Modeling dynamics of information networks

We propose an information-based model for network dynamics in which imperfect information leads to networks where the different vertices have widely different numbers of edges to other vertices, and where the topology has hierarchical features. The possibility to observe scale-free networks is linked to a minimally connected system where hubs remain dynamic.     

相对论哈密顿-雅可比方程及其应用

利用相对论哈密顿-雅可比方法求出了电子在激光场中的相对论性运动方程的解析解.并且在电子与激光脉冲散射的实验室参照系、电子初始静止参照系、电子平均静止系中,对于给定的任意椭圆偏振的激光场,得到了解析表达式.     

Investigation of the behavior of an Ising metamagnet under the influence of a field using Glauber dynamics

In this study, the kinetics of the Ising metamagnet where the interlayer interactions are ferromagnetic has been investigated under the mean field approximation. In describing the kinetics of the system, Glauber stochastic dynamics in the presence of an external field which performs time-dependent oscillations, has been utilized. Obtained results could be identified by two distinct types: the asymmetric solutions oscillating in the vicinity of finite values where the lattice magnetization has different values and the symmetric solutions being zero where the sublattice magnetizations are equal to each other. On the other hand, it has been observed that in the case where the system's initial state has a homogenous magnetization it exhibits two different periodical behaviors in the course of time.     

Canonical Analysis of Condensation in Factorised Steady States

We study the phenomenon of real space condensation in the steady state of a class of mass transport models where the steady state factorises. The grand canonical ensemble may be used to derive the criterion for the occurrence of a condensation transition but does not shed light on the nature of the condensate. Here, within the canonical ensemble, we analyse the condensation transition and the structure of the condensate, determining the precise shape and the size of the condensate in the condensed phase. We find two distinct condensate regimes: one where the condensate is gaussian distributed and the particle number fluctuations scale normally as L ^1/2 where L is the system size, and a second regime where the particle number fluctuations become anomalously large and the condensate peak is non-gaussian. Our results are asymptotically exact and can also be interpreted within the framework of sums of random variables. We further analyse two additional cases: one where the condensation transition is somewhat different from the usual second order phase transition and one where there is no true condensation transition but instead a pseudocondensate appears at superextensive densities. PACS numbers: 05.40.-a, 02.50.Ey, 64.60.-i.     

Dynamics of majority rule in two-state interacting spin systems

We introduce a two-state opinion dynamics model where agents evolve by majority rule. In each update, a group of agents is specified whose members then all adopt the local majority state. In the mean-field limit, where a group consists of randomly selected agents, consensus is reached in a time that scales ln(N, where N is the number of agents. On finite-dimensional lattices, where a group is a contiguous cluster, the consensus time fluctuates strongly between realizations and grows as a dimension-dependent power of N. The upper critical dimension appears to be larger than 4. The final opinion always equals that of the initial majority except in one dimension.     

On the mean free path for a periodic array of spherical obstacles

We prove theorems pertaining to periodic arrays of spherical, obstacles which show how the macroscopic limit of the mean free path depends on the scaling of the size of the obstacles. We treat separately the cases where the obstacles are totally and partially absorbing, and we also distinguish between two-dimensional arrays, where our results are optimal, and higher dimensional arrays, where they are not. The cubically symmetric arrays to which these results apply do not have finite horizon.     

Glassy synchronization in a population of coupled oscillators

A phase model for a population of oscillators with random excitatory and inhibitory mean-field coupling and subject to external white noise random forces is proposed and studied. In the thermodynamic limit different stable phases for the oscillator population may be found: (i) an incoherent state where all possible values of an oscillator phase are equally probable, (ii) a synchronized state where the population has a nonzero collective phase; (iii) a glassy phase where the global synchronization is zero but the oscillators are in phase with the random disorder; and (iv) a mixed phase where the oscillators are partially synchronized and partially in phase with the disorder. These predictions are based upon bifurcation analysis of the reduced equation valid at the thermodynamic limit and confirmed by Brownian simulation.     

The emergence of background geometry from quantum fluctuations

We show how the quantization of two-dimensional gravity leads to an (Euclidean) quantum space–time where the average geometry is that of constant negative curvature and where the Hartle–Hawking boundary condition arises naturally.     

Tachyon correlation functions in perturbative string theory

This work presents an analytical calculation of tachyon correlation functions in the non-critical string theory where the Liouville fields are important. The calculations are performed at large negative target space dimension D where there exists a perturbative expansion, and in the framework of the full Liouville theory where the curved measure for the Liouville field plays an important role, rather than in the effective theory. The correlation functions are obtained for any genus of the Riemann surface at one-loop order.     

Scientific Review: Interactions of PEO with Monovalent Electrolytes in Solvents of Different Hydrogen Bonding Capacities

Small-Angle Neutron Scattering (SANS) has been used in order to investigate the ion binding capacities of PEO in different solvents. Aprotic (acetonitrile) as well as protic (methanol and water) solvents, have been studied where methanol and water form an average two and four tetrahedrally oriented hydrogen bonds per molecule, respectively [1]. Unusual behavior of PEO has been observed in aprotic solvents and solvents with moderate hydrogen bonding where monovalent ions associate to the polymer backbone leading to a polyelectrolyte-like (where a certain fraction of monomers are charged) behavior. This is in marked contrast to behavior in aqueous solutions where water molecules associate via hydrogen bonding to the polymer and the ions are more preferentially coordinated by the solvent than the polymer.     

影响南丰蜜桔品质的土壤元素ICP-MS/ICP-AES分析

南丰蜜桔是原产于江西南丰的优良品种,但是品质随着种植地区的不同差异较大。文章借助ICP-MS/ICP-AES技术对江西6个不同地区,生产南丰蜜桔品质的土壤中植物的必需元素进行了分析,以期找到影响南丰蜜桔品质的土壤因素。结果显示, 品质较好的3个地区土壤中B, P, K, Mg和Ca含量均高于品质较差地区的含量,特别是B, P和K含量差异显著,而Fe, Mn, Si, Cu和Zn含量则低于品质差的地区。上述结果表明南丰蜜桔的品质主要受B, P, K, Mg和Ca控制,尤其是B, P, K影响较大;而Fe, Mn, Si, Cu和Zn对南丰蜜桔品质影响较小。所以在种植南丰蜜桔时应当适当增加B, P, K, Mg和Ca等肥料的施用量。     

Chameleon fields: awaiting surprises for tests of gravity in space

We present a novel scenario where a scalar field acquires a mass which depends on the local matter density: the field is massive on Earth, where the density is high, but is essentially free in the solar system, where the density is low. All existing tests of gravity are satisfied. We predict that near-future satellite experiments could measure an effective Newton's constant in space different from that on Earth, as well as violations of the equivalence principle stronger than currently allowed by laboratory experiments.     

Limit cycles in a forced Lorenz system

We consider a Lorenz system where the control parameter is sinusoidally modulated. Limit cycles appear where previously there were strange attractors. Perturbation theory is used to estimate the critical amplitude of the modulation for which limit cycles appear.     

Wormholes and the construction of compactified phases

In the context of Classical General Relativity, assuming the positive energy condition, we study the possibility of connecting a region where some dimensions are compact to another region where compactification does not exist. In some simple models, where compactification is achieved through the condensation of gauge fields, we find that the matching of these two regions implies the existence of a wormhole. We also discuss the possibility of spontaneous quantum nucleation of a compactified phase in the midst of an uncompactified space.Awarded an honorable mention by the Gravity Research Foundation, 1991     

Anomalous latent heat in nonequilibrium phase transitions

We study first-order phase transitions in a two-temperature system, where due to the time-scale separation all the basic thermodynamical quantities (free energy, entropy, etc.) are well defined. The sign of the latent heat is found to be counterintuitive: it is positive when going from the phase where the temperatures and the entropy are higher to the one where these quantities are lower. The effect exists only out of equilibrium and requires conflicting interactions. It is displayed on a lattice gas model of ferromagnetically interacting spin-1/2 particles.     

Crackling noise in plasticity

Plastic deformation is a paradigmatic problem of multiscale materials modelling with relevant processes ranging from the atomistic scale up to macroscopic scales where deformation is treated by continuum mechanics. Recent experiments, investigating deformation fluctuations under conditions where plastic deformation was expected to occur in a smooth and stable manner, demonstrate that deformation is spatially heterogeneous and temporally intermittent, not only on atomic scales, where spatial heterogeneity is expected, but also on mesoscopic scales where plastic fluctuations involve collective events of widely different amplitudes. Evidence for crackling noise in plastic deformation comes from acoustic emission measurements and from deformation of micron-scale samples both in crystalline and amorphous materials. Here we provide a detailed account of our current understanding of crackling noise in crystal and amorphous plasticity stemming from experiments, computational models and scaling theories. We focus our attention on the scaling properties of plastic strain bursts and their interpretation in terms of non-equilibrium critical phenomena.     

Kinetic theory for sheared granular flows

Rapid granular flows are far-from-equilibrium-driven dissipative systems where the interaction between the particles dissipates energy, and so a continuous supply of energy is required to agitate the particles and facilitate the rearrangement required for the flow. This is in contrast to flows of molecular fluids, which are usually close to equilibrium, where the molecules are agitated by thermal fluctuations. Sheared granular flows form a class of flows where the energy required for agitating the particles in the flowing state is provided by the mean shear. These flows have been studied using the methods of kinetic theory of gases, where the particles are treated in a manner similar to molecules in a molecular gas, and the interactions between particles are treated as instantaneous energy-dissipating binary collisions. The validity of the assumptions underlying kinetic theory, and their applicability to the idealistic case of dilute sheared granular flows are first discussed. The successes and challenges for applying kinetic theory for realistic dense sheared granular flows are then summarised.     

Partial measurement in the Bohm-Bub hidden-variable theory

The Bohm-Bub hidden-variable theory is able to predict the results of measuring a quantum system only in the special case where the set of commuting observables being measured is complete. To handle the much more common case where the set is incomplete, Tutsch has proposed a generalization of the Bohm-Bub model. Unfortunately, as we show here, Tutsch's original method does not yield the correct quantum mechanical transition probabilities. On the other hand, Belinfante's modification of Tutsch's method does yield the correct probabilities, and it gives a satisfactory hidden-variable theory of partial measurement for the case where one or more commuting variable(s) are measured at a single space-time point. In the case where the variables are measured at different space-time points, the theory is inadequate, due to the fact that it is not relativistically covariant, and does not take relaxation of the hidden variables into account.     

Submonolayer island growth with adatom exchange

Submonolayer epitaxy is studied with two simple theoretical models where adatom exchange with a surface atom yields a stable nucleus for island growth. The results are relevant to systems where surface layer inclusions are formed by alloying and where buried islands are formed in the presence of surfactants. Rate equations and Monte Carlo simulations are used to study the evolution of the island size distributions. The rate equations reproduce all of the qualitative features found in both the simulations and in recent experiments when the coverage-dependent rate of adatom capture by islands is calculated self-consistently.