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Urea transporters are a family of membrane proteins that transport urea molecules across cell membranes and play important roles in a variety of physiological processes. Although the crystal structure of bacterial urea channel dvUT has been solved, there lacks an understanding of the dynamics of urea transport in dvUT. In this study, by using molecular dynamics simulations, Monte Carlo methods, and the adaptive biasing force approach, we built the equilibrium structure of dvUT, calculated the variation in the free energy of urea, determined the urea-binding sites of dvUT, gained insight into the microscopic process of urea transport, and studied the water permeability in dvUT including the analysis of a water chain in the pore. The strategy used in this work can be applied to studying transport behaviors of other membrane proteins.

Urea transporters (UTs) are transmembrane proteins that transport urea molecules across cell membranes and play a crucial role in urea excretion and water balance. Modeling the functional characteristics of UTs helps us understand how their structures accomplish the functions at the atomic level, and facilitates future therapeutic design targeting the UTs. This study was based on the crystal structure of Desulfovibrio vulgaris urea transporter (dvUT). To model the binding behavior of urea molecules in dvUT, we constructed a cooperative binding model. To model the substitution of urea by the urea analogue N,N'-dimethylurea (DMU) in dvUT, we calculated the occupation probability of DMU along the urea pore and the ratio of the occupation probabilities of DMU at the external (Sext) and internal (Sint) binding sites, and we established the mutual substitution rule for binding and substitution of urea and DMU. Based on these calculations and modelings, together with the use of the Monte Carlo (MC) method, we further modeled the urea flux in dvUT, equilibrium urea binding to dvUT, and the substitution of urea by DMU in the dvUT. Our modeling results are in good agreement with the existing experimental functional data. Furthermore, the modelings have discovered the microscopic process and mechanisms of those functional characteristics. The methods and the results would help our future understanding of the underlying mechanisms of the diseases associated with impaired UT functions and rational drug design for the treatment of these diseases.

Airport networks are a kind of complex systems that display significant fluctuations. To describe this kind of phenomena a dynamical fluctuation model is proposed. In this model the fluctuations in growth rates of weight are exponential. There are two adjustable parameters: the exponent β and the creation probability P d of a new node. β characterizes the tendency to retain an “optimal” allocation of weights (size of components) for a given kind of networks. P d reflects the interactive effect between the weight fluctuation and variation of nodes and links (topological structure) for each real network. For airport networks the exponent β is 0.4 and the creation probability P d is equal to 0.018 (China), 0.025 (US), 0.03 (Brazil) and 0.04 (Europe). This model quantitatively describes and reproduces these real airport networks.

SnO2 nanotube arrays have been synthesized by means of a simple and low-cost method. The ZnO nanorod arrays prepared by aqueous chemical growth method were used as templates. By liquid phase deposition, SnO2 nanotubes were obtained with proper deposition time. Scanning electron microscopy, transmission electron microscopy and X-ray diffraction were used to characterize the morphologies and structures of the products, and the formation mechanism was discussed according to the experimental results.

We successfully fabricated a novel highly regular ZnO hierarchical nanostructure with six rows of single crystal ZnO nanowire (NW) arrays in double 3-fold-symmetry, using a two-stage synthesis scheme without any catalyst and chemical reagent. Our synthesis employs a simple thermal evaporation of Zn powder and chemical vapor deposition (CVD) followed by post-annealing. In the first stage, Zn-rich ZnO nanotubes are formed; then in the annealing stage, the resulting Zn-rich ZnO nanotubes provide the backbones and the supply of Zn to grow ZnO NWs. A growth model for ZnO hierarchical nanostructure based on dense arrangement principle is proposed. This novel nanostructure has strong violet emission, high surface area and specific geometric structures. These make it suitable for application on chemical sensors, battery electrodes, solar cells and optoelectronic devices.

The highly crystalline core–shell ZnO/MgO nanowires (NWs) were achieved by using a two-step CVD method. The related crystal growth model is proposed. The epitaxial growth of cubic MgO shells on the surfaces of hexagonal ZnO NWs benefits from the close interplanar distances of MgO (111) and ZnO (0002) planes. Comparing with bare ZnO NWs, more than 10 times enhancement of ultraviolet (UV) emission intensity is obtained from ZnO/MgO NWs with a shell thickness of 25 nm, owing to the improvement of crystal quality of ZnO NWs surface layers and the passivation of remained surface defects after forming high crystallization MgO shells.

TiO2 nanotube arrays were prepared using template-based liquid phase deposition method. Their morphologies and structures were investigated by scanning electron micro¬scopy, transmission electron microscopy and X-ray diffraction. The photocatalytic properties of the samples were evaluated with the degradation of methylene blue under UV irradiation. It was found that the TiO2 nanotube arrays annealed at 900 °C showed the highest photocatalytic activity.

A three-state, multiion kinetic model was proposed to enable the conduction properties of the mammalian channel ClC-0 to be well characterized. Using this rate-theory based model, the current-voltage and conductance-concentration relations were obtained. The five parameters needed were determined by fitting the data of conduction experiments of the wild-type ClC-0 and its K519C mutant. The model was then tested against available calculation and simulation data, and the energy differences between distinct chloride-occupancy states computed agreed with an independent calculation on the binding free energies solved by using the Poisson-Boltzmann equation. The average ion number of conduction and the ion passing duration calculated closely resembled the values obtained from Brownian dynamics simulations. According to the model, the decrease of conductance caused by mutating residue K519 to C519 can be attributed to the effect of K519C mutation on translocation rate constants. Our study sets up a theoretical model for ion permeation and conductance in ClC-0. It provides a starting point for experimentalists to test the three-state model, and would help in understanding the conduction mechanism of ClC-0.

Using electrochemical deposition, Ni–P nanorod arrays with a series of aspect ratios have been successfully fabricated in the pores of anodic aluminum oxide (AAO) membranes. The aspect ratio of Ni–P nanorods was controlled by the deposition time. The morphologies were analyzed by scanning electron microscopy and transmission electron microscopy. The dependence of the optical absorbance upon the aspect ratio was studied by UV–vis spectra. The results show that the absorbance increases in visible region and decreases rapidly in ultraviolet region as the aspect ratio of nanorods increases, which qualitatively agree with the prediction of Maxwell–Garnett (MG) theory and the simulation based on the Mie scattering theory, respectively. The dependence of photoluminescence emission (PL) spectra upon the aspect ratio is also obtained. These investigations show that the optical properties of nano-array composite structure can be modified by changing the aspect ratio of nanorods.

TiO 2 nanotube arrays doped by Sn up to 12 at% have been prepared using template-based liquid phase deposition method. Their morphologies, structures and optical properties have been investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, UV–vis absorption spectroscopy and photoluminescence spectroscopy. The photocatalytic properties of the samples were evaluated with the degradation of methylene blue under UV irradiation. The result shows that doping an appropriate amount of Sn can effectively improve the photocatalytic activity of TiO 2 nanotube arrays, and the optimum dopant amount is found to be 5.6 at% in our experiments.

Porous anodic alumina membranes (AAMs) were prepared in oxalic acid and then carried on an etch-treatment in phosphoric acid. Using the etch-treatment the photoluminescence (PL) intensity of AAMs increases by a factor of 1/3. The effect of etch-treatment upon the intensity and peak position of photoluminescence (PL) spectra was investigated. It was found that the intensity of the photoluminescence (PL) spectra increased with the etching time increasing. A PL spectrum can be divided into two subbands with the peak at 434 and 460 nm, respectively. As the etching time prolongs, the intensity of the peak of 434 nm subband increases and that of the 460 nm subband rises firstly and then decreases. It can be explained by that two luminescence centers (F and F+ centers) coexist in AAMs. F centers are concentrated in the surface layer and F+ centers are enriched in the depth of pore wall. The increment of the PL intensity comes from the contribution of F+ photoluminescence centers concentrated in the depth of pore wall in AAMs. This work will be beneficial to improving the photoluminescence intensity and understanding the light-emitting mechanisms for related materials.

Ni–P/AAO nano-array composite structure assemblies with Ni and P grown in the pores of anodic aluminum oxide (AAO) membranes were prepared by electroless deposition. The results of SEM, TEM and SAED show that as-deposited Ni–P nanowires have an amorphous structure and a few nanocrystallites form after annealing. The optical absorption spectra reveal that, as the annealing temperature increases, the absorption band edge of the Ni–P/AAO composite structure is obviously blue shifted, which is attributed to a decrease of the internal pressure after heat treatment. Meanwhile, the annealed Ni–P/AAO nano-array composite structure exhibits the absorption behavior of a direct band gap semiconductor. Details of this behavior are discussed together with the implications for potential device applications.

An increasing attention has been dedicated to the characterization of complex networks within the protein world. Before now most investigations about protein structures were only considered where the interactive cutoff distance R c =5 or 7 A. It is noteworthy that the length of peptide bond is about 1.5 A, the length of hydrogen bond is about 3 A, the range of London-van der Waals force is about 5 A and the range of hydrophobic effect can reach to 12 A in protein molecule. Present work reports a study on the topological properties of the amino acid network constructed by different interactions above. The results indicate that the small-world property of amino acid network constructed by the peptide and hydrogen bond, London-van der Waals force and the hydrophobic effect is strong, very strong and relatively weak, respectively. Besides, there exists a precise exponential relation C ∝ k −0.5 at R c =12 A. It means that the amino acid network constructed by the hydrophobic effect tend to be hierarchical. Functional modules could be the cause for hierarchical modularity architecture in protein structures. This study on amino acid interactive network for different interactions facilitates the identification of binding sites which is strongly linked with protein function, and furthermore provides reasonable understanding of the underlying laws of evolution in genomics and proteomics.

The tubular tetrapod MgO has been successfully synthesized by simple thermal evaporation of Mg metal power with the pre-growing tetrapod ZnO template. The phase transformation, morphologies, and photoluminescence evolution of the MgO products were carefully investigated with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectra. These studies indicated that the tetrapod ZnO played a template role in formation of the tubular MgO and determined the dimension and morphology of the final product. Our approach present here is simple and may open a new route to synthesis of other tubular oxides.

The cobweb-like network was constructed, and its structure properties and synchronizability were studied by numerical simulation and probability theory. For cobweb-like networks, the behaviors of structure properties with the adding probability are similar to those for the small-world network. However, the properties of cobweb-like networks also distinctly depend on the spoke–ring ratio r . With increasing r , the average path length decreases, and the average clustering coefficient increases. Simultaneously, the connectivity distribution becomes heterogeneous. Moreover, in the case of bounded synchronized region, the synchronizability shows complicated behaviors with r , and is enhanced favorably at r = 2.28 with homogeneous load distribution. The reason is that homogeneous load distribution has an advantage over the communication between oscillators, which efficiently leads to global synchronization. This work could be useful for design and kinetic property research of cobweb-like networks.

Porous anodic aluminum oxide (AAO) Bragg stacks were fabricated by a modified two-step anodization, and the optical transmittance spectra of AAO Bragg stacks soaking in varied analytes (air, series...

The preparation of Zn deposits has been performed by thin-layer electrodeposition in acidic zinc sulphate solution with and without agar, respectively. The morphological and structural characteristics of the deposits have been investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The study shows that the presence of agar has a significant influence on the morphology of the Zn deposits. Under the chosen conditions and without agar, the deposit shows a dendritic morphology, which is made of orderly arranged grains with a preferred orientation in [0001]. In the presence of agar, the deposit shows a dense branch morphology, which has a randomly oriented grain texture and diminished grain size in comparison with that of the dendritic morphology. This work contributes to understanding the influence of agar gel on the pattern formation in thin-layer electrodeposition.

In this paper we consider the evolutionary minority game with different capacities. With the increase of capacity level ρ 1 , the probability γ n of room1 with n agents changes from one normal distribution to two normal distributions and back to one normal distribution again. When room2 is the basic strategy, the probability of room1 with n agents is a small normal distribution. And when room1 is the basic strategy the probability of room1 with n agents is a large normal distribution. We calculate the integral of the normal distributions and explain the characters in the figures. For instance, the room with more capacity represents the interest of the majority and the room has more probability to win.

Prediction of protein domain structural classes is an important topic in protein science. In this paper, we proposed a new conception: structural class tendency of polypeptides (SCTP), which is based on the fact that a given amino acid fragment tends to be presented in certain type of proteins. The SCTP is obtained from an available training data set PDB40-B. When using the SCTP to predict protein structural classes by Intimate Sorting predictive method, we got the predictive accuracy (jack knife test) with 93.7%, 96.5%, and 78.6% for the testing data set PDB40-j, Chou&Maggiora and CHOU. These results indicate that the SCTP approach is quite encouraging and promising. This new conception provides an effective tool to extract valuable information from protein sequences. (c) 2007 Elsevier B.V. All rights reserved.

Some highly designable protein structures have dented on the surface of their native structures, and are not full compactly folded. According to hydrophobic-polar (HP) model the most designable structures are full compactly folded. To investigate the designability of the dented structures, we introduce the hydrogen bond energy in the secondary structures by using the secondary-structure-favored HP model proposed by Ou-yang etc. The result shows that the average designability increases with the strength of the hydrogen bond. The designabilities of the structures with same dented shape increase exponentially with the number of secondary structure sites. The dented structures can have the highest designabilities for a certain value of hydrogen bond energy density.

An urchin-like ZnO/MgO hierarchical structure was synthesized successfully via one-step thermal evaporation of the mixture of metal Zn and Mg powders under designed conditions. The morphology observations and structure analysis of ZnO/MgO hierarchical structures and the related byproducts revealed that there existed a morphology evolution linkage as MgO spheres—ZnO/MgO hierarchical structures—ZnO flowers. The detailed investigations suggested that the temperature and ZnO x concentration in gas flow played crucial roles in the formation of these structures, especially for the hierarchical structure. The photoluminescence spectra showed a regular change corresponding to the morphology evolution.

Based on the high resolution protein structures taken from the Protein Data Bank, the mean backbone torsion angle of each protein is calculated. Then the statistical characters of the mean backbone torsion angles of proteins are investigated. On φ – ψ plane, the representing points of the proteins, i.e., the mean backbone torsion angles ( φ ¯ , ψ ¯ ) , separate into four clusters according to four main structural classes. Each cluster has a determinate centroid, which associates to the relative content of two types of popular secondary structural elements, α -helices and β -strands. It is also found that α / β structural class exhibits greater concentricity of the partial mean backbone torsion angle relative to other classes. An intuitive explanation is that the α / β structural class has high level of average lengths of both α -helices and β -strands. These results provide a further understanding of protein structures.

Electrodeposition of Pb0.5Sn0.5 alloy is carried out in a quasi-2D electrochemical cell. As the growth proceeds the morphologies of the deposits transit from cake-like to branched and finally to the compact morphology. We show that these morphological transitions arise from the changes in the transport mechanisms of the ions in the electrolyte cell. In addition, it is found that the current density on the growth interface can vary spontaneously due to the irregular shape of the deposit and the generation of hydrogen gas. It causes the formation of the complex microstructure with non-uniform composition. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We study the dynamical behavior of the epidemiological model with pathogen mutation on small-world networks, and discuss the influence of the immunity duration τ R , the cross-immunity threshold h thr , and system size N on epidemic dynamics. A decaying oscillation occurs because of the interplay between the immune response and the pathogen mutation. These results have implications for the interpretation of longitudinal epidemiological data on strain abundance, and they will be helpful to assess the threat of highly pathogenic and mutative viruses, such as avian influenza.

Networks grow and evolve when new nodes and links are added in. There are two methods to add the links: uniform attachment and preferential attachment. We take account of the addition of links with mixed attachment between uniform attachment and preferential attachment in proportion. By using numerical simulations and analysis based on a continuum theory, we obtain that the degree distribution P(k) has an extended power-law form P(k) ~ (k + k0)−γ. When the number of edges k of a node is much larger than a certain value k0, the degree distribution reduces to the power-law form P(k) ~ k−γ; and when k is much smaller than k0, the degree distribution degenerates into the exponential form . It has been found that degree distribution possesses this extended power-law form for many real networks, such as the movie actor network, the citation network of scientific papers and diverse protein interaction networks.

The motion of carriers in an external field is modelled by Monte Carlo simulation in two-dimensional continuous space. The mean square displacement 〈 R 2 〉 of carriers as functions of the relative field strength λ and time t is carried out by theoretical calculation and numerical simulation. It is shown that the motion of carriers is a combination of diffusion and drift in a determinate proportion. As time t increases, there exists a crossover from dominant diffusion to dominant drift. The crossover time t c , diffusion coefficient D and drift velocity v as a function of the relative field strength λ are obtained by analysis and simulation. The drift velocity can be quantitatively compared with experimental data. The motion of electrons in semiconductors and magnetron sputter ion deposition plasma provides perfect experimental support to this model.

The two-dimensional growing self-avoiding walk on percolation was investigated by statistical analysis and Monte Carlo simulation. We obtained the expression of the mean square displacement and effective exponent as functions of time and percolation probability by statistical analysis and made a comparison with simulations. We got a reduced time to scale the motion of walkers in growing self-avoiding walks on regular and percolation lattices.

The dynamics of the blackmail propagation model based on small-world networks is investigated. It is found that for a given transmitting probability λ the dynamical behavior of blackmail propagation transits from linear growth type to logistical growth one with the network randomness p increases. The transition takes place at the critical network randomness p c = 1 / N , where N is the total number of nodes in the network. For a given network randomness p the dynamical behavior of blackmail propagation transits from exponential decrease type to logistical growth one with the transmitting probability λ increases. The transition occurs at the critical transmitting probability λ c = 1 / 〈 k 〉 , where 〈 k 〉 is the average number of the nearest neighbors. The present work will be useful for understanding computer virus epidemics and other spreading phenomena on communication and social networks.

Random walk on percolation under an external field has been investigated by using statistical analysis and Monte Carlo simulation. The mean square displacement 〈R2〉 as a function of time t was obtained. There exist some steps in the log〈R2〉–logt plot. The defect in the percolation plays the part of the trap for the walker. Each step corresponds to a type of trap. The height of the steps indicates the mean square displacement before the walker enters the trap and the width of the step expresses the trapping time spent in the trap. The calculated height and width by the probability theory are in agreement with simulation results quite well.

Electrodeposition is an efficient technique for producing new material with specific chemical and physical properties. These properties stem from the novel morphology and microstructure of deposits. In this paper, we study the morphology and microstructure of the Pb–Sn codeposit by quasi-two-dimensional electrodeposition. A codeposition mechanism is suggested from the analysis by the electrochemical reaction dynamics. Based on this mechanism, the proposal for the microstructure-controlled electrodeposition is offered and an artificial multilayered microstructure is prepared in Pb–Sn alloy system.

In this paper we report a novel phenomenon taking place in the thin layer electrodeposition of Pb. A segment of dendrite deposit, which was segregated from the cathode, moved and shortened spontaneously in the electrochemical cell. We find that this behavior arises from the concurrent electrodissolution and electrodeposition reactions taking place at two ends of the isolated segment of the deposits. A mechanism inducing this phenomenon is suggested.

Deposition, diffusion, and aggregation (DDA) on a two-dimensional small-world network have been investigated by computer simulations. This model is characterized by two parameters: the clustering exponent α and long-range connection rate ϕ . The results show that as α and ϕ vary there exists a continuous crossover in the fractal dimension D f from 1.65 to 2, which corresponds to the crossover from the DDA pattern to dense one. The change of the aggregation pattern results from the long-range connection in the network, which reduces the effect of screening during the aggregation. With primitive analysis, we obtain the expressions of the fractal dimension D f and the crossover point α c . These results may be useful to describe the vapor deposition, molecular-beam epitaxy, and similar experiments on defective substrates.

The Pb–Sn codeposits were prepared by electrochemical deposition. SEM, XRD, and EPMA were applied to study morphologies and microstructure of the deposits. With the proportion of two kinds of cations in electrolyte solution varies, the deposits exhibit abundant morphologies and abnormal nonequilibrium microstructure. The Pb0.9Sn0.1 dendritic deposit consists of the center part with Pb-based solid solution and outer part with pseudo-eutectic, whereas the tip of the side-branch is covered with Pb-based solid solution. The Pb–Sn deposit with rich Sn consists of branches, subbranches, and globules forming on the tip of each subbranch. The texture of the globule transits from pseudo-eutectic to Pb-based solid solution with the growth of the globule. The formation mechanisms are discussed based on the electrochemical reaction dynamics.

The effects of interaction strength and range on the wetting behavior in two-dimensional binary fluid (which is composed of water-like and water–oil particles) confined between two parallel plane walls have been investigated by using the free energy analysis and discontinuous molecular dynamic simulations. Some rules are found. When the concentration of water-like particles c w is comparable to that of oil-like particles c o , the concave-water-lens may exist. As the strength or range of the preferential attraction between the walls and water-like particles increase, the system undergoes the transition from the partial wetting to complete wetting, and the occupied rate of water-like particles on the wall η varies gradually from a low fractional value to unity. When c w is very smaller or larger than c o , the concave-water-lens exist no long, and η increases abruptly from a low fractional value to unity.

xProtein folding in a two-dimensional lattice with an unrestricted boundary is simulated by means of the simplified HP model. The proteins are regarded as peptide chains and fold into compact structures. These structures are classified by the number of core sites. It is found that the number of structures with the given designability and given number of core sites versus designability appears as the normal distribution. The simulation shows that the structures with a large number of core sites have a high designability.

Pattern of diffusion-limited aggregation (DLA) on nonuniform substrate was investigated by computer simulations. The nonuniform substrates are represented by Leath percolations with the probability p. p stands for the degree of nonuniformity and takes values in the range pc⩽p⩽1, where pc is the threshold of percolation. The DLA cluster grows up on the Leath percolation substrate. The patterns of the DLA clusters appear asymmetrical and nonuniform, and the branches are relative few for the case p is close to pc. In addition, the pattern depends on the shape of substrate. As p increases from pc to 1, cluster changes to pure DLA gradually. Correspondingly, the fractal dimension increases from 1.46 to 1.68. Also, the random walks on Leath percolations through the range pc⩽p⩽1 were examined. Our simulations show the Honda–Toyoki–Matsushita relation is still reasonable for fractional dimensional systems.

The effect of temperature on the emulsification has been investigated by discontinuous molecular dynamic simulation. When a large oil drop is put in water, on one hand the mixing entropy makes it divide into small oil drops; on the other hand the interactions among particles drives the small oil drops fowards aggregation. The evolution of the mean size of oil drops obeys the exponential delay law. There exist an active temperature, at which, the addition of surfactants has obvious effect on the emulsification. The surfactants with low HLB value (e.g. H 1 T 3) make the dispersity of emulsion decrease, and the surfactants with high HLB value (e.g. H 2 T 2 and H 3 T 1) make a contribution to increase the dispersity of emulsion.

The glass transition for the soft sphere system with Morse potential was investigated based on molecular dynamics simulation and partition function analysis. The dependence of the glass transition temperature on the density and the softness of the potential was obtained.

Epidemic spreading in percolation worlds has been investigated by Monte Carlo simulations, based on a correlated percolation model. It is found that the spreading behavior is greatly influenced by the spreading worlds. When the correlation changes from the weak limit to a strong one, the pattern consisting of sick individuals converts from the pattern of site percolation to that of Leath percolation in a percolation world. Correspondingly, the fractal dimension varies from the dimension of the random pattern to that of dense growth morphology. The critical correlation exponent α c = d w , where d w is the fractal dimension of the percolation world. Furthermore, the critical behavior of epidemic spreading is obviously affected by the spreading world also. The threshold of pathogenic ratio s c =1 (for uniform world) and 0.593 (for the critical percolation one), respectively, in the strong correlation limit.

Self-attracting walk (SATW) on non-uniform substrates has been investigated by Monte Carlo simulations. The non-uniform substrates are described by Leath percolation clusters with occupied probability p. p stands for the degree of non-uniformity, and takes on values in the range pc≲p ≤1 where pc is the threshold of percolation. For the case of strong attractive interaction u, p has little influence on the walk which is dominated by attractive interactions. Furthermore, in the case of small scales, the exponent ν of the mean end-to-end distance 2(t)> versus time t is given by ν≃1/(ds+1), while the exponent k of visited sites versus t is given by k≃ds/(ds+1), where ds are the fractal dimensions of the substrates. For u ≃ 0, the walk reduces to the random walk on percolations with p in pc≲p≤1. Also, ν and k decrease sensitively with the reduction of p. It is found, the blocked sites in the substrates (i.e. defects) have much greater influence on the walk driven by thermal flunctuation than that dominated by the attractive interaction.

Using NVT molecular dynamics method, we investigated the critical scaling and universality in the short-time dynamics for the two-dimensional vapor–liquid fluid system by the evolution of the potential energy. Our results for the NVT ensemble confirmed that there exist universal scaling behaviors already in the short-time regime. The critical exponents θ , z and β/ν were determined from the short-time dynamic scaling relations. It showed that the static critical exponent β/ν obtained from the present short-time dynamics is consistent with that of the two-dimensional Ising model.  2002 Elsevier Science B.V. All rights reserved.

Particle–cluster aggregation on nonuniform substrates was investigated by Monte Carlo simulations. The nonuniform substrates are represented by percolations with occupied probability p. Elastic repulsive interactions between particles through the substrates have been involved. It was found, for uniform substrates (p∼1), the aggregates change from diffusion-limited aggregates to thick net-like branched structures with the increase of repulsive interaction. As p decreases, the effect of repulsive interaction on aggregates lessens gradually. When p is close to the critical value pc, the cluster changes very little for variant repulsive interactions.

A particle–cluster aggregation model is presented, in which particle motion is controlled by randomness and directive correlation. The directive correlation means that the walking direction of the particle at next step relates to the moving direction at previous step. The influence of competition between randomness and directive correlation of particle motion on aggregation is investigated by Monte Carlo simulations.

Diffusion-limited aggregation (DLA) on nonuniform substrates was investigated by computer simulations. The nonuniform substrates are represented by Leath percolations with the occupied probability ...