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We present a computer model of diffusion limited aggregation with linear seed. The clusters with varying linear seed lengths are simulated, and their pattern structure, fractal dimension and multifractal spectrum are obtained. The simulation results show that the linear seed length has little effect on the pattern structure of the aggregation clusters if its length is comparatively shorter. With its increasing, the linear seed length has stronger effects on the pattern structure, while the dimension Df decreases. When the linear seed length is larger, the corresponding pattern structure is cross alike. The larger the linear seed length is, the more obvious the cross-like structure with more particles clustering at the two ends of the linear seed and along the vertical direction to the centre of the linear seed. Furthermore, the multifractal spectra curve becomes lower and the range of singularity narrower. The longer the length of a linear seed is, the less irregular and nonuniform the pattern becomes.

We investigate the magnetic transitions in a (La1-xBx)(2/3)Ca1/3MnO3 system, which consists of paramagnetic and ferromagnetic domains, based on a magnetic theoretical percolation model. In the mean-field approximation, the resistance as a, function of temperature and magnetic field has been derived analytically and simulated numerically. It is found that the dependence of the critical temperature on magnetic field is linear when applied magnetic field is not too strong. Our theoretical predications are in good agreement with recent experimental observations.

By using the replica method and the functional integral technique, the quantum XY spin glass model with ferromagnetic coupling is investigated numerically. From the numerical results of the thermodynamic and magnetic quantities we found that these quantities do not vary with the mean exchange interaction when the mean exchange interaction is lower than 1. This feature demonstrates that there are the mean interaction translational symmetries in the spin-glass and paramagnetic phases.

With the help of the replica method and imaginary-time functional-integrate technique, the spin glass model with the vibrations of crystal lattices is investigated. In the limit of the replica symmetry and the imaginary-time static approximation, the magnetic and thermodynamic quantities have been obtained. By the numerical calculations, we found that the magnetization of the system has the typical spin-glass behaviour. A peak is found in the susceptibility–temperature curve and is shifted to lower temperature with increasing applied field. Due to the lattice contribution, the specific heat increases strongly at high temperature. Due to the magnetic contribution, the anomaly in the specific heat–temperature curve forms a λ-type peak, which agrees with the observation of Rojo et al. [Phys. Rev. B 66 (2002) 094406].

We investigate the electrical properties of Sm-doped Bi4−xSmxTi3O12 (BST) ceramics prepared by a conventional electroceramic technique. The x-ray diffraction analysis reveals the Bi-layered perovskite structure in all samples. The SEM micrographs show randomly oriented and plate-like morphology. For the samples with x = 0.4 and 1.0, the current–voltage characteristics exhibit negative differential resistance behaviour and the P–V hysteresis loops are characterized by large leakage current, whereas for the samples with x = 0.6 and 0.8, the current–voltage characteristics show simple ohmic behaviour and the P–V hysteresis loops are of the saturated and undistorted hysteresis. The remanent polarization and coercive field of the BST ceramic with x = 0.8 are above 32 μC/cm2 and 70 kV/cm, respectively.

We have studied the densification behaviour, microstructure and electrical properties of WO3 ceramics with V2O5 as the additive ranging from 0.5 to 15mol%. Scanning electron microscopic photos indicated that the grain size of WO3-V2O5 specimens is smaller than that of pure WO3. The addition of V2O5 to WO3 showed a tendency to enhance the densification rate and to restrict the grain growth. Electrical properties of all specimens were measured for different electrodes at different temperatures. The formation of the grain boundary barrier layer was confirmed by the non-ohmic I-V behaviour. The nonlinear coefficient was obtained at the current density J=0.01, 0.1 and 1mA/cm(2) for a series of WO3-V2O5 samples. The V0.5mol% specimen showed an abnormal phenomenon that the nonlinear characteristics appeared at 350degreesC and disappeared at lower and higher temperatures. This implies that it could be applied as a high-temperature varistor. The double Schottky barrier model was adopted to explain the phenomena for the WO3-V(2)o(5) varistors.

The full-potential linearized augmented plane wave method was applied to study the electronic and the magnetic properties of the compound pipz-H-2[MnF4(HF2)](pipz=piperazine). The band structure, the total density of states, the partial density of states and the electron density were calculated to explain the electronic and the magnetic properties of pipz-H-2[MnF4(HF2)] in the ferromagnetic state. It is found that the magnetic moment of the molecule mainly comes from the Mn atoms with partial contribution from the F atoms. The symmetrical sigma/sigma, bonds via H atoms along Mn-F-H-F-Mn chains and the weak direct-exchange interaction between F(2), F(3) and Mn atoms have effect on the electronic structure and the magnetism of pipz-H-2[MnF4(HF2)].

Using an exact diagonalization method, we study an extended Hubbard model with an electron-lattice interaction for an organic ferromagnetic chain with radical coupling. The result shows that the ferromagnetic ground state originates from the antiferromagnetic correlation between adjoining sites, which is enhanced by the on-site e-e repulsion. The intersite e-e repulsion induces the inhomogeneous distribution of the charge density. The dimerization is decreased by the e-e interaction and the radical coupling. The electron-lattice interaction and the radical coupling can transfer the spin density and charge density between the main chain and the radicals.

The quantum infinite range XY spin glass model with the infinite range planar Dzyaloshinskii-Moriya interaction in external field for spin S=1/2 is investigated theoretically. Numerical calculations show that, the specific heat depending on the temperature has crossover behavior; the weak field dependence of the specific heat can be fitted by the parabolic approximation, C/T = A + Bh2, the coefficient B is peaked near the transition point.

By using replica method and Matsubara imaginary-time functional-integral technique, the quantum infinite range Heisenberg model is solved. The solution shows that the quantum infinite range Heisenberg model also has phase transition.

The percolation clusters with varying occupy probability were constructed in this paper. Viscous fingering (VF) in percolation cluster, based on the assumption that bond radii are Rayleigh distribution, is investigated by means of successive over-relaxation technique. The fractal dimension for VF in percolation cluster is calculated. The result shows that it can increase fractal dimension of VF as increase of percolation probability of reduce of viscous ratio. VF's fractal dimension of porous media in the limit viscous ratio → ∞ is found to be identical with that in diffusion limited-aggregation. We have found that the topology and the geometry of the porous medium have strong effects on the displacement processes and the structure of the VF. We find that the sweep efficiency of the displacement processes mainly depends upon the length of the network system and also on the viscosity ratio. Moreover, the fractional flow of injected fluid as a function of mean saturation is obtained.

A new method?mapping dilation method is proposed in this paper to construct Sierpinski carpet. Viscous fingering (VF) in Sierpinski carpet, based on the assumption that bond radii are beta distribution, is investigated by means of successive over-relaxation techniques. The topology and the geometry of the porous media have a strong effect on displacement processes. In the Sierpinski network, the VF pattern of porous media in the limit M???? is found to be similar to the diffusion-limited-aggregation pattern. The fractal dimension for VF in fractal space is calculated and the fractal dimension D can be reasonably regarded as a useful parameter to evaluate the sweep efficiencies and oil recoveries. We have also found that the geometry of the porous medium also has strong effects on the displacement processes and the structure of the VF. Moreover, we find that the sweep efficiency of the displacement processes mainly depends upon the length of the network system and also on the viscosity ratio M. This shows that the current method can be used to solve VF problems in complex structures if the structures are self-similar, or they can be reduced to a self-similar structure.

The total reflection characteristics of plane waves from the interface including a chiral medium have been studied with complex chiral material parameters. The possible values of chirality admittance ζc are determined for left-circularly polarized (LCP) and right-circularly polarized (RCP) total reflections at fixed incident angles from an interface between free space and a chiral medium. It is found that there exists a region of parameter ζc, in which neither LCP nor RCP modes can be totally reflected for any incident angle θ. It is demonstrated that for ζ1 = Re(ζc) > 0, total reflection is preferred for LCP mode whereas RCP total reflection is favored for ζ1

We report a comparative study between two kinds of polyaniline, PANI-H3PO4 and PANI-C4H6O6. We have measured the temperature dependence of the dc-conductivity σdc(T) and magnetic susceptibility χT(T). The structure of polyaniline was characterized by Fourier transform infrared technique, electron-spin-resonance and x-ray diffraction. Polyaniline synthesized with phosphoric and tartaric acids leads to high magnetic susceptibility χT (at T = 295 K) ≈ 10-4 emu/mol.2rings. The dc-conductivity of both kinds of PANI shows a semiconductor behavior and follows the quasi-one-dimensional variable-range-hopping model. A comparison of the magnetic susceptibility shows greater electron localization in PANI-C4H6O6, which is in agreement with the lower conductivity at room temperature for PANI-C4H6O6.

The reflection from and transmission characteristic of the plane waves are studied at the interface between media including chiral media. The co-polarized and cross-polarized reflection and transmission coefficients are derived from the chiral constitutive relations. Possible values of chirality admittance ζc are determined for fixed Brewster angles. In addition, the features of reflection and transmission in some typical cases including the normal incidence case and that containing a mirror-conjugated medium are discussed in detail. For example, complex chiral parameters for minimal reflection coefficient in the case of normal incidence are optimized.

A computer model of capillary and viscous fingering in a porous media is presented, which treats the media as a square lattice connected with randomly chosen radius. The fractal properties of the model are studied for shell-shell aggregation method by Monte Carlo simulation. The simulation results show that the dimension D increases along with increasing of M and decreasing of mu, where M and mu are the ratios of the viscosity of the two fluids and the most probable radius of the throat in porous media respectively. It is found that there exist foul regions for fluid.

Based on a theoretical model proposed for quasi-one-dimensional organic polymer ferromagnets, the next-nearest neighbor hopping interactions of π-electrons are considered. Allowing for full lattice relaxation, a set of self-consistent equations is established to study the system. The spin-density-wave (SDW) and the possible ferromagnetic ground state of the system are investigated in detail. It is found that the next-nearest neighbor hopping interactions will make the SDW stronger and consequently make the ferromagnetic state more stable as compared with the nonmagnetic reference state.

A new kind of organic polymer ferromagnet based on polaron is proposed. In this kind of polymer, there are no organic free-radicals, which are rather reactive and unstable, instead spins are provided by polarons. Allowing for full lattice relaxation, the system is studied self-consistently by Peierls-Hubbard model. The formation energies of polarons are calculated. The possible ferromagnetism in polymers of this type is demonstrated.

A new quasi-one-dimensional organic ferromagnet model is proposed. Magnon excitations for finite and infinite on-site repulsion of electrons on main carbon chain are investigated. It is found that the lowest branch of spectrum preserves the characteristics of the ferromagnetic magnon. It is also shown that with increasing of the on-site repulsion energy, the itinerant π-electrons become tightly localized.

Based on a theoretical model proposed for quasi-one-dimensional organic polymer ferromagnet poly-BIPO, the effects of electron-electron interaction and electron-phonon coupling on the spin-density-wave (SDW) state of poly-BIPO system are studied. It is found that the SDW state is the stable ground state of the system, in which the system shows ferromagnetic order. And the larger electron-electron interaction and the smaller electron-phonon coupling will make the SDW state more stable than the nonmagnetic state.

Based on the replica method and the imaginary time functional-integral technique, we investigate the infinite-range quantum Dzyaloshinskii–Moriya spin glass model. It is found that the quantum Dzyaloshinskii–Moriya spin glass model behaves in a Heisenberg-like manner. The specific heat has the crossover behaviour. The broad Maximum in specific heat is shifted to higher temperature with increasing applied field. These features are in good agreement with the observation of Brodale et al. [J. Magn. Magn. Matter. 31-34 (1983) 1331] The susceptibility of the system has the typical spin glass feature.

The percolation clusters with varying occupy probability are constructed. Invasion percolation (IP) in percolation cluster is investigated by means of IP algorithm without trapping. The pattern constructions of IP in percolation clusters are obviously different from that of viscous fingering (VF) in percolation clusters. The fractal dimension Df of IP increases with increasing the percolation probability P. The geometry and the topology of the porous media have strong effects on the pattern structure of IP. For large M (the node numbers occupied by the injected fluid), the rescaled value is Rg/M1/Df, which asymptotically approaches a constant value, and Rg is the gyration radius of IP cluster. Moreover, the chemical dimension Dl and the shortest path exponent dmin are obtained.

The localized vibrational modes around a bipolaron in cis-(CH)x are studied by using a two-dimensional extension of the SSH model that includes the bond-bending term. A number of additional modes have been found, compared with the results based on the standard SSH model. The amplitudes of the two directions (x and y direction) are comparable for most of the modes as in the trans-(CH)x case. The number of localized modes and their frequencies depend not only on the coupling constant, but also on the bond-bending term and the parameter t1 in removing the degeneracy of the ground state.

A modified method of calculating the end-to-end distance of segments with a given number of units in a single polymer chain is presented and numerical studies of some fractals by using Havlin and Ben-Avraham's and our methods are given. The results show that our method can remove the fluctuations in the end-to-end distances of the segments arising in Havlin and Ben-Avraham's method.

The electron-lattice coupling vibrational modes are calculated using a two-dimensional extension of the Su-Schrieffer-Heeger model that includes the bond-bending term, the electron-electron interactions and the electrostatic pinning for doped samples. The result shows that all ten localized modes exist after turning on the e-e interactions and doped pinning effects, but their localizations has been strengthened and the frequencies have been moved slightly.

By means of the renormalized vertex procedure for the motion Green's function developed by the authors, the vertex function of magnetic alloys, based on the s-d exchange interaction, is solved exactly and the corresponding Hall conductivity tensors are obtained. It is found that the renormalized modification of the conductivity is very important in the cases of not too weak external magnetic field and slow relexaction time.

With the help of the decimation ansatz of the renormlization group, the dependence of critical temperature on a transverse magnetic field is calculated analytically for a quasi-one-dimensional disordered superconductor model, based on the de Gennes-Skal-Shklovskii (dGSS) picture of the large cluster in a percolation system. Our results are in good agreement with those given by Halley's scaling theory.

A new computer model of viscous fingering (VF) in a porous medium is presented. The simulation results show that the VF pattern is in agreement with the experimental results. The simulation on the sweep efficiency also agrees with experiment results. The surface fractal dimension as a function of viscous ratio is found.

By using the generalized static replica symmetry approximation, the quantum XY spin-glass model in a longitudinal field is investigated. The thermodynamic quantities, spin-glass and self-interaction order parameters are calculated numerically. The local susceptibility depending on temperature has the typical spin-glass plateau characteristic; the specific heat against temperature display a crossover feature which was discovered experimentally in the CuMn sample by Brodale et al. (J. Magn. Magn. Mater. 31-34 (1983) 1331) and cusps sharper than that in the model with the Dzyaloshinskii-Moriya interaction.

A new porous media model with correlated sites-bonds has been constructed. Taking into account both the pore and throat geometries, the viscous fingering (VF) in porous media has been investigated by using the standard over-relaxed Gauss-Seidel scheme. The simulation results show that the VF's structure varies with the correlation parameter epsilon and the viscous ratio M. The sweep efficiency epsilon decreases along with the increase of the correlation parameter E and the lattice size R-1s. The surface fractal D-s gradually increases as the correlation parameter epsilon increases, whatever the viscous ratio M is. Also, D-s gradually increases as M increases whatever epsilon is. This means that not only the viscosity ratio but also the topology and the geometry of the porous media have a strong effect on the displacement process, the VF's structure, the sweep efficiency and the surface pattern.

A two-dimensional single-mode laser model is investigated, with cross-correlations between the real and imaginary parts of the quantum noise as well as the pump noise. The general closed form of the laser intensity Langevin equation (GILE) is obtained under a stable locked phase resulting from the cross-correlation λq between the real and imaginary parts of the quantum noise. Because of the presence of a new term containing λq, we can unify the two opposite intensity Langevin equations which correspond to the two special cases for |λq|→0 and |λq|→1 in the GILE. It is expected that the transient and stationary properties of the laser model can be changed qualitatively when λq varies.

A model of random porous media degradation is investigated via several fluid displacing, freezing and thawing cycles. The fluid transport is based on the deterministic method with dispersion effect. Research shows that the topology and the geometry of the porous media have a strong effect on displacement processes. The distribution of throat size N(r) after displacement but before freezing damage shows that the major change, after successive cycles, happens at the throat radius r > 0.9. The distribution of velocities normal to the interface of viscous fingering in percolation cluster is also studied. When iterations n greater than or equal to 10, the scaling function distribution is very sharp.

Using the full-potential linearized augmented plane wave method based on the density functional theory, spin-polarized calculations of electronic structure for the zinc-blende CrS and CrSe are performed. Zinc-blende CrS and CrSe at their respective equilibrium lattice constants are half-metallic with the same total magnetic moment of 4.00B. The electronic structures of zinc-blende CrS and CrSe are calculated under uniform strains from -10% to +10% relative to the equilibrium lattice constant. The calculated results indicate that zinc-blende CrS and CrSe can maintain half-metallic ferromagnetism and keep the same total magnetic moment of 4.00B from -1% to 10% and from -4% to 10% uniform strain, respectively.

The influence of inhomogeneous interaction energy between deposited atoms and substrate atoms on island film growth is investigated by Monte Carlo simulation on a triangular lattice substrate. The Gaussian distribution is employed to describe the inhomogeneity of interaction energy. The results illustrate that the influence of inhomogeneous interaction energy on the growth of thin film is related to the degree of the inhomogeneity and the experimental conditions (such as substrate temperature).At medium temperature the inhomogeneity of interaction energy has notable influence on the island number and the island size. Increasing in temperature could counteract the influence of the inhomogeneity of interaction energy.

The effect of low-energy deposition particles on the initial stage of thin film growth is studied by Monte Carlo simulation in this paper. The energy range of deposition particles is from 0 to 0.7eV. Three processes are considered: atom deposition, adatom diffusion and re evaporation. The effect of nearest adatoms and next near adatoms is also considered. The results show that the low-energy ion irradiation strongly affects the island film growth process at low temperature. Morphologies and size distributions of islands have significantly changed with the increase of incident ion energy.

In this paper, a single-charge tunneling simulator, the Monte Carlo simulator of two-dimensional quantum dot array using standard single electron tunneling theory and Monte-Carlo method is introduced. The simulated results show that the two-dimensional quantum dot array has Coulomb charging effect at low temperatures. The quantum effect of the dot array exhibits great prospect in research and applications.

Based on our interchain coupled theoretical model for quasi-one-dimensional organic ferromagnet, we took into account the nearest and the next nearest hopping interactions between neighboring chains, to study the charge density wave and the spin density wave along the main chain. The calculated results showed that the interchain coupling results in the transfers of charge density and spin density between the main chain and the side radicals of the two coupled chains.

In this paper,the effect of the anisotropy diffusion on the growth of diffusion-limited aggregation(DLA) clusters is discussed.Our computer simulation results verify that DLA clusters grown with anisotropic diffusion rules have a striking overall diamond shape.A new anisotropic diffusion equation of particles is derived.The Hausdorff dimension of a two-dimensional DLA cluster in the anisotropic diffusion is calculated.The results show that the effective angle βeff=min(βix,βiy).In addition,the generalized dimension Dq of the anisotropic diffusion DLA is also discussed and an expression of the generalized dimension Dq is obtained using the modified wedge model.

Starting from the extensional discrete model SSH Hamiltonian containing an external Coulomb potential arising from interchain charged solitons and the counterions, the intrachain electron-electron interaction, the energy spectra and electron states of soliton lattice have been studied in trans-polyacetylene. The results show that: two bound states have been found at the bottom of valence band and several other states at the top of conduction band. With the increasing of the dopant concentration, the localization of bound states are weakened and the discrete soliton energy levels in the forbidden band move into the soliton band. When the dopant concentration is up to 16.67%，all the discrete electron states of soliton lattice disappear and become extended ones. It is found that the forbidden band width increases and the gap (between the top of the soliton band and the bottom of conduction band) namows with the doping level increasing. Furthermore, the gap (from the bottom of the soliton band to the top of valence band) has a maximum at the critical doping level. Finally, the effect of e-e interaction on the energy spectra of soliton lattice is discussed.

The ferromagnetic state in quasi-one-dimensional organic ferromagnet poly-SIPO has been studied. We consider the electron hoping, electron-electron correlation and Pierls instability in one-dimensional system. And self-consistent calculations are performed to investigate the structure of energy band and the distribution of spin density. The effects of the above aspects on the ferromagnetic state are studied. The results show that the ground state is a stable ferromagnetic state in this system.

利用稳态量子ｒｅｐｌｉｃａ对称自旋玻璃理论，研究了具有Ｄｚｙａｌｏｓｈｉｎｓｋｉｉ－Ｍｏｒｉｙａ（缩写为ＤＭ）各向异性相互作用的Ｓｈｅｒｒｉｎｇｔｏｎ－Ｋｉｒｋｐａｔｒｉｃｋ自旋玻璃在外场中的热力学性质。数值计算了不同外场和各向异性作用的自旋为１／２和１的熵、比热、局域磁化率和相应的序参数随温度的变化。发现局域磁化率与热场动力学的结果相符合。特别地，本文的比热－温度曲线能满意地解释Ｂｒｏｄａｌｅ等实验观察到的不同磁场下的交叉特征。

The static Mahan-H?nsch quantum transport equation in applied magnetic fields is extended to spin glass systems through introducing physical self-energies of elastic and inelastic scattering. In the quasi-elastic scattering limit, the Hall conductivity for spin glass model with the s-d exchange interaction between electrons and localized moments is evaluated by using this equation. The relation between resistivity and the Edwards-Anderson (EA) spin glass parameter and local susceptibility is obtained. Finally, thermoelectric power of spin glass::s and some interesting characteristic temperatures are discussed.

We have studied electronic bound states and the localized modes around the soliton after turning on the next-neighbor hopping interaction, based on SSH model. The results show that (1) the electronhole symmetry of the energy band structure implied by SSH model is broken ; (2) the number and location of the bound states trapped by the soliton have changed; (3) a new localized mode have been found; (4)the frequencies of modes have shifted and their localization are strengthened.

The dynamic theory for disordered superconductivity is suggested based on the fracton-electron interaction. It has been demonstrated that electrons in disordered superconductors can feel an attractive interaction by exchange of virtual fractons. A normal state is unstable with respect to such an interaction, and a superconducting state is formed through the association of electrons in pairs with opposite wave vectors and spins. The critical temperature for percolation superconducting model can be derived from this theory.

On the basis of the diagnostics about the axial distribution of plasma electron temperature and electron density in an axial flow RF PCVD reactor by using electrical probe, a model for two-dimension fluid kinetics concerned with major PCVD parameters is proposed. A kinetic analysis about how deposition profiles are influenced by major PCVD parameters is presented by means of the analysis of plasma parameters. The model has been applied to study the deposition process of SnO2 films obtained from a gases mixture of SnCl4 and O2. The theoretical calculation are in good agreement with the experiments of deposition.

In this paper, we use the renormalisation group approach and Monte-Carlo simulation to treat the problem of percolation on a two-dimensional square lattice with next-nearest-neighbour interactions. The critical probability pc and the critical exponents α,β,γ and so forth are obtained. It is shown that the two-dimensional percolation problem with next-nearest-neighbour interactions belongs to different universality class from that only with nearest-neighbour interactions.

A formula of the Josephson current in the presence of microwave and static magnetic field, taking finite wave-number effect into account, is derived. Finite wavenumber effect on ac Josephson current is discussed according to this formula. It can be used to explain such anomalous phenomena as missing of some rf-induced steps in the I-V curve, asymmetry of the I-V curves.

The authors propose a new method, the alternating translational-dilation method (ATDM), and use it in combination with the Monte Carlo technique to calculate the critical percolation probability for Sierpinski gaskets (SG). They obtain numerical evidence of the critical percolation probability Pc=1 for site problems on SG and an approximate relation Pc=1-1/N in two-dimensions, where N is the number of stages of SG.

The critical behaviour of fully directed Levy flight on a square lattice is studied using the Monte Carlo method. The obtained critical exponents nu , nu /sub /// and nu perpendicular to are independent of the parameter u. This seems to be interesting compared with the Levy flight previously discussed by Halley and Nakanishi (1985), for which nu depends on u in addition to d. It also indicates that the introduction of the direction plays a dominant role in directed Levy flight just as in directed SAW, with nu , nu /sub /// and nu perpendicular to independent of d.