基于“教—学—评”一体化的大单元教学设计与实施

在当今学科素养时代,大单元教学成为必然趋势。针对大单元教学中出现的误区,基于“教—学—评”一体化理念,提出大单元教学设计与实施应力求“真教学”,主要围绕三个方面展开:以“学”为主线,瞄准“真需求”;以“教”为推力,落地“真实践”;以“评”为标尺,实现“真反馈”。

RESEARCH ON NONLINEAR DISTORTION IN AMPLIFIERS

Transistors are nonlinear devices, which can produce nonlinear distortion in amplifier while amplifying signals. For weak nonlinear distortion, the expressions of total harmonic distortion (THD), the second order intermodulation distortion(IM2 ), the third order intermodulation distortion(IM 3) and intercept point(IP 3) are deduced. With the aid of software Multisim, we simulate transistor common emitter amplifier, transistor common emitter amplifier with resistor in emitter, differential amplifier and differential amplifier with resistor between emitters. The simulational results and theoretical analyses are almost the same.

A robot simulation system with virtual force display and feedback based on master manipulator

This paper describes a virtual environment, which can present dynamic force transformation during the control of objects. A 5-DOF haptic interface with the capability to generate kinesthetic effect is combined. In this system, the operator manipulates an object in a virtual environment by using the 5-DOF master arm. When contacting with the virtual object, the contact force can be calculated and shown in the graphic interface. The contact response and deformation of the virtual object, which are usually called haptic rendering, also can be performed. The study supplies an approach to improve the operator’s immersion and can be used in many tele-robot control fields.

A novel intra refresh scheme for wireless video transmission

The burst error of wireless channels and the two-state Markov wireless model are analyzed. Based on this model and the coding modes of the video encoder,the channel distortion of inter-coding and intra-coding due to burst error is deduced. Then we propose a novel intra refresh scheme in rate-distortion (R-D) framework. This scheme optimizes the error resilience and coding efficiency of wireless video transmission system. It can also stop error propagation and reduce channel distortion effectively. Simulations under different channel conditions verify the improvements of the proposed scheme with respect to error resilience for wireless video communication.

Microscopic simulation of multi-lane traffic under dynamic tolling and information feedback

To investigate drivers' lane-changing behavior under different information feedback strategies,a microscopic traffic simulation based on the cellular automaton model was made on the typical freeway with a regular lane and a high-occupancy one. A new dynamic tolling scheme in terms of the real-time traffic condition on the high-occupancy lane was further designed to enhance the whole freeway's flow throughput. The results show that the mean velocity feedback strategy is generally more efficient than the travel time feedback strategy in correctly guiding drivers' lane choice behavior. Specifically,the toll level,lane-changing rate and freeway's throughput and congestion coefficient induced by the travel time feedback strategy oscillate with larger amplitude and longer period. In addition,the dynamic tolling scheme can make the high-occupancy lane less congested and maximize the freeway's throughput when the regular-lane inflow rate is larger than 0.45.

Evaluation of cracking potential for concrete arch dam based on simulation feedback analysis

It is still very difficult for researchers and engineers to implement the simulation analysis including a complete process and a full model with the complicated arch dam and the foundation, and to evaluate the cracking potential in the construction and service periods. To take Xiaowan project of China for an example, a practical system of simulation feedback analysis, a specific cracking criterion, and a resolution for the conflicting requirements of temperature and stress/strain simulation are presented, which are put into a successful practice. The simulation results of temperature, stress, and cracking are identical well with the monitor data. A modified temperature control measure is propounded, and the significant effect is gained by adopting the new scheme.

An invading annual plant benefits less from soil biota and has reduced competitive power with a resident grass

Aims Interactions between plants and their soil biota,arbuscular mycorrhizal fungi(AMF)in particular,may play a vital role in the establishment and the range expansion of exotic plants in new environments.However,whether there are post-introduction shifts in dependence on AMF and how dependency interacts with competition remains poorly understood.Methods We conducted a common garden greenhouse experiment to examine how native(USA)and invasive(China)populations of the plant species Plantago virginica,respond to soil biota,and whether these responses change in the presence of a competitor.Important Findings We found that while native populations consistently had a higher AMF colonization rate and benefited from AMF in both biomass and seed production,invasive populations received less benefit from AMF,and even showed reduced biomass with AMF in the presence of a competitor.This low mycorrhizal dependency in invasive populations correlated with greater suppression by an indigenous competitor for the invader.The different responses of the invasive and native populations to AMF suggest that alteration of mycorrhizal dependency has occurred during the invasion of P.virginica into China.Our findings suggest that this reduced dependency incurs a cost during interspecific competition.