Jia-Sheng , Sun Xinyu , Li Neinyi , White B. E. , Klotzkin David
Published: February 2012

Semiconductor quantum dots have very low thermal conductivities compared with bulk materials or quantum well structures. In this paper, thermal conductivity of InAs quantum dot laser active regions was determined using two different approaches. Measured conductivity is between 0.03 and 0.05 W/(m-K) for both approaches, in reasonable agreement considering the approximations used in the measurement method. This reduced thermal conductivity of the active region in quantum dot lasers has a significant effect on the laser operating characteristics.
Surface temperature effect on the scattering of D2(v = 0, j = 0)-Cu(111) system
Authors: Sahoo Tapas , Mukherjee Saikat , Adhikari Satrajit
Published: February 2012

We perform four-dimensional (4D⊗2D) as well as six-dimensional (6D) quantum dynamics on a parametrically time- and temperature-dependent effective Hamiltonian for D2(v, j)-Cu(111) system, where such effective potential has been derived through a mean-field approach between molecular degrees of freedom and surface modes with Bose-Einstein probability factor for their initial state distribution. We present the convergence of the theoretically calculated sticking probabilities employing 4D⊗2D quantum dynamics with increasing number of surface atoms as well as layers for rigid surface and the surface at a particular temperature, where the temperature-dependent sticking probabilities appear exclusively dictated by those surface modes directed along the Z-axis. The sticking and state-to-state transition probabilities obtained from 6D quantum dynamics are shown as a function of initial kinetic energy of the diatom at different surface temperature. Theoretically calculated sticking probabilities display the similar trend with the experimentally measured one.
Rapid fabrication of a microdevice with concave microwells and its application in embryoid body formation
Authors: Xu Youchun , Xie Fengbo , Qiu Tian , Xie Lan , Xing Wanli , Cheng Jing
Published: February 2012

Here, we report a novel method for the fabrication of polydimethylsiloxane microdevices with complicated 3-D structures, such as concave and crater shapes, using an easily machined polymethyl methacrylate mold combined with a one-step molding process. The procedure presented here enables rapid preparation of complex 3-D microstructures varying in shape and dimensions. To regulate embryoid body (EB) formation, we fabricated a microfluidic device with an array of concave microwells and found that EBs growing in microwells maintained their shape, viability, and a high degree of homogeneity. We believe that this novel method provides an alternative for rapid prototyping, especially in fabricating devices with curved 3-D microstructures.
Narrow linewidth tunable external cavity diode laser using wide bandwidth filter
Authors: Thompson Daniel J. , Scholten Robert E.
Published: February 2012

We demonstrate single mode operation of an external cavity diode laser (ECDL) employing an interference filter with multimode bandwidth for mode selection. A cateye reflector maximizes feedback efficiency and reduces susceptibility to intra-cavity optical misalignment. Narrow linewidths of 26 kHz are observed, and the laser can be tuned over 14 nm using a single 785 nm filter, without alteration of the output beam direction. The cateye reflector and filter allow a mechanically rigid design free of significant mechanical resonances, illustrated by comparison of the frequency noise spectrum with that of a common Littrow ECDL design using a diffraction grating and kinematic mount.
The impact of Ge codoping on the enhancement of photovoltaic characteristics of B-doped Czochralski grown Si crystal
Authors: Arivanandhan Mukannan , Gotoh Raira , Watahiki Tatsuro , Fujiwara Kozo , Hayakawa Yasuhiro , Uda Satoshi , Konagai Makoto
Published: February 2012

The effect of Ge codoping on minority carrier lifetime in boron (B)-doped Czochralski-silicon (CZ-Si) crystals was investigated. The minority carrier lifetime increased from 110 to 176 µs as Ge concentration was increased from zero to 1 × 1020 cm−3 in B/Ge codoped CZ-Si crystals. Light-induced degradation (LID) experiments showed that B-doped CZ-Si degrades rapidly, while B/Ge codoped CZ-Si degrades more slowly. Moreover, the flow pattern defect (FPD) density of grown-in micro-defects (GMD) in as-grown B/Ge codoped CZ-Si decreased with increasing Ge concentration. From the infrared (IR) absorption studies, it was observed that the interstitial oxygen (Oi) concentration decreased as Ge concentration increased in the crystal. The suppressed LID effect in the B/Ge codoped CZ-Si appears to be related to the low concentration of B-O associated defects, possibly because Ge doping retards the Oi diffusion in addition to the low Oi concentration present (evidenced from IR studies). The mechanism by which the Ge concentration influences the reduction of FPDs and Oi concentration is discussed in terms of Ge-vacancy defect formation during post-growth cooling of the ingots.
Ferromagnetism in thin-film Cr-doped topological insulator Bi2Se3
Authors: Haazen P. P. J. , Laloë J.-B. , Nummy T. J. , Swagten H. J. M. , Jarillo-Herrero P. , Heiman D. , Moodera J. S.
Published: February 2012

We report on the observation of ferromagnetism in epitaxial thin films of the topological insulator compound Bi2Se3 with chromium doping. The structural, magnetic, and magnetoelectrical properties of Bi2Se3 were investigated for Cr concentrations up to 10%. For a Cr content up to ∼5% the films are of good crystalline quality, with the lattice parameter a decreasing and the lattice parameter c increasing with increasing Cr concentration. The Curie temperature reached a maximum TC = 20 K for 5.2% Cr. Well-defined ferromagnetic hysteresis in the magnetization and in the magnetoresistance was also observed in these films.
Temperature effect on electrical characteristics of negative capacitance ferroelectric field-effect transistors
Authors: Xiao Y. G. , Tang M. H. , Li J. C. , Cheng C. P. , Jiang B. , Cai H. Q. , Tang Z. H. , Lv X. S. , Gu X. C.
Published: February 2012

The electrical properties of negative capacitance (NC) ferroelectric field-effect transistors (FeFETs) were theoretically investigated in the temperature range from 280 to 360 K. The derived results indicate that for a fixed thickness of ferroelectric thin film the amplification of surface potential can be tuned by temperature. The transfer and output characteristics degrade with increasing temperature due to the gradual loss of ferroelectric NC effect. It is expected that the derived results may provide some insight into the design and performance improvement for the low power dissipation applications of FeFETs.
Quasi-omnidirectional electrical spectrometer for studying spin dynamics in magnetic tunnel junctions
Authors: Yamaguchi Akinobu , Fukushima Akio , Kubota Hitoshi , Yuasa Shinji
Published: February 2012

We report an omnidirectional electrical spectroscopy setup for studying the spin dynamics in a nanoscale magnet. It has a measureable solid angle range comprising about 50% of the total range and allows the magnetoresistance and spin-torque diode signal to be measured simultaneously at any angle to the magnetization. This setup can provide detailed information about the spin-wave resonance modes excited in a nanoscale magnet.
Droplet jumping by electrowetting and its application to the three-dimensional digital microfluidics
Authors: Jun Lee Seung , Lee Sanghyun , Hyoung Kang Kwan
Published: February 2012

We introduce droplet jumping by electrowetting (DJE), which stretches droplets to store energy for jumping by electrowetting. The capillarity-driven droplet jumping is effective to overcome the energy barrier, where the threshold for jumping is less than 100 V. We studied the detailed jumping mechanisms with regard to the jumping height and the energy conversion and demonstrated the transport of sessile droplets to upper surfaces under diverse electrode configurations. While the droplet jumping on the superhydrophobic surface is the primary focus of our research, DJE is also found to be possible on conventional Teflon surfaces, envisioning the three-dimensional droplet-based digital microfluidics.
Nonvanishing turn-on delay in quantum dot lasers
Authors: Sokolovskii G. S. , Dudelev V. V. , Kolykhalova E. D. , Deryagin A. G. , Maximov M. V. , Nadtochiy A. M. , Kuchinskii V. I. , Mikhrin S. S. , Livshits D. A. , Viktorov E. A. , Erneux T.
Published: February 2012

A turn-on of a quantum dot semiconductor laser is analyzed in detail both theoretically and experimentally. We show that quantum dot lasers have a nonlinear damping rate which strongly affects laser turn-on dynamics due to the non-instantaneous capture of carriers to a dot. It results in nonvanishing turn-on delay even at very high pumping in good agreement with experiment.
Ultrasonic variable-focus optical lens using viscoelastic material
Authors: Koyama Daisuke , Isago Ryoichi , Nakamura Kentaro
Published: February 2012

A variable-focus lens that employs acoustic radiation force and a viscoelastic material and that has no mechanical moving parts is investigated. The lens has a simple and thin structure that consists of an annular ultrasonic transducer and silicone gel. An axially symmetric acoustic standing wave can be generated in the gel by exciting a vibration mode in the radial direction on the transducer. The lens profile can be altered by varying the acoustic radiation force of the transducer. The focal length can be controlled by varying the transducer input voltage so that the lens functions as a variable-focus lens.
Electron emission mechanism during the nanosecond high-voltage pulsed discharge in pressurized air
Authors: Levko D. , Yatom S. , Vekselman V. , Krasik Ya. E.
Published: February 2012

A comparison between the results of x-ray absorption spectroscopy of runaway electrons (RAEs) generated during nanosecond timescale high-voltage (HV) gas discharge and the simulated attenuation of the x-ray flux produced by the runaway electron spectrum calculated using particle-in-cell numerical modeling of such a type of discharge is presented. The particle-in-cell simulation considered the field and explosive emissions (EEs) of the electrons from the cathode. It is shown that the field emission is the dominant emission mechanism for the short-duration (<2.5 ns) high-voltage pulses, while for the long-duration (>5 ns) high-voltage pulses, the explosive emission is likely to play a significant role.
AlGaN-based ultraviolet light-emitting diodes using fluorine-doped indium tin oxide electrodes
Authors: Ju Chae Dong , Yoon Kim Dong , Geun Kim Tae , Mo Sung Yun , Doeck Kim Moon
Published: February 2012

In this paper, improved electrical and optical properties of aluminum gallium nitride (AlGaN)-based ultraviolet light-emitting diodes using fluorine-doped indium tin oxide (F-ITO) electrodes are reported. F-doping was found to increase the work function as well as the energy bandgap of the ITO and, thereby, reduce the Shottky barrier height in contact with p-(Al)GaN. As a result, the optical transmittance increased from 79.7% to 86.9% at 380 nm, while the specific contact resistance decreased from 1.04 × 10−3 Ω·cm2 to 9.12 × 10−4 Ω·cm2 after F-doping, which led to an increase in the output power from 2.41 mW to 5.99 mW.
The vibration dipole: A time reversed acoustics scheme for the experimental localisation of surface breaking cracks
Authors: Van Damme Bart , Van Den Abeele Koen , Bou Matar Olivier
Published: February 2012

A combination of time reversed acoustics and nonlinear elastic wave spectroscopy techniques is introduced to localize surface breaking defects in a non-destructive manner. Reciprocal time reversal is applied at two neighbouring positions in order to create a vibration dipole with high amplitudes. At surface breaking cracks, nonlinear elastic effects are triggered by the shear forces due to induced friction of the crack interfaces. By mapping the nonlinearity generated by the vibration dipole over the sample surface, the position of a surface breaking crack can be visualized. The technique is tested on an industrial steel sample containing a closed crack.
Formation of ordered one-dimensional microstructures of dislocations in near-surface layer of semiconductor, under laser radiation with microstructured distribution of intensity
Authors: Banishev A. F. , Banishev A. A.
Published: February 2012

The paper presents the results of investigation the process of formation of the ordered microstructures of dislocations in the near-surface layer a single-crystal plate of silicon under the action of pulsed laser radiation with microstructured distribution intensity. It has been found that generation of the ordered one-dimensional microstructures of dislocations takes place. The period of these ordered microstructures is d≈3÷4 μm. A combination of one-dimensional structures of dislocations produces ordered two-dimensional structure of dislocations.
Judging a patient's decision to seek emergency healthcare: clues for managing increasing patient demand
Authors: Morgans Amee , Burgess Stephen
Published: February 2012

Objective. In recent years, the concept of an ‘inappropriate’ emergency department or ambulance user has arisen. This discussion paper explores definition and measurement of inappropriate emergency healthcare utilisation, and the effect on demand. Method. A comprehensive literature review of published articles was conducted. Results. Exploration of the definitions of ‘inappropriate’ emergency healthcare utilisation identified two patient cohorts; emergency healthcare utilisation by those who are not experiencing a health emergency, and those who do not seek emergency healthcare who should. Several position papers from Australian and international sources emphasised the patient’s right to access emergency healthcare when they feel the need, and the responsibility of emergency healthcare workers to provide treatment to all patients. Differences between medical classifications of urgency based on physiological measures are contrasted with patient-based determination of urgency, which is defined by psychosocial factors. Conclusions. This literature review raises questions about patients’ understanding of the role of emergency healthcare services in an emergency. This has implications for determining the patient’s point of access to the health system in an acute health event, and offers an opportunity to selectively educate patients and carers to change help-seeking behaviours to suit the health system resources and moderate patient demand. What is known about the topic? There is a public health issue where some patients seek emergency healthcare when they are not acutely unwell (inappropriate health service users) and some patients who fail to seek emergency healthcare when they are acutely unwell (patients who ‘delay’ or avoid using emergency health services). There is a difference in understanding between health professionals and patients about what a health emergency is and when it is appropriate to seek emergency healthcare. There is an increasing demand for emergency health services both nationally and internationally. What does this paper add? This paper provides a review of Australian and international rates of ‘inappropriate’ healthcare utilisation. This paper identifies the limitations on the ability to determine whether patients were appropriate or inappropriate, and instead identifies what motivates patients to seek emergency healthcare for non-acute events and fail to seek healthcare for acute events. What are the implications for practitioners? There is a high demand for health services, which is increasing, and understanding patient motivations to seek healthcare may assist the development of demand management strategies. This paper will enhance practitioner understanding of patient motivation to seek emergency healthcare. This paper concludes with educational information that practitioners can use to change patient healthcare utilisation patterns.
Near-Infrared Properties of Type Ia Supernovae
Authors: Phillips M. M.
Published: February 2012

The photometric properties of Type Ia supernovae (SNe Ia) in the near-infrared as garnered from observations made over the last 30 years are reviewed. During this period, light curves for more than 120 nearby SNe Ia have been published, revealing considerable homogeneity but also some fascinating differences. These data have confirmed that, for all but the fastest declining objects, SNe Ia are essentially perfect standard candles in the near-infrared, displaying only a slight dependence of peak luminosity on decline rate and color.
SRY (sex determining region Y)-box2 (Sox2)/poly ADP-ribose polymerase 1 (Parp1) complexes regulate pluripotency
Authors: Lai Yi-Shin , Chang Chia-Wei , Pawlik Kevin M. , Zhou Dewang , Renfrow Matthew B. , Townes Tim M.
Published: February 2012

To gain insight into mechanisms controlling SRY (sex determining region Y)-box 2 (Sox2) protein activity in mouse embryonic stem cells (ESCs), the endogenous Sox2 gene was tagged with FLAG/Hemagglutinin (HA) sequences by homologous recombination. Sox2 protein complexes were purified from Sox2/FLAG/HA knockin ESCs, and interacting proteins were defined by mass spectrometry. One protein in the complex was poly ADP-ribose polymerase I (Parp1). The results presented below demonstrate that Parp1 regulates Sox2 protein activity. In response to fibroblast growth factor (FGF)/extracellular signal-regulated kinase (ERK) signaling, Parp1 auto-poly ADP-ribosylation enhances Sox2-Parp1 interactions, and this complex inhibits Sox2 binding to octamer-binding transcription factor 4 (Oct4)/Sox2 enhancers. Based on these results, we propose a unique mechanism in which FGF signaling fine-tunes Sox2 activity through posttranslational modification of a critical interacting protein, Parp1, and balances the maintenance of ESC pluripotency and differentiation. In addition, we demonstrate that regulation of Sox2 activity by Parp1 is critical for efficient generation of induced pluripotent stem cells.
Eye Movements Reveal no Immediate “WOW” (“Which One's Weird”) Effect in Autism Spectrum Disorder
Authors: Benson Valerie , Castelhano Monica S. , Au-Yeung Sheena K. , Rayner Keith
Published: February 2012

Autism spectrum disorder (ASD) and typically developed (TD) adult participants viewed pairs of scenes for a simple “spot the difference” (STD) and a complex “which one's weird” (WOW) task. There were no group differences in the STD task. In the WOW task, the ASD group took longer to respond manually and to begin fixating the target “weird” region. Additionally, as indexed by the first-fixation duration into the target region, the ASD group failed to “pick up” immediately on what was “weird”. The findings are discussed with reference to the complex information processing theory of ASD (Minshew & Goldstein, 1998).
Sarcoplasmic reticulum Ca2+ permeation explored from the lumen side in mdx muscle fibers under voltage control
Authors: Robin Gaëlle , Berthier Christine , Allard Bruno
Published: February 2012

Under resting conditions, external Ca2+ is known to enter skeletal muscle cells, whereas Ca2+ stored in the sarcoplasmic reticulum (SR) leaks into the cytosol. The nature of the pathways involved in the sarcolemmal Ca2+ entry and in the SR Ca2+ leak is still a matter of debate, but several lines of evidence suggest that these Ca2+ fluxes are up-regulated in Duchenne muscular dystrophy. We investigated here SR calcium permeation at resting potential and in response to depolarization in voltage-controlled skeletal muscle fibers from control and mdx mice, the mouse model of Duchenne muscular dystrophy. Using the cytosolic Ca2+ dye Fura2, we first demonstrated that the rate of Ca2+ increase in response to cyclopiazonic acid (CPA)–induced inhibition of SR Ca2+-ATPases at resting potential was significantly higher in mdx fibers, which suggests an elevated SR Ca2+ leak. However, removal of external Ca2+ reduced the rate of CPA-induced Ca2+ increase in mdx and increased it in control fibers, which indicates an up-regulation of sarcolemmal Ca2+ influx in mdx fibers. Fibers were then loaded with the low-affinity Ca2+ dye Fluo5N-AM to measure intraluminal SR Ca2+ changes. Trains of action potentials, chloro-m-cresol, and depolarization pulses evoked transient Fluo5N fluorescence decreases, and recovery of voltage-induced Fluo5N fluorescence changes were inhibited by CPA, demonstrating that Fluo5N actually reports intraluminal SR Ca2+ changes. Voltage dependence and magnitude of depolarization-induced SR Ca2+ depletion were found to be unchanged in mdx fibers, but the rate of the recovery phase that followed depletion was found to be faster, indicating a higher SR Ca2+ reuptake activity in mdx fibers. Overall, CPA-induced SR Ca2+ leak at −80 mV was found to be significantly higher in mdx fibers and was potentiated by removal of external Ca2+ in control fibers. The elevated passive SR Ca2+ leak may contribute to alteration of Ca2+ homeostasis in mdx muscle.
Matrix and quantum confinement effects on optical and thermal properties of Ge quantum dots
Authors: Chang J E , Liao P H , Chien C Y , Hsu J C , Hung M T , Chang H T , Lee S W , Chen W Y , Hsu T M , George Tom , Li P W
Published: February 2012

The influence of SiO2 and Si3N4 dielectric matrices on the structural, phonon, luminescence and thermal properties of Ge quantum dots (QDs) has been experimentally investigated. Compared with the case of QDs in SiO2 layers, Si3N4 matrix imposes large interfacial surface energy on QDs and enhances their Ostwald ripening rate, appearing to be conducive for an improvement in crystallinity and a morphology change to a more perfectly spherical shape of Ge QDs. Quantum confinement induced electronic structure modulation for Ge QDs is observed to be strongly influenced not only by the QD size but also by the embedded matrix. Both matrix and surface effects offer additional mechanisms to QD itself for controlling the optical and thermal properties of the QDs.
Synthesis, structure and electric properties of Pb(Yb1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 ternary ceramics
Authors: He Chao , Wang Zujian , Li Xiuzhi , Liu Ying , Shen Dongquan , Li Tao , Long Xifa
Published: February 2012

The ternary ceramics of Pb(Yb1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PYMNT) solid solution system is prepared by a two-step synthetic process. Its structure and electrical properties are studied. All the obtained ceramics have pure perovskite structure. It is noted that the morphotropic phase boundary (MPB) of the PYMNT ternary system is not a linear region which is between the MPB compositions of PMNT and PYNT binary systems. The Curie temperature T
C of the ternary system varies in the range 165–370 °C and the piezoelectric coefficient d
33 varies in the range 335–505 pC N−1. With increasing PYNT content, the dielectric constants ε′ decrease and the coercive field E
c increases. Therefore, the electric properties and T
C can be adjusted by selection of composition. The results show that the PYMNT ceramic exhibits higher Curie temperature, larger coercive field and good piezoelectric properties, making it a promising material for high-power electromechanical transducers that can operate in a large temperature range.
Macroscopic effects of tunnelling barriers in aggregates of carbon nanotube bundles
Authors: Salvato M , Cirillo M , Lucci M , Orlanducci S , Ottaviani I , Terranova M L , Toschi F
Published: February 2012

We report on experiments conducted on single-walled carbon nanotube bundles aligned in chains and connected through a natural contact barrier. The dependence upon the temperature of the transport properties is investigated for samples having different characteristics. Starting from two bundles separated by one barrier deposited over four-contact probes, we extend the study of the transport properties to samples formed by chains of several bundles. The systematic analysis of the properties of these aggregates shows the existence of two conduction regimes in the barrier. We show that an electrical circuit taking into account serial and parallel combinations of voltages generated at the junctions between bundles can model the samples consistently.
Computing the table of marks of a cyclic extension
Authors: Naughton L. , Pfeiffer G.
Published: February 2012

The subgroup pattern of a finite group

G
G

is the table of marks of

G
G

together with a list of representatives of the conjugacy classes of subgroups of

G
G

. In this article we present an algorithm for the computation of the subgroup pattern of a cyclic extension of

G
G

from the subgroup pattern of

G
G

. Repeated application of this algorithm yields an algorithm for the computation of the table of marks of a solvable group

G
G

, along a composition series of 

G
G

.
The relative importance of shallow and deep shelf spawning habitats for the South African chokka squid (Loligo reynaudii)
Authors: Roberts Michael J. , Downey Nicola J. , Sauer Warwick H.
Published: February 2012

Roberts, M. J., Downey, N. J., and Sauer, W. H. 2012. The relative importance of shallow and deep shelf spawning habitats for the South African chokka squid (Loligo reynaudii). – ICES Journal of Marine Science, 69: 563–571. It is well known that the spawning grounds of chokka squid Loligo reynaudii lie along the shallow inshore regions of South Africa's south coast. However, egg masses have been found in deeper water on the Agulhas Bank, and hydroacoustic targets deemed to be large aggregations of spawning squid have been identified. The aim of this study was to investigate the extent, depth range, and importance of deep spawning. Trawl data collected during demersal research surveys between Port Nolloth on the west and Port Alfred on the south coast were examined for egg capsules. No spawning was found on the west coast. Data showed that chokka squid preferred the eastern Agulhas Bank for spawning. Spawning occurred not only inshore but also on the mid-shelf extending to depths of 270 m near the shelf edge. Squid egg biomass markedly decreased beyond 70 m, suggesting delineation between the inshore and offshore spawning grounds. Total egg biomass calculations for depths shallower and deeper than 70 m indicated the coastal area to be strongly favoured, i.e. 82 vs. 18%. These results contest the commonly accepted notion that L. reynaudii is an inshore spawner and redefine the spawning grounds to extend across the shelf.
Atlantic water in the Faroe area: sources and variability
Authors: Larsen Karin Margretha H. , Hátún Hjálmar , Hansen Bogi , Kristiansen Regin
Published: February 2012

Larsen, K. M. H., Hátún, H., Hansen, B., and Kristiansen, R. 2012. Atlantic water in the Faroe area: sources and variability. – ICES Journal of Marine Science, 69: 802–808. The inflow of Atlantic water (AW) across the Greenland–Scotland Ridge and into the Nordic Seas controls both physical and biological conditions in the northeastern Atlantic through its transport of heat, salt, and other properties. The two main branches of this flow pass through the Iceland–Faroe Gap and the Faroe–Shetland Channel, respectively. Regular monitoring along four standard sections crossing these flows provides time-series of the AW temperature and salinity variability since the late 1980s. The analysis of these series presented shows a persistent increasing trend in both temperature and salinity, modulated by smaller subdecadal oscillations. Using supplementary data sources, the previously established link between the large-scale circulation in the North Atlantic and Atlantic inflow properties is supported. Salinity is also impacted by large changes in the Bay of Biscay source waters, and upstream air–sea heat fluxes modulate temperature. Relationships between changes in transport and associated residence time, and the modifying strength of the air–sea interaction and mixing, are also discussed.