Individual’s strategy characterized by local topology conditions in prisoner’s dilemma on scale-free networks

We introduce a “gradient” to find out the defectors, and further a “topology potential” to characterize the individual’s strategy preference in the prisoner’s dilemma on scale-free networks. It is shown that the cooperators typically locate on the nodes with high topology potential and the defectors are mainly found on the nodes with small topology potential. A critical topology potential is found for the nodes where cooperators are nip and tuck with defectors. So the information of node’s degree, gradient and topology potential together can predict individual’s strategy decision in the prisoner’s dilemma on the complex networks.     

Interplay of wetting and phase separation at surfaces

We review our understanding of surface-directed spinodal decomposition (SDSD), i.e., the interplay of wetting and phase separation in an unstable AB mixture placed in contact with a wetting surface. In this context, we present results for two problems, viz., SDSD in a semi-infinite geometry with a completely wet surface; and SDSD in a thin-film geometry with partially wet surfaces.     

Study of thermal properties of the metastable supersaturated vapor with the restricted ensemble

The pressure and internal energy data at different densities of the supersaturated Argon vapor at the reduced temperatures 0.7 and 0.8 are obtained by the restricted canonical ensemble Monte Carlo simulation method [D.S. Corti, P. Debenedetti, Chem. Eng. Sci. 49 (1994) 2717]. In order to maintain the system in its one-phase state, different constraints on the density fluctuations have been imposed, varying with densities approaching and beyond the spinodal. The results are comparable with a molecular dynamics simulation study [A. Linhart, C.C. Chen, J. Vrabec, H. Hasse, J. Chem. Phys. 122 (2005) 144506] on the same system. The current study verifies the conclusion drawn by the simulation work that clustering of Argon atoms exists even in the vicinity of the spinodal. Compared with molecular dynamics simulations, our method can give the equilibrium properties of a metastable fluid, for example internal energies.     

Two-dimensional chiral segregation of the bent hard needles model with Lennard-Jones sites

Assuming the aggregates of a single chiral component as a pure phase, chiral segregation can be considered as a coexistence of two phases, therefore the formalisms of phase transitions in Statistical Mechanics can be applied. That is, chiral segregation can be considered as phase equilibrium. The standard mechanism to understand phase equilibrium considers the complete van der Waals forces, including repulsions and attractions. However, during the last few years, a particular kind of fluid-fluid equilibrium, explained in terms of only excluded volume effects, has gained important interest. This kind of phenomenon is known as depletion forces. In this paper, the contribution of these two mechanisms is investigated. In order to analyze the effect that repulsions and attractions have on chiral segregation we study a two-dimensional model, bent hard needles model. In one case only infinitely repulsive interactions are considered while in the second case, one and two Lennard-Jones (LJ) sites are added to model the complete van der Waals forces. In the first case, because of the nature of the model, the cause for chiral segregation is due to excluded volume effects that appear when the density of the system is sufficiently high. In the second case, the model proposed is more complex and besides the density the temperature also affects the phase separation. Monte Carlo simulations in the Gibbs ensemble (GMC) are used to perform this comparison. As a result, the segregation phase diagram is obtained for the infinitely repulsive model and that with two LJ sites. The important conclusions are that for some particular molecular geometries, repulsions are not able to produce chiral segregation at all, independently of density. However, when attractions are included the effect of repulsion is complemented and phase separation can be achieved even for those molecular geometries where infinitely repulsions were not able.     

Improving mixture of grains by using bi-dimensional Galton boards

This paper presents an experimental and numerical study that deals with the problem of mixing grains falling down through a bi-dimensional Galton board (BGB). The special issue addressed here is the influence of the presence of lateral walls in the BGB. Disks of equal diameters but different species are launched from the top of the device. During the fall, disks collide with obstacles (arranged to form a triangular lattice) and with the lateral walls. The exit distribution of particles at the bottom of the board is determined and the incidence of the presence of walls in the mixing quality is studied as a function of W the relative separation between lateral walls. Two types of indexes are evaluated to characterize the efficiency in the obtained mixture. The presence of walls has proven to be crucial to enhance the quality of the mixture of particles.     

Structural phase transitions and sodium ordering in Na0.5CoO2: a combined electron diffraction and Raman spectroscopy study

The nonstoichiometric Na_xCoO₂ system exhibits extraordinary physical properties that correlate with temperature and Na concentration in its layered lattice without evident long-range structure modification when conventional crystallographic techniques are applied. For instance, Na_0.7CoO₂, a thermodynamically stable phase, shows large thermoelectric power; water-intercalated Na_0.33CoO₂·1.3H₂O is a newly discovered superconductor with T_c∼4 K, and Na_0.5CoO₂ exhibits an unexpected charge ordering transition at around T_co∼55 K. Recent studies suggest that the transport and magnetic properties in the Na_xCoO₂ system strongly depend on the charge carrier density and local structural properties. Here we report a combined variable temperature transmission electron microscopy and Raman scattering investigation on structural transformations in Na_0.5CoO₂ single crystals. A series of structural phase transitions in the temperature range from 80 to 1000 K are directly identified and the observed superstructures and modulated phases can be interpreted by Na-ordering. The Raman scattering measurements reveal phase separation and a systematic evolution of active modes along with phase transitions. Our work demonstrates that the high mobility and ordering of sodium cations among the CoO₂ layers are a key factor for the presence of complex structural properties in Na_xCoO₂ materials, and also demonstrate that the combination of electron diffraction and Raman spectroscopy measurements is an efficient way for studying the cation ordering and phase transitions in related systems.     

Molecular Dynamical Simulation of Water/Ice Phase Transitions within Carbon Nanotubes under Various Pressures

A molecular dynamics simulation is performed for water confined within carbon nanotubes with diameters 11.00 A and 12.38A. Under pressures from 0.1 MPa to 500MPa the simulations are carried out by cooling from 300 K to 240K. Water molecules tend to transform from disordered to ordered with different configurations （square, pentagonal, hexagonal and hexagonal plus a chain）. It is concluded that denser structures may appear under high pressures.     

Molecular Dynamics Simulation of Water Confined in Carbon Nanotubes

Molecular dynamics simulations are performed for water confined in carbon nanotubes with various diameters （11.0-13.8 A ）. The simulations under an isobaric pressure （one atmosphere） by lowering temperatures from 300 K to 190K are carried out. Water molecules within variously sized tubes tend to transform from disorder to order with different configurations （four-water-molecule ring, six-water-molecule ring and seven-water-molecule ring） at phase transition temperatures, which may be lowered by the increasing tube radius. It is also found that the configurations of water in （10, 10） tube are not unique （seven-molecule ring and seven-molecule ring plus water chain）.     

Influence of nucleation on the kinetics of boron precipitation in silicon

A study of the precipitation of boron implanted into pre-amorphized silicon has been carried out following several thermal processes in the temperature range between 550 and 900 °C. It will be shown that the formation of inactive boron takes place even during a low-temperature solid-phase epitaxy of the regrowing layer, when the starting concentration level exceeds about 3.5×10²⁰ atoms/cm³. The presence, at the beginning of the annealing process, of inactive atoms in the form of small aggregates which behave as nucleation centers, markedly affects the precipitation kinetics during the thermal treatments. In these conditions the experimental data follow the Ham's theory of precipitation. On the contrary, if all the dopant is incorporated in the lattice side, nucleation is the limiting factor for boron deactivation.     

Immunization of susceptible-infected model on scale-free networks

In this paper, we investigate two major immunization strategies, random immunization and targeted immunization, of the susceptible-infected (SI) model on the Barabási-Albert (BA) networks. For the heterogeneous structure, the random strategy is quite ineffective if the vaccinated proportion is small, while the targeted one which prefers to vaccinate the individuals with the largest degree can sharply depress the epidemic spreading even only a tiny fraction of population are vaccinated. The analytical solution is also obtained, which can capture the trend of velocity change vs. the amount of vaccinated population.     

A class of stable spectral methods for the Cahn–Hilliard equation

In this work, the initial-boundary value problem of two-dimensional Cahn–Hilliard equation is considered. A class of fully discrete dissipative Fourier spectral schemes are proposed. Moreover, semi-implicit prediction–correction schemes are presented. The numerical simulations are performed to demonstrate the effectiveness of the proposed schemes.     

On the cleaning of monocrystalline metallic samples from impurities

The problem of sample cleaning is essential for all the scientists using ultra-high vacuum (UHV) techniques. The paper explores the issue of how the real structure of the monocrystalline sample affects its cleaning procedure. The mosaic structure of a monocrystalline sample should be taken into account in the interpretation of segregation and adsorption phenomena studies carried out under UHV conditions. Some examples of the cleaning of an Fe(1 1 1) sample from sulphur and carbon impurities are presented in the paper. Cleaning may result in obtaining two different states: clean surface and clean defects or clean surface but filled defects. According to these studies, the number of adsorption sites in the defects equals approximately 50% of the number of adsorption sites on the surface.     

Intrinsic inhomogeneity and non-linear conduction in charge-ordered Bi0.5Ca0.4Sr0.1MnO3

Systematic studies of X-ray, magnetic, electronic transport, and elastic properties have been performed on polycrystalline Bi_0.5Ca_0.4Sr_0.1MnO₃ sample. The sample exhibits charge ordering (CO) state below T_CO (=304 K), accompanied by a distinct maximum in magnetization. The softening of Young's modulus in the vicinity of T_CO indicates that there is a strong coupling of electron-phonon due to Jahn-Teller (JT) effect. The dynamic ferromagnetic spin correlations are observed at high temperatures above T_CO, which are replaced by antiferromagnetic (AFM) spin fluctuations at a concomitant CO transition. Below 32 K, a spin-glass (SG) state dominates at low temperatures. The voltage-current (V-I) characteristics measurement results indicate that the non-linear conduction starts above a threshold current, giving rise to a region of negative differential resistance (NDR). The origin of the non-linear conduction is discussed in view of current induced collapse of CO state associated with phase-separation mechanism.     

Phase stability in substitutionally Mn-doped GaAs: Role of lattice constraint

Phase stability of Ga_xMn_1−xAs alloy with a zincblende structure over the whole Mn composition is investigated by means of the full-potential linearized augmented plane-wave method and the cluster expansion method, and role of a lattice constraint from substrate on the phase stability is discussed. The calculated results demonstrate a phase separated type phase diagram with a miscibility gap even when the lattice constraint by changing the lattice constant is imposed, where the critical temperature is found to decrease with increasing the lattice constant. Thus, the elastic constraint from the substrate acts to help stabilize a solid solution so as to realize the magnetic semiconductor with higher Mn composition.     

Nonlinearities in sedimentation: a microscopic study

Effect of temperature and surface tension on surface during sedimentation is studied using atomic force microscopy. Effects of surface tension is incorporated by using ∼1 mm radius water droplets. Surface tension of water droplet directed the deposition of dissolved particles around the perimeter of the droplet; leaving almost hollow circle in the middle with light deposition due to the particles being close to the surface. Evaporating shallow water solutions left random salt structures on the surface. Growth exponents are calculated along with the fractal dimension. For sedimentation process in shallow water (depth of ∼2 mm), a transition is observed from continuum model (1.88±0.2) to KPZ (0.406±0.082) universality class around ∼1 μm at room temperature. For droplets evaporation, turbulent (multi-affine) to self-affine transition is observed. Fractal dimensions (FD) for the droplets are found to be between one and two. The FD values are consistent with the fact that competing nonlinear terms are present in the system.     

Spatial arrangements of particles with different mobility tendencies in a model glass-former

The use of the isoconfigurational method has enabled one to determine the existence of particles with high and low dynamic propensity (tendency to be mobile) and particles with preferred directionality for motion (directional particles) in supercooled liquids. On the other hand, dynamical studies have shown that the relaxation of such systems evolves by means of rapid crossings between metabasins of the potential energy surface (a metabasin being a group of mutually similar, closely related structures which differ markedly from the ones belonging to other metabasins), as collectively relaxing units (d-clusters) take place. Here we determine the spatial arrangements of such particles in a model three dimensional glass-forming system. We show that both the highest and the lowest propensity particles form compact clusters, which are separated from each other by the high directionality particles. The particles of this interfacial region seem to behave as to help make room for the enhanced (expansion) movement of the high propensity cluster and to keep the local density constant. Finally, we also find that only the high propensity particles (but not the directional ones) exhibit a great tendency to take part in d-cluster events.     

Theory of solid solubility for rare earth metal based alloys

Both parabola and ellipse separating schemes are used to study the solid solubilities for the binary alloy systems based on the 13 rare earth metals. It has been found that the soluble elements can be separated from the insoluble ones by a parabolyy ₁=a−bx ₁ ² or an ellipse(x ₂−m)²/c²+(y₂−n)²/d²=1. The results show that the overall reliabilities of the solid solubilities for the 897 binary alloys based on the rare earth metals are 89.2% and 92.8% for the parabola and ellipse regularities respectively. The constants a and b in the parabola equation, andm, n, c andd in the ellipse equation are discussed, which can be related to some appropriate parameters for each host metal respectively.     

Giant electroresistance and nonlinear conduction in electron-doped Ca0.9Ce0.1MnO3

We report a large resistance drop induced by Dc electrical currents in charge-ordered Ca_0.9Ce_0.1MnO₃. A giant electroresistance (ER) of ∼90% at 100 mA current below charge ordering (CO) transition temperature (T_CO) is found. Nonlinear conduction, which starts above a threshold current, gives rise to a region of negative differential resistance (NDR). The nonlinear conduction cannot be explained by homogeneous Joule heating of the sample. The origin of these phenomena is discussed in view of current induced collapse of CO state associated with phase-separation mechanism. This work can be useful for the potential applications of ER such as nonvolatile memory elements.     

Early stages of laser mixing process in Sb/Ge multilayer thin films

The onset of mixing at the interfaces between Sb and Ge in thin multilayered films containing two or four layers has been studied. The films were irradiated with nanosecond laser pulses in order to trigger mixing, and in situ reflectivity measurements were used to follow the transformation in real-time. Cross sectional transmission electron microscopy analysis was used to study both the structure and the composition profile before and after irradiation.A threshold irradiation energy exists for the onset of mixing, below which roughening of the interface between the layers is observed, together with recrystallization of the surface Sb layer following melting. The results are consistent with a melting/diffusion process which is inhomogeneously nucleated at the interface between the top Sb and Ge layers. Once mixing is initiated an amorphous Sb-Ge layer of constant thickness is formed, corresponding to mixing along a well defined planar melt front. Voids are observed at the former Sb/Ge interface, which may be related to interfacial stress in the as-grown configuration.     

The influence of the solubility limit on diffusion of as implants in silicon

Enhanced diffusion of implanted arsenic impurities in silicon during subsequent thermal annealing can be interpreted in terms of a system of reaction-diffusion equations. It is shown that for high doses the local solubility limit can considerably influence the reactions between the defects involved and thus markedly change the effective diffusion of As donors. A similar effect can be brought about by the presence of predoped donors/acceptors, which also can significantly accelerate/retard the effective diffusion of As implants. Furthermore, an explanation of some precipitation/clustering processes during a rapid/slow cooling-down is proposed. Finally, several contradictory experimental results published previously will be shown to be compatible with the present model.