bluuebunny/crossref_metadata_2025 huggingface dataset:
Timescale for the formation of the cold‐dense plasma sheet: A case study
Authors: Wing Simon , Johnson Jay R. , Fujimoto Masaki
Published: December 2006

The timescale for the formation of cold‐dense plasma sheet ions was investigated with an event in which the interplanetary magnetic field (IMF) was northward for almost one day. The plasma sheet dawn and dusk flanks appear to reach cold dense states (n > 1 cm−3; T < 2 keV) within a few hours after IMF northward turning. Closer to the center (midnight meridian), the ion temperatures reach < 2 keV within a few hours of IMF northward turning, but the ion densities do not reach above 1 cm−3 for at least ∼8 hours after IMF northward turning. The connection between solar wind ions and plasma sheet cold‐component ions is demonstrated. The plasma sheet dawn flank ions appear to lag the solar wind ions by about 3 hours. This study confirms the previous statistical results: (a) the densification of the plasma sheet can be attributed to the influx of the cold‐component (magnetosheath/solar wind origin) ions; and (b) the cooling of the plasma sheet can be attributed not only to the influx of the solar wind ions, but also to the cooling of the hot components. Order of magnitude calculations of the plasma sheet filling rate from reconnection and diffusion suggest that both entry mechanisms could result in roughly comparable filling rates. Hence, the dawn‐dusk asymmetries would be key in distinguishing the roles of the various proposed entry mechanisms.
Downward transport of ozone‐rich air near Mt. Everest
Authors: Zhu Tong , Lin Weili , Song Yu , Cai Xuhui , Zou Han , Kang Ling , Zhou Libo , Akimoto Hajime
Published: December 2006

High ozone concentrations (70–80 ppb) were found from late afternoon to midnight at sites at ca. 5000 m above sea level (m.a.s.l.) on Mt. Everest. Observational data suggest that katabatic wind from Mt. Everest was “pumping down” ozone‐rich air from the upper troposphere. Numerical modelling demonstrates that cooling of glaciers and snow on the northern mountain slopes and heating of the valley surface play important roles in forming katabatic winds and accelerating vertical exchange between the upper atmosphere and surface air. These results suggest that the “pump‐down” mechanism at high mountains covered with snow/glaciers is an important process in terrestrial intercontinental transport of ozone and atmosphere–land exchanges of masses and energy.
Observed timescales of evapotranspiration response to soil moisture
Authors: Teuling A. J. , Seneviratne S. I. , Williams C. , Troch P. A.
Published: December 2006

The sensitivity of evapotranspiration (ET) to soil moisture storage plays an important role in the land‐atmosphere system. Yet little is known about its magnitude, or its dependence on vegetation, soil, and/or climate characteristics. Here we relate the sensitivity to the timescale of ET decay in absence of rainfall, and show that it can thus be derived from time series of ET alone. We analyze ET observations from 15 vegetated sites covering a range of climates conditions, yielding timescales of 15–35 days. Longer timescales (weaker ET sensitivity) are found in regions with seasonal droughts, or at sites with woody vegetation. We compare observed values with output of different land surface models (LSMs) from the Second Global Soil Wetness Project, revealing large inter‐model differences and significant differences with observations. Our methodology can lead to improved representation of soil moisture effects on ET in LSMs.
Coronal prominence structure and dynamics: A magnetic flux rope interpretation
Authors: Gibson S. E. , Fan Y.
Published: December 2006

The solar prominence is an example of a space physics phenomenon that can be modeled as a twisted magnetic flux tube or magnetic flux “rope.” In such models the prominence is one observable part of a larger magnetic structure capable of storing magnetic energy to drive eruptions. We show how a flux rope model explains a range of observations of prominences and associated structures such as cavities and soft X‐ray sigmoids and discuss in particular the observational and dynamic consequences of three‐dimensional reconnections in and around the evolving magnetic flux rope. We demonstrate that the flux rope model can describe the prominence's preeruption structure and dynamics, loss of equilibrium, and behavior during and after an eruption in which part of the flux rope is expelled from the corona.
Low‐temperature magnetic behavior of multidomain titanomagnetites: TM0, TM16, and TM35
Authors: Carter‐Stiglitz Brian , Moskowitz Bruce , Solheid Peter , Berquó Thelma S. , Jackson Michael , Kosterov Andrey
Published: December 2006

An unpredicted effect of the Verwey transition in magnetite is that a field‐cooled (FC) remanent magnetization can be less intense than a zero‐field cooled (ZFC) isothermal remanence. The effect, only documented in a handful of multidomain (MD) samples, is thought to be unique to MD material. Data for new MD samples all show an elevation of ZFC over FC remanences. Current theory suggests that the FC easy axis bias alone produces the effect. We measured hysteresis loops after three cooling pretreatments; the results are inconsistent with the aforementioned theory. They are, however, consistent with a previous hypothesis which cites the absence of transformational twins in FC samples as an important factor. Our initial low‐temperature domain observations in FC and ZFC magnetite further support this theory. We also present data for MD titanomagnetites (x = 0.16, 0.35). These samples also show elevated ZFC remanences below a critical temperature (Tcrit). The titanomagnetites' frequency dependence of susceptibility around Tcrit, the suppression of the amplitude dependence of susceptibility below Tcrit, and Mössbauer data suggest that the change in magnetic anisotropy at Tcrit is related to a suppression of B site electron hopping at low temperature, at least on the timescale of the magnetic measurements. Given our remanence data, field cooling must affect the orientation of the new low‐temperature magnetic easy axis. We appeal to the same process as we did for magnetite to explain the elevation of ZFC moments, noting that the exact nature of the transition across Tcrit is not completely understood.
Timing of meltwater pulse 1a and climate responses to meltwater injections
Authors: Stanford Jennifer D. , Rohling Eelco J. , Hunter Sally E. , Roberts Andrew P. , Rasmussen Sune O. , Bard Edouard , McManus Jerry , Fairbanks Richard G.
Published: December 2006

The temporal relationship between meltwater pulse 1a (mwp‐1a) and the climate history of the last deglaciation remains a subject of debate. By combining the Greenland Ice Core Project δ18O ice core record on the new Greenland ice core chronology 2005 timescale with the U/Th‐dated Barbados coral record, we conclusively derive that mwp‐1a did not coincide with the sharp Bølling warming but instead with the abrupt cooling of the Older Dryas. To evaluate whether there is a relationship between meltwater injections, North Atlantic Deep Water (NADW) formation, and climate change, we present a high‐resolution record of NADW flow intensity from Eirik Drift through the last deglaciation. It indicates only a relatively minor 200‐year weakening of NADW flow, coincident with mwp‐1a. Our compilation of records also indicates that during Heinrich event 1 and the Younger Dryas there were no discernible sea level rises, and yet these periods were characterized by intense NADW slowdowns/shutdowns. Clearly, deepwater formation and climate are not simply controlled by the magnitude or rate of meltwater addition. Instead, our results emphasize that the location of meltwater pulses may be more important, with NADW formation being particularly sensitive to surface freshening in the Arctic/Nordic Seas.
Structural model of full‐length human Ku70–Ku80 heterodimer and its recognition of DNA and DNA‐PKcs
Authors: Rivera‐Calzada Angel , Spagnolo Laura , Pearl Laurence H , Llorca Oscar
Published: December 2006

Recognition of DNA double‐strand breaks during non‐homologous end joining is carried out by the Ku70–Ku80 protein, a 150 kDa heterodimer that recruits the DNA repair kinase DNA‐dependent protein kinase catalytic subunit (DNA‐PKcs) to the lesion. The atomic structure of a truncated Ku70–Ku80 was determined; however, the subunit‐specific carboxy‐terminal domain of Ku80—essential for binding to DNA‐PKcs—was determined only in isolation, and the C‐terminal domain of Ku70 was not resolved in its DNA‐bound conformation. Both regions are conserved and mediate protein–protein interactions specific to mammals. Here, we reconstruct the three‐dimensional structure of the human full‐length Ku70–Ku80 dimer at 25 Å resolution, alone and in complex with DNA, by using single‐particle electron microscopy. We map the C‐terminal regions of both subunits, and their conformational changes after DNA and DNA‐PKcs binding to define a molecular model of the functions of these domains during DNA repair in the context of full‐length Ku70–Ku80 protein.
Isotope selective photoionization of NaK by optimal control: Theory and experiment
Authors: Schäfer-Bung Boris , Bonačić-Koutecký Vlasta , Sauer Franziska , Weber Stefan M. , Wöste Ludger , Lindinger Albrecht
Published: December 2006

We present a joint theoretical and experimental study of the maximization of the isotopomer ratio Na23K39∕Na23K41 using tailored phase-only as well as amplitude and phase modulated femtosecond laser fields obtained in the framework of optimal control theory and closed loop learning (CLL) technique. A good agreement between theoretically and experimentally optimized pulse shapes is achieved which allows to assign the optimized processes directly to the pulse shapes obtained by the experimental isotopomer selective CLL approach. By analyzing the dynamics induced by the optimized pulses we show that the mechanism involving the dephasing of the wave packets between the isotopomers Na23K39 and Na23K41 on the first excited state is responsible for high isotope selective ionization. Amplitude and phase modulated pulses, moreover, allow to establish the connection between the spectral components of the pulse and corresponding occupied vibronic states. It will be also shown that the leading features of the theoretically shaped pulses are independent from the initial conditions. Since the underlying processes can be assigned to the individual features of the shaped pulses, we show that optimal control can be used as a tool for analysis.
Effect of rapid thermal annealing on electrical and optical properties of Ga doped ZnO thin films prepared at room temperature
Authors: Kim Jong Hoon , Ahn Byung Du , Lee Choong Hee , Jeon Kyung Ah , Kang Hong Seong , Lee Sang Yeol
Published: December 2006

Ga doped ZnO (GZO) thin films were prepared by pulsed laser deposition on glass substrate at room temperature. Structural, optical, and electrical properties of these films were analyzed in order to investigate their dependence on oxygen pressure and rapid thermal annealing (RTA) temperature. High quality GZO films with a low resistivity of 2.92×10−4Ωcm and a transparency above 94% were able to be formed at an oxygen pressure of 3×10−2Torr and a RTA temperature of 400°C. A four point probe method, x-ray diffraction, atomic force microscopy, and ultraviolet–near-infrared grating spectrometer are used to investigate the properties of GZO films.
Simulation studies of the fidelity of biomolecular structure ensemble recreation
Authors: Lätzer Joachim , Eastwood Michael P. , Wolynes Peter G.
Published: December 2006

We examine the ability of Bayesian methods to recreate structural ensembles for partially folded molecules from averaged data. Specifically we test the ability of various algorithms to recreate different transition state ensembles for folding proteins using a multiple replica simulation algorithm using input from “gold standard” reference ensembles that were first generated with a Gō-like Hamiltonian having nonpairwise additive terms. A set of low resolution data, which function as the “experimental” ϕ values, were first constructed from this reference ensemble. The resulting ϕ values were then treated as one would treat laboratory experimental data and were used as input in the replica reconstruction algorithm. The resulting ensembles of structures obtained by the replica algorithm were compared to the gold standard reference ensemble, from which those “data” were, in fact, obtained. It is found that for a unimodal transition state ensemble with a low barrier, the multiple replica algorithm does recreate the reference ensemble fairly successfully when no experimental error is assumed. The Kolmogorov-Smirnov test as well as principal component analysis show that the overlap of the recovered and reference ensembles is significantly enhanced when multiple replicas are used. Reduction of the multiple replica ensembles by clustering successfully yields subensembles with close similarity to the reference ensembles. On the other hand, for a high barrier transition state with two distinct transition state ensembles, the single replica algorithm only samples a few structures of one of the reference ensemble basins. This is due to the fact that the ϕ values are intrinsically ensemble averaged quantities. The replica algorithm with multiple copies does sample both reference ensemble basins. In contrast to the single replica case, the multiple replicas are constrained to reproduce the average ϕ values, but allow fluctuations in ϕ for each individual copy. These fluctuations facilitate a more faithful sampling of the reference ensemble basins. Finally, we test how robustly the reconstruction algorithm can function by introducing errors in ϕ comparable in magnitude to those suggested by some authors. In this circumstance we observe that the chances of ensemble recovery with the replica algorithm are poor using a single replica, but are improved when multiple copies are used. A multimodal transition state ensemble, however, turns out to be more sensitive to large errors in ϕ (if appropriately gauged) and attempts at successful recreation of the reference ensemble with simple replica algorithms can fall short.
Light-polarization characteristics of electroluminescence from InGaN∕GaN light-emitting diodes prepared on (112¯2)-plane GaN
Authors: Masui Hisashi , Baker Troy J. , Iza Michael , Zhong Hong , Nakamura Shuji , DenBaars Steven P.
Published: December 2006

Light polarization and emission spectra from InGaN∕GaN quantum-well light-emitting diodes (LEDs) were investigated. The LEDs were prepared on the (112¯2) plane of wurtzite GaN. Polarization and spectrum measurement was performed at different observation angles with respect to the LED surface. Partially polarized electroluminescence was confirmed at any angle of observation, where the emission intensity tended to be greater when a polarizer was aligned along the c axis of the InGaN∕GaN LED structure. The results clearly indicated the inclination of the c axis relative to the LED surface. As a result, two light polarizations were identified and they were assigned to two different electronic transitions in relation to emission peak energies. Possible alteration of the valence-band structure was suggested due to the induced strain.
High-current vacuum arc under axial magnetic field: Numerical simulation and comparisons with experiments
Authors: Wang Lijun , Jia Shenli , Shi Zongqian , Rong Mingzhe
Published: December 2006

Based on a magnetohydrodynamic model, a numerical simulation of high-current vacuum arc (HCVA) is carried out. In this model, the kinetic energy terms and ion viscosity terms in energy conservation equations are considered. Compared with the supersonic constricted vacuum arc, the ion flow in HCVA is in the subsonic status. Therefore, boundary conditions of cathode and anode sides have to be adjusted for HCVA. According to the simulation results of HCVA, we can find that the maximal plasma pressure appears near the cathode side. The characteristics of HCVA are significantly different from those of supersonic vacuum arc. Then, we make the comparisons between simulation results and experimental results (such as electron number density, electron temperature, ion temperature, high speed charge-coupled device photographs, and so on). The simulation results are in agreement with the experimental results. In addition, we also analyze the influence of different arc models on the distribution of current density in the anode side.
Sound absorption characteristics of porous aluminum fabricated by spacer method
Authors: Hakamada Masataka , Kuromura Tetsunume , Chen Youqing , Kusuda Hiromu , Mabuchi Mamoru
Published: December 2006

Porous Al specimens with porosities of 85%–95% and pore sizes of 212–300to610–700μm were fabricated by the spacer method, and their sound absorption coefficients were investigated by the transfer function method. The sound absorption coefficient increased with porosity. However, there was no apparent correlation between pore size and sound absorption coefficient. Also, the sound absorption coefficient depended on the thickness. The sound absorption coefficient of a specimen was significantly improved by the modification of aperture size, even if the porosity and pore size were unchanged. Therefore, it is suggested that sound absorption behavior is strongly affected by not only the porosity and pore size but also the aperture size for porous Al fabricated by the spacer method.
Enhanced Zn–Cd interdiffusion and biexciton formation in self-assembled CdZnSe quantum dots in thermally annealed small mesas
Authors: Margapoti E. , Worschech L. , Forchel A. , Slobodskyy T. , Molenkamp L. W.
Published: December 2006

By controlled annealing of small ZnSe mesas with embedded CdZnSe quantum dots (QDs) at considerably low temperatures, significant changes of the QD luminescence have been observed. To investigate the spectral evolution of single exciton lines several thermal annealing steps were performed successively, and large energy shifts of single exciton (X) lines due to annealing were traced. In annealed QDs the biexciton (XX) emission is drastically enhanced. Biexciton binding energies less than 10meV were recorded for the thermally annealed CdZnSe QDs, indicating a considerable change in the QD confinement. The pronounced energy shifts of the QD luminescence is attributed to the Cd–Zn interdiffusion between the CdZnSe QDs and the surrounding ZnSe matrix. In small mesas interdiffusion activation energy (EA) of less than 1eV was determined. This value of EA is half of that recorded for the Cd–Zn interdiffusion in large QD ensembles, indicating that the sidewalls of the etched mesas play an important role in the observed diffusion process.
Preparation, structures, and multiferroic properties of single phase Bi1−xLaxFeO3 (x=–0.40) ceramics
Authors: Zhang Shan-Tao , Pang Ling-Hua , Zhang Yi , Lu Ming-Hui , Chen Yan-Feng
Published: December 2006

A simple and effective method that solid state reaction followed by quenching process is developed to prepare multiferroic La-substituted BiFeO3 (Bi1−xLaxFeO3 (BLFOx) with x=0–0.40) ceramics. X-ray diffraction, x-ray photoelectron spectroscopy, and inductively coupled plasma studies show that the ceramics prepared under the optimized conditions are single phase. A phase transition from rhombohedral to orthorhombic phase is observed near x=0.30. This transition has great effects on the multiferroic properties. Magnetic and electric measurements reveal that the BLFO0.30 has enhanced multiferroic properties with two times remnant magnetization and polarization of 0.041emu∕g and 22.4μC∕cm2, respectively. The enhanced multiferroic properties are attributed to the enhanced magnetoelectric interaction, which results from the La substitution-induced destruction of the spin cycloid. These results show that BiFeO3-based perovskite solid solution with no other ferroelectric end member can have improved multiferroic properties via enhancing magnetoelectric interaction. This work may provide some guidelines for further study on BiFeO3 and BiFeO3-based solid solutions.
Propensity rules for inelastic electron tunneling spectroscopy of single-molecule transport junctions
Authors: Troisi Alessandro , Ratner Mark A.
Published: December 2006

Using a perturbative approach to simple model systems, we derive useful propensity rules for inelastic electron tunneling spectroscopy (IETS) of molecular wire junctions. We examine the circumstances under which this spectroscopy (that has no rigorous selection rules) obeys well defined propensity rules based on the molecular symmetry and on the topology of the molecule in the junction. Focusing on conjugated molecules of C2h symmetry, semiquantitative arguments suggest that the IETS is dominated by ag vibrations in the high energy region and by out of plane modes (au and bg) in the low energy region. Realistic computations verify that the proposed propensity rules are strictly obeyed by medium to large-sized conjugated molecules but are subject to some exceptions when small molecules are considered. The propensity rules facilitate the use of IETS to help characterize the molecular geometry within the junction.
Lennard-Jones sticks: A new model for linear molecules
Authors: Vesely Franz J.
Published: December 2006

We consider the anisotropic interaction between two line segments consisting of a homogeneous distribution of Lennard-Jones centers. The potential energy of such a pair cannot be expressed in closed form. However, we show that it may be approximated in a way that renders this intuitively appealing model competitive both for simulations and theory.
Band gap tuning and high electrical conductivity in amorphous and polycrystalline films of the Cux(CdTe)yOz system
Authors: Jiménez-Sandoval S. , Garnett-Ruiz G. E. , Santos-Cruz J. , Jiménez-Sandoval O. , Torres-Delgado G. , Castanedo-Pérez R. , Morales-Sánchez E.
Published: December 2006

Thin films of the semiconductor alloy Cux(CdTe)yOz system were grown by reactive rf cosputtering. The effects of incorporating both copper and oxygen into a CdTe matrix were investigated. The films were polycrystalline, however, for the highest oxygen concentrations used in this work the grain size was reduced to nanometric dimensions. It is shown in this work that the optical and charge transport properties of the polycrystalline and amorphous films may be tailored by controlling the relative chemical composition. Remarkably, unusual p-type resistivity and mobility values have been measured for the amorphous films.
Effects of substrate on the dielectric and tunable properties of epitaxial SrTiO3 thin films
Authors: Hao J. H. , Luo Zhi , Gao J.
Published: December 2006

Tunable dielectric thin films of SrTiO3 (STO) were prepared on different single-crystalline substrates, including insulating LaAlO3, conductive Nb-doped STO (NSTO), and superconducting YBa2Cu3O7−δ. Substrate effects including morphology, orientation, and lattice mismatch induced strains were investigated. We found that a change of substrate used for STO thin films can strongly affect the dielectric properties of STO thin films in terms of dielectric constant, loss tangent, and tunability. Effects of substrate properties on the temperature dependence of dielectric constant and loss tangent were investigated. At low temperatures, STO thin films under minimal strain yield high dielectric constant and low loss tangent while the thin films under either tensile or compressive strain exhibit the reduced dielectric constant and high loss. The tunability of about 77% in STO∕NSTO system, close to the value found in STO single crystal, was observed at 10K. Physical origin of observed phenomena was discussed.
Heterogeneous porous media as multiscale structures for maximum flow access
Authors: Lorente Sylvie , Bejan Adrian
Published: December 2006

Natural porous structures are heterogeneous with multiple scales that are distributed nonuniformly. Few large pores (fissures, channels, and cracks) are accompanied by numerous finer channels. Can this type of flow architecture be attributed to a principle of maximization of global flow access? Features similar to those of multiscale porous structures are exhibited by tree-shaped flow structures. Trees have been deduced from the maximization of flow access between a point and a volume, a point and an area, and a point and a curve (e.g., circle). In this paper we invoke the same principle and consider fundamentally the question of how to bathe with minimal flow resistance a microchannel structure that globally behaves as a porous medium. We develop completely multiscale configurations that guide the flow from one side of the porous structure to the other (line to line and plane to plane) and show analytically the advantages of tree structures over the usual stacks of parallel microchannels. The “porous medium” that has tree-shaped labyrinths is heterogeneous, with multiple scales that are distributed nonuniformly. These features justify comparisons with the design of natural porous structures.
Behavior of oblately deformed droplets in an immiscible dielectric liquid under a steady and uniform electric field
Authors: Sato Hiromi , Kaji Nobufuji , Mochizuki Takaaki , Mori Yasuhiko H.
Published: December 2006

The deformation and breakup of droplets in a steady and uniform electric field were experimentally investigated. Droplets of silicone oil suspended in more electric-conducting caster oil undergoes the three following modes of deformation when subjected to an electric field: oblate deformation with a symmetric axis oriented close to parallel with the electric field, oblate deformation with a symmetric axis oriented obliquely to the electric field, and an oscillatory oblate–prolate deformation synchronized with a sit-up motion. Each droplet during the oscillatory motion is simultaneously observed from two directions, and the flow in the droplet is visualized by a tracer particle method. The oscillatory motion is revealed to involve electrorotation of the droplet. The conditions under which each of the three deformation modes or droplet breakup occurs are identified.
A new chaotic communication scheme based on adaptive synchronization
Authors: Xiang-Jun Wu
Published: December 2006

A new chaotic communication scheme using adaptive synchronization technique of two unified chaotic systems is proposed. Different from the existing secure communication methods, the transmitted signal is modulated into the parameter of chaotic systems. The adaptive synchronization technique is used to synchronize two identical chaotic systems embedded in the transmitter and the receiver. It is assumed that the parameter of the receiver system is unknown. Based on the Lyapunov stability theory, an adaptive control law is derived to make the states of two identical unified chaotic systems with unknown system parameters asymptotically synchronized; thus the parameter of the receiver system is identified. Then the recovery of the original information signal in the receiver is successfully achieved on the basis of the estimated parameter. It is noticed that the time required for recovering the information signal and the accuracy of the recovered signal very sensitively depends on the frequency of the information signal. Numerical results have verified the effectiveness of the proposed scheme.
Design of multidirectional multiscroll chaotic attractors based on fractional differential systems via switching control
Authors: Deng Weihua , Lü Jinhu
Published: December 2006

This paper proposes a saturated function series approach for generating multiscroll chaotic attractors from the fractional differential systems, including one-directional (1-D) n-scroll, two-directional (2-D) n×m-grid scroll, and three-directional (3-D) n×m×l-grid scroll chaotic attractors. Our theoretical analysis shows that all scrolls are located around the equilibria corresponding to the saturated plateaus of the saturated function series on a line in the 1-D case, a plane in the 2-D case, and a three-dimensional space in the 3-D case, respectively. In particular, each saturated plateau corresponds to a unique equilibrium and its unique scroll of the whole attractor. In addition, the number of scrolls is equal to the number of saturated plateaus in the saturated function series. Finally, some underlying dynamical mechanisms are then further investigated for the fractional differential multiscroll systems.
Significant change of alignment effect by dimer formation in the dissociative energy transfer reaction of Ar(P23)+(N2O)n and (H2O)n
Authors: Watanabe D. , Ohoyama H. , Matsumura T. , Kasai T.
Published: December 2006

An alignment effect in the dissociative energy transfer reaction of Ar(P23)+(X2O)n(X=N,H) was directly measured using an oriented Ar(P23,MJ=2) beam. The chemiluminescence intensity of N2(B,Πg3) for (N2O)n and OH(A,Σ+2) for (H2O)n was measured as a function of the magnetic orientation field direction in the collision frame. The relative reaction cross section for each magnetic substate in the collision frame, σMJ′, was determined. In both the reaction systems, it is observed that the dimer formation significantly enhances the alignment effect and decreases the reactivity, especially for σ∣1∣ and σ∣2∣. A significant contribution of rank 4 moment is recognized in the dimer reaction.
Solid state self-assembly of nanocheckerboards
Authors: Yeo S. , Horibe Y. , Mori S. , Tseng C. M. , Chen C. H. , Khachaturyan A. G. , Zhang C. L. , Cheong S.-W.
Published: December 2006

The authors introduce an emergent method to fabricate a few-nanometer-size columnar superlattice with a checkerboard pattern in inorganic spinels by harnessing the Jahn-Teller structural distortion. Transmission electron microscope images reveal that the fundamental building blocks are two types of long nanorods with the ∼4×4×70nm3 size, which are alternatively stacked in a way that the cross sectional and side views show checkerboard and herringbone patterns, respectively. The authors discuss that the strain induced by the Jahn-Teller distortion causes this peculiar self-assembled nanostructure in the coherent mixture of two spinel phases. This pure solid state self-assembly can be implemented to fabricate heterogeneous nanostructures with practical functionalities.
Controlled manipulation and actuation of micro-objects with magnetotactic bacteria
Authors: Martel Sylvain , Tremblay Charles C. , Ngakeng Serge , Langlois Guillaume
Published: December 2006

Bacterial actuation and manipulation are demonstrated where Magnetospirillum gryphiswaldense magnetotactic bacteria (MTB) are used to push 3μm beads at an average velocity of 7.5μms−1 along preplanned paths by modifying the torque on a chain of magnetosomes in the bacterium with a directional magnetic field of at least 0.5G generated from a small programmed electrical current. But measured average thrusts of 0.5 and 4pN of the flagellar motor of a single Magnetospirillum gryphiswaldense and MC-1 MTB suggest that average velocities greater than 16 and 128μms−1, respectively could be achieved.
Determination of aggregates as charge trapping and recombination centers in poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene] by time-resolved electroluminescence spectroscopy
Authors: Tseng Hao-En , Liu Ching-Yang , Chen Show-An
Published: December 2006

A presence of aggregates can give critical influences on photophysical properties of conjugated polymer. For poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene], the authors found that the aggregates can serve as charge traps and recombination centers by using time-resolved electroluminescence spectroscopy, and that the emissions from isolated chains and aggregates show different dynamics. The authors also found that the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of aggregates lie within the band gap of isolated chains. Thus, the aggregates act as shallow traps for both electron and hole so that a reexcitation to HOMO and LUMO of isolated chains is possible.
Ti
Si
2
∕
Si
heteronanocrystal metal-oxide-semiconductor-field-effect-transistor memory
Authors: Zhu Yan , Li Bei , Liu Jianlin , Liu G. F. , Yarmoff J. A.
Published: December 2006

Ti Si 2 ∕ Si heteronanocrystals with a density of 5×1011cm−2 were formed on a thermally oxidized p-type Si substrate by using self-aligned silicide technique. Metal-oxide-semiconductor-field-effect-transistor (MOSFET) memory devices were fabricated using these heteronanocrystals as floating gates. As compared to Si nanocrystal MOSFET memory, TiSi2∕Si heteronanocrystal memories exhibit higher charge storage capacity, longer retention, better writing efficiency, less writing saturation, and faster erasing speed.
Band gap energy determination by photoacoustic spectroscopy under continuous light excitation
Authors: Astrath N. G. C. , Sato F. , Pedrochi F. , Medina A. N. , Bento A. C. , Baesso M. L. , Persson C. , Ferreira da Silva A.
Published: December 2006

In this work the authors used the photoacoustic spectroscopy under continuous light excitation to determine the optical band gap of semiconductors. The experiments were performed in lead iodide PbI2 and hexagonal silicon carbide 4H-SiC samples. The nonradiative relaxation processes are discussed in terms of the generated signal. A mechanism to describe the signal increase/decrease under the continuous excitation is presented. The results showed that the method was useful to locate the band gap directly from the optical absorption spectra.
Array of dielectric nanocomposite devices using photoepoxy Su-8 as the polymeric phase
Authors: Li Fang , Wang Qing-Ming
Published: December 2006

An array of dielectric nanocomposite devices in which negative tone photoepoxy Su-8 is used as the polymeric matrix and Ba0.5Sr0.5TO3 nanoparticles as the inclusions is fabricated on silicon substrate. The use of Su-8 necessitates a single step process for both the top electrode deposition and ultraviolet exposure using a shadow mask and direct-current magnetron sputtering in the device fabrication. Scanning electron microscopy examination indicates a uniform distribution of nanoparticles in Su-8 matrix. Effective dielectric constant of the nanocomposites increases with loading concentration with a good agreement with the Maxwell-Garnett and Bruggeman approximations at low concentrations, while dielectric loss is low for all compositions.
Optical emission from C60-coupled β-FeSi2 nanocomposites
Authors: Wu X. L. , Xue F. S. , Zhang Z. Y. , Chu Paul K.
Published: December 2006

C 60 -coupled β-FeSi2 nanocomposite structures were fabricated and their photoluminescence (PL) properties were investigated. The nanocomposites exhibit a pinned PL peak at 570nm and a band edge at ∼370nm. Spectral analyses suggest that the pinned PL behavior is closely related to both the β-FeSi2 nanocrystals and the coupled C60. A band-mixing model based on the direct and indirect gaps in a nanoenvironment consisting of mainly β-FeSi2 nanocrystals and C60 is proposed and used to derive the electronic states. Good agreement is achieved between the theoretical calculation and experimental results.
Fabrication of GaN nanowire arrays by confined epitaxy
Authors: Wang Xin , Sun Xinyu , Fairchild Michael , Hersee Stephen D.
Published: December 2006

The authors report the fabrication of GaN nanowire arrays inside a thick SiNx, selective growth mask that was patterned by interferometric lithography and dry etching. The GaN nanowires are molded by the apertures in the selective growth mask and the growth is epitaxial with respect to the underlying GaN layer. The precise location and diameter of each nanowire in the array are controlled by the growth mask patterning, and the resulting array has a long-range order that is compatible with photonic crystal applications. This process uses conventional metal organic precursors and does not require any additional metal catalysts.
Microstructure and enhanced in-plane ferroelectricity of Ba0.7Sr0.3TiO3 thin films grown on MgAl2O4 (001) single-crystal substrate
Authors: Zhou X. Y. , Heindl T. , Pang G. K. H. , Miao J. , Zheng R. K. , Chan H. L. W. , Choy C. L. , Wang Y.
Published: December 2006

The microstructure and in-plane dielectric and ferroelectric properties of highly oriented Ba0.7Sr0.3TiO3 (BST) thin film grown on MgAl2O4 (001) single-crystal substrate through pulsed laser deposition were investigated. X-ray diffraction measurements indicated that BST had a distorted lattice with a tetragonality a∕c=1.012. The cross-sectional observation under transmission electron microscope revealed that, while most of BST grains grew epitaxially on MgAl2O4, the film also contained a noticeable amount of misoriented grains and dislocations. The electrical measurements indicated that the film had a shifted Curie temperature (TC=78°C) and an enhanced in-plane ferroelectricity (remnant polarization Pr=7.1μC∕cm2) when compared with BST ceramic (TC≈33°C and Pr≈0).
Pentacene field-effect transistors with a laminated Mylar™ foil as gate dielectric
Authors: Diallo Karim , Erouel Mohsen , Tardy Jacques
Published: December 2006

This work reports on pentacene based organic field-effect transistors with a gate dielectric made of a thin foil of Mylar™ transferred by a lamination process at moderate temperature. The process described here enabled the process of both bottom and top gate transistors, thus demonstrating the feasibility of laminating a dielectric film onto an organic semiconductor. Furthermore the authors point out the importance of the organic/insulator interface through the beneficial deposition of polymethyl methacrylate layer on the Mylar before evaporation of the pentacene layer in the case of bottom gate devices. A comparison is given with devices having a spun on organic dielectric.
Electronic composite of sulfonated tetrafluorethylene copolymer with potassium ferricyanide exhibiting room-temperature negative differential resistance
Authors: Choi Yongki , Wang Gang , Yau Siu-Tung , Choi Yongki
Published: December 2006

A two-phase composite material was prepared by mixing the polymer Nafion with an electroactive molecule, potassium ferricyanide. The current-voltage characteristic of the material shows a finite conductance about zero bias, indicating a metal-like electrical conduction. The conductance is found to be proportional to the concentration of the potassium ferricyanide molecule and temperature. A conductance peak is present at a low bias voltage, providing a region of negative differential resistance. A peak-to-valley current ratio of 1.8 was obtained with a current density of 30μA∕cm2. A conduction mechanism based electron tunneling between the active sites of the molecule is proposed.
Hybrid coupled cluster and molecular dynamics approach: Application to the excitation spectrum of cytosine in the native DNA environment
Authors: Valiev Marat , Kowalski Karol
Published: December 2006

Evolution of the excited state energies of cytosine base in the native DNA environment was investigated using a hybrid coupled cluster and classical molecular dynamics approach. The time averaged excitation energies obtained with the variant of the completely renormalized equation-of-motion with singles, doubles, and non-iterative triples approach that includes a bulk of the correlation effects for excited states, are compared with the analogous calculations in the gas phase. Significant blue shifts for the two lowest singlet excitation energies can be observed as a result of the interaction of the quantum system with the surrounding environment.
Passive mode locking by carbon nanotubes in a femtosecond laser written waveguide laser
Authors: Della Valle Giuseppe , Osellame Roberto , Galzerano Gianluca , Chiodo Nicola , Cerullo Giulio , Laporta Paolo , Svelto Orazio , Morgner Uwe , Rozhin A. G. , Scardaci V. , Ferrari A. C.
Published: December 2006

The authors report on the first demonstration of mode locking in an active waveguide laser manufactured by femtosecond laser writing. The active waveguide is fabricated in an Er–Yb-doped phosphate glass, and the mode locker is a fiber-pigtailed saturable absorber device based on single-wall carbon nanotubes specially designed to efficiently operate at 1.5μm. Transform-limited 1.6ps pulses were observed in a ring laser cavity configuration.
Well-aligned zinc sulfide nanobelt arrays: Excellent field emitters
Authors: Lu Fang , Cai Weiping , Zhang Yugang , Li Yue , Sun Fengqiang , Heo Sung Hwan , Cho Sung Oh
Published: December 2006

Large-scale, well-aligned and oriented wurtzite ZnS nanobelt arrays are fabricated by a simple solvothermal reaction and subsequent heat treatment. The nanobelts grow along the [0001] direction perpendicularly on a zinc substrate, which are about 30nm in thickness, several hundreds of nanometers in width, and up to 4μm in length. Importantly, such nanostructured arrays show a good field emission property with low turn-on field (3.8Vμm−1) and high field enhancement factor (∼1800), which is ascribed to the top edges and corners of the freestanding and well aligned nanobelts, and good electric contact with the conducting substrate where they grow.
Near-field optical properties of single plasmonic nanowires
Authors: Laroche Thierry , Girard Christian
Published: December 2006

The authors apply the finite difference time domain method to study the propagation of a local excitation along metallic nanowires of subwavelength cross section. The metallic nanowires are elongated cylinders deposited on a transparent substrate. A tightly focused Gaussian beam illuminates one end of the nanowires. The localized surface plasmon excitations propagate along the nanowire over distances much larger than the incident wavelength. According to recent experimental studies, they show that such nanostructures behave like a Fabry-Pérot cavity with large value of surface plasmon propagation length.
Theoretical and experimental studies of parameter estimation based on chaos feedback synchronization
Authors: Zhang Yu , Tao Chao , Jiang Jack J.
Published: December 2006

In this paper, we perform theoretical and experimental studies of parameter estimation based on chaos feedback synchronization. The Chua chaotic system is applied as the original system, and its time series of a single variable is applied as a feedback variable to drive a simulative system. The simplex method is employed to minimize the synchronization error in the simulative system to iteratively approach the original system parameters. Furthermore, the effects of feedback function, feedback weight, and noise are investigated. The parameter estimation method based on feedback synchronization shows its robustness to noise perturbation. Finally, the circuit experiment of parameter estimation is implemented in order to examine its practical applicability. The original Chua circuit parameters can be well approached from its recorded time series of a single variable. The results show the parameter estimation method based on feedback synchronization may be capable of estimating real system parameters from a chaotic time series.
Self-assembled monolayer-modified Ag anode for top-emitting polymer light-emitting diodes
Authors: Chong Lai-Wan , Lee Yuh-Lang , Wen Ten-Chin , Guo Tzung-Fang
Published: December 2006

A self-assembled monolayer (SAM), 4-fluorothiophenol (4-FTP), is employed to modify the Ag anode of a top-emitting polymer light-emitting diode (T-PLED) to enhance the hole injection and the performance of a T-PLED device. The results show that the reflectivity of the Ag anode does not decrease due to the formation of a SAM. A brightness of 68981cd∕m2 and a luminous efficiency of 10.3cd∕A have been achieved for the 4-FTP-modified device. The improved performance is attributed to the work function increase of the Ag/4-FTP anode due to the presence of fluorine atoms at the outer surface of the modified anode.
Resonance Raman intensity analysis of the excited state proton transfer dynamics of 2-nitrophenol in the charge-transfer band absorption
Authors: Wang Ya-Qiong , Wang Hui-Gang , Zhang Shu-Qiang , Pei Ke-Mei , Zheng Xuming , Lee Phillips David
Published: December 2006

Resonance Raman spectra were obtained for 2-nitrophenol in cyclohexane solution with excitation wavelengths in resonance with the charge-transfer (CT) proton transfer band absorption. These spectra indicate that the Franck-Condon region photodissociation dynamics have multidimensional character with motion along more than 15 normal modes: the nominal CCH bend+CC stretch ν12 (1326cm−1), the nominal CCC bend ν23 (564cm−1), the nominal CO stretch+NO stretch+CC stretch ν14 (1250cm−1), the nominal CCH bend+CC stretch+COH bend ν15 (1190cm−1); the nominal CCH bend+CC stretch ν17 (1134cm−1), the nominal CCC bend+CC stretch ν22 (669cm−1), the nominal CCN bend ν27 (290cm−1), the nominal NO2 bend+CC stretch ν21 (820cm−1), the nominal CCO bend+CNO bend ν25 (428cm−1), the nominal CC stretch ν7 (1590cm−1), the nominal NO stretch ν8 (1538cm−1), the nominal CCC bend+NO2 bend ν20 (870cm−1), the nominal CC stretch ν6 (1617cm−1), the nominal COH bend+CC stretch ν11 (1382cm−1), nominal CCH bend+CC stretch ν9 (1472cm−1). A preliminary resonance Raman intensity analysis was done and the results for 2-nitrophenol were compared to previously reported results for nitrobenzene, p-nitroaniline, and 2-hydroxyacetophenone. The authors briefly discuss the differences and similarities in the CT-band absorption excitation of 2-nitrophenol relative to those of nitrobenzene, p-nitroaniline, and 2-hydroxyacetophenone.
An exact solution in sedimentation under an inclined wall
Authors: Kerr Oliver S.
Published: December 2006

When a particle-laden fluid is introduced below a flat sloping boundary, as the sediment particles fall a layer of clear, relatively buoyant fluid can form adjacent to the boundary. This fluid can rise and lead to enhanced overall sedimentation rates, the so-called “Boycott effect.” When this layer of fluid flows up the boundary it does so in two stages. The first stage involves a unidirectional flow that does not vary along the wall, and the second stage occurs when the influence of the lower end of the wall is felt and a steady nonuniform boundary layer is established. The exact solution to the governing equations for the first stage is found when some standard assumptions are made.
Role of molecular charge and hydrophilicity in regulating the kinetics of crystal growth
Authors: Elhadj S. , De Yoreo J. J. , Hoyer J. R. , Dove P. M.
Published: December 2006

The composition of biologic molecules isolated from biominerals suggests that control of mineral growth is linked to biochemical features. Here, we define a systematic relationship between the ability of biomolecules in solution to promote the growth of calcite (CaCO
3
) and their net negative molecular charge and hydrophilicity. The degree of enhancement depends on peptide composition, but not on peptide sequence. Data analysis shows that this rate enhancement arises from an increase in the kinetic coefficient. We interpret the mechanism of growth enhancement to be a catalytic process whereby biomolecules reduce the magnitude of the diffusive barrier,
E
k
, by perturbations that displace water molecules. The result is a decrease in the energy barrier for attachment of solutes to the solid phase. This previously unrecognized relationship also rationalizes recently reported data showing acceleration of calcite growth rates over rates measured in the pure system by nanomolar levels of abalone nacre proteins. These findings show that the growth-modifying properties of small model peptides may be scaled up to analyze mineralization processes that are mediated by more complex proteins. We suggest that enhancement of calcite growth may now be estimated
a priori
from the composition of peptide sequences and the calculated values of hydrophilicity and net molecular charge. This insight may contribute to an improved understanding of diverse systems of biomineralization and design of new synthetic growth modulators.