bluuebunny/crossref_metadata_2025 huggingface dataset:
Density functional study of methanol decomposition on clean and O or OH adsorbed PdZn(111)
Authors: Huang Yucheng , He Xiang , Chen Zhao-Xu
Published: May 2013

Methanol is the future and clean fuel, and its chemistry on metal surfaces has received much attention. In this paper we explore methanol dissociation on the clean and O or OH covered PdZn(111) that mimics Pd/ZnO catalyst studied as a promising catalyst for methanol steam reforming, using density functional theory at PW91 level and slab model. Our study demonstrates that unlike the situation on Pd (111), methanol preferentially undergoes the O–H bond scission on the PdZn (111). The presence of O and OH species hinders the C–H bond dissociation, but significantly reduces the O–H bond-breaking barrier. The present results indicate that in the course of methanol steam reforming, methanol first loses the hydrogen atom of the hydroxyl group, forming methoxy. This step is greatly enhanced when there are O and/or OH species (i.e., after water dissociation happens). Analyses reveal that CH2O is formed mainly from CH3O, not from CH2OH.
Mesoscopic mechanism of the domain wall interaction with elastic defects in uniaxial ferroelectrics
Authors: Morozovska Anna N. , Eliseev Eugene A. , Svechnikov G. S. , Kalinin Sergei V.
Published: May 2013

The role of elastic defects on the kinetics of 180° uncharged ferroelectric domain wall motion is explored using continuum time-dependent Landau-Ginzburg-Devonshire equation with elastic dipole coupling. In one dimensional case, ripples, steps, and oscillations of the domain wall velocity appear due to the wall-defect interactions. While the defects do not affect the limiting-wall velocity vs. field dependence, they result in the minimal threshold field required to activate the wall motions. The analytical expressions for the threshold field are derived and the latter is shown to be much smaller than the thermodynamic coercive field. The threshold field is linearly proportional to the concentration of defects and non-monotonically depends on the average distance between them. The obtained results provide the insight into the mesoscopic mechanism of the domain wall pinning by elastic defects in ferroelectrics.
Growth mechanism of photoreduced silver nanostructures on periodically proton exchanged lithium niobate: Time and concentration dependence
Authors: Craig Carville N. , Manzo Michele , Denning Denise , Gallo Katia , Rodriguez Brian J.
Published: May 2013

Photodeposition of metallic nanostructures onto ferroelectric surfaces, which have been chemically patterned using a proton exchange process, has recently been demonstrated. By varying the molar concentration of the AgNO3 solution and the illumination time, one can determine the initial nucleation sites, control the rate of nucleation and the height of silver nanostructures formed, and study the mechanisms by which these processes occurs. The nanoparticles are found to deposit preferentially in the boundary between ferroelectric and proton exchanged regions, in an area proton exchanged via lateral diffusion under the masking layer used for chemical patterning, consistent with our previous results. Using a short illumination time (3 min), we are able to determine that the initial nucleation of the silver nanostructure, having a width of 0.17 ± 0.02 μm and a height of 1.61 ± 0.98 nm, occurs near the edge of the reactive ion etched area within this lateral diffusion region. Over longer illumination times (15 min), we find that the silver deposition has spread to a width of 1.29 ± 0.06 μm, extending across the entire lateral diffusion region. We report that at a high molar concentration of AgNO3 (10−2 M), the amount of silver deposition for 5 min UV illumination is greater (2.88 ± 0.58 nm) compared to that at low (10−4 M) concentrations (0.78 ± 0.35 nm), however, this is not the case for longer time periods. With increasing illumination time (15 min), experiments at 10−4 M had greater overall deposition, 6.90 ± 1.52 nm, compared to 4.50 ± 0.76 nm at 10−2 M. For longer exposure times (30 min) at 10−2 M, the nanostructure height is 4.72 ± 0.59 nm, suggesting a saturation in the nanostructure height. The results are discussed in terms of the electric double layer that forms at the crystal surface. There is an order of magnitude difference between the Debye lengths for 10−2 and 10−4 M solutions, i.e., 3.04 vs. 30.40 nm, which suggests the Debye length plays a role in the availability of Ag+ ions at the surface.
Enhanced piezoelectric performance of composite sol-gel thick films evaluated using piezoresponse force microscopy
Authors: Liu Yuanming , Lam Kwok Ho , Kirk Shung K. , Li Jiangyu , Zhou Qifa
Published: May 2013

Conventional composite sol-gel method has been modified to enhance the piezoelectric performance of ceramic thick films. Lead zirconate titanate (PZT) and lead magnesium niobate–lead titanate (PMN-PT) thick films were fabricated using the modified sol-gel method for ultrasonic transducer applications. In this work, piezoresponse force microscopy was employed to evaluate the piezoelectric characteristics of PZT and PMN-PT composite sol-gel thick films. The images of the piezoelectric response and the strain-electric field hysteresis loop behavior were measured. The effective piezoelectric coefficient (d33,eff) of the films was determined from the measured loop data. It was found that the effective local piezoelectric coefficient of both PZT and PMN-PT composite films is comparable to that of their bulk ceramics. The promising results suggest that the modified composite sol-gel method is a promising way to prepare the high-quality, crack-free ceramic thick films.
Mechanical stress modified ferroelectric aging behavior
Authors: Xu Tingting , Kan Yi , Jin Yaming , Sun Hui , Du Yingchao , Wu Xiumei , Bo Huifeng , Cai Wei , Huang Fengzhen , Lu Xiaomei , Zhu Jinsong
Published: May 2013

Mechanical stress effect on aging behavior of Bi3.25La0.75Ti3O12 (BLT) and PbZr0.53Ti0.47O3 (PZT) films was investigated. It is found that the remnant polarization decreases with time while the coercive field increases in stress-free BLT films. For unconfined PZT films, both the remnant polarization and the coercive field decrease as time elapses. The applied tensile stress weakens the aging of remnant polarization of BLT films but strengthens the aging of coercive field, while the applied tensile stress possesses opposite effect. In contrary, the applied compressive stress simultaneously improves the aging behavior of both remnant polarization and coercive field of PZT films. Mechanical-stress-induced variation of domain wall mobility in different materials was suggested as the possible origin of these observations. This work indicates that the aging behavior modification using stress could be realized, and it is helpful for promoting the reliability of ferroelectric films for industrial applications.
Atomic vapor deposition of bismuth titanate thin films
Authors: Deepak Nitin , Zhang Panfeng F. , Keeney Lynette , Pemble Martyn E. , Whatmore Roger W.
Published: May 2013

c-axis oriented ferroelectric bismuth titanate (Bi4Ti3O12) thin films were grown on (001) strontium titanate (SrTiO3) substrates by an atomic vapor deposition technique. The ferroelectric properties of the thin films are greatly affected by the presence of various kinds of defects. Detailed x-ray diffraction data and transmission electron microscopy analysis demonstrated the presence of out-of-phase boundaries (OPBs). It is found that the OPB density changes appreciably with the amount of titanium injected during growth of the thin films. Piezo-responses of the thin films were measured by piezo-force microscopy. It is found that the in-plane piezoresponse is stronger than the out-of-plane response, due to the strong c-axis orientation of the films.
Multicomponent diffusive-convective fluid motions in porous layers: Ultimately boundedness, absence of subcritical instabilities, and global nonlinear stability for any number of salts
Authors: Rionero Salvatore
Published: May 2013

Either for its great geophysical relevance or the frequent occurrence of porous materials in real life, research on convective-diffusive fluid motions in porous horizontal layers has a notable relevance, which is increasing with the number of salts dissolved in the fluid. In the present paper, porous horizontal layers heated from below and salted by m salts partly from above and partly from below are studied \documentclass[12pt]{minimal}\begin{document}$\forall m\in \mathbb {N}$\end{document}∀m∈N. In the Darcy-Boussinesq scheme it is shown that: (i) the L2 solutions are bounded, uniquely determined, and asymptotically converging toward an absorbing set; (ii) for each Fourier component of the perturbations to the thermal conduction solution, there exists an own nonlinear admissible evolution system; (iii) subcritical instabilities do not exist and the conditions of linear stability also guarantee the global nonlinear stability; (iv) global nonlinear stability is guaranteed by the general condition (1.2) holding \documentclass[12pt]{minimal}\begin{document}$\forall m\in \mathbb {N}$\end{document}∀m∈N; (v) condition (1.2) is hidden in the Darcy-Boussinesq equations, it can be found by substituting the salt concentration fields via new suitable unknown fields and looking for symmetries and skew-symmetries in the new system of equations. The present paper – originating from Rionero [“Absence of subcritical instabilities and global nonlinear stability for porous ternary diffusive-convective fluid mixtures,” Phys. Fluids 24, 104101 (2012)]10.1063/1.4757858 – generalizes the properties (ii)–(iv) (obtained for m = 2) to any \documentclass[12pt]{minimal}\begin{document}$m\in \mathbb {N}$\end{document}m∈N and furnishes the newly obtained properties (i) and (v). We stress the relevant physical meaning of (1.2). In fact (1.2) – in simple algebraic closed form – guarantees that the onset of convection cannot occur and appears to be useful not only for theoreticians but also for experimentalists in the research field of physics of fluids. Analogously, conditions guaranteeing the onset of convection – in simple algebraic closed form (cf. (6.18) and (6.19) reversed) – are furnished.
Interface control of surface photochemical reactivity in ultrathin epitaxial ferroelectric films
Authors: Chen Jason , Lu Haidong , Liu Heng-Jui , Chu Ying-Hao , Dunn Steve , (Ken) Ostrikov Kostya , Gruverman Alexei , Valanoor Nagarajan
Published: May 2013

Asymmetrical electrical boundary conditions in (001)-oriented Pb(Zr0.2TiO0.8)O3 (PZT) epitaxial ultrathin ferroelectric films are exploited to control surface photochemical reactivity determined by the sign of the surface polarization charge. It is shown that the preferential orientation of polarization in the as-grown PZT layer can be manipulated by choosing an appropriate type of bottom electrode material. PZT films deposited on the SrRuO3 electrodes exhibit preferential upward polarization (C+) whilst the same films grown on the (La,Sr)CoO3-electrodes are polarized downward (C−). Photochemical activity of the PZT surfaces with different surface polarization charges has been tested by studying deposition of silver nanoparticles from AgNO3 solution under UV irradiation. PZT surfaces with preferential C+ orientation possess a more active surface for metal reduction than their C− counterparts, evidenced by large differences in the concentration of deposited silver nanoparticles. This effect is attributed to band bending at the bottom interface which varies depending on the difference in work functions of PZT and electrode materials.
Delocalized Davydov D1 Ansatz for the Holstein polaron
Authors: Sun Jin , Duan Liwei , Zhao Yang
Published: May 2013

An efficient, yet very accurate trial wave function, constructed from projecting the well-known Davydov D1 Ansatz onto momentum eigenstates, is employed to study the ground state properties of the generalized Holstein Hamiltonian with simultaneous diagonal and off-diagonal coupling. Ground-state energies have been obtained with a precision matching that of the computationally much more demanding density-matrix renormalization group method. The delocalized D1 Ansatz lowers the ground-state energies at the Brillouin zone boundary significantly compared with the Toyozawa and Global-Local Ansätze in the weak coupling regime, while considerable improvement is demonstrated to have been achieved over the entire Brillouin zone in the strong coupling regime. Unique solutions are obtained with the delocalized D1 for different initial conditions when the transfer integral is 20 times the phonon frequency at the zone center, implying the absence of any self-trapping discontinuity. The scaled correlation variance is found to fit satisfactorily well with the predictions of the perturbation theories.
Failure behavior of Pb(Zr0.95Ti0.05)O3 ferroelectric ceramics under shock compression
Authors: Zhang Fuping , He Hongliang , Liu Gaomin , Liu Yusheng , Yu Yin , Wang Yonggang
Published: May 2013

PZT 95/5 ferroelectric ceramics have been used in shock-driven pulsed-power supplies for many years; their mechanical failure under shock compression plays an important role in dielectric breakdown. Shock experiments have been conducted to understand such failure by measuring the velocity of the free surface or the PZT/sapphire interface. Results confirm that delayed failure exists in PZT 95/5 before dynamic yielding at 2.4 GPa; multipoint measurements indicate that the failure layer in PZT 95/5 was not a plane but a rough front. The delay time and velocity of this layer had been determined by measuring samples of varying thicknesses at fixed pressure; results indicate that this velocity is the same as the shock-wave speed and the delay time decreases with increasing shock stress. At a shock stress of 4.9 GPa, the delay time falls to zero and a ramp wave is observed. This kind of failure is a new phenomenon in electric breakdown of PZT 95/5 under shock compression.
Effect of confining wall potential on charged collimated dust beam in low-pressure plasma
Authors: Kausik S. S. , Kakati B. , Saikia B. K.
Published: May 2013

The effect of confining wall potential on charged collimated dust beam in low-pressure plasma has been studied in a dusty plasma experimental setup by applying electrostatic field to each channel of a multicusp magnetic cage. Argon plasma is produced by hot cathode discharge method at a pressure of 5×10−4 millibars and is confined by a full line cusped magnetic field confinement system. Silver dust grains are produced by gas-evaporation technique and move upward in the form of a collimated dust beam due to differential pressure maintained between the dust and plasma chambers. The charged grains in the beam after coming out from the plasma column enter into the diagnostic chamber and are deflected by a dc field applied across a pair of deflector plates at different confining potentials. Both from the amount of deflection and the floating potential, the number of charges collected by the dust grains is calculated. Furthermore, the collimated dust beam strikes the Faraday cup, which is placed above the deflector plates, and the current (∼pA) so produced is measured by an electrometer at different confining potentials. The experimental results demonstrate the significant effect of confining wall potential on charging of dust grains.
Investigation of the magnetic properties of FeAu nanoclusters in a W matrix: Evidence for exchange-bias phenomenon
Authors: Folcke E. , Le Breton J. M. , Lefebvre W. , Bran J. , Lardé R. , Golkar F. , Shield J. E.
Published: May 2013

Equiatomic FeAu nanoclusters were produced by inert-gas condensation and embedded in a W matrix. Transmission electron microscopy investigation shows that three kinds of clusters are present: mono-crystalline, polycrystalline, and partially crystalline clusters. It demonstrates that during their formation, the structure of nanoclusters evolves from an amorphous to a crystalline structure. Crystallisation starts at the surface of nanoclusters and currently leads to the formation of poly-crystalline nanoclusters in the end. Most of the investigated objects consist in a duplex amorphous core-crystalline shell structure. Their magnetic properties were investigated by magnetization measurements as a function of magnetic field (hysteresis loops) or temperature (ZFC/FC curves). They show evidence at low temperatures of ferromagnetic and antiferromagnetic states, and ordering as well as superparamagnetism or spin-glass behaviour. Measurements performed after cooling the samples under various applied fields reveal the occurrence of exchange-spring phenomenon, related to the presence of the W matrix, through RKKY coupling between ferromagnetic and antiferromagnetic nanoclusters.
Sideband separation experiments in NMR with phase incremented echo train acquisition
Authors: Walder Brennan J. , Dey Krishna K. , Kaseman Derrick C. , Baltisberger Jay H. , Grandinetti Philip J.
Published: May 2013

A general approach for enhancing sensitivity of nuclear magnetic resonance sideband separation experiments, such as Two-Dimensional One Pulse (TOP), Magic-Angle Turning (MAT), and Phase Adjust Spinning Sidebands (PASS) experiments, with phase incremented echo-train acquisition (PIETA) is described. This approach is applicable whenever strong inhomogeneous broadenings dominate the unmodulated frequency resonances, such as in non-crystalline solids or in samples with large residual frequency anisotropy. PIETA provides significant sensitivity enhancements while also eliminating spectral artifacts would normally be present with Carr-Purcell-Meiboom-Gill acquisition. Additionally, an intuitive approach is presented for designing and processing echo train acquisition magnetic resonance experiments on rotating samples. Affine transformations are used to relate the two-dimensional signals acquired in TOP, MAT, and PASS experiments to a common coordinate system. Depending on sequence design and acquisition conditions two significant artifacts can arise from truncated acquisition time and discontinuous damping in the T2 decay. Here we show that the former artifact can always be eliminated through selection of a suitable affine transformation, and give the conditions in which the latter can be minimized or removed entirely.
Transient behavior of a model fluid under applied shear
Authors: Costa Dino , Sergi Alessandro , Ferrario Mauro
Published: May 2013

We study the transient behavior of a model fluid composed by soft repulsive spheres subjected to a planar uniform shear. To this aim, we use a dynamical non-equilibrium molecular dynamics method originally developed by Ciccotti and Jacucci [Phys. Rev. Lett. 35, 789 (1975)10.1103/PhysRevLett.35.789] and recently applied to the study of the transient regimes in various fluid systems. We show that the dynamical method allows one to study the transient behavior of the viscous time-dependent response over a wide range of applied shear rates, provided that a temperature control is enforced on the system. In this study, we adopt in particular the configurational thermostat of Braga and Travis [J. Chem. Phys. 123, 134101 (2005)10.1063/1.2013227]. The initial behavior of the dynamical response to a θ-like perturbation is characterized by a rapid increase, culminating in a pronounced peak, later relaxing to a plateau value. The latter positively reproduces the values of the viscosity observed in standard steady-state non-equilibrium molecular dynamics.
Exact wave solutions for Bose–Einstein condensates with time-dependent scattering length and spatiotemporal complicated potential
Authors: Kengne E. , Lakhssassi A. , Vaillancourt R. , Liu Wu-Ming
Published: May 2013

We consider a cubic-quintic Gross–Pitaevskii equation which governs the dynamics of Bose–Einstein condensate matter waves with time-dependent scattering length and spatiotemporal complex potential. By introducing phase-imprint parameters in the system, we present the integrable condition for the equation and obtain the exact analytical solutions, which describe the propagation of a solitary wave. By applying specific time-modulated feeding/loss functional parameter, various types of magnetic trap strengths, and phase-imprint parameters, the dynamics of the solutions can be controlled. Solitary wave solutions with breathing and snaking behaviors are reported.
Hirshfeld density partitioning technique: A first application to the transition metal compounds, HScO, TiO, VO
Authors: Miliordos Evangelos , Harrison James F.
Published: May 2013

We apply a variant of the Hirshfeld density partitioning technique, HI, to calculate the atomic charges and decompose the dipole moments into the part due to the charges and the induced dipoles developed on each atom for three different transition metal (TM) containing molecules. Additionally, the α and β spin densities are treated separately developing a new variant (spin-adapted HI) of the fractional occupation HI version proposed recently. We also study the dependence of HI charges on the atomic state of the TM employed in the promolecule. The VO case exhibits a strong dependence of the atomic charge on the V or V+ state used. Although the bonding in the ground high spin electronic state and the first excited low spin state in TiO and VO is essentially identical, the dipole moments differ significantly and we find that this is due entirely to the σ electron distribution localized on the transition metal. Finally, the mechanism for the rapid change of the dipole moment of HScO upon bending is confirmed to occur mainly due to the induced atomic charges.
Coupling efficiency in piezoelectric actuators with direct current and alternating current excitation
Authors: Blackburn J. F. , Cain M. G.
Published: May 2013

This paper gives a theoretically rigorous description of energy coupling in piezoelectric actuators considering both DC and AC excitations. It is shown that these different excitations schemes give different actuator efficiencies, in general, but that DC and AC efficiencies converge at low frequencies given a suitable definition of efficiency in each case. This result is plausable but non-obvious: the DC and AC calculations are different since the former is transient and the latter based on a steady state excitation. In the low frequency analytical results presented here, the system efficiency can be expressed solely in terms of the piezoelectric's coupling factor and a factor which relates to the load the piezoelectric is attached to. However, we show that this simple formalism breaks down at high frequencies and then efficiency depends on all material and geometric properties separately. In that case, the calculated efficiency can differ significantly from what may be expected from a simpler DC analysis. At high frequencies, we therefore recommend the use of the high frequency efficiency formulas presented here. We also give a comparison between the theory and experimental results showing good agreement with no fitting parameters used. Hence, advice is given on how to optimise efficiency and absolute energy coupled. In this paper, we do not make the assumption that strain or electric field is spatially constant: piezoelectrics will, in fact, show both spatial and temporal variations of stress, strain, and electric fields—and these are accounted for correctly. In fact, an analytical calculation, in both the DC and AC regimes, can be made without making such assumptions. We show the reasons why this is the case.
Structure factor and rheology of chain molecules from molecular dynamics
Authors: Castrejón-González Omar , Castillo-Tejas Jorge , Manero Octavio , Alvarado Juan F. J.
Published: May 2013

Equilibrium and non-equilibrium molecular dynamics were performed to determine the relationship between the static structure factor, the molecular conformation, and the rheological properties of chain molecules. A spring-monomer model with Finitely Extensible Nonlinear Elastic and Lennard-Jones force field potentials was used to describe chain molecules. The equations of motion were solved for shear flow with SLLOD equations of motion integrated with Verlet's algorithm. A multiple time scale algorithm extended to non-equilibrium situations was used as the integration method. Concentric circular patterns in the structure factor were obtained, indicating an isotropic Newtonian behavior. Under simple shear flow, some peaks in the structure factor were emerged corresponding to an anisotropic pattern as chains aligned along the flow direction. Pure chain molecules and chain molecules in solution displayed shear-thinning regions. Power-law and Carreau-Yasuda models were used to adjust the generated data. Results are in qualitative agreement with rheological and light scattering experiments.
Rate equation model for the time dependence of the reflectance of a Ge2Te2Sb5 film during optical switching processes
Authors: Gericke F. , Flissikowski T. , Katmis F. , Braun W. , Grahn H. T.
Published: May 2013

We apply a rate equation model in order to simulate the measured change of the reflectance of an epitaxially grown Ge2Te2Sb5 (GST) film during optically induced switching between the amorphous and crystalline phases of the material. The amorphization and the re-crystallization process are considered to exhibit different switching rates, which depend on the actual value of the energy fluence of the applied laser pulse. The measured time dependence of the reflectance of the GST film as a measure of its degree of crystallinity is qualitatively reproduced by the rate equation model demonstrating that both processes can occur simultaneously during the switching process, but with different rates.
Long-range specific ion-ion interactions in hydrogen-bonded liquid films
Authors: Enami Shinichi , Colussi Agustín J.
Published: May 2013

Anions populate fluid interfaces specifically. Here, we report experiments showing that on hydrogen-bonded interfaces anions interact specifically over unexpectedly long distances. The composition of binary electrolyte (Na+, X−/Y−) films was investigated as a function of solvent, film thickness, and third ion additions in free-standing films produced by blowing up drops with a high-speed gas. These films soon fragment into charged sub-micrometer droplets carrying excess anions detectable in situ by online electrospray ionization mass spectrometry. We found that (1) the larger anions are enriched in the thinner (nanoscopic air-liquid-air) films produced at higher gas velocities in all (water, methanol, 2-propanol, and acetonitrile) tested solvents, (2) third ions (beginning at sub-μM levels) specifically perturb X−/Y− ratios in water and methanol but have no effect in acetonitrile or 2-propanol. Thus, among these polar organic liquids (of similar viscosities but much smaller surface tensions and dielectric permittivities than water) only on methanol do anions interact specifically over long, viz.: ⟨ri − rj⟩/nm = 150 (c/μM)−1/3, distances. Our findings point to the extended hydrogen-bond networks of water and methanol as likely conduits for such interactions.
Volume crossover in deeply supercooled water adiabatically freezing under isobaric conditions
Authors: Aliotta Francesco , Giaquinta Paolo V. , Pochylski Mikolaj , Ponterio Rosina C. , Prestipino Santi , Saija Franz , Vasi Cirino
Published: May 2013

The irreversible return of a supercooled liquid to stable thermodynamic equilibrium often begins as a fast process which adiabatically drives the system to solid-liquid coexistence. Only at a later stage will solidification proceed with the expected exchange of thermal energy with the external bath. In this paper we discuss some aspects of the adiabatic freezing of metastable water at constant pressure. In particular, we investigated the thermal behavior of the isobaric gap between the molar volume of supercooled water and that of the warmer ice-water mixture which eventually forms at equilibrium. The available experimental data at ambient pressure, extrapolated into the metastable region within the scheme provided by the reference IAPWS-95 formulation, show that water ordinarily expands upon (partially) freezing under isenthalpic conditions. However, the same scheme also suggests that, for increasing undercoolings, the volume gap is gradually reduced and eventually vanishes at a temperature close to the currently estimated homogeneous ice nucleation temperature. This behavior is contrasted with that of substances which do not display a volumetric anomaly. The effect of increasing pressures on the alleged volume crossover from an expanded to a contracted ice-water mixture is also discussed.
Magnetic resonance imaging study on near miscible supercritical CO2 flooding in porous media
Authors: Song Yongchen , Zhu Ningjun , Zhao Yuechao , Liu Yu , Jiang Lanlan , Wang Tonglei
Published: May 2013

CO2 flooding is one of the most popular secondary or tertiary recoveries for oil production. It is also significant for studying the mechanisms of the two-phase and multiphase flow in porous media. In this study, an experimental study was carried out by using magnetic resonance imaging technique to examine the detailed effects of pressure and rates on CO2/decane flow in a bead-pack porous media. The displacing processes were conducted under various pressures in a region near the minimum miscibility pressure (the system tuned from immiscible to miscible as pressure is increasing in this region) and the temperature of 37.8 °C at several CO2 injection volumetric rates of 0.05, 0.10, and 0.15 ml/min (or linear rates of 3.77, 7.54, and 11.3 ft/day). The evolution of the distribution of decane and the characteristics of the two phase flow were investigated and analyzed by considering the pressure and rate. The area and velocity of the transition zone between the two phases were calculated and analyzed to quantify mixing. The area of transition zone decreased with pressure at near miscible region and a certain injection rate and the velocity of the transition zone was always less than the “volumetric velocity” due to mutual solution and diffusion of the two phases. Therefore, these experimental results give the fundamental understanding of tertiary recovery processes at near miscible condition.
Polaron dynamics in a two-dimensional Holstein-Peierls system
Authors: Mozafari E. , Stafström S.
Published: May 2013

A semiclassical model for studying charge transport in a two-dimensional molecular lattice is presented and applied to both a well ordered system and a system with disorder. The model includes both intra- and inter-molecular electron-lattice interactions and the focus of the studies is to describe the dynamics of a charge carrier in the system. In particular, we study the dynamics of the system in which the polaron solution is dynamically stable. It is found that the parameter space for which the polaron is moving through the system is quite restricted and that the polaron is immobile for large electron-phonon coupling and weak intermolecular electron interactions and dynamically unstable and disassociates into a delocalized electronic state decoupled from the lattice for small electron-phonon coupling and strong intermolecular electron interactions. Disorder further limits the parameter space in which the polaron is mobile.
An efficient implementation of two-component relativistic exact-decoupling methods for large molecules
Authors: Peng Daoling , Middendorf Nils , Weigend Florian , Reiher Markus
Published: May 2013

We present an efficient algorithm for one- and two-component relativistic exact-decoupling calculations. Spin-orbit coupling is thus taken into account for the evaluation of relativistically transformed (one-electron) Hamiltonian. As the relativistic decoupling transformation has to be evaluated with primitive functions, the construction of the relativistic one-electron Hamiltonian becomes the bottleneck of the whole calculation for large molecules. For the established exact-decoupling protocols, a minimal matrix operation count is established and discussed in detail. Furthermore, we apply our recently developed local DLU scheme [D. Peng and M. Reiher, J. Chem. Phys. 136, 244108 (2012)]10.1063/1.4729788 to accelerate this step. With our new implementation two-component relativistic density functional calculations can be performed invoking the resolution-of-identity density-fitting approximation and (Abelian as well as non-Abelian) point group symmetry to accelerate both the exact-decoupling and the two-electron part. The capability of our implementation is illustrated at the example of silver clusters with up to 309 atoms, for which the cohesive energy is calculated and extrapolated to the bulk.
Effect of laser light polarization on generation of relativistic ion beams driven by an ultraintense laser
Authors: Domanski Jaroslaw , Badziak Jan , Jabłoński Sławomir
Published: May 2013

The effect of laser light polarization on properties of proton and carbon ion beams generated from a CH target irradiated by a 130 fs laser pulse of ultra-relativistic intensity (∼1022–1023 W/cm2) is investigated using particle-in-cell simulations. It is shown that only circular light polarization ensures the production of quasi-monoenergetic relativistic beams of both protons and carbon ions from such a target while using the linear one results in the generation of quasi-monoenergetic protons accompanied with carbon ions of complex and broad energy spectrum. The influence of the target thickness and laser intensity on the ion energy spectrum and the laser-ions energy conversion efficiency is examined.
Visualization of hydration layers on muscovite mica in aqueous solution by frequency-modulation atomic force microscopy
Authors: Kobayashi Kei , Oyabu Noriaki , Kimura Kenjiro , Ido Shinichiro , Suzuki Kazuhiro , Imai Takashi , Tagami Katsunori , Tsukada Masaru , Yamada Hirofumi
Published: May 2013

A three-dimensional interaction force mapping experiment was carried out on a muscovite mica surface in an aqueous solution using a high-resolution and low-thermal drift frequency-modulation atomic force microscope. By collecting oscillatory frequency shift versus distance curves at the mica/solution interface, complicated hydration structures on the mica surface were visualized. Reconstructed two-dimensional frequency shift maps showed dot-like or honeycomb-like patterns at different tip-sample distances with a separation of 0.2 nm with each other, which agree well to the water molecule density maps predicted by a statistical-mechanical theory. Moreover, site-specific force versus distance curves showed a good agreement with theoretically calculated site-specific force curves by a molecular dynamics simulation. It is found that the first and second hydration layers give honeycomb-like and dot-like patterns in the two-dimensional frequency shift images, respectively, corresponding to the lateral distribution function in each layer.
A decomposition of irreversible diffusion processes without detailed balance
Authors: Qian Hong
Published: May 2013

As a generalization of deterministic, nonlinear conservative dynamical systems, a notion of canonical conservative dynamics with respect to a positive, differentiable stationary density ρ(x) is introduced: \documentclass[12pt]{minimal}\begin{document}$\dot{x}=j(x)$\end{document}ẋ=j(x) in which ∇·(ρ(x)j(x)) = 0. Such systems have a conserved “generalized free energy function” F[u] = ∫u(x, t)ln (u(x, t)/ρ(x))dx in phase space with a density flow u(x, t) satisfying ∂ut = −∇·(ju). Any general stochastic diffusion process without detailed balance, in terms of its Fokker-Planck equation, can be decomposed into a reversible diffusion process with detailed balance and a canonical conservative dynamics. This decomposition can be rigorously established in a function space with inner product defined as ⟨ϕ, ψ⟩ = ∫ρ−1(x)ϕ(x)ψ(x)dx. Furthermore, a law for balancing F[u] can be obtained: The non-positive dF[u(x, t)]/dt = Ein(t) − ep(t) where the “source” Ein(t) ⩾ 0 and the “sink” ep(t) ⩾ 0 are known as house-keeping heat and entropy production, respectively. A reversible diffusion has Ein(t) = 0. For a linear (Ornstein-Uhlenbeck) diffusion process, our decomposition is equivalent to the previous approaches developed by Graham and Ao, as well as the theory of large deviations. In terms of two different formulations of time reversal for a same stochastic process, the meanings of dissipative and conservative stationary dynamics are discussed.
Differentiating bonding and caging in a charged colloid system through rheological measurements
Authors: Zong Yiwu , Yuan Guangcui , Zhao Chuanzhuang , Han Charles C.
Published: May 2013

The linear and nonlinear rheological measurements were utilized to study the mechanical response of concentrated mixtures of colloidal particles with opposite charges. The particle volume fraction ($\iPhi$Φ) spans the region from low volume fraction ($\iPhi$Φ = 0.18) gel to high volume fraction ($\iPhi$Φ = 0.53) glass. In the linear viscoelastic region, the storage moduli G′ exhibits deferent $\iPhi$Φ dependence at low and high $\iPhi$Φ’s. It follows a power law relationship as G′ ∼ $\iPhi$Φ6.2±0.2 for $\iPhi$Φ < 0.46, and follows an exponential relationship as G′ ∼ exp[(13.8 ± 0.6)$\iPhi$Φ] for $\iPhi$Φ ≥ 0.46. The difference can be taken as a distinction between a colloidal gel and an attractive glass (or dense gel) for the present system. The loss moduli G″ is almost frequency independent within the whole experimental frequency range (10−1–102 rad/s) for colloidal gel, and G″ exhibits a weak minimum for attractive glass. In the nonlinear large amplitude rheological measurement, samples with $\iPhi$Φ < 0.46 show one-step yielding, and samples with $\iPhi$Φ ≥ 0.46 exhibit two-step yielding which is in agreement with numerous experiments in attractive glassy systems. The first yielding is due to the breaking of short range interactions which bond the interconnected clusters or local clusters, while the second yielding is attributed to the breaking of long range interaction, normally the caging forming or glass forming interactions. The qualitative distinction between attractive glass and gel in terms of their yielding behavior is consistent with the linear rheological results. The particle-particle interactions were modulated by salt concentration. It was found that, when the attraction interaction is enhanced, both yielding points in attractive glass shift to higher strain amplitude and the gap between the two yielding points become more separated.
Effect of oxygen environment on formation of modulated Ag nanostructures along the interface of a Ag-Si heterostructure
Authors: Boyerinas Brad M. , Balsam Joshua M. , Bruck Hugh A. , Roytburd Alexander L.
Published: May 2013

Ag nanostructures were formed along the interface between Ag foil and Si wafer. These structures form when heated in the presence of air below the melting temperature of Ag, while heating above the melting temperature results in Ag foil melting with no nanostructure growth. Nanostructure morphology is determined by Si wafer orientation, while the size and periodicity of the structures depend on the duration of thermal processing. Electron backscatter diffraction (EBSD) analysis shows an epitaxial relation between Ag nanostructures and Si. Annealing specimens in vacuum above the Ag-Si eutectic but below pure Ag melting temperature results in solidification of melted foil without any interfacial nanostructure growth.
Size effect of out-of-plane thermal conductivity of epitaxial YBa2Cu3O7−δ thin films at room temperature measured by photothermal radiometry
Authors: Ikeda Tatsuya , Ando Tetsu , Taguchi Yoshihiro , Nagasaka Yuji
Published: May 2013

The out-of-plane (c-axis) thermal conductivities of high-temperature superconducting thin films (YBa2Cu3O7-δ: YBCO) have been measured by photothermal radiometry (PTR) at room temperature. The YBCO samples are in c-axis-aligned epitaxially grown thin films with thicknesses of 250, 500, and 1000 nm. PTR is a noncontact measurement technique for the thermal conductivity and is based on the detection of infrared radiation emitted from a sample heated by a frequency-modulated laser beam. By changing the modulation frequency up to about 1 MHz, the thermal conductivity of thin film can be determined by a curve-fitting analysis of phase-lag data in the frequency domain. The uncertainty of measured thermal conductivity is estimated to be better than ±7%. The experimental results for thermal conductivity exhibit apparently positive film thickness dependence, and their absolute values are less than half of those for single crystal at the smallest thickness. The results indicate a size effect that cannot be explained by the very short phonon mean free path that the kinetic theory predicts. By employing a simple model taking into account phonon boundary scattering, the possible mean free path to interpret the present results is substantially larger than the prediction. The conclusion supports the validity of quite broad spectral distribution of phonons responsible for the thermal conductivity of YBCO.
Impurity mixing and radiation asymmetry in massive gas injection simulations of DIII-D
Authors: Izzo V. A.
Published: May 2013

Simulations of neon massive gas injection into DIII-D are performed with the 3D MHD code NIMROD. The poloidal and toroidal distribution of the impurity source is varied. This report will focus on the effects of the source variation on impurity mixing and radiated power asymmetry. Even toroidally symmetric impurity injection is found to produce asymmetric radiated power due to asymmetric convective heat flux produced by the 1/1 mode. When the gas source is toroidally localized, the phase relationship between the mode and the source location is important, affecting both radiation peaking and impurity mixing. Under certain circumstances, a single, localized gas jet could produce better radiation symmetry during the disruption thermal quench than evenly distributed impurities.
Searching for low-workfunction phases in the Cs-Te system: The case of Cs2Te5
Authors: Ruth Anthony , Németh Károly , Harkay Katherine C. , Terdik Joseph Z. , Spentzouris Linda , Terry Jeff
Published: May 2013

We have computationally explored workfunction values of Cs2Te5 surfaces, an existing crystalline phase of the Cs-Te system and a small bandgap semiconductor, in order to search for reduced workfunction alternatives of Cs2Te that preserve the exceptionally high quantum efficiency of the Cs2Te seasoned photoemissive material. We have found that the Cs2Te5(010) surface exhibits a workfunction value of ≈1.9 eV when it is covered by Cs atoms. Cs2Te5 is analogous to our recently proposed low-workfunction materials, Cs2TeC2, and other ternary acetylides [J. Z. Terdik et al., Phys. Rev. B 86, 035142 (2012)], in as much as it also contains quasi one-dimensional substructures embedded in a Cs-matrix, forming the foundation for anomalous workfunction anisotropy and low workfunction values. The one-dimensional substructures in Cs2Te5 are polytelluride ions in a tetragonal rod-like packing. Cs2Te5 has the advantage of simpler composition and availability as compared to Cs2TeC2; however, its low workfunction surface is less energetically favored to the other surfaces than in Cs2TeC2. A significant and remarkable advantage of Cs2Te5 as compared to Cs2Te is its high optical absorption of visible photons that can allow for high quantum efficiency electron emission at visible photon energies.
Note: Single-polarity high-voltage amplifier to drive coarse-approach slip-stick piezoelectric motors
Authors: Belussi Cristian H. , Gómez Berisso Mariano , Fasano Yanina
Published: May 2013

Scanning probe microscopies typically rely on coarse-approach slip-stick piezoelectric motors that work by exciting piezoelectric stacks with sawtooth signals of hundreds of V and some kHz. For this application, we introduce a single-polarity high-voltage amplifier based on discrete MOSFET-technology components with improved output current desirable for low-temperature actuation. The amplifier has an output signal of 600 V, 100 mA output current, noise level below 2 μV/\documentclass[12pt]{minimal}\begin{document}$\sqrt{{\rm Hz}}$\end{document} Hz , 4 kHz high-voltage bandwidth, 2 V/μs slew-rate, and rise and fall times of 80 μs (when loaded with 30 nF). The circuit was successfully applied to drive a home-made scanning tunnelling microscope.
Effective hybrid graphene/carbon nanotubes field emitters by electrophoretic deposition
Authors: Koh Angel T. T. , Chen Ting , Pan Likun , Sun Zhuo , Chua Daniel H. C.
Published: May 2013

Hybrid graphene and carbon nanotube (CNT) field emitters were fabricated with electrophoretic deposition (EPD). The combination of both materials was used to improve the turn-on field for pure carbon nanotubes emitters and the reliability of pure graphene emitters deposited by the same method. The CNT was envisioned to hold down the graphene flakes, like a safety belt or Velcro, at high voltages to prevent an early short circuit at relatively low voltages. These hybrid emitters were studied for their field emission performance in relation to the EPD deposition duration. It was observed that the emitters performed better when the EPD duration was increased due to the increase in the amount and density of graphene flakes. Possible reasons for the improvement of field emission performance were suggested. The roles of graphene and CNT in these hybrid emitters were also discussed.
Multi-water-bag models of ion temperature gradient instability in cylindrical geometry
Authors: Coulette David , Besse Nicolas
Published: May 2013

Ion temperature gradient instabilities play a major role in the understanding of anomalous transport in core fusion plasmas. In the considered cylindrical geometry, ion dynamics is described using a drift-kinetic multi-water-bag model for the parallel velocity dependency of the ion distribution function. In a first stage, global linear stability analysis is performed. From the obtained normal modes, parametric dependencies of the main spectral characteristics of the instability are then examined. Comparison of the multi-water-bag results with a reference continuous Maxwellian case allows us to evaluate the effects of discrete parallel velocity sampling induced by the Multi-Water-Bag model. Differences between the global model and local models considered in previous works are discussed. Using results from linear, quasilinear, and nonlinear numerical simulations, an analysis of the first stage saturation dynamics of the instability is proposed, where the divergence between the three models is examined.
A complete theory for the magnetism of an ideal gas of electrons
Authors: Biswas Shyamal , Sen Swati , Jana Debnarayan
Published: May 2013

We have explored Pauli paramagnetism, Landau diamagnetism, and de Haas-van Alphen effect in a single framework, and unified these three effects for all temperatures as well as for all strengths of magnetic field. Our result goes beyond Pauli-Landau result on the magnetism of the 3-D ideal gas of electrons, and is able to describe crossover of the de Haas-van Alphen oscillation to the saturation of magnetization. We also have obtained a novel asymptotic series expansion for the low temperature properties of the system.
Manipulating ice crystallization of 0.9 wt. % NaCl aqueous solution by alternating current electric field
Authors: Ma Yahong , Zhong Lisheng , Gao Jinghui , Liu Lin , Hu Huiyu , Yu Qinxue
Published: May 2013

In this paper, we propose a physical method to manipulate the ice crystallization by applying an AC electric field during the liquid-solid transition of 0.9 wt. % NaCl aqueous solution. By using optical microscopic observation, we found that the ice grains are miniaturized in the presence of AC electric field during freezing process. Further study suggests that the grain size and the associated ice crystallization fraction are dependent on the field strength as well as frequency. And AC electric field can reduce the grain size and the crystallization fraction down to 35 μm and 71%, respectively, on the optimal condition (with field strength E = 100 kV/m, frequency f = 106 Hz). Moreover, the dielectric spectrum measurement of our sample close to transition temperature implies that such an optimal condition corresponds with a dielectric relaxation state, which might be the reason for the reduction of crystallized ice. Our finding may provide a potential way for cryoprotective application.