bluuebunny/crossref_metadata_2025 huggingface dataset:
In-grown stacking faults in 4H-SiC epilayers grown on off-cut substrates
Authors: Hassan J. , Henry A. , Ivanov I. G. , Bergman J. P.
Published: June 2009

Different and novel in-grown stacking faults have been observed and characterized in 4H-SiC epitaxial layers grown on 4° or 8° off-cut substrates. Two different kinds of triangular stacking faults were observed in the epilayers grown on 4° off-cut substrates. The faults were formed during the epitaxial growth close to the episubstrate interface and increased continuously in size during the growth. Their structural and optical properties were however different as seen from both synchrotron white beam topography and low temperature photoluminescence. The luminescence spectra were similar but appeared in different energy regions of 2.85–2.95 eV and 2.48–2.64 eV, respectively, which have not been observed for previously reported stacking faults. A third stacking fault was observed in 8° off-cut as-grown epilayers, sometime with higher density. A combination of back polishing, etching in molten KOH, and optical microscopy revealed the geometrical structure of the stacking fault inside the epilayer. Also this fault started close to the episubstrate interface, expanded rapidly but changed geometry after some time and reduced in size during further growth. The optical spectrum from this fault is identical with the emission from the stacking faults previously only observed and formed in bipolar diodes during forward voltage operation.
Applications of automata and graphs: Labeling operators in Hilbert space. II.
Authors: Cho Ilwoo , Jorgensen Palle E. T.
Published: June 2009

We introduced a family of infinite graphs directly associated with a class of von Neumann automaton model AG. These are finite state models used in symbolic dynamics: stimuli models and in control theory. In the context of groupoid von Neumann algebras, and an associated fractal group, we prove a classification theorem for representations of automata.
Chromium doping of epitaxial PbZr0.2Ti0.8O3 thin films
Authors: Feigl L. , Pippel E. , Pintilie L. , Alexe M. , Hesse D.
Published: June 2009

Epitaxial ferroelectric PbZr0.2Ti0.8O3 thin films were grown by pulsed laser deposition. PbZr0.2Ti0.8O3 was doped with Cr acting as acceptor ion. Microstructural characterization was performed by (high resolution) transmission electron microscopy. The voltage dependence of polarization, dielectric constant, and leakage current were measured with respect to the Cr content. To derive the electronic properties, PZT was considered as a wide-gap semiconductor which allows treating the metal-PZT interface as a Schottky contact. The Cr was found to facilitate the elastic relaxation of the film. Furthermore, the leakage current was increased through a reduction of the Schottky barrier.
Breakdown current density of graphene nanoribbons
Authors: Murali Raghunath , Yang Yinxiao , Brenner Kevin , Beck Thomas , Meindl James D.
Published: June 2009

Graphene nanoribbons (GNRs) with widths down to 16 nm have been characterized for their current-carrying capacity. It is found that GNRs exhibit an impressive breakdown current density, on the order of 108 A/cm2. The breakdown current density is found to have a reciprocal relationship to GNR resistivity and the data fit points to Joule heating as the likely mechanism of breakdown. The superior current-carrying capacity of GNRs will be valuable for their application in on-chip electrical interconnects. The thermal conductivity of sub-20 nm graphene ribbons is found to be more than 1000 W/m K.
In situ formation of tin nanocrystals embedded in silicon nitride matrix
Authors: Huang Shujuan , So Yong Heng , Conibeer Gavin , Green Martin A.
Published: June 2009

Tin (Sn) nanocrystals (NCs) embedded in a silicon nitride (Si3N4) matrix have been fabricated in a cosputtering process employing low temperature (100 °C) substrate heating. Transmission electron microscopy (TEM) showed the formation of uniformly sized Sn NCs of 5.2±0.9 nm evenly distributed in the Si3N4 matrix. Both TEM and x-ray diffraction measurements showed that the Sn NCs adopted the semimetallic tetragonal β-Sn structure rather than the cubic semiconducting alpha-Sn structure. X-ray photoelectron spectroscopy revealed that the semimetallic state (Sn0) is the major component of Sn in the sample films. Our investigation demonstrates a pronounced effect of the substrate temperature on the formation of Sn NCs. The mechanism of in situ formation of Sn NCs is discussed. We suggest that the formation of uniformly sized Sn NCs is correlated with lowering the surface mobility of the nuclei due to the presence of the cosputtered Si3N4.
Magnetic nanoparticle migration in microfluidic two-phase flow
Authors: Wu Liqun , Zhang Yong , Palaniapan Moorthi , Roy Partha
Published: June 2009

Continuous separation of superparamagnetic nanoparticles in a microfluidic system has numerous applications, especially in novel sensors based technology platforms. We have studied a simple microfluidic system with two fluidic inlets, resulting in two-phase flow of identical aqueous fluids. Magnetic nanoparticles were entrained in de-ionized water entering one inlet channel, while the other inlet channel had only de-ionized water input. The application of a magnetic field using a simple permanent magnet causes increased migration of nanoparticles into the pure fluid channel. In the absence of the magnetic field, the particles are able to diffuse into the particle free phase. A steady state convection diffusion model describes the transport of nanoparticles in the microchannel. Particle velocities are estimated from magnetic and hydrodynamic interaction forces. It is shown how particle separation is affected by Péclet number, channel length to width ratio, and magnetic field strength and field gradient. Experiments were conducted with three particle sizes, 1000, 500, and 100 nm. Results revealed a significant discrepancy between theoretical and experimental particle separations under the applied magnetic field. A correction term was introduced into the magnetic force equation. Experiment and theory could be reconciled with the insight that the correction term scales linearly with the volume of the nanoparticle core.
Time-delayed transformation of defects in zinc oxide layers grown along the zinc-face using a hydrothermal technique
Authors: Noor Hadia , Klason P. , Nur O. , Wahab Q. , Asghar M. , Willander M.
Published: June 2009

A study of deep level defects in a hydrothermally grown, intrinsically n-type zinc oxide (ZnO) device has been carried out using conventional deep level transient spectroscopy (DLTS). Performed under variable measurement conditions, DLTS demonstrates two electron trap levels, E1 (dominant) and E2, with activation energies Ec−0.22±0.02 eV and Ec−0.47±0.05 eV, respectively. A time-delayed transformation of shallow donor defects zincinterstitial and vacancyoxygen (Zni-VO) into the E1 level has been observed. While the x-ray diffraction measurements reveal that the preferred direction of ZnO growth is along the (101¯0) plane, i.e., the (Zni-VO) complex, it is assumed that the (Zni-VO) complex is transformed into a zinc antisite (ZnO) under favorable conditions. As a result, the free carrier concentration decreases with increasing trap concentration. Henceforth, the E1 level exhibiting the increase in concentration is attributed to ZnO.
Insights into thermal degradation of organic light emitting diodes induced by glass transition through impedance spectroscopy
Authors: Nenna G. , Barra M. , Cassinese A. , Miscioscia R. , Fasolino T. , Tassini P. , Minarini C. , della Sala D.
Published: June 2009

Highly sensitive alternate current (ac) impedance measurements with variable temperature have been performed to investigate the optical and electrical failure mechanisms during the glass transition phenomena in the archetypal ITO/TPD/Alq3/Al organic light emitting diode (OLED) structure. Since the device degradation is mainly related to the lower glass transition temperature (Tg) of the N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD), this study is focused on the frequency response of thin TPD films approaching the glassy region. The related experimental data are discussed in the framework of the universal dielectric response model. By ac measurements, TPD glass transition temperature is located and temperature regions with different OLED behaviors are evidenced. The relation between the behaviors of TPD frequency response and of the OLED electro-optical response, while the temperature approaches the glass transition region, is discussed.
Direct observation of photonic jets and corresponding backscattering enhancement at microwave frequencies
Authors: Zhao L. , Ong C. K.
Published: June 2009

We report the direct observation of photonic nanojets that emerged from the shadow side of a dielectric cylinder illuminated by plane waves in the microwave frequencies (8–13 GHz). Using our recently developed two-dimensional spatial field mapping system, we carried out a point-by-point measurement of both the phase and intensity of spatial electric field distribution inside and around scattering dielectric cylinders. The direct electric field maps confirm the subwavelength waist of the photonic jet. In addition, we also confirmed the superbackscattering enhancement induced by the presence of a particle much smaller than the initial focusing cylinder within the photonic jet.
Hybridized quantum dot-wetting layer states in photoluminescence of In(Ga)As/GaAs dot chain samples
Authors: Dorogan V. G. , Mazur Yu. I. , Marega E. , Tarasov G. G. , Ware M. E. , Salamo G. J.
Published: June 2009

The effects of electronic wave function hybridization are studied in In(Ga)As/GaAs dot chain samples by means of continuous wave and time resolved photoluminescence (PL). A set of wetting layer (WL) states strongly coupled with the quantum dot (QD) heavy hole states is revealed in the PL. The hybridization of states is favored by the presence of a specific one-dimensional postwetting layer that strings together the QDs in each chain. It is demonstrated that the strength of hybridization is significantly weakened for states deep in the WL gap. The hybridization of the WL states and the QD hole states substantially affects the rates of carrier trapping by the QDs and the carrier distribution. Specific convex shape of the PL transients is related to the presence of long living localized states in the WL energy gap.
Origin of magnetic field effect enhancement by electrical stress in organic light emitting diodes
Authors: Bagnich S. A. , Niedermeier U. , Melzer C. , Sarfert W. , von Seggern H.
Published: June 2009

Recently, it has been discovered that the magnetic field effect (MFE) in organic light emitting diodes (OLEDs) based on poly(para-phenylene vinylene) can be enhanced by exposing the diode to moderate electrical stress. Here, we disclose the mechanism behind this way of improving the MFE. We first show that electronic traps in general play an important role for the MFE. Optical depletion of available trap states by infrared illumination leads to a decrease in the MFE. Furthermore, we demonstrate that annealing of the OLED at high temperatures eliminates the MFE improvement of the previously performed electrical conditioning. However, the improvement can be restored by subsequent conditioning at higher current or voltage. Thus it is likely that electrical stress is accompanied by a transformation of the polymer morphology or conformation resulting in a formation of energetic traps for charge carriers.
The dependence of vircator oscillation mode on cathode material
Authors: Li Limin , Liu Lie , Cheng Guoxin , Xu Qifu , Wan Hong , Chang Lei , Wen Jianchun
Published: June 2009

This paper presents the effects of cathode materials on the oscillation mode of a virtual cathode oscillator (vircator). In the case of the stainless steel cathode, an oscillation mode hopping appeared with two separate frequencies. Interestingly, the vircator using the carbon fiber cathode exhibited an almost unchanged microwave frequency throughout the microwave pulse. To understand this phenomenon, several parameters are compared, including the diode voltage, accelerating gap, emitting area, and beam uniformity. It was found that a flat-top voltage and a relatively stable gap will provide a possibility of generating a constant microwave frequency. Further, the cathode operated in a regime where the beam current was between the space-charge limited current determined by Child–Langmuir law and the bipolar flow. On the cathode surface, the electron emission is initiated from discrete plasma spots and next from a continuing area, while there is a liberation process of multilayer gases on the anode surface. The changes in the emitting area of carbon fiber cathode showed a self-quenching process, which is not observed in the case of stainless steel cathode. The two-dimensional effect of microwave frequency is introduced, and the obtained results supported the experimental observations on the oscillation mode. By examining the cross section of electron beam, the electron beam for carbon fiber cathode was significantly centralized, while the discrete beam spots appeared for stainless steel cathode. These results show that the slowed diode closure, high emission uniformity, and stable microwave frequency tend to be closely tied.
Failure mechanism analysis of electromigration dominated damage in TiSi2 nanowires
Authors: Zou Chen-Xia , Xu Jun , Zhang Xin-Zheng , Song Xue-Feng , Yu Da-Peng
Published: June 2009

Electromigration-induced damage has been an important concern in very large scale integrated circuit design for a long time and will be a major road block in the pursuit of nanoelectronics devices and next generation power electronics. In this letter, the failure mechanism analysis on two-terminal TiSi2 nanowire devices was reported. Electromigration dominant mass migration is observed and verified by energy dispersive spectroscopy. The contribution of thermomigration is discussed based on temperature simulation. This work provides useful reference for future devices and the failure analysis on nanostructures.
Near-field excitation and near-field detection of propagating surface plasmon polaritons on Au waveguide structures
Authors: Dallapiccola R. , Dubois C. , Gopinath A. , Stellacci F. , Dal Negro L.
Published: June 2009

The propagation of surface plasmon polaritons guided along Au metal waveguides fabricated by electron-beam lithography is experimentally investigated using simultaneous near-field excitation and detection of plasmon-polariton modes localized at the air/Au interface. The directly measured propagation characteristics of surface plasmon-polaritons agree well with simulation results obtained using full-vector calculations and the analytic dispersion of asymmetric plasmonic waveguides for thin Au films. Our results demonstrate that near-field excitation/detection schemes are well suited for direct imaging and characterization of propagating surface plasmon-fields bound to thin-film metal layers, and can be used for fast and reliable characterization of plasmonic waveguide elements and nanodevices.
OH produced from o-nitrophenol photolysis: A combined experimental and theoretical investigation
Authors: Cheng Shi-Bo , Zhou Can-Hua , Yin Hong-Ming , Sun Ju-Long , Han Ke-Li
Published: June 2009

Photodissociation dynamics of o-nitrophenol in the gas phase at different photolysis wavelengths (361–390 nm) is investigated, and the nascent OH radical is observed by the single-photon laser-induced fluorescence technique. At all the photolysis wavelengths, the OH radicals are formed in vibrationally cold state (υ″=0) and have similar rotational state distributions. The average rotational temperature for all the photolysis wavelengths is approximately 970±120 K, corresponding to a rotational energy of 1.9±0.2 kcal mol−1. The spin orbit and Λ-doublet states of the OH fragments formed in the dissociation are measured to have nonstatistical distributions. To get an insight into the dissociative mechanism leading to OH formation in the photolysis of o-nitrophenol, the potential energy surfaces of the OH-forming channels are mapped by ab initio theoretical calculations. According to both experimental and theoretical results, a possible mechanism for OH formation is proposed.
Sound transmission within the Bragg gap via the high-order modes in a waveguide with periodically corrugated walls
Authors: Tao Zhiyong , He Weiyu , Xiao Yumeng , Zhang Weihe , Wang Xinlong
Published: June 2009

The well-known Bragg resonance in periodic waveguides always leads to the creation of the so-called Bragg gap, within which sound propagations are effectively forbidden. Here we report the possibility of sound energy transmission in the Bragg gap via the high-order transverse modes, which penetrate through the forbidden band due to the interactions between different sound modes in an acoustic duct with periodically corrugated walls. The theoretical analysis indicates that in the waveguides with transverse scales comparable to its period, the guided wave modes can interact with the Bragg gap so that the forbidden band undergoes an abnormal change, giving rise to both a considerable compression in the band width and a sharp descent of the transmission loss on the upper edge of the stopband. The experiment confirms the existence and the significance of the interacting effect, and the measurements of the transmission loss and the radial distribution of sound fields agree quite well with the theoretical predictions.
Generalized van der Waals theory for the twist elastic modulus and helical pitch of cholesterics
Authors: Wensink H. H. , Jackson G.
Published: June 2009

We present a generalized van der Waals theory for a lyotropic cholesteric system of chiral spherocylinders based on the classical Onsager theory for hard anisometric bodies. The rods consist of a hard spherocylindrical backbone surrounded with a square-well potential to account for attractive (or soft repulsive) interactions. Long-ranged chiral interactions are described by means of a simple pseudoscalar potential which is appropriate for weak chiral forces of a predominant electrostatic origin. Based on the formalism proposed by Straley [Phys. Rev. A 14, 1835 (1976)], we derive explicit algebraic expressions for the twist elastic modulus and the cholesteric pitch for rods as a function of density and temperature. The pitch varies nonmonotonically with density, with a sharp decrease at low packing fractions and a marked increase at higher packing fractions. A similar trend is found for the temperature dependence. The unwinding of the helical pitch at high densities (or low temperatures) originates from a strong enhancement of the local nematic order and the corresponding increase in the twist elastic resistance associated with near-parallel local rod configurations. This contrasts with the commonly held view that the increase in pitch with decreasing temperature as often observed in cholesterics is due to layer formation resulting from presmectic fluctuations. The increase in pitch with increasing temperature is consistent with an entropic unwinding as the chiral interaction becomes less significant than the thermal energy. The variation of the pitch with density, temperature, and contour length is in qualitative agreement with recent experimental results on colloidal fd rods.
Wavelet-based analysis of enstrophy transfers in two-dimensional turbulence
Authors: Fischer Patrick , Bruneau Charles-Henri
Published: June 2009

Two-dimensional turbulence admits two different ranges of scales: a direct enstrophy cascade from the injection scale to the small scales and an inverse energy cascade at large scales. It has already been shown in previous papers that vortical structures are responsible for the transfers of energy upscale while filamentary structures are responsible for the forward transfer of the enstrophy. Here we propose an original mathematical tool, the interaction function, for studying the space localization of the enstrophy fluxes. It is defined using an orthogonal two-dimensional wavelet decomposition.
Ultrafast rerouting of light via slow modes in a nanophotonic directional coupler
Authors: Kampfrath T. , Beggs D. M. , White T. P. , Burresi M. , van Oosten D. , Krauss T. F. , Kuipers L.
Published: June 2009

We demonstrate that two coupled photonic-crystal waveguides can route two subsequently arriving light pulses to different output ports even though the pulses are only 3 ps apart. This rerouting of light is due to an ultrafast shift in the transmittance spectrum triggered by the generation of electrons and holes in the Si base material by a femtosecond laser pulse. The use of slow-light modes allows for a coupler length of only 5.2 μm. Since these modes are not directly involved, the 3 ps dead time is solely determined by the duration of the input pulse rather than its transit time through the device.
Anomalous lattice parameter of magnetic semiconductor alloys
Authors: Caetano Clóvis , Marques Marcelo , Ferreira Luiz G. , Teles Lara K.
Published: June 2009

The addition of transition metals to III-V semiconductors radically changes their electronic, magnetic, and structural properties. We show by ab initio calculations that in contrast to the conventional semiconductor alloys, the lattice parameter in magnetic semiconductor alloys, including those with diluted concentration, strongly deviates from Vegard’s law. We find a direct correlation between the magnetic moment and the anion-transition metal bond lengths and derive a simple and general formula that determines the lattice parameter of a particular magnetic semiconductor by considering both the composition and magnetic moment. This dependence can explain some experimentally observed anomalies and stimulate other kind of investigations.
Correlation of mass fractal dimension and asymmetry
Authors: Schneider Gerald Johannes
Published: June 2009

Small-angle X-ray experiments reveal the structure and structural changes of silica embedded in a rubbery host matrix due to the deformation of the surrounding elastomer. The experiments prove that the silica is initially isotropic and becomes anisotropic due to the deformation of the matrix. Increasing the elongation ratio of the polymer results in a larger mass fractal dimension of the silica clusters. The growing mass fractal dimension can be explained simply by a rearrangement of the primary particles within the clusters. However, for the first time, mathematical reasons are presented which clearly demonstrate that self-affine clusters have to be used instead of self-similar ones in order to describe the experiments correctly.
Car–Parrinello density matrix search with a first principles fictitious electron mass method for electronic wave function optimization
Authors: Li Xiaosong , Moss Christopher L. , Liang Wenkel , Feng Yong
Published: June 2009

In spite of its success in molecular dynamics and the advantage of being a first order propagation technique, the Car–Parrinello method and its variations have not been successful in self-consistent-field (SCF) wave function optimization due to slow convergence. In this article, we introduce a first principles fictitious mass scheme to weigh each individual density element differently and instantaneously. As an alternative to diagonalization in SCF, the Car–Parrinello scheme is implemented as a density matrix search method. Not only does the fictitious mass scheme developed herein allow a very fast SCF convergence, but also the Car–Parrinello density matrix search (CP-DMS) exhibits linear scaling with respect to the system size for alanine helical chain test molecules. The excellent performance of CP-DMS holds even for very challenging compact three-dimensional quantum particles. While the conventional diagonalization based SCF method has difficulties optimizing electronic wave functions for CdSe quantum dots, CP-DMS shows both smooth and faster convergence.
Measurement of work in single-molecule pulling experiments
Authors: Mossa Alessandro , de Lorenzo Sara , Huguet Josep Maria , Ritort Felix
Published: June 2009

A main goal of single-molecule experiments is to evaluate equilibrium free energy differences by applying fluctuation relations to repeated work measurements along irreversible processes. We quantify the error that is made in a free energy estimate by means of the Jarzynski equality when the accumulated work expended on the whole system (including the instrument) is erroneously replaced by the work transferred to the subsystem consisting of the sole molecular construct. We find that the error may be as large as 100%, depending on the number of experiments and on the bandwidth of the data acquisition apparatus. Our theoretical estimate is validated by numerical simulations and pulling experiments on DNA hairpins using optical tweezers.
Cones of positive maps and their duality relations
Authors: Skowronek Łukasz , Størmer Erling , Życzkowski Karol
Published: June 2009

The structure of cones of positive and k-positive maps acting on a finite-dimensional Hilbert space is investigated. Special emphasis is given to their duality relations to the sets of superpositive and k-superpositive maps. We characterize k-positive and k-superpositive maps with regard to their properties under taking compositions. A number of results obtained for maps are also rephrased for the corresponding cones of block positive, k-block positive, separable, and k-entangled operators due to the Jamiołkowski–Choi isomorphism. Generalizations to a situation where no such simple isomorphism is available are also made, employing the idea of mapping cones. As a side result to our discussion, we show that extreme entanglement witnesses, which are optimal, should be of special interest in entanglement studies.
Tuning of structure inversion asymmetry by the δ-doping position in (001)-grown GaAs quantum wells
Authors: Lechner V. , Golub L. E. , Olbrich P. , Stachel S. , Schuh D. , Wegscheider W. , Bel’kov V. V. , Ganichev S. D.
Published: June 2009

Both structure and bulk inversion asymmetry in modulation-doped (001)-grown GaAs quantum wells were investigated employing the magnetic field induced photogalvanic effect. We demonstrate that the structure inversion asymmetry (SIA) can be accurately tailored by the delta-doping layer position. Symmetrically doped structures exhibit a substantial SIA due to impurity segregation during the growth process. Tuning the SIA by the delta-doping position, we can grow samples with almost equal degrees of structure and bulk inversion asymmetry.
Extracting the Richardson constant: IrOx/n-ZnO Schottky diodes
Authors: Sarpatwari K. , Awadelkarim O. O. , Allen M. W. , Durbin S. M. , Mohney S. E.
Published: June 2009

A method is proposed to account for the effects of Schottky barrier height inhomogeneities on the Richardson constant (A∗) extracted from current-voltage-temperature (I-V-T) measurements. Our approach exploits a correlation between the extracted Richardson constant and effective barrier height. As a test case, the method is applied to I-V-T measurements performed on IrOx/n-ZnO Schottky diodes. A homogeneous A∗ value of 27±7 A cm−2 K−2 is obtained, in close agreement with the theoretically expected value of 32 A cm−2 K−2 for n-type ZnO.
Multistate storage through successive phase change and resistive change
Authors: Wu Liangcai , Song Zhitang , Rao Feng , Gong Yuefeng , Feng Songlin
Published: June 2009

Combination of phase change and resistive change was proposed to achieve multistate storage in one cell and Ge2Sb2Te5 (GST)/tungsten oxide (WOx) stack was fabricated. In reset process, three resistance staircases were observed, corresponding to the device transition from low-resistance-state (LRS) to a medium-resistance-state (MRS) first, and then transition from the MRS to high-resistance-state (HRS). In set process, two S-shaped negative-differential-resistances were observed, corresponding to the device transition from HRS to MRS first, and then transition from MRS to LRS. The GST/WOx architecture with successive phase change and resistive change is considered to have potential for multistate storage.
Enhanced exchange anisotropy between antiferromagnetic PtMn and ferromagnetic Co system by AuCu underlayer
Authors: Soeya Susumu
Published: June 2009

The introduction of a Au50Cu50 (in at. %) seed and dynamic-stress-induced Pt50Mn50 ordered-assisting layer into PtMn/Co exchange-coupled films resulted in a unidirectional anisotropy constant Ke≒0.37 erg/cm2, approximately 20% larger than the previous reported results and in a strong PtMn(111) crystalline orientation even after thermal annealing. It was considered that the former was due to the increase in exchange-coupling density with the strong PtMn(111) orientation and to the increase in lattice distortion of the PtMn film with excessive dynamic-stress-induced PtMn ordered-assisting effect of the AuCu film. The cause of the latter was that the AuCu film effectively functioned as a seed layer of the PtMn film.
Reader as a contact detector
Authors: Zhang Mingsheng , Liu Bo , Hu Shengbin
Published: June 2009

The response of reader in thin film magnetic head is studied experimentally when thermal actuated slider contacts with disk without magnetic transition. The reader signal shows quick response and high sensitivity to the continuous and intermittent contact. The spectrum analysis of reader signal shows the peaks to be corresponding to the harmonic frequencies of a slider’s resonance frequency.
A model of atom dense packing for metallic glasses with high-solute concentration
Authors: Lu Bao-Chen , Yao Jia-Hao , Xu Jian , Li Yi
Published: June 2009

Taking the chemical ordering in the metallic glasses into consideration, we have extended the efficient cluster packing model to predict the composition in high-solute concentration alloys with atomic dense packing. Its validity is supported by the good agreements between the predicted compositions with the maximum packing efficiency and the experimentally optimized bulk metallic glass formers in the Cu–Zr, Cu–Hf, and Ni–Nb binary systems. Despite its simplicity, it seems that the structure predicted by our model reflects in certain way the averaged structural configuration of metallic glasses.
Exciton-related electroluminescence from ZnO nanowire light-emitting diodes
Authors: Zimmler Mariano A. , Voss Tobias , Ronning Carsten , Capasso Federico
Published: June 2009

The authors study the microscopic origin of the electroluminescence from zinc oxide (ZnO) nanowire light-emitting diodes (LEDs) fabricated on a heavily doped p-type silicon (p-Si) substrate. By comparing the low-temperature photoluminescence and electroluminescence of a single nanowire LED, bound- and free-exciton related recombination processes, together with their longitudinal-optical phonon replicas, can be identified as the origin of both electroluminescence and photoluminescence.
Fabrication and characterization of all-thin-film magnetoelectric sensors
Authors: Zhao Peng , Zhao Zhenli , Hunter Dwight , Suchoski Richard , Gao Chen , Mathews Scott , Wuttig Manfred , Takeuchi Ichiro
Published: June 2009

ac magnetic field sensors based on thin-film magnetoelectric (ME) devices operating at room temperature have been fabricated. The ME layers consist of a sol-gel derived Pb(Zr0.52Ti0.48)O3 film and a sputter deposited Fe0.7Ga0.3 film on Si cantilevers. The ME coupling is substantially improved by depositing a Pt layer at the interface. The ME coefficient up to 1.81 V/Oe cm is obtained at the mechanical resonant frequency of 333 Hz and at dc bias magnetic field of 90 Oe. Clear reduction in the substrate clamping effect is observed as the Si cantilever thickness is systematically reduced down to 35 μm.
Ultraviolet coherent random lasing in randomly assembled SnO2 nanowires
Authors: Yang H. Y. , Yu S. F. , Lau S. P. , Tsang S. H. , Xing G. Z. , Wu T.
Published: June 2009

Although nanostructured SnO2 exhibited ultraviolet stimulated emission at room temperature, the low emission intensities and occurrence of gain saturation restricted them to be considered as luminescent materials for semiconductor lasers. In this letter, we find that a large ultraviolet excitonic gain can be obtained from SnO2 nanowires coated with an amorphous layer. Under effective pumping, ultraviolet coherent random lasing can be realized from randomly assembled SnO2 nanowires at room temperature.
A review of terms and definitions to categorise estuaries, lagoons and associated environments
Authors: Tagliapietra Davide , Sigovini Marco , Ghirardini Annamaria Volpi
Published: June 2009

Estuaries, rias, fjords, coastal lagoons, bahiras, river mouths, tidal creeks, deltas and similar coastal environments are often regarded as a single broad conceptual class. ‘Brackish’, ‘estuarine’, ‘paralic’ and ‘transitional’ are terms used in different contexts to designate collectively this class of environments. Nevertheless every term, generated from different historical perspectives and scientific points of view, excludes some of the above-mentioned environments. These terms and definitions were examined with regard to their meaning and history. The main attributes have been extracted from definitions and arranged in a conceptual scheme giving an overall direct perception of their relationships. This analysis provided evidence for the occurrence of two major groups of attributes: hydrological and geomorphic. Although the significance of hydrological attributes is instantly recognisable, geomorphic attributes imply subjacent concepts of geographical scale and hydrological features not expressly formulated in definitions, such as a limited supply of seawater to the system.
Mitochondrial DNA supports the identification of two endangered river sharks (Glyphis glyphis and Glyphis garricki) across northern Australia
Authors: Wynen Louise , Larson Helen , Thorburn Dean , Peverell Stirling , Morgan David , Field Iain , Gibb Karen
Published: June 2009

The river sharks (genus Glyphis) are a small group of poorly known sharks occurring in tropical rivers and estuarine waters across northern Australia, south-east Asia and the subcontinent. The taxonomy of the genus has long been unclear due to very few individuals having been caught and examined, resulting in a paucity of data regarding their distribution, biology and ecology. Only recently has attention focussed on the two Australian species, G. glyphis and G. garricki. This study is a result of a rare opportunity to collate the few samples that have been collected from these species and the bull shark Carcharhinus leucas, which shares an overlapping range. These samples were analysed using the DNA barcoding approach (cox1 mitochondrial gene), compared with six other species of carcharhinids and evaluated in light of the current taxonomic classification. Nine species-specific nucleotide differences were found between G. glyphis and G. garricki and no intra-specific variation provides strong support for the separation into distinct species. Significant differences were also observed at the inter-generic level, with Glyphis forming a distinct clade from Carcharhinus. This study provides the basis for future molecular studies required to better address conservation issues confronting G. glyphis and G. garricki in Australia.
Sustainability assessment for fishing effects (SAFE) on highly diverse and data-limited fish bycatch in a tropical prawn trawl fishery
Authors: Zhou Shijie , Griffiths Shane P. , Miller Margaret
Published: June 2009

A new sustainability assessment for fishing effects (SAFE) method was used to assess the biological sustainability of 456 teleost bycatch species in Australia’s Northern Prawn Fishery. This method can quantify the effects of fishing on sustainability for large numbers of species with limited data. The fishing mortality rate of each species based on its spatial distribution (estimated from detection/non-detection data) and the catch rate based on fishery-dependent or fishery-independent data were estimated. The sustainability of each species was assessed by two biological reference points approximated from life-history parameters. The point estimates indicated that only two species (but 21 when uncertainty was included) had estimated fishing mortality rates greater than a fishing mortality rate corresponding to the maximum sustainable yield. These two species also had their upper 95% confidence intervals (but not their point estimates) greater than their minimum unsustainable fishing mortality rates. The fact that large numbers of species are sustainable can be attributed mainly to their wide distributions in unfished areas, low catch rates within fished areas and short life spans (high biological productivity). The present study demonstrates how SAFE may be a cost-effective quantitative assessment method to support ecosystem-based fishery management.
Ecology and comparison of coastal and offshore bottlenose dolphins (Tursiops truncatus) in California
Authors: Bearzi Maddalena , Saylan Charles A. , Hwang Alice
Published: June 2009

Populations of coastal and offshore bottlenose dolphins (Tursiops truncatus) are considered to differ ecologically, with implications for their protection and management. We assessed occurrence, distribution and behaviour of coastal and offshore populations of dolphins during a photo-identification study in Santa Monica Bay and nearby areas (1997–2007). Bottlenose dolphins occurred year-round and were encountered on 44.2% of all surveys (n = 425). We photo-identified 647 individuals; of these, 375 (58.0%) were coastal (<1 km from shore), 241 (37.2%) offshore (1–65 km from shore) and 31 were both (4.8%). Dolphins mostly travel (69.0%) and travel-dive (61.5%), with offshore dolphins socialising more (22.6%) than coastal. There were low re-sighting rates for both coastal and offshore dolphins. Low re-sighting rates of coastal individuals provide little evidence of year-round site fidelity, suggesting their range is greater than the study area. Several individuals were re-sighted between and over 1-year periods, often foraging. This suggests that coastal dolphins: (1) are highly mobile within inshore waters, but spend time foraging in the study area, and (2) range >1 km from shore, contrary to what has been previously reported.
Nursery grounds, movement patterns and growth rates of dusky sharks, Carcharhinus obscurus: a long-term tag and release study in South African waters
Authors: Hussey Nigel E. , McCarthy Ian D. , Dudley Sheldon F. J. , Mann Bruce Q.
Published: June 2009

Knowledge of movement patterns of sharks in coastal waters is critical for the structuring of regional management plans. Through a long-term tag–recapture program, 9716 dusky sharks (Carcharhinus obscurus) were tagged and released along the east coast of South Africa. A total of 648 C. obscurus, principally small sharks (<100 cm PCL), were recaptured. Most recaptures were within 100 km of the tagging location in the nursery habitat in KwaZulu-Natal (KZN) with small scale movements occurring throughout the year. Forty-eight C. obscurus undertook movements >200 km that indicated a southerly migration between KZN and Eastern/Southern Cape (E/SC) between June and November. Seasonal northerly migrations were less well defined. The largest southerly and northerly movements were 1323 km and 1374 km, respectively. For sharks moving 1–100 km south from their tagging locality in KZN, an increase in displacement occurred between June and September identifying animals beginning their migration to the E/SC. With increasing displacement, there was also an increase in minimum swimming speed. Calculated growth rates of small sharks of 10.3–11.5 cm year–1 were in agreement with current literature values. Established tag–recapture programs provide an important tool in understanding the ecology of early life-stages of coastal shark species.
Livestock water productivity in the Blue Nile Basin: assessment of farm scale heterogeneity
Authors: Haileslassie A. , Peden D. , Gebreselassie S. , Amede T. , Wagnew A. , Taddesse G.
Published: June 2009

A recent study of the livestock water productivity (LWP), at higher spatial scales in the Blue Nile Basin, indicated strong variability across regions. To get an insight into the causes of this variability, we examined the effect of farm households’ access to productive resources (e.g. land, livestock) on LWP in potato–barley, barley–wheat, teff–millet and rice farming systems of the Gumera watershed (in the Blue Nile Basin, Ethiopia). We randomly selected 180 farm households. The sizes of the samples, in each system, were proportional to the respective system’s area. Then we grouped the samples, using a participatory wealth ranking method, into three wealth groups (rich, medium and poor) and used structured and pre-tested questionnaires to collect data on crops and livestock management and applied reference evapotranspiration (ET0) and crop coefficient (Kc) approaches to estimate depleted (evapotranspiration) water in producing animal feed and food crops. Then, we estimated LWP as a ratio of livestock’s beneficial outputs to water depleted. Our results suggest strong variability of LWP across the different systems: ranging between 0.3 and 0.6 US$ m−3 year−1. The tendency across different farming systems was comparable with results from previous studies at higher spatial scales. The range among different wealth groups was wider (0.1 to 0.6 US$ m−3 year−1) than among the farming systems. This implies that aggregating water productivity (to a system scale) masks hotspots and bright spots. Our result also revealed a positive trend between water productivity (LWP and crop water productivity, CWP) and farm households’ access to resources. Thus, we discuss our findings in relation to poverty alleviation and integrated land and water management to combat unsustainable water management practices in the Blue Nile Basin.
Assessing the importance of livestock water use in basins
Authors: Cook S. E. , Andersson M. S. , Fisher M. J.
Published: June 2009

Recent concern over food prices has triggered a renewed interest in agricultural production systems. While attention is focused mainly on cropping, a complete analysis of food production systems should recognise the importance of livestock as major consumers of resources – in particular water – and as providers of food and other products and services. We propose that there is a need to examine not just food systems in isolation, but combined food and water systems, both of which are described as in a critical condition. From this broader perspective, it appears even more important to understand livestock systems because first, a total evaluation of agricultural water productivity – the gain from water consumed by agriculture – cannot be made without understanding the complexities of livestock-containing systems and; second, because in most tropical river basins, livestock systems are the major consumers of water.
To identify total water productivity of livestock-containing systems, we describe concepts of agricultural water productivity and review the complexities of tracking the flow of water through livestock-containing systems: from inputs as evapotranspiration (ET) of forage and crops to outputs of valued animal products or services. For the second part, we present preliminary results from water use accounts analysis for several major river basins, which reveal that for Africa at least, livestock systems appear to be the major water consumers. Yet, little is known about the fate of water as it passes through these systems.
We propose that livestock-containing systems offer substantial scope for increasing total water productivity and that there is considerable merit in improving the capacity to analyse water consumption and water productivity through such systems. Without removing this major source of uncertainty, the potential for systemic improvement to meet the world food and water crisis remains undefined and hence under-acknowledged.
Enabling the uptake of livestock - water productivity interventions in the crop - livestock systems of sub-Saharan Africa
Authors: Amede Tilahun , Geheb Kim , Douthwaite Boru
Published: June 2009

Livestock–water productivity (LWP) refers to a set of innovations that could contribute towards reducing the amount of water needed per unit of output generated. But what does it take to get these ideas adopted by livestock keepers in crop–livestock systems? In this paper, we treat LWP as an innovation, and consider in what ways it may be introduced and/or developed among the crop–livestock agricultural systems by drawing on successful examples of change. In the first part of this paper, we introduce relevant tenets of the innovation systems literature, and introduce a three-component conceptual framework for the adoption of LWP technologies. In the second part, we describe three successful cases of resources use change. In the final section, we identify what we consider to be necessary components in successful change, and relate these to LWP. We argue that, in the under-regulated crop–livestock systems of eastern Africa, key areas for focus include social institutions, political systems, gender and leadership.
Enhancing local innovation to improve water productivity in crop - livestock systems
Authors: Waters-Bayer Ann , Bayer Wolfgang
Published: June 2009

In their efforts to adapt to changing conditions and grasp opportunities, small-scale farmers have been innovating since time immemorial. With increasing scarcity of water, harnessing water productivity in crop–livestock systems will require enhancing such local innovation processes, including both endogenous development and local adaptation of exogenous interventions. The paper highlights the importance of taking an innovation systems perspective in this endeavour. The various actors involved in agricultural production, extension, research, education, policymaking and trade who can contribute to or constrain innovation processes need to be recognised and their interactions understood. Particularly in the realm of working with water – often the task of women and girls – gender aspects must be addressed, including women’s role in innovation processes and the impact of change in water access and use on women’s workloads and decision-making.
The paper presents examples of technical and socio-institutional innovation to improve crop–livestock water productivity that have been developed by local resource users. It demonstrates how scientists and technical advisors in research and development organisations can harness these dynamics in local knowledge by identifying local innovations, exploring together with local people the rationale behind them, and explaining in scientific terms why they work. It argues for an approach to research that allows farmers to be creative and that strengthens their capacities to continue to adapt to changing conditions.
It stresses the role of researchers in revealing how farmers are developing solutions that challenge official policy, and then joining forces with farmers to bring about policy change to accommodate and encourage local innovation. Thus, it presents one ‘intervention’ that could enhance crop–livestock water productivity: promoting an approach of recognising local innovation and engaging in participatory research with local people who are developing their own ways to make the most of scarce water.