Tensile behavior and deformation mechanisms of bulk ultrafine-grained copper

The tensile behaviors of the ultrafine-grained (UFG) pure copper prepared by cold rolling have been investigated. The UFG-Cu exhibited high strengths and low ductility. The ductile dimple-like fracture surfaces and persistent-slip-bands (PSBs)-like local shear bands in the tension-deformed UFG-Cu were observed, both of which typically spanned tens of grain sizes. This observation indicated that the fracture mechanisms operated at a larger scale than the grain size and eventually involved collective grain activities. Moreover, localized shear bands provided the experimental evidence to the localized plastic deformation, which was the one of the dominant reasons, causing the low ductility in the UFG-Cu.     

A hybrid computational strategy for identification of structural parameters

By identifying parameters such as stiffness values of a structural system, the numerical model can be updated to give more accurate response prediction or to monitor the state of the structure. Considerable progress has been made in this subject area, but most research works have considered only small systems. A major challenge lies in obtaining good identification results for systems with many unknown parameters. In this study, a non-classical approach is adopted involving the use of genetic algorithms (GA). Nevertheless, direct application of GA does not necessarily work, particularly with regards to computational efficiency in fine-tuning when the solution approaches the optimal value. A hybrid computational strategy is thus proposed, combining GA with a compatible local search operator. Two hybrid methods are formulated and illustrated by numerical simulation studies to perform significantly better than the GA method without local search. A fairly large structural system with 52 unknown parameters is identified with good results, taking into consideration the effects of incomplete measurement and noisy data.     

Contact Friction Compensation for Robots Using Genetic Learning Algorithms

In this paper, the issues of contact friction compensation for constrained robots are presented. The proposed design consists of two loops. The inner loop is for the inverse dynamics control which linearizes the system by canceling nonlinear dynamics, while the outer loop is for friction compensation. Although various models of friction have been proposed in many engineering applications, frictional force can be modeled by the Coulomb friction plus the viscous force. Based on such a model, an on-line genetic algorithm is proposed to learn the friction coefficients for friction model. The friction compensation control input is also implemented in terms of the friction coefficients to cancel the effect of unknown friction. By the guidance of the fitness function, the genetic learning algorithm searches for the best-fit value in a way like the natural surviving laws. Simulation results demonstrate that the proposed on-line genetic algorithm can achieve good friction compensation even under the conditions of measurement noise and system uncertainty. Moreover, the proposed control scheme is also found to be feasible for friction compensation of friction model with Stribeck effect and position-dependent friction model.     

Least-Squares, Moment-Based, and Hybrid Polynomializations of Drag Forces

In order to carry out nonlinear dynamic analyses of fixed offshore structures in the frequency domain, polynomial approximations of the distributed drag term, u∣u∣, and inundation drag term, ηu∣u∣, of the Morison forces are studied. The methods of least-squares and moment-based approximations are considered for cases with and without current. Numerical results and analytical expressions of the polynomial coefficients are presented for the cubic approximations of u∣u∣ and quartic approximations of ηu∣u∣. The curve shapes, first four central moments, and probability density functions of the different approximations are evaluated and compared with the corresponding exact solutions. For the nonmonotonic inundation drag term with the current effect included, a hybrid polynomialization, based on the least-squares approximation for the odd-order polynomial coefficients and the moment-based approximation for the even-order coefficients, is proposed.     

Effect of Al on the NiAl-Type B2 Precipitates in Ferritic Superalloys

Ultra-small-angle X-ray scattering (USAXS) is employed to quantify the average size, interparticle spacing, and volume fraction of the primary B2 precipitates in Fe-based superalloys with varying Al concentration. The results are analyzed with a model incorporating polydispersity and interference effects and verified by transmission electron microscopy (TEM) characterizations. As the Al amount increases from 4 to 10?mass pct, there is an approximately 40?pct decrease in the average interparticle spacing and?~30?pct reduction in the average particle diameter.     

Asymptotic stabilization of driftless systems

Issues of asymptotic stabilization of a class of non-linear driftless systems are presented. In addition to the necessary and sufficient condition for the existence of a smooth time-invariant asymptotic stabilizer, sufficient condition for the existence of a quadratic-type Lyapunov function candidate is also proposed herein to alleviate the construction of stabilizing control laws. Following the deduction of the equivalence of the sufficient condition and the determination of the local definiteness of a defined scalar function, the stabilizability checking conditions are then derived in terms of system dynamics and its derivatives at the origin only. These are achieved by taking Taylor's series expansion on system dynamics. The derived conditions are shown to be consistent with those obtained by Brockett. Comparative results of Liaw and Liang are also included. Finally, examples are given to demonstrate the use of the main results.     

Bibliometric analysis for development of research strategies in agricultural technology: the case of Taiwan

Due to rapid environmental change, policymakers no longer choose foresight issues based on their own experience. Instead, they need to consider all the possible factors that will influence new technological developments and formulate an appropriate future technological development strategy to the country through the technology foresight system. For the sake of gathering more objective evidence to convince stakeholders to support the foresight issues, researchers can employ bibliometric analysis to describe current scientific development and forecast possible future development trends. Through this process, a consensus is reached about the direction of future technology development. However, we believe that bibliometric analysis can do more for technology policy formulation, such as (1) offer quantitative data as evidence to support the results of qualitative analysis; (2) review the situations of literature publication in specific technological fields to seize the current stage of technology development; and (3) help us grasp the relative advantage of foresight issues development in Taiwan and the world and develop profound strategic planning in accordance with the concept of Revealed Comparative Advantage. For those reasons, our research will revisit the role that bibliometric analysis plays for nations while choosing the foresight issues. In addition, we will analyze the development of the technology policy in Taiwan based on bibliometric analysis, and complete the foresight issues selection by processing key issue integration, key word collection related to this field, the searching and confirmation of literature, development opportunities exploration, comparative development advantage analysis and the innovation-foresight matrix construction, etc.     

Ozonation of Pyrolytic Aqueous Phase: Changes in the Content of Phenolic Compounds and Color

Ozonation on the phenols present in pyrolytic aqueous phases attained from biomass thermochemical conversion was evaluated. During ozonation, the dark color of original samples was found to decrease as a function of ozonation time. The oxidation kinetics of phenols was quantified by a method based on the color changes of samples. The oxidation profiles showed different behaviors and in some cases the phenols presented a positive correlation with the relative R color parameter, except eugenol, syringol, and vanillin which were markedly different. Finally, the color changes observed seem to be associated with the changes in the overall content of phenols and with the change in the molecular weight of the heavy fractions that include lignin oligomers.