Simulation of structure and mobility of aggregates formed by simultaneous coagulation,sintering and surface growth

In this work, a new model for the simulation of nanostructured aggregates by simultaneous coagulation, sintering and surface growth is presented. Coagulation is treated as cluster–cluster agglomeration along the line connecting the center of mass of both agglomerates and is implemented using a Monte Carlo algorithm. Sintering is modeled as successive overlapping of spheres which cause reduction in the surface area based on a rate law for surface reduction. Surface growth is modeled as an increase in primary particle diameter, e.g. as a result of surface reactions. The evolved aggregates are analyzed by calculating their fractal dimension, radius of gyration, mobility diameter and mobility shape factor. It is found that the aggregates structure tends to be more compact when introducing the surface growth in shorter time comparing to the coagulation-sintering step only. Fractal dimension and the mobility shape factor of the resulting aggregates are correlated to an effective dimensionless time that combines the characteristic times of these three fundamental mechanisms. It is shown that the mobility diameter in the free molecular regime is not proportional to the radius of gyration. A power law relation that correlates the aggregates projected area and the equivalent number of primary particles is found to be in a very good agreement with estimates published in literature.     

Combined effect of viscous dissipation and joule heating on the coupling of conduction and free convection along a vertical flat plate

An analysis is presented to investigate the influences of viscous dissipation and Joule heating in the entire thermo-fluid dynamic field resulting from the coupling of bouncy forced flow with conduction along one side of a heated flat plate of thickness ‘b’. The governing equations are transformed into dimensionless non-similar equations by using set of suitable transformations and solved numerically by the finite difference method along with Newton's linearization approximation. Numerical results for the velocity profiles, temperature profiles, skin friction coefficient and the surface temperature distributions are shown both on graphs and in tabular form for different values of the parameters.     

SimRDH: A Modeling and Simulation Environment With Component Hybrid Dynamic Nets, Elevator Application

Component hybrid dynamic nets (CHDNs) are a graphic model for hybrid dynamic systems, which allow every component of the hybrid system to be individually represented. On the basis of this methodology, a software tool dedicated to electrical engineering simulations has been developed. Thus, the aim of this paper is to present a brief review of the model structure and to describe the developed software called SimRDH. In order to show the applications of this software tool, a hydraulic system, a mechanical system, and finally, an elevator system powered by supercapacitors have been studied.     

Verification of minimum-redundancy prefix codes

We show that verifying a given prefix code for optimality requires /spl Omega/(nlogn) time, indicating that the verification problem is not asymptotically easier than the construction problem. Alternatively, we give linear-time verification algorithms for several special cases that are either typical in practice or theoretically interesting.     

Design consideration of low temperature differential double-acting Stirling engine for solar application

This paper presents design considerations to be taken in designing of a low temperature differential double-acting Stirling engine for solar application. The target power source will be a thermosiphon solar water heater with integrated storage system, which will supply a constant source temperature of 70 °C. Hence, the system design is based on a temperature difference of 50 °C, assuming that the sink is kept at 20 °C. During the preliminary design stage, the critical parameters of the engine design are determined according to the Schmidt analysis, while the third order analysis was used during the design optimisation stage in order to establish a complete analytical model for the engine. The heat exchangers are designed to be of high effectiveness and low pressure-drop, and are made from a 0.015 m tube, while the porosity of the steel wool of 0.722 is used for the regenerator matrix. Upon optimisation, the optimal engine speed is 120 rpm with the swept volume of 2.3 l, and thus the critical engine parameters are found to be the bore diameter of 0.20 m. In addition, the volumes of heater, cooler and regenerator are 1.3 l, 1.3 l and 2.0 l volumes, respectively.     

Assembly of a protein "brush" by end-grafting titin fragments to liposomes

Titin is a giant filamentous protein of striated muscle composed of >300 immunoglobulin-like domains linked in tandem. Here, we demonstrate that a six-immunoglobulin fragment of titin carrying a poly-histidine tag forms a protein "brush" on liposomes containing metallochelating lipids. These specimens might allow the direct visualization by cryo-EM of frozen hydrated and unstained titin chains with preserved architectural features.     

Synthesis and Physico-Chemical Studies of Ester-Quat Surfactants in the Series of (Dodecanoyloxy)propyl n-Alkyl Dimethyl Ammonium Bromide

Ester-quat surfactants in the series of (dodecanoyl oxy) propyl n-alkyl dimethyl ammonium bromide referred to here as LC₃Cm (where m is the hydrocarbon chain lengths 8, 12 and 14) were synthesized and characterized by the usual spectroscopic methods (NMR, IR, MS…). Their physico-chemical properties were investigated by surface tension and conductimetric measurements. From surface tension measurements, isotherms and thermodynamic adsorption parameters were determined. The critical micelle concentration (CMC), the degree of counter ion dissociation (α) of micelles in the water and the standard Gibbs free energy $( \Updelta G_{\text{m}}^{0}) $ , of micellization were also determined by conductimetric measurements. The results obtained from both methods were compared to the similar surfactants in the series of quaternary ammonium surfactants. Optical microscopy was also used to study the behavior of anhydrous surfactants and the binary water/surfactant system as a function of temperature.     

Preparation and Characterization of Some NR and SBR Formulations Containing Different Modified Kaolinite

Kaolinite clay (KC) surface was modified with different surface modifiers such as methacrylic acid (MAA), polymethacrylic acid (PMAA1, mol wt 10,000) and polymethacrylic acid (PMAA2, mol wt 11,500). The adsorption isotherms of the above modifiers on the surface of KC were determined. The concentrations required for building up monolayer coverage of these modifiers on the surface of KC were determined from the adsorption isotherms. The optimum amount of modifier required for monolayer surface coverage on kaolinite was equal to 31 × 10^?5 mol/g for MAA, 35 × 10^?5 mol/gfor PMAA and 23.5 × 10^?5 mol/g for PMA. Different rubber mixes containing unmodified and modified KC were prepared. The rheometric characteristics of the rubber mixes and physico-mechanical properties of the rubber vulcanizates were measured. There was remarkable decrease in both the optimum cure time (tc₉₀) and scorch time (ts₂), following increase in the maximum torque of the SBR mixes by adding unmodified or modified KC. With the maximum torque increase, the values of both of the optimum cure time (tc₉₀) and scorch time (ts₂) decreases for the NR mixes by adding unmodified and modified KC. Also the mechanical properties of the investigated rubber vulcanizates as tensile strength and hardness were improved using unmodified KC and modified KC.     

Study of the drying behavior of high load multiphase droplets in an acoustic levitator at high temperature conditions

Experimental data on the drying behavior of suspension droplets is limited, despite its importance in industrial applications for material processing, chemical or the food industry involving spray dryers. This fact is particularly significant for high load and temperature conditions, as found in such industrial applications. In this work, the drying behavior of acoustically levitated multiphase droplets has been experimentally investigated. The acoustic tube levitator has been modified in order to allow experiments to be performed at high temperature conditions. The flow rate, temperature and relative humidity of this air stream can be controlled by an air conditioning system. A CMOS camera and a back-light illumination system are used to measure the droplet cross-sectional area and vertical position of the droplet during the drying process. The experiments have been performed using water–glass particle suspensions. The glass particles have a mean particle size and relative density of 13 μm and 2.5, respectively. The effect of the air temperature (60 °C<T<120 °C), initial volume of the droplet (0.05 μl<V₀<0.7 μl), initial solid mass load (0.01<Y_S<0.5) and relative humidity of the air (0.05<HR<0.45) on the mean porosity of the grain, first drying period duration and liquid evaporation rate has been analyzed by means of a parametric screening matrix and also by means of a central composite design (CCD) experimental design. The most important parameters to be considered for the porosity and the drying behavior in the range of variables analyzed are the initial solid mass load and the initial droplet volume. The relative humidity of the air exerts a moderate influence on the drying behavior of the droplet and the temperature has only a very low impact on the mean porosity. In addition, particular attention should be given to the drying behavior of small droplets, which result in a very low mean porosity values for high solid mass loads. The CCD confirms that the initial droplet volume, the solid mass load and their interaction exert significant influence on the three responses.     

In vitro studies on antioxidant activity of lignans isolated from sesame cake extract

The antioxidant activity of compounds isolated from a methanolic extract of commercial sesame cake was studied using a peroxidation model and a radical‐scavenging method. Pure compounds were isolated from the extract by preparative high‐performance liquid chromatography (HPLC) and identified and confirmed as sesamol, sesamin, sesamolin, sesaminol diglucoside and sesaminol triglucoside by HPLC, infrared, nuclear magnetic resonance and mass spectrometry. When the rate of inhibition of lipid peroxidation and the superoxide radical‐scavenging power of the individual compounds were evaluated, the compounds showed antioxidant activity to different extents. The antioxidant activity of compounds by the β‐carotene‐bleaching assay followed the order sesamol > sesamolin ≥ sesamin > butylated hydroxytoluene (BHT) > sesaminol triglucoside > sesaminol diglucoside. By the thiocyanate method the inhibition of linoleic acid peroxidation shown by sesamol, sesamin, sesamolin, sesaminol triglucoside, sesaminol diglucoside and BHT at 200 mg l^?1 was 77, 60, 69, 32, 25 and 49% respectively. A concentration–dependent superoxide–scavenging effect was also shown by these compounds. Sesamolin had an appreciable effect at 300 and 500 mg l^?1, while the other compounds were more effective at 100 mg l^?1. The study also established the occurrence of sesamol in the methanolic extract of defatted sesame cake for the first time. Copyright © 2005 Society of Chemical Industry