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.     

Air Quality Profile of Inorganic Ionic Composition of Fine Aerosols at Two Sites in Mumbai City

The levels of PM ₁₀ , PM _2.5 , and NO ₂ were studied at a kerbsite and ambient site in Mumbai. Measurements were also made for eight inorganic ions (F ^? , Cl ^? , NO ₃ ^? , SO ^2? ₄ , Na ⁺ , K ⁺ , NH ₄ ⁺ , Ca ²⁺ , and Mg ²⁺ ) in the PM _2.5 fraction. During the study period, PM _2.5 , PM ₁₀ and NO ₂ levels ranged between 11–91, 18–125, and 8–64 μ g m ^{? 3} at a ambient site whereas at the kerbsite the ranges were 10–176, 21–189, and 4–55 μ g m ^?3 respectively. Average PM _2.5 values were 42 μ g m ^{? 3} at ambient and 69 μ g m ^?3 at the kerbsite. The measured ions accounted for about 50% of the PM _2.5 mass. Non-sea-salt (nss) sulfate contributed 91% and 85% of the ionic mass at the ambient and kerbsite sites respectively. Due to biomass sources of K, only about 5% of K ⁺ was from seas salt. The average equivalent ratio of NH ₄ ⁺ to nss- SO ² ₄ ^? , and NO ₃ ^? was over 1, indicating high source strength of ammonia.     

微铣刀刀刃轨迹预测模型及影响因素分析

微铣削是一种柔性很强的微加工方法,可对多种材料进行微器件的加工.但由于微铣刀具有独特的几何特征,微铣削时的刀刃轨迹与传统意义上的铣削刀刃轨迹有明显区别.针对2刃微铣刀,开发了一个考虑刀具回转误差和转子振动效应的刀刃轨迹预测模型,并分析了其对加工过程的影响.同时提出了一种基于刀柄测量结果,计算刀尖回转误差和刀具装夹不平衡量的方法.将这两个结果输入刀刃轨迹模型后,可以准确地预测刀尖中心和两个刀刃的轨迹,并以此来计算即时切屑厚度、切削力、铣槽宽度(加工误差)和表面质量.实验结果很好地验证了模型的预测.分析结果表明,在微铣削过程中,单刃切削经常发生;刀刃角和进给角这两个模型参数对加工误差和刀具磨损非常重要,刀刃角的最优值为±90°,进给角可根据加工要求进行选择.     

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.     

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.     

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...     

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.     

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.     

High-temperature oxidation of titanium silicide coatings on titanium

Coatings of Ti ₅Si₃ on titanium have been prepared by means of decomposition of silane SiH₄ on heated titanium ribbons. Oxidation of the coated titanium specimens was much slower than that of the noncoated ones. Gravimetric and morphological experiments allowed to propose a mechanism describing the oxidation process.     

A two-parameter parsimonious bathtub model for the analysis of system failure times with illustrations to reliability data

In this study, a two-parameter, upper-bounded probability distribution called the tau distribution is introduced and its applications in reliability engineering are presented. Each of the parameters of the tau distribution has a clear semantic meaning. Namely, one of them determines the upper bound of the distribution, while the value of the other parameter influences the shape of the cumulative distribution function. A remarkable property of this new probability distribution is that its probability density function, survival function, hazard rate function (HRF), and quantile function can all be expressed in terms of its cumulative distribution function. The HRF of the proposed probability distribution can exhibit an increasing trend and various bathtub shapes with or without a low and long-flat phase (useful time phase), which makes this new distribution suitable for modeling a wide range of real-world problems. The constraint maximum likelihood estimation, percentile estimation, approximate Bayesian computation, and approximate quantile estimation computation are proposed to calculate the unknown parameters of the model. The suitability of the estimation methods is verified with the aid of simulation and real-world data results. The modeling capability of the tau distribution was compared with that of some well-known two- and three-parameter probability distributions using two data sets known from the literature of reliability engineering: time between failures data of a machining center, and time to failure of data acquisition system cards. Based on empirical results, the new distribution may be viewed as a viable competitor to the Weibull, Gamma, Chen, and modified Weibull distributions.