bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular beam epitaxy grown (Ga,Mn)(As,P) with perpendicular to plane magnetic easy axis
Authors: Rushforth A. W. , Wang M. , Farley N. R. S. , Campion R. P. , Edmonds K. W. , Staddon C. R. , Foxon C. T. , Gallagher B. L.
Published: October 2008

We present an experimental investigation of the magnetic, electrical, and structural properties of Ga0.94Mn0.06As1−yPy layers grown by molecular beam epitaxy on GaAs substrates for y≤0.3. X-ray diffraction measurements reveal that the layers are under tensile strain, which gives rise to a magnetic easy axis perpendicular to the plane of the layers. The strength of the magnetic anisotropy and the coercive field increases as the phosphorous concentration is increased. The resistivity of all samples shows metallic behavior with the resistivity increasing as y increases. These materials will be useful for studies of micromagnetic phenomena requiring metallic ferromagnetic material with perpendicular magnetic anisotropy.
Theoretical investigation of intramolecular vibrational energy redistribution in HFCO and DFCO induced by an external field
Authors: Pasin Gauthier , Iung Christophe , Gatti Fabien , Richter Falk , Léonard Céline , Meyer Hans-Dieter
Published: October 2008

The present paper is devoted to a full quantum mechanical study of the intramolecular vibrational energy redistribution in HFCO and DFCO. In contrast to our previous studies [Pasin et al., J. Chem. Phys. 124, 194304 (2006) and 126, 024302 (2007)], the dynamics is now performed in the presence of an external time-dependent field. This more closely reflects the experimental conditions. A six-dimensional dipole surface is computed. The multiconfiguration time-dependent Hartree method is exploited to propagate the corresponding six-dimensional wave packets. Special emphasis is placed on the excitation of the out-of-plane bending vibration and on the dissociation of the molecule. In the case of DFCO, we predict that it is possible to excite the out-of-plane bending mode of vibration and to drive the dissociation to DF+CO with only one laser pulse with a fixed frequency and without excitation of an electronic state.
Numerical simulation of phase separation coupled with crystallization
Authors: Zhou Douglas , Shi An-Chang , Zhang Pingwen
Published: October 2008

The kinetics of liquid-liquid phase separation and polymer crystallization observed in double-quench experiments with blends of poly(ethylene-co-hexene) and poly(ethylene-co-butene) are studied using time-dependent Ginzburg–Landau Model. Numerical simulations demonstrate that our model can successfully reproduce three experimental phenomena: The decrease in number and size of crystallized spherulites with increasing time in phase separation, the preponderance of nuclei near the domain interface, and the subphase separation and subcrystallization occurring when the second quench is very deep. Moreover, the simulations are consistent with the recently proposed mechanism of “phase separation fluctuation assisted nucleation” in the crystallization process.
Incoherent control of locally controllable quantum systems
Authors: Dong Daoyi , Zhang Chenbin , Rabitz Herschel , Pechen Alexander , Tarn Tzyh-Jong
Published: October 2008

An incoherent control scheme for state control of locally controllable quantum systems is proposed. This scheme includes three steps: (1) amplitude amplification of the initial state by a suitable unitary transformation, (2) projective measurement of the amplified state, and (3) final optimization by a unitary controlled transformation. The first step increases the amplitudes of some desired eigenstates and the corresponding probability of observing these eigenstates, the second step projects, with high probability, the amplified state into a desired eigenstate, and the last step steers this eigenstate into the target state. Within this scheme, two control algorithms are presented for two classes of quantum systems. As an example, the incoherent control scheme is applied to the control of a hydrogen atom by an external field. The results support the suggestion that projective measurements can serve as an effective control and local controllability information can be used to design control laws for quantum systems. Thus, this scheme establishes a subtle connection between control design and controllability analysis of quantum systems and provides an effective engineering approach in controlling quantum systems with partial controllability information.
Nanopatterned CoPt alloys with perpendicular magnetic anisotropy
Authors: Makarov D. , Bermúdez-Ureña E. , Schmidt O. G. , Liscio F. , Maret M. , Brombacher C. , Schulze S. , Hietschold M. , Albrecht M.
Published: October 2008

CoPt alloy films with perpendicular magnetic anisotropy were grown on SiO2 nanoparticle arrays with particle sizes as small as 10 nm. In order to induce perpendicular magnetic anisotropy in the CoPt film, a MgO seed layer was sputter deposited. Despite the fact that neighboring CoPt film caps are interconnected, individual caps appear as single domain and for most of them their magnetization orientation can be reversed individually. This behavior might be caused by domain wall nucleation and pinning preferentially at the rim of each cap. Thus, arrays of magnetic caps with defined pinning sites can be considered as a percolated perpendicular medium.
Effects of series and parallel resistances on the current-voltage characteristics of small-area air-bridge resonant tunneling diode
Authors: Hou Y. , Wang W.-P. , Li N. , Lu W. , Fu Y.
Published: October 2008

We have studied experimentally and theoretically the effects of series and parallel resistances on the current-voltage (I-V) characteristics of the resonant tunneling diode (RTD) in the format of a small-area freestanding air bridge. It has been shown by standard quantum mechanical considerations that the I-V characteristics consists of a simple resonant current peak (without bistability) and the voltage at the current peak is quite low, whereas experiments show not only a much high current-peak voltage, but also the bistability. Furthermore, experimental peak-to-valley ratio is in general quite low. By analyzing material and device structures, it has been demonstrated that the series resistance in the RTD contacts shifts the peak in current to higher voltage, it also creates the experimentally observed bistability effect in the region of the tunneling resonance. The parallel resistance induces a leakage current and reduces the peak-to-valley ratio. We have further performed similar analyses to many RTD structures reported in the literature and the conclusions remain the same.
Growth optimization for low residual carriers in undoped midinfrared InAs/GaSb superlattices
Authors: Haugan H. J. , Elhamri S. , Brown G. J. , Mitchel W. C.
Published: October 2008

Reducing residual background carriers in InAs/GaSb superlattices (SLs) is an essential task to increase the operating temperature of photoconductive devices. This paper discusses how low-temperature Hall measurements were used to tune several SL growth parameters for the minimum residual carriers in a typical midinfrared 21 Å InAs/24 Å GaSb SLs designed for the 4 μm cutoff wavelength. Among the three growth parameters studied, neither growth temperature nor in situ postannealing significantly affected the intrinsic carrier type and doping concentration. The lowest carrier density of 1.8×1011 cm−2 was achieved at 400 °C. All SLs grown at 400 °C maintained the lowest density around 1.6×1011 cm−2 with or without postannealing. However, in-plane carrier mobility showed a slight improvement with annealing, especially at temperatures above 450 °C. The growth parameter most sensitive to the carrier density was interface control. With a minor variation in interface shutter sequence, the carrier density dramatically increased from ∼2×1011 to 5×1012 cm−2, and the corresponding mobility dropped from 6600 to 26 cm2/V s, indicating dramatic degradation of interfacial quality. All SLs investigated in this study were residually p-type.
Chirped porous silicon reflectors for thin-film epitaxial silicon solar cells
Authors: Kuzma-Filipek Izabela J. , Duerinckx Filip , Van Kerschaver Emmanuel , Van Nieuwenhuysen Kris , Beaucarne Guy , Poortmans Jef
Published: October 2008

The studies of porous silicon as a one-dimensional photonic crystal have led to solutions allowing the fabrication of broad photonic band gaps as large as several hundreds nanometers for various types of applications. In this work we demonstrate the use of the chirping process, i.e., the gradual increase in the spatial period of the structure, as it is used in image processing, to design porous silicon broad-band reflectors for thin-film silicon solar cells. Modeling of those layers is done using linear design method and a simulation software. Such chirped structures are fabricated by an anodization process. Samples are prepared on mono and multicrystalline silicon substrates with 15, 40, 60, and 80 layers. The reflectance spectra of such prepared porous reflectors are evaluated and the results show an increase in bandwidth of over 50% of the total width in comparison with the conventional, unchirped reflectors. We demonstrate clear advantages of introducing chirped multilayer structures over conventional ones. Although some understanding of chirping exists mainly in the field of image processing and photonics, detailed study of chirped porous structures as broad-band reflectors is needed for their implementation in thin-film epitaxial silicon solar cells.

A record efficiency of almost 14% was reached for those types of reflectors on a large area 71 cm2 epitaxial Si solar cell, giving a boost in efficiency of 0.6% absolute in comparison with the solar cells containing conventional reflectors.
Fluid dynamical analysis of the distribution of ink jet printed biomolecules in microarray substrates for genotyping applications
Authors: Dijksman J. Frits , Pierik Anke
Published: October 2008

Oligonucleotide microarrays are tools used to analyze samples for the presence of specific DNA sequences. In the system as presented here, specific DNA sequences are first amplified by a polymerase chain reaction (PCR) during which process they are labeled with fluorophores. The amplicons are subsequently hybridized onto an oligonucleotide microarray, which in our case is a porous nylon membrane with microscopic spots. Each spot on the membrane contains oligonucleotides with a sequence complementary to part of one specific target sequence. The solution containing the amplicons flows by external agitation many times up and down through the porous substrate, thereby reducing the time delaying effect of diffusion. By excitation of the fluorophores the emitted pattern of fluorophores can be detected by a charge-coupled device camera. The recorded pattern is a characteristic of the composition of the sample. The oligonucleotide capture probes have been deposited on the substrate by using noncontact piezo ink jet printing, which is the focus of our study. The objective of this study is to understand the mechanisms that determine the distribution of the ink jet printed capture probes inside the membrane. The membrane is a porous medium: the droplets placed on the membrane penetrate in the microstructure of it. The three-dimensional (3D) distribution of the capture probes inside the membrane determines the distribution of the hybridized fluorescent PCR products inside the membrane and thus the emission of light when exposed to the light source. As the 3D distribution of the capture probes inside the membrane eventually determines the detection efficiency, this parameter can be controlled for optimization of the sensitivity of the assay. The main issues addressed here are how are the capture probes distributed inside the membrane and how does this distribution depend on the printing parameters. We will use two model systems to study the influences of different parameters: a single nozzle print head jetting large droplets at a low frequency and a multinozzle print head emitting small droplets at a high frequency. In particular, we have investigated the effects when we change from usage of the first system to the second system. Furthermore, we will go into detail how we can obtain smaller spot sizes in order to increase the spot density without having overlapping spots, leading eventually to lower manufacturing costs of microarrays. By controlling the main print parameters influencing the 3D distribution inside the porous medium, the overall batch-to-batch variations can possibly be reduced.
High mobility single crystalline ScN and single-orientation epitaxial YN on sapphire via magnetron sputtering
Authors: Gregoire John M. , Kirby Steven D. , Scopelianos George E. , Lee Felix H. , van Dover R. Bruce
Published: October 2008

The mechanical, chemical, and electronic properties of the lanthanoid nitrides give this class of materials many potential applications. While ScN research activity has sharply increased recently, investigations of growth methods for optimizing structural and, more importantly, electronic properties are still needed. YN has received some theoretical but very little experimental attention. We present results of x-ray diffraction and atomic force microscopy analyses of film structure as well as Hall effect measurements of electronic properties for sputter-deposited ScN and YN. Films are deposited at select values of sputter gas stoichiometry, gas pressure, and substrate temperature, and optimal values are suggested. Additionally, the role of deposition geometry is investigated. Grown under optimal conditions, ScN films are single crystalline and YN films are singly oriented with both nitrides exhibiting the same epitaxial relation to α-Al2O3(11¯02) substrates. Our films also exhibit the highest documented electron mobility for the respective materials, despite their high carrier concentration.
Organic single-crystal transistors with secondary gates on source and drain electrodes
Authors: Nakayama K. , Hara K. , Tominari Y. , Yamagishi M. , Takeya J.
Published: October 2008

Rubrene and tetracyanoquinodimethane single-crystal transistors are fabricated incorporating secondary gates (split gates) on source and drain electrodes to reduce the interfacial barriers at the metal/semiconductor contacts. Separating the effect of the injection barriers, the intrinsic carrier transport in the semiconductor channels is extracted for the p-type rubrene crystal transistors and the n-type tetracyanoquinodimethane crystal transistors. The transconductance of the tetracyanoquinodimethane devices is drastically improved by activating the split-gate electrodes, indicating significant injection barriers in the n-type transistors. The result demonstrates that the technique is useful to improve transistor performance when it is restricted by the injection barriers.
Whistler turbulence: Particle-in-cell simulations
Authors: Saito Shinji , Gary S. Peter , Li Hui , Narita Yasuhito
Published: October 2008

Two-dimensional electromagnetic particle-in-cell simulations in a magnetized, homogeneous, collisionless electron-proton plasma demonstrate the forward cascade of whistler turbulence. The simulations represent decaying turbulence, in which an initial, narrowband spectrum of fluctuations at wavenumbers kc∕ωe≃0.1 cascades toward increased damping at kc∕ωe≃1.0, where c∕ωe is the electron inertial length. The turbulence displays magnetic energy spectra that are relatively steep functions of wavenumber and are anisotropic with more energy in directions relatively perpendicular to the background magnetic field Bo=x̂Bo than at the same wavenumbers parallel to Bo. In the weak turbulence regime, the primary new results of the simulations are as follows: (1) Magnetic spectra of the cascading fluctuations become more anisotropic with increasing fluctuation energy; (2) the wavevector dependence of the three magnetic energy ratios, ∣δBj∣2∕∣δB∣2 with j=x,y,z, show good agreement with linear dispersion theory for whistler fluctuations; (3) the magnetic compressibility summed over the cascading modes satisfies 0.3≲∣δBx∣2∕∣δB∣2≲0.6; and (4) the turbulence heats electrons in directions both parallel and perpendicular to Bo, with stronger heating in the parallel direction.
Penetration and radial force balance in field-reversed configuration with large rotating magnetic field
Authors: Ohnishi M. , Hugrass W. , Fukuhara M. , Masaki T. , Osawa H. , Chikano T.
Published: October 2008

A field-reversed configuration (FRC) is formed by applying a rotating magnetic field (RMF) much larger than the axial magnetic field to a cylindrical glass vacuum chamber filled with 10Pa argon gas without a preionization. The FRC with the plasma density 2.2×1019m−3, the temperature 8.0eV, the separatrix length 0.45m, and the separatrix radius 0.035m is sustained for the notably long period of 40ms. It is observed that the antenna current which produces the RMF is reduced by about half after the FRC is formed. The interaction between the plasma and the antenna circuit increases the antenna resistance and changes the inductance of the antenna so that the circuit becomes nonresonant. The RMF is sufficiently large to fully penetrate to the center during the period and drive the current with a rigid rotor profile. The RMF is shown to play a major role in sustaining the plasma pressure.
Direct laser writing of three-dimensional photonic structures in Nd:yttrium aluminum garnet laser ceramics
Authors: Ródenas Airán , Zhou Guangyong , Jaque Daniel , Gu Min
Published: October 2008

We report on the direct laser writing of a three-dimensional photonic structure in a neodymium doped yttrium aluminum garnet laser ceramic. The fabricated structure consists of a voxel-based face centered cubic lattice showing a stop band centered at 2.4 μm. Confocal luminescence imaging was used to study the submicron low refractive-index voxels constituting the photonic structure, as well as to elucidate how the luminescence properties of the neodymium laser ions are modified by the writing process.
Glass supported ZnSe microring strongly coupled to a single CdSe quantum dot
Authors: Renner Johannes , Worschech Lukas , Forchel Alfred , Mahapatra Suddhasatta , Brunner Karl
Published: October 2008

By means of molecular beam epitaxy a single layer of self-assembled CdSe quantum dots (QDs) embedded in a ZnSe/ZnMgSSe heterostructure was grown on a GaAs substrate. Electron beam lithography and etching techniques were then applied to pattern microrings. Afterward the microstructures were glued on a glass support and the GaAs was totally removed. The photoluminescence of such glass supported rings was studied for different temperatures, and tuning of single QD lines into resonance with a cavity photon mode was achieved. Strong coupling was found with a Rabi splitting of 0.7 meV attributed to the strong oscillator strength of CdSe quantum dots.
Forces on a rotating particle in a shear flow of a highly rarefied gas
Authors: Liu Nan , Bogy David B.
Published: October 2008

The determination of the forces on a particle is required for the simulation of the particle’s motion, which in turn is necessary for the simulation of particle contamination in a hard disk drive. In this paper, the forces on a rotating sphere in a shear flow of a highly rarefied gas are investigated analytically. The Chapman–Enskog distribution function is used to describe the molecules in the shear flow and a Maxwell-type boundary condition is assumed on the surface of the sphere. Expressions are obtained for the drag force as well as lift forces for the special case where the gradient of the shear flow is along the same direction as the axis of the particle’s rotation. The effects of particle rotation and shear flow are shown to be decoupled. These lift forces also turn out to be in the opposite directions from their corresponding forces when the fluid is modeled as a continuum.
Heat flux characteristics in an atmospheric double arc argon plasma jet
Authors: Tu Xin , Yu Liang , Yan Jianhua , Cen Kefa , Chéron Bruno
Published: October 2008

In this study, the axial evolution of heat flux excited by a double arc argon plasma jet impinging on a flat plate is determined, while the nonstationary behavior of the heat flux is investigated by combined means of the fast Fourier transform, Wigner distribution, and short-time Fourier transform. Two frequency groups (<1 and 2–10 kHz) are identified in both the Fourier spectrum and the time-frequency distributions, which suggest that the nature of fluctuations in the heat flux is strongly associated with the dynamic behavior of the plasma arc and the engulfment of ambient air into different plasma jet regions.
Magnetic-field-induced strain assisted by tensile stress in L1 martensite of a Ni–Fe–Ga–Co alloy
Authors: Masdeu F. , Pons J. , Cesari E. , Kustov S. , Chumlyakov Y. I.
Published: October 2008

Magnetic-field-induced strains larger than 2% have been obtained in the nonlayered L10 martensite of a Ni49Fe18Ga27Co6 single crystal, under an assisting tensile stress around 16 MPa and fields below 15 kOe. In martensitic samples previously compressed, application of a constant tensile stress along the same axis together with a perpendicular magnetic field produces the elongation of the sample, as one of the variants rotates its c axis from the field direction to the stress-axis direction. An estimated magnetostress of ∼0.8 MPa is in good agreement with the theoretical value given by the ratio of magnetocrystalline anisotropy constant and twinning shear.
Enhanced particle filtration in straight microchannels using shear-modulated inertial migration
Authors: Bhagat Ali Asgar S. , Kuntaegowdanahalli Sathyakumar S. , Papautsky Ian
Published: October 2008

In this work, we introduce a novel method for enhanced particle filtration using shear-modulated inertial migration in straight microchannels. Depending on their size, inertial lift causes particles to migrate toward microchannel walls. Using microchannels with high aspect ratio cross sections, the fluidic shear can be modulated, resulting in preferential equilibration of particles along the longer microchannel walls. Due to large lift forces generated in these high aspect ratio channels, complete particle filtration can be achieved in short distances even at low flow rates (Re<50). Based on this principle, we use a straight microfluidic channel with a rectangular cross section to passively and continuously filter 1.9 μm polystyrene particles. Overall, the proposed technique is versatile and can be easily integrated with on-chip microfluidic systems for filtration of a wide range of particle sizes, from micro- to nanoparticles.
Dewetting of nanometer thin films under an electric field
Authors: Hu Guo-Hui , Xu Ai-Jin , Xu Zhen , Zhou Zhe-Wei
Published: October 2008

The dewetting of a nanoscale water film under the action of an electric field is studied with molecular dynamics simulation. Results show that the onset of film rupture is induced by a spontaneous instability mechanism. After the rupture, the rim of the film recedes with a dynamic contact angle. The transient streamlines at a typical moment show that the liquid molecule near the rim moves almost vertically upwards, driven by the repulsive force from the solid surface. The oscillatory behavior of the density profile, resulting from the interaction between attractive and repulsive potentials, is observed near the solid surface. The analyses of the dewetting process demonstrate that the applied electric field will increase the wettability of graphite walls, thus suppressing the rupture, reducing the dynamic contact angle, and raising the liquid density adjacent to both the solid and liquid-vacuum surfaces. Owing to the polarity of water, the positive voltage produces stronger influences than the negative one.
Real-time atomic force microscopy using mechanical resonator type scanner
Authors: Seo Yongho , Choi C. S. , Han S. H. , Han Seung-Jin
Published: October 2008

The real-time atomic force microscope for biological sample is a challenging research field. We have demonstrated a real-time atomic force microscope by implementing a mechanical resonator type scanner called by “microscanner” The microscanner was designed to have a resonance frequency in the range of 5–10 kHz and an amplitude of 1–3 μm. The resonant vibration of the microscanner was served as a fast-scan directional motion, and an image acquisition rate of 30 frames/s with 256×256 pixels per frame was achieved. Time-varying sequential images of a poly(ethylene-oxide) sample were taken as a demonstration of potential for excellence in real-time imaging a moving nano-object.
Direct evidence of trap-mediated excitation in GaN:Er3+ with a two-color experiment
Authors: Bodiou Loic , Braud Alain
Published: October 2008

We report a direct confirmation of the generally proposed rare-earth excitation model in GaN. The intermediate step involving the formation of excitons bound to rare-earth ions prior to the rare-earth excitation is demonstrated. Using a two-color experiment, we show that the erbium photoluminescence decay following a pulsed laser excitation is quenched when an additional continuous-wave (cw) laser is applied. As the two beams excite the sample, the cw beam perturbs the intermediate step of the Er excitation mechanism either by photoionization of Er-related trapped carriers or by inducing an Auger effect between the trapped carriers and free carriers.
Stochastic model for photoinduced surface relief grating formation through molecular transport in polymer films
Authors: Juan M. L. , Plain J. , Bachelot R. , Royer P. , Gray S. K. , Wiederrecht G. P.
Published: October 2008

We use a stochastic model to study photoinduced surface relief grating (SRG) formation due to molecular transport in azobenzene polymer films. The model is shown to reproduce the essential experimental features of SRG formation. In particular, it predicts SRG formation under both p and s polarizations, and the double peaked topographies that can occur at early times of the process. The evolving molecular positions and orientations during exposure are also followed, providing a useful mechanistic picture of SRG dynamics.
Electronic structure of La1−xSrxScO3 probed by soft-x-ray absorption spectroscopy
Authors: Higuchi T. , Nagao Y. , Liu J. , Iguchi F. , Sata N. , Hattori T. , Yugami H.
Published: October 2008

The electronic structure of La1−xSrxScO3 single crystal has been studied by x-ray absorption spectroscopy (XAS). The conduction band is mainly composed of Sc 3d state hybridized with O 2p state. The O 1s XAS spectrum exhibits the existence of the Sc 3d-defect-induced state under the Sc 3d conduction band. The intensity of Sc 3d-defect-induced state increases with Sr substitution. The energy separation between the top of the valence band and the bottom of the Sc 3d-induced unoccupied state is in accordance with the energy gap that is expected from optical absorption.
Self-quenching and self-recovering InGaAs∕InAlAs single photon avalanche detector
Authors: Zhao Kai , You Sifang , Cheng James , Lo Yu-hwa
Published: October 2008

To prevent device damage through thermal runaway, conventional III–V single photon avalanche diodes (SPADs) operate in gated mode where the device is biased above breakdown only for a short gating period. Here a free-running In0.53Ga0.47As∕InAlAs SPAD with built-in negative feedback mechanism is reported. A physical model is also developed to formulate the avalanche process with negative feedback. Introducing negative feedback enables the device to possess self-quenching and self-recovering capabilities. Such devices have demonstrated free-running single photon detection at 1550nm wavelength with single photon detection efficiency of 11.5%, dark count rate of 3.3M∕s, and a self-recovery time of 60ns at 160K.
Switching magnetic vortex core by a single nanosecond current pulse
Authors: Yamada Keisuke , Kasai Shinya , Nakatani Yoshinobu , Kobayashi Kensuke , Ono Teruo
Published: October 2008

In a ferromagnetic nanodisk, the magnetization tends to swirl around in the plane of the disk and can point either up or down at the center of this “magnetic vortex.” This binary state can be useful for information storage. It is demonstrated that a single nanosecond current pulse can switch the core polarity. This method also provides the precise control of the core direction, which constitutes fundamental technology for realizing a vortex core memory.
Electric field induced phase transition in charge-ordered LuFe2O4
Authors: Li Changhui , Zhang Xiangqun , Cheng Zhaohua , Sun Young
Published: October 2008

The measurements of resistance under various applied voltages as well as the highly nonlinear current-voltage characteristics reveal that a small electric field is able to induce an insulating to metallic phase transition in LuFe2O4. The threshold field at which the phase transition occurs decreases exponentially with the increasing temperature. We interpret this transition as a consequence of the breakdown of the charge-ordered state triggered by applied electric field. This electrically driven phase transition results in a colossal electroresistance effect around room temperature which makes LuFe2O4 a very promising material for many applications.
Sixfold symmetry of excitonic transition energies in c-plane for wurtzite GaN
Authors: Hao Guo-Dong , Chen Y. H. , Hao Y. F.
Published: October 2008

The optical properties of the strained wurtzite GaN are investigated theoretically within the nearest neighbor tight-binding method. The piezoelectric effect is also taken into account. The empirical rule has been used in the strained band-structure calculation. The results show that the excitonic transition energies are anisotropic in the c-plane in a high electronic concentration system and have a 60° periodicity, which is in agreement with experiment.
Consumer assessment of eating quality - development of protocols for Meat Standards Australia (MSA) testing
Authors: Watson R. , Gee A. , Polkinghorne R. , Porter M.
Published: October 2008

Meat Standards Australia sought a consistent measure of the beef eating experience to the consumer. Rather than objective measurements or trained panel sensory assessment, it was decided to proceed with direct consumer assessment. Consumer-based assessment has much greater variation, but it has the decided advantage of validity. This paper summarises the path taken to obtain consistent consumer assessment. What meat samples to present to consumers? What responses to ask for? What to do with these responses when they were obtained? The answers to these questions have led to the MQ4 measure of consumer assessment of meat eating quality, which now forms the basis of the MSA predictive model.
Measuring the effectiveness of protected area networks in reducing deforestation
Authors: Andam Kwaw S. , Ferraro Paul J. , Pfaff Alexander , Sanchez-Azofeifa G. Arturo , Robalino Juan A.
Published: October 2008

Global efforts to reduce tropical deforestation rely heavily on the establishment of protected areas. Measuring the effectiveness of these areas is difficult because the amount of deforestation that would have occurred in the absence of legal protection cannot be directly observed. Conventional methods of evaluating the effectiveness of protected areas can be biased because protection is not randomly assigned and because protection can induce deforestation spillovers (displacement) to neighboring forests. We demonstrate that estimates of effectiveness can be substantially improved by controlling for biases along dimensions that are observable, measuring spatial spillovers, and testing the sensitivity of estimates to potential hidden biases. We apply matching methods to evaluate the impact on deforestation of Costa Rica's renowned protected-area system between 1960 and 1997. We find that protection reduced deforestation: approximately 10% of the protected forests would have been deforested had they not been protected. Conventional approaches to evaluating conservation impact, which fail to control for observable covariates correlated with both protection and deforestation, substantially overestimate avoided deforestation (by over 65%, based on our estimates). We also find that deforestation spillovers from protected to unprotected forests are negligible. Our conclusions are robust to potential hidden bias, as well as to changes in modeling assumptions. Our results show that, with appropriate empirical methods, conservation scientists and policy makers can better understand the relationships between human and natural systems and can use this to guide their attempts to protect critical ecosystem services.
Azatryptophans endow proteins with intrinsic blue fluorescence
Authors: Lepthien Sandra , Hoesl Michael G. , Merkel Lars , Budisa Nediljko
Published: October 2008

Our long-term goal is thein vivoexpression of intrinsically colored proteins without the need for further posttranslational modification or chemical functionalization by externally added reagents. Biocompatible (Aza)Indoles (Inds)/(Aza)Tryptophans (Trp) as optical probes represent almost ideal isosteric substitutes for natural Trp in cellular proteins. To overcome the limits of the traditionally used (7-Aza)Ind/(7-Aza)Trp, we substituted the single Trp residue in human annexin A5 (anxA5) by (4-Aza)Trp and (5-Aza)Trp in Trp-auxotrophicEscherichia colicells. Both cells and proteins with these fluorophores possess intrinsic blue fluorescence detectable on routine UV irradiations. We identified (4-Aza)Ind as a superior optical probe due to its pronounced Stokes shift of ≈130 nm, its significantly higher quantum yield (QY) in aqueous buffers and its enhanced quenching resistance. Intracellular metabolic transformation of (4-Aza)Ind into (4-Aza)Trp coupled with high yield incorporation into proteins is the most straightforward method for the conversion of naturally colorless proteins and cells into their blue counterparts from amino acid precursors.
Selection and gene flow on a diminishing cline of melanic peppered moths
Authors: Saccheri Ilik J. , Rousset François , Watts Phillip C. , Brakefield Paul M. , Cook Laurence M.
Published: October 2008

Historical datasets documenting changes to gene frequency clines are extremely rare but provide a powerful means of assessing the strength and relative roles of natural selection and gene flow. In 19th century Britain, blackening of the environment by the coal-fired manufacturing industry gave rise to a steep cline in the frequency of the black (carbonaria) morph of the peppered moth (Biston betularia) across northwest England and north Wales. Thecarbonariamorph has declined across the region following 1960s legislation to improve air quality, but the cline had not been comprehensively described since the early 1970s. We have quantified changes to the cline as of 2002, equivalent to an interval of 30 generations, and find that a cline still exists but that it is much shallower and shifted eastward. Joint estimation of the dominant fitness cost ofcarbonariaand dispersal parameters consistent with the observed cline change indicate that selection againstcarbonariais very strong across the landscape (s≈ 0.2), and that dispersal is much greater than previously assumed. The high dispersal estimate is further supported by the weak pattern of genetic isolation by distance at microsatellite loci, and it implies that in addition to adult dispersal, wind-dispersed first instar larvae also contribute to lifetime dispersal. The historical perspective afforded by this study of cline reversal provides new insight into the factors contributing to gene frequency change in this species, and it serves to illustrate that, even under conditions of high dispersal and strong reverse selection acting against it, complete erosion of an established cline requires many generations.
The systematization and typology of the instant messaging writing system used by young Israeli Arabs
Authors: Habib Sandy , Kurzon Dennis
Published: October 2008

This study investigates a new writing system based on the Roman script that has been used by Israeli Arabs in Israel for about ten years. This system is associated with instant messaging (IM); people usually use it when sending SMSs or when utilizing any of the computer-mediated communication forms, such as Messenger. The paper focuses on the systematization and the typology of this writing system based on data collected from about 40 participants studying in the same school. The results show that most of the participants have used this system systematically, and that this system can be classified as a developing alphabet.
The Protein Interaction Network of the Epithelial Junctional Complex: A System-Level Analysis
Authors: Paris Luca , Bazzoni Gianfranco
Published: October 2008

To acquire system-level understanding of the intercellular junctional complex, protein–protein interactions occurring at the junctions of simple epithelial cells have been examined by network analysis. Although proper hubs (i.e., very rare proteins with exceedingly high connectivity) were absent from the junctional network, the most connected (albeit nonhub) proteins displayed a significant association with essential genes and contributed to the “small world” properties of the network (as shown by in vivo and in silico deletion, respectively). In addition, compared with a random network, the junctional network had greater tendency to form modules and subnets of densely interconnected proteins. Module analysis highlighted general organizing principles of the junctional complex. In particular, two major modules (corresponding to the tight junctions and to the adherens junctions/desmosomes) were linked preferentially to two other modules that acted as structural and signaling platforms.
Parsing, Semantic Networks, and Political Authority Using Syntactic Analysis to Extract Semantic Relations from Dutch Newspaper Articles
Authors: van Atteveldt Wouter , Kleinnijenhuis Jan , Ruigrok Nel
Published: October 2008

Analysis of political communication is an important aspect of political research. Thematic content analysis has yielded considerable success both with manual and automatic coding, but Semantic Network Analysis has proven more difficult, both for humans and for the computer. This article presents a system for an automated Semantic Network Analysis of Dutch texts. The system automatically extracts relations between political actors based on the output of syntactic analysis of Dutch newspaper articles. Specifically, the system uses pattern matching to find source constructions and determine the semantic agent and patient of relations, and name matching and anaphora resolution to identify political actors. The performance of the system is judged by comparing the extracted relations to manual codings of the same material. Results on the level of measurement indicate acceptable performance. We also estimate performance at the levels of analysis by using a case study of media authority, resulting in good correlations between the theoretical variables derived from the automatic and manual analysis. Finally, we test a number of substantive hypotheses with regression models using the automatic and manual output, resulting in highly similar models in each case. This suggests that our method has sufficient performance to be used to answer relevant political questions in a valid way.
When microbes and consumers determine the limiting nutrient of autotrophs: a theoretical analysis
Authors: Cherif Mehdi , Loreau Michel
Published: October 2008

Ecological stoichiometry postulates that differential nutrient recycling of elements such as nitrogen and phosphorus by consumers can shift the element that limits plant growth. However, this hypothesis has so far considered the effect of consumers, mostly herbivores, out of their food-web context. Microbial decomposers are important components of food webs, and might prove as important as consumers in changing the availability of elements for plants. In this theoretical study, we investigate how decomposers determine the nutrient that limits plants, both by feeding on nutrients and organic carbon released by plants and consumers, and by being fed upon by omnivorous consumers. We show that decomposers can greatly alter the relative availability of nutrients for plants. The type of limiting nutrient promoted by decomposers depends on their own elemental composition and, when applicable, on their ingestion by consumers. Our results highlight the limitations of previous stoichiometric theories of plant nutrient limitation control, which often ignored trophic levels other than plants and herbivores. They also suggest that detrital chains play an important role in determining plant nutrient limitation in many ecosystems.
Vision and touch in relation to foraging and predator detection: insightful contrasts between a plover and a sandpiper
Authors: Martin Graham R , Piersma Theunis
Published: October 2008

Visual fields were determined in two species of shorebirds (Charadriiformes) whose foraging is guided primarily by different sources of information: red knots (
Calidris canutus
, tactile foragers) and European golden plovers (
Pluvialis apricaria
, visual foragers). The visual fields of both species showed features that are found in a wide range of birds whose foraging involves precision pecking or lunging at food items. Surprisingly, red knots did not show comprehensive panoramic vision as found in some other tactile feeders; they have a binocular field surrounding the bill and a substantial blind area behind the head. We argue that this is because knots switch to more visually guided foraging on their breeding grounds. However, this visual field topography leaves them vulnerable to predation, especially when using tactile foraging in non-breeding locations where predation by falcons is an important selection factor. Golden plovers use visually guided foraging throughout the year, and so it is not surprising that they have precision-pecking frontal visual fields. However, they often feed at night and this is associated with relatively large eyes. These are anchored in the skull by a wing of bone extending from the dorsal perimeter of each orbit; a skeletal structure previously unreported in birds and which we have named ‘supraorbital aliform bone’,
Os supraorbitale aliforme
. The larger eyes and their associated supraorbital wings result in a wide blind area above the head, which may leave these plovers particularly vulnerable to predation. Thus, in these two shorebirds, we see clear examples of the trade-off between the two key functions of visual fields: (i) the detection of predators remote from the animal and (ii) the control of accurate behaviours, such as the procurement of food items, at close quarters.
Juveniles exposed to embryonic corticosterone have enhanced flight performance
Authors: Chin Eunice H , Love Oliver P , Verspoor Jan J , Williams Tony D , Rowley Kyle , Burness Gary
Published: October 2008

Exposure to maternally derived glucocorticoids during embryonic development impacts offspring phenotype. Although many of these effects appear to be transiently ‘negative’, embryonic exposure to maternally derived stress hormones is hypothesized to induce preparative responses that increase survival prospects for offspring in low-quality environments; however, little is known about how maternal stress influences longer-term survival-related performance traits in free-living individuals. Using an experimental elevation of yolk corticosterone (embryonic signal of low maternal quality), we examined potential impacts of embryonic exposure to maternally derived stress on flight performance, wing loading, muscle morphology and muscle physiology in juvenile European starlings (Sturnus vulgaris). Here we report that fledglings exposed to experimentally increased corticosteronein ovoperformed better during flight performance trials than control fledglings. Consistent with differences in performance, individuals exposed to elevated embryonic corticosterone fledged with lower wing loading and had heavier and more functionally mature flight muscles compared with control fledglings. Our results indicate that the positive effects on a survival-related trait in response to embryonic exposure to maternally derived stress hormones may balance some of the associated negative developmental costs that have recently been reported. Moreover, if embryonic experience is a good predictor of the quality or risk of future environments, a preparative phenotype associated with exposure to apparently negative stimuli during development may be adaptive.
Mid-Pliocene equatorial Pacific sea surface temperature reconstruction: a multi-proxy perspective
Authors: Dowsett Harry J , Robinson Marci M
Published: October 2008

The Mid-Pliocene is the most recent interval of sustained global warmth, which can be used to examine conditions predicted for the near future. An accurate spatial representation of the low-latitude Mid-Pliocene Pacific surface ocean is necessary to understand past climate change in the light of forecasts of future change. Mid-Pliocene sea surface temperature (SST) anomalies show a strong contrast between the western equatorial Pacific (WEP) and eastern equatorial Pacific (EEP) regardless of proxy (faunal, alkenone and Mg/Ca). All WEP sites show small differences from modern mean annual temperature, but all EEP sites show significant positive deviation from present-day temperatures by as much as 4.4°C. Our reconstruction reflects SSTs similar to modern in the WEP, warmer than modern in the EEP and eastward extension of the WEP warm pool. The east–west equatorial Pacific SST gradient is decreased, but the pole to equator gradient does not change appreciably. We find it improbable that increased greenhouse gases (GHG) alone would cause such a heterogeneous warming and more likely that the cause of Mid-Pliocene warmth is a combination of several forcings including both increased meridional heat transport and increased GHG.
Mid-Pliocene sea level and continental ice volume based on coupled benthic Mg/Ca palaeotemperatures and oxygen isotopes
Authors: Dwyer Gary S , Chandler Mark A
Published: October 2008

Ostracode magnesium/calcium (Mg/Ca)-based bottom-water temperatures were combined with benthic foraminiferal oxygen isotopes in order to quantify the oxygen isotopic composition of seawater, and estimate continental ice volume and sea-level variability during the Mid-Pliocene warm period,
ca
3.3–3.0 Ma. Results indicate that, following a low stand of approximately 65 m below present at marine isotope stage (MIS) M2 (
ca
3.3 Ma), sea level generally fluctuated by 20–30 m above and below a mean value similar to present-day sea level. In addition to the low-stand event at MIS M2, significant low stands occurred at MIS KM2 (−40 m), G22 (−40 m) and G16 (−60 m). Six high stands of +10 m or more above present day were also observed; four events (+10, +25,+15 and +30 m) from MIS M1 to KM3, a high stand of +15 m at MIS K1, and a high stand of +25 m at MIS G17. These results indicate that continental ice volume varied significantly during the Mid-Pliocene warm period and that at times there were considerable reductions of Antarctic ice.