An analysis of the pressure build-up inside a reacting pellet during gas solid reactions

A method has been outlined for the calculation of the pressure gradient that can exist within the reacted shell when a spherical pellet reacts with a gas and undergoes a transport controlled topochemical reaction. It is known that pressure gradients can arise because of Knudsen flow existing in the reacted shell with small pores and the reactant gas having a different diffusivity than that of the product gas. The phenomena can be represented by a boundary value problem involving a set of partial differential equations with a moving boundary, incorporating time and positional dependence of diffusivities of the reactant and product gases. In the present work, the resulting equations have been solved numerically. A study has been made of the influence of the relevant parameters like total and Knudsen diffusivity ratios of the reactant and product gases, the porosity to tortuosity ratio of the reacted shell, the Biot modulus, the equilibrium constant of the reaction and the viscous flow parameter on the pressure build up inside the reacted shell.     

Equilibrium shapes and quasi-static formation of bubbles at submerged orifice

A detailed analysis of the effect of chamber volume, orifice radius, orifice submergence and contact angle on quasi-static formation of bubbles is presented. It is shown, that many aspects of slow bubble formation, involving phenomena leading to various modes of the bubble release, as well as the maximum orifice diameter which sustains a bubble at equilibrium, can be explained on the basis of information on equilibrium shapes and conditions. Scaling rules enabling adoption of results for water to other liquids are also presented.     

New frontiers for mid-infrared sensors: towards deep sea monitoring with a submarine FT-IR sensor system

A sub-sea deployable fiber-optic sensor system for the continuous determination of a range of environmentally relevant volatile organic compounds in seawater has been developed. The prototype of a robust, miniaturized Fourier transform infrared (FT-IR) spectrometer for in situ underwater pollution monitoring was designed, developed, and built in our research group. The assembled instrument is enclosed in a sealed aluminium pressure vessel and is capable of maintenance-free operation in an oceanic environment down to depths of at least 300 m. The whole system can be incorporated either in a tow frame or a remotely operated vehicle (ROV). A suitable fiber-optic sensor head was developed, optimized in terms of sensitivity and hydrodynamics, and connected to the underwater FT-IR spectrometer. Due to a modular system design, various other sensor head configurations could be realized and tested, ensuring facile adaptation of the instrument to future tasks. The sensor system was characterized in a series of laboratory and simulated field tests. The sensor proved to be capable of quantitatively detecting a range of chlorinated hydrocarbons and monocyclic aromatic hydrocarbons in seawater down to the low ppb (microg/L) concentration range, including mixtures of up to 6 components. It has been demonstrated that varying amounts of salinity, turbidity, or humic acids, as well as interfering seawater pollutants, such as aliphatic hydrocarbons or phenols, do not significantly influence the sensor characteristics. In addition, the sensor exhibits sufficient long-time stability and a low susceptibility to sensor fouling.     

Polysaccharide production by kefir grains during whey fermentation

Fermentation of deproteinised whey with kefir grains CIDCA AGK1 was studied focusing on polysaccharide production from lactose. Kefir grains were able to acidify whey at different rates depending on the grain/whey ratio. During fermentation, kefir grains increased their weight and a water-soluble polysaccharide was released to the media. Exopolysaccharide concentration increased with fermentation time, reaching values of 57.2 and 103.4 mg/l after 5 days of fermentation in cultures with 10 and 100 g kefir grains/l, respectively. The polysaccharide fraction quantified after fermentation corresponded to the soluble fraction, because part of the polysaccharide became a component of the grain. Weight of kefir grains varied depending on the time of fermentation. Polysaccharide production was affected by temperature. Although the highest concentration of polysaccharide in the media was observed at 43 degrees C at both grain/whey ratios, the weight of the grains decreased in these conditions. In conclusion, kefir grains were able to acidify deproteinised whey, reducing lactose concentration, increasing their weight and producing a soluble polysaccharide.     

DESIGN OPTIMIZATION OF INDUCTION MOTORS WITH DIFFERENTIAL EVOLUTION ALGORITHMS WITH AN APPLICATION IN TEXTILE SPINNING

This article deals with the design optimization of a squirrel-cage three-phase induction motor, selected as the driving power of spinning machines in the textile industry, using three newly developed versions of differential evolution (DE) algorithms called modified DE versions (CMDE, GMDE, and LMDE). Efficiency, which decides the operating or running cost of the motor (industry), is considered as the objective function. First, the algorithms are applied to design a general purpose motor with seven variables and nine performance-related parameters with their nominal values as constraints. To make the machine feasible, practically acceptable to serve in textile industries, and less costly to operate, certain constraints are modified in accordance with the demands of the spinning application. Comparison of the optimum designs with the industrial (existing) motor reveals that the motor designed by the proposed algorithms consumes less power input.     

Linking perceived external prestige and collective identification to collaborative behaviors in R&D teams

Research efforts have long been directed at understanding variations in collaborative behaviors among work teams with burgeoning interest in teams operating in knowledge-intensive settings. One of the largely unexplained issues is how does team image and collective identification facilitate collaborative behaviors. Here, survey data were collected from nineteen highly technical work teams engaging in software development in an R&D division of a multinational NASDAQ firm involved in multimedia communications and information processing technology. The relationships between perceived external prestige, collective team identification and team collaborative behaviors were examined. The results of the team-level analyses suggest that perceived external prestige augments collective team identification (measured at Time 1), which in turn engenders a high degree of collaboration and interaction within the team (measured at Time 2). When past team performance was controlled for, the results consistently supported the hypothesized model.     

Electrochemical studies of ferrocene in a lithium ion conducting organic carbonate electrolyte

We carried out a detailed study of the kinetics of oxidation of ferrocene (Fc) to ferrocenium ion (Fc⁺) in the non-aqueous lithium ion conducting electrolyte composed of a solution of 1 M LiPF₆ in 1:1 EC:EMC solvent mixture. This study using cyclic (CV) and rotating disk electrode (RDE) voltammetry showed that the Fc⁰/Fc⁺ redox couple is reversible in this highly concentrated electrolyte. The ferrocene and ferrocenium ion diffusion coefficients (D) were calculated from these results. In addition, the electron transfer rate constant (k⁰) and the exchange current density for the oxidation of ferrocene were determined. A comparison of the kinetic data obtained from the two electrochemical techniques appears to show that the data from the RDE experiments are more reliable because they are collected under strict mass transport control. A Tafel slope of c.a. 79 mV/decade and a transfer coefficient α of 0.3 obtained from analysis of the RDE data for ferrocene oxidation suggest that the structure of the activated complex is closer to that of the oxidized specie due to strong interactions with the carbonate solvents. The experiments reported here are relevant to the study of redox reagents for the chemical overcharge protection of Li-ion batteries.