bluuebunny/crossref_metadata_2025 huggingface dataset:
First demonstration of collimation and monochromatisation of a laser accelerated proton burst
Authors: Ter-Avetisyan S. , Schnürer M. , Polster R. , Nickles P.V. , Sandner W.
Published: November 2008

Laser produced ion beams have a large divergence angle and a wide energy spread. To our knowledge, this is the first demonstration of collimation and monochromatisation of laser accelerated proton beams, using a permanent quadrupole magnet lens system. It acts as a tunable band pass filter by collimating or focusing the protons with the same energy. Because it gathers nearly the whole proton emission, a strong enhancement of the beam density appears. For the collimated beam, an increase of the proton density in the (3.7 ± 0.3) MeV energy band up to a factor of ~30, from possible 40, relative to the non-collimated beam is demonstrated. With the help of this simple, reliable, and well established technique new perspectives will be opened for science and technology, monoenergetic ion beams can be attained in any lab, where a source of laser accelerated ions exist. This finding enables to apply afterward well known beam steering techniques to the formed ion beam, which are applied in conventional accelerators to manipulate the beam parameters or to transport the beams and make them use in many application.
Eric Wolfensohn: Pioneer of Twentieth-Century British Theatre Lighting Design
Authors: Morgan Nigel
Published: November 2008

Eric Wolfensohn was one of a small group of British lighting designers to emerge in the 1940s. In this article, Nigel Morgan records how, as he plied his trade, Wolfensohn established a blueprint for the working pattern of the modern freelance lighting designer. Starting as a technician and operator, he progressed to designer and consultant, crossing between the genres of ballet, opera, and plays, and moving seamlessly into shop display, exhibition, film and television, borrowing techniques from each particular form and fusing styles in a quest for aesthetic satisfaction. Nigel Morgan qualified as a music teacher, and playing in a rock band introduced him to the stage and a fascination for stage design and technology. For the next twenty years he followed a career in theatre, lighting world premieres of plays by Caryl Churchill, Stephen Jeffreys and Tom Kempinski. He developed a highly successful lighting business in retail, with Harrods and Daks-Simpsons the principal London clients. Parallel to this, he was the innovator of lighting programmes in higher education, including the first European undergraduate programme in lighting design at Rose Bruford College in 1996. Nigel gained a PhD in 2003 for researching the origins of lighting design in Britain, and has published Stage Lighting for Theatre Designers and Stage Lighting in Britain: the Emergence of the Lighting Designer.
Neurotic disorders
Authors: Lindesay James , Winston Tony
Published: November 2008

This paper updates a previous review of the topic published in this series in 1992. There are no major advances in knowledge, understanding or treatment to report, but there has been a steady growth in interest, articles, chapters and textbooks dealing with neurotic disorders in the elderly, which is an encouraging sign that these common, disabling and treatable conditions are now being taken more seriously by health professionals.
Channelized melt flow in downwelling mantle: Implications for 226Ra‐210Pb disequilibria in arc magmas
Authors: Petford N. , Koenders M. A. , Turner S.
Published: November 2008

We present the results of an analytical model of porous flow of viscous melt into a steadily dilating “channel” (defined as a cluster of smaller veins) in downwelling subarc mantle. The model predicts the pressure drop in the mantle wedge matrix surrounding the channel needed to drive melt flow as a function of position and time. Melt is sucked toward the dilatant region at a near‐constant velocity (10−5 s−1) until veins comprising the channel stop opening (t = τ). Fluid elements that complete their journey within the time span t < τ arrive at a channel. Our results make it possible to calculate the region of influence sampled by melt that surrounds the channel. This region is large compared to the model size of the channelized region driving flow. For a baseline dilation time of 1 year and channel half width of 2 m, melt can be sampled over an 80‐m radius and has the opportunity to sample matrix material with potentially contrasting chemistry on geologically short timescales. Our mechanical results are consistent with a downgoing arc mantle wedge source region where melting and melt extraction by porous flow to a channel network are sufficiently rapid to preserve source‐derived 238U‐230Th‐226Ra, and potentially also 226 Ra‐210Pb, disequilibria, prior to magma ascent to the surface. Since this is the rate‐determining step in the overall process, it allows the possibility that such short‐lived disequilibria measured in arc rocks at the surface are derived from deep in the mantle wedge. Stresses due to partial melting do not appear capable of producing the desired sucking effect, while the order of magnitude rate of shear required to drive dilation of ∼10−7 s−1 is much larger than values resulting from steady state subduction. We conclude that local deformation rates in excess of background plate tectonic rates are needed to “switch on” the dilatant channel network and to initiate the sucking effect.
On the modification of tides in a seasonally ice‐covered sea
Authors: St‐Laurent P. , Saucier F. J. , Dumais J.‐F.
Published: November 2008

New observations from eight moorings located in Foxe Basin, Hudson Strait, and Hudson Bay are used to study the seasonal variability of the M2 tide. Significant seasonal variations of the M2 surface elevation are found in all these regions and at all seasons. The largest variations occur during winter while both elevation increase (Hudson Strait) and decrease (Hudson Bay, Foxe Basin) are observed. These variations are found recurrent at the stations where multiyear observations are available. Observations from a velocity profiler are consistent with a seasonal damping of the tides because of friction under ice. Numerical simulations with a sea ice‐ocean coupled model and realistic forcing qualitatively reproduce most of the features of the observed variability. The simulations show that the winter M2 variations are essentially caused by the under‐ice friction, albeit with strong regional differences. Under‐ice friction mostly occurs in a limited region (Foxe Basin) and can account for both increased and decreased M2 elevations during winter.
On turbulence closures for two‐phase sediment‐laden flow models
Authors: Chauchat Julien , Guillou Sylvain
Published: November 2008

Recent experimental studies show that there exists a difference between horizontal velocity components of particles and of fluid in sediment‐laden open channel flows. For suspended particles with sufficient inertia, volume fraction profile cannot be represented without the introduction of empirical parameters in passive scalar sediment transport models. The aim of this paper is to propose a two‐phase model that allows representation of the main features of sediment‐laden flows: the existence of a horizontal velocity difference between particles and fluid, the dispersion of particles by fluid turbulent motion, and the damping of fluid turbulent kinetic energy. A 2‐D vertical numerical model for suspended particle transport in open channels using a two‐phase approach is used in conjunction with experimental measurements. Different turbulence models for both phases are presented. The fluid phase turbulence is modeled by a k − ɛ model. Two models for the solid phase turbulence are used: a first‐order model, based on the kinetic theory of granular flows, and an algebraic model based on an homogeneous, isotropic, and steady fluid turbulence assumption. We demonstrate that a modeling approach of the coupling between fluid and solid turbulence allows reproduction of the main features of sediment‐laden flows. We show this approach represents an improvement compared with the classical approach. We show that a simple algebraic model based on the homogeneous, isotropic, and steady fluid turbulence assumption for the solid phase turbulence allows the physical phenomenon to be reproduced with very slight differences compared with a first‐order model.
A prelanding assessment of the ice table depth and ground ice characteristics in Martian permafrost at the Phoenix landing site
Authors: Mellon Michael T. , Boynton William V. , Feldman William C. , Arvidson Raymond E. , Titus Timothy N. , Bandfield Joshua L. , Putzig Nathaniel E. , Sizemore Hanna G.
Published: November 2008

We review multiple estimates of the ice table depth at potential Phoenix landing sites and consider the possible state and distribution of subsurface ice. A two‐layer model of ice‐rich material overlain by ice‐free material is consistent with both the observational and theoretical lines of evidence. Results indicate ground ice to be shallow and ubiquitous, 2–6 cm below the surface. Undulations in the ice table depth are expected because of the thermodynamic effects of rocks, slopes, and soil variations on the scale of the Phoenix Lander and within the digging area, which can be advantageous for analysis of both dry surficial soils and buried ice‐rich materials. The ground ice at the ice table to be sampled by the Phoenix Lander is expected to be geologically young because of recent climate oscillations. However, estimates of the ratio of soil to ice in the ice‐rich subsurface layer suggest that that the ice content exceeds the available pore space, which is difficult to reconcile with existing ground ice stability and dynamics models. These high concentrations of ice may be the result of either the burial of surface snow during times of higher obliquity, initially high‐porosity soils, or the migration of water along thin films. Measurement of the D/H ratio within the ice at the ice table and of the soil‐to‐ice ratio, as well as imaging ice‐soil textures, will help determine if the ice is indeed young and if the models of the effects of climate change on the ground ice are reasonable.
A state‐dependent parameterization of saturated‐unsaturated zone interaction
Authors: Bogaart P. W. , Teuling A. J. , Troch P. A.
Published: November 2008

The relevance of groundwater as an important source of root zone moisture by means of capillary rise is increasingly being recognized. This is partly reflected in many current land surface schemes, which increasingly replace a one‐way (i.e., downward) drainage of water by a two‐way interaction flux between the root zone and a groundwater system. A fully physically correct implementation of this two‐way saturated‐unsaturated interaction flux requires transient simulations using the highly nonlinear Richards' equation, which is a computationally demanding approach. We test a classic simple approximation that computes the root zone–groundwater interaction flux as the net effect of a downward drainage flux and an upward capillary rise flux against the Darcy equation for quasi steady state conditions. We find that for a wet root zone and/or shallow groundwater, the errors within this approximation are significant and of the same magnitude as the interaction flux itself. We present a new closed‐form parameterization of the Darcy equation–based fluxes that accounts both for root zone soil moisture and depth to the water table. Parameter values for this parameterization are listed for 11 different, widely applied soil texture descriptions. The high numerical efficiency of the proposed method makes it suitable for inclusion into demanding applications, e.g., a Monte Carlo framework, or high spatial resolution.
Plio‐Pleistocene denitrification in the eastern tropical North Pacific: Intensification at 2.1 Ma
Authors: Liu Zhonghui , Altabet Mark A. , Herbert Timothy D.
Published: November 2008

Global climate has changed substantially over the past ∼4 million years (Ma) toward, on average, colder conditions and higher amplitude oscillation between glacial and interglacial periods. Corresponding changes in marine biogeochemistry could have linked oceanic circulation changes to the global carbon cycle, but remain poorly understood. We report a high‐resolution, 4‐Ma‐long δ15N record from Ocean Drilling Program Site 1012 on the California margin, which monitors denitrification intensity in one of the principal Oxygen Minimum Zones (OMZs) of the open ocean. The δ15N record demonstrates that eastern tropical North Pacific (ETNP) denitrification was weak for much of the late Pliocene. Though there was no apparent change associated with Northern Hemisphere glaciation (NHG) at ∼2.7 Ma, denitrification strengthened substantially (by ∼2‰ in δ15N) at ∼2.1 (Ma). Since 2.1 Ma, intense denitrification in the ETNP occurred during interglacial periods and was generally very climate‐sensitive. We infer that two oceanic changes, the shoaling of the thermocline in the eastern Pacific (and thus the strengthened Walker circulation) and the development of a modern‐like frontal system in high‐latitude southern ocean around ∼2.1 Ma provided favorable conditions for intensification of ETNP denitrification that was also likely mirrored south of the equator. Intermediate water circulation changes likely created the poorly ventilated zones susceptible to the suboxic condition required by denitrification. 2.1 Ma thus marks a critical point for the reorganization of the ocean's nitrogen cycle in which open ocean denitrification became a significant loss term during interglacial phases of climate. Given linkage between the ocean's N and C cycle, ETNP denitrification changes probably contributed to Plio‐Pleistocene climatic changes.
Glacier, fjord, and seismic response to recent large calving events, Jakobshavn Isbræ, Greenland
Authors: Amundson J. M. , Truffer M. , Lüthi M. P. , Fahnestock M. , West M. , Motyka R. J.
Published: November 2008

The recent loss of Jakobshavn Isbræ's extensive floating ice tongue has been accompanied by a change in near terminus behavior. Calving currently occurs primarily in summer from a grounded terminus, involves the detachment and overturning of several icebergs within 30–60 min, and produces long‐lasting and far‐reaching ocean waves and seismic signals, including “glacial earthquakes”. Calving also increases near‐terminus glacier velocities by ∼3% but does not cause episodic rapid glacier slip, thereby contradicting the originally proposed glacial earthquake mechanism. We propose that the earthquakes are instead caused by icebergs scraping the fjord bottom during calving.
Recent radical shifts of atmospheric circulations and rapid changes in Arctic climate system
Authors: Zhang Xiangdong , Sorteberg Asgeir , Zhang Jing , Gerdes Rüdiger , Comiso Josefino C.
Published: November 2008

Arctic climate system change has accelerated tremendously since the beginning of this century, and a strikingly extreme sea‐ice loss occurred in summer 2007. However, the greenhouse‐gas‐emissions forcing has only increased gradually and the driving role in Arctic climate change of the positively‐polarized Arctic/North Atlantic Oscillation (AO/NAO) trend has substantially weakened. Although various contributing factors have been examined, the fundamental physical process, which orchestrates these contributors to drive the acceleration and the latest extreme event, remains unknown. We report on drastic, systematic spatial changes in atmospheric circulations, showing a sudden jump from the conventional tri‐polar AO/NAO to an unprecedented dipolar leading pattern, following accelerated northeastward shifts of the AO/NAO centers of action. These shifts provide an accelerating impetus for the recent rapid Arctic climate system changes, perhaps shedding light on recent arguments about a tipping point of global‐warming‐forced climate change in the Arctic. The radical spatial shift is a precursor to the observed extreme change event, demonstrating skilful information for future prediction.
Multiscale relationships between fracture length, aperture, density and permeability
Authors: Neuman Shlomo P.
Published: November 2008

Fractured rocks exhibit a hierarchical structure which renders their attributes scale‐dependent. In particular available data indicate a tendency for fracture length scales to be distributed according to a power law, average fracture aperture to be given by a power of the fracture length scale, and fracture density as well as log permeability to behave as random fractals. To date, no consistent theoretical relationship has been developed between fracture type (as categorized, for example, by length scale and/or aperture) and corresponding fractal attributes (such as density and log permeability). We develop and explore multiscale relationships between these fracture categories and attributes on the basis of a theory recently proposed by the author, which allows linking them in a formal way.
Evaluation of MODIS NDVI and NDWI for vegetation drought monitoring using Oklahoma Mesonet soil moisture data
Authors: Gu Yingxin , Hunt Eric , Wardlow Brian , Basara Jeffrey B. , Brown Jesslyn F. , Verdin James P.
Published: November 2008

The evaluation of the relationship between satellite‐derived vegetation indices (normalized difference vegetation index and normalized difference water index) and soil moisture improves our understanding of how these indices respond to soil moisture fluctuations. Soil moisture deficits are ultimately tied to drought stress on plants. The diverse terrain and climate of Oklahoma, the extensive soil moisture network of the Oklahoma Mesonet, and satellite‐derived indices from the Moderate Resolution Imaging Spectroradiometer (MODIS) provided an opportunity to study correlations between soil moisture and vegetation indices over the 2002–2006 growing seasons. Results showed that the correlation between both indices and the fractional water index (FWI) was highly dependent on land cover heterogeneity and soil type. Sites surrounded by relatively homogeneous vegetation cover with silt loam soils had the highest correlation between the FWI and both vegetation‐related indices (r∼0.73), while sites with heterogeneous vegetation cover and loam soils had the lowest correlation (r∼0.22).
Multiple problems push LHC start to next spring
Authors: Guinnessy Paul
Published: November 2008

CERN engineers are relieved to have more time to finish constructing the LHC.
Inherent paramagnetic defects in layered Si/SiO2 superstructures with Si nanocrystals
Authors: Jivanescu M. , Stesmans A. , Zacharias M.
Published: November 2008

An extensive electron spin resonance (ESR) analysis has been carried out on structures comprised of Si nanoparticles (∼2 nm across) embedded in a regular pattern in an amorphous SiO2 matrix, fabricated by the SiO/SiO2 superlattice approach, with the intent to reveal and quantify occurring paramagnetic defects. The as-grown state is found to exhibit only a Si dangling bond (DB) signal, which through combination of first and second harmonic X-, K-, and Q-band observations in combination with computer spectra simulation, could be conclusively disentangled as solely comprised of overlapping powder pattern spectra of Pb(0) and Pb1 defects, the archetypal intrinsic defects of the Si/SiO2 interface, with no evidence for a D line (Si DBs in disordered Si). This indicates a full crystalline system of randomly oriented Si nanocrystals (NCs). The Pb(0)/Pb1 defect system, pertaining to the NC-Si/SiO2 interfaces, is found to be both qualitatively and quantitatively much alike that of standard (high-quality) thermal Si/SiO2. The system is inherent, remaining unaffected by subsequent UV/vacuum UV irradiations. Relying on the known properties of Pb-type defects in standard microscopic Si/SiO2, the data would comply with Si nanocrystallites, in average, predominantly bordered by (111) and (100) facets, perhaps with morphology, schematically, of [100] truncated (111) octahedrons. Based on independent NC particles counting, there appears a Pb-type center at ∼71% of the Si NCs indicating the latter to be comprised of two subsystems–with or without an incorporated strain relaxing interface defect–which in that case will exhibit drastically different defect-sensitive properties, such as, e.g., photoluminescence (PL). Upon additional optical irradiation, two more defects appear, i.e., the SiO2-associated Eγ′ and EX centers, where the observed density of the former, taken as criterion, indicates the SiO2 matrix to be of standard thermal oxide quality. Thus, the properties of the revealed crucial intrinsic point defects bear out a high quality of both the NC-Si/SiO2 interfaces and the embedding SiO2, alike that of standard thermal Si/SiO2. In combination with H passivation/depassivation treatments, the degrading impact of the optical excitation (∼360 nm) itself used during PL measurements has been studied, revealing weak ESR reactivation of Pb(0), Pb1, and Eγ′ defects.
Three-dimensional modeling of the plasma arc in arc welding
Authors: Xu G. , Hu J. , Tsai H. L.
Published: November 2008

Most previous three-dimensional modeling on gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) focuses on the weld pool dynamics and assumes the two-dimensional axisymmetric Gaussian distributions for plasma arc pressure and heat flux. In this article, a three-dimensional plasma arc model is developed, and the distributions of velocity, pressure, temperature, current density, and magnetic field of the plasma arc are calculated by solving the conservation equations of mass, momentum, and energy, as well as part of the Maxwell’s equations. This three-dimensional model can be used to study the nonaxisymmetric plasma arc caused by external perturbations such as an external magnetic field. It also provides more accurate boundary conditions when modeling the weld pool dynamics. The present work lays a foundation for true three-dimensional comprehensive modeling of GTAW and GMAW including the plasma arc, weld pool, and/or electrode.
Structure and magnetic properties of bulk nanocrystalline Dy metal prepared by spark plasma sintering
Authors: Yue M. , Wang K. J. , Liu W. Q. , Zhang D. T. , Zhang J. X.
Published: November 2008

The structure and magnetic properties were studied for bulk nanocrystalline dysprosium (Dy) metal prepared by spark plasma sintering method. All the as-prepared samples have hexagonal close packed structure. A decrease in grain size results in remarkable changes in magnetic ordering temperature of the nanocrystalline Dy metal. At 5K, the magnetization drops by 3.35%, and the coercive force increases by three times for nanocrystalline Dy compared to those of coarse-grained bulk Dy sample. These results indicate the remarkable influence of the nanostructure on the magnetism of Dy due to finite size effect.
Laser mode effects on the ion acceleration during circularly polarized laser pulse interaction with foil targets
Authors: Chen M. , Pukhov A. , Sheng Z. M. , Yan X. Q.
Published: November 2008

Ion acceleration by circularly polarized laser pulses interacting with foil targets is studied using two dimensional particle-in-cell simulations. It is shown that laser pulses with transverse super-Gaussian profile help in avoiding target deformation as compared with the usual Gaussian pulse. This improves monochromaticity of the accelerated ion spectrum. Two kinds of surface instabilities have been found during the interaction. These instabilities can potentially break the target and destroy the quasimonoenergetic character of the final ion spectrum. Combined laser pulses with super-Hermite and Gaussian modes are used to improve the ion acceleration and transverse collimation.
Dynamics of optically injected two-dimensional currents
Authors: Sherman E. Ya. , Abrarov R. M. , Sipe J. E.
Published: November 2008

We investigate the charge and spin dynamics of optically injected currents in multiple quantum well structures using a hydrodynamic model. The dynamics is very complex even on time scales of the order of 1 ps due to the interplay of Coulomb forces, electron-hole drag effects, and nonlinearity of the equations of motion. Our analysis is based on a numerical approach employing an expansion of the calculated quantities in a Hermite–Gaussian basis. We calculate the evolution of the density of injected carriers, analyze the pattern of charges after the injection, and extract the parameters that characterize the overall charge displacement in the optical pump-probe and terahertz radiation experiments. While these two parameters would take on the same value if the injected charge distributions moved rigidly, we find that their observed values should be different due to the complex behavior of the carrier motion. The spin flows arising from the spin-dependent skew scattering of electron by holes and corresponding spin density distributions are calculated and analyzed.
Deep traps in GaAs/InGaAs quantum wells and quantum dots, studied by noise spectroscopy
Authors: Kunets Vas. P. , Morgan T. Al. , Mazur Yu. I. , Dorogan V. G. , Lytvyn P. M. , Ware M. E. , Guzun D. , Shultz J. L. , Salamo G. J.
Published: November 2008

Remotely doped In0.35Ga0.65As layers of different coverages 6, 9, 11, and 13 ML were grown by molecular beam epitaxy on (100) GaAs. Quantum dot (QD) nucleation was observed in situ by reflection high-energy electron diffraction at 8 ML growth of In0.35Ga0.65As, while for 6 ML, only two-dimensional (2D) growth was observed. Atomic force microscopy, low temperature photoluminescence, and Hall effect measurements confirmed this transition from 2D to three-dimensional growth. Low-frequency noise studies have been performed to probe defects in such heterostructures throughout the transition from a highly strained quantum well to QDs. Results were compared to a bulk n-type GaAs reference sample. We revealed three main defects in GaAs with activation energies of 0.8, 0.54, and 0.35 eV. These defects with the same activation energies were found in all samples. However, structures containing In0.35Ga0.65As QDs show an additional peak at low temperatures due to the presence of defects which are not observed for reference GaAs and quantum well samples. Detailed analysis shows that for 9 and 11 ML In0.35Ga0.65As QD samples this peak corresponds to the well known M1 defect in GaAs with an activation energy of 0.18 eV, while for a coverage of 13 ML the defect was found to have an activation energy of 0.12 eV. All defects were characterized quantitatively in terms of their activation energy, capture cross section, and density. These studies indicate that noise spectroscopy is a very sensitive tool for electronic material characterization on the nanoscale.
The effect of SiO2 addition and measurement temperature on the high-field electrical behavior of BaTiO3-based positive temperature coefficient thermistors
Authors: Zubair M. A. , Leach C.
Published: November 2008

The effects of SiO2 addition, in the range 0–3 at. %, on the high field electrical characteristics of positive temperature coefficient of resistance (PTC) thermistors have been characterized at several temperatures above the ferroelectric transition temperature TC. It was found that decreases in SiO2 content and increases in measurement temperature both decreased the field dependency of the current-voltage response. The electrical data were analyzed in terms of existing current-flow models and found to exhibit reasonable agreement only with the model based on diffusion limited transport across a double Schottky barrier. The maximum value of voltage drop per grain boundary for fit to the diffusion limited model Vmax increased with increasing measurement temperature within the PTC region, but leveled off beyond the temperature of maximum resistance. This behavior directly parallels the variation of electrostatic barrier height with temperature. A reduction in Vmax with increasing SiO2 content was observed and attributed to a concomitant reduction in electrostatic barrier height.
Comparison of sensitivities of carbon nanotube field-effect transistor biosensors with and without top metal gate
Authors: Abe Masuhiro , Murata Katsuyuki , Ataka Tatsuaki , Matsumoto Kazuhiko
Published: November 2008

The sensitivities of biosensors using top-gate-type carbon nanotube field-effect transistors (CNT-FETs) with and without a top metal gate were compared. The CNT-FET biosensor without the top metal gate (sensor I) showed about three times higher transconductance than the one with the top metal gate (sensor II) when they were modulated by a reference gate electrode placed in a solution. Further, the sensitivity of sensor I was three times higher than sensor II. These results were attributed to the shielding effect of the top metal gate electrode placed in the solution, which was proved by a numerical simulation.
X-ray in-plane scattering investigation of GaN nanorods
Authors: Horák L. , Holý V. , Staddon C. R. , Farley N. R. S. , Novikov S. V. , Campion R. P. , Foxon C. T.
Published: November 2008

An x-ray method is described for the structure characterization of semiordered GaN nanorods. In contrast to other works based on synchrotron radiation, the method uses a standard x-ray laboratory equipment so that it is suitable for a rapid characterization of the nanorods in a technological laboratory. The method uses a grazing-incidence diffraction setup and it makes it possible to determine the mean size of the rods and their angular twist with respect to the crystalline substrate. The applicability of the method is demonstrated on a series of GaN nanorod samples and the parameters of the nanorods are compared with the results of scanning electron microscopy.
Magnetic structures and phase transitions in PrMn2−xFexGe2
Authors: Wang J. L. , Campbell S. J. , Studer A. J. , Avdeev M. , Hofmann M. , Hoelzel M. , Dou S. X.
Published: November 2008

The magnetic properties and magnetic structures of PrMn2−xFexGe2 compounds (space group I4/mmm) have been investigated using magnetic, F57e Mössbauer effect (x=1.0,1.3,1.6), and neutron diffraction measurements (x=0.4,0.6,0.8,1.3) over the temperature range of 3–410 K. This has enabled the existing magnetic phase diagram for PrMn2−xFexGe2 to be extended from Fe concentration x=0–1 to the full range x=0–2 in terms of concentration and dMn–Mn, the intralayer distance. Analysis of the Mössbauer spectra (4.5–300 K) using a model which takes nearest-neighbor environments into account confirms the nonmagnetic nature of Fe atoms in these compounds, and leads to hyperfine parameters which deviate around the magnetic transition temperatures derived from the magnetic and neutron investigations while also enabling the Debye temperatures of PrMn2−xFexGe2 (x=0.4–1.6) to be determined. The experimental values for TCinter are found to decrease rapidly with increasing Fe concentration in the range x=0.0–0.6 compared with calculated TCinter values due to pressure (and therefore geometric) effects only. This behavior demonstrates that electronic effects and replacement of the magnetic Mn atoms with nonmagnetic Fe atoms contribute to the overall magnetic behavior of PrMn2−xFexGe2 compounds. Compared with intralayer Mn–Mn interactions, the interlayer Mn–Mn interactions play the major role in the anomalous thermal expansion observed at magnetic transition in these layered systems, with the interlayer Mn–Mn interactions governing the significant magnetovolume effects.
Nanoindentation-induced plastic deformation and fracture behavior difference between a- and c-domains of BaTiO3 single crystal
Authors: Sun Z. H. , White K. W.
Published: November 2008

The plastic deformation and fracture behavior of individual a- and c-domains of (001) oriented BaTiO3 single crystal are studied with nanoindentation and atomic force microscopy. Consistent with previous observations in rocksalt and perovskite crystals, square-shaped pileups directly surround the residual indents, and rosette arm patterns extend beyond these pileups. These features have been ascribed to dislocation activities on the {110}⟨11¯0⟩ slip systems induced by nanoindentations. We observed rosette screw arms only in c-domains, inside which 90° ac-domain switching is confirmed. We conclude that indentation-induced cracks on {110}90 planes most likely nucleate by dislocation pileups on two neighboring {110}45 planes, which create a sessile dislocation. Significantly shorter cracks in the c-domain under the same indentation load suggest a higher apparent toughness of the c-domain. However, we attribute the different crack lengths to the lower crack driving force resulting from indentation-induced plasticity in c-domains rather than an inherent difference in the crack growth resistance.
Ultrasonic generation and rotation of a small droplet at the tip of a hypodermic needle
Authors: Tan Zhi Wen , Teo Su Gui Gisela , Hu Junhui
Published: November 2008

We show that a hypodermic needle can generate and rotate a small droplet of water around its needle tip when the hypodermic needle is mechanically driven by an acoustic needle. The water droplet increases in size with the driving time and begins to rotate around the tip of the hypodermic needle when the diameter of the droplet is large enough. The rotating droplet falls off when its diameter is larger than a critical value of several millimeters. For a given operating voltage, the revolution speed, maximum diameter, and lifetime of a droplet can be controlled by the operating frequency of the ultrasonic transducer. A revolution speed of up to 16.7 revolutions/s has been achieved.
Stress dependence and scaling of subcoercive field dynamic hysteresis in 0.5Pb(Zr1/2Ti1/2)O3–0.5Pb(Zn1/3Nb2/3)O3 ceramic
Authors: Yimnirun R. , Wongdamnern N. , Triamnak N. , Unruan M. , Ngamjarurojana A. , Ananta S. , Laosiritaworn Y.
Published: November 2008

Stress dependence and scaling behavior of subcoercive field dynamic ferroelectric hysteresis were investigated in rhombohedral 0.5Pb(Zr1/2Ti1/2)O3–0.5Pb(Zn1/3Nb2/3)O3 (0.5PZT–0.5PZN) bulk ceramic with profound relaxor characteristics. The scaling relation of hysteresis area ⟨A⟩ against frequency f, field amplitude E0, and stress σ for the minor loops takes a form of ⟨A−Aσ=0⟩∝f−0.34E03.68σ0.35, which is very similar to that of soft and hard lead zirconate titanate ceramics with the same disrupted domains. This study suggests that the domain structures play a significant role in controlling the dynamic hysteresis behavior of ferroelectric materials.
Stability of a two-layer binary-fluid system with a diffuse interface
Authors: Frolovskaya O. A. , Nepomnyashchy A. A. , Oron A. , Golovin A. A.
Published: November 2008

The phase separation of a binary fluid can lead to the creation of two horizontal fluid layers with different concentrations resting on a solid substrate and divided by a diffuse interface. In the framework of the Cahn–Hilliard equation, it is shown analytically and numerically that such a layered system is subject to a transverse instability that generates a slowly coarsening multidomain structure. The influence of gravity, solutocapillary effect at the free boundary, and Korteweg stresses inside the diffuse interface on the stability of the layers is studied using the coupled system of the hydrodynamic equations and the nonlinear equation for the concentration (H model). The parameter regions of long-wave instabilities are found.
Converging and wave guiding of Gaussian beam by two-layer dielectric rods
Authors: Dai W. , Soukoulis C. M.
Published: November 2008

We have shown that a two-layer dielectric structure can give excellent beaming and enhanced transmission simultaneously of a Gaussian source. The front surface of the layer of dielectric rods supports surface states and the rear grading layer couples the surface states to radiation modes. By repeating periodically this two-layer structure, one can obtain excellent beaming and enhanced transmission for very long distances.
Simulation of electromechanical responses of ferroelectric ceramics driven by alternating compressive stress and static electric field
Authors: Chow Simon Ching-kin , Lo Veng-cheong
Published: November 2008

The effect of static electric field on mechanical and dielectric properties of a lead zirconate titanate (PbZrxTi1−xO3) piezoceramic sample driven by an alternating compressive stress has been experimentally investigated by Zhou et al. [J. Am. Ceram. Soc. 88, 867 (2005)]. Numerical simulation for this experimental result using two-dimensional four-state Potts model is presented in this article. Upon polarization switching, the dipole in the perovskite cell undergoes 90° rotation, which is in turn associated with the switching of ferroelastic strain state. Consequently, the stress-strain relation and hence the mechanical stiffness are strongly influenced by the magnitude of the dc bias. Optimal mechanical and piezoelectric responses can be obtained by the suitable selection of biasing field.
Relaxation time effects on dynamic conductivity of alloyed metallic thin films in the infrared band
Authors: Shelton D. J. , Sun T. , Ginn J. C. , Coffey K. R. , Boreman G. D.
Published: November 2008

The behavior of nanoscale infrared antenna elements depends upon the dynamic conductivity of thin metallic films. Spectroscopic ellipsometer measurements of noble metal films show that when the product of the incident radiation frequency and the relaxation time is greater than unity, anomalous dynamic electron transport effects occur. In this regime electron scattering increases the conductivity of alloyed metallic films as demonstrated by ellipsometry measurements of films from the Au-Cu system. A binary alloy thin film was fabricated with equal parts of Au and Cu, and the dynamic conductivity was measured to be 300% larger than the high frequency conductivity of pure Au or pure Cu films at wavelengths in the 3–5 μm band. When electronic scattering is reduced, ellipsometer measurements of Au and Cu films taken near 4 K demonstrate that the IR conductivity decreases to 20% of the value measured at 300 K at wavelengths in the 3–5 μm band. Using measured dc relaxation times, a model to explain deviations from Drude behavior was developed using the theory of the anomalous skin effect and frequency dependent relaxation time. This model was in quantitative agreement with the measured data. The ability to design an alloyed metallic thin film using a calculated ideal dc relaxation time to produce the greatest possible dynamic conductivity for infrared antennas and metamaterials was demonstrated.
Experimental determination of valence band offset at PbTe/CdTe(111) heterojunction interface by x-ray photoelectron spectroscopy
Authors: Si Jianxiao , Jin Shuqiang , Zhang Hanjie , Zhu Ping , Qiu Dongjiang , Wu Huizhen
Published: November 2008

Lattice-matched PbTe/CdTe(111) heterojunction interfaces were studied using x-ray photoelectron spectroscopy. A type-I band alignment with a valence band offset of ΔEV=0.135±0.05 eV and a conduction band offset of ΔEC=1.145±0.05 eV is concluded. Within experimental error the determined valence band offset is in agreement with theoretical prediction by inclusion of spin-orbit interaction.
Temperature dependence of the low frequency noise in indium arsenide nanowire transistors
Authors: Sakr M. R. , Gao X. P. A.
Published: November 2008

We studied the low frequency noise in indium arsenide (InAs) nanowire field effect transistors at different temperatures and gate voltages. Mostly, the excess noise had 1/f dependence except at low temperatures and gate voltages close to the threshold value where the noise changed gradually to Lorentzian. The Hooge’s parameter showed thermally activated behavior with minimum value ∼5×10−4. The distribution of activation energies of the fluctuators responsible for the noise was found to have broad minima associated with the characteristic temperature of the thermally activated Hooge’s parameter.
Enhanced Jahn–Teller distortion in the orthorhombic phase of La0.15Ca0.85MnO3 and Y0.15Ca0.85MnO3
Authors: Tong P. , Kim Bongju , Kwon Daeyoung , Kim Bog G. , Ahn G. Y. , Park J. M. S. , Kim Sung Baek , Cheong S-W.
Published: November 2008

We report the results of neutron powder diffraction experiments on La0.15Ca0.85MnO3 and Y0.15Ca0.85MnO3. After an incomplete orthorhombic-monoclinic phase transition, the residual orthorhombic phase undergoes an enhancement of Jahn–Teller distortion of MnO6 octahedra. The degree of Jahn–Teller distortion is strongly influenced by coexisting monoclinic phase. Furthermore, ferromagnetism is closely associated with this Jahn–Teller distortion, rather than the buckling effect in the orthorhombic phase. Despite the low concentration of Jahn–Teller active Mn3+ ions, our result indicates an important role of Jahn–Teller effect on physical properties of the lightly electron-doped manganites.
Aerially applied citric acid reduces the density of an invasive frog in Hawaii, USA
Authors: Tuttle Nathania C. , Beard Karen H. , Al-Chokhachy Robert
Published: November 2008

The Puerto Rican frog (Eleutherodactylus coqui) is an invasive pest in Hawaii. Citric acid is approved for controlling these frogs, but has been limited to terrain accessible by foot or vehicle. We determined the effectiveness of helicopter applications of 16% citric acid and repeated 11% citric acid treatments for eradicating and/or reducing densities of E. coqui by monitoring populations before and after treatment using mark–recapture. We also evaluated the effects of the marking technique, toe-clipping, and weather changes on population parameter estimates. We found that a 16% citric acid treatment appears to have reduced adult E. coqui density 3-fold in a plot, T1, completely covered with citric acid, but did not reduce adult density in a plot, T2, where 6% of the plot was unintentionally not treated. Preadults were reduced 3- to 5-fold in treated plots. The apparent reduction in adults in T1 lasted at least 5 months. Repeated treatments of 11% citric acid were studied in T2 and likely reduced adults 440-fold while preadults were reduced 9-fold. E. coqui that had fewer toe-clips had greater recapture probability and survival estimates, while weather had no effect on parameter estimates. In summary, we found that 16% and 11% citric acid treatments can reduce E. coqui density, treatment effects can last 5 months for adults, and repeated treatments appear more effective for reducing density than single applications.
The characteristics of den trees used by the squirrel glider (Petaurus norfolcensis) in temperate Australian woodlands
Authors: Crane M. J. , Montague-Drake R. M. , Cunningham R. B. , Lindenmayer D. B.
Published: November 2008

Being able to recognise critical habitat features such as nesting and denning sites is essential for wildlife conservation. It is particularly true for the den trees of species threatened by habitat loss, such as the squirrel glider (Petaurus norfolcensis). Measurements of 146 den trees of the squirrel glider were made in fragmented woodlands of the South-west Slopes of New South Wales and data compared with random trees to quantify the key characteristics of den sites. The likelihood of use as a den tree increased with increasing numbers of visible tree hollows and tree size. Dieback was also a positive indicator of den use. However, when visible hollows within a tree are abundant, dieback-free trees were preferred. Measures of den tree context such as basal area, the number of neighbouring large trees and distance to the next nearest tree, were also found to be important determinants of the likelihood of usage. The above variables were combined into a multiple regression model. The squirrel glider favoured particular Eucalyptus species and some broader eucalypt groups. We believe such variations were most likely due to interspecific differences in hollow development and dieback among the various groups, rather than bark type, a factor previously cited as an important determinant of den tree usage. The ‘best’ model had high negative predictive power, suggesting it would be useful for identifying (1) trees that could be felled without a loss of this critical habitat resource (e.g. at development sites) and (2) areas unsuitable for potential squirrel glider relocation or habitat enhancement. Squirrel gliders show preference for a combination of tree and tree context features in selecting den trees. Understanding these features will help managers enhance and protect denning resources for this species.
The effect of exclusion of terrestrial predators on short-term survival of translocated European wild rabbits
Authors: Rouco C. , Ferreras P. , Castro F. , Villafuerte R.
Published: November 2008

Many translocation methods have been tested in southern Europe in recent decades to increase the translocation success of the European wild rabbit (Oryctolagus cuniculus L.) for both conservation and game purposes. The main problem experienced during such translocations is the high short-term (7 days) mortality attributed to predation during the days immediately following rabbit release. In this study, we test the effect of the exclusion of terrestrial predators on the survival of translocated rabbits for recovery purposes. Four translocation plots (4 ha with 18 artificial warrens each) were constructed, two of them with a fence to exclude terrestrial predators. In all, 724 rabbits were released to the translocation plots in five batches and forced to remain inside warrens for 7 days. Following liberation, exclusion of predators did not increase rabbit survival in the short term. Contrary to expectations, three months after release, survival of rabbits in the unfenced plot was slightly, but not significantly, higher than in the fenced plot (0.57 and 0.40 respectively). Although predator control is a frequent management practice associated with rabbit translocations, our results suggest that it may not favour rabbit survival rate as much as the adaptation of rabbits to the release site.
Koalas on North Stradbroke Island: diet, tree use and reconstructed landscapes
Authors: Woodward W. , Ellis W. A. , Carrick F. N. , Tanizaki M. , Bowen D. , Smith P.
Published: November 2008

North Stradbroke Island lies 4 km off the coast of Queensland, Australia. It is home to one of the only naturally occurring island populations of koalas and it is mined for mineral sands. We analysed the diet and day use tree selections of koalas and recorded the tree species composition of revegetated and undisturbed landscapes at this location. We used faecal cuticle examination to compare the diet of koalas that used reconstructed landscapes with that of koalas that used undisturbed areas. Reconstructed landscapes that were composed of more than 95% diet and/or roost tree species had evidence of use by koalas. Eucalyptus robusta was the most commonly eaten and utilised species and there was no difference in general diet composition between koalas that used the revegetated landscape and those inhabiting undisturbed areas. Other species that were used for roosting and forage included E. racemosa, E. pilularis, Lophostemon confertus and Melaleuca quinquinerva. We observed individual differences and seasonal variation in the diet composition of radio-tracked koalas. These results suggest either flexibility in the diet choices of koalas, or individual preferences within groups of koalas. Our results also indicate that post-mining landscapes can provide habitat that will be used by koalas, which should encourage further efforts into habitat re-creation for native species.