Computations of mixed convection slip flow around the surface of a sphere: Effects of thermophoretic transportation and viscous dissipation

The effects of thermophoretic motion and viscous dissipation on the two-dimensional fluid flowing along different positions of a sphere are inspected by considering slip flow. The leading set of partial differential equations is altered as a set of nonlinear primitive partial differential equations utilizing primitive variable transformation. The finite difference method is used to solve the governing equations numerically. The impacts of appropriate parameters, such as Eckert number slip flow parameters, mixed convection parameter, and thermophoresis parameter on unknown variables, such as velocity profile, mass concentration, and temperature profile are analyzed and displayed with the help of graphs by using the highly technical software, Tecplot 360. And also, we have observed the effects of the identical parameters on skin friction coefficient, rate of heat, and rate of mass transfers by means of graphs. From the outcomes, we noted that (a) the velocity profile is dominant at position $X=1.5$ rad and the temperature distribution and mass concentration are dominant at position $X=\pi$ rad for increasing values of Eckert number. (b) Slip parameter boosts the velocity at position $X=2.095$ rad but temperature and mass concentration are maximum at position $X=\pi$ rad. (c) The thermophoretic parameter is also having a very strong impact on heat and fluid flow mechanics. The slip flow provides benefits in improving heat and mass transfer mechanisms along with skin friction. It is also predicted that the concentration boundary layer will be thinner during thermophoresis around the different positions. The novelty of the predicted work is holding slip flow with the inclusion of mechanical energy and thermophoretic motion around different positions of the sphere. It is worth mentioning that the obtained results predicted in graphs are satisfied by the prescribed boundary conditions, which yield the corrected skin friction, rate of heat transfer, and rate of mass transfer.     

New aramid‐based nanocomposites: Synthesis and characterization

New type of nanocomposites containing various proportions of montmorillonite in aromatic polyamide was prepared via solution intercalation method. Aramid chains were synthesized by reacting 4,4′‐oxydianiline with isophthaloyl chloride in N,N′‐dimethyl acetamide. Dodecylamine was used as swelling agent to change the hydrophilic nature of montmorillonite into organophilic. Appropriate amounts of organoclay were mixed in the polymer solution using high‐speed mixer for complete dispersion of the clay. Thin films cast from these materials after evaporating the solvent were characterized by XRD, TEM, mechanical, thermal, and water absorption measurements. The structure and morphology of the nanocomposites determined by XRD and TEM revealed the formation of exfoliated and intercalated clay platelets in the aramid matrix. Mechanical data indicated improvement in the tensile strength and modulus of the nanocomposites with clay loading up to 6 wt%. The glass transition temperature increased up to 12 wt% clay content and thermal stability amplified with increasing clay loading. The water absorption reduced gradually as a function of organoclay and approached to zero with 20 wt% organoclay in the aramid. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Thermal and mechanical properties of SEBS-g-MA based inorganic composite materials

Organic-inorganic hybrids based on a triblock copolymer [polystyrene-b-poly (ethylene-ran-butylene)-b-polystyrene-g-maleic anhydride] (SEBS-g-MA) with silica and clay were prepared using sol-gel and solution intercalation methods respectively. Reinforcement in the first system was achieved by the in-situ hydrolysis/condensation of tetraethoxysilane in the copolymer matrix yielding hybrid materials. The interaction between organic and inorganic phases was developed through a coupling agent. In another system, copolymer was reinforced by organoclay and compatibility between copolymer and hydrophilic montmorillonite was achieved by intercalation of clay with dodecylamine which increased the organophilicity of the clay. Thin transparent films of these hybrids materials were characterized for their mechanical, thermal and thermomechanical behavior. The tensile strength of hybrids improved relative to the pure copolymer in all the systems. Dynamic mechanical thermal analysis carried out gave α-relaxation temperature associated with glass transition temperature (T_g). The results indicate a shift in T_g values with the addition of silica in the matrix, which suggests an increased interfacial interaction between organic and inorganic phases while this effect is less pronounced in polymer–clay system. Thermal decomposition temperatures of the hybrids were found in the range of 450–500 °C. The weights of the residues left at 700 °C were nearly proportional to the inorganic contents in the original hybrids.     

Sampling from repairs of conditional functional dependency violations

Violations of functional dependencies (FDs) and conditional functional dependencies (CFDs) are common in practice, often indicating deviations from the intended data semantics. These violations arise in many contexts such as data integration and Web data extraction. Resolving these violations is challenging for a variety of reasons, one of them being the exponential number of possible repairs. Most of the previous work has tackled this problem by producing a single repair that is nearly optimal with respect to some metric. In this paper, we propose a novel data cleaning approach that is not limited to finding a single repair, namely sampling from the space of possible repairs. We give several motivating scenarios where sampling from the space of CFD repairs is desirable, we propose a new class of useful repairs, and we present an algorithm that randomly samples from this space in an efficient way. We also show how to restrict the space of repairs based on constraints that reflect the accuracy of different parts of the database. We experimentally evaluate our algorithms against previous approaches to show the utility and efficiency of our approach.     

A new route for the synthesis of CuIn0.5Ga0.5Se2 powder for solar cell applications

In this paper, a new and simple method is described that does not use an autoclave to synthesize copper indium gallium diselenide (CuIn_0.5Ga_0.5Se₂) particles from the constituent elements. The process also does not require a post-synthesis selenization step. A solvo-thermal route is followed in which the constituent element powders are dissolved and made to react in a solvent such as ethylenediamine (ED), or triethylenetetramine (TETA). Crystal structure, morphology, composition, and particle size distribution of prepared particles were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), and dynamic light scattering (DLS), respectively. The band gap energies of the prepared particles were determined using an UV-VIS-NIR spectrophotometer. The results indicate that the solvent temperature and the synthesis time significantly affect the formation of single-phase CuIn_0.5Ga_0.5Se₂ and the crystallinity of the particles. Further, the measured band gap energy for the prepared particles is close to that of the bulk material. For example, the single-phase plate-like CuIn_0.5Ga_0.5Se₂ particles with an average particle size of 413.9 nm which can be successfully synthesized at a temperature of 250 °C in 15 h, have a band gap energy of 1.15 eV.     

An efficient multistage switching node architecture for broadband ISDNs

This paper proposes and analyses a new and efficient multistage switching node architecture for high‐speed communication networks such as Broadband Integrated Services Digital Networks (BISDNs). The proposed architecture has several superior features as compared to the existing switching nodes based on Banyan architecture. The architecture uses a reduced number of stages in an attempt to reduce the delay. Each switching element has its own input buffer and that reduces the blocking probability. Performance of the proposed architecture has been evaluated using simulation. The performance results are presented in the form of utilization, and delay, with different buffer sizes. The results show that the proposed architecture provides better performance in terms of reduced delay and higher throughput. This revised version was published online in June 2006 with corrections to the Cover Date.     

The design of robust multi-loop-cascaded hydro governors

In the present paper, a new multi-loop-cascaded governor is proposed for hydro turbine controls. A turbine model is obtained that covers the effects of the water hammer, travelling waves, inelastic water penstocks and head loss due to the friction. Plant parameter uncertainties are taken into account to investigate stability robustness. The polynomial H robust control design method is used to design the multi-loop-cascaded governor. Water and load disturbance, and permanent oscillations in the power systems such as inter-area modes are included in the robust design procedure. Robust performance is achieved by using parameterised dynamic weighting functions of the design theory. The designed governor ensures that the overall system remains asymptotically stable for all norm-bounded uncertainties. Simulation results show that the system performance specifications and stability margins are improved significantly even in the presence of parameter uncertainties.Nomenclature - Polynomial notation is employed and the polynomials are assumed to be functions of the complex s variable. X^* denotes complex conjugate of the X. - a. S: complex frequency and is the frequency. - b. R₊: Set of all positive real numbers - c. R: Set of all real numbers - d. R(.): Set of all real rational functions - e. R[.]: Set of finite polynomials with real coefficients - f. R^mxm(.): Set of all real (mxm) matrices - g. R^mxm[.]: Set of polynomial (mxm) matrices.     

An exact analysis of radiative heat transfer and unsteady MHD convective flow of a second‐grade fluid with ramped wall motion and temperature

The influence of simultaneously applied ramped boundary conditions on unsteady magnetohydrodynamic natural convective motion of a second‐grade fluid is investigated and analyzed in this study. The motion of the fluid is considered near an infinite upright plate that is nested in a porous medium subject to nonlinear thermal radiation effects. The Laplace transformation technique is utilized to acquire the exact solutions of momentum and energy equations. To effectively examine the rate of heat transfer and shear stress, the Nusselt number and skin friction coefficient are also established. The outcomes of mathematical computations are elucidated through tables and figures to highlight some physical aspects of the problem. Some limiting models of the present problem are also deduced and presented. On comparison, it is observed that the fluid exhibits lower temperature and velocity profiles under ramped boundary conditions. It is also found that wall shear stress can be controlled by choosing large values of the magnetic parameter (M) and Prandtl number (Pr). In addition, the heat transfer rate specifies inverse trends for growing values of radiation parameter (Nr) and Prandtl number (Pr), while it increases rapidly under a ramped surface condition and decreases slowly under a constant surface condition.     

Dilemmas of integrated water resources management implementation in the Awash River Basin,Ethiopia: irrigation development versus environmental flows

Environmental flows allocation is an intrinsic part of Integrated Water Resources Management (IWRM). This paper analyses socio‐political issues and effects of environmental flows integration on water availability under the context of increased agricultural intensification in an effort to tackle food insecurity. Lack of appropriate framework comprising the procedural requirements and strategic directions as well as prevalence of politically motivated ad hoc development programmes are among major challenges identified. Introducing environmental flows to a perceived satisfactory level would result in a significant increase of unmet irrigation water demand, yet, “productivity first” norm overtakes. This is presumed to be due to skewed focus on irrigation expansion and low awareness on the possible consequences. The particular challenges highlighted generally unveil the inherent contradictions in the IWRM concept putting its claim that the set of principles and entire course stand universally accepted as a means to balance socio‐economic and environmental outcomes under question.