bluuebunny/crossref_metadata_2025 huggingface dataset:
Neogene magmatism northeast of the Aegir and Kolbeinsey ridges, NE Atlantic: Spreading ridge–mantle plume interaction?
Authors: Breivik Asbjørn Johan , Faleide Jan Inge , Mjelde Rolf
Published: February 2008

According to mantle plume theory the Earth's interior cools partly by localized large vertical mass transport, causing extensive decompression melting. The Iceland melt anomaly is regarded as a typical example of a mantle plume. However, there are centers of Miocene to recent magmatism in the Norwegian‐Greenland Sea not easily explained by the plume theory. Here we present new data to document diffuse late Miocene magmatic underplating of older oceanic crust located mostly north of the Aegir Ridge, an extinct seafloor spreading axis in the Norway Basin. There is also a region with similar magmatism northeast of the presently spreading Kolbeinsey Ridge north of Iceland. Intraplate magmatism in these locations is not easily explained by local plume models, edge‐driven convection, or by asthenosphere flow–lithosphere thickness interaction. On the basis of correlation between the magmatism and the active or extinct spreading ridges, we propose the mid‐ocean ridge basalt–capture model, in which this magmatism can be understood through plume–spreading ridge interaction: The asthenosphere flow out from Iceland captures deeper, low‐degree partially molten asthenospheric regions from underneath the spreading ridges and carry these across the terminating fracture zones, to subsequently underplate oceanic crust or to intrude and build seamounts. This model is similar to lithospheric cracking models for intraplate magmatism in requiring that low‐degree partial melt can be retained in the asthenosphere over time but differ in that the magma is extracted by internal magma movement processes and not by external tectonic forces.
Sea ice, high‐latitude convection, and equable climates
Authors: Abbot D. S. , Tziperman Eli
Published: February 2008

It is argued that deep atmospheric convection might occur during winter in ice‐free high‐latitude oceans, and that the surface radiative warming effects of the clouds and water vapor associated with this winter convection could keep high‐latitude oceans ice‐free through polar night. In such an ice‐free high‐latitude ocean the annual‐mean SST would be much higher and the seasonal cycle would be dramatically reduced ‐ making potential implications for equable climates manifest. The constraints that atmospheric heat transport, ocean heat transport, and CO2 concentration place on this mechanism are established. These ideas are investigated using the NCAR column model, which has state‐of‐the‐art atmospheric physics parameterizations, high vertical resolution, a full seasonal cycle, a thermodynamic sea ice model, and a mixed layer ocean.
GOES sounding improvement and applications to severe storm nowcasting
Authors: Li Zhenglong , Li Jun , Menzel W. Paul , Schmit Timothy J. , Nelson James P. , Daniels Jaime , Ackerman Steven A.
Published: February 2008

An improved clear‐sky physical retrieval algorithm for atmospheric temperature and moisture is applied to the Geostationary Operational Environmental Satellite‐12 (GOES‐12) Sounder. A comparison with the microwave radiometer (MWR) measured total precipitable water (TPW) at the Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) site from June 2003 to May 2005 shows that the TPW retrievals are improved by 0.4 mm over the legacy GOES Sounder TPW product. The Lifted Index (LI) derived product imagery (DPI) from the improved soundings better depicts the pre‐convective environment surrounding a tornadic supercell at Eagle Pass, Texas on 24 April 2007. Another severe storm case from 13 April 2006 demonstrates that the improved physical algorithm successfully detects low‐level moisture. Both cases show the new retrievals along with the derived products will help the forecasters with short‐term severe storm nowcasting.
A model‐dye comparison experiment in the tidal mixing front zone on the southern flank of Georges Bank
Authors: Chen Changsheng , Xu Qichun , Houghton Robert , Beardsley Robert C.
Published: February 2008

A process‐oriented model‐dye comparison experiment was conducted to examine the ability of a numerical ocean model to simulate the observed movement of dye across the tidal mixing front on the southern flank of Georges Bank during 22–26 May 1999. The experiment was made using the unstructured‐grid Finite‐Volume Coastal Ocean Model (FVCOM) with varying horizontal resolution. The results indicate that the observed cross‐isobath movement of the dye patch was primarily controlled by meso‐scale temporal and spatial variability of the water temperature and salinity fields. Onset of vertical stratification tended to slow down an upward stretching of the dye column and trapped the dye within the bottom mixed layer. To reach a convergent numerical solution that reproduced the observed lateral turbulent dispersion of dye, the FVCOM grid required a horizontal resolution of ∼500 m in the dye study region. Within the tidal mixing front of Georges Bank, the movement of the center of the dye patch was mainly driven by the ensemble velocity integrated over the dye volume, with a first‐order contribution from vertical shear of the dye's horizontal velocity.
A study of the slope probability density function of the ocean waves from radar observations
Authors: Hauser D. , Caudal G. , Guimbard S. , Mouche A. A.
Published: February 2008

Radar observations of the sea surface at C‐Band and small incidence angles are used to investigate some properties of the surface slope probability density function (pdf). The method is based on the analysis of the variation of the radar cross‐section with incidence angle, assuming a backscattering process following the Geometrical Optics theory. First, we assess the limit of this model in our experimental configuration by using simulations of radar cross‐sections with a more accurate backscattering model, namely the Physical Optics model. We show that roughness properties with scales larger than 12 cm can be analyzed in our configuration (C‐Band, incidence 7 to 16°). The radar data are then analyzed in terms of filtered mean square slope under the assumption of a Gaussian slope pdf. Dependence of the radar‐derived mean square slopes (mss) with wind speed is analyzed, thanks to wind estimates obtained by using coincident observations of the same radar at larger incidence (around 32°). Furthermore an analysis of the anisotropy of the mean square slope is proposed. The results are discussed in comparison with those of Cox and Munk (1954a, 1954b), and with the mean square slopes derived from two surface models (Elfouhaily et al., 1997 and Kudryavtsev et al., 2003). We find that the radar‐derived values are in good agreement with Cox and Munk results, taking into account the filtering effect on radar‐derived values. We also show that the surface model of Elfouhaily et al. yields good agreement for the omni directional mss, but a too large anisotropy of the mss. The model of Kudryavtsev provides a reasonable anisotropy of the mss, but overestimates the mss values in all directions. Finally, we propose an analysis of the radar data under a non‐Gaussian assumption for the slope pdf, by applying the compound model suggested by Chapron et al. (2000) to our observations. To our knowledge, it is the first time that peakedness values are explicitly derived from radar observations, and documented as a function of azimuth and wind speed. We show that the peakedness (or kurtosis) of the slope pdf is not zero but weak (peakedness factor reaching about 0.20), and slightly increases with wind speed.
Secondary acidification: Changes in gas‐aerosol partitioning of semivolatile nitric acid and enhancement of its deposition due to increased emission and concentration of SOx
Authors: Kajino Mizuo , Ueda Hiromasa , Nakayama Shinji
Published: February 2008

Secondary acidification, or the indirect enhancement of semivolatile air pollutant deposition associated with increased SO42− concentrations, is shown to occur in general air pollution using data collected from six stations of the Acid Deposition Monitoring Network in East Asia (EANET) in Japan. This effect was first detected as a result of volcanic SO2 plumes in our previous studies. Results indicate that as SO42− concentration increases, gas‐aerosol partitioning of nitric acid shifts to the gas phase, increasing the HNO3 gas concentration. Since the dry and wet deposition rates of HNO3 gas are very high, deposition can be enhanced even when the emission of NOx remains unchanged. In western Japan, the indirect effect for wet deposition is most apparent from spring to autumn, when the Asian continental outflow carries sulfate‐rich contaminated air masses. However, it is not pronounced in air masses containing abundant sea‐salt particles and related cation components in aerosols. In areas such as forests or farmlands with low surface resistance, dry deposition of nitric acid is more pronounced than wet deposition as the dry deposition velocity of HNO3 gas is high. Increased dry deposition of t‐NO3 due to the indirect effect and consequent vegetation damage is thus of considerable concern in such regions. The deposition of other semivolatile components, such as hydrochloric acid and ammonia, can be altered and can also induce secondary acidification.
The nucleolar SUMO‐specific protease SENP3 reverses SUMO modification of nucleophosmin and is required for rRNA processing
Authors: Haindl Markus , Harasim Thomas , Eick Dirk , Muller Stefan
Published: February 2008

The ubiquitin‐like SUMO system functions by a cyclic process of modification and demodification, and recent data suggest that the nucleolus is a site of sumoylation–desumoylation cycles. For example, the tumour suppressor ARF stimulates sumoylation of nucleolar proteins. Here, we show that the nucleolar SUMO‐specific protease SENP3 is associated with nucleophosmin (NPM1), a crucial factor in ribosome biogenesis. SENP3 catalyses desumoylation of NPM1–SUMO2 conjugates in vitro and counteracts ARF‐induced modification of NPM1 by SUMO2 in vivo. Intriguingly, depletion of SENP3 by short interfering RNA interferes with nucleolar ribosomal RNA processing and inhibits the conversion of the 32S rRNA species to the 28S form, thus phenocopying the processing defect observed on depletion of NPM1. Moreover, mimicking constitutive modification of NPM1 by SUMO2 interferes with 28S rRNA maturation. These results define SENP3 as an essential factor for ribosome biogenesis and suggest that deconjugation of SUMO2 from NPM1 by SENP3 is critically involved in 28S rRNA maturation.
Small-angle neutron scattering from giant water-in-oil microemulsion droplets. I. Ternary system
Authors: Foster Tobias , Sottmann Thomas , Schweins Ralf , Strey Reinhard
Published: February 2008

To investigate the kinetics of biochemical transformations in confined environments, compartments with a radius of the order of 10–50nm are needed. Giant water-in-oil microemulsions provide such nanoscale reaction compartments and allow furthermore to control the degree of compartmentalization by an external tuning parameter such as temperature. With this motivation we investigated the phase behavior and the microstructure of oil-rich microemulsions. In this approach we focused on oil-rich microemulsions of the ternary system D2O-cyclohexane(d12)-C12E6. Measurements of the phase behavior revealed that up to 20wt% of water can be solubilized by less than 3wt% of surfactant. Small-angle neutron scattering experiments were performed to determine the length scales and microstructure topologies of the oil-rich microemulsions. To analyze the scattering data, we derived the form factor for polydisperse spherical Gaussian shells with a scattering contribution of the droplet core. The quantitative analysis of the scattering data with this form factor shows that the radius of the largest droplets amounts up to 36nm.
BETSI, a new test bench for ion sources optimization at CEA SACLAY
Authors: Tuske O. , Adroit G. , Delferrière O. , De Menezes D. , Gauthier Y. , Gobin R. , Harrault F.
Published: February 2008

In the framework of several International HPPA projects (such as IFMIF, IPHI, and Spiral2) the CEA handles the design and the developments of several electron cyclotron resonance (ECR) ion sources. For the IFMIF EVEDA demonstrator, a 140mA cw extracted deuteron beam will be required for high yield of neutron production. For radioactive ion production in the Spiral2 project, several milliamperes of deuterons will be delivered with a permanent magnet source. The optimization of the beam quality at the entrance of the radio frequency quadropole (RFQ) accelerator system triggered the need of a new test bench for ion source optimization and beam qualification. The BETSI ion source test bench will operate up to 50kV and ignite cw or pulsed hydrogen plasma with a 2.45GHz magnetron. Great care has already been taken to design electrostatic optics of the extraction system to minimize the emittance growth. Plasma diagnostics will be inserted in the source chamber and several beam diagnostics (emittance and current measurements, beam species analysis) will also be implemented on the low energy beam line transport (LEBT). These diagnostics allow the simultaneous analysis of the beam quality with the plasma parameters of the source. Regional funding request will also be needed to improve the LEBT for space charge compensation measurements. The design of the present and upgraded test bench will be reported as well as the first extracted beam analysis.
Uniform H− ion beam extraction in a large negative ion source with a tent-shaped magnetic filter
Authors: Tobari H. , Hanada M. , Kashiwagi M. , Taniguchi M. , Umeda N. , Watanabe K. , Inoue T. , Sakamoto K. , Takado N.
Published: February 2008

Based on previous studies on the spatial uniformity of the negative ion beam, the external magnetic filter was replaced to a novel tent-shaped magnetic filter in the JAEA 10A negative ion source. The line-cusp field configuration on the source chamber was also changed to form a symmetric magnetic field like many of positive ion sources aiming at high proton yield. This magnetic field configuration allows fast electrons emitted from filament cathodes to rotate azimuthally inside the source chamber. The source configuration thus prevents localization of fast electrons due to their B×gradB drift in the filter field. As a result, the H− ion beam profile extracted from a wide region of 340×170mm2 showed reduction of standard deviation from 16% in the original to 7.9% with the tent filter. The negative ion source with the tent filter satisfied the requirement of the beam uniformity for a large negative ion source in the ITER neutral beam injection.
Spectroscopic observations of beam and source plasma light and testing Cs-deposition monitor in the large area negative ion source for LHD-NBI
Authors: Oka Y. , Tsumori K. , Ikeda K. , Kaneko O. , Nagaoka K. , Osakabe M. , Takeiri Y. , Asano E. , Komada S. , Kondo T. , Sato M. , Shibuya M. , Grisham L. R. , Ikeda Y. , Hanada M. , Umeda N.
Published: February 2008

In the large area negative ion source for the LHD negative-ion-(H−)-based neutral beam system, (I) we used the spectrometer to measure caesium lines in the source plasma during beam shots. (II) With Doppler-shifted measurements, the Hα line at three different locations along the beam as well as the spectrum profile for cases of different plasma grid areas. (III) Caesium deposition monitor with a high speed shutter was tested to measure the weight of the deposited Cs layer. In the observation, cleaner spectra of Doppler-shifted Hα line with only a small level of background light were obtained at a new observation port which viewed the blueshifted light in the drift region after the accelerator of a LHD ion source. Both the amounts of CsI (852nm, neutral Cs0) and CsII (522nm, Cs+) in the source plasma light rose sharply when beam acceleration began, and continued rising during a 10s pulse. It was thought that this was because the cesium was evaporated/sputtered from the source back plate by the back-streaming positive ions. Cs deposition rate to the crystal sensor measured by adjusting the shutter open time was evaluated to be 2.9nanograms∕scm2 for preliminary testing. More neutral Cs tended to be evolved in the source after arc discharge. Much Cs could be consumed in a high rate-pulsed operation (such as LHD source).
Long pulse production of high current D− ion beams in the JT-60 negative ion source
Authors: Hanada M. , Kamada M. , Akino N. , Ebisawa N. , Honda A. , Kawai M. , Kazawa M. , Kikuchi K. , Komata M. , Mogaki K. , Noto K. , Ohshima K. , Takenouchi T. , Tanai Y. , Usui K. , Yamazaki H. , Ikeda Y. , Grisham L. R.
Published: February 2008

The first long pulse production of high power D− ion beams has been demonstrated in the JT-60 U negative ion sources, each of which was designed to produce 22A, 500keV D− ion beams. Voltage holding capability and the grid power loading were examined for long pulse production of high power D− ion beams. From the correlation between voltage holding and the light intensity of cathodoluminescence from the Fiber Reinforced Plastic insulators, the acceleration voltage for stable voltage holding capability was found to be less than 320–340kV where the light was sufficiently suppressed. By tuning the extraction voltage, the grid power loadings in the ion sources were decreased to the allowable levels for long pulse injection without a significant reduction of the beam power. After tuning the acceleration and extraction voltages, D− ion beams of 12.5 and 9.8A were produced at 340keV with cesium seeding at a rate of ∼14μg∕s into the ion sources. The pulse duration of these D− ion beams was extended step by step, and then was successfully extended up to 18s without degradation of the negative ion production. The D− ion beams were neutralized to yield 3.6MW D0 beams by a gas cell, and then injected into the JT-60 U plasma. Further, a slight reduction of D− ion beam power allowed the longer injection duration of 21s at a D0 beam power of 3.2MW. The success in the long pulse production of a high power D− ion beam shows that negative ion beams can be produced during a few tens of seconds without degradations of negative ion production and the voltage holding in a large Cs-seeded negative ion source.
Development of an 18GHz superconducting electron cyclotron resonance ion source at RCNP
Authors: Yorita Tetsuhiko , Hatanaka Kichiji , Fukuda Mitsuhiro , Kibayashi Mitsuru , Morinobu Shunpei , Okamura Hiroyuki , Tamii Atsushi
Published: February 2008

An 18GHz superconducting electron cyclotron resonance ion source has recently been developed and installed in order to extend the variety and the intensity of ions at the RCNP coupled cyclotron facility. Production of several ions such as O, N, Ar, Kr, etc., is now under development and some of them have already been used for user experiments. For example, highly charged heavy ion beams like Kr21+,23+86 and intense O5+,6+16 and N6+15 ion beams have been provided for experiments. The metal ion from volatile compounds method for boron ions has been developed as well.
Prospects of nanorods as an emulsifying agent of immiscible blends
Authors: Hore Michael J. A. , Laradji Mohamed
Published: February 2008

Immiscible binary fluids containing rigid nanorods that are preferentially immersed in one of the two fluids are systematically investigated via dissipative particle dynamics simulations. For sufficiently high volume fraction and/or aspect ratio, nanorods lead to a pronounced slowing down of the phase separation process, and yield microphase-separated structures with a characteristic length scale that decreases as either the nanorods length or their volume fraction is increased. The slowing down of the dynamics is attributed to a disordered jamming of the nanorods in the preferred component and a dramatic reduction in their diffusion due to kinetic conformational hindrance. The final characteristic length scale of the dispersion, reduced by the nanorods length, is found to depend only on Onsager’s dimensionless parameter ψν, where ψ and ν are the nanorods volume fraction and aspect ratio, respectively. These results indicate that nanorods may be used as an effective emulsifying agent of binary polymer blends.
A Monte Carlo algorithm to study polymer translocation through nanopores. I. Theory and numerical approach
Authors: Gauthier Michel G. , Slater Gary W.
Published: February 2008

The process during which a polymer translocates through a nanopore depends on many physical parameters and fundamental mechanisms. We propose a new one-dimensional lattice Monte Carlo algorithm that integrates various effects such as the entropic forces acting on the subchains that are outside the channel, the external forces that are pulling the polymer through the pore, and the frictional effects that involve the chain and its environment. Our novel approach allows us to study the polymer as a single Brownian particle diffusing while subjected to a position-dependent force that includes both the external driving forces and the internal entropic bias. Frictional effects outside and inside the pore are also considered. This Monte Carlo method is much more efficient than other simulation methods, and it can be used to obtain scaling laws for various polymer translocation regimes. In this first part, we derive the model and describe a subtle numerical approach that gives exact results for both the escape probability and the mean translocation time (and higher moments of its distribution). The scaling laws obtained from this model will be presented and discussed in the second part of this series.
Fragmentation channels of K-shell excited rare-gas clusters studied by multiple-ion coincidence momentum imaging
Authors: Murakami H. , Iwayama H. , Nagaya K. , Yao M.
Published: February 2008

Multiple-ion coincidence momentum imaging experiments were carried out for K-shell (1s) excited Ar clusters containing about 130 atoms and Kr clusters containing about 30, 90, and 160 atoms. The time-of-flight spectra reveal that the major products of the Coulomb explosion are singly charged ions. With increasing the number of charges generated in clusters, the momentum of monomer ions such as Ar+ and Kr+ increases, while that of cluster ions such as Ar3+, Kr2+, and Kr3+ decreases. This observation indicates the site-specific decay process that the heavier ions appear in the central part of clusters. We have also investigated the momentum distribution in various fragmentation channels and the branching ratio of each channel at the Coulomb explosion. When the number Ncoin of coincidently detected ions is four, for example, the most frequent channel from Kr clusters containing 30 atoms is to emit simply four Kr+ ions, but Kr2+ ions participate in the fragmentation from the larger Kr clusters. The fragmentation channel in which two Ar2+ ions are emitted becomes dominant with increasing Ncoin, and the average momentum of Ar2+ ion in this channel is larger than that in the channels where only single Ar2+ is emitted.
C 13 – C 13 and N15–C13 correlation spectroscopy of membrane-associated and uniformly labeled human immunodeficiency virus and influenza fusion peptides: Amino acid-type assignments and evidence for multiple conformations
Authors: Bodner Michele L. , Gabrys Charles M. , Struppe Jochem O. , Weliky David P.
Published: February 2008

Many viruses which cause disease including human immunodeficiency virus (HIV) and influenza are “enveloped” by a membrane and infection of a host cell begins with joining or “fusion” of the viral and target cell membranes. Fusion is catalyzed by viral proteins in the viral membrane. For HIV and for the influenza virus, these fusion proteins contain an ∼20-residue apolar “fusion peptide” that binds to target cell membranes and plays a critical role in fusion. For this study, the HIV fusion peptide (HFP) and influenza virus fusion peptide (IFP) were chemically synthesized with uniform C13, N15 labeling over large contiguous regions of amino acids. Two-dimensional C13–C13 and N15–C13 spectra were obtained for the membrane-bound fusion peptides and an amino acid-type C13 assignment was obtained for the labeled residues in HFP and IFP. The membrane used for the HFP sample had a lipid headgroup and cholesterol composition comparable to that of host cells of the virus, and the C13 chemical shifts were more consistent with β strand conformation than with helical conformation. The membrane used for the IFP sample did not contain cholesterol, and the chemical shifts of the dominant peaks were more consistent with helical conformation than with β strand conformation. There were additional peaks in the IFP spectrum whose shifts were not consistent with helical conformation. An unambiguous C13 and N15 assignment was obtained in an HFP sample with more selective labeling, and two shifts were identified for the Leu-9 CO, Gly-10 N, and Gly-10 Cα nuclei. These sets of two shifts may indicate two β strand registries such as parallel and antiparallel. Although most spectra were obtained on a 9.4T instrument, one C13–C13 correlation spectrum was obtained on a 16.4T instrument and was better resolved than the comparable 9.4T spectrum. More selective labeling and higher field may, therefore, be approaches to obtaining unambiguous assignments for membrane-associated fusion peptides.
Waterlike hierarchy of anomalies in a continuous spherical shouldered potential
Authors: de Oliveira Alan Barros , Franzese Giancarlo , Netz Paulo A. , Barbosa Marcia C.
Published: February 2008

We investigate by molecular dynamics simulations a continuous isotropic core-softened potential with attractive well in three dimensions, introduced by Franzese [J. Mol. Liq. 136, 267 (2007)], that displays liquid-liquid coexistence with a critical point and waterlike density anomaly. Besides the thermodynamic anomalies, here we find diffusion and structural anomalies. The anomalies, not observed in the discrete version of this model, occur with the same hierarchy that characterizes water. We discuss the differences in the anomalous behavior of the continuous and the discrete model in the framework of the excess entropy, calculated within the pair correlation approximation.
On geometric discretization of elasticity
Authors: Yavari Arash
Published: February 2008

This paper presents a geometric discretization of elasticity when the ambient space is Euclidean. This theory is built on ideas from algebraic topology, exterior calculus, and the recent developments of discrete exterior calculus. We first review some geometric ideas in continuum mechanics and show how constitutive equations of linearized elasticity, similar to those of electromagnetism, can be written in terms of a material Hodge star operator. In the discrete theory presented in this paper, instead of referring to continuum quantities, we postulate the existence of some discrete scalar-valued and vector-valued primal and dual differential forms on a discretized solid, which is assumed to be a triangulated domain. We find the discrete governing equations by requiring energy balance invariance under time-dependent rigid translations and rotations of the ambient space. There are several subtle differences between the discrete and continuous theories. For example, power of tractions in the discrete theory is written on a layer of cells with a nonzero volume. We obtain the compatibility equations of this discrete theory using tools from algebraic topology. We study a discrete Cosserat medium and obtain its governing equations. Finally, we study the geometric structure of linearized elasticity and write its governing equations in a matrix form. We show that, in addition to constitutive equations, balance of angular momentum is also metric dependent; all the other governing equations are topological.
Energy relaxation of the amide-I mode in hydrogen-bonded peptide units: A route to conformational change
Authors: Pouthier Vincent
Published: February 2008

A one-site Davydov model involving a CO group engaged in a hydrogen bond is used to study the amide-I relaxation due to Fermi resonances with a bath of intramolecular normal modes. In the amide-I ground state, the hydrogen bond behaves as a harmonic oscillator whose eigenstates are phonon number states. By contrast, in the amide-I first excited state, the hydrogen bond experiences a linear distortion so that the eigenstates are superimpositions of number states. By assuming the hydrogen bond in thermal equilibrium at biological temperature, it is shown that the amide-I excitation favors the population of these excited states and the occurrence of coherences. Due to the interaction with the bath, the vibron decays according to an exponential or a biexponential law depending on whether the Fermi resonance is wide or narrow. Therefore, each excited state relaxes over a set of number states according to specific pathways. The consequence is twofold. First, the relaxation leads to a redistribution of the number state population which differs from the initial Boltzmann distribution. Then, it allows for coherence transfers so that, although the vibron has disappeared, the hydrogen keeps the memory of its initial distortion and it develops free oscillations.
Post-heat-treated spin-spray plated MnxZnyFe3−x−yO4 films exhibiting high resistivity and noise suppressing properties
Authors: Subramani A. K. , Matsushita N. , Watanabe T. , Kondo K. , Tada M. , Abe M. , Yoshimura M.
Published: February 2008

Mn x Zn y Fe 3 − x − y O 4 films with a tailored microstructure were prepared by the spin-spray technique. The films were then heat treated (260°C for 3min) in a similar way to that of the reflow soldering process. The as-prepared and heat-treated films were studied for their structural, electrical, and magnetic properties. By using an oxidizing solution of CH3COONa+(NH4)2CO3+NaOH+NaNO2 (in contrast to that of CH3COONa+NaNO2 in the conventional spin spray), Mn concentration (CMn) in the film was increased and a narrow columnar structure was obtained. This structure resulted in an increased surface resistivity (ρs), thereby good noise suppressing properties even after the heat treatment. The films exhibited a high deposition rate of up to 63nm∕min with a good adhesion to the substrate. A slight decrease in the saturation magnetization (Ms) and increase in the uniaxial anisotropy field (Hk), and coercivity (Hc) were observed due to the heat treatment. The films also exhibited a decrease in imaginary permeability in the lower frequencies and the resonance frequency (fr) shifted to a higher frequency range. The film characteristics were as follows: Ms of 450–570emu∕cm3, Hc of 18–45Oe, Hk of 43–86Oe, ρs of 103–107Ω∕sq, initial permeability μ′ of 25–60, imaginary permeability μ″ of 20–38, and resonance frequency fr of 530–750MHz. The films prepared at optimum condition exhibited reflection loss (S11) less than −10dB and the transmission loss (ΔPloss) of up to 50% at 10GHz. ΔPloss exhibited uniform distribution up to 1GHz even after the heat treatment.
Design aspects of a high-speed sensorless brushless dc motor using third harmonic back-emf for sensorless control
Authors: Wang Kai , Shen Jianxin , Zhou Fengzheng , Fei Weizhong
Published: February 2008

There is increasing interest in high-speed permanent magnet (PM) brushless dc motors for a wide range of applications. Back-emf is often utilized for sensorless operation of permanent magnet brushless dc motors, by detecting the emf zero crossings. However, in high-speed motors, the free-wheeling diode conduction can last more than 30edeg. This can obscure the zero crossings of the phase EMF; therefore, it is preferable to utilize the third harmonic emf instead of the phase emf. In this paper, some design aspects related to this high-speed sensorless operation are presented, including a special nonoverlapping winding arrangement and magnet segmenting technique. Finally, the experimental results confirmed the validity of the proposed design method.
Effects of geometries on permeability spectra of CoTaZr magnetic cores for high frequency applications
Authors: Lee D. W. , Wang S. X.
Published: February 2008

The permeability of the magnetic core is closely related to the inductance improvement for integrated inductors. Simulation data indicate that the effective permeability of the finite-sized magnetic core can be significantly reduced from the relative permeability of the magnetic material due to the demagnetization effect. The observed trend in the permeability of the patterned CoTaZr magnetic cores, however, shows that the demagnetization effect alone is not sufficient to predict the effective permeability and that the magnetic domain patterns need to be considered as well. The measured permeability was found to decrease as the patterned magnetic core was narrowed or shortened.
Determining vortex chirality in ferromagnetic ring by lateral nonlocal spin valve
Authors: Chen D. C. , Yao Y. D. , Wu J. K. , Yu C. , Lee S. F.
Published: February 2008

We demonstrate detecting chirality of vortex state in a magnetic ring by lateral nonlocal spin-valve (NLSV) measurement. A Permalloy (Py) ring, a Py narrow wire, and copper contacts were used as spin injector, detector, and the normal-metal diffusive channel, respectively. By comparing the anisotropic magnetoresistance loop of the individual ring with NLSV loop, the vortex chirality and the related switching field of the ring can be determined. Both onion-to-vortex transition field and vortex chirality were found to alternate in both the same and different current probe arrangements on the magnetic ring.
Detection of DNA labeled with magnetic nanoparticles using MgO-based magnetic tunnel junction sensors
Authors: Shen Weifeng , Schrag Benaiah D. , Carter Matthew J. , Xie Jin , Xu Chenjie , Sun Shouheng , Xiao Gang
Published: February 2008

We have demonstrated the detection of 2.5μM target DNA labeled with 16nm Fe3O4 nanoparticles (NPs) and 50nm commercial MACS™ NPs using arrays of magnetic tunnel junction sensors with (001)-oriented MgO barrier layers. Signal-to-noise ratios of 25 and 12 were obtained with Fe3O4 and MACS™ NPs, respectively. These data show conclusively that MgO-based MTJ sensor arrays are very promising candidates for future applications involving the accurate detection and identification of biomolecules tagged with magnetic nanoparticles.
Multidimensional solid state NMR of anisotropic interactions in peptides and proteins
Authors: Wylie Benjamin J. , Rienstra Chad M.
Published: February 2008

Accurate determinations of chemical shift anisotropy (CSA) tensors are valuable for NMR of biological systems. In this review we describe recent developments in CSA measurement techniques and applications, particularly in the context of peptides and proteins. These techniques include goniometeric measurements of single crystals, slow magic-angle spinning studies of powder samples, and CSA recoupling under moderate to fast MAS. Experimental CSA data can be analyzed by comparison with ab initio calculations for structure determination and refinement. This approach has particularly high potential for aliphatic C13 analysis, especially Cα tensors which are directly related to structure. Carbonyl and N15 CSA tensors demonstrate a more complex dependence upon hydrogen bonding and electrostatics, in addition to conformational dependence. The improved understanding of these tensors and the ability to measure them quantitatively provide additional opportunities for structure determination, as well as insights into dynamics.
Nanodipole photovoltaics
Authors: Shvydka Diana , Karpov V. G.
Published: February 2008

We propose a principle of photovoltaics utilizing the built-in electric field generated by aligned nanosize dipoles in a semiconductive host, either polymer or liquid, or amorphous, or polycrystalline. Such dipoles are readily found with the wurtzite CdS, CdSe, and some other nanoparticles. We show that their generated field can be uniform and strong enough, ∼3×104V∕cm, to separate electron-hole pairs and run significant drift currents. Our suggested structure does not rely on p-n or Schottky junctions and can be tunable in a broad range of parameters.
Incremental analysis of the magnetization behavior in iron-filled carbon nanotube arrays
Authors: Müller C. , Elefant D. , Leonhardt A. , Büchner B.
Published: February 2008

We show an efficient way to investigate the magnetic behavior of nanotube stubs based on the embedding of aligned iron-filled carbon nanotubes in silicon oxide using thermal chemical vapor deposition and gradual mechanical polishing afterwards. On the one hand, during the covering process the saturation magnetization moment rises due to the transformation of Fe3C into body-centered-cubic-Fe and graphite. On the other hand, the coercivity drops, mainly induced by changes in the shape of the nanowires. Further magnetization measurements of the embedded sample point to most of the ferromagnetic nanowires being located near the surface of the substrate. The coercivity increases when reducing the thickness of the nanotube array. The anomalous high coercivity of the Fe nanowires encapsulated by non magnetic carbon nanotubes make them suitable for high density data storage applications.
Asymptotic theory of wall-attached convection in a horizontal fluid layer with a vertical magnetic field
Authors: Busse F. H.
Published: February 2008

A horizontal fluid layer heated from below in the presence of a vertical magnetic field is considered. A simple asymptotic analysis is presented which demonstrates that a convection mode attached to the side walls of the layer sets in at Rayleigh numbers much below those required for the onset of convection in the bulk of the layer. The analysis complements an earlier analysis by Houchens et al. [J. Fluid Mech. 469, 189 (2002)] which derived expressions for the critical Rayleigh number for the onset of convection in a vertical cylinder with an axial magnetic field in the cases of two aspect ratios.
Time-of-arrival probabilities and quantum measurements. II. Application to tunneling times
Authors: Anastopoulos Charis , Savvidou Ntina
Published: February 2008

We formulate quantum tunneling as a time-of-arrival problem: we determine the detection probability for particles passing through a barrier at a detector located a distance L from the tunneling region. For this purpose, we use a positive-operator-valued measure (POVM) for the time of arrival determined in C. Anastopoulos and N. Savvidou, J. Math. Phys. 47, 122106 (2006). This only depends on the initial state, the Hamiltonian, and the location of the detector. The POVM above provides a well-defined probability density and an unambiguous interpretation of all quantities involved. We demonstrate that for a class of localized initial states, the detection probability allows for an identification of tunneling time with the classic phase time. We also establish limits to the definability of tunneling time. We then generalize these results to a sequential measurement setup: the phase-space properties of the particles are determined by an unsharp sampling before their attempt to cross the barrier. For such measurements the tunneling time is defined as a genuine observable. This allows us to construct a probability distribution for its values that is definable for all initial states and potentials. We also identify a regime in which these probabilities correspond to a tunneling-time operator.
Magnetic domains and magnetization process of amorphous granular (CoFeB)–SiO2 thin films
Authors: Takezawa M. , Shiota A. , Morimoto Y. , Yamasaki J. , Munakata M. , Yagi M.
Published: February 2008

The domain structure and magnetization process of a granular film were explored using a Kerr microscope. Narrow line-shaped reversal domains were observed in a granular (Co25Fe66B9)75–(SiO2)25 film, and no increase in the width of the domains was observed during the magnetization reversal process by applying a dc field along the easy axis. In addition, no wall displacement was observed in an ac field along the hard axis because only magnetization rotation occurs due to wall pinning. It was found that wall motion that causes excess eddy current losses at high frequencies is hard to occur by the granular structure.
Reducing the color shift of a multidomain vertical alignment liquid crystal display using dual threshold voltages
Authors: Lu Ruibo , Wu Shin-Tson , Lee Seung Hee
Published: February 2008

A multidomain vertical alignment liquid crystal display (MVA LCD) with reduced color shift is proposed. Each pixel is divided into a main region and a subregion. A thin electric shielding layer is embedded in the subregion to generate a higher threshold voltage than that of the main region. As a result, the final gamma curve is a superposition of two different-shaped gamma curves. Such a MVA LCD exhibits a reduced color shift while only requires a single thin-film transistor. Its potential application for LCD TVs is emphasized.
Carrier distribution in (0001)InGaN∕GaN multiple quantum well light-emitting diodes
Authors: David Aurélien , Grundmann Michael J. , Kaeding John F. , Gardner Nathan F. , Mihopoulos Theodoros G. , Krames Michael R.
Published: February 2008

We study the carrier distribution in multi quantum well (multi-QW) InGaN light-emitting diodes. Conventional wisdom would assume that a large number of QWs lead to a smaller carrier density per QW, enabling efficient carrier recombination at high currents. We use angle-resolved far-field measurements to determine the location of spontaneous emission in a series of multi-QW samples. They reveal that, no matter how many QWs are grown, only the QW nearest the p layer emits light under electrical pumping, which can limit the performances of high-power devices.
Correlation of In–Ga intermixing with band-tail states in InAs∕GaAs quantum dots
Authors: Chung Hung-Chin , Lai Yi-Feng , Liu Chuan-Pu , Lai Yen-Lin , Fang Yu-Ching , Hsu Li
Published: February 2008

We have investigated the shape and composition profiles of buried and surface InAs∕GaAs Stranski–Krastanov quantum dots (QDs) by using the spectrum-imaging (SI) method with energy-filtered transmission electron microscopy (EFTEM). Indium maps from EFTEM SI reveal lens and truncated pyramid shapes for the surface and buried QDs, with an increase in composition variations for the buried QDs. Photoluminescence measurements reveal an emission at 1.075eV, associated with confined states in the buried QDs, along with a high energy shoulder, associated with band-tail states due to In–Ga intermixing in the vicinity of the buried QDs.
Improved performance of polymer/TiO2 nanorod bulk heterojunction photovoltaic devices by interface modification
Authors: Lin Yun-Yue , Chu Tsung-Hung , Chen Chun-Wei , Su Wei-Fang
Published: February 2008

In this article, the polymer photovoltaic devices based on the poly(3-hexylthiophene)/TiO2 nanorods hybrid material is present. An enhancement in the device performance can be achieved by removing or replacing the insulating surfactant on the TiO2 nanorod surface with a more conductive ligand, which can play the role to assist charge separation efficiency or also to prevent from back recombination, giving a large improvement in the short circuit current and fill factor. The relatively high power conversion efficiency of 1.7% under simulated AM 1.5 illumination (100mW∕cm2) can be achieved, providing a route for fabricating low-cost, environmentally friendly polymer photovoltaic devices by all-solution processes.
193
nm
deep-ultraviolet solar-blind cubic boron nitride based photodetectors
Authors: Soltani A. , Barkad H. A. , Mattalah M. , Benbakhti B. , De Jaeger J.-C. , Chong Y. M. , Zou Y. S. , Zhang W. J. , Lee S. T. , BenMoussa A. , Giordanengo B. , Hochedez J.-F.
Published: February 2008

Deep-ultraviolet (DUV) solar-blind photodetectors based on high-quality cubic boron nitride (cBN) films with a metal/semiconductor/metal configuration were fabricated. The design of interdigitated circular electrodes enables high homogeneity of electric field between pads. The DUV photodetectors present a peak responsivity at 180nm with a very sharp cutoff wavelength at 193nm and a visible rejection ratio (180 versus 250nm) of more than four orders of magnitude. The characteristics of the photodetectors present extremely low dark current, high breakdown voltage, and high responsivity, suggesting that cBN films are very promising for DUV sensing.
Hugoniot measurement of gold at high pressures of up to 580GPa
Authors: Yokoo Manabu , Kawai Nobuaki , Nakamura Kazutaka G. , Kondo Ken-ichi
Published: February 2008

Hugoniot for Au was measured over a pressure range from 190to580GPa using a two-stage light-gas gun. The accuracy for impactor velocity was 0.2% and that for shock velocity ranged from 1.0% to 2.3%. Symmetric-impact experiments were performed to obtain shock compression data that are independent of those of other materials. The relationship between the shock and the particle velocity shows that our data for shock velocity deviate upward from the previously established relationship by up to 2.7% at up=3.5km∕s. Moreover, we also report data obtained by impedance matching using Ta and Cu.
Influence of gas pressure in the voids during charging on the piezoelectricity of ferroelectrets
Authors: Qiu Xunlin , Mellinger Axel , Gerhard Reimund
Published: February 2008

Cellular polypropylene ferroelectrets were subjected to vacuum and high air pressures. The capacitance of the samples was measured as a way to monitor their thickness. It was found that both in vacuum and in high-pressure air, the thickness of the samples recovers to its original value after a sufficient storage time (typically, several hours), indicating that the internal and external pressures equalize as a result of gas diffusion. Optimal piezoelectricity is achieved by charging at a pressure of 170kPa, which is explained by means of the void-height distribution function in combination with Townsend’s model of the Paschen breakdown.
Ferroelectric properties of Bi4−xCexTi3O12 (<x<4) thin film array fabricated from Bi2O3∕CeO2∕TiO2 multilayers using multitarget sputtering
Authors: Kim Ki Woong , Kim Tai Suk , Jeon Min Ku , Oh Kwang Seok , Jung Chang Hwa , Woo Seong Ihl
Published: February 2008

We fabricated a ferroelectric Bi4−xCexTi3O12 thin film library by solid-state mixing of Bi2O3∕CeO2∕TiO2 multilayers using a multitarget rf magnetron sputtering equipped with an automated shutter. Polarization-electrical field and the structure are mapped as a function of Ce content (x) from 0 to 4. The remnant polarization decreases as Ce content increases, and at x⩾0.8, Bi4−xCexTi3O12 samples exhibit a paraelectric property due to the formation of impurity phases such as Bi2Ti2O7 and CeO2. Among the thin film samples of the library, Bi3.85Ce0.15Ti3O12 exhibited the largest remnant polarization of 13.0μC∕cm2.
Conformal oxide coating of carbon nanotubes
Authors: Kawasaki S. , Catalan G. , Fan H. J. , Saad M. M. , Gregg J. M. , Correa-Duarte M. A. , Rybczynski J. , Morrison F. D. , Tatsuta T. , Tsuji O. , Scott J. F.
Published: February 2008

The International Roadmap for Ferroelectric Memories requires three-dimensional integration of high-dielectric materials onto metal interconnects or bottom electrodes by 2010. Here, we demonstrate the possibility of conformally coating carbon nanotubes with high-dielectric oxide as a first step toward ultrahigh integration density of three-dimensional ferroelectric random access memories.
Formation and role of cool flames in plasma-assisted premixed combustion
Authors: Kim W. , Mungal M. G. , Cappelli M. A.
Published: February 2008

The structure of a plasma-assisted laminar premixed flame is studied numerically. The initial radical yield generated by a nonequilibrium discharge serves as the boundary condition for a one-dimensional flame code predicting the formation of a cool flame which pilots the premixed methane/air combustion. The ignition of the surrounding unactivated methane-air mixture by this cool flame is modeled as an opposed diffusion flame. Our findings indicate that the nonequilibrium discharge is an in situ reformer of the fuel for the production of the cool flame, producing primarily H2 and CO, thus, facilitating the burning of the lean methane-air mixture.