bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser ablation characteristics of yttria-doped zirconia in the nanosecond and femtosecond regimes
Authors: Heiroth S. , Koch J. , Lippert T. , Wokaun A. , Günther D. , Garrelie F. , Guillermin M.
Published: January 2010

The laser ablation characteristics of yttria-stabilized zirconia (YSZ) have been investigated as a function of the target microstructure and dopant level for different nanosecond- [ArF, KrF, and XeCl excimers; Nd:YAG (yttrium aluminum garnet) (fourth harmonic)] and femtosecond-laser sources [Ti:sapphire (fundamental and third harmonic)]. Particle ejection, which compromises the quality of coatings prepared by pulsed laser deposition (PLD), was analyzed in detail. Nanosecond-laser pulses cause a severe thermomechanical surface cracking and exfoliation of micron-sized fragments on a microsecond to millisecond time scale in the case of 8–9.5 mol % Y2O3-doped, fully stabilized zirconia (8YSZ and 9.5YSZ) targets. As a consequence of the intrinsic material brittleness, fully stabilized YSZ coatings deposited by PLD contained particles for all tested conditions. Lower doped partially stabilized zirconia (3YSZ) exhibits a superior fracture toughness attributed to a laser-induced partial transition to the monoclinic phase, detected by Raman spectroscopy, which enables the deposition of particle-free dense thin films by conventional PLD using nanosecond-UV laser radiation at moderate fluences of 1.2–1.5 J/cm2. The ablation dynamics of ultrashort laser pulses differ fundamentally from the nanosecond regime as evidenced, e.g., by time-resolved shadowgraphy and light scattering experiments. Femtosecond pulses prevent the exfoliation of micron-sized fragments but result invariably in a pronounced ejection of submicron particles. The resulting PLD coatings are porous and reveal a large surface roughness as they consist of an agglomeration of nanoparticles. Femtosecond-NIR pulses provide a factor of 2.5–10 higher material removal rates compared to nanosecond- and femtosecond-UV pulses. The ablation metrics, i.e., threshold fluence and effective absorptivity, mainly depend on the laser wavelength while the pulse duration, target microstructure, and dopant level are of minor importance. Evidence is presented that incubation effects play a significant role in nanosecond- and femtosecond-laser ablations of YSZ enabling material removal at comparatively low fluences for sub-bandgap photon energies.
Secondary electron doping contrast: Theory based on scanning electron microscope and Kelvin probe force microscopy measurements
Authors: Volotsenko I. , Molotskii M. , Barkay Z. , Marczewski J. , Grabiec P. , Jaroszewicz B. , Meshulam G. , Grunbaum E. , Rosenwaks Y.
Published: January 2010

The secondary electron emission flux in a scanning electron microscope is a powerful tool for delineation of electrically active dopant concentration, built-in potentials, and surface electric fields in semiconductor junctions. In all the secondary electron images of p-n junctions, the p-doped regions appear brighter than n-doped regions. We present a theory for the doping contrast in p-n junctions that is based on the secondary electron emission yield and surface band bending extracted from Kelvin probe force microscopy measurements. We show that the contrast is governed by the secondary electron escape depth, and their escape probability which is related to the secondary electron energy distribution and the effective electron affinity. It is found that the escape depth is the main factor determining the dopant contrast, and the escape probability has a smaller effect. In addition, our theory explains the logarithmic dependence of the measured contrast on the acceptor concentration in silicon reported by many groups.
Multiple-lobed bifurcation of rotating liquid drops levitated by ultrasound
Authors: Lü Y. J. , Xie W. J. , Wei B.
Published: January 2010

It is previously predicted that the equilibrium shape of a rotating liquid drop evolves from the axisymmetric to the two-, three-, and four-lobed morphologies as the angular velocity increases. Although the two- and three-lobed shape bifurcations have been observed in experiments, the four-lobed equilibrium shape is scarcely reported. Here, we investigate the multiple-lobed shape bifurcations of rotating drops by using acoustic levitation, and in particular, follow the evolution of the four-lobed equilibrium shape. A new shape family of rotating drops characterized by five-lobed bifurcation is also observed, which is unexpected in the theoretical predictions. A numerical method is employed to simulate the shape evolution of acoustically levitated and rotating drops. And the results validate the existence of bifurcation point shifts among all the lobed-shape families due to the initial drop flattening induced by the acoustic radiation pressure, which plays a decisive role in the emergence of the five-lobed shape.
Lateral hot electron transport and ion acceleration in femtosecond laser pulse interaction with thin foils
Authors: Psikal J. , Tikhonchuk V. T. , Limpouch J. , Klimo O.
Published: January 2010

Hot electron transport along the target surface out of the laser-irradiated spot plays an important role in such applications as ion acceleration or fast ignition of fusion reactions. In this paper, the lateral electron transport in a thin foil, limited in transverse sizes, is studied by numerical particle-in-cell simulations for two linear polarizations (p and s) of femtosecond laser pulse incident on a foil at various angles. Two mechanisms of the transport are identified: the first one is due to hot electron recirculation across the foil and the second is electron guiding along the foil surface by quasistatic magnetic and electric fields. It is demonstrated that the second mechanism takes place for larger incidence angles, although the recirculation is still important. The ions accelerated from a lateral foil edge, which is out of the laser focal spot, can have higher energies than the ions from the rear foil side.
Manipulation of magnetism by electrical field in a real recording system
Authors: Zhou Tiejun , Leong S. H. , Yuan Z. M. , Hu S. B. , Ong C. L. , Liu B.
Published: January 2010

We report an electrically controlled magnetism in a real recording system with CoCrPt–TiO2 nanocomposite thin films as recording medium. We show that in a spin-stand test, with a small voltage of 3 V applied across the head-media gap during recording, a 13% reduction of saturation current was observed and the read back waveforms showed sharper transitions. These account for the 3 dB improvement in read back signal-noise-ratio of the written magnetic information. The improved recording performance is mainly attributed to the reduction of anisotropy of the recording medium in the presence of electrical field. Simulations were carried out to understand the magnetization reversal process under applied electric and magnetic fields.
Controllable optical emission spectroscopy diagnostic system for analysis of process chemistries
Authors: Thamban P. L. Stephan , Hosch Jimmy , Goeckner M. J.
Published: January 2010

Optical emission spectroscopy (OES) diagnostics have been employed for many years in plasma etch end point detection schemes. Unfortunately some newer process systems have much lower optical emission or limited optical access. To overcome such limitations, an OES diagnostic system making use of variable e-beam has been developed. That system is described and initial experimental results are presented. A strong correlation is observed between the optical emission intensity and e-beam current, a measurable electrical parameter. This correlation offers means to normalize optical signal and to be used as a feedback input to the electronics that control the plasma source. In addition there is a measurable response from the different lines due to energy of the electrons, indicating a new degree of freedom in the diagnostic that can be tapped for more precise analysis of end point.
Microcantilever sensors for monitoring the evaporation of microdrops of pure liquids and mixtures
Authors: Liu Chuanjun , Bonaccurso Elmar
Published: January 2010

We describe in detail a nonimaging technique that allows the measurement of the mass, the radius, and the contact angle of evaporating sessile microdrops of pure liquids and binary mixtures. The microdrops were deposited onto hydrophobized silicon microcantilevers whose bending and resonance frequency were monitored during drop evaporation. We verify the laws of evaporation kinetics for microdrops with diameters from 80 down to 10 μm. The evaporation of mixtures of water/ethanol drops confirmed previous results with millimeter sized drops. N,N-dimethylformamide drops undergo a transformation from an initial spherical shape to a thin film. Flattening of the drop causes a slowdown of the evaporation kinetics at the end. Two concurring factors are at its origin: the rising disjoining pressure stabilizes the thin liquid film and the increasing radius of curvature of the drop reduces the vapor pressure.
On the influence of wakefields on three-dimensional particle arrangements
Authors: Kroll M. , Schablinski J. , Block D. , Piel A.
Published: January 2010

The role of wakefields on the three-dimensional (3D) particle arrangement in finite dust clouds at low neutral gas pressures is investigated experimentally. Using a novel stereoscopic digital in-line holography approach for the instantaneous measurement of the 3D particle positions, the structural properties of finite dust clouds are studied. The competition of a nested shell structure (known from Yukawa balls) and vertical particle chains (known for particle clouds confined in the plasma sheath) results in a markedly different particle arrangement. With experiments studying the dynamical response in a two-particle system for identical plasma and confinement conditions, we show that the presence of an ion focus in the wake of the particle is responsible for the observed structural differences.
Geometric criterion for RR↔MR transition in hypersonic double-wedge flows
Authors: Hu Z. M. , Gao Y. L. , Myong R. S. , Dou H. S. , Khoo B. C.
Published: January 2010

In a previous research article [Z. M. Hu et al., Phys. Fluids 21, 011701 (2009)], an overall Mach reflection (oMR) configuration with double inverse Mach reflection patterns was computationally confirmed when a double-wedge geometry interacts with a hypersonic flow. Extended computations are conducted in this paper and compared to analytical solutions based on the classical two- and three-shock theories. A geometric criterion is proposed for the transition between regular reflection and Mach reflection occurring inside the parameter space where a type V interaction of shock wave presents in hypersonic double-wedge flows. An oMR solution is allowed by the geometric criterion, while it is theoretically inadmissible. In the vicinity of symmetric condition, regular to Mach reflection transition can also be triggered prior to the theoretical criterion by disturbance generated by a slight increase in the second wedge angle.
Effects of subconduction band excitations on thermal conductance at metal-metal interfaces
Authors: Hopkins Patrick E. , Beechem Thomas E. , Duda John C. , Smoyer Justin L. , Norris Pamela M.
Published: January 2010

Increased power densities combined with the decreased length scales of nanosystems give rise to large thermal excitations that can drastically affect the electron population near the Fermi surface. In light of such conditions, a model is developed for electron thermal boundary conductance (eTBC) that accounts for significant changes in the electron and hole populations around the Fermi level that occur at heightened temperatures. By including the contribution of subconduction band electrons to transport and evaluating the transmission coefficient based upon the total number of available states, an extension of eTBC predictions to high temperatures is made possible.
Sense toxins/sewage gases by chemically and biologically functionalized single-walled carbon nanotube sensor based microwave resonator
Authors: Tooski S. B.
Published: January 2010

In this work the complex permittivity and microwave absorption of toxins/sewage gases and functionalized single-walled carbon nanotube sensors in a perturbed microwave resonant cavity are studied with the aid of a kinetic model. The results show that the real permittivity decreases and the imaginary permittivity increases with increasing the electron density; however, the real permittivity increases and the imaginary permittivity decreases with the collision frequency increasing. The results furthermore show that low electron density and high collision frequency can greatly reduce the microwave absorption, while high electron density and low collision frequency can increase the microwave absorption. The microwave absorption shifts to high frequency with increasing the electron density. The microwave absorption, in contrast, shifts to low frequency with the collision frequency increasing. The kinetic model may be used to study the effects of gas pressure on the complex permittivity and microwave absorption.
Theoretical studies of absorption cross sections for the C̃ B12-X̃ A11 system of sulfur dioxide and isotope effects
Authors: Tokue Ikuo , Nanbu Shinkoh
Published: January 2010

The C̃ B12-X̃ A11 photoexcitation of SO2 was studied to investigate excited-state dynamics and the effects of the initial vibrational state. Ultraviolet photoabsorption cross sections (σ's) of seven isotopologues (S32 O162, S33 O162, S34 O162, S36 O162, S32O16O17, S32O16O18, S34O16O18) were computed using the wave packet propagation technique based on the three-dimensional potential energy surfaces of the X̃ and C̃ states, which were calculated using the ab initio molecular orbital configuration interaction method. Numerous wave packet simulations were carried out under the adiabatic approximation and used to calculate the σ’s of the seven isotopologues at 298 K; we concluded that the absorption spectrum of SO2 can be reliably modeled within the adiabatic framework based on the analysis of the time evolution of the wave packet. The calculated σ’s are in reasonable agreement with the recent experiment in the 190–228 nm region, and the isotope shifts of the peaks for S33 O162 and S34 O162 relative to the corresponding peaks for S32 O162 are in good agreement with the observed data. Relative to the σ of S32 O162, isotopic substitution shows a significant increment for those of S34 O162 and S36 O162 in the 190–228 nm region. This trend is consistent with the observed data.
Effect of shear on nanoparticle dispersion in polymer melts: A coarse-grained molecular dynamics study
Authors: Kalra Vibha , Escobedo Fernando , Joo Yong Lak
Published: January 2010

Coarse-grained, molecular dynamics (MD) simulations have been conducted to study the effect of shear flow on polymer nanocomposite systems. In particular, the interactions between different components have been tuned such that the nanoparticle-nanoparticle attraction is stronger than nanoparticle-polymer interaction, and therefore, the final equilibrium state for such systems is one with clustered nanoparticles. In the current study, we focus on how shear flow affects the kinetics of particle aggregation at the very initial stages in systems with polymers of different chain lengths. The particle volume fraction and size are kept fixed at 0.1 and 1.7 MD units, respectively. Through this work, shear has been shown to significantly slow down nanoparticle aggregation, an effect that was found to be a strong function of both polymer chain length and shear rate. To understand our findings, a systematic study on effect of shear on particle diffusion and an analysis of relative time scales of different mechanisms causing particle aggregation have been conducted. The aggregation rate obtained from the time scale analysis is in good agreement with that determined from the aggregation time derived from the pair correlation function monitored during simulations.
Quantum oscillations in adsorption energetics of atomic oxygen on Pb(111) ultrathin films: A density-functional theory study
Authors: Hu Ziyu , Yang Yu , Sun Bo , Shao Xiaohong , Wang Wenchuan , Zhang Ping
Published: January 2010

Using first-principles calculations, we have systematically studied the quantum size effects of ultrathin Pb(111) films on the adsorption energies and penetration energy barriers of oxygen atoms. For the on-surface adsorption of oxygen atoms at different coverages, all the adsorption energies are found to show bilayer oscillation behaviors. It is also found that the work function of Pb(111) films still keeps the bilayer-oscillation behavior after the adsorption of oxygen atoms, with the values being enlarged by 2.10–2.62 eV. For the penetration of the adsorbed oxygen atoms, it is found that the energy barriers are all oscillating with a bilayer period on different Pb(111) films because of the modulation of quantum size effects. Our studies indicate that the quantum size effect in ultrathin metal films can modulate a lot of processes during surface oxidation.
Instability of shock-induced nozzle flow separation
Authors: Johnson Andrew D. , Papamoschou Dimitri
Published: January 2010

We investigate experimentally the causes of jet plume instability and enhanced mixing observed in the exhaust of shock-containing convergent-divergent nozzles. Key features of the internal flow are the separation shock, separation shear layers, and pattern of alternating expansion and compression waves downstream of the shock. We focus on two possible reasons for this instability—the motion of the separation shock and the wave pattern downstream of the shock. The nozzle flow was generated in a planar facility with variable area ratio and pressure ratio, and the motion of the shock was tracked using time-resolved wall pressure measurements. The isolated effect of the wave pattern was investigated in a separate facility wherein a sonic shear layer, simulating the nozzle separation shear layer, was disturbed with compression and expansion waves emanating from a wavy wall. In both instances, the instability of the shear layer was characterized by time-resolved measurements of the total pressure. In the nozzle flow, the amplitude of shock motion increases with shock strength. Correlation of shock motion with shear layer total pressure is virtually absent for weak shocks but becomes significant for strong shocks. However, impingement of stationary waves on the shear layer had no impact on its growth rate. We conclude that the enhanced shear layer instability is strongly coupled to shock motion, and that the wave pattern by itself is not a cause of enhanced mixing. The occurrence of asymmetric separation at large shock strengths is a further contributor to the enhancement of instability.
Modified shock velocity in heterogeneous wetted foams in the strong shock limit
Authors: Elbaz D. , Dias F. , Canaud B. , Ballereau P.
Published: January 2010

Shock propagation in wetted foams described by a regular square alignment of fibers of heavy medium immersed in a light medium is studied. A two-dimensional Eulerian adaptative mesh refinement code is used. The equation of state is assumed to be that of perfect gases. The variation of the presence ratio of fibers—the ratio of the dry-foam density to the solid density—leads to an increase in the shock velocity in comparison to the speed that the shock would have in a homogeneous medium with the same average density. This departure from the homogeneous case exhibits a maximum when the presence ratio is roughly 70%. Only three independent parameters seem to have an effect on the shock velocity: the presence ratio, the density ratio between both fluids, and the adiabatic exponent. The numerical results seem to be consistent with a thermodynamic description of turbulence.
Infrared dielectric response and Raman spectra of tunable Ba0.5Sr0.5TiO3–Mg2TiO4 composite ceramics
Authors: Zhang Jingji , Zhai Jiwei , Wang Jiangying , Shao Jun , Lu Xiang , Yao Xi
Published: January 2010

Dielectric properties of (1−y)Ba0.5Sr05TiO3–yMg2TiO4 (y=0.5–0.8) composite ceramics were studied by using spectroscopic techniques. Increasing the concentration of Mg2TiO4 resulted in hardening of the softest mode, which is responsible for the decrease in the intrinsic permittivity and dielectric loss with increasing y. The soft mode hardens with y and becomes harmonic, which caused the reduction in tunability of the Ba0.5Sr05TiO3–Mg2TiO4 composite ceramics. Raman spectra revealed that linewidth of the MgO4 bending vibration decreases with increasing y, confirming the increase in intrinsic quality factor with y.
Electric field induced sp3-to-sp2 conversion and nonlinear electron transport in iron-doped diamond-like carbon thin film
Authors: Liao Xing , Zhang Xiaozhong , Takai Kazuyuki , Enoki Toshiaki
Published: January 2010

The electron transport was investigated at different temperatures and voltages for Fe-doped diamond-like carbon (DLC) thin films on Si substrate. The I-t curves show saturation at a low bias voltage, where the increasing rate and time needed for the saturation increase with the elevation of temperature. When the bias voltage exceeds a threshold voltage, the I-t curves show a three-stage process: the current increases, takes a plateau, and finally increases divergently in the last stage. These phenomena, which are not observed in the nondoped DLC/Si system, can be explained in terms of the electric-field-induced sp3-to-sp2 conversion, in which embedded Fe works as catalyst.
Chain dynamics of poly(ethylene-alt-propylene) melts by means of coarse-grained simulations based on atomistic molecular dynamics
Authors: Pérez-Aparicio R. , Colmenero J. , Alvarez F. , Padding J. T. , Briels W. J.
Published: January 2010

We present coarse-grained molecular dynamics simulations of poly(ethylene-alt-propylene) (PEP) melts, ranging in chain length from about Ne (the entanglement length) to N=6Ne. The coarse-grained parameters, potential of mean force and bare friction, were determined from fully atomistic molecular dynamics simulations carried out on a PEP cell containing 12 chains of 80 monomers each and subjected to periodic boundary conditions. These atomistic simulations were previously validated by means of extensive neutron scattering measurements. Uncrossability constrains were also introduced in the coarse-grained model to prevent unphysical bond crossing. The coarse-grained simulations were carried out at 492 K and focus on chain dynamics. The results obtained were analyzed in terms of Rouse coordinates and Rouse correlators. We observe deviations from Rouse behavior for all chain lengths investigated, even when the chain stiffness is incorporated in the Rouse model. These deviations become more important as the chain length increases. The general scenario emerging from the results obtained is that the deviations from Rouse-like behavior are due to correlations among the forces acting upon a chain bead, which seem to be related with the constraint of uncrossability among the chains. As consequence, nonexponentiality of the Rouse correlators and mode- and time-dependent friction are observed. It seems that, in the molecular weight explored, these effects still give not raise to reptation behavior but to a crossover regime between Rouse and reptation. On the other hand, the results obtained are in qualitative agreement with those expected from the so-called generalized Rouse models, based on memory function formalisms.
Macroscopic description of the isotropic to antiferroelectric B2 phase transition in banana-shaped liquid crystals
Authors: Mukherjee Prabir K.
Published: January 2010

We present a mean-field description of the phase transitions, which are obtained when cooling from the isotropic liquid to the first liquid crystalline phase in compounds composed of achiral banana-shaped molecules. We put special emphasis on the isotropic to antiferroelectric B2 phase transition. The free energy is written in terms of the coupled order parameters including the antiferroelectric polarization. We present a detailed analysis of the different phases that can occur and analyze the question under which conditions a direct isotropic to antiferroelectric B2 phase transition is possible when compared with other phase transitions. The theoretical results are found to be in qualitative agreement with all published experimental results.
Nanoscopic spontaneous motion of liquid trains: Nonequilibrium molecular dynamics simulation
Authors: Bahrami Amir Houshang , Jalali Mir Abbas
Published: January 2010

Macroscale experiments show that a train of two immiscible liquid drops, a bislug, can spontaneously move in a capillary tube because of surface tension asymmetries. We use molecular dynamics simulation of Lennard-Jones fluids to demonstrate this phenomenon for NVT ensembles in submicron tubes. We deliberately tune the strength of intermolecular forces and control the velocity of bislug in different wetting and viscosity conditions. We compute the velocity profile of particles across the tube and explain the origin of deviations from the classical parabolae. We show that the self-generated molecular flow resembles the Poiseuille law when the ratio of the tube radius to its length is less than a critical value.
On spread extent of sessile droplet into porous medium: Numerical solution and comparisons with experiments
Authors: Markicevic B. , D’Onofrio T. G. , Navaz H. K.
Published: January 2010

The spread of a wetting liquid sessile droplet into porous medium is solved numerically using the capillary network model with a microforce balance boundary condition at the liquid/gas free interface in the porous medium. The spread starts as the porous medium imbibes the sessile liquid, followed by liquid additionally being spread inside the porous medium itself. After there is no remaining sessile liquid, the net flow across the porous medium boundaries is equal to zero. Either spread, with or without sessile liquid present at the porous medium surface, is rendered by local differences in capillary pressure. These local differences are accounted for by implementing the numerical solution over a heterogeneous capillary network, consisting of pores connected by throats. Both pores and throats follow predefined distribution functions. Once there is no sessile liquid present on the porous medium surface, it is found from a numerical solution that the liquid front can extend significantly in time, wetting very large volumes of the porous medium. This is also measured in experiments, in which over time, an increase in wetted volume of more than 16 times is observed compared to the wetted volume right after the disappearance of sessile liquid on the porous medium surface. The numerical and experimental results for the time changes of (i) volume of liquid remaining at the porous medium surface, (ii) porous medium surface wetted area of the droplet imprint, and (iii) liquid protrusion depth into porous medium are compared, with very good qualitative and quantitative agreement found.
Effect of chain stiffness on ion distributions around a polyelectrolyte in multivalent salt solutions
Authors: Wei Yu-Fu , Hsiao Pai-Yi
Published: January 2010

Ion distributions in dilute polyelectrolyte solutions are studied by means of Langevin dynamics simulations. We show that the distributions depend on the conformation of a chain while the conformation is determined by the chain stiffness and the salt concentration. We observe that the monovalent counterions originally condensed on a chain can be replaced by the multivalent ones dissociated from the added salt due to strong electrostatic interaction. These newly condensed ions give an important impact on the chain structure. At low and at high salt concentrations, the conformation of a semiflexible chain is rodlike. The ion distributions show similarity to those for a rigid chain, but difference to those for a flexible chain whose conformation is a coil. In the midsalt region, the flexible chain and the semiflexible chain collapse but the collapsed chain structures are, respectively, disordered and ordered structures. The ion distributions, hence, show different profiles for this three chain stiffness with the curves for the semiflexible chain lying between those for the flexible and the rigid chains. The number of the condensed multivalent counterions, as well as the effective chain charge, also shows similar behavior, demonstrating a direct connection with the chain morphology. Moreover, we find that the condensed multivalent counterions form triplets with two adjacent monomers and are localized on the chain axis at intermediate salt concentration when the chain stiffness is semiflexible or rigid. The microscopic information obtained here provides a valuable insight to the phenomena of DNA condensation and is very useful for researchers to develop new models.
On mean coordination and structural heterogeneity in model amorphous solids
Authors: Zaccone Alessio , Del Gado Emanuela
Published: January 2010

We propose a simple route to analytically evaluate the average coordination of model disordered solids with maximally homogeneous distribution of the particles in space. The model yields the average number of contacts (z) as a function of volume fraction (ϕ) of a hard-sphere connected system and recovers the critical jamming point of hard spheres (z=6 at ϕ=0.64). Numerical simulations of Lennard-Jones glasses with a varying attraction range are used to investigate the volume fraction dependence of the average coordination in the presence of attraction. It is observed that upon decreasing ϕ below 0.6, structural heterogeneity is reflected in values of the coordination number which are higher than those predicted by the model for a statistically homogeneous distribution of particles in space due to the attraction-induced local aggregation. Thus the model can be usefully employed as a quantitative reference to assess the degree of structural heterogeneity in glasses in terms of a directly accessible structural parameter such as the mean number of contacts.
Lipid membranes with transmembrane proteins in shear flow
Authors: Khoshnood Atefeh , Noguchi Hiroshi , Gompper Gerhard
Published: January 2010

The effects of embedded proteins on the dynamical properties of lipid bilayer membranes are studied in shear flow. Coarse-grained molecular simulations are employed, in which lipids are modeled as short polymers consisting of hydrophilic head groups and hydrophobic tail monomers; similarly, transmembrane proteins are modeled as connected hydrophobic double- or triple-chain molecules with hydrophilic groups at both ends. In thermal equilibrium, rigid proteinlike molecules aggregate in a membrane of flexible lipids, while flexible proteins do not aggregate. In shear flow parallel to the membrane, the monolayers of lipid bilayer slide over each other. The presence of transmembrane proteins enhances the intermonolayer friction. The friction coefficient depends on the chain lengths of lipids, the membrane tension, the length of the protein, and the cluster size. It is found to increase with protein length (with positive mismatch, i.e., proteins which are longer than the membrane thickness) and protein cluster size. In flow, proteins get oriented in the flow direction to reduce friction, with large fluctuations of the orientation angle.
Applicability of envelope model equations for simulation of narrow-spectrum unidirectional random wave field evolution: Experimental validation
Authors: Shemer Lev , Sergeeva Anna , Slunyaev Alexey
Published: January 2010

Combined experimental and numerical study of spatial evolution of unidirectional random water-waves is performed. Numerous realizations of wave fields all having identical initial narrow-banded Gaussian power spectrum but random phases for each harmonic were generated by a wavemaker in a 300 m long wave tank. The measured in the vicinity of the wavemaker temporal variation of the surface elevation was used to determine the initial conditions in the numerical simulations. The cubic Schrödinger equation (CSE) and the modified nonlinear Schrödinger (MNLS) set of equations due to Dysthe were used as the theoretical models. The detailed comparison of the evolution of the wave field along the tank in individual realizations, measured by wave gauges at different distances from the wavemaker and computed using the two theoretical models, was performed. Numerous statistical wave parameters were calculated based on the whole ensemble of realizations. Comparison of the spatial variation of the computed statistical characteristics of the random wave field with laboratory measurements indicates that contrary to the deterministic case, ensemble averaged statistical parameters derived from the CSE simulations compare reasonably well with the experiments and with the results derived from the MNLS model simulations. In particular, simulations based on both models indicate that the statistical characteristics of the random wave field depend on the local width of frequency spectrum and deviate from the Gaussian statistics: the probability of extremely large (the so-called freak) waves is highest when the local spectral width attains maximum. In view of the satisfactory agreement of the numerical results with the laboratory experiments, the computational domain was extended to distances exceeding twice the actual length of the tank and long-scale (at distances approaching 200 dominant wavelengths) variation of the statistical parameters is studied.
Contact resistance in few and multilayer graphene devices
Authors: Venugopal A. , Colombo L. , Vogel E. M.
Published: January 2010

The contact resistance of metals on backgated graphene field-effect transistors is studied. The residual resistance obtained at high backgate voltage is found to be in excellent agreement with the extracted values of contact resistance from transfer length measurements on graphene flakes. The contact resistance is found to be a significant contributor to the total resistance of graphene-based devices. The specific contact resistance is shown to be independent of the applied backgate voltage and the number of graphene layers.
Electroviscous effects in nanofluidic channels
Authors: Wang Moran , Chang Chi-Chang , Yang Ruey-Jen
Published: January 2010

This paper presents a systematical study of electroviscous effects in nanofluidic channels using a triple layer model and a numerical framework. A chemical dissociation layer is introduced at solid-liquid interfaces to bridge the surface charge condition with the local properties of both solid surfaces and the ionic liquid. The electrokinetic transport in the electrical double layers is modeled by a lattice Poisson–Boltzmann method. The results indicate that there is an ionic concentration leading to the maximum electroviscosity for a given channel height, pH value, and environmental temperature. For a very high ionic concentration, a smaller channel height leads to a higher electroviscosity. When the bulk concentration reduces from 10−3M to 10−6M, there is a critical channel height that maximizes the electroviscosity for a given ionic concentration, and the critical height increases with the decreasing ionic concentration. The electroviscosity increases with the pH of electrolyte solutions and is nearly proportional to the environmental temperature. The present study may help to improve the understanding of electrokinetic transport in nanofluidic channels.
Microstructure and superconductivity of Ir-doped BaFe2As2 superconductor
Authors: Wang X. L. , Shi H. Y. , Yan X. W. , Yuan Y. C. , Lu Z.-Y. , Wang X. Q. , Zhao T.-S.
Published: January 2010

Polycrystalline samples with nominal composition of Ba(Fe1−xIrx)2As2 (x=0.10, 0.15, and 0.20) were investigated by means of x-ray diffraction (XRD), scanning electron microscopy (SEM), electrical resistivity, and magnetization measurements. XRD and SEM results showed that almost single phase samples were obtained. Bulk superconductivity with TC∼28 K was observed in the x=0.10 sample. TC∼28 K is the highest superconducting critical temperature among the reported data for electron-doped AFe2As2-type (A=Ca, Sr, and Ba) superconductors. The upper critical field Hc2(0) reaches as high as 65 T for the x=0.10 sample. The underlying physics is discussed in connection with Co-doping case.
Roller-style electrostatic printing of prepatterned few-layer-graphenes
Authors: Liang Xiaogan , Giacometti Valentina , Ismach Ariel , Harteneck Bruce D. , Olynick Deirdre L. , Cabrini Stefano
Published: January 2010

Electrostatic exfoliation of patterned few-layer-graphenes was demonstrated using a method compatible with high throughput roll-to-roll manufacturing. A patterned graphite template was placed on a roller and used to exfoliate patterned graphene on a planar substrate. The exfoliated graphene features were subsequently characterized by Raman spectroscopy. In comparison with previously demonstrated planar electrostatic exfoliation approach, the roller-style method can create a narrower distribution of thickness of few-layer-graphenes, which is attributed to the combinational action of tangential rolling friction and electrostatic forces. This roller-style electrostatic printing technique could be applied for roll-to-roll manufacturing of graphene-based devices in the future.
Oxygen concentration and its effect on the leakage current in BiFeO3 thin films
Authors: Yang H. , Wang Y. Q. , Wang H. , Jia Q. X.
Published: January 2010

Epitaxial c-axis oriented BiFeO3 (BFO) films were fabricated on (001) oriented SrTiO3 substrates by pulsed laser deposition. Nuclear resonance backscattering spectrometry was used to directly measure the oxygen concentration of as-deposited and annealed BFO films. Compared to the ideal stoichiometry of BFO, the as-deposited BFO film shows more than 10% oxygen deficiency. However, postannealing the as-deposited BFO films reduces the oxygen deficiency almost half. The reduced oxygen vacancies in annealed BFO films are believed to be responsible for the different leakage mechanisms and the two orders of magnitude drop in leakage current density.
Improved ferroelectric properties of Pb(Zr0.52,Ti0.48)O3 thin film on single crystal diamond using CaF2 layer
Authors: Liao Meiyong , Nakajima Kiyomi , Imura Masataka , Koide Yasuo
Published: January 2010

The authors report the integration of perovskite Pb(Zr0.52,Ti0.48)O3 thin film on single crystal diamond by using a nonoxide single CaF2 buffer layer. The CaF2 buffer layer plays a dual role in the lead zirconate titanate Pb(Zr,Ti)O3 (PZT) film deposition. The first is that the CaF2 layer leads to a preferentially (100)-oriented PZT thin film on diamond, improving the ferroelectric properties significantly. The PZT film exhibits a remanent in-plane polarization of 2Pr=68 μC/cm2 and a coercive field of 33 kV/cm. The remanent polarization is much larger than that of PZT films deposited on diamond by using SrTiO3/Al2O3 buffer layer. The second is that the CaF2 layer acts as an efficient energy barrier for the metal-ferroelectric-insulator-diamond capacitor due to its wide band gap. The leakage current in the capacitor is reduced to be lower than 10−6 A/cm2 in the forward bias mode.
Turbulent drag reduction via a transverse wave traveling along streamwise direction induced by Lorentz force
Authors: Huang Leping , Fan Baochun , Dong Gang
Published: January 2010

Lorentz force can be used to induce motion in the electrically conducting fluids which might then lead to turbulence suppression and drag reduction. In this paper, drag reduction in turbulent channel flow via a transverse wave traveling along streamwise direction induced by Lorentz force is investigated numerically by direct numerical simulation. It is found that the intrinsic and induced flows are modified each other due to the two-way coupling when the transverse wavy Lorentz force is utilized to modulate the near-wall turbulent flow. There is an optimal wave number kx in flow control, in which the influence of the intrinsic flow on the induced flow is weakest, and on the contrary, the intrinsic turbulent flow is modified strongly by the induced flow. The variable-interval space averaging detective technique (a spatial version of the VITA technique) and conditionally sampled and ensemble averaging method are used to obtain the frequency and intensity of the turbulent bursts which mainly contribute to the turbulent skin-friction drag. The results show that the frequency and intensity vary with kx in the contradictious tendencies. Therefore, the turbulent skin-friction reduction can be optimized with kx. It is also shown that the maximum drag reduction is affected by the oscillation parameters.
Morphological instability of the solid-liquid interface in crystal growth under supercooled liquid film flow and natural convection airflow
Authors: Ueno Kazuto , Farzaneh Masoud
Published: January 2010

Ringlike ripples on the surface of icicles are an example of morphological instability of the ice-water interface during ice growth under supercooled water film flow. The surface of icicles is typically covered with ripples of about 1 cm in wavelength, and the wavelength appears to be almost independent of external temperature, icicle radius, and volumetric water flow rate. One side of the water layer consists of the water-air surface and growing ice is the other. This is one of the more complicated moving phase boundary problems with two interfaces. A recent theoretical work [K. Ueno, Phys. Rev. E 68, 021603 (2003)] to address the underlying instability that produces ripples is based on the assumption of the absence of airflow around icicles. In this paper, we extend the previous theoretical framework to include a natural convection airflow ahead of the water-air surface and consider whether the effect of natural convection airflow on the wavelength of ripples produced on an ice surface is essential or not.
Liquid crystal-carbon nanotubes mixtures
Authors: Popa-Nita V. , Kralj S.
Published: January 2010

The self-organizing properties of nematic liquid crystals (LCs) can be used to align carbon nanotubes (CNTs) dispersed in them. In the previous paper [P. van der Schoot, V. Popa-Nita, and S. Kralj, J. Phys. Chem. B 112, 4512 (2008)], we have considered the weak anchoring limit of the nematic LC molecules at the nanotube’s surface, where the CNT alignment is caused by the anisotropic interfacial tension of the nanotubes in the nematic host fluid. In this paper, we present the theoretical results obtained for strong enough anchoring at the CNT-LC interface for which the nematic ordering around nanotube is apparently distorted. Consequently, relatively strong long-range and anisotropic interactions can emerge within the system. In order to get insight into the impact of LC ordering on the alignment of nanotubes we treat the two mixture components on the same footing and combine Landau–de Gennes free energy for the thermotropic ordering of the liquid crystal and Doi free energy for lyotropic nematic ordering of carbon nanotubes caused by their mutually excluded volume. The phase ordering of the binary mixture is analyzed as a function of the volume fraction of the carbon nanotubes, the strength of coupling, and the temperature. We find that the degree of ordering of the nanorods can be tuned by raising or lowering the temperature or by increasing or decreasing their concentration.
Measurement of thermopower and current-voltage characteristics of molecular junctions to identify orbital alignment
Authors: Tan Aaron , Sadat Seid , Reddy Pramod
Published: January 2010

We report an experimental technique that concurrently measures the Seebeck coefficient and the current-voltage (I-V) characteristics of a molecular junction to determine the identity and the effective energetic separation of the molecular orbital closest to the electrodes’ Fermi level. Junctions created by contacting a gold-coated atomic force microscope tip with a monolayer of molecules assembled on a gold substrate were found to have a Seebeck coefficient of (+16.9±1.4) μV/K. This positive value unambiguously shows that the highest occupied molecular orbital (HOMO) dominates charge transport. Further, by analyzing the (I-V) characteristics, the HOMO level is estimated to be ∼0.69 eV with respect to the Fermi level.
Ferromagnetic ordering of silicon vacancies in N-doped silicon carbide
Authors: Zhao Mingwen , Pan Fengchun , Mei Liangmo
Published: January 2010

We perform first-principles calculations to investigate the roles of silicon vacancy (VSi) and nitrogen impurity in the magnetic properties of silicon carbide (3C-SiC). High-spin configurations are predicted for the negatively-charged (VSi) defects. The coupling is ferromagnetic between the (VSi) defects at −2e charge state, whereas the (VSi) defects at -e charge state prefer to interact antiferromagnetically. Substituting C with N atoms can manipulate the charge states of (VSi) defects and the magnetic interactions between them. Our work offers a possible route toward high Curie temperature (Tc) ferromagnetism in metal-free 3C-SiC materials.
Mixed-power scaling of whole-plant respiration from seedlings to giant trees
Authors: Mori Shigeta , Yamaji Keiko , Ishida Atsushi , Prokushkin Stanislav G. , Masyagina Oxana V. , Hagihara Akio , Hoque A.T.M. Rafiqul , Suwa Rempei , Osawa Akira , Nishizono Tomohiro , Ueda Tatsushiro , Kinjo Masaru , Miyagi Tsuyoshi , Kajimoto Takuya , Koike Takayoshi , Matsuura Yojiro , Toma Takeshi , Zyryanova Olga A. , Abaimov Anatoly P. , Awaya Yoshio , Araki Masatake G. , Kawasaki Tatsuro , Chiba Yukihiro , Umari Marjnah
Published: January 2010

The scaling of respiratory metabolism with body mass is one of the most pervasive phenomena in biology. Using a single allometric equation to characterize empirical scaling relationships and to evaluate alternative hypotheses about mechanisms has been controversial. We developed a method to directly measure respiration of 271 whole plants, spanning nine orders of magnitude in body mass, from small seedlings to large trees, and from tropical to boreal ecosystems. Our measurements include the roots, which have often been ignored. Rather than a single power-law relationship, our data are fit by a biphasic, mixed-power function. The allometric exponent varies continuously from 1 in the smallest plants to 3/4 in larger saplings and trees. Therefore, our findings support the recent findings of Reich et al. [Reich PB, Tjoelker MG, Machado JL, Oleksyn J (2006) Universal scaling of respiratory metabolism, size, and nitrogen in plants. Nature 439:457–461] and West, Brown, and Enquist [West GB, Brown JH, Enquist BJ (1997) A general model for the origin of allometric scaling laws in biology.Science276:122 -126.]. The transition from linear to 3/4-power scaling may indicate fundamental physical and physiological constraints on the allocation of plant biomass between photosynthetic and nonphotosynthetic organs over the course of ontogenetic plant growth.