bluuebunny/crossref_metadata_2025 huggingface dataset:
Creeping motion and pending breakup of drops and bubbles near an inclined wall
Authors: Griggs Andrew J. , Zinchenko Alexander Z. , Davis Robert H.
Published: September 2009

The gravity-driven motion of a three-dimensional deformable drop or bubble in the vicinity of an inclined wall is investigated for low Reynolds number by computational and experimental methods. The velocity, shape, and distance from the wall for a nonwetting drop moving due to gravity are examined for different values of the drop-to-medium viscosity ratio, λ, the wall inclination angle from horizontal, θ, and Bond number, B, the latter which gives the relative magnitude of the buoyancy to capillary forces. The steady nondimensional velocity, scaled with the isolated settling drop velocity, is found to vary nonmonotonically with the Bond number for small inclination angles and intermediate viscosity ratios. For the same range of Bond numbers, the steady velocity was found to be an increasing function for bubbles and a decreasing function for highly viscous drops. Depending on the parameter values, steady motion of the drop may not exist. In particular, the critical Bond number, above which the droplet experiences unrestricted elongation and the possible onset of breakup, is found to be smallest at moderate inclination angles and to be a nonmonotonic function of the viscosity ratio. The underlying mechanism of breakup for this problem is described as a hydrodynamic “pinning” effect, through which the drop tail cannot move away from the wall as fast as the bulk or nose of the drop, which gives rise to the unsteady behavior. Experimental observations of drop shapes, velocity, and critical conditions for breakup show good agreement with the simulations.
Terahertz carrier dynamics and dielectric properties of GaN epilayers with different carrier concentrations
Authors: Guo H. C. , Zhang X. H. , Liu W. , Yong A. M. , Tang S. H.
Published: September 2009

Using terahertz time-domain spectroscopy, we measured the complex conductivity and dielectric function of n-type GaN with various carrier concentrations on sapphire substrate. The measured complex conductivity, which is due to the free carriers, is well fitted by simple Drude model. The contribution from the lattice vibration to the complex dielectric function increases with the decrease in free carrier concentration. A better fitting of the frequency-dependent complex dielectric response was obtained by considering both of the Drude and the classical damped oscillator model.
A global search algorithm of minima exploration for the investigation of low lying isomers of clusters from density functional theory-based potential energy surfaces: The example of Sin (n=3,15) as a test case
Authors: Marchal Rémi , Carbonnière Philippe , Pouchan Claude
Published: September 2009

Using an effective generation algorithm coupled with a PBE0/LANL2DZdp level of theory, 905 stable structures of Sin (n=3,15) have been found. This global search algorithm of minima exploration includes two original parts: the spheroidal generation, allowing the generation of rings, sphericals, m rings cylinders, and planar structures, and the raking optimization, which discards step by step the conformations that become physically unreasonable during the optimization process. The 142 isomers lying below 1 eV are reported and include the 28 structures reported in the literature. Conformational energies are well reproduced with respect to the values previously published (ΔE=0,00±0,09 eV).
Thermodynamically stable, size selective solubilization of carbon nanotubes in aqueous solutions of amphiphilic block copolymers
Authors: Nagarajan R. , Bradley R. Ashton , Nair Bindu R.
Published: September 2009

Two molecular modes of amphiphilic block copolymer-carbon nanotube interactions have been identified in the literature, one involving the adsorption of individual block copolymer molecules on the carbon nanotubes and the other involving the adsorption of multimolecular, spherical micelles. In both cases, the nature of stability imparted to the dispersion of carbon nanotubes in the aqueous medium is kinetic, controlled by the steric barrier imposed by the adsorbed individual block copolymer molecules or the adsorbed micelles. In this study, we propose another mode of molecular interaction, wherein the block copolymer molecules self-assemble around the nanotube, generating aggregates in which the nanotubes are solubilized. In this case, the resulting system is a thermodynamically stable nanocolloidal solution, similar to aqueous surfactant solutions, in contrast to the kinetically stabilized nanotube dispersions. To examine whether such solubilization of nanotubes is possible, we have constructed a simple phenomenological theory for the free energy change associated with solubilization and have performed illustrative numerical simulations based on the theory. The calculated results for the commercially available symmetric PEO-PPO-PEO triblock copolymers and for the PEO-PPO diblock copolymers having the same composition and molecular weight as the triblocks show that indeed the block copolymer molecules are capable of solubilizing the carbon nanotubes. While the block copolymers whose natural curvature is cylindrical are the best candidates to solubilize the nanotubes, other block copolymers whose natural curvature is spherical or lamellar, are also found capable of solubilizing the nanotubes. Most interestingly, the solubilization is found to be size specific suggesting that this can be developed into a practical method to fractionate carbon nanotubes by their diameter. These results are applicable to both single-walled and multiwalled carbon nanotubes and the general conclusions are valid also for other diblock and triblock copolymers.
Metal-insulator-metal capacitor with high capacitance density and low leakage current using ZrTiO4 film
Authors: Wu Yung-Hsien , Chen Bo-Yu , Chen Lun-Lun , Wu Jia-Rong , Wu Min-Lin
Published: September 2009

Thin amorphous and orthorhombic ZrTiO4 film with a high-work-function Ni top electrode has been explored in metal-insulator-metal (MIM) capacitors for analog circuit applications. It has been found that even though the permittivity can be as high as 78.9 for orthorhombic ZrTiO4, the extraordinarily high quadratic voltage coefficient of capacitance (VCC), and leakage current make it ineligible for reliable MIM capacitors. On the other hand, amorphous ZrTiO4 demonstrates a high capacitance density of 29.12 fF/μm2 and a low VCC of 2341 ppm/V2. Because of the amorphous phase and the conduction mechanism of Schottky emission, a low leakage current of 1.3×10−7 A/cm2 at −2 V and a good thermal leakage up to 125 °C has also been obtained. Besides these promising characteristics, amorphous ZrTiO4 holds a great potential for high-performance MIM capacitors not only in its process simplicity but also in the full compatibility with incumbent backend integrated circuit technology.
Radiation loss of photonic crystal coupled-cavity waveguides
Authors: Jágerská J. , Zhang H. , Le Thomas N. , Houdré R.
Published: September 2009

We experimentally investigate the out-of-plane radiation losses of photonic crystal coupled-cavity waveguides. We observe a strong variation in the losses along the dispersion curve and show that such variation is closely linked with the specific far-field radiation pattern of a single cavity constituent. A simple theoretical model based on tight-binding approximation is used to describe this behavior.
Anomalous properties of the local dynamics in polymer glasses
Authors: Casalini R. , Roland C. M.
Published: September 2009

We show how changes in a local, high frequency dynamic process are correlated with the macroscopic behavior of glassy polymers. Polyvinylethylenes vitrified by different chemical and thermodynamic pathways exhibit different densities in the glassy state. We find that the rate and amplitude of a high frequency relaxation mode (the Johari–Goldstein process involving local motion of segments of the chain backbone) can either correlate or anticorrelate with the density. This implies that neither the unoccupied (free) volume nor the configurational entropy governs the local dynamics in any general sense. Rather it is the magnitude of the fluctuations in local density that underlie these nanometer-scale motions. We show how properties of the dynamics and the density fluctuations can both be interpreted in terms of an asymmetric double well potential. Although the results herein are for polymers, the principles are expected to be generally applicable to glassy materials.
Cluster size effects on sintering, CO adsorption, and implantation in Ir/SiO2
Authors: Kaden W. E. , Kunkel W. A. , Anderson Scott L.
Published: September 2009

A series of planar model catalysts have been prepared via deposition of Irn+ on thermally grown amorphous SiO2/Si(100) and ion scattering spectroscopy was used to probe surface structure as a function of cluster size, impact energy, and surface temperature. Deposition of Ir2 or Ir10 at low energies and room temperature results in stable clusters forming one- or two-dimensional single layer islands on the oxide surface. Heating the samples to 750 K leads to agglomeration, forming multilayer structures on the surface. Ir1 deposited under similar conditions sinters into large clusters at room temperature. Deposition at 110 K at least partially stabilizes the Ir atoms with respect to diffusion and sintering. At higher deposition energies, partial implantation into the surface is observed, but this appears to be insufficient to stabilize the clusters against sintering at elevated temperature. At low temperatures, substrate-mediated adsorption of CO is found to be highly efficient, leading to near saturation coverages of CO bound atop the Irn clusters. The CO can be removed by careful He+ sputtering. The deposition/binding behavior of Irn on SiO2 is quite different from Irn/TiO2(110), for which the clusters bind in three-dimensional morphology, starting at Ir5. That system also shows substrate-mediated adsorption of CO, but the CO preferentially binds at the periphery of the clusters rather than on top.
Casimir chemistry
Authors: Sheehan D. P.
Published: September 2009

It is shown that, at the nanoscale, the Casimir effect can be used to mechanically tune critical aspects of chemical reactions (e.g., energies, equilibrium constants, activation energies, transition states, reaction rates) by varying the spacing and composition of reaction vessel boundaries. This suggests new modalities for catalysts, nanoscale chemical manufacturing, chemical-mechanical engines, and biochemical processes in organisms.
Carbonyl mediated attachment to silicon: Acetaldehyde on Si(001)
Authors: Belcher Daniel R. , Schofield Steven R. , Warschkow Oliver , Radny Marian W. , Smith Phillip V.
Published: September 2009

A detailed understanding of the chemical reactions of organic molecules with semiconductor surfaces will greatly aid schemes for the incorporation of organic functionality into existing technologies. In this paper we report on the reaction of acetaldehyde (CH3CHO) with silicon (001) as revealed by a combination of temperature-dependent scanning tunneling microscopy (STM) experiments and density functional theory (DFT). We observe that low-coverage exposures at room temperature result almost exclusively in the formation of a single adsorbate species. Conversion of this structure into thermodynamically favored bridge-bonded structures is achieved through temperature anneals between 150–250 °C. We determine the chemical identity of each of the experimentally observed species by comparison with DFT total energy calculations and simulated STM images. Calculations of transition states are used to formulate a full reaction pathway explaining the formation of the observed species. Excellent agreement is found between our experimental measurements and theoretical calculations. The results also present a picture consistent with our previous work on acetone and reveal a general reaction pattern for molecules containing the acetyl COCH3 functional group, where the initial attachment to the surface is mediated by a carbonyl C=O group. This suggests that modification of the residue R will facilitate in binding other electronically active molecules to the surface in a controlled fashion.
High dielectric permittivity of percolative composites based on onion-like carbon
Authors: Macutkevic J. , Seliuta D. , Valušis G. , Banys J. , Kuznetsov V. , Moseenkov S. , Shenderova O.
Published: September 2009

The broadband dielectric properties of the onion-like carbon (OLC) and polyurethane based composites of different compositions are presented for the frequency range of 20 Hz–3 GHz and 250–450 K temperatures. It is shown that an abrupt increase in the complex dielectric permittivity at the volume fraction of OLC 10% is associated with the onset of percolation. The revealed critical exponent and percolation point reasonably agree with theoretically predicted values. Composites with 10% of OLC exhibit dielectric permittivity as high as 2000 and conductivity as high as 0.01 S/m at 100 Hz.
Lanthanide-based graded barrier structure for enhanced nanocrystal memory properties
Authors: Chan M. Y. , Chan T. K. , Osipowicz T. , Chan L. , Lee P. S.
Published: September 2009

A memory structure comprising Ge nanocrystals and lanthanide-based charge trapping dielectric stack was fabricated to realize a self-aligned graded barrier structure. By exploiting efficient charge trapping of the nanocrystals embedded in the heterogeneous high-k dielectric, strong memory effect was manifested by a large counterclockwise capacitance-voltage hysteresis of 2.7 V under a low voltage operation of ±4 V. The high-k barrier with graded composition provides a favorable confinement barrier for improved hole retention with simultaneous enlargement of the memory window.
Memristive switching of MgO based magnetic tunnel junctions
Authors: Krzysteczko Patryk , Reiss Günter , Thomas Andy
Published: September 2009

Here we demonstrate that both, tunnel magnetoresistance (TMR) and resistive switching (RS), can be observed simultaneously in nanoscale magnetic tunnel junctions. The devices show bipolar RS of 6% and TMR ratios of about 100%. For each magnetic state, multiple resistive states are created depending on the bias history, which provides a method for multibit data storage and logic. The electronic transport measurements are discussed in the framework of a memristive system. Differently prepared MgO barriers are compared to gain insight into the switching mechanism.
Blister formation in ion-implanted GaAs: Role of diffusivity
Authors: Collino R. R. , Dick B. B. , Naab F. , Wang Y. Q. , Thouless M. D. , Goldman R. S.
Published: September 2009

We have investigated the influence of substrate temperature during implantation, Timplant, on blister formation in GaAs:N layers produced by N ion implantation followed by rapid thermal annealing. Similar depths of popped blisters (craters) and damage profiles were observed for both low and high Timplant. This is in contrast to reports of Timplant-dependent blister formation in higher-diffusivity systems such as GaAs:H and Si:H. The apparent Timplant-insensitivity of blister formation in GaAs:N is likely due to the lower diffusivity of N in GaAs in comparison to that of H in GaAs and Si.
High-density amorphous ice: Molecular dynamics simulations of the glass transition at 0.3 GPa
Authors: Seidl M. , Loerting T. , Zifferer G.
Published: September 2009

Based on several force fields (COMPASS, modified TIP3P and SPC/E) high-density amorphous ice is simulated by use of isothermal-isobaric molecular dynamics at a pressure of p≈0.3 GPa in the temperature range from 70 to 300 K. Starting at low temperature a large number of heating/cooling cycles are performed and several characteristic properties (density, total energy, and mobility) are traced as functions of temperature. While the first cycles are showing irreversible structural relaxation effects data points from further cycles are reproducible and give clear evidence for the existence of a glass-to-liquid transition. Although, the observed transition temperatures Tg are dependent on the actual force field used and slightly dependent on the method adopted the results indicate that high-density amorphous ices may indeed be low-temperature structural proxies of ultraviscous high-density liquids.
High performance binderless TiO2 nanowire arrays electrode for lithium-ion battery
Authors: Li Yueming , Lv Xiaojun , Li Jinghong
Published: September 2009

Binderless lithium ion battery electrode fabricated by anodizing Ti foil, in which TiO2 nanowire serves as active materials and unreacted Ti foil as the current collector, exhibited high electrochemical performance.
Reshaping of intense laser pulse with a capillary
Authors: Cao Lihua , Yu Wei , Yu M. Y. , Wang Xin , Gu Yuqiu , He X. T.
Published: September 2009

The reshaping of intense laser pulse by vacuum capillary is studied by particle-in-cell simulation. It is shown that as an intense laser pulse propagates from free space into a capillary, its profile is reshaped due to laser-plasma interaction near the entrance of capillary. As a result, the free-space mode is self-consistently converted into a capillary mode. Only the relatively low-intensity periphery of the reshaped pulse interacts with the capillary-wall plasma, so that the high-intensity center of the pulse can propagate in the narrow vacuum channel over a distance much larger than the Rayleigh length. The mechanism is then applied to reshape a radially imperfect laser pulse having two wings around the center spot. Most of the output light energy is concentrated in the center spot, and the wings are almost completely removed. That is, the quality of the laser pulse can be greatly improved by a capillary.
Diffusion of hydrogen vacancy in Na3AlH6
Authors: Wang Jianchuan , Du Yong , Xu Honghui , Sun Lixian , Liu Zi-kui
Published: September 2009

We perform first-principles calculations to investigate neutral and charged H vacancies dynamics involving vacancy formation and diffusion in Na3AlH6. We find that the activation barrier for local diffusion (diffusion within AlH5 unit) is smaller than that of nonlocal diffusion (diffusion between AlH6 and AlH5 units) for all types of H vacancies; H diffusion in Na3AlH6 is dominated by mobility of positively charged H vacancies. Furthermore, our results confirm that the observed highly mobile species by anelastic spectroscopy measurements is probably the positively charged H vacancies in the form of local diffusion.
Multispot point spread function for multiphoton fluorescence microscopy
Authors: Mondal Partha Pratim
Published: September 2009

We propose and demonstrate an imaging technique capable of generating multiple excitation spot for multiphoton fluorescence microscopy. The point spread function (PSF) is generated by interfering two counterpropagating extended depth of focus beams along the optical axis. At an illumination wavelength of 976 nm and aperture angle of 60°, five distinct nanospots of dimension ≈210 nm is obtained along the optical axis. The resulting PSF has the ability to simultaneously excite multiple planes, and overcomes the sidelobe problem associated with single-photon variant. The proposed multiple-excitation-spot-based-optical imaging technique may find potential application in nanobioimaging and three-dimensional fluorescence microscopy.
Creating perfectly ordered quantum dot arrays via self-assembly
Authors: Shi Feng , Sharma Pradeep , Gunaratne Gemunu H.
Published: September 2009

Several applications involving quantum dots require perfect long-range ordered arrays. Unfortunately, self-assembly (the choice method to fabricate quantum dots) leads to patterns that, although short range ordered, exhibit defects equivalent to grain boundaries and dislocations on a large scale. We note that rotational invariance of film growth is one reason for formation of defects, and hence study an anisotropic model of quantum dot formation. However, nonlinear stability analysis shows that even in the extreme limit of anisotropy, square arrays whose orientations are in a finite range are linearly stable; consequently structures created in the film continue to have defects. Building on insights developed by the authors earlier on a simpler monolayer self-assembly model, we propose controlling the deposition through a mask to generate ordered quantum dots arrays. General principles to estimate geometrical characteristics of the mask are given. Numerical integration of the model shows that perfectly ordered square arrays of quantum dots can indeed be created using masked deposition.
The effect of dust size distribution on quantum dust acoustic wave
Authors: El-Labany S. K. , El-Siragy N. M. , El-Taibany W. F. , Behery E. E.
Published: September 2009

Based on the quantum hydrodynamics theory, a proposed model for quantum dust acoustic waves (QDAWs) is presented including the dust size distribution (DSD) effect. A quantum version of Zakharov–Kuznetsov equation is derived adequate for describing QDAWs. Two different DSD functions are applied. The relevance of the wave velocity, amplitude, and width to the DSD is investigated numerically. The quantum effect changes only the soliton width. A brief conclusion is presented to the current findings and their relevance to astrophysics data is also discussed.
Anomalous parallel momentum transport due to E×B flow shear in a tokamak plasma
Authors: Casson F. J. , Peeters A. G. , Camenen Y. , Hornsby W. A. , Snodin A. P. , Strintzi D. , Szepesi G.
Published: September 2009

Nondiffusive anomalous momentum transport in toroidal plasmas occurs through symmetry breaking mechanisms. In this paper the contribution of sheared E×B flows to parallel momentum transport [R. R. Dominguez and G. M. Staebler, Phys Fluids B 5, 3876 (1993)] is investigated with nonlinear gyrokinetic simulations in toroidal geometry. The background perpendicular shear is treated independently from the parallel velocity shear to isolate a nondiffusive, nonpinch contribution to the parallel momentum flux. It is found that the size of the term depends strongly on the magnetic shear, with the sign reversing for negative magnetic shear. Perpendicular shear flows are responsible for both symmetry breaking and suppression of turbulence, resulting in a shearing rate at which there is a maximum contribution to the momentum transport. The E×B momentum transport is shown to be quenched by increasing flow shear more strongly than the standard linear quench rule for turbulent heat diffusivity.
Engineering double-shifted hysteresis loops in Co/IrMn/Cu/Co films
Authors: Cichelero R. , Pereira L. G. , Dias T. , Schmidt J. E. , Deranlot C. , Petroff F. , Geshev J.
Published: September 2009

Co ( 3   nm ) / IrMn ( 15   nm ) / Cu ( d Cu ) / Co ( 7   nm ) films were subjected to magnetic annealing where its temperature and duration as well as the direction and amplitude of the applied field were varied. We demonstrate that the exchange-bias field magnitude and sign of the subloop of the bottom-pinned Co layer can be tailored in a controlled manner allowing the whole hysteresis loop to be tuned from a double negatively/negatively shifted to a double negatively/positively shifted with the shifts of the subloops in antiphase.
Direct immobilization of enzymes in GaN and InN nanocolumns: The urease case study
Authors: Sofikiti N. , Chaniotakis N. , Grandal J. , Utrera M. , Sanchez-Garcia M. A. , Calleja E. , Iliopoulos E. , Georgakilas A.
Published: September 2009

In this work, the development of potentiometric urea biosensors through the entrapment of urease enzyme within the cavities of nanocolumnar GaN and InN wurtzite semiconductor substrates, is being described. The biosensing capabilities of these materials are compared with biosensors based on the corresponding flat surfaces, in order to check the increased sensitivity and enzyme stabilization properties expected from the nanocolumns. The obtained results proved that the electrochemically active nanocolumns serve both as highly sensitive transducer, as well as stabilizing nanoenvironment within which urease retains its catalytic activity for a prolonged period of time.
A computationally less demanding charge-on-spring model for the water molecule
Authors: Baranyai András
Published: September 2009

We developed a new charge-on-spring model for the water molecule with the advantage of being computationally less demanding. We start from the basic geometry of Lamoureux et al. [J. Chem. Phys. 119, 5185 (2003); Chem. Phys. Lett. 418, 245 (2006)] in order to have a good approximation for the quadrupole moment of the gas phase molecule, but we use only four charged sites. We polarize the molecules in two steps. First, the three sites of the equilibrium gas phase molecule are polarized and this process is accompanied by a charge rearrangement. This step creates the massless spring particle connected to the uncharged oxygen atom. The equilibrium position of the spring particle is found by iteration. We describe the construction of the model and present details of the results obtained by molecular dynamics simulation for the properties of liquid water, hexagonal ice, and gas clusters. Our results are comparable in quality to that of Lamoureux et al. [Chem. Phys. Lett. 418, 245 (2006)] and show good agreements with experiments.
Efficiency enhancement in a single-pass Raman free electron laser
Authors: Rouhani M. H. , Maraghechi B.
Published: September 2009

Efficiency enhancement in free electron laser (FEL) with ion channel and axial magnetic field is compared. By using Maxwell’s equations and nonwiggler averaged equation of motion of electron beam, a set of coupled nonlinear differential equations is derived in the slowly varying amplitude and wave number approximation. Because of using nonwiggler averaged equation of motion, it is possible to treat the injection of the beam into the wiggler. The electron beam propagates with a relativistic velocity, ions are assumed immobile and slippage is ignored. The final set of nonlinear first-order differential equations describing the nonlinear evolution of the FEL is solved by the Runge–Kutta method. Efficiency enhancement in group I orbits is almost the same for both ion channel and axial magnetic field cases, with somewhat larger growth rate for the latter. In group II orbits, efficiency enhancement is not possible for the ion-channel guiding; however, the intrinsic efficiency can be larger than that of the axial magnetic field case.
The structure of nanochannels formed by block copolymer solutions confined in nanotubes
Authors: Chen Houyang , Ruckenstein Eli
Published: September 2009

Monte Carlo simulations are employed to obtain information about the radius and the roughness of the inner surface of the channels, which are generated by a family of block copolymer solutions confined in nanotubes. The fluctuations of the above quantities also have been calculated. The simulations have been carried out by varying the interactions between various kinds of segments and those between segments and the wall of the nanotubes, as well as the chemical structure of the copolymer and the nanotube diameter. The present simulations provide insight regarding the structure of ionic and water channels formed by protein in the phospholipid bilayers of the cell membrane.
On the structure and dynamics of secondary n-alkyl cations
Authors: East Allan L. L. , Bučko Tomáš , Hafner Jürgen
Published: September 2009

A variety of computational studies was undertaken to examine and establish the relative importance of open versus closed structures for unbranched secondary n-alkyl cations. First, the PW91 level of density functional theory was used to optimize over 20 minimum-energy structures of sec-pentyl, sec-hexyl, and sec-heptyl ions, demonstrating that closed structures are more stable than open ones on the potential energy surface (PES). Second, PW91 was used with a theoretical Andersen thermostat to perform a molecular dynamics simulation (150 ps) of C9H19+ at a typical catalytic temperature of 800 K, demonstrating that the structure preference is inverted on the free-energy surface. Third, both quantum (rigid-rotor/harmonic oscillator) and classical partition functions were used to demonstrate that the simulated structure-opening at catalytic temperatures is due to the floppiness of the open forms, which improves its free energy by both lowering its zero-point vibrational energy and increasing its molecular entropy. The particular conformer of the preferred open form (at 800 K) is dependent on length of alkyl ion, with pentyl ions preferring syn/anti structures but longer ions preferring open-clinal ones. These results, plus an additional set of PES optimized structures from an alternative level of theory (MP2/6-31G(d,p)), are used to discuss the likely nature of secondary n-alkyl ions.
Graphene on gold: Electron density of states studies by scanning tunneling spectroscopy
Authors: Klusek Z. , Dabrowski P. , Kowalczyk P. , Kozlowski W. , Olejniczak W. , Blake P. , Szybowicz M. , Runka T.
Published: September 2009

Graphene devices require electric contacts with metals, particularly with gold. Scanning tunneling spectroscopy studies of electron local density of states performed on mono-, bi-, and trigraphene layer deposited on metallic Au/Cr/SiO2/Si substrate shows that gold substrate causes the Fermi level shift downwards which means that holes are donated by metal substrate to graphene which becomes p-type doped. These experimental results are in good accordance with recently published density function theory calculations.
Transmission electron microscopy investigation of inversion domain boundary in Al0.65Ga0.35N grown on AlN/sapphire template
Authors: Sang L. W. , Fang H. , Qin Z. X. , Wang X. Q. , Shen B. , Yang Z. J. , Zhang G. Y. , Zhang X. P. , You L. P. , Yu D. P.
Published: September 2009

A kind of inversion domains (IDs) which originated from the tips of threading dislocations were observed in the Al0.65Ga0.35N layer by transmission electron microscopy (TEM). The IDs showed columnar structures with diameters of 10–20 nm. We find that the dislocations evolved into V-shape boundaries then form IDs. By high resolution TEM analysis, the atomic structure at the boundary was proved to be the IDB∗ structure, in which each atom remains fourfold coordinated without the formation of Ga–Ga or N–N bonds.
A model for jumping and bubble waves in the Belousov–Zhabotinsky-aerosol OT system
Authors: Vanag Vladimir K. , Epstein Irving R.
Published: September 2009

We develop a four-variable model, based on the classic Field–Kőrös–Noyes mechanism for the oscillatory Belousov-Zhabotinsky (BZ) reaction, that describes recently discovered jumping waves and bubble waves in the BZ reaction in aerosol OT microemulsion and provides insight into their origins. Contrary to suggestions based on previous models, it appears that these phenomena can arise from interaction between a Turing instability and either excitability or a Hopf instability of the steady state, rather than requiring a wave instability. The model should be useful for studying other patterns in BZ microemulsions as well as the behavior of systems of BZ microdroplets coupled through bromine diffusion.
Multiple quantum NMR dynamics of spin-12 carrying molecules of a gas in nanopores
Authors: Doronin S. I. , Fedorova A. V. , Fel’dman E. B. , Zenchuk A. I.
Published: September 2009

We consider the multiple quantum (MQ) NMR dynamics of a gas of spin carrying molecules in nanocavities. MQ NMR dynamics is determined by the residual dipole-dipole interactions, which are not averaged completely due to the molecular diffusion in nanopores. Since the averaged nonsecular Hamiltonian describing MQ NMR dynamics depends on only one coupling constant, this Hamiltonian commutes with the square of the total spin angular momentum Î2. We use the basis of common eigenstates of Î2 and the projection of I on the external magnetic field for investigation of MQ NMR dynamics. This approach allows us to study MQ NMR dynamics in systems consisting of several hundreds of spins. The analytical approximation of the stationary profile of MQ coherences is obtained. The analytical expressions for MQ NMR coherence intensities of the five-spin system in a nanopore are found. Numerical investigations allow us to find the dependencies of intensities of MQ coherences on their orders (the profiles of MQ coherences) in systems consisting of 600 spins and even more. It is shown that the stationary MQ coherence profile in the considered system is an exponential one.
Effects of Ti top electrode thickness on the resistive switching behaviors of rf-sputtered ZrO2 memory films
Authors: Wang Sheng-Yu , Lee Dai-Ying , Tseng Tseung-Yuen , Lin Chih-Yang
Published: September 2009

In this study, we propose a simple method to produce the various interface thicknesses within Ti/ZrO2 by changing the thickness of the Ti top electrode. As the Ti thickness increases, the induced interface thickness also increases to degrade the dielectric strength of the ZrO2, further lowering the forming voltage. However, when the interface layer is thick enough, it will trap sufficient charges to build up an opposite electric field to increase the forming voltage. The induced interface thickness is found to obviously affect the bias polarity of the resistive switching behavior and the device reliability. A fluctuant ON process is also demonstrated to be attributed to the competition between the formation and rupture of the conducting filaments.
Ab initio study of ferroelectric and nonlinear optical performance in BiFeO3 ultrathin films
Authors: Ju Sheng , Cai Tian-Yi
Published: September 2009

Density functional theory within the local density approximation plus on-site Coulomb repulsion is applied to investigate the crystal structure, electronic structure, multiferroism, linear, and nonlinear optical response in BiFeO3 ultrathin films, which are fabricated via epitaxial growth on (001)-oriented SrTiO3 substrates and have a strained P4mm phase. Born effective charges are calculated within the Berry-phase method and the spontaneous electric polarization is found to be 79 μC/cm2. The second-harmonic generation susceptibility, which can reach 7.5×10−7 esu, undergoes a substantial change between different magnetic orderings. Our calculations demonstrate the existence of robust ferroelectric distortion and nonlinear optical response in these ultrathin films.
Aging and the Discrimination of Object Weight
Authors: Norman J Farley , Norman Hideko F , Swindle Jessica M , Jennings L RaShae , Bartholomew Ashley N
Published: September 2009

A single experiment was carried out to evaluate the ability of younger and older observers to discriminate object weights. A 2-alternative forced-choice variant of the method of constant stimuli was used to obtain difference thresholds for lifted weight for twelve younger (mean age = 21.5 years) and twelve older (mean age = 71.3 years) adults. The standard weight was 100 g, whereas the test weights ranged from 85 to 115 g. The difference thresholds of the older observers were 57.6% higher than those of the younger observers: the average difference thresholds were 10.4% and 6.6% of the standard for the older and younger observers, respectively. The current findings of an age-related deterioration in the ability to discriminate lifted weight extend and disambiguate the results of earlier research.
Detection of DNA Damage Induced by Hydroquinone and Catechol Using an Electrochemical DNA Biosensor
Authors: Wang Chuanhu , Zhao Jun , Zhang Dapeng , Yang Zhousheng
Published: September 2009

DNA damage induced by hydroquinone and catechol was detected by an electrochemical method. Calf thymus DNA was immobilized onto the surface of a pretreated glassy carbon electrode (GCE(ox)) to form a DNA/GCE(ox) modified electrode. Then the DNA/GCE(ox) was incubated in acetate buffer solution containing hydroquinone or catechol at a constant potential for the desired time. Differential pulse voltammetric experiments were then performed. The anodic peaks corresponding to the oxidation of guanisine and adenosine on the electrode could be observed on voltammetric curves. The experimental results showed that DNA damage could be detected using electrochemical DNA biosensors. The extent of DNA damage could be electrochemically recognized via the change of the anodic peak current. DNA damage induced by hydroquinone was greater than that by catechol. The response conditions were optimized with respect to DNA concentration, pH, ionic strength, and other variables.
Flexibility of Short-Strand RNA in Aqueous Solution as Revealed by Molecular Dynamics Simulation: Are A-RNA and A´-RNA Distinct Conformational Structures?
Authors: Ouyang Defang , Zhang Hong , Herten Dirk-Peter , Parekh Harendra S. , Smith Sean C.
Published: September 2009

We use molecular dynamics simulations to compare the conformational structure and dynamics of a 21-base pair RNA sequence initially constructed according to the canonical A-RNA and A′-RNA forms in the presence of counterions and explicit water. Our study aims to add a dynamical perspective to the solid-state structural information that has been derived from X-ray data for these two characteristic forms of RNA. Analysis of the three main structural descriptors commonly used to differentiate between the two forms of RNA – namely major groove width, inclination and the number of base pairs in a helical twist – over a 30 ns simulation period reveals a flexible structure in aqueous solution with fluctuations in the values of these structural parameters encompassing the range between the two crystal forms and more. This provides evidence to suggest that the identification of distinct A-RNA and A′-RNA structures, while relevant in the crystalline form, may not be generally relevant in the context of RNA in the aqueous phase. The apparent structural flexibility observed in our simulations is likely to bear ramifications for the interactions of RNA with biological molecules (e.g. proteins) and non-biological molecules (e.g. non-viral gene delivery vectors).
Chiral Amine-Mediated Asymmetric Conjugate Additions to Vinyl Sulfones
Authors: Zhu Qiang , Lu Yixin
Published: September 2009

Chiral molecules containing sulfone groups are useful intermediates and have found wide applications in organic synthesis. In this account, recent progress in the use of vinyl sulfones as Michael acceptors in the asymmetric organocatalytic conjugate addition is summarized.
Base-Sensitivity of Arginine Alpha-Ketoamide Inhibitors of Serine Proteases
Authors: Stoermer Martin J. , Leung Donmienne , Young Paul R. , Fairlie David P.
Published: September 2009

Serine protease enzymes use a serine hydroxyl group to catalyze hydrolysis of polypeptides. They are important in immunity, blood clotting, digestion, and as therapeutic or diagnostic targets for cancer, diabetes, stroke, inflammatory diseases, and viral infections. Their inhibitors typically possess an electrophile that reacts with the nucleophilic hydroxyl group of the catalytic serine. The α-ketoamide is a valuable electrophile in inhibitor discovery as it permits synthetic elaboration to both sides, unlike other electrophiles. Here we show that an α-ketoamide is unstable above pH 7 when adjacent to the C-terminus of arginine – the guanidine side chain condenses with the α-ketoamide at the keto group rather than the amide carbonyl to form a six-membered hemiaminal rather than a seven-membered lactam.
The Enantiocontrolled Synthesis of a Highly Functionalized Cyclohexenone Related to the A-Ring of the Furanosteroid Viridin
Authors: Findlay Alison D. , Gebert Antje , Cade Ian A. , Banwell Martin G.
Published: September 2009

A seven-step reaction sequence has been used to convert the enantiomerically pure cis-1,2-dihydrocatechol 10 into the cyclohexenone 17a. A near equivalent sequence involving the same starting material has allowed for the synthesis of the regioisomeric system 17b. Compound 17a is related to the A-ring of ent-viridin (ent-1), the non-natural enantiomer of the furanosteroid viridin (1).
Structure of 4,4-Bisphenylsulfonyl-N,N-dimethylbutylamine: Interplay of Intramolecular C–H···N, C–H···O=S, and ?···? Interactions
Authors: Ran Jiong , Wong Ming Wah
Published: September 2009

Conformations of 4,4-bisphenylsulfonyl-N,N-dimethylbutylamine (BSDBA) were examined by ab initio calculations. Intramolecular C–H···N, C–H···O, and π···π interactions are found to play an important role in governing the conformational properties. This finding is supported by charge density analysis based on the theory of atoms in molecules. The calculated molecular structure and 1H chemical shifts of the methyl derivative (BSTBA) are in excellent agreement with experimental findings. The intramolecular C–H···N hydrogen bond in BSDBA is estimated to have a significant interaction energy of 25 kJ mol–1. The sulfonyl oxygens in BSDBA interact readily with neighbouring methylene, methyl and phenyl hydrogens via C–H···O=S hydrogen bonds. In agreement with experiment, solvent effect calculations indicate that these weaker intramolecular interactions prevail in an aprotic polar medium.
A state-mutating genetic algorithm to design ion-channel models
Authors: Menon Vilas , Spruston Nelson , Kath William L.
Published: September 2009

Realistic computational models of single neurons require component ion channels that reproduce experimental findings. Here, a topology-mutating genetic algorithm that searches for the best state diagram and transition-rate parameters to model macroscopic ion-channel behavior is described. Important features of the algorithm include a topology-altering strategy, automatic satisfaction of equilibrium constraints (microscopic reversibility), and multiple-protocol fitting using sequential goal programming rather than explicit weighting. Application of this genetic algorithm to design a sodium-channel model exhibiting both fast and prolonged inactivation yields a six-state model that produces realistic activity-dependent attenuation of action-potential backpropagation in current-clamp simulations of a CA1 pyramidal neuron.
Structure of apo-CAP reveals that large conformational changes are necessary for DNA binding
Authors: Sharma Hitesh , Yu Shaoning , Kong Jilie , Wang Jimin , Steitz Thomas A.
Published: September 2009

The binding of cAMP to the
Escherichia coli
catabolite gene activator protein (CAP) produces a conformational change that enables it to bind specific DNA sequences and regulate transcription, which it cannot do in the absence of the nucleotide. The crystal structures of the unliganded CAP containing a D138L mutation and the unliganded WT CAP were determined at 2.3 and 3.6 Å resolution, respectively, and reveal that the two DNA binding domains have dimerized into one rigid body and their two DNA recognition helices become buried. The WT structure shows multiple orientations of this rigid body relative to the nucleotide binding domain supporting earlier biochemical data suggesting that the inactive form exists in an equilibrium among different conformations. Comparison of the structures of the liganded and unliganded CAP suggests that cAMP stabilizes the active DNA binding conformation of CAP through the interactions that the N
6
of the adenosine makes with the C-helices. These interactions are associated with the reorientation and elongation of the C-helices that precludes the formation of the inactive structure.
Modulation of neuronal responses during covert search for visual feature conjunctions
Authors: Buracas Giedrius T. , Albright Thomas D.
Published: September 2009

While searching for an object in a visual scene, an observer's attentional focus and eye movements are often guided by information about object features and spatial locations. Both spatial and feature-specific attention are known to modulate neuronal responses in visual cortex, but little is known of the dynamics and interplay of these mechanisms as visual search progresses. To address this issue, we recorded from directionally selective cells in visual area MT of monkeys trained to covertly search for targets defined by a unique conjunction of color and motion features and to signal target detection with an eye movement to the putative target. Two patterns of response modulation were observed. One pattern consisted of enhanced responses to targets presented in the receptive field (RF). These modulations occurred at the end-stage of search and were more potent during correct target identification than during erroneous saccades to a distractor in RF, thus suggesting that this modulation is not a mere presaccadic enhancement. A second pattern of modulation was observed when RF stimuli were nontargets that shared a feature with the target. The latter effect was observed during early stages of search and is consistent with a global feature-specific mechanism. This effect often terminated before target identification, thus suggesting that it interacts with spatial attention. This modulation was exhibited not only for motion but also for color cue, although MT neurons are known to be insensitive to color. Such cue-invariant attentional effects may contribute to a feature binding mechanism acting across visual dimensions.
Long-term natural variability and 20th century climate change
Authors: Swanson Kyle L. , Sugihara George , Tsonis Anastasios A.
Published: September 2009

Global mean temperature at the Earth's surface responds both to externally imposed forcings, such as those arising from anthropogenic greenhouse gases, as well as to natural modes of variability internal to the climate system. Variability associated with these latter processes, generally referred to as natural long-term climate variability, arises primarily from changes in oceanic circulation. Here we present a technique that objectively identifies the component of inter-decadal global mean surface temperature attributable to natural long-term climate variability. Removal of that hidden variability from the actual observed global mean surface temperature record delineates the externally forced climate signal, which is monotonic, accelerating warming during the 20th century.
Beyond the Bosphorus?
Authors: Wimmel Andreas
Published: September 2009

This article examines the impact of national borders on public discourses, based on a case study of the struggle surrounding Turkey’s application to join the European Union (EU). Comparing opinions, reasons and interpretation patterns in quality press commentaries about enlarging the EU beyond the Bosphorus, the article confirms the importance and robustness of national cleavages between the German and the French public spheres on the one hand and the British public sphere on the other. Whereas Turkish membership was predominantly rejected on the continent, the British commentators strongly and almost unanimously supported Ankara’s request. These similarities and divergences, I argue, are first and foremost the result of competing visions of Europe’s finality, especially regarding various constitutional ideas and cultural principles. Against this background, the Turkey question was partly exploited as an instrument to advance or to suppress different concepts on the future of European integration.
The schematic structure of Spanish PhD thesis introductions
Authors: Carbonell-Olivares María , Gil-Salom Luz , Soler-Monreal Carmen
Published: September 2009

Since the 1990s written academic genres have received considerable attention in discourse and rhetorical studies, especially texts written in English. Although few studies describe PhD theses as a genre, some work has been carried out on their macrostructure and the rhetorical moves of certain sections. In the Spanish literature, genre studies on academic writing are scarce relative to those in English, especially in the case of doctoral theses. We analyse the introductions of 21 doctoral theses in computing written in Spanish using Bunton’s model (2002) for thesis introductions in English. The results indicate that most of the steps in this model are applicable to our corpus, but several new steps and sub-steps have been distinguished to account for the observed moves of Spanish PhD thesis introductions. The complexity of the thesis introduction is related to the scope and depth of the research carried out for a doctoral thesis, the need to display extensive knowledge of the field and to justify the relevance of the research.