International Journal of Modern Physics C

The world evolution of the severe acute respiratory syndrome coronavirus 2 (SARS-Cov2 or simply COVID-19) led the World Health Organization to declare it a pandemic. The disease appeared in China in December 2019, and it has spread fast around the world, especially in European countries like Italy and Spain. The first reported case in Brazil was recorded in February 26, and after that the number of cases grew fast. In order to slow down the initial growth of the disease through the country, confirmed positive cases were isolated to not transmit the disease. To better understand the early evolution of COVID-19 in Brazil, we apply a Susceptible–Infectious–Quarantined–Recovered (SIQR) model to the analysis of data from the Brazilian Department of Health, obtained from February 26, 2020 through March 25, 2020. Based on analytical and numerical results, as well on the data, the basic reproduction number is estimated to $R_0=5.25$. In addition, we estimate that the ratio between unidentified infectious individuals and confirmed cases at the beginning of the epidemic is about 10, in agreement with previous studies. We also estimated the epidemic doubling time to be $2.72$ days.

Necklace-ring solitons have gained much attention due to their potential applications in optics and other scientific areas. In this paper, the numerical investigation of the nonlinear Schrödinger equation by using the curvilinear coordinate lattice Boltzmann method is proposed to study necklace-ring solitons. Different from those used in the general curvilinear coordinate lattice Boltzmann models, the lattices used in this work are uniform in two- and three-dimensional space. Furthermore, the model contains spatial evolution rather than time evolution to avoid the complexity of dealing with higher-order time derivative terms as well as to maintain the simplicity of the algorithm. Numerical experiments reproduce the evolution of two- and three-dimensional necklace-ring solitons. The truncation error analysis indicates that our model is equivalent to the Crank–Nicolson difference scheme.

The exponential synchronization and anti-synchronization of nonautonomous chaotic systems with uncertain parameters are studied. The adaptive controller is designed and analytic expression of the controller and the adaptive laws of parameters are given. Based on the Lyapunov stability theory, the exponential stability of the error system is proved. Numerical simulations of two nonautonomous chaotic systems with uncertain parameters are presented to illustrate the ability and effectiveness of the proposed method.

This paper addresses an autonomous facial expression recognition system using the feature selection approach of the Quantum-Inspired Binary Gravitational Search Algorithm (QIBGSA). The detection of facial features completely depends upon the selection of precise features. The concept of QIBGSA is a modified binary version of the gravitational search algorithm by mimicking the properties of quantum mechanics. The QIBGSA approach reduces the computation cost for the initial extracted feature set using the hybrid approach of Local binary patterns with Gabor filter method. The proposed automated system is a sequential system with experimentation on the image-based dataset of Karolinska Directed Emotional Faces (KDEF) containing human faces with seven different emotions and different yaw angles. The experiments are performed to find out the optimal emotions using the feature selection approach of QIBGSA and classification using a deep convolutional neural network for robust and efficient facial expression recognition. Also, the effect of variations in the yaw angle (front to half side view) on facial expression recognition is studied. The results of the proposed system for the KDEF dataset are determined in three different cases of frontal view, half side view, and combined frontal and half side view images. The system efficacy is analyzed in terms of recognition rate.

For networks with fixed network topology, when the total coupling strength between nodes is limited and the coupling strength between nodes is saturated, the global optimization algorithms including genetic algorithm (GA) and particle swarm optimization (PSO) algorithm are used to adjust the coupling strength between nodes to improve the synchronizability of the network, respectively. Simulation results show that in WS small-world network, when the edge betweenness centrality of the edge is large, the coupling strength of the edge after optimization is greater. Furthermore, compared with GA, PSO has better performance.

The Susceptible, Infected and Recover (SIR) model is a very simple model to estimate the dynamics of an epidemic. In the current pandemic due to Covid-19, the SIR model has been used to estimate the dynamics of infection for Bangladesh, India, Pakistan and compared with that of China. Numerical solutions are used to obtain the value of parameters for the SIR model. It is predicted that the active case in Pakistan due to the SARS-CoV-2 will be comparable with that in China whereas it will be low for Bangladesh and India. The basic reproduction number, with fluctuations, for South Asian countries are predicted to be less than that of China. The susceptible population is also estimated to be under a million for Bangladesh and India but it becomes very large for Pakistan.

The main aim of this paper is to examine the discharging process with insertion of wavy surface and changing shape of nanoparticles. Contours were presented in the form of contours and profiles of energy and temperatures. To get the acceptable accuracy, adaptive grid is employed and time steps for each iteration are variable. The outputs indicate that augmenting A and selection of platelet shape lead to a faster solidification. With augment of $A$, 14% reduction has been reported for ($m=3$). Such percentage augments with the rise of $m$ and 14.03% reduction were reported for ($m=5.7$). At $m=5.7$, augmenting $A$ from 0.1 to 0.3 makes the time to reduce from 44.16s to 37.96s. Lower level of energy was reported for platelet shapes, which means higher liquid fraction of domain. Temperature declines with augment of $A$ and $A=0.1$ prolongs process of about 14.03% in the existence of platelet shape.

In this paper, a mathematical model describing the transmission dynamics of onchocerciasis with distributed delays in infection incubation and recovery in humans and blackfly host population is formulated. We showed that the delayed model is positively invariant and bounded. Also, we obtain the onchocerciasis-free and endemic steady-state solutions as well as the basic reproduction number $R_{hb}$ of the delayed onchocerciasis model. We found that the delayed onchocerciasis model is locally asymptotically stable whenever $R_{hb}<1$. The findings suggest that, for $R_{hb}$ to be less than unity, effective use of ivermectin drug for treatment, distribution of treated nets and cloths, etc., is necessary for the minimization and possible elimination of onchocerciasis infection.

When monolayer (ML) MoS₂ is placed on a substrate, the proximity-induced interactions such as the Rashba spin-orbit coupling (RSOC) and exchange interaction (EI) can be introduced. Thus, the electronic system can behave like a spintronic device. In this study, we present a theoretical study on how the presence of the RSCO and EI can lead to the band splitting, the lifting of the valley degeneracy and to the spin polarization in $n$- and $p$-type ML MoS₂. We find that the maxima of the in-plane spin orientation in the conduction and valence bands in ML MoS₂ depend on the Rashba parameter and the effective Zeeman field factor. At a fixed Rashba parameter, the minima of the split conduction band and the maxima of the split valence band along with the spin polarization in ML MoS₂ can be tuned effectively by varying the effective Zeeman field factor. On the basis that the EI can be induced by placing the ML MoS₂ on a ferromagnetic substrate or by magnetic doping in ML MoS₂, we predict that the interesting spintronic effects can be observed in $n$- and $p$-type ML MoS₂. This work can be helpful to gain an in-depth understanding of the basic physical properties of ML MoS₂ for application in advanced electronic and optoelectronic devices.

The exact controllability can be mapped to the problem of maximum algebraic multiplicity of all eigenvalues. In this paper, we focus on the exact controllability of deterministic complex networks. First, we explore the eigenvalues of two famous networks, i.e. the comb-of-comb network and the Farey graph. Due to their special structure, we find that the eigenvalues of each network are mutually distinct, showing that these two networks are optimal networks with respect to exact controllability. Second, we study how to optimize the exact controllability of a deterministic network. Based on the spectral graph theory, we find that reducing the order of duplicate sets or co-duplicate sets which are two special vertex subsets can decrease greatly the exact controllability. This result provides an answer to an open problem of Li et al. [X. F. Li, Z. M. Lu and H. Li, Int. J. Mod. Phys. C 26, 1550028 (2015)]. Finally, we discuss the relation between the topological structure and the multiplicity of two special eigenvalues and the computational complexity of our method.

From the stock markets of six countries with high GDP, we study the stock indices, S&P 500 (NYSE, USA), SSE Composite (SSE, China), Nikkei (TSE, Japan), DAX (FSE, Germany), FTSE 100 (LSE, Britain) and NIFTY (NSE, India). The daily mean growth of the stock values is exponential. The daily price fluctuations about the mean growth are Gaussian, but with a nonzero asymptotic convergence. The growth of the monthly average of stock values is statistically self-similar to their daily growth. The monthly fluctuations of the price follow a Wiener process, with a decline of the volatility. The mean growth of the daily volume of trade is exponential. These observations are globally applicable and underline regularities across global stock markets.

We present Star–Triangle Relations (STRs), a Mathematica® package designed to solve Feynman diagrams by means of the method of uniqueness in any Euclidean space-time dimension. The method of uniqueness is a powerful technique to solve multi-loop Feynman integrals in theories with conformal symmetry imposing some relations between the powers of propagators and the space-time dimension. In our algorithm, we include both identities for scalar and Yukawa type integrals. The package provides a graphical environment in which it is possible to draw the desired diagram with the mouse input and a set of tools to modify and compute it. Throughout the use of a graphic interface, the package should be easily accessible to users with little or no previous experience on diagrams computation. This manual includes some pedagogical examples of computation of Feynman graphs as the scalar two-loop kite master integral and a fermionic diagram appearing in the computation of the spectrum of the $\gamma$-deformed ${𝒩}=4$ SYM in the double scaling limit.

Segregation of granular particles affects the quality of end products in the pharmaceutical, chemical and food processing industries. Many researchers have worked on controlling the mechanical properties of granular particles to minimize segregation. In this paper, we studied different chute-related factors — inclination angle, friction, fill, channel geometry and base profile — and their effects on segregation. We conducted a small-scale experiment with chute inclined at different angles, and also numerical simulations performed using an open-source discrete element method (DEM) code — LIGGGHTS. We found the optimal condition for minimum segregation of a binary granular mixture. We concluded that segregation is minimized if the stream-wise velocity is low, for example, by keeping the chute at a low inclination $10^{\circ }$ and increasing the wall roughness to 0.14.

In this paper, we study and simulate the effect of individual social responses, as a collective factor, on the epidemic spreading processes. We formally define the problem based on the traditional $SI$ and $SIR$ compartmental models considering the time-varying infection probability dependent on the social responses. In this study, models of generic and special case scenarios are developed. While in the generic case the effective parameter of behavioral response is demonstrated as one collective factor, in the special case the behavioral response is assumed as the combination of two collective factors: social cost and transfer rate of social awareness. With social cost, we refer to the costs incurred by a certain population to prevent or mitigate an epidemic. With transfer rate of social awareness, we describe the averaged rate of received information and knowledge regarding a disease that individuals hold and make use to avoid negative consequences. We show that, while in both $SI$ and $SIR$ models the density of infected agents grows exponentially during the initial time steps, the inclusion of our models of social responses, either generic or special one, leads to mitigation of the spreading. As a result of both generic and special cases, the density of infected agents in the stationary state and the maximum number of infected agents decrease according to power-law functions for different values of collective factors. In the special case results, we also witnessed significant changes in the slope of decreasing trends of stationary density of states happening for a critical value of transfer rate of social awareness, approximately at about the inverse of the time interval of transmission rate update. With this result, we point out that increasing the transfer rate of social awareness to about this critical point outperforms any slight increase in social cost in reducing the number of infected agents.

Modified three-derivative Runge–Kutta (MTHDRK) methods for the numerical solution of the resonant state for the Schrödinger equation are investigated. Order conditions are presented and oscillation-fitting conditions are derived. Two practical fifth-order explicit MTHDRK methods are constructed and the error analysis is carried out for large energy. The numerical results are presented for the numerical solution of the Schrödinger equation to show the robustness of our new methods.

In this work, theoretical analysis is carried out on fully developed hydromagnetic flow of heat generating/absorbing fluid in a vertical microchannel in the presence of Hall and ion-slip effects. The governing coupled flow equations are obtained in dimensional form and thereafter simplified by employing some similarity transformation variables and quantities. The transformed coupled equations are solved by adopting the Adomian Decomposition Method (ADM) and their solution represented in closed form. Interesting influences of some active parameter on different flow features are shown using line graphs and Table. The numerical values for the results obtained in this work using ADM were validated with results obtained from existing benchmark. Results from the analysis reveal that in the existence of heat generation/absorption, the primary velocity and the temperature distribution could be enhanced by growing the ion-slip and Hall current parameter, whereas its influence on velocity is contrary along the secondary direction.