Papers by Keyword: Stagnation

Abstract: Currently ,most of traditional Ant Colony Optimization algorithms that we are using were proved to be some critical issues, such as slow convergence and long time computation, search stagnation etc. A new improved ACO algorithm based on scholarship mechanism to balance between the search data processing and stagnation was addressed.Besides,the improved ACO alorithm was deeply analyzed and proved that the optimal solution can maintain ability for other path detection.The theoretical analysis and comparative experiments demonstrate that the imroved ACO has much better performance and can be used to solve the problems of convergence and search stagnation efficiently.

Abstract: In the current study, the material corrosion behavior and degradation of a closed-loop copper piping systems were investigated taking temperature and flow parameters into consideration. To simulate the practical environment conditions, two identical copper closed-loop piping systems were constructed with three types of joints. Both systems were filled with 3% sodium chloride solution and run for about eleven months period. They were heated to a temperature of 80°C for eight hours a day and for 5 days a week. Outside that heating period, systems were maintained at room temperature (23± 2°C). Within such a heating interval, the contained solution for one system was kept in stagnation condition while it was flowing at input velocity of 0.27 m/s for the other. For both systems, the corrosion was then assessed and quantified using different evaluation techniques: Potentiodynamic test, Pourbaix diagrams, light microscope and scanning electron microscopy (SEM). The experimental results confirmed a diverse significant influence of solution flowing conditions on the damage of copper pipes.

Abstract: A calibration method of a contact sensor for displacement with a piezo nanopositioning stage is presented in this paper. The experiment system is set up, and an old contact sensor for displacement is calibrated by a P-622.ZCD precision vertical nanopositioning stage, which is tested for a good using status in the end. The calibrating results indicate the error regularity existed in the output values, and there is the stagnation phenomenon during the descending process of the stage after elevation.

Abstract: In order to overcome the shortcomings of precocity and stagnation in ant colony optimization algorithm, an improved algorithm is presented. Considering the impact that the distance between cities on volatility coefficient, this study presents an model of adjusting volatility coefficient called Volatility Model based on ant colony optimization (ACO) and Max-Min ant system. There are simulation experiments about TSP cases in TSPLIB, the results show that the improved algorithm effectively overcomes the shortcoming of easily getting an local optimal solution, and the average solutions are superior to ACO and Max-Min ant system.

Abstract: Molecular dynamics simulations of bicrystals show that grain boundaries undergo a thermal roughening transition, and the grain boundary mobility increases abruptly when the boundary roughens. The roughening transition temperature varies widely from boundary to boundary, ranging from less than 0.4 to more than 0.9 of the melting temperature. Thus, at typical annealing temperatures we expect polycrystals to contain both smooth (slow) and rough (fast) boundaries, with the fraction of each type varying with temperature.

Abstract: The study of microstructural evolution in polycrystalline materials has been active for many decades so it is interesting to illustrate the progress that has been made and to point out some remaining challenges. Grain boundaries are important because their long-range motion controls evolution in many cases. We have some understanding of the essential features of grain boundary properties over the five macroscopic degrees of freedom. Excess free energy, for example, is dominated by the two surfaces that comprise the boundary although the twist component also has a non-negligible influence. Mobility is less well defined although there are some clear trends for certain classes of materials such as fcc metals. Computer simulation has made a critical contribution by showing, for example, that mobility exhibits an intrinsic crystallographic anisotropy even in the absence of impurities. At the mesoscopic level, we now have rigorous relationships between geometry and growth rates for individual grains in three dimensions. We are in the process of validating computer models of grain growth against 3D non-destructive measurements. Quantitative modeling of recrystallization that includes texture development has been accomplished in several groups. Other properties such as corrosion resistance are being related quantitatively to microstructure. There remain, however, numerous challenges. Despite decades of study, we still do not have complete cause-and-effect descriptions of most cases of abnormal grain growth. The response of nanostructured materials to annealing can lead to either unexpected resistance to coarsening, or, coarsening at unexpectedly low temperatures. General process models for recrystallization that can be applied to industrial alloys remain elusive although significant progress has been made for the specific case of aluminum alloy processing. Thin films often exhibit stagnation of grain growth that we do not fully understand, as well as abnormal grain growth. Grain boundaries respond to driving forces in more complicated ways than we understood. Clearly many exciting challenges remain in grain growth and recrystallization.