Making irrigation management pro-poor: lessons from China and Vietnam

Irrigation management / Poverty / Irrigation systems / Water delivery / Participatory management / Farmer participation / Institutions / Water users’ associations / Water rates / China / Vietnam / Nam Duong Irrigation System / Ningxia Province / Qingtongxia Irrigation District

THE EFFECT OF MICROSTRUCTURE AND TEXTURE ON HIGH CYCLE FATIGUE PROPERTIES OF AL ALLOYS

High cycle fatigue tests were carried out on a medium strength continuous casting AA 5754 Al alloy, and new generation high strength AA 2026 and AA 2099 Al alloys. The effect of texture on fatigue properties and short crack behavior were studied. The strengthening mechanisms were also thoroughly investigated for the two high strength alloys.Texture played an important role in the anisotropy of fatigue strength for the AA 5754 Al alloy. Being a solution strengthened alloy, it had a fatigue strength of 120% σy. High strength Al alloys had a strong tendency for planar slip due to the high density of coherent and shearable precipitates in the alloys. Texture was a key factor controlling the crack initiation and propagation. The crack path and the possible minimum twist angles were measured using EBSD and calculated theoretically by a crystallographic model. Based on the micro-texture measured by EBSD, the crack paths were predicted for the AA 2099 alloy and confirmed by the observed values.The excellent balance of superior fatigue properties and high tensile strength of AA 2026 and AA 2099 was attributed to the reduced population of Fe-containing particles, homogeneously distributed precipitates and dislocations. The addition of Zr coupled with the optimized thermo-mechanical treatment strongly restrained the recrystallization, refined the grain structure and promoted the homogenization of the precipitates. Moreover, the retainment of the deformation texture developed during the hot extrusion provided significant orientation strengthening in the high strength Al alloys.Fatigue cracks tended to initiate at coarse second phase particles on sample surfaces and the crack population varied markedly with the applied stresses in the high strength Al alloys. The relationship between of the crack population and the applied stress level was studied and quantified by a Weibull distribution function. Since the measured cracknumbers were associated with the crack initiate sites (i.e., the weakest links) in an alloy, the fatigue weakest-link density, which is defined as the crack population per unit area when stress close to the ultimate tensile stress, and the weakest-link strength distribution can all be calculated and regarded as a property of the studied materials

Product Design Process and Methods

Suitable design procedures and methods will lead to twice the result with half the work. Hence, good products need a good beginning in the design process. The design procedure is the basis for guiding the steps of design process, while the design method is the guarantee for effectively developing the design process and improving its quality. A clear and reasonable process can lead to a simple and smooth way in design, while the proper use of creating techniques can let the designer find a better way to solve the problems in a wider range, so as to develop and design a good product

AN INVESTIGATION OF US AND CHINESE PROSPECTIVE ELEMENTARY TEACHERS’ PROBLEM POSING WHEN INTERACTING WITH PROBLEM-SOLVING ACTIVITIES

This study examined the patterns of problem posing shown by United States (US) and Chinese prospective elementary teachers during problem-posing processes when problem-solving activities were involved in an alternating manner. It further explored the features of the relationship between problem posing and problem solving. Data were collected by asking 32 US and 55 Chinese prospective elementary teachers to pose problems for Translating, Comprehending, Editing, and Selecting processes (Christou, Mousoulides, Pittalis, Pitta-Pantazi, & Sriraman, 2005) before a problem-solving task, and then to pose two more problems after that problem-solving task, namely, problem posing after the problem solving process. All participants completed the first set of tasks, and 43 of them completed the similarly structured second set of tasks. Participants’ posed and solved problems were quantitatively analyzed. For problem solving, the results showed that (1) 25% of the 32 US participants and 98% of the 55 Chinese participants completely solved the given problem during the first task administration, and (2) 19% of the 16 US participants and 89% of the 27 Chinese participants correctly solved the given problem during the second task administration. In their problem posing, Chinese participants posed a much higher percentage of solvable mathematical problems in the Comprehending and Selecting processes compared to their US counterparts, while their US counterparts were challenged most by these two processes. Additionally, both US and Chinese participants’ best performance in problem posing did not occur during problem posing after the problem solving process. In qualitative analysis, US and Chinese participants’ problem-posing performance shared some similar patterns regarding (1) features of posed problems, (2) capability of posing problems with creative ideas, and (3) progression of problem-posing performance throughout all five problem-posing processes. The US and Chinese participants also showed some differences during the problem-posing process as follows: (1) figure visualization; (2) calculation interpretation; (3) habitual preference of posing a sequence of problems; (4) perception of a given answer based on previously posed or solved problems; and (5) problem-posing strategy selection for integrating given information. This study further examined the features of the relationship between problem posing and problem solving. Different types of problem-posing tasks needed different amounts of problem-solving effort and they had different impacts on problem-solving performance. In addition, problem solving before problem posing had a positive influence on participants’ subsequent problem-posing performance. This study suggests recommendations for future research to understand other forms of interactions between problem posing and problem solving, explore specific impacts of cultural or academic background on problem-posing performance, and develop models or frameworks that could help problem posers overcome the difficulties involved in posed problems that were ill-structured, unsolvable, or not mathematical problems. For teacher preparation, this study advocates that prospective elementary teachers need more exposure to multiple types of problem-posing tasks, practices involving interactions between problem posing and problem solving, opportunities to work with ill-structured mathematical problems, as well as opportunities to recognize and analyze different types of mathematical problems before posing their own problems