bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiscale unit‐memory convolutional codes
Authors: Nagaraj Santosh V. , Bell Mark R.
Published: August 2013

In this study, authors propose structure to unit memory (UM) convolutional codes that greatly simplify their decoding when using sequential or suboptimal L‐decoders. The multiscale structure proposed in this study preserves the word‐oriented nature of unit memory codes (UMCs), but allows for processing the code in blocks of sizes less than the memory of the code with non‐Viterbi‐type decoders. At one end of the multiscale structure are generic UMCs. At the other end are structured systematic UMCs that can be decoded with the same ease as conventional multimemory convolutional codes with sequential or L‐decoders. As a special case, the authors show quick‐look parity check systematic codes of arbitrary rates that are better than previously known optimum minimum distance systematic convolutional codes. These codes are derived from block codes and the convolutional code can be decoded using the syndrome decoder of the underlying block code. The authors present simulation results and analysis to support the proposed multiscale UM convolutional codes.
Single feed circularly polarised omnidirectional bifilar helix antennas with wide axial ratio beamwidth
Authors: Amin Muhammad , Yousaf Jawad , Iqbal Sana
Published: August 2013

This study presents design and analysis of single feed omnidirectional circularly polarised resonant side‐fed bifilar helix antennas with wide axial ratio (AR) beamwidth that does not require a ground plane. The simulation results show that side‐fed helix antennas of various radii give polarisation beamwidth (for AR ≤3 dB) from 170° to 178° in elevation planes at a certain turn angle where area of the loop equals the product of pitch and radianlength of the helix. Circularly polarised helix antennas with smaller radii are of higher turn angle, have lower value of resonant input impedances but AR is less sensitive to inaccuracy in turn angle and vice versa for helix with larger radii. The gain and 3 dB beamwidth of the antennas are 2 dBi and 90°, respectively. The polarisation bandwidth (for AR ≤3 dB) varies from 34 to 65%. The simulated results are verified by experimental measurements.
Ultra‐wideband slot antenna with a stop‐band notch
Authors: Ojaroudi Nasser , Ojaroudi Mohammad
Published: August 2013

In this study, a simple and compact ultra‐wideband (UWB) printed slot antenna with band‐notch performance is designed and manufactured. To increase the impedance bandwidth of the square slot antenna, the authors use an S‐shaped parasitic structure inside the rectangular slot on the feed line. By using this structure UWB frequency range can be achieved. Additionally, by using square‐ring stub with two L‐shaped protruded strip inside the square‐ring stub, a frequency notched band performance has been obtained. The designed antenna has a small size of 20 × 20 mm2, wheeas showing the radiation performance in the frequency band of 3.05 to over 12.76 GHz with a band rejection performance in the frequency band of 5.13 to 6.04 GHz, which has a frequency bandwidth increment of 13% with respect to the previous similar antenna.
Microwave signal conditioning through non‐reciprocal phase shifting
Authors: Palomba Mirko , Limiti Ernesto
Published: August 2013

Two non‐reciprocal microwave signal conditioning circuits, a non‐reciprocal phase shifter and a quasi‐circulator, are proposed as based on the use of active microwave devices. Analytical expressions are derived to demonstrate the principles of operation and prototypes are presented both in hybrid and monolithic form. The hybrid structures operate in the L‐band, whereas the monolithic ones are designed for X‐band operation, and demonstrate the compactness and performance of the proposed topologies.
Multiscale modelling of coupled Ca2+ channels using coloured stochastic Petri nets
Authors: Liu Fei , Heiner Monika
Published: August 2013

Stochastic modelling of coupled Ca2+ channels is a challenge, especially when the coupling of the channels, as determined by their spatial arrangement relative to each other, has to be considered at multiple spatial scales. In this study, the authors address this problem using coloured stochastic Petri nets (𝒮𝒫𝒩𝒸) as high‐level description to generate continuous‐time Markov chains. The authors develop several models with increasing complexity. They first apply 𝒮𝒫𝒩𝒸 to model single clusters of coupled Ca2+ channels arranged in a regular or irregular lattice, where they describe how to represent the geometrical arrangement of Ca2+ channels relative to each other using colours. They then apply this modelling idea to construct more complex models by modelling spatially arranged clusters of channels. The authors’ models can be easily reproduced and adapted to different scenarios.
Electroactive hydrogel comprising poly(methyl 2-acetamido acrylate) for an artificial actuator
Authors: Ha Eun-Ju , Kim Bong-Soo , Park Chun-ho , Lee Jang-Oo , Paik Hyun-jong
Published: August 2013

A poly(methyl 2-acetamidoacrylic acrylate) (MAA) hydrogel was developed for use in an artificial actuator. The equilibrium swelling ratio of the MAA hydrogel was observed at different pH values with different concentrations of cross-linking agent; the hydrogel containing 2% cross-linking agent exhibited the maximum equilibrium swelling ratio at pH 10. The bending behavior of the MAA hydrogel under an electric field was measured in aqueous NaCl. The actuation response of the MAA hydrogel occurred via reversible bending behavior at 6 V. It was found that the MAA hydrogel features stable bending behavior over consecutive cycles in aqueous NaCl at different voltages depending on the cross-linking agent. Hence, the MAA hydrogel can be utilized as an artificial actuator using electrical stimulus.
Two fluid shear-free composites
Authors: Krisch J. P. , Glass E. N.
Published: August 2013

Shear-free composite fluids are constructed from two Letelier rotated unaligned perfect fluids. The component fluid parameters necessary to construct a shear-free composite are investigated. A metric in the Stephani-Barnes solution family and a simple stationary metric are discussed.
Conservative parameterization schemes
Authors: Bihlo Alexander , Bluman George
Published: August 2013

Parameterization (closure) schemes in numerical weather and climate prediction models account for the effects of physical processes that cannot be resolved explicitly by these models. Methods for finding physical parameterization schemes that preserve conservation laws of systems of differential equations are introduced. These methods rest on the possibility to regard the problem of finding conservative parameterization schemes as a conservation law classification problem for classes of differential equations. The relevant classification problems can be solved using the direct or inverse classification procedures. In the direct approach, one starts with a general functional form of the parameterization scheme. Specific forms are then found so that corresponding closed equations admit conservation laws. In the inverse approach, one seeks parameterization schemes that preserve one or more pre-selected conservation laws of the initial model. The physical interpretation of both classification approaches is discussed. Special attention is paid to the problem of finding parameterization schemes that preserve both conservation laws and symmetries. All methods are illustrated by finding conservative and invariant conservative parameterization schemes for systems of one-dimensional shallow-water equations.
Effective interactions between solid particles mediated by free polymer in solution
Authors: Shvets A. A. , Semenov A. N.
Published: August 2013

Effective potentials of interaction between solid non-adsorbing surfaces in semidilute or concentrated polymer solutions are calculated using two approaches: the numerical self-consistent-field theory (SCFT) and the analytical theory generalizing the ground-state dominance approximation by taking into account the finite chain-length (chain-end) effects (GSDE). A good agreement between the two approaches is demonstrated within the natural region of validity of the asymptotically exact GSDE theory. It is shown that in most cases the interaction potentials involve the short-range depletion attraction which is replaced by the polymer-mediated repulsion at longer separations ranging from roughly 10ξ to 3Rg (ξ is the concentration correlation length and Rg is the polymer coil gyration radius). For a given polymer concentration and molecular weight the highest repulsion energy barrier, Um, is predicted for ξ/Rg ∼ 0.2 and in the theta-solvent conditions. The fluctuation-induced (anti-Casimir) polymer-mediated repulsion forces are analyzed as well. It is shown that the overall polymer-mediated repulsion energy between naked spherical particles of radius Rc = 200 nm is typically not enough for their kinetic stabilization. There are, however, a few special cases where colloidal stability can be imparted by free polymers only.
Development of multi-environment dual-probe atomic force microscopy system using optical beam deflection sensors with vertically incident laser beams
Authors: Tsunemi Eika , Kobayashi Kei , Oyabu Noriaki , Hirose Masaharu , Takenaka Yoshiko , Matsushige Kazumi , Yamada Hirofumi
Published: August 2013

We developed a dual-probe atomic force microscopy (DP-AFM) system with two cantilever probes that can be operated in various environments such as in air, vacuum, and liquid. The system employs the optical beam deflection method for measuring the deflection of each cantilever mounted on a probe scanner. The cantilever probes mounted on the probe scanners are attached to inertia sliders, which allow independent control of the probe positions. We constructed three types of probe scanners (tube, shear-piezo, and tripod types) and characterized their performance. We demonstrated AFM imaging in ambient air, vacuum, and ultrapure water, and also performed electrical measurement and pick-up manipulation of a Au nanorod using the DP-AFM system.
Non-Levi closed conjugacy classes of SO
q(N)
Authors: Mudrov Andrey
Published: August 2013

We construct explicit quantization of semisimple conjugacy classes of the complex orthogonal group SO(N) with non-Levi isotropy subgroups through an operator realization on highest weight modules of the quantum group \documentclass[12pt]{minimal}\begin{document}$U_q\bigl (\mathfrak {s}\mathfrak {o}(N)\bigr )$\end{document}Uqso(N).
Status and characterization of the lithium beam diagnostic on DIII-D
Authors: Stoschus H. , Thomas D. M. , Hudson B. , Watkins M. , Finkenthal D. F. , Moyer R. A. , Osborne T. H.
Published: August 2013

The 30 keV lithium beam diagnostic on DIII-D is suitable to measure both the radial electron density and poloidal magnetic field profiles in the pedestal. The refurbished system features a new setup to measure the Doppler shift allowing accurate alignment of the spectral filters. The injector has been optimized to generate a stable lithium neutral beam with a current of I = 15−20 mA and a diameter of 1.9 ± 0.1 cm measured by beam imaging. The typical temporal resolution is Δt = 1−10 ms and the radial resolution of ΔR = 5 mm is given by the optical setup. A new analysis technique based on fast Fourier transform avoids systematic error contributions from the digital lock-in analysis and accounts intrinsically for background light correction. Latest upgrades and a detailed characterization of the system are presented. Proof-of-principle measurements of the poloidal magnetic field with a statistical error of typically 2% show a fair agreement with the predictions modeled with the Grad-Shafranov equilibrium solver EFIT within 4%.
Enhanced thermoelectric performance of Mg2Si0.4Sn0.6 solid solutions by in nanostructures and minute Bi-doping
Authors: Zhang Xin , Liu Hongliang , Lu Qingmei , Zhang Jiuxing , Zhang Feipeng
Published: August 2013

n-type Mg2(Si0.4Sn0.6)Bix (0 ≤ x ≤ 0.04) solid solutions with minute amounts of Bi were prepared by induction melting, melt spinning (MS), and spark plasma sintering (SPS) method, namely the non-equilibrium technique MS-SPS, using bulks of Mg, Si, Sn, Bi as raw materials; the phase components, microstructures as well as the thermoelectric properties were systematically investigated. The multiple localized nanostructures within the matrix containing nanoscale precipitates and mesoscale grains were formed, resulting in remarkably decreasing of lattice thermal conductivities, particularly for samples with the nanoscale precipitates having the size of 10–20 nm. Meanwhile, the electrical resistivity was reduced and the Seebeck coefficient was increased by Bi-doping, causing improved electrical performance for the Mg2(Si0.4Sn0.6)Bix (0 ≤ x ≤ 0.04) compounds. The dimensionless figure of merit ZT was significantly improved and the maximum value reaches 1.20 at 573 K for the Mg2(Si0.4Sn0.6)Bi0.03 sample, greatly higher than that of the non-doped samples.
Magnetic dipole discharges. I. Basic properties
Authors: Stenzel R. L. , Urrutia J. M. , Teodorescu-Soare C. T. , Ionita C. , Schrittwieser R.
Published: August 2013

A simple discharge is described which uses a permanent magnet as a cold cathode and the metallic chamber wall as an anode. The magnet's equator is biased strongly negative, which produces secondary electrons due to the impact of energetic ions. The emitted electrons are highly confined by the strong dipolar magnetic field and the negative potential in the equatorial plane of the magnet. The emitted electrons ionize near the sheath and produce further electrons, which drift across field lines to the anode while the nearly unmagnetized ions are accelerated back to the magnet. A steady state discharge is maintained at neutral pressures above 10−3 mbar. This is the principle of magnetron discharges, which commonly use cylindrical and planar cathodes rather than magnetic dipoles as cathodes. The discharge properties have been investigated in steady state and pulsed mode. Different magnets and geometries have been employed. The role of a background plasma has been investigated. Various types of instabilities have been observed such as sheath oscillations, current-driven turbulence, relaxation instabilities due to ionization, and high frequency oscillations created by sputtering impulses, which are described in more detail in companion papers. The discharge has also been operated in reactive gases and shown to be useful for sputtering applications.
Magnetic dipole discharges. II. Cathode and anode spot discharges and probe diagnostics
Authors: Stenzel R. L. , Urrutia J. M. , Ionita C. , Schrittwieser R.
Published: August 2013

The high current regime of a magnetron-type discharge has been investigated. The discharge uses a permanent magnet as a cold cathode which emits secondary electrons while the chamber wall or a grounded electrode serves as the anode. As the discharge voltage is increased, the magnet develops cathode spots, which are short duration arcs that provide copious electrons to increase the discharge current dramatically. Short (1 μs), high current (200 A) and high voltage (750 V) discharge pulses are produced in a relaxation instability between the plasma and a charging capacitor. Spots are also observed on a negatively biased plane Langmuir probe. The probe current pulses are as large as those on the magnet, implying that the high discharge current does not depend on the cathode surface area but on the properties of the spots. The fast current pulses produce large inductive voltages, which can reverse the electrical polarity of the magnet and temporarily operate it as an anode. The discharge current may also oscillate at the frequency determined by the charging capacitor and the discharge circuit inductance. Each half cycle of high-current current pulses exhibits a fast (≃10 ns) current rise when a spot is formed. It induces high frequency (10–100 MHz) transients and ringing oscillations in probes and current circuits. Most probes behave like unmatched antennas for the electromagnetic pulses of spot discharges. Examples are shown to distinguish the source of oscillations and some rf characteristics of Langmuir probes.
Permutation invariant polynomial neural network approach to fitting potential energy surfaces
Authors: Jiang Bin , Guo Hua
Published: August 2013

A simple, general, and rigorous scheme for adapting permutation symmetry in molecular systems is proposed and tested for fitting global potential energy surfaces using neural networks (NNs). The symmetry adaptation is realized by using low-order permutation invariant polynomials (PIPs) as inputs for the NNs. This so-called PIP-NN approach is applied to the H + H2 and Cl + H2 systems and the analytical potential energy surfaces for these two systems were accurately reproduced by PIP-NN. The accuracy of the NN potential energy surfaces was confirmed by quantum scattering calculations.
Characterization of a high pressure, high temperature modification of ammonia borane (BH3NH3)
Authors: Nylén Johanna , Eriksson Lars , Benson Daryn , Häussermann Ulrich
Published: August 2013

At elevated pressures (above 1.5 GPa) dihydrogen bonded ammonia borane, BH3NH3, undergoes a solid-solid phase transition with increasing temperature. The high pressure, high temperature (HPHT) phase precedes decomposition and evolves from the known high pressure, low temperature form with space group symmetry Cmc21 (Z = 4). Structural changes of BH3NH3 with temperature were studied at around 6 GPa in a diamond anvil cell by synchrotron powder diffraction. At this pressure the Cmc21 phase transforms into the HPHT phase at around 140 °C. The crystal system, unit cell, and B and N atom position parameters of the HPHT phase were extracted from diffraction data, and a hydrogen ordered model with space group symmetry Pnma (Z = 4) subsequently established from density functional calculations. However, there is strong experimental evidence that HPHT-BH3NH3 is a hydrogen disordered rotator phase. A reverse transition to the Cmc21 phase is not observed. When releasing pressure at room temperature to below 1.5 GPa the ambient pressure (hydrogen disordered) I4mm phase of BH3NH3 is obtained.
Effective protein-protein interaction from structure factor data of a lysozyme solution
Authors: Abramo M. C. , Caccamo C. , Cavero M. , Costa D. , Pellicane G. , Ruberto R. , Wanderlingh U.
Published: August 2013

We report the determination of an effective protein-protein central potential for a lysozyme solution, obtained from the direct inversion of the total structure factor of the system, as extracted from small angle neutron scattering. The inversion scheme rests on a hypernetted-chain relationship between the effective potential and the structural functions, and is preliminarily tested for the case of a Lennard-Jones interaction. The characteristics of our potential are discussed in comparison with current models of effective interactions in complex fluids. The phase behavior predictions are also investigated.
Direct observation of internal energy distributions of ${\rm C}_5^-$C5−
Authors: Goto M. , Sundén A. E. K. , Shiromaru H. , Matsumoto J. , Tanuma H. , Azuma T. , Hansen K.
Published: August 2013

Photon induced decay of \documentclass[12pt]{minimal}\begin{document}${\rm C}_5^-$\end{document}C5− has been measured in an electrostatic storage ring. The time dependence of the photo-enhanced decay is close to a 1/t decay which indicates a thermal process. The deviation from the expected power of −1 is quantitatively explained by the small heat capacity of the anion. Measurements of the photo-enhanced decay at different storage times and photon energies allow a determination of the radiative cooling rate and the energy distribution of the ions. The average energy content between 15 and 70 ms is found to vary as time to the power −0.72, and at 50 ms the ions contain an average excitation energy of 0.5 eV. The time dependent energy distribution is consistent with cooling by infrared photon emission if published oscillator strengths are reduced by a factor 2.5, in contrast to cooling of larger molecular carbon-based ions where electronic transitions cause a much stronger cooling.
A new design of indirectly heated cathode based strip type electron gun
Authors: Maiti Namita , Lijeesh K. , Barve U. D. , Quadri Nishad , Tembhare G. U. , Mukherjee S. , Thakur K. B. , Das A. K.
Published: August 2013

A new design of indirectly heated solid cathode based electron gun (200 kW, 45 kV, 270° bent strip type electron gun) has been presented. The design issue addressed is the uniformity of temperature on the solid cathode using (a) a multi-segmented filament with variable height as the primary heat source and (b) trapezoidal shaped single long filament as the primary heat source. The proposed design in this paper is based on computer simulation and validated by extensive experimentations. The design emphasis is on maintaining uniform temperature on the solid cathode. The designed multi-segment filament and the single long filament provide a temperature uniformity on the solid cathode of about 250 K and 110 K, respectively. The better temperature uniformity inspite of the thermal expansion, in case of a single long filament tightly clamped at two ends, has been possible due to shaping of the single filament with a number of constituent sections such that the thermal expansion of different sections forming the actual filament takes care of not only the mechanical stability but also does not affect the emitting surface of the filament. Experiments show that the modified design achieves a one to one correspondence of the solid cathode length and the electron beam length emitted from the solid cathode.
Generation of single bubbles of various sizes using a slitting elastic tube
Authors: Sanada T. , Abe K.
Published: August 2013

The generation of single bubbles is often required in laboratory research. However, it is very difficult to control bubble production, especially for a required bubble size, by using the same orifice. In this study, we demonstrate the control of bubble formation by combining a pulsed acoustic pressure wave in a gas phase and a slitting elastic tube. By elastically deforming the tube using the acoustic wave, we can control the bubble radius in the range from 300 μm to 5 mm by using the same tube without liquid flow. This method can produce bubbles with good repeatability and small individual differences in the tubes.
Magnesium cluster film synthesis by helium nanodroplets
Authors: Emery Samuel B. , Rider Keith B. , Little Brian K. , Schrand Amanda M. , Lindsay C. Michael
Published: August 2013

Atomic and molecular clusters are a unique class of substances with properties that differ greatly from those of the bulk or single atoms due to changes in surface to volume ratio and finite size effects. Here, we demonstrate the ability to create cluster matter films using helium droplet mediated cluster assembly and deposition, a recently developed methodology that condenses atoms or molecules within liquid helium droplets and then gently deposits them onto a surface. In this work, we examine magnesium nanocluster films, which exhibit growth behavior comparable to low-energy cluster beam methods, and demonstrate physical properties and morphology dependent on helium droplet size.
Stability of the Mn photoluminescence in bifunctional ZnS:0.05Mn nanoparticles
Authors: Beltran-Huarac Juan , Wang Jingzhou , Tanaka Hiroki , Jadwisienczak Wojciech M. , Weiner Brad R. , Morell Gerardo
Published: August 2013

We investigate the stability of the orange band photoluminescence (PL) of bifunctional nanoparticles of Mn2+-doped ZnS at 5% (ZnS:0.05Mn). These 4-nm nanoparticles are synthesized via a one-step inorganic chemical route under ambient conditions. The phase, crystallinity, and morphology are analyzed via X-ray and electron diffractions and high-resolution electron microscopy. Based on the thermally activated carrier-transfer model, it is found that orange emission is rather stable at low temperatures and possesses thermal activation energy of ∼18 meV. The analysis of the PL decay curves suggests the coexistence of multiple lifetimes, that the shortening observed in PL lifetime is not due to the Mn2+ ions, and that the orange band decay is stable in temperature range from 10 K to 300 K. The measured M-H hysteresis loops demonstrate that ZnS:0.05Mn nanoparticles exhibit ferromagnetic ordering below 30 K, unlike its bulk counterpart. No magnetic field dependence of the Mn2+ PL intensity is observed up to 1 T. The stability of the PL signal when subject to an applied magnetic field is discussed. This study offers experimental evidence to test low-dimensional dilute magnetic semiconductor models and widens the range of applications of ZnS:Mn nanostructures beyond optoelectronics.
Structural and electronic properties of Ni26–p
X
p clusters (X = Pd, Pt): A density-functional-theoretic study
Authors: Aguilera-Granja F. , Gallego L. J.
Published: August 2013

We performed density-functional-theoretic calculations to investigate the structural, energetic, and electronic properties of the binary clusters Ni26–pXp (X = Pd, Pt) at T = 0 K. For small p, Pd and Pt clusters exhibit similar polyicosahedral structures and similar chemical order, the Pd or Pt atoms occupying positions with the lowest possible coordination numbers, forming “islands” separated from each other on the cluster surface. For intermediate and large p, there are marked differences between the Pd and Pt clusters. Notably, all the Ni26–pPdp clusters are polyicosahedral, whereas Ni26–pPtp clusters transition from polyicosahedral to cubic between p = 18 and p = 22. Also, whereas Pd atoms continue to constitute separated surface islands for as long as possible as p increases, until the islands eventually coalesce to form a shell surrounding an Ni core, Ni26–pPtp clusters transition from the “separated surface islands” configuration to the all-Pt structure via a series of configurations featuring Pt and Ni layers.
Polarization relaxation and charge injection in thin films of poly(vinylidene fluoride/trifluoroethylene) copolymer
Authors: Mai Manfang , Martin Bjoern , Kliem Herbert
Published: August 2013

Polarization relaxation effects and charge injection in poly(vinylidene fluoride/trifluoroethylene) thin films are investigated in a thickness range between 60 nm and 400 nm. In time domain measurements of polarization reversal, the switching transients exhibit two stages: a rapid increase of polarization followed by a continuous slow increase lasting for several decades. This continuous increase of the polarization corresponds to a t−α (Kohlrausch law) behaviour of the current density in the long time range. For a constant electric field, these currents in the long time range are independent of the sample thickness as expected for a relaxational volume polarization effect. Furthermore, the isochronal polarization and depolarization currents saturate at high fields. We described the experiments using an asymmetric double well potential model with a distribution of relaxation times in which dipoles are fluctuating thermally activated between the two minima. As temperature increases, charge injection sets in. The charging currents then deviate from the t−α behaviour and become constant in time. The discharging currents are found to be a superposition of dipole relaxational currents and space charge relaxational currents. In the short time range, only the dipole relaxational currents are found. After several seconds, a space charge relaxation current with a pronounced minimum in time sets in, whose time constant shifts to shorter values with increasing temperature.
Imaging of the relative saturation current density and sheet resistance of laser doped regions via photoluminescence
Authors: Yang Xinbo , Macdonald D. , Fell A. , Shalav A. , Xu Lujia , Walter D. , Ratcliff T. , Franklin E. , Weber K. , Elliman R.
Published: August 2013

We present an approach to characterize the relative saturation current density (Joe) and sheet resistance (RSH) of laser doped regions on silicon wafers based on rapid photoluminescence (PL) imaging. In the absence of surface passivation layers, the RSH of laser doped regions using a wide range of laser parameters is found to be inversely proportional to the PL intensity (IPL). We explain the underlying mechanism for this correlation, which reveals that, in principle, IPL is inversely proportional to Joe at any injection level. The validity of this relationship under a wide range of typical experimental conditions is confirmed by numerical simulations. This method allows the optimal laser parameters for achieving low RSH and Joe to be determined from a simple PL image.
Multi-jump magnetic switching in ion-beam sputtered amorphous Co20Fe60B20 thin films
Authors: Raju M. , Chaudhary Sujeet , Pandya D. K.
Published: August 2013

Unconventional multi-jump magnetization reversal and significant in-plane uniaxial magnetic anisotropy (UMA) in the ion-beam sputtered amorphous Co20Fe60B20(5–75 nm) thin films grown on Si/amorphous SiO2 are reported. While such multi-jump behavior is observed in CoFeB(10 nm) film when the magnetic field is applied at 10°–20° away from the easy-axis, the same is observed in CoFeB(12.5 nm) film when the magnetic field is 45°–55° away from easy-axis. Unlike the previous reports of multi-jump switching in epitaxial films, their observance in the present case of amorphous CoFeB is remarkable. This multi-jump switching is found to disappear when the films are crystallized by annealing at 420 °C. The deposition geometry and the energy of the sputtered species appear to intrinsically induce a kind of bond orientation anisotropy in the films, which leads to the UMA in the as-grown amorphous CoFeB films. Exploitation of such multi-jump switching in amorphous CoFeB thin films could be of technological significance because of their applications in spintronic devices.
A thousand-fold enhancement of photoluminescence in porous silicon using ion irradiation
Authors: Azimi S. , Song J. , Dang Z. Y. , Breese M. B. H.
Published: August 2013

A large increase in the porosity of highly doped p-type silicon is observed at the end-of-range depth of high-energy ions after subsequent electrochemical anodization. This occurs under certain conditions of irradiation geometry and fluence, owing to the dual effects of increased wafer resistivity and a locally increased current density during anodization. This results in the creation of highly porous, sub-surface zones which emit photoluminescence with an intensity of more than three orders of magnitude greater than the surrounding mesoporous silicon, comparable to that produced by microporous silicon. This provides means of selectively enhancing and patterning the photoluminescence emission from micron-sized areas of porous silicon over a wide range of intensity.
Probing the laser wakefield in underdense plasmas by induced terahertz emission
Authors: Hu Z. D. , Sheng Z. M. , Wang W. M. , Chen L. M. , Li Y. T. , Zhang J.
Published: August 2013

Terahertz (THz) radiation can be produced from a laser wakefield driven in underdense plasmas in the presence of a transverse DC magnetic field. It is shown that the radiation usually contains a component at the electron plasma frequency and its harmonics when the wakefield is excited at high amplitudes. In the highly nonlinear bubble/blowout regime, the radiation contains a smooth component peaked at the reduced electron plasma frequency and an irregular spectrum extending to tens of the electron plasma frequency. The latter is due to the broken-wave structure behind the bubble. A theoretical model is presented and validated via two-dimensional particle-in-cell simulations. The measurement of such THz emission may provide a diagnostic of the laser wakefield structure.
Femtosecond laser desorption of ultrathin polymer films from a dielectric surface
Authors: Mercadier Laurent , Peng Jiahui , Sultan Yasir , Davis Thomas A. , Rayner David M. , Corkum Paul B.
Published: August 2013

By focusing femtosecond pulses on the front and rear surface of a fused silica coverslip, we desorb 8-nm thick polymer films at submicron scale. To determine the role of the substrate in the desorption process, we measure the threshold for nonlinear absorption in fused silica and compare it to the threshold for desorption, taking into account the enhancement of the field at the dielectric-air interface. The results indicate that absorption of energy only occurs in the film. We then measure the beam radius in situ by the knife-edge technique and characterize the desorption by atomic force microscopy. The radius of the laser desorbed area is determined by the desorption threshold intensity and can be a factor of 5 smaller than the beam waist.
Simulation of malaria-infected red blood cells in microfluidic channels: Passage and blockage
Authors: Wu Tenghu , Feng James J.
Published: August 2013

Malaria-infected red blood cells (iRBCs) become less deformable with the progression of infection and tend to occlude microcapillaries. This process has been investigated in vitro using microfluidic channels. The objective of this paper is to provide a quantitative basis for interpreting the experimental observations of iRBC occlusion of microfluidic channels. Using a particle-based model for the iRBC, we simulate the traverse of iRBCs through a converging microfluidic channel and explore the progressive loss of cell deformability due to three factors: the stiffening of the membrane, the reduction of the cell's surface-volume ratio, and the growing solid parasites inside the cell. When examined individually, each factor tends to hinder the passage of the iRBC and lengthen the transit time. Moreover, at sufficient magnitude, each may lead to obstruction of narrow microfluidic channels. We then integrate the three factors into a series of simulations that mimic the development of malaria infection through the ring, trophozoite, and schizont stages. These simulations successfully reproduce the experimental observation that with progression of infection, the iRBC transitions from passage to blockage in larger and larger channels. The numerical results suggest a scheme for quantifying iRBC rigidification through microfluidic measurements of the critical pressure required for passage.
The onset of magnetic reconnection in three dimensions
Authors: Pritchett P. L.
Published: August 2013

The onset of collisionless magnetic reconnection in current sheets containing a localized enhancement of the initial normal magnetic field component is examined using 2D and 3D particle-in-cell simulations that treat a closed system. In the 2D case, the current sheet is found to remain stable for at least several hundred inverse ion cyclotron times. In 3D, however, the system is found to be unstable to a ballooning/interchange type of mode with wavenumber kyρin∼1 (where ρin is the ion gyroradius in the normal field Bz). These modes evolve to form intense “heads” of strongly enhanced Bz; in the wake of the heads are regions of strongly reduced or reversed Bz. These local field reversals lead to the onset of reconnection with reconnection electric fields several times more intense than typical values seen for 2D reconnection.
Electrochromic π-Conjugated Copolymers Derived from Azulene, Fluorene, and Dialkyloxybenzothiadiazole
Authors: Lim Shaun Zhi Hao , Neo Wei Teng , Cho Ching Mui , Wang Xiaobai , Tan Angeline Yan Xuan , Chan Hardy Sze On , Xu Jianwei
Published: August 2013

A series of random π-conjugated copolymers P1, P2, and P3 were synthesised from 1,3-dibromoazulene, 4,7-dibromo-5,6-bis(dodecyloxy)benzo-2,1,3-thiadiazole, and 9,9-dioctylfluorene-2,7-bis(trimethyleneborate) via Suzuki coupling reactions. The copolymers P1–3 had molecular weights in the range of 17000–30900 g mol–1 with polydispersity indexes of 1.45–2.03. Thermal analysis showed that the polymers P1–3 had good thermal stability with decomposition temperatures ranging from 341 – 363°C both in air and in nitrogen. Photoluminescence studies showed that polymer P1 and P2 are weakly fluorescent with low quantum yields of 0.013 and 0.0029 for P1 borne with 30 % azulene and P2 borne with 50 % azulene in the polymer backbone, respectively. P3 borne with 70 % azulene resulted in complete quenching of fluorescence. The electrochemical band gaps for P1–3 are very close to their corresponding optical band gaps. Electrochromic study showed that three polymer thin films displayed the same colour change from yellowish green at the neutral and electrochemically-reduced state to greyish brown at the electrochemically-oxidised state. In particular, electrochromic contrasts of 17 % and 13 % for P2 and P3, respectively, were recorded in the near infrared region.
Temperature-Responsive Self-Assemblies of ‘Kinked' Amphiphiles
Authors: Squire Jennifer S. , Durand Grégory , Waddington Lynne , Sutti Alessandra , Henderson Luke C.
Published: August 2013

The synthesis of novel norbornane-based amphiphiles and the thermal response of their corresponding colloids is presented. It was found that the hydrodynamic diameter (DH) expansion or contraction of 1–4 in response to increasing temperature was governed by the length of the hydrophobic region possessed by the amphiphile (a 12 or 16 carbon chain). These data were used as a starting point to extend into an active tumour targeting system whereby two amphiphiles were modified to incorporate the oestrogen receptor antagonist Tamoxifen at the polar head group. This was achieved by a triazole moiety while both the C12 (18) or C16 (19) hydrophobic chains were incorporated as the hydrophobic region in an attempt to retain the response to thermal stimuli observed in our preliminary findings. These functionalised novel amphiphiles possessed critical aggregation concentration values of 510 and 19 µM, while aqueous self-assemblies of 56 and 106 nm for 18 and 19 were observed. Imaging by cryogenic transmission electron microscopy showed 18 to possess liposomal morphology, while 19, bearing a C16 hydrophobic portion, formed non-defined amorphous aggregates. Finally, the response to temperature of these assemblies was investigated with only the C12 variant 18 displaying a temperature response in the 5–55°C thermal window investigated.
Virus diseases of perennial pasture legumes in Australia: incidences, losses, epidemiology, and management
Authors: Jones Roger A. C.
Published: August 2013

This article reviews current knowledge for Australia over the occurrence, losses caused, epidemiology, and management of virus diseases of perennial pasture legumes. Currently, 24 viruses have been found infecting perennial pasture legumes, and one or more viruses have been detected in 21 of these species. These viruses are transmitted by insect vectors, non-persistently or persistently, by contact or via seed. Their modes of transmission are critical factors determining their incidences within pastures in different climatic zones. Large-scale national or state surveys of lucerne (alfalfa) (Medicago sativa) and white clover (Trifolium repens) pastures revealed that some viruses reach high incidences. Infection with Alfalfa mosaic virus (AMV) was very widespread in lucerne stands, and with AMV and White clover mosaic virus (WClMV) in white clover pastures. Several other viruses are potentially important in pastures in these and other perennial temperate/Mediterranean pasture species. Data demonstrating herbage yield losses, diminished pasture persistence, and impaired nitrogen fixation/nodule function are available for AMV in lucerne, and AMV, WClMV, and Clover yellow vein virus in white clover. Integrated Disease Management approaches involving phytosanitary, cultural, chemical, and host resistance control measures are available to minimise virus infection in lucerne and white clover. Research on virus diseases of perennial tropical–subtropical pasture legumes has focussed almost entirely on virus identification, and information on their incidences in pastures, the losses they cause, and how to control them is lacking. Overall, viruses of perennial pasture legumes are least studied in South Australia and the Northern Territory. These and other critical research and development gaps that need addressing are identified.
Virus diseases of pasture grasses in Australia: incidences, losses, epidemiology, and management
Authors: Jones Roger A. C.
Published: August 2013

This paper reviews current knowledge for Australia over the occurrence, losses caused, epidemiology, and management of virus diseases of pasture grasses. It also reviews all records of viruses in wild grasses likely to act as alternative host reservoirs for virus spread to nearby pastures or crops. Currently, 21 viruses have been found infecting 36 pasture or forage grass species and 59 wild grass species. These viruses are transmitted by arthropod vectors (mites or insects) or, in one instance, via grass seeds. Their modes of transmission are critical factors determining their incidences within pastures in different climatic zones. Large-scale surveys of perennial grass pastures growing in regions with temperate–Mediterranean climates revealed that Barley yellow dwarf virus (BYDV), Cereal yellow dwarf virus (CYDV), and Ryegrass mosaic virus (RyMV) sometimes reach high infection incidences. The same was true for BYDV and CYDV when perennial pasture grasses and wild grasses growing outside pastures were surveyed to establish their occurrence. Smaller scale surveys of grasses growing both inside and outside annual pastures found that Wheat streak mosaic virus (WSMV) infection could also reach high incidences in some annual grass species. Herbage yield loss data are available demonstrating potentially serious impacts on pasture production under Australian conditions from BYDV infection in perennial ryegrass swards, and from RyMV infection in both perennial and Italian ryegrass swards. Also, infection with BYDV or RyMV diminished the ability of infected pasture grass plants to compete with pasture legumes or weeds. Host resistance to BYDV, CYDV, and/or RyMV has been identified within a few temperate–Mediterranean pasture grasses, and is available for use in Australian pasture breeding programs. Integrated Disease Management tactics involving phytosanitary, cultural, chemical, and host resistance measures were devised against BYDV, CYDV, and RyMV infection in mixed species pasture, but no field experiments were undertaken with pasture grasses to validate their inclusion. Several other grass viruses that occur in other countries, but have not been looked for in Australia, are potentially important, especially in temperate–Mediterranean pasture grass species. With few exceptions, research on viruses of perennial or annual tropical–subtropical pasture or wild grass species growing within or outside pastures has focussed only on virus identification and characterisation studies, and information on incidences in pastures, losses caused, epidemiology, and management is lacking. Critical research and development gaps that need addressing are identified.
Genetic approaches to enhancing phosphorus-use efficiency (PUE) in crops: challenges and directions
Authors: Bovill William D. , Huang Chun Y. , McDonald Glenn K.
Published: August 2013

Many soils have intrinsically low concentrations of available phosphorus (P), which is a major limitation to crop and pasture growth. Regular applications of P have underpinned agricultural productivity internationally, and fertiliser use now constitutes one of the largest variable input costs to farming. Globally, high-quality reserves of P are being depleted and price increases are likely in the future. In addition, the effects of P pollution on water quality are attracting legislative regulation. Hence, there is a need to improve P-use efficiency (PUE) in farming systems. Progress in improving PUE has been limited for several reasons, including: inconsistent definitions of PUE, inappropriate phenotyping, incomplete understanding of the controls of P uptake, lack of field validation, and little consideration of genotype × environment interactions that affect the expression of PUE. With greater consideration of these limitations, the powerful array of molecular and genomic tools currently available promises considerable advances in developing more P-efficient crops. Stronger interaction between molecular science and the traditional disciplines of plant breeding, crop physiology, soil science, and agronomy will allow new opportunities to study genetic differences in PUE, bringing P-efficient crops closer to reality.
Establishing a clinic for young people in a rural setting: a community initiative to meet the needs of rural adolescents
Authors: Ervin Kaye , Phillips Jacqueline , Tomnay Jane
Published: August 2013

This paper describes the establishment and evaluation of a rural clinic for young people. A conceptual approach to community development was used to establish the clinic in a small north Victorian rural health service, with qualitative methods used to evaluate services. Study participants were members of an operational committee and advisory committee for the establishment of the rural clinic for young people. The clinic was evaluated against the World Health Organization framework for the development of youth-friendly services. With robust community support, the clinic was established and is operational. Most consultations have been for sexual and mental health. Qualitative evaluation identifies that not all the World Health Organization benchmarks have been met, but this is hampered predominantly by financial constraints. In conclusion, establishing clinic for young people in a small rural setting can be achieved with community support and the development of referral pathways.