初中数学活动课操作策略初探

数学活动课可安排学生进行探索性的活动,通过一些具体的操作,亲自实践,然后由学生对问题进行思考,得出数学结论,培养学生解决问题的能力和探索问题的精神。学习的过程,不仅是一个学生主动参与的过程,更是一个学生创造的过程。学生在这个探索空间里,不仅是一个发现者、探索者,更是一个创造者。     

SEISMIC RESPONSE CONTROL OF CABLE-STAYED BRIDGE USING DIFFERENT CONTROL STRATEGIES

The goal of this research is to study the effect of cable vibration through a number of control cases of a cable-stayed bridge. In order to consider the complicated dynamic behaviour of the full-scale bridge, a three-dimensional numerical model of the MATLAB-based analysis tool has been developed by the complete simulation of the Gi-Lu bridge. The dynamic characteristics of cables in the cable-stayed bridge are verified between the field experiment and the result from numerical simulation using geometrically nonlinear beam elements in MATLAB program. Three types of control devices are selected to reduce the response of the bridge deck which includes: actuators, viscous-elastic dampers with large capacity, and base isolations. Moreover, two types of control devices, MR dampers and viscous dampers, are installed either between the deck and cables and/or between two neighbouring cables for controlling the cable vibration. A modified bi-viscous model combined with convergent rules is used to describe the behaviour of MR dampers. Finally, through evaluation criteria the control effectiveness on the cable-stayed bridge using different control strategies is examined.     

SLIDING MODE CONTROL OF BUILDING FRAMES UNDER RANDOM GROUND MOTION

A sliding mode control theory is presented to control the response of building frames to predominant frequency components of the random ground motions. The control algorithm is derived based on a sliding surface which is a function of a state vector containing the structural displacements and velocities and variables that dictate the predominant frequency components of the excitation. Three control mechanisms are employed to control the response of the building frame namely, (1) active mass damper (AMD) placed at the top storey of the building, (2) an actuator placed at a storey level and, (3) an actuator placed at a storey level along with a tuned mass damper (TMD) situated at the top storey level. Responses obtained by the proposed control strategy are compared with those obtained by the linear feedback and feedforward-feedback control strategies (conventional control strategies). Also, they are compared with those obtained by the sliding mode control strategy that considers in its state vector only structural displacements and velocities. It is shown that the proposed control strategy generally performs better than other control strategies in the higher range of control forces. For the lower range of control forces, conventional control strategies are more effective.     

Converting a large lecture class to an active blended learning class: why,how, and what we learned

Faced with diminished faculty resources and increased student enrolment from 2010 to 2017, we sought to use blended learning to achieve active learning in a large c.400-student introductory geography class. Working iteratively over seven years and eight classes and using smart classrooms, better timetabling, experimentation with peer review and learning management system (LMS) technologies, as well as the expertise of Queen’s University Continuing and Distance Studies instructional design team to improve integration between course elements, we closely approached the quality of learning achieved in a much smaller enrolment class. It is possible to teach large classes of 400 students in an active and engaged manner. The greatest obstacle to the development and maintenance of this model is institutional culture.     

Experimenting with Active Learning in Geography: Dispelling the Myths that Perpetuate Resistance

While some geographers have embraced active learning as a means to engage students in a course, many others stick to conventional teaching methods. They are often deterred by suggestions that it can be difficult to implement active learning where students have no prior knowledge of a subject, that active learning requires too much work of lecturers and students, and that there are significant institutional constraints to implementing active learning. In this article the authors draw on their experiences of utilizing active learning in five different countries before dispelling myths which continue to constrain the uptake of active learning methods. Finally, they provide simple guidelines for successful integration of active learning in geography courses.     

Archeoseismicity and environmental crises at the Sialk Mounds,Central Iranian Plateau,since the Early Neolithic

During the long-lasting cultural sequences of the Shurābeh and Sialk archeological mounds (6200–550 BC) the inhabitants encountered numerous diversified crises along a narrow fertile passageway at the edge of the Central Iranian Plateau Great Desert. Some of the threats may be attributed to earthquakes, drastic climatic changes, and man-made environmental deterioration, which possibly led to the settlement withdrawing at different stages toward a more suitable location. Our study identified the occurrence of a large-magnitude earthquake around 3800 BC along the Kāshān fault, which is well-documented by various lines of circumstantial evidence, including: (i) numerous contemporaneous smashed skeletons and artifacts underneath collapsed walls and ceiling debris in several different areas; (ii) tilted and collapsed walls; (iii) nearly N–S oriented fallen large storage jars; and (iv) nearly vertical deep ground fractures cutting walls and floors of the Sialk III₅ South Mound settlement. Archeological data also shows additional stratigraphic discontinuities and damages that may be attributed to earthquakes. However, damage features in limited exposed trenches are less conclusive and require additional careful excavations. Apparent ancient paleo-architectural innovative attempts to enhance the coherency/elasticity of the structures and minimize earthquake damage to buildings were also noted, suggesting the indigenous earthquake hazard mitigation endeavor. There seems to be a correlation between some site abandonment dates and possible drastic regional draught/cooling events. The natural and anthropogenic impacts addressed in this study constituted major threats to the sensitive archeological settlements at the fringe of the desert and the vicinity of the Kāshān active fault since antiquity.     

The 1561 Earthquake(s) in Southern Italy: New Insights into a Complex Seismic Sequence

In the summer of 1561, a strong seismic sequence struck southern Italy, then the Spanish-ruled Kingdom of Naples. Both the Italian seismological tradition and the latest catalogues locate it in the Vallo di Diano (Diano Valley), a low-seismicity intermontane basin 100 km south-east of Naples. We explore the hypothesis that current perception of the 1561 earthquake is distorted by the nature of the historical dataset from which its parameters have been assessed, and which mostly derive from a single—albeit very detailed—primary source. We present and discuss several previously unconsidered original accounts. Our results cast doubts on the traditional interpretation of the earthquake, which could have been either one Vallo di Diano mainshock or several strong earthquakes within a time/space window compact enough for contemporary viewers to perceive them as one. Unquestionably, there is much more to the 1561 earthquake(s) than previously appeared. We hope that this groundbreaking effort will rekindle the interest of the seismological community in this seismic episode, our knowledge of which is still far from complete.     

Engaging students and maintaining quality in the era of massification: strategies and approaches for teaching large first-year courses

This article examines the nature of first-year international relations (IR) teaching in Australia. Cost pressures in the university sector have been met by economies of scale with foundational classes becoming very large, often with hundreds of students. The article critically reflects on current strategies for teaching these courses to meet the challenge of providing an engaging and high quality learning environment in large classes with widely fluctuating student entry scores, university preparedness, and educational capital and language competence. The article argues that a successful approach to improving the quality of first-year IR teaching and to accommodating the diverse learning needs of all students is to run these courses in multiple streams, with one dedicated to providing a richer, more active IR learning experience. In the era of ‘massification’, allowing students a level of guided autonomy in aligning their learning preferences with teaching methods is likely to increase engagement and motivation, thereby improving retention and degree progression.     

ACTIVE/PASSIVE SEISMIC CONTROL OF STRUCTURES

In civil engineering, structural integrity and safety are of utmost importance as the consequences of failure are devastating. Maintaining the structural integrity becomes particularly important when the structures are subjected to severe earthquakes and strong wind-loading. Various passive and active control means have been considered to avoid catastrophic failure due to seismic or wind excitations. In this paper, a new class of hybrid actuators is presented which consists of a piezoelectric stack actuator combined with a viscoelastic damper to form a passive/active brace system (PAB). The actuator is used for mitigating structural dynamic responses of a three-storey structure subjected to simulated earthquakes loading. The proposed hybrid actuator is selected because it combines the attractive attributes of active and passive systems as well as because it has high stiffness-weight ratio, high frequency bandwidth, and low power consumption. The theoretical and experimental performance characteristics of the three-storey structure with the hybrid PAB actuator are presented. Comparisons are also included when the structure is controlled with conventional viscoeiastic dampers or conventional active control braces that operate without any viscoelastic damping. These comparisons emphasize the effectiveness of the hybrid actuator in damping out simulated seismic vibrations.     

Parametric Sensitivity of Ground Motion Pulse Filter for Response Control of Base-Isolated Buildings

Recently, the authors have proposed ground motion pulse filters for designing effective active and semi-active controllers for base-isolated structures subject to near-field earthquakes. The controller design is realized by augmenting the structural system equation with state-space model of the pulse filter. It has been observed that the resulting controllers are capable of simultaneously reducing peak values of base displacement, superstructure drift, and accelerations of the base and the superstructure simultaneously within practical range of control forces. Since the pulse model depends on ground pulse period, ground pulse decay factor, and the pulse shape factor, a parametric sensitivity analysis is carried out to find pulse parameters for a broad range of earthquakes. It is found that the performance of the controller doesn't vary significantly if the pulse period is underestimated by 50% or overestimated by 20% with respect to the actual ground pulse period, the ground decay factor is between 0.15 and 0.35 and the pulse shape factor is between 1 and 3.