Numerical modeling of natural convection in an open cavity with two vertical thin heat sources subjected to a nanofluid

This paper presents a numerical study of natural convection cooling of two heat sources vertically attached to horizontal walls of a cavity. The right opening boundary is subjected to the copper–water nanofluid at constant low temperature and pressure, while the other boundaries are assumed to be adiabatic. The governing equations have been solved using the finite volume approach, using SIMPLE algorithm on the collocated arrangement. The study has been carried out for the Rayleigh number in the range 10⁴ ≤ Ra ≤ 10⁷, and for solid volume fraction 0 ≤ φ ≤ 0.05. In order to investigate the effect of heat source location, three different placement configurations of heat sources are considered. The effects of both Rayleigh numbers and heat source locations on the streamlines, isotherms, Nusselt number are investigated. The results indicate that the flow field and temperature distributions inside the cavity are strongly dependent on the Rayleigh numbers and the position of the heat sources. The results also indicate that the Nusselt number is an increasing function of the Rayleigh number, the distance between two heat sources, and distance from the wall. In addition it is observed that the average Nusselt number increases linearly with the increase in the solid volume fraction of nanoparticles.     

Transportation ontology definition and application for the content personalization of user interfaces

Ontologies have been largely exploited in many domains and studies. In this paper, we present a new application of a domain ontology for generating personalized user interfaces for transportation interactive systems. The concepts, relationships and axioms of transportation ontology are exploited during the semi-automatic generation of personalized user interfaces. Personalization deals with the capacity of adaptation of a user interface, reflecting what is known about the user and the domain application. It can be performed on the interface container presentation (e.g., layout, colors, sizes) and in the content provided in their input/output (e.g., data, information, document). In this paper, the transportation ontology is used to provide the content personalization. This paper presents the ontology and how it is used for the personalization of user interfaces for developing transportation interactive systems by model-driven engineering.     

Influence of ageing on the internal friction of magnesium

The internal friction of cp- (99.8 wt.%) and hp- (99.99 wt.%) magnesium was determined by measuring the logarithmic decrement of free vibrations of bending beams, which were clamped at one end. Independently of the purity and the thermomechanical pretreatment, for all samples the logarithmic decrement increases with increasing strain amplitude. The damping in hp-magnesium is generally higher than in cp-magnesium. This can be explained by the model of Granato and Lücke, assuming that the successive unpinning of dislocation segments between weak pinning points is the reason of the increment of damping with increasing strain amplitude. The weak pinning points are assumed to be solute atoms or vacancies. Based on this model, other effects, found also in time and stress dependent internal friction measurements, can be explained qualitatively. The damping decreases at room temperature with ageing time and annealing temperatures up to 150°C. For higher annealing temperatures the damping increases monotonously with the temperature of the heat treatment. The effect of ageing can also be reverted by dynamic strain in the range of about 10⁻⁴–10⁻³, which increases the internal friction of aged samples before they can age again.     

Sampled-data modelling and analysis of the power stage of PWM DC-DC converters

The power stage of the PWM DC–DC converter is modelled and analysed using the sampled-data approach. The work addresses both continuous and discontinuous conduction mode under voltage mode control, and continuous conduction mode under current mode control. For each configuration, nonlinear and linearized sampled-data models, and control-to-output transfer functions are derived. Using this approach, both current mode control and discontinuous conduction mode can be handled systematically in a unified framework, making the modelling for these cases simpler than with the use of averaging. The results of this paper are similar to results of Tymerski, but they are presented in a simpler manner tailored to facilitate immediate application to specific circuits. It is shown how sampling the output at certain instants improves the obtained phase response. Frequency responses obtained from the sampled-data model are more accurate than those obtained from various averaged models. In addition, a new (‘lifted’) continuous-time switching frequency-dependent model of the power stage is derived from the sampled-data model. Detailed examples illustrate the modelling tools presented here and also provide a means for comparing results obtained from the sampled-data approach with those obtained from averaging.     

Decentralized collaborative business process execution using blockchain

World Wide Web - Blockchain technology enables several untrustworthy parties to execute inter-organizational business processes in a tamper-proof manner. Existing approaches are based on smart...     

Analysis of double-diffusive hydrothermal flow in a domestic stack: The effect of side walls patterns

Domestic stack is considered to investigate the double-diffusive laminar natural convection. The working fluid is a gaseous mixture that has similar physical properties to carbon dioxide. Knowing the patterns of gaseous mixture distribution and determining the carbon deposit regions can help in carbon capture problems. The present study uses the finite element method to numerically examine the double ratio-diffusive physical phenomena in a rectangular-trapezoidal enclosure and to simulate the stack under a wide range of dimensionless parameters, such as buoyancy ratio $1\le N_{\mathit{BR}}\le 7$, Lewis number $2\le \mathit{Le}\le 8$, and Rayleigh number ${10}^3\le \mathit{Le}\le {10}^5$ for different aspect ratios. Nine different cases of the geometrical ratio are selected to cover most possible design configurations. The results indicate that increasing the Lewis number leads to augmented solutal transport but reduces heat transfer. However, both heat and mass transfer are observed by increasing the buoyancy ratio. It is worth mentioning that increasing the ratio of upper side length to base length $\left(\frac{d}{D}\right)$ from $\left(\frac{1}{4}\right)$ to $\left(\frac{3}{8}\right)$ leads to a significant increase in mass transfer by 75% and heat transfer enhancement ratio by around 50%.     

A fully implicit conjugate heat transfer method

Abstract

This article deals with the development of an implicit and conservative method for conjugate heat transfer at solid-fluid interfaces. The technique is applicable for both conformal and non-conformal meshes. The method, which is implemented within a fully coupled in-house code, is symmetric in its treatment of the solid and fluid regions and is shown to be very robust for highly complex configurations. To demonstrate the performance of the method, two compressible turbulent conjugate heat transfer test cases, the Mark II and C3X with film cooling, which are benchmarks for simulating the hydrodynamic and thermal fields around and inside turbine blades, are used. Numerical results generated are in good agreement with available experimental measurements.     

Functional Characterization of Cardiac Actin Mutants Causing Hypertrophic (p.A295S) and Dilated Cardiomyopathy (p.R312H and p.E361G)

Human wild type (wt) cardiac α-actin and its mutants p.A295S or p.R312H and p.E361G correlated with hypertrophic or dilated cardiomyopathy, respectively, were expressed by using the baculovirus/Sf21 insect cell system. The c-actin variants inhibited DNase I, indicating maintenance of their native state. Electron microscopy showed the formation of normal appearing actin filaments though they showed mutant specific differences in length and straightness correlating with their polymerization rates. TRITC-phalloidin staining showed that p.A295S and p.R312H exhibited reduced and the p.E361G mutant increased lengths of their formed filaments. Decoration of c-actins with cardiac tropomyosin (cTm) and troponin (cTn) conveyed Ca²⁺-sensitivity of the myosin-S1 ATPase stimulation, which was higher for the HCM p.A295S mutant and lower for the DCM p.R312H and p.E361G mutants than for wt c-actin. The lower Ca²⁺-sensitivity of myosin-S1 stimulation by both DCM actin mutants was corrected by the addition of levosimendan. Ca²⁺-dependency of the movement of pyrene-labeled cTm along polymerized c-actin variants decorated with cTn corresponded to the relations observed for the myosin-S1 ATPase stimulation though shifted to lower Ca²⁺-concentrations. The N-terminal C0C2 domain of cardiac myosin-binding protein-C increased the Ca²⁺-sensitivity of the pyrene-cTM movement of bovine, recombinant wt, p.A295S, and p.E361G c-actins, but not of the p.R312H mutant, suggesting decreased affinity to cTm.     

Thermodynamic Consistent Formulations of Viscoplastic Deformations in FCC Metals

A general consistent thermodynamic framework for small strain thermoviscoplastic deformations of face-centered cubic (FCC) metals is presented in this study. An appropriate and consistent Helmholtz free energy definition is incorporated, after considering the strain rate effect imbedded through the hardening definition, in deriving the proposed three-dimensional kinematical model. Microstructural physically based thermal and athermal yield function definitions (von Mises type) are utilized in this work for dynamic and static deformations of FCC metals. A length scale parameter introduced implicitly through the viscosity parameter is related to the waiting time of dislocations at an obstacle. The role of material dependence in setting the character of the governing equations is illustrated in the context of a simple uniaxial tensile problem in order to check the effectiveness and the performance of the proposed framework and its finite-element implementation. Results obtained for OFHC copper at low and high strain rates and temperatures show, generally, good comparisons with experimental results.     

Supramolecular association of acid terminated polydimethylsiloxanes

Summary. Benzoic acid terminated polydimethylsiloxanes (PDMS) have been synthesized by hydrosilylation of allyloxybenzylbenzoate with SiH terminated precursors followed by deprotection. These oligomers have been characterized by ¹H, ¹³C and ²⁹Si NMR, by FTIR and by SEC in tetrahydrofurane. Because of the flexibility and low polarity of the siloxane backbone, they are ideally suited to study the effect of hydrogen bonding on macromolecular properties. Received: 17 July 1997/Revised: 22 July 1997/Accepted: 6 August 1997