Distributed biological computation: from oscillators,logic gates and switches to a multicellular processor and neural computing applications

Neural Computing and Applications - Ever since its foundational years, synthetic biology has been focused on the implementation of biological computing structures. In the beginning, engineered...     

Robustness as a criterion for use of hollow clay masonry units in seismic zones: an attempt to propose the measure

In order to provide adequate seismic behavior of masonry walls, local brittle failure of masonry units in the most stressed zones of structural walls should be prevented. Although robust behavior is required by the code, no specifications are given regarding the criteria to fulfill this requirement. To propose such criteria, a series of 28 masonry walls, built with six different types of hollow clay masonry units, currently available on the market, have been tested by subjecting them to cyclic lateral load at two levels of constant precompression. Besides, the strength characteristics of the units, like compressive strength orthogonal and parallel to the bed joints and tensile and shear strength of the units have been determined by standardized and specifically designed testing procedures. By correlating the parameters of seismic resistance of the walls and strength characteristics of the units, no specific indicator for robustness could have been determined on the basis of the mechanical characteristics of the tested units. It has been found that in all cases the level of precompression, i.e. the ratio between the compressive stresses in the walls and the compressive strength of masonry, represents the governing parameter.     

A Meshless Approach Towards Solution of Macrosegregation Phenomena

The simulation of macrosegregation as a consequence of solidification of a binary Al-4.5%Cu alloy in a 2-dimensional rectangular enclosure is tackled in the present paper. Coupled volume-averaged governing equations for mass, energy, momentum and species transfer are considered. The phase properties are resolved from the Lever solidification rule, the mushy zone is modeled by the Darcy law and the liquid phase is assumed to behave like an incompressible Newtonian fluid. Double diffusive effects in the melt are modeled by the thermal and solutal Boussinesq hypothesis. The physical model is solved by the novel Local Radial Basis Function Collocation Method (LRBFCM). The involved physical relevant fields are represented on overlapping 5-noded sub-domains through collocation by using multiquadrics Radial Basis Functions (RBF). The involved first and second derivatives of the fields are calculated from the respective derivatives of the RBFs. The fields are solved through explicit time stepping. The pressure-velocity coupling is calculated through a local pressure correction scheme. The evolution of the solidification process is presented through temperature, velocity, liquid fraction and species concentration histories in four sampling points. The fully solidified state is analyzed through final macrosegregation map in three vertical and three horizontal cross-sections. The results are compared with the classical Finite Volume Method (FVM). A surprisingly good agreement of the numerical solution of both methods is shown and therefore the results can be used as a reference for future verification studies. The advantages of the represented meshless approach are its simplicity, accuracy, similar coding in 2D and 3D, and straightforward applicability in non-uniform node arrangements. The paper probably for the first time shows an application of a meshless method in such a highly non-linear and multi-physics problem.     

Modeling of the Coupling of Microstructure and Macrosegregation in a Direct Chill Cast Al-Cu Billet

The macroscopic multiphase flow and the growth of the solidification microstructures in the mushy zone of a direct chill (DC) casting are closely coupled. These couplings are the key to the understanding of the formation of the macrosegregation and of the non-uniform microstructure of the casting. In the present paper we use a multiphase and multiscale model to provide a fully coupled picture of the links between macrosegregation and microstructure in a DC cast billet. The model describes nucleation from inoculant particles and growth of dendritic and globular equiaxed crystal grains, fully coupled with macroscopic transport phenomena: fluid flow induced by natural convection and solidification shrinkage, heat, mass, and solute mass transport, motion of free-floating equiaxed grains, and of grain refiner particles. We compare our simulations to experiments on grain-refined and non-grain-refined industrial size billets from literature. We show that a transition between dendritic and globular grain morphology triggered by the grain refinement is the key to the explanation of the differences between the macrosegregation patterns in the two billets. We further show that the grain size and morphology are strongly affected by the macroscopic transport of free-floating equiaxed grains and of grain refiner particles.

     

Prediction of Macrosegregation in Steel Ingots: Influence of the Motion and the Morphology of Equiaxed Grains

Although a significant amount of work has already been devoted to the prediction of macrosegregation in steel ingots, most models considered the solid phase as fixed. As a result, it was not possible to correctly predict the macrosegregation in the center of the product. It is generally suspected that the motion of the equiaxed grains is responsible for this macrosegregation. A multiphase and multiscale model that describes the evolution of the morphology of the equiaxed crystals and their motion is presented. The model was used to simulate the solidification of a 3.3-ton steel ingot. Computations that take into account the motion of dendritic and globular grains and computations with a fixed solid phase were performed, and the solidification and macrosegregation formation due to the grain motion and flow of interdendritic liquid were analyzed. The predicted macrosegregation patterns are compared to the experimental results. Most important, it is demonstrated that it is essential to consider the grain morphology, in order to properly model the influence of grain motion on macrosegregation. Further, due to increased computing power, the presented computations could be performed using finer computational grids than was possible in previous studies; this made possible the prediction of mesosegregations, notably A segregates. This article is based on a presentation given at the International Symposium on Liquid Metal Processing and Casting (LMPC 2007), which occurred in September 2007 in Nancy, France.     

Influence of Ag on the Composition and Electromagnetic Properties of Low-Temperature Cofired Hexaferrites

We have studied the compatibility of Ag and (Co,Cu)Z-hexaferrite with the composition Ba₃Co_1.4Cu_0.6Fe₂₄O₄₁ (Z). In order to do this, the (Co,Cu)Z-hexaferrite was cofired with various amounts of Ag at 900°C. The degradation of the (Co,Cu)Z-hexaferrite to Y- and U-hexaferrite occurred during the cofiring and was confirmed by X-ray diffraction as well as by thermomagnetic measurements. The permeability and permittivity of the cofired ceramics were measured in the range 1 MHz to 10 GHz. For the (Co,Cu)Z-hexaferrite, both these properties were significantly influenced by the Ag when the amount of Ag exceeded a minimum of 4.5 wt%. The influence of the Ag and the degradation of the (Co,Cu)Z-hexaferrite on the permeability were evaluated using the Bruggeman effective media theory.     

The mechanism of the low-temperature formation of barium hexaferrite

We have investigated the formation of barium hexaferrite via the coprecipitation method. Fine precursor powders were obtained with coprecipitation from water and ethanol solutions of various reagent salts. The coprecipitates were calcined at 300–800 °C for 0–50 h. The samples were characterized with X-ray powder diffraction, thermal analysis, electron microscopy and magnetometry. The formation of barium hexaferrite was a combination of two competing mechanisms and was not influenced by the reagent salts or the solvent. The formation temperature of the barium hexaferrite was reduced to 500 °C by optimizing the coprecipitation conditions.