“思考题前置教学法”在环境科学实验中的应用研究

探讨思考题前置教学法在环境科学实验教学中的运用,并提高学生发现问题、分析问题和解决问题的能力,提高学生综合素质,以及实验课的教学质量。     

Age-related difference in the use of mobile phones

This study examined the difference between younger adults and older adults in requirements for mobile phones and acceptance of new functions. A survey was conducted among 351 older adults and 140 younger adults in China. Four major findings were derived. Firstly, older adults perceived ease to understand manuals, font size, icon size, and feedback of the operation as more important compared with younger adults. Secondly, younger adults placed more emphasis on most non-visual aspects of mobile phones than older adults, while older adults placed more emphasis on visible attributes. Thirdly, the biggest age-related difference lays in connectivity. Younger adults perceived Internet access and the connection between mobile phones and other devices as much more important compared with older adults. Fourthly, older adults had more difficulties using soft keys and multi-tap than younger adults, which implied that smart phones with changing button labels and the touch & hold operation would be confusing for older adults. These results were interpreted in the context of the transition from feature phones to smart phones.     

基于全年动态负荷分析的冷热源方案设计

以北京某酒店为例,对该建筑进行全年逐时动态负荷计算分析。根据计算分析结果,确定制冷季梯级利用离心式冷水机组、螺杆机组和空气源热泵机组作为空调系统冷源,供热季利用板式换热器和空气源热泵机组作为空调系统热源,以达到系统节能的目的。     

Cold pre-compression of membrane electrode assembly for PEM fuel cells

Direct compression from the land structure of bipolar plate in a PEM fuel cell is considered as an important factor for the higher performance under the land than under the channel areas. Therefore the objective of this study is to determine if a cold pre-compression treatment on the whole membrane electrode assembly (MEA) area may have a significant positive effect on the overall performance of the cell. Five different levels of cold pre-compression have been applied and the experimental results show that the overall performance of the cell first increases with the level of compression to a maximum, and then decreases. These results clearly show that cold pre-compression of the MEA can significantly enhance the performance of the entire cell and there exists an optimal level of compression. Results of electrochemical impedance spectroscopy (EIS) show that the cold pre-compression results in a significant reduction in charge transfer resistance, especially in the high current density region. Further study by the cyclic voltammetry (CV) shows that the electro-chemical area (ECA) is changed with the different cold pre-compressed MEAs and there exists an optimal compression that results in the maximum ECA.     

Combined Vector Field Approach for 2D and 3D Arbitrary Twice Differentiable Curved Path Following with Constrained UAVs

Path following is an essential requirement for unmanned aerial vehicles (UAVs). Path following problems of 2-dimensional (2D) straight lines and planar circles have been studied and many approaches have been proposed during the past few years. In this paper the problem of following arbitrary twice differentiable curved paths in both 2D and 3D spaces is investigated. Based on the Helmholtz theorem, respective combined guidance vector fields for any given 2D and 3D arbitrary twice differentiable curved paths are constructed by trading off the respective conservative and solenoidal vector fields making use of the defined distance between the UAV and the desired path. Conditions for the two combined vector fields to be globally feasible are given. UAV input constraints and constant wind disturbance are assumed to be present. By tracking the constructed combined vector fields, a saturated course rate controller for 2D curved path following and a jointly saturated course rate and climb rate controller for 3D curved path following are designed. The Lyapunov stability of the saturated course rate controller for 2D curved path following is proved. Numerical simulations are given to assess the proposed approach.     

API-based two-dimensional dispatching decision-making approach for semiconductor wafer fabrication with operation due date–related objectives

This paper presents an adjacent pairwise interchanges (API)-based two-dimensional dispatching decision-making approach for semiconductor wafer fabrication with operation due date-related objectives. Each time when a machine becomes idle, the proposed dispatcher chooses a target processing job from the competing jobs and assigns it a start time. Giving the operation due date information of each competing job, we formulate this dispatcher as the mean absolute deviation problem to keep the jobs finished around their operation due dates in a proactive way. Dominance properties of this problem are established using proof by APIs. Then, a heuristic comprised of job selection within candidate set, movement of job cluster and local search is designed to solve this problem more efficiently. Numerical experiments validate the efficiency of the proposed heuristic in a single-machine environment as well as in a simulated wafer fab abstracted from practice. In comparison with four most referenced due date-related dispatching rules, the simulation study reveals the benefits brought by the two-dimensional dispatching decision with different due date tightness taken into account.     

Factors that influence the performance of two-chamber microbial fuel cell

The two-chamber microbial fuel cell (MFC) was operated in batch mode, using acclimated hydrogen-producing mixed bacteria as the anodic inoculum, artificial sucrose wastewater as the substrate (sucrose concentration 10.0 g/L). The performance of the MFC was analyzed at different anodic pH microenvironments, such as the initial pH of the anolyte of 8.57, 7.3, 7.0 and 6.0, respectively, while anodic pH-controlled of 7.3 and 7.0. It showed that the best performance was obtained when the MFC was carried out at anodic pH-controlled of 7.3. Taking the interaction of factors into consideration, we adopted response surface methodology (RSM) to investigate the effects of sucrose concentration, operating temperature and ferrous sulfate concentration on the performance of MFC. The optimum condition for maximum output voltage of the two-chamber MFC (external resistance 1000 Ω) was thus obtained.     

Adaptive variable universe of discourse fuzzy control for a class of nonlinear systems with unknown dead zones

In this paper, based on an adaptive nonbackstepping design algorithm, we proposed a novel variable universe of discourse fuzzy control (VUDFC) approach for a class of single‐input–single‐output strict‐feedback nonlinear systems with unknown dead‐zone inputs. Firstly, we convert the form of system into a normal form on the basis of some new state variables and coordinate transformation; at the same time, state‐feedback control is changed to output‐feedback control. Secondly, we design observers to estimate the new unmeasurable states. Then, different from considering the traditional backstepping‐based fuzzy control scheme, we introduce a direct VUDFC scheme, which is mainly based on changing of contraction‐expansion factors to modify the universe of discourse online, and fuzzy rules can automatically reproduce to develop the control performance; thus, the size of initial rule base is greatly reduced. This new algorithm can alleviate tracking error, improve the accuracy of the system, and strengthen robustness. Lastly, according to Lyapunov theorem analysis, we prove that all the signals in the closed‐loop system can be guaranteed to be stable, and the output can track the reference signal very well. Simulation results illustrated the effectiveness of the proposed VUDFC approach.     

工程造价专业开展 BIM 实训课程的问题及解决办法

BIM(建筑信息模型)在工程造价管理中精密、自动、可视、高效、智能的优点已经逐渐被大家所认同,本文结合自己在工程造价教学中应用BIM技术的体会,和在此过程中遇到的问题,寻找相应的解决办法,探索工程造价专业中BIM技术的应用更加便利的实训通道。     

Modeling the temperature-dependent mode I fracture behavior of adhesively bonded joints

An ethylene propylene diene monomer (EPDM) rubber film has been used as an inhibitor and insulation in solid rocket motors (SRMs) due to its excellent heat-insulating property. EPDM is wrapped on the surface of the grain layer-by-layer via an adhesive; thus, the adhesive property between EPDM films is one of the key factors that influence the structural integrity of an SRM. The adhesive properties are largely temperature dependent, therefore, it is essential to study the effect of temperature on the properties of the bonding interface between EPDM films. In this article, double cantilever sandwich beam (DCSB) and uniaxial tensile experiments were performed to study the temperature-dependent mode I fracture of the bonding interface, in the service temperature range of the SRMs. A comparison of experimental and numerical results obtained using experimental parameters indicates that the fracture parameters determined by the simple beam theory (SBT) and the compliance-based beam method (CBBM) are not accurate. Next, we obtained accurate parameters using an inverse analysis method. Moreover, we made an initial attempt to establish a temperature-dependent cohesive zone model to predict the temperature-dependent fracture behavior of adhesively bonded joints. Good agreement between experimental and numerical results demonstrates that this temperature-dependent model is applicable.