The Hall effect on an unsteady flow due to a rotating infinite disc

An analysis of the effects of Hall currents on the unsteady flow of an electrically conducting, viscous, incompressible fluid due to a rotating disk has been carried out. It is assumed that the flow is under the action of a transverse magnetic field and the magnetic Reynolds number is small. Approximate solutions to the velocity and the torque are derived for small values of the time t. They are shown graphically. It is observed that the torque-coefficient decreases with an increase in the Hall parameter.     

Numerical analysis of natural convection for a porous rectangular enclosure with sinusoidally varying temperature profile on the bottom wall

Numerical investigations of steady natural convection flow through a fluid-saturated porous medium in a rectangular enclosure with a sinusoidal varying temperature profile on the bottom wall were conducted. All the walls of the enclosure are insulated except the bottom wall which is partially heated and cooled. The governing equations were written under the assumption of Darcy-law and then solved numerically using finite difference method. The problem is analyzed for different values of the Rayleigh number Ra in the range 10 ≤ Ra ≤ 1000, aspect ratio parameter AR in the range 0.25 ≤ AR ≤1.0 and amplitude λ of the sinusoidal temperature function in the range 0.25 ≤ λ ≤ 1.0. It was found that heat transfer increases with increasing of amplitude λ and decreases with increasing aspect ratio AR. Multiple cells were observed in the cavity for all values of the parameters considered.     

Numerical analysis of natural convection in an inclined trapezoidal enclosure filled with a porous medium

A theoretical study of buoyancy-driven flow and heat transfer in an inclined trapezoidal enclosure filled with a fluid-saturated porous medium heated and cooled from inclined walls has been performed in this paper. The governing non-dimensional equations were solved numerically using a finite-difference method. The effective governing parameters are: the orientation or inclination angle of the trapezoidal enclosure , which varies between 0° and 180°, the Rayleigh number Ra, which varies between 100 and 1000, the side wall inclination angle θ_s and the aspect ratio A. The side wall inclination parameter θ_s is chosen as 67°, 72° and 81° and the calculations are tested for two different values of A=0.5 and 1.0. Streamlines, isotherms, Nusselt number and flow strength are presented for these values of the governing parameters. The obtained results show that inclination angle is more influential on heat transfer and flow strength than that of the side wall inclination angle θ_s. It is also found that a Bénard regime occurs around =90°, which depends on the inclination of the side wall, Rayleigh number and aspect ratio.     

Scheduling with bus access optimization for distributed embeddedsystems

In this paper, we concentrate on aspects related to the synthesis of distributed embedded systems consisting of programmable processors and application-specific hardware components. The approach is based on an abstract graph representation that captures, at process level, both dataflow and the flow of control. Our goal is to derive a worst case delay by which the system completes execution, such that this delay is as small as possible; to generate a logically and temporally deterministic schedule; and to optimize parameters of the communication protocol such that this delay is guaranteed. We have further investigated the impact of particular communication infrastructures and protocols on the overall performance and, specially, how the requirements of such an infrastructure have to be considered for process and communication scheduling. Not only do particularities of the underlying architecture have to be considered during scheduling but also the parameters of the communication protocol should be adapted to fit the particular embedded application. The optimization algorithm, which implies both process scheduling and optimization of the parameters related to the communication protocol, generates an efficient bus access scheme as well as the schedule tables for activation of processes and communications     

Influence of wet milling conditions on the structural and magnetic properties of Ni3Fe nanocrystalline intermetallic compound

Nanocrystalline Ni₃Fe compound is obtained by dry and wet milling under argon atmosphere, using benzene as surfactant. X-ray diffraction patterns show that the Ni₃Fe phase is formed after 2 h of milling followed by annealing (350 °C for 4 h). The mean size of the crystallites is 12 ± 2 nm for 40 h of wet milling. Iron and chromium contamination was evidenced by X-ray microanalysis. The increase in benzene quantity shifts the powder particle size distribution towards smaller particle size ranges. DSC analysis revealed the presence of benzene in the wet milled powders. Spontaneous magnetization decreases with increasing milling time and benzene quantity. Annealing at 350 °C for 4 h leads to a substantial increase of the spontaneous magnetization.     

The effects of thermal treatment on the physical properties of Sr2FeMo1−xMxO6 perovskite with M = W, Ta and x ≤ 0.3

The Sr₂FeMo_1−xM_xO₆ double perovskites with M = W and Ta and x ≤ 0.3, were obtained by sintering at 1300 °C, during 4 and 8 h, respectively. The perovskites crystallize in a tetragonal structure having I4/mmm space group. The grains are more homogeneous when sintering time is increased. The samples sintered longer time show higher values of saturation magnetizations, resistivities and magnetoresistivities than the samples sintered during 4 h. The intergrain tunnelling magnetoresistance as well as the intragrain contributions, respectively were analysed as function of temperature and external field. The changes in the physical properties, when the sintering time is increased, have been correlated with the number of antisite defects as well as the nature of grain boundaries.     

BiFeO3-synthesis,characterization and its photocatalytic activity towards doxorubicin degradation from water

Pure bismuth ferrite was successfully obtained through the thermolysis of new bismuth ferrioxalate coordination compound, namely BiFe(C₂O₄)₃·3H₂O. The synthesized precursor was characterized by chemical analysis, infrared spectroscopy and thermal analysis. The bismuth ferrite obtained after a heating treatment of the precursor for at 450–800?°C/1?h was investigated by X-ray diffraction, FE-SEM, TEM and HRTEM. The obtained pure bismuth ferrite nanoparticles (480?°C) was tested as photocatalyst towards the degradation of doxorubicin (DOX), a well-known anti-cancer drug commonly used for the treatment of various cancer types, which has been detected in hospital effluent water. The comparative results of DOX degradation through photolysis and photocatalysis under UV irradiation showed a great photocatalytic activity of bismuth ferrite towards DOX degradation and mineralization from water. The kinetics aspects were discussed based on the first-order kinetics model that fitted the best the experimental photocatalysis results.     

A proposed mixed-mode fracture specimen for wood under creep loadings

A mixed-mode fracture specimen was designed in this paper. This geometry is a judicious compromise between a modified Double Cantilever Beam specimen and Compact Tension Shear specimens. The main objective is to propose a specimen which traduces a stable crack growth during creep loading taking into account viscoelastic behaviour under mixed-mode loadings. The numerical design is based on the instantaneous response traduced by a crack growth stability zone. This zone is characterized by a decrease of the instantaneous energy release rate versus the crack length. In order to obtain a mixed-mode separation, the paper deals with the use of the M-integral approach implemented in finite element software, according to energetic fracture criterions. In these considerations, a numerical geometric optimization is operated for different mixed-mode ratios. Finally, a common specimen which provides to obtain fracture parameters, viscoelastic properties and creep crack growth process for different mixed-mode configurations is proposed.     

Finite element method used in contact problems with dry friction

In this paper, we present a formulation of numerical approximations of the frictional quasi-contact problem with dry friction between a deformable body and a foundation with possibility to consider the case of two deformable bodies. We consider numerical approximations of 3D static contact problem with dry friction, using finite contact elements. Saddle-point algorithm, Lagrange incremental multipliers method and penalty functions are used to enforce finite element surface contact constrains for incremental formulation of the frictional quasi-static problem. Some typical examples in the elastic contact problems with dry friction are presented.     

Stretchable, transparent graphene interconnects for arrays of microscale inorganic light emitting diodes on rubber substrates

This paper describes the fabrication and design principles for using transparent graphene interconnects in stretchable arrays of microscale inorganic light emitting diodes (LEDs) on rubber substrates. We demonstrate several appealing properties of graphene for this purpose, including its ability to spontaneously conform to significant surface topography, in a manner that yields effective contacts even to deep, recessed device regions. Mechanics modeling reveals the fundamental aspects of this process, as well as the use of the same layers of graphene for interconnects designed to accommodate strains of 100% or more, in a completely reversible fashion. These attributes are compatible with conventional thin film processing and can yield high-performance devices in transparent layouts. Graphene interconnects possess attractive features for both existing and emerging applications of LEDs in information display, biomedical systems, and other environments.