《物质结构与性质》模块的学科认知理解及其教学启示

现代物理实验技术是物质结构研究的重要手段,理论与实验事实相互拟合与佐证是物质结构研究的基本范式,作用与能量是物质结构研究的核心话题,解释与预测是物质结构理论的功能旨向。高中《物质结构与性质》模块的教学要以这种本原性和结构化的认识为依托,用"技术—方法—创新"、"实验—数据—推理"、"微粒—作用—能量"和"结构—性能—应用"等观念统整教学,让学生充分认识和理解学科认知与推理方式,实现素养为本的课堂教学。

Genetic algorithm tuned PI controller on PMSM simplified vector control

A simple control structure in servo system is occasionally needed for simple industrial application which precise and high control performance is not exessively important so that the cost production can be reduced efficiently. Simplified vector control, which has simple control structure, is utilized as the permanent magnet synchronous motor control algorithm and genetic algorithm is used to tune three PI controllers used in simplified vector control. The control performance is obtained from simulation and investigated to verify the feasibility of the algorithm to be applied in the real application. Simulation results show that the speed and torque responses of the system in both continuous time and discrete time can achieve good performances. Furthermore, simplified vector control combined with genetic algorithm has a similar perfofmance with conventional field oriented control algorithm and possible to be realized into the real simple application in the future.

Application of Non-destructive Testing to Evaluate the Performance of Bridges Structures

Bridges are important elements in road system and can influence the entire economy of cities and region. Usually, these structures have high financial investments for their constructions, in this way, maintenance and conservation become so important. Inspection is a technical activity that covers several operations, including performance analysis; examination; final performance report, other operations may be necessary, such as maintenance work, recovery, strengthening and rehabilitation. Technical examination together with some test methods allows a critical and parametric judgment of the bridge performance by minimizing the subjectivity of visual evaluations, and permits a more detailed diagnosis. This paper discusses the methodology to perform tests to complement the assessment recommended by DNIT （Brazilian National Department of Transport Infrastructure）, which consists only on a visual judgment. This approach provides technical basis to classify the bridges as its need and urgency of maintenance.

Performance of Steel Structures under Fatigue Cyclic Loading

A component or structure, which is designed to carry a single monotonically increasing application of static load, may fracture and fail if the same load or even smaller load is applied cyclically a large number of times. For example a thin rod bent back and forth beyond yielding fails after a few cycles of such repeated bending. The fatigue failure is due to progressive propagation of flaws in steel under cyclic loading. This is partially enhanced by the stress concentration at the tip of such flaw or crack. The presence of a hole in a plate or simply the presence of a notch in the plate has created stress concentrations at the center points. These stress concentrations may occur in the material due to some discontinuities in the material itself. At the time of static failure, the average stress across the entire cross section would be the yield stress. However when the load is repeatedly applied or the load fluctuates between tension and compression, the center points experience a higher range of stress reversal than the applied average stress. These fluctuations involving higher stress ranges, cause minute cracks at these points, which open up progressively and spread with each application of the cyclic load and ultimately lead to rupture. Fatigue failure can be defined as the number of cycles and hence time taken to reach a pre-defined or a threshold failure criterion. Low cycle fatigue could be classified as the failures occurring in few cycles to a few tens of thousands of cycles, normally under high stress/strain ranges. High cycle fatigue requires about several millions of cycles to initiate a failure. The type of cyclic stresses applied on structural systems and the terminologies used in fatigue resistant design are illustrated in this paper. The common form of presentation of fatigue data is by using the S-N curve, where the total cyclic stress （S） is plotted against the number of cycles to failure （N） in logarithmic scale. The point at which the S-N curve flattens off is called the ＂endurance limit＂. To carry out fatigue life predictions, a linear fatigue damage model is used in conjunction with the relevant S-N curve.

2D hetero-structures based on transition metal dichalcogenides:fabrication,properties and applications

Recently,two dimensional transition metal dichalcogenides MX_2(M = Mo,W,etc; X = S,Se,Te) have ignited immense interests because of their unique structural and physical properties for the potential applications in the nano-optoelectronics,valley-spintronics etc. In terms of the structural compatibility and van der Waals interaction,two dimensional(2D) MX_2 layers can be fabricated into various lateral and vertical hetero-structures. The atomically-thin hetero-structures comprising different layered MX_2 provide a new platform for exploring fundamental physics and device technologies with unprecedented phenomenon and extraordinary functionalities. In this review,we report the recent progress about the fabrication,properties and applications of 2D hetero-structures based on transition metal dichalcogenides.