Two-stage Turing model for generating pigment patterns on the leopard and the jaguar

Based on the results of phylogenetic analysis, which showed that flecks are the primitive pattern of the felid family and all other patterns including rosettes and blotches develop from it, we construct a Turing reaction-diffusion model which generates spot patterns initially. Starting from this spotted pattern, we successfully generate patterns of adult leopards and jaguars by tuning parameters of the model in the subsequent phase of patterning

Oscillatory Turing Patterns in a Simple Reaction-Diffusion System

Turing suggested that, under certain conditions, chemicals can react and diffuse in such a way as to produce steady-state inhomogeneous spatial patterns of chemical concentrations. We consider a simple two-variable reaction-diffusion system and find there is a spatio-temporally oscillating solution (STOS) in parameter regions where linear analysis predicts a pure Turing instability and no Hopf instability. We compute the boundary of the STOS and spatially non-uniform solution (SSNS) regions and investigate what features control its behavior

An Improved Method of Computing Multistate Survivorship Proportions for the Terminal Age Groups

The aging of populations is a phenomenon which has become an important research topic. Demographers, however, have given inadequate attention to the projection of the number of old people and their future age composition. This paper shows that the conventional method for estimating the survivorship proportions of the very old tends to produce misleading results with respect to the size and composition of the aged. Several alternatives are suggested here to overcome these problems. An empirical example is used to point out the problems of the conventional approach and to evaluate the suggested improvements

Compression-compression fatigue of Pd_(43)Ni_(10)Cu_(27)P_(20) metallic glass foam

Compression-compression fatigue testing of metallic-glass foam is performed. A stress-life curve is constructed, which reveals an endurance limit at a fatigue ratio of about 0.1. The origin of fatigue resistance of this foam is identified to be the tendency of intracellular struts to undergo elastic and reversible buckling, while the fatigue process is understood to advance by anelastic strut buckling leading to localized plasticity (shear banding) and ultimate strut fracture. Curves of peak and valley strain versus number of cycles coupled with plots of hysteresis loops and estimates of energy dissipation at various loading cycles confirm the four stages of foam-fatigue

Oxidation Behavior of a Pd_(43)Cu_(27)Ni_(10)P_(20) Bulk Metallic Glass and Foam in Dry Air

The oxidation behavior of both Pd_(43)Cu_(27)Ni_(10)P_(20) bulk metallic glass (Pd4-BMG) and its amorphous foam containing 45 pct porosity (Pd4-AF) was investigated over the temperature range of 343 K (70 °C) to 623 K (350 °C) in dry air. The results showed that virtually no oxidation occurred in the Pd4-BMG at T < 523 K (250 °C), revealing the alloy’s favorable oxidation resistance in this temperature range. In addition, the oxidation kinetics at T ≥ 523 K (250 °C) followed a parabolic-rate law, and the parabolic-rate constants (k_p values) generally increased with temperature. It was found that the oxidation k_p values of the Pd4-AF are slightly lower than those of the Pd4-BMG, indicating that the porous structure contributes to improving the overall oxidation resistance. The scale formed on the alloys was composed exclusively of CuO at T ≥ 548 K (275 °C), whose thickness gradually increased with increasing temperature. In addition, the amorphous structure remained unchanged at T ≤ 548 K (275 °C), while a triplex-phase structure developed after the oxidation at higher temperatures, consisting of Pd_2Ni_2P, Cu_3P, and Pd_3P

Effect of Particle Orientation on the Elastic Anisotropy of Al/SiCp Metal Matrix Composites

Metal matrix composites (MMCs) are promising new materials for structural applications because of their high specific stiffness and strength, and high temperature stability. Of particular interest are the discontinuous silicon carbide (SiC) reinforced aluminum metal matrix composites. The improved mechanical properties are governed by the properties of the constituent phases, as well as the SiC particle characteristics such as shape, aspect ratio and orientation. The particle characteristics have a major effect on the anisotropic properties of these composites. The overall properties also depend on the manufacturing process of these composites since it determines the orientation of the particles and may produce internal defects such as porosity and intermetallic compounds [l]. Thus it is important to experimentally characterize the effective elastic properties and to theoretically predict them from the knowledge of the constituent properties and the microstructures

Elastic Moduli of Silicon Carbide Particulate Reinforced Aluminum Metal Matrix Composites

The mechanical properties of metal matrix composites (MMCs) reinforced by discontinuous silicon carbides are governed by the properties of the reinforcing phase, as well as their morphology (whisker vs. particulate), orientation and volume fraction. The morphology of SiC particles and their orientation are major variables affecting the anisotropic properties of these composites. SiC whisker (SiCW) reinforced aluminum MMCs tend to have higher strengths and moduli in the extrusion direction due to the high degree of whisker alignment in that direction, and these values are higher than those for SiC particulate (SiCp) reinforced composites at a given reinforcement level [1]. SiCpreinforced MMCs are known to be more isotropic in the extrusion plane. In situations requiring multidirectional reinforcement, particulate reinforced composites can outperform whisker reinforced composites. Thus, it is important to characterize the mechanical properties of these composites in order to develop the criteria for selecting microstructural design variables