International Journal of Modern Physics C

Mobile ad-hoc networks (MANETs) are random, self-configurable and rapidly-deployable networks. The main goal of developing the MANETs is not only obtaining better service, but also having networks that can serve in situations in which no other means of communications can operate. Examples include networks that are used in battlefields, in search-and-rescue operations, and networks of sensors. We propose a percolation model for studying the properties of the MANETs. The model is based on a random network of sites, distributed in space, which represent the mobile nodes. Two nodes are linked if they are within each other's transmission ranges. A node may be lost or become inactive if, for example, it runs out of energy (provided by its batteries). A link can be lost if, for example, one of its two end nodes moves outside of the other's transmission range. Extensive Monte Carlo simulations are carried out to study the properties of the model. The network's topology is characterized by a critical transmission range, which is the analogue of the percolation threshold. It is shown that not only can the model take into account several important features of the real MANETs and explain them in physical terms, but also leads to the development of efficient protocols for self-configuration, adaptability, and disaster survival, which are of utmost importance to the practical applications.

We investigate imbibition of a wetting liquid in power-law-shaped channels by numerical simulations with a two-phase lattice Boltzmann model. At short times, the dynamics of the imbibition follows diffusive scaling similar to that in uniform capillaries, but at longer times power-law behavior with exponent depending on the channel shape changes is observed. The observed behavior is in exact agreement with a recent theory of Reyssat and co-workers.¹

The nonlinear phenomena of supratransmission and bistability in harmonically forced arrays of anharmonic oscillators are studied in the present article. Employing a finite-difference scheme with multiple properties of consistency, we show that these processes are actually present in such nonlinear systems. We show that, for every frequency in the forbidden band-gap of the medium, there exists a critical forcing amplitude above which the propagation of energy into the system from the boundary is inevitable. We provide diagrams of total energy vs amplitude for several values of the parameters of the model studied in this work, as well as a graph establishing the relationship between the critical amplitude at which supratransmission starts vs frequency. Likewise, we establish the existence of a bistable region, where a conducting and an insulating regimes coexist.

In this paper, based on a weighted projection of the user-object bipartite network, we study the effects of user tastes on the mass-diffusion-based personalized recommendation algorithm, where a user's tastes or interests are defined by the average degree of the objects he has collected. We argue that the initial recommendation power located on the objects should be determined by both of their degree and the user's tastes. By introducing a tunable parameter, the user taste effects on the configuration of initial recommendation power distribution are investigated. The numerical results indicate that the presented algorithm could improve the accuracy, measured by the average ranking score. More importantly, we find that when the data is sparse, the algorithm should give more recommendation power to the objects whose degrees are close to the user's tastes, while when the data becomes dense, it should assign more power on the objects whose degrees are significantly different from user's tastes.

In this work, we establish computationally the existence of the process of nonlinear supratransmission in the simplest generalization of the classical β-Fermi–Pasta–Ulam chain to two-space dimensions, subject to harmonic boundary data in one end of the Dirichlet form. Our simulations employ a finite-difference scheme with multiple properties of consistency in the domains of the solutions, the local energy density and the total energy of the system. Moreover, our results establish the presence of the phenomenon of nonlinear infratransmission or lower-transmission, thus proving the existence of a bistable region where a conducting and an insulating regimes coexist.

Pedestrian behavioral modeling is an important topic to reproduce rich pedestrian dynamics phenomena. In this paper, a modified lattice gas model is proposed to simulate pedestrian counter flow under periodic boundary conditions by considering the variable transition probability, which can quantitatively describe complex human subconscious behaviors and distinguish the individual and common characteristics of pedestrians. Four types of walkers are involved in the model, and their dynamical characteristics are discussed in some complex situations. The simulation results show that the presented model can reproduce some essential features of pedestrian counter flows, such as the lane formation, segregation effect and phase separation. For the mixed pedestrian flows, the comparison between the subconscious behaviors of obeying the traffic rules and those of breaking the traffic rules indicates that the former could effectively reduce the occurrence of jam cluster. In addition, it is found that with increase of the strength of drift D₁, the jam transition threshold decreases. Finally, the simulation results are compared with our previous study (see Ref. 32). It is shown that the mean velocity and the mean flow are always larger at the free moving phase, and the underlying mechanism is discussed in detail.

In this study, we develop a fuzzy back-propagation (BP) neural network controller for active vibration control of a centrifugal pendulum vibration absorber (CPVA). The fuzzy BP neural network controller systems can be viewed as a conventional fuzzy algorithm for coarse tuning. The BP algorithm can also be applied for fine tuning, in this case to regulate the anti-resonance frequency in an active pendulum vibration absorber (APVA), by suppressing vibration of the carrier. The dynamic model of the APVA was developed and simulated using MATLAB. In the simulation results, when the frequency of the disturbance changes, the outputs of the fuzzy BP neural network controller are used to determine an appropriate value for the torque of the active pendulum such that the vibration amplitude of the carrier is minimized. A comparison of the carrier vibration results for the CPVA, the fuzzy algorithm and the fuzzy BP algorithm is performed. The simulation results demonstrate the effectiveness of the proposed fuzzy BP neural network APVA for reducing the carrier vibrations.

The major factor that drives a protein toward collapse and folding is the hydrophobic effect. At the folding process a hydrophobic core is shielded by the solvent-accessible surface area of the protein. We study the behavior of the numbers in 5526 protein structures present in the Brookhaven Protein Data Bank. The first digit of mass, volume, average radius and solvent-accessible surface area are measured independently and we observe that most of these geometric observables obey the Newcomb–Benford law. That is volume, mass and average radius obey the Newcomb–Benford law. Nevertheless, the digits of the solvent-accessible surface area do not agree with the Newcomb–Benford law. The present findings indicate that the hydrophobic effect is responsible for the anomalous first digit behavior of solvent-accessible surface areas.

The effect of the damaged car evacuation on the traffic flow behavior is investigated, in the one-dimensional deterministic Nagel–Schreckenberg model, using parallel dynamics. A realistic model applied to the cars involved in collisions is considered. Indeed, in this model we suppose that the damaged cars must be removed from the ring with a probability P_exit. This investigation enables us to understand how the combination of the two probabilities, namely P_col and P_exit, acts on density and current. It is found that the current and density at the steady state, depend strongly on the initial density of cars in the ring. However, for the intermediate initial density ρ_i, the current J decreases when increasing either P_exit and/or P_col. While, for high initial density, J increases passes through a maximum and decreases for large values of P_exit. Furthermore, the current can decrease or increase with the collision probability depending on the initial density.

We study totally asymmetric simple exclusion process (TASEP) where particles move on a single-chain lattice which diverges into two parallel lattice branches. At the branching point, the particles move to one of the two branches with equal rate r/2. The phase diagram and density profiles are investigated by using mean-field approximation and Monte Carlo simulations. It is found that the phase diagram can be classified into three regions at any value of r. However, a threshold is identified. In cases of r > r_c and r < r_c, the phase diagram exhibits qualitatively different phases. The analytical results are in good agreement with the results of Monte Carlo simulations.

Web encounter facilitate contacts between people from different communities outside space and time. Implicit Community Structure is exhibited because of highly connected links within community and sparse encounters between communities. Considering the imperceptible influence of encounter on opinions, Sznajd updating rules are used to mimic people's behaviors after encountering a stranger in another community. We introduce a model for opinion evolution, in which the interconnectivity between different communities is represented as encounter frequency, and leadership is introduced to control the strength of community's opinion guide. In this scenario, the effects of Implicit Community Structure of contact network on opinion evolution, for asymmetric and random initial distribution but with heterogeneous opinion guide, are investigated respectively. It is shown that large encounter frequency favors consensus of the whole populations and successful opinion spreading, which is qualitatively agree with the results observed in Majority model defined on substrates with predefined community structure.

The assessment of the skin surface is of a great importance in the dermocosmetic field to evaluate the response of individuals to medical or cosmetic treatments. In vivo quantitative measurements of changes in skin topographic structures provide a valuable tool, thanks to noninvasive devices. However, the high cost of the systems commonly employed is limiting, in practice, the widespread use of these devices for a routine-based approach. In this work we resume the research activity carried out to develop a compact low-cost system for skin surface assessment based on capacitive image analysis. The accuracy of the capacitive measurements has been assessed by implementing an image fusion algorithm to enable a comparison between capacitive images and the ones obtained using high-cost profilometry, the most accurate method in the field. In particular, very encouraging results have been achieved in the measurement of the wrinkles' width. On the other hand, experiments show all the native design limitations of the capacitive device, primarily conceived to work with fingerprints, to measure the wrinkles' depth, which point toward a specific re-designing of the capacitive device.