Modeling of multi gas-solid reactions; effect of bulk environment parameters on solid conversion

A unified gas-solid reaction model that considers multi gas-solid components is developed for reactions in porous pellets with multiple reactants. The transient variables and properties of the reactants and transport parameters are continually updated in the simulation. Temperature, pressure, solid conversions, and concentration profiles are well predicted. Structural changes are also considered. Heat, mass, and reaction front tracking equations for all the components are solved simultaneously through a combination of solution techniques. Illustrative validation results for the model are presented for hematite/nickel oxide reduction at 608 K. The importance of bulk temperature and pressure on the overall and individual grain conversions is explored for a range of interest. The response of system parameters to dynamic changes in boundary conditions is studied.     

On partial-information optimal singular control problem for mean-field stochastic differential equations driven by Teugels martingales measures

This paper is concerned with partial-information mixed optimal stochastic continuous–singular control problem for mean-field stochastic differential equation driven by Teugels martingales and an independent Brownian motion, where the Teugels martingales are a family of pairwise strongly orthonormal martingales associated with Lévy processes. The control variable has two components; the first being absolutely continuous, and the second singular. Partial-information necessary and sufficient conditions of optimal continuous–singular control for these mean-field models are investigated. As an illustration, this paper studies a partial-information linear quadratic control problem of mean-field type involving continuous–singular control.     

Use of Endostemon tereticaulis (Pear.) M.Ashby and Hyptis spicigera Lam. Plant Extracts as Corrosion Green Inhibitors for Mild Steel in 1M HCl: Electrochemical and Surface Morphological Studies

Protection of Metals and Physical Chemistry of Surfaces - In the present study, we evaluated the effect of corrosion inhibition of ethanol extracts from Endostemon tereticaulis and Hyptis spicigera...     

Experimental study of complex two-phase instabilities during the start-up of a vertical thermosyphon reboiler operating under vacuum

This paper reports experimental studies of the start-up at reduced pressures (0.105–0.171 bar) and low heat fluxes (1.23–1.55 kW m⁻²) of the thermosyphon reboiler research facility in the Morton Laboratory at the University of Manchester. This is a full scale replica of an industrial sized natural circulation thermosyphon reboiler comprising 50 vertically mounted 25 mm OD tubes of 3 m length with water as the process fluid in the tubes and with steam condensing in the shell side of the reboiler. Unstable behaviour is obtained at start-up with flow-induced instabilities (geysering) when the level of the liquid within the tubes of the bundle is up to the top tubesheet (100% submergence) and also at 83% submergence of the tubes irrespective of the process pressure. At 100% submergence of the tubes, intermittent reversed flows in the entire loop with substantial vibrations are obtained. Chaotic behaviour is obtained at the lower submergence level of 83%. However, start-up at process pressures of 0.22 and 1.04 bar, and low heat fluxes with the entire thermosyphon loop flooded with liquid completely alleviated the flow-induced instabilities observed at the lower submergence levels within the tubes. The flow in the closed loop of liquid is induced very soon after the steam is introduced into the reboiler due to the buoyancy forces emanating from differences in density around the loop. The start-up is smooth and relatively quick, but further instrumentation and control are required for the introduction of the feed to the thermosyphon system once vapour is generated. A control strategy and procedure is proposed which will avoid the instabilities that inherently occur with start-up procedures currently practised in industry.     

Robot Dynamic Modeling Using a Power Flow Approach with Application to Biped Locomotion

In this paper, we present a method for robots modeling called bidirectional dynamic modeling. This new method takes into account the gear efficiency and the direction of power transmission in the gears. Epicyclic gearboxes have often different efficiencies in the two directions of power transmission. The characteristics of the chain of transmission must then be taken into consideration in order to describe the dynamic behavior of robots. The two directions of power flow can indeed occur in robot motions. Depending on that direction the dynamic model is different. The bidirectional dynamic modeling is experimentally applied to a bipedal walking robot. Our method exhibits a better accuracy over classical modeling. Moreover, when applied to computed torque control, the bidirectional model increases the tracking performances.     

Capacity Optimization of MIMO Wireless Communication Systems Using a Hybrid Genetic-Taguchi Algorithm

The purpose of this paper is to use a hybrid Taguchi-genetic algorithm to optimize the capacity of MIMO systems with different linear array geometrical configurations at both communication ends (Transmitter and Receiver). The method combines the traditional genetic algorithm, known to have a powerful global exploration capability, and the Taguchi method, which can exploit the optimum offspring and thus, enhance the genetic algorithm. The idea is to use the spatial channel model where the effect of mutual coupling is considered. Each array geometrical configuration has its own contribution in the total channel matrix depending on its physical parameters. The end result is to find out which combination(s) produce the highest capacity value.     

A new worm propagation threat in BitTorrent: modeling and analysis

Peer-to-peer (P2P) networking technology has gained popularity as an efficient mechanism for users to obtain free services without the need for centralized servers. Protecting these networks from intruders and attackers is a real challenge. One of the constant threats on P2P networks is the propagation of active worms. Recent events show that active worms can spread automatically and flood the Internet in a very short period of time. Therefore, P2P systems can be a potential vehicle for active worms to achieve fast worm propagation in the Internet. Nowadays, BitTorrent is becoming more and more popular, mainly due its fair load distribution mechanism. Unfortunately, BitTorrent is particularly vulnerable to topology aware active worms. In this paper we analyze the impact of a new worm propagation threat on BitTorrent. We identify the BitTorrent vulnerabilities it exploits, the characteristics that accelerate and decelerate its propagation, and develop a mathematical model of their propagation. We also provide numerical analysis results. This will help the design of efficient detection and containment systems.     

Mathematical analysis of a disease transmission model with quarantine,isolation and an imperfect vaccine

A new mathematical model for the transmission dynamics of a disease subject to the quarantine (of latent cases) and isolation (of symptomatic cases) and an imperfect vaccine is designed and analyzed. The model undergoes a backward bifurcation, where a stable disease-free equilibrium co-exists with a stable endemic equilibrium when the associated reproduction threshold is less than unity. It is shown that the backward bifurcation phenomenon can be removed if the vaccine is perfect or if mass action incidence, instead of standard incidence, is used in the model formulation. Further, the model has a unique endemic equilibrium when the threshold quantity exceeds unity. A nonlinear Lyapunov function, of the Goh–Volterra type, is used to show that the endemic equilibrium is globally-asymptotically stable for a special case. Numerical simulations of the model show that the singular use of a quarantine/isolation strategy may lead to the effective disease control (or elimination) if its effectiveness level is at least moderately high enough. The combined use of the quarantine/isolation strategy with a vaccination strategy will eliminate the disease, even for the low efficacy level of the universal strategy considered in this study. It is further shown that the imperfect vaccine could induce a positive or negative population-level impact depending on the size (or sign) of a certain associated epidemiological threshold.     

Pattern and antibiotic susceptibility of bacteria in pyogenic meningitis in a children's emergency room population in Maiduguri, Nigeria, 1988-1992

From January 1988 to November 1992, 107 (3.5%) of 3074 postneonatal children admitted to the Children's Emergency Room, University of Maiduguri Teaching Hospital, Nigeria, had sporadic pyogenic meningitis; 66 (61.7%) were aged < or = 12 months. Streptococcus pneumoniae, Neisseria meningitidis and Haemophilus influenzae together were responsible for 77.3% (58) of 75 culture-proven cases, 13.4% (10) had Enterobacteriaceae, 5.3% (4) had Staphylococcus aureus and 4% (3) untyped alpha-haemolytic streptococci. Fifty percent of 62 bacteria were resistant to ampicillin, 47.2% of 36 to penicillin and 10.7% of 56 to chloramphenicol; none of 21 bacteria was simultaneously resistant to all three antibiotics. Up until 1992, we have encountered treatment failure with a regimen containing chloramphenicol in only 2 of 53 patients; the 2 patients had coliform meningitis. Non-meningococcal bacteria are an important cause of sporadic pyogenic meningitis in sub-Saharan Nigeria and chloramphenicol is the most appropriate initial drug of choice at the present time for the management of sporadic meningitis.     

Structural Stabilities and Elastic Thermodynamic Properties of SrTe Compound and SrTe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Alloy Under High Pressure

The effect of pressure on the structural, elastic, and thermodynamic properties of SrTe in both B1 (rocksalt) and B2 (CsCl-type) phases and the SrTe_1?x Ca _x alloys with Ca dopant concentrations at x = 0.16667, 0.20, 0.33333, 0.42857, 0.44444 and 0.50 have been investigated using the two new gradient-corrected functional developed by Perdew, J.P.; Burke, K.; Ernzerhof named Density-Gradient Expansion for Exchange in Solids (PBEsol) and generalized Wu–Cohen (WC), in a significant range of pressure from 0 GPa to 30 GPa. The structure parameters, elastic stiffness constants c _ij , the bulk modulus (B), Kleinman parameter (\( \xi \)), shear anisotropies A _shear are also determined. Furthermore, as reported in this study, the aggregate elastic modulus (B, G, E), Poisson’s ratio (ν) and the Lame’s coefficients (λ) are estimated. On the other hand, the ductility, brittleness, longitudinal, transverse sound velocities and the Debye temperature Θ_D(T) are also obtained. Importantly, our results are in reasonable agreement with the available theoretical and experimental data. To the best of our knowledge, this is the first study of the effect of the composition on the properties of the SrTe_1?x Ca _x alloys which may encourage other works for the confirmation of the reported results.