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We propose a simple swarm model to study collective behaviour of a group of mobile autonomous agents interacting through a long range attraction and short range repulsion function. It is shown that the individuals (agents) will aggregate and eventually form a cohesive cluster of finite size around the swarm centre in a finite time, and the size depends only on the parameters of the swarm model. Furthermore, it is also shown that all the individuals will converge to equilibrium positions of the swarm model, and thus the configuration of the swarm converges to a constant constellation. Numerical simulations are also worked out to illustrate the analytical results.

We study the antiferromagnetic phase transition in the quasi-two-dimensional Hubbard model at half filling for a wide range of the Coulomb interaction U. By using the fluctuation-exchange approximation, we calculate the Neel transition temperature of the system as a function of the Coulomb interaction U. For weak-to-intermediate Coulomb interactions, the present calculation provides a reasonable result for the Neel temperature.

We study the effects of the energy band structure of conduction-electron on the transport properties of an interacting quantum dot system. By applying the nonequilibrium Keldysh Green function technique, we show that the finite width of electron band in leads causes the negative differential conductance in some regions of the applied voltage. We also show that the van Hove singularities in the density of states of conduction-electron do not qualitatively change the differential conductance of the system, and hence can be safely ignored. Therefore, the wide band approximation used in the previous investigations is partially justified.

TiO2 thin films are prepared on fused silica with conventional electron beam evaporation deposition. After annealed at different temperatures for 4h, the spectra and XRD patterns of the TiO2 thin film are obtained. Weak absorption of coatings is measured by the surface thermal lensing technique, and laser-induced damage threshold (LIDT) is determined. It is found that with the increasing annealing temperature, the transmittance of TiO2 films decreases. Especially when coatings are annealed at high temperature over 1173K, the optical loss is very serious. Weak absorption detection indicates that the absorption of coatings decreases firstly and then increases, and the absorption and defects play major roles in the LIDT of TiO2 thin films.

TiO2 coatings are prepared on fused silica with conventional electron beam evaporation deposition. After annealed at different temperatures for four hours, the spectra and XRD patterns of TiO2 thin film are obtained. XRD patterns reveal that only anatase phase can be observed in TiO2 coatings regardless of the different annealing temperatures, and with the increasing annealing temperature, the grain size gradually increases. The relationship between the energy gap and microstructure of anatase is determined and discussed. The quantum confinement effect is observed that with the increasing grain size of TiO2 thin film, the band gap energy shifts from 3.4 eV to 3.21 eV. Moreover, other possible influence of the TiO2 thin-film microstructure, such as surface roughness and thin film absorption, on band gap energy is also expected.

Superionic conductor RbAg4I5 crystalline grain films were prepared by vacuum thermal evaporation on NaCl crystalline substrates. The surface morphology, microstructure and the electronic energy states of the films were examined by atomic force microscopy, transmission-electron microscopy, x-ray diffraction and x-ray photoelectron spectroscopy. The results show that the obtained RbAg4I5 layer has an epitaxial film of perfect crystalline structure, and the unit cell of crystalline grain RbAg4I5 films belongs to cubic crystal system. The principal x-ray diffraction peaks at d = 3.7447 and 1.8733 A are related to the structure of ternary compound RbAg4I5 films.

The absorption spectra of the A1 low-frequency exciton band in quaternary compound Rb0.5Cs0.5Ag4I5 thin films have been measured by an UV-2100 spectrophotometer at the temperature (T) range from 78 to 289 K. The measurements at intermediate temperatures are performed within an interval of photon energies from 3.44 to 3.70 eV. The spectra have been computer-processed to separate the A1 band from the interband absorption edges, and to determine their parameters: the spectral peak position (Em), the half-width (G) of the exciton band, and the Gaussian shape ratio in the spectrum. The results show that at T 107 K, dEm/dT = -3.01×10-4 eVK-1, dG/dT = 5.47×10-4 eVK-1. It is emphasized that the phase transition γ→β in this material is carried out at a temperature of 107 K.

In this paper, a one-dimensional short-ranged spin-glass model in a random magnetic field is studied. Noticing convexity of the partition function, we use Jensen's inequality to obtain a lower bound to the averaged free energy density and the slope inequality for an upper bound. These bounds are derived under very general conditions and they can be used as tests for various approximate methods such as the replica method.

Various ionizing radiations, such as electrons and alpha particles, transfer their energy to media by produced secondary electrons and induce double- or single-strand break of DNA, which result in variable effects. To understand how the ionizing radiations interact with DNA and break it, several models have been developed, most of them consider the water as a vapor state. Actually, the ionizing particles interact with DNA which is solved in liquid water. To compare the difference of vapor and liquid water models, we calculate the stopping power, continuous slowing down approximation (CSDA) range and S value of electrons and alpha particles at cellular scale in liquid and vapor by Monte Carlo simulations, respectively. Our data show that the stopping power and CSDA range are different in liquid and vapor water in a special energy range. For many S values, the liquid model is better than the vapor model when the energy of the electrons is higher than 100 keV and the vapor model is higher than the liquid model for the 1 MeV alpha particles.

Coherent electronic transport properties of silver–C60–silver molecular junctions in different configurations are studied using hybrid density function theory. The experimentally measured current flows of C60 molecules adsorbed on the silver surface are well reproduced by theoretical calculations. It is found that the current–voltage characteristics of the molecular junctions depend strongly on the configurations of the junctions. Transmission spectra combined with density of states can help us to understand in depth the transport properties. Different kinds of electrode construction are also discussed. With the help of the calculation, two possible configurations of silver–C60–silver molecular junctions are suggested.