bluuebunny/crossref_metadata_2025 huggingface dataset:
Along‐strike trace element and isotopic variation in Aleutian Island arc basalt: Subduction melts sediments and dehydrates serpentine
Authors: Singer Brad S. , Jicha Brian R. , Leeman William P. , Rogers Nick W. , Thirlwall Matthew F. , Ryan Jeff , Nicolaysen Kirsten E.
Published: June 2007

Trace element and Sr‐Nd‐Pb isotope compositions of basaltic lavas from 11 volcanoes spanning 1300 km of the Aleutian Island arc provide new constraints on the recycling of elements in melts and fluids derived from subducted oceanic crust and sediment. Despite a nearly twofold variation in the flux of sediment subducted along the Aleutians, proxies indicating the presence of sediment melt in the magma source, including Th/La and Th/Nd, do not vary systematically along strike. In contrast, ratios including B/La, B/Nb, B/Be, Cs/La, Pb/Ce, and Li/Y suggest that the quantity or composition of fluid transferred from the slab into the mantle wedge varies an order of magnitude along strike and is apparently correlated with sediment flux. However, the most distinctive fluid addition corresponds spatially with subduction of the Amlia Fracture Zone (AFZ), a likely repository for H2O‐rich serpentinite. Sr, Nd, and Pb isotope ratios, together with Th/Nd and B/La ratios, show that the majority of these basalts reflect a common baseline metasomatism of the mantle that accumulated, perhaps over millions of years, via small additions of both slab fluids and partially melted sediment. The paradox of requiring slab surface temperatures high enough to melt a layer of sediment, while lower‐temperature dehydration reactions that supply water occur sufficiently deep to flux melting >80 km beneath the volcanoes is reconciled in a four‐stage model: (1) as sediment and altered ocean crust is carried to ∼60 km depth and temperatures increase to ∼650°C, metamorphic dehydration reactions release most of the fluid and B to the shallow mantle wedge beneath the fore arc, but some of this mantle is metasomatized and flows downward; (2) the uppermost layer of sediment begins to melt at ∼750°C and >60 km depth; this small volume of melt physically mingles with the overlying metasomatized mantle wedge as it flows further downdip; (3) below the sediment veneer, the uppermost 1 km of ocean crust reaches 650°C at ∼90 km depth where antigorite breaks down, releasing B‐rich H2O; and (4) this fluid infiltrates the layer of residual unmelted metasediment leaching the remaining inventory of fluid mobile elements and ascends into the modified mantle lowering its solidus and inducing partial melting. Where antigorite is likely abundant at the surface of the Pacific plate along the AFZ, deep H2O flux to the mantle is enhanced. This is reflected in higher B and lower incompatible element contents in the magmas, a relationship that links the amount of serpentine subducted to the extent of partial melting and the major element composition of arc basalt.
The onboard imagers for the Canadian ACE SCISAT‐1 mission
Authors: Gilbert K. L. , Turnbull D. N. , Walker K. A. , Boone C. D. , McLeod S. D. , Butler M. , Skelton R. , Bernath P. F. , Chateauneuf F. , Soucy M.‐A.
Published: June 2007

The Atmospheric Chemistry Experiment (ACE) onboard the Canadian Space Agency’s SCISAT‐1 satellite has been in orbit since August of 2003. Its broad objective is to study the problem of stratospheric ozone depletion, particularly in the Arctic. The main instruments are two spectrometers, one an infrared Fourier Transform Spectrometer and the other a dual optical spectrophotometer sensitive in the UV and visible. Also included are two filtered imagers used to measure altitude profiles of atmospheric extinction and detect thin clouds. The nominal center wavelengths of the filters are 525 nm for the visible (VIS) imager and 1020 nm for the near‐infrared (NIR) imager. With the decommissioning of other satellite instruments used to monitor global aerosols [i.e., Stratospheric Aerosol and Gas Experiment II (SAGE II), SAGE III, Polar Ozone and Aerosol Measurement (POAM) III, Halogen Occultation Experiment (HALOE)], the imagers provide much needed continuity in this data record. The data product from the imagers is still, however, in a preliminary state. Funding restrictions in the prelaunch period were responsible for an incomplete characterization of the imagers’ optics and electronics and prevented corrections being made for the problems found during testing. Postlaunch data analysis to correct for image artifacts is ongoing. A comparison with coincidental measurements from SAGE II shows that systematic errors from the preliminary analysis are within 5 and 20% for the VIS and NIR imagers, respectively, for uninverted profiles of optical depth. Despite the preliminary nature of the imager results, a paper describing the imagers and the initial operational data processing code is timely because the data are already being used.
Robustness of proxy‐based climate field reconstruction methods
Authors: Mann Michael E. , Rutherford Scott , Wahl Eugene , Ammann Caspar
Published: June 2007

We present results from continued investigations into the fidelity of covariance‐based climate field reconstruction (CFR) approaches used in proxy‐based climate reconstruction. Our experiments employ synthetic “pseudoproxy” data derived from simulations of forced climate changes over the past millennium. Using networks of these pseudoproxy data, we investigate the sensitivity of CFR performance to signal‐to‐noise ratios, the noise spectrum, the spatial sampling of pseudoproxy locations, the statistical representation of predictors used, and the diagnostic used to quantify reconstruction skill. Our results reinforce previous conclusions that CFR methods, correctly implemented and applied to suitable networks of proxy data, should yield reliable reconstructions of past climate histories within estimated uncertainties. Our results also demonstrate the deleterious impact of a linear detrending procedure performed recently in certain CFR studies and illustrate flaws in some previously proposed metrics of reconstruction skill.
Ground surface temperature scenarios in complex high‐mountain topography based on regional climate model results
Authors: Salzmann Nadine , Nötzli Jeannette , Hauck Christian , Gruber Stephan , Hoelzle Martin , Haeberli Wilfried
Published: June 2007

Climate change can have severe impacts on the high‐mountain cryosphere, such as instabilities in rock walls induced by thawing permafrost. Relating climate change scenarios produced from global climate models (GCMs) and regional climate models (RCMs) to complex high‐mountain environments is a challenging task. The qualitative and quantitative impact of changes in climatic conditions on local to microscale ground surface temperature (GST) and the ground thermal regime is not readily apparent. This study assesses a possible range of changes in the GST (ΔGST) in complex mountain topography. To account for uncertainties associated with RCM output, a set of 12 different scenario climate time series (including 10 RCM‐based and 2 incremental scenarios) was applied to the topography and energy balance (TEBAL) model to simulate average ΔGST for 36 different topographic situations. Variability of the simulated ΔGST is related primarily to the emission scenarios, the RCM, and the approach used to apply RCM results to the impact model. In terms of topography, significant influence on GST simulation was shown by aspect because it modifies the received amount of solar radiation at the surface. North faces showed higher sensitivity to the applied climate scenarios, while uncertainties are higher for south faces. On the basis of the results of this study, use of RCM‐based scenarios is recommended for mountain permafrost impact studies, as opposed to incremental scenarios.
Monogenic Vessel Diseases Related to Ischemic Stroke: A Clinical Approach
Authors: Ballabio E , Bersano A , Bresolin N , Candelise L
Published: June 2007

The identification of stroke cases caused by monogenic disorders is important both for therapeutic decisions and genetic counselling, although they represent less than 1% of all stroke patients. The purpose of this review is to summarize genetic, pathological, and clinical features of single-gene disorders related to ischemic stroke. The following monogenic disorders are considered: cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy, cerebral autosomal-recessive arteriosclerosis with subcortical infarcts and leukoencephalopathy, hereditary endotheliopathy with retinopathy, nephropathy, and stroke, Fabry disease, pseudoxanthoma elasticum, Neurofibromatosis type 1, familial MoyaMoya disease, Ehlers-Danlos syndrome type IV, Marfan syndrome. For each monogenic disorder, mode of inheritance, pathophysiological aspects, clinical phenotype, and diagnostic tools are carefully described. Furthermore, the classification of monogenetic disorders is presented according to stroke mechanisms, which include small vessel diseases, large artery diseases, and arterial dissections. This review could be useful to identify specific diagnostic pathways for patients with a suspicion of monogenic disease.
Interaction of an unconfined vortex with a solid surface
Authors: Parras L. , Fernandez-Feria R.
Published: June 2007

The interaction of an open vortex with a solid plane perpendicular to the axis of the vortex is analyzed numerically. We solve the axisymmetric, incompressible Navier-Stokes equations with boundary conditions that far from the axis correspond to the near-inviscid far-field of Long’s similarity solution for an open vortex. Continuation techniques are used to solve the equations of motion for varying Reynolds numbers. When this parameter is large enough, a vortex breakdown phenomenon occurs, producing a small region of reversed flow at the axis. This region increases in size and migrates toward the solid plane for increasing Reynolds numbers. The subsequent intensification of the swirl near both the axis and the surface generates a bifurcation with nonuniqueness of the solution corresponding to a new, more intense, vortex breakdown. At the end, for Reynolds numbers above a critical value, the flow acquires a two-celled structure, with a region of reversed flow all along the axis surrounded by an annular updraft region with intensified swirl. For large Reynolds numbers this flow structure tends, far above from the plane, to Long’s self-similar solution of Type II. Thus, we show that of the two different similarity solutions for high Reynolds numbers found by Long for a given flow force, only that with negative axial velocity at the axis (Type II solution) is compatible with the viscous interaction of the vortex with a solid surface. We also find that the corresponding flow force increases linearly with the Reynolds number, so that the solution tends for large Reynolds numbers to the similarity solution with the most negative axial velocity at the axis. This transition from one-cell to two-cell flow configuration, and its relation to the intensification of the swirl in the flow, is in agreement with observations of intense tornado-like vortices, where the flow at the axis is directed downward, while the rotation of the flow is intensified in an annular updraft.
Calculation of the distribution of eigenvalues and eigenvectors in Markovian state models for molecular dynamics
Authors: Hinrichs Nina Singhal , Pande Vijay S.
Published: June 2007

Markovian state models (MSMs) are a convenient and efficient means to compactly describe the kinetics of a molecular system as well as a formalism for using many short simulations to predict long time scale behavior. Building a MSM consists of grouping the conformations into states and estimating the transition probabilities between these states. In a previous paper, we described an efficient method for calculating the uncertainty due to finite sampling in the mean first passage time between two states. In this paper, we extend the uncertainty analysis to derive similar closed-form solutions for the distributions of the eigenvalues and eigenvectors of the transition matrix, quantities that have numerous applications when using the model. We demonstrate the accuracy of the distributions on a six-state model of the terminally blocked alanine peptide. We also show how to significantly reduce the total number of simulations necessary to build a model with a given precision using these uncertainty estimates for the blocked alanine system and for a 2454-state MSM for the dynamics of the villin headpiece.
A surface photovoltage spectroscopy study of GaAs∕AlAs complicated nanostructures with graded interfaces
Authors: Donchev V. , Kirilov K. , Ivanov Ts. , Germanova K.
Published: June 2007

We present a surface photovoltage (SPV) spectroscopy study of the optical properties and the bound states of graded interface AlAs∕GaAs superlattices (SLs) containing two GaAs embedded quantum wells (EQWs) with different widths. SPV spectra are measured in the metal-insulator-semiconductor operation mode under super-band-gap optical excitation at room temperature. In spite of the relatively large absorption of the GaAs substrate, the SPV spectra exhibit clearly resolved features superimposed on the substrate smooth background. These features have been identified as free exciton transitions in the EQWs and in the SL. This interpretation is based on a detailed comparison of the SPV results with those of electronic structure calculations and photoluminescence spectral measurements. The calculations are performed in frames of the envelope function approximation, employing a model structure very similar to the real one and taking into account the interface grading. The mechanisms of the SPV signal generation have been discussed. An experimental confirmation is given to the theoretical model developed by others, about the SPV behavior in quantum wells. Our study demonstrates further the SPV spectroscopy powerful potentialities for nondestructive contactless characterization at room temperature of complicated nanostructures with graded interfaces.
Alternans amplification following a two-stimulus protocol in a one-dimensional cardiac ionic model of reentry: From annihilation to double-wave quasiperiodic reentry
Authors: Comtois P. , Vinet A.
Published: June 2007

Electrical pacing is a common procedure in both experimental and clinical settings to study and/or annihilate anatomical reentry. A previous study [Comtois and Vinet, Chaos 12, 903 (2002)] has described new ways to terminate reentry in a one-dimensional loop model by a protocol consisting of only two stimulations. Annihilation of the reentrant activity was much more likely with these new scenarios than through a unidirectional block. This paper investigates the sensitivity of these scenarios of annihilation to the length of the pathway. It shows that double-pulse stimulation can stop the reentry if the circuit is shorter than a limiting length. Beyond this upper limit, stimulation rather yields sustained double-wave reentry. The same dynamical mechanism, labeled alternans amplification, is found to be responsible for these two types of post-stimulus dynamics.
Analytical solution for relativistic charged particle motion in a circularly polarized electromagnetic wave
Authors: Kong Ling-Bao , Liu Pu-Kun
Published: June 2007

The relativistic motion of a charged particle in a uniform magnetic field and a circularly polarized electromagnetic wave propagating along the direction of magnetic field is studied. By manipulating the integrals of motion, some typical quantities of particle motion have been presented analytically in terms of explicit functions of three free parameters. The results may be of great importance for high-power microwave generation or particle acceleration.
Real time correlation function in a single phase space integral beyond the linearized semiclassical initial value representation
Authors: Liu Jian , Miller William H.
Published: June 2007

It is shown how quantum mechanical time correlation functions [defined, e.g., in Eq. (1.1)] can be expressed, without approximation, in the same form as the linearized approximation of the semiclassical initial value representation (LSC-IVR), or classical Wigner model, for the correlation function [cf. Eq. (2.1)], i.e., as a phase space average (over initial conditions for trajectories) of the Wigner functions corresponding to the two operators. The difference is that the trajectories involved in the LSC-IVR evolve classically, i.e., according to the classical equations of motion, while in the exact theory they evolve according to generalized equations of motion that are derived here. Approximations to the exact equations of motion are then introduced to achieve practical methods that are applicable to complex (i.e., large) molecular systems. Four such methods are proposed in the paper—the full Wigner dynamics (full WD) and the second order WD based on “Wigner trajectories” [H. W. Lee and M. D. Scully, J. Chem. Phys. 77, 4604 (1982)] and the full Donoso-Martens dynamics (full DMD) and the second order DMD based on “Donoso-Martens trajectories” [A. Donoso and C. C. Martens, Phys. Rev. Lett. 8722, 223202 (2001)]—all of which can be viewed as generalizations of the original LSC-IVR method. Numerical tests of the four versions of this new approach are made for two anharmonic model problems, and for each the momentum autocorrelation function (i.e., operators linear in coordinate or momentum operators) and the force autocorrelation function (nonlinear operators) have been calculated. These four new approximate treatments are indeed seen to be significant improvements to the original LSC-IVR approximation.
An experimental and quasiclassical trajectory study of the rovibrationally state-selected reactions: HD+(v=–15,j=1)+He→HeH+(HeD+)+D(H)
Authors: Tang X. N. , Houchins C. , Xu H. F. , Ng C. Y. , Chiu Y. , Dressler R. A. , Levandier D. J.
Published: June 2007

The absolute integral cross sections for the formation of HeH+ and HeD+ from the collisions of HD+(v,j=1)+He have been examined over a broad range of vibrational energy levels v=0–13 at the center-of-mass collision energies (ET) of 0.6 and 1.4eV using the vacuum ultraviolet (VUV) pulsed field ionization photoelectron secondary ion coincidence method. The ET dependencies of the integral cross sections for products HeH+ and HeD+ from HD+(v=0–4)+He collisions in the ET range of 0–3eV have also been measured using the VUV photoionization guided ion beam mass spectrometric technique, in which vibrationally selected HD+(v) reactant ions were prepared via excitation of selected autoionization resonances of HD. At low total energies, a pronounced isotope effect is observed in absolute integral cross sections for the HeH++D and HeD++H channels with significant favoring of the deuteron transfer channel. As v is increased in the range of v=0–9, the integral cross sections of the HeH++D channel are found to approach those of HeD++H. The observed velocity distributions of products HeD+ and HeH+ are consistent with an impulsive or spectator-stripping mechanism. Detailed quasiclassical trajectory (QCT) calculations are also presented for HD+(v,j=1)+He collisions at the same energies of the experiment. The QCT calculations were performed on the most accurate ab initio potential energy surface available. If the zero-point energy of the reaction products is taken into account, the QCT cross sections for products HeH+ and HeD+ from HD+(v)+He are found to be significantly lower than the experimental results at ET values near the reaction thresholds. The agreement between the experimental and QCT cross sections improves with translational energy. Except for prethreshold reactivity, QCT calculations ignoring the zero-point energy in the products are generally in good agreement with experimental absolute cross sections. The experimental HeH+∕HeD+ branching ratios for the HD+(v=0–9)+He collisions are generally consistent with QCT predictions. The observed isotope effects can be rationalized on the basis of differences in thermochemical thresholds and angular momentum conservation constraints.
Interplay of host volume variations and internal distortions in the course of intercalation into disordered matrices
Authors: Vakarin E. V. , Garcia-Belmonte Germà , Badiali J. P.
Published: June 2007

Based on a combination of the distortive lattice gas model and the maximum information entropy approach, the thermodynamics of insertion into disordered hosts is analyzed. It is found that the isotherm specificities can be explained as a cooperative interplay of the host volume expansion and the internal distortions, which tend to optimize the host structure inducing a local lowering of the insertion energetic cost. Behavior of amorphous LixWO3 films of different thicknesses is discussed in this context.
Effects of laser-induced heating on Raman stress measurements of silicon and silicon-germanium structures
Authors: Georgi Carsten , Hecker Michael , Zschech Ehrenfried
Published: June 2007

The authors investigate the effect of laser-induced heating on Raman measurements for different unpatterned and patterned substrates, including pure silicon, strained-silicon-on-insulator, and silicon-germanium layers on silicon. The relationship between heating and incident power of the laser used for Raman measurements is derived for unpatterned substrates, and the much stronger heating effects for line and island structures are shown. Additionally, the enormous heating of isolated silicon particles within the laser beam was investigated. The measured shifts clearly show that heating has to be considered even for moderate laser intensity when accurate stress measurements on such substrates are performed by Raman spectroscopy.
Detection of charged particles with charge injection devices
Authors: Fletcher Kurtis A. , Apker Benjamin , Hammond Samantha , Punaro John , Marshall Frederic J. , Laine Jonathan , Forties Robert
Published: June 2007

A method for using charge injection devices (CIDs) for detection of high-energy charged particles from inertial-confinement fusion reactions is described. Because of the relatively small depletion region of the CID camera (depletion depth of ∼7μm), aluminum foils are placed in front of the device to reduce the energy of the charged particles and maximize the energy deposited in the CID. Simultaneous measurements of H2(d,p)3H protons with a CID and a surface barrier detector indicate that the CID is an efficient detector of charged fusion products. Tests using high energy alpha particles emitted from a radium-226 source are also reported.
Optimizing the physical contribution to the sensitivity and signal to noise ratio of extraordinary magnetoresistance quantum well structures
Authors: Shao Y. , Solin S. A. , Ram-Mohan L. R. , Yoo Keon-Ho
Published: June 2007

For applications to extraordinary magnetoresistance (EMR) quantum well sensor design, the electron areal density n2D, the mobility μ, and the products n3D1∕2μ2 and n3D1∕2μ5∕2 are key physical parameters to be optimized for enhanced device sensitivity and signal to noise ratio. We model the electron areal density and carrier mobility in a two-dimensional electron gas layer developed in a δ-doped AlInSb∕InSb heterostructure. The nonparabolic band structure due to the nature of the small energy band gap of InSb is accounted for. The detailed description of the energy dispersion and the energy dependent effective mass are obtained by the k∙P method of band structure calculation. The transport properties are calculated by including contributions of scattering from ionized impurities, the background neutral impurities, the deformation potential acoustic phonons, and the polar optical phonons. We calculate the dependencies of n2D, μ, n3D1∕2μ2, and n3D1∕2μ5∕2 on temperature, spacer layer thickness, doping density, and the quantum well thickness. This has important implications for EMR sensor design.
Reply to “Comment on ‘Theory of the photodissociation of ozone in the Hartley continuum: Potential energy surfaces, conical intersections, and photodissociation dynamics’ ” [J. Chem. Phys. 123, 014306 (2005)]
Authors: Balint-Kurti Gabriel G. , Baloïtcha Ezinvi
Published: June 2007

We share the concerns of Grebenshchikov and Schinke at the differences between our calculations especially in view of the similarity between our potential energy surfaces. Despite the differences between the methods used, our results should agree if both calculations are properly converged.
Development of high-pressure, high-field and multifrequency electron spin resonance system
Authors: Sakurai T. , Taketani A. , Tomita T. , Okubo S. , Ohta H. , Uwatoko Y.
Published: June 2007

The electron spin resonance (ESR) system which covers the magnetic field region up to 16T, the quasicontinuous frequency region from 60to700GHz, the temperature region from 1.8to4.2K, and the hydrostatic pressure region up to 1.1GPa has been developed. This is the first pulsed high-field and multifrequency ESR system with the pressure region over 1GPa as far as we know. Transmission ESR spectra under hydrostatic pressure can be obtained by combining a piston-cylinder-type pressure cell and the pulsed magnetic field ESR apparatus. The pressure cell consists of a NiCrAl cylinder and sapphire or zirconia inner parts. The use of sapphire or zirconia as inner parts enables us to observe ESR under pressure because these inner parts have high transmittance for the electromagnetic wave with millimeter and submillimeter wavelengths. We have successfully applied this system for the pressure dependence measurements of an isolated spin system NiSnCl6∙6H2O up to 1.1GPa. It was found that the single ion anisotropy parameter D of this compound strongly depends on pressure. The parameter D is approximately proportional to the pressure up to 0.75GPa, and the relation between D and the pressure can be used for the pressure calibration of this high-field and high-pressure ESR system.
Ultraviolet semiconductor laser diodes on bulk AlN
Authors: Kneissl Michael , Yang Zhihong , Teepe Mark , Knollenberg Cliff , Schmidt Oliver , Kiesel Peter , Johnson Noble M. , Schujman Sandra , Schowalter Leo J.
Published: June 2007

Current-injection ultraviolet lasers are demonstrated on low-dislocation-density bulk AlN substrates. The AlGaInN heterostructures were grown by metalorganic chemical vapor deposition. Requisite smooth surface morphologies were obtained by growing on near-c-plane AlN substrates, with a nominal off-axis orientation of less than 0.5°. Lasing was obtained from gain-guided laser diodes with uncoated facets and cavity lengths ranging from 200 to 1500 μm. Threshold current densities as low as 13 kA/cm2 were achieved for laser emission wavelengths as short as 368 nm, under pulsed operation. The maximum light output power was near 300 mW with a differential quantum efficiency of 6.7%. This (first) demonstration of nitride laser diodes on bulk AlN substrates suggests the feasibility of using such substrates to realize nitride laser diodes emitting from the near to deep ultraviolet spectral regions.
Effect of surface oxidation on electron transport in InN thin films
Authors: Lebedev V. , Wang Ch. Y. , Cimalla V. , Hauguth S. , Kups T. , Ali M. , Ecke G. , Himmerlich M. , Krischok S. , Schaefer J. A. , Ambacher O. , Polyakov V. M. , Schwierz F.
Published: June 2007

The chemical and electron transport properties of oxidized indium nitride epilayers and indium oxide/indium nitride heterostructures are reported. It is shown that the accumulation of electrons at the InN surface can be manipulated by the formation of a thin surface oxide layer using an ozone-assisted oxidation processing. It results in improved transport properties and in a reduction of the electron sheet concentration of the InN epilayer caused by a passivation of the surface donors and a shift of the electron density distribution peak from the surface toward the bulk InN. Using the ensemble Monte Carlo simulation method, the electron mobility for different dislocation densities and surface band bending values has been calculated. The theoretical results correlate well with our experimental data. In opposition to the ozone treatment, in epitaxial oxide/nitride heterojunctions the electron sheet concentration of InN raises due to the increasing band bending at the heterointerface affecting adversely the electron transport properties.
Experimental validation of negative refraction of metamaterial composed of single side paired S-ring resonators
Authors: Wang Dongxing , Ran Lixin , Chen Hongsheng , Mu Mingkai , Kong Jin Au , Wu Bae-Ian
Published: June 2007

A one-dimensional metamaterial structure is realized by printing subwavelength paired S-shaped metallic strips only on one side of a dielectric substrate. The simultaneously negative effective permittivity and permeability of such metamaterial are retrieved from the scattering parameters yielded in the numerical simulation. Experiments aimed to verify the transmission and refraction properties of the metamaterial are conducted, and the results show the existence of the negative refraction within the same frequency band, as indicated in the simulation. The proposed structure design makes it easy to fabricate and provides feasibilities for making controllable metamaterial by incorporating itself with lumped active elements.
Evidence of negative bias temperature instability in 4H-SiC metal oxide semiconductor capacitors
Authors: Marinella M. J. , Schroder D. K. , Isaacs-Smith T. , Ahyi A. C. , Williams J. R. , Chung G. Y. , Wan J. W. , Loboda M. J.
Published: June 2007

Generation lifetimes and interface state densities of n-type 4H-SiC metal oxide semiconductor (MOS) capacitors are characterized by using the pulsed MOS capacitor technique. A decrease in lifetime and increase in interface state density occurs when the devices are negatively biased at 400°C. This behavior is consistent with an effect seen in Si∕SiO2 devices known as negative bias temperature instability. A portion of the lifetime degradation caused by this effect can be recovered by removing the negative bias as well as by positively biasing the device.
Spin-wave propagation and transmission along magnetic nanowires in long wavelength regime
Authors: Xi Haiwen , Xue Song
Published: June 2007

In this study, we start with the Landau-Lifshitz-Gilbert equation to describe the spin waves in magnetic nanowires using the linearization approach. In the long wavelength regime, the spin-wave propagation and attenuation along a uniform magnetic nanowire are first investigated. Then, the study is extended to magnetic nanowires composed of multiple segments. Spin waves are found to be reflected and transmitted at the interfaces. In particular, resonance behavior of the spin-wave transmission can be observed in a three-piece magnetic nanowire structure. The resonance is then characterized in terms of resonance wavelength and linewidth and analyzed based on the interface coupling and the structural and magnetic properties of the nanowires.
Deviations from the local field approximation in negative streamer heads
Authors: Li Chao , Brok W. J. M. , Ebert Ute , van der Mullen J. J. A. M.
Published: June 2007

Negative streamer ionization fronts in nitrogen under normal conditions are investigated both in a particle model and in a fluid model in local field approximation. The parameter functions for the fluid model are derived from swarm experiments in the particle model. The front structure on the inner scale is investigated in a one-dimensional setting, allowing reasonable run time and memory consumption and high numerical accuracy without introducing superparticles. If the reduced electric field immediately before the front is ⩽50kV∕(cmbar), solutions of fluid and particle model agree very well. If the field increases up to 200kV∕(cmbar), the solutions of particle and fluid model deviate, in particular, the ionization level behind the front becomes up to 60% higher in the particle model while the velocity is rather insensitive. Particle and fluid model deviate because electrons with high energies do not yet fully run away from the front, but are somewhat ahead. This leads to increasing ionization rates in the particle model at the very tip of the front. The energy overshoot of electrons in the leading edge of the front actually agrees quantitatively with the energy overshoot in the leading edge of an electron swarm or avalanche in the same electric field.
Nonlithographic patterning through inkjet printing via holes
Authors: Xia Yajun , Friend Richard H.
Published: June 2007

The authors demonstrate a patterning technique, through creating via-hole structures on insulator-coated substrates via inkjet printing, the resolution of which meets the requirements for flat-panel display applications. The authors also fabricate polymer light-emitting diode arrays by subsequently inkjet printing light-emitting polymers onto the inkjet-patterned substrate. The resultant devices exhibit good performances. Hence, this nonlithographic patterning technique provides a way of patterning large-area substrates for applications such as flat-panel displays.
Effects of polyethylene oxide on the dynamics of the α and α′ relaxations observed in polystyrene by low-frequency anelastic spectroscopy
Authors: Wu Xuebang , Zhu Zhengang
Published: June 2007

The relaxation dynamics in amorphous polystyrene and blends with polyethylene oxide (PEO) has been investigated by low-frequency anelastic spectroscopy. The dissipation spectra exhibit two relaxation peaks, corresponding to the α relaxation and the α′ (liquid-liquid) transition, respectively. The origin of the liquid-liquid transition is the inhomogeneity in the melt due to the chain clustering. With increasing PEO content, the peak temperature Tα′ and the relaxation strength Δα′ decrease, while Tα decreases and Δα increases. Moreover, the fractional free volume sharply increases above Tα′ for all the samples, due to the bigger value of thermal expansion coefficient αf.
Surface plasmon polariton waveguiding: From multimode stripe to a slot geometry
Authors: Satuby Yinon , Orenstein Meir
Published: June 2007

Surface plasmon polariton (SPP) photonic waveguiding along laterally wide and 20nm thick gold stripes, at λ=1.55μm, exhibited multimodal behavior with some localizations of the field near the stripe’s edges. This was leveraged in a configuration comprised of two adjacent edges, creating slot waveguide geometry. The measured slot mode was predominantly a TM mode—which corresponds to the coupled fields of the two edges as was also confirmed by numerical simulation.
Observation of Fabry-Pérot-type surface plasmon on Ag film with perforated short-range 3×3 hole array arranged in long-range periodic structure
Authors: Chang Yi-Tsung , Chuang Tzu-Hung , Tsai Ming-Wei , Lai Mu-Jen , Lee Si-Chen
Published: June 2007

This letter elucidates enhanced optical transmission through a Ag film with perforated short-range 3×3 hole arrays arranged in a long-range periodic structure. The 3×3 squared hole array constitutes an individual microcell. The measured transmission peak wavelength reveals that the surface plasmons are generated by Fabry-Pérot-type waveguide resonances with integer order. The ratio of periodicity between the superperiodic structure p and the 3×3 microcell d determines the integer order. Namely, when p∕d>3, the order 3, 4, and 5 surface plasmon modes with average hole spacings p∕3, p∕4, and p∕5 are observed. The transmission intensities of order 3 modes are the strongest, and those of order 5 modes are barely seen. But as p∕d approaches 4, the order 3 modes gradually disappear with the emergence of order 4 and 5 modes. These phenomena suggest that the surface plasmons are Fabry-Pérot-type resonance within a super unit cell.
Characterization of ferroelectric domains in morphotropic potassium sodium niobate with scanning probe microscopy
Authors: Herber Ralf-Peter , Schneider Gerold A. , Wagner Susanne , Hoffmann Michael J.
Published: June 2007

Lead-free piezoceramic potassium sodium niobate in its morphotropic composition was synthesized with abnormal grain growth. Ferroelectric domain patterns were imaged with piezoresponse force microscopy. Analysis of the domain structure at the morphotropic phase boundary revealed a coexistence of tetragonal and orthorhombic polarized domains in a single grain.
Multifunctional ferrimagnetic-ferroelectric thin films for microwave applications
Authors: Heindl R. , Srikanth H. , Witanachchi S. , Mukherjee P. , Heim A. , Matthews G. , Balachandran S. , Natarajan S. , Weller T.
Published: June 2007

Ferrimagnetic and ferroelectric structures based on barium strontium titanate and barium hexaferrite are investigated for potential applications in tunable microwave devices. Thin film bilayers were grown on MgO and sapphire, and their underlying crystallographic, microstructural, and magnetic properties were analyzed and compared. Microcircuits were fabricated using optical lithography, and microwave properties and electrical tunability were measured in the range of 1–50GHz. Overall, the studies demonstrate the possibility of realizing high quality multifunctional microwave materials that combine tunable magnetic and dielectric properties.
Ba
0.9
Sr
0.1
Ti
O
3
-based optical microcavities fabricated by chemical solution deposition
Authors: Hong X. K. , Hu G. J. , Shang J. L. , Bao J. , Chu J. H. , Dai N.
Published: June 2007

Single or coupled optical microcavities have been prepared by inserting one or two dense Ba0.9Sr0.1TiO3 layers, respectively, in the quasiperiodic Ba0.9Sr0.1TiO3 multilayers fabricated based on phase separation. The single microcavities exhibit well-defined resonant modes in the investigated wavelength range with a quality factor no less than 60. The resonant frequency of the mode can be tuned through varying the spinning rate during the spin-coating process to change the thickness of the inserted layer. The mode properties of the coupled microcavities strongly depend on the mismatch parameter of the inserted defect layers. The approach reported here offers a simple, inexpensive, and flexible route for fabricating high quality microcavities.
Long range influence of an excess proton on the architecture of the hydrogen bond network in large-sized water clusters
Authors: Mizuse Kenta , Fujii Asuka , Mikami Naohiko
Published: June 2007

Infrared spectra of completely size-selected protonated water clusters H+(H2O)n are reported for clusters ranging from n=15 to 100. The behavior of the dangling OH stretch bands shows that the hydrogen bond structure in H+(H2O)n is uniquely different to that of (H2O)n up to the size of n=100, at least. This finding indicates that the presence of an excess proton creates a characteristic morphology in the hydrogen bond network architecture of more than 100 surrounding water molecules.
Simultaneous monitoring of multimetallic atom densities in plasma processes employing a multimicrohollow cathode lamp
Authors: Ohta Takayuki , Ito Masafumi , Tachibana Yoshihiro , Taneda Satoshi , Takashima Seigo , Hori Masaru , Kano Hiroyuki , Den Shoji
Published: June 2007

The authors have developed a simultaneous measurement technique of multimetallic atom densities in process plasmas using absorption spectroscopy employing a multimicrohollow cathode plasma as a light source. The optical emissions of four metallic atoms of Cu, Zn, Fe, and Mo were simultaneously produced from the multimicrohollow cathode plasma of millimeter size. The absolute densities of Cu and Mo in the magnetron sputtering plasma were simultaneously measured using this technique. The simultaneous monitoring of multimetallic atoms is very useful for controlling the plasma processes precisely.
Switchable titanate-nanotube electrode sensitive to nitrate
Authors: Liu Aihua , Zhou Haoshen , Honma Itaru , Ichihara Masaki
Published: June 2007

The redox peak current of the Ti(IV)∕Ti(III) pair for titanate-nanotube (TNT) film-covered basal plane pyrolytic graphite disk electrode (PGE) was found sensitive to the varying concentration of nitrate in the acetate buffer solution. The TNT/PGE shows stable redox peak in 0.1M acetate buffer, which disappeared when changed into the same buffer solution containing over 5.6mM nitrate. The return of the TNT/PGE into bare acetate buffer induced a full recovery of the redox peak of Ti(IV)∕Ti(III). These effects can be repeated, just as a switch with on/off function. The electrochemical activity of titanium oxide on the electrode surface can be reversibly retrieved between 0.1M acetate buffer solution (pH 5.5) and nitrate. This system may be applicable to designing nitrate sensor.
Ferrite-film nonlinear spin wave interferometer and its application for power-selective suppression of pulsed microwave signals
Authors: Ustinov Alexey B. , Kalinikos Boris A.
Published: June 2007

A theoretical model of the nonlinear spin wave interferometer has been developed. An experimental prototype of the device has been manufactured and investigated. The device application for power-selective suppression of pulsed microwave signals has been demonstrated. The obtained experimental data are in good agreement with the theory.
Complexation of TbIII with size fractions of humic acid: evidence from luminescence sensitisation and anisotropy measurements
Authors: Riggle Jeremy , von Wandruszka Ray
Published: June 2007

Environmental context. Organic ligands, especially those derived from humic acid (HA), play a major role in the fate and transport of metal ions in the environment. For the modelling of subsurface pollutant transport, it is important to understand which components of a heterogeneous humic material interact most strongly with multivalent cations.
Abstract. The luminescence sensitisation and anisotropy characteristics of a series of TbIII complexes with a leonardite humic acid (LHA) were investigated in order to evaluate the interactions between the metal and different components of the humate. Ultrafiltration was used to separate LHA into six size fractions, which ranged from 500 Da to 0.2 μm, and were then used to form the TbIII complexes. Each fraction was first characterised by 13C NMR and UV-Vis spectroscopy, which showed that the smaller ones (<3 kDa) had a significantly lower aliphatic content than the larger ones. These smaller components were good energy donors, which could effectively sensitise TbIII luminescence. At the same time, the luminescence anisotropy of TbIII increased significantly when these LHA fractions were added, which indicated the formation of tightly bound complexes. In this sense, the smaller LHA fractions were comparable to ethylenediaminetetraacetate, although their effect was not as strong. In contrast, the larger LHA sizes had little or no influence on TbIII sensitisation or anisotropy. The results obtained suggest that the sizes and aliphatic content of humic polymers play a major role in their aqueous interactions with trivalent metal ions. Divalent metals are expected to behave in a similar way.
Mapping of arsenic species and identification of a novel arsenosugar in giant clams Tridacna maxima and Tridacna derasa using advanced mass spectrometric techniques
Authors: Nischwitz Volker , Pergantis Spiros A.
Published: June 2007

Environmental context. Arsenic is known to accumulate in various marine organisms. The high acute toxicity of inorganic arsenic species and the potential chronic toxicity of some organoarsenic species require detailed knowledge about the occurrence and metabolism of arsenic compounds in marine organisms. The application of advanced analytical techniques still allows, even after decades of arsenic speciation, the identification of novel species. In addition, comprehensive mapping of all arsenic species present in marine organisms may allow for a more detailed understanding of arsenic metabolism.
Abstract. Because of their symbiotic microalgae, giant clams (Tridacna species) exhibit a unique arsenic metabolism, which has been shown in previous studies to involve a large number of arsenic species. This study demonstrates the application of liquid chromatography (HPLC) online with electrospray tandem mass spectrometry (ES-MS/MS) as well as inductively coupled plasma mass spectrometry (ICP-MS) for arsenic speciation analysis in giant clam extracts. Selected reaction monitoring (SRM) was used for sensitive and selective detection of a large number of arsenic species in a single chromatographic run. Novel aspects are the analysis of 10 tissue fractions from one clam and the analysis of kidney extracts both from T. maxima and T. derasa with the same method thus offering the possibility for direct comparisons. Moreover, HPLC-ES-MS/MS in the precursor ion scan mode and product ion scan mode allowed the identification of a novel sulfonated dimethylarsenosugar and the partial characterisation of another unknown arsenic species. The results indicate that most arsenic species are accumulated in the kidneys. However, arsenobetaine was found at similar contents in all analysed tissue fractions of one T. maxima clam.
Efficient supervised learning in networks with binary synapses
Authors: Baldassi Carlo , Braunstein Alfredo , Brunel Nicolas , Zecchina Riccardo
Published: June 2007

Recent experimental studies indicate that synaptic changes induced by neuronal activity are discrete jumps between a small number of stable states. Learning in systems with discrete synapses is known to be a computationally hard problem. Here, we study a neurobiologically plausible on-line learning algorithm that derives from belief propagation algorithms. We show that it performs remarkably well in a model neuron with binary synapses, and a finite number of “hidden” states per synapse, that has to learn a random classification task. Such a system is able to learn a number of associations close to the theoretical limit in time that is sublinear in system size. This is to our knowledge the first on-line algorithm that is able to achieve efficiently a finite number of patterns learned per binary synapse. Furthermore, we show that performance is optimal for a finite number of hidden states that becomes very small for sparse coding. The algorithm is similar to the standard “perceptron” learning algorithm, with an additional rule for synaptic transitions that occur only if a currently presented pattern is “barely correct.” In this case, the synaptic changes are metaplastic only (change in hidden states and not in actual synaptic state), stabilizing the synapse in its current state. Finally, we show that a system with two visible states and
K
hidden states is much more robust to noise than a system with
K
visible states. We suggest that this rule is sufficiently simple to be easily implemented by neurobiological systems or in hardware.
Mechanisms of photoswitch conjugation and light activation of an ionotropic glutamate receptor
Authors: Gorostiza Pau , Volgraf Matthew , Numano Rika , Szobota Stephanie , Trauner Dirk , Isacoff Ehud Y.
Published: June 2007

The analysis of cell signaling requires the rapid and selective manipulation of protein function. We have synthesized photoswitches that covalently modify target proteins and reversibly present and withdraw a ligand from its binding site due to photoisomerization of an azobenzene linker. We describe here the properties of a glutamate photoswitch that controls an ion channel in cells. Affinity labeling and geometric constraints ensure that the photoswitch controls only the targeted channel, and enables spatial patterns of light to favor labeling in one location over another. Photoswitching to the activating state places a tethered glutamate at a high (millimolar) effective local concentration near the binding site. The fraction of active channels can be set in an analog manner by altering the photostationary state with different wavelengths. The bistable photoswitch can be turned on with millisecond-long pulses at one wavelength, remain on in the dark for minutes, and turned off with millisecond long pulses at the other wavelength, yielding sustained activation with minimal irradiation. The system provides rapid, reversible remote control of protein function that is selective without orthogonal chemistry.