Backward wellposedness of nonuniform Timoshenko beam equation

In this paper, we consider the Timoshenko equation of a nonuniform beam, with clamped boundary condition at one end and with feedback controls at the other end. It is proved that the system is backward wellposedness when the feedback controls are weak enough. Project supported partially by the National Key Project of China and the Natural Science Foundation of China (No. 69874034).     

变价格下的单向捕获模型

主要考虑具有变价格下 ,开放渔场的自反馈控制问题 ,体现价格因素对系统的影响 ,进而考虑其持久的产出 .     

Influence of Design Reference on Tracking Performance of Feedback Control

In this paper, we present an investigation on the tracking performances of feedback control as a function of reference signals. We use multi-objective optimal designs of feedback controls as a fair basis for comparing different control designs, and examine step, ramp, and periodic signals at various frequencies. Through comparing the tracking performances of controls designed with different reference signals,we find that the controls designed with ramp signals perform better in tracking step and ramp references than those designed with step signals. To track periodic signals, we find that the controls designed with periodic signals at the same frequency generally provide the best performance, and those designed with step and ramp signals perform comparably.     

气候系统中的反馈机制与气候的稳定性

在气候系统中,存在着很多的正负反馈机制．由于正反馈机制的存在,加之影响气候的外部因素的经常变动,以及大气的流体性质,使气候表现出不稳定性,同时,由于负反馈的广泛存在,从较长一段时间看,气候又具有一定的稳定性,而人则是现代气候不稳定的一个最重要因素     

具有反馈控制的非自治两种群浮游生物相克系统的持久性

研究一类具有反馈控制的非自治两种群浮游生物相克系统．借助干微分方程的比较原理和一个积分不等式,得到了一组保证系统持久的充分性条件．结果表明在原系统持久下,反馈控制变量对系统的持久性没有影响．所得结果说明文献[2]的持久性条件中有关反馈控制变量的条件限制是多余的,由此实质性地改进了文献[2]的结果．     

反馈控制对一类Gilpin-Ayala竞争系统的影响

研究一类具反馈控制的无穷时滞的Gilpin-Ayala竞争系统,利用比较原理,证明了该系统的持久性,说明了通过适当的反馈控制可以改变系统的绝灭性,进而避免物种的绝灭.     

关于英语精读课教师提问与学生反馈的研究--以中国地质大学（北京）外语系为例

本研究采用定性和定量相结合的方法,通过对中国地质大学（北京）英语专业某班进行课堂录音和学生访谈,从课堂提问分类、学生对不同类型提问的应答参与度以及不同类型提问对学生语言输出的影响这三个方面,对英语精读课教师提问与学生反馈的状况进行了研究。基于研究结果,笔者提出了一些提高课堂提问效果的建议。     

An analysis of the effectiveness of feedback to students on assessed work

This paper presents the views of students, from a range of schools and disciplines, on the effectiveness of current assessment feedback practices at Flinders University. We also report on a workshop on feedback with teachers. Overall, individual written comments were found to be the most useful form of feedback. However, there was significant variation with the level of satisfaction with feedback and the relative usefulness of different forms of feedback across the different schools and disciplines. This research suggests both the need to improve the effectiveness of such feedback and to tailor the forms of feedback offered to students according to the distinctive teaching and learning environments in different schools and disciplines. To that end, innovation and further research on feedback are justified, and some suggestions are offered.     

Effects of exteroceptive feedback and safe-box confinement durations on escape behavior in rats

In Experiment 1, rats received escape training in which an exteroceptive feedback cue occurred in the safe box, and safe-box confinement durations of 5 or 20 sec were combined orthogonally with shock-box confinement durations of 5 or 20 sec. Exteroceptive feedback reliably facilitated escape performance relative to no-feedback controls when safe-box confinement was relatively longer than shock-box confinement. Confinement duration also facilitated performance in the absence of exteroceptive feedback. In Experiment 2, escape training with or without feedback was followed by extinction either with the feedback condition of prior training or with the opposite feedback condition. Feedback presentations in extinction reliably increased responding. Feedback removal reliably decreased responding relative to feedback controls. Introduction of feedback in extinction reliably enhanced performance relative to no-feedback controls.     

University teachers’ reflections on the reasons behind their changing feedback practice

This study investigated the changing feedback practices of teachers in an elite university in China. Drawing on teacher cognition theory and recent research developments in effective feedback practices, fourteen teachers were invited to reflect and explain their feedback practices in semi-structured interviews. Which identified three trends: their use of feedback practices appear to change: (1) from addressing specific tasks with detailed comments to addressing a combination of issues within and beyond task level, (2) from providing feedback at the end of a learning cycle to instructing on common problems at the beginning, and (3) they appear to make their feedback more timely and interactive by using social networking software and new course formats. Teachers seem to be willing to experiment with a wide range of feedback. They constantly evaluate the effectiveness of these practices based on two criteria: improving student academic performance and teaching all the content from the curriculum as scheduled. Recommended or experimental feedback practices were unlikely to be sustainably adopted by teachers unless they were confirmed to be effective by the teachers’ own evaluations.     

球头铣刀铣削过程的物理建模与仿真

给出了球头铣刀刃线几何模型,采用理论切削力分析与实验-系数识别相结合的方法,建立了新的螺旋刃球头铣刀的铣削力模型;建立了考虑刀杆柔性的球头铣刀铣削振动模型;考虑刀具动态变形和工件表面波纹对切削厚度的再生反馈,建立了球头刀铣削动力学模型,对动态铣削过程进行了仿真,证明离线仿真可以对铣削过程动特性做出准确的预测.     

对外汉语课堂中教师的消极反馈语研究——以云南师范大学为例

反馈语在对外汉语课堂中扮演着重要的角色。反馈语可以是书面反馈语、口语反馈语,也可以是体态语,而反馈语又分为积极反馈和消极反馈。在课堂中,学生犯错是不可避免的,老师不当的消极反馈会挫伤学生的自信心,降低学生的学习积极性。本文将对对外汉语课堂中的消极反馈展开研究,对比四位教师课堂中的消极反馈,并提出改善建议。     

学生社团在校企文化互动中的作用研究——对湖北省部分高职院校的调查与思考

对湖北省高职院校的调查表明,当前学生社团与企业的互动,主要在于获取资源、拓展空间,社团则以自身的资源和优势,为企业提供反馈服务,开展合作开发。在校企文化互动中,学生社团发挥着中介、过滤、再殖等作用,少数社团以其特有的“黏合力”推动着校企合作的深化和发展,校企共同组建的新型社团开始出现;同时,受企业文化的影响,学生社团也存在过度“市场化”的风险。总体看来,学生社团的文化价值亟需得到校企双方的重新认识,其作用的发挥也将取决于校企双方共同创设的良好机制。     

How Do Faculty Make Formative Use of Student Evaluation Feedback?: A Multiple Case Study

This multiple case study explored faculty formative use of student evaluation feedback. Results were based on interviews of ten education faculty members at a midwestern research university and reviews of relevant documents. It was found that end of semester student evaluation, originally used for summative evaluation, was also used by faculty for teaching improvement purposes. Faculty cared for student evaluation feedback and used discretion in using the feedback to improve their teaching. Faculty also experienced anxiety and tensions in the context of a mandated summative evaluation. Variations were found in faculty use of evaluation feedback, as a result of difference in background and experience.     

The Interactive Effects of Personal Achievement Goals and Performance Feedback in an Undergraduate Science Class

The authors explored whether manipulating feedback influenced cognition, motivation, and achievement in an undergraduate chemistry course. They measured students’ (N = 250) achievement goals, test anxiety, self-efficacy, and metacognitive strategy use at the beginning and end of the semester. After completing the first set of questionnaires, students were randomly assigned to 1 of 4 conditions: (a) control, (b) mastery feedback, (c) performance-approach feedback, and (d) combined mastery/performance-approach feedback. In each condition, students received a raw performance score for each weekly quiz they completed online and, for the treatment conditions, additional feedback reflective of that specific feedback condition. Results provide evidence for the multiple goals perspective (specialized pattern) wherein performance-oriented feedback was beneficial for some outcomes, whereas mastery feedback was beneficial for other outcomes.     

Effects of duration of feedback on signaled avoidance

Two experiments were carried out to study vertical jumping avoidance learning in rats. In particular, we examined the effects of the duration of a feedback stimulus and of the interval between the end of the feedback stimulus and the start of the next trial on acquisition and extinction of avoidance. In Experiment 1, the duration of feedback was manipulated while intertriai interval (feedback plus no-feedback) was held constant. Animals with feedback lasting more than 1 sec needed fewer trials to reach the acquisition criteria than did animals with no feedback or with 1-sec feedback. No differences were observed in extinction. In Experiment 2, the durations of both feedback and no-feedback were manipulated. Animals without feedback needed more trials to reach the acquisition criterion than did animals with feedback, but the performance of the feedback animals did not differ as a function of feedback duration, no-feedback duration, or total intertrial interval. Again, no differences were observed in extinction. These results indicate that the presentation of feedback improves the acquisition of vertical jumping avoidance, but that this effect is independent of the temporal characteristics of feedback.     

Developing knowledge-in-action with a learning progression: Sequential analysis of teachers' questions and responses to student ideas

Researchers have argued that teachers' knowledge can be evidenced by the ways they elicit and respond to student ideas. We analyze data from a four-year study of nine high school teachers who designed formative assessment tasks and learned about student thinking with a learning progression for natural selection. We coded teacher questions, student responses, and teacher feedback in classroom videos collected across four years. Through sequential analysis, we found that teachers came to ask more questions that elicited student ideas, and also became more likely to respond to student ideas with pushing feedback at the end of the study.     

Ten Years of Puzzling about Audience Awareness

The decisions evaluators make regarding how to work with teachers through the annual evaluation process can have a positive impact on teacher growth and student learning. In this article, the author examines the quality of feedback and how administrators use and provide this feedback to teachers through the evaluation process. What constitutes quality feedback? How does quality feedback support teachers' instruction? How can the supervision and evaluation process offer both teachers and administrators an opportunity to work together to improve student learning? The evaluation process should support the goal of maintaining a high level of quality instruction. In the end, the goal is to increase student learning by improving the effectiveness of teaching.     

负反馈放大电路稳定性动态仿真研究

利用运放构建有3个极点的开环放大电路,由Multisim的AC Analysis获得该电路的频率响应,找到对应相位差为-180°的开环电压放大倍数。根据放大电路稳定工作条件,分析出反馈系数范围,据此计算出电压串联负反馈的反馈电阻,构成反馈放大电路。改变反馈电阻,用Multisim中的示波器同时观察输入输出波形,并用Fourier Analysis对输出信号进行傅里叶分析。结果显示振荡波形主要由两部分频率成分迭加而成,一部分是对输入信号放大产生的输出信号;另一部分是由于自激振荡产生的输出信号,其频率值与理论分析一致,除此之外,还包含幅值较小的其他频率成分的谐波分量。通过仿真,同时还可以观察到自激振荡的起振过程,随反馈电阻增大,振荡幅度减小到振荡消失等过程。     

Using observational feedback to promote academic development

The purpose of this paper is to illustrate how professional consultants can use observational feedback to improve instructional effectiveness and to strengthen the academic identity of university teachers. To this end, a three-step approach is presented together with guidelines for giving feedback. A case example, based on the author's own practice, is used to highlight the complexities involved and to draw attention to the need for professionals to use their expert-power base judiciously.