Effects of particle loading on a reduced pressure inductively coupled radio frequency plasma torch

Our previous attempts in the modeling of the heat transfer and fluid flow in radio frequency (RF) plasma torches considered dilute particle-loading conditions. It was assumed that the injected particles have no effect on the plasma temperature and velocity profiles. However, in practice, the plasma deposition process is carried out under fairly high loading conditions to achieve high energy efficiency. The plasma gas experiences significant local cooling and deceleration due to high particle injection rates. To this end, a numerical model has been developed which considers the coupling effects between the plasma temperature and velocity fields and injected particles. In this study, effort has been focused on the particle-loading effect in an inductively coupled RF plasma torch under a reduced pressure environment. The temperature and flow fields in an inductively coupled RF plasma torch are solved using an axisymmetric, variable property formulation of the Navier-Stokes equations. Pseudo two-dimensional electrical and magnetic field equations were considered. In addition, an integral constraint condition is used to maintain a specified discharge power in the plasma torch. The interaction between the plasma gas and injected particles is considered using the well-known “Particle-Source-In-Cell” (PSI-Cell) method. The exchanged mass, momentum, and energy between the plasma gas and injected particles are accounted for through additional source terms in the governing equations. The effect of particle loading on the resulting torch flow, thermal profiles, and particle-melting characteristics are presented and discussed.     

Stability and Exponential Synchronization of High-Order Hopfield Neural Networks with Mixed Delays

This paper investigates the problems of stability and synchronization for high-order recurrent neural networks with mixed delays. Firstly, we establish sufficient conditions to ensure the asymptotic stability and then the exponential synchronization. Furthermore, our results are applied to two chosen systems to demonstrate the effectiveness of the obtained theoretical results.     

A declarative language to support dynamic evolution of web service business protocols

We investigate the problem of web service instances migration in the context of business protocol evolution, i.e., how to convert active instances of web services from an old version of a business protocol into a new one? We propose a framework based on a declarative approach to support service providers in defining fine-grained migration strategies of active instances. While the existing approaches for instances migration force the migrated instances to reflect the original ones as accurately as possible, in our approach we give to service providers the ability to declaratively define the constraints that drive the instances migration process. A migration strategy is expressed as a set of instances migration rules which are specified using an instance mapping language made of a set of generic migration patterns. The proposed approach has been implemented in a software tool that provides useful functionalities for protocol managers.     

Reactions of 4-[4′-(1′,3′-Diphenylpyrazolyl)methylene]-2-phenyl-5-oxo-2-oxazoline with grignard reagents and diazoalkanes

The title compound reacts with two moles of Grignard reagents with 1,2-addition to give the alcohol 4 , and/or the oxazoline 5 , or with 1,4-addition to give the amino ketone 6 . A reaction mechanism is proposed. Diazomethane is always added to the exocyclic double bond in 1 , but diphenyldiazomethane, in addition, replaces the carbonyl-oxygen by a benzhydrylidene group to give compound 9 .     

An effective scheduling scheme for multi-hop multicast in wireless mesh networks

With the utilization of concurrent transmission strategy, a throughput-enhanced scheduling scheme is devised for multicast service in wireless multi-hop mesh networks. Since the performance of a multicast mechanism is constrained in a wireless setting due to the interference among local wireless transmissions, the interference relationships are first characterized by introducing a graph transformation method. Based on the graph transformation, the multicast scheduling problem is converted to the graph coloring problem, and then a capacity greedy algorithm is designed to provide concurrent transmission scheduling so that the demanded multicast transmission rate can be achieved. Moreover, the necessary and sufficient conditions of multicast schedulable feasibility are derived. Through corresponding simulations, it is shown that the proposed strategy can enhance the throughput of wireless multi-hop multicast systems significantly.     

The effect of variation of angle of inclination on the performance of low-concentration-ratio compound parabolic concentrating solar collectors

Thermal heat transfer in line-axis, symmetric, compound parabolic concentrating solar energy collectors (CPCs) has been investigated and a theoretical numerical model has been developed. The model allows the effect of the angle of axial inclination of an east-west aligned CPC and hence the effect of the latitudinal and tracking configuration of the CPC system on performance to be determined. The internal and external convective heat transfer correlations employed are angular dependent. The variation of convective, radiative, conductive and overall heat transfer coefficients and system efficiency for a range of angular inclinations, concentration ratios, total insolations and beam to diffuse insolation factors are presented graphically. The results demonstrate that there is a 10% variation in convective heat transfer with angle of inclination for low concentration CPCs (i.e. C = 1.5).     

Numerical simulations of transport processes in a pulse tube cryocooler: Effects of taper angle

A numerical model is developed for the prediction of the performance and transport characteristics in an orifice pulse tube refrigerator (OPTR). The OPTR is studied for a two specific geometries. In the first geometry (A), only the taper angle of the pulse tube is changed. In the second geometry (B), the taper angle of the pulse tube is varied along with the diameter of the hot heat-exchanger. The taper angle of the pulse tube is shown to have significant effects on the secondary streaming patterns observed in the pulse tube. Tapering the pulse tube improved the performance of the OPTR only for Geometry-B. In this case, suppression of velocity streaming is achieved in the warm end of the pulse tube.     

NATURAL CONVECTION-RADIATION INTERACTIONS IN A CUBE FILLED WITH A NONGRAY GAS

A three-dimensional numerical study was performed on interactions of natural convection and radiation in a cubical enclosure filled with carbon dioxide gas. The enclosure was heated differentially by two opposing vertical walls. Gas radiation was analyzed by the P₁ differential approximation method and the weighted sum of gray gas model. Computations were carried out over a range of the Rayleigh number, Ra, between 10⁵ and 10⁹. The Prandtl number and the overheat ratio were held fixed at 0·68 and 1·0, respectively. Unsteady transitional flows were computed by a direct simulation method, without using any explicit turbulence models. From the predictions, a mean heat transfer correlation has been proposed as Nu = 0·323 Ra^0·342 in the surface/gas radiation mode, where Nu is the time and spatially averaged Nusselt number at the isothermal walls.     

NOx formation in post-flame gases from syngas/air combustion at atmospheric pressure

Species concentration measurements specifically those associated with nitrogen oxides (NO_x) can act as important validation targets for developing kinetic models to predict NO_x emissions under syngas combustion accurately. In the present study, premixed combustion of syngas/air mixtures, with equivalence ratio (Φ) from 0.5 to 1.0 and H₂/CO ratio from 0.25 to 1.0 was conducted in a McKenna burner operating at atmospheric pressure. Temperature and NO_x concentrations were measured in the post-combustion zone. For a given H₂/CO ratio, increasing the equivalence ratio from lean to stoichiometric resulted in an increase in NO and decrease in NO₂ concentration near the flame. Increasing the H₂/CO ratio led to a decrease in the temperature as well as the NO concentration near the flame. Based on the axial profiles above the burner, NO concentration increases right above the flame while NO₂ concentration decreases through NO₂-NO conversion reactions according to the path flux analysis. In addition, the present experiments were operated in the laminar region where multidimensional transport effects play significant roles. In order to account for the radial and axial diffusive and convective coupling to chemical kinetics in laminar flow, a multidimensional model was developed to simulate the post-combustion species and temperature distribution. The measurements were compared against both multidimensional computational fluid dynamics (CFD) simulations and one-dimensional burner-stabilized flame simulations. The multidimensional model predictions resulted in a better agreement with the measurements, clearly highlighting the effect of multidimensional transport.     

The use of response surface method to optimize the extraction of natural dye from winery waste in textile dyeing

Grape pomace, which is a winery waste is studied and experimented to serve as a source of natural dyes that could be utilized in textile dyeing. The present study aims at developing and optimizing an extraction method of natural dye derived from grape pomace in order to dye silk fabrics. The water-acidified ethanol (20–40%) mixture is used mainly for the extraction of anthocyanins at different durations and at different temperatures (20–40 °C) from grape pomace. Effects of these independent variables (percentage of acidified ethanol, temperature, and duration of extraction) and their interactions during the extraction are determined by response surface methodology based on three-level three-factorial Box–Behnken design. Optimized values of percentage of acidified ethanol, temperature, and the duration of extraction for the optimization of monomeric anthocyanins concentration (75 mg L^?1) are found as 40%, 32,7 °C, and 38 h, respectively. The extract has been used for silk fabrics dyeing. The effects of some parameters (temperature, pH, and salt addition) on dyeing silk fabrics have been studied and optimized. The use of tannic acid as a natural mordant to improve the dye fastness proprieties has been investigated.