A comparison of conductive and crystallographic effects of the phase transition in electrochemical nickel-boron layers

Experimental data related to the variations with temperature in the film resistivity of amorphous nickel-boron layers (electrochemically deposited) and its temperature coefficient are used for identifying the temperature for the phase transition. Suggestions are presented for interpreting the observed shifts in the resistivity and in the product of resistivity and its temperature coefficient.     

Static and incremental dynamic approaches for multi-objective bitmap join indexes selection in data warehouses

The Journal of Supercomputing - Data warehouses are very large databases and play key role in intelligent decision making in enterprises. The bitmap join indexes selection problem is crucial in the...     

Empirical Correlations for Slightly Heated Decaying Passive-Grid Turbulence

For homogeneous isotropic turbulence approximated by grid turbulence, velocity and temperature fluctuations decay under the effects of viscosity and thermal diffusivity of the fluid. In the self-similar region of grid flow, there is no mean shear and no turbulence production, and the decay rate is well represented by a power law; this is supported by the present measurements in three different grid flows and by previously published data for passive-grid turbulence obtained over different ranges of streamwise distance and/or Reynolds number. The grid flow is slightly heated so that temperature acts as a passive scalar. From dimensional analysis and empirical power-law correlations, relations for basic flow parameters, such as the Kolmogorov, Taylor, and Corrsin microscales, and the Reynolds and Péclet numbers, are established as functions of the normalized streamwise distance downstream of the grid. With these relations, it is possible to determine the flow parameters for a specific passive-grid geometry or, more generally, a specific set of initial conditions.     

Particle swarm optimization for bitmap join indexes selection problem in data warehouses

Data warehouses are very large databases usually designed using the star schema. Queries defined on data warehouses are generally complex due to join operations involved. The performance of star schema queries in data warehouses is highly critical and its optimization is hard in general. Several query performance optimization methods exist, such as indexes and table partitioning. In this paper, we propose a new approach based on binary particle swarm optimization for solving the bitmap join index selection problem in data warehouses. This approach selects the optimal set of bitmap join indexes based on a mathematical cost model. Several experiments are performed to demonstrate the effectiveness of the proposed method on the bitmap join index selection problem. Further testing of the method is performed using a database environment specific cost function. The binary particle swarm optimization is found to be more effective than both the genetic algorithm and data mining based approaches.     

Study of interface influence on crack growth: Application to Solid Oxide Fuel Cell like materials design

In the present work a mesh free method is used to study the effect of interfaces on the crack propagation path in multilayered like Solid Oxide Fuel Cells (SOFCs) materials. The partition of unity principle was introduced to model the crack tip singularity. The penalty method is used to model the materials discontinuity along the interfaces. The stress intensity factors (SIF) were computed using the interaction integral. The mesh free method is implemented and verified using results from the literature. A parametric study of crack propagation in mono-layer and bi-layer material is conducted. Finally an application to SOFC unit shows that crack initiated in the anode propagates towards the anode/electrolyte interface.     

Investigation of flow around a pair of side-by-side square cylinders using the lattice Boltzmann method

The low-Reynolds number flow around two square cylinders placed side-by-side is investigated using the lattice Boltzmann method (LBM). The effects of the gap ratio s/d (s is the separation between the cylinders and d is the characteristic dimension) on the flow are studied. These simulations reveal the existence of regimes with either synchronized or non-synchronized vortex-shedding, with transition occurring at s/d ≈ 2, which is larger than for circular cylinders. Detailed results are presented at Re = 73 for s/d = 2.5 and 0.7 corresponding to the synchronized and flip-flop regimes, respectively. Vortex-shedding from the cylinder occurs either in-phase or in-antiphase in the synchronized regime. However, linear stochastic estimate (LSE) calculations show that in-phase locking is the predominant mode. LSE is also employed to educe the underlying modes in the flip-flop regime, where evidence for both in-phase and anti-phase locked vortices is found, indicating that this regime is in a quasi-stable state between these two modes. The merging of the wakes, which is gradual for the synchronized regime, occurs rapidly in the flip-flop regime. The mean pressure on the upstream surface is symmetric and asymmetric for the synchronized and flip-flop regimes, respectively. Differences in results between the two regimes are interpreted in terms of the interaction of the jet formed between the cylinders with the adjoining wakes, the strength of this interaction depending on the spacing.     

An XFEM model for cracked porous media: effects of fluid flow and heat transfer

In this work, a numerical model is developed to investigate the influence of fluid flow and heat transfer on the thermo-mechanical response of a cracked porous media. The fluid flow, governed by the Darcy’s law, is discretized with the nonconforming finite element method. Time splitting is used with the energy conservation equation to solve the fluid and the solid phases separately. A combination of Discontinuous Galerkin (DG) and multi-point flux approximation methods is used to solve the advection-diffusion heat transfer equation in the fluid phase. While the conductive heat transfers equation in the solid phase is solved using the eXtended finite element method (XFEM) to better handle the temperature discontinuities and singularities caused by the cracks. Further, the resulted temperature is used as body force to solve the thermo-mechanical problem using the XFEM. In the post processing stage, the thermal stress intensity factor is computed using the interaction integral technique at each time step and used to validate the obtained results. A good agreement was found when the results were compared with the existing ones in the literature.     

Energy dependence of the theoretical expressions of Ziman transport parameters in the Mayadas-Shatzkes model

The macroscopic transport parametersK _n (n=0, 1, 2) defined by Ziman are calculated in the framework of the Mayadas-Shatzkes model from two opposite assumptions: whether or not the reflection coefficient depends on electron energy. In the case of metal and semi-metal films asymptotic formulations are given. It is only in the case of fine-grained film that the equations strongly differ whether or notR is energy dependent. A comparison with several experiments related to the thermoelectric power of noble metal films and the temperature coefficient of resistivity of semi-metal films suggests thatR must be physically regarded as energy independent.