International Journal of Modern Physics C

The population growth in big urban centers generates the necessity for tall buildings. This phenomenon happens also in tourist regions where it is necessary to host many people. However, locations with high buildings interfere with the flow of the wind and can affect the comfort and safety of pedestrians at street level. Tall buildings barrier reduces the natural ventilation in regions far from the beach. This work presents the results concerning the effects created by tall buildings on Mucuripe beach, Fortaleza, Brazil. We performed numerical simulations to verify the wind interference with buildings in an area of $1.6\times 10^5$m², using the OpenFOAM toolbox, to solve the Reynolds Averaged Navier–Stokes (RANS) equations with the $k$–$ϵ$ turbulence model. The results showed how the obstacles alter the airflow. From them, one can identify the regions with reduced safety and pedestrian comfort, and also the weak wind zone created by the downstream of the constructions for the different wind directions that are locally observed.

The asymmetric simple exclusion process (ASEP) is a paradigmatic model for nonequilibrium systems and has been used in many applications. Airplane boarding provides another interesting example where this framework can be applied. We propose a simple model for boarding process, in which a particle moves along a one-dimensional aisle after being injected, and finally is removed at a reserved site. Different from the typical ASEP model, particles are removed in a disorderly or a parallel way. Detailed calculations and discussions of some related characteristics, such as mean boarding time and parallelism indicator, are provided based on Monte-Carlo simulations. Results show that three phases exist in the boarding process: free-flow, jamming and maximum current. Transitions between these phases are governed by the difference between the injection and removal rate. Further analysis shows how the scaling behavior depends on the system size and the boarding conditions. Those results emphasize the importance of utilizing the whole length of the aisle to reduce the boarding time when designing an efficient boarding strategy.

In this work, we study a simple model of social contagion that aims to represent the dynamics of social influences among politicians in an artificial corrupt parliament. We consider an agent-based model with three distinct types of artificial individuals (deputies), namely honest deputies, corrupt deputies and inflexible corrupt deputies. These last agents are committed to corruption, and they never change their state. The other two classes of agents are susceptible deputies, that can change state due to social pressure of other agents. We analyze the dynamic and stationary properties of the model as functions of the frozen density of inflexible corrupt individuals and two other parameters related to the strength of the social influences. We show that the honest individuals can disappear in the steady state, and such disappearance is related to an active-absorbing nonequilibrium phase transition that appears to be in the directed percolation universality class. We also determine the conditions leading to the survival of honesty in the long-time evolution of the system, and the regions of parameters for which the honest deputies can be the either the majority or the minority in the artificial parliament.

Considering congestion effects in realistic network environments, we give a new method to adjust dynamically adjust the weight of the congested edge. We calculate the load on an edge based on the revised betweenness method and propose a novel model with three states of edges to investigate the dynamics of cascading failures in the ring network, the BA scale-free network, and the real traffic networks in London. By two robust metrics, we surprisingly observe the abnormal dynamics of cascading propagation, especially compared with that in the unadjustable weight, the curves of cascading dynamics in the adjustable weight are more irregular, which means that enhancing the capacity of each edge is not always better to avoid the cascading propagation. In addition, our simulation results show that the dynamical change of the edge’s weight makes the heterogeneous BA networks more vulnerable.

Equivalence between algebraic equations of motion may be detected by using a $p$-adic method, methods using factorization and linear algebra, or by systematic computer search of suitable Tschirnhausen transformations. Here, we show standard polynomial interpolation to be a competitive alternative method for detecting orbital equivalences and field isomorphisms. Efficient algorithms for ascertaining equivalences are relevant for significantly minimizing computer searches in theoretical and practical applications.

This three-dimensional (3D) numerical work based on the volume control method quantifies the convective heat transfer occurring in a hemispherical cavity filled with a ZnO–H₂O nanofluid saturated porous medium. Its main objective is to improve the cooling of an electronic component contained in this enclosure. The volume fraction of the considered monophasic nanofluid varies between 0% (pure water) and 10%, while the cupola is maintained isothermal at cold temperature. During operation, the active device generates a heat flux leading to high Rayleigh number reaching $7.29\times 10^{10}$ and may be inclined with respect to the horizontal plane at an angle ranging from 0${}^{\circ }$ to 180${}^{\circ }$ (horizontal position with cupola facing upwards and downwards, respectively) by steps of 15${}^{\circ }$. The natural convective heat transfer represented by the average Nusselt number has been quantified for many configurations obtained by combining the tilt angle, the Rayleigh number, the nanofluid volume fraction and the ratio between the thermal conductivity of the porous medium’s solid matrix and that of the base fluid. This ratio has a significant influence on the free convective heat transfer and ranges from 0 (without porous media) to 70 in this work. The influence of the four physical parameters is analyzed and commented. An empirical correlation between the Nusselt number and these parameters is proposed, allowing determination of the average natural convective heat transfer occurring in the hemispherical cavity.

Properties of one-dimensional discrete-time quantum walks (DTQWs) are sensitive to the presence of inhomogeneities in the substrate, which can be generated by defining position-dependent coin operators. Deterministic aperiodic sequences of two or more symbols provide ideal environments where these properties can be explored in a controlled way. Based on an exhaustive numerical study, this work discusses a two-coin model resulting from the construction rules that lead to the usual fractal Cantor set. Although the fraction of the less frequent coin $\to 0$ as the size of the chain is increased, it leaves peculiar properties in the walker dynamics. They are characterized by the wave function, from which results for the probability distribution and its variance, as well as the entanglement entropy, were obtained. A number of results for different choices of the two coins are presented. The entanglement entropy has shown to be very sensitive to uncovering subtle quantum effects present in the model.

We present a statistical characterization of the morphological features emerging from the complex processes governing the growth of the road network, particularly in a mostly self-organized urban setting. Apart from the usual fractal analysis, the roads are quantified by their lengths and straightnesses, while the segmented blocks are characterized by their areas, perimeters and circularities. When applied to the Metro Manila conurbation, one of the megacities in Asia with the fastest growing populations, we observe dense space-filling and nontrivial statistical distributions of roads and blocks that can be attributed to the geographical constraints of the metropolis. The emergence of the scale-free regimes is explained using a simple rule-based model patterned after the assumed dynamical interplay between the local and global factors involved in individual street formation. By viewing road network growth from a quantitative complex systems perspective, we can gain insights into the underlying rules operating at the local scales that give rise to the global spatial patterns.

Bose–Einstein condensates of repulsive Bose atoms in a one-dimensional harmonic trap are investigated within the framework of a mean field theory. We solve the one-dimensional nonlinear Gross–Pitaevskii (GP) equation that describes atomic Bose–Einstein condensates. As a result, we acquire a family of exact breather solutions of the GP equation. We numerically calculate the number density $n(z,t,N)$ of atoms that is associated with these solutions. The first discovery of the calculation is that at the instant of the saddle point, the density profile exhibits a sharp peak with extremely narrow width. The second discovery of the calculation is that in the center of the trap ($z=0$ m), the number density is a U-shaped function of the time $t$. The third discovery of the calculation is that the surface plot of the density $n(z,t)$ likes a saddle surface. The fourth discovery of the calculation is that as the number $N$ of atoms increases, the Bose–Einstein condensate in a one-dimensional harmonic trap becomes stabler and stabler.

It is essential to model the crowd movement considering complex building structures coupling different psychological perceptions. To model the interaction between individual perception and surroundings, a perception floor field cellular automata (PFFCA) is proposed in this paper. Here, the forerunners imitation behavior is introduced into the traditional FFCA to explore the influence of motion similarity (MS) perception of dual-exit bottleneck on passing efficiency. It is found that the MS perception works effectively when pedestrians move toward dual exits. The simulation shows that the entry restriction (i.e. partition fence) shortens the average passing time by forming a “transition area”. The phase transitions of specific outflow and crowd density under different fence lengths are investigated, to examine the effectiveness of partition fences in facilitating the usage efficiency of varying exits. The simulation is in accordance with a recent observation. These conclusions are summarized by a comprehensive assessment, which is applicable for practical improvement of dual-exit bottleneck.

Many practical systems, such as heart and neural systems, are described by excitable media or networks. Various oscillations of coupled excitable units are typical system states, determining some important functions in realistic processes. Excitable units do not oscillate individually, while oscillations of coupled excitable cells can appear after the self-organizations of collective motions via mutual interactions. Therefore, different mechanisms underlying oscillations turn to be very crucial issues under investigation. So far, all mechanisms of the oscillations of excitable networks rely, with no exception, on the existence of the oscillation sources formed by successive excited units on loops. Here, we explore a novel oscillation mechanism in diffusively coupled excitable networks where loop existence is no longer required, and oscillations can be sustained due to the excitation propagations between two hubs linked by a chain of low-degree nodes. Some necessary conditions for the sustained oscillations on hub size, chain length and coupling strength are analyzed in detail. And the possible application and significance of the explored mechanism for realistic oscillations of practical excitable networks are briefly discussed.

Tritium adsorption in the irradiation defects of the Li₂ZrO₃ is a fundamental problem to understand the tritium behavior during the release process. A comprehensive computational study of tritium/helium adsorption in the lithium vacancy of bulk Li₂ZrO₃ is presented by the density functional theory calculations. The most stable tritium adsorption position has been found and it is determined by the neighboring lithium–oxygen interactions. The results reveal that the intrinsic defect is the lithium vacancy with one electron and it transforms to be the neutral state after a tritium atom is adsorbed. Moreover, helium is adsorbed almost in the center of lithium vacancy without bonding with surrounding oxygen atoms, which could diffuse easily in the bulk Li₂ZrO₃. Therefore, we predict that the intrinsic Li vacancy tends to adsorb a positive ion T${}^{+}$ other than a neutral T atom. Our results provide theoretical support to understand the T behavior in the Li₂ZrO₃ crystal.

The well-known Green’s function method has been recently generalized to nonlinear second-order differential equations. In this paper, we study possibilities of exact Green’s function solutions of nonlinear differential equations of higher order. We show that, if the nonlinear term satisfies a generalized homogeneity property, then the nonlinear Green’s function can be represented in terms of the homogeneous solution. Specific examples and a numerical analysis support the advantage of the method. We show how, for the Bousinesq and Kortweg–de Vries equations, we are forced to introduce higher order Green’s functions to obtain the solution to the inhomogeneous equation. The method proves to work also in this case supporting our generalization that yields a closed form solution to a large class of nonlinear differential equations, providing also a formula easily amenable to numerical evaluation.

In this work, we consider bounded one-dimensional systems consisting of particles with relativistic potentials and nonlocal interactions. The systems are initially at rest and at equilibrium, and are perturbed sinusoidally at one end. Meanwhile, we consider an absorbing boundary at the other end. A Hamiltonian computational method is employed in this work to simulate the dynamics of the continuous-time system. We show here that the driving boundary propagates energy into the system in the form of nonlinear modes. For each driving frequency at the forbidden band-gap, this process occurs at a critical amplitude: the supratransmission threshold. We find that supratransmission occurs for all frequencies in the forbidden band-gap independently of whether nearest-neighbor or global interactions are considered. Several qualitative conclusions are obtained in this work based on our computational results.