A remark on the condensation in the hard-core lattice Bose gas

We point out that Bose-Einstein condensation occurs at sufficiently low temperature in a hard-core ^d-lattice Bose gas for d3 and particle density 1/2, by exploiting its equivalence to a spin-1/2XY model.     

Evolution of cooperation in lattice population with adaptive interaction intensity

We study the evolutionary Prisoner’s Dilemma game among individuals endowed with adaptively interaction intensity. Individuals adjust their interaction intensity according to the rules “payoff increase-high intensity, payoff decrease-low intensity”: if an individual’s payoff increases compared with that in the previous generation, he raises his interaction intensity; otherwise, he reduces the probability of interaction. We find that if individuals can adjust their interaction intensity with a proper scale, cooperation can be promoted. Interestingly, individuals with low interaction intensity usually hold the boundary of cooperator cluster. Such spatial distribution can alleviate the exploitation from defectors to cooperators since the interaction between cooperators and defectors is weakened. We hope our work can yield some insight into investigation of the evolution of cooperation in structured population.     

Manifestations of random lattice deformations in the spectra of crystals with rare earths ions

The splitting of zero-phonon lines of rare-earth impurity centers is observed in the optical spectra of dielectric crystals. It is shown that the primary contribution to such splitting comes from random deformations associated with point defects in the crystals.     

Thermal configurations of oxygen in silicon

The central position and the infrared absorption coefficient of the 9 m band of Si samples were measured with Fourier transform infrared spectroscopy (FTIR) at temperatures from T=77 K to 775 K. The infrared absorption coefficients were corrected by considering background absorption and free carrier absorption calculated from the increased free carrier concentration and from the resistivity determined from Hall effect measurements. We found the central position of the 9 m band to shift to longer wavelengths with increasing temperature. The concentration [O_i] of interstitial oxygen is almost constant for T<600 K, but decreased rapidly for T>600 K. These results verified there are two types of thermal configurations of oxygen in silicon: The bonded Si₂O configuration with a binding energy E _b0.8 to 1.0 eV at T77 K to 600 K, and the Si₂O configuration coexists with a quasi-free interstitial oxygen (QFIO) state for T>600 K. The lattice potential barrier E _L, which retards QFIO atoms from migrating in the lattice, is estimated to be 1.5 to 1.6 eV. From these configurations the anomalous diffusivity of oxygen in silicon can be explained quite well.     

The influence of graded interfaces in the electronic spectrum of nanometer silicon dots

The effects imposed to the electron energy levels of Si/SiO₂ quantum dots by the presence of smooth graded interfaces and interfacial carriers trap is studied. For small diameter quantum dots, while the existence of graded interfaces strongly blue shifts the carrier energy states (up to a few hundred meV), the effect of the interfacial carriers trap is to red shift the energies, but to a lesser extend (under 50 meV). In addition, slight changes in the distance of the carriers trap in relation to the center of the dot does not alter significantly the energy spectrum.     

The study of the influence of uniaxial stress on impurity complexes in silicon

The influence of external uniaxial stress on the different indium-donor complexes in silicon has been studied using the perturbed γ –γ angular correlation (PAC) method. Such effect of an applied stress is detected by means of the probe atoms situated at different complexes in the sample. The current results showed that the responses of the probes in an extrinsic silicon samples are found to be dissimilar for the same value of stress. Such change in the local environments of the probe atoms could be associated with the various strain field created by the implantations of varied size of impurities. The phosphorous implantation in silicon has even lead to the complete absence of observable effect of the applied stress suggesting significant lose of the elasticity of the sample.     

The influence of anharmonicities to the lattice structure of rare gas crystals

The zero-point energy and the leading anharmonic terms of the free energy retained in second-order perturbation theory are calculated numerically at temperature zero for the two closest-packed structures, the face-centered cubic (fcc) and the hexagonal closest-packed (hcp). In agreement with experiment we get the fcc lattices energetically favoured relative to the hep lattices.     

The impact of large-scale computing on lattice statistics

The use of computers in theoretical physics has grown dramatically over the years; this is as true in lattice statistical mechanics as anywhere. This paper is concerned with one such aspect with which the name of C. Domb has been closely associated: the enumeration of embeddings of connected structures in an unlimited crystal lattice. An informal account is given of a recent computer project originating in the combinatorial shadow method developed by M. F. Sykes: the determination of the numbers and the properties ofcluster embeddings in crystal lattices. Sykes' approach has opened a way to information which was earlier considered to be forever beyond reach. The principles are given and the algorithms sketched; the detailed FORTRAN programming is not given. The methods used have had to be specially developed, but some have a wider application for computer algebra when the computational task is massive. Provided the computer is large enough and fast enough, impressive results may be obtained in return for a reasonable effort. In practice, this implies that the computer may have to be one of the largest and fastest, or else that it is dedicated to the task.     

稀土（Tb，Gd）掺杂多孔硅的光致发光性能研究

用电化学方法对多孔硅薄膜进行了稀土（Tb，Gd）离子的化学掺杂.利用荧光分光光度计测试了样品的光致发光特性.用扫描电子显微镜研究了薄膜的表面形貌.用卢瑟福背散射谱分析了稀土离子在多孔硅薄膜中的分布情况.结果表明，Tb的掺入显著增强了多孔硅的发光强度，并且发光峰位出现蓝移.这是由于Tb³⁺的4f能级⁵D_{4—⁷F3，⁵D4—⁷F关键词： 多孔硅 稀土掺杂 光致发光}     

The influence of some optical parameters on IR spectroscopy of oxygen in silicon

The influence of optical parameters involved in the determination of impurity concentrations in single crystalline silicon by IR spectroscopy was evaluated. Variations of the refractive index with wavelength have a negligible effect. Contributions by the coefficient of extinction and reflectivity of the sample surface cannot be ignored. The influence of sample surface morphology was investigated experimentally and results indicate that errors up to ~30% can occur if a constant value of reflectivity R = 0.30 is employed in calculations of the absorption coefficient.     

Velocity autocorrelation function in lattice gases from the ring kinetic theory. Comparison with numerical simulations

We obtain the complete time dependence of the velocity autocorrelation function (VACF) for lattice gas cellular automata, usingring kinetic theory. This theory accounts for the simplest correlated collisions that improve on the molecular chaos approach, and yields a closed equation for the VACF that we evaluate for both infinite and finite systems. We compare our analytical results with numerical simulations at all times, as well as with long-time results of the mode coupling theories, finding a very good agreement for all times at all densities.     

The mechanism of PEO process on Al–Si alloys with the bulk primary silicon

This study focuses on mechanism of ceramic coating on Al–Si alloys with bulk primary Si using plasma electrolytic oxidation (PEO) technology. Al–Si alloys with 27–32%Si in weight were used as substrates. The morphologies, composition and microstructure of PEO coatings were investigated by scanning electron microscopy (SEM) with energy dispersive X-ray system (EDX). Results showed that the PEO process had four different stages. The effect of bulk Si is greatly on the morphology and composition of coatings at first three stages. Anodic oxide films formed on Al and Si phases, respectively. When the voltage exceeded 40 V, glow appeared and concentrated on the localized zone of interface of Al and Si phase. Al–Si–O compounds formed and covered on the dendrite Si phase surface, and the coating on bulk Si, which was silicon oxide, was rougher than that on other phase. If the treatment time was long enough, the coatings with uniform surface morphologies and elements distribution will be obtained but the microstructure of inner layer is looser due to the bulk Si.     

Diffusion in a lattice of randomly placed sites and application to ac conductivity

The transition probability for a carrier hopping between randomly placed sites is determined for a system in thermodynamic equilibrium. The effect of the first waiting time is included and the result is shown to be consistent with the theory of statistical thermodynamics. Furthermore, a comparison is made with the master equation approach, which is shown to be exact when the waiting times are exponentially distributed. The application to ac conductivity is discussed.     

晶格常数与掺杂YBCO体系超导电性的关系

依据现有的YBCO掺杂实验,对掺杂YBCO体系超导电性与其晶格常数进行了研究,发现它们之间具有较好的规律性。因此提出用晶格常数作为掺杂YBCO超导电性的一个判断标准,这对探索超导机制及对今后实验工作掺杂元素和掺杂比例的选取有很好的指导意义。     

The effect of Magic Angle Spinning on proton spin–lattice relaxation times in some organic solids

Proton spectra of solids are usually broadened by strong proton homonuclear dipolar interactions. However, substantial line narrowing may be achieved by Magic Angle Spinning (MAS) in systems of low proton density or in systems in which rapid molecular motions occur. In such conditions, T₁(H) measurements are often used to characterise the dynamics of each resolved proton site. We show that T₁(H) values measured for solid organic compounds with high proton abundance, such as adamantane and glycine, may be strongly dependent on the spinning rate employed, so that care is required when values are compared. The effects of molecular motion and proton density on T₁(H) and its dependence on spinning rate were investigated. We found that an increase in molecular motion leads to an increase of T₁(H) at higher spinning rates. The opposite is found for systems with low proton densities which show relatively lower T₁(H), at higher spinning rates. A possible interpretation is suggested in terms of the reduced spin diffusion efficiency at higher spinning rates.     

Rotational invariance in the three-dimensional lattice Boltzmann method is dependent on the choice of lattice

The lattice Boltzmann method has recently gained popularity as a tool for simulating complex fluid flows. It uses discrete sets of velocity vectors, or lattices, to create a reduced model of the molecular dynamics of a continuum fluid. While several lattices are believed to behave isotropically, there are reports of qualitatively incorrect results. However, thus far, the reason as to why a lack of isotropy occurs is not known. Based on the hypothesis that lower order lattices may not display rotational invariance, this study tests the isotropy of the D3Q15, D3Q19 and D3Q27 lattices by performing simulations at intermediate Reynolds numbers (50–500) and low Knudsen number (<0.0005) in an axisymmetrical geometry with a nozzle leading to a throat followed by a sudden expansion. The symmetry properties of the results were examined. It was found that at Re ? 250 the D3Q15 and D3Q19 lattices produced different results depending on the plane of the lattice with which the flow was aligned. Lattice planes with fewer than six velocity vectors consistently produced results which were qualitatively different from the planes with six or more velocity vectors. These errors were not observed at Re = 50 or when a D3Q27 lattice was used. They appeared to be independent of grid density, collision operator and Ma. This suggests that the lattices which contain these planes are not fully isotropic and therefore do not properly replicate the behavior of a real fluid in this particular situation, notably downstream from the expansion. Predictions made using these models in more complex geometries may therefore be affected by the orientation of the lattice. When using LBM in CFD simulation (including validation) this study highlights the need for caution to ensure that the solution obtained is independent of the lattice orientation throughout the domain.     

Surface diffusion of particles adsorbed on an inhomogeneous lattice with two non-equivalent sites

We investigate surface diffusion in a system of particles with the nearest neighbor pairwise lateral interaction adsorbed on a two-dimensional inhomogeneous lattice of square symmetry with deep and shallow sites. General analytical expressions for the chemical and jump diffusion coefficients have been derived in case of strong inhomogeneity. The expressions are valid for the inhomogeneous lattices with different geometries and dimensionalities. We have calculated the coverage dependencies of the tracer, jump and chemical diffusion coefficients for different temperatures using the real-space renormalization group (RSRG) method and compared the data with the numerical results obtained by the MC simulations. The coincidence between the data obtained by these quite different methods is rather good.     

Y2O3:Er3的共沉淀法制备和pH值对发光性质的影响

采用共沉淀法,通过氨水调节沉淀剂碳酸氢铵的pH值,制备了一系列Y<,2>O<,3>:1%Er样品.傅里叶变换红外光谱以及兀素分析表明,沉淀剂pH值在8.0～9.5之间变化时,前驱沉淀物化学结构基本不变;而X射线荧光潜仪分析与SEM形貌表征的结果表明,pH值改变时不仅会导致前驱沉淀物中Er含量的变化.而且使得煅烧后粉末颗粒的粒径及其分布发生改变.测量煅烧后粉末样晶的荧光光谱,结果显示,pH值变化引起的Er含最和颗粒粒径的变化,都会导致粉末样品发光性质产生差异.     

Pairs of chiral quarks on the lattice from staggered fermions

A new formulation of chiral fermions on the lattice is presented. It is a version of overlap fermions, but built from the computationally efficient staggered fermions rather than the previously used Wilson fermions. The construction reduces the four quark flavors described by the staggered fermion to two quark flavors; this pair can be taken as the up and down quarks in Lattice QCD. A domain wall formulation giving a truncation of this overlap construction is also outlined.