OH*-chemiluminescence during autoignition of hydrogen with air in a pressurised turbulent flow reactor

Autoignition of hydrogen in air was studied in a turbulent flow reactor using OH*-chemiluminescence. High-speed imaging was used to visualise the formation of autoignition kernels in the flow, and to analyse the conditions under which temporary stabilisation of the flame kernels occurred. The experiments were carried out at temperatures of 800–850 K, pressures of 0.8–1.2 MPa and an equivalence ratio of φ = 0.25. Measurements of the autoignition delays yielded values in the range of τ = 210–447 ms. The autoignition delay results indicated that, over the range of conditions studied, ignition delays reduced with decreasing pressure. This observation contradicted homogeneous gas-phase kinetic calculations, which predicted an increase in autoignition delay with decreasing pressure. If the kinetic model was altered to include surface reactions at the reactor walls, the calculations could be qualitatively reconciled with the experimental data, suggesting that wall reactions had a significant influence on autoignition delays.     

Novel nanocomposite membranes based on PBI and doped-perovskite nanoparticles as a strategy for improving PEMFC performance at high temperatures

In this work, Sr²⁺ dopant effects of Ba_0.9Sr_0.1TiO₃ and La_0.9Sr_0.1CrO_3-δ doped-perovskite nanoparticles on increasing proton conductivity, fuel cell performance, and mechanical and thermal stability of polybenzimidazole-based nanocomposite membranes were studied. The Sr²⁺ dopant creates cation vacancies in Ba_0.9Sr_0.1TiO₃ doped-perovskite nanoparticles and oxygen vacancies in La_0.9Sr_0.1CrO_3-δ doped-perovskite nanoparticles. The oxygen vacancies, which decrease columbic repulsion between protons and positive ions, have a more important role than the cation vacancies. They provide high surface area and high interfacial interaction between La_0.9Sr_0.1CrO_3-δ doped-perovskite nanoparticles, phosphoric acid, and polybenzimidazole for proton transfer and increase the proton conductivity of the nanocomposite membranes. In addition, the results of relative humidity effects showed that the ordered arrangement of oxygen vacancies of the La_0.9Sr_0.1CrO_3-δ doped-perovskite nanoparticles creates a specific pathway in the nanocomposite membranes for increasing proton transfer in the presence of relative humidity. Furtheremore, at phosphoric acid doping level of 13 mol phosphoric acid per monomer unit, proton conductivity of the nanocomposite membranes containing 8 wt.% La_0.9Sr_0.1CrO_3-δ doped-perovskite nanoparticles was obtained as 126 mS cm^-1 at 180°C and 6% relative humidity. The nanocomposite membrane showed the best performance and the power density of 0.62 W cm^-2 at 180°C and 0.5 V.     

Factors Motivating Citizen Engagement in Mobile Sensing: Insights from a Survey of Non-Participants

Mobile sensing uses features of mobile technology to monitor the environment and if a community participates in such monitoring, there can be community improvements in the quality of life. Despite the numerous potential benefits, the rate of citizen engagement in mobile sensing is generally low. Using the urban sensing project called “2Loud?,” this study was designed to uncover the reasons for non-participation and to discuss the motivations for intention to participate. A survey was administered to citizens who had been invited to participate but had decided not to participate. Examining the four motivational factors of “Concern,” “Belief,” “Technology,” and “Time” through a series of Kruskal-Wallis H Tests indicated that respondents had a statistically significant favorable attitude toward “Intention to Participate” if they had some concern and belief, and if they had access to technology and available time, compared to those who did not. However, binary logistic regression analysis indicated that only “Time” and “Technology” were significant predictors of “Intention to Participate.” These findings are discussed in light of social psychology and information technology theories, and recommendations for improved communication and engagement strategies are suggested.     

Study of the motion of a spheroidal drop in a linear shear flow

The motion of a spheroidal deformable drop in a simple shear flow is simulated using a finite-difference/front-tracking method. The effect of surface tension coefficient, viscosity ratio and inertia on lateral migration and deformation of the drop is investigated. It is revealed that the deformation of a spheroidal drop is directly related to the capillary and Reynolds numbers. In the limit of finite Reynolds numbers, the equilibrium position of prolate drops depends strongly on the viscosity ratio; the final position of more viscous drops is closer to the wall in contrast with the spherical ones. As the deformability of drops increases and the inertial force decreases, the rate of migration of the prolate drops increases. Although the steady-state position does not depend on the capillary and Reynolds numbers, the migration rate depends considerably on these dimensionless parameters. In addition, the rate of migration is a decreasing function of the aspect ratio due to different direction of the lift force acting on the drop.     

Solving a new fuzzy multi-objective model for a multi-skilled manpower scheduling problem by particle swarm optimization and elite tabu search

Manpower scheduling is a complicated problem to solve that strives to satisfy employers’ objectives and employees’ preferences as much as possible by generating fairly desirable schedules. But sometimes, objectives and preferences may not be determined precisely. This problem causes manpower scheduling takes the fuzzy nature. This paper presents a new fuzzy multi-objective mathematical model for a multi-skilled manpower scheduling problem considering imprecise target values of employers’ objectives and employees’ preferences. Hence, a fuzzy goal programming model is developed for the presented mathematical model and two fuzzy solution approaches are used to convert the fuzzy goal programming model to two single-objective models. Since the complexity of a manpower scheduling problem is NP-hard, the single-objective models are solved by two meta-heuristics, namely particle swarm optimization and elite tabu search. Eventually, the performance of the proposed algorithms is verified and the results are compared with each other to select the best schedules.     

Some new efficient multipoint iterative methods for solving nonlinear systems of equations

It is attempted to put forward a new multipoint iterative method of sixth-order convergence for approximating solutions of nonlinear systems of equations. It requires the evaluation of two vector-function and two Jacobian matrices per iteration. Furthermore, we use it as a predictor to derive a general multipoint method. Convergence error analysis, estimating computational complexity, numerical implementation and comparisons are given to verify applicability and validity for the proposed methods.     

Recent advances on akermanite calcium-silicate ceramic for biomedical applications

Owing to great biocompatibility and high capacity of apatite formation, bioceramics, especially calcium silicate-based compounds, were extensively employed in orthopedic and dental uses concerning biomedical applications. Lately, akermanite (AK; Ca₂MgSi₂O₇), as a bioceramic containing Ca-, Mg- and Si, has gained an increased level of attention because of its more tunable mechanical characteristics and degradation rate. All studies indicate that this magnesium incorporating Ca-silicate ceramic has a great capacity to use as a bone graft material to fulfill the necessity of bone reconstruction. Despite the rising interest in using these materials in biomedical fields, there has not yet been an extensive overview of this bioceramic property and its potential benefits. Thus, it has been speculated that this concept and the emergence of akermanite bioactive ceramics might lead to significant upcoming advancements in the field of bone tissue engineering (BTE). Definitely, the approach still requires additional advances to considerably better respond to the vital concerns regarding the clinical application. The review tackles the present research trends on akermanite ceramics for biomedical purposes such as bone scaffold, coating materials, bone cement, and treatment of osteoporotic bone defects, commencing with recent status and shifting to upcoming developments.     

Copper chloride modified copper electrode: Application to electrocatalytic oxidation of methanol

Copper chloride modified copper (CCMC) electrode was prepared as a new electrode. For the preparation of the modified electrode, the polished copper electrode was placed in 0.1 M CuCl₂ solution for 20 s. In this step, a layer of copper (I) chloride was formed at the surface of copper electrode. Then, the electrode was placed in 0.1 M NaOH and the electrode potential was cycled between −250 and 1000 mV (vs. SCE) at a scan rate of 50 mV s⁻¹ for 5 cycles in a cyclic voltammetry regime until a featureless voltammogram was obtained. Surface physical characteristics of the modified electrode were studied by scanning electron micrographs (SEM). Results showed that considerable amounts of microcrystals have been formed on the copper surface during the modification. Surface elemental analysis of electrode were performed by energy dispersive X-ray (EDX) technique. The results showed that in addition to copper and chloride elements, there is also oxygen at the surface of CCMC electrode. This indicates that a layer of (ClCu)₂O was formed at the surface of the modified electrode. The electrocatalytic activity of the modified electrode for the oxidation of methanol, in aqueous basic solution was studied by using cyclic voltammetry. Results showed that, copper chloride modified electrode can improve the activity of Cu towards the oxidation of this small organic molecule, showing the possibility of attaining good electrocatalytic anodes for fuel cells. The modified electrode shows a stable and linear response in the concentration range of 5 × 10⁻³ to 8 × 10⁻² M with a correlation coefficient of 0.9958.     

Thermorheological and mechanical behavior of polylactide and its enantiomeric diblock copolymers and blends

In this study, different compositions of nearly monodispersed diblock copolymers of dl-lactide or d-lactide and l-lactide were synthesized by living ring-opening polymerization with a dinuclear indium catalyst. The effects of molecular weight and block length ratio on the rheological behavior of dl and l-lactide diblock copolymers in the disordered state were investigated. For comparison, blends of PDLLA and PLLA homopolymers of equivalent molecular weights to the diblock copolymers were prepared. We found that the time–temperature (t–T) superposition principle is applicable to the diblock copolymers PLLA-b-PDLLA and blends in the disordered state. However, the t–T superposition failed at low temperatures close to the temperature of crystallization. In contrast, diblock copolymers PLLA-b-PDLA formed stereocomplex crystallites of high melting point (slightly above 200 °C) that causes a viscosity enhancement. The failure of t–T superposition was found due to existing of micro homo or stereocomplex crystallites. The non-isothermal crystallization behavior was investigated using differential scanning calorimetry (DSC). The DSC thermograms of blends exhibited a single glass transition at 50–60 °C followed by melting point of PLLA at 177 °C. With decreasing of the PLLA content in the blends, the intensity of the melting peak decreased. In addition, different crystallization behavior was observed for diblock copolymers compared to their equivalent blends. Specifically, low temperatures and enthalpies of melting peaks were observed for diblock copolymers. These also show improvement in elongation at break and tensile strength as compared to their counterpart homopolymer blends.