bluuebunny/crossref_metadata_2025 huggingface dataset:
Earthquake evidence for along‐arc extension in the Mariana Islands
Authors: Heeszel David S. , Wiens Douglas A. , Shore Patrick J. , Shiobara Hajime , Sugioka Hiroko
Published: December 2008

Analysis of data from a deployment of ocean bottom and land seismographs in 2003–2004 detected four swarms of earthquakes in the overriding plate of the Mariana subduction system between the fore‐arc and the back‐arc spreading center. Two additional shallow swarms were identified by analyzing the teleseismic earthquake catalogs from 1967 to 2003. Focal mechanism solutions for these swarms, determined from regional waveform inversion for the 2003–2004 events or retrieved from the Centroid Moment Tensor catalog for previous years, suggest a complex system of deformation throughout the arc. We observe arc‐parallel extension near volcanic cross chains, arc‐perpendicular extension along the frontal arc, and arc‐parallel compression farther into the back arc near the Mariana Trough. A swarm beneath the middle and eastern summits of the Diamante cross chain may have recorded magmatic activity. Volcanic cross chains showing evidence of adiabatic decompression melting from extensional upwelling are localized at regions of enhanced along‐strike extension. The earthquake data are consistent with recent GPS results indicating 12 mm/a of extension between Guam and Agrihan. The along‐arc extension may result from either increasing curvature of the Mariana system with time or from deformation induced by oblique subduction in the northernmost and southernmost regions of the arc.
First arrival stochastic tomography: Automatic background velocity estimation using beam semblances and VFSA
Authors: Hu Chaoshun , Stoffa Paul , McIntosh Kirk
Published: December 2008

We present a new tomography method based on the local beam semblance and the very fast simulated annealing (VFSA) global optimization method. The data space is the local beam semblance calculated using local slant stacks for overlapping offset windows, i.e. beam windows, of the original common‐shot or common‐receiver gathers. On each beam semblance panel, the first coherency peak can be identified with a particular ray parameter, first‐arrival traveltime and beam center position. The forward problem can be solved with any ray tracer to find arrivals matching the identified peaks. Our inversion scheme uses VFSA to find the maximum‐a‐posteriori (MAP) solution and estimates the uncertainty by applying Bayesian analysis of all the sampled models for a specified model parameterization. This integration of automatic local semblance evaluation instead of first‐arrival picking and a fast forward modeling method combined with VFSA to determine the optimal model makes our method robust, efficient and accurate.
Is the North Atlantic hurricane season getting longer?
Authors: Kossin James P.
Published: December 2008

In the 2008 North Atlantic hurricane season, July was anomalously active with four tropical storms, of which two intensified to become hurricanes. The 2007 season experienced an uncommon May storm and an equally uncommon December storm. The 2005 season was the most active in the secular record, and was also anomalously active during the typically quiescent early and late portions of the season. This recent increase in early‐ and late‐season activity has raised questions about the effect that climate change may be having on the length of the hurricane season. Here I report on the observed trends in the annual distribution of North Atlantic tropical storm formation events and their relationship with tropical Atlantic sea surface temperatures (SST). I find an apparent tendency toward more common early‐ and late‐season storms that correlates with warming SST, but the uncertainty in these relationships is high.
Overview of the Dust and Biomass‐burning Experiment and African Monsoon Multidisciplinary Analysis Special Observing Period‐0
Authors: Haywood J. M. , Pelon J. , Formenti P. , Bharmal N. , Brooks M. , Capes G. , Chazette P. , Chou C. , Christopher S. , Coe H. , Cuesta J. , Derimian Y. , Desboeufs K. , Greed G. , Harrison M. , Heese B. , Highwood E. J. , Johnson B. , Mallet M. , Marticorena B. , Marsham J. , Milton S. , Myhre G. , Osborne S. R. , Parker D. J. , Rajot J.‐L. , Schulz M. , Slingo A. , Tanré D. , Tulet P.
Published: December 2008

The African Monsoon Multidisciplinary Analysis (AMMA) is a major international campaign investigating far‐reaching aspects of the African monsoon, climate and the hydrological cycle. A special observing period was established for the dry season (SOP0) with a focus on aerosol and radiation measurements. SOP0 took place during January and February 2006 and involved several ground‐based measurement sites across west Africa. These were augmented by aircraft measurements made by the Facility for Airborne Atmospheric Measurements (FAAM) aircraft during the Dust and Biomass‐burning Experiment (DABEX), measurements from an ultralight aircraft, and dedicated modeling efforts. We provide an overview of these measurement and modeling studies together with an analysis of the meteorological conditions that determined the aerosol transport and link the results together to provide a balanced synthesis. The biomass burning aerosol was significantly more absorbing than that measured in other areas and, unlike industrial areas, the ratio of excess carbon monoxide to organic carbon was invariant, which may be owing to interaction between the organic carbon and mineral dust aerosol. The mineral dust aerosol in situ filter measurements close to Niamey reveals very little absorption, while other measurements and remote sensing inversions suggest significantly more absorption. The influence of both mineral dust and biomass burning aerosol on the radiation budget is significant throughout the period, implying that meteorological models should include their radiative effects for accurate weather forecasts and climate simulations. Generally, the operational meteorological models that simulate the production and transport of mineral dust show skill at lead times of 5 days or more. Climate models that need to accurately simulate the vertical profiles of both anthropogenic and natural aerosols to accurately represent the direct and indirect effects of aerosols appear to do a reasonable job, although the magnitude of the aerosol scattering is strongly dependent upon the emission data set.
A study of X‐ray emission from laboratory sparks in air at atmospheric pressure
Authors: Dwyer J. R. , Saleh Z. , Rassoul H. K. , Concha D. , Rahman M. , Cooray V. , Jerauld J. , Uman M. A. , Rakov V. A.
Published: December 2008

We present a detailed investigation of X‐ray emission from long laboratory sparks in air at atmospheric pressure. We studied 231 sparks of both polarities using a 1‐MV Marx generator with gap lengths ranging from 10 to 140 cm. The X rays generated by the discharges were measured using five NaI/PMT detectors plus one plastic scintillator/PMT detector, all enclosed in 0.32‐cm‐thick aluminum boxes. X‐ray emission was observed to accompany about 70% of negative polarity sparks and about 10% of positive polarity sparks. For the negative sparks, X‐ray emission was observed to occur at two distinct times during the discharge: (1) near the peak voltage, specifically, about 1 μs before the voltage across the gap collapsed, and (2) near the time of the peak current through the gap, during the gap voltage collapse. Using collimators we determined that the former emission emanated from the gap, while the latter appeared to originate from above the gap in the space over the high‐voltage components. During individual sparks, the total energy of the X rays that was deposited in a single detector sometimes exceeded 50 MeV, and the maximum energy of individual photons in some cases exceeded 300 keV. X‐ray emission near the peak voltage was observed for a wide range of electrode geometries, including 12‐cm‐diameter spherical electrodes, a result suggesting that the X‐ray emission was the result of processes occurring within the air gap and not just due to high electric fields at the electrode.
Short‐term effects of agriculture on air pollution and climate in California
Authors: Jacobson Mark Z.
Published: December 2008

This paper discusses the short‐term effects of irrigation and albedo differences due to agriculture on California and Los Angeles air pollution and climate. High‐resolution irrigation, land use, soil, albedo, and emission data were applied at the subgrid scale in the nested global‐through‐urban GATOR‐GCMOM model to examine these issues following a comparison of baseline model results with data. In August, irrigation alone was found to increase soil moisture, thereby increasing nighttime but decreasing daytime ground temperatures more, causing a net ground cooling in California and Los Angeles. Agriculture was calculated to increase the albedo of the northern Central Valley but decrease that of the southern valley more relative to nonagricultural land today, offsetting part of the cooling due to irrigation alone. The spatial maximum day‐night average August cooling in the Central Valley due to irrigation plus albedo differences from agriculture was 0.9 K at 30 m height and 2.3 K at the ground, in range of an historic 0.74–2.4 K cooling at 2 m attributed to heavily irrigated agriculture in an independent data study. When averaged over all model cells containing >0% irrigation, irrigation alone and irrigation plus albedo differences decreased day‐night average 2‐m temperatures by 0.44 K and 0.16 K, respectively, indicating greater local than regional effects of agriculture. In the Central Valley, irrigation increased the relative humidity, cloud water, and precipitation, shifting aerosol and soluble gas mass to clouds and rain. In the valley and Los Angeles, agriculture stabilized air, decreasing wind speeds and turbulence, increasing pollution in the absence of rain. Thus, when enhancing clouds and precipitation, agriculture decreased pollution; otherwise, agriculture increased pollution. Agriculture in parts of the polluted eastern Los Angeles basin increased fine particulate matter by ∼2% and ozone by ∼0.1%. All results were robust to a change in the simulation date, although further evaluation is needed to better quantify effects of agriculture on climate and air quality.
Mineralogical composition, structure, morphology, and geological history of Aram Chaos crater fill on Mars derived from OMEGA Mars Express data
Authors: Massé M. , Le Mouélic S. , Bourgeois O. , Combe J.‐P. , Le Deit L. , Sotin C. , Bibring J.‐P. , Gondet B. , Langevin Y.
Published: December 2008

Aram Chaos is a crater 280 km in diameter centered at 2.5°N, 338.5°E. It is filled by chaotic terrains overlain by a dome‐shaped, layered 900 m thick formation displaying spectral signatures of ferric oxides on Thermal Emission Spectrometer (TES) and Observatoire pour la Mineralogie, L'Eau, les Glaces et L'Activite (OMEGA) medium spatial resolution data. We describe in detail the mineralogical composition, structure, and morphology of this crater fill using high‐resolution data (OMEGA, Mars Orbiter Laser Altimeter, Mars Orbiter Camera, TES, Thermal Emission Imaging System, and High‐Resolution Imaging Science Experiment). We infer the following formation scenario: the crater was first filled by a geological formation, the composition of which remains unclear because it is covered by dust. Widespread fracturing of this formation led to the development of chaotic terrains. Later, a second layered formation, presently dome shaped, was emplaced unconformably on the chaotic terrains. This younger unit is composed of a bright, poorly consolidated material that contains both monohydrated sulfates and ferric oxides according to OMEGA data. The surface of this formation is partially covered by dust and displays landforms indicating that the bright material has been mobilized by wind during or after its deposition. After its emplacement, this formation has been grooved down to various depths by large eolian erosion corridors. In these corridors, eolian removal of the bright material with a sulfate‐rich matrix has left debris fans, sand sheets, and dunes, which display some of the strongest spectral signatures of ferric oxides on Mars. Similar residual deposits enriched in ferric oxides, overlying a layered formation containing both ferric oxides and sulfates, have been observed by the Opportunity rover in Meridiani Planum, suggesting a common formation process.
Methylmercury production in a Chesapeake Bay salt marsh
Authors: Mitchell Carl P. J. , Gilmour Cynthia C.
Published: December 2008

In a detailed study of the biogeochemical factors affecting the methylation of mercury in a Chesapeake Bay salt marsh, we examined relationships between mercury methylation and numerous variables, including sulfate reduction rates, organic carbon mineralization rates, iron and sulfur chemistry, and the character of dissolved organic matter (DOM). Our data show that salt marshes are important sites of de novo methylmercury (MeHg) production in coastal ecosystems. Some of the controls on MeHg production that have been well‐described in other ecosystems also impacted MeHg production in this salt marsh, specifically the effect of sulfide accumulation on mercury bioavailability. We observed some novel biogeochemical relationships with Hg(II)‐methylation and MeHg accumulation, particularly the positive association of Hg(II)‐methylation with zones of microbial iron reduction. On the basis of this relationship, we suggest caution in wetland and groundwater remediation approaches involving iron additions. Aqueous phase Hg complexation appeared to be the dominant control on Hg bioavailability across the marsh sites examined, rather than Hg partitioning behavior. A detailed examination of DOM character in the marsh suggested a strong positive association between Hg(II)‐methylation rate constants and increasing DOM molecular weight. Overall, our results indicate that net MeHg production is controlled by a balance between microbial activity and geochemical effects on mercury bioavailability, but that a significant zone of MeHg production can persist in near surface salt marsh soils. Production of MeHg in coastal marshes may negatively impact ecosystems via export to adjacent estuaries or through direct bioaccumulation in birds, fish and amphibians that feed in these highly productive ecosystems.
Electrical resistivity imaging of the architecture of substream sediments
Authors: Crook N. , Binley A. , Knight R. , Robinson D. A. , Zarnetske J. , Haggerty R.
Published: December 2008

The modeling of fluvial systems is constrained by a lack of spatial information about the continuity and structure of streambed sediments. There are few methods for noninvasive characterization of streambeds. Invasive methods using wells and cores fail to provide detailed spatial information on the prevailing architecture and its continuity. Geophysical techniques play a pivotal role in providing spatial information on subsurface properties and processes across many other environments, and we have applied the use of one of those techniques to streambeds. We demonstrate, through two examples, how electrical resistivity imaging can be utilized for characterization of subchannel architecture. In the first example, electrodes installed in riparian boreholes and on the streambed are used for imaging, under the river bed, the thickness and continuity of a highly permeable alluvial gravel layer overlying chalk. In the second example, electrical resistivity images, determined from data collected using electrodes installed on the river bed, provide a constrained estimate of the sediment volume behind a log jam, vital to modeling biogeochemical exchange, which had eluded measurement using conventional drilling methods owing to the boulder content of the stream. The two examples show that noninvasive electrical resistivity imaging is possible in complex stream environments and provides valuable information about the subsurface architecture beneath the stream channels.
Simulation of chemical reaction via particle tracking: Diffusion‐limited versus thermodynamic rate‐limited regimes
Authors: Benson David A. , Meerschaert Mark M.
Published: December 2008

Chemical reactions may be simulated without regard to local concentrations by applying simple probabilistic rules of particle interaction and combination. The forward reaction A + B→ C is coded by calculating the probability that any A and B particles will occupy the same volume over some time interval. This becomes a convolution of the location densities of the two particles. The backward reaction is a simple exponential decay of C particles into A and B particles. When the mixing of reactants is not a limiting process, the classical thermodynamic reaction rates are reproduced. When low mixing (as by diffusion) limits the reaction probabilities, the reaction rates drop significantly, including the rate of approach to global equilibrium. At long enough times, the law of mass action is reproduced exactly in the mean, with some irreducible deviation in the local equilibrium saturations (the equilibrium constant divided by the mass action expression) away from unity. The saturation variability is not sensitive to numerical parameters but depends strongly on how far from equilibrium the system is initiated. This is simply due to a relative paucity of particles of some species as the reaction moves far to one side or the other.
Potential importance of alterations in hydrogen sulphide (H2S) bioavailability in diabetes
Authors: Lefer D J
Published: December 2008

British Journal of Pharmacology (2008) 155, 1308; doi:10.1038/bjp.2008.377
Universal structures in some mean field spin glasses and an application
Authors: Bolthausen Erwin , Kistler Nicola
Published: December 2008

We discuss a spin glass reminiscent of the random energy model (REM), which allows, in particular, to recast the Parisi minimization into a more classical Gibbs variational principle, thereby shedding some light into the physical meaning of the order parameter of the Parisi theory. As an application, we study the impact of an extensive cavity field on Derrida’s REM: Despite its simplicity, this model displays some interesting features such as ultrametricity and chaos in temperature.
Oxygen vacancy kinetics in ferroelectric PbZr0.4Ti0.6O3
Authors: Gottschalk S. , Hahn H. , Flege S. , Balogh A. G.
Published: December 2008

Oxygen vacancy kinetics in ferroelectric PbZr0.4Ti0.6O3 were studied by oxygen18 (O18) tracer self-diffusion in epitaxial thin films as well as bulk polycrystalline samples. O18 exchange annealing was carried out at an oxygen partial pressure of 250mbar and temperatures between 250 and 400°C. Isotope depth profiling was performed by secondary ion mass spectrometry as well as neutral secondary mass spectrometry. The observed concentration depth profiles of the polycrystalline samples show two distinct diffusion paths, namely, bulk diffusion and grain boundary (GB) diffusion. It appears to be of type B-kinetics in the investigated temperature range, with DGB∕Dbulk⪢100. Donor doped samples with different levels of Nb5+ (1–4mol.%) were also investigated. The effect on the diffusion depth profiles, however, were negligible and can solely be attributed due to the change in the samples microstructure as induced by the dopants. A diffusion coefficient for the bulk diffusion of the O18 isotope, Dbulk=10±5×10−8cm2∕sexp(−0.87±0.1eV∕kT) was found. The faster GB diffusion process shows an activation enthalpy of only EA=0.66±0.2eV.
The effect of matrix and substrate on the coercivity and blocking temperature of self-assembled Ni nanoparticles
Authors: Abiade Jeremiah T. , Oh Sang Ho , Kumar Dhananjay , Varela Maria , Pennycook Stephen , Guo Haizhong , Gupta Arunava , Sankar Jagannathan
Published: December 2008

We have shown that the magnetic properties of nanoparticles may be tuned from superparamagnetic to ferromagnetic by changing the substrate or thin film matrix in which they are embedded. Nickel nanoparticles were embedded into alumina, titanium nitride, and cerium oxide matrices on both silicon and sapphire substrates via pulsed laser deposition. The laser ablation time on the nickel target was kept constant. Only nickel nanoparticles in cerium oxide showed characteristics of ferromagnetism (room temperature coercivity and remanence). Ni nanoparticles, in either alumina or titanium nitride, possessed blocking temperatures below 200 K. Detailed scanning transmission electron microscopy analysis has been conducted on the samples embedded into cerium oxide on both substrates and related to the magnetic data.
Intrinsic electron mobilities in CdSe, CdS, ZnO, and ZnS and their use in analysis of temperature-dependent Hall measurements
Authors: Yang Xiaocheng , Xu Chunchuan , Giles N. C.
Published: December 2008

Intrinsic electron mobilities and intrinsic Hall r factors for n-type wide band gap II–VI semiconductors CdSe, CdS, ZnO, and ZnS are predicted from 60 to 400 K using the relaxation-time approximation including scattering due to polar-optical phonons and acoustic phonons (piezoelectric and deformation potentials). Experimental deformation potentials (E1) are used and the relative importance of deformation-potential scattering in these II–VI compounds is clarified. At 300 K, intrinsic Hall electron mobilities (in cm2/V s) are about 600 (CdSe), 440 (CdS), 230 (ZnO), and 250 (ZnS). The intrinsic predictions are applied to fitting of temperature-dependent Hall effect measurements from n-type CdSe, CdS, and ZnO bulk crystals including extrinsic scattering due to both neutral and ionized impurities. Donor and acceptor concentrations and activation energies are obtained, and Coulomb screening is included to yield donor ionization energies for isolated centers. The intrinsic mobility predictions establish upper limits for these compounds, especially important for thin film studies where sample inhomogeneities can produce anomalously high results.
Contact-resonance atomic force microscopy for viscoelasticity
Authors: Yuya P. A. , Hurley D. C. , Turner J. A.
Published: December 2008

We present a quantitative method for determining the viscoelastic properties of materials with nanometer spatial resolution. The approach is based on the atomic force acoustic microscopy technique that involves the resonant frequencies of the atomic force microscopy cantilever when its tip is in contact with a sample surface. We derive expressions for the viscoelastic properties of the sample in terms of the cantilever frequency response and damping loss. We demonstrate the approach by obtaining experimental values for the storage and loss moduli of a poly(methyl methacrylate) film using a polystyrene sample as a reference material. Experimental techniques and system calibration methods to perform material property measurements are also presented.
Polarization offset of homogeneous Bi3.15Nd0.85Ti3O12 ferroelectric thin films
Authors: Wu Hao , Wu Di , Li Aidong
Published: December 2008

In this report, the polarization offset usually observed in compositionally graded ferroelectric thin films was observed in homogeneous Bi3.15Nd0.85Ti3O12 thin films sandwiched in Pt electrodes. The observed polarization offset was studied as functions of temperature and of the driving voltage amplitude using a modified Sawyer–Tower circuit. The polarization offset is obvious only at temperatures above 150 °C and increases with increasing testing temperature and amplitude of driving voltage. The reported phenomena demonstrate that the composition gradient is not a necessity for such a polarization offset. The strong temperature and voltage dependence indicates that the polarization offsets may be related to thermionic charge injection, which is asymmetric to top and bottom electrodes.
Subband gap photoresponse of nanocrystalline silicon in a metal-oxide-semiconductor device
Authors: Hossain S. M. , Anopchenko A. , Prezioso S. , Ferraioli L. , Pavesi L. , Pucker G. , Bellutti P. , Binetti S. , Acciarri M.
Published: December 2008

In this paper we report on the photoconduction and photovoltaic properties of nanocrystalline silicon. Silicon nanocrystals (Si-ncs) have been prepared by using plasma-enhanced chemical vapor deposition on a p-type silicon substrate. The Si-ncs have been formed into the dielectric of a metal-oxide-semiconductor device. I-V characteristics of the devices have been studied under dark and illumination. Illumination was performed with light in the wavelength range of 350–1630 nm. A photovoltaic effect has been observed in the illuminated I-V characteristics in the range of 350–1100 nm. For longer wavelengths no measurable photovoltaic effect has been observed, but considerable photocurrent has been measured for 1300–1630 nm light under reverse bias condition. This photoresponse is attributed to absorption through subband gap states at the Si-nc and silicon oxynitride matrix interface.
Underwater microdischarge in arranged microbubbles produced by electrolysis in electrolyte solution using fabric-type electrode
Authors: Sakai Osamu , Kimura Masaru , Shirafuji Tatsuru , Tachibana Kunihide
Published: December 2008

Pulsed microdischarge was generated in microbubbles produced by electrolysis in an electrolyte solution without external gas feed by using a fabric-type electrode. The electrode structure not only allowed low-voltage ignition of the atmospheric-pressure discharge in hydrogen or oxygen containing microbubbles but also worked effectively in producing and holding the bubbles on its surface. The generation of reactive species was verified by optical emissions from the produced microplasmas, and their transport into the solution was monitored by the change in hydrogen concentration.
Fluence-dependent formation of Zn and ZnO nanoparticles by ion implantation and thermal oxidation: An attempt to control nanoparticle size
Authors: Amekura H. , Ohnuma M. , Kishimoto N. , Buchal Ch. , Mantl S.
Published: December 2008

For possible control of the size of nanoparticles (NPs), the fluence-dependent formation of Zn and ZnO NPs by ion implantation with and without thermal oxidation was investigated by optical absorption spectroscopy, Rutherford backscattering spectrometry, and small-angle x-ray scattering (SAXS). The mean diameter and number density of Zn NPs in the as-implanted state in silica (SiO2) were determined by SAXS as 7 nm and 13×1017 cm−3, 12 nm and 3.8×1017 cm−3, and 12 nm and 3.2×1017 cm−3 for fluences of 0.50, 1.0, and 2.0×1017 ions/cm2, respectively. With increasing fluence, the mean diameter of the NPs increases and the number density decreases. However, an upper limit of the NP size and Zn concentration in SiO2 is observed above the fluence of 1.0×1017 ions/cm2 due to sputtering loss. Thermal annealing in oxygen gas at 700 °C for 1 h induces the transformation of Zn NPs to both ZnO NPs and the Zn2SiO4 phase. With decreasing fluence, the branching ratio to the ZnO component decreases. This is because the reaction between tentatively formed ZnO NPs and the SiO2 substrate is enhanced by the higher surface-to-volume ratio of smaller NPs. At a fluence of 0.20×1017 ions/cm2, almost no ZnO component was detected. The size control of Zn and ZnO NPs is therefore possible only in a limited fluence region.
Dislocation nucleation during nanoindentation of aluminum
Authors: Wagner R. J. , Ma L. , Tavazza F. , Levine L. E.
Published: December 2008

Through multiscale simulations, we explore the influence of both smooth and atomically rough indenter tips on the nucleation of dislocations during nanoindentation of single-crystal aluminum. We model the long-range strain with finite element analysis using anisotropic linear elasticity. We then model a region near the indenter atomistically and perform molecular dynamics with an embedded atom method interatomic potential. We find that smooth indenters nucleate dislocations below the surface but rough indenters can nucleate dislocations both at the surface and below. Increasing temperature from 0 to 300 K creates prenucleation defects in the region of high stress and decreases the critical depth.
Landau damping in relativistic plasmas with power-law distributions and applications to solar wind electrons
Authors: Podesta J. J.
Published: December 2008

The relativistic plasma dispersion relation is derived for Langmuir waves in a spatially homogeneous unmagnetized plasma in which the electrons have an isotropic power-law distribution in momentum space. The theory is applied to the study of Langmuir waves in the quiescent solar wind near the orbit of the Earth assuming that the electron distribution function can be approximated as a power-law from thermal energies ∼10eV to relativistic energies ≳100keV. Numerical solutions of the dispersion relation show that in the regime of weak Landau damping the phase speeds of the waves match the velocities of the high-energy particles, known in the solar wind literature as the superhalo, which lie in the range 0.09<v∕c<0.8. While this result raises the question of whether wave-particle interactions with a spectrum of Langmuir waves plays a role in the formation of the superhalo, the observed energy density of the waves near the orbit of the Earth at 1AU is so small that active acceleration of superhalo electrons by Langmuir waves, if it occurs at all, has ceased by the time the solar wind reaches the Earth.
Exponential frequency spectrum and Lorentzian pulses in magnetized plasmas
Authors: Pace D. C. , Shi M. , Maggs J. E. , Morales G. J. , Carter T. A.
Published: December 2008

Two different experiments involving pressure gradients across the confinement magnetic field in a large plasma column are found to exhibit a broadband turbulence that displays an exponential frequency spectrum for frequencies below the ion cyclotron frequency. The exponential feature has been traced to the presence of solitary pulses having a Lorentzian temporal signature. These pulses arise from nonlinear interactions of drift-Alfvén waves driven by the pressure gradients. In both experiments the width of the pulses is narrowly distributed resulting in exponential spectra with a single characteristic time scale. The temporal width of the pulses is measured to be a fraction of a period of the drift-Alfvén waves. The experiments are performed in the Large Plasma Device (LAPD-U) [W. Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] operated by the Basic Plasma Science Facility at the University of California, Los Angeles. One experiment involves a controlled, pure electron temperature gradient associated with a microscopic (6mm gradient length) hot electron temperature filament created by the injection a small electron beam embedded in the center of a large, cold magnetized plasma. The other experiment is a macroscopic (3.5cm gradient length) limiter-edge experiment in which a density gradient is established by inserting a metallic plate at the edge of the nominal plasma column of the LAPD-U. The temperature filament experiment permits a detailed study of the transition from coherent to turbulent behavior and the concomitant change from classical to anomalous transport. In the limiter experiment the turbulence sampled is always fully developed. The similarity of the results in the two experiments strongly suggests a universal feature of pressure-gradient driven turbulence in magnetized plasmas that results in nondiffusive cross-field transport. This may explain previous observations in helical confinement devices, research tokamaks, and arc plasmas.
Electric detection of ferromagnetic resonance in single crystal iron film
Authors: Hui Xiong , Wirthmann A. , Gui Y. S. , Tian Y. , Jin X. F. , Chen Z. H. , Shen S. C. , Hu C.-M.
Published: December 2008

We report electric detection of ferromagnetic resonance (FMR) in epitaxially grown single crystal iron film through microwave photovoltage generation technique. The experimental results agree well with the established theory about FMR in iron films, showing excellent extendability of such a technique onto different ferromagnets as an effective way to study magnetocrystalline anisotropy and spin excitations. Furthermore, the information about the phase of magnetization precession is implicated in the lineshape of photovoltage, which makes it possible to probe in details into magnetic phase dynamics that is of significance for devising spintronic devices.
Convectively induced shear instability in large amplitude internal solitary waves
Authors: Carr M. , Fructus D. , Grue J. , Jensen A. , Davies P. A.
Published: December 2008

Laboratory study has been carried out to investigate the instability of an internal solitary wave of depression in a shallow stratified fluid system. The experimental campaign has been supported by theoretical computations and has focused on a two layered stratification consisting of a homogeneous dense layer below a linearly stratified top layer. The initial background stratification has been varied and it is found that the onset and intensity of breaking are affected dramatically by changes in the background stratification. Manifestations of a combination of shear and convective instability are seen on the leading face of the wave. It is shown that there is an interplay between the two instability types and convective instability induces shear by enhancing isopycnal compression. Variation in the upper boundary condition is also found to have an effect on stability. In particular, the implications for convective instability are shown to be profound and a dramatic increase in wave amplitude is seen for a fixed (as opposed to free) upper boundary condition.
A comparative study of two classical force fields on statics and dynamics of [EMIM][BF4] investigated via molecular dynamics simulations
Authors: Dommert Florian , Schmidt Jochen , Qiao Baofu , Zhao Yuanyuan , Krekeler Christian , Delle Site Luigi , Berger Robert , Holm Christian
Published: December 2008

The influences of two different commonly employed force fields on statical and dynamical properties of ionic liquids are investigated for [EMIM][BF4]. The force fields compared in this work are the one of Canongia Lopes and Padua [J. Phys. Chem. B 110, 19586 (2006)] and that of Liu et al. [J. Phys. Chem. B 108, 12978 (2004)]. Differences in the strengths of hydrogen bonds are found, which are also reflected in the static ion distributions around the cation. Moreover, due to the stronger hydrogen bonding in the force field of Liu et al., the diffusive motions of cations and anions and the rotational behavior of the cations are slower compared with those obtained with the force field of Canongia Lopes and Padua. Both force fields underestimate the zero-field electrical conductivity, while the experimental dielectric constant can be reproduced within the expected statistical error boundaries.
In-plane anisotropy characteristics of GaN epilayers grown on A-face sapphire substrates
Authors: Kim-Chauveau Hyonju , De Mierry Philippe , Cabane Hugues , Gindhart Dave
Published: December 2008

We report on the structural in-plane anisotropy of GaN films grown on A-plane sapphire substrates by metal organic chemical vapor deposition. It is found that GaN:Si grown on A-face sapphire exhibits a strongly anisotropic wafer bending in the two orthogonal in-plane directions, with a ∼24% larger curvature along the c-axis of sapphire than along the m-axis. Using a model developed for an elastically anisotropic bilayer structure and using our curvature data, the anisotropic biaxial stresses in the two in-plane directions have been estimated as σ1x≅−1.3 GPa and σ1y≅−1.1 GPa along parallel and perpendicular to c-axis of sapphire, respectively. This anisotropic stress is also responsible for the distortion of the GaN hexagonal basal plane, as evidenced by x-ray diffraction measurements. The broadening of full width at half maximum of the GaN (0002) x-ray reflections varies with different azimuthal angles, correlated with the tilt of the c-axis of GaN. The in-plane epitaxial relationships between the GaN (0001) and A-face sapphire are found as a-axis of GaN aligned with c-axis of sapphire and m-axis of GaN aligned with m-axis of sapphire.
Band bending at the surfaces of In-rich InGaN alloys
Authors: Bailey L. R. , Veal T. D. , King P. D. C. , McConville C. F. , Pereiro J. , Grandal J. , Sánchez-García M. A. , Muñoz E. , Calleja E.
Published: December 2008

The band bending and carrier concentration profiles as a function of depth below the surface for oxidized InxGa1−xN alloys with a composition range of 0.39≤x≤1.00 are investigated using x-ray photoelectron, infrared reflection, and optical absorption spectroscopies, and solutions of Poisson’s equation within a modified Thomas–Fermi approximation. All of these InGaN samples exhibit downward band bending ranging from 0.19 to 0.66 eV and a high surface sheet charge density ranging from 5.0×1012 to 1.5×1013 cm−2. The downward band bending is more pronounced in the most In-rich InGaN samples, resulting in larger near-surface electron concentrations.
Giant geometrically amplified piezoresistance in metal-semiconductor hybrid resistors
Authors: Hansen Ole , Reck Kasper , Thomsen Erik V.
Published: December 2008

We show that very high geometrically amplified piezoresistance can indeed be obtained in microstructured metal-semiconductor hybrid devices, even significantly higher amplification factors than the factor of approximately 8 demonstrated recently by Rowe and co-workers may be achieved. However, we also show that this amplification cannot be used to realize high sensitivity sensor devices due to limitation of the applied voltage across the device when the transfer resistance is smaller than the total resistance of the device. In that case, the sensitivity in units of V V−1 Pa−1 is always less than the sensitivity of conventional piezoresistors fabricated in the same piezoresistive material.
Predicting Young’s modulus of nanowires from first-principles calculations on their surface and bulk materials
Authors: Wang Guofeng , Li Xiaodong
Published: December 2008

Using the concept of surface stress, we developed a model that is able to predict Young’s modulus of nanowires as a function of nanowire diameters from the calculated properties of their surface and bulk materials. We took both equilibrium strain effect and surface stress effect into consideration to account for the geometric size influence on the elastic properties of nanowires. In this work, we combined first-principles density functional theory calculations of material properties with linear elasticity theory of clamped-end three-point bending. Furthermore, we applied this computational approach to Ag, Au, and ZnO nanowires. For both Ag and Au nanowires, our theoretical predictions agree well with the experimental data in the literature. For ZnO nanowires, our predictions are qualitatively consistent with some of experimental data for ZnO nanostructures. Consequently, we found that surface stress plays a very important role in determining Young’s modulus of nanowires. Our finding suggests that the elastic properties of nanowires could be possibly engineered by altering the surface stress of their lateral surfaces.
Relativistic E×T Jahn–Teller effect in tetrahedral systems
Authors: Poluyanov Leonid V. , Domcke Wolfgang
Published: December 2008

It is shown that E2 states in tetrahedral systems exhibit a linear E×T Jahn–Teller effect which is of purely relativistic origin (that is, it arises from the spin-orbit-coupling operator). The electrostatic interactions give rise to a Jahn–Teller effect which is quadratic in the T displacements. The 4×4 Hamiltonian matrix in a diabatic spin-electron basis is derived by an expansion of the electrostatic electronic Hamiltonian and the Breit–Pauli spin-orbit operator in powers of the Jahn–Teller active normal mode and taking account of symmetry selection rules for the matrix elements. The adiabatic potential-energy functions of the E2×T system are doubly degenerate (Kramers degeneracy). For small displacements from the tetrahedral reference geometry, the adiabatic potential-energy surfaces represent a double cone in four-dimensional space, which is a novel topography of Jahn–Teller potential-energy surfaces. The topological phases of the adiabatic electronic wave functions are discussed.
Reconstruction of depth profiles of thermal conductivity of case hardened steels using a three-dimensional photothermal technique
Authors: Qu Hong , Wang Chinhua , Guo XinXin , Mandelis Andreas
Published: December 2008

A method of retrieving thermophysical depth profiles of continuously inhomogeneous materials is presented both theoretically and experimentally using laser infrared photothermal radiometry. This method represents the three-dimensional (3D) extension of earlier one-dimensional thermal-wave inverse-problem techniques for reconstructing inhomogeneous thermal-conductivity or diffusivity depth profiles. A 3D theoretical model suitable for characterizing solids with arbitrary continuously varying thermophysical property depth profiles and finite (collimated or focused) laser beam spotsize is developed. A numerical fitting algorithm to retrieve the thermophysical profile was demonstrated with three case hardened steel samples. The reconstructed thermal conductivity depth profiles were found to be well anticorrelated with microhardness profiles obtained with the conventional indenter method.
Crack-free GaAs epitaxy on Si by using midpatterned growth: Application to Si-based wavelength-selective photodetector
Authors: Huang Hui , Ren Xiaomin , Lv Jihe , Wang Qi , Song Hailan , Cai Shiwei , Huang Yongqing , Qu Bo
Published: December 2008

A monolithically integrated wavelength-selective photodetector, which consists of an 11.86 μm thick GaAs-based Fabry–Pérot filter and a 3.84 μm thick InP-based p-i-n absorption structure (with a 0.3 μm In0.53Ga0.47As absorption layer), was grown on a Si substrate. A crack-free and high-quality epilayer with an area of 800×700 μm2 was obtained by using midpatterned growth and thermal-cycle annealing. Long dislocations running parallel to the GaAs/Si interface were formed by thermal annealing. This kind of dislocation may effectively alleviate the thermal stress across a large patterned area and be responsible for the crack-free epilayer. A photodetector with a spectral linewidth of 1.1 nm (full width at half maximum) and a quantum efficiency of 9.0% was demonstrated.
Oscillating Ponomarenko dynamo in the highly conducting limit
Authors: Peyrot Marine , Gilbert Andrew , Plunian Franck
Published: December 2008

This paper considers dynamo action in smooth helical flows in cylindrical geometry, otherwise known as Ponomarenko dynamos, with periodic time dependence. An asymptotic framework is developed that gives growth rates and frequencies in the highly conducting limit of large magnetic Reynolds number, when modes tend to be localized on resonant stream surfaces. This theory is validated by means of numerical simulations.
Dielectric response of multiwalled carbon nanotubes as a function of applied ac-electric fields
Authors: Basu Rajratan , Iannacchione Germano S.
Published: December 2008

The complex dielectric constant (ε∗) is reported for multiwalled carbon nanotubes (MWCNTs) up to 105 Hz as a function of ac-electric field amplitudes Erot (in phase and same frequency as the measurement) and Eac (different phase and fixed frequency with respect to the measurement). A slow relaxation process (mode 1) is observed, which shifts to higher frequency with increasing Erot but is independent of Eac. A fast relaxation process (mode 2) is also observed, which is independent of Erot but shifts to higher frequency with increasing Eac (opposite to that of mode 1). An ac-conductivity analysis of MWCNT reveals insights on how Erot and Eac influence the dissipation.
Role of the strain in the epitaxial regrowth rate of heavily doped amorphous Si films
Authors: D’Angelo D. , Romano L. , Crupi I. , Carria E. , Privitera V. , Grimaldi M. G.
Published: December 2008

Solid phase epitaxial regrowth (SPER) of p-doped preamorphized Si was studied by time resolved reflectivity. Strain and dopant concentration were opportunely varied by implanting neutral (Ge) and isovalent (B, Ga) impurities in order to disentangle the two different effects on SPER. Larger SPER rate variations occurred in strained doped Si with respect to undoped samples. The generalized Fermi level shifting model was implemented to include the role of the strain and to fit the experimental data over a large range of temperature for p- and n-type doping. We introduced a charged defect, whose energy level is independent of the dopant species.
Long-range and superfast trapping of DNA molecules in an ac electrokinetic funnel
Authors: Du Jiong-Rong , Juang Yi-Je , Wu Jie-Tang , Wei Hsien-Hung
Published: December 2008

In this work we report a microfluidic platform capable of trapping and concentrating a trace amount of DNA molecules efficiently. Our strategy invokes nonlinear electro-osmotic flow induced by charge polarization under high-frequency ac fields. With the asymmetric quadrupole electrode design, a unique converging flow structure can be created for generating focusing effects on DNA molecules. This focusing in turn transforms into a robust funnel that can collect DNA molecules distantly from the bulk and pack them into a compact cone with the aid of short-range dipole-induced self-attraction and dielectrophoresis. Our results reveal that not only can DNA molecules be concentrated within just a few seconds, but also they can be focused into threads of 1mm in length, demonstrating the superfast and long-range trapping capability of this funnel. In addition, pico M DNA solutions can be concentrated with several decades of enhancement without any continuous feeding. Alternating concentration and release of DNA molecules is also illustrated, which has potentials in concentrating and transporting biomolecules in a continuous fashion using microdevices.
Cathodoluminescence microanalysis of diamond nanocrystals in fused silicon dioxide
Authors: Stevens-Kalceff M. A. , Prawer S. , Kalceff W. , Orwa J. O. , Peng J. L. , McCallum J. C. , Jamieson D. N.
Published: December 2008

MeV carbon ion implantation followed by thermal annealing in a hydrogen-containing atmosphere produces a layer of diamond nanocrystals within fused quartz (SiO2). Cathodoluminescence (CL) microanalysis in a scanning electron microscope has revealed at least three previously unreported low intensity CL emissions from carbon implanted and thermally annealed fused SiO2. The CL emissions are observed at 2.78 eV [full width at half maximum (FWHM) of 0.08 eV], ∼3 eV (FWHM of 0.4 eV), and 3.18 eV (FWHM of 0.11 eV). The peak widths and energies of these emissions are incompatible with any known defects associated with the silicon dioxide host lattice. Nondestructive depth resolved CL microanalysis investigations confirm that these CL emissions originate from the near-surface region, consistent with their association with the layer of diamond nanocrystals.
Manipulation of microparticles in colloidal liquids by Z-scan-based optical trapping
Authors: Liu Jin , Dai Qiao-Feng , Feng Tian-Hua , Liu Hai-Ying , Wu Li-Jun , Guo Qi , Hu Wei , Liu Song-Hao , Lan Sheng , Gopal Achanta Venu , Trofimov Vyacheslav A.
Published: December 2008

Manipulation of microparticles in colloidal liquids by using Z-scan-based optical trapping is systematically investigated. A physical model for the creation and annihilation of ordered structures in Z-scan-based optical trapping is presented theoretically and verified experimentally. Disordered, ordered, and intermediate states appearing in Z-scan trapping experiments are discussed and the conditions for realizing phase transition and observing self-induced transparency are clarified. We experimentally demonstrate the high quality and good stability of the formed structures, the sequential trapping of individual microparticles, and the multiple trapping processes. The dependence of the quality of the formed structures on trapping power, scanning speed, and the size and material of microparticles are identified.