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Liu J.,Polytechnic University of Mozambique
Nonlinear Dynamics | Year: 2011

In this paper, a periodic epidemic model is proposed in order to simulate the dynamics of HFMD transmission. We consider the effects of quarantine in the children population. We obtain a threshold value which determines the extinction and uniform persistence of the disease. Our results show that the disease-free equilibrium is globally asymptotically stable if the threshold value is less than unity. Otherwise, the system has a positive periodic solution and the disease persists. Numerical simulations show that quarantine has a positive impact on the spread of disease, i.e., quarantine is beneficial to the intervention and control of the disease outbreak in the children population. © 2010 Springer Science+Business Media B.V. Source


Zappelli L.,Polytechnic University of Mozambique
IEEE Transactions on Microwave Theory and Techniques | Year: 2012

An equivalent circuit for discontinuities exciting evanescent accessible modes is proposed. The key feature of this equivalent circuit is its capability for simplification if a port relative to an accessible evanescent mode is matched, or connected to a very long line. Circuit drawing is simple, fast, and based on a regular polygon with as many susceptances as the sides and diagonals. Each side is connected with a line of electrical length θ k to the terminal ports, and if the port refers to an evanescent accessible mode, a series reactance is added. This reactance is the key to the evanescent part of the circuit because it is able to cancel the effect of the evanescent mode if the relative port is matched or connected to a very long evanescent line, reducing the complexity of the circuit by one degree. With the help of the proposed equivalent circuit, we can define some approximating functions for the elements of a circuit representing a post in a waveguide, which can be used to speed up the optimization of complex structures, like filters or diplexers, based on posts. © 2012 IEEE. Source


Goncharov P.R.,Polytechnic University of Mozambique
Nuclear Fusion | Year: 2015

Semianalytical calculations of fusion neutron spectra in case of the presence of substantial suprathermal tails in fuel nuclei velocity distributions have been implemented using two different approaches. Numerical techniques are described. Results for a variety of isotropic and anisotropic distributions of suprathermal fuel nuclei are presented. Verification of calculated fusion product spectra has been performed using several methods. © 2015 IAEA. Source


Snegirev A.Yu.,Polytechnic University of Mozambique
Combustion and Flame | Year: 2015

The paper focuses on developing and justification of the flame extinction model for large eddy simulations of under-resolved turbulent diffusion flames. The model is based on the perfectly stirred reactor (PSR) concept, in which the residence time is coupled with the local strain rate, and the radiative losses from the reaction zone are taken into account. The single-step global reaction of fuel oxidation is considered. A possible way to calibrate the kinetic parameters is that by fitting measured values of flame temperature and strain rate at diffusive extinction (blow-off). By comparing the simulation results with experimental data available for methane-air and heptane-air flames and with the published predictions made by the activation energy asymptotics for the ethylene-air flame, it is demonstrated that the PSR model is capable of evaluating flammability bounds of the diffusion flame, including high-strain blow-off and low-strain quenching (i.e., diffusive and radiative extinction). The confluence of these bounds is shown to produce the minimum extinguishing concentration of an inert diluent. For the flames diluted by nitrogen, carbon dioxide, water vapor, or argon, the minimum extinguishing concentrations predicted in this way by the non-adiabatic PSR model are shown to agree with the measured values. Possibility of formulating a unified extinction criterion, the Damköhler number, is confirmed. © 2015 The Combustion Institute. Source


Jimenez J.,Polytechnic University of Mozambique | Jimenez J.,Stanford University
Annual Review of Fluid Mechanics | Year: 2011

The kinematics and dynamics of wall-bounded turbulence are surveyed, with emphasis on the multiscale processes associated with the logarithmic layer and with its interactions with the wall. It is shown that the logarithmic law reflects a momentum cascade and that its structure agrees reasonably well with Townsend's (1961) model of a self-similar family of attached eddies, each of which contains, on average, a sweep-ejection pair, a segment of a large velocity streak, and disorganized vorticity. Those logarithmic eddies are themselves turbulent objects and can be studied in minimal simulation boxes that are much larger than those in the buffer layer. It is argued that, near the wall, the logarithmic eddies are probably the same as the vortex packets identified by experiments, but that their dynamics does not appear to be especially linked to the buffer layer. Further from the wall, they align into longer superstreaks, although the mechanism remains unclear. Source

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